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DUBLIN CITY UNIVERSITY School of Electronic Engineering

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1. gt T m m Recommended setting E0000 8 1 0 0 O Used VGA performance setting on Vectra ES 1000 9 10 E3000 10 10 000 lb A Used by performance setting on Vectra ES Used performance setting on Vectra ES Used by VGA performance setting on Vectra ES F0000 12 WIE Reserved for system ROM gt F4000 13 11 Reserved for system ROM F8000 14 1 1 1 Qj Reserved for system ROM 000 15 64 Reserved for system ROM have more than one HP IB interface only one can use this setting table 3 3 The Address and Select Code The interrupt switches 5 and 6 determine the level at which the HP IB Interface interrupts the Interrupt level 3 is the factory setting 30 3 3 6 Connecting Peripherals An HP IB system can accommodate up to 14 peripherals in addition to the computer which is the controller of the system The peripherals have been connected using RS 489 368 cables 1 meter long That was done by follow the following instructions 1 As referred in the peripheral manual to find out how to set up the peripheral its power cable was connected and it was switched on before connecting it to the computer 2 Then it was turned off 3 A bus address for the peripheral that does not conflict with the addresses of other peripherals was determined Each peripheral must have a unique addr
2. y CO 3 E SE anle ENE ODER MA a LOGIC ANALYZER 1 IALL SENDING 7 15kTUP Vd ue a E t t C NAM 0 ie poSNRRCT fuo CHANNEL 19 687 i CALL SKETCH SCHEMATIC DIAGRAMI 7 CALL SKETCH THE LAYOUT CIRCUII amp i GOOM POINT D ki i 1 GETTING i COMPARING SIGNAL 11 gt d M ua TES 5 oteFERENGE z d PROBLEM iH 1 THE rig SAT NO ARRAY t SENDI EA 7 CONNECT POD 18 CHANNEL 140 10 POINT GRD i HANNEL 1 are AM CALL A THE CiRCHIT 2098 CRUE EUN amp por memes EXPECTED DAMAGED f COMPONERT am 55 FT 7i 4 p CONNECY 10 i CHANREL 40 Go 3 i 1 v m E CL SKETCH THE 1 4 SCHEMAT LC D LAGRAN 1 p ui 6 m i Hor 3 2 Aw jf C f SY 5 YES j EXPECTED 1 T DAMAGED ZOMPONENT 1 THE FAPER i t DRIUF MOTOR E ua 5 DAMAGED
3. THE BUS amp 5 THE CONTROL FROM REMOTE 1 YES ir ERROR 3 9 ew NO PROCESS THE CAPTURED DATA PROCESSED tO 1225 STONA TIONS SAUE po EASH ON TEMPORARY FILE Tanta DDCUALUE 2091 19 m RESULT VARIABLE aem SAU 1 VANE Ju n 1 _ TEST fad ON THE MAIN POWER E CHANGE THE EXT ad 7 CHECK PORER 27 T DH Y DISCORNECT THE aT T Pop nc lt lt ete rketeh ennewarto niauram Tie Sac t 2 Li lt sketeh rhe ciment 4 vont il 1 CALL GETTIN AND COMPARIN 519 G G saa ese AU bs DLEFERENCE TRANSFORMER aLLOUA BL 1OLERR ye d A PUT THE PROB al 2 ooo CALL sketen t the sircurt X i pom nint 64 3 E ERE 21 CALL GETTING aND D COMPARING NAL 2 E rd Pd 185 DIFFERENCES LLOWABL p NA Mo E i PROBLEM
4. independent of the need for an expert service engineer 3 Achieve a quick and easy corrective maintenance to any CNC machine 4 Decrease the number of service engineers and technicians that are needed for maintenance 5 Decrease the downtime of any CNC equipment 6 Transfer the knowledge between service engineers CHAPTER 2 WORKSTATION SPECIFICATION 2 1 Introdu on As mentioned in the previous chapter CNC machine has high output which increases the significance of breakdown time since the breakdown of a single CNC machine can result in the production of an entire workshop being halted The maintenance workstation associated with a workshop has more significance than a workstation inside other workshops where linked production is not going on This chapter will describe the CNC machine maintenance workstation specification and the software tools which are designed to reduce breakdown time 2 2 General Workstation Specification In general every workstation will have a number of specifications to achieve its aims In this case they can be broken down into 1 Service engineer specifications 2 Test equipment specifications 2 2 1 Service Engineer Specifications For the propose of maintaining the CNC machine which is a very complex machine expert service engineer who will have worked in the maintenance field for a long time following a training course at a CNC machine manufacturer is necessary
5. DZSCOPE SIGNAL START i iMITIALIZE ThE sS amp MST RUMENT i HARE e gt CHOM REMOTE e ee 455 ERROR gt N rd Y GET DATA FROM THE NSTRUMENT CAL IND Y VAN or ratarino 7 st 77 Fact THE OLEREREN Wb 1 i ERANCE ar SANE THE RESULT 3 Bares Tm EXP f wt 1111 et T END x 2 AND CUMPARING LOGIC SIONAL START THE HSTRUNENT PHAM DUE CONTROL EROM ESMOTE oe cec T y pm att CATA WHOM HE 1 BSTRUMENT NP coto PR PROCESS THE 1 CAPTURED DATA Md PROCESSED BATA 18 TEMPORARY FILE GIVE THE CONTROL BACK TO LOCAL PRONT PANEL praen 3 T N gt up 4 ptit T me OPE MM EF Fil 3 rirapenoe amoorary JU DIFFERENCE f ranis ens rart SAVE THE RESULT EN VALVE if FULE GRTTING SIGNALS FROM THE LOGTC ANA LYE AND PROVING THAT INPUT GUT i aim
6. starting point well as some possible intermediate steps an expert system can produce an optimum plan for achieving that goal For very complex projects planning is a difficult human task But for an expert system with the appropriate knowledge and inputs planning is an easy task 57 4 3 9 8 Prediction Predicting means to foretell the future A prediction system receives input data about a given situation Then it deduce the outcomes Weather forecasting is good example of an expert system of this type 4 3 9 9 Repair Repair is the process of returning broken device to its original state A repair expert system implements automatic repair of the system That accomplish by building the capability of diagnosis debugging and planning into it The system locates the trouble suggests the fault candidate list works out a plan and then implements it 68 4 4 Electronic Fault Diagnosis Diagnosis is concerned with producing a hypothesis to explain why the observed behavior of a system is different from its expected behaviour This definition of diagnosis is particularly suitable in the area of electronic fault diagnosis In general diagnosis has two tasks The first task is to find hypothesis a fault that explains the malfunctioning of the device or to produce a hypothesis a disease that explains a particular set of symptoms The second task in both cases is the extraction of extra information that is requir
7. ATN The ATN or attention is issued only by the controller to indicate that the byte on the bus is a command address and not data SRO The SRQ or service request is issued by any device needing service from the controller REN The remote enable connections is issued by the controller when it wants remote control over all the instruments on the bus EOI The EOI or end or identify send by the talker with the last byte of a data stream to indicate end of data 3 3 4 Addressing As all instruments share a common bus there must a method of selecting an instrument from others to make it do something specific The IEEE 488 bus protocol does this by allowing the controller to send an address down the bus before some command data is sent The addressed instrument recognizes its address and prepares itself for some kind of activity An address may sent down the bus by making low at the same time as transmitting a Hex address in the range 20 to 3E corresponding to address 0 to 30 in decimal if the instrument is to become a listener Alternatively making ATN low with Hex 40 to will make the addressed instrument a talker 28 Instruments generally have the same address for talk or listen set by the address selecting DIL switch or by the other ways depending on the instrument it self For example selecting 04 on the DIL switch will cause the instrument to respond to address Hex 24 for listen
8. i CALL AND COMPARING i sib um d y Pa NS VES M is 3 d 7 EXPECTED t DAMAGED z E PRONLEM IN THE 1 ib ER 6406 GAY ARRAY 1 3 SOLENOID yrs 121 Net bu E CHECK 9 1 BAMURLLY ay HE i J85CELLUSC ORE Is NO E PUE PER i DAMAGED THE i quis ao i cabh SEND 1 10 THE j CALL GETTING 1 COMPARING 1 SIGNAL 4413 7 TES DIFFERENCE bd N 48 PROBLEN iN Mo our PROBLEM IN 15 A H 3 GETTING amp 625 PW C528 of y Muf YES EXPECTED i DAMAGE COMPONENT 18 ae LONNECT n d f 8NNEL 180 12 1 2 POINT 9 1 B id CHANNEL 10 POINTOD 1 NES ws cer SKETCH THEI DINGRAM i aLL SKETCH THEG vi 200 POINDSCD H LU THE DRIUE 15 DAMAGED pem DAMAGED COMPONENT a PON CHECK ENCODER I MANUALLY BY THE 980808001
9. Deckert J C L K Alexandridis M G Lougee W P Confidante A Computer Based Design Aid for the Optimal Synthesis analysis and operation of maintenance facilities Proceedings of Autotest Con 84 Cat No 84 CH1921 6 PP 390 404 Nov 1984 Smirnov N Experience in Organizing the Servicing of NC Machine Tools Sov Eng Res GB Vol 2 No 2 Feb 1982 Mikhailov p Veselov V Promising Developments Microprocessor Drives for Machine Tools Sov Eng Res GB Vol 3 No 12 Dec 1983 Chapurlat A de Bonnieres P Kretzschmar J Billiau R Editors Moise Expert Svstem for NC Machine Tool Trouble Diaanosis Proceedings of Operative Expert Syetems International Seminar Exhibition April 1987 Keller A 7 Kamath A R R Perera U D Reliability Analvsis of CNC Machine Tools Reliab Eng GB Vol 3 No 6 Nov 1982 Padraig Cunningham Michael Brady Knowledge Based Systems for Fault Diagnosis AICS Irish Conference on and 142 36 37 38 39 40 41 42 43 44 45 46 Cognitive Science UCD Dublin Sep 1988 Brown J S Bruton R R deKleer J Pedagocial Natural Language and Knowledge Engineering Techniques in SOPHIE and 111 Intelligent tutoring system eds D Sleeman J s Brown PP 227 282 Academic Press 1982 Clancey W J The Evistemology of Rule Based Expert Syste
10. Martin D J Development of to Diaanose the Health of Metal Cutting Machinarv Sensors 85 Conference MS85 1000 1 12 Nov 1985 Rault A Brunet J Deviq Ephraim P Modelling and Identification for Machine Tool Fault Detection and Diagnosis Proceeding of the 25th IEEE Conference on Decision and Control Cat No 86 CH 2344 0 PP 808 12 Vol 2 Dec 1986 James S Bennett DART An Expert System for Computer Fault Diaanosis Augast 1981 Randall Davis Howard Shrobe Walter Hamscher Diagnosis Based on Description of Structure and Function AAAI 1982 Vol 82 PP 137 142 1982 Davis H Shrobe The Hardware Troubleshooting Group SIGART Newsletter Vol 93 PP 17 20 July 1985 Robert Neches William R Swartout Johanna Moore Explainable and Maintenable Expert Systems IJCAI 85 PP 141 28 29 30 31 32 33 34 35 382 389 August 1985 Los Angles Beichelt F Fischer K Optimum Control of Automatic Svstems Under Uncertaintv Control Science and Technology for the Progress of society Proceedings of the Eighth Triennial World Congress Of the International Federation of Automatic control PP 875 880 Vol 2 Aug 1981 Dormer Real Time Process Optimisation Factory 2000 Integrating Information and Material Flow Publ No 80 31 Aug 2 Sep 1988 Pattipati R Shaw J J
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12. Asynchronous Asynchronous Asynchronous Asynchronous Synchronous Synchronous Synchronous TTY Telety pewriter data is accomplished by of data is being transmitted character at the end of transmission it This assumes that Application Baudot TTY ASCII TTY FSK MODEM FSK MODEM FSK MODEM PSK MODEM PSK MODEM PSK MODEM Commonly Used Baud Rates in these devices All other systems transmitted with clock bits transmitting of information by asynchronous the start of transmission and extended period of time synchronous communication is obviously much more efficient Since this synchronous communication can computer manufacturers have developed 20 take standard forms 1 start and 1 In a synchronous requires communications protocols such BISYNC binary synchronous communications and HDLC high level data link control Syncronizauion End of transmission Bisyne data format Information N bits Opening address control _________ Error check fig 3 3 Two Forms of Synchronous Serial Communications Protocols closing 16 bit CRC 01111110 HDLC SDLC data format These type of protocols are illustrated in fig 3 3 BISYNC is a byte oriented protocol SDLC and HDLC are both bit oriented protocols 76 3 3 2 The Solution The IEEE 488 parallel data transfer standard was developed by the Hewlett Packard Corpora
13. Embedded system This program is just a portion of another larger program First the expert system is built into an algorithmic program This is illustrated in fig 4 1 Second an algorithmic program is built into an expert system This is illustrated in fig 4 1B 28 COMPUTER MEMORY MEMORY rear tr m ALGORITHMIC PROGRAM EXPERT SYSTEM fig 4 1 Types of Embedded Systems VP Expert is a real example of the embedded system It links to an external software package such as a TURBO C system During the inferencing process the VP Expert system may reach out and access data in TURBO C to get enough knowledge to reach a solution While these programs are not really embedded the effect is the same They usually share memory with the expert system have program links to it 48 4 3 5 Expert System Architecture An expert system is simply an arrangement of software components that permits an expert s knowledge to be used by others for problem solving and decision making in a specific domain The main components of an expert system are the knowledge base the inference engine the data base and the user interface A general block diagram is shown in fig 4 2 Each of these elements will be explained in the following sections DATA BASE KNOMLEDGE BASE mA WORKING MEMORY 1 USER INTERFACE 2 X i USER i x a fig 4 2 A General Block Di
14. jump delay or reset action 3 Data display in state table or timing diagram formats 4 Simple menu oriented user interface featuring a front panel keyboard and a display screen with touch sensitive on screen softkeys 5 Auto acquisition mode for repeated acquisitions without manually restarting the instrument 6 Expandable acquisition memory depth with memory chaining feature 7 Data search and compare functions 8 Non volatile memory ensures that two instrument setups the current setup and another setup of the user choice are not lost when power is turned off 9 Full programmable by adding the GPIB COMM pack to the Logic Analyzer 37 3 5 1 Addressing 1241 Logic Analyzer The operations of the 1241 Logic Analyzer are controlled through menus displayed on the screen Use the MENU keys on the front panel to select general menu groups select individual menus through on screen soft keys Each soft key is outlined on the screen and has a label describing its function The menu groups as illustrated in fig 3 13 consist of five keys to select from CONFIG TRIGGER DATA EDIT UTILITY EXECUTE SCROLL START STOP MENU CONFIG 2 cor 8 Lid e GLITCH DON T CARE Ce w UTILITY fig 3 13 The Front Panel of the 1241 Logic Analyzer 38 The UTILITY menu key should pressed
15. lt 1 7 CALL GETTING AND COMPARING SIGNAL 3 1 5 p ALLORARE EXPECTED DAMAGED COMPONENTS W y 1 I 19m 3 C2 COMPONENTS 1 98586 2 a E 17 EXIT i j AME NN 4 THE PROB AT i j POUT i sath 1 SKET THE CIRCUIT amp 200M PAINI f 1 CALL AND COMPARING 314691 1 4 3 1 A Ny MFFERENCEN 125 bos QU SHEE iNO PUT THE PROB SOTHE 1 2 3 LL SMETON ch Tae CIRCUIT ZOOM HOINT 112 1 SETTING AND COMPARING 1 7 d ALLORABL M TOLERA 555 lt HO 2 MOTORS WORK gt 27 i E 5 s a i ES E MS 2 2 9 59 nE H h Arve EXPECTED DAMAGED COMPONENTS CL URS 2 723 3 4 17 uw P PROBLEM HE s EEN 72733 PUT 260 T THE PROB at AINT 13 ae mame ne JES 170 ULL s rim SCHEMATIC af AGHRM a ur 7 SKETCH TAE Layout CIRCUIT 4 2 ZION POLNT 13 a
16. DRIVE MOT OTOA Q r 4 CONTROL OPTICAL INDICATORS ENCODER 12V 95 7325 ONLY FRONT PANEL fig 7 1 7475A Simplified Block Diagram The two drive motors reversible motors Encoders on each motor transmit rotation data back to their respective servo IC One motor drives grit wheels which moves the plotting medium while the other motor moves the pen across the plotting surface The most of the plotter s faults usually happen in the power supply motors and in the motor servo systems Because of that EXP Test System attempted in its electronic fault diagnosis to cope with all these faults and define the damaged components inside these units Two identical servo systems are used to drive the motors Fig 7 2 shows the block diagram of a motor servo system 113 FROM PROCESSOR THROUGH GATE ARRAY SERVO CONDITION CIRCUIT IPART OF GATE ARRA YI OPTICAL ENCODER MOTOR DRIVERS 18 26V UNREGULATED OF GATE ARRAYI PROCESSOR fig 7 2 Motor Servo System Block Diagram Digital move commands are generated and sent by the microprocessor through the gate arrays to the servo chips The servo chips provide the interface to the microprocessor decodes the encoder signals sums position errors estimates velocity and sums Yt and transforms the servo error to pulse width modulated output The servo chips output the pulse w
17. Database for Diagnostic Expert System Computer Sep 1984 L F Pau Survev of Expert Svstems for Fault Detection Test Generation and Maintenance Expert Systems Vol 3 No 2 April 1986 Dana S Nau Expert Computer Systems Computer Feb 1983 Randall Davis Howard Shrobe Representing Structure and Behaviour of Digital Hardware Computer Oct 1983 Padraig Cunningham Knowledge representation Electronic Fault Diagnosis P HD Thesis Trinity College Dublin 1989 Gleeson J F J _ An EMYCIN Based Expert Syste or Electronic Fault Diagnosis M Sc Thesis Dept of Computer Science Trinity College Dublin 1986 Wally Wang John Mueller Illustrated VP Expert Wordware Pub Inc 1989 Paperback Software VP Expert 1987 J L Alty J Coombs Expert Systems Concepts and Examples The National Computing Centre Limited 1984 Louis E Frenzel Jr Crash Course in Artificial Intelligence and Expert Systems USA 1987 John D 1 Handbook of Practical Microcomputer Troubleshooting Reston Pub Company Inc 1979 Allen Buckroyd Computer Intearated Testing BSP UK 1989 S J Cahill Designing Microprocessor Based Digital Circuitry PHI 1985 Paul C Barr Ronald L Krimper Michael R Lazear Christopher Stammen _ CAD Principles and Applications W 145 73 74 75 76 77 78 79 80 81 82 Systeems Inc 1985 Patrick Carberry CAD CAM with Personal Comp
18. If the expert system was developed using modern development tools it is a simple matter to modify the knowledge base by writing new rules or removing rules 4 3 6 3 Transportability The wider the availability of an expert system the more useful it will be The more different types of computers for which the expert system is available the more widely the expertise can be used 4 3 6 4 Adaptive Learning Ability This is an advanced feature of some expert systems that allows them to learn from their own use As the expert system is being operated the inference engine will draw conclusions that 54 produce new knowledge This new knowledge is stored temporarily in the data base but in some systems they can lead to the creation of a new rule which can be stored in the knowledge base and used again in a future problem 4 3 7 Uncertainty Expert systems has the ability to deal with uncertain information If an expert system in collecting its initial inputs ask a question for which the user does not has answer the user can simply say that he does not know Expert systems are designed to deal with inputs such as this There are several methods of dealing with uncertain information In rule based expert systems numerical factors indicating the probability of conclusion are used as a measure for uncertainty These numerical factors are known as certainty factors CF 4 3 8 Fuzzy Logic Fuzzy logic is another method of d
19. LOUTPHT Y Pig tu THE PROB aT FREE EDGE 10 1 1 1 CALL i 4 ke TIME t ZOOM 66 4 1 M 3 uETTING AND COMPARING i SLGRAL 16 i EE as DIFFERENCE YES aLLOWABL a TOLERA NACE 7 41 S74 EXPECTED DARAGED EN TS ti 4 638 39 049 7 2 CR 3 CRIA CRIS y vd DAMAGED COMPONENTS 41 631 014 7 EXIT maama oo amp s t PROBLEM I POLNE o Lek i P PHRDCOMNECT 5422 1 TS ipn THE PROB pun t aT i VES A ow FERENCE S uan ie TOLERA M EXPECTED DAMAGED i COMPONENTS 1 i n 2 DLEFERENCE ALLOWABL S TOLERG UC lt FRORLEM of THERM 1 E i i Zoom POINT 09 7 80 1 uRTTING SMD COMPARING SiGHAL 3 m 91 LOHARL COLERA g SHE p p 4 1 yes i D DT 2 E wd E m1 x cuo e THE 1 0 1 1 OL EFENENCI EN Ho i UN CIRC cut 00 PAINT
20. M iN THE 591 OUTPUT BRTMERM l POEMT 30 i ND y 1 4 COLL sketch the amp point 13 CALL GETTING AND COMPARING SIGMAL 63 i hao o 28 Y p DIFFERENCES 1 ALLOMABL 2 3 APOLERA 27 E d THE EXPECTED DAMAGED COMPONENTS Fi dg Qu i m 3 628 038 PROBLEM 700 53 6 Bue i ie POINT CI amp POINICL Y 3 Ec PUT b PROB AT ONT CALL sketch the einem amp znom Paint 3 i CALL GETTING AND COMPARING SIGNAL 143 un d THE EXPECTED tHE EXPECTED DAMAGED AGED t COMPONENTS 1 COMPONENTS Ci d i 15 d i0 632 3 C37 y EXPECTED DAMAGED COMPONENTS t1 3 2 7 Pu THE PROB POINT 5 m ji call 1 8x T SOOM 01 5 i CALL GETTING uM COMPARING SEGNAL 45 i PUT THE PROB AT i 1 7 1 i 3 Le came 7 R 1 CALL SEETCH MR CIRCUIT amp ZOOM POINT 273 v CALL SETTING AND COMPARING SIGNAL ci 7 Ne uz Td MLFFERENCESN _5 STOLE N Yao 9 3 PROBLEM
21. NO 134 CONNECT POD 0 CHANNEL 0 TO POINT A AND PRESS START BUTTON ON THE LOGIC ANALYZER FRONT PANEL WAIT TILL THE ANALYZER GET DATA ON IT S SCREEN THEN CHOOSE YES AND PRESS lt ENTER gt OTHERWISE CHOOSE NO AND PRESS lt ENTER gt YES NO THE INPUT OF THE PAPER MOTOR DRIVERS IS OK YOU SHOULD MAKE TEST TO ANOTHER POINTS DEFINE THE DAMAGED COMPONENTS PRESS ANY KEY TO CONTINUE The user should press any key CHOOSE YES THEN PRESS ENTER TO SEND THE SUITABLE SETUP OTHERWISE CHOOSE NO AND PRESS ENTER YES NO CONNECT POD 0 CHANNEL 0 TO POINT A AND POD 0 CHANNEL 1 TO POINT E AFTER THAT RUN THE INTERNAL TEST PROGRAM AND PRESS START BUTTON ON THE LOGIC ANALYZER FRONT PANEL WAIT TILL THE ANALYZER GET DATA ON IT S SCREEN THEN CHOOSE YES AND PRESS lt ENTER gt OTHERWISE CHOOSE NO AND PRESS lt ENTER gt XES NO THE PROBLEM IS DEFINED THE EXPECTED DAMAGED COMPONENTS ARE 1 U2 2 04 08 3 CR5 PRESS ENTER THEN Q TO EXIT 135 The preceding examples are just some of the examples of fault cases with which EXP Test System has been tested These tests indicate that it is reasonable to expect the EXP Test System to be able to diagnosis better than 70 of faults in the HP 7475A Graphics plotter The flow chart of EXP Test System is shown in appendix A Some conclusions on this research and some directions for further research will be given i
22. Schedulina of Generating Units J Inst Eng India Electr Eng Div Vol 66 pt EL1 41 45 Aug 1985 Konstantionova Raikin A L Optimal Scheduling of atio volvi ipment Stoppa in Continuous Process Svstems Avtom and Telemekh USSR Vol 42 No 6 PP 170 180 June 1981 Vergin R C Scriabin Maintenance Scheduling for Multicomponent Equipment AIIE Trans USA Vol 9 No 3 PP 297 305 Sept 1977 Park K S Optimal Scheduling ef Multiple Preventive Maintenance Activities Microelectron and Reliab GB Vol 23 No 2 PP 351 354 July 1983 Yamayee 7 Sidenblad Yoshimura M A Computationallv Efficient Optimal Maintenance Schedulina Method IEEE Trans Power Appar and Syst USA Vol PAS 102 No 2 PP 330 338 Feb 1983 140 18 19 20 21 22 23 24 25 26 27 Sivazlian D Optimum Scheduling of a New Maintenance Proar U Stochastic Degradation Microelectron Reliab UK Vol 29 No 1 PP 57 71 1989 Smiley G Rotation Machinarv Monitoring and Fault Diagnosis Sound and Vib USA Vol 17 No 9 PP 26 28 Sept 1983 Roger T Hartly CRIB Computer Fault finding Through Knowledge Engineering Computer March 1984 Sylla C Diagnosis Interval Estimation in Process Analysis for Troubleshooting Tasks Computer Ind Eng UK Vol 17 PP 519 524 1989 Neun J A Walter
23. between the test and the reference signals to calculate the difference In the end it will define the allowable tolerance and save it with the difference in a text file called RESULT The second part get the test digital signals from U U T through the IEEE Interface Card by using the Logic Analyzer Then this program will convert the captured data the raw data in ASCII code to a useful interpretation After that it will call the reference file and compare between the test and the reference signals to calculate the sum of the total difference which equals zero if the plotter is in good condition In the end it will save the sum of the total difference value in a text file called RESULT Getting and Proving Input Output This program will get the test digital signals from U U T through the IEEE Interface Card by using the Logic Analyzer The input and the output signals of the inverter 123 can be captured by using the multi channels pod of the Logic Analyzer Then this program will convert the captured data the raw data in ASCII code to a useful interpretation After that it will check that the input signal is opposite to the output signal to prove that the inverter is ok and save the result in RESULT 5 Getting the Setup Information from the Logic Analyzer This program will just get the setup information from the Logic Analyzer and save it in a setup file 6 Sending the Setup Information to the Logic Analyzer
24. circuits Real digital circuits are more complex than this So it seems likely that pure model based expert systems for fault diagnosis will be estimately very difficult for the expected future This is very similar to the case with analog circuits where quantitative models are very complex 24 40 42 4 9 Advantages and Disadvantages of Shallow and Deep Knowledge Based Systema The advantages and the disadvantages of both deep and shallow knowledge based systems will be presented in summary in this section 65 4 9 1 Advantages and Disadvantages of Shallow Knowledge Based Systems The advantages of the shallow knowledge based systems are 1 Speed of execution 2 Ease of representation of expert knowledge shallow rules The disadvantages of the shallow knowledge based systems are 1 Difficult to extend the knowledge base 2 Will not perform well on problem cases not considered in system construction 3 Knowledge may be distributed throughout the system and therefore difficult to alter 4 9 2 Advantages and Disadvantages of Deep Knowledge Based Systems The advantages of the deep knowledge based systems are 1 Should be able to perform reasonably well cases not considered explicitly in the construction of the system 2 Easily altered to operate in another problem situation by changing the model The disadvantages of the deep knowledge based systems are 1 Slow of execution 2 Reasoning mechanism w
25. comes up with a corrective solution 4 3 9 3 Design Design information for certain types of products can be stored in an expert system A user can then call the expert system to design the product 4 3 9 4 Diagnosis Expert systems can be used to diagnose a malfunction in device or system From this aspect they are similar to debugging expert systems except that they do not give solution to the problem A diagnosis system observes the behavior of the device or 56 system and makes note of improper performance 4 3 9 5 Instruction An expert system domain can be used in teaching students how to solve problems in the field of expertise The student can work through different problems with the expert system By using the explanation subsystem the student can notice the sequence of rules being used to reach a conclusion So the student can get idea about what knowledge an expert needs and how it is used to solve problems 4 3 9 6 Interpretation Interpretation is one of the best applications for an expert system Interpretation systems are given inputs that consist of observations and other data Then using its knowledge base and inferencing system the interpretation system attempts to deduce particular situation from the input data It attempts to explain the situation which it represents 4 3 9 7 Planning A planner attempts to come up with a method or approach that will achieve a goal Given the objective
26. complete automation of some of the design processes In the early 1970s interactive computer graphics became a practical tool for supporting graphics based design Presently the great majority of computer based work stations supporting design are of the interactive computer graphics type During the preceding twenty year period the acronym CAD has been used to apply to any or all of the various application areas 72 Computer aided design CAD or designing with the aid of a computer has evolved to the point where each one will be exposed to its capabilities Today designing with the aid of a computer is not reserved for a chosen few Anybody who has a popular personal computer could purchase a CAD package for a few hundred dollars and begin designing today 73 c Svst 6 2 1 Overview The objective of CAD is to increase productivity by utilizing computers in the design process The meaning of productivity here is the ratio of labor hours required for a manual design function to the labor hours required if a computer is used to support the 89 function CAD is a broad subject that fits into a broad spectrum of automated methods The following diagram fig 6 1 shows the place of CAD in the spectrum of automated methods Automated methods Construction Group MRP Engineering Manufacturing management technology and design CAM Simulation Optimization Computer Computer aided aided engr design CAD Computer aided Computer a
27. conditions are found the rules are fired As the rules continue to fire they will reference one another and form an inference chain Each time a new rule is examined it is checked against the current status of the problem solution stored in the data base The firing of a particular rule may add new facts to the data base This gives the inference engine additional information to go This process continues until the solution is found The inference engine can take two basic approaches to search for an answer These are forward and backward chaining 51 Forward Chaining In this case the inference engine attempts to match a fact in the data base to the situation stated in the IF part of the rule Once a fact has been matched the rule is fired The action stated could produce a new fact that is stored in the knowledge base This new fact may then be used to search out the next appropriate rule This searching and matching process continues until a final conclusion rule is fired Backward Chaining In this case the inference engine starts with the hypothesis in the data base Then it begins examining the THEN parts of rules looking for a match The inference engine searches for evidence to support the hypothesis originally stated If a match is found the data base is updated recording the conditions that the rule stated as necessary for supporting the matched conclusion The chaining process continues with the system attempting to mat
28. facts contained in the knowledge base 42 4 2 1 Application of Artificial Intelligence The artificial intelligence software can be adopted to any problem requiring its special qualities a problem with no algorithmic solution because of the unbelievable flexibility of the artificial intelligence process Non numerical problems and problems with uncertainty which are often not suitable for the algorithmic process are both easily solved with artificial intelligence techniques With algorithmic software the problem is guaranteed to be solved with AI there can be partial solutions or even no solution As a result AI often fits the disorganized imperfect real world better than conventional software because it can deal with shades of gray 68 The most important applications to artificial intelligence are 1 Games 2 General Problem Solving 3 Expert Systems 4 Natural Language Processing 5 Computer Vision 6 Robotics 7 Education 4 3 Expert Svstems The major use of artificial intelligence nowadays is in expert systems Expert systems are the artificial intelligence programs that act as intelligent advisors or consultants By using the stored knowledge in a specific domain a non expert user can solve problems and make decisions in a subject area nearly as well as an expert 43 An expert system permits the knowledge and experience of one or more experts to be captured and stored in a computer This knowled
29. information not contained in the knowledge base Then the inference engine will search for a CHOICES 70 statement naming the same variable which creates a menu of options to accompany the question during a consultation In the studied case the ASK statement will ask the user TO CHECK THE TRANSFORMER DISCONNECT THE TRANSFORMER S OUTPUT FROM 029 THEN PUT THE OSCILLOSCOPE S PROBE AT POINT 1 TO LOCATE POINT 1 AND CONTINUE THE TEST CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER The choices will be YES NO Here the user makes choice so if he chooses YES YES becomes the value of CHECK TRANSFORMER Since the inference engine has found a value for CHECK TRANSFORMER it will go back to rule POWER SUPPLY to give CHECK TRANSFORMER the defined value Since the value of CHECK TRANSFORMER is YES the inference engine will fire POWER SUPPLY When POWER SUPPLY is fired the inference engine will calls first of all the SKETCH1 file which draw the schematic diagram of the circuit then the inference engine calls the SKETCH2 file which draw the layout diagram of the circuit then the inference engine calls the EXP T1 file which get the signal from the peripheral instruments and compare it with the reference signal and give the result value to variable deltal and calculate the allowable tolerance and give its value to standerl then EXP T1 program saves deltal and standerl in a text file FILE9 The inference e
30. intelligent workstation captures the important part of the deep knowledge of the system because the Graphic element is very important we will devote a complete chapter to explain the integrating graphic CAD knowledge with expert system and on line test Technician The technician being considered is a practitioner with limited experience This means a technician with only a brief training period on guided service procedures is suitable So an expert with a high level of performance is not required The union of these three elements comprises the intelligent mobile workstation As mentioned the intelligent mobile unit contains the shallow knowledge and the deep knowledge It is very difficult to incorporate all the knowledge inside the knowledge base of the system in a short time or during the creation of the system So just the shallow knowledge is included in the production rules IF THEN of EXP Test System at the early stage By using the system it would be essential for the user to refine the shallow knowledge and to add new cases which are encountered during the use of this system The shallow knowledge is updated and it expands continuously while the system is being used EXP Test System contains nearly one hundred production rules these rules contain the knowledge of the expert in the CNC machine A two dimensional Graphic facility has been incorporated in this work the physical dimension layout diagram and the functional dimension s
31. is being added continually Experts continue to gain different experiences and improved problem_solving methods All of this should be incorporated regularly into the expert system to keep it up to date The rule format makes this easy because it breaks the knowledge down into small pieces So an old rules can be rewritten to accommodate changes Also a new knowledge is added by simply writing new rules and storing them in the knowledge base 72 5 INTEGRATING EXPERT SYSTEM AND ON LINE TEST 5 1 Introduct The term expert system refers to a computer program that is largely a collection of heuristic rules rules of thumb and detailed domain facts that have proven useful in solving the special problems of some technical field Expert systems to date are an outgrowth of artificial intelligence AI a field that has for many years been devoted to the study of problem solving using heuristics to the construction of symbolic representations of knowledge about the world to the process of communicating in natural language and to learn from experience Expertise is often defined to be that body of knowledge that is acquired over many years of experience with a certain class of problem One of the hallmarks of an expert system is that it is constructed from the interaction of two very different people a domain expert a practicing expert in some technical domain and a knowledge engineer an AI specialist skilled in analyz
32. outputs then it is faulty 35 The strategy which EXP Test System uses to trace electronic faults depends on regressing along a faulty line This is very similar to that which the technician does in the diagnosis of electronic faults So for example a bad signal is found at the 5V output of the power supply the EXP Test System will trace all the signals on that line with the intention of defining the damaged components 7 2 U U T description As mentioned EXP Test System was developed for electronic fault diagnosis in CNC machines Because of the unavailability of a CNC machine in the electronic school the HP 7475A Graphics plotter has been used as U U T unit under test The HP 7475A Graphics plotter has the same principle of the CNC machines Fig 7 1 shows the block diagram of HP 7475A Graphics plotter The HP 7475A Graphics plotter uses microprocessor based logic to convert digital instructions into a graphic plot The microprocessor receives instructions from either an internal ROM read only memory program external controller through the I O input output circuits It then issues data to the pen drive and paper drive motor servo systems and the pen down circuit to produce the plot 112 SIX CAROUSEL CAROUSEL MOTOR PEN DOWN ORIVER Jata BUS ier i CONTROLLER 3208655 BUS MOTOR i e MOTOR 5 DRIVER GATE 2 ARRAYS OPTICAL ENCODER PAPER
33. printed circuit boards in both time and cost The productivity gained by using a printed circuit CAD system compared to the manual method can be up to four to one A printed circuit CAD system automates repetitive and time consuming tasks such generating bills of materials and manual design checking The application programs for printed circuit design aid the designer in drawing the schematic diagram directly on the screen A library of circuit symbols available on line are used to place components on the schematic diagram When finished the drawing can be reproduced by high quality pen plotter or a simple printer A CAD method allows a design engineer to create on line finished schematic diagram drawings CAD systems contain pre stored chip descriptions and component symbols in a library These library symbols become the building blocks 92 for schematic diagram design A CAD system must consist of a cpu a storage device like a floppy disk drive a monitor an input device such as digitizer or mouse and a keyboard The software required is an operating system for example for a personal computer MS DOS graphics software for example OrCAD SDT III System and a database to control the storage or the drawings produced All the graphic installations have two basic parts hardware and software The hardware is the computer and its associated peripherals 6 2 2 OrCAD SDT III System OrCAD SDT III System is complete an
34. purpose hardware The appearance of micro computerization and more user friendly computer program languages led us to investigate the application of these new techniques to corrective maintenance of NC machine tools 33 2 Summarv of the Project Usually any workshop which contains a large number of CNC machines has its special workstation This workstation is controlled by a service engineer who is responsible for solving any problems that might happen to any of the machines in the workshop In the case of a breakdown to any machine the service engineer will collect all the information about the machine and equiped with service catalogues and some testing devices will go to the machine location to fix it That work may take or two weeks with a non expert person and may only take hours with expert As a result maintenance engineers are forced to keep up with advances in any technology that will reduce downtime But as mentioned in the case of the absence of the expert person the maintenance will depend on the non expert who will take a long time to fix the broken machine This project concentrated on CNC machine corrective maintenance So an intelligent mobile workstation was developed for this purpose Fig 1 1 shows the intelligent mobile workstation mobile unit inside the CNC machine workshop This intelligent mobile workstation is controlled by EXP Test System the expert system MACHINE MACHINE CHC
35. sec 2 2 1 and may only take hours with an expert person who has the service engineer s specification 2 4 The Alternative Solution To solve the problems which will face any manufacturer when installing workstations inside his plant which contain CNC machines and to allow service engineers or technicians to carry out the necessary maintenance to any of the machines an intelligent mobile unit was developed controlled by expert system Two situations have been mentioned viz 1 Maintenance where the skill level of the maintenance engineer or technician is uncertain 2 Maintenance where the skill level of the maintenance engineer is high In specifying the workstation the intention is to assume the realistic situation of an uncertain skill level in the maintenance staff arising through inadequate training turnover etc whilst attempting through maximum support in the workstation to achieve the level of performance possible with the highly skilled maintenance person Translating this intention into appropriate technology hardware and software is the essence of this project The make up of the hardware has already been hinted at The major components are 1 A controller Personal Computer 11 2 Digital Oscilloscope 3 Logic Analyzer 4 A suitable hardware interface 5 Probes and other ancillary equipment In chapter three the hardware make up of the workstation is dealt with in more detail In defin
36. the reference signal Then calculating the difference and the allowable tolerance and save them in a text file called RESULT EXP Test System will take these two values from RESULT and will compare them to define the problem and the solution In the case of using the logic analyzer to get the test signals EXP Test System will call the Sending Setup Information program which gets the setup information from the setup file and sends it to the logic analyzer EXP Test System will call Getting and Proving input output program for testing the condition of the inverters in the motor servo systems To test the output of the encoders the feedback signals EXP Test System will ask the user to put the oscilloscope s probe at the 121 encoder s output and define the quality of the signals This is the only case which EXP Test System asks the user for the quality of the signal That is because of the confusion which the feedback causes during testing the motor servo systems The motor usually stops in the case of any fault in the motor servo system that will cause the feedback signal to vanish So if EXP Test System calls Getting and Comparing the Test Signals program to compare the feedback signal with a reference signal it will conclude that the problem is always in the encoder whereas it might be in any part of the motor servo system 7 4 2 1 Supporting Software The supporting software was developed to enhance the automatic work o
37. this project the role of expert systems in electronic fault diagnosis has been reviewed the significance of electronic systems 137 failure in machine downtime determination has been stated workshop facility suited to repair with maximum support has been defined and an example workstation implemented based on an integration of hardware and software with instrument interrogation complementing instruction or direction from expert system and circuit data reproducible on request from a CAD data base Substantial additional work is required to produce a flexible and usable system that will enable the development of a workstation that will accommodate the updating necessary to cope with new repair situations However with CAD data base information available from machine manufacturers it is conceivable that a flexible intelligent repair station can be produced 138 1 2 3 4 5 6 71 81 91 REFERENCES Berutti A Decentralized Maintenance for Automated Plant Electr Constr and Maint USA Vol 83 No 3 PP 65 69 March 1984 Barbara Y White and John R Frederiksen Qualitative Understanding of Electrical System Troubleshooting SIGART NEWSLETTER Journal paper 1985 Webb A Solving the Maintenance Problem MOD MACH SHOP USA Vol 52 No 2 PP 90 94 July 19 Moorhead J Getting the Handle on NC VII Programming Maintenance Operation MOD MACH SHOP
38. what is wanted from the user is to test these components and change the faulty one The previous test was one of many tests which applied the EXP Test System to improve its capability in troubleshooting faults in the plotter s power supply The second fault was simulated by getting the input point A and the output point E signals of the inverter paper motor drivers from the input only This will indicate that the paper motor drivers which invert the input signals is faulty This is because the input and the output signals will be the same two signals from the same source This example will show the capability of EXP Test System in defining the damaged components in the digital circuits motor servo system The motor servo system fails test P D MOTOR5 The dialogue was as follow the underlined text is the user choice 130 WELCOME TO EXP Test SYSTEM SYSTEM FOR TESTING CNC MACHINE PRESS ANY KEY TO CONTINUE The user should press any key CHECK THE MAIN POWER PLUG 220 ACV IF THE MAIN POWER IS OFF MOVE THE CURSOR TO OFF AND PRESS ENTER IF ON PRESS ENTER QN OFF TO CHECK THE TRANSFORMER DISCONNECT THE TRANSFORMER S OUTPUT FROM J9 THEN PUT THE OSCILLOSCOPE S PROBE AT POINT 1 TO LOCATE POINT 1 AND CONTINUE THE TEST CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER XES NO THE TRANSFORMER IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE The
39. will close the data file At this stage a complete schematic will appear on the screen So the Sketch Program will draw a blinking rectangle around the test point to draw the attention of the user to the wanted place This blinking rectangle will continue for 20 seconds then the Sketch Program will clear the screen and will zoom onto the area inside the rectangular Also the test point will be shown blinking on the screen to notify the user of the correct position of the test point After a while in addition to the schematic diagram a PRESS ANY KEY TO CONTINUE sentence will appear the screen to force The Sketch Program to wait until the user presses any key on the keyboard 107 the user pressed any key the Sketch Program will shut down the graphics mode and exit The convert function consists of two functions The first one is x conv function which convert x values from the plotter scale to the screen scale The second function is y conv function which convert y values from the plotter scale to the screen scale In the beginning when the plot file is created the size of the paper which the plotter will plot the schematic on is defined to A4 The location of the coordinate origin 0 0 plotter units and the orientation of the X and Y axis is shown in fig 6 4 tY P2 11888 7721 Jen LM 22 8 ORIGIN Y fig 6 4 The Location of the 0 0 Plotter Units The A4 size paper area is di
40. 9 Repair Electronic Fault Diagnosis Shallow Knowledge Shallow Knowledge Based Systems Deep Knowledge Deep Knowledge model based systems Based Systems 9 1 Advantages Disadvantages Based Systems 9 2 Advantages and Disadvantages Systems Knowledge 10 1 Exp Test System Introduction 58 60 60 61 63 Advantages and Disadvantages of Shallow and Deep Knowledge 65 of Shallow Knowledge of Deep Knowledge Based 66 73 73 2 Using Expert System in Building Intelligent Workstation Improving the Productivity Developing an Intelligent Mobile Workstation for On Line Test 6 INTEGRATING GRAPHIC CAD KNOWLEDGE WITH EXPERT SYSTEM AND ON LINE TEST 6 1 6 2 INTRODUCTION CAD System 2 1 Overview 2 2 OrCAD SDT III System 2 3 OrCAD Plot File Programs Integrating OrCAD SDT III System with EXP Test System 7 IMPLEMENTATION 75 Introduction description Approach Adopted Design and Development 4 1 Introduction 4 2 Structure 7 4 2 1 Supporting Software 7 4 2 2 Designing the Rule Set 7 4 2 3 Domain expertise 7 4 2 4 Knowledge Engineering Certainty Factors 74 76 76 89 89 89 99 109 111 111 112 117 117 127 7 6 EXP Test System in Operation 127 8 CONCLUSION 137 REFERENCES 139 APPENDIX CHAPTER 1 INTRODUCTION 1 1 Motivation for the Project During
41. ACHINE PRESS ANY KEY TO CONTINUE The user should press any key CHECK THE MAIN POWER PLUG 220 ACV IF THE MAIN POWER IS OFF MOVE THE CURSOR TO OFF AND PRESS ENTER IF ON PRESS ENTER oN OFF 128 TO CHECK THE TRANSFORMER DISCONNECT THE TRANSFORMER S OUTPUT FROM 49 THEN PUT THE OSCILLOSCOPE S PROBE AT POINT 1 TO LOCATE POINT 1 AND CONTINUE THE TEST CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER XES NO THE TRANSFORMER IS OK PRESS ANY KEY CONTINUE TESTING THIS DEVICE The user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT 2 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER YES NO THE 5 OUTPUT IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE The user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT 5 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER XES NO THE 12V OUTPUT IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE The user should press any key 129 PUT THE OSCILLOSCOPE S PROBE AT POINT 7 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER XES NO THE PROBLEM IS DEFINED THE EXPECTED DAMAGED COMPONENTS ARE 1 c3 2 VR2 PRESS ENTER THEN Q TO EXIT The EXP Test System has defined the fault candidate list which is C3 VR2 All
42. BE AT POINT 3 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER YES NO If the user chooses YES then EXP Test System will call EXP T3 which will get the signal at point 3 compare it with the reference signal and return deltal and standerl If the user 83 chooses the system will wait until the user is ready and it will prompt him again If deltal gt standerl EXP Test System will display THERE IS PROBLEM BETWEEN POINT 3 AND POINT 1 TO BE MORE SPECIFIC PRESS ANY KEY TO CONTINUE TESTING 5V LINE But if deltal lt standerl EXP Test System will display the fault candidate list THE EXPECTED DAMAGED COMPONENTS ARE 1 021 2 VR1 3 c30 4 c28 5 C5 7 That work will take by experience about 5 minutes Ifa new defect is encountered EXP Test System will be terminated after several trials and a message will be given showing that a new problem is being processed The following example explains how EXP Test System ask the user for more information and tell him that a new case is encountered This example will check the drive motors of the U U T to define if the malfunction is from one of the motors from the motor s driver 84 SWITCH THE PLOTTER U U T PUT BLANK PAPER ONE AT LEAST NO1 THEN PRESS P1 amp P2 AT THE SAME TIME SWITCH ON THE PLOTTER THE TEST PROGRAM WILL RUN TESTING TH
43. CHC oc i MACHINE 1 Tha iu MACHINE fig 1 1 The Intelligent Mobile Workstation which was developed inside VP Expert system shell EXP Test System is a highly flexible user friendly and pattern_directed inference system that is adequate for hardware fault diagnosis and is accompanied by a two dimensions graphic system a functional dimension and a physical dimension The physical dimension sketches the circuit layout and the functional dimension sketches the circuit schematic this is important for accessing any component on the circuit As a result this will reduce the breakdown time of the CNC machine and will allow any maintenance engineer or technician with little experience to repair the machine quickly This he can do without returning to the service manual for information about the broken machine having an integrated system which contains complete information procedural and graphic The intelligent mobile workstation mobile unit has five SERUICE ENGINEER USER INTERFACE EXPERT SYSTEM 7 TOURBO C GRAPHIC EST SIGNALS fig 1 2 The Components of the Mobile Unit components as shown in fig 1 2 1 User interface P C screen 2 Expert system VP EXPERT 3 TURBO C system TC2 4 Graphic system OrCAD 5 Hardware system controller IEEE interface card Digital Oscilloscope and Logic Analyzer In the case of a problem the
44. DUBLIN CITY UNIVERSITY School of Electronic Engineering Master of Engineering Thesis THE DEVELOPMENT OF AN INTELLIGENT MOBILE MAINTENANCE WORKSTATION FOR APPLICATION IN AUTOMATED CNC MACHINE REPAIR Author Mustafa Houreh B Eng Supervisor Dr Charles McCorkell September 1991 THIS THESIS IS BASED ON THE AUTHORS OWN RESEARCH RESULTS ABSTRACT The project focuses electronic repair in machine This is justified given that electronic causes determine a high percentage of automated CNC machine failures An intelligent maintenance workstation is proposed as a vehicle for redressing the problem of uncertainty in the skill level of repair staff and as a means of enhancing the pace of repair under normal circumstances The suitability of expert systems in electronic fault diagnosis is established through a review of the literature and a realistic role for an expert system in the definition of the workstation is determined Circuit interrogation is carried out using a combination of instruments probes and driving software written in C Procedural guidance available from the expert system and detailed circuit knowledge is reproducible in the workstation from pre stored CAD data base files In the absence of a CNC machine to carry out the implementation a partial implementation only was possible However all of the elements were included and credibility given to the proposal ACKNOWLEDGEMENTS Iam indebted to my pro
45. Data 3 3 2 The Solution 3 3 3 The IEEE 488 Bus Lines 3 3 3 1 Data Connections 10 11 15 15 15 16 335 3 3 4 APPLICATI 4 1 Int 4 2 Int 4 2 1 4 3 Exp 4 3 1 4 3 2 4 3 5 4 3 4 3 4 3 4 3 4 3 6 4 3 4 3 4 3 4 3 3 2 Handshaking Connections 3 3 Interface Management Connections Addressing Setting the DIL Switch on HP IB Interface Card Connecting Peripherals Digital Oscilloscope Addressing HP 54501A Oscilloscope Logic Analyzer Addressing 1241 Logic Analyzer ON OF EXPERT SYSTEM IN DIAGNOSTICS roduction roduction to Artificial Intelligence Application of Artificial Intelligence ert Systems Widely Used Expert Systems Advantages of Expert Systems Disadvantages of Expert Systems Expert System s Expert System Architecture 5 1 The Knowledge base 5 2 The Data Base 5 3 The Inference Engine 5 4 User Interface Expert System Features 6 1 Explanation Facility 6 2 Ease Of Modification 6 3 Transportability 6 4 Adaptive Learning Ability 32 36 41 41 42 43 5 4 4 4 4 4 10 Systems Incorporating both Deep and Shallow 4 INTEGRATING EXPERT SYSTEM AND ON LINE TEST 5 1 3 7 Uncertainty 3 8 Fuzzy Logic 3 9 Expert System Applications 4 3 9 1 Control 4 3 9 2 Debugging 4 3 9 3 Design 4 3 9 4 Diagnosis 4 3 9 5 Instruction 4 3 9 6 Interpretation 4 3 9 7 Planning 4 3 9 8 Prediction 4 3 9
46. E OPERATION OF EVERY MOTOR THAT CALLED THE INTERNAL TEST PROGRAM BY LOOKING CAREFULLY TO THE MOTORS PRESS lt ENTER gt IF ALL OF THEM WORK PERFECTLY OR MOVE THE CURSOR TO PROBLEM AND PRESS lt ENTER gt NO_PROBLEM PROBLEM If the user finds a problem in the performance of any motor he will select PROBLEM In this case EXP Test System will print out on the screen ONE OF THE DRIVE MOTORS DOESN T WORK PRESS ANY KEY TO DEFINE WHICH ONE Now the system will ask the user MOVE THE CURSOR TO THE SUITABLE DRIVE MOTOR WHICH YOU NOTICED DOESN T WORK AND PRESS ENTER PAPER DRIVE MOTOR PEN DRIVE MOTOR PEN SOLENOID CAROUSEL STEPPER MOTOR If the user selects PAPER DRIVE MOTOR EXP Test System will display PRESS ANY KEY TO DEFINE THE DAMAGED COMPONENTS When the user presses any key the system displays 85 PUT THE OSCILLOSCOPE S PROBE AT POINT ENCAX OR THEN ROTATE THE MOTOR MANUALLY BY USING ONE OP THE BUTTONS ON THE FRONT PANEL OF THE PLOTTER IF THERE IS A SQUARE SIGNAL PRESS ENTER IF THERE IS NO SIGNAL MOVE THE CURSOR TO NO AND PRESS ENTER YES NO If the user observes the square signal on the oscilloscope s screen he will select YES In this case EXP Test System will display THE ENCODER IS OK PRESS ANY KEY TO CONTINUE TESTING THIS UNIT The user should press any key to continue then the system displays SWITCH ON THE LOGIC ANALYZER TH
47. E NO AND PRESS ENTER YES NO THE PEN COIL SUPPLY OUTPUT IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE The user should press any key SWITCH THE PLOTTER U U T OFF PUT BLANK PAPER ONE PEN AT LEAST NO1 THEN PRESS P1 amp P2 AT THE SAME TIME SWITCH ON THE PLOTTER THE TEST PROGRAM WILL RUN TESTING THE OPERATION OF EVERY MOTOR THAT CALLED THE INTERNAL TEST PROGRAM BY LOOKING CAREFULLY TO THE MOTORS PRESS ENTER IF ALL OF THEM WORK PERFECTLY OR MOVE THE CURSOR TO PROBLEM AND PRESS ENTER NO PROBLEM PROBLEM 133 ONE OF THE DRIVE MOTORS DOESN T WORK PRESS ANY KEY TO DEFINE WHICH ONE The user should press any key MOVE THE CURSOR TO THE SUITABLE DRIVE MOTOR WHICH YOU NOTICED DOESN T WORK AND PRESS ENTER PAPER DRI MOTOR PEN DRIVE MOTOR PEN SOLENOID CAROUSEL STEPPER MOTOR PRESS ANY KEY TO DEFINE THE DAMAGED COMPONENTS The user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT ENCAX ENCBX THEN ROTATE THE MOTOR MANUALLY BY USING ONE OF THE BUTTONS ON THE FRONT PANEL OF THE PLOTTER IF THERE IS A SQUARE SIGNAL PRESS ENTER IF THERE IS NO SIGNAL MOVE THE CURSOR TO NO AND PRESS ENTER YES NO THE ENCODER IS OK lt PRESS ANY KEY gt TO CONTINUE TESTING THIS UNIT The user should press any key SWITCH ON THE LOGIC ANALYZER THEN CHOOSE YES AND PRESS lt ENTER gt OTHERWISE CHOOSE NO AND PRESS lt ENTER gt YES
48. EE software system By including all the information which is important for fixing CNC machines plus the schematic diagram and layout circuit diagram inside the data base of the expert system and by making the data base follow the maintenance tree the CNC machine maintenance can be made very easy As a result this will reduce the breakdown time of the CNC machine and will allow any maintenance engineer or technician with limited experience of repair of machines to complete the service without having to refer to paper based information 14 8 HARDWARE CONFIGURATION 3 1 Introduction As mentioned in chapter 1 the intelligent mobile unit has five components which are 1 User Interface 2 Expert System 3 TURBO C System 4 Graphic System 5 Hardware System This chapter will give a more specific discussion about the hardware system which is illustrated in fig 3 1 and consists of five parts 1 Controller P C 2 IEEE Interface Card 3 Digital Oscilloscope 4 Logic Analyzer 5 Cables 3 2 Controller The controller sends the command signals to the test equipment Digital Oscilloscope and Logic Analyzer through the IEEE card those command signals cause 1 Initialize the IEEE bus and the instruments 2 Sending the setup information to the test equipments 3 Command the instruments to get the information from the 15 pIGITAL OSCILLOSCOPE HNIT HHDER
49. EN CHOOSE YES AND PRESS lt ENTER gt OTHERWISE CHOOSE NO AND PRESS lt ENTER gt YES NO Now the system will call EXP_SET1 program which will setup the Logic Analyzer When the Logic Analyzer is ready EXP Test System displays CONNECT POD 0 CHANNEL 0 TO POINT A AND PRESS START BUTTON ON THE LOGIC ANALYZER FRONT PANEL WAIT TILL THE ANALYZER GET DATA ON IT S SCREEN THEN CHOOSE YES AND PRESS lt ENTER gt OTHERWISE CHOOSE NO AND PRESS lt ENTER gt YES NO 86 At this point the expert system will call _ 11 program which will get the signal from the Analyzer and compare it with the reference signal Then EXP T11 calculates the total difference save it in variable deltal and return deltal to EXP Test System If deltal gt 0 wrong signal is received EXP Test System will display THERE IS A PROBLEM IN THE INPUT OF THE PAPER MOTOR DRIVER THIS IS A NEW CASE TO DEFINE WHICH COMPONENTS CAUSE THE PROBLEM YOU SHOULD DO SOME OTHER TESTS TO THE INPUT AND OUTPUT OF U6 GATE ARRAY PRESS lt ENTER gt THEN lt Q gt TO EXIT It is a very difficult job for an expert to know of all the types of problems which might occur to a machine That means there is always a lack in the knowledge base of EXP Test System This lack can be compensated for by integrating EXP Test System s knowledge base with the knowledge which is included in the Graphic subsystem and the knowledge of the technician So if EXP Test Sy
50. H ON THE MAIN POWER AND BE SURE OF THE CONNECTION BETWEEN THE MAIN POWER AND THE DEVICE PRESS lt ENTER gt TO RETRY THE PREVIOUS TEST But if the main power is on EXP Test System display TO CHECK THE TRANSFORMER DISCONNECT THE TRANSFORMER S OUTPUT FROM 49 THEN PUT THE OSCILLOSCOPE S PROBE AT POINT 1 TO LOCATE POINT 1 AND CONTINUE THE TEST CHOOSE YES AND PRESS lt ENTER gt OTHERWISE CHOOSE NO AND PRESS lt ENTER gt YES NO If the user presses YES EXP Test System will do the following procedures First of all it will call SKETCH1 program from the TURBO C system TO draw the schematic diagram of the circuit The user should press any key then EXP Test System will call SKETCH2 program from TURBO C system Also this program draws the layout diagram of the circuit and will cause the transformer area and point 1 to flash hence locating point 1 After that the SKETCH2 program will zoom onto the flashing the transformer area around point 1 and will display PRESS ANY KEY TO CONTINUE The user should put the probe at point 1 then he should press 81 any key on the keyboard EXP Test System will call EXP T1 program which as mentioned will return two variables deltal and standerl If deltal gt standerl if the received signal is wrong EXP Test System will tel the user that there is a problem in the transformer so it will display THERE IS A PROBLEM IN THE TRANSFORMER I SUGGEST Y
51. If the content of Comp array is AA this will signal to an arc command in the HP formatted plot file In this case some difficult work has carried out to modify the captured data to put it in the suitable format for the arc function in TURBO C The arc command in HP formatted plot file has two formats 1 PA x1 y1 AA x y start angle the arc index 2 1 1 start angle the arc index AA x y start angle the arc index The function in TURBO C has the format arc x y start angle end angle r The first format of the arc command contains the start point of the arc point 1 1 the centre of the current arc point x y the direction of the arc the start angle and the arc index The second format of the arc command contains the centre of the previous arc point 1 1 no matter what the other information inside the first part of data in this case The second part of data contains the centre of the current arc point x y the direction of the arc the start angle and the arc index While the arc format contains the centre of the arc point x y the start angle the end angle and the radius r There are two ways to calculate the end angle of the arc from the components of the arc command format If the arc index was equal 103 30 the end angle start angle 180 But if the arc index was equal 15 the end angle start angle 90 To calculate the radius of the arc f
52. OU TO REPLACE IT PRESS lt ENTER gt THEN lt Q gt TO EXIT But if deltal lt standerl if the received signal is correct EXP Test System will display THE TRANSFORMER IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE At this stage if the user presses any key EXP Test System will display PUT THE OSCILLOSCOPE S PROBE AT POINT 2 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER YES NO The Graphic facility has been connected just to point 1 to prove the capability of integrating EXP Test System with Graphic facility 82 If the user chooses YES after he puts the oscilloscope probe at point 2 EXP Test System will call EXP T2 which will get the signal at point 2 and return deltal and standerl to EXP Test System If deltal gt standerl if the received signal is wrong EXP Test System will display inside flashing window THERE IS A PROBLEM IN THE 5V OUTPUT TO DEFINE WHICH COMPONENTS CAUSE THIS PROBLEM YOU SHOULD MAKE TEST TO SOME OTHER POINTS BETWEEN POINT 1 AND POINT 2 PRESS ANY KEY TO CONTINUE But if deltal standerl then EXP Test System will display THE 5V OUTPUT IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE Assume that deltal gt standerl in the previous case wrong signal is received at point 2 If the user presses any key EXP Test System will display PUT THE OSCILLOSCOPE S PRO
53. Program will draw the schematic Sketchl or the layout diagram Sketch2 when it is called from inside EXP Test System The difference between Sketchl and Sketch2 is that Sketchl reads the data file which contains the graphical information for drawing the schematic diagram while Sketch2 reads the data file which contains the graphical information for drawing the layout diagram Fig 6 3 shows the flow chart of the Sketch Program In the beginning the Sketch Program initializes the graphics system and puts the system in the graphics mode Then it selects the style of the line which will be used for writing the text Also it will set the color of the current drawing and the current background color After that the Sketch Program will open the data file and read it Then it will check the data file to ensure that it is not empty The Sketch Program will print on the screen ERROR OPEN FILE and exit if the data file is empty If the data file isn t empty the Sketch Program will go to the next stage In the next stage the Sketch Program will scan the first three characters of the first line in the data file and save them in character array Comp Also by using strcmp function in TURBO C the Sketch Program will compare between the content of Comp and pointer to options which contains the different types of the first three characters for every line in the data file 105 SKETCH THE SCHEMATIC DIAGRAM Qe STRR
54. RAH SCHEMATIC amp LAYOUT DIAGRENS 3 ON THE SCHEEN SEARCH PROGRAM if DATA SKETCH PROGRAM 9 p EXP TEST ae eee 6 GETTING AHD 4 1 GETTING AND FROVI COMPARING THE TEST SIGNALS ET ee reterence H GETTING NPYT OUTPUT REFERENCE t FROM IHE cij To am HFG ION To HE LAL setup IM SETUP INFOR FROM ith ho fig 7 4 The Complete Software Configuration 120 First of all EXP Test System asks the user to check the main power supply This work should be done before testing any point in the plotter s circuitry After that EXP Test System will ask the user to put the probe of the oscilloscope for testing the analogue signals in the plotter s circuitry or of the logic analyzer for testing the digital signals in the plotter s circuitry on one of the test points Immediately after that EXP Test System will call SKETCH program which will draw the schematic and the layout diagrams on the screen EXP Test System will ask the user now if he has put the probe at the wanted test point When the user choose YES from the choice list EXP Test System will call the Getting and Comparing the Test signals program The work of this program is to get the signal from the test point and compare it with
55. RT next one indicates that the output of X1 is connected to the first input of X2 The behavioural information is represented as follows IF AND ORG d VAL IN 2 d t ON VAL OUT 1 d t ON If the device is an OR gate and the second input is on then the output is on The process for tracing through this model to find a fault is described in fig 4 5 Compute Suspects no Generate Test yes Execute Test and Draw Conclusions fig 4 5 Flowchart of the DART Diagnostic System 64 The computation of suspects produces a suspect set which has the following form OR NOT p1 NOT pn Where pi is a statement from the circuits design description not known to be true For instance if the diagnosis had reached a stage where it knows that either of the XOR gates X1 or X2 is broken the set will be OR NOT XORG X1 NOT XORG X2 Clearly the diagnosis is complete when the set of suspects contains only one entry The set of suspects is reduced by generating distinguishing tests between them The difference between qualitative and quantitative models is not important with digital electronics where the basic one zero model is the only reasonable representation On the other hand analog devices have an infinite number of possible states so there is a considerable difference between quantitative and qualitative models These digital fault diagnosis systems are presented working simple
56. So the service engineer would typically have as minimum specification 1 A good knowledge in maintenance from experience 2 A specific background in fixing CNC machines 3 Because circuit complexity is increasing doubling about every two years he must be able to keep up with advances in any technology that will reduce downtime 2 2 2 Test Equipment Specification Usually in any workshop which deals with manually controlled machines the basic test tools which are adequate for testing power supply some electrical components and simple logic circuits should be available These tools include 1 Analog multimeter 2 Digital multimeter 3 Oscilloscope 4 Function generator 5 Power supply The test or service equipment used in CNC machine troubleshooting is basically the same as that used in other fields of electronics That is most procedures are performed using conventional meters including high voltage meters for measurement of video terminal CRT voltages multitrace oscilloscopes for measurement of pulses on data and address buses clock and other control lines etc and assorted clips patchcords power supplies and hand tools Theoretically all CNC machine troubleshooting problems can be solved using such instruments However there are some specialized test instruments that greatly simplify microcomputer service just as they do for any programed digital device composed mostly of ICs such specialized equipmen
57. T Nes PUT THE SYSTEM GRAPHICS MODE OPEN THE DATA FILE DATA FILE ym a SCAN THE FIRST THREE CHARACTERS OF DATA LINE SCAN THE LINE COMPONENTS DRAH LINE SCAN THE TEXT COMPONENTS WRITE TEXT SCAN D s COMPON DRAM CIRCLE ES CLOSE DATA FILE CLEAR SCREEN SHUT DOWN THE GRAPHICS MODE fig 6 3 The Flowchart of the Sketch Program 106 If the content of Comp array is LIN this will indicate that the data file contains data for drawing a line The Sketch Program will scan the rest of the current data line put the graphics information in array of character Temp Then the Sketch Program scans Temp separates its content to 1 1 2 2 By using convert function which converts the coordinates from the plotter scale to the screen scale and using line function the Sketch Program will draw line on the screen If the content of Comp array is TEX CIR OR the same procedure will take place But outtextxy function will be used for writing the specified text circle will be used for drawing a circle and arc function will be used for drawing an arc Then the Sketch Program will make the end of file test to ensure that the file hasn t reached the end If the Sketch Program pass this test it will return back to scan another line of data inside the data file But if it didn t pass the end of file test the Sketch Program
58. TEST LOGIC ANALYZER fig 3 1 The Hardware Configuration UTUST 4 Command the instruments to send data to the controiler 5 Check that the correct information was received After the controller receives the information from the instruments it compares that information with the reference 3 3 I te ec The intention is to look into automating a test procedure for a volume product so to reduce costs This calls for some kind of computer program and some interface to particular pieces of test equipment needed for this job Unfortunately each piece of test equipment has a different number and type of control input this will require a number of different 16 interface cards in the computer each with different software driver All this interfacing is an overhead to actually doing the real job of specifying and writing the program that manipulates the test instruments to automate the test procedure What is required 1 that every test instrument have the same interface cards It would be preferable if communication via a common bus into one card in the computer were available Before the solution is described a brief review of Digital Communication principle is given 3 3 1 Introduction to Digital Communication Serial and parallel data transfer are the two basic methods of communicating digital information between microprocessors and peripheral equipment Both techniques in widespread use thr
59. This program will call the setup file and send the setup information to the Logic Analyzer The flow charts of all the previous mentioned programs are in appendix A 7 4 2 2 Designing the Rule Set Developing the rules to be used by EXP Test System was the largest development task representing approximately four months work which formed the core of the project The result is about one hundred rules A fuller description is provided in section 4 10 1 A typical rule from this expert system is shown here RULE POWER_SUPPLY12 IF CHECK_PEN_SUPPLY YES THEN CALL TC2 SKETCH1 CALL TC2 SKETCH2 CALL TC2 EXP_T10 LOADFACTS FILE9 FIND THE_PEN_SUPPLY THE_12V_TEST FOUND 124 RULE POWER SUPPLY13 IF deltal gt standerl THEN WOPEN 4 15 1 8 60 14 ACTIVE 4 DISPLAY THERE IS A PROBLEM IN THE PEN COIL SUPPLY S OUTPUT TO DEFINE WHICH COMPONENTS CAUSE THE PROBLEM YOU SHOULD MAKE TEST TO ANOTHER POINT PRESS ANY KEY TO CONTINUE WCLOSE 4 RESET deltal RESET standerl THE PEN SUPPLY FOUND FIND MOR PEN SUPPLY ELSE CLS DISPLAY THE PEN COIL SUPPLY IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE RESET deltal RESET standerl 7 4 2 3 Domain expertise There were two clear stages in developing the rule set First there was the task of developing domain expertise in other words becoming familiar with various aspects of the plotter s electronic circuitry It was important to understand the actual construction of the p
60. USA Vol 52 No 6 PP 118 122 Nov 1979 Switzer G Hydraulic Maintenance Program Boosts NC Productivity Tool and Prod USA Vol 43 No 1 PP 60 62 April 1977 Kolenaty G Holland M SYS PLANR Decision Support Svstem for Managing Software Development Softfair A conference on software development tools Techniques and Alternative Proceedings PP 99 108 25 28 July 1983 Thrasher D Giomi M Drill Machine Maintenance Service Circuits Manuf USA Vol 22 No 6 PP 58 59 June 1982 Davis W J Carnahan J V Decision Support for Road Surface maintenance Dmega GB Vol 15 No 4 313 322 1987 Stuart C Shapiro Sargur Srihari Ming Ruey Taie James Geller Development of an Intelligent Maintenance Assistant SIGART Newsletter Vol 92 PP 48 49 April 1985 139 10 11 12 13 14 15 16 17 Eva Hudlika and Victor R Construction and use of a Causal Mode of a 5 11 Svstem SIGART Newsletter acm Vol 93 July 1985 Kothari D P Girotra S N New Optimal and Reliable Generator Maintenance Scheduling Algorithm J Inst Eng India Electr Eng Div India Vol 67 pt EL4 PP 171 173 Feb 1987 Escudero L F Qn Maintenance Scheduling of Production Units Eur J Oper Res Netherlands Vol 9 No 3 March 1982 Kathari D Girotra S N Yadava G S Some Aspects of Optimal Maintenance
61. agram of an Expert System 4 3 5 1 The Knowledge base The knowledge base is the heart of any expert system There are different ways for representing knowledge in expert system such as frames semantic networks and production rules It is proved that production rules is the best way for representing knowledge It has been determined through considerable experience that one of the best methods of knowledge representation for expert systems is 49 production rules Most commercial experimental expert systems use the popular IF THEN rules format 68 Production Rules Production rules are generally easy to write and it is quick to built the desired knowledge base Rules is formatted into two parts The first the left hand side of the rule IF part states some premise or condition The second the right hand side of a production rule THEN part states a conclusion or action that will take place if the conditions on the left hand side of the rule have been met When the right hand side of the rule is implemented the rule is said to be fired As an example of representing knowledge by using production rule IF the patient has headache THEN the patient needs aspirin CF 7 Each rule is made up of clauses There is one IF clause and one THEN clause to every rule The IF part of the rule may contain more than one clause These are called compound clauses and they are linked by AND or OR The certainty factor CF is a number b
62. ance costs also that technician will increase his knowledge day by day by fixing machines using the intelligent workstation If he adds the acquired new knowledge to the knowledge base of the expert system he will be able to help himself and other technicians after him to achieve a quick fault diagnosis in the future That of course will reduce the breakdown time and increase the productivity and the benefit to the whole plant 5 4 Developing an Intelligent Mobile Workstation for On Line Test As illustrated in fig 1 1 the intelligent mobile workstation is a mobile unit which can be easily moved from the service station to any CNC machine inside the workshop The total system configuration which is shown in fig 5 1 consist Of 1 EXP Test System 2 Graphics 3 Technician 76 INTELLIGENT HORRSTATION TECHNICIAN Y 2 EXP TEST SYSTEM Saal CNC fig 5 1 System Configuration of the Intelligent Workstation Exp Tast System The highly specialized piece of software that attempts to duplicate the function of an expert in some field of expertise The program acts as an intelligent consultant or advisor in the domain of interest capturing the knowledge of one or more experts in its knowledge base Non experts can then tap the EXP Test System to solve repair problems and make decisions in that repair domain 77 Graphics As mentioned the Graphic element in the
63. and library directory 17 PSpice analog simulation shell PSpice not included 18 String searching 19 Vertical text placement 20 Suspension of session for DOS command execution 21 Supports A through E and custom size worksheets Part Libraries Included with OrCAD SDT III are extensive part libraries of the most commonly used devices in the industry Creating Custom Libraries OrCAD SDT III enables the user to create his own custom libraries or modify existing ones in two easy ways First the user can invoke the graphical object editor called LIBEDIT With this editor the user use commands similar to those of OrCAD SDT III to construct or modify a part on the screen 94 and add it to a new or existing library Second the user can use a text editor to create a library source file A library source file is an ASCII text file that contains instructions in the OrCAD Symbol Description Language Utility Programs OrCAD SDT III s flexibility continues after the schematic design process with easy to use utility programs including ANNOTATE This program scans a hierarchy or flat file and automatically updates all part reference designators BACKANNO The BACKANNO utility updates part reference designators in the user design The input to the program list of old and new reference designators is used to update the user schematic worksheets CLEANUP This utility checks the worksheet for wires buses
64. ated with EXP Test System in such a way that EXP Test System plots the desired circuit board on the screen Then it shows the point which needs to be checked EXP Test System At this stage there are two possibilities 79 1 If the type of fault which is the machine is included within the knowledge base of EXP Test System EXP Test System will define the problem and will print out the fault candidate list This will depend on the information which is provided by the technician and on the result of comparing the test signals with the reference signals of each point The following example explains how EXP Test System asks the user for information ask him also to move the oscilloscope s probe from point to another how it defines the fault candidate list When the user start EXP Test System it will display WELCOME TO EXP TEST SYSTEM SYSTEM FOR TESTING CNC MACHINE PRESS ANY KEY TO CONTINUE The user must follow all the instructions which appear on the Screen so if he is ready for testing the machine he will press any key on the keyboard If that happened EXP Test System will display CHECK THE MAIN POWER PLUG 220 ACV IF THE MAIN POWER IS OFF MOVE THE CURSOR TO OFF AND PRESS ENTER IF ON PRESS ENTER ON OFF In this case the user should check the main power and notify 80 EXP Test System what is the result If the main power is OFF EXP Test System will display SWITC
65. beginning the Search Program opens the OrCAD plot file to read it and opens a data file to save the modified data in it Then the Search Program makes checks the plot file to ensure that it is not empty At this stage if the plot file is empty the search program will print on the screen 99 SEARCH PROGRAM M X t START SEARCH FOR THE OF DATA IN THE PLOT FILE FOR FIRST SAVE F CHAR SEARCH FOR SECOND PART OF DAIA SAU IN ARRY OF CHAR rt AUE entry THE para Pit THE FORMAT RA lus x3 ul x2 921 MODIFY THE DATA SAVE THE DATA MITH THE FORMAT TEX x y tents ERROR READING FROM PLOT fig 6 2 The Flowchart of the Search Program ERROR OPEN PLOT FILE Then it will close the plot data files and exit But if the plot file contains the graphical information the Search Program will start searching for the start point of the data which is for HP format the term 5 1 After finding SP1 inside the plot file the Search Program checks the plot file to ensure that it hasn t reached its end If the Search Program encountered EOF inside the plot file it will close the plot and the data files and exit This check for the end of file will be accomplished after every search for new data in the plot file Now if it is not the end of the file the Search Program will start to search for the first part of the
66. ch the right side of the rule against the current system s status The corresponding IF sides of the rules matched are used to generate new intermediate hypothesis which are recorded in the data base The backward chaining continues until the hypothesis is proved 4 3 5 4 User Interface The user interface is a piece of software that lets the user communicate with the system It asks questions or presents menu choices for entering initial information in the data base It provides a menus of communicating the answer or solution once it has been found Any intermediate communications during the problem_solving process are taken care of by the user interface The clauses used in the rules are used as outputs with appropriate 52 prefaces in simple systems Some expert systems also VP Expert can include blocks of text with each rule and at the beginning or the end of the expert system These are used to provide additional information or explanations 4 3 6 Expert System Features Expert systems more useful if they have some additional features These include an explanation facility ease of modification transportability and adaptive learning ability 4 3 6 1 Explanation Facility Usually the first time users of the expert system are surprised at how quickly it comes up with a conclusion They clearly don t believe it Users frequently want to know just how the expert system arrived at that answer Most of the expert sys
67. chematic diagram of the circuit board which is going to be checked The deep knowledge resides in the Graphics facility which contain 78 the structural information about the U U T unit under test circuitry and the intelligence of the technician A very important part is played by this technician in analyzing the schematic diagram of the circuit and in defining the solution if new case is encountered By integrating the EXP Test System with the accompanying Graphics facility and with the intelligence and the knowledge of the technician the intelligent mobile workstation will incorporate both deep and shallow knowledge This incorporation will give the intelligent mobile workstation the capability of solving all the problems which might occur Now let us ask this question How can that accomplish In the case of a breakdown to a CNC machine the user of the machine will call the service technician who of course immediately will move the intelligent mobile workstation to the location of the broken down machine There he will switch the workstation and call EXP Test System EXP Test System will begin to guide the technician to diagnosis the problem The user interface will help the EXP Test System to ask the technician for some information and will ask him also to move the Digital Oscilloscope s probe or the Logic Analyzer s probe from one point to another to get some test signals The Graphic facility has been integr
68. cuits can be based on either deep or shallow knowledge An electronic fault diagnosis system can be model based or it can be built using shallow rules linking symptoms to causes 64 There are two types of human experts the design engineer and the test technician Their reasoning strategies for diagnosis may be completely different In addition that one expert might use different strategies at different stages A technician will start 59 off reasoning the first principles of what he knows about electronics and will proceed to learn shallow rules of thumb linking symptoms to possible causes as he becomes more familiar with the circuit So he might operate like a qualitative model based system A design engineer might be considered similar toa model based expert system So he might operate like a quantitative model based system The architecture for a knowledge based system for electronic fault diagnosis should reflect one of these approaches 35 4 5 Shallow Knowledae Conclusions are drawn directly from facts that describe the problem in shallow reasoning Shallow knowledge is best considered as rules of thumb that describe a particular problem domain These would be simple rules linking symptoms to causes in diagnosis Human experts may acquire their knowledge at this level or they may acquire them at a deeper level where the knowledge is based on a model of the system and the reasoning is done from the first principles in this mo
69. d LF OR EOL If EOI is selected messages are terminated by sending EOI concurrent with the last byte of the message During message reception receiving an EOL is the only recognized message terminator if LF OR EOI is selected a CR followed by LF concurrent with EOI is sent as a message terminator In this project the address 1 was selected for the 1241 Logic Analyzer and the EOI as a message terminator 40 CHAPTER 4 APPLICATION OF EXPERT SYSTEM IN DIAGNOSTICS 4 1 Introductio Diagnosis has been considered a task well suited to expert systems solutions since early in the short history of expert systems This is because diagnostic problems not clearly defined and not well suited to algorithmic solutions The emphasis with expert systems has not been on specific problem solving procedures but on knowledge about the problem domain and general procedures that reason with this knowledge Diagnostic tasks can easily be represented in this format 35 The main components of diagnosis can be summarized as follows Givens 1 A case of malfunctioning unusual symptoms 2 A standard set of diagnostic tests Goals 1 To fit case into known disease fault classes 2 To find probable causes of symptoms 3 To recommend treatment methods Constraints 1 The tests may be numerous and difficult to select 2 The tests may be costly in time or money 3 The tests may be unreliable Operations 1 De
70. d flexible schematic capture package Easy to use menu driven commands help the user to create edit save print and plot electronic schematics It is developed specifically to run on IBM personal computers and compatibles OrCAD SDT III supports most of the popular graphics boards printers and plotters This eliminates the need for special proprietary hardware by enabling the user to use standard output equipment The OrCAD SDT III software package consists of the schematic drafting program DRAFT a graphical library object editor called LIBEDIT netlist design check part listing and other utility and library programs DRAFT DRAFT is the schematic drafting program that enables the user to create edit and save schematic worksheet The major features of DRAFT include 1 User definable template dimensions at 1 mil resolution 2 User definable text size 93 3 Eight part fields 4 Over 3500 Unique library parts 5 DeMorgan Equivalent parts 6 Placement of wires buses connectors labels and junctions 7 Real time rubberbanding of wires and buses when objects are moved 8 Part rotation and mirroring 9 Moving replicating and deleting objects or blocks of objects 10 Powerful step and repeat command 11 Visible grid dots and angled bus entries 12 Automatic panning of the worksheet 13 Five zoom levels 14 Over 100 user assignable macros 15 Unlimited levels of hierarchy 16 On Line part browsing
71. d up even if not used nowadays bus extenders exist to both extend the bus in length and to increase the number of instruments on the bus 3 3 3 The IEEE 488 Bus Lines Referring to fig 3 4 the bus comprises a number of lines connected to each instrument in turn The electrical nature of the interface at each instrument is show in this figure As a wire OR function is implemented the bus line is active or true when low i e at 0 4v or less When nothing is driving that particular bus line it will sit at about 3 3v and be read as inactive or false The maximum bus transfer speed is supposed to be one million transfers per second In actual fact very few measurement set_ups 22 THE IEEE 488 BUS LINES 5 3K rh 5 Q 6K RX 0 DATA DATA CONTROLLER BUS LINE INACTIVE Va 3 3 BUS LINE ACTIVE 0 4 5 5V 3K 3K 6K 6 Ov Ov INSTRUMENT 1 INSTRUMENT 2 come anywhere near this speed Referring to fig 3 5 the bus is made up of 16 lines and 8 grounds making 24 lines in all 0 08 DATA BUS NRFD DAV NDAC GPIB CONNECTOR HANDSHAKE BUS REN MANAGEMENT BUS 12056 3917 17 fig 3 5 The GPIB Bus Lines Ignoring the grounds for the meantime the 16 lines are divided into three groups named transfer control lines or Handshake Bus Management lines and the Data Bus The Data Bus consists of eight lines carrying all commands data and addresses bi direc
72. ddress buses simultaneously Second and more important a typical data byte is 8 bits and thus requires 8 clock pulses or 8 one at a time pushes of the single step button Since all program steps require at least one byte and often two or three bytes possibly 24 bits you must push that button many times if the malfunction occurs at step 3333 of the program This means that you must spend endless hours comparing program lists against binary readouts at addresses If you are already familiar with troubleshooting of any programmed device you know that the most time consuming part of the task is in making such comparison The logic analyzer overcomes this basic problem by permitting you to select the data at a particular address for display The logic analyzer will then run through the program at near the normal system speed a fraction of a second and display the selected data at the desired breakpoint or between two breakpoints in the program 69 2 3 Breakdown Time In the case of a breakdown to CNC machine in the mentioned workshop the service engineer will collect all the information about the broken machine and equipped with the service catalogues and all the test equipment which have just been mentioned will go to the machine location to fix it 10 That work may take or two weeks with non expert person service engineer or technician who doesn t meet the previous specification for the service engineer
73. ddressing HP 54501A Oscilloscope 3 5 The Logic Analyzer The Tektronix 1241 was used in this project as a logic Analyzer because it is a portable general purpose digital design and troubleshooting tools that offers similar feature sets The 1241 Logic Analyzer uses a liquid crystal color shutter LCCS to produce a three color display screen it also has vertical expansion feature that doubles the height of the timing diagram traces Two types of data acquisition cards allow the instrument to be configured to meet the specific requirements 124001 card supports high speed hardware analysis with 9 acquisition channels at 100 MHZ 10 ns and 6 ns glitch detection The 1240D2 has 18 acquisition channels at 50 MHZ and includes a bus demultiplexing feature 36 Instrument configurations include any combination of 124001 and 124002 acquisition cards up to maximum of four cards 1241 configured with both card types is an effective tool for evaluating hardware software integration The 1241 Logic Analyzer provide the following features 1 Acquisition with one or two timebases Asynchronous or synchronous selections are available 2 Powerful triggering with two event recognizers that can be used independently or together The global event recognizer triggers on a single event in one or two timebases The sequential event recognizer consist of up to 14 separate levels Each level specifies its own event and a trigger wait
74. del If a particular problem is unsolvable with the shallow knowledge available in a system then the knowledge base can be extended to cover that problem This extension will cover that particular problem only This explain the main problem with shallow representations A shallow knowledge based system will not perform well on cases not considered in its construction 4 6 Shallow Knowledge Based Systems Shallow knowledge based systems are usually rule based systems The knowledge of a particular domain is represented as IF THEN 60 rules The shallow knowledge is considered to have some advantages including 1 Shallow rules are an easy way of representing the domain knowledge of an expert 2 The knowledge base can be easily extended by adding new rules 3 The use of a backward chaining rule based system facilitates the development of a user interface as the inference engine will automatically ask the user for any information that is not available to the system 39 4 It is easy to have a rule based system explain its line of enquiry The advantages and disadvantages of shallow rules based systems can be considered using the PROCESSEX system which is an expert system for fault diagnosis in digital electronics It is written in EMYCIN which is a backward chaining system PROCESSEX contains about one hundred and fifty rules which are written in both English and the Lisp like code used by the system EMYCIN use the English rep
75. del based expert systems for electronic fault diagnosis This is an important difference between knowledge based systems for medical diagnosis and those for electronic fault diagnosis Most medical diagnosis systems are shallow knowledge based systems because deep models of the problem domain would be very complex and are not used by human experts Instead experts use models of the various pathologies of the system This is reflected in an expert system for diagnosis of glaucoma called CASNET stands for causal associational network and is semantic network based system 48 The equivalent to these pathological models in electronic fault diagnosis are fault models these are models of the various different types of fault that can occur in a circuit Classes of failure as used by Davis are general fault models but are peripheral to the model based diagnosis system 41 Davis main model is a model of the structure and behaviour of the system The advantages and disadvantages of deep knowledge based systems can be considered using the DART system Consider the full adder represented by the circuit diagram in fig 4 4 The structural information about this circuit is represented by Lisp like expressions of which the following are examples XORG X1 CONN OUT 1 X1 IN 1 X2 The first of these expressions indicates that X1 is an OR gate The 63 lt al 5 XN Co fig 4 4 Schematic of the Full Adder in DA
76. duce possible causes of symptoms 41 2 gather data about symptoms and characteristics of the case 3 Classify possible causes into disease or fault hypotheses 4 Distinguish competing hypotheses 5 Take account of the interactions of several causes 52 4 2 Introduction to Artificial Intel ence Artificial intelligence gives computers extra computing capability allowing them to exhibit more intelligent behavior Intelligence the ability of a human being to acquire knowledge and apply it means the capability of thinking and reasoning To a certain degree artificial intelligence allows computers to accept knowledge from human input then use that knowledge through reasoning processes to solve problems The main element of any artificial intelligence application is knowledge an understanding of some subject area obtained through education or experience The problem that the computer cannot have experiences or learn as the human mind can So it can acquire knowledge given to it by human experts This knowledge consists of facts procedures and information that has been organized to make it understandable and applicable to problem solving or decision making Most knowledge bases typically concentrate on some specific domain After building the knowledge base artificial intelligence techniques will be used to give the computer reasoning capability So the computer will be able to think reason and reach conclusions based on the
77. ealing with uncertain knowledge It is a system conceived by computer scientist Lotfi Zadeh for dealing in unreliable information In this method an attempt is made to assign numerical ranges with a possibility value between zero and one to concepts such as tall good hot and other elements with values that are hard to determine 82 4 3 9 Expert System Applications The applications that fit the way an expert system represents knowledge will be explained in details in this section to determine whether a particular application 15 suitable for expert system Expert systems are definitely not suitable for all 55 situations 4 3 9 1 Control The computer in this application is interfaced to other system There are two basic types of control open loop and closed loop The computer in an open loop system follows step by step procedure to cause a particular type of behavior to occur in the system A closed loop control uses feedback that monitors the system status This feedback is the key to use the expert systems in control applications because it gives the expert system inputs to use in making decisions With this kind of input information in addition to its own knowledge base an expert system adapt to changing conditions It can also diagnose problems and correct them by develop plans for overcoming them 4 3 9 2 Debugging Debugging is the process of troubleshooting that finds problems system and
78. ed to formulate the hypothesis There are three stages in the diagnostic process Abduction arrive at a hypothesis to explain the symptoms Deduction derive experimental outcomes of the hypothesis and carry out tests 58 Induction conclude the hypothesis to be true or false 77 MYCIN system is one of the early famous expert systems for medical diagnosis 47 It is a backward chaining rule based system for diagnosing and treating infectious blood diseases The knowledge about the problem domain is represented as IF THEN rules thus it is shallow knowledge This shallow knowledge representation is characteristic of diagnostic expert systems in medicine 46 On the other hand some of the expert systems developed for electronic fault diagnosis have been model based 44 or 36 This gives the fundamental difference in the nature of the reasoning involved in medical diagnosis and in electronic fault diagnosis Medical diagnosis is based on models of the pathology of the system under diagnosis these are shallow models whereas electronic fault diagnosis is based on models of a correctly functioning circuit This distinction does not only exist in the way human experts perform these tasks but is also reflected in the way expert systems are designed to operate in these domains That mean that expert systems for medical diagnosis need to be based on shallow knowledge representations while those developed for troubleshooting electrical cir
79. ei CALL GETTING on COMPARING A DIFFERENCES NO aLLoaBh 7 T 12 ALI 4 NCE v E YES 7 DAMAGED ean Ine j E 5 gm gt 3 z oSFINE WITCH MOTOR i WORK i 4 t E 4 2 Pod Ed AROUSEL HO PEH STEPPER 08116 MOTOR Pi M fo x UES VES VES Y 3 et Pm CM 181 12d 191 4 4 2 0 renee 7 ns D N OLENDI b 5 E 9 CALL S NDIMG 1 prone 1 10 4 gt IDTSCOHNECT THE hat CONNECT k ALYZER S pape 19 LH UM TRE LINE SDE AH t A m CH 8 p LUE SARL GETTING i CORPARIRG i iia of y EXPECTED DAMAGED COMPONENTS 3 CR T CRIB CRIS 3 THE CAROUSEL DRIVE STEPPER MOTOR mir ea ove ZENDING TAA Y DISCONNECT N WE i Lat POIMIS ONNECT THE ANALYSER S 0 ON THE i 1 CALL SKETCH i THE CIRCUIT amp 20 cD
80. ematic of the circuit while the physical part corresponds to the circuit layout EXP Test System was developed as a system for electronic fault diagnosis It has the advantages of the both types of knowledge shallow and deep knowledge The shallow knowledge is the knowledge about fault procedure and the deep knowledge is the knowledge about electronic circuitry The following example will describe the way EXP Test System represent the shallow and deep knowledge this example checks the output of the transformer 67 This statement eliminates the Rules and Values windows when the user runs the rule base ACTIONS This statement and FIND clause define the steps for solving a problem DISPLAY WELCOME TO EXP TEST SYSTEM SYSTEM FOR TESTING CNC MACHINE PRESS ANY KEY TO START gt CLS This clause clears the consultation window FIND THE PROBLEM RULE POWER SUPPLY IF CHECK TRANSFORMER YES THEN CALL TC2 SKETCH1 CALL TC2 SKETCH2 CALL 2 _ 1 LOADFACTS FILES FIND THE TEST THE PROBLEM FOUND RULE POWER SUPPLY1 IF deltal gt stander1 THEN 1 15 1 8 60 4 This clause define the position size and background color of a window ACTIVE 1 This clause displays a window on the screen DISPLAY THERE IS A PROBLEM IN THE TRANSFORMER I SUGGEST YOU TO REPLACE IT PRESS ENTER THEN Q TO EXIT WCLOSE 1 This clause removes a window from the screen RESET deltal 1 The RESET
81. er for a DEC VAX 11 780 series computer system into complete final system specifications 45 XSEL is another DEC CMU expert system with knowledge of VAX 11 780 computer systems XSEL was designed to help DEC sales persons select components for a VAX system Prospector Prospector is an expert system that helps geologists locate ore deposits EL This expert system analyzes electronic circuits consist of transistors diodes and resistors A schematic diagram of the circuit is entered into the computer and EL analyzes it SOPHIE SOPHIE was designed to help students learn to troubleshoot electronic circuits The system presents a simulated electronic circuit and a problem then permits the student to troubleshoot it 36 DELTA DELTA was Developed by the General Electric Company to assist maintenance personnel in locating problems in diesel electric locomotive engines FOLIO This is an expert system that helps stock brokers handling investments for their clients VP Expert VP Expert represents the first low cost expert system program For the first time personal computer owners can develop powerful expert systems on their own with little or no knowledge of a Special programming language VP Expert can create expert systems for providing advice for legal consultation financial planning medical diagnoses or electronic 46 fault diagnosis 65 66 4 3 2 Advantages of Expert Systems The previous programs point o
82. ess the HP IB Command Library uses address 30 for the controller address so it should not be used 4 After that the peripherals were connected Here are some points which are important when connecting several peripherals to the interface 1 Up to 14 peripherals can be connected to a single interface 2 Devices can be interconnected in any scheme as long as there is an unbroken path between each peripheral and the controller Several devices can be connected at connector or each device can be connected to the next 3 The total cable length on one interface should not exceed 2meters 6 feet times the number of connected devices the computer is considered as one device and it should not exceed 20 meters 66 feet For high speed data transfer the length should not exceed 1 meter 3 feet times the number of devices and not more than 15 meters 50 feet 31 3 4 The Digital Oscilloscope In this project the HP 54501A Oscilloscope was used as a Digital Oscilloscope because it is a general purpose digitizing oscilloscope that is fully programmable and transportable It is an excellent general purpose digitizing oscilloscope because of the friendly user interface yet it has many sophisticated capabilities and multiple triggering functions 3 4 1 Addressing HP 54501A Oscilloscope The front panel of the HP 54501A is separated into six functional areas as shown in fig 3 9 The Menus Section consists of nine
83. etween 0 and 1 that indicates the confidence in the validity of the conclusion While each production rule represents an individual piece of knowledge it is usually related to many other rules The rules link together to establish a line of reasoning This collection of rules will form the knowledge base Finally with production rules it 13 very easy to modify or a new knowledge to the knowledge base 4 3 5 2 The Data Base The data base contains a broad range of information about the 50 current status of the problem being solved is portion of working memory where the current status of the problem solving process is stored Also the data base records facts about the problem Initially the Known facts are stored there Then the new facts which picked up from the inference process are added The initial conditions of the problem to be solved are also stored in the data base Usually the expert system asks the user for some beginning input This information gives the expert system a starting point to begin the search process The inference engine begins its search matching the rules in the knowledge base against the information in the data base 4 3 5 3 The Inference Engine The inference engine is software that implements a search and pattern_matching operation It examines the rules in a particular sequence looking for matches to the initial and current conditions given in the data base As rules matching these
84. eying for a different definition of baud rate as it applies to that form of data For example a bit time of 9 09 ms would have a rate of 110 baud except for PSK If the serial message consists of a start bit 8 data bits and 2 stop bits a system working at this rate would be capable of transferring 10 bytes of data per second Table 3 1 illustrates some commonly used baud rates along with the number of stop bits data bits type of transmission and the normal application of each Note that all of the baud rates listed are multiples except 110 baud which is used for communications between electromechanical teletypewriters which are quickly disappearing The only systems employing 2 stop bits or 1 5 stop bits were designed for mechanical devices The extra time allowed by additional stops was required 19 5 7 P 7 7 7 Variable Variable Variable NOTE P Parity MODEM MOdulator DEModulator table 3 1 for mechanical synchronization use 1 stop bit 3 3 1 5 Synchronous Serial Data In synchronous transmission pulses so it is not necessary to send synchronization with the data as with the asynchronous system Synchronization can be information periodically For example transferring 100 bytes methods would take 1000 bit times stop bit per byte system that sends 1 sync byte before end of message only 816 bit times If information is transmitted for any Asynchronous
85. f EXP Test System It is divided into six different types each type supports EXP Test System in side of the automatic test brief explanation on each type will be mentioned These types are 1 Search and Sketch programs An expanded explanation has been already given about these two programs which support the graphics facility accompanying EXP Test System 2 Getting the Reference Signals from the U U T This software was divided into two programs The first one get the reference analogue signals from U U T through the IEEE Interface Card by using the oscilloscope This program will convert the captured data the raw data in ASCII code to a useful interpretation After that it will save the processed data in a text file called REFERENCE The second one get the reference digital signals from 122 3 4 U U T through the IEEE Interface Card by using the Logic Analyzer Then this program will convert the captured data the raw data in ASCII code to a useful interpretation After that it will save the processed data in a text file also called REFERENCE Getting and Comparing the Test Signals This software was divided into two parts The first part gets the test analogue signals from U U T through the IEEE Interface Card by using the oscilloscope Then this program will convert the captured data the raw data in ASCII code to a useful interpretation After that it will call the reference file and compare
86. ge can then be used by anyone requiring it The purpose of an expert system is not to replace the experts but to make their knowledge and experience more widely available So the expert system permits non expert users to increase their productivity and solve problems when an expert is not available An expert system consists of three major components a knowledge base an inference engine and a user interface The knowledge base contains all the facts and ideas of a specific domain The inference engine analyzes the knowledge and extracts conclusions from it The user interface implements communication with the user and permits new knowledge to be entered into the knowledge base To use an expert system the user starts up the expert system software The expert system then asks the user various questions to collect some initial information about the problem to be solved The user can key in the information requested or select it from alternatives presented in menu form Once the expert system has the input it needs it starts searching for a solution and reaching a conclusion Usually users do not trust expert systems so they direct them to explain the process by which the conclusion was reached An expert system can be created to help users troubleshoot and repair a complex devices The various troubles and symptoms can be given to expert system which then identifies the problem and suggests the solution Expert systems also can be used
87. graphical data which always has one of the following formats 1 PA x y the normal case 2 AA x y start angle the arc index in the case of drawing a chain of arcs Then it will save the captured data in an array of character First After that the Search Program makes the end of file check on the plot file If it is passed the Search Program will start searching for the second part of the graphical data which will take one of the following formats 1 PA x y for drawing line 2 LB text for writing a text 3 CI r for drawing a circle 4 AA x y start angle the arc index for drawing an arc Then it will save the captured data in another array of character Second Also the Search Program will check for EOF after the previous search 101 Now the Search Program has a complete information for drawing a line a circle an arc or writing a text To define the type of the captured data the Search Program scans the first two characters in the array Second The first two characters in the second part of the data always defines the type of graphical information Then the Search Program will save these two characters in character array Comp After that the Search Program begins to extract the main information about the captured data dimensions coordinates text angles Then saves them in two arrays of character C contains the extracted information from the first part of graphical data D contai
88. he overall structure and also for visualizing how the system would appear to the user The first stage of the knowledge engineering process was to develop the overall structure of the system this was done along conventional knowledge engineering lines The localisation technique is very similar to that which an expert 126 would be expected to take 7 5 Certainty Factors EXP Test System didn t use certainty factors in its rules The reasons for this are very interesting a reflection on the fault domain In most instances the system asks the user to move the probe from one test point to another or if there is a signal in some test point feedback signals this is a simple YES NO query where there is very little vagueness There is a signal or there is not If the expected signal is not there then there is a fault or problem in the circuit which produces or uses that signal so the system localizes to that part of the circuit and tests another point or section of the circuit There is very little room for uncertainty in electronic circuits especially in digital circuits A line is generally either high low or carrying a signal The nature of digital test equipment also leads to precise results of tests the user either sees a signal on an oscilloscope screen or he doesn t This is very different to the situation in medical diagnosis where estimates and qualitative judgements must be made without clear quantitative result
89. he deep knowledge is the knowledge about electronic circuitry The shallow knowledge EXP Test System was represented ina number of the IF THEN rules These IF THEN rules give the system an easy way of representing the domain knowledge of the expert in the maintenance also it gives the system a high speed execution with the ability to extend the system easily by adding some rules The deep knowledge is included in the union of the Graphics facility and the intelligence of the technician Diagnosis is intrinsically a goal directed reasoning process goal being to prove that a particular module or component in a circuit is faulty 63 The procedure for testing the plotter s circuitry in EXP Test System was defined in cooperation with the maintenance expert in the school of electronic engineering at Dublin City University As mentioned different experts use different strategies for solving electronic faults In NODAL the expert system which was developed in Trinity College Dublin for testing the switching mode power supply different strategies were used for electronic fault diagnosis 111 The model within NODAL is hierarchical containing at least two levels a module level and a component level If the modules are large or complex then they may be subdivided into sub modules in the model 63 At a module level the fundamental principle is that if a module has good signals at its input and a bad signal at one of its
90. he layout diagram do that in conjunction with EXP Test System the CALL clause from inside VP Expert should be used The CALL clause should added to the IF THEN rules in the suitable place to increase the competence of EXP Test System As shown in the following example 109 RULE POWER SUPPLY IF CHECK TRANSFORMER YES THEN CALL TC2 SKETCH1 CALL TC2 SKETCH2 CALL TC2 EXP_T1 LOADFACTS FILE9 FIND THE TEST THE PROBLEM FOUND In response to the previous rule EXP Test System will display TO CHECK THE TRANSFORMER DISCONNECT THE TRANSFORMER S OUTPUT FROM J9 THEN PUT THE OSCILLOSCOPE S PROBE AT POINT 1 TO LOCATE POINT 1 AND CONTINUE THE TEST CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER YES NO when POWER SUPPLY rule is fired by choosing YES the inference engine will call first of all the SKETCH1 file which draws the schematic diagram of the circuit then the inference engine calls the SKETCH2 file which draws the layout diagram of the circuit The user should put the probe at point 1 then he should press any key on the keyboard to continue testing the broken down machine 110 7 IMPLEMENTATION 1 1 ntr EXP Test System was developed system for electronic fault diagnosis It has an advantage through the inclusion of both types of knowledge shallow and deep knowledge The shallow knowledge is the knowledge about fault diagnosis and t
91. ided design and drafring drafting CADD CAD fig 6 1 Place of CAD in the Spectrum of Automated Methods CAD systems may be either two dimensional or three dimensional and they may be designed to provide either special purpose or general purpose applications Although there is no strict use of the acronyms generally refers to 3D three dimensional systems that build a model of a design and tend to automate drafting Computer aided design CAD generally refers to 2D two dimensional systems that support drafting more directly A special purpose application refers to a system dedicated toa specific narrow application such as PCB boards piping and the like Special purpose CAD systems are often referred to as vertical systems 90 general purpose application 13 a more general application such higher level language that can be applied in a number of application areas General purpose CAD systems are often referred to as horizontal systems The great majority of CAD systems in use today are general purpose 2D systems that are being applied to help drafting in any discipline architecture mechanical civil electrical or electronic All CAD systems that in any way aid or automate drafting have the following components 1 Computer 2 Graphics screen 3 Graphics input such as a digitizer keyboard mouse 4 Graphics output such as a plotter Computer graphics is used in art engineering construc
92. idth modulated signal back to the gate array where the motor drive pulses are stretched to the proper width in the digital gain circuit The servo conditioning circuit also in the gate array then passes the pulses on to the motor drivers through either the or XC line depending on the direction of rotation indicated by the sign voltage from the servo chip As the mechanical system moves optical encoders mounted on the shaft of eacb motor send back digital pulses to the servo chip to close the servo loop To maintain a consistent and predictable movement it is essential to control the amount of power applied to the motor by each pulse 114 The pulse amplitude depends on the actual voltage output of the motor drive power supply The pulse width is modified to compensate for pulse amplitude so that the pulse represents the proper amount of power Five major voltages are generated by the 7475A circuitry Low current linear supplies provide the 12V and 5V required for the servo IC s The 5V supply provides the power for the remaining logic circuitry Regulation for the 5V linear supply is provided The unregulated 18 26V supplied to the main drive motors and the pen carousel drive motor The fifth supply is the 12V source used in conjunction with the 12V supply to operate the r o input output line drivers Fig 7 3 shows the 7475 Graphics plotter s power supply 115 OF At MAIN EA Roit Sorri y F
93. ill be difficult to generate because of its generality 35 4 10 Svstems Incorporating both Deep and Shallow Knowledge A deep knowledge based system would be the ideal solution were it not for the problem of performance It seems unavoidable that a system that reasons about circuit from first principles will be slow The obvious solution is to incorporate some shallow knowledge 66 into the system in order to short cut some of this reasoning from first principles This approach is supported in 38 and 45 This project will be described as an example of a knowledge based system for electronic fault diagnosis incorporating both deep and shallow knowledge 4 10 1 EXP Test System Electronic fault diagnoses is considered a suitable area for expert systems applications the research in this area is well documented 38 41 45 It is considered that the best approach to the problem generating expert systems for troubleshooting electronic circuitry is to incorporate both deep and shallow knowledge in the system 45 This approach recognizes the usefulness of both types of knowledge and utilizes both in the troubleshooting process Given symptoms of misbehaviour the expert system must be able to determine the structural defects responsible for the fault from the deep knowledge base 55 The structural knowledge has two components a functional part and a physical part The functional part is similar to the sch
94. ime of implementation VP Expert system has special features including 1 An inference engine that uses backward and forward chaining for problem solving 2 Optional development windows that let the user observe the behind the scenes path of the inference engine as it navigates the knowledge base to solve problems during a consultation 3 Confidence factors that let the user account for uncertain information in a knowledge base 4 Simple English rule construction 5 The ability to explain its actions during a consultation 6 Knowledge base chaining which lets the user create knowledge bases that would otherwise be too large to fit in memory 7 built in text Editor 8 Automatic question generation 9 The ability to record and graphically display the rule by rule search pattern used behind the scenes during a consultation 10 Rapid execution of the knowledge base 11 The ability to execute external DOS programs 12 Floating point math functions 66 One of the main problems at the outset of design and development 118 was the complete lack of any examples or previously implemented systems either in EMYCIN or in any similar expert system shell Although there is a large amount of information in papers and books about expert systems there is very little information available anywhere on actual design and implementation of working systems 64 7 4 2 Structure The goal of EXP Test System thro
95. ing an expert s problem solving process and encoding them in a computer system The best human expertise 15 the result of years perhaps decades of practical experience and the best expert system is one that has profited from contact via the knowledge engineer with human expert 52 Repair of electronic systems and electromechanical equipment is a domain well suited to expert systems technology Expert systems 73 have been built in a wide variety of domains 78 including systems that specifically deal with repair For example expert systems for troubleshooting have been developed for computer installations and minicomputers Dart 24 54 is a system used to assist a technician in finding faults in a computer system Two versions of Dart have been recently reported that use different expert system tools as basic building blocks Emycin 79 rule based system was employed in the first Dart version 24 while a meta level reasoning system 80 was used in the second system 54 IDT 56 an Intelligent Diagnostic Tool is a system designed to assist in identifying faults in PDP 11 03 computers This system was built using OPS 5 81 a rule based system developed at Carnegie Mellon 53 In this research on repair systems It was hypothesized that expert systems can capture the repair knowledge of the best qualified human experts in a particular domain A successfully implemented service advisory system would allow a technicia
96. ing the software many more issues arise such as 1 What routine software is necessary to drive the instruments 2 How should the man machine interface be defined 3 What level of support is possible with an expert system 4 If an expert system is to be used can an off the shelf expert system be integrated with a standard programing language such as C 5 How do we define the knowledge base given the context electronic circuit knowledge is usually documented graphically yet maintenance procedures may be stated linguistically 6 Maintenance procedures and solutions can be at two very distinct levels shallow and deep how do we accommodate that These are examples of the many unfolding issues that arise in any attempt to define the software Most of the agonizing centres around the question of knowledge encapsulation and representation Following considerable reading in this area we concluded that any attempt to encapsulate known diagnostic procedures in a linguistic based expert system would be impossible given the near infinity of loops and breakdown possibilities in even modestly complex electronic and electromechanical systems The partitioning of knowledge into shallow and deep is useful and has been used as 12 follows Routine isolated faults that constitute the largest group of all faults power supply problems for example are classifiable as shallow from a knowledge point of view Any problem which requires info
97. ject supervisor Dr Charles McCorkell for his continued help and encouragement Thanks to all the staff of the School of Electronic Engineering at Dublin City University especially Mr John Whelan Mr Noel Murphy for their help To my fellow Postgrads and friends at Dublin City University I wish you good luck with your respective careers I must acknowledge the great help given by Mr John Whelan in advising me during builting my project Finally my sincerest gratitude to my wife for her patience constant support and understanding throughout Declaration I hereby declare that this thesis is entirely of my own work and has not been submitted as an exercise to any other university M __ Mustafa Houreh DEDICATION To my parents as they enter their golden years CONTENTS 1 INTRODUCTION 1 1 1 1 Motivation for the Project 2 Summary of the Project 3 Aim of the Project 2 WORKSTATION SPECIFICATION 2 2 2 2 1 Introduction 2 General Workstation Specification 2 2 1 Service Engineer Specification 2 2 2 Test Equipment Specification 3 Breakdown Time 4 The Alternative Solution 3 HARDWARE CONFIGURATION 3 3 3 1 Introduction 2 Controller 3 IEEE Interface Card 3 3 1 Introduction to Digital Communication 3 3 1 1 Serial Data Transfer 3 3 1 2 Parallel Data Transfer 3 3 1 3 Asynchronous Serial Data 3 3 1 4 Baud Rate 3 3 1 5 Synchronous Serial
98. junctions labels module ports and other objects that are placed on top of each other COMPOSER If the user choose to create library parts using a text editor COMPOSER is the library utility that converts the user custom library source files into the highly compressed library object files used by DRAFT CROSSREF This utility scans through the schematic files gathers information for all parts used in the schematic files and creates a cross reference listing that tells the user where each part is located DECOMP If the user choose to create library parts using a 95 text editor DECOMP is a library de compiler that enables the user to convert the OrCAD supplied library object files to library source files ERC This is a utility that performs an electrical rules check of the user schematic worksheets LIBARCH This utility takes all the library parts used in the schematic files and makes single library source an archived library containing only parts which are usable for those schematic files LIBEDIT This utility enables the user to create library components on the screen NETLIST This program generates a netlist of the worksheet signal and part connections PARTLIST This utility summarizes all the parts used ina schematic or group of schematic sheets PLOTALL PLOTALL plots a schematic or group of schematic sheets in batch mode PRINTALL PRINTALL prints a schematic or group of schematic shee
99. keys to select from Timebase Channel Trigger Display Waveform Math Waveform Save Define Measure Utilities Delta t Delta v The Display Section contains the screen and selection keys Ina vertical column on the right side of the screen is the function display The functions that are displayed at any one time will correspond to a key in the selection column These keys can select any available function or field that is displayed in halfright The Utilities Menu Key should be pressed to address the HP 54501A This will give access to the calibration and service functions 32 Display and Selection Keys Setup E Input Entry Devices and Knob fig 3 9 The Front Panel of the HP 54501 as well as setup the HP IB Interface The submenus which appear at this time includes as illustrated in fig 3 10 UTILITY HP IB menu seiftest menu clicker off on fig 3 10 The Submenus of the Utilities Menu 33 HP IB menu Selftest menu Probe cal menu Self cal menu Service menu So if the selection kev which matches the HP IB submenu is pressed it will allow the user to make settings so the HP 54501A can talk to peripheral devices As illustrated in fig 3 11 this interface includes Talk only mode Addressed mode EOI Form feed Paper length form feed off on paper length 11 in 12 in fig 3 11 The HP IB
100. keyword sets the value of a 68 RESET stander1l variable to unknown THE TEST FOUND ELSE CLS DISPLAY THE TRANSFORMER IS PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE RESET deltal RESET stander1 ASK CHECK TRANSFORMER CHECK THE TRANSFORMER DISCONNECT THE TRANSFORMER S OUTPUT FROM J9 THEN PUT THE OSCILLOSCOPE S PROBE AT POINT 1 TO LOCATE POINT 1 AND CONTINUE THE TEST CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE AND PRESS lt gt CHOICES CHECK TRANSFORMER YES NO The previous example contain the two types of knowledge deep shallow knowledge The shallow knowledge in EXP Test System was represented in nearly one hundred of the IF THEN rules These IF THEN rules gave the system an easy way to represent the domain knowledge of the expert in the maintenance also it gave the system a high speed execution and the ability to extend the system easily by adding some rules The system backward chains through these rules with the goal of discovering which of fault candidates is faulty The clauses on the left hand side of the rules must be found true in order to prove the clause on the right hand side If the information in the clauses on the left hand side is not known to the system then it 69 will query the user for that information So the system get the extra information that it needs to isolate a fault by asking the user The ultimate problem or goal of consu
101. le in this integration process The main drawing entities represented in this format are as follow 1 The line command PA x1 y1 PD PA x2 vy2 this command ask HP Plotter to draw line between point 1 1 and point x2 y2 2 The text command PA x y LB text this command ask HP Plotter to write the defined text at point x y 3 The circle command PA x y CI r this command ask HP Plotter to draw a circle with the 97 radius at point x y 4 The arc command PA x1 y1 AA x y start angle the arc index Or 1 1 start angle the arc start angle the arc index this command ask HP Plotter to draw an arc at point x y In the first format Point xl yl1 define the start point where the plotter s pen start drawing the arc In the second format which is encountered in the case of drawing a chain of arcs coil point xl y1 define the centre of the previous arc define the direction of the draw for clockwise for unti clockwise A software has been developed using TURBO C Compiler to read the graphical format of the plot file to be used in EXP Test System This software is divided into two main parts The first part of the program searches and extracts all the data of the drawing entities After manipulating and modifying these data it saves them in a data file to be used later The function of the other part of the software is to read this data from the data file a
102. lotter s circuitry as will as understanding the circuitry s working at a logical and digital level This included a wide knowledge about the problems and the 125 components which would be most likely to be at fault A great deal of the information knowledge gathered at this stage of the project seemed extremely difficult to put into rule format Details of the particular things which could be wrong with the plotter and how they might be checked confirmed and fixed The second stage of the development consisted of organizing this information and constructing rules from it 7 4 2 4 Knowledge Engineering One approach to design rules is by attempting to construct consultation trees on paper by writing out lists of useful questions which could be asked and linking them with arrows representing the order in which they should be presented to the user so that they would be most intelligible to him A rule with two possible answers eg YES or NO would have two arrows from it for the two possible answers These arrows would go to more questions or if enough information had been collected then they would point to a fault and associated solution The approach which used to design rules in this project was by drawing the initiative flow chart of EXP Test System This flow chart was containing the useful questions which could be asked to the user and the expected answers This was found to be a very useful approach for developing t
103. lt WRONT PANEL 7 PNOCESS IHE CAPTURED DATA i y Ett i 1 E PROG PARED DATA IT A TEXT FILE GETTING SETUP 1 FROM THE LOGIS ANALYZER stant Li pem c i i i ERN P 5S 10 T dye E 455 v 1 308 4 INSTRUMENT 2 IRANE THE CONTMOL FROM REMOTE yes C ERROR 5 9 eee SEIP ANFORMATION FROM ME ANALYZER ES 245 X lt gt 40 T GIUE THE CONTROL BACK LOCAL FRONT PANEL i Li 1 N WS 3 yggon Nt NO 3 3 SAVE THE i te loert ion e JIN MASS MERORY 1 t TING TROM THE VUT SETUP IMFORMATIOS nOurc ANALYZER ron 4 b 5 i i 5 4 a E 2 EU YES THE Sls amp eG ERNMENT i MAKE CONTROL FROM REMOTE 4 i 1 7 av 4 a0 4 SETUP nora tT FROM UE ANALYZER 1 3 f THE CONTROL BACK TO LOCAL CERONT PANEL ri SS SETUP TREORMATLON E p gt jn 8 MASS MEMORY 1 1 lt lt Pi i
104. ltation is defined in a FIND clause in the ACTIONS block of the knowledge base This clause instructs the inference engine to FIND a value for a given variable which we call the goal variable The goal variable named in the FIND clause of EXP Test System s ACTIONS block is THE PROBLEM Once THE PROBLEM has been identified as the goal variable the inference engine searches the knowledge base for the first rule that can assign a value to the goal variable Since the goal variable is THE PROBLEM the inference engine looks for the first rule containing the variable THE PROBLEM in its conclusion This is the rule POWER SUPPLY Once the rule is found the inference engine looks at the first variable named in the premise of the rule If it does not know the value of the variable it looks for the first rule containing that variable in its conclusion The only variable named in the premise of POWER SUPPLY is CHECK TRANSFORMER Since the inference engine doesn t know the value of CHECK TRANSFORMER it scans the knowledge base for the first rule which might provide the value in other words the first rule which might contains the variable THE TRANSFORMER in its conclusion Because there is no such rule in the knowledge base the inference engine after scanning all the rules for one that can assign a value to the variable THE TRANSFORMER looks for ASK statement that can provide a value for THE TRANSFORMER ASK statement will prompt the user for
105. m a Framework for explanation Artificial Intelligence Vol 20 PP 215 251 1983 Cunningham P et al Diaqnostic Heuristics and Perspectives Expert Systems PP 242 253 1986 Padraig Cunningham A_ Taxonomv of Knowledge Representation Formalisms Trinity College Dublin Computer Science Report No CSC 87 01 1987 Dague P Raiman Deves P Troubleshooting When Modeling is the Trouble AAAI 1987 Davis R Diagnostic Reasoning Based on Structure and Behavior Artificial Intelligence Vol 24 PP 347 410 1984 deKleer J How Circuits Work Artificial Intelligence Vol 24 PP 205 280 1984 Feigenbaum E A Art of Artificial Intelligence Themes and Case Studies of Knowledge Engineering IJCAI 77 PP 1014 1029 1977 Genesereth M R The Use of Design Descriptions in Automated Diagnosis Artificial Intelligence Vol 24 PP 411 436 1984 Giovannini F Malabocchia F Model Based Expert System for HW Troubleshooting Driven by Compiled Control Knowledge Expert Systems PP 65 77 1985 Pople H E Jr Myers J D Miller R A DIALOG A Model of 143 47 48 49 50 51 52 53 54 55 56 57 58 Diagnostic Logic for Interne Midicine IJCAI PP 848 855 1975 Shortliffe E H Computer Based Medical Consultation MYCIN American Elsevier 1976 Weiss S M Kulikowski C A Safir A A Model Based Consultation Svstem for the Lo
106. n the next chapter 136 8 CONCLUSION Faults due to electronic system failure or malfunction are the major cause of downtime in highly automated machine tool workshops Failure detection and repair is problematic if highly Skilled and well trained local maintenance staff are not in constant supply In this dissertation it is proposed that the enhancement of the rate of repair notwithstanding uncertainty about the skill level is possible with an extension of the basic tool kit so that expert knowledge is available in an intelligence based workstation Based on the conclusion that total maintenance repair knowledge may not be encapsulated a priori the role of an expert system is rendered limited However acknowledging that deep knowledge of electronic circuitry is normally documented in graphical form a system has been proposed and implemented that allows the user to call on graphical information available froma CAD data base whilst proceeding with linguistic diagnostic instruction from the expert system Integrating graphical circuit knowledge and facilitating interrogation of the problem against the background of a workstation defined in this way establishes the context and reflects the normal repair situation The normal repair situation in electronics is characterized by uncertainty incomplete knowledge mixed causality and in consequence a rate of convergence to fault diagnosis varying widely In
107. n with only a brief training period to conduct expertly guided service procedures Reduction of service time and overall maintenance costs improved and uniformly applied service strategies and automated record keeping are among the expected benefits of the use of such an expert service advisory system 5 2 Using Expert System in Building Intelligent Workstation An expert system is the intelligent element among the main elements which assist in building an intelligent workstation Using an expert system in constructing an intelligent workstation will mean implementing the artificial intelligence techniques this workstation This will give the workstation an intelligence 74 attribute and will lead to a powerful workstation Electromechanical systems such as CNC machines have service manuals which describe repair procedures at certain practical level of detail eg about board or electromechanical unit replacement Repair of such systems is normally accomplished by direct replacement of Field Replaceable Units FRUs Detection and replacement of defective FRUs are the basic objectives of the repair task in these systems Depending on the type of system serviced service manuals vary considerably in complexity For some systems complex decision ttrees and flowcharts are part of the manual while in other systems only rudimentary information on repair is provided 53 An expert s intuition and efficiency are not found
108. nd prepare it that it can be drawn on the Screen The screen is set to the graphic mode using a suitable scale according to the drawing TURBO C built in functions have been used to create the schematic diagram on the screen These functions are 1 The line function line x1 y1 x2 y2 which draw line on the screen between point xl yl and point x2 y2 98 2 The text function outtextxy x y text which write the defined text on the screen at point x y 3 The circle function circle x y r which draw circle on the screen at point x y with radius r 4 The arc function arc x y start angle end angle r which draw arc on the screen at point x y beginning at the Specified start angle and finishing at the specified end angle with radius r Several tests have been carried out using these programs and as a result both the drawings created by OrCAD SDT III and the one extracted from the plot file were identical 6 3 Programas The software which reads the graphical format of the plot file and draws the graphics the screen is divided into two main parts The first part is called the Search Program The second part is called the Sketch Program Fig 6 2 shows the flow chart of the Search Program The work of the Search Program is to search and extract all the data of the drawing entities inside the plot file Then the Search Program will save these data in a data file after manipulating and modifying them In the
109. ng Term Managment of Glaucoma IJCAI PP 826 832 1977 Padraig Cunningham Michael Brady Qualitative Reasoning in Electronic Fault Diagnosis 1987 PP 443 445 G M D A Bell The Coexistence Approach to Knowledge Representation Expert Systems Vol 2 No 4 Oct 1985 A S Pollitt Reducing Complexity by Rejecting the Consultation Model as a Basis for the Design of Expert Systems Expert Systems Vol 3 No 4 Oct 1986 Michael D Rychener Expert Systems for Engineering Design Expert Systems Vol 2 No 1 Jan 1985 M Hofmann J Caviedes J Bourne G Beale A Brodersen Building Expert Svstems for Repair Domains Expert Systems Vol 3 No 1 Jan 1986 Michael Genesereth Diagnosis Using Hierarchical Design Models AAAI PP 278 283 Aug 1982 Johan de Kleer Brian C Williams Reasoning About Multiple Faults AAAI PP 132 139 1986 Hal Shubin John Wade Ulrich IDT An Intelligent Diagnostic Tool AAAI PP 290 295 Aug 1982 Ramesh S Patil Peter Szolovits William B Schwartz Causal Understanding of Patient Illness in Medical Diagnosis IJCAI PP 893 899 Aug 1981 Addis Towards an Expbert Diagnostic System ICL 144 59 60 61 62 63 64 65 66 67 68 69 70 71 72 Technical Journal Vol 2 1980 Sanjay Mittal Chandrasekaran Jon Sticklen Patrec Knowledae Directed
110. ngine then gate FILE9 from TURBO C give the value FOUND to the goal variable THE PROBLEM which just was an index to tel that the match is found The FIND statement inside POWER SUPPLY rule lead the inference engine through the knowledge base by giving a new goal 71 After that the inference engine go to POWER SUPPLY1 rule which contain the goal variable in its conclusion Depending the comparison between the value of deltal and the value of standerl the inference engine will fire the POWER SUPPLYl rule or it will not The deep model should contain a structural and behavioural description of the circuit The deep knowledge was represented in the graphic accompany to each test applying on the circuit this graphic has two dimension the physical dimension layout diagram and the functional dimension schematic diagram In addition to representing the deep knowledge in the graphic the deep knowledge can be represented in the intelligence of the technician and the production rules As mentioned with production rules it is very easy to modify or add a new knowledge to the knowledge base The key to the success of an expert system is the integrity of its knowledge base If the knowledge base is incomplete the system will poor problem solver and it may lead to wrong solutions Therefore it is important that the knowledge base be kept up to date at all times In electronic fault diagnosis a new knowledge
111. ns the extracted information from the second part of graphical data By using strcmp function in TURBO C the Search Program will compare between the content of Comp and a pointer to options contains the first two characters to every expected graphical entities PA LB CI AA If the content of Comp array was PA this will indicate to a line command in the HP formated plot file In this case the Search Program will do the suitable manipulation and modification to the format of the captured data to put it in the suitable format for the line function in TURBO C the new formated data LIN 1 1 2 2 Then the Search Program will save the new formated data in the data file If the content of Comp array was LB this will indicate toa text command in the HP formatted plot file Also in this case the suitable manipulation and modification will take part to put the captured data in the suitable format for the text function in TURBO the new formated data TEX x y text Then the Search Program will save the new formated data in the data 102 file If the content of Comp array is CI this will signal to a circle command in the HP formatted plot file Also the suitable manipulation and modification will take a part to put the captured data in the suitable format for the circle function in TURBO C the new formatted data CI x y r Then the Search Program will save the new formatted data in the data file
112. nt M fait Ms FALE Fa i 9 A E v TES HODIFV THE DATA TEXT E i EAE THE x po amm THE FORMAT ICIR di 53 E pon C CTRCL hs Va THE BATA SAUE THE DATA DIR FORMAT 1 i leh e u sta amuia pes 2 end sale i READING 1 FES EROM FLOP gt FILE NON com 71 9 CONUERT THE COORDINATES FROH THE PLOTTER Dine _ NSION i io THE SCREEN DIMENSION y E M ANT C ZOOM THE aaia INSIDE RECTANGHLAR ye HALT TEL THE HSER PRESS 1 KEY ON KEYBOARD SHUT DOWN THE GRAPHICS WODE i 4 Li END 1 SCAN THE CIR THE YSTEM SGRAPHICS HODE 1 Y OPEN THE FILE JES 27 COMPONENTS 2 DRAN CIRCLE 1 vU urn LNO 6 DRAW SCAN THE ORC COMPONENTS ARC pma lt CLEAR SCREEN THE OGSGGiLuicSGCQOPRE THE ANALYZER TART Y l i By 2 P g Za YES INICIALIZE THE i 1348 amp INSTRUMENT 1 MAKE THE CONTRO i REMUT NEM URS IRET FROM THE iNSTRUMENT 1 GIVE THE CONTROL BACK TO LOCAL 1
113. o restore equipment to operating condition within an hour or two when parts were available instead of the two or three days But when this technician left the plant the situation reverted to its original status The search for a more practical solution led some plants to a nation wide CNC maintenance service that means they signed a contract with the manufacturer s for minor and major preventive maintenance which is the key to improve operational efficiency 3 JACK MOORHEAD 4 recommended the provisions for programming maintenance and operation to be made before the CNC machine tool arrive on the shopfloor and the CNC users should be in a position to support and sustain CNC operation internally even though there is considerable assistance available from the outside He said that to develop this internal capability it is important to select the right people and train them thoroughly Three groups are involved 1 part programmer 2 machine operators 3 maintenance technicians He added a minimum number of adequately trained people can keep the CNC running Also when these trained people left the plant the situation reverted to its original status and the breakdown time will cause a halt of the production to the entire workshop To solve the problem of depending on expert people some companies developed expert systems however until the early eighties expert systems required tremendous development work and often special
114. or Hex 44 for talk It should be remembered that more than one listener can be active on the bus at any one time but not more than one talker 3 3 5 Setting the DIL switch on HP IB Interface Card The configuration switches on the HP IB interface card set the interface s operating parameters They are set at the factory as shown below fig 3 8 N CA gt N fig 3 8 The Configuration Switches This setting specifies select code 7 memory address DC000 and interrupt level 3 As a procedure to check the HP IB interface card configuration a comparison has been made between the switch setting of this card and with those shown above As this configuration is satisfactory 29 for most systems it was kept as it is The address switches 1 through 4 determine the memory address and select code of the interface If it is wished to change the recommended setting an address or select code that isn t the same as the address or select code of any other card installed in the system should be chosen Table 3 3 help for set the address and select code it shows addresses used by some common system components Memory Select Switches Address Code 1 2 3 4 Potential Conflicts 00 Used and C4000 1 1000 1 by C8000 2 0 0 1 Q Used by hard disk controller on pre 1935 Vectra PC 2C000 3 0 0 1 1 D0000 4 10100 04000 5 101 D3000 6 0110
115. or RS 232 AB Aplicar 91 267 Fi cer C cour 3 134 820v gt con I v 1 T s exa jer 9 4 em ieee v i WS ar tat vna e 14 1 4 te RA vs b Lr 4 a 2 n M e t imm CES t 39 n 47 te M rv e 4 n 42 4 1 T E 4 1 1 x eu 69 LOS Cig 3 45 28 20 48 3 m ax asd aide nna 19 sev V lt lt A 2 TI Xm POS 847 un 4 V ED cu am n ety or roe y 1 ie we mi pt T Lee I 6 4 a V he amp c9 yv magro JI Te gp tm 41 x _ lt 2 x w 2 E IM asav lotter s Power Supply 116 fig 7 3 The 7475 Graphics P 7 3 opted The development of the EXP Test System proceeded in two stages The First stage was to study the domain which was the design of the 7475A Graphics plotter its construction and the problems which might be encountered during it s use deep study to the 7475A Graphics plotter s circuitry was done The contact with the manufacturer s service board concluded by a list of some previous faults
116. oughout the industry and each has its advantages and disadvantages 3 3 1 1 Serial Data Transfer Serial data transfer is commonly used whenever digital information must be relayed over a relatively long distance The data is often transferred through the telephone wires or over the airwaves via some form of radio carrier The main reason for long distance serial transfer is the reduction in the number of wires required to carry the information Unfortunately the speed at which this data can be transferred serially is normally limited to at present no more than 4 800 bits per second over commercial voice grade telephone equipment Leased service is available for rates of 9 600 bits per second 17 In theory a voice grade channel can carry up to about 20 000 bits per second Higher speeds are attainable if special digital communications links are leased from the telephone company 3 3 1 2 Parallel Data Transfer Parallel transmission is used for short distances where the speed of information transfer is critical This form of data communication is found in newer types of computer peripheral equipment with transfer speeds of up to one million characters per second This equipment includes printers disk drivers and various other forms of peripheral components 3 3 1 3 Asynchronous Serial Data Serial data is transferred in either the asynchronous or synchronous form In asynchronous transmission some times referred to as start sto
117. p transmission start and stop bit intervals are transmitted with each byte of information for the purpose of synchronization No clock waveform is transmitted with asynchronous data since the start and stop bits are used for synchronization In synchronous data transmission synchronization is effected by transmitting a synchronization character or two followed by a large block of data In addition to the sync characters a clock waveform must also be transmitted Therefore synchronization occurs for a block of data in a synchronous system and for each piece of data in an asynchronous system Fig 3 2 illustrates the typical format used for transmitting data asynchronously Each piece of information is preceded by a start bit that is at a logic zero or by definition a space This is 18 STOP START STOP Di D D oe a rx SETS yq 4 4 4 fig 2 2 Asynchronous Serial Data followed by data bits that comprise the information that is always transmitted with the least significant bit first The stop bit or bits in some older systems follows the data and is always at the logic one level or by definition a mark 3 3 1 4 Baud Rate The speed at which serial data is transferred is referred to as its baud rate The baud rate is arrived at by taking the reciprocal of the bit time interval for most application Refer to the section on PSK phase shift k
118. resentation in its explanation facility The rule set has a reasonably complex structure as shown in fig 4 3 This complex structure inherent in the rule base is characteristic of most rule based systems and contradicts that rule base systems are easily extended If an extra rule is to be added to the system then care must be taken to ensure that it fits into the existing structure 64 4 7 Deep Knowledge A model based system is more general than the equivalent shallow knowledge based system as specific heuristics which handle 61 INITIALISATION AND LOCALISATION CONTROL SYSTEM SOLUTIONS fig 4 3 The Complex Structure of PROCESSEX individual cases need not be encoded It should be able to perform well on problems not clearly considered in its construction At the same time a model based system should perform reasonably well on problems on the periphery of its knowledge The reasoning mechanism should be able to draw conclusions in all cases from the first principles described in the model The control structures required are more complex because of this generality They also take longer to execute That because of this complexity and because the inference chains are longer due to the small size of the knowledge 63 62 4 8 Deep Knowledge model based systems Knowledge elicitation difficulties with shallow knowledge based systems are probably a factor contributing to the amount of effort invested in producing mo
119. rmation with detailed circuit information which is normally preserved graphically is classified as deep from a knowledge point of view The following assumptions underpin the proposed intelligent maintenance workstation 1 Shallow knowledge with diagnostic procedures can be encapsulated in a standard expert system shell and will enhance the pace of early fault diagnosis 2 The normal context applying in the diagnosis of complex faults must be acknowledged in the sense that a Graphical information is available and used b convergence to fault identification is open ended uncertain interactive involves learning whilst persueing the fault and the outcome is unpredictable The conclusion reached in defining the software specification therefore is that all of the following elements must be available 1 Routine software for signal detection and instrument driving 2 An expert system shell for shallow knowledge encapsulation and user guidance 3 graphical facility to allow the introduction of deep knowledge in the context of complex fault diagnosis Specifically the following hardware and software elements constitute the workstation 13 This unit consists of four hardware parts which are 1 Controller personal computer 2 IEEE interface card 3 Digital oscilloscope 4 Logic analyzer And from four software packages which are 1 VP EXPERT system 2 TURBO C system 3 Orcad system 4 IE
120. rom the components of the arc command xr xl x yr yl y for the first format of the arc command r sqrt pow x 2 0 pow y 2 0 for the second format of the arc command 1 0 2 0 sqrt pow x 2 0 pow y 2 0 The new formatted data ARC x y start angle end angle r Then the Search Program will save the new formatted data in the data file If the content of Comp wasn t one of the previous characters the Search Program will print on the screen ERROR READING FROM PLOT FILE The three characters in the beginning of every new formated data was added to simplify the recognition of the data type in the second part of the software In the end of this search the Search Program will make an EOF test If the Search Program encounters EOF inside the plot file it will close the plot and the data files and exit If the Search Program doesn t encounter EOF it will return and repeat the previous work So it will search for the first and second parts of graphical information then it will manipulate modify them and save the new formatted data in the data file The data is organized in lines inside the data file each line contains information for drawing one graphic entity 104 LIN 1 1 2 2 x y text CIR x y r ARC x y start angle end angle r The work of the Sketch Program is to read the new formatted data from the data file and prepare it so that it can be drawn on the screen The Sketch
121. s 64 7 6 EXP Test System in Operation To test the performance of EXP Test System and to improve its ability in electronic fault diagnosis some experiences were applied on it To do that wires were connected from the test points A B C D E F G H I J K L M on the motor servo systems to an external breadboard to simplify getting the test signals from that points But it was very difficult to reach the defined test points inside the plotter s power supply and changing the signal s 127 characteristics to simulate the faults So a function generator and a power supply was used to simulate the signals of the plotter s power supply The function generator s signals were used to simulate the transformer s output to give 10 5 ACV The power supply s signals were used to simulate all the continuous voltages appearing on the plotter s power supply board So by using the front panels of the function generator the power supply the amplitude of the signals can be changed increase or decrease the volt values to simulate the fault cases The following examples will explain how EXP Test System diagnoses the electronic faults to achieve the solution The first fault was simulated by decreasing 5V DCV and making it less than the allowable tolerance The plotter s power supply fails test POWER SUPPLY4 The dialogue was as follows the underlined text is the user choice WELCOME TO EXP Test SYSTEM SYSTEM FOR TESTING CNC M
122. service Manuals and such information is normally not provided to the end_user In fact complex repair procedures are difficult to provide in a manual For example basic operations such as setting up hypothesis based on symptoms proving hypothesis and suggesting and verifying corrective actions are often complicated by the presence of subclasses or subproblems which require a changing focus of attention and or changing strategies when solving a problem Effective focusing mechanisms and flexible solution strategies cannot be readily suggested in a service manual due to lack of contextual information However these methods that a human expert readily performs can be implemented using artificial intelligence techniques 53 That mean that the main task of the expert system is to capture the repair knowledge of the best qualified human experts in its knowledge base So the existence of the expert system inside the intelligent 75 workstation gives successfully implemented service advisory system which is the best solution to stop calling in the expert person every time a breakdown happened to any of the machines in the workshop 5 3 Improving the Productivity By building the intelligent workstation which includes all the repair knowledge in its expert system s knowledge base we can depend on a technician with a limited experience to solve any machine s breakdown problems That will reduce the service time and overall mainten
123. service engineer will move the mobile unit to the location of the broken machine switch on the unit and follow the instruction of the expert system The main input to the system is the test signal from the test equipment This signal is compared with the reference signal inside TURBO C system then the result is chained through the function test rules and a list of components in which the fault might lie is produced this is the fault candidate list The expert system will inform the user and guide him on were to put the probe to get the test signal In addition it will call a program in TURBO C which converts an OrCAD program for drawing the schematic and layout diagrams by HP plotter and sketch the mentioned diagrams on the screen of the P C using the graphic library in TC2 The system backward chains through these rules with the goal of discovering which of the fault candidates 13 indeed faulty If it is difficult to get some information using the test equipment the Expert System will query the user for that information So the system gets the extra information that it needs to isolate a fault by asking the user about the faulty device and the existence nature of signals at various points in the circuit 1 3 Aim of the Prodect The aim of the project was to develop a mobile intelligent workstation that will 1 Include an expert system for electronic fault diagnosis which incorporates both deep and shallow knowledge 2
124. stem didn t come to any solution the technician has to analyze the schematic diagram of the circuit and try to find out the fault However there are two reasons why this will not take too long The first one because EXP Test System has already completed part of the analyses The second is the great help which will the graphics facility give When this technician comes up with the solution he will update EXP Test System which may be easily accomplished by adding the new case to it s knowledge base 87 As mentioned it is very easy to update EXP Test System by adding or modifying it because it consists of many production rules IF THEN ie it is modular Up dating EXP Test System will provide new insights different experiences improve problem solving methods and increase the depth of the knowledge inside it s knowledge base at the same time That will ease the task for the new technician in the case of absence retirement or death of the previous technician The new technician technician2 in fig 5 1 will get the advantages of all the knowledge of the expert and the knowledge of the previous technician He will find them inside the knowledge base of EXP Test System CHAPTER 6 INTEGRATING GRAPHIC CAD KNOWLEDGE WITH EXPERT SYSTEM AND ON LINE TEST 6 1 INTRODUCTION Computers have been used to facilitate the design process since the early 1960s Applications have included analysis of designs simulation and even the
125. submenu 1 Talk oniy mode Set the oscilloscope to talk only when a hardcopy without 34 intervention from an external controller is wished The attached printer must be set in the listen only or listen always mode 2 Addressed mode This mode allows a controlling device to selectively address the HP 54501A for talking or listening The address of the HP 54501A can be selected while the instrument is in the addressed mode 3 EOI key The EOI End or Identify key toggles this function on or off EOI is a line on the HP IB asserted with the last data byte of a message If this function is on EOI will be asserted by the HP 54501A on the last byte of each message sent If it is off EOI will not be asserted This function only affects messages sent from the HP 54501A The HP IB will accept any of the legal 488 message terminators regardless of the setting of this function IEEE 488 requires that EOI is asserted Therefore with EOI off the HP 54501A will send messages that do not follow IEEE 488 rules concerning EOI EOI should only be turned off if the controller does not deal with EOI appropriately 4 Form Feed key and Paper Length key Are useful when the oscilloscope is connected to a printer In this project the addressed mode was selected then address 7 was given to the oscilloscope and case on for the EOI was selected as illustrated in fig 3 12 35 HP IB menu ADDRESSED ADDRESS 7 fig 3 12 A
126. t includes 1 2 3 4 5 6 LOGIC PROBE Such probes will detect and indicate high and low 1 or 0 logic levels as well as intermediate or bad logic levels including an open circuit on a single line of CNC machine circuit LOGIC PULSER Such pulsers are hand held logic generators used for injecting controlled pulses into digital logic circuits CURRENT TRACER Such current tracers are hand held probes that enable the precise localization of low impedance faults in electrical systems including typical CNC machine printed circuit wiring LOGIC CLIP Such clips are designed for logic level determination only on ICs using TTL and DTL circuits Generally clips can test flip flops gates counters buffers adders shift registers and the like but will not test ICs with nonstandard input levels or expandable gates LOGIC COMPARATOR Such comparators clip onto 16 pin ICs and through comparison scheme instantly display any logic state differences between the test IC and a reference IC Logic differences are identified to the specific pin or pins of the IC with the comparator s display of 16 LEDs A lighted LED corresponds to a logic difference LOGIC ANALYZER Although single stepping check of system timing can pinpoint many CNC machine problems there are two obvious problems First present day multitrace oscilloscopes do not have enough traces to accommodate all the lines in data and a
127. tems have a means for explaining their conclusion Typically this takes the form of showing the rules involved in the decision and the sequence in which they were fired When users want to know the expert system s line of reasoning they can read the rules and follow the logic themselves The explanation facility is important because it helps the user feel more comfortable with the outcome VP Expert has very powerful explanation facility These include BECAUSE HOW WHY BECAUSE The because keyword appears in the rule base It provides explanation of the expert system s rules during execution It lets us add reasons to the rules in rule base These reasons describe how the rule works and why the rule requires specific answers from 53 the user HOW The HOW command lets us ask how VP Expert assigned a specific value to a variable If VP Expert assigned the value to a variable the HOW command displays the BECAUSE text If the rule does not contain a BECAUSE keyword and text VP Expert displays the rule WHY The WHY command lets us ask VP Expert why it is asking a specific question If the rule contains the BECAUSE keyword and text VP Expert displays the BECAUSE text If the rule does not contain the BECAUSE keyword VP Expert displays the rule 65 4 3 6 2 Base Of Modification In domains where rapid changes take place it is important that some means be provided for quickly and easily incorporating this knowledge
128. the last 20 years the complexity of the mechanical aspect of machine tools has significantly increased this has been accompanied by a corresponding complexity of electronics In the early 1970 s Alfred Herbert limited introduced a variety of computer numerical control CNC turning machine tools These were continuously modified in the light of experience gained in the field subsequently updated models were developed and more recently microprocessor control together with manual data input CNC systems were introduced Because of its considerable inherent flexibility a CNC machine is capable of producing an output machining rate of up to three to four times the output of manually operated conventional machines Because of the high output of these machines breakdowns have an increased significance since the breakdown of a single CNC machine can result in the production of an entire workshop being halted 34 In short CNC equipment availability seldom reached much beyond the 60 percent level because nine times out of ten the maintenance people could not make the necessary repairs So it was necessary to call in the machine manufacturer s maintenance people who of course were not immediately available so the down time was measured in days To solve the maintenance problem technician was hired to specifically cope with control unit emergencies and maintenance So he instituted a preventive maintenance program and he was able t
129. tion manufacturing business management education and many other areas An architect can lay out or design a building using a computer and specialized graphic software Animated cartoons and movies also take advantage of computers and graphic application program One of the most basic forms of computer graphics is the bar chart or graph Simulation and training of pilots is another area where computer graphics has had great payoffs With three dimensions representations of an aircraft s controls and an airport s landing strip student pilots can learn the basics of flying without wasting expensive fuel The simulation of an aircraft and an airstrip allow student to experience the visual aspect of flying without having to step into a plane 91 CAD Applications A variety of CAD applications are currently in use on computers from mainframes to personal computers The industry is growing so fast that it s now necessary to specialize in a specific application area just to maintain a good knowledge of that field One of The most important applications is Printing Circuit Design If there is a single field in CAD that has benefitted most it is the printed circuit design process With the electronics industry becoming more competitive in developing new electronic products the need for taking a designer s first sketches to final artwork is essential A printed circuit CAD system can reduce everything from design to manufacturing the
130. tion for use in their instruments It was adopted as a general purpose instrumentation bus GPIB by IEEE in 1975 This standard is like the RS 232C standard because it defines the pin connections protocol standard messages for communications The IEEE 488 interface bus is a means of connecting a number of instruments to a common input output port of a computer An 8 line bus carries addresses data and commands between instruments and the computer Each instrument has an address or addresses assigned to it usually by means of a DIL switch on the 21 instrument and can be called up by the computer After activation the addressed instrument may either send data talk or receive data listen before being de activated untalk unlisten and the next instrument activated An instrument that can send data is called a talker Likewise one that can receive data is a listener and one that can send or receive is called a talker listener The computer is called the controller There may be only one controller active on the bus at time although control may be transferred from one controller to another Also there may be only one talker active on the bus at any one time although there may be many listeners if desired Physical electrical limitations are up to 15 devices connected to the bus with no more than 2 meters between them or 20 meters bus length overall Also more than 50 of the instruments connected must be powere
131. tionally between instruments and controller The Handshake lines are manipulated to ensure that each 8 bit byte is successfully read by the listener The Bus Management lines are primarily used to differentiate between data commands and addresses on the bus as well number of miscellaneous control functions regarding the passing of data status and command streams between devices 24 3 3 3 1 Data Connections The data connections may be open collector or three state logic In most applications these lines use three state bidirectional data transceivers since they increase the usable frequency range of the bus The frequency range is increased because a three state driver contains a low impedance pullup network that charges the line capacitance more quickly This reduction in zero to one transition time allows higher data transmission rates The data pins are labeled DIO1 through DIO8 where DIO1 is the least significant bit position 76 The actual pin numbers are illustrated in fig 3 6 SIGNAL GROUND 4 SHIELD ATN GND 23 ATN SRQ GND 2 SRQ SFC GND 21 9 IFC NDAC GND 20 8 NDAC NRFD GND 19 7 NRFD DAV GND 18 6 DAV REN 7 5 EOI DIO8 6 4 2 DIO4 2107 5 3l 2106 4 28 0102 DIOS 3 19 0101 TWISTED PAIR WITH SIGNAL CABLE OF SAME NAME fig 3 6 GPIB Interface Connec
132. to address the 1241 Logic Analyzer This will give access to the STORAGE MEMORY MANAGER menu a COMM PORT CONTROL menu if COMM Pack is installed and ROM Pack menu if ROM Pack is installed So once the COMM Pack has been installed as shown in fig 3 14 enter the menu pressing the UTILITY key and then the COMM PORT CONTROL soft key RETAINING SPURS Snap the handle on the pack over these purs to secure the pack firmly 10 the 1240 CAUTION wen n INTERFACE CONNECTOR HANDLE Pull the handle to remove the pack Secure the pack firmly to the 1240 by snapping the handle over the retaining spurs fig 3 14 The COMM Pack installation Fig 3 15 shows a typical COMM port control menu display The port status GPIB address and message termination type can be selected by using the COMM port control menu GPIB port status Valid selections are ONLINE and OFFLINE in OFFLINE no communication occurs between the controller and 1241 before changing any other parameters the 1241 39 must be OFFLINE When the 1241 goes ONLINE it sends service request to the controller notifying the controller SERVICE REQUEST KNOB SELECT PORT STATUS ONG TNE 124075 GPIB ADDRESS s MESSAGE TERMINATION fig 3 15 A Typical COMM Port Control Menu Display of its ONLINE status x 1241 s GPIB Address Valid addresses are 0 30 Message Termination Valid types are EOI an
133. to aid in diagnosing medical cases Symptoms and test results can be given to the expert system which 44 then searches its knowledge base in an attempt to match these input conditions with a particular disease This results in a conclusion about the illness and some possible suggestions on how to treat it Such an expert system doesn t replace doctors but helps them confirm their own decisions Expert systems have been used to help locate oil and mineral deposits 4 3 1 Widely Used Expert Systems There are few number of expert systems available now in operation they represent just a small percentage of all computer software in use Some of these expert systems played an important part in artificial intelligence development they make good models for studying the structure of an expert system MYCIN MYCIN is probably the best known of all the expert systems It was designed by Edward Shortliffe of Stanford University in the mid 1970s It is medical expert system that diagnoses bacterial infections 47 DENDRAL DENDRAL is another early expert system it is a product of researchers at Stanford University DENDRAL was developed to identify the molecular structure of unknown compounds 54 XCON and XSEL XCON is an expert system that helps configure large computer Systems Developed jointly by Digital Equipment Corporation DEC and researchers at Carnegie Mellon University CMU helps translate a customer s ord
134. tor Plug 25 3 3 3 2 Handshaking Connections To ensure that bytes pass from talker to listener s a three line handshake is implemented with DAV NDAC and NRFD DAV The DAV data available is issued by the talker to indicates the availability or validity of data the data bus connections NRFD The NRFD connection or not ready for data pin is issued by the listener to indicates the readiness of the device or devices connected to the bus to receive data NDAC The NDAC or not data accepted is issued by the listener to indicates the condition of acceptance by the devices connected to the bus This handshake allows bytes to be passed at the rate that the slowest listener can take them The handshake occurs for every byte transfer irrespective of whether that transfer is data commands or addresses Before a byte is sent from the talker to the listeners the three handshake lines should be in the states given by table 3 2 LINE STATE MEANING ST EDI TI UTR e an Ea High Ready for data table 3 2 Quiescent State of the Handshake Lines Referring to fig 3 7 when the talker is ready to output data it inputs NRFD and NDAC A B and providing they are in the state 26 given in table 3 2 it outputs a byte onto the data bus After allowing few nanoseconds settling time it drives DAV low C signalling that data is valid on the bus Mean
135. ts in batch mode TREELIST A program that scans a hierarchical organization of sheets to display the structure sheet names and sheet path names of the hierarchy 6 2 3 OrCAD Plot File During the last twenty years CAD Computer Aided Design has been used as a powerful tool in all engineering disciplines specially in electronic engineering field and printed circuit board design It was very important to incorporate CAD system in this work to 96 achieve the interactivity integrity and generality The OrCAD SDT III which is a computer aided drafting package capable of drawing 2D diagrams has been adopted OrCAD SDT III package is a complete and flexible schematic capture package being used in the department It has an easy to use menu driven commands which help to draft and plot electronic schematics In order to integrate OrCAD with the EXP Test System it was necessary to adopt a neutral file which can be produced by OrCAD SDT III and read by an external program The plot files are the ideal files to be used in this process because of its capabilities to represent all the entities which can be drawn on the screen Also these files are written in text files which can easily be read and translated to other formats OrCAD SDT III has the capability to create several types of OrCAD plot files These files command plotters to create hardcopy of the drawings HP formatted plot file has been chosen to be used as a neutral fi
136. ughout are to detect faults and find solutions To approach these goals and build the automatic test system supporting software has been developed in TURBO C with EXP Test System This software reduces the dependency on the user of EXP Test System in defining the quality of the signals In NODAL it is very important that the user give help to the system in defining the fault NODAL usually asks the user about the nature of the signals at various points in the power supply circuit In order to prove this the clauses in the rule premise have to be proved true The information that the module is of type one one is available in the module frame The user will have to be asked for the other information The output is found to be connected to Node 12 so the user is asked for the quality of the signal at Node 12 and at A to which the input is connected If the signal on the output is bad and the signal on the input is good then the module is concluded to be faulty Setup for Test Vector 1 What is the SIGNAL of A Good What is the SIGNAL of B Good 119 pd SYSTEM ud 1 What is the SIGNAL of NODE 12 Good 63 EXP Test System usually asks the user to move the probe from one test point to another and it will ask him for some extra information about the quality of the signals in a few places Fig 7 4 shows the complete software which was developed to achieve the project s goals THE P C PLOT 5 til it D
137. user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT 2 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER YES NO 131 THE OUTPUT IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE The user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT 5 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER XES NO THE 12V OUTPUT IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE The user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT 7 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER XES NO THE 5V OUTPUT IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE The user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT 8 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER YES NO THE 418 26V OUTPUT IS OK PRESS ANY KEY TO CONTINUE TESTING THIS DEVICE 132 The user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT 11 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOSE NO AND PRESS ENTER XES NO THE 12V OUTPUT IS OK lt PRESS ANY KEY gt TO CONTINUE TESTING THIS DEVICE The user should press any key PUT THE OSCILLOSCOPE S PROBE AT POINT 12 IF YOU ARE READY CHOOSE YES AND PRESS ENTER OTHERWISE CHOOS
138. ut some of the main advantages of expert systems Like other conventional software expert systems offer some advantages as following 1 2 3 4 5 Permit experts to do the work of experts Improve productivity by improving efficiency Save time in accomplishing a specific objective Simplify some operations Automate repetitive or complex processes Expert systems offer some additional advantages over conventional software such as 1 2 3 Permit new kinds of problems to be solved Capture and store valuable knowledge that might be lost due to the resignation retirement or death of an expert Make expert knowledge available to a wider users 4 3 3 Disadvantages of Expert Systems The 1 2 3 4 disadvantages of expert systems are summarized as follow Expert systems are expensive is very difficult to develop an expert system and hard to find good experts Most expert systems still must be implemented a big mainframe or minicomputer Expert systems not 100 reliable So that the user should always provide the final judgment These disadvantages are significant but certainly not impossible to overcome 47 4 3 4 Expert System s There are two basic types of expert systems the stand alone system and the embedded type 1 Stand Alone system In this case the computer is totally dedicated to that program while it is running it 2
139. uters Book Inc 1985 Joe Rooney Philip Steadman _ Principles of Computer Aided Desian Open University 1987 Spyros G Tzafestas _ Knowledge Based System Diagnosis Supervision and Control Plenum Press New York 1989 Barry B Brey Microprocessor Hardware Interfacing and Applications Bell amp Howell Company 1984 Keravnou E T Johnson L Competent Expert Systems Kogan Page 1986 Hayse Roth D A Waterman Lenat Building Expert Systems Addison Wesly Reading MA 1983 Buchanan Shortliffe Rule Based Expert Systems Addison Wesly Publishing Co Inc 1984 M R Genesereth An Overview of MBS for AI Experts Standford Heuristic Programming project Memo HPP 82 27 Dept of Computer Science 1982 C L Forgy OPS5 User s Manual Carnegie Mellon University 1981 Lotfi Zadeh Fuzzv Lodic Computer PP 83 92 April 1988 146 APPENDIX A pj di iu ei A S lai 431 Tk 4 gt awd T E E E 8 4 ji oe E m 1 Pui CO ee 24 Ta Li p SES i CLOSE PLOT amp 3 BAER FILE 4 7 2 Y THEO d TYPE 1 4 4 HODITE THE AE a THE DAT EO 8 mA WITH EHE FO DRPRT 2 B Zu te
140. vided to 11000 in X direction and to 7721 in Y direction The initialize of the graphic system defines the screen to be divided to 320 in X direction and to 200 in Y direction Fig 6 5 shows the location of the coordinate origin 0 0 screen units and the orientation of the X and Y axis 9 0 ORIGIN ex 5 1 1 TN 2 328 200 fig 6 5 The Location of the 0 0 Screen Units 108 The x conv function multiply the value which originally come from the HP formatted plot file the coordinates shown in fig 6 4 by x conversion rate x conversion rate 320 11000 0 029 X value in screen scale x conversion rate x value in plotter scale Then x conv function returns the x value in the screen scale Because the orientation of Y axis in the plotter scale 1 opposite that of the orientation of Y axis in the screen scale The y conv function subtracts the value which originally come from the HP formatted plot file from the maximum value to y in the plotter scale 7721 Then multiply the result by y conversion rate y conversion rate 200 7721 0 026 y value in screen scale y conversion rate 7721 y value in plotter scale Then y conv function returns the y value in the screen scale 6 4 Integrating OrCAD SDT III Svstem with EXP Test System Now the Sketch program Sketchl and Sketch2 is ready for drawing the schematic or t
141. which happened during the history of the plotter The second phase of the project which required much more original thought and work was to design and built the supporting programs in TURBO C and the final expert system with VP Expert The design structure imposed by VP Expert meant that in general the system would have knowledge about what should be happening if the plotter were in perfect working order So the system looks for what should be there and when there is a discrepancy between the expected behaviour and the actual behaviour of the plotter it tries to localize the source of this discrepancy When the system has done this it then proposes a hypothesis about the cause of the fault based on the location of the discrepancy Therefore the fault is diagnosed not by what is happening but by what is not happening in the plotter s circuitry 7 4 Design and Development 7 4 1 Introduction Once VP Expert system was adopted as the shell for EXP Test System the appearance of the system to the user and the style of consultation had also been decided VP Expert system dictates 117 this to the builder of the expert system This is due to the rigid question and answer framework which VP Expert system provides as its only means of communication with the user VP Expert system was selected as the development environment for EXP Test System because it was the only expert system shell available in the electronic school at the t
142. while the listeners are looking at DAV waiting for it to go low and when it does they take low the NRFD line D signalling to the talker that it must not change it s data At the same time the listeners latch in the data byte and having done so release the NDAC line E signalling that they have accepted data Due to the party line nature of the bus NDAC will not go high until the slowest listener has accepted the data MEANING NOT VALID DAY DATA VALID listener READY FOR DATA READY FOR DATA response 0146 51 iPastest Listener noc b tesis tar dta listener DATA ACCEPTED MDAC E N EE uc DATA NOT ACCEPTED fig 3 7 The Handshake Once the NDAC goes high the talker initiates a reset sequence to prepare for the next byte transfer if any This happens by it taking DAV high again F and removing data from the bus The listeners in response to DAV going high let NDAC go low 6 signalling that they have not yet accepted the subsequent data byte because it hasn t yet been sent and they let NRFD go high to signal to the talker that they are ready for new data 27 3 3 3 3 Interface Management Connections These connections IFC ATN SRQ REN and EOI manage the flow of information through the GPIB IFC The interface clear is issued by the controller to initialize all instruments on the bus to their known states

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