Prototype Software for Automatic Generation of On
Contents
1. 1981 C L Beck Modeling and Simulation of Flexible Control Structures for Automated Manufacturing Systems Tech report Robotics Institute Carnegie Mellon University 1985 C L Beck and B H Krogh Models for Simulation and Discrete Control of Manufacturing Systems IEEE International Conference on Robotics and Automation San Francisco April 1986 B H Krogh and C L Beck Synthesis of Place Transitions Nets for Simulation and Control of Manufacturing Systems 4th IFAC IFORS Symposium Large Scale Systems International Federation of Automatic Control Zurich August 1986 International Electrotechnical Commission Standard for Programmable Controllers Part 8 Programming Languages 1982 Technical Committee 65 Industrial Process Measurement and Control2. about an operation A INSERT assoc actuator for this operation P INSERT an out op cond OR header for this operation C INSERT an out op cond AND header for this operation O INSERT an in op cond OR header for this operation H INSERT an in op cond AND header for this operation L LIST all of the names present Q Quit and look at another data base List all of the commands availabel Pu will generate the structure for an output transition and name that transition TRANS _ n where n is a number DBBUILD maintains Once the transition has been named DBBUILD will ask if there are any resource states that you want to attach to this transition Upon entering a state DBBUILD will generate a structure to hold the state name DBBUILD will name this structure STATE_ n much in the same way it names the transitions C can be used to add additional resource states to an existing output transition DBBUILD will first ask for th output transition name TRANS_1 TRANS_ 2 etc and then allow you to enter a resource state O and H perform the same as P and C respectively but are used for input transitions rather than output transitions NOTE 1 The words OR and AND used in the menus refer to transitions and resource states associated with that operation respectively OR is used for transitions because they represent the different enabling or resulting sets of resource states AND is used for resource states within a transition beca
3. an experienced programmer would feel quite comfortable using DBBUILD without first reading this manual However DBBUILD will query for information that may seem irrelevant this manual tries to explain the need for these queries II 2 Structure The data base is comprised of four major record types l operations containing information on input and output transitions resource states and actuators 2 resources containing information on the resource states and the sensors data required to define each state 3 sensors containing the address label of the sensor input port and 4 actuators containing the address label for the actuator output port Schematics of the records are shown in figures 4 through 7 The topics discussed in this part of the manual are for use by those who have an understanding of a structured language Comprehension of the material is not required to use DBBUILD II 2 1 Operation Records The following is the top level structure in the operation record typedef struct operation type char name NAME SIZE operation name defined by user char desc DESC_SIZE operation description int num_in_op holds the number of input transitions int num out op holds the number of output transitions int num_assoc act holds number of associated actuators struct operation_type next struct operation type prev struct in_ op in_ op ptr pointer to list of input transitions struct out _op out_op ptr pointer to list
4. associated with the resultant resource states within a transition and is performed to maintain the system state as defined in the Petri net The instructions within IL are used to develop conditional branches based on the system state For example IF limit switch 1 LS1 is activated AND limit switch 2 LS2 is not OR limit switch 1 is activated AND limit switch 3 LS3 is activated THEN turn on solenoid 1 S1 OPERATIONS POINTER TO BEGINNING OF OPERATION LIST OPERATION NAME NEXT OPERATION DESCRIPTION NOOF INPUT TRANS NO OF OUTPUT TRANS NO OF ACTUATORS PREVIOUS POINTER TO ONE OF POINTER TO ASSOCIATED ACTUATORS THE INPUT OR OUTPUT TRANSITIONS NEXT TRANSITION STRUCTURE NAME STRUCTURE NAME DESCRIPTION DESRIPTION NO OF INPUT OR ACTUATOR OUTPUT TRANS TTS TYPE OF OUTPUT POINTER TO EACH OF THE RESOURCE STATES STRUCTURE NAME DESRIPTION RESOURCE NAME STATE NAME NEXT PREVIOUS STRUCTURE NAME DESRIPTION RESOURCE NAME STATE NAME Figure 4 Database structures and pointers operation records RESOURCES POINTER TO BEGINNING OF RESOURCE LIST RESOURCE NAME DESCRIPTION NO OF STATES Previous POINTER TO ONE OF THE STATES NEXT STATE STATE NAME DESCRIPTION NO OF DIFFERENT SETS OF SENSORS USED TO DEFINE THIS STATE PREVIOUS POINTER TO ONE OF THE SETS OF SENSORS NEXT LIST STRUCTURE NAME EXT L DESCRIPTION NO OF SENSORS IN PE THIS LIST POINTER TO LIST OF THE RE
5. determine if deadlocks are present The program that performs the net analysis may be a simulation program that can simulate the nets operation given an initial marking or placing of the tokens Ultimately to allow the generated code to be used in a production environment an interface such as Ladder Diagram needs to be presented to the technician for use in on line debugging of the system One of the purposes of the IEC Language Specification is to provide consistency between controller codes This consistency should allow the development of linking programs that can change the controller code from IL to Structured Function Chart 5 to executable code etc and back again 19 I Sensors Actuators Resources and Operations for Conveyor Example The following two lists show the sensors and actuators used in the conveyor example SENSORS PLS1 PREP BOOTH LIMIT SWITCH 1 BLS1 BASE BOOTH LIMIT SWITCH 1 BLS2 BASE BOOTH LIMIT SWITCH 2 BLS3 BASE BOOTH LIMIT SWITCH 3 CLS1 CLEAR BOOTH LIMIT SWITCH 1 BPLS1 BASE PUSHER LIMIT SWITCH 1 BPLS2 BASE PUSHER LIMIT SWITCH 2 BLDO BASE LEFT DOOR OPEN LIMIT SWITCH BRDO BASE RIGHT DOOR OPEN LIMIT SWITCH BLDC BASE LEFT DOOR CLOSED LIMIT SWITCH BRDC BASE RIGHT DOOR CLOSED LIMIT SWITCH ACTUATORS PBSD PREP BOOTH STOP DOWN PBSU PREP BOOTH STOP UP BPEX BASE PUSHER EXTEND BPRET BASE PUSHER RETRACT RBDO RIGHT BASE DOOR OPEN LBDO LEFT BASE DOOR OPEN RBDC RIGHT BASE DOOR OPEN LBDC LEFT BA
6. of output transitions The authors would like to thank Wayne Figurelle for developing the C code for DBBUILD 23 struct act list assoc_act_ptr pointer to list of actuators affected by the operation The following structure contains information on the associated actuators typedef struct act list char name NAME SIZE structure name defined by DBBUILD char desc DESC_SIZE not used char act_name NAME SIZE name of the actuator char assoc op name NAME SIZE not used char act_cond COND_SIZE the condition of the actuator defined by user struct act list next struct act list prev The following structure holds information on the input transitions typedef struct in_op char name NAME SIZE DBBUILD name of the transition char desc DESC_SIZE not used int num_in_op_ AND number of resource states associated with the transition struct in_op next struct in_op prev struct in_op AND in_op AND ptr points to a list of the resource states associated with the transition The following structure holds information on the output transitions typedef struct out op char name NAME SIZE char desc DESC_SIZE int hum_out_op_AND struct out op next struct out_op prev struct out_op AND out_op_ AND ptr The following structure holds the input transition s resource states typedef struct in_op AND char name NAME SIZE structure name defined by DBBUILD char desc DESC_SIZE not used
7. sensor type Char name NAME SIZE sensor name Int wire _num Char desc DESC_SIZE description of the sensor optional Int cond condition the sensor will be in when actuated Struct sensor type next Struct sensor _type prev Int num_assoc_ res Number of resources for which this sensor is used Struct assoc res assoc res ptr Pointer to associated resources The following structure contains information on resource states in which the sensor is used Typedef struct assoc _res Char name NAME SIZE DBBUILD structure name Char desc DESC_SIZE not used Char res_name NAME SIZE Resource name Char state_name NAME SIZE State name Struct assoc Tes next Struct assoc res prev 11 3 Menus The menus used to prompt the user use terms used to describe elements of Petri nets Most menu options are self explanatory however those options that are not will have a brief explanation following the menu listing The top level menu and therefore the first one you see allows you to choose which record you want to investigate This menu is as follows For sensor data type For resource data type For operation data type For actuator data type To quit this program oOrown Hone aw me tt Which type do you want to alter or look at 27 II 3 1 Operation Menu If at the top level you decide to look at operations the following menu will appear I INSERT new operation D DELETE an operation F FIND an operation or some info
8. DBBUILD and PROGGEN In section 3 we describe the structure and use of DBBUILD and in section 4 we describe PROGGEN and discuss its performance in terms of the generated controller code The performance criteria is based on correctness and gains or losses in efficiency compared to code developed manually by a programmer In section 5 we propose methods for incorporating additional utilities such as timers counters and external functions into DBBUILD and PROGGEN The structure of the database built by DBBUILD corresponds to a PN model of the system Thus PN techniques can be applied to determine if deadlocks or inconsistencies exist in the control logic Current research into the application of PN theory for automatic evaluation and diagnosis of programming errors is discussed in the concluding section 2 Control of an Automatic Conveyor In this section we illustrate the Petri net methodology for an automatic conveyor system at the General Motors Truck amp Bus Assembly Plant in Baltimore MD This example is used as an illustration throughout the remainder of the report The conveyor system illustrated in figure 1 indexes vans through a painting module consisting of a preparation booth a base coat booth a clear coat booth and an observation booth The preparation booth is used for final preparation of the vans before painting Coats of pigment and resin are applied in the base coat booth followed by the application of a coat of clear resin in t
9. OCIATED WITH THIS OUTPUT TRANSITION Figure FLOW continued 14 In IL would be represented as follows LD LS1 ANDN LS2 OR LS1 AND LS3 ST S1 To simply enable the actuator when the input resource state conditions are satisfied is not sufficient Actuators vary in types some are required to remain enabled for the duration of the operation while others are required to remain enabled until another motion of the same actuator is needed Enabling the actuator output for the duration of an operation is established by the fact that the input states to the operation remain true until an output transition becomes true as defined by the associated resource state sensors and new states are defined Other types of actuators must remain rigid even after its motion is complete For example the doors between the booths in the conveyor example must be held open after the door open limit switch has been activated This prevents the doors from drifting shut and possibly making contact with the van causing a paint defect The task of maintaining the output to the specified actuator is performed automatically by PROGGEN If an actuator has in its description more than one motion PROGGEN will first reset all outputs to the actuators then set the output for the desired motion Therefore for the case described above the operation that opens the door will set latch the output to the door open solenoid In the operation that the do
10. Prototype Software for Automatic Generation of On line Control Programs for Discrete Manufacturing Processes Gregg Ekberg and Bruce H Krogh CMU RI TR 87 3 Flexible Assembly Laboratory The Robotics Institute Carnegie Mellon University Pittsburgh Pennsylvania 15213 February 1987 Copyright 1987 Carnegie Mellon University This work has been supported in part by General Motors Corporation North American Philips Corporation and the National Science Foundation under research grant DMC 8451493 Table of Contents 1 Introduction 2 Control of an Automatic Conveyor 3 DBBUILD 4 PROGGEN 4 1 Description 4 2 Analysis 5 Additional Utilities 5 1 TIMERS 5 2 COUNTERS 5 3 EXTERNAL FUNCTIONS 6 Conclusion I Sensors Actuators Resources and Operations for Conveyor Example II DBBUILD User s Manual II 1 Introduction II 2 Structure II 2 1 Operation Records I 2 2 Resource Records II 2 3 Actuator Records II 2 4 Sensor Records II 3 Menus II 3 1 Operation Menu II 3 2 Resource Menu 11 3 3 Actuator Menu II 3 4 Sensor Menu NR we 17 17 17 18 18 19 22 22 22 22 24 25 26 26 27 29 30 31 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 il List of Figures Modular paint shop conveyor system Detail of conveyor stops and chain Petri net model of conveyor control logic for the base coat booth Database structures and pointers operation records Database structures and poin
11. QUIRED SENSORS STRUCTURE NAME DESCRIPTION SENSOR NAME SENSOR CONDITION NEXT PREVIOUS Figure 5 Database structures and pointers resource records 10 SENSORS POINTER TO BEGINNING OF SENSOR LIST NEXT SENSOR SENSOR NAME DESCRIPTION NO OF RESOURCES IN WHICH IT IS USED TYPE OF SENSOR WIRE NUMBER Figure 6 Database structures and pointers sensor records 11 POINTER TO BEGINNING OF ACTUATOR LIST NEXT ACTUATOR ACTUATOR NAME DESCRIPTION NO OF OPERATIONS IN WHICH IT IS USED TYPE OF OUTPUT WIRE NUMBER PREVIOUS Figure 7 Database structures and pointers actuator records START THE OPERATION ENABLING CONDITIONS WITH THE LD INSTRUCTION FOR THE FIRST ENABLING STATE IN THE FIRST INPUT TRANSITION START OR ENABLING CONDITIONS AND LOAD FIRST STATE FROM THIS TRANSITION LOAD THE REMAINING STATES WITH THE AND INSTRUCTION GET NEXT TRANSITION ARE THERE ANY MORE INPUT TRANSITIONS NO ENABLE THE OPERATIONS ASSOCIATED ACTUATORS TO NEXT PAGE FROM NEXT PAGE Figure 8 PROGGEN Flow Chart Continued on next page 13 FROM PREVIOUS PAGE 1S THERE ANOTHER OUTPUT TRANSITON YES LOAD THE OPERATIONS ENABLING STATES AGAIN LOAD AS AND INSTRUCTIONS THE SENSORS ASSOCIATED WITH THIS TRANSITIONS RESOURCE STATES RESET THE LATCHED STATES OF ALL RESOURCES ASSOCIATED WITH THIS TRANSITION USING THE RESET INSTRUCTION SET THE RESOURCE STATES ASS
12. SE DOOR CLOSE The following lists provide a brief description of the resource states and operations modeled by the PN in figure 3 VAN RESOURCE CYCLE SENSORS REQUIRED VO Van at prep booth stop PLS1 V1 Van arrived in base booth BLS1 V2 Van in base booth painting position BLS2 V3 Base coat applied to van NONE V4 Van at base booth doors BLS3 V5 Van arrived in clear booth CLS1 VE1 Failed to move into paint position BPLS2 and BLS1 VE2 Failed to move off grounding bars BPLS2 and BLS2 20 BASE BOOTH PUSHER RESOURCE CYCLE BP1 Base pusher retracted and waiting for van to arrive BP2 Base pusher extended with van in the back dog thus the van is in the painting position BP3 Base pusher retracted while the van is in the painting position BP4 Base pusher extended with van in the front dog thus the van is pushed past the painting position BASE BOOTH DOORS RESOURCE CYCLE BDOI1 Opened for van to pass through BDO2 Base doors open and van passed BDC1 Base doors closed for painting BDC2 Base doors closed painting complete BDOE Error base door open the doors did not open BDCE Error base doors close the doors did not close BASE BOOTH RESOURCE CYCLE BBF Base booth clear empty and waiting for the next van CONVEYOR RESOURCE CYCLE CS Conveyor stopped SENSORS REQUIRED BPLS1 BPLS2 BPLS1 BPLS2 SENSORS REQUIRED BLDO and BRDO BLDO BRDO CLS1 BLDC
13. SOR2 etc This version of DBBUILD does not contain additional information on sensors beyond what the S option provides II 3 3 Actuator Menu If at the top level you requested to enter the actuator record the following menu would appear I_INSERT new actuator D DELETE an actuator F FIND an actuator or some info about an actuator L LIST all of the names present Q Quit and look at another data base List all of the commands availabel The find command invokes the following menu D To see the description of the actuator S Get info about a particular assoc op M to list all of the motions this actuator has L To list all of the assoc op with this actuator Q To QUIT looking at this actuator to see these commands 31 1 3 4 Sensor Menu If at the top level you entered the sensor record the following menu would appear I INSERT new sensor D DELETE a sensor F FIND a sensor L LIST all of the sensors present W Change the WIRE number assoc with a sensor Q To quit and look at another data base List all of the commands availabel The find option will cause the following menu to appear D To see DESCRIPTION of the sensor L To LIST all of the states that this sensor is used to define W To see the WIRE number of this sensor Q When you are done looking at this particular sensor List these commands 32 References J L Peterson Petri Net Theory and the Modeling of Systems Prentice Hall Inc Englewood Cliffs NJ
14. and BRDC BLDC and BRDC BLS3 and NOT BLDO BLS2 and NOT BLDC and NOT BRDC SENSORS REQUIRED NONE SENSORS REQUIRED NONE 21 OPERATIONS OP1 Drop stop in prep booth and allow van to move into base booth OP2 Put van into base booth painting position by extending base pusher OP3 Retract base pusher OP4 Apply base coat to van OP5 Extend base pusher to push van past painting position OP6 Open base booth doors OP7 Retract base pusher to accept new van arriving in base booth OP8 Stop conveyor to prevent van from hitting base doors OP9 Move van from base doors to clear booth pusher OP10 Close base booth doors OPE1 Manual reset of base pusher and van in paint position OPE2 Manual reset of base pusher and van off grounding bars OPE3 Manually open of base doors and restart conveyor OPE4 Manually close base doors ACTUATORS REQUIRED PBSD BPEXT BPRET NONE BPRET RBDO and LBDO BPRET NONE NONE RBDC and LBDC NONE NONE NONE 22 Il DBBUILD User s Manual II 1 Introduction DBBUILD an interactive program used to obtain and store information concerning a discrete manufacturing system The structure of DBBUILD emulates a Petri net model to simplify analysis of the system logic using existing Petri net theories The purpose of this appendix is to familiarize the user with DBBUILD s structures and menues DBBUILD prompts the user for all information that is required and therefore
15. char res_name NAME SIZE the resource name char state name NAME SIZE the resource state name struct in_op AND next struct in_op_AND prev typedef struct char name NAME SIZE char desc DESC_SIZE char res_name NAME SIZE char state name NAME SIZE struct out _ op AND next struct out_op AND prev I 2 2 Resource Records Typedef struct resource type Char name NAME_SIZE Char desc DESC_SIZE Struct resource type next Struct resource type prev int num_state Struct state type Typedef struct state type Char name NAME SIZE Char desc DESC SIZE Char latched Struct state type next Struct state type prev Int num OR struct OR_type OR_ptr The following structure contains the name used to define a specified resource state Typedef struct OR type Char name NAME _ SIZE Char desc DESC_SIZE Struct OR_type next Struct OR_type prev Int num_AND state_ ptr The following structure holds the output transition s resource states out_op AND The following is the resource record and its components Name of the resource Description of the resource Holds the number of different states the resource has Points to the resource state structure The following structure contains information on the resource states The resource state structure Name of the state Description of the state Used for generating the IL code Number of sensors used to determine the
16. e compilation PROGGEN will allocate a timer to that operation internally and will attach to the variable state TIMER the address of the timer completed status word bit 15 of the timer address 5 The use of the variable TIMER allows the user to specify those output transitions that are dependent on the timer If the operation reaches an acceptable output transition the timer is automatically reset 5 2 COUNTERS Counters are often required to remember how many times an operation has been executed and based on the accumulated value of the counter initiate another operation For example in an automated paint shop the paint gun requires cleaning if the same color has been used N times If a different color is used a purge operation is performed which includes cleaning the gun We therefore want to count the number of consecutive times the same color has been used It is proposed to view the counter as a type of actuator The counter name would act as the label to the counter address within the controller code The state of the counter is then defined by two associated feedback words representing counting and finished states These states can be defined by the counter address bits 16 and 15 respectively 5 To allow the user to use the counter feedback words in other operations we define feedback words label cnt and label done as follows for countervalue lt N label cnt 1 label done 0 for countervalue N label cnt 0 label done 1 for c
17. e states We use Petri nets PN to model the discrete decision and control of a manufacturing system Previous research has shown that PN models are effective for modeling the evolution of the state transitions in discrete systems 1 PNs contain transitions representing operations or events places representing conditions or states in the process and directed arcs connecting the places and transitions In the graphical representation of PNs transitions are represented by vertical bars and places are represented by circles The conditions enabling an operation are the resource states associated with the operations input transition Upon completion of the operation the resources will be in the states associated within the output transition Recently a systematic methodology was developed for synthesizing PN models of discrete manufacturing systems 2 3 4 As presented by Beck 2 systematic approaches to developing the manufacturing system control logic can be synthesized from activity cycles for each resource The resource activity cycles are developed individually and then joined at common operations to synthesize the complete system control logic We use this approach to define information that is entered into the database using DBBUILD The report is organized as follows In section 2 we present an example of an automated conveyor system in an automobile paint shop which we use throughout the report to illustrate the functions of
18. ed by sensors 1 and 2 or by sensors 3 and 4 DBBUILD s terms for these sets of sensors is SERIES i e sensors 1 and 2 would be listed in SERIES_1 and sensors 3 and 4 would be listed in SERIES 2 DBBUILD uses the word SERIES __ n to label the structure that contains the pointer to each of the sensors See struct OR_ type in section 3 of this manual Additionally DBBUILD uses SENSOR _ n as the name of the structure that holds the actual sensor name See struct AND _ type in section 3 of this manual If the F option was chosen to find information about a resource the following menu will appear D To see the description of the state S To get info about a particular state L to list all of the states assoc with this resource Q To QUIT looking at this resource to see these commands 30 If at this level S is requested the following menu will appear D To see the description of the state L To list the SERIES of SENSORS assoc with this state O To see info about a particular SERIES Q You are done looking at this state To see these commands If the O option is chosen the following menu will appear L To list SENSORS assoc with this SERIES S To list all of the sensor names under this SERIES and their conditions A To see info about a particular associated sensor Q You are done looking at this SERIES To see these commands If at this level the A option is used DBBUILD will ask for the sensor name SENSOR _ 1 SEN
19. ed which are not required to maintain correctness For example the state V1 van entered base booth is explicitly defined by BLS1 At no other time is BLS1 activated nor will the state V1 exist if BLS1 is not activated Using the S set instruction is considered poor programming style primarily because if a power failure occurs the set or latched states will remain high thus resetting the system logic becomes very difficult Also with set instructions there is possibility of logic errors by forgetting to reset the word however PROGGEN removes this problem because it maintains the states of the latched words 17 5 Additional Utilities The prototype versions of DBBUILD and PROGGEN presented in this report have been developed to support automatic generation of controller code for systems with binary sensors and actuators Further work is required to implement the required software to support timers counters external functions add subtract logical comparison etc and non binary inputs and outputs Some ideas for possible implementations of these control structures are presented in this section 5 1 TIMERS Timers are often used to monitor the sequencing of a system A timer can be viewed as a function within an operation that is initiated when the operation is enabled We propose to have operations that can be specified as timed operations for which DBBUILD will prompt the user for the pre set timer duration During controller cod
20. ese records Each record is built using doubly linked lists established through pointers to structures For example and as shown in figure 4 within the operation structure there are pointers to the next and previous operations pointers to a list of the input transitions pointers to a list of the output transitions and pointers to a list of the associated actuators In turn these structures have pointers to structures that contain information on the resource states and the actuators Attached to each each input and output transition of an operation are the resource states that are required to enable the transition While building an operation the user does not need to specify the sensors required to define the resource state This information can be added at some other time as a function of the resource state Figure 1 Modular paint shop conveyor system PusveR POSNER Dos Fee Roue Ae Lindi D CONETOR Cuas SECTE AA Figure 2 Detail of conveyor stops and chain BDO TO CLEAR COAT BOOTH LOGIC OP 10 re eo BOOTH LOGIC FROM CLEAR COAT i OPt a a Figure 3 Petri net model of conveyor control logic for the base coat booth DBBUILD protects against entering incorrect conditions for identifying a resource state by accepting a sensor pointer only if the sensor has been entered in the data base Similarly an actuator cannot be referenced in an operation record unless it has been entered in the ac
21. he clear coat booth All painting is performed by robots The purpose of the observation booth is to allow sufficient flash time so that the majority of the solvents can vaporize before the vans enter an oven for baking The conveyor system is presently controlled by an Allen Bradley PLC 2 30 All sensor signals from limit switches and actuator commands to pushers and mechanical stops are binary The controller coordinates the motion of the vans and the opening and closing of the doors between the booths The doors must be closed during painting and a van must not be released into the next booth before the booth is availabel The conveyor chain shown in figure 2 is a roller flight chain which allows a van to be held in place by mechanical stops while the chain and other vans in the system continue to move Unpainted vans are held by a mechanical stop in the preparation booth and released when the base coat booth becomes availabel After entering the base coat booth the van skid moves up to a set of grounding bars where the rear dog on the pusher catches the push plate on the skid see figure 2 The van is then pushed into a secured painting position on the grounding bars Prior to initiating the base coat painting cycle the booth doors are closed and the pusher is retracted to prevent the buildup of paint on the cylinder shaft Following the completion of the base coat painting cycle the doors are opened and the van skid is pushed off t
22. he grounding bars by the front dog of the pusher if the clear coat booth is availabel This sequence of events is repeated in the clear coat booth When the van moves into the observation booth mechanical stops hold it in place while the solvents vaporize Using the PN methodology described in the introduction a PN model of this system was synthesized from single resource activity cycles for the van conveyor chain mechanical stops in the preparation and observation booths doors and pushers in the base coat and clear coat booths The base booth portion of the PN for the conveyor control logic is shown in figure 3 Descriptions of the resource states and operations for this part of the net are given in appendix I The PN for the clear coat and observation booths are similar 3 DBBUILD DBBUILD is an interactive program written in the C programming language and is used to enter the system description into a data base The database is comprised of four major record types 1 operations containing information on input and output transitions resource states and actuators 2 resources containing information on the resource states and the sensor data required to define each state 3 sensors containing the address label of the sensor input port and 4 actuators containing the address label for the actuator output port Diagrams of the four record types are shown in figures 4 through 7 DBBUILD consists of procedures to create and modify th
23. his software the manufacturing engineer can specify the control logic in terms of the physica devices and operations from which the computer generates the programs for real time control The prototype software described in this report is comprised of two programs DBBUILD and PROGGEN DBBUILD Data Base BUILDer is an interactive program used to build and modify a data base containing the system control description in terms of its physical devices and operations PROGGEN PROGram GENerator executed from within DBBUILD generates source code for the on line control computer Normally a skilled programmer performs the task of developing the controller program usually in the Ladder Diagram Language from the system designer s description of a discrete manufacturing system Several problems can arise from the transfer of information to the programmer and the manual encoding of the system control logic This is due to several factors including e the designer s description of the system can be misinterpreted e the programmer s implementation may be inflexibly structured around the specific sensor actuator realization whereas the design engineer will maintain flexibility to meet changes in the operation of the system e the functional description of the system operation is not clearly reflected in the low level control program These factors make it difficult to debug the control program or make changes in the sequencing of operatio
24. ne looking at this out _op To see these commands D To see the description of the in op L To list all of the ANDs present R To see the resource name and the state name of the AND Q You are done looking at this in_op To see these commands The following menu is presented when the F option is used in the previous menu D To see the description of the assoc act C To see the condition the sensor will be in after the op 29 L to list all info about the assoc actuator for this op Q You are done lookinga t this assoc act to see these commands II 3 2 Resource Menu If from the top level you decide to work on the resource record the following menu will be presented I INSERT new resource D DELETE a resource F FIND a resource or some info about a resource L LIST the name and descriptions of the resources present S Insert a STATE to a resource E ELIMINATE a state from a resource O ADD a new SERIES of SENSORS to a given state A ADD a SENSOR to a given series of a given state T TRASH delete a SERIES of SENSORS from a given state W Delete a SENSOR to a given series of a given state Q Quit and look at another data base List all of the commands availabel NOTE As a resource cycles or is cycled through the systems operations its state will change These states may or may not be defined by sensors and in addition some states may be defined by more than one set of sensors For example some arbitrary state may be defin
25. ns Future modifications may be made difficult because the programmer did not anticipate possible changes in operation sequencing The manufacturing engineer thinks more about how the sequencing of operations may affect future operating conditions The objective for developing the software described in this report is to eliminate the need for manually encoding the discrete control logic for manufacturing systems This task is accomplished by the computer allowing the system designer to specify and modify the control program using a high level functional representation of the system To maintain a systematic approach of generating system control programs the code is generated for one operation at a time using physical states of resources as enabling conditions It is not necessary for the user to specify when to enable and disable the operation actuators this task is performed automatically by PROGGEN Control of a discrete manufacturing system involves the coordination of multiple resources in a sequence of discrete operations The initiation of each operation depends on the states of physical parts and devices resources within the system A resource is any component within the manufacturing system that is involved in the system s operation robots fixtures raw materials controllers etc Following the execution of an operation the states of the resources involved in the operation are changed sensors are used to monitor changes the resourc
26. or is to be closed the output to the door open solenoid will be reset unlatch and the output to the door close solenoid will be set This method will also work for actuators with more than one motion not just two way actuators 4 2 Analysis When sensors are not associated with a resource state feedback words are needed to maintain the control logic Feedback words are words that are stored in memory and are used to remember if a resource is in a given state For example the state of the base booth in the conveyor example is not explicitly defined by sensors Therefore when its state is changed it is set with the S instruction latched and a location within its memory structure in DBBUILD is 15 updated with its latched state If an old state is still latched when a new state is to be latched PROGGEN will unlatch the old state and latch the new state This operation follows from the fact that a resource cannot be in more than one state at any given time Creating feedback words only for those states that are not defined by sensors does not provide sufficient information on the system state to enable the proper outputs In the current version of PROGGEN feedback words are created for all resource states Storing all resource states provides the required information for proper sequencing but leads to inefficient IL code To clarify the need for the storage of all resource state information consider operations 2 and 5 in the con
27. ountervalue gt N reset countervalue countervalue 1 18 where label is the counter name as defined by the system designer For example samecolor cnt would be the variable attached to bit 16 of the samecolor counter 5 3 EXTERNAL FUNCTIONS External functions are required to perform a series of operations that do not belong at the level of the system state description For example comparing the value of a sensor to some set point It is proposed to have the user define an external function label in the associated actuator list in an operation and it will remain his responsibility to generate code for that label Simple routines are easy to write in the Structured Text Language 5 and are easily accessible by the Instruction List code using the JMP instruction All variables will be the same names as those used in the system description level 6 Conclusion This report presents some initial work in the area of automatic programming of programmable controllers from high level descriptions The software developed illustrates the ability to interpret a data base that contains the system operation information and from it generate executable controller code Additional work is required in the area of simulation and analysis of the generated control logic The data base generated by DBBUILD is structured identically to the information contained within a PN model of the system This structure allows existing Petri net theories to be used to
28. state Points to the series of sensors used to define state of the series of sensors DBBUILD structure name not used Number of sensors in series Struct AND type AND_ptr Pointer to the sensors in the series The following structure contains the sensor names for a specified series Typedef struct AND type Char name NAME SIZE Char desc DESC SIZE Struct AND_type next Struct AND_type prev Char sensor_name NAME_ SIZE Char sensor cond COND SIZE Char assoc _res_name NAME SIZE If 2 3 Actuator Records The actuator record is defined as follows Typedef struct actuator Char name NAME SIZE Char desc DESC_SIZE Struct motion struct Int wire_num Struct actuator next Struct actuator prev Int num_assoc_ op Struct assoc_op DBBUILD structure name not used Sensor name The state of the sensor activated not activated not used Actuator structure Name of the actuator Actuates description Indicates different actuator motions Actual wire number Number of operation in which actuator is used Points to an operation The following structure holds information on the operations in which the actuator is used Typedef struct assoc op Char name NAME SIZE Char desc DESC_SIZE Char op_name NAME SIZE Char act list NAME SIZE Struct assoc op next Struct assoc op prev Name of the operation Not used 26 II 2 4 Sensor Records The sensor record is as follows Typedef struct
29. ters resource records Database structures and pointers sensor records Database structures and pointers actuator records PROGGEN Flow Chart omc 11 12 Abstract This report describes prototype software for automatically generating control programs for discrete manufacturing processes from a high level description of the system control logic The control logic is synthesized from a specification of the physical resource states required for each operation in the process The software described in this report allows the user to specify interactively the operation sequencing logic and the actuators and sensors for each stage of the process This information is then used to automatically generate code for on line control computers The current implementation supports binary sensor and actuator signals The methodology is illustrated for the automatic generation of instruction list IL code to control a conveyor system in an existing robotic assembly plant 1 Introduction The writing and debugging of computer programs for sequential control accounts for a major component of the cost in implementing automated manufacturing systems It is also time consuming and expensive to modify existing control programs This report describes prototype software for reducing the time and cost involved in developing discrete control programs by automatically generating executable computer code from a high level description of the system control logic With t
30. tuator database Additionally DBBUILD will inform the user if a state attached to an operation transition is or is not present in the resource data base These checks help prevent confusion for the user and prevents errors from occurring in the controller code that is generated by PROGGEN More information on DBBUILD is provided in the User s Manual in appendix II 4 PROGGEN 4 1 Description PROGGEN is written in the C programming language and is used to generate Instruction List IL code from a data base constructed using DBBUILD Instruction List programs are executed sequentially and repeatedly by a programmable logic controller to generate and maintain the correct outputs to the system The instructions used in this version of PROGGEN are per the International Electrotechnical Commission SC65A WG6 Standard for Programmable Controllers 5 The current version of PROGGEN supports the generation of a control program for a simple discrete process It does not yet support operations requiring timers counters arithmetic functions or logical comparison Possible methods for incorporating these functions are described in section 5 The basic logical flow of PROGGEN is shown in Figure 8 It looks at each operation separately generating code to check the required resource states Then conditional on these states code is generated to enable the desired actuator outputs Setting latching the resultant resource states is based on the sensors
31. use all of the resource states must be satisfied for that transition to be enabled NOTE 2 The labels TRANS__ n and STATE _ n are used by DBBUILD to search through the record 28 See struct in _op OR and struct in_op_AND in section 3 of this manual for more information F will cause DBBUILD to prompt the user for an operation name and will then display the next menu containing new options D To A To F To O To N To I To G To Q To To see the description of the operation list all of the assoc actuators with this operation find info about assoc actuators with this operation list all of the out ops assoc with this operation get info about the out ops assoc with this operation list all of the in ops assoc with this operation list all about the in ops assoc with this operation quit looking at this operation see these commands O will list the names of this operations output transistions TRANS _1 TRANS _ 2 etc N will cause DBBUILD to ask for the output transition name and then present the resource states associated with that transition I and G will perform the same tasks as O and N respectively except they are used for input transitions The following menus are presented when the N and G options are chosen from the previous menu D To see the description of the out_op L To list all of the ANDs present R To see the resource name and the state name of an AND Q You are do
32. veyor example move the van into the painting position and move the van out of the painting position The resulting IL code for only remembering those states that are not defined by sensors is as follows Note enabling conditions are now the sensors for those resource states that are defined by sensors OPERATION 2 OPERATION 5 Enabling Enabling LD BLS1 LD CBC AND BPLSi AND BPLS1 S BPEXT AND BLS2 S BPEXT Result Result LD BLS2 LD BLS3 AND BPLS2 AND BPLS2 R BPEXT R BBF R BPEXT S BBC S CBF Result Result LD BLS1 LD BLS2 AND BPLS2 AND BPLS2 R BPEXT R BPEXT s E1 S E2 We see that when both BLS2 and BPLS2 are high following completion of operation 2 E2 from operation 5 will be set which is not what we wanted To prevent this type of sequencing problem all resource states whether defined by sensors or not are used as feedback words This change produces the correct code as shown below 16 OPERATION 2 OPERATION 5 Enabling Enabling LD V1 LD CBC AND BP1 AND BP3 ST BPEXT AND v3 ST BPEXT Result Result LD Vi LD CBC AND BP1 AND BP3 AND BPL52 AND v3 AND BLS1 AND BPLS2 R V1 AND BLS2 R BP1 R CBC S E1 R BP3 S E2 Result Result LD Vi LD CBC AND BP1 AND BP3 AND BLS2 AND V3 AND BPLS2 AND BPLS2 R V1 R CBC S V2 R BP3 S BP2 S B3C S V4 S BP4 The inefficiency of using this method to maintain correct sequencing stems from the fact that many times feedback words are generat
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