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1771-6.5.25, Servo positioning Assembly User Manual

1. Figure 6 16 Connections to a Cat No 845N SJDN4 C Encoder and a Bulletin 1388 dc Servo Controller Drive 1771 ES Expander 8 to 15V de woe Hs Supply or Input Circuits L am customer Oo supplied O O O O O O LJO Cat no 845N aes T SJDN4 C Encoder rc 1 A3TBI o F 9 L Q 10 C Cc 9 5 158 A Q7 C 9 Q 6 AQ A Y CS 8 Bulletin 888 ot S 12 DC Servo Controller os A 5 Drive l 27K Sa c B 3 2 SS Ey i i AP Y LOH 1i5 14 Motor Tach P1 ae P2 NOTES b bj OP1 0 7 0 El Belden 8725 or equivalent 50ft max L Belden 8761 or equivalent 50ft max r 2 Bulletin 1888 Power Transformer 12303 Connect the bulletin 1388 dc servo controller drive and its bulletin 1388 power transformer to the 1771 ES expander as shown in Figure 6 16 Tachometer input terminal 12 on the 1771 ES expander and terminal 2 on the drive each connect to a dc common at ground potential therefore you must connect these terminals directly as shown Connect the analog output signal from terminal 3 of the 1771 ES expander to terminal 7 of the
2. Figure 2 2 Closed loop Axis Servo System Axis Motion q lt Motor Tach ee Velocity c i Feedback omman Position Data PC Velocity a Processor Command m gt Drive Disable rics Tach Input for h Loss ofFeedback a 8 eat Detection Position s 2 _ Feedback i e E z gi T Discrete Inputs EE Jog Forward L a To JH Jog Reverse Home Limit Switch Servo Controller Servo Expander cat no 1771 M3 cat no 1771 ES Hardware Stop Hardware Start NOTE Feedrate Enable Spuld be ingtaled in fis 10 Eases or control of a second and third axis Discrete Output Hardware Done 10998 The PC processor sends commands and user programmed data from the data table to the 1771 M3 controller as directed by a block transfer write instruction The 1771 M3 controller coordinates the block transfer automatically keeping ladder diagram programming to a minimum Based on information it receives from the processor the 1771 M3 controller sends axis motion commands to the 1771 ES expander The 1771 ES expander closes the servo positioning loop It commands axis motion by generating an analog voltage for your servo drive
3. 12002 3 4 Chapter 3 Positioning Concepts Feed forwarding requires an additional summing point and an amplifier The axis feedrate is multiplied by the feed forward gain K2 to produce the feed forward value The feed forward value is added to the following error multiplied by the gain to generate the velocity command Without feed forward the axis will not begin to move until the axis feedrate builds up enough following error to generate a sufficiently large velocity command to overcome friction and inertia to move the axis However the feed forward value could generate a velocity command to move the axis almost immediately This immediate response keeps the actual position closer to the position command thereby reducing the following error 3 5 Chapter 3 Positioning Concepts Leadscrew Pitch Leadscrew pitch is the linear distance from one peak of the screw thread to the next A leadscrew with a pitch of 1 4 inch is shown in Figure 3 5 Figure 3 5 Leadscrew Example Showing Pitch 4 threads per inch 4 pitch in this example Pitch is sol 1 4 inch in this example 12003 If the leadscrew has only one thread the pitch is also equal to the lead which is the distance the axis travels each revolution of the leadscrew You can see from Figure 3 5 that the axis will travel 1 4 inch per revolution if the pitch is 1 4 inch Since leadscrews normally have onl
4. Maximum D A voltage analog output voltage BCD format For 10 0V program 000 Least significant digit of excess following error percentage BCD format Excess following error percent should be greater than or equal to 6 The value entered here is the percent above rapid traverse following error at which Emergency Stop is to occur aws 7 31 Chapter 7 Formatting and Interpreting Data Blocks Feedrate Reduction When axis following error reaches 106 25 of rapid traverse following error the servo positioning assembly automatically reduces feedrate by 50 of the feedrate value This feedrate reduction provides an opportunity for following error to decrease Feedrate returns to the programmed value when following error is reduced to less than or equal to 106 25 of rapid traverse following error and the current move is completed Note that if the excess following error value you enter is less than or equal to 6 the axis executes immediate stop before following error reaches 106 25 of rapid traverse following error and D A Voltage Bits 00 thru 13 in words 15 and 16 34 and 35 53 and 54 specify the maximum servo output voltage that is available to command rapid traverse feedrate in the positive and negative directions Figure 7 21 Enter values for these parameters in BCD format in the range of 0 01V to 9 99V Programming 0 causes the D A voltage value to default to 10V
5. Left Wiring Arm of 1771 ES Expander 12020 Connecting a Single Ended Encoder Figure 6 11 shows details of how to connect a single ended encoder Connect each channel return line to common Chapter 6 Installing the Assembly Figure 6 11 Connection Details for a Single ended Encoder 5 to 30V DC Belden 8761 or cha Tina customer aly max supplied Ground the shield rs at the I O chassis end a i T CHA PNS Saar aaa aa i Output oF we A Encoder N CHB 6 IS Marker IO o ni Marker 6 S I Belden 8725 or Ground the shield i equivalent at the I O chassis end 50 ft max iS 6 29N Left Wiring Arm of 1771 ES Expander 121 If you switch channel A with channel B you reverse the direction of the feedback If the direction of the feedback does not correspond to the axis motion direction as you have defined it switch channel A with channel B Ground the shield at the I O chassis end Connecting the Analog Output Supply To connect the analog output supply follow these steps 1 Connect the plus side of the analog and hardware one output power supply to terminal 1 of the right wiring arm 2 Connect the minus side to terminal 6 6 21 Chapter 6 Installing the Assembly 6 22 3 Connect the common to te
6. In Position Axis is considered In Position Band value stored in the when it is within 10 increments parameter block is 5 of the programmed endpoint 11040 Rapid Traverse Rate The rapid traverse rate you enter Figure 7 19 is the highest feedrate the axis can attain It is associated with open travel of the axis The servo positioning assembly uses this rate for the go home operation and for moves that you program to use the global feedrate Chapter 7 Formatting and Interpreting Data Blocks Figure 7 19 Rapid Traverse Rate Word Rapid Traverse Rate 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 12 Axis 1 js N Word 31 Axis 2 4 7 Word 50 Axis 3 inch metric i decimal ial PERE point Multiplier point 001 x 10 This BCD value 0 999 ipm or 000 x 10 19 99 mmpm max times the 010 x 10 multiplier is the rapid traverse rate 100 x 10 n i 110 x 108 111 x 10 The rapid traverse rate is limited by several parameters The servo positioning assembly detects a programming error and inhibits axis motion when you enter a rapid traverse rate that violates any of the following formulas RR lt 12 500 x FR x FM x EL Table 7 A code 15 1 28 RR lt 1 5 x 10 x FR x FM Table 7 A code 14 1 28 RR lt 4x 106 x FRx D A Table 7 A code 12 RR lt 6 5 x 107 x FR x IG Table 7 A code 13 1 28 Where the following are parameters you ente
7. Words 45 63 specify same parameters as words 7 25 but for Axis 3 Values may be different Fixed Overhead Parameters for Axis 1 Parameters for Axis 2 Parameters for Axis 3 Chapter 7 Formatting and Interpreting Data Blocks The size of the parameter block you must provide depends on the number of axes Size of Number of Axes Parameter Block ee 2 44 words Your program must transfer the parameter block at power up After that the 1771 M3 controller calls for your program to send the parameter block again only when you issue a new parameter or reset command Parameter Control Word The parameter control word Figure 7 9 identifies the block as the parameter lock bits 10 17 a specifies the units as either inch or metric bit 7 identifies the number of axes in the system bit 0 1 and 2 Figure 7 9 Parameter Block Control Word Parameter Block Control word 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Wordi 0 1 0 0 0j 0 0 0 0 0 00 Identifies this as No of Axes a parameter block 0 0 1 1 0 1 q1 2 0 Inch 1 1 1 3 1 Metric 11031 Address Pointers Words 2 through 5 specify the starting addresses of the parameter command and first moveset block for each axis Figure 7 10 7 19 Chapter 7 Formatting and Interpreting Data Blocks Figure 7 10 Address Pointer Words Param
8. metric PE a decimal Least significant digits point 11044 Loss of Feedback Detection Enable Turn bit 15 off until you complete the open loop and closed loop axis integration procedures chapter 9 Then turn on bit 15 of the most significant home position word to enable the loss of feedback detection feature of the 1771 ES expander WARNING Once you have completed the axis integration procedures never turn this bit off Without loss of feedback detection if encoder or tachometer feedback is lost unexpected axis motion can occur resulting in damage to equipment and or injury to personnel External Synchronization of Feedrate Override Turn on bit 16 of the most significant home position word to have the 1771 ES expander recognize the feedrate override enable input Figure 7 22 7 33 Chapter 7 Formatting and Interpreting Data Blocks With this bit off you change the feedrate by the percentage you enter in the command block when you enable feedrate override in the command block However you change the feedrate for a particular move only if you had enabled feedrate override in the move block With the bit on you must still enable feedrate override in the command block and move block before feedrate changes However the 1771 ES expander will not change the feedrate until you close the feedrate override enable input This allows you to synchronize the feedrate override of several axes Global Accel Decel
9. ences Figure 4 1 Where the Servo Positioning Assembly Fits in a Positioning System Axis Motion Servo Positioning Assembly a ee i orwar K A Position Following Velocity Servo Drive he Command Ero ri Command Feedrate l gt S gt K gt DIA u Position Velocity Feedback Incremental Position Feedback 12005 Figure 4 2 shows where the servo positioning assembly fits in a PC system The PC processor constantly communicates with the servo 4 1 Chapter 4 Positioning with Allen Bradley PC positioning assembly through the I O scan The PC processor acts on a block transfer read instruction to receive status blocks Based on the status information received the PC processor acts on a block transfer write instruction to send either parameter blocks move blocks or control blocks Figure 4 2 Where the Servo Positioning Assembly Fits in a PC System Output Scan Outputs Parameter Moveset and Command Blocks Servo PC uae Processor Positioning lt Input Scan Assembly Inputs Status Blocks 12006 Independent of I O Scan Although the servo positioning assembly sends data to and receives data from the data table through the I O scan the positioning loop is closed on the 1771 ES expander at the positioning loop summing point This allows the 1771 ES expander to
10. its specifications and its compatibility with other hardware components you will need for a closed loop positioning system 6 Installing the Assembly installing the servo positioning assembly and interconnecting hardware 7 Formatting and formatting parameter move description Interpreting Data Blocks and control data for block transfer to the servo positioning assembly interpreting status and diagnostic data received in block transfer from the servo positioning assembly 8 Programming generating a ladder diagram program to transfer data blocks between the PC data table and the servo positioning assembly 9 Integrating Axes adjusting the servo positioning assembly for optimum operation with the machine axis it is to control 10 Troubleshooting using indicator status and status block information to diagnose and correct problems Chapter Objectives What is the Servo Positioning Assembly Introducing the Servo Positioning Assembly This chapter gives you an overview of the servo positioning assembly its applications functions and features A servo positioning assembly controls the motion of one of your axes It consists of one Servo Controller Module cat no 1771 M3 one Servo Expander Module cat no 1771 ES that includes two Field Wiring Arms cat no 1771 WB With a basic servo positioning assembly plus a servo drive motor tachometer and encoder you can control the motion of one user supplied machin
11. 7 35 Chapter 7 Formatting and Interpreting Data Blocks zero there are no software travel limits To guard against damage to equipment use caution when operating an axis without software travel limits A CAUTION If programmed values for software travel limits are Figure 7 25 Software Travel Limit Words Software Travel Limit Word 21 Axis 1 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 40 Axis 2 Word 59 Axis 3 metric inch decimal decimal point point Positive software travel limit An axis position value in inches or meters BCD format Software Travel Limit Word 22 Axis 1 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 41 Axis 2 7 e Word 60 Axis 3 metric inch decimal decimal point point Negative software travel limit An axis position value in inches or meters BCD format CAUTION If programmed values are zero there are no software travel limits To guard against damage to equipment exercise caution when operating an axis without software travel limits 41047 Backlash Takeup Backlash takeup helps minimize axis positioning inaccuracy caused by mechanical play in the axis positioning system Word 23 42 61 is the backlash takeup word Figure 7 26 7 36 Chapter 7 Formatting and Interpreting Data Blocks Figure 7 26 Backlash Takeup Word B
12. Allen Bradley Servo Positioning Assembly User Manual Cat No 1771 QC Series B Table of Contents Using This Manual wo ciceic ewe crew ceanen enews 1 1 Manual s Purpose 0 0 0 cee cece ee eee ee 41 1 AUGIONCE serege gale yew aw ted ont Lee eee eae eeredee 1 1 VOCaDUIANY si s iniiae aa a aE a i N 1 1 Manual Organization 2 ccsecceeuseeeuSadaededee beeen 1 2 Introducing the Servo Positioning Assembly 2 1 Chapter Objectives ic 26ucoence deeds dee iSewnd bee P ew eee 2 1 What is the Servo Positioning Assembly 2 1 ItS ApplicationS s 20 beeen ee eect eee EEEa ee neg 2 2 2 IS FUNCOM 22 aces tyes eek eee ea eke eh 2 2 Its Features 2 eee eee eee 2 4 SUMMA cvnseievendepineeseedsid ees Ee ati 2 7 Positioning Concepts 000c cece ee eee eens 3 1 Chapter Objectives cs eeeedaglecaaiwaesncaveedds 3 1 Closed Loop Positioning 00 0e cece eee 3 1 Leadscrew Pitch 00 c cece e eee eee 3 6 Encoder Feedback i 2 4 00d4se0es he G se ehave en Ges 37 SUMMA sodien ainnhs ieee sewn E seats Pea daa Oda S 3 11 Positioning With an Allen Bradley Programmable Controller 4 1 Chapter Objectives 2c ci ads cinod ieee et edawben educa vxedes 41 Where the Servo Positioning Assembly Fits In 41 Independent of I O Scan 00 c cece cece ees 4 2 Move Moveset 00 cece cece eee teens 4 2 IN POSHION v ec
13. Run Single Step Moves For run single step moves axis synchronization is dependent upon the axis response on each move The same is true for continuous moves with the next move in the opposite direction In both cases the 1771 ES expander executes the next move automatically as soon as the current move is done without waiting for a start signal However the time it takes for each move cannot be precisely calculated because the following error has to close before the move is done Auto Position Correction The auto position correction feature may prevent an accumulation of position error caused by occasional noise on the channel A and B inputs However if the environment is excessively noisy or if the cabling and shielding is not proper this feature causes the axis to jump or jerk This jump or jerk should indicate to you that a problem exists You enter the number of lines on the encoder and the feedback multiplier into the parameter block From this the 1771 ES expander knows how many feedback pulses it should receive each encoder revolution The module also receives a marker pulse each revolution Each time the 1771 ES expander receives a marker pulse it checks the value in the position register to see if it is an even multiple of the number of feedback pulses per revolution If the value is off the 1771 ES expander will automatically adjust it This feature corrects position errors caused by noise on the channel A and B enco
14. a D mY D lt e i io D N J D D se N h N par N _ N A Wigs s S D oS fa D iS i te co _ ee a ico i ico oS D E ico ss ia gt go N imsi is o _ co as co as Ko D Ko foe Ko lt o io ais io ahs io ee io D N io Po Table of Contents iii GIOSSdly cctiereiedecneernprneaee tr adedan eos A 1 Status Block cccead eek eee kee ene ee eee ee eee B 1 Parameter Block 000cceeeeueneeeceauueuee C i Moveset Block Command Block Manual s Purpose Audience Vocabulary Using This Manual This manual shows you how to use the series B Servo Positioning Assembly cat no 1771 QC If you have a series A Servo Positioning Assembly refer to publication 1771 817 To use the servo positioning assembly you must be able to program and operate an Allen Bradley PC processor In particular you must be able to program block transfer instructions In this manual we assume that you know how to do this If you don t refer to the appropriate manual for the PC processor you will be using Consult our Publication Index publication SD499 for a list of our publications Some inconsistency exists throughout industry in the nomenclature used for components of closed loop servo positioning sy
15. Following Error Error 50 Feed Suppression Starts at 6 25 above max Following Error Excess Error Determined by Excess Following Error Parameter 11038 Gain Reduction Factor Bits 0 7 of the in position band and gain break factor word Figure 7 17 specify the gain reduction factor The initial gain of the axis is multiplied by this factor to obtain the reduced gain value for axis speeds above the gain break speed Chapter 7 Formatting and Interpreting Data Blocks Figure 7 17 In position Band Gain Reduction Factor Word 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 11 Axis 1 Word 30 Axis 2 Word 49 Axis 3 V V A A This BCD value 99 max times 2 is Gain reduction factor the in position band in increments of feedback resolution 11039 Gain Reduction Factor Reduced Gain Initial Gain For example if the initial gain is one and you want the reduced gain to be 0 5 program 50 as the value for gain reduction factor Gain Reduction Factor D 50 1 The gain reduction factor must be less than 1 0 If you program zero the system gain for any axis speed will be the initial gain If gain break velocity is zero and you program a non zero gain reduction factor system gain for any axis speed is the initial gain times the gain reduction factor Enter the gain reduction factor in BCD format In Position Band The size of the in pos
16. Furthermore with an Allen Bradley Data Highway network you can send this diagnostic information to a computer or other Allen Bradley PC processors The servo positioning assembly provides specific fault responses if certain critical connections are broken Loss of Feedback The 1771 ES expander continuously monitors the tachometer and encoder feedback If it senses an imbalance between these signals it holds the velocity command output signal at zero and disables the servo drive through the drive disable circuit Therefore if the cable from either the encoder or the tachometer breaks the 1771 ES expander will disable the servo drive Hardware Stop You must connect a set of normally open contacts of your master control relay between the hardware stop input terminal and the input power supply common terminal Normally the master control relay would be energized pulling the hardware stop input low This allows the module to enable the servo drive However if the master control relay de energizes for any reason such as extreme overtravel limit or emergency stop the hardware stop input goes high This forces the module to hold the velocity command output signal at zero and disable the servo drive by turning off the drive disable circuit Therefore if a connection in the hardware stop circuit breaks the 1771 ES expander will disable the servo drive 5 9 Chapter 5 Hardware Description Loss of Power The 1771 ES expand
17. ccc cc eee een eae Parameter Block nics 600 50 Sei woe ted ceed ae ewe Moveset Block 00 0 0 ccc eee nee nes Command Block 0 0 ccc e eee eee eee eens SUMMAN cn those ota ceareeed cette satseeudetaee sees Programming cori vitae ra dien ewes e eee ee esas Chapter Onjecines cncicssstesscteseriiseingabasensd Programming Objectives 0 cece eee eee eee PLC 2 Family Block Transfer Instructions PLC 2 Family Block Transfer Timing 04 PLC 3 Block Transfer Instructions 0 e eee PLC 3 Block Transfer Timing 00eeeeeeeee Programming Example cee eee eee eee SUMMAN sey ipie epar tima kii a e bad Integrating Axes ase ise tae wiew wen ee ose wien eae Chapter Objectives 22 0422 shedeetdnwticeaderesua enon Open Loop Procedure 0 0 ccc c eee c eee eee Closed Loop Procedure 00 ccc cece cence eens Tachometer Calibration 0 0 00 c ccc ee ee ees SUMMA occ donee eia Ea te abe de inky A Troubleshooting usssusssnnnnnnnnnnnnnnnnn Chapter Objectives 2514442 sh ddert iheubewededtedee es Monitoring 1771 M3 Controller Indicators Monitoring 1771 ES Expander Indicators Monitoring the Status Block 0 cess Troubleshooting Flowchart 00 0 ee eee eee eee SUMMAY vanes eheiveselss eee bei exeeses ad dew ENE e r D op D
18. or x4 3 8 Chapter 3 Positioning Concepts The following equation shows how these factors determine feedback resolution leadscrew pitch feedback resolution encoder lines feedback multiplier You must select the leadscrew pitch encoder lines and feedback multiplier to provide desired feedback resolution and meet other requirements of your application The programming resolution of the servo positioning system is 0 0001 inch or 0 001 millimeter If you select a feedback resolution coarser than that round off your position commands so that the effective programming resolution is no finer than the feedback resolution you chose If you select a feedback resolution finer than the programming resolution positioning can be smoother However the maximum axis speed is directly proportional to the feedback resolution There is always a trade off between feedback resolution and maximum axis speed The maximum encoder input frequency for the servo positioning assembly is 250kHz Therefore to avoid a programming error you must limit the axis speed to conform to this formula programmed 1 5 x 107 axis speed lt 1 28 x feedback res x feedback mult The 1 28 factor allows for a 127 feedrate override value Each encoder line represents a fraction of a revolution of the leadscrew For example consider a 250 line encoder Each line represents 1 250 of a revolution of the leadscrew Also consider a 4 pitch per inch leadsc
19. 2 of the command block refer to Figure 7 44 and its associated text for more information on Axis Control Word 2 Turn off bits 11 and 15 to display the current axis position as shown in Figure 7 6 The maximum value is 999 9999 inch or 19999 999 mm If the axis exceeds the maximum it displays the maximum and the position valid bit goes off 7 13 Chapter 7 Formatting and Interpreting Data Blocks Figure 7 6 Position Following error Diagnostic Words with Position or Following error Selected Position or Following Error Most Significant Word 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 5 Axis 1 Word 9 Axis 2 0 0 Word 13 Axis 3 so ao inch decimal point Sign Most significant digits BCD position or following error value 999 9999 inches or 19999 99 mm max Position or Following Error Least Significant Word 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 6 Axis 1 Word 10 Axis 2 Word 14 Axis 3 metric decimal Least significant digits 11055 point Turn off bit 11 and turn on bit 15 to display the following error as shown in Figure 7 6 The maximum value is 999 9999 inch or 19999 999 mm If the axis exceeds the maximum it displays the maximum Turn on bit 11 to display the diagnostic status as shown in Figure 7 7 7 14 Word 5 Axis 1 Word 9 Axis 2 W
20. Every 2 4 milliseconds ms it updates this analog output voltage according to motion commands from the 1771 M3 controller discrete inputs and Chapter 2 Introducing the Servo Positioning Assembl Its Features 2 4 feedback from your encoder The 1771 ES expander is able to provide this fast servo sample rate because the update is independent of the I O scan A drive disable output provides a signal to disable the servo drive in conditions such as loss of feedback or a hardware stop signal A hardware done output signals the completion of each single step move Discrete hardware inputs include hardware stop jog forward jog reverse home limit feedrate enable hardware start The 1771 M3 controller sends axis status and diagnostic data to the data table as directed by a block transfer read instruction Because axis command and status data is stored in the data table axis motion control can interact with other axes discrete I O and report generation See the following table for a list of the many useful benefits you ss derive from an A B servo positioning assembly Feature incremental digital encoder feedback absolute or incremental positioning commands programmable gain break programmable acceleration deceleration programmable in position band programmable jog rates programmable dwell excess following detection loss of feedback detection software travel limits backlash ta
21. In the search home operation the axis moves until the servo positioning assembly detects the first encoder marker beyond the user installed home limit switch The 4 11 Chapter 4 Positioning with Allen Bradley PC axis stops on the marker The servo positioning assembly then sets it position register to the home position value you specify in the parameter block This initializes the axis position scale Figure 4 10 shows how the home position value you specify in the parameter block can affect the axis position scale This figure compares the scales for an axis after search home operations with different home position values form the parameter block representing the same physical position Figure 4 10 Axis Position Scales for 2 Home Position Values Home 2 0 3 00 9 Parameter Block Home Position Value 3 00 10 5 00 0 1 Parameter Block Home Position Value 5 00 11008 Preset Through a command block you can command the servo positioning assembly to preset a specified value into its position register When the servo positioning assembly executes a preset command it sets its position register to the specified value without causing axis motion This action effectively shifts the axis position scale Figure 4 11 shows an axis position scale before and after a preset operation Figure 4 11 Axis Position Scale before and after Preset After Preset 1 5 5 0 5 B
22. Polarity Select the polarity of each encoder input to allow your encoder to function properly with the 1771 ES expander Figure 6 1 Encoder Polarity Jumper Position High true Left Low True Right e 6 6 Keying Chapter 6 Installing the Assembly With a differential encoder the connections and the polarity jumper positions determine the polarity of the feedback signals With a single ended encoder the polarity jumper positions alone determine the polarity of the feedback signals The polarity selections are important to the marker logic Set the polarity so that the marker is true at the same time that channels A and B are true refer to Figure 3 7 Selecting Encoder Input Signal Mode Select the signal mode of each encoder input to match the encoder Figure 6 1 Encoder Signal Mode Jumper Position Single ended Left e e e Differential Right e e Selecting Marker Logic For almost all encoders set the marker logic jumper to the bottom position to gate the marker with channel A and channel B This gives the marker signal a level of noise immunity However if you cannot select the polarity so that the marker on your encoder is always true at the same time as the channel A and B signals set the market logic jumper to the top position A package of plastic Keys cat no 1771 RK is provided as standar
23. an escape move you must enter its address in the parameter block moveset address pointer word You must do this because the escape move must be the first moveset transferred to the 1771 M3 controller even though it is not the first moveset normally executed Feedback Resolution Feedback resolution is the smallest unit of axis motion that can be distinguished by the servo positioning assembly That is it is the distance the axis moves per feedback increment Enter the value of feedback resolution in the feedback resolution word of the parameter block Figure 7 11 As described in chapter 3 feedback resolution is determined by the number of encoder lines the feedback multiplier and leadscrew pitch Feedback Resolution Axis Displacement per Encoder Rev Encoder Lines Feedback Multiplier If the system has no gearing the axis displacement per revolution is the same as the leadscrew pitch or lead Figure 7 11 Feedback Resolution Word Feedback Resolution Word 7 Axis 1 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 26 Axis 2 Word 45 Axis 3 Feedback resolution BCD format 0010 minimum 0 inches x 10 1 millimeters x 10 11033 Chapter 7 Formatting and Interpreting Data Blocks Encoder Lines This word specifies the number of encoder lines per encoder revolution Figure 7 12 Figure 7 12 Encoder Lines Word Encoder Lines 17
24. and feedrate override enable Follow these steps 1 Provide a 3 pole selector switch to select between auto and manual mode 2 Connect one pole of the selector switch to a discrete input module terminal Use this input to control the auto manual bit in the control block This bit controls whether the 1771 ES expander is in the auto or manual mode 3 Connect a second pole of the selector switch to the jog reverse feedrate override enable terminal of the 1771 ES expander 4 Connect a momentary contact jog reverse switch to the selector switch contact corresponding to manual on the second pole 5 Connect a momentary contact feedrate override switch to the selector switch contact corresponding to auto on the second pole 6 17 Chapter 6 Installing the Assembly Figure 6 9 Connection Details for Jog Forward Hardware Start and Jog Reverse Feedrate Override Enable 3 Pole Selector Auto Switch oN Discrete input module Manual 5 Tg terminal to control the auto manual bit in the command block 5 to 30V dc To other axes ge jj 4 customer supplied m Hardware Start x i iQ e _ T p AO Jog l l S A S i I o Manual a ay Feedrate 41 I9 Overrid
25. ipm s maximum resolution 1 ipm s 99 99 mpm s maximum resolution 0 01 mpm s Initial Servo Gain Programmable Summary Chapter 5 Hardware Description 0 01 9 99 ipm mil following error 1 mil 001 inch 0 01 9 99 mmpm mil following error 1 mil x 001 mm Servo Sample Period 2 4ms Environmental Conditions Operational Temperature 0 to 60 C 32 to 140 F Storage Temperature 40 to 85 C 40 to 185 F Relative Humidity 5 to 95 without condensation Keying Servo controller slot between 2 and 4 8 and 10 Left servo expander slot between 2 and 4 14 and 16 Right servo expander slot between 4 and 6 32 and 34 Now that you have read about the function of each input and each output you are ready to install the servo positioning assembly Chapter 6 gives you this information Chapter Objectives Configuring the Modules Installing the Assembly The previous chapter described the hardware of the servo positioning assembly This chapter tells you how to install the servo positioning assembly As you install it you will make hardware selections to direct its operation to fit your application requirements The first step of installing a servo positioning assembly is to plan how to configure modules in the I O chassis Planning Module Combinations You can install one 1771 M3 controller in an I O chassis together with either one two or three 1771 ES expanders However the
26. noise free marker signal Although this feature may be able to prevent an accumulation of position error caused by occasional noise on the channel A and B inputs it cannot maintain position accuracy if the environment is excessively noisy or if the cabling and shielding is not proper If the environment is excessively noisy or if the cabling and shielding is not proper this feature will cause the axis to jump or jerk This jump or jerk indicates a problem Note that when the module detects a position error it does not necessarily disable the servo drive Specifications Chapter 5 Hardware Description Because this feature adjusts the position register to the closest even multiple of the number of feedback increments per revolution it is essential that the axis move less than half an encoder revolution per servo sample period 2 4ms Therefore to avoid a programming error you must limit the axis speed to conform to this formula programmed 12 500 f lt x FR x FM x EL axis speed 1 28 Where FR feedback resolution FM feedback multiplier 1 2 or 4 EL encoder lines per revolution Here is a list of specifications for the servo positioning assembly Servo Output Voltage a 10V dc maximum isolated D A Converter DAC Signed 12 bit resolution Encoder Input High 1 6V Low 1 0V sinking ImA Encoder Input Rate Differential 250k Hz maximum Single ended 20k Hz maximum Jumper selection
27. of differential or single ended input Encoder Multiplier xl x2 or x 4 programmable Tachometer Input For loss of feedback detection Full scale voltage 3V dc minimum 50V dc maximum Input impedance 20k ohmss Discrete Inputs 5 11 Chapter 5 Hardware Description 5 12 Resistance to high side of supply 11 2k ohms or 1 2k ohms switch selectable for each input For a low required sink current with 1 2k ohms resistance 4mA 5V 24mA 30V For a low required sink current with 11 2k ohms resistance 0 4mA 5V 2 7mA 30V High 40 of dc supply voltage low 20 of dc supply voltage Hardware Done Output a On 15V source thru 1k ohms resistance Off 15mA sink Drive Disable Output Current 100mA maximum source or sink Voltage 30V dc maximum to 5V dc minimum Backplane Current 1771 M3 controller 1 75A 1771 ES expander 1 70A External Power Supply Requirements External supply for inputs 4 75 dc minimum 30V dc maximum 500mA maximum External supply for DAC and hardware done output 15V dc 200mA maximum External supply for drive disable output 4 75V dc minimum 30V dc maximum 100mA maximum Maximum Programmable Position 999 9999 inches resolution 0 0001 inch 19999 999 millimeters resolution 0 001 mm Programmable Speed 0 0001 9990 0000 ipm resolution 0 0001 ipm 0 001 199900 000 mmpm resolution 0 001 mmpm Accel Decel 9999
28. of the left wiring arm as a low true feedrate override enable signal After setting a feedrate override value for the axis through the command block and enabling external synchronization of feedrate override through the parameter block you can enable the feedrate override through this input Do this by setting bit 16 of word 17 in the parameter block ON Axis 1 Set bit 16 of words 36 and 55 for axis 2 and 3 respectively This allows you to activate a preloaded feedrate override value to change speed on several axes at the same instant Jog Forward In the manual mode the module accepts the signal at terminal 8 of the left wiring arm as a low true jog forward signal When the module receives this signal it moves the axis in the positive direction at the rate established through block transfer External Power Supplies Chapter 5 Hardware Description Jog Reverse In the manual mode the module accepts the signal at terminal 9 of the left wiring arm as a low true jog reverse signal When the module receives this signal it moves the axis in the negative direction at the rate established through block transfer Home The module accepts the signal at terminal 10 of the left wiring arm as a low true home signal The module considers the first marker pulse after the home signal as the home position Hardware Stop The module accepts the signal at terminal 11 of the left wiring arm as a high true hardware stop signal Unless t
29. provide a servo sample period of 2 4ms independent of I O scan Move Moveset You must describe the axis motion you want in moveset blocks in the data table You can enter a maximum of 21 separate move blocks in a moveset block Figure 4 3 4 2 Chapter 4 Positioning with Allen Bradley PC Figure 4 3 A Moveset Block is Sent to the 1771 M3 Controller That Sends the Move Blocks Sequentially to the 1771 ES Expander Two Move Block register in the 1771 ES expander Current Move Next Move Move blocks sent in sequence as each current move is started Moveset block in the PC Processor data table Move 1 Move 1 Move 2 A complete moveset 21 Move 2 moves max is sent in a Move 3 single block transfer Move 3 Move 4 Move 4 e o e e e e Move 21 Move 21 Moveset register in the 1771 M3 controller 12007 The PC processor sends a complete moveset block to the 1771 M3 controller in a single block transfer The 1771 M3 controller can hold a moveset block for each of the three possible axes The 1771 ES expander can hold two move blocks the current move block available for execution and the next move block After the current move is completed and the next move is to be executed the next move block becomes the current move block Figure 4 4 Chapter 4 Positioning with Allen Bradley PC Figure 4 4
30. the entire block If additional moveset blocks are needed you also need a next moveset point word A moveset block can be 64 words long maximum and describe 21 moves maximum To describe 21 moves in a single moveset block all 21 7 3 Chapter 7 Formatting and Interpreting Data Blocks Status Block 7 4 moves would have to use the global accel decel and final rate values from the parameter block Upon request from the status block the PC processor sends a moveset block to the 1771 M3 controller which transfers each move description to the 1771 ES expander one at a time The 1771 ES expander generates the analog voltage to command axis motion as programmed Command Block The command block for a 1 axis system has up to four words a 2 axis system has up to eight words a 3 axis system has up to 12 words This block regularly transfers from the data table to provide commands such as start slide stop search home jog reset and offset for each axis unless the 1771 M3 controller needs a parameter or moveset block You must include the command block address in the parameter block Data Table Allocation You must allocate a sufficiently large data table area for the data blocks needed in the block transfer communication Furthermore the parameter block must start at least 63 words before the end of a contiguous data table area Also each moveset block regardless of size must start at least 64 words before the end of a con
31. the plus side of the power supply to terminal 8 on the right wiring arm of the 1771 ES expander Without this connection the drive disable circuit will not turn on the 1771 ES expander will not enable the servo drive Chapter 6 Installing the Assembly Connecting the Tachometer Figure 6 15 shows details of how to connect the tachometer Follow these steps Figure 6 15 Connection Details for Tachometer Right Wiring Arm of 1771 ES Expander i High Low High Low 7 Tach Servo Drive TS aS IO 15 55 S 7O 50V Max TS at Terminals 27KQ JO 1S WS 25 He 12025 1 Connect the tachometer directly to the servo drive 2 Connect the tachometer signal at the servo drive to the right wiring arm of the 1771 ES expander This allows the 1771 ES expander to detect loss of tachometer feedback at the servo drive Limit the voltage at the terminals to 5 0V maximum Tachometers typically generate much larger voltages than 50V at high speed Therefore you must drop the voltage thru a voltage divider 3 Unless you have access to a voltage divider in the servo drive place a 27k ohms 1 4 Watt potentiometer between the servo drive and terminal 11 of the 1771 ES expander 4 Set the potentiometer for maximum resistance until you perform the integration procedures chapt
32. to the 1771 M3 controller Words 3 thru 6 provide the status of axis 1 Words 7 thru 10 provide the status of axis 2 Words 11 thru 14 provide the status of axis 3 The following sections describe status block words The servo positioning assembly configures all words in the status block Address Pointer The address pointer word Figure 7 3 contains in BCD format the data table address of the next block to be transferred from the processor to the 1771 M3 controller Your ladder diagram program reads this address and uses itto configure a write block transfer instruction The 1771 M3 controller programs this word according to its requirements When it does 7 5 Chapter 7 Formatting and Interpreting Data Blocks 7 6 not need to request the parameter block or a moveset block it requests the command block Figure 7 3 Address Pointer Word Address Pointer Word 2 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Address of next block to be write transferred to the 1771 M3 controller BCD format 11052 The value that appears in this word is one of the pointer addresses you put into word 2 parameter block of the parameter block word 3 command block of the parameter block word 4 initial moveset block axis 1 of the parameter block word 5 initial moveset block axis 2 of the parameter block word 6 initial moveset block axis 3 of the parameter block the last word next moveset
33. 00 es Sete dee ee a ee eee eee ee 4 8 Synchronizing Axes o02cchcrepetadsiceselvissteeegeges 4 8 Specifying Axis Position 00 cece ee eee eee 4 10 SUMMA nnneicededeuaey ede seod pee TEEI AAT 4 13 Hardware Description ais siacsaw cence deine eae daadeass 5 1 Chapter Objectives 000 c eee eee eee eee 5 1 Indicators saa cine lia Ree Baesian kd dd aa a r disp a EA 2 5 1 Inputs Outputs 2 0 2 0 aidea ai ena aE 5 2 External Power Supplies onanan aaan 5 7 Compatible Processors 0 eeaeee 5 8 Fault Responses 00 00 c eee eee eee ees 5 9 Specifications es0cas s decee ones d barritas ce peusies 5 11 SUMMA ai mi a EE E A ER E EOE 5 1 Table of Contents Installing the Assembly 2 00eceeeeee eens Chapter Objectives 0 02 cece eee ee eee eee Configuring the Modules 0 0 c cece cece eee eee Setting Switches and Jumpers 0000 e eee ee eee KOYING se eee act Stara Mai wide ree cere dee E a ce Inserting the Module 0 cee eee ee eee Connecting to Terminals 02 cece cece eee Connecting A B Encoder and Drive 00 00e Start up Sequence 0 cece eee eects SUMMA 2 2iecceeetecdeneet ene seen ARESE SE REI Formatting and Interpreting Data Blocks Chapter Objectives 00 2 cece eee eee eee Relationship of Data Blocks 00 0 eee eeeaee Status Block 0
34. 1 M3 controller turns on this bit when communication between it and the 1771 ES expander is lost Bit 14 Following Error Valid This bit is on if the next two status block words for this axis contain axis following error Bit 15 Position Valid This bit is on if the next two status block words for this axis contain axis position If the axis position value exceeds the maximum allowable value 999 9999 in or 19999 999 mm the servo positioning assembly turns off both the position valid and following error valid bits bits 15 and 14 and sets the position value in the status block at the maximum value Chapter 7 Formatting and Interpreting Data Blocks Bit 16 Diagnostic Valid When you turn on the select diagnostic bit of axis control word 2 of the command block this bit goes on to indicate that the position or following error words in the status block contain diagnostic information Bit 17 Command Taken When you turn on the new parameter moveset override offset preset or get new preset value bit in the command block this bit goes on to indicate that the command has been taken When you detect this bit to be on you can turn off the command block bit Position Following Error Diagnostic Words The 3rd and 4th status words for an axis provide either current axis position following error or diagnostic information You can select which status to display by controlling the state of bits 11 and 15 of the axis control word
35. 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 8 Axis 1 Word 27 Axis 2 7 Word 46 Axis 3 The value of this word times the mulitplier specified by bit 15 of the next word must equal the actual number of encoder lines BCD format For 10 000 program 0000 11034 The value of this word times the encoder lines multiplier specified by bit 15 of the next higher word must equal the actual number of lines on the encoder You can enter values up to 10 000 with the x1 multiplier Entering zero 0000 specifies 10 000 lines You can enter higher values by using the x4 multiplier For example if your encoder has 12 000 lines you can enter 3000 in the encoder lines word and turn on bit 15 of the next word to indicate x4 3 000 x 4 12 000 lines The status block indicates a programming error after transfer of the parameter block if Encoder Lines x Feedback Multiplier x Encoder Lines Multiplier gt 32 767 Chapter 7 Formatting and Interpreting Data Blocks Initial Gain Multipliers Bits 0 thru 13 of this word Figure 7 13 specify the servo gain for this axis at speeds below the gain break speed specified in word 10 You must enter gain values in BCD format from 0 01 to 9 99 ipm mil or from 0 01 to 9 99 mmpm mil A mil is 0 001 inch or 0 001 mm Figure 7 13 Feedrate Multiplier Encoder Lines Multiplier and Initial Gain Word Feedback Multiplier E
36. 6 18 also Chapter 6 Installing the Assembly shows connections from the central ground bus to each chassis and to the T O chassis ground bus shown in Figure 6 17 Figure 6 18 AC Power and Ground Connections Incoming AC H1H2 H3 H4 Hz Ha Ht Isolation Transformer aren 1388 120V AC ower X xa xa Wal Transformer Xo round Bus ee 120V AC oe ae a a y2 Y3 Y1 Fuse 35 5V ac V A8TB1 7 8 9 A2TB1 Li iN Li iN Li N i 7A co Ge_ 10 Bulletin 1388 9 DC Servo Controller Power Power 15V de Drive Supply Supply for For DAC for Input 1 0 Chassis Customer G AZIB Circuits Backplane oe 4 5 e D I O Chassis Ground Bus ioe Motor l Start up Sequence 17966 After properly installing your servo positioning assembly formatting the data blocks entering the program and integrating each axis you start up the system in the following sequence 1 De energize the CRM relay Chapter 6 Installing the Assembly Summary 2 Turn on the dc power connected to the wiring arms 3 Turn on the power supply for th
37. Chapter 7 Formatting and Interpreting Data Blocks Code Definition Invalid motion command bit combination or command not allowed 33 Invalid command cannot process new parameters preset or offset commands while axis is in motion Attempted switch to auto mode before first marker is found Parameter Block Through the parameter block you specify axis parameters such as software travel limits home position value servo gain and rapid traverse rate You specify these parameters for each axis individually Figure 7 8 Chapter 7 Formatting and Interpreting Data Blocks 7 18 o o yy OAA ONI o 12 44 45 63 Figure 7 8 Parameter Block Showing Word Assignments Parameter Block Control Word Parameter Block Pointer Command Block Pointer Moveset Block Pointer Axis 1 Moveset Block Pointer Axis 2 Moveset Block Pointer Axis 3 Feedback Resolution Encoder Lines Feedback Mult Encoder Lines Mult Initial Gain Gain Break Speed In Position Band Gain Reduction Factor Rapid Traverse Rate High Jog Rate Low Jog Rate Excess Following Error D A Vlotage Excess Following Error D A Voltage Home Position MS Home Position LS Global Accel Decel Rates Decel Step Rate Software Travel Limit Software Travel Limit Backlash Take up Offset FE Reduction Tach Conversion Factor Words 26 44 specify same parameters as words 7 25 but for Axis 2 Values may be different
38. ES expanders and either an I O adapter or mini processor module the total would exceed 8A In that case you could not use a 1771 P1 or 1771 P2 power supply because they are rated at 6 5A If the total current exceeds 6 5A you can use Power Supply Modules cat no 1771 P3 P4 P5 to provide 8A 11A or 16A The following table lists the number of axes you can control with a servo positioning system in a 1771 A4 I O chassis based on power requirements and compatibility of other components used with the 1771 A4 I O chassis I O Adapter or Mini Processor Module Cat No 1771 AL 1771 P1 1771 P2 1771 P3 1771 P4 1771 P4 plus 1771 P3 or a second 1771 P4 Chapter 6 Installing the Assembly Planning Module Location The 1771 M3 controller requires one I O chassis slot You can install it in any I O in the I O chassis The 1771 M3 controller uses both the output image table byte and the input image table byte that correspond to its location address The 1771 ES expander requires two slots Install it in a pair of slots that make up an I O module group Setting Switches and Jumpers Through switches and jumpers on the 1771 ES expander you can select various aspects of the module s operation To access these switches and jumpers lay the 1771 ES expander on its right side and remove the left cover Locate the switches and jumpers through Figure 6 1 Figure 6 1 1771 ES Expander Switches and Jumpers Discrete Inp
39. I O chassis must not contain any other module combination of a master such as an analog module and its slave expander A master must communicate with its slaves through the backplane Two masters trying to communicate through the backplane interferes with each other If you have an illegal combination of 1771 ES expanders or a second master slave combination in the I O chassis the active indicator on the 1771 M3 controller blinks An illegal combination of 1771 ES expanders would be the number of 1771 ES expanders not matching the number of axes in the parameter block an axis 2 with no axis 1 an axis 3 with no axis 2 two axes with the same number Always use the same series level of 1771 M3 controller and 1771 ES expander You cannot use a series A 1771 M3 controller with a series B 1771 ES expander Likewise you cannot use a series B 1771 M3 controller with a series A 1771 ES expander 6 1 Chapter 6 Installing the Assembly 6 2 Avoiding Backplane Power Supply Overload For each module you plan to install in the I O chassis add up it current load on the backplane power supply Be sure that this total current is not so large as to overload the backplane power supply The backplane power supply current load of the servo positioning 1771 M3 1771 ES Total controller expanders Current 3 45A assembly is 5 15A 6 85A Note that if you add the total current draw of one 1771 M3 controller three 1771
40. In the 1771 ES Expander as Each Current Move is Completed the Next Move Block is Ready to Take its Place Start Start Start Start Start Start of of of of of of Move Move Move Move Move Move Current Move Block Move 1 Move 1 Move 2 Move 3 Move 20 Move 21 e Next Move Block Move 2 Move 3 Move 4 Time gt 12008 Initially the 1771 M3 controller sends the first move block to the 1771 ES expander Then as each move is started the 1771 M3 controller sequentially sends each of the remaining move blocks to the 1771 ES expander A move block for a move to position defines motion of the axis from one position to another Figure 4 5 shows the profile of an axis move The horizontal axis in the figure represents axis position The vertical axis represents axis velocity Moves plotted above the position axis are in the positive direction from left to right moves plotted below the position axis are in the negative direction right to left Figure 4 5 One move Profile for an Axis Rate Move Constant Velocity Final Velocity or Feedrate Acceleration Pa Deceleration Position Startpoint Endpoint er In the move shown in Figure 4 5 the axis starts from a resting position accelerates to a final velocity 4 4 Chapter 4 Positioning with Allen Bradley PC moves at the final velocity some distance decelerates to zero velocity at which time it has r
41. Initially set them to the maximum value the servo drive will accept The plus and minus D A voltage values needn t be equal You can enter them as different values to compensate for directional differences in drive performance during axis integration chapter 9 Home Position Value Words 17 and 18 36 and 37 55 and 56 specify the axis home position value Figure 7 22 Bits O through 14 of the first word contain the most significant digits Bit 17 of the first word specifies the sign of the home position value When the servo positioning assembly performs a search home or initialize home operation it sets the axis position register to the value you enter for this parameter Chapter 7 Formatting and Interpreting Data Blocks Figure 7 22 Home Position Words Most Significant Home Position 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 a inch Word 17 Axis 1 Word 36 Axis 2 i Word 55 Axis 3 out decimal e oin isz Loss of feedback Most significant digits P detection External _ 0 disable synchronization of 1 enable feedrate overide 0 disable BCD home position value 1 enable 999 9999 inches or 19999 99 mm max Home Position Least Significant Word 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 18 Axis 1 Word 37 Axis 2 Word 56 Axis 3
42. Rate Word 19 38 57 specifies the acceleration and deceleration rate the servo positioning assembly uses for all jogs and for moves in movesets for which you do not enter local acceleration and deceleration rates It is also the deceleration value used when executing a slide stop during manual mode operation of an axis or when you issue a reset command during axis motion Figure 7 23 Figure 7 23 Global Accel Decel Rate Word Global Accel Decel Rate 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 19 Axis 1 E d Word 38 Axis 2 Word 57 Axis 3 E inch Pa i decimal ecima point point BCD global accel dec rate 9999 ipm s or 99 99 mpm s max ma Decel Step Rate Word 20 39 58 specifies the deceleration step rate Figure 7 24 This parameter applies to deceleration of axis motion when the servo positioning assembly is in the manual mode At axis feed rates equal to or less than that specified by this word the servo positioning assembly ignores the programmed deceleration rate and steps axis feed rate directly to zero This parameter is not effective in auto mode and applies only to jog and search home operations Chapter 7 Formatting and Interpreting Data Blocks Figure 7 24 Deceleration Step Rate Word Decel Step Rate 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 20 Axis 1 7 Wo
43. WY z s i a 4 be lower than the high jog rate 11042 7 30 Chapter 7 Formatting and Interpreting Data Blocks Excess Following Error The excess following error parameter is a 2 digit BCD number that the 1771 ES expander interprets as a percentage above the following error allowed at the rapid traverse rate Programmable excess following error values can thus range from 0 through 99 Program the most significant digit in bits 14 through 17 of the first word and the least significant digits in bits 14 through 17 of the second word Figure 7 21 This parameter specifies maximum allowable axis following error When the following error reaches the maximum value permitted as specified by the excess following error parameter the servo positioning assembly stops axis motion by commanding immediate stop Figure 7 16 Figure 7 21 Excess Following Error D A Voltage Words Excess Following Error MSD D A Voltage 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 15 Axis 1 Word 34 Axis 2 Word 53 Axis 3 V Y Most significant digit of excess following error percentage BCD format Maximum D A voltage analog output voltage BCD format For 10 0V program 000 Excess Following Error LSD D A Voltage 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 16 Axis 1 Word 35 Axis 2 Word 54 Axis 3 V Y A
44. acklash Takeup Distance Word 23 Axis 1 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 42 Axis 2 7 e Word 61 Axis 3 A inch metric decimal decimal point point e Sign Distance axis overshoots when initial 0 4 approach to endpoint is from direction 1 opposite that specified in bit 17 Axis approaches all endpoints moving in the direction specified by the sign bit 17 11048 In this word bit 17 specifies the direction the axis is to move in approaching all programmed endpoints When the axis approaches an endpoint at which it is to stop while moving in the specified direction it simply stops at the endpoint If the axis approaches the endpoint from the opposite direction it overshoots the endpoint by the amount you specify in bits 00 thru 16 then returns to the endpoint from the opposite direction Consider the example of your entering 0010 in the backlash takeup word Ifthe axis is moving in the positive direction it stops at the programmed endpoint without overshoot Ifthe axis is moving in the negative direction it overshoots the endpoint by 0 001 inch then returns to the programmed endpoint Backlash takeup affects only halt moves that command the axis to stop at a move endpoint For blended moves backlash takeup has no effect Also backlash takeup is active only in auto mode Backlash takeup has no effect on axis motion in the man
45. aici Command oe CH B 5 I Servo L Output O CH B f S f S Return Drive Encoder foun Marker d I Customer oa Marker S S Supplied Joa Fwoul aes ll os is oO FS S Drive Disable Joc REV B HTE High Y O Low a L HO IH m 5 to 30V de Drive HOME LS 0O UP OMI 7 wae Disable Supply o Tach Customer a mardware STOP Supplied i a p Xo Belden 8761 or NOTES equivalent 50ft max If equipment permits one supply can be used for encoder and input circuits Current requirements depend on hardware configuration In the auto mode the module accepts this input as the hardware start signal figure 6 9 In the auto mode the module accepts this input as the feedrate enable signal figure 6 9 The module generates a hardware done signal at this 15V dc driver output terminal figure 6 12 E Refer to figures 6 10 and 6 11 Refer to figure 6 8 B Refer to figures 6 13 and 6 14 Refer to figure 6 15 12017 6 10 Chapter 6 Installing the Assembly This is a simplified diagram to give you an overall view of how you are to connect these terminals We give you further details in the following sections and their associated figures For all connections to the terminals limit the cable length to 50 feet Keep low level conductors separate from high level conductors This is particularly important for cable connections to the encoder Follow the practices outlined in the PC Grounding and Wir
46. al rate values Upon request from the status block the PC processor writes a moveset block to the 1771 M3 controller which transfers the move blocks to the 1771 ES expander one at a time The servo expander generates analog voltage to command axis motion as programmed The first word of a moveset block is the moveset control word MCW Following the MCW are the move blocks Each move block consists of a single move control word SMCW two position or dwell words and may contain words for local feedrate accel rate and decel rate depending on whether you select local or global rates by the SMCW You can leave words of zeros before and after move blocks This gives you flexibility For example you could remove a move block without changing the location of the other move blocks within the data table However you must respecify the number of moves in the moveset control word If the end of program bit is off the last word in a moveset block must be an address pointer in BCD format to the moveset block that should be executed next Moveset Control Word The MCW word identifies the block as a moveset block indicates whether you program the axis in inch or metric units specifies the number of moves in the moveset and whether or not the moveset defines an escape
47. als 8 9 and 10 on the right wiring arm provide connection points for a drive disable signal Figure 5 2 In chapter 6 we will show you how to connect this output to either source or sink 100mA maximum to enable the drive The module normally provides current thru this transistor to enable the drive However the module will turn off the current to disable the drive if the hardware stop input goes high a command block commands an immediate stop a firm ware or hardware watchdog timers times out the 1771 ES expander detects excess following error a loss of feedback or a power supply loss Figure 5 2 Schematic Diagram of the Drive disable Output Circuit 1771 ES Expander 8 2kQ DRIVE aT 8 DISABLE SUPPLY DRIVE j pl 9 ets S DRIVE 10 DISABLE Qi to COMMON 12011 The 1772 ES expander is compatible with a wide variety of servo drives including Allen Bradley Bulletin dc Servo Controllers refer to publication 1388 5 0 Allen Bradley also offers Bulletin 1326 dc servo Motors to match the Bulletin 1388 dc Servo Controllers 5 3 Chapter 5 Hardware Description 5 4 Tachometer Input Terminals 11 and 12 on the right wiring arm provide connection points for the velocity feedback signal from the tachometer Although the velocity loop is closed on the servo drive the 1771 ES expander uses the ve
48. ar Axis Motion Axis Motion Slide A Shaft f C wa lu Rotation 11999 The leadscrew assembly is referred to as the axis A leadscrew assembly consists of a long threaded shaft the leadscrew and slide having an internal thread that matches the leadscrew When the motor rotates the leadscrew clockwise the slide moves forward When the motor rotates the leadscrew counterclockwise the slide moves backward 3 1 Chapter 3 Positioning Concepts 3 2 Velocity Loop Most closed loop servo positioning installations use a dc motor to power the leadscrew To accurately control the velocity of the dc motor we need a velocity loop Figure 3 2 The velocity loop contains a summing point an amplifier and a tachometer A tachometer is a precision generator that produces a voltage signal directly proportional to the angular velocity of the motor shaft The output of the tachometer is the velocity feedback signal which is subtracted from the velocity command signal The difference is the velocity error signal that is amplified to provide power for the motor to run at the commanded velocity Figure 3 2 Velocity Loop Axis Motion 7 7 t S Motor Fuig b S Summing Point i Amplifier Velocity Velocity Command Error Velocity Feedback Velocity Error Velocity Command Velocity Feedback 12000 Whenever the velocity deviates from the
49. ation Fault This red indicator turns on when the module detects a fault in the communication between it and a 1771 ES expander Active This green indicator is normally on It turns off when a hardware fault is detected on a 1771 ES expander it blinks if you have not properly configured the modules There are six indicators on the 1771 ES expander With the PC processor operating in the run mode the indicators have the following functions Module Active This green indicator is on when the module is operating normally Marker This green indicator is on when the channel A channel B and marker signals are true simultaneously Home This green indicator is on when the axis is in the home position Tach Calibrate This green indicator is used in setting the adjustments for loss of feedback detection Hardware Stop This red indicator goes on when the hardware stop input opens It stays on until the input closes and the servo expander module is reset Diagnostic This red indicator goes on when a fault is detected at the servo expander module 5 1 Chapter 5 Hardware Description These indicators are useful troubleshooting aids described fully in chapter 9 Inputs Outputs The 1771 M3 controller requires no connections You will make all wiring connections to the 1771 ES expander Figure 5 1 shows the terminals on the 1771 ES expander These terminals provide the connection points for all the inputs a
50. block of a moveset block First Status Word Each bit of the first status word Figure 7 4 corresponds to a particular axis condition Chapter 7 Formatting and Interpreting Data Blocks Figure 7 4 First Status Word First Status Word Word 3 Axis 1 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 7 Axis 2 Word 11 Axis 3 q RRM UU URS Excess Error Loss of In Position Feedback Done Insufficient Data Ready Travel Limit Jog Hardware start Travel Limit Slide Stop Feed Reduction Jog Feedrate Override Enable Hardware Stop Home Immediate Stop 1 ve 0 Manua 11053 Bit 0 In Position The 1771 M3 controller turns on this bit when following error is less than twice the in position band value programmed in the parameter block word 11 When the in position bit is on it indicates that the axis has moved to within a specified distance of the programmed end point Bit 1 Done The 1771 M3 controller turns on this bit when the 1771 ES expander has finished feeding the axis for a programmed move or finished a dwell Bit 2 Ready The 1771 M3 controller turns off the ready bit after power up or after you execute the reset command The controller turns on this bit when it receives valid parameter block values When the ready bit is on the 1771 M3 controller is ready to respond to commands you issue thro
51. byte bits 00 thru 10 of the first diagnostic word is the error code The error code is a BCD number that references the errors listed in table 7 A 7 15 Chapter 7 Formatting and Interpreting Data Blocks Use the block pointer and word pointer to identify the location of the problem Then use the error code to determine the nature of the problem Table 7 A Diagnostic Code Definitions a or MS metric only bit set in inch format Can only change feedback multiplier from a power up rest Invalid axes used programmed a O w Invade toe aniesspaits O O o ieas o or B00oT mM O o nace mater seing O D A voltage too small for selected rapid rate Initial gain too small for selected rapid rate O e pome O 18 Posey or decel value so al or selected feedback resoluion Not as many valid SMCWs as there were moves declared in the MCW Local parameters or run at velocity not allowed for a preset or dwell Invalid preset position must be an absolute position 26 Invalid escape move block only moveset blocks identified in the parameter block can be escape move blocks 8 Cannot program a preset or dwell as an escape move 27 A valid next moveset pointer could not be found 28 Command results in overflow of offset accumulator Attempted context switch with dual meaning bits on 29 30 1 Attempted context switch while axis is commanding motion Manual mode only bit s on while in auto mode
52. commanded velocity the velocity feedback signal adjusts the velocity error signal until the velocity matches the velocity command signal Chapter 3 Positioning Concepts Positioning Loop When we want to move the slide a specific distance we can turn the motor on at a specific velocity for a specific length of time However this could produce imprecise positioning To accurately control the position of the slide we need a positioning loop Figure 3 3 Figure 3 3 Velocity Loop and Positioning Loop Axis Motion _ Encoder o Following Error Position Command Position A f amp S oe Tach eae 7 Following r omman pz Axis Error Velocity Amplifier eedtate S is K Command 1 Position Velocity Feedback 7 Incremental Position Feedback 12001 The positioning loop includes a summing point an amplifier a D A converter and an incremental digital encoder to produce a position feedback signal The axis feedrate is integrated in a register to produce the position command value Incremental position feedback is integrated in a register to produce the actual position value The position value is subtracted from the position command value The difference is the following error which is amplified and converted to an analog velocity command signal This s
53. cuit stops the axis abruptly stressing the servo drive the servo motor and the mechanical linkage just as the CRM would Use the hardware stop input only for backup to inform the 1771 ES expander of a condition that has already stopped the axis so that the expander can provide a controlled start up Connecting Home Limit Switch To connect a home limit switch follow these steps 1 Connect a normally open limit switch between the home limit switch terminal and common 2 Place the limit switch so that it closes as the axis reaches a point approximately one half of an encoder revolution from the point you want to establish as home position 3 Adjust the angular position of the encoder to have the marker pulse occur precisely at the point you want to establish as home position Through the command block transfer you can command a search home function sections titled Axis Control Word and Axis Control Word 2 The 1771 ES expander a moves the axis to the limit switch decelerates the axis Chapter 6 Installing the Assembly establishes the point of the next marker pulse following the limit switch as the home position stops the axis at the home position You must re establish the home position after each time power to the I O chassis backplane goes off because the encoder feedback is incremental Connecting Jog Reverse Feedrate Override Enable Figure 6 9 shows details of how to connect jog reverse
54. d with each I O chassis When properly installed these keys can guard against the seating of all but a selected type of module in a particular I O chassis module slot Keys also help align the module with the backplane connector 6 7 Chapter 6 Installing the Assembly Each module is slotted at the rear edge Position the keys on the chassis backplane connector to correspond to these slots to allow the seating of the module Insert keys into the upper backplane connectors Position the keys between the numbers at the right of the connectors Refer to Figure 6 5 for the 1771 M3 controller keying position Refer to Figure 6 6 for the 1771 ES expander keying positions Figure 6 5 Keying Diagram for the 1771 M3 Controller 2 4 Keying ae 6 Bands gt _ 8 Jio 12 Between i e pins 2 and 4 18 e pins 8 and 10 20 11005 6 8 Chapter 6 Installing the Assembly Figure 6 6 Keying Diagram for the 1771 ES Expander Upper Left Upper Right Connector Connector 2 2 eee 4 4 Keying 6 5 Bands x 8 10 10 12 12 i J14 14 16 16 Between 18 18 Between e pins 2 and 4 20 20 e pins 4 and 6 e pins 14 and 16 ee ae e pins 32 and 34 24 24 26 26 28 28 30 30 32 32 34 34 36 36 11006 Inserting the Module To insert a module into an T O chassis follow these steps 1 Remove power from the I O chassis before
55. der feedback signals However the function of this feature assumes a noise free marker signal The marker signal does have some noise protection because the 1771 ES expander only accepts a marker signal when the channel A and B signals are high unless you set the marker logic jumper to the not gated position To command axis motion you must be able to specify axis position by establishing an axis position scale or coordinate system for each axis Chapter 4 Positioning with Allen Bradley PC Figure 4 9 shows an example of an axis and its position scale Any axis position within the range of travel can be identified by a number For the servo positioning assembly the axis position scale can be either in inches or millimeters The position scale is an internal scale used by the servo positioning assembly to identify axis position It is not printed on the axis slide You can shift the axis position scale by entering through the command block any of the following commands search home preset initialize home Figure 4 9 Axis Position Scale MM 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 1 2 3 4 5 6 INCHES A 17967 Search Home Because the position feedback is incremental rather than absolute the servo positioning assembly does not know the axis position when it first receives power You must command a search home through the command block each time after powering up
56. drive Connect the analog return signal from terminal 4 of the 1771 ES expander to terminals 6 and 8 of the drive With this signal orientation when you connect the tachometer to the drive with the proper polarity for negative feedback the signal will also have Chapter 6 Installing the Assembly the proper polarity for loss of feedback detection at the 1771 ES expander If you use the opposite analog output signal orientation you will not be able to utilize the loss of feedback detection feature WARNING Always utilize the loss of feedback feature Without loss of feedback detection if encoder or tachometer feedback is lost unexpected axis motion can occur resulting in damage to equipment and or injury to personnel Limit the cable lengths to 50 feet If your application requires a cable length greater than 50 feet contact your local Allen Bradley representative Grounding Cable Shields Figure 6 17 is a pictorial representation of the shielded cable connections Mount a ground bus directly below the I O chassis to provide a connection point for cable shield drain wires and the common connections for the input circuits Connect the I O chassis ground bus through 8 AWG wire to the central ground bus to provide a continuous path to ground The tachometer cable is broken into three segments because of the connection to the drive and potentiometer in the middle of the cable Connect these cable shield segments together as shown Co
57. e Enable SO i G s Q Ol iS Jo O Reverse NS Auo HS i S i ji r ale o a i e o Manual fo 9 We 20 O O o Wiring Arm of 1771 OZ Contact Output Module Left Wiring Arm of 1771 ES Expander 12019 In the manual mode the jog reverse switch controls whether the input is high or low In the auto mode the feedrate override enable switch controls whether the input is high or low You can connect the same feedrate override enable signal to several 1771 ES expanders to coordinate the start of feedrate override for those axes Connecting Jog Forward Hardware Start Figure 6 9 also shows details of how to connect jog forward and hardware start Follow these steps Chapter 6 Installing the Assembly 1 Connect a third pole of the selector switch to the jog forward hardware start terminal of the 1771 ES expander 2 Connect a momentary contact jog forward switch to the selector switch contact corresponding to manual on the third pole 3 Connect an output terminal of a Contact Output Module cat no 1771 OZ to the selector switch contact corresponding to auto on the third pole In the manual mode the jog forward switch controls whether the input is high or low In the auto mode the hardware start output from the 1771 OZ module controls whether the input is high or low You can use the ladder diagram program to generate a hardware start signal by closing the contacts of 1771 OZ module
58. e I O chassis backplane 4 Energize the CRM relay 5 Generate a reset command through the command block Now that you have installed the servo positioning assembly you are ready to enter data blocks into the data table of the PC processor During installation you made hardware selections to direct module operation In chapter 7 we tell you how to make software selections to direct other aspects of module operation Chapter Objectives Relationship of Data Blocks Formatting and Interpreting Data Blocks The previous chapter told you how to install the modules During installation you made hardware selections through switch and jumper settings These hardware selections direct some aspects of module operation This chapter tells you how to make software selections through data blocks you set up in the data table Through data blocks you direct module operation This chapter also tells you how to monitor module operation through a data block that the module sends to the data table You must program the PC processor to communicate with the 1771 M3 controller through a block transfer read instruction and a block transfer write instruction The data blocks are status block parameter block moveset block command block The block transfer read instruction transfers status block data from the 1771 M3 controller to the data table The block transfer write instruction transfers the parameter block the moveset block and
59. e axis You can add a second 1771 ES expander to control a second axis and a third 1771 ES expander to control a third axis A 1771 I O chassis can accommodate one 1771 M3 controller and a maximum of three 1771 ES expanders The 1771 M3 controller requires one I O chassis slot it requires no wiring figure 2 1a You can install it at any I O slot in the I O chassis The 1771 ES expander requires a pair of slots that make up an I O module group Figure 2 1b You make all wiring connections to the 1771 ES expander 2 1 Chapter 2 Introducing the Servo Positioning Assembl Figure 2 1 Servo Positioning Assembly rp H eee pam 7 p 4 epal pea a Servo Controller Module b Servo expander Module cat no 1771 M3 cat no 1771 ES 17954 Its Applications Typical applications for a servo positioning assembly include positioning for grinding transfer lines material handling drilling riveting rotary indexing y belt cutting glass cutting Its Function Figure 2 2 shows a servo system for closed loop axis control The 1771 M3 controller communicates with the 1771 ES expander through T O chassis backplane connections 2 2 Chapter 2 Introducing the Servo Positioning Assembl
60. eached the programmed endpoint Move Values Each move block can specify several values The servo positioning assembly executes the move based on these items you enter endpoint acceleration final feedrate deceleration When you select a deceleration value the 1771 ES expander automatically calculates the point at which the deceleration must begin You can combine several single moves like that of Figure 4 5 to form a moveset Figure 4 6 shows an example that consists of four moves Move starts at position coordinate 0 and ends at position coordinate 2 Move 2 continues axis motion to position coordinate 5 Move 3 continues to position coordinate 7 Move 4 then causes the axis to reverse direction and move back to position 0 The axis stops after it returns to its initial starting position A drawing like that of Figure 4 6 is a moveset profile You can use such profiles as an aid in programming axis motion Figure 4 6 Moveset Profile with All Single step Moves m Move 1 Move 2 Move 3 Rate 0 1 2 3 4 5 6 7 8 Position Rate Move 4 11011 Chapter 4 Positioning with Allen Bradley PC You can program multiple movesets for a given axis Move Selection For each move you have each of the following selections Absolute or incremental positioning In an absolute move the endpoint value specifies a position coordinate relative to the current axis Zero posi
61. efore Preset 11009 4 12 Summary Chapter 4 Positioning with Allen Bradley PC Initialize Home Through a command block you can generate an initialize home command The initialize home operation assigns the home position value which you specify in the parameter block to the current axis position Its effect is the same as that of the preset operation except that the new position value is the home position value Now that you have been familiarized with the general concepts of how the servo positioning assembly functions in a closed loop positioning system and in a PC system you are ready for specific details of the servo positioning assembly in chapter 5 4 13 Chapter Objectives Indicators Hardware Description The previous chapter described how the servo positioning assembly fits into a positioning system as part of a programmable controller This chapter describes specific hardware of the servo positioning assembly and lists its specifications This chapter also describes other hardware items you need for a positioning system There are three indicators on the 1771 M3 controller With the PC processor operating in the run mode the indicators have the following functions Processor Communication Fault This red indicator turns on when the module detects a fault in the communication between it and the PC processor The I O adapter module or PC processor will not detect this as a fault Expander Communic
62. er 9 Connecting A B Encoder and Drive Chapter 6 Installing the Assembly 5 Connect the tachometer high signal to terminal 11 6 Connect the tachometer low signal to terminal 12 7 Connect the shields of the cable segments 8 Connect the shield to ground at the I O chassis end Figure 6 1 shows the jumpers in the position in which we place them for shipping the 1771 ES expander to you These channel polarity jumper settings select high true polarity These channel signal mode jumper settings select differential mode This marker logic jumper setting selects the marker to be gated with channel A and channel B If you use the Allen Bradley 845N SJDN4 C encoder leave the jumpers set to the position shown in Figure 6 1 With the jumpers set as shown in figure 1 connect the 845N SJDN 4 C encoder to the 1771 ES expander as shown in Figure 6 16 We show the channel A signal connection reversed with the not channel A connection and the channel B signal connection reversed with the not channel B connection This inversion of the channel A and B polarity allows the marker to be high at a time when both channels A and B are high Use an 8 to 15V dc power supply for the input circuits Connect the plus side of the supply voltage to pin E of the encoder With this configuration 5V dc power is generated at the encoder the signals from the encoder are 5V dc 6 27 Chapter 6 Installing the Assembly
63. er holds the velocity command output signal at zero and disables the servo drive by turning off the drive disable circuit if it is unable to sense the specified voltage as the following power supply terminals positive terminal for the input power supply common terminal for the input power supply positive terminal for the analog power supply negative terminal for the analog power supply Therefore if one of these power supplies connected to the 1771 ES expander terminal fails or if one of these connections from these power supply breaks the 1771 ES expander will disable the servo drive The drive disable circuit normally provides current to a sensing circuit on the servo drive to enable it However if the 1771 ES expander detects a fault it cuts off the current in the drive disable circuit thereby disabling the servo drive Therefore if a connection in the drive disable circuit breaks this disconnection will disable the servo drive Auto Position Correction Each time the 1771 ES expander receives a marker pulse it checks the value in the position register to see if it is an even multiple of the number of feedback increments per revolution If the value is off the 1771 ES expander will automatically adjust it to the closest even multiple This auto position correction feature corrects position errors caused by noise on the channel A and B encoder feedback signals However the function of this feature assumes a
64. eter Block Pointer 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 2 S J Data table address of parameter block BCD format Command Block Pointer 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 3 FSS Data table address of command block BCD format Axis 1 Moveset Block Pointer 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 4 FS Data table address of first moveset block to be transferred for axis 1 BCD format Axis 2 Moveset Block Pointer 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 5 SS 5 Data table address of first moveset block to be transferred for axis 2 BCD format Axis 3 Moveset Block Pointer 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 6 Data table address of first moveset block to be transferred for axis 3 BCD format 11032 7 20 Chapter 7 Formatting and Interpreting Data Blocks Important The address pointer value you enter in each of these words must be a BCD value other than 000 For each axis include only the address of the first moveset block in the parameter block Include address pointers to subsequent movesets in the blocks that precede them If you program
65. f move blocks through which it describes axis motion for a sequence of moves Figure 7 29 Figure 7 29 Moveset Block Showing Word Assignments Moveset Control Word MCW Single Move Control Word SMCW Position or Dwell Time MS Position or Dwell Time LS sarah Up to Local Acceleration 5 words 64 words Local Deceleration Single Move Control Word SMCW oolli j Mowe Block 2 Position or Dwell Time MS 3 words Position or Dwell Time LS t Single Move Control Word SMCW l Position or Dwell Time MS Move Block N 1 Position or Dwell Time LS 4 words Local Feedrate Single Move Control Word SMCW Position or Dwell Time MS Position or Dwell Time LS Move Block N Local Feedrate 6 words Local Acceleration Local Deceleration Next Moveset Pointer If Required 11216 Each move requires a move block of at least three words a single move control word and two words to define position or dwell time A move block may have as many as six words a single move control word two position words a rate word an accel word and a decel word In addition two words moveset control word and next moveset pointer apply to the entire moveset block Since the moveset block may contain no more than 64 words the largest possible number of moves a single Chapter 7 Formatting and Interpreting Data Blocks block can describe is 21 All 21 moves would have to use global accel decel and fin
66. hen all axes are in position you can send a start command to each axis through the hardware start input terminal of the 1771 ES expander Using the hardware start and done signals is faster than using block transfer for the status and command blocks Furthermore if the axis synchronization includes multiple servo positioning assemblies precise synchronization cannot occur through block transfer because two block transfers cannot occur simultaneously Continuous Moves For continuous moves with the next move in the same direction axis synchronization requires precise programming of feedrates acceleration rates and deceleration rates You must program the move blocks so that each axis takes the same amount of time for corresponding moves Furthermore you must plan the moves to be long enough to adhere to the following constraints Each move must take longer than the time it takes to transfer a move block from the 1771 M3 controller to the 1771 ES expander This time is a function of the number of axes as follows No of Axes Time 1 20ms 2 25ms 3 30ms Ifthe number of moves requires additional moveset blocks the last two moves of each preceding moveset block must not be too short They must take a long enough time for the following moveset block to be transferred from the data table Refer to chapter 8 for details about block transfer timing 4 9 Chapter 4 Positioning with Allen Bradley PC Specifying Axis Position
67. his input is pulled low the module holds the velocity command output signal at zero and disables the servo drive by turning off the drive disable circuit Encoder Inputs Terminals 2 3 4 5 6 and 7 on the left wiring arm provide connection points for input signals from the encoder Through jumpers on the module you can select each channel individually for either single ended or differential and for either high true of low true input signals If you use a single ended encoder limit the input pulse rate to 20k Hz If you use a differential encoder limit the input pulse rate to 250k Hz The 1771 ES expander is compatible with Allen Bradley Incremental Differential Line Driver Encoders cat no 845N SJDN4 C and with other encoders having current sinking 5 30V dc line driver outputs totem pole TTL outputs or open collector outputs You must provide at least two external dc power supplies to provide power for the input and output circuits 5 7 Chapter 5 Hardware Description Compatible Processors 5 8 Input Supply You must connect a 5 30V dc power supply between terminals 1 and 12 of the left wiring arm This provides power for the input circuits The input circuits require 500mA maximum at 30V You can use the same power supply to power the encoder if the power supply has enough additional current capacity for the encoder Drive Disable Supply Unless the servo drive provides its own dc voltage source for th
68. ide travel The first market pulse after the limit switch is activated could then designate the home position Figure 3 8 Summary Chapter 3 Positioning Concepts Figure 3 8 Marker Pulse Establishing a Home Position Limit Switch Marker Pulse Axis Motion _ gt Home Position 12004 Once we establish a home position we can use it as an absolute reference point for all moves In this chapter we described concepts of closed loop positioning Now you are ready for concepts of position with an Allen Bradley PC This material is covered in chapter 4 3 11 Positioning With an Allen Bradley Programmable Controller Chapter Objectives The previous chapter described concepts of closed loop positioning This chapter describes where the servo positioning assembly fits into a positioning system and how the servo positioning assembly communicates with the PC processor Where the Servo Positioning Figure 4 1 shows where the servo positioning assembly and a servo drive Assembly Fits In fit in the positioning system we described in the previous chapter The servo drive contains the velocity loop summing point and amplifier The servo positioning assembly contains the positioning loop summing point and the feed forward summing point The servo positioning assembly sends the analog velocity command signal to the servo drive Encoder
69. if you want to remove power Connect a set of normally open CRM contacts in series with servo transformer overload servo drive fault and servo motor overload contacts Connect this series of contacts between the hardware stop input terminal and common The opening of any of these contacts indicates that power to the servo motor is interrupted When any of these sets of contacts open the hardware stop circuit the following occur 1 When this circuit opens the 1771 ES expander immediately sets the velocity command output to zero and disables the serve drive by turning off the drive disable circuit 6 15 Chapter 6 Installing the Assembly 2 The 1771 M3 controller sends the hardware stop signal to the PC data table thru the status block transfer 3 After this circuit closes again the 1771 ES expander still holds the velocity command at zero and holds the servo drive disabled until you either send a reset signal through a command block transfer This allows the 1771 ES controller to maintain the accumulated axis position cycle I O chassis backplane power off then back on This clears the accumulated axis position When you restart the axis after a hardware stop the axis feedrate accelerates before reaching the final velocity rate This allows a smooth start up after a hardware stop Do not provide switch contacts in the hardware stop circuit for an operator to turn off the axis motion Opening the hardware stop cir
70. ignal directs the axis to move in the right direction the position value moves closer to the position command value The following error is a function of the axis velocity divided by the positioning loop gain K1 The following error is multiplied by the gain 3 3 Chapter 3 Positioning Concepts to generate the velocity command Gain is expressed in ipm mil where 1 mil 0 001 in or mmpm mil where 1 mil 0 001 mm For example with a velocity of 100 ipm and a gain of ipm mil the following error is velocity 100 ipm 2following error gain 1 ipm mil 100 mil When you increase the gain you decrease the following error and decrease the cycle time of the system However the gain that you can use is limited by the drive the motor and the machine a gain that is too large causes instability Feed Forward To decrease the following error without increasing the gain we can add a feed forward component Figure 3 4 Figure 3 4 Velocity Loop Positioning Loop and Feed Forwarding Velocity Command K following Error K Axis Feedrate Axis Motion J Encoder Feed K Forward S Motor ran ee 2 Position Following i Veloci Axis Command Error Command Feedrate i F a gt K gt gt DIA aa Velocity Feedback Position 7 Incremental Position Feedback
71. ing Guidelines publication 1770 980 Power Supplies Use shielded cable for connecting the input power supply and the analog power supply Route these cables only with low level conductors Keep these power supply cables as short as possible Ground the common terminal for each of these power supplies Encoder and Tachometer For an encoder or tachometer connection use only a single continuous shielded cable segment Do not break the cable for connection in a junction box Connect the cable directly from the encoder to the 1771 ES expander Important Ensure that the power supply for the encoder provides the voltage recommended by the encoder manufacturers Shielded Cables For many connections we tell you to use shielded cable Using shielded cables and properly connecting their shields to ground protects against electromagnetic noise interfering with the signals transmitted through the cables WARNING Use shielded cable where we tell you to use it and how we tell you to use it If you do not the axis motion in your positioning system could be unpredictable this could result in damage to equipment and or injury to personnel 6 11 Chapter 6 Installing the Assembly 6 12 Within a shielded cable pairs of wires are twisted together Using a twisted pair for a signal and its return path provides further protection against noise We show a twisted pair like this XX We show a shielded twisted pair li
72. inserting or removing a module 2 Open the module locking latch on the I O chassis and insert the module into the slot keyed for it 3 Press the module firmly to seat it into its backplane connector 4 Secure the module in place with the module locking latch CAUTION Do not force a module into a backplane connector if you cannot seat a module with firm pressure check the alignment and keying Forcing a module can damage the backplane connector or the module 6 9 Chapter 6 Installing the Assembly Connecting to Terminals Make connections to the 1771 ES expander as shown in Figure 6 7 Figure 6 7 Simplified I O Terminal Connection Diagram 5 to 30V DC 2 Input Power 7 wie costes D cnn Belden 8723 o 50 ft max n r supplied ar I O equivalent 50ft max O O Q Q 2 t 15V de For DAC XX Customer Belden 8761 or 8 Iden 8725 T gt Supplied equivalent dded i Ce Comm 50ft max To Servo 50ft max EEN EEn Motor CH A ESM 10V t B CH A z io
73. is circuit you ll need a 5 30V dc power supply to provide 100mA maximum for the drive disable circuit How you connect this power supply depends on whether the servo drive requires a current source or a current sink to enable it Analog Supply A separate 15V dc supply is needed to provide 200mA maximum for the digital analog converter DAC to generate the analog output signal and for the hardware done output circuit The servo positioning assembly can be used with PC processors that have block transfer capability and adequate data table size to contain the data blocks you need for your application Compatible PC processors include a Mini PLC 2 05 cat no 1772 LS LSP a Mini PLC 2 15 cat no 1772 LV a PLC 2 20 cat no 1772 LP2 PLC 2 30 cat no 1772 LP3 PLC 3 cat no 1775 L1 L2 Fault Responses Chapter 5 Hardware Description The servo positioning assembly provides a means for detecting and responding to faults in your servo positioning system Since the servo positioning assembly is part of a PC system diagnostic information about fault conditions detected by the servo positioning assembly can be block transferred to the PC processor At the PC processor you can use the ladder diagram program to respond to diagnostic information about fault conditions in any way you feel is appropriate for your application This may include turning off machinery turning on alarms or generating report printouts
74. it the loop contactor relay LCR circuit the dc power supplies and any ac I O chassis Provide a separate transformer for the servo drives to provide noise immunity Use normally open LCR contacts to switch power from the servo drive to the servo motor Also use normally closed LCR contacts to switch in the dynamic braking resistor across the servo motor whenever power is removed from the servo motor Check with the servo drive and servo motor manufacturer for the resistance and power rating for the dynamic braking resistor WARNING Without a dynamic braking resistor removing servo motor power while the axis is in motion allows momentum to keep the axis in motion In an emergency situation this could be dangerous A dynamic braking resistor can help stop the servo motor by quickly dissipating the energy of momentum Even with dynamic braking a vertical axis may also require an electric brake or counter balance An extreme overtravel limit switch or an emergency stop switch can de energize the LCR thereby turning off servo motor power However abruptly stopping an axis in this way stresses the servo motor and the mechanical linkage Therefore use the LCR to stop a moving axis only in an emergency To stop an axis in a non emergency situation use the slide stop bit in the command block thru the ladder diagram program A slide stop decelerates the axis feedrate before stopping it After a slide stop you can use an emergency stop switch
75. ition band is measured in increments of the feedback resolution of the axis Program a 2 digit BCD value that is half the desired in position band in bits 10 17 of the in position band and gain break factor word Figure 7 17 If you program zero as the in position band parameter value the servo positioning assembly automatically makes the active in position band 2 feedback increments The 1771 M3 controller turns on the in position bit when the done bit is on in the status block and the axis is within the in position band The axis must be in position before the following actions can take place Manual mode commands are not executed unless the in position bit is on In auto mode the start command is not executed unless the in position bit in the status block is on 7 27 Chapter 7 Formatting and Interpreting Data Blocks 7 28 When the direction of axis motion is reversed the in position bit in the status block must be on before axis motion in the reverse direction can occur Note that the value you enter for the in position band is actually half the desired in position band value For example if the in position band value you enter is 5 then the servo positioning assembly considers the axis in position if it is within 10 increments of feedback resolution of the programmed endpoint Figure 7 18 illustrates the concept of in position band Figure 7 18 In position Band Example Programmed Endpoint Position
76. k 1 auto O manual Bit 10 Immediate Stop When this bit is on it indicates that the 1771 ES expander is holding its analog output signal at zero and is disabling the servo drive through its drive disable output You can clear this immediate stop condition through a reset command or by cycling I O chassis backplane power off then on Commands and events that can cause the immediate stop condition are Chapter 7 Formatting and Interpreting Data Blocks software stop command hardware stop input open excess following error loss of feedback loss of power firmware or hardware watchdog timeout on the 1771 ES expander Bit 11 Hardware Stop The 1771 M3 controller turns on this bit only if the hardware stop input of the 1771 ES expander is open Note that the immediate stop bit bit 10 is also on if this bit is on You can turn off this bit with a reset command or by cycling power to the I O chassis backplane Bit 12 Feed Reduction This bit goes on when axis following error reaches 106 25 of rapid traverse following error resulting in 50 feedrate reduction but has not necessarily reached the excess error point When axis following error does reach the excess error point the feed reduction bit stays on and the immediate stop status bit goes on Important If the excess error point is less than 106 25 of rapid traverse following error immediate stop occurs before feed reduction Consequently the feedrate
77. ke this XX IK Connect each shield to ground at one end only At the other end cut the shield foil and drain wire short and cover them with tape to protect against their accidentally touching ground Keep the length of leads extending beyond the shield as short as possible Use cables with the proper number of individually shielded twisted pairs as follows Number of Individually Shielded To connect to Twisted Pairs Use Encoder 4 Belden 8725 or equivalent Analog power supply 2 Belden 8723 or equivalent All other shielded cable Belden 8761 or equivalent connections Connecting the Input Supply To connect the input power supply follow these steps 1 Connect the plus side of the input power supply to terminal 1 of the left wiring arm Chapter 6 Installing the Assembly 2 Connect the minus side to terminal 12 and to ground at the I O chassis 3 Connect the shields of the two cable segments if you use the same supply to power the encoder 4 Connect the shield to ground at the I O chassis end 5 Connect the power supply chassis to ground Connecting Hardware Stop Before you connect to the hardware stop input you should first consider overall power distribution including the master control relay and loop contactor relay Figure 6 8 Connect a suppression network across each relay coil Chapter 6 Installing the Assembly Figure 6 8 Simplified Power Distribution with the Maste
78. keup offset preset Chapter 2 Introducing the Servo Positioning Assembl Benefit precise closed loop positioning programming flexibility precise positioning at low speed with stability at high speed optimize the machine cycle time over varying loads flexible positioning accuracy flexible manual positioning precise dwell times automatic drive shutdown if the axis following error becomes too large allow automatic drive shutdown during a move if tachometer or encoder feedback is lost guards against axis overtravel compensates for mechanical backlash compensates for a variation in tool length or fixture dimension easy redefinition of axis coordinates Chapter 2 Introducing the Servo Positioning Assembl 2 6 Feature optically isolated analog output external hardware startl encoder input selectable for high true or low truel synchronized start of feedrate overridel sensing of customer power supply loss feed forwarding constant velocity command moveset overridel diagnostic words in the status block for Benefit guards against noise entering the backplane circuits and limits the potential for damage due to improper connection synchronizes moves with other axes compatibility with a wider range of encoders activates a pre loaded feedrate override value to change speed on several axes simultaneously an orderly shutdown of the servo sy
79. locity feedback signal to compare to the position feedback signal from the encoder If the module detects an imbalance between these signals it disables the servo drive and sends a loss of feedback signal through the status block The 1771 ES expander accepts a full scale tachometer signal of 3V to 50V dc If the full scale tachometer signal is greater than 50V dc you must reduce it through a voltage divider on the servo drive before connecting it to the module CAUTION Do not connect a signal greater than 50V dc across these terminals A signal greater than 50V dc could damage the 1771 ES expander Hardware Done Output Terminal 7 on the right wiring arm provides a connection point for a hardware done output signal Figure 5 3 Chapter 5 Hardware Description Figure 5 3 Schematic Diagram of the Hardware done Output Cirucit 1771 ES Expander anal ANALOG SUPPLY w 15Vdo 211 9 NOT USED ANALOG e 3a S 3 OUTPUT ANALOG all 4 RETURN N 5 15Vdc ar COMMON i 6 ANALOG SUPPLY 6 S 15Vdc 7 HDW DONE ms 12012 The output transistor normally on provides a 15mA maximum sink When the axis feed is done and the axis is in position the transistor is off and the circuit provides 15V dc through a 1k resistor This provides you with a hardware done signal that is high true In chap
80. n 12009 In Position For a continuous move with the next move in the same direction the move is complete when the axis feed is done The 1771 ES expander immediately begins the feedrate for the next move without waiting for the following error to close For any halt move single step move or a continuous move with the next move in the opposite direction the move is not complete until the axis is in position The axis is in position when the following conditions are met the axis feed is done following error has closed to within the in position band You establish the in position band in the parameter block The in position band is the largest distance from the endpoint at which you will allow the axis to be considered in position Synchronizing Axes In many applications it is important to synchronize the motion of two or more axes In the following sections we will tell you how to do this Halt Moves For halt moves axis synchronization is straightforward When an axis is in position after a move the next axis move will not begin until you send a start command 4 8 Chapter 4 Positioning with Allen Bradley PC You can monitor the in position signal of each axis through the status block When all axes are in position you can send a start command to each axis through the command block Alternatively you can monitor the in position signal of each axis through the hardware done output terminal of the 1771 ES expander W
81. n Break Speed Word Gain Break Speed 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 10 Axis 1 5 R Word 29 Axis 2 4 7 Word 48 Axis 3 inch i h metric j decimal decimal Multiplier point point 001 x 10 000 x 10 010 x 10 This BCD value 0 999 ipm or 100 x 10 19 99 mmpm max times the 110 x 107 multiplier is the gain break speed 111 x 10 11037 At speeds equal to and above the gain break value you enter into this word the servo positioning assembly reduces servo gain by the gain reduction factor specified in the next word of the parameter block The gain break plot of Figure 7 16 illustrates the concept of gain break Typically gain at axis speeds below the gain break velocity is relatively high to allow precise axis positioning Reduced gain at axis speeds above gain break velocity allows for better stability at higher axis speeds Gain break velocity can be no greater than rapid traverse rate If there is to be no gain break point for an axis program the rapid traverse speed in this word 7 25 Chapter 7 Formatting and Interpreting Data Blocks Figure 7 16 Gain Break Plot Emergency Stop Commanded Axis A Speed Rapid Traverse Speed gt corresponds to Analog Output Voltage specified in parameter block Gain Break Speed X Reduced _ Initial Gain Reduction Gain Gain Factor Slope IPM Mil Initial Gain gt Gain Break A Following Point Max
82. ncoder Lines Multiplier Loss of marker Initial Gain 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 9 Axis 1 Word 28 Axis 2 Word 47 Axis 3 y Loss of marker Feedback detection Multiplier 0 disabled 01 x1 1 enabled 10 x2 Encoder a n 00 x4 Lines Initial Gain ipm mil or Multiplier mmpm mil BCD format X i 1 mil 0 001 inch or 0 001 x as See preceding millimeter word 11035 Servo gain is the ratio of axis speed to following error Gain Axis Speed Following Error Following error is the difference between the axis position commanded by the servo expander and the actual axis position indicated by encoder feedback Servo gain affects axis response to positioning commands from the 1771 ES expander module Figure 7 14 shows how different gain values affect system responsiveness The horizontal axis represents following error The vertical axis represents analog output voltage Since analog output voltage is directly proportional to axis speed you can use the vertical axis to represent either variable If gain is relatively high following error will be relatively small because the system will be more sensitive to changes in following error If gain is 7 23 Chapter 7 Formatting and Interpreting Data Blocks low following error becomes relatively larger because the system is not as responsive to changes in followi
83. nd outputs of the servo positioning assembly Limit the cable length to 50 feet for all connections Figure 5 1 Terminals On the 1771 ES Expander Showing Input and Output Signals j CIC SEMO 5 O O elll S O All TS ia yO ie 1 Input Supply 5to 30V dc S QJ 1 Analog Supply 15V dc 2 Channel A 2 S Q 2 Not Used 3 Channel A 3 Q Q 3 Analog Output 4 Channel B 4 Q QJ 4 Analog Retun e 5 Channel B 5 Q Q 5 15V DC Common 6 Marker 6 Q Q 6 Analog Supply 15V dc gt 7 Marker 7 Q Q 7 aa Done ee 8 Jog Forward HDW Start 8 O Q 8 Drive Disable Supply 9 Jog Reverse FDRT ENBL 9 Q Q 9 Drive Disable Output 10 Home Limit Switch 10 Q Q 10 Drive Disable Common 11 Hardware Stop 11 Q 11 Tachometer 12 5to 30V dc Common 12 12 Tachometer __ 12010 5 2 Chapter 5 Hardware Description Outputs to Servo Drive Terminals 3 and 4 on the right wiring arm provide connection points for the velocity command signal to the serve drive This analog output is a 10V dc differential signal Termin
84. ng error Choose a gain value to match the capability of your axis drives motors and mechanics and provide adequate system response Figure 7 14 Following Error Vs Speed for Various Gains Analog Output Voltage Axis Speed High Gain Low Gain Following Error High Gain Low Gain Low Following Error High Following Error 11036 Parameter block values for gain and in position band must provide a stable system and maintain desired positioning accuracy If gain is too high the axis may overshoot programmed endpoints and oscillate or hunt about them If gain is too low the axis may stop before it is within the desired in position band You can increase in position band but this decreases positioning accuracy Use bit 15 of this word to select the encoder lines multiplier This encoder lines multiplier you select times the encoder lines value you select in the previous word must match the number of lines per revolution of the encoder 7 24 Chapter 7 Formatting and Interpreting Data Blocks Use bits 16 and 17 of this word to select the feedback multiplier The feedback multiplier you select affects the value you must enter for the feedback resolution word Gain Break Speed At axis speed below the gain break value you enter into the gain break word Figure 7 15 servo gain is the initial gain programmed in the preceding word Figure 7 15 Gai
85. nnect the shield to ground only at the I O chassis end Do not connect the shield to the drive Chapter 6 Installing the Assembly 8 to 15V de Power Supply for input Circuts customer supplied Shielded cables are not required for these discrete inputs However they can improve noise immunity NOTES Belden 8761 or equivalent Belden 8723 or equivalent Belden 8725 or equivalent 6 30 Figure 6 17 Shielded Cable Grounding Connections 15V de For DAC Customer Supplied Return 1771 ES Expander Twisted pair with shield or conduit a OO00000000 Bulletin 1388 DC Servo Controller Drive 27K Drive Disable Lr 8 AWG vire to central ground bus Encoder 1 0 Chassis Ground Bus 12304 Connecting AC Power Figure 6 18 shows ac power connections Incoming ac connects to the primary of the bulletin 1388 power transformer Both the 120V secondary and the 35 5V secondary connect to the bulletin 1388 dc servo controller drive Incoming ac also connects to the primary of an isolation transformer The secondary of the isolation transformer connects to the power supply for the input circuits the power supply for the I O chassis backplane the power supply for the analog output circuit Figure 6 18 shows a grounded ac system the low side of the isolation transformer is connected to the central ground bus Figure
86. ord 13 Axis 3 Word 6 Axis 1 Word 10 Axis 2 Word 14 Axis 3 Chapter 7 Formatting and Interpreting Data Blocks Figure 7 7 Position Following Error Diagnositc Words with Diagnostic Selected First Diagnostic Word 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word pointer This BCD Error code This BCD number tells you which word is number refers to the error in error within the block listed in Table 7 A Second Diagnostic Word 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 ON Block pointer This BCD number is the address of the block which is in error 12028 Also this diagnostic status displays automatically when the 1771 M3 controller detects an error in the parameter block immediately after power up or an invalid ID in a command block The diagnostic status displays automatically in that case because the error prevents your selecting it through the command block The second diagnostic word is the block pointer The block pointer is a BCD number that indicates the starting address of the block in error The 1771 M3 controller gets these block pointers you enter into the parameter block or the moveset block The high byte bit 10 thru 17 of the first diagnostic word is the word pointer The word pointer is a BCD number 1 thru 64 that indicates which word is in error within the block The low
87. output when each of several axes generates a hardware done signal You can connect the same hardware start signal to several 1771 ES expanders to coordinate the start of motion following halt moves for these axes Connecting a Differential Encoder Figure 6 10 shows details of how to connect a differential encoder With a differential encoder reversing the connections on a channel or changing the position of the polarity jumper for the channel reverses the polarity of the signal on that channel Set the polarity so that the marker is true at the same time that channels A and B are true If you switch channel A with channel B you reverse the direction of the feedback If the direction of the feedback does not correspond to the axis motion direction as you have defined it switch channel A with channel B Ground the shield at the I O chassis end Chapter 6 Installing the Assembly Figure 6 10 Connection Details for a Differential Encoder 5 to 30V DC Belden 8761 or mpa ri equivalent pp y 50 ft max customer supplied Ground the shield p at the I O chassis end CH A al endl Differential o CH B Output CHB Encoder o Marker oS Marker i l Belden 8725 or Ground the shield equivalent at the I O chassis end 50 ft max abdaooabdba i 2
88. r RR rapid traverse rate FR feedback resolution FM feedback multiplier 1 2 or 4 EL encoder lines per revolution 7 29 Chapter 7 Formatting and Interpreting Data Blocks D A maximum D A voltage IG initial gain These formulas include an allowance for a 127 feedrate override factor These formulas apply to both ipm and mmpm Jog Rate The high and log jog rate words Figure 7 20 specify the speeds at which you can jog the axis You can jog the axis only in manual mode Program the values in BCD format The operator can select jog speed high or low by controlling the jog rate select bit in the command block Figure 7 20 Jog Rate Words High Jog Rate 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 13 Axis 1 Word 32 Axis 2 i i Word 51 Axis 3 inch naik Multiplier poini geemal 001 x 10 000 x10 This BCD value 0 999 ipm or 010 x10 19 99 mmpm max times the 100 x 10 multiplier is the high jog rate It must 110 x 103 not be higher than the rapid traverse 111 x10 rate Low Jog Rate 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 14 Axis 1 Word 33 Axis 2 4 j Word 52 Axis 3 Y inch metric ceama decimal Multiplier point point n x10 This BCD value 0 999 ipm or 010 x 10 19 99 mmpm max times the 100 x 10 multiplier is the low jog rate It must
89. r Control Relay Loop contactor Relay and Hardware Stop Incoming L i i e d 1 d 2 i 3 Wa F F F u u u S S s e e e e e Hy H4 nti Isolation Isolation ______ Step Down Step Down i i Transformer Transformer A X1 X2 a F F F u u 3 Extreme s Overtravel Limit Switches negel TOOT O O O crm LCR A Servo Drive Use any number PE of E stop switches H Hi je in series CRM Dynamic i a I A Fa CRM LCR Braking LCR ap ay ek en Resistor LCR Q Q QO 1 Cae y Help aa aen t a shor tse ctay He Fea Backplane Motor Power Supply ia nae aad Power Supply for fe H 9 Analog Output Circuit a OMe 15V DC Common 15V de Servo Xformer Thermal Overload Power Supply for Input Circuits TF CRM 1771 ES Expander aie 5 30V de Servo Drive E CRM Fault T O Y Y Servo Motor Tol O Maules P Input Circuits Thermal Overload l 42 5 30V de Common NOTE _ To minimize EM generation connect a suppression network for 120V ac Allen Bradley ae ee See cat no 700 N24 fo r220 240V ac Electrocube part no RG 1676 13 12018 6 14 Chapter 6 Installing the Assembly Provide one transformer for the master control relay CRM circu
90. rd 39 Axis 2 Word 58 Axis 3 V Y inch metric Poe decimal decimal ed point point moan This BCD value 0 999 ipm or 010 x 10 19 99 mmpm max times the 100 x 102 multiplier is the decel step rate 110 x 103 During deceleration the axis feed 111 x 10 rate steps directly to zero once the rate drops to this level This only applies to jog and search home 11046 Software Travel Limits Words 21 and 22 40 and 41 59 and 60 specify the axis position values of the axis software travel limits Figure 7 25 When a programmed move calls for the axis to move beyond a software travel limit if there is time the servo positioning assembly automatically decelerates the axis at the programmed rate for the current move so that it stops at or before the software travel limit position If there is no time to decelerate the axis before the limit is exceeded the servo positioning assembly executes an immediate stop This could occur following a continuous move because the next move starts with the feedrate of the previous move rather than zero Software travel limit values are axis position values Note that if zero is the programmed travel limit value there is no software travel limit The absolute positions of the software travel limit vary with changes in axis position value due to preset or home commands In addition to the software travel limit you must have extreme axis overtravel limit switches wired in the master control relay circuit
91. re done output power supply common to the 1771 IB input module common terminal This power supply provides the 15V dc source for the hardware done signal Examine the hardware done signal thru the ladder diagram program You can synchronize the motion of several axes after each halt move send a hardware start signal to all axes when you have received the hardware done signal from each axis Chapter 6 Installing the Assembly Connecting Drive Disable Figure 6 13 shows details of how to connect drive disable for two basic types of configurations Some servo drives require a current source connected to an input to enable the drive Some require a current sink connected to an input to enable the drive We provide all three connection points base emitter and collector of the drive disable circuit to provide you with a flexibility of connecting it in a configuration that applies to your servo drive Figure 6 13 Connection Details for Two Basic Drive Configurations a Current Sourcing Configuration Drive Enable Q1 on Current is sourced from terminal 10 into the servo drive 8 2k Drive Disabled Q1 off Current into the servo drive is inhibited Customer s Drive Disable Power Supply 5 to 30V dc Drive Disable Input on Customer s Servo Drive b Current Sinking Configuration Drive Enable Q1 on Current is sunk thru terminal 9 and Q1 8 2k Drive Disabled Q1 off Current th
92. reduction bit in the status block does not turn on Bit 13 14 and Travel Limits These bits are on when the axis is at the corresponding software travel limit positions You enter the travel limits in the parameter block Bit 15 Insufficient Data When the servo positioning assembly receives a command to execute axis motion such as start or begin but does not have moveset data to execute a move it turns on the insufficient data bit It also turns on this bit when you issue an escape command even though you had never stored an escape move on the 1771 ES expander This insufficient data bit stays on until the 1771 M3 controller receives a new moveset block and then a start or begin command 7 9 Chapter 7 Formatting and Interpreting Data Blocks Bit 16 Loss of Feedback This bit is meaningful only if you enable the loss of feedback detection feature by setting bit 15 of the most significant home position word of the parameter block If loss of feedback is enabled and the servo positioning assembly detects a loss of feedback it turns on the loss of feedback bit in the status word If this bit is on then the immediate stop bit in the status block is on indicating that the 1771 ES expander has executed an immediate stop after detecting the loss of feedback Bit 17 Excess Error If following error equals or exceeds the excess following error value you enter in the parameter block the 1771 M3 controller turns on this bi
93. rew for this example The slide moves 1 4 inch for each revolution With an x1 multiplier each feedback increment represents 1 250 of 1 4 inch or 0 001 inch slide movement This is the feedback resolution 0 25 in rev feedback resolution 250 lines rev x 1 increment line 0 001 in increment 3 9 Chapter 3 Positioning Concepts Therefore if we cause the leadscrew to move the slide 2 inches we will get 2 000 feedback pulses Now consider replacing the 250 line encoder with a 500 line encoder By doubling the number of feedback pulses per revolution of the leadscrew we improve the feedback resolution from 0 001 inch to 0 0005 inch Another way to improve feedback resolution is to use a higher feedback multiplier You can select a multiplier of x1 x2 or x4 For example with the 4 pitch per inch leadscrew and the 250 line encoder if you select an x2 multiplier you get the same feedback resolution improvement of from 0 001 inch to 0 0005 inch With an x4 multiplier you improve the feedback resolution to 0 00025 inch Marker Besides the channel A and B output an incremental encoder has a marker output Figure 3 6 and Figure 3 7 The marker pulse occurs once every revolution With a 4 pitch leadscrew the marker pulse occurs at each 1 4 inch interval of slide travel We can use a market pulse to establish a home position somewhere along the slide travel For example we can place a limit switch near the end of the sl
94. rminal 5 4 Connect the shield to ground at the I O chassis Connecting Velocity Command Connect the analog velocity command output signal from terminals 3 and 4 on the right wiring arm to the corresponding terminals of the servo drive Reversing these connections reverses the direction the axis moves in response to the velocity command Connect this signal so that the direction of motion that results from it matches the correct direction of motion as you have defined it Connect the shield to ground at the servo drive end Chapter 6 Installing the Assembly Connecting Hardware Done Figure 6 12 shows details of how to connect hardware done Follow these steps Figure 6 12 Connection Details for Hardware Done Output 15V de For DAC customer supplied Comm Right Wiring Arm f 1771 ES E 0 S Expander HBV 45V Wiring Arm of 1S 1771 IB Input Module I Is Belden 8761 or aa T 9 equivalent aN TO 50ft max nel AS F S I s Q Hardware Done z S i Q S i amp 9 JO lO EQ 10 9S E S i Q 2 9 2S e lS vq 12022 1 Connect the hardware done output from terminal 7 on the right wiring arm to an input terminal of a dc 12 24V Input Module cat no 1771 IB 2 Connect the analog and hardwa
95. ru Q1 is inhibited Terminal 9 is pulled up to the potential of terminal 8 e 9 Customer s Drive Disable Power Supply at Drive Disable 6 to 30Vde ae Input on Customer s Servo Drive 40 12023 For the drive disable circuit you must provide a 5 30V dc power supply which can provide 100mA maximum The power supply can be separate or an integral part of the servo drive Each of the configurations of figure 6 13 includes a separate power supply 6 24 Chapter 6 Installing the Assembly Figure 6 13a shows a current sourcing configuration Normally the drive disable circuit is on sourcing current into the drive thru terminal 10 When the drive disable circuit turns off the drive is disabled Figure 6 13b shows a current sinking configuration Normally the drive disable circuit is on sinking current from the drive thru terminal 9 When the drive disable circuit turns off the drive is disabled Figure 6 14 shows how to connect the drive disable circuit to the Bulletin 1388 servo drive which has an internal power supply and requires a current source to enable it Figure 6 14 Connection Details for Providing a Drive disable Signal to the Bulletin 1388 Servo Drive 8 2k 9 d Qi e 40 43 Right Wiring Arm of Bulletin 1388 1771 ES Expander Servo Drive 12024 Note that whatever configuration your drive requires you must connect
96. side of the input power supply To select 1 2k ohms set the switch on To select 11 2k ohms set the switch off Figure 6 3 Figure 6 3 Discrete input resistance Switch Assembly Jog Forward hardware start Jog Reverse Hardware feedrate enable Home Limit Stop Switch 1 2 3 4 on ON 0 ON 1 2KQ input N OFF pull up resistance H L F F ON OFF 11 2kQ input pull up resistance OFF OFF 12015 With 1 2k ohms your input device must sink 4mA for a 5V power supply to 25mA for a 30V power supply With 11 2k ohms your input device must sink 0 5mA for a 5V power supply to 2 7mA for a 30V power supply Unless your input device cannot sink enough current select 1 2k ohms because it provides better noise immunity than an 11 2k ohms input resistance 6 5 Chapter 6 Installing the Assembly Selecting Axis Number Select the axis number as shown in Figure 6 4 Figure 6 4 Axis number Switch Assembly Axis 1 Axis 3 is 2 Axi 1 2 3 ON ON 0 Set one switch to ON N OFF to select that axis number ji LL F ON Set the other F a two to OFF z OFF OFF 12016 Set to on the switch corresponding to the number for the axis Set to off the other two switches in the assembly Set each 1771 ES expander in an T O chassis to a unique axis number starting with 1 Selecting Encoder Input
97. stablish the address for the status block through the block transfer read instruction Because axis command and status data is stored in the data table axis motion control can interact with other axes discrete I O and report generation Parameter Block The parameter block for a 1 axis system has 25 words a 2 axis system has 44 words a 3 axis system has 63 words You specify parameters for each axis separately You specify parameters such as software travel limits home position servo gain global accel decel rate rapid traverse rate In the parameter block you also specify the address of the parameter block the command block and the first moveset block for each axis With these addresses the 1771 M3 controller can ask through the status block for the block it needs at any particular time The processor transfers the parameter block to the 1771 M3 controller through a block transfer write This provides axis parameter information after a power up and after a command block commands a reset or new parameters Moveset Block A moveset block describes a sequence of axis moves You can program axis motion to provide either single step moves or continuous moves Each move requires a minimum of three words a single move control word and two words to define position or dwell time and can include three optional words a rate word an accel word and a decel word for a total of six A moveset control word applies to
98. stem and to provide you with this diagnostic information to allow you to reduce following error by up to 99 9 without increasing instability runs an axis continuously at a selected velocity could apply to controlling a conveyor with no programmed end point Modifies a moveset while it is being executed provide your ladder diagram program with access to diagnostic information hardware and program troubleshooting Chapter 2 Introducing the Servo Positioning Assembl 1IThese features are only available on the series B servo positioning assembly Summary This chapter was intended to be very general Upcoming chapters cover these topics in greater detail To prepare for those details read about positioning concepts in chapter 3 2 7 Chapter Objectives Closed Loop Positioning Positioning Concepts This chapter presents positioning concepts and terminology If you are thoroughly familiar with the concepts of closed loop servo positioning you can skip ahead to chapter 4 Closed loop positioning is a precise means of moving an object from one position to another Typically an electric motor supplies the mechanical power and the needed motion is linear Therefore we must convert the rotary motion of the motor s shaft to linear motion Axis Motion One common method of converting rotary motion to linear motion is with a leadscrew Figure 3 1 Figure 3 1 Leadscrew Converting Rotory Motor Motion Into Line
99. stems Therefore as you read this manual you should be aware of the names we use for these components We refer to the Servo Controller Module cat no 1771 M3 as the 1771 M3 controller We refer to the Servo Expander Module cat no 1771 ES as the 1771 ES expander We refer to the device that receives the velocity command signal from the 1771 ES expander as the servo drive The servo drive converts ac power to dc power for the servo motor in proportion to the velocity command signal What we refer to here as the servo drive others may refer to as a servo controller So if you refer to this device as a servo controller be aware of our nomenclature as you read this manual PC refers to programmable controller For an extensive list of terms we use this publication refer to the glossary in appendix A Chapter 1 Troubleshooting Manual Organization This manual is organized into the following chapters Chapter Title What s Covered 2 Introducing the Servo an overview of the servo positioning Positioning Assembly assembly its applications functions and features 3 Positioning Concepts concepts of closed loop positioning including velocity loop positioning loop and feed forward 4 Positioning with the servo positioning assembly s position in Allen Bradley PC s a servo system and the servo positioning assembly s communication with the PC processor 5 Describing Hardware describing the servo positioning assembly
100. t Since excess following error turns on immediate stop the immediate stop bit in the status block is also on Additionally if the 1771 ES expander applies feedrate reduction to an axis for which excess error is greater than the 106 25 built in excess error value then the feedrate reduction bit bit 12 of the first status word for the axis is on If however the excess error point you enter is less than 106 25 then the feedrate reduction bit is not on Second Status Word The second status word Figure 7 5 identifies the active moveset and move as well as providing additional status bits CAUTION The function of bits 06 16 and 17 are different from the function of the corresponding bits for the series A servo positioning assembly If you replace a series A assembly with a series B assembly without changing your program accordingly you may cause unexpected results Word 4 Axis 1 Word 8 Axis 2 Word 12 Axis 3 Chapter 7 Formatting and Interpreting Data Blocks Figure 7 5 Second Status Word Second Status word 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 k T 7 Command Taken Diagnostic Valid e ee Position Valid Following Loss of Power Error Valid Programming Error Axis Fault Block ID 11054 Bit 0 5 Move Number These bits indicate the active move within the moveset in BCD format Bit 6 Loss of Power When se
101. t this bit indicates a loss of power across one of the following sets of terminals terminals 1 and 12 input supply of the left wiring arm terminals 1 and 6 analog supply of the right wiring arm If this bit is on then the immediate stop bit in the status block is on indicating that immediate stop has been executed after detection of the loss of power Bit 7 Programming Error If the 1771 M3 controller detects an illegal bit combination such as a non BCD value where one is expected or an illegal bit combination in the command block it turns on the programming error bit When this bit is on bits 10 thru 12 of this status word provide a code to identify the block containing the programming error 7 11 Chapter 7 Formatting and Interpreting Data Blocks When you detect that this bit is on you may want to turn on bit 11 of axis control word 2 in the command block to display diagnostic status in the 3rd and 4th status words for the axis Bits 12 11 10 Block ID These bits are the block ID of the moveset block currently being executed unless the diagnostic valid bit bit 6 is on When the programming error bit is on bits 10 thru 12 indicate the block in which the error was detected ID Bits 12 11 10 000 Parameter 001 Axis 1 Odd Moveset 010 Axis 2 Odd Moveset 011 Axis 3 Odd Moveset 100 Axis 1 Even Moveset 101 Axis 2 Even Moveset 110 Axis 3 Even Moveset 111 Command Bit 13 Axis Fault The 177
102. ter 6 we will show you how to connect the hardware done signal to a dc 12 24V Input Module cat no 1771 IB for axis synchronization of halt moves Discrete Inputs Terminals 8 9 10 and 11 on the left wiring arm provide connection points for discrete input signals The module accepts a discrete input signal as being high when it reaches 40 of the input power supply voltage The module accepts a discrete input signal as being low when it reaches 20 of the input power supply voltage 5 5 Chapter 5 Hardware Description 5 6 Each discrete input has an internal pull up resistor In chapter 6 we will show you how to select an internal pull up resistor of 1 2k or 11 2k You select each input individually through a switch setting For a high signal the input device you connect to a discrete input does not have to source current For a low signal the input device you connect to a discrete input has to sink current through the pull up resistor Hardware Start In the auto mode the module accepts a high to low transition at terminal 8 of the left wiring arm as a low true hardware start input signal After completing a halt move the 1771 ES expander will not execute the next move until it receives a start command The start command could come through block transfer of a control block or through the hardware start signal Feedrate Override Enable In the auto mode the module accepts a high to low transition at terminal 9
103. the command block data from the data table to the module Figure 7 1 7 1 Chapter 7 Formatting and Interpreting Data Blocks Figure 7 1 The Status Block Transfers to the Data Table the Parameter Moveset and Command Blocks go to the 1771 M3 Controller Data Table 1771 M3 Controller Status p Block Transfer Read Status Block Block Parameter Parameter Block Block Block Transfer Write Moveset gt Moveset Block Block Command Command Block j Block 12029 Status Block The status block is regularly transferred to the data table to provide updated information about the current status of each axis This status includes actual axis position in position at home position slide stop emergency stop software travel limit exceeded feed reduction excess following error auto manual mode address pointer to tell the program which block parameter moveset or control to write transfer to the 1771 M3 controller next diagnostic status that tells you where programming errors are in parameter moveset and command blocks 7 2 Chapter 7 Formatting and Interpreting Data Blocks The first block transfer after power up writes a 6 word status block into the data table After that the status block consists of 6 words for a 1 axis system 10 words for a 2 axis system or 14 words for a 3 axis system You e
104. tiguous data table area For a PLC 2 family processor assign data block addresses of 200 or greater to avoid processor work areas The status block which is the only block transferred from the 1771 M3 controller to the processor contains information about axis and servo positioning assembly status The first block transfer after power up writes a 6 word status block into the data table After that the status block consists of word assignments Figure 7 2 Size of Number of Axes Status Block 6 words 10 words 14 words Chapter 7 Formatting and Interpreting Data Blocks Figure 7 2 Status Block Showing Word Assignments Status Block Format Address Pointer Status Word 1 Axis 1 Status Word 2 Axis 1 MS Position FE Diagnostic Axis 1 LS Position FE Diagnostic Axis 1 Status Word 1 Axis 2 Status Word 2 Axis 2 The module sends diagnostic 7 information in this word when you MS Position FE Diagnostic Axis 2 request it thru the command block or E l when the module detects an error in LS Position FE Diagnostic Axis 2 the parameter block immediately after k power up Status Word 1 Axis 3 Status Word 2 Axis 3 MS Position FE Diagnostic Axis 3 LS Position FE Diagnostic Axis 3 iais We reserve the first word of the status block for future use It contains all zeros when returned by the 1771 M3 controller The second word is an address pointer that identifies the next block the processor is to transfer
105. tion In an incremental move the endpoint value specifies a position coordinate relative to the last programmed endpoint achieved by the axis Global or local values You enter a global final feedrate value and a global accel decel rate value These global rates apply to all moves except those for which you select to specify local rates A local rate applies only to a single move Halt or run After completing a move for which you have selected halt the 1771 ES expander will not execute the next move until it receives a begin or start command After completing a move for which you have selected run the 1771 ES expander will immediately execute the next move without waiting for a start command With halt selected the module executes a single step move With run selected you can select moves to be either single step moves or continuous moves Single step or continuous When the 1771 ES expander executes a single step move it decelerates the axis to zero velocity at the programmed endpoint When it executes a continuous move it attempts to blend the move smoothly with the final feedrate of the next move if the next move is in the same direction The moves in Figure 4 6 are all programmed as single step moves Figure 4 7 shows the same moveset with all moves programmed as continuous A moveset can contain a mix of single step and continuous moves 4 6 Chapter 4 Positioning with Allen Bradley PC Figure 4 7 Moveset Profile
106. tion of axis motion Also the phase relationship of these signals allow the decoding circuit to count either 1 2 or 4 feedback pulses for each line of the encoder Figure 3 7 This provides flexibility in establishing feedback resolution Figure 3 7 Encoder Signals Showing Phase Relationship Forward Reverse Channel A E L Channel A J L Channel B Channel B Marker Marker x1 J xi x2 LAA LLL x2 al OU UUU UUU ad UUU O UUU U Note For the servo positioning assembly the encoder marker must be high when both channel A and channel B are high or the marker is not recognized unless you set the marker logic jumper to the not gated position 11001 Feedback Resolution The following discussion of feedback resolution assumes that you are using a leadscrew and that the encoder is coupled directly to the leadscrew with no intermediate gearing These assumptions apply to many applications If your application differs be sure to account for the differences Feedback resolution is the smallest axis movement the servo positioning system can detect Itis determined by leadscrew pitch axis displacement per revolution encoder lines number of lines per revolution feedback multiplier selected as x 1 x2
107. ual mode This parameter has a 4 digit BCD value in the range of 0 0001 to 0 7999 inches or 0 001 to 7 999 mm Offset Word 24 43 62 specifies the value the servo positioning assembly adds to the offset accumulator when the servo positioning assembly executes one of the following Chapter 7 Formatting and Interpreting Data Blocks a position with offset move in a moveset a an offset command from the command block This parameter has a 4 digit BCD value that can be in the range 0 0001 to 0 7999 inches or 0 001 to 7 999 mm Figure 7 27 Figure 7 27 Offset Word Word 24 Axis 1 Word 43 Axis 2 Word 62 Axis 3 Offset 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 e e inch metric decimal decimal Sion point poini Offset value inches or 0 9 i millimeters BCD format 1 11049 Tachometer Conversion Factor The servo positioning assembly uses bits 00 thru 03 of word 25 44 63 for its loss of feedback detection feature Figure 7 28 The tachometer calibration procedure explains how to select the value for this word Chapter 7 Formatting and Interpreting Data Blocks Figure 7 28 Following Error Reduction Tachometer Conversion Factor Word FE Reduction Tach Conversion Factor 17 16 15 14 13 12 11 10 07 06 05 04 03 02 01 00 Word 25 Axis 1 e Word 44 Axis 2 A Word 63 Axis 3
108. ugh the command block 7 7 Chapter 7 Formatting and Interpreting Data Blocks 7 8 The processor must not transfer the command or moveset blocks to the servo controller until the ready bit is on Bit 3 Hardware Jog Hardware Start The 1771 M3 controller turns on this bit when the 1771 ES expander recognizes a jog plus or hardware start input signal Bit 4 Slide Stop The 1771 M3 controller turns on this bit when it receives a slide stop request from the command block word 1 bit 5 The slide stop status bit stays on even after the slide stop command is no longer present in the command block This bit turns off when you command axis motion or reset A reset command while the axis is in motion will also turn on this bit and cause a slide stop When the axis stops this bit turns off Bit 5 Hardware Jog Feedrate Override Enable The 1771 M3 controller turns on this bit when the 1771 ES expander recognizes a jog minus or feedrate override enable input signal Bit 6 Home The 1771 M3 controller turns on this bit when the axis feed is done after any command to move to the home position if you have established a home position You establish a home position through an initialize home or search home command This bit turns off when the axis moves away from the home position Bit 7 Auto Manual This bit indicates the current mode of the axis based on the status of the auto manual bit word 1 bit 7 in the command bloc
109. ut Resistance p Switch Assembly co E Cr Axis Number Switch Assembly High True Low True CH A Polarity Jumper e CH B Polarity Jumper Marker Polarity Jumper _e CH A Signal Mode Jumper e CH B Signal Mode Jumper e Marker Signal Mode Jumper e m Single Ended Differential k Not Gated Marker e Logic Jumper Gated with CH A and CHB 12013 6 3 Chapter 6 Installing the Assembly This publication shows and describes switches as being on or off Printed on the actual switch assemblies are the words ON and OFF or the word OPEN OPEN corresponds to OFF Use a blunt pointed instrument such as a ball point pen to set these switches Never use a pencil graphite could jam the switch Figure 6 2 shows details of a jumper connecting two pins Each jumper connects two of a set of three pins To change a jumper setting follow these steps 1 Pull the jumper straight up 2 Position the jumper over the pins you want to connect 3 Push the jumper straight down If you position the jumper correctly it slides down over the pins easily Figure 6 2 Jumper in the Left Position 12014 6 4 Chapter 6 Installing the Assembly Selecting Discrete Input Resistance Select the resistance between each discrete input terminal and the high
110. vV EA BCD following error reduction value 0 99 9 a 0 0 1 0 125 0 0 Total value is the sum of the ie selected values 0 0 1 0 500 Used if full scale analog output A voltage is greater than tachometer voltage for a given rpm Refer to the tachometer calibration procedure in chapter 9 11050 Each of bits 0 thru 3 corresponds to a factor The total factor used by loss of feedback detection equals the sum of the individual factors selected If you are not using the loss of feedback detection feature or if tachometer voltage is greater than or equal to 10V program zero for all bits of this word Following Error Reduction The servo positioning assembly accepts the BCD value you enter into bits 04 thru 17 as the following error reduction value Figure 7 28 You can command a reduction of the following error by 0 through 99 9 The 1771 ES expander reduces the following error through feed forwarding without increasing the positioning loop gain Consider an example in which you have entered an initial gain value of 1 00 With an axis speed of 10 ipm without following error reduction the following error would be 10 mils 7 39 Chapter 7 Formatting and Interpreting Data Blocks Moveset Block 7 40 FE speed 10ipm 10 mils gain 1 ipm mil However if you enter a following error reduction value of 70 0 the following error at 10 imp is reduced from 10 mils to 3 mils A moveset block contains a number o
111. with all Continuous Moves m Move 1 i_ Move2 Move3 Rate Position 0 1 2 3 4 5 6 7 8 Rate Moe 4 11012 11012 Move Alternatives In place of a move to position in any move block you can select one of the following Dwell Instead of an endpoint and rates you can program a time in seconds in the move block When the 1771 ES expander executes a dwell move block it stops axis motion for the programmed amount of time Preset to Position You can program an axis position preset value in the command block When the 1771 ES expander executes a preset to position it sets its axis position register to the programmed preset value No axis motion occurs Move to Position with Offset The parameter block contains an offset value When the 1771 ES expander executes a move to position with offset it adds this offset value to an offset accumulator For every move it adds the value stored in the accumulator to the programmed endpoint then executes the move Constant Velocity This command clears the position register to zero before moving the axis to the position you specify By repeatedly generating continuous constant velocity moves you can cause uninterrupted motion which could for example be applied to a conveyor Figure 4 8 Chapter 4 Positioning with Allen Bradley PC Figure 4 8 Moveset Profile for Constant Velocity Moves Rate gt Positio
112. y one thread and pitch is a more common term than lead in this publication we use the term pitch to refer to the distance the axis travels for each revolution of the leadscrew Do not confuse leadscrew pitch with its inverse which is the number of pitch threads per inch In the example of Figure 3 5 the leadscrew has 4 pitch threads per inch A leadscrew with a pitch of 1 4 inch is often described as being a 4 pitch per inch leadscrew 3 6 Chapter 3 Positioning Concepts Encoder Feedback An incremental digital encoder provides feedback that indicates the magnitude and direction of any change of axis position As shown in Figure 3 6 the encoder shaft is attached to a transparent disc marked with uniformly spaced lines Strategically located photodiodes detect light As the disc rotates the lines break up the light reaching the photodiodes As a result the output channel A channel B and marker from each photodiode is a series of electrical pulses Figure 3 6 Incremental Encoder Showing How Signals Are Generated Photodetectors Light Source De 4 Channel A A Channel B Marker K Marker A B Marker 11000 3 7 Chapter 3 Positioning Concepts Channel Phase Relationship The photodetectors are placed so that the channel A and channel B output signals are out of phase by 90 Figure 3 7 The lead lag relationship of these signals indicates the direc

1771-6.5.25, Servo positioning Assembly User Manual

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