QCI-TD054 Servo Tuning - QuickSilver Controls, Inc.
Contents
1. Kuff xT arget _ Velocity _ only _upper _ word _ used Ev2x512 gt Lyry Position kali zh Kez ae d 1 KP 1 AF Kax512 ht x Positi Ka if yy ee AF7 osition Kaff xT arget _ Acceleration _ only _upper _ word _ used Kp x 7 arg t _ Position Position Where _ Ayl 32768 _ F2 32768 e Fa 32768 T _the_sample _ period 1202 seconds QuickSilver Controls Inc Page 6 of 29 OUL slo uoO JAAIISYOIND JO SHCWAPEN BE w JUNHBUY PUL wy SiOJjuoO J AIIS39InO wiWIAd wISNCOAITS wul8BBnNud AIIS yi OPONIS 9ul S OMUOD JOAIISYOIND JO syseWAEpes PasajsiHay 91e IOO pue OUOOyIINH o 9010U noy m BHueyo o 15 qns si JUsLUNDOP SIU wespeq 4901G wVIAd JEAIISHIINO pu 7 weeg yoo g yoojg apu 04 13d o sn QZ 490ld L SlvZ gt X gt Slv 4 keja y4 sig 94 334w yoolg ule yoolg uoneuuuns Glv2 ly K L ueg 40 e163 U 10 e169 U p lluur1 xew gt X gt XewL Joy yndyno nbio L un ik w19 apow 42013A L GLvZ gt X gt GLvz lt d K A s4q 94 19417 s apow uonisod TA jeuonodold ueg puemuoypse4 AOA aj0A9 s 4 e y q Jepooug w19 spon ISoI A a Ne su spon uolysod Suu1 eJB lul uoN Jo win xew gt X gt XBW L sq 9L sew OUI S O NUOD L GlvZ gt X gt GlvZ a 0K9 si yen lt ey q 1eBJe L S j ueg pi2. the servo calculates the motion profile defined by a command and its parameters During each servo cycle the target position is updated in the servo control loop The trajectory generator also calculates a target velocity The target velocity value is used to compensate for lag in position that is induced by the Velocity Feedback terms Kv1 and Kv2 QuickSilver Controls Inc Page 17 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Velocity Feedforward is a positive value used to anticipate the velocity necessary for a given move Setting the gain value to zero eliminates the Velocity Feedforward term Usually this gain value is set equal to the sum of the Velocity 1 Feedback Kv1 and Velocity 2 Feedback Kv2 gain values Kvff 3 produces the following chart 5200 00 4875 00 4550 00 Target 4225 00 Position 3900 00 3575 00 3250 00 2925 00 2600 00 2275 00 1950 00 vem ja e l Positions T E a o75 0 fT 650 00 tie 20 00 40 00 60 00 80 00 100 00 120 00 140 00 160 00 180 00 200 00 Time s Kp 10 Kv2 3 Kvff 3 The actual velocity follows the desired velocity very well To further reduce position error Kp can be increased With a dampener in place Kv2 increasing Kp should not cause the system oscillation In the next plot the value of Kp is increased For applications that require zero overshoot and faster response Kvff may be slightly reduced to force
3. 00 160 00 180 00 200 00 Timetims Kp 1 A large amount of error is required to make the motor move Setting Kp 2 doubles the torque and produces the following profile Target 200 00 Position 4675 00 4550 00 4225 00 3900 00 3575 00 3250 00 2925 00 2600 00 2275 00 1350 00 1625 00 1300 00 975 00 650 00 325 00 0 00 T 000 20 00 4000 60 00 80 00 100 00 120 00 140 00 160 00 180 00 200 00 Time ins Kp 2 Although less error is required to generate sufficient torque the servo overshoots once the servo gets moving The servo does not come back until enough negative torque is generated Increasing Kp will continue to have this effect QuickSilver Controls Inc Page 15 of 29 Technical Document QCI TD054 QuickSilver Controls Inc 5200 00 4875 00 Target 4550 00 Position 4225 00 3900 00 3575 00 3250 00 2925 00 2600 00 2275 00 1950 00 Actual 1625 00 Position 1300 00 975 00 650 00 325 00 0 00 0 00 20 00 40 00 6000 80 00 100 00 120 00 140 00 160 00 150 00 200 00 Timerms Kp 10 Using the spring analogy again by increasing Kp the spring stiffness is increased Typically Kp is increased to achieve the desired stiffness and reduce position error Although the servo is moving to the target in a timely manner there is not
4. QuickSilver Controls Inc Torque Saturation Torque saturation is another common issue encountered while tuning Common signs of saturation are the servo being unable to complete a motion in the required time or accruing excessive amounts of error Saturation can occur because of two limits Either the required torque exceeds the software based torque limits or the servo cannot output sufficient torque due to physical constraints such as the actual maximum torque output In the case of a software torque limit the TQL command can be edited to increase the limits If the servo is limited by physical constraints then the torque cannot be increased other than by selecting another motor If the total available power torque at speed is not sufficient it may be increased by increasing the power supply voltage up to 48v if a lower supply voltage is being used No amount of tuning or varying of parameters can change the physical amount of torque the servo can output An example of torque saturating taken with the Strip Chart tool is shown below The torque saturation is a result of the closed loop moving torque limit set to 25 2nd Y axis right hand axis Notice how the position error 1st Y Axis left had axis deviates significantly from the near zero values when the torque saturates at the 25 mark As this example shows torque saturation greatly hinders the precision control Thus torque safety margin should always be included when selecting a mot
5. Tuning the servo a certain way for one system may not work for another system In order to help facilitate the tuning of different systems several application specific recommendations are provided These suggestions are meant to be a starting point None of these recommendations are an end all solution because all systems are truly unique Inertial Ratios Up To 5 1 For a load inertia to motor inertia ratio of 1 1 to 5 1 the default tuning parameters should be sufficient These have been optimized for each device for this nominal load range assuming a relatively tight coupling servo class coupler or a stiff belt Aramid type Higher Inertia Ratios The servo can be tuned to handle huge inertial loads with mismatches of 1000 1 or even 3000 1 category The limiting factor is not the control loop but the electric motor s maximum torque At some point the electric motor will just not have enough torque to move the mass in the desired time frame For high inertia loads the load inertia will dominate the response Therefore the velocity estimator should have a lower bandwidth low Fv2 because fast variations seen at the servo are not good estimates of the actual load response Reducing Fv2 reduces the high frequency gain of the system This suppresses the high frequency resonance modes allowing Kv2 to be increased to improve the low frequency damping of the system QuickSilver Controls Inc Page 24 of 29 Technical Document QCI TD054
6. a following error This forces the servo to approach the commanded position from the starting side without overshooting QuickSilver Controls Inc Page 18 of 29 Technical Document QCI TD054 QuickSilver Controls Inc The system responds very well with Kp 40 5200 00 Target Position Actual Position 1625 00 1300 00 975 00 650 00 325 00 0 00 0 00 2000 4000 60 00 80 00 100 00 120 00 140 00 160 00 180 00 200 00 Time ms Kp 40 Kv2 3 Kvff 3 Acceleration Feedback Ka The acceleration feedback value is derived from the Velocity 1 post filter value And the Acceleration filter term The Acceleration Feedback term functions as an electronic damper improving the overall system smoothness and decreasing the system settling time Ka amplifies high rates of change of the velocity feedback This counteracts any rapid changes in shaft velocity Ka can be thought of as a virtual viscous inertial damper flywheel with a viscous coupling to to the shaft The larger the value of Ka the larger the virtual flywheel becomes The higher the frequency settings for Fv1 and Fa the stiffer the virtual coupling to shaft A larger flywheel increases the virtual inertia of the system and resists rapid acceleration Thus Ka smoothes out the velocity ripple Excessive Ka can introduce noise into the system as the individual encoder counts are emphasized Excessive Ka combined with high Fv1 and Fa act as a lar
7. drive signal to operate the motor However when the velocity feedback term is included the loop is not just looking at the error but also the measured velocity times the velocity feedback term and the system gain The velocity term if compared to driving a car acts to apply the brakes earlier and earlier for higher and higher velocities to prevent going past the intended stopping point where as the proportional term would not even get off the gas pedal until it had already passed the destination ignoring it is still moving way too fast However with the two operating together in the absence of feedforward the braking of the velocity feedback term must be offset by a larger following error to produce more requested torque from the proportional term such that their sum produces sufficient output to drive the motor As the error reduces the proportional drive decreases As the velocity slows the braking action of the velocity feedback term decreases If properly balanced the result is a smooth stop at the desired target However in the process of the motion a following error was introduced proportional to velocity Adding an offsetting feedforward velocity term corrects the forced but predictable error that was caused by the velocity feedback it does this without affecting the system stability The result is a stable system with smaller error throughout its motion The acceleration feedback is calculated so as to approximate a viscou
8. factor s magnitude corresponds to a faster maximum rate of current torque change and slower for a lower K factor By default K factor is set to 0 1 or 0 2 depending on the motor type The K factor can be set as high as 1 0 or as low as 0 02 To access the K factor open the Initialization Wizard tool in QuickControl select Motor Motor And Phase Advance Constants then press the Advanced button Another window titled Edit K Factor appears Clicking the arrow expands the table i i of available K factors ranging from 0 02 to 1 AlowerK asas ai factor may help in stabilizing high inertia loads or 3 systems with backlash The lower rate of torque change Cance helps minimize the rate of change of torque which EA l translates into rate of change of acceleration also known NOTE The following are only valid if the attached device as jerk allowed in the control loop Internally K is has been initialized using the Initialization Wizard increased as motor speed increases to allow the motor Gaei 60 u torque to be achieved at higher speeds fo Mod A Auto default Uses voltage read at time of xl ies actor Select a Te Select K Factor OK Manual aqe bai Advanced Cancel Edit Native C Nati j Edi 0 02 z Description Ei Pee EEN QuickSilver Controls Inc Page 23 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Tuning Notes Proper tuning depends on the specific properties of the system
9. 2 and Kvff are adjusted until there is some noise during the move but not at rest QuickSilver Controls Inc Page 27 of 29 Technical Document QCI TD054 QuickSilver Controls Inc 6 Reduce Fv1 and Fv2 Reduce Fv1 by 3 times the default setting and set Fv2 to three times Fv1 The factor of 3 reduction corresponds approximately to the square root of 10 where 10 was the shift in resonant frequency We only shift by 3 approximately the square root of 10 to keep the filter point roughly centered at the geometric mean of the anti resonant and the resonant frequencies Example Default Fv1 209Hz Fv2 209Hz Change to Fv1 70Hz Fv2 210Hz This helps reduce the high frequency noise in the system Test the move Most noise should have quieted and the overshoot minimized Keep decreasing the velocity filters until almost all the noise goes away Remember to keep Fv2 three times greater than Fv1 Typically Fv2 should be well above the total time of the system s shortest move For example if a 100ms move is as fast as the servo will go 100ms 10 rad sec 10 2n Hz 1 6Hz then Fv2 should be set to about 50Hz Note that there is a tradeoff between bandwidth response time and noise a wider bandwidth corresponds to faster settling response give adequate servo torque but a wider bandwidth also allows more encoder noise hearing each encoder increment pass through 7 Adjust Ka and Fa Typically adjust Fa down by the same fact
10. 3 times lower As the two filters Fv1 and Fv1 are cascaded their roles are sometimes reversed i e Fv1 is made higher rather than lower This is done to allow more flexibility in setting ratios between Fv1 and Fa See below Acceleration Filter Fa Like the Velocity Feedback terms the Acceleration Feedback term also has a low pass filter that reduces undesired high frequency noise as well as affects the tuning of the system Fa is typically set to about 5 times Fv1 if Fv1 lt Fv2 or 5 times lower if Fv2 lt Fv1 A physical viscous inertial damper has an optimal range of frequencies over which it aids damping so does our simulated damper This range is centered on the geometrical mean of Fv1 and Fa The a larger ratio of Fv1 to Fa taking the larger of the two over the smaller produces a greater damping value phase boost up to a ratio of approximately 5 1 however the wider the ratio the more acoustical noise is heard This is due to less filtering allowing more of the noise associated with individual encoder edges to pass through to the drivers QuickSilver Controls Inc Page 22 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Acceleration 1 Filter Fa1 SD08 Acceleration 2 Filter Fa2 SD08 Fa1 is the same as Fa Faz2 is the filter feedback term associated with the second filtered acceleration term second synthetic inertial damper term Fa filters the acceleration used by Ka2 Voltage Dependant Paramet
11. CTC FLC commands directly Press Test to send to the commands to the selected servo Control Panel Tools gt Control Panel Use Control Panel to execute the same moves as used in your application Use the panel s Strip Chart to chart such things as Position Error and Torque while you are using the Initialization Wizard see above to change the tuning parameters See the SilverLode User Manual for more details on using Control Panel Note the servo can be commanded to a constant velocity by releasing the Jog slider with the shift key pressed QuickSilver Controls Inc Initialization Wizard xj Advanced If neither Basic nor Intermediate tuning Exit w Save produced the desired results edit the tuning parameters directly Initialization Wizard Tuning Wizard I Default Tuning Parameters Basic Intermediate Advanced CTC cmd Kp po K 5 Ky1 Ka fio Kv2 20 Kvff 20 Karl FLC cmd Fvi 6 Hz Fa 180 Hz Fyv2fi2 Hz Control Panel Device ID 16 UID 16 Type A23H1 Rev 45 11 Serial 1716 r Device Status Position p counts Velocity o cps Pos Ero 7 counts counts Torquel30 Dive eae Temp 38 1 c Target Pojo counts r Tuning Cycles ms I O forever delay r Move Type C MAT C MRT C Cycle G May C MRY TestMove 1 Acceleration feon cps s Velocity pm cps Test Move 2 Position counts Acceleration 17000 cps s Velocity js cps Cycle Positi
12. Position error feedback enters the servo loop and Kp scales the error The product of the error and Kp produces a torque that minimizes error This concept is the basis of most servomechanisms Thus the larger the error grows the more torque the motor produces Torque Kpx Target Position Actual Position or Torque Kp Position _ Error The best analogy to Kp is a simple spring If the servo were to be replaced by a spring Kp would be the spring s stiffness If the shaft were rotated the spring would be winding or unwinding The more the shaft was rotated the more the spring would fight back The next Strip Chart plot from the QuickControl Control Panel demonstrates the effects of Kp The filter constants are set at their default values and the control constants are set as follows Kp Kv1 Kv2 Kvff Ka Kaff Ki Hl H H H lH HH II SO OcCOOEOPOEDPO QuickSilver Controls Inc Page 14 of 29 Technical Document QCI TD054 QuickSilver Controls Inc The Strip Chart plots a 4000 count 100 millisecond ms move with a 25 ms ramp time MAT command The channels plotted are Position and Target Position The Target Position is where the shaft is supposed to be and the Position is where the shaft actually is Target 5200 00 Position 4875 00 4550 00 4225 00 3900 00 3575 00 3250 00 2925 00 2600 00 2275 00 1950 00 1625 00 1300 00 975 00 x 650 00 Position 325 00 0 00 sg 0 00 20 00 40 00 680 00 80 00 100 00 120 00 140
13. Technical Document QCI TD054 Quicksilver Controls Inc Date 3 April 2009 www QuickSilverControls com Servo Tuning The factory default servo loop parameters have been optimized for a nominal load range inertial mismatch up to 10 1 for each servo motor Given a fairly tight coupling the default tuning parameters meets the performance requirements of most systems Generally 19 out of 20 applications can use the factory default tuning parameters Some applications require servo loop tuning to match the target system One of the biggest challenges for a servo system is maintaining stable control in spite of a large mismatch between the motor s rotor inertia and the load inertia of the system The QuickSilver PVIA servo control algorithm can be tuned to provide stable operation over a very broad range In addition it can be tuned for precise control with mismatch ratios greater than 100 1 This Technical Document contains information necessary to properly tune QuickSilver control systems It covers the PVIA servo control loop commands associated with tuning control loop parameters and the effects of each parameter on motion The document concludes with a section that provides tuning recommendations for specific applications Initialization Wizard a x QuickControl Tools Press Download to initialize servo or change the Primarily two QuickControl tools are used for servo Sedan e e i a ulus pile eee the Initialization Wiz
14. ard Kaff 0 200 0 200 Integrator Gain Ki 0 2000 0 2000 Damping Factor Kd OO SAIT ee ping Default 21300 Default 65 2 Fsi 32768 Ksi Stiffness Per Inertia Factor Ksi 123 28672 Fsi 5 2758 Hz QuickSilver Controls Inc Page 12 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Anticipated Acceleration Kaa 0 32767 0 100 Factor Default 25 of Ksi Default 25 of Ksi Velocity 2 Feedback Filter Fv2 4096 32767 70Hz 400Hz aoe 1 Feedback Fat 4096 to 32767 OHz 2758Hz a 2 Feedback 4096 to 32767 OHz 2758Hz These parameters are used in the calculations of the PVIA algorithm that controls the position of the servo when in motion or stopped Each parameter has its own individual influence on the servo operation but most of the parameters work in conjunction with one another For example velocity and acceleration feedback filters have a frequency setting for rolling off high frequencies that may cause system instabilities and noise Velocity and acceleration feedback serve to stabilize a control system but they tend to force error into the system during non zero velocity and non zero acceleration stages of the move respectively To understand this we will consider a constant velocity motion using only a proportional term and a velocity feedback term Assuming a fairly large system gain requiring only a small torque a small position error when amplified would produce sufficient
15. ard and the Inliefeaion Wize Turing Wea ontro anel Device UID 16 Options Download File Initialization DEVICE DETECTED Unit ID 16 Motor Cable SilverDust D2 IGB sn 1716 Length m Grade Motor Detected A23H1 CPR 8000 j ft Tools gt Initialization Wizard 7 actory Default Initialization gep A aie ae Initialize P ter B As described in the User Manual the Initialization on Wizard is used to initialize the controller for such Save W Motor things as communications error limits and servo saveas lasa tuning The servo tuning part of the wizard is Control Constants documented here while the rest of the wizard is documented in the User Manual Cancel a Kp 50 m e Description ee Description The file Factory Default Initialization qcp contains two n E e servo tuning commands J aiem gt Control Constants CTC ra di He K pm te L J Default For q Device Filter Constants FLC CTC and FLC by default have Default For Device checked which means use the factory default servo tuning settings You could edit the servo tuning parameters manually by un checking this box but we will show you how to use the Tuning Wizard instead Property of QuickSilver Controls Inc Page 1 of 29 This document is subject to change without notice QuickControl and QCI are Registered Trademarks of QuickSilver Controls Inc SilverLode SilverNugget Si
16. ation filters Velocity 1 Feedback Filter Fv1 Velocity 2 Feedback Filter Fv2 Acceleration Feedback Filter Fa CT2 FL2 SilverDust Rev 08 SD08 SD08 includes alternative servo tuning commands e Control Constants 2 CT2 e Filter Constants 2 FL2 Filter Constants 2 FL2 changes the servo loops actual velocity and actual acceleration calculations from an estimator model to a more efficient observer model and enables the addition of a second acceleration feedback term In simple terms the estimator model calculates actual acceleration and velocity by differentiating the position while the observer model calculates acceleration and velocity using commanded torque and integration In both models the actual velocity and acceleration are only approximations of the real velocity and acceleration FL2 overrides any previous Filter Constants FLC command and enables the use of CT2 s Acceleration 2 Feedback Gain Ka2 parameter CT2 overrides any previous Control Constants CTC command Property of QuickSilver Controls Inc Page 8 of 29 This document is subject to change without notice QuickControl and QCI are Registered Trademarks of QuickSilver Controls Inc SilverLode SilverNugget SilverDust PVIA QuickSilver Controls and AntiHunt are trademarks of QuickSilver Controls Inc Technical Document QCI TD054 QuickSilver Controls Inc The Tuning Wizard automatically detects which set of comma
17. d and therefore is disabled and the integrator acts on the difference in velocities between the target velocity and the actual velocity These changes allow the servo to smoothly recover from a motion stoppage without overrunning the target velocity Single Loop Control SLC The SLC command configures the servo to run in a single feedback control loop All information for commutation position velocity and acceleration control is derived from the internal encoder If a motion is running the Trajectory Generator must be shut down before executing this command When entering single loop control the servo sets the current target position to the actual position The servo uses single loop control by default The Dual Control Loop command is used for cases where external encoder position control is required Switching between Single Loop and Dual Loop control usually requires changing the control loop tuning QuickSilver Controls Inc Page 10 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Dual Loop Control DLC The DLC command configures the servo to run in a dual feedback control loop With a dual feedback control loop the servo uses an external Secondary encoder signal for position info SilverLode motor commutation velocity and acceleration feedback information are still derived from the internal primary encoder however moving and holding error limit flags are also based on the external encoder for triggering the Kill M
18. e position error becomes zero In the next plot the integrator gain term is set to a small value Ki 5 QuickSilver Controls Inc Page 20 of 29 Technical Document QCI TD054 Quicksilver Controls Inc Target Position 375 00 750 00 1125 00 1500 00 1875 00 2250 00 2625 00 3000 00 Time ms Kp 7 Ki 5 The integrator gain greatly reduced the steady state error The product of Ki and Kp generally sets the steady state accuracy of a system In other words if Kp is doubled halving the Ki value achieves approximately the same amount of steady state error A good starting point for determining the ideal Ki for a system is to take a look at the default Kp and Ki values For example if a custom tuned system has Kp 200 and the default tuning parameters had Kp 100 and Ki 1000 a good starting value for Ki would be 500 Damping Factor Kd SD08 Kd is a damping factor feeding back from the observer raw velocity into the observer raw acceleration used to damp the 2 order observer system Setting this value to 100 full scale native units of 32767 will approximate the response of the standard velocity filter system overdamped Reducing the value to approximately 65 of full scale makes the velocity estimate closer to critically damped allowing the control loop to see the velocity sooner which has the effect of increasing the phase margin of the system Stiffness Per Inertia Factor K
19. easing the Fa filter to a frequency above the belt resonance typically 1500 to 2000HZ Operation from an External Encoder Tuning a the servo that is operating from external secondary encoder requires adjustments to the proportional gain Kp It must be properly adjusted in relation to the resolution of the external encoder If the external encoder resolution is double 2X the resolution of the internal encoder then the default Kp value should be decreased by one half 0 5X If the external encoder is one third 0 33X the resolution of the internal encoder then the default Kp value should be increased by a factor of three 3X QuickSilver Controls Inc Page 26 of 29 Technical Document QCI TD054 Quicksilver Controls Inc Tuning a 100 1 Inertial Mismatch Advanced The following procedure describes how to tune a servo for high inertial mismatch by modifying the individual tuning parameters of the CTC and FLC commands Tuning Wizard Advanced tab High resolution fast following applications require maximum bandwidth and gain but no minimal oscillations When tuning the servo it is important to keep the Velocity Feedforward Kvff term equal to the sum of the two velocity feedback terms Kv1 amp Kv2 The Acceleration Feedforward Kaff and feedback terms Ka should also be equal 1 Determine Motion Profile To Be Tuned Before beginning to tune the servo determine the motion profile for the system Absolute moves may be u
20. ers SilverLode servos have several control loop parameters in the Motor Constants MCT command that depend solely on voltage level of the external power supply Thus these parameters must be configured for the correct operating voltage of the servo Incorrect initialization or power supply voltage level deviation can cause unstable operation QuickControl takes care of most of the work During initialization QuickControl polls the servo for the current voltage level QuickControl then sets the voltage dependant parameters based on the voltage sensed by the servo If the servo will be operated at a different voltage than the current supply voltage the Motor Constants voltage setting should be manually set to the expected operating voltage This forces QuickControl to use the manually set voltage when configuring the Motor Constants rather than the detected voltage K Factor The SilverLode servo varies torque by changing the estimated current fed to the windings The rate at which the servo changes the requested current is controlled by the K factor This factor can be denoted by the term di dt or rate of current change per unit change of time K is the fraction of the requested change permitted in each 120uS sample period when the motor is operating at low speeds As the motor speed increases an internal calculation gradually adjusts the permitted change from K up to 100 so as to allow the motor to produce torque at higher speeds Increasing K
21. ewuojpa93 uone19 9099V q 94 1947 A ueg yoeqp 4 Z IOOl8A S ueg n yoeqp 4 L ISOI SA ueg N yoeqp 4 uone19 999V I A IS3O InO 6z Jo bed OU S OLJUOD JOAIISHOIIND JO Alu9doiq L GlLvz Aq pajusseide ose yoro JO sanjea wnwixew y 42y Yons payeos oue Ayooja 2e pue uone1 955v Jape 1013 uont soq uonisoq 981e 1 JO E1 9U9S APOojeA Jobe L JoyefesL uone1ajao0y BIe L J1 l4 SSed M07 yoeqp 4 90 A puo5 s p 1J ll d Balm I9O J A Slvd Ad AA 5 n4 000h eys poseyi4 3 Koel Ni Le JoyOU WO SuO II9OJ SA Se aad LAAN ij uonisod Slve LAd AM J Iqd SSEqg MO7 yoeqpss lool A SJl4 uoleseje007 lt K paseyy uone1 l o5v SlvZ e3 AV JOY I4 SSEd M07 yoeqpes_ uoljelejso0y pSOGL IOO JUaWIND0G IeS9 uuo Technical Document QCI TD054 QuickSilver Controls Inc Tuning Commands Primary Commands The following two commands set the primary tuning parameters See the Command Reference for the specific details of each command Control Constants CTC This command specifies values for the servo loop gain constants Proportional Kp Velocity 1 Feedback Kv1 Velocity 2 Feedback Kv2 Velocity Feedforward Kvff Acceleration Feedback Ka Acceleration Feedforward Kaff Integrator Ki Filter Constants FLC This command selects the cutoff frequency for the velocity and acceler
22. ge inertia with tight coupling and may cause high frequency instability exhibited by a high pitch squeal The relative values of Fv1 and Fa are also important See Velocity Filters below Ka is most useful when tuning out vibrations or resonance modes induced by system components e g a belt drive See the section on tuning belt drives at the end of this document for an example Acceleration 1 Feedback Ka1 SD08 Acceleration 2 Feedback Ka2 SD08 Ka1 is the same as Ka Ka2 is a second acceleration feedback term second virtual viscous inertial damper The acceleration for Ka2 is filtered by Fa2 Acceleration Feedforward Kaff The Acceleration Feedforward value is derived from the Velocity Feedforward value It functions similarly to the Velocity Feedforward term by compensating for the position lag QuickSilver Controls Inc Page 19 of 29 Technical Document QCI TD054 Quicksilver Controls Inc induced by Acceleration Feedback term Ka Normally Kaff is set equal to Ka although it may be set slightly higher than Ka to assist with the acceleration of high inertial loads Integrator Gain Ki The integrator parameter is the most important term for controlling steady state position error The integrator works over time to eliminate position error The longer there is position error the larger the effect of Ki to get rid of the error This term is commonly referred to as the l term in the traditional PID control loop Un
23. he more damping the shock absorber provides With Kp only the servo would oscillate to a stop during every move Even the smallest amount of Kv2 adds noticeable damping to the system The following plot has the same settings as the previous chart except Kv2 1 QuickSilver Controls Inc Page 16 of 29 Technical Document QCI TD054 Quicksilver Controls Inc 5200 00 4875 00 4550 00 4225 00 3900 00 3575 00 3250 00 2925 00 2600 00 2275 00 1950 00 1625 00 1300 00 Position 975 00 650 00 325 00 0 00 stir a 0 00 2000 40 00 6000 380 00 10000 120 00 140 00 160 00 180 00 200 00 Timefme Kp 10 Kv2 1 The Kv2 parameter has a significant damping effect on the system Setting Kv2 to 3 will provide even more damping Target Position 40 00 60 00 80 00 100 00 120 00 140 00 160 00 180 00 200 00 Time ms Kp 10 Kv2 3 Although the system has more damping it is unable to match the velocity of the calculated trajectory Velocity feedback subtracts some component of the velocity Kv2 x velocity from the calculated torque As Kv2 increases the velocity feedback will cause a greater velocity error in the system To compensate for this a Velocity Feedforward Kvff term is added to the system Velocity Feedforward Kvff The servo contains an internal target generator called the trajectory generator In real Time
24. iceable overshoot Thus if Kp is large the servo will start vibrating as it overcompensates for small errors This is the same principle as a car with no shock absorbers The springs work fine but every time the car hits a bump the car bounces several times To eliminate the bounce shock absorbers are added to the car In the PVIA algorithm the Velocity Feedback parameters Kv1 and Kv2 act as shock absorbers Velocity Feedback Kv1 amp Kv2 Velocity values are derived from the position information read every servo cycle 120 microseconds Velocity is calculated from the change in position each servo cycle Velocity data is filtered by two cascaded low pass filters providing a once filtered value Velocity 1 and a twice filtered value Velocity 2 Both velocity values have a gain setting that is used to adjust the amount of velocity feedback Velocity feedback is negative feedback used to dampen the servo control loop Setting the velocity feedback gain values to zero removes all velocity feedback from the control loop Kv1 is typically set to 0 Most applications have no need for a Kv1 greater than zero Kv1 is only necessary for high frequency response applications i e 10ms move In these situations the extra filtering done to calculate Velocity 2 does not accurately represent the load s velocity Kv2 is typically the only velocity feedback used Kv2 is analogous to a shock absorber coupled with a spring The more Kv2 increases t
25. iffness until the servo is stable Initialization Wizard Tuning Wizard Default Tuning Parameters Control Panel Basic Intermediate Advanced Use the Control Panel to test the servo in motion Stepl Step2 Step 3 Step 4 Step5 Advanced Step 2 Adjust Damper fi d stif til the system i Sabi erdichist les Cono Panola test stabiny while timation The Damper Frequency is the geometric mean between Fv1 and Fv2 Press Advanced to change the frequency order and ratios of Fv1 Fv2 and Fa Damper Frequency Fv1 Fv2 Fa Advanced 5 2 Hz Damper Stiffness Kv2 Kvff Advanced J 20 QuickSilver Controls Inc Page 3 of 29 Technical Document QCI TD054 Step 3 Inertial Damper Increase the Inertial Damper to further eliminate noise If the system is already stable leave the default Initialization Wizard E xi Intermediate If Basic tuning did not produce the desired results go through Steps 1 5 below Initialization Wizard Tuning Wizard Default Tuning Parameters Control Panel Basic Intermediate Advanced Step 1 Step 2 Step 3 i Step 5 Step 4 Increase Stiffness Kp to eliminate position error If system becomes noisey go back and adjust the dampers Stiffness Kp Advanced jn 75 Step 5 Holding Stiffness Increase Holding Stiffness Ki to reduce Position Error while the servo is holding not moving The effects of Ki on Position Error is best seen by charti
26. like a PID servo loop the PVIA integrator term can be increased greatly without causing hunting or oscillation In the PVIA system the velocity error position error and the acceleration error are all integrated This action keeps the system poles and zeros from moving as rapidly while still providing the increased gain The integrator is also configured to reset to the level at which it may maintain linear operation through the limiters any level higher than this merely adds to recovery time from a torque limiting process This allows the motor to rapidly recover with minimum overshoot even when mechanically offset and released The integrator gain should be set to zero when first tuning the other control constants This allows a best effort tuning of the proportional velocity and acceleration terms Once these have been tuned the Ki term may be increased until it causes overshoot etc with the value then backed down to a level to where those effects are avoided This chart shows a 500 count move run with Kp set to 7 all other gains set to 0 Target Position Actual E Position 375 00 750 00 1125 00 1500 00 1875 00 2250 00 2625 00 3000 00 Time rms Kp 7 all other K values gains 0 The shaft never gets to the target position because there is not enough torque generated by Kp to move the shaft into position By using Ki more and more torque will be added until th
27. lverDust PVIA QuickSilver Controls and AntiHunt are trademarks of QuickSilver Controls Inc Technical Document QCI TD054 QuickSilver Controls Inc Tuning Wizard IT xi a Default Tuning Parameters are good for most applications ve The Tuning Wizard by default has the Default If your servo motor is not moving smoothly uncheck the P h box to use the Tuning Wizard Tuning Parameters checked which is the same wan as the FLC CTC Default For Device checkbox _IiisiesionWea_ Tunina Ward Default Tuning Parameters Control Panel Uncheck this box to use the Tuning Wizard The Tuning Wizard provides three methods or a levels of tuning Basic Intermediate or Se ee E Advanced Although they present three different interfaces in the end they edit the same two Initialization Wizard Turing Wizard servo tuning commands i e CTC FLC Control Pane Basic Intermediate Advanced Basic The Basic tab allows the user to select from one of several standard system types Press Preset Tuning Param and select one of the Seno Pes Select Presets x Select type of system for preset o Once you press OK CTC and FLC will be set to factory defaults for the selected system type Cancel These commands will also be sent to the selected Heavy Load fie high inertial mismatch gt 501 x servo Use the Control Panel see below to test the new servo tuning parameters F
28. nds is being used in the initialization file and changes the dialog boxes accordingly Control Constants 2 CT2 Proportional Kp Velocity 1 Feedback Kv1 Velocity 2 Feedback Kv2 Velocity Feedforward Kvff Acceleration 1 Feedback Kal Acceleration 2 Feedback Ka2 Acceleration Feedforward Kaff Integrator Ki Filter Constants 2 FL2 Damping Factor Kd Stiffness Per Inertia Factor Ksi Anticipated Acceleration Factor Kaa Velocity 2 Feedback Filter Fv2 Acceleration 1 Feedback Filter Fa1 Acceleration 2 Feedback Filter Fa2 Associated Commands The following commands set parameters associated with tuning Anti Hunt Constants AHC The Anti hunt constants set the thresholds used to determine if the current position is sufficiently close to the target to allow the motor to enter into and remain in Anti Hunt The first parameter is the maximum error allowed in the Anti Hunt before the unit will revert to normal closed loop operation The second parameter is the maximum error allowed at the end of motion before going into Anti Hunt These two parameters should be set to zero before tuning the servo This allows the true settling response of the servo to be monitored Once the tuning is complete the two parameters should be set back to there original values S Curve Factor SCF With the SCF command the shape of the motion profile acceleration can be varied from a linear profile to a full S curve profile All basic moti
29. ng Position Error see Control Panel Note increasing Ki too much will cause the servo to oscillate QuickSilver Controls Inc Page 4 of 29 QuickSilver Controls Inc Initialization Wizard x Intermediate If Basic tuning did not produce the desired Exit w Save results go through Steps 1 5 below Initialization Wizard Tuning Wizard TI Default Tuning Parameters Control Panel Basic Intermediate Advanced Step 1 Step 2 Step 4 Step 5 Step 3 Increase Inertial Damper Stiffness to futher eliminate noise This is typically required for belt drives Inertial Damper Ka Kaff Advanced s Step 4 Stiffness Increase Stiffness Kp to reduce Position Error The effects of Kp on Position Error is best seen by charting Position Error see Control Panel Note increasing Kp too much will cause the servo to become noisy Initialization Wizard xj Intermediate If Basic tuning did not produce the desired Exit w Save results go through Steps 1 5 below Law Save Initialization Wizard Tuning Wizard i Default Tuning Parameters Control Panel Basic Intermediate Advanced Step 5 Increase Holding Stiffness Ki to eliminate holding position error Only increase this as much as needed as it will cause the system to become noisey Holding Stiffness Ki Advanced a Aa fie Technical Document QCI TD054 Advanced Use the Advanced method to edit the
30. of the second filter By adding this filtering the velocity gains can be increased for greater damping capacity In applications with large inertial mismatches 100 1 gt the velocity gains are increased greatly The filters provide a means to stabilize the high gain servo control loop As the control system would ideally act upon the velocity of the load with any high frequency shaft torsions being ignored high inertia loads are typically tuned with Fv1 and Fv2 at lower cutoff frequencies A good example of this technique is the application of an equalizer to an audio system If the upper half of the frequency range is reduced to minimum levels reducing the high notes a low pass filter has effectively been introduced into the system The only sounds allowed to pass through the audio system would be the lower tones i e bass For a typical system the first velocity filter Fv1 is placed at the lowest frequency The second filter Fv2 is 2 to 5 times higher with 3 times higher being typical These tuned filters help reduce the high frequency resonance modes of widely mismatched systems 20 1 to 200 1 A good rule of thumb is to start with the upper cutoff frequency geometrically centered between the system s anti resonant and resonant frequencies For example a system with a large flywheel setting these filters at 1000Hz is unreasonable low hundreds of Hz for the upper frequency would be more appropriate the lower frequency some 2 to
31. on 8000 counts Strip Chart 20000 Motor Driver Enabled C Disabled Inputs Outputs Set Shift L Click Clear Cnt L Click Tri State L Click mh w Ja a ja s ja E oor Fa a JE eee fE JE JE fea fe Jea Ja Ja E fE Analog 1 3 29 2 327 33 25 4 319 Note keep an eye on the torque If the move requires more torque than the servo has no amount of tuning will stabilize the system QuickSilver Controls Inc Page 5 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Control System Overview QuickSilver s PVIA Servo Algorithm Internal to the SilverLode servos is a unique servo loop algorithm called Position Velocity Feedback Feedforward Integral and Acceleration Feedback Feedforward PVIA In the PVIA algorithm position information is used to perform closed loop control of rotor position by detecting and correcting for errors in actual position versus the target position Actual velocity and actual acceleration are calculated from the time history data of rotor position Actual position actual velocity and actual acceleration data are passed in real Time to the PVIA algorithm along with target position target velocity and target acceleration data see diagram on following 2 pages These variables are used in calculating the motor torque needed to correct any motor position error The exact transfer function when not limiting is Torque Xvi x512 yj EZ x Position
32. on commands incorporate the s curve factor This command can be set at any time except during a motion allowing each motion profile to be tailored for the best shape It is suggested that SCF be set to 0 no S Curve during the initial stages of tuning Once the system is stable with SCF set to 0 some S Curve can be added as desired with minimal adjusted to the tuning parameters QuickSilver Controls Inc Page 9 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Torque Limits TQL This command specifies the torque limits for the different operating states of the servo The two operating modes are Open Loop and Closed Loop with each mode having both a Moving or Holding condition state The four parameters for the torque limits are Closed Loop Holding Closed Loop Moving Open Loop Holding and Open Loop Moving For most applications the Closed Loop Moving torque limit is set to 100 and the Open Loop Holding torque limit is set to 20 30 Normally the Closed Loop Holding torque limit is set about 10 higher than the Open Loop Holding torque limit Open Loop Moving torque is used less frequently but is sometimes used combined with a short Anti Hunt delay to snap down a small residual error See Torque Limits Control Loop Mode CLM The CLM command closes the control loop around position or around velocity When the servo loop is closed around motor velocity rather than motor position the proportional gain Kp is ignore
33. or i e 3 as Fv1 was adjusted Ka may be adjusted up in value by approximately 10 as was Kv2 The combination of these changes makes the simulated inertial damper appear to have 3x lower critical frequency and about 10x the inertia of the default system Increase Ka until it introduces noise and or a squeal too much gain and then reduce by a factor of 2 The tolerable encoder noise level is an application dependent choice Test the system for fast medium and slow operation 8 Iterate Kv2 and Kvff Fv1 Fv2 With noise gone or greatly reduced increase Kv1 and Kvff to decrease the overshoot When noise and overshoot have been minimized go to the next step 9 Reduce Kv2 and Kvff by 10 Loosen up the system by decreasing both velocity terms by 10 Test the move Bring up the Strip Chart and observe the position error incurred from the motion 10 Kp x 2 To decrease the Position Error double the Position Gain Test the move Some oscillation may begin to occur Bring up the Strip Chart and chart the position error and torque Kp can be increased more if the position error is too great but QuickSilver Controls Inc Page 28 of 29 Technical Document QCI TD054 QuickSilver Controls Inc watch the torque If the torque saturates no amount of tuning will allow the servo to provide more torque 11 Set Ki and Reduce Kp Kv2 Kvff by 25 A good starting place for Ki is a value that keeps the product of Ki and Kp the same as the fact
34. or many applications this all that is needed If the servo is performing as required go back to the Initialization Wizard to tab e Press Download File To Device to download the file to the servo s non volatile memory e Press Save to save the file to your PC note if you are still using Factory Default Initialization qcp you will be prompted to change the name QuickSilver Controls Inc Page 2 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Intermediate x If the Basic method did not work try the I Intermediate If Basic tuning did not produce the desired Intermediate method which is a 5 step iterative results go through Steps 1 5 below process Initialization Wizard Tuning Wizard Step 1 System Type Default Tuning Parameters Much like the Basic method Step 1 allows the user Basic Intermediate Advanced to select a system type Think of this as a starting Stepl Step2 Step 3 Step 4 Step5 place a Step 1 Select type of system and test tuning parameters Select you system type and press Test CTC and FLC will be sent to the selected servo Heavy Load i e high inertial mismatch gt 50 1 Press Test to set tuning parameters to starting values for above system type Initialization Wizard x Intermediate If Basic tuning did not produce the desired results go through Steps 1 5 below Step 2 Damper Adjust the Damper Frequency until the servo is quiet Adjust the Damper St
35. or type Strip Chart olx Fie Edit View Setup sml ib lala Yminpe imas 4228 Sample ms 500 Select Channels Repeat Last Move j B Position Error _ ss is counts Position Error sz r anko l Torque 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500 Time ms QuickSilver Controls Inc Page 25 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Anti Hunt Settings Experiment with the Anti Hunt settings to optimize operation The typical Open to Closed value of 20 counts and Closed to Open value of 8 counts are a good start assuming a 8000 count encoder If normal operation involves overcoming the motor torque by hand or with a load such as would happen with a gripper or going against a hard stop then set up the servo to check holding currents before going into Anti Hunt Mode This makes the transition into and out of Anti Hunt Mode smoother Checking holding currents forces the closed loop torque to be less than the open loop torque setting before the servo enters Anti Hunt Mode Checking holding currents also forces the error to be less than the magnitude of the limit before Anti Hunt Mode begins This usually requires the load to settle down on its own as even a slight error will cause the torque command to go to its limits when the integrator is on This makes the servo go to zero error befo
36. ory default In other words if Kp is twice the default Kp then start with Ki at half its default value Set the Integrator Gain and reduce all gains by 25 to provide system stability Increasing Ki will make the system stiffer when holding a position Increasing Ki too much will cause oscillation during motion Test the move The move should be stable If excessive low frequency oscillation occurs reduce Ki 12 Save Results Record the results Then download all the new control and filter constants to the servo Reboot and test the servo again to verify that the correct parameters are being used QuickSilver Controls Inc Page 29 of 29
37. otor Conditions Anti Hunt Mode uses the position error derived from the external encoder to establish when to move in and out of open loop holding torque When precise position control is needed an external encoder allows direct position control of the motor Attaching an encoder directly to the driven device avoids the backlash and flexure present in the coupling between motor and the load When using a linear slider for example a linear encoder can be used for the external encoder signal When entering dual loop control the servo sets the current target position to the current actual position in order to prevent a sudden motion The servo must be configured for closed loop control for this command to take effect The servo uses single loop control by default but the DLC command can be placed anywhere in a user program to change the servo to DLC Executing a move with single loop control before entering dual loop control may be used to verify that the external encoder is connected and operational The external encoder settings must be initialized before using this command The Select External Encoder SEE command configures the servo for external encoder usage The Control Constants typically need to be configured differently for dual loop operation The default control constants are optimized for single loop operation Motion parameters become related to external encoder counts rather than internal encoder counts Only the position error term i
38. re the torque is reduced meaning that the servo must delay entering Anti Hunt Mode until the load has settled Turning off the holding currents check bypasses the torque test allowing the transition to Anti Hunt Mode to be based solely on position error Special Step and Direction Tuning For systems using step and direction inputs the Anti Hunt delay setting will delay the transition into the holding state to a time that is consistent with the step rate For example if the minimum step rate is 100 Hz then the delay should be at least 10 or 20 milliseconds This keeps the servo from transitioning between the moving and holding states while still moving The velocity feedforward term must equal the sum of the two velocity feedback terms Making it anything else will create a velocity dependent following error if the feedforward is less or leading error if the feedforward is greater than the sum of the other two Belt Driven Positioning Tables Direct Drive The high torque of the servo coupled with its PVIA servo technology is ideal for direct drive belt applications Direct drive belt applications have two challenges high inertial mismatch and vibrations from flexure of the belt QCI recommends tuning the high inertial mismatch first After the high inertial mismatch is tuned the vibration caused by belt resonance can be tuned out of the system This is accomplished by increasing the Ka gain value to 5 or 10 times the default value and incr
39. s derived from the external encoder the velocity and acceleration terms are still calculated from the internal encoder Typically using an external encoder with twice the resolution would result in needing to reduce the proportional gain by a factor of 2 Typically the feedforward and feedback gains are set equal to each other Some motions may require intentional under damping of the response such as when moving liquids with a compliant pumping mechanism Removing or reducing the feedforward term will introduce a moving error at velocity that will decay more slowly at the tail This may help to prevent overshoot in a loosely coupled system At the other extreme heavy tightly coupled loads may be moved with lower error if the feedforward acceleration term is increased to be larger than the feedback term this causes the requested torque to jump in response to requested acceleration even before any error has accumulated in the system The use of the Strip Chart under the Control panel is a great aid in tuning A clamp circuit is often useful while tuning a system as this step often presents some of the highest acceleration and deceleration moves that the system will experience as engineering attempts to determine the full capabilities of the system QuickSilver Controls Inc Page 11 of 29 Technical Document QCI TD054 Quicksilver Controls Inc Overview of the Control System Parameters A good understanding of the control parameters and se
40. s inertial damper that is a flywheel coupled to the shaft through a viscous coupling means This type of a load produces a vibration dissipation effect To understand the effect consider a system running at speed Both the motor shaft and the inertial load are spinning at the same speed If a disturbance causes a decrease in shaft speed the inertial load end up spinning at a higher speed adding torque to offset a portion of the disturbance Because of the viscous coupling between the shaft and the inertial load some shearing will occur which will dissipate heat Now view a vibration on the shaft as a series of speeding up stages followed by slowing down stages each time the speed changes energy is dissipated in the viscous material Removing the vibrational energy from the system damps the system and makes it more stable For slower acceleration and decelerations the viscous coupling does not significantly slip and the damper appears to act more as a flywheel QuickSilver Controls Inc Page 13 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Now the mathematics of the corrective action of the acceleration term closely mimic that of a physical inertial damper However rather than actually accelerating a physical mass which would reduce the torque available to the user load the control acts to reduce the motor torque at those instants in time at which the simulated inertial load would be accelerating and to increase the torque a
41. sed to produce a fast move in one direction and a slow move in the other while helping to ensure that hard stops are not hit Make sure the move is within the torque limits of the servo One of biggest problems with tuning a high inertial mismatch system is insufficient torque While the servo is trying to move a very large load 100 times the rotor inertia monitor the torque with the strip chart to make sure it does not max out 2 Disable Anti Hunt and Drag Mode Turn off Anti Hunt Mode feature and Drag mode while performing the tuning process Anti Hunt and Drag Mode can hide clues needed for optimal tuning 3 Start with the Factory Defaults Run the Initialization Wizard using factory defaults 4 Set Ki to zero Start with Ki 0 It is important to optimize the system for the non integrator terms first we will add the integrator term in later 5 Increase Kv2 and Kvff Increase both velocity terms to 10 times the default values This factor of 10 corresponds to the natural frequencies of the system typically lowering by the square root of 100 in a system with 100 1 mismatch Adjust accordingly for other mismatch ratios Test the move Note any changes in operation or sound If a high frequency screeching occurs in a low inertia system lower the Kv2 and Kvff until the sounds subside If excessive overshoot occurs increase Kv2 and Kvff Typical adjustments are by a factor of 2 i e either divide by 2 or multiply by 2 Typically Kv
42. si SD08 Ksi can either be thought of in terms of a stiffness factor between an internal position change and the internal raw acceleration estimate The acceleration is integrated twice to calculate the observer motion such that the average calculated velocity corresponds to the average measured velocity Ksi an also be thought of as a filter Fsi where Ksi 32768 Fsi Mathematically speaking Fsi is the same as FLC s Fv1 for the same frequency roll off Larger values of Ksi correspond to stiffer systems i e thick shafts and low inertial loads corresponding to faster wider bandwidth systems When using QuickControl the user may set Ksi in terms of Fv1 by selecting Normal Units QuickSilver Controls Inc Page 21 of 29 Technical Document QCI TD054 QuickSilver Controls Inc Anticipated Acceleration Factor Kaa Kaa allows the observer to anticipate the acceleration that is about to occur as the result of the commanded torque Kaa should typically be between 10 and 80 of Ksi Larger values of Kaa correspond to the expected response of a stiff system that is a higher acceleration bandwidth When using QuickControl Kaa is set as a percentage QuickControl automatically multiplies the percentage by Ksi at time of download Velocity Filters Fv1 and Fv2 Both Velocity Feedback values are filtered using two low pass filters The first one cascades into the second providing a steeper frequency roll off on the output
43. t those instants in time at which the simulated inertial load would be decelerating The result is an improved system stability without the physical size cost or lost system torque required by a physical system As with the velocity feedback term the acceleration feedback introduces a predictable error which may be offset by adding an acceleration feedforward term Further the acceleration feedforward term may be increased to help command the motor to produce an expected needed torque in response to a commanded acceleration given a knowledge of the approximate inertia of the system This allows a significant percentage of the system drive to be commanded using the prior knowledge of the system rather than waiting for the system error increase to produce the needed torque Note Kv1 gain term adds in a singly filtered velocity estimate where as Kv2 feeds in a doubly filtered velocity estimate Most applications work well using only a Kv2 term Some very light very fast acting system may benefit by splitting the gains approximately 20 KV1 80 Kv2 with Kff typically being set to the sum of Kv1 plus Kv2 This configuration allows a portion of the faster responding Kv1 to act on the system However if driving significant inertial loads torsional oscillations in the shaft may be accentuated by the lighter filtering and a high frequency oscillation may occur Proportional Gain Kp Proportional gain Kp is the simplest component of the servo loop
44. ttings is useful when figuring what changes should be made to optimize the operation of the servo QCI recommends that all users read the parameter descriptions and their functions in the control system before tuning the servo The typical parameter ranges listed in the table below represents values that have been implemented in working applications and are to be utilized as a guide for user applications Some applications may need values outside the typical range listed in the table The table below lists user adjustable tuning parameters in the PVIA algorithm Tuning Parameters Symbol Typical Parameter Range Proportional Gain 40 400 40 400 Velocity 1 Feedback Gain 0 0 Velocity 2 Feedback Gain 5 50 5 50 Velocity Feedforward Gain 5 50 5 50 Acceleration Feedback Gain paged Feedforward 0 200 0 200 Integrator Gain i 0 2000 0 2000 Velocity 1 Feedback Filter 0 to 32767 OHz 200Hz Velocity 2 Feedback Filter 0 to 32767 70Hz 400Hz Scene Feedback 0 to 32767 30Hz 2000Hz 0 200 0 200 Optional tuning parameters for SD08 Tuning Parameters Symbol Typical Parameter Range Proportional Gain Kp 40 400 40 400 Velocity 1 Feedback Gain Kv1 0 0 Velocity 2 Feedback Gain Kv2 5 50 5 50 Velocity Feedforward Gain Kvff 5 50 5 50 eee 1 Feedback Kat 0 200 0 200 e 2 Feedback Ka2 0 200 0 200 oo Feedforw
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