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1. the user can specify a holding and moving torque The combination of these modes results in TQL s four 4 torque limit parameters one for each torque mode as discussed above e Closed Loop Holding e Closed Loop Moving e Open Loop Holding e Open Loop Moving In a simple application TQL is edited as part of the Initialization Wizard However it is perfectly acceptable to vary torque limits at any time by inserting a TQL anywhere in an application program However TQL is a class D command See Command Reference for command classifications This means TQL can only be executed from within a program or sent from a host while the servo is idle For direct access to the torque limits even during program execution see Register Control below 100 Torque is permitted for continuous duty assuming adequate heat sink and 25C ambient Maximum torque above 100 is permitted but at a reduced duty cycle and duration typically 10 duty cycle depending on application The primary difficulty with high torque and high duty cycle application is servo motor overheating Short duty cycles less than 10 at Maximum torque can usually be used without restriction The exact time depends entirely on the operating environment If sufficient external cooling is provided a SilverLode servo can operate at the Maximum setting indefinitely A slight amount of air movement over the servo motor and controller can have a significant effect on temperature To d2. Open Loop GOL and Go Closed Loop GCL commands See Command Reference for details on GOL and GCL Anti Hunt Anti Hunt is enabled using the Anti Hunt Constants AHC command and is used to automatically switch between Closed Loop mode and Open Loop mode based on position error and torque level Using the Anti Hunt Mode AHM command the servo can be set to enter Anti Hunt only when holding a position or it can be set to enter Anti Hunt any time position error is low enough When using open loop control to hold position the controller applies a constant torque to the motor ignoring small position errors When using Open Loop mode during a move the servo ignores small errors and applies torque to the motor based only on the motion profile from the Trajectory Generator Anti Hunt can make the servo operate more smoothly but it also limits the final position accuracy The following commands are important to Anti Hunt operation Typically they are edited in the Initialization Wizard but may be added to application programs e Anti Hunt Constants AHC Anti Hunt Delay AHD Anti Hunt Mode AHM Torque Limits TQL Error Limits ERL The AHC and AHD commands set the conditions under which the servo enters and exits Anti Hunt while the AHM command sets the type of Anti Hunt operation the device uses See Anti Hunt Feature in User Manual for more details QuickSilver Controls Inc Page 2 of 11 Technical Document QCI TD051 Quick
3. Moving whenever the servo is in motion Target Generator active and is Holding otherwise The transition from Moving to Holding takes a pre defined time to allow for settling See Torque Mode Details below Note It is possible for the motor to be moving while in the Holding mode i e turning the shaft by hand or not moving while in the Moving mode i e if the shaft was jammed The Moving and Holding modes are used only for control purposes and are not related to the actual state of the shaft Open Loop Vs Closed Loop Torque Mode In Closed Loop mode torque is calculated using the difference between target position and actual position The greater the difference or error the greater the torque In Open Loop mode torque is set using the TQL command see Torque Limits below and the actual position is ignored A simple example of closed loop control is a car s cruise control Property of QuickSilver Controls Inc Page 1 of 11 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 TD051 QuickSilver Controls Inc Typically the servo automatically switches between Open and Closed Loop modes based on the Anti Hunt settings see below but the mode may be directly selected with the Go
4. Silver Controls Inc Torque Mode Details A different torque limit can be set for each of the four torque modes see Torque Limits below Described below are the conditions that determine which torque mode to use Torque Modes Anti Hunt Disabled Torque Modes Anti Hunt Disabled Closed Loop Closed Loop Closed Loop Closed Loop Holding Mode Moving Mode Moving Mode Holding Mode ERL Delay To Holding Time Start of Move Change from Moving to Holding Torque With Anti Hunt disabled using AHC as shown the edit AHC Anti Hunt Constant x only torque modes used are Closed Loop Holding and ET oe Closed Loop Moving The above diagram illustrates Pe A tia sii how the torque modes change during a typical move TA ae ra ae Cmca Anti Hunt Description At the beginning the servo is stopped and holding in Doo i o Test Closed Loop Holding mode When commanded to Check move the servo goes into Closed Loop Moving mode Biel A j m Closed to Open until the move completes The ERL command s E ETE Ue etaukt For Delay To Holding timer starts running to allow the pialti eA motor to settle The timer allows a higher moving jo counts torque limit to persist up to seven seconds after the U last motion After the timer expires the servo goes into Closed Loop Holding mode x Cancel Moving Error Limit 500 counts Description Holding Error Limit 200 counts r Units Delay to Holding fizo mSe
5. Technical Document QCI TD051 Quicksilver Controls Inc Date 4 January 2008 www QuickSilverControls com Torque Control This Technical Document describes how the SilverLode Controller Drivers control torque Typically a SilverLode servo generates torque based on position error target position minus actual position inputs from the Trajectory Generator desired motion profile and the commands e Anti Hunt Constants AHC e Anti Hunt Mode AHM e Anti Hunt Delay AHD e Torque Limits TQL By default all motion occurs with torque being constantly adjusted This is referred to as Closed Loop mode or the servo loop This allows the servo to use only as much torque as required for any given move It is also possible to operate the servo without the benefits of the servo loop which is called Open Loop mode In Open Loop mode the servo has no feedback and constantly applies the torque specified by a programmed limit see TQL below The closed loop torque equation as well as a flow chart the PVIA servo loop can be found in Technical Document QCI TD054 Servo Tuning on our website Torque Modes A servo may be operated in either Closed or Open loop mode In each of these modes there are two sub modes Holding and Moving The combination results in the following for torque modes e Closed Loop Holding e Closed Loop Moving e Open Loop Holding e Open Loop Moving Moving Vs Holding Torque Mode In simple terms the servo is
6. ally higher moving torque if needed at the end of a move so that any final vibrations may be settled before dropping to a lower torque level Closed Loop Moving Typically a higher permissible torque level is desired for this mode to allow motion when commanded Open Loop Holding This torque setting is frequently referred to as the Anti Hunt torque see Anti Hunt in User Manual for details The torque should normally only be set a margin above what is needed to hold the unit to minimize heating however setting too low may cause the unit to cycle between open and closed loop in the Anti Hunt mode due to not having sufficient torque in the open loop mode This is an open loop mode so the current required to generate the torque specified is always flowing through the windings This current flow generates heat increasing the temperature of the servo If the servo is experiencing excessive heating while at rest lowering this value can decrease the amount of heat generated Excessive holding current contributes solely to the heating of the servo so remember that less torque means less current decreasing the operating temperature In addition torque is proportional to current but heat is proportional to the square of current Therefore decreasing the torque setting by 30 will generally decrease the heat generated at rest by almost 50 setting the torque to 30 reduces the heat to approximately 9 as compared to the 100 setting QuickSil
7. alue contained in a single register Torque Curve A typical torque speed curve is shown below When the 34HC 2 motor type is operating at 48 VDC 30 000 STU corresponds to 1650 oz in at 0 RPM However 30 000 STU also corresponds to 780 oz in at 1000 RPM At higher speeds the 150 30 000 and the 100 20 000 settings produce the same torque This is caused when the commanded torque levels can not be reached due to the back EMF of the motor reaching the power supply voltage The flat portion of the curve represents the constant torque operation while the sloping section approximates a fixed power hyperbolic curve slightly lower due to losses increasing with speed This spoeed dependant torque relationship is a result of the design of the motor It is important because the torque limits set with the TQL command limit the relative torque the servo will apply not the actual torque The relative nature of the torque representation must be considered on applications with critical maximum torque requirements 34HC 2 Torque vs Speed Data 1800 1600 l 48V MAX 48V 100 1400 36V 100 1200 r 24V 100 12V 100 0 500 1000 1500 2000 2500 Speed rpm The high pole count motor used with the SilverLode controller driver is one of the QuickSilver s distinguishing features A SilverLode servo can produce a large amount of torque for its size at lower speeds The high torque constant o
8. c Normal Drag Mode D C Native QuickSilver Controls Inc Page 3 of 11 Technical Document QCI TD051 QuickSilver Controls Inc Torque Modes w Anti Hunt Enabled Torque Modes w Anti Hunt Enabled Open Loop Closed Loop Closed Loop Closed Loop Open Loop Holding Mode Moving Mode Moving Mode Holding Mode Holding Mode Anti Hunt Anti Hunt IERL Delay To Holding Time iChange from i i i 1 i 1 i 1 i 1 i i i i 1 i Moving to Start of Move Holding Torque AHD Anti Hunt Delay i Change from f Closed Loop to Settling Open Loop Torque With Anti Hunt enabled using AHC and AHM as edit AHC Anti Hunt Constant ST shown the only torque modes used are Closed Anti Hunt disabled when both parameters 0 Loop Holding Closed Loop Moving and Open i m Open to Closed Cancel Loop Holding The above diagram illustrates how A eh rO AAA the torque modes change during a typical move clad ale Description fo counts Test At the beginning the servo is stopped and holding Im p eo F v Holding in Open Loop Holding mode When commanded to tiesedto Open Currents move the servo goes into Closed Loop Moving Amount of eror required to go into oe mode until the move completes and ERL s Delay iiaii Dae To Holding timer expires at which time the servo f am goes into Closed Loop Holding mode AHD s Anti J Hunt Delay timer starts after the motor se
9. ctual torque The most linear torque range is from 20 to 80 of the torque rating 10 to 80 for SilverDust I Grade controllers with an I Grade motor The nominal speed range lies on the torque plateau at the lower speed end of the torque curves This is the area of the torque curve where the torque remains roughly constant as the speed increases Temperature has a slight effect on the rotor magnetic strength as well as motor winding resistance Lower temperatures and torque speed usage in the nominal regions improves torque accuracy The power supply in use must also be taken into consideration A supply in compliance with QCI specifications is highly recommended and required to maintain the warranty Further variation in the voltage level up to 10 may vary the output torque similarly These minimum power supply requirements are meant to ensure the servo can operate optimally If all four of these requirements are met torque variation is minimized Note The SilverDust I Grade controllers when mated to an I Grade Motor enable the use of factory calibration values stored in the memory onboard the I Grade motor These calibration values significantly reduce the torque ripple of the system and resulting velocity variations as compared to previous systems QuickSilver Controls Inc Page 11 of 11
10. etermine the actual torque that may be applied to the load refer to the torque curve charts The 100 torque applied to the load depends on the motor speed See Torque Curve below QuickSilver Controls Inc Page 7 of 11 Technical Document QCI TD051 QuickSilver Controls Inc Unit Normal vs Native Typically servos have a 100 torque level corresponding to a native value of 20 000 SilverLode Torque Units STU and a Maximum torque of 30 000 STU The following I Grade motors are the exceptions In QuickControl the TQL command automatically scales percentage values to STU see Scaling in User Manual depending on motor type Grade Motors With Non Standard 100 and Maximum Torque Limits NOTE All other l Grade motors have 20 000 STU for 100 torque and 30000 STU for Maximum torque Non STU STU Standard 100 Maximum Motors QCI A34N 1 20 000 22 500 QCI A34H 1 16 383 24 575 A STU does not directly correlate to a physical torque units i e ounce inches because torque changes as speed changes Therefore QCI gives torque in percentage of available torque at current speed as defined by the published torque curves See Torque Curve below Closed Loop Holding Typically a reduced torque level is desired as no motion is active the lower level here can permit manual movement of an axis or may reduce motor heating if a jam occurs The purpose of the Delay to Holding is to permit the typic
11. f the motor however directly corresponds to a high motor constant i e volts radian second value At higher speeds the losses increase and the voltage head between the power supply voltage and the back EMF of the motor drops QuickSilver Controls Inc Page 10 of 11 Technical Document QCI TD051 QuickSilver Controls Inc causing a reduction in torque at moderate to high speeds For this reason operating the device from higher voltages up to 48 VDC allows the system to attain higher speeds and greater output torque Understanding torque speed relationship is extremely important to properly using and sizing a SilverLode servo system Reading Actual Torque The servo s actual torque can be obtained from the low word of register 9 and is updated every servo cycle 120 uSec In closed loop control the torque value can be anything between plus or minus the torque limit setting The torque value during open loop control will be the exact value in the TQL command This is a read only data register Chart vs Actual Torque The SilverLode servo it is not intended for use as a precision torque sensor Attempting to set a servo to a precise torque i e 200 oz in using TQL and the motor s torque curve will get you within about 10 The torque curves are de rated from actual readings to insure all motors can meet the torque and efficiency changes a little from motor to motor Speed power supply drift and temperature also affect the a
12. isters 206 and 207 can be updated from any internal and external source To change torque limits internally use the CLC or CLX command to move the data CLC has the ability to write to either the low word or high word of a register Thus an individual torque limit can be changed with CLC The procedure for changing torque limits is to first copy or write the desired torque limit value into register 10 the accumulator Be sure that the value is in native torque units Copy this number from the Accumulator to the corresponding 16 bit half of torque limit register using CLC In the CLC example below CLC updates the closed loop moving torque limit the low word of register 206 CLC Calculation x OK Cancel Register Description Operation Copy Word Reg L Word LO Acc 7 Updating the torque limits externally requires some type of host Use the Write Register Immediate WRI command to write a value to a register and Read Register RRG to read the value of a register see Command Reference QuickSilver Controls Inc Page 9 of 11 Technical Document QCI TD051 Quicksilver Controls Inc See technical document QCI TD053 Serial Communications on our website for details on host level communications Torque Input Mode The Torque Input Mode TIM command is an advanced topic described in Application Note QCI AN047 Input Mode Joystick In brief TIM configures the servo for direct torque control based on the v
13. losed Loop Open Loop Holding Mode Holding Mode Holding Mode Holding Mode Anti Hunt Anti Hunt Load Causes Motor Shaft to Move AHD Anti Hunt Delay Change from Closed Loop to Settling t Open Loop Torque Command The above diagram illustrates what happens in Anti Hunt when the load causes the motor shaft to move without a move command As soon as the position error is greater than AHC s Open to Closed parameter the torque mode changes to Closed Loop Holding As long as the position error is less than AHC s Open to Closed parameter the Anti Hunt Delay timer runs Once the timer expires the servo goes back to Open Loop Holding mode Note since there is no move ERL s Delay to Holding timer does not run QuickSilver Controls Inc Page 6 of 11 Technical Document QCI TD051 Quicksilver Controls Inc Torque Limits Command TQL x Torque limits have broad uses including protecting machine parts at hard stops web tensioning allowing the shaft to free wheel a Canca and reducing power consumption by the Closed Loop Holding 75 m Description servo and hence its temperature when SF Defaut holding position Closed Loop Moving 100 i a Torque limits are primarily changed using l the Torque Limits TQL command ei 20 5 om J nits f N A servo may be operated in either closed Or apentoop Moving 20 x r z ae ative open loop mode In each of these modes
14. ttles to within the Closed to Open limits specified by AHC After x the Anti Hung Delay timer expires the servo goes into OPEN Detemine whether or not Anti Loop Holding mode Hunt is active while in motion Cancel x Description Delay bef ing into Anti Hunt paw efore moving into Anti Hun H only when stopped Cacal default 150 mSec Description s idad mana or Units Normal Native QuickSilver Controls Inc Page 4 of 11 Technical Document QCI TD051 Quicksilver Controls Inc Torque Modes w Anti Hunt Enabled and Long Delay To Holding Time Torque Modes w Anti Hunt Enabled Open Loop Closed Loop Closed Loop Open Loop Holding Mode Moving Mode Moving Mode Holding Mode Anti Hunt Anti Hunt Time IERL Delay To Holding Time iChange from Moving to Holding Torque L Start of Move i i AHD Anti Hunt Delay i i i I Change from Closed Loop to Open Loop Torque Settling i The above diagram illustrates what happens if ERL s Delay to Holding timer is set longer than AHD s Anti Hunt Delay timer Note that the torque mode changes from Closed Loop Moving to Open Loop Holding without ever going to Closed Loop Holding QuickSilver Controls Inc Page 5 of 11 Technical Document QCI TD051 Quicksilver Controls Inc Torque Modes w Anti Hunt Enabled and Position Error Without Move Toraue Modes w Anti Hunt Enabled Open Loop Closed Loop C
15. ver Controls Inc Page 8 of 11 Technical Document QCI TD051 QuickSilver Controls Inc Open Loop Moving This torque is only used when a move is commanded and the AHM command is set to when moving or stopped as shown zl In this Anti Hunt mode the servo uses Open Loop Moving SEA E aie en mode during moves as long as the position error stays within Cancel the limits setin AHC As this is an open loop mode all the Description heating issues discussed above apply Anti Hunt Mode C only when stopped default when moving or stopped Register Control The four torque limits set by TQL are stored in four 16 bit words in two data registers as shown both registers are read write capable Upper 16 BitWord Lower 16 Bit Word Reg 206 Closed Loop Holding Closed Loop Moving Reg 207 Open Loop Holding Open Loop Moving When the TQL command is executed it simply writes its four parameters to registers 206 and 207 Use of the TQL command could be replaced with direct writes to these registers allowing the torque limits to be updated in real time The servo will begin using the new torque limit value within of one servo cycle 120 usec of the register update Direct editing also allows individual limits to be adjusted without changing any of the other three limits Note that when writing to either register 206 or 207 the torque limits must be in SilverLode Torque Units STU i e 20 000 STU 100 Reg
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