Baldor MN1903 installation manual Servo axis tuning for velocity control, Calculating Kvelff

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5.7 Servo axis - tuning for velocity control

Drives designed for velocity control incorporate their own velocity feedback term to provide system damping. For this reason, KDERIV (and KVEL) can be set to zero.

Correct setting of the velocity feed forward gain KVELFF is important to get the optimum response from the system. The velocity feed forward term takes the instantaneous velocity demand from the profile generator and adds this to the output block (see Figure 11). KVELFF is outside the closed loop and therefore does not have an effect on system stability. This means that the term can be increased to maximum without causing the motor to oscillate, provided that other terms are setup correctly.

When setup correctly, KVELFF will cause the motor to move at the speed demanded by the profile generator. This is true without the other terms in the closed loop doing anything except compensating for small errors in the position of the motor. This gives faster response to changes in demand speed, with reduced following error.

5.7.1 Calculating KVELFF

To calculate the correct value for KVELFF, you will need to know:

HThe speed, in revolutions per minute, produced by the motor when a maximum demand (+10V) is applied to the drive.

HThe setting for LOOPTIME. The factory preset setting is 1ms.

HThe number of encoder lines for the attached motor. Baldor BSM motors use either 1000 or 2500 line encoders.

The servo loop formula uses speed values expressed in quadrature counts per servo loop. To calculate this figure:

1.First, divide the speed of the motor, in revolutions per minute, by 60 to give the number of revolutions per second. For example, if the motor speed is 3000rpm when a maximum demand (+10V) is applied to the drive:

Revolutions per second

=

3000 / 60

=50

2.Next, calculate how many revolutions will occur during one servo loop. The factory preset servo loop time is 1ms (0.001 seconds), so:

Revolutions per servo loop

=

50 x 0.001 seconds

=0.05

3.Now calculate how many quadrature encoder counts there are per revolution. The NextMove PCI counts both edges of both pulse trains (CHA and CHB) coming from the encoder, so for every encoder line there are 4 ‘quadrature counts’. With a 1000 line encoder:

Quadrature counts per revolution

=

1000 x 4

 

=

4000

4. Finally, calculate how many quadrature counts there are per servo loop:

Quadrature counts per servo loop

=

4000 x 0.05

 

=

200

5-22 Operation

MN1903

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Contents NextMove PCI Motion Controller Page Contents Operation Appendices Iv Contents MN1903 General Information Safety Notice PrecautionsNextMove PCI features MN1903 IntroductionIntroduction MN1903 Installed Receiving and inspectionIdentifying the catalog number Catalog number PCI001Phase Units and abbreviationsOther information needed for installation IntroductionHardware requirements Tools and miscellaneous hardwareLocation requirements Installation This completes the basic installationInstalling the NextMove PCI card NextMove PCI Expansion card and can Bracket boardBasic Installation MN1903 100-pin edge connector Outline1 100-pin connector pin assignment Pin Signal100-pin connector pin assignment Analog I/O Location Analog inputsPin Name MintMT keyword / description Analog input wiring, AIN0 shown Analog outputs Drive Demand/Command Pin Name DescriptionDigital I/O Input Common Breakout module connectorDigital input arrangement Stepperio Digital inputs Pin Name MintMT keyword Common DescriptionINX.4 Digital input circuit fast interrupts Digital outputs OUTX.0 Other I/O Encoder interfaces X12, X13, X14, X15Encoder input frequency Power Relay and can power Relay connectionsStepper drive outputs X10 Pin X10 Name X11 Name DescriptionCan Connections Cable length Maximum bit Resistance Conductor Rate Area1 CAN1 CANopen Baldor proprietary can interface using a RJ45 connector 2 CAN2 Baldor canEmulator connection Reset statesSystem watchdog Connection summary minimum system wiring Example minimum system wiringThis completes the input/output wiring Module Signal ConnectorConnector details for minimum system wiring shown in Figure Breakout Pin Name FunctionInput / Output MN1903 Installing the driver software Windows 95, 98 and ME Drivers\nmPCI\win9xInstalling the driver software Windows NT Installing the driver software WindowsInstalling WorkBench \startStarting WorkBench MN1903 Operation Operation MN1903 WorkBench Help fileChoosing an axis 1, 2, 3 and 4 axis cards Configuring an axisChoosing an axis 8 axis card Selecting a scale Setting the drive enable output Testing the drive enable output Servo axis testing and tuning Testing the drive command outputAn introduction to closed loop control Summary, the following rules can be used as a guide NextMove PCI servo loop Servo axis tuning for current control Selecting servo loop gainsMN1903 Operation Underdamped response Underdamped responseOverdamped response Overdamped responseCritically damped response Critically damped ideal responseServo axis eliminating steady-state errors Servo axis tuning for velocity control Calculating KvelffKvelff Correct value of Kvelff Adjusting Kprop Correct value of Kprop Stepper axis testing JOG.0=2Digital input/output configuration Digital input configurationDigital output configuration Saving setup information 10.1Loading saved information Operation MN1903 Problem diagnosis SupportMet featureNextMove PCI indicators Status and can LEDsCommunication Symptom CheckMotor control Output polarity Mechanical specifications Digital inputs X1 Relay output Encoder interfaces X1210CANopen interface Stepper outputs X1011Baldor can interface NextMove PCI Expansion card NextMove PCI Expansion cardAxis numbering when using expansion cards Main Expansion cardsWith no One 4-axis One 8-axis Two 4-axis Expansion Expansion cardExpansion card status LEDs NextMove PCI Breakout module Catalog number Description PCI003-501CBL021-501 CBL021-503Digital output modules NextMove PC system adapterSpares Catalog Description Number OPT025-508Baldor can nodes NextMove PCI can Bracket board Encoder Splitter/Buffer boardCatalog Description Number OPT008-501 OPT029-501Accessories MN1903