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A.1.6 Tuning the position loop for a velocity servo drive
The MintDrive can be tuned as a velocity servo drive, passing the profiled demand components through
the speed and current loops only. To do this the MintDrive keyword CONFIG should be set to 1 by
typing:
CONFIG=1
The gain term KVELFF should be set to the value derived from the following equation:
KVELFF = (32767 / (((MaxMotorSpeed / 60) / Servo Frequency) x (4 x MotorEncoderLines))) / 16
where:
Servo Frequency is the reciprocal of the time period set using the Mint keyword LOOPTIME;
MotorEncoderLines is 1024 for a resolver motor;
MaxMotorSpeed is found from the motor specifications.
A.1.7 Tuning the position loop for a servo drive
The MintDrive can be tuned as a servo drive, passing the profiled demand components through the
position, speed and current loops. To do this the MintDrive keyword CONFIG should be set to 1 by
typing:
CONFIG=1
There are two types of move that can be used to help tune the position loop; step and trapezoid.
A step move performs an instantaneous position demand change. This is useful for tuning the motor to
overcome following error and decrease response time.
The trapezoid move type performs a trapezoidal move based on a given acceleration, slew speed and
deceleration profile. This is equivalent to a positional move generated by using the keywords MOVEA or
MOVER.
A.1.7.1 Position Loop gain terms
The output from the position loop is effectively a speed command. This command is a 16 -bit signed
value scaled such that 32767 represents the maximum motor speed.
Before starting, it may be necessary to increase the Following Error Fatal limit, the threshold at which
the drive will trip with a Following Error. The default value is 1000 counts which may not be sufficient
whilst initially tuning the motor.
KVELFF - Velocity Feedforward gain
This is applied to the demand speed. The profiler will generate a demand speed based upon the
current move. This term should be used to scale that demand speed to the equivalent speed command
for the speed loop - this is related to the specified maximum speed of the motor and of the position
(servo) loop frequency:
The gain term KVELFF should be set to the value derived from the following equation:
KVELFF = (32767 / (((MaxMotorSpeed / 60) / Servo Frequency) x (4 x MotorEncoderLines))) / 16