THORLABS KBD101 User Manual page 47

Brushless DC Servo Driver K-Cube
Derivative Recalculation Time – Time over which derivative is calculated. Under
normal circumstances, the derivative term of the PID loop is recalculated at every
servo cycle. However, it may be desirable to increase the sampling rate to a higher
value, in order to increase stability. The Derivative Time parameter is used to set the
sampling rate. For example if set to 10, the derivative term is calculated every 10
servo cycles. The value is set in cycles, in the range 1 to 32767 (1 cycle = 102.4 µs).
Typically increasing the derivative time increases sensitivity to noise.
Output Gain – This parameter is a scaling factor applied to the output of the PID loop.
It accepts values in the range 0 to 65535, where 0 is 0% and 65535 is 100%. Typically
used to tighten a control loop for increased positional performance at the expense of
stability.
Vel. Feed Forward and Acc. Feed Forward – These parameters are velocity and
acceleration feed-forward terms that are added to the output of the PID filter to assist
in tuning the motor drive signal. They accept values in the range 0 to 32767.
Position Error Limit – Under certain circumstances, the actual encoder position may
differ from the demanded position by an excessive amount. Such a large position
error is often indicative of a potentially dangerous condition such as motor failure,
encoder failure or excessive mechanical friction. To warn of, and guard against this
condition, a maximum position error can be set in the Position Error Limit parameter,
in the range 0 to 65535. The actual position error is continuously compared against
the limit entered, and if exceeded, the Motion Error bit (bit 15) of the Status Register
is set, the associated axis is stopped and the GUI panel Position Error LED is lit.
Note
The position error limit is monitored only when the motor is enabled (i.e.
the feedback loop is active).
Position PID Settings Summary
Stage overshoots the intended position - reduce Int and increase Deriv and Prop terms.
Stage doesn't attain final position - increase the Int and Prop terms.
Motion is unstable - reduce Prop and Int, increase Deriv.
Stage sounds noisy - reduce Deriv.
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