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HA0364T Rev C Aug 2022
Chapter 6
this can lead to overshoot and general instability. If this is too low it can result in a
sloppy response. It accepts values in the range 0 to 32767.
Integral
term - Increasing the integral (Int) term minimises following error and final
position error. If Integral is too high this will typically lead to motion overshoot during
and at end of move. If the integral term is too low final position may take a long time
to reach, if at all. It accepts values in the range 0 to 32767.
Integral
limit - Limits the wind up limit for the integral term such that excessive
overshoots are prevented. Typically used to prevent runaway integral calculations
due to stiction and other such physical forms of random forces. Normally set as low
as possible, but high enough that with the given integral term final position can be
reached. It accepts values in the range 0 to 32767. If set to 0 then the integration term
in the PID loop is ignored.
Derivative
term - Increasing the derivative (Deriv) term decreases the rate of change
of driver output. Typically this is used to reduce the overshoot from a given motion. If
derivative is too high it can become sensitive to noise from the measured position
error. If derivative is too low, velocity fluctuations may arise during motion. It accepts
values in the range 0 to 32767.
Derivative
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 Err. 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 Err. 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)..
