Motion Control
MultiFlex PCI 1000 Series User's Manual
121
When feed forward is incorporated into the digital PID filter it becomes the primary component in
generating the servo command output voltage. Typically the setting of the other terms of the filter will be:
Proportional gain – reduced by 25% to 50%
Integral gain – reduced by 5% to 25%
Derivative gain – set to zero, if the axis is too responsive reduce the gain of the amplifier
Acceleration and Deceleration Feed Forward
For most applications, velocity feed forward is sufficient for accurately positioning the axis. However for
applications that require a very high rate of change, acceleration and deceleration gain must be used to
reduce the following error at the beginning and end of a move.
Acceleration and deceleration feed forward values are calculated using a similar algorithm as used for
velocity gain. The one difference is the velocity is expressed as encoder counts per second, while
acceleration and deceleration are expressed as encoder counts per second per second.
controller output = Accel./Decel. (encoder counts/sec/sec.) * Feed forward term (encoder counts *
volt/sec./sec.)
i
Acceleration and deceleration feed forward values should be set prior to using
the Servo Tuning Utility to set the proportional and integral gain.
i
Acceleration feed forward and deceleration feed forward are not supported
during Contour Mode (multi-axes lines and/or arcs).
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