Chapter 5: MEI Software
25
Integral Gain
The integral gain parameter is used to integrate static errors and "fine tune" the position at rest.
The motor command (analog voltage or pulse rate) will increase with increasing error and time.
The maximum amount of gain due to integration is limited to prevent "windup".
With proper tuning, motor sizing and a low-friction mechanical system, 0-1 encoder count (step)
error is possible. The range of values for integral gain is 0 to 32,767.
See appendix C, “Tuning Your System,” for more information on setting integral gain.
Derivative Gain
The derivative gain affects the analog command voltage or pulse rate based on the amount of
position error change occurring in the last two samples. The derivative gain term acts as a
damping factor. The range of values for the derivative gain is 0 to 32,767.
See appendix C, “Tuning Your System,” for more information on setting derivative gain.
Acceleration Feed Forward
The acceleration feed forward term is used to add extra output during acceleration to reduce
following error. The range of values for the acceleration feed forward is 0 to 32,767.
See appendix C, “Tuning Your System,” for more information on setting acceleration feed
forward.
Velocity Feed Forward
The velocity feed forward term is used to add extra output during constant velocity to reduce
following error. The range of values for the velocity feed forward is 0 to 32,767.
See appendix C, “Tuning Your System,” for more information on setting velocity feed forward.
I Maximum
This parameter sets the maximum voltage output by the integration term of the PID algorithm.
The limit is used to prevent "windup". Generally, "windup" occurs in systems where (very) high
friction cannot be overcome without entering an oscillation mode. The range of values for the
integration limit is 0 to 32767.
See appendix C, “Tuning Your System,” for more information on setting the integration limit.
Offset
This parameter sets the DAC output level. It can be used to compensate for other system offsets.
The offset parameter should be set at 0 in most cases.
Note that each axis also has an internal offset, which is in series with the digital filter offset
described here and visible on the SETUP program tuning screen. The offset is used to zero the
DAC and Voltage-to-Frequency converter outputs to prevent motion when the axis is placed in
idle mode.
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