Rockwell Automation 1771-QB Linear Pos. - Manual (Page 101)

Formatting Module Data (WRITES)
Chapter 7
7Ć22
The integral term alters response to positioning errors. If the integral gain is
relatively high, the system will be more sensitive to positioning errors.
However, if the gain is too high, the axis may overshoot and oscillate around
programmed endpoints. On the other hand, if the gain is too low, the system will
take longer to compensate for positioning errors.
Derivative Gain (words 21 and 50)
The derivative gain factor K
D
is used by the derivative component during final
axis positioning, i.e., when the desired velocity is zero and the axis is in the PID
band.
Figure 7.29
Derivative Gain Word
50072
Derivative gain,
BCD or binary
0.9999 max, unitless
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
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The module uses derivative control to increase system stability by opposing
changes to positioning error. Derivative gain reduces overshoots and oscillations
around an endpoint caused by proportional and integral control, but too large a
derivative gain will actually cause oscillations instead of reducing them.
Derivative control is also very susceptible to electrical noise. We recommend
that you set derivative gain to zero if it isn’t required to improve system
performance.
Feedforward Gain (words 22 and 51)
The percentage of the axis velocity applied through feedforwarding determines
the corresponding reduction in the following error. The magnitude of the
feedforward contribution is calculated as follows:
feedforward velocity = (Kf)(speed)
where,
Kf = feedforward gain
Speed = desired axis speed