Yaskawa DR2 Sigma Servo - Manual (Page 450)

B.3 Adjusting a Servopack for Position Control
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3) Functions to Improve Response
The mode switch, feed-forward, and bias functions improve response.
However, they are not certain to improve response and may even worsen it in some
cases. Follow the points outlined below and observe the actual response while making
adjustments.
a) Mode Switch
The mode switch improves the transition characteristics when the torque references
become saturated during acceleration or deceleration.
Above the set level, the speed loop control switches from PI (proportional/integral)
control to P (proportional) control.
b) Feed-forward Function
Use feed-forward to improve the response speed. However, feed-forward may be in-
effective in systems where a sufficiently high value of position loop gain is not pos-
sible.
Follow the procedure below to adjust the feed-forward amount (Cn-1D).
(1) Adjust the speed loop and position loop, as described above.
(2) Gradually increase the feed-forward amount (Cn-1D), such that the positioning
complete (COIN) signal is output early.
At this point, ensure that the positioning complete (COIN) signal breaks up (alternate-
ly turns ON/OFF) and that the speed does not overshoot. These problems can arise if
the feed-forward is set too high.
For all types of Servopack except DR1, a primary delay filter can be applied to feed-
forward. This filter can be used to correct breakup (alternatingly turning ON/OFF) of
the positioning complete (COIN) signal or speed overshoot arising when feed-for-
ward is activated.
c) Bias Function
When the lag pulses in the error counter exceeds the positioning complete width
(Cn-1B), the bias amount (Cn-1C) is added to the error counter output (speed refer-
ence). If the lag pulses in the error counter lies within the positioning complete width
(Cn-1B), the bias amount (Cn-1C) is no longer added.
This reduces the number of pulses in the error counter and shortens the positioning
time.
The motor speed becomes unstable if the bias amount is too large.
Observe the response during adjustment as the optimum value depends on the load,
gain, and positioning complete width.
Set Cn-0C to zero (0) when the bias is not used.
Bias Function
Speed
Speed
Reference
Positioning Complete
(COIN) Signal
Motor Speed with No Bias
Motor Speed with Bias
Time
B