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Sigma II User's Manual
The response increases if the position loop gain is set to a high value, and the
time required for positioning will be shortened. In order to set the position loop
gain to a high value, the rigidity and natural frequency of the mechanical system
must be high.
The responsiveness of the whole servo system may become unstable if only the
position loop gain is increased. Because the speed reference, as output from the
position loop, is likely to become unstable. Increase the speed loop gain while
observing the response.
Adjustment Method
1. Set the position loop gain to a comparatively low value. Then increase the speed
loop gain set in Pn100 to within a range where there is no noise or oscillation.
2. Decrease the speed loop gain a little from the value set in step 1. Then increase
the position loop gain to within a range where there is no overshooting or oscilla-
tion.
3. Set the speed loop integral time constant in Pn101 while observing the position-
ing settling time and the vibration of the mechanical system. If the constant is
too large, the positioning settling time will be too long.
4. Set the torque reference filter to a small value in Pn401 if the mechanical system
has shaft torsional resonance. If the mechanical system generates oscillation
noise in a high-pitched tone, shaft torsional resonance may occur. In that case,
set Pn401 to a larger value.
5. Finally, progressively make fine adjustments to parameters such as the position
loop gain, speed loop gain, and integral time constant to find the optimal points.
n
Function to Improve Response Characteristics
The mode switch, feed-forward, and bias functions can improve the response of the
servo system only if they are used properly. If they are used improperly, they will
worsen the response. Refer to the following instructions and make adjustments to
these functions while observing the change in the actual response.
Mode Switch
Use the mode switch function to improve the transient characteristics of the servo
system if there is torque reference saturation at the time of acceleration or decelera-
tion. The speed loop in PI (proportional and integral) control is switched over to P
(proportional) control when the operation speed exceeds the set value in this func-
tion.
6-31
Chapter 6: Servo Adjustment
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