User manual of EL8-EC***F AC Servo
251
6.8.1 Velocity feedforward
Velocity feedforward can be used in position control mode. When the function is enabled,
it can increase velocity responsiveness, reduce position deviation during constant velocity.
Pr1.10
Name
Velocity feed forward
gain
Mode
PP
HM
CS
P
Range
0~1000
Unit
0.10% Default
300
Index
2110h
Activation
Immediate
Used for decreasing following error caused by low responsiveness of velocity loop. Might cause
overshoot or increase in noise if set value is too high.
Pr1.11
Name
Velocity feed forward
filter time constant
Mode
PP
HM
CS
P
Range
0~6400
Unit 0.01ms Default
50
Index
2111h
Activation
Immediate
Set velocity feed forward low pass filter to eliminate high or abnormal frequencies in velocity feed
forward command. Often used when position command with low resolution or high electronic gear
ration to smoothen velocity feed forward.
Position deviation under constant velocity can be lowered with higher velocity feed forward gain.
Please to refer to the equation below.
Position deviation[Uint]=
Velocity feedforward application
Set Pr1.11 to around 50 (0.5ms), then tune Pr1.10 from 0 to bigger values until the velocity
feedforward achieves better performance. Under constant velocity, the position deviation
in a motion will decrease as the velocity feedforward gain increase.
Steps to tuning:
1. Increase Pr1.10 to increase responsiveness but velocity overshoot might occur
during acc-/deceleration.
2. By reducing Pr1.11, velocity feedforward would be more effective and vice versa.
Pr1.10 and Pr1.11 need to be tuned to a balance.
3. If mechanical noise exists under normal working conditions, please increase Pr1.11
or use position command filter (1 time delay/ FIR smoothing filter)
