
B-65150E/04 3. α SERIES PARAMETER ADJUSTMENT
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(5) Velocity feed-forward coefficient adjustment (example using a square
figure with 1/4 arcs)
[Purpose of adjustment]
Feed-forward coefficient adjustment can reduce positional
deviation and figure errors. If the response of the velocity loop for
executing a velocity command is low, velocity control cannot be
exercised as specified where the specified acceleration varies to a
large extent, thus causing a figure error. The response of the
velocity loop can be improved by increasing the velocity loop gain
and by adjusting the velocity feed-forward coefficient.
Velocity feed-forward multiplies a specified rate of variation
(acceleration) by an appropriate coefficient for torque command
compensation. In the servo velocity loop (PI control), a
compensation torque occurs only when a difference (velocity
deviation) between a specified velocity and actual velocity
actually occurs. On the other hand, velocity feed-forward
performs torque command compensation according to an
acceleration value specified beforehand. So, a figure error that
occurs due to a velocity loop delay can be reduced.
[Guideline for adjustment value setting]
The formula below is applicable. In actual adjustment, however,
make an adjustment starting with a velocity feed-forward
coefficient of 100.
(Motor rotor inertia + load inertia)
(Velocity feed-forward coefficient) = 100 ×
Motor rotor inertia
Fig. 3.4.3 (c) Effect of velocity loop gain
Velocity loop gain: 200%
Advanced preview feed-forward coefficient: 98%
FAD time constant: 24 ms (linear type)
Fig. 3.4.3 (d) Effect of velocity loop gain
Velocity loop gain: 300%
Advanced preview feed-forward coefficient: 99%
FAD time constant: 24 ms (linear type)