
B-65270EN/05 APPENDIX H.DETAILS OF HIGH-SPEED AND HIGH-PRECISION ADJUSTMENT
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(3) 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.
(Velocity feed-forward coefficient) =
100 × (Motor rotor inertia + load inertia) / Motor rotor inertia
[Actual adjustment]
Make a velocity feed-forward coefficient adjustment by using a
square figure with four 1/4 arcs of a 5-mm radius. In this
adjustment, disable the velocity clamp function based on an arc
radius. (Disable the function, or in the example below, ensure
that a velocity equal to or greater than F4000 can be specified.)
G91;
G08P1;
G01X10.F4000;
G02X5.Y-5.R5.;
G01Y-20.;
G02X-5.Y-5.R5.;
G01X-20.;
G02X-5.Y5.R5.;
G01Y20.;
G02X5.Y5.R5.;
G01X10.;
G08P0;
G04X3.;
M99;
5 mm
5 mmStart, End
Fig. H (e) Programmed figure
When the actual path is measured in a mode for displaying a reference
path, the actual path and reference path are plotted at the same time as
shown below: