
H.DETAILS OF HIGH-SPEED AND HIGH-PRECISION ADJUSTMENT APPENDIX B-65270EN/05
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H DETAILS OF HIGH-SPEED AND
HIGH-PRECISION ADJUSTMENT
(1) Overview
This chapter explains in detail the adjustment procedure described in
Section 3.3, "ADJUSTING PARAMETERS FOR HIGH-SPEED
AND HIGH-PRECISION MACHINING".
(2) Feed-forward coefficient adjustment (using an arc of R10/F4000)
[Purpose of adjustment]
In a conventional position control loop where feed-forward
control is not exercised, a velocity command is output based on
(positional deviation) × (position loop gain). This means that the
machine moves only when there is a difference between the
specification of a command and the machine position. When the
position gain is 30 [1/s], for example, a feedrate of 10 m/min
generates a positional deviation of 5.56 mm. In linear feed, this
positional deviation does not cause a figure error. For an arc or
corner, however, this positional deviation causes a large figure
error.
A function for eliminating such a positional deviation is
feed-forward. Feed-forward converts the position command from
the CNC to a velocity command for velocity command
compensation. Feed-forward can reduce a positional deviation (to
almost 0, theoretically). Accordingly, feed-forward can reduce
arc and corner figure errors. However, the servo response is
improved, so that a shock can occur. To prevent a shock from
occurring, acc./dec. before interpolation must be used at the same
time.
[Guideline for adjustment value setting]
Theoretically, a feed-forward coefficient of 100% leads to a
positional deviation of 0, and eliminates figure errors. Actually,
however, there is a delay in velocity loop response. So, a value
slightly less than 100% produces a specified figure. Usually, a
value between 95% to 99% (settings of 9500 to 9900) is
optimum. As the default, use 9800.
First, adjust the feed-forward coefficient while viewing an arc
figure. (Set a velocity feed-forward coefficient of 50% before
starting adjustment.)