
B-65150E/04 3. α SERIES PARAMETER ADJUSTMENT
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(4) 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 a 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,
acceleration/deceleration 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.)
[Actual adjustment]
Create a program as indicated below for circular movement by
R10/F4000, and measure the path with SD. G08P1 and G08P0 in
the program are G codes for starting and ending the advanced
preview control mode in Series 16, respectively. For a mode to be
used, select the corresponding G codes from Table 3.4.3 (b).
G91;
G08P1;
G17G02I-10.F4000.;
I-10.;
I-10.;
G08P0;
G04X3.;
M99;