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9. Adjustment
9 - 6
(2) Setting the speed loop leading compensation
The speed loop leading compensation (SV008 (VIA)) determines the characteristics of the speed
loop mainly at low frequency regions. 1364 is set as a standard, and 1900 is set as a standard
during SHG control. The standard value may drop in respect to loads with a large inertia.
When the VGN1 is set lower than the standard value because the load inertia is large or because
machine resonance occurred, the speed loop control band is lowered. If the standard value is set in
the leading compensation in this status, the leading compensation control itself will induce vibration.
In concrete terms, a vibration of 10 to 20Hz could be caused during acceleration/deceleration or
stopping, and the position droop waveform could be disturbed when accelerating to a constant
speed and when stopped. (Refer to the following graphs.)
This vibration cannot be suppressed by the vibration suppression functions. Lower the VIA in
increments of 100 from the standard setting value. Set a value where vibration does not occur and the
position droop waveform converges smoothly. Because lowering the VIA causes a drop in the position
control's trackability, the vibration suppression is improved even when a disturbance observer is used
without lowering the VIA. (Be careful of machine resonance occurrence at this time.)
If VIA is lowered, the position droop waveform becomes smooth and overshooting does not occur.
However, because the trackability in respect to the position commands becomes worse, the
positioning time and accuracy are sacrificed. VIA must be kept high (set the standard value) to
guarantee precision, especially in high-speed contour cutting (generally F = 1000 or higher). For
machines which aim to attain a high speed and high accuracy, set VGN1 to a sufficiently large value
so that VIA does not need to be lowered. When adjusting, the cutting precision will be better if
adjustment is carried out to a degree where overshooting does not occur and a high VIA is maintained,
without pursuing position droop smoothness.
If there are no vibration or overshooting problems, the high-speed contour cutting precision can be
further improved by setting the VIA higher than the standard value. In this case, adjust by raising
the VIA in increments of 100 from the standard value.
Setting a higher VIA improves the trackability regarding position commands in machines for which
cycle time is important, and the time to when the position droop converges on the in-position width
is shortened.
It is easier to adjust the VIA to improve precision and cycle time if a large value (a value near the
standard value) can be set in VGN1, or if VGN1 can be raised equivalently using the disturbance
observer.
No. Abbrev. Parameter name Explanation Setting range
SV008 VIA Speed loop lead
compensation
Set the gain of the speed loop integration control.
The standard setting is "1364". During the SHG control, the standard
setting is "1900". Adjust the value by increasing/decreasing it by about
100 at a time.
Raise this value to improve contour tracking precision in high-speed
cutting. Lower this value when the position droop vibrates (10 to 20Hz).
1 to 9999
POINT
Position droop vibration of 10Hz or less is not leading compensation control
vibration. The position loop gain must be adjusted.
Vibration waveform with leading compensation control Adjusted position droop waveform
0
0
Speed FB
0
T mei
0
D/A output range
Time
Time
Time
Position
droop