Mitsubishi Electric MELDAS MDS-B-SVJ2 Series Specifications And Instruction Manual page 113

(2) Setting the speed loop lead compensation
The speed loop lead 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 as shown in the graph in section 4-2-3 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 and 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.)
Speed FB
0
Position
0
droop
Vibration waveform with leading compensation control
If VIA is lowered, the position droop waveform becomes smooth and overshooting does not occur.
However, because the trackability regarding the position commands becomes worse, that amount
of positioning time and precision 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). In
other words, a large enough value must be set in VGN1 so that the VIA does not need to be
lowered in machines aimed at high-speed precision. 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
SV008 VIA Speed loop lead
compensation
POINT
Chapter 5 Adjustment
D/A output range
1364 is set as a standard. 1900 is set as a standard during SHG
control. Adjust in increments of approx. 100.
Raise the VIA and adjust to improve the contour tracking precision in
high-speed cutting. If the position droop vibrates (10 to 20Hz), lower the
VIA and adjust.
Position droop vibration of 10Hz or less is not leading compensation control
vibration. The position loop gain must be adjusted.
0
Time
0
Time
Adjusted position droop waveform
Explanation
5-5
Time
Time
Setting range
1 ~ 9999