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4 Servo Adjustment
MITSUBISHI CNC
4-3-2 Speed loop gain
(1) Setting the speed loop gain
The speed loop gain 1 (SV005: VGN1) is an important parameter for determining the responsiveness of
the servo control. During servo adjustment, the highest extent that this value can be set to becomes
important. The setting value has a large influence on the machine cutting precision and cycle time.
[1] Refer to the following standard VGN1 graphs and set the standard VGN1 according to the size of
the entire load inertia (motor and machine load inertia).
[2] If the standard VGN1 setting value is exceeded, the current command fluctuation will increase even
if the speed feedback fluctuates by one pulse. This can cause the machine to vibrate easily, so set
a lower value to increase the machine stability.
<When machine resonance does not occur at the standard VGN1>
Set the standard VGN1. Use the standard value if no problem (such as machine resonance)
occurs. If sufficient cutting precision cannot be obtained at the standard VGN1, VGN1 can be
raised above the standard value as long as a 70 percent margin in respect to the machine
resonance occurrence limit is maintained. The cutting accuracy can also be improved by adjusting
with the disturbance observer.
<When machine resonance occurs at the standard VGN1>
Machine resonance is occurring if the shaft makes abnormal sounds when operating or stopping,
and a fine vibration can be felt when the machine is touched while stopped. Machine resonance
occurs because the servo control responsiveness includes the machine resonance points. (Speed
control resonance points occur, for example, at parts close to the motor such as ball screws.)
Machine resonance can be suppressed by lowering VGN1 and the servo control responsiveness,
but the cutting precision and cycle time are sacrificed. Thus, set a vibration suppression filter and
suppress the machine resonance (Refer to section "4-4-2 Vibration suppression measures"), and
set a value as close as possible to the standard VGN1. If the machine resonance cannot be
sufficiently eliminated even by using a vibration suppression filter, then lower the VGN1.
【#2205】 SV005 VGN1 Speed loop gain 1
Set the speed loop gain.
The higher the setting value is, the more accurate the control will be, however, vibration tends to
occur.
If vibration occurs, adjust by lowering by 20 to 30%.
The value should be determined to the 70 to 80% of the value at which the vibration stops.
The value differs depending on servo motors.
Aim at the standard value determined by the servo motor type and load inertia ratio to adjust.
---Setting range---
1 to 9999
Suppressing the resonance with the vibration suppression function and increasing the VGN1 setting
is effective for adjusting the servo later.
POINT