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5 Servo Adjustment
MITSUBISHI CNC
5.2.2 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 "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 30000
POINT
Suppressing the resonance with the vibration suppression function and increasing the VGN1 setting is effective for
adjusting the servo later.