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4 Servo Adjustment
MITSUBISHI CNC
(3) SHG control
If the position loop gain is increased or feed forward control (NC function) is used to shorten the settling
time or increase the precision, the machine system may vibrate easily.
SHG control changes the position loop to a high-gain by stably compensating the servo system position
loop through a delay. This allows the settling time to be reduced and a high precision to be achieved.
(SHG: Smooth High-Gain)
(Feature 1) When the SHG control is set, even if PGN1 is set to the same value as the conventional
gain, the position loop gain will be doubled.
(Feature 2) The SHG control response is smoother than conventional position control during
acceleration/deceleration, so the gain can be increased further with SHG control compared to
the conventional position control.
(Feature 3)With SHG control, a high gain is achieved so a high precision can be obtained during contour
control.
The following drawing shows an example of the improvement in roundness characteristics with
SHG control.
Shape error characteristics
During SHG control, PGN1, PGN2 and SHGC are set with the following ratio.
PGN1 : PGN2 : SHGC = 1 : 8/3 : 6
During SHG control even if the PGN1 setting value is the same, the actual position loop gain will be
higher, so the speed loop must have a sufficient response. If the speed loop response is low, vibration
or overshooting could occur during acceleration/deceleration in the same manner as conventional
control. If the speed loop gain has been lowered because machine resonance occurs, lower the position
loop gain and adjust.
No. Abbrev. Parameter name
Setting
ratio
Setting example Explanation
Setting
range
SV003
(SV049)
PGN1
(PGN1sp)
Position loop gain 1 1 21 27 33 39 48
Always set with a combination
of these three parameters.
1 to 200
(rad/s)
SV004
(SV050)
PGN2
(PGN2sp)
Position loop gain 2 8/3 56 72 88 104 128
0 to 999
(rad/s)
SV057
(SV058)
SHGC
(SHGCsp)
SHG control gain 6 126 162 198 234 288
0 to 1200
(rad/s)
(F=3000mm/min ,
ERROR=5.0µm/div)
-50.0 50.00.0
0.0
-50.0
50.0
[1] :
C
ommanded path
[2] : SHG control (PGN1=47)
[3] : Conventional control (PGN1=33)
Conventional
control
SHG control
Control
method
Roundness error (Ǵm)
2.5
22.5
<Effect>