Basics Of The Servo System - Mitsubishi Electric MELSERVO-J2 Series Instruction Manual

9. ADJUSTMENT

9.1.2 Basics of the servo system

Position command
generation section
Speed Operation
A general servo system configuration is shown above. The servo control system consists of three loops:
current loop, speed loop and position loop. Among these three loops, the response of the inside loop must
be increased 4 to 6 times higher. If this condition is not satisfied, vibration will be generated. If the
condition further worsens, hunting will occur.
(1) Current loop
For the servo amplifier, the response level of the current loop is factory-set to a high value and need
not be adjusted. If the motor is installed to the machine, the response of the current loop will hardly
vary.
(2) Speed loop
Response will vary according to the inertia moment of the machine. When the load inertia moment
increases, the response of the speed loop will reduce. Use the speed loop gain (VG2) to compensate for
the reduction of the response level.
Speed loop response fv[rad/s]
m : Loop inertia moment ratio
J load inertia moment
L
J servo motor shaft inertia moment
M
(3) Position loop
The response level will not vary according to machine conditions.
Position loop response fp[rad/s]
When the motor is installed to the machine, the gain must be adjusted to satisfy fv
to the load inertia moment ratio m.
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pattern
Deviation
counter
Time
Position loop
Amplifier gain setting VG2[rad/s]
J
L
J
M
amplifier gain setting PG2[rad/s]
search engine
PG2 VG2
Position Speed
control control
section section
Current loop
Speed loop
1 m
9 - 2
Servo motor
Current Power
control control Motor
section section
Encoder
4 to 6fp according