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Sigma II User's Manual
6.4 Servo Gain Adjustments
This section describes information on the basic rules of gain adjustments in the servo
amplifier, adjustment methods in a variety of cases, and reference set values.
6.4.1
Servo Gain Parameters
The following parameters must be set properly for servo gain adjustments.
•
Pn100: Speed loop gain
•
Pn101: Speed loop integral time constant
•
Pn102: Position loop gain
•
Pn401: Torque reference filter time constant
If the servo amplifier is used in the speed control mode with the analog voltage refer-
ence, the position loop is controlled by the host device. Therefore, position loop
gain is adjusted through the host device.
If the host is not available for adjustments of position loop gain, set the speed refer-
ence input gain in parameter Pn300. If the set value is improper, the servomotor
may not run at top speed.
6.4.2
Basic Rules of Gain Adjustment
The servo system consists of three feedback loops (i.e., position loop, speed loop,
and current loop). The innermost loop must have the highest response speed and the
middle loop must have higher response speed than the outermost. If this principle is
not followed, it will result in vibration or poor responsiveness.
The servo amplifier is designed to ensure that the current loop has good response
performance. The user needs only to adjust the position loop and speed loop gain.
The servo system block diagram consists of the position, speed, and current loops, as
shown below.
Speed
Speed control mode
Position control mode
In case of position control
Pulse
train
Speed pattern
+
Error
-
counter
Time
Position loop
Host controller (prepared by the user)
Host controller
(prepared by the user)
In case of speed control
Analog
voltage
K
+
P
Speed K
V
control
(D/A con-
-
block T
verter)
i
Speed loop
Servo amplifier
Servo amplifier
K
= Position loop gain
P
K
= Speed loop gain
V
T
= Integral time constant
i
6-26
Chapter 6: Servo Adjustment
Motor
+
Power
Current
SM
conver
-
limit
sion block
block
PG
Encoder
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