YASKAWA SGM-A3 User Manual page 23

(4) Servo amplifier
A servo amplifier is required to operate an AC servomotor.
The following figure illustrates the configuration of a servo amplifier:
Reference
input
A servo amplifier consists of the following two sections:
(a) Comparator
A comparator consists of a comparison function and a control function. The com-
parison function compares reference input (position or speed) with a feedback
signal and generates a differential signal.
The control function amplifies and transforms the differential signal. In other
words, it performs proportional (P) control or proportional/integral (PI) control.
(It is not important if you do not understand these control terms completely at this
point.)
(b) Power Amplifier
A power amplifier runs the servomotor at a speed or torque proportional to the
output of the comparator. In other words, from the commercial power supply of
50/60 Hz, it generates alternating current with a frequency proportional to the ref-
erence speed and runs the servomotor with this current.
Proportional/integral (PI) control
TERMS
PI control provides more accurate position or speed control than proportional control, which
is more commonly used.
Servo amplifier
Power
amplifier
Comparator
Feedback
Commercial AC power
1.1 Basic Understanding of AC Servos
Motor driving AC power
Servomotor
1
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