Yaskawa Large Capacity Sigma II Series - Manual (Page 23)

1.2 Configuration of Servo System
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4. Servo Amplifier
A servo amplifier is required to operate an AC servomotor. The following figure illus-
trates the configuration of a servo amplifier:
A servo amplifier consists of the following two sections:
• Comparator
A comparator consists of a comparison function and a control function. The comparison
function compares reference input (position or speed) with a feedback signal and gener-
ates 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 1 . (It is not impor-
tant if you do not understand these control terms completely at this point.)
• 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 gen-
erates alternating current with a frequency proportional to the reference speed and runs
the servomotor with this current.
5. Host Controller
A host controller controls a servo amplifier by specifying a position or speed as a set
point.
For speed reference, a position control loop may be formed in the host controller when a
position feedback signal is received. Yaskawa machine controller MP920 is a typical
host controller.
1 Proportional/integral (PI) control
PI control provides more accurate position or speed control than proportional control, which is more
commonly used.
Servo amplifier
Reference
input
Motor driving AC power
Comparator
Power
amplifier
Feedback Servomotor
Commercial AC power
TERMS