Yaskawa Large Capacity Sigma II Series - Manual (Page 17)

1.1 Basic Understanding of AC Servos
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To develop such a servo system, an automatic control system involving feedback control 1
must be designed. This automatic control system can be illustrated in the following block
diagram:
This servo system is an automatic control system that detects the machine position (output
data), feeds back the data to the input side, compares it with the specified position (input
data), and moves the machine by the difference between the compared data.
In other words, the servo system is a system to control the output data to match the specified
input data.
If, for example, the specified position changes, the servo system will reflect the changes.
In the above example, input data is defined as a position, but input data can be any physical
quantities such as orientation (angle), water pressure, or voltage.
Position, speed, force (torque), electric current, and so on are typical controlled values for a
servo system.
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Feedback control
A control method in which process variables are returned to the input side to form a closed loop. It is
also called closed-loop control. If a negative signal is returned to the input side, it is called negative
feedback control. Normally, negative feedback control is used to stabilize the system. If feedback is
not returned, the control method is called open-loop control.
TERMS
Configuration of Servo System
Specified position
input
Servo
amplifier
+
-
Servo-
motor
Controlled
machine
(load)
Machine position
output
Feedback part
Detector