Omron SYSMAC CJ Series, Operation Manual

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Servo system principles Section 1-4
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1-4 Servo system principles
The servo system used by and the internal operation of the CJ1W-MCH72 are
briefly described in this section.
1-4-1 Semi-closed loop system
The servo system of the CJ1W-MCH72 uses a semi-closed or inferred closed
loop system. This system detects actual machine movements by the rotation
of the motor in relation to a target value. It calculates the error between the
target value and actual movement, and reduces the error through feedback.
1-4-2 Internal operation of the CJ1W-MCH72
Inferred closed loop systems occupy the mainstream in modern servo systems
applied to positioning devices for industrial applications. The figure shows the
basic principle of the servo system as used in the CJ1W-MCH72.
1 The CJ1W-MCH72 performs actual position control. The main input of the
controller is the Following Error, which is the calculated difference between
the demand position and the actual measured position.
2 The Position Controller calculates the required speed reference output
determined by the Following Error and possibly the demanded position and
the measured position. The speed reference is provided to the Servo
Driver.
3 The Servo Driver controls the rotational speed of the servo motor
corresponding to the speed reference. The rotational speed is proportional
to the speed reference.
4 The rotary encoder generates the feedback pulses for both the speed
feedback within the Servo Driver speed loop and the position feedback
within the CJ1W-MCH72 position loop.
The labels in the figure are:
A CJ1W-MCH72.
B Servo system.
C Demand position.
D Position control.
E Speed reference.
F Speed control.
G Motor.
H Encoder.
I
Measured speed.
J Measured position.
A B
C
D
J
I
E
F
G
H
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