Motor Runaway - Omron CS1W-MC221 - 02-2008 Operation Manual

Wiring
2-3-9

Motor Runaway

Runaway Due to Faulty
Wiring
1,2,3...
130
tions between the analog control voltage ground (AG) and the 24-V system
ground (DC GND).
In a servo system employing a Servomotor, faulty or disconnected wiring may
cause the servomotor to run out of control. Therefore, careful attention must
be paid to preventing faulty or disconnected wiring. Also implement the mea-
sures explained in 2-4 Failsafe Circuits for preventing motor runaway due to
such problems.
When the wiring is correct, the servomotor maintains the stopped position
through corrective operations as long as a position loop is formed and servo-
lock is in effect.
Error
counter
Direction
discrimination
circuit
If the motor rotates in the CW direction due to a factor such as temperature
drift, it is detected by the encoder and the internal error counter of the Motion
Control Unit is notified of the direction and amount of rotation by means of
feedback signals given by the encoder.
The count of the error counter is ordinarily zero unless otherwise designated.
When the motor moves in the CW direction, the feedback signal transfers the
direction and travel distance as a count to the error counter. Then the Motion
Control Unit outputs a control voltage to rotate the motor in the CCW direction
so as to zero this count figure.
The control voltage is output to the servo driver, and the motor rotates in the
CCW direction. Again, when the motor rotates in this CCW direction, the
encoder detects the direction and travel distance and notifies the error counter
in the Motion Control Unit with feedback signals to subtract and zero the count
figure.
This position loop subtracts the count in the error counter to maintain it at
zero.
If the phase-A and phase-B feedback input lines are wired in reverse (crossed
dotted lines at 1 in the figure), the servolock will not be effective and the motor
will run out of control.
1. If the motor rotates in the CW direction due to drift or some other cause,
the encoder detects the direction and travel distance and transmits feed-
back signals to the error counter in the Motion Control Unit.
Amp
Control voltage
(2)
Phase A feedback
(1)
Phase B feedback
Section 2-3
Servomotor
Servo
driver
Encoder