Omron CS1W-MC221 -, Operation Manual

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131
Wiring Section 2-3
2. If the phase A and phase B feedback input lines are wired in reverse, the
error counter receives the information as a rotation in the CCW direction.
3. As a result, the error counter having a count in the CCW direction attempts
to zero the count by outputting a control voltage to the motor driver in the
CW direction.
4. The servomotor rotates in the CW direction, repeating the above steps 1.
to 3. Eventually, the motor runs out of control.
Runaway can occur not only from reversed wiring of phases A and B of the
feedback inputs, but also from reversed wiring of the speed control voltage
and the ground lines (crossed dotted lines at 2 in the figure above).
Runaway Due to
Disconnected Wiring The servomotor runs out of control not only when the position loop is not cor-
rectly formed but also when the position loop is not interrupted due to discon-
nected wiring.
1,2,3... 1. Wire breakage while the servomotor is rotating:
While the servomotor is rotating, the speed control voltage is not 0 V be-
cause of the signal from the error counter. If the feedback line is broken,
no feedback signals will be given to the error counter and the speed control
voltage remains unchanged from the value existed before the line break-
age, causing motor runaway.
2. Wire breakage while the motor is stopped:
If the feedback line is broken while the servomotor is stopped and correct
feedback signals cannot be returned, the speed control voltage remains at
zero without changing. Therefore, the servomotor also remains stopped. In
fact, however, the motor may move in one direction without stopping.
This is caused by a discrepancy between the 0 V of the MC Unit’s control volt-
age and the 0 V of the servo driver’s voltage input.
When the two 0 voltages do not match, an electric potential difference is gen-
erated, resulting in a false control voltage. This in turn causes the servomotor
to move in one direction without stopping.
Error
counter
Amp
Direction
discrimination
circuit
Control voltage
Servo
driver
Servomotor
Phase A feedback
Phase B feedback
Encoder
Broken lines
Speed control
voltage (0 V)
Difference in electric
potential
Servo driver
voltage input (0 V)