Omron CJ1W-C113 - REV 02-2008, Operation Manual

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Z-phase Margin Section 6-8
Therefore, the Origin Stop Flag will not turn ON when the present position
passes through 0, such as occurs when positioning from –100 pulses to 100
pulses.
6-8 Z-phase Margin
6-8-1 Description
Although there will be some variations for different settings, the PCU origin
search basically works by stopping pulse output with the first encoder Z-
phase after confirming ON/OFF for the origin proximity signal, outputting error
counter reset, and determining that position as the origin.
In cases where the time (distance) from when the origin proximity signal
changes from OFF to ON until the first Z-phase is detected is extremely short
or is almost the same as the time taken for one rotation, the position at which
the Z-phase is detected may be displaced by one phase due to discrepancies
in the ON response of the origin proximity sensor or the Servo Drive speed.
This displacement is avoided by confirming the “Z-phase margin.” The Z-
phase margin indicates in pulses the amount by which the motor rotated dur-
ing the time from when the origin proximity signal changed from ON to OFF
until the Z-phase was detected. If this value is close to 0 or close to one motor
rotation, there is a possibility of origin displacement during origin search. A
simple way of reducing the probability of this is to adjust the motor’s mounting
angle and the origin proximity sensor’s mounting position so that this value is
approximately half a rotation.
Origin Search Operation
6-8-2 Calculating the Z-phase Margin (Example)
One way of obtaining the Z-phase margin is to, after origin search, perform
jogging in the opposite direction to origin search, stop operation at the point
where the origin proximity signal changes from OFF to ON, and read the
value of the present position at that point. The value of this present position
will be equal to the Z-phase margin. If the speed at the point where the origin
proximity signal changes from OFF to ON is fast, there will be some inaccu-
racy in the value read for the Z-phase margin. Try to reduce the speed of the
jog feeding in the neighborhood of the point where the origin proximity signal
changes from OFF to ON. By adjusting mounting positions and angles so that
this position corresponds to approximately half the distance moved for one
rotation of the motor.
Motor rotation
Origin proximity signal
Z-phase
Time
This distance is the Z-phase margin.