Omron CJ1W-NC271 - 12-2009, Operation Manual

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Phase Z Margin
Section 8-5
8-5 Phase Z Margin
8-5-1 Description
Although there are some variations for different settings, the PCU's origin
search basically works by latching (detecting) the first encoder phase Z after
confirming ON/OFF status of the origin proximity signal, performing position-
ing for the final travel distance to return to the origin, and then setting that
position as the origin.
When the time (distance) from when the origin proximity signal changes from
ON to OFF until the first phase Z is detected is extremely short or is almost
the same as the time taken for one rotation of the Servomotor, the position at
which the phase Z is detected may be displaced by one phase due to discrep-
ancies in the ON response of the origin proximity sensor or the Servo Drive
speed. This displacement is prevented by confirming the “phase Z margin.”
The phase Z margin indicates the amount by which the Servomotor rotated
during the time from when the origin proximity signal changed from ON to
OFF until the phase Z 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 proba-
bility of this is to adjust the Servomotor's mounting angle or the origin proxim-
ity sensor's mounting position so that this value is approximately half a
rotation of the Servomotor.
Example: Final travel distance to return to zero point = 0
8-5-2 Calculating the Phase Z Margin (Example)
One method used to obtain the phase Z margin is to perform jogging after ori-
gin search in the opposite direction to origin search, with the final travel dis-
tance to return to origin set to 0. Then 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 is equal to the
phase Z margin.
If the speed at the point when the origin proximity signal turns ON is fast,
there will be some inaccuracy in the value read for the phase Z margin.
Reduce the speed of the jogging in the vicinity of the point where the origin
proximity signal turns ON.
The required phase Z margin can be obtained by adjusting mounting positions
and angles so that this position corresponds to approximately half the dis-
tance moved for one rotation of the motor.
Time
Servomotor rotation
This distance is the phase Z margin.
Phase Z signal
1
0
Origin proximity
input signal