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or misuse of techniques shown in this web page. We simply publish information
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You Say You Can't Make Your Machine Zero Return?
by Michael Saylor of CNC Engineering and Service
For most of the Fanuc Series Controllers (FS) OT,16/18T,10/11T you can have
a condition where upon every time you attempt a Zorn (Zero Return), a Soft Limit
Over Travel occurs. This is especially troublesome with the Z axis of vertical
machining centers and the X axis of turning centers. These axes tend to drift
during the night. When this happens, here's what you do:
Release NC Soft OT alarm by Jogging away from the limit. Turn the control's
power off. Depress the "P" key and the "CAN" (cancel) key
and keep them depressed when you turn the control on (continue holding P and
CAN until CRT Display comes on. Release "P" and "Can" keys.
Attempt Zero Return again. Pressing P and CAN makes the control ignore the soft
limit, and resets at Decel via prox. If the axis over travels again, more than
likely you have a bad Zrn Switch. Usually a Proximity Limit Switch. Check the
machine maintenance drawing for schematic and DGN associated. Check the DGN I/O
bits or ladder while placing a metal object in "Proximity" of the
switch face. Note: Even though an indicating led works, it doesn't always mean
the switch is good.