[howd]

After loss of ACP (dead batteries) I can't get HOME REFERENCE POSITION to stay where I set it with parameter 1815. Okuma lathe with Fanuc 18T controller, sure is drivin me crazy.

[HuFlungDung]

Is this an absolute positioning system with encoder power backed up by battery to maintain track of position?

[howd]

Yes, as best as I can tell. There are 2 C-size lithium batteries hooked in series to make 6 volts. Power is to maintain track of position; and I have been goin at this like it was absolute positioning. I have been into parameters, and can't really tell if it is absolute. I do know for sure that there are no decelleration switches, just the over travel switches.

[HuFlungDung]

I have absolute positioning on my Mits, but I don't know how the setting procedure compares to yours. Something to this effect: first one must find the parameter to turn off absolute positioning (not referring to G90 programming but rather to non-stop monitoring of the position.) Then, the control must be powered down and powered back up. Then, you may need to run through some sort of procedure to reestablish the reference position. Maybe you'll be lucky, and its already set. Anyway, you run through that procedure, then find the parameter to turn on absolute position, power the control off and on again, and it should then be ready to go.

[howd]

Hey HuFlungDung(long name with much meaning), thanks so much for the reply. So far that sounds just like we've been doin, but the home still wanders around. The great thing is, we can move it where we want it, set the parameter to 'position set' and move axis's around and the next thing you know HOME is moved again. I need some super glue. I imagine that there is some stupid and insignificant thing I don't do that then allows things to shift.

[HuFlungDung]

How much 'wander' are you getting? Are you powering down, and then powering back up? Do you see any warnings about the reference position being lost when you reboot?

[howd]

Usually several inches in X or Z, sometimes both are off. Yes, we have been powering down, although not always at the cabinet main disconnect. No warnings, messages, or alarms upon reboot, just an alarm 90(reference position not established). This alarm doesn't show up till we've already noticed our 'distance to go' numbers are way off, then we know we will be seeing ALARM 90.If we are in 'manual mode', home doesn't move, but if we run thru a program, it does. Program could have some problems, but I don't see that as a home movement problem.

[sinha_nsit]

REFERENCE SETTING PROCEDURE
My machine (Fanuc 0i Mate TC) also has absolute encoder, and I am also anticipating this problem, though the battries are still new, so there has been no such problem till date. But, I discussed it with the vendor and he gave the following reply:

THE FOLLOWING IS THE PROCEDURE FOR SETTING REFERENCE POSITION (FOR MACHINES WITH ABSOLUTE ENCODER) IN CASE THE REFERENCE POSITION IS DISTURBED BY ANY REASON :
SET PARAMETER 1815 # 4 (APZ) FOR THE CORRESPONDING AXIS (X OR Z) = 0
SWITCH THE POWER OFF AND THEN ON AFTER A FEW SECONDS.
MESSAGE “---- (X OR Z)-AXIS NEED ZRN” WILL APPEAR ON CRT (NC ALARM).
MOVE THE AXIS TO THE REFERENCE POSITION BY MANUAL JOGGING
(NORMALLY 10 MM AWAY FROM THE EMERGENCY POSITION).
SET PARAMETER 1815 # 4 (APZ) FOR THE CORRESPONDING AXIS (X OR Z) = 1
SWITCH THE POWER OFF AND THEN ON AFTER A FEW SECONDS.
NOW THIS POSITION WILL BECOME THE MACHINE REFERENCE VALUE FOR THIS AXIS.

I am still discussing this issue with the vendor. This method might work, but the new reference position will be different from the old reference position. AS A RESULT, ALL THE PREVIOUS TOOL OFFSET SETTINGS WILL BECOME INCORRECT AND WILL HAVE TO BE DONE AGAIN.
There should be some way to acquire the previous position exactly.
Can you run G28 U0 W0 in the MDI mode (G91 G28 X0 Y0 Z0 on a milling machine) and see if the tool goes to the reference position. If the machine does execute this command, and the previous referencing was done in a similar way, then correct position will be reached, and everything will be okey. It will be like working with incremental encoder.