Fanuc 18i with right angle head

[blackx-runner]

We got a new to us, but used machine at work. Vanguard vertical bridge mill running a fanuc 18i control. Absolute encoders. Also has a 4th axis (C) right angle head. The issue we are having is in referencing the C axis. Manually referencing the C-axis after a power down it does as expected. Rotates a couple revolutions and picks up a position and the control shows the axis as referenced. Where we run into problems is when a G28 C0 is commanded. It will rotate to the correct position, but then throw an alarm 90 error - Reference Return Incomplete-

Fanuc's Alarm Description: The reference position return cannot be performed normally because the reference position return start point is too close to the reference position or the speed is too slow. Separate the start point far enough from the reference position, or specify a sufficiently fast speed for reference position return. Check the program contents.

The axis rotates as it should, so I would assume we don't have an issue with the start point being too close. As for the speeds, its programmed with a G0 and all the over rides - even though I don't think they do anything - are set to 100%. The parameters for the speed all check out as fast enough per the book.
Just seems odd that it will pick up a position and appear correct manually homing, but using a G28 throws a Reference Return Incomplete alarm. Anyone got any ideas on this one?

[fordav11]

your thinking logic is not correct.
G28 is used to home an axis VIA another position.
C is absolute so you are telling it to go to C0 then it tries to zero return
But at this point you are already at zero return C0 so you get that alarm.
You can try incremental G28 H0 (H is the incremental axis for C so there's no movement then it should go home). This is equivalent to G28 U0 V0 W0
Or go home via another absolute position like G28 C10
Or just G0 C0 in the program.
On later controls with battery-backed position encoders you don't need to zero return an axis unless it is out of position or not already zero returned. Even if it's not battery-backed you don't need to zero return any axis unless you power off/on. It'll run all day to the correct positions just using G0/G1 as long as it has been zero returned once.

[blackx-runner]

your thinking logic is not correct.
G28 is used to home an axis VIA another position.
C is absolute so you are telling it to go to C0 then it tries to zero return
But at this point you are already at zero return C0 so you get that alarm.
You can try incremental G28 H0 (H is the incremental axis for C so there's no movement then it should go home). This is equivalent to G28 U0 V0 W0
Or go home via another absolute position like G28 C10
Or just G0 C0 in the program.
On later controls with battery-backed position encoders you don't need to zero return an axis unless it is out of position or not already zero returned. Even if it's not battery-backed you don't need to zero return any axis unless you power off/on. It'll run all day to the correct positions just using G0/G1 as long as it has been zero returned once.

The reason for the necessary zero return of the C-axis is to re-sync everything after running the spindle. Get the spindle drive dogs oriented to the correct angle the head is locked into.

G0 C0 will not work correctly. If we are running with our C-axis head at 0 degrees the C axis absolute position remains at 0 while the spindle is running. when the spindle stops and we activate the c-axis and give it a G0C0 command to get the drive dogs in the proper postion they will remain in whatever postition they stopped at. This is the reason we are using the G28 command.

[hitachibos]

G28 has to be done incrementally on a mill .......G91 G28 C0
G28 U0 or W0 only works on a lathe

then dont forget to go back to G90

[blackx-runner]

G28 has to be done incrementally on a mill .......G91 G28 C0
G28 U0 or W0 only works on a lathe

then dont forget to go back to G90

same results either way. The C-axis does move to the correct position, then after doing so it will throw the alarm code 90. It almost seems like it expects a marker or switch to be at that location. When it doesn't get the expected signal it gives the alarm.
What we can't figure out is if there is actually a marker its looking for that isn't working correctly. And if there is why when we manually refernce the C-axis it finds a postion - same postion every time - without throwing any alarms.

[hitachibos]

did you try G28 H0

??

[blackx-runner]

did you try G28 H0

??

Ya, didn't do anything.
We found a parameter right at the end of the day that didn't seem right. Got that changed and did a quick test and didn't throw any alarm. We'll have to check a little closer tomorrow make sure everything is working correctly, but right now things are looking a little better.