Rotary 4th axis home position problem

Hello everyone.

Im having an issue with our 4th axis rotary table. Everytime i power off the machine then turn it on again the home position of the rotary table changes by about +|- 2 deg.

The machine is a DOOSAN 5700 mill With fanuc oi control

The actual rotary table is from TJR .

I tried adjusting the zero position stop (the one that works with the proximity switch )

Did not solve issue.

Im hoping someone whos had the same issue can enlighten me with this.

Might have to add some value to a grid shift parameter for that axis. I'm thinking that if the proximity switch happens to trigger too close to when the encoder index also triggers, then the servo will turn almost an additional full turn. Or it may not. Hence the discrepancy in the home position. Grid shift should force a consistent directionality to the servo's homing direction in relation to the encoder index. Just my WAG.

Well, TJR tables are Chinese manufactured. that might give you a clue. Have you tried contacting TJR?. The machine make and model have nothing to do with this. I work for Doosan, wish I could help. You need to take this up with TJR or the the people that sold you this rotary table. We sell and support Koma Precision and Lehman.

Regards,
Paul

qrovin said:

Hello everyone.

Im having an issue with our 4th axis rotary table. Everytime i power off the machine then turn it on again the home position of the rotary table changes by about +|- 2 deg.

The machine is a DOOSAN 5700 mill With fanuc oi control

The actual rotary table is from TJR .

I tried adjusting the zero position stop (the one that works with the proximity switch )

Did not solve issue.

Im hoping someone whos had the same issue can enlighten me with this.

Click to expand...

Is the brake functioning properly?

I'm curious on this one. I have a Haas HRT210 that does this. It's error is .753 degrees.. Just enough to corn hole you if you're not paying attention

The brake seems ok because as long as u dont turn off machine it goes back to same position.
Only when u power off then on is when it changes

To be clear:

Is it drifting off when you go into E-stop?
The DRO follows the movement, but doesn't stop it?
Shirley this doesn't happen with the brake set?
If you have an A0 move in the next line - it will move back to position - no?

Or is it moving, w/o the DRO seeing the movement?

Or it is moving when you power down the control?


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Think Snow Eh!
Ox

If his problem is like mine. You can home it out. Set up a zero.. Shut it down and rehome and have the zero point be off a smidge.

I've had that happen when my proximity switch was too far away from the metal block that it was designed to detect. I didn't need to move it very much closer, but I haven't had the problem since.

ARB said:

If his problem is like mine. You can home it out. Set up a zero.. Shut it down and rehome and have the zero point be off a smidge.

Click to expand...

Then you are saying that the HOMING process is not repeatable?

[not that either of you can likely answer this] but if it is looking for a signal from the platter (L/S / Prox) and THEN a signal from the HOME pulse on the servo motor, then it would need to be a full turn of the motor off. Very possible if the platter pulse is not far away from the home pulse. (180* target differential)
I kan't imagine that you have 1 turn / .753* ???

So - maybe your machines are set up with a piss poor homing routine or something is loose or slipping in the drivetrain between the servo and the worm?


FWIW - I have an axis on one machine that bounces back and forth .015" when homing.
And yes - I believe that axis uses a prox as well. I have had one of the other axi's on that machine home off as well, but not in quite a while now. The machine uses lots of prox's for homing.


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Think Snow Eh!
Ox

Might be worth checking if either the 4th or the interface card has a battery that is low or dead.