[ragman]

Hi all. I have an old Yang HMC / Fanuc OMD which has developed a problem with zero return on Y.
Despite using P/Cancel, it continues to go into overtravel when I try to Zero Return it. It decelerates when it initially hits the first trip dog, but refuses to find zero. To release it from O/T, I hold in the O/T release button and manually wind it away. X and Z axes are working perfectly. Does anyone have any ideas on what to look for next?

[ben_heinman]

It may just be that the soft limit switch is getting stuck in when it runs over the dog. If you spray some WD-40 onto the button of the limit switch and work it in and out may solve your problem. If a stuck switch is not the problem. You probably just need to open your Y axis positive stroke limit. They are usually set around 2000 - 6000. I'm not sure what the parameter # for this control would be, but you should be able to find it in your parameter or maintainence manual. Open that limit to 999999 and then home the machine with the overides turned down low. Once the machine has found that home position you can change the parameter back to the original setting.

[Al_The_Man]

With an 0MD you should have the ladder available, also you can check the inputs with the diagnostic screen for the home limit.
If you trip the dog manually prematurely the axis should go into the zero routine and look for the marker, if the marker is not present for some reason it will keep on going, if the grid shift is too large you will see the effect also by the premature tripping.
Al.

[ragman]

I can manually activate the limit switch (before it reaches the trip dog) and the machine will stop and indicate that it is at Zero Return. If I let the switch run up and aong the trip dog, the axis will just continue on into overtravel.

[Al_The_Man]

0507 - 0511 is the grid shift for each axis (Y=508).
You can either try lowering this or moving the dog farther away from the O.T. switch.
Al.

[ragman]

Thanks for the replies to date! What gets me is why has it changed?? Switched off the previous day after a faultless run, then next day at start up........no way!

[ragman]

Late News - All good..........Chips are flying again. Thanks to all.

By the way Al, I found the Grid shift Parameter for Y to be 509.

[stevo1]

So what was the fix?? Was it the gridshift parameter??

Stevo

[ragman]

So what was the fix?? Was it the gridshift parameter??

Stevo

I ended up changing the grid shift amount on Y and also moved the trip dog down a little. I also found that the reference position on the job I had set up as well as the G30 tool change position needed to be reset - not a big problem, but something to keep in mind. (Y only).