Zero return does not work on a fanuc 6m

[alfaguilar]

I have an acroloc machining center, that sudenly did not want to home, I do the Zero return but it always overtravels on X, Y and Z, I have checked the limit switches but they seem to be ok, when it hits the middle switch it does not slow down, any help will be appreciated.

[Al_The_Man]

Have you checked power on the switches?
Sounds like you have lost the power to all somewhere.
Al.

[mfgbydesign]

First thing I usually check is the inputs. Don't remember exactly how to do it on that control, but there is a page you can bring up that shows the I/O. Toggle the switch manually and see if you get a bit to change zero to one. If no input its a switch circuit. If input is working you need to check the ladder logic to see what other condition is not being met.

[Al_The_Man]

Originally Posted by mfgbydesign First thing I usually check is the inputs. If input is working you need to check the ladder logic to see what other condition is not being met.

Good idea, the status is on the diagnostic page, if you have the schematic of the inputs it will tell you the bit number to check.
Unfortunately the ladder does not display on the 6.
Al.

[Dan Fritz]

Sounds like the control can't see the ZRN (Zero Return) input. If you jog or rapid toward the limit switches, it will just overtravel like you describe. If you turn on the ZRN input, it's supposed to slow down when it hits the zero-return switch cam, then drop off the cam, then find the "1 pulse per rev." signal on the pulse coder.

You didn't mention what model CNC this is. Some controls use encoder feedback with battery backup, so the "zero" point is never supposed to be lost. Older controls must manually zero-return every time you power up, or they won't know where machine zero is.

Acroloc used several different Fanuc models, starting with the 3000C and system 6M. Those had resolver feedback with no battery backup. Let us know what control you have and we can give you the diagnostic bit for that ZRN signal. If the panel switch for ZRN is not seen by the control, that would explain your problem.

[alfaguilar]

Thank you very much for your prompt response.
I will discribe more what I have done.
Originally The machine would go over the limit switch and make a noise like something being forced (it even crashed against the hard stopper making a big noise while running a program), then it would alarm, I had to turn off the whole machine then it could recover from that, I looked at the limit switches and I found out there was an open wire, I resoldered it to the switch then it did overtravel but the limit switch would work stoping the movement.

So, my situation right now is that the machine does not slow down when pressing the decel switch (it seems that the decel switch is not there) then overtravels, when making the zero return on all 3 axis.

I have checked the " Pressing P and CAN keys while boots up" and makes no difference I have also pushed the decel switch down and check diagnostic #32 bit 5 for X axis , #33 bit 5 for Y axis and #34 bit 5 for Z axis and they all change from 1 to 0 when the switch is pressed.

Before all this I was playing with parameters 24 25 and 26 to make the RS232 comunication, I did make that to work but now I dont know if I messed up another parameter related with the zero return because I only realized this after downloading my program, once I was ready to test the program machine gave me the alarm 010, for any program we try to run it gives this alarm, then we figured out the machine needed to be home, so here we go with this problem.
My controller only goes up to parameter 166, some other posts talk about parameter 1815 bit 5 I guess but this machine does not have it.
I am running out of ideas, any help I will appreciate it

[alfaguilar]

Yes I did not say what control it has.

Here is what the machine has.
On the CRT screen appears Sistem 6m 991 VER. 2
On the control panel it says GN series

[Dan Fritz]

You have an early model Fanuc 6M (sometimes called the "6M-A") with resolver feedback.

Press the DGNOS key and page up to show diagnostic 101. This is an 8-bit register where you can see the status of some input signals. The bit on the FAR LEFT is for the ZRN input. When you rotate the operator's panel mode switch to the "Zero return" position, that bit should change from "0" to "1". If it does not, there may be a problem with the panel switch, or you may have a bad input for the ZRN input on the I/O board.

Hope this helps.

[alfaguilar]

Dan thank you very much,
I will check that tomorrow.
I am new with this, sorry to ask you but where is the I/O card located? aslo I don't have any documentation for this control, where could I get something, that would help me troubleshoot the Zrn switch signal.

[alfaguilar]

I checked the signal on the DGNOS key to show diagnostic 101.
The bit on the FAR LEFT "Zero return" position, changes from "0" to "1".
so that means the signal from the zero return switch goes to where it is supposed, the signal from the decel switch goes to were it is supposed to.
what else do I need to check?
is there any parameter that that could be causing this?
Thanks in advance

[mfgbydesign]

I do not have an answer for you but suggest now that DNC is working backup your parameters. There should also be a paper copy in the control that shows factory original settings. You could compare to see what's changed.

[alfaguilar]

how do I make a back up?