Fanuc 5T Zero Return Problem

[Stu-Jitsu]

When attempting to do a Zero Return, the machine stops immediately when the decel switch is pressed and refuses to move any more as it should to complete the Zero Return routine. The Zero return indicator does not come on. What could my problem be?

Any help would be appreciated.

[NC Cams]

Did the system work and then all of a sudden quit or is this a problem noted after a return to service after an equipment move?

The ZRN switch inputs and the DECEL inputs are not readily understandble if you read the manual as much or as intently as one can or should. I've read it until I"m blue in the face and STILL don't quite understand it.

My take at this point is that there is an input that should tell the machine to slow down as you approach the end limit stop switch - I finally concluded that this is the DECEL switch.

IT should engage and remain engaged (slow down fast jog to very slow speed) once you get close to either end limit so that the jog won't drive the axis thru the end limit stops and break something.

I came to the conclusion that the ZRN (zero return) switch is actually the HOME switch although it is definitely NOT labeled as such. When tripped, ZRN should immediately stop the machine. As the instructions are in Jinglish, it is not the easiest thing to understand.

Now if the ZRN indicator light does not come on, you could have other problems. However, I seem to recall that the ZRN light is dependant on some other logic conditions to be in effect at the same time for the indicator to come on - it has been a while since I read the manual so I'm perhaps giving bad info here.

First things to do are to power down and then clean and retighten ALL the connector pins from the P/S to the A and B boards - a poor ground will cause all kinds of things to not function well as will bad connections to any of the boards.

Check to see if your switches are truly functioning at the pins where the outside world meets the I/O of the Fanuc (usually at one of the 3 the Honda connnectors at the bottom middle/right of the control cabinet)

Have someone trip the switch and see if the switch changes state NO to NC or vice versa where the switch ties into the machine harness at the Honda connectors.

Make sure you have the proper pull up power going to the ZRN and DECEL switches - my unit has a separate power supply that provides the power for the safety circuit logic.

I hope you have a wiring diagram for the lathe and a Fanuc manual - you'll be hard pressed to figure out what's going on without it, especially if you don't know which pin to look for at the Honda connectors that they used at the machine to outsider world interface.

If you dont' have Honda connectors, you should have something that resembles a MIL connector. Pinouts are different and they are identified either way in the service manual.

If you find that you toasted something on the board, Glen Rowe at Billor Ent in Texas (they have a website) can repair the boards for you. I paid for mine when he did my 5T repairs and I have no other affiliation of any sort with him/them. He can also bench test the boards for a modest fee.

I hope this helps

[Dan Fritz]

The 5T zero return switch is supposed to SLOW the axis to a "creeping" feedrate and then, when the switch drops off the cam it's supposed to stop on the 1-pulse per rev signal from the pulse coder.

To display parameters on the 5T, run the address LED under the letters "PRM", and set the parameter number with the 2-digit display.

It sounds like the parameter that sets that "creeping" speed (parameter 10) is zeroed out. Look at parameter #10. If it's all zeros, then that's your problem.

Other parameters that can mess up zero-return are:

Parameter 00 bit 4 (5th bit from the right). Should be a "1" for the zero return option.

Parameter 00 bit 3 (4th bit from the right). For automatic zero return (G28). should be a "1"

Parameter 09, bits 0 and 1 (two bits on the far right). Bit 0 is for Z axis and bit 1 is for X axis. Both bits should be "0". A "1" is only set for the seldom used magnetic-switch method of zero return.

Parameter 09, bits 2 (Z) and bit 3 (X). Sets the direction of zero-return. Should be "0" if you zero return the axis in the "+" direction, and "1" if you zero return in the "-" direction.

Parameter 10, bits 0, 1, 2, and 3. Sets the creeping speed after the zero return switch is actuated. Must not be all zeros. This is a binary number set in pulses per second (PPS). Set any binary number from 0001 to 1100

Good luck!

[Stu-Jitsu]

Thanks for the replies! The machine has not been moved. This problem has just cropped up.

Unfortunately we have not got to the bottom of it yet. The description given by Dan matches my understanding of how the zero return routine is suppose to work.

I have checked the parameters suggested by Dan and all look OK.

This is what is in the machine:
PRM 00 0111011
PRM 09 0000000
PRM 10 0000010

I have also checked DGN 12, bit 2 (3 from right) (zero return decel switch) and the switch is operating properly.

Do you have any more suggestions? Is there something else in the logic that must be satisfied?

Thanks for your help!