[mccafferty]

We are having a problem with a Fanuc O-T controller on a SuperMax lathe. Part way through a program that has been used for years, it generates an error. The diagnostic code indicates an over current on the Z axis (bit 5 of the 0721 diag param). We have changed the servo, the servo amp, the axis board, and the associated cables. It does not happen at the same point in the program, but always happens when it is cutting metal in the Z axis. The servo stall current is rated at 5.9 amps. With an AC current clamp on the servo motor, we get from 1 - 2.2 amps. However, it will be running along and trip out.

I have a list of the original parameter list. The parameters from 8245 to 8265 have to do with the digital servo. I have the values, but do not have a description of what the parameters are. Does anyone know if one of these parameters deal with the current trip value?

On the schematic of the servo amp, there are 50m Ohm series resistors used to measure the phase current. There are traces on each side of the resistor for this measurement, but I can't tell where they go. Is the A/D conversion to determine the current don on the servo amp module, the axis board, or somewhere else in the controller?

Like I say, we have replaced everything that we (as well as a couple of support services) think has to do with Z axis overcurrent. The carriage moves very nice and smooth and the program has been used to make the same part for years.

We are at our wits end. Does anyone have any ideas?

Thanks,

Terry

[DocHod]

I'm not familiar to this problem and this might be a shot in the dark but it may not have to do with your servo , but if there is a heat overload it may be as simple as a bad fan in the main cabinet.

[ktb100]

We had the same problem with a Miyano, Fanuc OT-C. We found out the thrust bearings on the ball screw were bad. Really strange because it would still cut and hold good size. After replacing them, we never saw the alarm again (2 years now) Our best guess was that the servo motor had to be fighting for position and causing the over current.

Good luck and please post back to let us know what you find.