[Geof]

I fired up my TL2, pushed Auto Restart and wandered away. After a few minutes I noticed the carriage was making its way slowly but steadily toward the chuck.

A pile of chips had been swept up by the guards at the back and was clustered around the proximity detector so it was giving a false signal.

[Donkey Hotey]

I understand the false home signal but why was it heading back toward the chuck? Was it jogging the carriage to get it away from the prox sensor and the chips were preventing that signal from happening?

And I'm curious: you don't 'Auto Shutdown' your TL at night? I find it helpful to have it parked at the tailstock and ready to zero-out right after startup.

[Geof]

If you watch the homing movement the axis moves positive until it activates the proximity detector then reverses direction and moves negative. As soon as it leaves the proximity detector the controller starts counting pulses and waits for the Z channel signal, (Don't confuse this with the machine Z; the Z channel on an encoder is a single pulse once every revolution that gives an absolute position for the encoder.) this signal is what defines the home position. There is a minimum and maximum number of counts that the controller expects to see before the Z channel signal and if either of these are wrong it gives a Zero Return Margin error.

What happened with mine was that the chips activated the proximity detetctor which is what the controller was looking for so it started heading negative. But the proximity detector stayed active so the machine never started counting or looking for the Z signal, it just kept going.

I have had this occur on mills with both microswitches and proximity detectors. If you don't catch it all that happens most times is the axis runs into the hard stop and the servo overloads.

EDIT: Yes I do normally park the machine home for shut down; this is standard practice on all our machines. Bring up Warm-Up program, G28, Power Off.

[Mark Hockett]

Geof,
My TL-1 has done that a few times, now I check it and clean if necessary every time I grease the Z ball-screw.

Mark Hockett

[Geof]

Grease the ball screw? You mean I should be doing that???

Just joking; yes, it will become a standard procedure from now on.

[alain aleman]

Clean the position sensors.

[Geof]

Clean the position sensors.

I did.