Centroid Community CNC Support Forum

Hi Folks,
I inadvertently over torqued my Clearpath motors running a job. After I cleared the motor fault with the MSP I gave the machine a G28 MDI and it didnt even come close to coming to machine zero. I then powered the whole system down and back up again. When Acorn was opened, I hit the green button to home and off it went to the limit switches as normal.

Im a novice to this kind of thing so go easy on me, but what is the difference between a G28 and the Acorn homing routine?

Thanks in advance,
Doug

Due to the fault, your machine coordinates were no longer accurate and you needed to "Reset Home" first (which is why restarting corrected it). G28 is a specific machine coordinate location that can be set as needed in the WCS config screen.

From the manual....

G28 moves to the first reference point, by way of an intermediate point. The location of the reference
point, in machine coordinates, may be set in Work Coordinate System Configuration. The intermediate
point is specified in the local coordinate system, and may be at the current location (resulting in a move
directly to the reference point). If an intermediate point is specified, only those axes for which positions are
specified will be moved. If no axes are specified, all axes will be moved.The location of the intermediate
point is stored for later use with G29. Movement is executed at the maximum (rapid) rate but can be
changed using the L word.

FWIW G
The default G28 position is machine home (machine 0's) but you can set it to what ever you like.

As Scott(Sword) pointed out, because you are running an open loop system, when your motors stalled the control had no way of knowing the axes hadn't actually moved to the position they had been commanded to go to. Once that happens the only way to rectify it is by re-homing the machine - theoretically you could just set a new part zero and squeak by but if you do that your travel limits, park position, any other WCS in use and everything else that uses machine position as a reference will no longer be reliable.

Ok, that makes sense. After I rebooted, the G28 brought it back to machine zero. Losing the steps is kinda what I figured happened. Just wanted to make sure. Since the wizard is set to limit switches, I couldn’t figure why it just wouldn’t continue to run till those tripped.
That’s for the input.
Doug

As noted, there is a button, RESET HOME. You should do that immediately after a crash or fault. Once you crash, 1 or more of your coordinates will be wrong, and if you send the machine back to "HOME", it will more than likely crash into the limit switch, etc.

If you crash a machine, rehome it. "When in doubt, home it out" applies to Acorn and open loop systems.
How accurately the machine homes is dependent on the quality of the switches on the machine and the machine's repeatability.
Good proximity sensors will generally be better than mechanical switches. But there are some good quality mechanical microswitches out there.

Marty

Thanks Marty.
Appreciate everyone’s advice.