Axis re-homes during operation - only using soft limits

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09 Aug 2018 03:51 #115838 by stoneumbrella
We have a Probotix CNC carver using a PBX-2 board. It’s a little long in the tooth but runs very well except for a strange bug we have been experiencing recently.

While carving, the system will suddenly re-home the X-axis about 2 inches from where it should be. This always happens on the X-axis and seems to occur when the carve is planning to mcve to a new depth (change in Z).

The system is not hanging up nor does it show any error messages. The X-home just changes value resulting in the machine moving to the touch-off value which is now about 2 inches away from where it should be. As an example:

Start of Cut:
X home: 0.5
Touch off X = 0.0

Random X home change at some point in cut:
X home: 2.5
Touch off: 0.0

So, now the machine moves 2 inches (back to zero) and then begins the cut - cutting right through the stock in totally the wrong place.

This does not always occur in the same place. Does the sytstem lsiten for some homing instruction? Could noise be triggering a signal? We have no homing or limit switches. We set the home by hand and use software limits.

We are cutting in “negative” space (0, -18) along the x and y axes. This is so we can start in the back corner of our carver and face stock that is too talll for our gantry. Perhaps cutting in negative directions is somehow causing this.

Thanks for your help.
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12 Aug 2018 00:38 #115931 by cmorley
When you say 'rehome' do you mean linuxcnc goes into homing mode or do you mean your home position moved.
The first would be super odd.
The second sounds like missed steps.

Chris M
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16 Aug 2018 11:37 #116127 by andypugh
Or something funny in the G-code. G92, G10, one of those.
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