Automatically limiting Z travel distance to soft limits during Z probing

[tommaso-b]

When performing Z probing for PCB engraving I often ran into the problem that the G38.2Z command caused a soft limit violation, accompanied by the requirement to perform a new homing cycle.
During Z probing the given Z distance in the G38.2Z command is anyhow not expected to be reached.
Instead the Z probe making contact with the PCB stops travel immediately.
So why not making Z probing more intelligent and avoiding soft limit violations ?

I implemented an automatic limiting of Z travel distance during Z probing. In case Z travel would exceed the soft limits, the Z movement is limited to the Z soft limit. Thus a soft limit error is avoided and the travel does not exceed the soft limit values.

Now I can start at any height a simple Z probing, without running into soft limit violations.

Example for my machine which has Z soft limit of 80:
G21G91G38.2Z-99F100

The given distance value -99 is automatically set to 80 during probing, i.e. no soft limit error will be triggered.

I have seen that other GRBL users are disabling the soft limits during Z probing to avoid the limit error.
My proposed solution is safer as limits are still in place.