Hijacking position control with a laser or other sensor signal?

Hi

This will be a pretty unusual request, so apologies if this seems strange.

Our application is not actually machining, we are using LCNC to drive a machine across a surface and our process is more akin to 3d printing.

I would like to use a single point laser to measure the distance from the "print head" to the surface, and then have the head move to preserve a set distance, by overriding the commanded position along our z axis by some small amount.

I am guessing this is unlikely to be something you would normally want in a CNC package, but can you suggest which LCNC software modules I might look into modifying to send an "on the fly" modifier to the commanded position, as well as if LCNC can accept sensor inputs? I know this is all a little vague, I am collecting ideas around how to do this at the moment so any suggestions are welcome!

Cheers

Ross

Something like feed back from an encoder, is that one way of descrbing it ?
The distance you have to move to preserve the distance could be considered an error ?

This is almost identical to Plasma THC (Torch Height Control)
This also "hijacks" the Z position to maintain the plasma torch at
a fixed distance above the work (that may be uneven or warp)

One way this is implemented is by using "External Offsets"
Which I believe is now integrated into LinuxCNC 2.8:

linuxcnc.org/docs/2.8/html/motion/external-offsets.html

I thought that would be a better description just before I looked at your answer.

Note that a number of sims are provided to show how external offsets can be used.

So if your sensor outputs an analog voltage denoting distance, you could use a Mesa THCAD and an encoder input to accurately measure that voltage. then you can calculate the required offset to apply.

Thanks guys, this sounds super promising! I will check it out today and revert back with any further questions.

Really appreciate the help!