engraving depth setting in realtime

While engraving large (ok, 30cm is not really "large") objects, the
thickness of the objects often differs a little bit. Now I will try to change
the settings of the Z-axis in realtime the following way:

A little china-vernier-caliper is read by a pic-microcontroller which sends
the results of a probe near the milling-cutter via serial port/usb to linuxcnc.
Then the Z-axis is raised/lowered based on this values.

The microcontroller delivers the values in freely definable format.
This may be inches, millimeters, motorsteps or what else.

Of course, the major problem will be the mechanical construction of the
probe (vibrations/filings/dust) - but where is the best/easiest place, to
implement the movement of Z ?

Is it in the kins, in HAL or is it possible, to do it in an own background-thread?

I think, it is something like
wiki.linuxcnc.org/cgi-bin/wiki.pl?Torch_Height_Control

but it should be possible, to do it with less overhead - I think....

Yes, look at the plasma torch height control for ideas. The torch height control reads the voltage of the arc which varies with the distance between the torch tip and the work and makes adjustments to the Z axis on the fly. Sample configurations are included with linuxcnc.

Rick G

@wiki,

do you know GCoderipper ?

Why not probe before engraving and just change the origin gcode.
Might be a lot easier.

Norbert

newbynobi wrote:

Why not probe before engraving and just change the origin gcode.
Might be a lot easier.

Yes, I know it.
But I want to do it with only one movement.
I wrote a china-vernier-caliper-readout a long time ago - now this
would be a task to use it for....

First I've tried to manipulate the moving axis by halcmd. That seems
to be impossible.

andypugh wrote:

wicki wrote:

While engraving large (ok, 30cm is not really "large") objects, the
thickness of the objects often differs a little bit. ..

Here is an idea that nearly worked:

wiki.linuxcnc.org/cgi-bin/wiki.pl?ProbeKins

What do you mean nearly worked?

I have had perfect results with probekins.

First I've tried to manipulate the moving axis by halcmd. That seems
to be impossible.

It is possible, look at the moveoff comp.

Norbert

andypugh wrote:

For manual adjustment of an axis position the "Offset" HAL component is probably simpler.

Oh yes - but it only sounds simpler (for me).
I was unable to get it working....

And I also was unable to find even one working example of the use of the offset-compoment.

The number of pins, signals and functions is really overwhelming.....