Re: Probing

["Dean L. Hedin" <dhedin-at-vsi.net>]

> I need to get onto EMC, if for no other reason than that the development I
> do can be shared.  I'm running with regular linux, with the clock rate
> turned up to 1000 HZ.  This works well for me, especially with the new
> motor drivers I should be getting back from the PCB shop in a about two
> weeks.

So does this mean you are using some kind of comercial controlling
software?

> Doug (I think it was Doug) has a nice optical interrupter probe.  Thanks
> for the pictures.  Your probe should give good repeatability.  I opted for
> a switch (partially because I had a bag of them), and did some limited
> repeatability testing.  For me, it was a good thing, as I have distroyed
> three switches so far.  Programming errors have jammed them into the work
> surface and crushed the switches.  As you can see from the picture, I chuck
> the switch in place of a cutting tool.  Once, I got the sequences wrong and
> turned on spindle power with the probe installed.  Fortunately, it wasn't
> so out of balance that everything self-destructed.
>
> This is a picture of my probe:
> http://files/cgi-bin/next-res.pl?home_album=/Processed/Carl%27s%20Projects&;
>b
> asedir=./Processed/Carl%27s%20Projects/Stewart%20Platform/Truck%20Signs&res
>= svga&name=PA250761.JPG&album_name=Truck%20Signs

Tried the link but I could'nt get there.  Sure would like to see it.

>
> My application was much simpler than determining the 3D shape of a model.
> I needed to carve some line art, photographs, and lettering into cherry
> panels.  For the photograph to look good, I needed to be able to carve
> closely to the surface, which required that I know where the surface was.
> Being glued-together wood boards, there was warpage and more unevenness
> that I could ignore.  I used the probe to map the surface height in a grid,
> and then bilinear interpolated the Z offset I needed at each point.
>

Interesting.  I was thinking of making a similiar utility to take the Deskcam 
Font output and use the probe "point cloud" so that you could conform the text
onto a curved surface.

> Does EMC include a provision for surface mapping?

This is what we are presently discussing.  At this point EMC supports a single
probe move.  We would like to automate it so as to cover regions and to 
collect the probe data (aka "point cloud" ) and to store it within a generic 
file format so as to allow post processing utilities to operate on this data, 
like your bilinear interpolater.

We believe initial coding will be easy.  The tough part is defining the file 
format and a probing strategy that it is generic for all n-axis machines.

The external programming interface to EMC is through tcl/tk interpreter 
extensions.   Using this scripting language one can use commands to
execute what would otherwise require g-code, including the probe command.

It should also be possible to call the tcl/tk EMC extensions directly from "C"
using the mktclapp tool  http://www.hwaci.com/sw/mktclapp/.   

I am hoping that Ray could contribute to the tk gui "probe setup" and I could 
write the probing stuff in "C".    If for some reason mktclapp does not work
then the whole thing will be in tcl/tk. I am going to do some initial code 
testing on Friday.  I am going to take the existing "single shot" probe script
and see if I can spawn a "C' program to perform some EMC commands
on my mill.