Re: Probing

[Doug Fortune <pentam-at-home.com>]

Pete Cook wrote:
> 
> Has anyone thought of a non-contact probe - One of the infrared type prox
> switches might work - they bounce a signal off the surface and trip at some
> distance from the surface - might have to be close to perpendicular for the
> best results - Might be a bit more pricy but somewhat harder to smash...

These analog sensors are not too expensive: 
Inexpensive: $15, cheaper in packs of four   
Simple to Use 
Small (3 x 1.5 x 1.4 cm) 
Connects directly to any microcontroller with A/D 
Detection range: 10 cm to 80 cm (4" to 31") 
Low microprocessor overhead (uses only 1 I/O line and a few
                       lines of code) 
Probably a great use for the analog input of a
Scenix SX28 microcontroller!  

http://www.hvwtech.com/sensors.htm

They also have digital output ones for $25, but 
the analog ones would be better because of the 
continuous output (I think for the digital ones 
you'd have to stop, take a reading, read in the 
serial stream, and then go again) leading to 
much (100 times?) faster data aquisition using the
analog version. 

I am considering them to do a pre-pass scan 
in order to have the computer plan a detailed 
run with a physical touch probe. 

Regarding probe software, I was giving away C 
code last week to convert from a 'point grid' 
(ie a regular X*Y matrix of Z elevations) to 
STL (which of course can be converted to GCode 
by a number of programs including Millwizard and 
Deskproto).  It has a limit of several hundred 
million points, so that should keep your digitizers 
humming for a long long time! 

If you want the code (compilable for Linux, and 
also I've got an .exe for Windoze), please email 
me offline (from my website), and I'll email you 
a copy Sunday when I get back to town. 

BTW, I reserve the term "point cloud" to refer 
to an arbitary grouping of XYZ data points. 

Doug Fortune 
http://www.cncKITS.com 

http://www.cncKITS.com