Re: Scanner/Digitizer skip function/probe details?

Alan M wrote:

>Yes, I was thinking about that, an encoder wheel on a dial
>indicator, or a photo-interrupter actuated by a vane (needle) moved
>by a contact. Or strain guages. What I haven't figured out is
>how to get 3D. 2D from the strain guages, but 3rd is tough.
>Maybe if object was on a rotary table (C axis), then we could
>approach in more limited directions? Any ideas?

Alan,

Check back in the archive for the last time we talked about this.
IMO,the most easily attainable method (besides the maxNC 'christmas
tree'tripod switch arrangement) is to set the probe tip in high
frequency motion of VERY small amplitude, and watch for a freq shift
(upon contact). This appears to be the way the roland digitisers
work. Cheap, fast, repeatable. The potential problem is "what happens
when you change probe length? Or mass?" On the rolands', the probe is
a fixed wire (piano/music wire??).

Re strain gauges. The problem here is accomodating overtravel.
Otherwise, the xy (as you say) is easy, just split a rod into three
parts, join w/ S/G's and encase in some firm 2 part urethane. The
third axis could be done as follows:

Mill a slot across the end of a 2 rods. fasten a square thin metal
diaphragm across the slot of the first rod(by pins/screws thru the
corners into the 'forks' of the rod). Mount the S/G to this. Now
fasten the other two corners of the diaphragm to the 2nd fork the
same way. This second fork will mount the rod previously described.
The first rod mounts to the machine.

Depending on the size/thickness of the diaphragm, and if overtravel
is not a concern, one S/G MAY be enough used this way. Remember, we
want to know if we hit ANYTHING, in ANY direction!

>I'm thinking each G61 move "collects" a data point, and they are
>saved in .DLG format (Digital Line Drawing), .DEM (Digital Elevation
>Map), .DXF or Gcode.

Always good to accomodate multiple file formats, as long as the
project still gets done!?!

Hope this helps.

Ballendo