Where should I head on a probe? (Was:Digitizer probe progress)

Now that I understaand the flexability of a probe (thanks to
Graham), it has landed on my "to do" list of things to obtain and/or
build. So I've got some questions:

1) Where do you find a probe or what major components for a home
built one are redily available? Is there something used for another
funtion (joystick turned upside down? ;-) that could provide parts?

2) OK, lets say a probe is obtained/built. Grahams process to
digitize an object is clever and works, but an easier way with less
steps would be more useful for mear mortals like me. The ability to
find the boundries of a piece of material (for use as a reference
point) would be helpful most CNC programs (MACH2 for example). I
may be wrong, but it should remove the requirement to hand measure
everything when beginning a new project.

3) While I understand that tool paths will not be optomized, and
tools/feeds/speeds will have to be hand entered, it would offer the
oportunity for a CNC program to act as a duplicator. Once the
boundries of the original probed, a marix of points (of a user
selected resolution) could be collected. The program could then
suggest an appropriate size/shape tool based on "best fit" of three
tool botton shapes, of 3 user selected sizes each to create a
duplicate of the work with a simple tool back and forth (don't know
technical term for it) path.

I think having this work done within the context of either CAM or
CNC software would be beneficial to all. While the final results
would be better served if this function was done at the CAM (or even
CAD) level, since only the CNC software has the ability to control
the tool, this is the only loigical place to start. The ability to
export the probed grid in a couple of popular formats for importing
into CAM packages (DXF, etc.) may be helpful for those people who
prefer to use their CAM software for better optimization and then re-
import back into the CNC system.

What are proples views on the above and where do you think I should
be heading/looking from this perspective.

Thanks and regards,
Jeff

With apologies to Graham, I have copied a number of his explanations
below so that I can find them easily.

I have uploaded the file digitizer_result.jpg to the files section.
It shows my homemade digitizer probe mentioned a few posts ago and
the results of some digitizing.

I wanted something small, easy to recognise to digitize and the
raised text on this spanner seemed to fit nicely.

The scan was over a 6mm X 10mm area with a 0.2mm grid size.

The computerized results are from Rhino. Here is my process:

Open the surface .dat file produced by TurboCNC ($20 and excellent)
in excel as a tab delimited file. Remove the header and the X, Y
and
Z columns. i.e. the format used is X 1.0 Y 2.0 Z 4.0 you need to
have 1.0 2.0 4.0 with just tabs between. So just remove the columns
with the letters.

Copy the data and paste into notepad, save as a .txt

Start Rhino and import as a point file.

To get at the points select the cloud and use the explode command to
seperate them. The grid type view was created from poly lines using
create polyline from points. This was done in both directions. It
saves time to do this from the side views as there is less dragging.

The rendered version was done by lofting a surface over the lines
but
in one direction only. I can't do rendering so it looks a little
tatty. I should also mention that the lofting often fell down and
it
was done in sections.

cheers,

Graham Stabler


I realise my example digitize wasn't a good one as it was a metalic
object and could have been digitized in just the same way as you
describe. I should have gone for a plastic object really.

Cheers,

Graham

p.s. Next one is going to have to be ultrasonic.

Graham:

Thanks! Your description was extremely helpful.
Now I "get it." The patent number 6553682 (from
a subsequent post) was useful too.

Again, thanks!

-Wayne

Yes, it detects where the tool is. it (should) slowly crash into the
work. so slowly and so carefully that it doesnt hurt anything or
move anything. In CNC EDM, we use detect voltage drop to determine
when the tool
(plus) touches the work (-). When the voltage difference dissapears,
we know we 'touched, and record this data.
For what? well we can touch the top to determine the surface
height. We can touch a bunch of tool to some surface to find tool
length differences. We can touch two sides to find a middle, or 4 to
find a center.
Some mills do this with a 'skip cycle'. So if you can insulate the
work or the tool ( either one ) a 12 volt dc source at maybe 50 to
100 mA can be used as the sense voltage, and it's absense can be
detected to trigger a position capture in the CNC. tomp

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@n...>
wrote:

>
> OK, the probe itself is screwed into a hub and from this hub

protrude

> three metal arms. These arms are insulated electrically. Each

arm

> sits between two bearings and hence makes an electrical connection
> between them. The PCB clamps down onto the balls, holding them in
> place and also making an electrical connection to them. There are
> two wires from the probe one connects to one part of the pcb which
> goes to just one of the balls, the current goes from the pcb to

ball

> to rod to ball ... until it leaves by the other wire.
>
> i.e.
>
> Wire
> pcb
> ball-rod-ball
> pcb
> ball-rod-ball
> pcb
> ball-rod-ball
> pcb
> wire
>
> So if the probe tilts in any direction or is pushed up then the
> circuit is broken and the computer knows to stop moving. The hub

is

> held against the contacts using a spring BTW.
>
> I have uploaded pics of results now, see my other post.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "tomp_tag" <tomp_tag@i...>
wrote:

> Yes, it detects where the tool is. it (should) slowly crash into

the work.

> so slowly and so carefully that it doesnt hurt anything or move

anything.

> In CNC EDM, we use detect voltage drop to determine when the tool
> (plus) touches the work (-). When the voltage difference

dissapears,

> we know we 'touched, and record this data. For what? well we can
> touch the top to determine the surface

height.

> We can touch a bunch of tool to some surface to find tool length
> differences. We can touch two sides to find a middle, or 4 to find

a

> center. Some mills do this with a 'skip cycle'. So if you can
> insulate the

work

> or the tool ( either one ) a 12 volt dc source at maybe 50 to 100

mA

> can be used as the sense voltage, and it's absense can be detected

to

> trigger a position capture in the CNC.
> tomp