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ToyMaker
06-10-2003, 07:13 PM
Here's an idea for a cheap HiRes encoder.
An inexpensive optical mouse can be had for US$ 10-20. An optical mouse has an inherent resolution of 400 dpi ( 0.0025" ).
Machine a disk 3.183 inches in diameter. Fasten the disk to the end of your lead screw. Mount the mouse so that it reads the outside edge of the disk.
The circumference of the disk is 10.00 inches. That will give you 4000 counts per revolution! Which with 10 tpi lead screws is 40,000 counts per inch! Or 0.000 025 inch resolution.
This should be enough for the Tim Allen in everyone :)

robotic regards,

Tom

p.s. or, if you machine the end of your lead screw to 0.3183 inches diameter, forget the disk and just read the screw surface for 4,000 counts per inch.

T

HuFlungDung
06-10-2003, 07:17 PM
That is the germ of a good idea, but you need to be sure that the detector reads a known number of irregularities of the surface to get its count, do you not?

ToyMaker
06-11-2003, 12:12 AM
I have tried my optical mouse on every surface I can find including slick coated paper and 'clear' plastic. It works flawlessly on all except a mirror (although I haven't tried on steel). So if the surface finish is not too fine it should work.
In the worst case, you might be able to get away with a piece of paper (or other suitably textured stuff) around the shaft or disk.
But a bigger problem I see is getting just the pulses out of the mouse. By design the beasts encode x motion, y motion, and the switch closures into a serial data stream.

robotic regards,

Tom

HuFlungDung
06-11-2003, 12:44 AM
A lot of CAD programs will give some kind of coordinate output directly proportional to mouse movement.

I'd have to try pushing an optical mouse using my cnc, to find out how repeatable it would be. I would find it surprising if the mouse would not "lose or stretch the distance" for a few pulses every once in a while, depending on the surface, which would be kind of irrelevant for normal mouse usage, but very relevant when using it as an encoder. It would be interesting to know.

balsaman
06-11-2003, 12:48 AM
Buying an encoder for $26.00 would be easier.

:)

But not as fun.

Eric

cbcnc
06-11-2003, 03:04 AM
Hey, there's an answer for a low cost digitizer. Move your mill to a certain spot, drop a probe and read out a straight distance. :)
Or use a $26 encoder connected to a probe as a rack and pinion.

Chris