So i was brainstorming one night a couple months ago on how to build the ultimate edge finder for my cnc router. It had to be small, low cost and easy to interface.
and then in a moment of genius?, i thought - what about those little pointing devices found on IBM laptop keyboards, otherwise known as trackpoints.
essentially these devices are 2 axis (sometimes 3) strain gauges, with a on board micro controller to interface the analog signal into a mouse movement.
I made up a mount using an air cylinder and linear slide bearing, which allows me to bring the probe up and down about 2 inches.
On the end of the strain gauge, i made an adapter to attach a standard indicator probe
I stole the trackpoint from an old IBM laptop i had (you could buy used keyboards on ebay for under 10 bucks), and wired up a mouse cable to it. It also allows you to plug in your standard mouse - so you don't loose that capability. (just don't move your standard mouse while the edge find routine is running)
in the end, i'm pretty happy with the outcome. It seems to repeat within +/-.001" or so, and with some tweaking it be capable of less error. Sorry i'm lacking many pictures at the moment, but i did put up a quick video
general operation is.. get the probe close to the object (.030" or so). lower it. tell it which axis and direction to move in. it then moves in .001" increments until mouse movement is detected. zeros axis, and moves away from edge in opposite direction.
[ame]http://youtube.com/watch?v=1yN3G4da6VI[/ame]
feedback welcome