As I was merrily mousing away on my computer, it occured to me that I was holding a precision(?) position sensing device. I wonder if you could somehow lash a mouse (or two) to a mill or lathe and use the output to run a DRO-like app on a laptop. Sort of a poor man's Trav-a-dial. With an appropriate surface finish, you might even be able to use the guts of an optical mouse so you wouldn't have to worry about oils attacking the rubber mouse ball. I checked on-line, and some optical mice are running at over 500 signals per inch, so that would get you to the 0.002" accuracy level.
The trick would be attaching the hardware, and then making use of the signals. You might be able to use the touchpad/joystick for regular mouse input, but you'd need a way to snag the mouse signals and get them into a program with readouts & a calibration routine.
Here's a link to a site to do your own computer-based DRO using a few simple parts and the software to make it work. Not exactly what you were asking for but might gove you some ideas. Respectfully, Ron Moore
Check out the Logitech Laser - very high accuracy.
Kinda nice - have one in the shop for CAD.
I think the issue will be the target it senses - an optical grating...
Martin
Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder
Place two objects as stops on your mouse pad, perhaps two cups of latte. (I used drillpress vises.) Move your optical mouse from stop to stop and back, observe how well (not!) the cursor on the screen returns to where you started.
A mouse is a "man-in-the-loop" device we learn to use by watching the cursor and responding appropriately. They might have .002 resolution but they definitely don't have that level of repeatability or accuracy.
The above test is a fallacy. For user convenience, the mouse driver accelerates the cursor exponentially to the mouse acceleration. For example, to move your cursor a fixed distance diagonally from corner to corner of the screen, the distance the mouse has to travel is less, if the mouse is moved "fast", than it is if the mouse is moved "slow". Or, put another way, the mouse driver software varies the resolution inversely proportional to mouse acceleration.
The above test failed because the acceleration of the mouse going forward was not the same as the accerleration of the mouse coming back. Note that we are talking about acceleration, not speed. There is a difference.
The original poster's idea would actually work, if:
a) it were an optical mouse and
b) the mouse driver only counted pulses and ignored the change in rate per unit time they were coming in at.
To bring this idea to fruition, you would have to write your own mouse driver for this specific application or, better still, skip the computer completely and hook the mouse up directly to a pulse counter circuit that feeds a DRO of some sort. Off the top of my head, I'd say that a circuit like this, complete with DRO, could be built for about $100 per axis, mouse included.
You can find a building block circuit for a DRO here:
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You can hook together as many building block circuits as you need, one building block circuit per digit.
Here is a mouse that produces 1000 pulses per inch:
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a 5-digit DRO constructed from the building block circuit above will allow you to read up to 99.999 inches of travel directly off the display without any additional circuitry to handle conversions from pulses per inch to inches of travel.
The question of the day is whether or not the mouse produces EXACTLY
1000 pulses per inch; although, you can probably fudge things with a correction factor and a pocket calculator if it doesn't. The pulses coming out of the mouse should be very close to the advertized 1000 per inch.
Interesting! I tried it again moving ver-r-r-ry slowly, and it did repeat quite well. Further, if it were constrained to move over the same fairly high-contrast optical path each time I can see how it should repeat.
The counting, scale factor correction and display driving could be done with a microcontroller available for well under 10 bux. A serial mouse (rather than USB) would probably be easiest to work with. I'd want a DRO to be repeatable to better than .001", but this mouse scheme might be OK for woodworking.
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