Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!ucsd!telesoft!rlk
From: rlk@telesoft.com (Bob Kitzberger @sation)
Newsgroups: sci.electronics
Subject: X-Y detection of moving metal ball?
Message-ID: <1225@telesoft.com>
Date: 30 Mar 91 05:48:37 GMT
Organization: TeleSoft, San Diego, CA.
Lines: 75


Hi All,

I've got a 'pet project' problem that is generating a lot of ideas among
colleagues at work, but NO concrete solutions.  (concrete solution ==
part numbers and source for parts ;-)  

And no, this isn't a school project ;-)

Problem: I want to detect the X and Y coordinates of a metal ball bearing
(magnetized or not) in motion within a box.  The data collection must
occur in a fashion that allows me to derive the velocity vector of the ball
bearing in the X-Y plane.  The size of the box is approximately one foot by one
foot.  Also, I should mention that the detection must occur in real-time.

We have a few ideas so far, but all of them use parts which are, to me,
hypothetically available.  I would appreciate any other ideas, or even
more importantly, sources for these 'hypothetical' parts.

1. Array of LEDs and corresponding phototransistors, one array for the
   X direction and one for Y:

        +-L-L-L-L-L-L-L-+
        |               |
        L               P
        |    B          |               L = LED
        L               P               P = phototransistor
        |               |               B = Ball
        L               P
        |               |
        +-P-P-P-P-P-P-P-+

    The idea is to detect when the ball bearing breaks the light path for
    a L/P combination.  The timing between light path breaks allows
    determination of the velocity vector.

    This is my cleanest solution, but I haven't been able to find a source
    for the LED/phototransistor pairs that won't disperse over the 
    distance involved (one foot).  Ideas/sources?

2. Laser detection.  Admittedly high-cost/complexity, this approach would
   use a laser pointed down at the box, with stepper motors to deflect 
   X/Y mirrors, and hence deflect the laser position.  As the laser
   bounces off of the ball bearing, it would be sensed by a sensor mounted
   next to the laser's 'head'.

   Problems: incident angle of laser light on a round ball bearing; source
   for inexpensive (<$100) laser setup, including relatively accurate
   positioning mechanism.  Fun, though ;-)

3. Matrix of 'energized' wires, detecting a magnetized ball in a manner
   similar to core memory devices.  These wires would be equally spaced,
   under the surface that the ball rolls on, parllel to both X and Y axis.
   This seems like it would work, but nobody here has a strong enough 
   electrical background to tell me how to detect when the ball rolls 
   over one of these wires.

4. Hundreds of Hall-effect switches under the surface that the (magnetized)
   ball rolls on.  Distasteful soluution, in my mind, due to the cost of
   hundreds of Hall-effect switches, and the drudgery of soldering them 
   all onto a PC board 1x1 feet.  Anybody have a source for _cheap_ 
   hall effect switches?

5. Video camera mounted above.  Perform pattern recognition for a ball bearing.
   Just kidding!  I know this option is silly.

That's it.  Thanks for any help!!

	.Bob.
-- 
Bob Kitzberger               Internet : rlk@telesoft.com
TeleSoft                     uucp     : ...!ucsd.ucsd.edu!telesoft!rlk
5959 Cornerstone Court West, San Diego, CA  92121-9891  (619) 457-2700 x163
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