Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!caen!uflorida!mailer.cc.fsu.edu!sun13!murray
From: murray@sun13.scri.fsu.edu (John Murray)
Newsgroups: sci.electronics
Subject: Re: X-Y detection of moving metal ball?
Message-ID: <2642@sun13.scri.fsu.edu>
Date: 31 Mar 91 21:18:39 GMT
References: <1225@telesoft.com>
Organization: SCRI, Florida State University
Lines: 68

In article <1225@telesoft.com> rlk@telesoft.com (Bob Kitzberger @sation) writes:
|
|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?

Standard solution: put the phototransistors down an inch or two of tube.
Depending on how professional you want it to look, you could probably
use black-painted soda straw... You don't *have* to put the leds down 
tubes, but you might want to, to even up the acreage chewed up around the
box.

Anyway, this is your cheapest solution.

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

Silly? What's so silly about it? ;-) (paint the floor black and the ball
white, and it's a piece of cake.. with a fast enough computer..)

|That's it.  Thanks for any help!!
|
|	.Bob.
|-- 
|Bob Kitzberger               Internet : rlk@telesoft.com
|TeleSoft                     uucp     : ...!ucsd.ucsd.edu!telesoft!rlk
|"Wretches, utter wretches, keep your hands from beans!"	-- Empedocles

-- 
*Standard Disclaimers Apply*|        ---Get Out Of HELL Free!---
John R. Murray              |The bearer of this card is entitled to forgive
murray@vsjrm.scri.fsu.edu   |Himself of all Sins, Errors and Transgressions.
Supercomputer Research Inst.|                                -- D. Owen Rowley