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From: rlk@telesoft.com (Bob Kitzberger @sation)
Newsgroups: sci.electronics
Subject: Re: X-Y detection of moving metal ball?
Message-ID: <1227@telesoft.com>
Date: 4 Apr 91 05:26:55 GMT
References: <1225@telesoft.com> <970024@hpdmd48.boi.hp.com>
Organization: TeleSoft, San Diego, CA.
Lines: 72

Thanks for everyone's help on this!  USEnet comes through once again...
Many have responded via e-mail, and I'm still wading through it all (this
project is done in my 'copious' spare time ;-) so if I neglect to 
send my thanks individually... THANKS.

The 'best fit' to budgetary and time constraints seems to be to go with 
the LED and phototransistor pairings, but, as several folks have pointed 
out, STROBE the LEDs one at a time to remove the dispersion problem.   
Thanks much for that idea (looks obvious in hindsight ;-)

If I can't get this to work (can't see why not) then I'll try a video
approach (gulp).

Andy Hill writes:
> 
>   As stated, the problem is a bit too fuzzy still.  Could you give us more
> details? (such as):
> 
>  1) How big is the ball bearing? (i.e., weight & diameter).

This is flexible, though I'd like to keep it in the 1/4" to 3/4" diameter.

>  2) What kind of resolution are you looking for?

1/4 the width of the ball, approximately.  This really depends on the 
velocity and acceleration of the ball, and hence resolution of the
velocity vector.  I haven't figured out the physics of this application 
yet.

>  3) How "real time" do you want it?  (i.e., what is the maximum velocity of
>     this ball?)

Not very fast... maybe 1-10 inches per second.


Rainer Malzbender writes:

> [whizzy video camera controller setup.  neat]

I should have mentioned that I don't want to spend more than $100 total
for this portion of the project.

> We were interested in obtaining accurate velocities, and hence looked
> into doing better than video rate resolution. Our idea was to use a
> laser bouncing off two piezo-controlled mirrors (x and y) which would
> bounce off the sphere and be detected with a photodiode. Using
> feedback one should be able to keep the beam on the sphere, and the
> control signals going to the piezo mirrors give a direct readout of
> position. Unfortunately we never actually got around to implementing
> this, and I think the optics of the spherical reflection would be
> pretty tricky, but it ought to work.

I spent a little time experimenting with a laser (from R&D Electronics) 
that had a stepper-motor controlled mirror on the x axis, and a fixed
mirror on the y.  $79 (the Right Price).  Not nearly accurate/steady
enough, and the stepper motor moved the laser much too far at each step
(piezo is probably a must here).  But the idea was quite exciting,
more so than any other idea.  I was also concerned, as you point out,
about the spherical reflections... the incident angle would have to be 
very close to zero to deflect the laser properly, no?  This means a 
very small laser step rate.

Again, thanks for all of the help.  Several of you were interested in 
the results, so I'll post a follow up.

	.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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