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From: toto@fwi.uva.nl (Toto van Inge)
Subject: Re: A sense of balance
Message-ID: <1993Feb5.142808.3339@fwi.uva.nl>
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Organization: FWI, University of Amsterdam
References: <1993Jan31.072524.14704@adobe.com> <VBFeyB5w165w@lcraft.ersys.edmonton.ab.ca>
Date: Fri, 5 Feb 1993 14:28:08 GMT
Lines: 59

cduguay@lcraft.ersys.edmonton.ab.ca (Claude Duguay) writes:

>epperson@adobe.com (Mark Epperson) writes:

>> I have been thinking of a sensor for center-or-gravity (balance).  The genera
>> idea is some form of rolling ball inside of a sphere or parabaloid.
>> 
>>    One idea is to use a thin plastic, a rolling magnet, and have a grid of 
>> magnus effect transistors glued to the underside to sense the magnetic flux. 
>> The grid would be scanned to get the values, convert to digital then 
>> interpolate to determine the exact location.
>> 
>>   A similar thing could be done with a LED hanging on a string and an array
>> of photo-diodes.
>> 
>>    Another idea is to put some form of conductive grid on the inside surface
>> and let the ball's weight complete the circuit (or change the capacitance). T
>> trouble with this is I can't thing of an easy way to make the grid.
>> 
>>    A similar approach has a grid of contact switches (button type) poking
>> through the surface, but this may not have the resolution I require.
>> 
>> 
>> What do you think?  How would you solve the problem(s)?
>> - Mark Epperson

>I'm no engineer, but one thing that comes to mind would be to use mercury in
>a bowl container (or sphere) with contacts that would close circuits when
>the mercury overlapped. As a primitive model, you could use wires sticking
>up through the bowl or if you want to get more ellaborate, you could etch a
>grid onto the inner surface. Let me know if you decide to use this idea,
>and please put my name as co-creator on the pattent when you take it out :-).

>Claude Duguay              cduguay@lcraft.ersys.edmonton.ab.ca 

Now lets see, take a ball say, a half one, make a high ohmic layer on the
inner side with for instance a carbon coating. Put three conducting balls
in it (copper, steel) with a size an order smaller than the half ball.
Make four (6,8?) contacts on the edge of the half ball and measure the
resistance across the diameter of it on the 4 (or 6, 8) contacts.
Because the three balls will touch each other they will create an
ohmic dip in the carbon coating. This will influence the measurements
on the edge of the half ball.
Experimenting with size of the three balls and thickness of the
carbon coating is still needed, because I have no idea how accurate
this set-up will be.

However, this thing will behave terrible if it is put into a moving
object that bumps up and down, the three balls will be dancing around
not giving nice results.
And finaly put me also on this pattent as a co-creator, it could be
a nice list :-)

Toto van Inge
-- 
Anthony van Inge Phone: +31 20 525 7533/fax:7490 
EMAIL:           toto@fwi.uva.nl
SNAIL:           Dept. of Math. and Computing Science, University of Amsterdam,
                 Kruislaan 403, 1098 SJ  Amsterdam, The Netherlands
