Newsgroups: comp.robotics
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From: nagle@netcom.com (John Nagle)
Subject: Re: Stretch sensors?
Message-ID: <nagleD86qv9.94D@netcom.com>
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
References: <3oblel$m48@linda.teleport.com> <3oe8gc$10ma@newsgate.sps.mot.com>
Date: Sun, 7 May 1995 01:59:33 GMT
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Sender: nagle@netcom4.netcom.com

rxjf20@email.sps.mot.com (Doug Shade) writes:
>In article <3oblel$m48@linda.teleport.com>
>nyquist@teleport.com (Nyquist Newave) writes:

>> Does anyone know of some kind of sensor that can return a measurable 
>> value when it is stretched?

     Sure.  Strain gauges are used that way.  Ones of both wire and silicon
are available; the silicon ones generate much larger outputs.  Strain
gauges are generally suited to measuring the stretch of materials like
steel, rather than, say, rubber.  Signals from straing gauges are typically
small, and good low-noise amplifiers are required.

     For larger stretch motions, try conductive elastomers.  The Atari
PowerGlove uses conductive elastomer stretch sensors.  Not too accurate,
and there are hysteresis problems, but cheap, simple, and easy to do.

     There's a cute sensor from Bonneville Scientific which measures
the thickness of a piece of rubber by ultrasonic means.  A sheet of Kynar
is used as driver and receiver.  I have one of these, and it works, but
the drive electronics is complex and subject to interference from AM 
broadcast stations.

     There are other approaches.  What are you trying to do?

     Don't have sources handy, but look in Thomas' Register or SENSORS
magazine.

					John Nagle

    
