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From: macminn@powertool.crd.ge.com (Stephen R MacMinn)
Newsgroups: comp.robotics,comp.lsi,sci.electronics
Subject: Re: velocity sensing for robotic joints
Message-ID: <10848@crdgw1.crd.ge.com>
Date: 8 Aug 90 03:11:46 GMT
References: <1990Aug7.205751.21206@ecf.utoronto.ca>
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Reply-To: macminn@powertool.crd.ge.com (Stephen R MacMinn)
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Organization: General Electric Corp. R&D, Schenectady, NY
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In article <1990Aug7.205751.21206@ecf.utoronto.ca> apollo@ecf.utoronto.ca (Vince Pugliese) writes:
>assuming one is using optical encoders (with 2-phase output)
>to measure position of a (rotary) robotic joint, what should one use
>to then measure velocity??
>
>two possibilities come to mind:
>
>1) use the position encoders with some sort of digital differentiator

This is pretty common.  You could (for instance) just look at the
frequency
of the pulse train coming from one channel of your encoder, although
that wouldn't give you direction.  Its a little more tricky in your
application because the joint probably spends a lot of time loitering
near zero velocity.  In that case there is a minimum speed that you
can control to, determined by your encoder resolution, with a stable
control system.

>2) a specialized velocity encoder 

...also pretty common.  A DC tachometer is probably well suited to
this application.  If you wanted to change sensors, you could get both
position and velocity information from a resolver with R/D converter
at up to 16 bits of accuracy.