Help identifying shaft encoder technology

Feb 17, 2010 6 Replies
M

I took a look inside the shaft encoder attached to a DC servo motor and was rather expecting to see a standard A/B quadrature optical assembly with a glass wheel, an LED illuminator and the usual optical pickup assembly.



Whet is ended up with is

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which looks a bit more like a tape head mounted close to a roller wheel.



The head appears to be thin film, and I assume that the wheel is some form of electromagnetic assembly - possibly like a resolver. There is a small air gap separating the two.



Any idea what the name of this technology is and who might be manufacturing it ?



Thanks,



Mark


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R

No idea who made that one but the technique is pretty common. I've seen it used in wind measurement instruments and IIRC the other one was in some domestic application with a magnetoresistive sensor. The wind measurement was single channel only for speed, ie not quadarature.

Looks like quite a few conductors going to the sense head.

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P

The wheel may have several 'tracks' to give better angular resolution.

Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ Rube Goldberg is alive and working for Microsoft.
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F

Usually a fairly broad track, covered by two reading heads, displaced to give quadrature between. It's easier to make than trying to lay down two quadrature tracks.

Probably also a one-pulse per rev "index Z" track, usually a raised cosine pulse shape.

Magnetic encoders are usually high resolution, so there are possibly more than one set of quadrature signals at differing PPR.

"Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)
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A

Googling for "magnetic shaft encoder" finds many, eg:

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Regards, Adrian Jansen adrianjansen at internode dot on dot net Note reply address is invalid, convert address above to machine form.
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R

These guys have some cool mag encoder ICs. I've got a sample kit I must play with one day....

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J

Helpful at least. Looking at the photo i believe it is an at least 8 bit= =20 absolute position encoder. Many of these thing use Gray code.

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