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Re: Absolute Rotary Encoders


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Thanks for the information Adam, do you recommend any specific brands?.
The Sick Stegman unit I was looking at has a metal disc of nickel alloy,
something like invar I assume, would it be likely to last longer?.

Re: Absolute Rotary Encoders


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I couldn't say for sure as I've no experience with that product. If the
atmosphere in the encoder was inert (eg argon) then that would help.
I'd definitely want extended warranty.

Data Devices Corporation (US) manufacture the Resolver to Digital
converter cards & IC chips. There are some export restrictions that can
apply, to prevent their use in missile guidance systems and the like.

Harrowe make resolvers but It's been a while and I'm not sure if they
make dual speed units or not (electrically geared not mech gearing).

Re: Absolute Rotary Encoders


A little more on why not optical.

The least significant bit in the optical wheel will (assuming binary
encoding and not BCD etc). will change state 2^18 times per rotation.
this means cutting a slot for the LSB every 2nd place or ever 2^17.

Lets assume our optical encoder is 1 meter in diameter (a bit rediculous
but anyway) the circumference will be 1xPI simplifies to PI.

lets change to millimeters 3141.5mm so our graticule spacing is
3141.5/(2^17) = 0.02mm spacing, pretty bloody fine spacing.

As always when putting maths on the web it's probably full of in correct
assumption and mistakes, so take it with a grain of salt, and do your
own calcs.

Cheers
Adam

On 26/03/2010 10:28 AM, Adam Anderson wrote:
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Re: Absolute Rotary Encoders


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The optical spot size of a Blu-ray disk is 580nm, over four orders of
magnitude smaller. Shouldn't be an issue to get 2^18 resolution.

David

Re: Absolute Rotary Encoders


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A lot of these discs are glass with a sputtered aluminium mask, any
moisture and you'll get corrosion or fungus. I've found a unit which
may work but lower in resolution, it comes with a 2 year warranty.

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