Position Encoding.

Tim Wescott · 2011-12-21T23:13:06+00:00

So, I'm working on an interesting problem. It's somewhat self-assigned, but it'll make it's way into some customer equipment. It's not quite DSP, not quite circuits, but I'm posting it to these groups anyway.The application is an optical encoder -- shine light through a disk at some photosensors, look at the result, and tell the processor where the disk is. There are some tried-and-true methods, but I want to do better.I want to be able to use an encoder to rapidly -- but not immediately -- figure out the absolute position of a wheel. Sort of a hybrid absolute/relative encoder, that's not as expensive as using N strips to get the 2^N precision of an absolute encoder, but that gets you an absolute position quicker than the "go around until you see an index pulse" that you get from a pure relative encoder.My thought is to use a quadrature encoder in the usual way to figure out the relative motion of the wheel, and then back that up by a strip that is encoded in binary (dark = 0, light = 1) with some scheme such that any consecutive string of N positions is unique.And I figured out one such scheme! Take the output of an N-bit LFSR, and lay it down in order. If the idea of having 2^N - 1 bits bothers you, then augment the LFSR such that it has one string of N zeros on its output, giving you a nice even 2^N positions.Then, to figure out the absolute position of the wheel, use the quadrature encoder to to run by N bits in either direction. Use the looked-up bits to determine the position (which you can, because they're unique), and voila! You have the absolute position and can now just use the relative encoder.So my question is: has anyone seen this done? Are there better variations? Is there anyone who makes some sort of off-the-shelf solution that does all that, but cheaper than I could ever roll my own from individual components? My ideal would be a sensor that I could buy off the shelf, and specify to my customer how their code disk would have to be made,...

Dec 21, 2011 446 Replies

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hamilton 14 years ago

The male determines the sex of a new born child.

So you think you have a say in the matter ?

LOL

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krw 14 years ago

No, as my father used to tell my mother (four boys, they were waiting for a girl), it's the woman who chooses.

I say "yes", but...

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Bill Sloman 14 years ago

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Really? Where? Do you exchange e-mails with Jim Thompson - who is also a long way out of touch with reality - in which you swap delusions?

You keep on posting this absurd claim, but you have yet to come up with any lie that I've posted.

This is a lie. Your boot is in the US and any part of me that you might like to kick is in the Netherlands. You may dream of some kind of intellectual equivalent of kicking ass, but - intellectually speaking - you haven't got a leg to stand on, let alone kick with.

You do have these minor cognitive difficulties. If you bothered reading to the end of the posts that you claim to be responding to, you'd find that mine - unlike those coming from AlwaysWrong - all end like this

-- Bill Sloman, Nijmegen

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Bill Sloman 14 years ago

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I'm not stupid enough to do your work for you. If you want to try to present a case that "proves" I'm a liar, you've got to collect and present the data that demonstrates the point. You've established that you'd like us to think that such evidence exists, but until you actually present it, any rational observer will balance your apparent conviction against the - high - probability that you are either deluding yourself, or trying to delude us.

The fact that you haven't is persuasive evidence that you can't.

-- Bill Sloman, Nijmegen

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Jim Thompson 14 years ago

Latest from Agent support...

"No promises but I escalated the feature.

Nice work on the regular expressions. Nice organization so you know what's what." ...Jim Thompson

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Michael A. Terrell 14 years ago

How would 'you' know how Christians think?

You can't have a sense of humor, if you have no sense.

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hamilton 14 years ago

Catching up on old posts ??

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