High resolution, low cost, quadrature encoders

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We can I source (I'm in Australia), high resolution (better than 10000 steps
per revolution) quadrature encoders prefereby with index signal ?



Re: High resolution, low cost, quadrature encoders



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I can't tell you, off-hand.  But I did work on 10000 count/rev optical
quadrature encoders for medical infusion pumps (actually writing the
software for testing them in real-time at up to 300 rpm while
adjusting and aligning them against their cams and then tightening
them and gluing them once they met spec.)  These included the homing
pulse (and more, actually.)  So that may be one market area to examine
for sources of these units.  It wasn't _more than_ 10000 counts,
though.  So if you are looking for better, I haven't experienced it.

Jon

Re: High resolution, low cost, quadrature encoders



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steps

A question if I may. Why so many steps? Has it to do with how fine the
infusion adjustment needs to be?

Jason



Re: High resolution, low cost, quadrature encoders


On Tue, 30 Aug 2005 19:10:50 GMT, "Jason James"

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I can't say for sure.  I was worried about the details of monitoring
both the A and B quadrature inputs at rates of 50000 counts/second or
roughly every 20us -- but since there could be sloppy +/- 25%
variations in A or B timing, I had to be good enough to sample at
rates better than 5us or so to be sure to catch everything.  Reality
was even better than that, luckily.

But I was mired in the details and didn't ask the big questions like
"why?"  I merely assumed that they had a reason for it.

Jon

Re: High resolution, low cost, quadrature encoders



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The size of the encoder sets limits. There used to be a company near me in
the UK (Gaebridge), who made the encoder disks, and would even do 'custom'
units. On the 50mm model, they offered up to 36000ppr 'off the shelf', and
could go even higher in a larger casing model. The company died a couple
of years ago, but models of similar resolution are available from
encoders-uk. Two things limit the resolution. The disk size (obvious), and
the support accuracy of the shaft. If (for instance), you have a 50mm
encoder disk, running full quadrature decoding on a 36000ppr disk (giving
potentially 144000 positions), The steps at the edge of the disk,
correspond to just 1um, and if the shaft moves laterally by this amount,
the count will change. Hence the high accuracy units have very tight
specifications on the shaft loadings, and use very expensive bearing
designs...
Why worry about the source being in Australia?. Most companies will ship
anywhere, and may even have agents. Search for the product first, then
worry about where it is.

Best Wishes



Re: High resolution, low cost, quadrature encoders



[snip]

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Then there are absolute sin/cosine wave encoders, no steps are
lost, thanks to their absolute nature.

Here's a nice encoder:
http://www.usa.canon.com/html/industrial_encoders/x1mnonrot.html

230 million pulse per revolution, no less ;)

--
Thanks, Frank.
(remove 'q' and '.invalid' when replying by email)




Re: High resolution, low cost, quadrature encoders


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Looks nice, but it really worries me when I see a spec for something
like resolution quoted to 4 significant digits accuracy.  Implies that
the writer knows nothing about what figures mean.


--
Regards,

Adrian Jansen           adrianjansen at internode dot on dot net
We've slightly trimmed the long signature. Click to see the full one.
Re: High resolution, low cost, quadrature encoders


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In this case, it may make sense. Say you have an encoder with 99 steps per
revolution. That would be ( 360 * 60 / 99 ) = 218.181818181818 arcminutes per
step. Who wants to quote resolution as a fraction?


Re: High resolution, low cost, quadrature encoders


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There are 1,296,000 arc seconds per revolution.

The encoder resolves 230,000,000 counts per revolution.

Accumulative accuracy is +/- 1 arc second or +/- 177.46913 counts.

Resolution of 0.005625 arc seconds or 0.998263 counts.

Don't get me wrong. This encoder is a very impressive piece of engineering.

It's just that if you are going to spec a resolution of one count in 230
million in arc seconds to 6 decimal places you should at least get the math
right.

The correct answer is 1,296,000 / 230,000,000
 or 81 / 14375 exactly,
 or 0.0056347826086956521739130434782609 approximately.




Re: High resolution, low cost, quadrature encoders


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Agilent offers an analog quadrature sensor that can give resolutions in
the range of 10k counts/rev. They will require a microprocessor with a
pair of A/D converters in addition to a standard quadrature counter
system running off a pair of comparators looking at the analog signals.
By using the analog outputs, you can interpolate the position to get at
least 64 "fractional" parts of a digital count.

If that is more effort than it is worth, the Cannon encoder that another
poster mentioned work well. They are what we used to proof our
interpolation scheme. They offer resolutions lower than the monster that
was mentioned.

Good Luck,
Bob

Re: High resolution, low cost, quadrature encoders


Check out
http://www.austriamicrosystems.com/03products/20_rotary_encoders.htm

But only up ro 12bit    406 bits res.

JG
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Re: High resolution, low cost, quadrature encoders



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These guys sell 10,000 count encoders online (in Australia) not sure if
you'd consider them cheap though:

http://www.wildcard-innovations.com.au/ (in the products / accessories
menu)

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