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[DPRG] More quad encoder stuff

Subject: [DPRG] More quad encoder stuff
From: Sluggy slugmusk at linuxlegend.com
Date: Thu Aug 30 12:39:44 CDT 2001

Yesterday, I wrote:

> I drew a 10 division wheel, but just then, the linuxlegend.com server
> seems to have gone away

Ok, linuxlegend.com is back up (after replacing a CPU fan!) so those 
interested will find three pictures at 

enc-7.gif is just a plain wheel with 14 divisions, 7 white, 7 black. 
After the discussion on the list, I now see where mounting the 
detectors physically 180 degrees appart will not work like we thought. 
Mounting them 90 degrees apart will, however.

enc-90.gif is a 10 division wheel with two rings of bands to provide 
signals 90 degrees appart with two detectors mounted parallel to one 
another along a radius line from the center.

Just for the fun of it, 6bitgray.gif is a 6 bit Gray code disk pattern. 
It is designed to have 6 sensors on the radius line and to increment 
as the disk turns clockwise.

In other news, I have revisited a Hewlett-Packard (Now Agilent 
Technologies) part that I looked into quite a while back, the HEDR-8000. 
These are surface mounted 8 pin (S08 package) devices with all optics 
and electronics to read, reflectively, a 75 or 150 line-per-inch 
pattern and provide a quadrature output. There are a couple of minor 
varieties, the biggest differences being LPI count and resolution. They 
specify an optical radius of 11mm, even for linear use, so I think it 
must be a minimum radius rating.

The URLs on the site are torturously long, so I have put the PDF for 
the part on my site: http://www.linuxlegend.com/~slugmusk/hedr8000.pdf

To check them out on your own, start with 
and look under Motion Control.

The actual rating of the 75 LPI part is 70-75 lines per inch, so I 
printed a 72 line per inch pattern on a 1 inch diameter disk. Assuming 
I did the math right (113 black/white divisions around the 
circumference of a 1 inch diameter disk), it looks pretty usable. As a 
matter of practical concern, I may need to adjust the size of the dark 
regions to keep them balanced with the light regions, as at this size, 
it bleeds over a bit. I will try a 150 line disk later today, but I 
think that may be approaching the practical resolution of my laser 
printer on plain paper.

In any case, this looks like a promising way to dodge the entire issue 
of mounting two sensors while keeping the simplicity of a printed disk 
attached with glue. I requested a sample kit (3 pieces) directly from 
Agilent (800 235 0312) and can expect it in 3-5 days.


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