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[DPRG] More quad encoder stuff

Subject: [DPRG] More quad encoder stuff
From: Dan Miner miner at centtech.com
Date: Thu Aug 30 13:19:52 CDT 2001

Great ideas - I especially like the enc-90 idea as you
CAN mount the sensors 180 degrees apart (but with a different
radius from the center) and it works with any # of divisions.

However, in a moment of nit-picking, your 6bitgray.gif is 
not really gray code - it's binary code.  The definition of 
gray code is that only 1 bit changes at a time.  Yours changes 
many bits at once - especially at the 12, 3, 6, and 9 o'clock 
positions.  5 bit gray code (left to right) would be:

LSB: 01100110011001100110011001100110 
     00111100001111000011110000111100 
     00001111111100000000111111110000 
     00000000111111111111111100000000 
MSB: 00000000000000001111111111111111 

Note that when going from any column to the next one, only 1
bit changes - including when you wrap around from last to first.

Also note that if you look at only the first two lines, you'll
see the "classic" quadrature encoder waveforms - which are 
really just 2-bit gray code.

				- Dan Miner

> -----Original Message-----
> From: Sluggy [mailto:slugmusk at linuxlegend.com]
> Sent: Thursday, August 30, 2001 12:40 PM
> To: dprg
> Subject: [DPRG] More quad encoder stuff
> 
> 
> 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 
> http://www.linuxlegend.com/~slugmusk/encpix
> 
> 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 
> http://www.semiconductor.agilent.com/cgi-bin/morpheus/home/home.jsp 
> 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.
> 
> Sluggy!
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