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From: ear@wpi.WPI.EDU (Eric A Rasmussen)
Newsgroups: comp.robotics
Subject: Re: What is the cheapest shaft encoder you know of?
Message-ID: <1991Jun19.044959.23200@wpi.WPI.EDU>
Date: 19 Jun 91 04:49:59 GMT
References: <966@agcsun.UUCP> <3755@intvax.UUCP> <6185@ptsfa.PacBell.COM>
Organization: Worcester Polytechnic Institute
Lines: 28

In article <6185@ptsfa.PacBell.COM> dmturne@PacBell.COM (Dave Turner) writes:
>The photo disk was available for $1.00 from the author. The 50 mark disk
>was about 2.5 inches in diameter; the 100 mark disk was 3.5 inches diameter.

Excuse me if I am missing some subtle flaw in reasoning, but I think I have
just come up with a very simple and cheap method of producing the optical disk
part of an optical encoder.

Steps
-----
1) Use a CAD package, drawing program, or whatever to design the simple radial
lines and circle pattern which will appear on the disk.
2) Make a good dark printout of said design on a laser printer.
3) Convert this to a transparency such as used for overhead projectors with
one of those thermal things often found in the office closet.
4) Cut the design out of the plastic.

Bingo, you have a clear plastic disk with your lines.  Some reenforcement
might be needed, such as using a transparent glue to attach it to a second
layer of clear plastic or glass, but other than that I can't think of a good
reason why it wouldn't work.  Furthermore, you could easily customize the
resolution to suit your needs.

+---------< Eric A. Rasmussen - Mr. Neat-O (tm) >---------+ +< Email Address >+
|   A real engineer never reads the instructions first.   | | ear@wpi.wpi.edu |
|   (They figure out how it works by playing with it.)    | | ear%wpi@wpi.edu |
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