On Saturday, June 02, 2012 03:49:49 PM cogoman did opine:
> While I can see the need (sometimes) for a durable metal encoder
> disc, and I have cut some out of .016" copper (was on hand, and never
> got tested), I wonder how useful, or how durable laser printed
> transparency film would be for many applications. Two of them glued
> back to back with the printing on the inside might be reasonably
> durable. all but the fingers could be clamped between an aluminum
> mounting piece giving some physical stability. The resolvers on our
> Shizuoka are located in sealed coffee can shaped bins, so reasonably
> protected from swarf. One could take a .JPG to Staples and have them
> print out a few with whatever resolution you choose (make THEM keep the
> stock of laser transparency film).
>
> The original encoder code was borrowed by a guy doing robotic
> encoders for some surplus Pittman gearmotors for robotics, though he
> used reflective sensors with less than 30 segments. I borrowed the code
> from him and made changes to make it easier to center a large encoder
> wheel. I have printed out samples (though I haven't used any yet) and
> get reasonable looking prints with 512 segments or more. I haven't
> added the index wedge yet, but I will insert the code that I do have
> here.
>
>
> %! Postscript utility for printing an encoder wheel
> %
> /inch {72 mul} def % #points/inch (don't change me)
> /size 3.9 inch def % radius of encoder wheel
> /segments 1024 def % number of segments (black and white)
> /angle 360 segments div def
> /wedge
> { /radius exch def
> /angle_s exch def
> /angle_e exch def
> newpath 0 0 moveto
> 0 0 radius angle_s angle_e arc
> closepath
> } def
>
> % ADD IN THE ENCODER WHEEL AT THE SPECIFIED DIAMETER
> gsave
> %THIS LINE SPECIFIES WHERE TO PUT THE CENTER
> 4.0 inch 4.0 inch translate
> 0 1 segments {
> 360 segments div rotate
> angle 0 size wedge
> 2 mod 0 eq {1} {0} ifelse
> setgray fill
> } for
> grestore
>
> %THIS ROUTINE FILLS THE CENTER WITH WHITE, AND SOMEHOW PUTS A SOLID
> CIRCLE
> % INSIDE THE GROUP OF WEDGES
> %THIS LINE SPECIFIES WHERE TO PUT THE CENTER
> 4.0 inch 4.0 inch 3.0 inch 0 360 arc
> gsave
> stroke
> grestore
> 9 setgray fill
>
> %THIS ROUTINE PUTS A TINY DOT IN THE CENTER TO AID IN MOUNTING THE
> DISC %THIS LINE SPECIFIES WHERE TO PUT THE CENTER
> 4.0 inch 4.0 inch .01 inch 0 360 arc
> gsave
> stroke
> grestore
> 0 setgray fill
>
> showpage
>
I scaled this down to the size I needed, and added enough to do it 2 up
which didn't come close to occupying the full 8.5x11 page. I was about to
add the index track too when I gave up due to poor resolution from the eps
fixed pixel size.
But when imported into gimp at 72 dpi, the resolution turns it into pretty
fuzzy stuff, with or without the anti-aliasing turned on.
So I thought I'd see what it might be able to do in inkscape, but its
crashing as it opens its screen on this box.
Back to cutting brass I believe, now that I have small enough bits.
Thanks cogoman. This would be useful if I had room for a 6" OD wheel, but
my limit in the space I have is about 2.7" in diameter.
> I open the .eps file in Gimp. Most Linuxes come with ghostscript
> installed, and that's what Gimp uses to write it out to a .JPG. To get
> good resolution, you need to print out a lot of dots, and that requires
> a lot of RAM, or a long time swapping to/from available RAM. I think I
> remember using 8000 by 8000 for the final file size. If Staples has a
> printer that handles postscript directly, you should be able to size and
> position the disc in the .eps code, and print it directly from .eps with
> much better resolution. With some care you should be able to get
> multiple encoders per sheet, depending on how big you want them.
>
> Hopefully this will be useful for someone. It sure is quicker than
> cutting that ultra thin aluminum, and the segments /should/ be equal in
> size (for 50% duty cycle).
>
> For test purposes, if you have clear spray paint on hand (Krylon
> works well here) printing on paper will give you the black. Several
> very light coats of Krylon on the print side will stabilize the print,
> then a heavier coat from the back will soak into the paper and make it
> more transparent. All the paint should make the disc stiffer, and seal
> it against some moisture. You could mount the disc in between
> cardboards with a hole cut in the middle to keep it flat while the paint
> dries.
>
> Does anyone think that this needs to go in the knowledgebase? I
> searched for encoder and didn't find any references that appeared to
> have this information.
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Cheers, Gene
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
My web page: <http://coyoteden.dyndns-free.com:85/gene>
If the rich could pay the poor to die for them, what a living the poor
could make!
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