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 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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