looking for rotary optical encoder disc

[colin]

Hi,
Im looking for an encoder disc 50mm OD, 12mm ID,
need about 50 slots, im tempted to make my own,
I need to arrange the two quadrature detectors to be on oposite
sides of the disc ~180' apart to offset bearing play.

at the moment I have one of the heds6100/9100 sets,
but they dont go down to 50cpr,
I need a lowish cpr in order for the quadrature signals to stay in a
quadrature fashion without needing super critical alignemt.

slots would only be 3mm pitch, so im contemplating makign my own as
ive not been able to find one.

anyone got any suggestions of sources or best way to make one?
im thinking maybe a reflective type opto and just a printed pattern on white
paper ...
hmm and need something for the shaft mount ...

Colin =^.^=

 

[John Larkin]

Hi,
Im looking for an encoder disc 50mm OD, 12mm ID,
need about 50 slots, im tempted to make my own,
I need to arrange the two quadrature detectors to be on oposite
sides of the disc ~180' apart to offset bearing play.

at the moment I have one of the heds6100/9100 sets,
but they dont go down to 50cpr,
I need a lowish cpr in order for the quadrature signals to stay in a
quadrature fashion without needing super critical alignemt.

slots would only be 3mm pitch, so im contemplating makign my own as
ive not been able to find one.

anyone got any suggestions of sources or best way to make one?
im thinking maybe a reflective type opto and just a printed pattern on white
paper ...
hmm and need something for the shaft mount ...

Colin =^.^=

Fotofab may have something standard.

John

 

[nospam]

anyone got any suggestions of sources or best way to make one?

If you search the web you will find a free program for creating images of
rotary encoder discs. Can't remember what it is called or where but it was
some kind of homebrew robotics site so you will probably find other useful
info about home brewing encoders and discs.

--

 

[Robert Latest]

Im looking for an encoder disc 50mm OD, 12mm ID,
need about 50 slots, im tempted to make my own,
I need to arrange the two quadrature detectors to be on oposite
sides of the disc ~180' apart to offset bearing play.

at the moment I have one of the heds6100/9100 sets,
but they dont go down to 50cpr,
I need a lowish cpr in order for the quadrature signals to stay in a
quadrature fashion without needing super critical alignemt.

slots would only be 3mm pitch, so im contemplating makign my own as
ive not been able to find one.

anyone got any suggestions of sources or best way to make one?

You could have the disk exposed onto lith film in a print shop (you'd have
to glue the film onto a tranparent disc afterwards), or have it laser-cut
from thin metal. Or have it milled from PCB material in one run with the
next PCB you make...

robert

 

[Paul Burke]

You could have the disk exposed onto lith film in a print shop (you'd have
to glue the film onto a tranparent disc afterwards),

If he's worried about bearing play, kitchen table methods won't help.

or have it laser-cut
from thin metal. Or have it milled from PCB material in one run with
the next PCB you make...

HP or whatever they are called this week do a most comprehensive range
of disks- what kind of speed is the OP working at if he's getting edge
separation problems? They won't go down to 50cpr, as this would make the
disk prohibitively small- the sensors are positioned 90 optical degrees
apart, where the size of the optical degree is governed by the slot pitch.

50cpr- that's 200 states per rev, or 1.8 degrees. I can't see bearing
play affecting this, unless the shaft fits in the hole like the
proverbial prick in a top hat.

I suspect that a good look at the electronics will save you much grief.

Paul Burke

 

[Tony Williams]

You could have the disk exposed onto lith film in a print shop
(you'd have to glue the film onto a tranparent disc afterwards),
or have it laser-cut from thin metal. Or have it milled from PCB
material in one run with the next PCB you make...

Etched pcb material is relatively transparent to
infra-red but copper is not. My homemade bobbin
winder just used a 10 'slot' etched pcb for the
turns counter.

 

[Fred Bartoli]

Le Fri, 17 Aug 2007 10:15:33 +0100, Tony Williams a écrit:

Etched pcb material is relatively transparent to infra-red but copper
is not. My homemade bobbin winder just used a 10 'slot' etched pcb for
the turns counter.

Relying on FR4 transparency won't help jitter, and I think it's a pb to
colin. But it's very possible to keep all the copper and strategically
place a bunch of holes, not plated to limit reflexion pbs.
Using 0.8mm thickness may slightly improve things too.

 

[colin]

If he's worried about bearing play, kitchen table methods won't help.

I have a pilar drill and a soldering iron, oh and a dremel too...
its amasing what you can do acuratly if you have enough inginuity.
(even if i cant spell well)

I have a buisiness card made from one of those chemical milling companies
its realy cool.

thats quite a good idea actually.

HP or whatever they are called this week do a most comprehensive range of
disks- what kind of speed is the OP working at if he's getting edge
separation problems? They won't go down to 50cpr, as this would make the
disk prohibitively small- the sensors are positioned 90 optical degrees
apart, where the size of the optical degree is governed by the slot pitch.

as I said I am at the moment using a heds6100/9100 set. 2000cpr
but as you cortectly say they dont go down to 50cpr.
i think its avago these days (have a go ?)

im using them upto 10krpm and they perform quite well at well over their
spec of 100khz.

I have a 40cpr plastic encoder wich came off an old dot matrix printer,
shame I havnt got 2., im also using it for one of the other axis of
rotation.
I could use it to make a spray paint image onto something.

50cpr- that's 200 states per rev, or 1.8 degrees. I can't see bearing play
affecting this, unless the shaft fits in the hole like the proverbial
prick in a top hat.

the heds 6100 have an ID of upto about 6mm, I had to bore them out to 12mm
I was amased I did it carefully enough not to scratch the film disc.

if I put another heds 9100 sensor on the oposite side
it would require centering the disc to a very small tolerance
or will likely change by more than 90' electrical phase
or as the shaft rotates.

this is a possibility I was considering but would require
more electronics to use pulses from oposite sides and cope with them not
being in quadrature.
such as QEI absolute position tracking logic,
.... im hoping to just xor them.

I might take the plunge and add an fpga where I can just feed all the
signals in
from 4 encoders, but this solution seemed atractivly simple.

I suspect that a good look at the electronics will save you much grief.

ah yes well the electronics does quite a lot too,
it spins at 10krpm and is averaged by a dspic33
over several hours, so thats a lot of points.

its compared to another identical encoder to give an average difference of
position to a truly ridiculous resolution.
eqv time is sub ps.

ive made other posts about this project were it is pointed out how futile
this is,
but nevertheless I have acheived sub ps resolution,
but im trying to remove some more of the noise.

as long as the pulses from the encoders either side stay in quadrature
doesnt matter about the absolute positional acuracy as long as it doesnt
change.

im painstakingly trying to get the 1M 12mmdia shaft straight to within 1um.
but it tends to go back to its original shape after an hour

Colin =^.^=

 

[colin]

If you search the web you will find a free program for creating images of
rotary encoder discs. Can't remember what it is called or where but it was
some kind of homebrew robotics site so you will probably find other useful
info about home brewing encoders and discs.

thanks
ive had a look before, and ive tried some graphics programs but it seems
dificult to get them to output something usable.

I also asked in a post somewhere for same sort of thing,
id apreciate it if you could remember something to reference it by.

Colin =^.^=

 

[colin]

Etched pcb material is relatively transparent to
infra-red but copper is not. My homemade bobbin
winder just used a 10 'slot' etched pcb for the
turns counter.

ive used a reflective IR opto device elsewhere
and put black crepe paper pcb tape on a white plastic disc,
but this was only 1 cpr, worked adequatly,
exept the tape didnt like to stick to the plastic so well.

im not sure how close the lines could be for the reflective device.
Id like to make the disc larger,
maybe use a 5" disc platter but id have to modify things a fair bit.

Colin =^.^=

 

[Martin Griffith]

Hi,
Im looking for an encoder disc 50mm OD, 12mm ID,
need about 50 slots, im tempted to make my own,
I need to arrange the two quadrature detectors to be on oposite
sides of the disc ~180' apart to offset bearing play.

at the moment I have one of the heds6100/9100 sets,
but they dont go down to 50cpr,
I need a lowish cpr in order for the quadrature signals to stay in a
quadrature fashion without needing super critical alignemt.

slots would only be 3mm pitch, so im contemplating makign my own as
ive not been able to find one.

anyone got any suggestions of sources or best way to make one?
im thinking maybe a reflective type opto and just a printed pattern on white
paper ...
hmm and need something for the shaft mount ...

Colin =^.^=

anything here?
http://www.usdigital.com/products/modules-disks-linear-strips.shtml


Martin

 

[colin]

anything here?
http://www.usdigital.com/products/modules-disks-linear-strips.shtml


Martin

yes thanks thats super

however I was just thinking id go for a plastic geer wheel and reflective ir
sensor.

I played around with some gear wheels and a sensor I have,
seems the plastic type rather than the metal type give a better signal,
and with the sensor on the outside of the wheel.

the advantage is that the gear can be withdrawn without having to move the
sensor,
and is very tolerant to axial alignment.

I can get 48teeth 50mm acetal geer with 8m bore,
I gues I can bore this out to 12mm somehow,
maybe with a soldering iron !
although I need to ensure very good radial acuracy.

I wonder if those disks from usdigital will work in reflective mode ?
I need a sensor on each side rather than 2 next to each other.

I also played around with some sheet tin metal and some lines drawn with a
felt tip pen
the sensor picked that up quite well,
so a printed image shld work OK too.

the gear seems easiest to try as its only a day away from a local supplier.

thanks
Colin =^.^=

 

[[email protected]]

thanks
ive had a look before, and ive tried some graphics programs but it seems
dificult to get them to output something usable.

If you want to try laser printing onto overhead transparency film (at
least for a prototype),
Postscript is a fairly easy language to write a code generator for.
Just look up the applicable primitives and write a program in your
favorite language that writes the commands to a .ps file.

I did do this at one point, but needed a higher resolution than
producable by a printer... the results turned out more like a moire
(?) pattern -undersampling of the geometry at the printer resolution.
(Actually I made an 8" diameter disk figuring I'd later modify to
generate only the diamter I actually intended to cut out and use...
but within the middle two inches it was not useable at the number of
CPR I coded).

 

[nospam]

thanks
ive had a look before, and ive tried some graphics programs but it seems
dificult to get them to output something usable.

I also asked in a post somewhere for same sort of thing,
id apreciate it if you could remember something to reference it by.

http://users.adelphia.net/~skbosko/Robot_top.htm
--

 

[James Beck]

Hi,
Im looking for an encoder disc 50mm OD, 12mm ID,
need about 50 slots, im tempted to make my own,
I need to arrange the two quadrature detectors to be on oposite
sides of the disc ~180' apart to offset bearing play.

at the moment I have one of the heds6100/9100 sets,
but they dont go down to 50cpr,
I need a lowish cpr in order for the quadrature signals to stay in a
quadrature fashion without needing super critical alignemt.

slots would only be 3mm pitch, so im contemplating makign my own as
ive not been able to find one.

anyone got any suggestions of sources or best way to make one?
im thinking maybe a reflective type opto and just a printed pattern on white
paper ...
hmm and need something for the shaft mount ...

Colin =^.^=

See if you have a Coin-Op distributor in your town.
Some of the encoder wheels used in the large trak-balls are pretty close
to what you are talking about. You might see if they have repair parts
for rebuilding them.
See : http://www.happcontrols.com/trackballs/560110e.htm

Jim

 

[colin]

http://users.adelphia.net/~skbosko/Robot_top.htm
--

wow thanks for that, thats realy cool
ive got it to draw a simple one,
but my inkjet printer is realy ancient.

Ive been meaning to get a test print of one of these latest epson injets,
you can send them an image and get a test print back

however the resolution of the drawing seems rather low at 1:1
it wont do the inkjet resolution of >1000dpi much justice
so I need to scale it up, but ive no idea how to make sure the
image wil come out the right size,
I gues I just need to make the slots long enough and then trim as necessary.


thanks
Colin =^.^=

 

[nospam]

wow thanks for that, thats realy cool

however the resolution of the drawing seems rather low at 1:1

I have never used it in anger and yes the results seem a bit 'jaggy'. I
played with it briefly and it seems to be limited to creating an image the
size of the white screen rectangle it is drawn in.

Looks like the best you can do is scale to fill that square then somehow
scale back down with the printer driver or print to an image file and edit
that.
--

 

[Palinurus]

You could have the disk exposed onto lith film in a print shop (you'd have
to glue the film onto a tranparent disc afterwards), or have it laser-cut
from thin metal. Or have it milled from PCB material in one run with the
next PCB you make...

robert

-
Lith film itself, including the "black" areas, is pretty transparent to
infrared. You can use it to make a cheesy sort of IR filter, but for an
encoder wheel, you'll have to find something else.

Heh. I remember, way back when, maintaining an old Anorad CNC machine
that used visible light in its encoders. It was controlled by an DEC
LSI-11 of about 9 cubic feet running FORTRAN, a machine which today
would be considered an inferior pocket calculator.

 

[ChairmanOfTheBored]

-
Lith film itself, including the "black" areas, is pretty transparent to
infrared. You can use it to make a cheesy sort of IR filter, but for an
encoder wheel, you'll have to find something else.

Heh. I remember, way back when, maintaining an old Anorad CNC machine
that used visible light in its encoders. It was controlled by an DEC
LSI-11 of about 9 cubic feet running FORTRAN, a machine which today
would be considered an inferior pocket calculator.

I have exactly what he needs, except that there are two sensors on the
same side, slightly offset by degrees to actually double the resolution
of the reader electronics.

I will post a picture in alt.binaries.schematics.electronic soon to
show it.

It has a much higher res than he mentioned as there are about 200 slots
around the disc. Almost the exact dimensions he refers to, however, and
the clamping mechanism as well. Sits on a 3/8" shaft IIRC.

If he wants it, I'll perhaps put it up on ebay so he can grab it.

 

[ChairmanOfTheBored]

I will post a picture in alt.binaries.schematics.electronic soon to
show it.

Said picture has been posted.

I think the idea of putting two sensors 180 degrees apart is not
needed.

If there is that much damned slop in your shaft <sic> you are going to
have some serious errors anyway you "look" at it.