RE: [CAD_CAM_EDM_DRO] DRO ENCODER TOOL

Ok, let me throw some of my ignorance in on this subject! When you say
absolute encoder are do you mean a strip that really has say 1000 lines per
inch for example? If so then would that mean that a 250 line per inch strip
with a quadrature reader would give you .001 or better resolution?

John Guenther

-----Original Message-----
From: D.F.S. [mailto:dfs@...]
Sent: Monday, March 13, 2000 3:58 PM
To: CAD_CAM_EDM_DRO@onelist.com
Subject: Re: [CAD_CAM_EDM_DRO] DRO ENCODER TOOL

From: "D.F.S." <dfs@...>

>
> From: stratton@...
>
> > All you get for you money from US Digital is a strip of plastic with

lines

> > printed on it.
> >
> > All you get from HP for 30 bucks is $2.00 worth of LEDs and Photo

Transistors

> > in a plastic block.
>
> Fine. Have you or anyone you know personally built their own?

Liner No.

Absolute position rotary Rotary Gray Code. Yes.

The idea is no different, and an Encoder strip is a lot easier
to design than a rotary one.

>
> In theory it might be simple - in practice, making two tiny slits a
> precise distance apart is going to be tricky.

You ignored the statements in my previous posts about the
photo typesetting of BOTH the strip and the shadow mask.

If you can typeset encoder strip or wheel, by definition, if the lines
are at least 2 pixels wide, you can accurately print the shadow mask.

If you can't keep tolerance between 2 white squares 1/2" apart your
30" strip is not worth squat anyway.

>
> Also, the HP read head is more than simply optoelectronics - there are
> threshold comparators to give a digital output. Again, not too
> complicated, but time consuming to figure out.

Weren't we just bitchin' the analog output from the transistors
were not brought out on the HP sensor?

I never bothered,
I just feed the output to a gate with schotty inputs.
Nice square edges.

These type of features may be an issue when readers are expected to
read high count wheels at high RPMs.

Do you REALLY expect to need to run you mill at the 170 MPH! those
readers are speced at with a .0005 resolution?

> But if someone wants to figure out how to crank out read head
> enclosures on their CNC mill and contract with the owner of a
> photolithography machine to have say 500 cpi (2000 counts/inch) strips
> made, there certainly would be a market for them here.

John has a machine on his web page that should be able to do it, if it
is as accurate as advertised.

In any event, this does not need to be any more complicated than sending
a postscript file to a local printer.

I'm not looking for a job or business, I have one, and this type of
stuff would never pay enough to bother with.

On the other hand, sharing experience and resources doing what I
like to do for fun is another story.

>
> I doubt you would beat the US digital prices by much - but you could
> provide a more useful resolution.

That is exactly the point, 2 bucks an inch is a non-issue..
It isThe fact all you get is a strip of plastic, you can easily have made
locally for the same cost, in an appropriate resolution, not something
derived from 30 year old dot matrix pin spacings.

Also as I mentioned, without a lot of extra work, this same method
could be used to generate an absolute encoder as well.


Marc


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