Re: Rotary to linear translation - an interesting idea.

On 10 Apr 00 at 23:11, CAD_CAM_EDM_DRO@egroups.com scribbled
furtively:

> Message: 8
> Date: Mon, 10 Apr 2000 09:57:41 -0700 (PDT)
> From: beer@...
> Subject: Rotary to linear translation - an interesting idea.
>
>
> A long time ago, someone I don't know emailed me the details of his
> homemade DRO that used rotary encoders. I've long since lost the
> emails, so I can't tell you his name .. too bad.
> Here's the interesting part, that I haven't been able to get my head
> around.

[swarfed]

> The guy claims that by pressing the pulley farther and farther into the
> shim stock, causing greater and greater deflections ( adjusting tension
> as required ), the pulley diameter is effectively changed - a given
> amount of linear travel will cause more or less rotation.

yes it will. kinda hard to put into words.... but I'll try...
if the shim is flat, meaning the encoder only just touches it with
enough force to be turned, then the shim stock is still travelling
'flat' and so it's travel will equal the travel of the bed.

but
if you have a big kink of shim going around the encoder wheel (and
made more by the supoprting rollers), that linear motion is now
converted to radial motion, ie, a point on the shim is moving around
a curve which now not parallel to the bed motion, and must be longer
in fact. ergo the travel of the encoder will be different for
different levels of deflection, and by adjusting the deflection you
can indeed adjust the 'encoder counts per linear unit travel'.

I do wonder just how much adjustment you have though, can't be a
lot... but can be precise I think....

I have a Calcomp plotter at home that uses a steel band to drive the
head and it's stretched 'twang' tight, even though the plotter must
be 20 years old.
--
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