Re: Magnetic encoders

I rather think it's worth playing with. Get some definitive results.

The main issue is that a pickup head won't read anything when stationery.
You'd have to use hall effect devices.
Other than that, the magnetic tape could be glued to a glass strip, or steel
measuring tape. The steel backing may even accentuate the poles.
All this would all go into an aluminium channel just like a regular linear
encoder.

As far as the resolution goes, I think a normal tape cassette moves at
1in/sec. Thus a 1KHz wave gives 1/1000 in. OK, if I'm out, record at 2KHz.

The way to record it would be to put a magnetic strip around a heavy steel
wheel. 300mm OD gives ~ 1m . Then drive it with a small DC motor. This will
keep jitter low. Then you need a stable oscillator, and a circuit to record
on one rev.

All very do-able...

Regards
Roland


2009/4/23 Jon Elson <elson@...>

>
>
> dandumit wrote:
> >> this stuff is NOT
> >> cheap. The read heads all run around $300 - 400 each, and the tapes are
> >> a couple
> >> hundred $ per meter.
> >>
> >> Jon
> >>
> >>
> > Does anybody knows if this kind of tape can be homemade ? from what is
> made of ? a casette tape can be used ? I have seen some new products from
> same company which has some new devices for linear encoders.
> >
> An audio tape is not a very sturdy material, and the stuff in cassettes
> is so thin that somebody moving around in the shop will blow it around.
> Also, it is prone to stretching, humidity changes, temperature changes,
> etc. as well as deterioration in the presence of oil and coolant, not to
> mention HOT metal chips!
> The Sony magnescale and similar tapes are some kind of mild steel (so it
> can be magnetized) with an adhesive backing. You just stick it down to
> the edge of the machine table. Even if the audio tape were OK, how
> would you put accurate megnetic stripes on it? Feed a sine wave into a
> tape recorder? You might as well use a steel ruler for all the
> long-term accuracy you'd get with that technique.
>
> Jon
>
>

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