andy pugh wrote:
> I have a rather interesting datasheet from Allegro. They have a sensor
> that detects either a magneic codewheel, or a gear tooth (with a
> biasing magnet behind the sensor).
> The neat part is that the pulse width is 45uS in one direction, and
> 90uS in the other.
> It is intended for crankshaft sensing, where index is done by a missing tooth.
>
> The typical code-wheel is a pressed steel part 100m diameter with a
> 70mm bore. This is pressed on to a hub with a 30mm bore in the case of
> the one I have on my desk at the moment.
>
> The encoding scheme seems compatible with software/parport sensing,
> and the form-factor seems ideal for a lathe spindle encoder.
>
> I wonder if it is worth adding support to the encoder driver?
>   
You can rig three Allegro ATS667 or similar gear tooth sensors to many 
spindles
and use traditional quadrature plus index sensing.  The A and B sensors 
need to be
adjusted to give the right quadrature phasing, and some kind of once/rev 
mark
(either a peg or a dimple) needs to be made for the index sensor.  This 
has worked
very well on my Bridgeport, where a traditional encoder was pretty much
impossible to connect.  I'm not sure the software sensing of such a sensor
as you mention would be completely reliable.

Jon

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