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.
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