On 06/30/2017 11:45 AM, Peter C. Wallace wrote:
This does show that a relatively small quadrature error
causes a large velocity modulation is the relative time
between edge changes so much
Good encoders have very close to 50% duty cycle on the
individual A and B outputs, at least when new. Depending on
the optical technology, the duty cycle can drift as the LED
ages. The phase angle between A and B is pretty well set by
mechanical features of the encoder, and is not likely to
drift. But, it could be off on poorly-built encoders.
Also, older encoders had mechanical adjustments for the
sensor gratings, and if dropped or handled roughly, that
factory adjustment could break loose.
Some very old encoders had 4 sensors and gratings such that
the sensors got differential light for each signal, and then
used a comparator. This pretty much eliminated the drift as
the LED (or bulb!) aged.
Anyway, I think many encoders have a spec of no more than 5%
duty cycle error, and maybe 5 or 10 electrical degrees in
the quadrature.
Jon
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