Re: rotary hand encoder wheels with detent

Bob wrote:

> I posted the links to show some people are using steppers
> as encoders and that they do work in some applications!

Marris wrote:

> I'm OK with that ... I guess I'm just looking at it
> from the point of view it has to work all the way down
> to zero speed. It's a shame it can't do that.

OK then, we're back to my original suggestion:

- use a stepper essentially for the mechanical 'feel' only

- however it can be used to conveniently mount a big knob
on the top, the stepper to the underside of your front panel,
and an encoder on the bottom (of a dual shafted stepper).

- the steppers can have the coils permanently (or I suggested:
intermittantly) shorted to create a harder feeling 'detent'
for slower rotational speeds for 'sneaking up' on a position,
and open circuited to get a freer feel for traversing longer
distances (ie many spins).

- encoders are a well known commodity, and do not need any
R & D to get it working. I might whip one up tonight!

- Scot Rogers suggested using a 3.6 degree stepper to get an
even 360/3.6 = 100 detents per revolution, and each step
could represent 0.1", 0.01", 0.001", 0.000 10" depending on
which of four modes it is in.

1.8 degree steppers (200 steps/rev) are more common, and thus
each step could represent 0.05", .005", 0.000 50", 0.000 05"
instead (for a total of 1"/rev .1"/rev, 0.01"/rev and 0.001"/rev).

- finally, such quadrature outputs from the encoder can be sent
back directly to two input bits on the parallel port (or game
port) for sensing by your favourite gcode interpreter program.

Some new people are wondering if & how the two quadrature bits
can specify direction: yes they can (two square waves are
generated, but offset from each other) - depending if you are
going CW or CCW (ie left or right) makes one channel 'lead' or 'lag'
the other. Of course the distance is determined by counting the
actual number of pulses going by.

Note:
Not only can this technique be used for a rotary 'jog' handwheel,
but also for fine-grained 'feedrate over-ride' (but I prefer a
potentiometer for that, fed back into the analog game port).

Doug Fortune
http://www.cncKITS.com


































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