Re: [CAD_CAM_EDM_DRO] Re: mounting encoder with pulley

caudlet wrote:

>The problem with building a divider for the encoder signal is that
>you are actually dealing with two channels. Their relationship to
>each other determines direction. Simple divider circuits (flop flop
>or binary divider chips) would probably alter the phase relationship
>with the two channels. The output of a channel gives squarewaves that
>vary in width depending on the rotation speed. There is a
>transision on the rising waveform and another transision on the
>falling edge. The two sensors are ofset from each other so the
>depending on the direction of rotation, the signal leads/lags the
>other. You have to maintain that phase relationship. It might be
>possible to build a circuit that ignores the trailing edge
>transisiton on both signals and divides everything in half. Who
>knows, you migh be able to further divide those signals down as long
>as the phase relationship is maintained.
>

I know there are difficulties - that's why I've responded to several
people saying that input multipliers are the better answer. I do have a
situation that suggests using an encoder divider, though.

The method I would use would be to do the full 4X decoding (or possibly
just use the encoder phases as step and direction signals, giving a
"free" divide by 4), then divide down the resulting count. This counter
would then drive a set of quadrature signals - essentially, I would
decode the encoder pulses, divide the decoded count, then output a set
of faked quadrature signals with the divided count. I think I would do
this with a microcontroller, so I could have better control of the
divide ratio, and different options for output. It's probably possible
in discrete logic, but I'm a software guy. :)

>On the other hand the
>fastest and cheapest way might to be to find another servo motor with
>an encoder count of 250 or 500. The last possibility is to shaft
>couple a 100 count encoder to the back of the servo motor (if you
>remove the existing encoder).
>

Either of those two options isn't that easy, since the encoder is
installed inside the motor housing, and the encoder signals are included
on the MIL-C-5015 series circular connector. The setscrew for the shaft
coupler is only accessible if you remove the connector, and it's
difficult to get in there (with the 0.050 allen key) to break the
loctite on the setscrew. It's a PITA to remove the old encoder and
install a new one.

>I don't think belt coupling a rotary
>encoder is the answer since they are not designed for even light
>radial loading. You can get lower count rotary encoders from US
>Digital at a reasonable cost.
>
>

That's what I was saying :) (in response to Dave's original question in
this thread)

- Steve