Re: Encoder for stepping motor

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "poppey_au" <gjo@...> wrote:

>
> Hi
> I'm in the planning phase (got most of the parts) to upgrade my X3
> mill to CNC. I'm basically following the instructions given in MEW
> article. Before I start putting the parts together I would like to be
> able to manually control it via an encoder and make a control box. A
> colleague of mine came with a Sanyo Denki stepping motor Type 103-770-
> 6 8 wire. The motor is mounted on a bracket and equipped with a 55 mm
> plastic hand wheel. He claims it has been used to manual control a CNC
> machine. The motor wires are terminated 2 by 2 on a terminal plug (4
> off) and together with a wire that goes to a 9 ways computer
> connector. 3 of the computer connectors wires are terminated together
> with 3 wire cable that has been cut off.
> Could this work as an encoder? Moreover, how should it be terminated?
> Gaute
>

Making an encoder out of a stepper works but takes electronics since
the voltage out is proportional to RPM. You can get anything from a
100 millivolts at slow RPM to 10V at high rpm. In addition the
quadrature signal is developed from two coils and it's possible to
generate one signal and if it's slow enough the phase gets messed up
and you get a direction reversal signal.

The coil becomes a voltage generator and loading it will decrease the
volts at low RPM. You circuit has to be tolerant of a wide range of
input and only output logic correct TTL levels (5V max).

We designed and sold a hand controller for MACH (MPG-02) that used a
small stepper as the encoder. It worked but it took a lot of design
and testing.

You could probably program up a PIC to recognize the signals and make
sure the low speed pulses don't get out of phase BUT at that point you
might as well do you pulsing from the PIC based on the position of an
analog signal.

My advice (having been there) is just buy a real rotary optical
encoder (Grayhill makes some with Detents). It's setup to do exactly
what you want....


TOM CAUDLE
www.CandCNC.com