Re: brushless servos without hall commutation

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "bluecoast1"
<bluecoast@h...> wrote:

>
> Hi,
>
> I have a number of brushless servos I've collected to build some

cnc

> machines. All of them have optical encoders of some resolution, but
> none have hall-effect sensors for commutation.
>
> What I am wondering is if there is any reason (I can't think of

any) why

> I couldn't divide the optical encoder output with a PIC or

something

> to get a faked hall-effect commutation output I could use for a
> generic controller.
>
> Has anyone faked the hall-sensor arrangement somehow?
>
> bluecoast

Dear Bluecoast:

We run brushless servomotor air-bearing tables
without halls as standard practice. Granted, our
Delta-Tau controller costs big bucks, but the
principle of operation is straight forward.

The controller needs to know how many poles in
the motor, and how many encoder counts in a single
revolution. At startup, the controller energizes
one motor coil, and waits for the rotor to settle.
It then records the encoder reading, then energizes
the next coil and records the position. From this
data, the controller knows the direction of rotation
and the encoder position of one set of poles. Once the
initialization process is completed, commutation
is then computed purely from encoder position.

Regards... Jeff