Re: DC Brushless Motors and Drives

Hi,
Some motors have 'Hall Effect Sensors' (for example 3 of them
labeled A,B,C) & extra wires for these. The drive uses these to find
out the rough starting angle of the rotor (1 of 3 OFF, or 1 of 3 ON
as the case may be). It can then SLOWLY move the motor until a Z
pulse is found. From there, everything is based on the encoder.

Jeff
www.xylotex.com

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
>
>
> Nicolas Benezan wrote:
>
> >Jon Elson wrote:
> >
> >
> >>encoder provides the right signals for the motor's commutation.
Most
> >>modern servo amps figure
> >>out the commutation by counting out encoder ticks from the index,
but
> >>then they need to
> >>know how many poles the motor is and how many lines the encoder
has.
> >>
> >>
> >
> >Hi Jon,
> >
> >just another dump question to you as expert: Do they need absolute
> >encoders for this to work? If not, how do they handle the
commutation
> >before the first index impulse is encountered?
> >
> >
> I'm not a great expert on this. But, there are a number of
schemes.
> Some do need encoders
> with separate commutation channels, some don't need any encoder
info at
> all, they sense
> the voltages from the motor windings. Others take a guess and move
the
> motor a little
> until the encoder passes the index position. So, you just have to
read
> the manufacturer's
> info on how this all works.
>
> Jon