Re: [CAD_CAM_EDM_DRO] AC servo motor project - encoder problems

toolspindoctor wrote:

>I have an AC servo motor from Yaskawa USASEM-08TV12 which I am trying
>to control with a Yaskawa servo amp. The amp is giving an error that
>the encoder is not wired correctly. Fortunately I have 2 amps and
>motors. The second one is functioning. With an oscilloscope I have
>examined the outputs from both encoders and they are identical on
>Phase A, and B. The good motor has a Phase C output that pulses at a
>rate similar to that on the other 2 phases. However, the new motor
>that I am trying to get to function has an origin pulse once per
>revolution. Thus the only difference I can see between the two
>encoders is on the Phase C channel.
>
>
>

Yaskawa, and a number of other manufacturers, use proprietary encoder
schemes that embed the commutation information in a "C" channel on the
encoder. This also provides the function of the index pulse. Using
this, there
is no need for the traditional Hall-effect sensors used on brushless motors.
The phase relationship between the C channel and the others gives the
commutation
info, so the motor only needs to move a couple of encoder counts for the
drive to know
which quadrant of a pole it is in. Without this info, the drive will
not function.
The drive applies power randomly to a winding and attempts to move the motor
a tiny amount. If it sees 4 encoder counts on the A/B quadrature
channel and no
signal change on C, it goes to fault status.

Without a signal on the C channel, how can the drive know which winding to
apply power to?

Jon