Re: [CAD_CAM_EDM_DRO] Re: AC Servo Motors and Drives

aussiedude36 wrote:

>Hi and thanks for your reply. I have read your reply a few times and
>it has become apparent that I have no idea what you said. So perhaps
>I can trouble you again or some one else may be able to help. My
>gecko drives have a simple 2 wire output, pwm'd dc that reverses
>polarity to change direction.
>

Yes, that is for a standard, permanent magnet brush DC motor.

> My new motors say AC servo motor and appear to have 4
>input wires not counting the encoders.
>

One wire is either a safety ground or a center tap on a wye winding.
Most AC servo motors are wound with a delta winding, so there are only
3 wires connected to the windings coming out.

> I was told by some one who
>may or may not be correct that AC servo motors use a kind of 3 phase
>signal and that they do not have brushes. Is this true and does that
>some how tie into the sinusoidally or trapezoidaly commutated stuff
>you said that is wy over my head.
>

Well, there are 2 types of motors that can be listed as AC servo. One has
permanent magnets and usually has an encoder with A,B and C outputs
to control the commutation of the AC servo drive. These used to be
called DC brushless motors, but that term is somewhat of a misnomer.
It did reliably identify the motor design, however. The other is almost
identical to standard 3-phase induction motors, and has no magnets at
all. This requires a flux-vector drive to control it, as the rotor
magnetization
that allows the motor to work is not fixed at any particular location
related to the rotor. It will not have the ABC outputs for commutation
on the encoder, but will have a standard incremental encoder.
The most definitive and correct terms would be Permanent Magnet
AC servo motor and AC Induction servo motor, but yours don't specify!

There is a wayto find out, though, if you have ratings. For instance,
if the
motor has a rating of 3000 RPM and 240 V, then if you spun the motor at
1000 RPM, and measured between any two motor wires, you should
get 80 V AC if it is a PM motor. If it is an induction motor, you would
likely get 10 -20 V maximum, because the rotor only has remanent
flux.

> Any body have ideas on a step and
>direction iput ac servo drive?
>
>
>

Rutex makes a drive for PM AC servo motors. But, you will have to
figure out
the encoder wiring to get the motor hooked up properly, and get the phasing
of the encoder commutation to match the motor windings to make it work
right. If your motor does not have the commutation channels on the encoder,
or from hall effect devices in the motor, then it is almost certainly not a
PM motor, and you are looking at very expensive flux vector drives.

Jon