Re: AC Servo Motors and Drives

Hi David,

The four input wires are probably one for each of the three phases
and one frame ground. (The three phases are usually connected
together like a Y, with one end of each phase connected toghether at
the middle, and the remaining three ends accessible in the three
wires coming from the motor.)

This kind of motor do not have brushes but are electronically
commutated (preferrably with a sinusoidal waveform for smooth
performance). You need a 3-phase servo drive that watches the encoder
output from the motor to keep track of where the rotor is, and
rotates the magnetic field within the motor correspondingly. This
means that you cannot use a DC motor drive to power these motors.

Unfortunately I don't know where to find a reasonable cheap AC servo
drive, but if you do find one, you have very nice servos indeed!

Good luck,

Arvid


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "aussiedude36"
<aussiedude@e...> 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. This is normally connected to a DC
> servo motor. My new motors say AC servo motor and appear to have 4
> input wires not counting the encoders. 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. Any body have ideas on a step

and

> direction iput ac servo drive?
>
> Sincerely
>
> David
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Madhu Annapragada"
> <mapr@c...> wrote:
> > When one talks about AC servo motors , it usually refers to the
> commutation
> > of the phases. If the commutation is sinusoidal then the motor is
> referred
> > to as an AC servo motor or a sinusoidally commutated DC servo
> motor. If the
> > commutation waveform is not mentioned explicitly, one assumes

that

> the
> > waveform is six step or trapezoidal (using hall effect sensors
> directly for
> > the commutation information). That said, to run these motors you
> can use
> > both sinusoidal or trapezoidal commutation although the sinusoidal
> > commutation has a number of advantages (lower cogging etc) and a

few

> > disadvantages (primarily the processing required to produce the
> switching
> > sequence for the six MOSFETS to produce a sinusoidal output).

Most

> servo
> > drives support both types of commutation and I am not sure if the
> Geckos do.
> > Madhu
> >
> > >-----Original Message-----
> > >From: aussiedude36 [mailto:aussiedude@e...]
> > >Sent: Wednesday, September 24, 2003 1:18 AM
> > >To: CAD_CAM_EDM_DRO@yahoogroups.com
> > >Subject: [CAD_CAM_EDM_DRO] AC Servo Motors and Drives
> > >
> > >
> > >Hi group, I have been playing with CNC stuff for a while and have
> > >built a couple of systems with steppers and Dc servos utilizing
> > >Geckos but I recently ended up with some AC Servo motors. As I
> > >understand it they are kind of like 3 phase motors in the way

they

> > >work, 1) am I right & 2) are there any gecko / inexpensive type

of

> > >drives to run these motors using step and direction pulses?
> > >Any direct answers or pointing in the right direction would be
> > >greatly appreciated.
> > >
> > >David