Building your own PM AC servo driver? (was: AC Servo Motors and Drives)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:

> > 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!


Has anyone here tried to build their own drive for a Permanent Magnet
AC servo motor? There are several microcontrollers and DSP chips out
there with multiple PWM channel outputs. Texas Instruments, Motorola
and Analog Devices all make dedicated DSPs with built in encoder
inputs, six PWM channels, A/D channels for measuring current in the
windings etc. I can buy single pieces (a TI one, the TMS320LF2407A),
at my local electronics shop for about $25.
TI also has several application notes on the subject, for
example "SPRA588 - Implementation of a Speed Field Oriented Control
of 3-phase PMSM Motor using TMS320F240". Field Oriented Control (FOC)
seems to be the latest in servo drives, and gives very precise
control over the motor.

Any thoughts about this?

// Arvid Brodin