Re: [CAD_CAM_EDM_DRO] Re: Question on Power Supply - regulated notes

Patrick J wrote:

>From: "Les Newell" <lesnewell@...>
>
>
>>When you get down to basics all motors are pretty much the same. They
>>all rely on the rotor following a rotating magnetic field. The only
>>difference is in how the field is generated. Brush motors use a
>>mechanical commutator while the commutation is done electronically for
>>steppers and brushless servos.
>>
>>
>
>
>So does a brushless servo motor have alot of wires then, just like a stepper?
>A brushed servo motor has 2 wires ?
>
>

Yes. Most brush DC motors have 2 wires. Some 4-pole DC brush motors
bring each
brush out, so you have 4 wires. (Don't confuse these with motors that
have TWO
commutators, and have 2 brushes at each END of the motor. Those are
motor/tachometers. You read speed from the tachometer, and don't
send any power to it.)

For 4-pole brush motors, you connect diametrically opposite brushes
together.
Then, they work exactly like any other 2-wire DC permanent magnet motor.

Brushless motors don't have such simple standards. Most are 3-phase, and
often have 3 stator wires. But, some odd ones are 2-pole, usually with 4
power wires. The 3-phase motors can have all 6 wires brought out, too.

Since the electronic commutation has to stay in sync with the motor's
position,
there has to be a position sensor of some sort on these motors. Early ones
used 3 Hall-effect sensors to actually sense the rotor's magnets. These
requires
a minimum of 5 wires, usually. +5 V power, ground, and the 3 pole sensing
wires. These could be decoded pretty simply by a brushless drive to turn on
the right transistors for the direction the motor needed to produce
torque in.

Later motors often integrated the position sensing in 3 extra tracks in
the optical
encoder. these signals were usually the same as the Hall effect signals.

Later, and especially "proprietary" motors, such as Yaskawa's ServoPack
motors and drives use a scheme that usually integrates the commutation
sensing with the index channel of the encoder, so you don't need ANY extra
channels, tracks or wires from the encoder. The index track looks much the
same as the A or B tracks, but its phase relationship to the A and B
waveforms
tells which part of the commutation sequence the motor is in. At
power-up, the
motor only has to move a couple encoder counts to get the absolute motor
position. Unfortunately, these schemes are proprietary, so in most
cases these
motors and drives can only be used with compatible units from the same
manufacturer.

The 3-phase motors with hall effect or optical commutation signals are
somewhat
interchangable, within the current and voltage ratings of the motors and
drives.

Jon