[SwampDonkey]

Can someone explain how these channels apply to the type of motor these encoders are applicable for? I understand an index is merely a count of RPM but also gives position of all the other slots relative to the Index. What does the Z channel do?

Are these required for brushless motors? What are the requirements for brushless and AC servo encoders?

Thanks in advance. I figured I'd just ask directly and get the benefit of our experienced members rather than try to decipher the info and possibly make expensive mistakes/ purchases.

[Al_The_Man]

The Z or marker pulse is just that, a once per rev pulse.
It is not needed for commutation.
It is used the same as commercial CNC zeroing procedure. This entails initiating the home sequence where the axis moves in rapid to the home switch, the axis then slows and looks for the first Z marker, at which point the axis stops and then uses this as a very accurate zero reference point.
Now modern quadrature encoders also have commutation tracks, that simulate the older Hall effect switches. But much more accurate.
AC servo's are practically identical to BLDC but instead of 3 phase sinusoidal,the three windings are powered two at a time.
Al.

[SwampDonkey]

The Z or marker pulse is just that, a once per rev pulse.
It is not needed for commutation.
It is used the same as commercial CNC zeroing procedure. This entails initiating the home sequence where the axis moves in rapid to the home switch, the axis then slows and looks for the first Z marker, at which point the axis stops and then uses this as a very accurate zero reference point.
Now modern quadrature encoders also have commutation tracks, that simulate the older Hall effect switches. But much more accurate.
AC servo's are practically identical to BLDC but instead of 3 phase sinusoidal,the three windings are powered two at a time.
Al.

Excellent info! Is there any "dead giveaway" as to which is for AC or BLDC? I dont typically see "sinusoidal" in the descriptions of encoders for sale.

[engnerdan]

AC servo's are practically identical to BLDC but instead of 3 phase sinusoidal,the three windings are powered two at a time.
Al.

So to add to this and better define the differnece between a BLDC and a AC (induction motor). A BLDC motor will have an rotor (the shaft assembly) made of a permanent magnet. An AC motor, which is properly called an AC Induction Motor, will have a rotor made of steel laminates and often aluminum.

Here is a BLDC motor rotor
Attachment 296034
Source: Brushless DC Motors ? Part I: Construction and Operating Principles | EDN


Here is a AC motor rotor

Source: AC motor rotor/electric motor rotor/induction motor/rotor China (Mainland) Machinery

-Dan

[mactec54]

So to add to this and better define the differnece between a BLDC and a AC (induction motor). A BLDC motor will have an rotor (the shaft assembly) made of a permanent magnet. An AC motor, which is properly called an AC Induction Motor, will have a rotor made of steel laminates and often aluminum.

Here is a BLDC motor rotor
Attachment 296034
Source: Brushless DC Motors ? Part I: Construction and Operating Principles | EDN


Here is a AC motor rotor

Source: AC motor rotor/electric motor rotor/induction motor/rotor China (Mainland) Machinery

-Dan

No one is talking about an AC Induction motor, AC Servo Rotor is almost the same construction as the BLDC Rotor, what you are showing is a regular Rotor for a AC motor, this type of Rotor is not used in an AC servo motors

[Al_The_Man]

So to add to this and better define the differnece between a BLDC and a AC (induction motor). A BLDC motor will have an rotor (the shaft assembly) made of a permanent magnet. An AC motor, which is properly called an AC Induction Motor, will have a rotor made of steel laminates and often aluminum.

-Dan

Yes if you notice I said AC servo's not induction motor.
BTW the rotor of an induction motor has embedded aluminum bars acting as shorted turns, they were at one time made of copper.
SwampD the commutation of a AC servo is often done with a resolver or other means rather than the three commutation pulses,
You can turn a AC servo into a BLDC by fitting the 3 commutation pulse encoder.
Al.

[engnerdan]

Al_The_man,
I do apologize, in the context you were talking about, AC servos are permanent magnet motors. At the same time there are AC induction servos, granted they are not as common. I fell victim of the one tack mind for a few minutes and forgot to add PMAC motors to my list.


ABB HDP (High Dynamic Performance) induction servo motors are an example.

Or from Lesson
"AC induction motors designed for servo operation are wound
with two phases at right angles. A fixed reference winding
is excited by a fixed voltage source, while a variable control
voltage from a servo-amplifier excites the winding. "
Source: http://www.leeson.com/documents/PMAC_Whitepaper.pdf


-Dan