3 Phase Stepper Motor Microstepping

[Jim Donaldson]

Hi All,

A quick question regarding microstepping control of a 3 phase hybrid
stepper motor (4 wire star wiring.)

A have a microstepping controller which produces 3 phases of 50/50
PWM, and I need to design an amplifier circuit.

What I'm thinking is that I need something like the following (per
phase.)

+Vcc

|
|
_|

 

[Jim Donaldson]

Hi All,

A question regarding microstepping control of a 3 phase hybrid
stepper motor (4 wire star wiring.)

A have a microstepping controller which produces 3 phases of 50/50
PWM, and I need to design an amplifier circuit.

What I'm thinking is that I need something like the following (per
phase.)

+Vs _________
|
R1
|
__|
|
|__
|
|________PHASE 1 WINDING __________ 0V
|
__|
|
|__
|
|
R2
-Vs ____|______


The above diagram is supposed to represent a half bridge, with two
current sensing resistors (R1, R2.) The star point on the motor is
connected to ground.

In this scheme we can split the PWM 50/50 into direction and magnitude
signals. The direction signal (ANDed with the chopper controller)
turns on either the top transistor, or the bottom transistor. The
magnitude is used as a reference voltage input to the chopper.

My application is quite cost sensitive and I'm not sure how to do this
cheaply.
Additionally, I have two motors to drive, and not a lot of space on
the board.

It looks like I need per motor...

3 half bridges with sense resisitors
Level shifting on each of voltages comming from the resistors
3 chopper controllers (or do I need six?)
A bit of logic (couple of and gates on the transistors)
Mosfet drivers

What would be the best way to do this?

I'm not expecting a full solution but any ideas would be gratefully
appreciated.

All the best,

Jim Donaldson