Re: Phase Drive Control?

Bob,

The 4-phase drive is simply individual control of the four "leads" of a
unipolar stepper motor. The driver in this case (MAXNC's low end
package, for example) has four darlington TIP 120 transistors for each
axis. think of it as a "low level" interface.

Step and direction (S&D) is a "higher level" interface. Drivers must
take these two signals, walk a counter (step) through four (full step),
or eight (half step) counts, and decode when and which motor lead(s) to
turn on. The direction tells the counter which way to count. The
driver can drive unipolar or bipolar stepper motors, depending on its
design.

Unipolar (I knew you'd ask that) may be simply thought of as four
windings, all with one end connected together, and one winding at a time
turned on to make the motor step. Bipolar brings out two pairs of
windings. In this case, each winding can be energized (driven) in two
directions. In the simplest case, there are therefore four possible
combinations of driving the windings. It gets more complicated after
that. half step and other "micro step" implementations (more advanced)
engage more then one winding at a time (often with overlap, hence more
states), and even various levels of drive to achieve micro steps of 10
or even 256.

Other drivers (still more advanced) are "chopper drives", which use high
voltages to get the di/dt's up on the windings (overcomes the
inductance), instead of our simple unipolar 4-phase example, which uses
a 10 ohm resistor, a 24v motor, and a 24v transformer. Choppers may use
80v power supplies and 2v motors!

For further information, check out Jones:

http://www.cs.uiowa.edu/~jones/step/

Hope this helps.

Alan

Robert Bachman wrote:

> Will someone please explain 'Phase Drive Control' as opposed
> to 'Step & Direction'? I know what step and direction is.
>
> Thanks,
> Bob
>