Re: Microstepping

--- In CAD_CAM_EDM_DRO@egroups.com, "Ian Wright" <Ian@i...> wrote:

> Hi,
>
> Since I haven't seen a 'technical' reply yet, I'll add my

two-pennorth for

> what its worth.
>
> If I understand it right the principle is as follows:-
> In a 'normal' stepper driver, a fixed voltage is applied to each

coil in

> turn but in alternating directions. This makes the adjoining

polepieces in

> the motor'flip' from one magnetic state to the other - i.e. either

North or

> South poles of equal strength. This makes the motor move in definite

jerks

> or 'full steps'.
> Now, in a microstepping drive, the same principle applies except

that the

> voltages applied to the poles are not equal. So, rather than always

applying

> full voltage to the windings, the voltage is reduced so that one

winding

> might get, say, 3/4 the voltage while the other gets 1/4. Doing this

means

> that, rather than the armature flipping completely from one

polepiece to the

> next, the relative difference in magnetic strength fo the poles will

make

> the armature turn only 1/4 step and 'hover' between the poles. The

next step

> would be produced by altering the voltages to 1/2 - 1/2 and then 1/4

- 3/4

> before the next full voltage change produces the full step.
>
> I may not have the technicalities exactly right but I'm sure others

will

> correct me. I think this is usually still done as discrete steps

but, if a

> true sine wave is applied, the motor should run as a synchronous

motor.

> I may be wrong???

No, you're right! A stepper will run well as
a synchronous AC motor provided the 2 AC
waveforms are 90' opposed and the drive is
current regulated rather than voltage.

Our new product uses sophisticated "current
slewing" at lower speeds where the computer
chip in the driver "ramps" the current from
one microstep to the next. The inbuilt computer
adjusts the ramp speed to suit the current
motor speed and allows for standard acceleration
rates etc. At lower speeds the motor is fed
with an almost perfect sinewave.

This give phenomenal performance, with full
torque but no "steps". Noiseless and without
resonance, and with 8x resolution over full
stepping. About as close to a servo as you get,
but only open loop of course.

You will see a lot of this new technology hit
the mills fairly soon, cheap high speed
embedded micros are allowing the perfect
stepper technology to become a reality. :o)
-Roman

PS. Possibly the hardest bit will be the
re-learning needed within the die hard
"microstepping doesn't work" crowd! ;o)