Re: stepper-servo system

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> I hoping someone might know a bit about using a stepper motor within a
> servo loop. Of course the feedback is to be implemented digitally
> which makes things even more tricky for me, I can remember the term z
> transform but not much else.
>
> Graham
>

Actually it's pretty easy. Your define a target voltage. You compare
that with the scaled gap voltage. If it's higher you set the
processor to flip the DIR pin the correct dir and then output a ramped
STEP rate from another pin. Drive a standard Step and Dir motor drive
OR get fancy and figur out all the electronics to do the power. That
is why some designs use a simple DC motor. Yould even use a relay for
direction on a DC motor. Not as elegent but a lot quicker to build!

For lower it just gets the DIR flipped the other way. It's important
to have a dead zone (no step pulses) to kill oscillations. The gap
voltage becomes the feedback. The coupling is loose rather than
like in a postional loop. If you try to do it by an encoder feedback
you will have to deal with loop gain and dampening.

You can profile the response rate and error tolerance in firmware on
the chip.

You can also accomplish the same thing with a quad comparator chip and
a handful of external components. Provides an UP or DOwn signal based
on the preset (via pot) target voltage. The pulsing can be gated on
from a 555 or similar chip.

Sometimes the process of working in an analog world works best with
analog technology.