Subject: stepper motors
From: bern
[email protected]9.co.uk
Date: 5/8/2004 3:11 PM Central Standard Time
Message-id: <
[email protected]>
would anyone know of a way to turn a signal meant to drive a stepper
motor into a pulse witdh modulation duty cycle (mapped to the start/end
parameter of the original stepper controls
That's a pretty interesting problem, mostly because there are only a few
circumstances in which the solution you want would be useful. Steppers give
angular control of motor shaft position by counting steps. Most applications
using stepper motors are actually trying to provide positional control of some
kind. In order to do that with another kind of motor drive, you would need
some kind of feedback from the motor shaft. That feedback is usually provided
with a resolver or an encoder, and the whole closed-loop system is called a
servo. It's necessary because motor speed curves are non-linear, and are
usually bent way out of shape by load torque requirements. That kind of thing
is not for the faint of heart, and requires more expertise than you'll probably
get from free advice on a newsgroup. Your statement at the end of your post
about mapping to the start/end parameter of the original stepper controls
indicates that you'll probably need a servo-type solution.
Packaged servo systems exist which accept the step/direction-type signals
common to stepper motor drivers. They're not cheap, though. You'll have to
purchase a motor with feedback encoder built-in along with your servo driver.
The application$ people who $ell the $ervo $ystem to you will be happy to help
with $etup and any nece$$ary fiddling (their $uper application$ help i$
$sometime$ built into the price).
If your control system is just controlling motor speed rather than position,
with neither angular shaft position or number of turns being important, you
might be able to do this. You'll also need some latitude as far as response
time (frequency-to-voltage converters have inherent lag). The easiest solution
would be reading the pulse frequency and outputting PWM with a cheap
microcontroller. There are also a number of analog methods for accomplishing
this, but from your description, they don't sound like what you need. If you'd
like more advice, a good description of your control system would be in order.
Good luck
Chris