Re: stepper version

[Fred Proctor <proctor-at-cme.nist.gov>]

Dan Falck wrote:

> You said that you have a stepper version built into EMC that uses the
> parallel port.  Do you have any docs that describe it?  On the website,
> there is a very good description of the servo system, but nothing about the
> stepper version.  Does it use encoders? Open loop? Limit switches? Home
> switches? I'm sorry to be so repetitive, but I would like to know something
> about it before I attempt to install Linux (again).

I just put some more documentation of the stepper motor setup on the EMC
web page,

	http://www.isd.cme.nist.gov/projects/emc/emcsoft.html

Look at the Figure 1 for a short block diagram comparing servos with
steppers, and the section "Setting up Stepper Motors" for how to do it.
There's a pinout for the parallel port bits there also.

It doesn't use encoders, and is therefore open-loop. Limit and home
switches are looked at, but the limit on input bits means we've ganged
the positive limits together, negative limits together, and homes
together. This can be changed easily (in emc/src/emcmot/extsmmot.c) if
you can get more bits either through a second parallel port card or by
using bidirectional parallel ports that let you read C0-C3 as inputs.

I will probably end up changing how the code runs bits to the steppers
based on a better method used by John Storrs. I haven't done this yet,
though. This won't change the pinouts or anything.

Matt Shaver asked about outputting the stepper phases directly, instead
of using step-and-direction bits as we do now. This should not be a
problem, but I need the phase diagrams and also a setup to test on. I
have a stepper test stand from Microkinetics. When Matt gets his stepper
motor Bridgeport working, I could try phasing on that.

> I would be interested in the archive version of the EMC list, so that I
> might not bother you with things that you have probably answered over and
> over before.

The mail list archive should be available to non-NISTers in the next few
days.

--Fred