I have a simple application for a stepper as a wire feeder(of course). I
have a 34 frame stepper with a 12:1 gear box and a Axidyne (tolomatic) 80v
5A microstepper drive. All I need it to do is run the motor 5 revolutions
(5/12ths rev on the gear box) whenever a limit switch is hit. That will be
about 100 times per minute.
What do I do that's reliable and cheap?
In the first place, using a switch which operates 100 times a second is
ludicrous. You are just asking for failure. This is
especially true when you have so many options to create electronic event
triggers. secondly. Stepper motors are prone to
undetected error slip when the load changes, as well as being notoriously
inefficient because half the current is used to brake
As I do not know the application, I cannot be very specific for a design, but I
would consider using magnetic clutches and brakes
as well as some feedback device to flag motion error. Please keep in mind that
cheap is relative to the loss of production. Being
penny wise and pound foolish is dumb.
This may be a good question to ask over on sci.engr.control. That group
is dying, but there are still lots of lurkers with experience in
industrial control. I'd bet that you'd find at least two if not more
folks who know the answer right off the bat.
It seems like one of those PLC's that you've been asking about --
particularly with the (fairly) high-level language support that Lloyd
was talking about -- would do this in a snap. Get the switch pulse,
emit the right number of pulses to the stepper at the right timing, repeat.
(Not, mind you, that I've ever worked with PLCs -- I've got extensive
control experience, but it always started with a blank piece of paper
and ended up with custom software on custom hardware. It comes from
working on small, high-performance equipment that always needed
semicircular boards doing impressive jobs in minimal space).
Control system and signal processing consulting
What's that Lassie? You say that Buerste fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue
by Mon, 14 Jun 2010 01:14:36 -0400:
you mean 100 steps per min. right?
If you have the driver circuit for the stepper motor and just need the
pulses, you could use two 555 timers(or one 556) to create the pulses.
The first timer is set to the frequency needed to run the stepper at
the required speed, and the second is used to enable the first timer
for the appropriate length of time.
The second timer is activated by your limit switch.
First, use an optointerrupter instead of a mechanical switch. Either a
complete unit with led on one side of a slot and phototransistor on the
other, or make your own. Then either go discrete logic with a clock through
a gate that gets triggered by the switch and goes to a counter that resets
the gate when it hits the target count. Can either count up or down (just
changes the reset logic on the counter outputs), and you can vary the count
in case you need one or two more or fewer pulses on the stepper motor. Or,
use a PIC or other microcontroller to read the switch and output the pulses.
If getting exactly the right number of steps is vital put an encoder wheel
on the motor with another optointerrupter and read that with the PIC and
count the resultant pulses; step until you hit your target.
Buy one of these controllers , http://www.splatco.com/controllers.htm and
use a Magnetic Proximity Like these
http://www.omron.com.au/technical_guide/proximity_sensor/index.asp as a
The controller is a bit of overkill, but it can give you delays or logic if
you require it.
There are some good tutorials on the Splatco website
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