Stepper control

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?
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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 and hold.
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. Steve

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Steve Lusardi wrote:

"Buerste" said "100 times a MINUTE'.

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Time is relative!
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Buerste wrote:

Even so, that is still a very high rate for a mechanical switch and a good target for replacement with something electronic. Even a switch with a 10M cycle rating will be failing in ~200 8hr shifts.
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the following:

Hah! I sincerely doubt you're doing your relatives 100 times a minute, either.
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<snip>

I'm done with my relatives, send pictures of yours!
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wrote the following:

Compliance.
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Buerste wrote:

Yeah, but try to get your relatives to stick to a time limit! ;-)
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Oops.... I meant per minute, not per second.....and it is still way too high for a mechanical switch. Steve

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Here's what I use now: http://www.grainger.com/Grainger/items/2F947?Pid=search
They last at least 6 months then they just bind-up. Kinda' surprising, isn't it? I'm sure the manufacturer didn't have my application in mind but I'm happy with the service life.
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On 06/13/2010 10:14 PM, Buerste wrote:

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).
--
Tim Wescott
Control system and signal processing consulting
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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.
--

Dan H.
northshore MA.
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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.
----- Regards, Carl Ijames

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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 position sensor. 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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