Re: [CAD_CAM_EDM_DRO] Basic stepper control question

Seems like you will need to incorporate a mechanical brake, actuated by your control at the time of final location, THEN power down. Hopefully you have room.

I would guess that there is no sure fire way to apply or remove power to a stepper without the risk of movement without some mechanical locking device. It would certainly sound like running Full Step is helpful as MicroSteps would be worse.

Even then, "re-powering" could allow for a step off either way but it sounds like that wouldn't matter...........

Chris

Tom Kulaga wrote:

> I've got a problem, and I know you guys can help me out. I'm involved in a project at work that uses a stepper motor to drive a mechanism. The motor only runs to get the machine to an optimal position, then stays there indefinately. Nothing fancy, full step mode, low current, little bitty NEMA 17 motors, etc, but once we get it into position, it absolutely cannot go moving around. I've done a ton of mechanical design to get all the backlash out of the system, and to thermally compensate the whole fixture so the critical point stays right where we want it even when the air temp goes WAY up.
>
> Here's the problem: in order to keep the controller and motor temps down, the electrical engineer on the team instructed the software guy to kill all current to the motor once the move is complete. Now, our test engineer is seeing random jumps right about when the power is cut. None of us knew that the current was being shut off till just recently, and when I heard about it, I theorized that shutting off the current causes the motor to fall off the intended position, but only some of the time.
>
> I came up with this theory while playing with a 200 step per rev motor, and noting that you only feel 50 little "clicks" per rev when you spin it by hand. If you shut off the current, wouldn't you expect the motor to drop back to the nearest "click" position, moving you 1-2 steps away from where you really want to be?
>
> The easiest thing to do would be to test it by leaving the current on, but the engineer I'm disagreeing with is also the project leader and a really opinionated "I'm never wrong" kind of guy. If I, a mechanical engineer, question the electrical aspects of the design, I damn well better have something to back me up. That's where you come in. Am I wrong or right? If I'm right, is there some reference material, white papers, or other fact-based evidence I can use to support my conclusion? Frankly, I don't think this guy knows steppers from a hole in the ground, but I'm pretty sure he'll argue with me anyway. Having proof that I'm right would simultaneously fix a serious problem as well as shut him up. That would be, well, enjoyabl e to say the least. :)
>
> Thanks for anything you can offer, guys.
>
> Tom Kulaga
>
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