Re: Stepper driver question - roller controller

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Marv Frankel" <Dcdziner@p...>
wrote:

>
> Guys,
> To explain a little further, a laminating machine has product
> coming off two rolls and they go through two pressure rollers.
> Sometimes the product on the bottom roll wanders to one side or the
> other, and gets out of registration with the upper product. The
> photocells will detect which way the product is going, and the stepper
> will skew the shaft to center the product.
> The stepper motor is a bipolar 440 oz.in, 4-lead, that will run on
> 24 or 48 volts. Since I'm "electronically deprived", I need the
> controller explained in simple terms. Does anyone have a simple
> schematic for a driver, or point me in the right direction. I know
> that the GRex that Gecko is coming out with will do the job, but I
> think it's slightly overkill for this application.
> Thanks for your help.
>
> Marv Frankel
> Los Angeles

Hi Marv,

440 oz-in, 48 volts is Gecko Territory, no doubt.

For the controller, you need, as you stated, a pair of sensors. one
for each side.

the logic is simple, either one off- do nothing. either one on, do
something.

here is the rub. you almost require a microcontroller. consider that
a slight adjustment will stop the progression of the part from moving
sideways. so, a sensor would have to be tripped to say, 'out of
bounds' once that sensor has tripped, a small adjustment might halt
the progression, another slight adj would send it back to the good
area, but it also might sent is back to the far sensor. This would
actually create an instability of control.

That rules out single point end switches entirely.

a pair of switches on each end would allow for a stepped response.
the first one closes and you are approaching the out of bounds area.
so a few steps go out. IF the sensor has not cleared in "X" time,
another few steps go out. this VERY gentle nudge to center would
prevent the control induced errors of a sloppy control.

Analogue sensors would be better. even a POT on an arm could ride the
edge. an analogue photo sensor would work as well, but dust will
effect it.


As I see your project, you would need
sensors on both sides,
a logic controller
a stepper driver (Gecko)
motor (you have)

Also, the device would have to have a means of adjustment. a simple
method would be to move the sensors. Or, pots on the controller.

As Alan mentioned, we are working on a different project that would
lend itself to this application very easily.

2 line LCD so on START, you can see the reading of the sensors. ie:
if they are dusty they would report a low signal.

Consider also that photo sensors would be subject to voltage spikes
and the natural loss of lumens of the bulb.

But, it sounds very interesting.

Dave