Re: New Article Posted

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@...> wrote:

>

<SNIP>

> >but does not lose any steps when in sync mode. I've been using this
> >setup in half-step mode for months and have not had any problems.
>
> Yes, in HALF STEP mode it will work fine. BUT you WILL lose steps if
> you try to microstep whilst using the sync mode. (or going into and
> out of it).
>

I thought about that today a little. I have a 13 tpi screw on a 1:1
pulley on a 200 step motor. that puts me at 2,600 full steps and some
high number of microsteps. I think the driver is 8x ? 20,400
microsteps ?

Assuming the sync pulls the motor to the nearest 1/2 step, we can
assume that anything one microstep closer than 'center' will fall back
and anything one mircrostep past 'center' will fall forward. Center
being that value equally between half steps.

in my case, 1 inch = 1/2600th of an inch or about 0.0003846"
a microstep would be 8 times that or 0.00004807

Now, assuming there are 4 microsteps between each half step, and the
first two will fall back and the second two will fall forward.

assuming further that I have 100 pauses across a part and in every
case, the driver was on 2 microsteps. that would mean the sync mode
would have pulled the position back 2 microsteps each of those 100
times for 200 total microsteps.

with a microstep being 0.000048077 (rounded), then 200 microsteps
would be 0.01" or 10 thou.

the assumptions are;
#1) that the drive actually does pull to the nearest half step when in
sync mode.
#2) that every sync mode would drive from the greatest distance from a
half step
#3) that every sync mode would drive the same way.
#4) that the driver does not automatically recover.

If the sync mode were split 50/50 all errors would effectively cancel
themselves out.

As for my PCB etcher, I move to 1.000" or 4.500" or 0.01" some other
whole number or simple decimal that will be divided evenly by half
stepping. (10 tpi screw on that) in those cases the sync mode would
never have any effect.


Probability would favor that the plus errors and minus errors would
cancel each other out to a large degree.

And, even if one had 1/3 one way, and 2/3 the other, my 200 would drop
to 66. And, if half were one micorstep away and half were 2
microsteps away, then those 66 times is only 99 microsteps or
0.0048077. or just under 5 thou.

5 thou is certainly enough to measure, but in so many cases, I would
never even fall on a microstep that it might be a rare occurance.

Also, if one were drilling a bunch of 80 pin DIP chips or such, the
first hole would be off by a max of 2 microsteps, but the driver would
have the axis pulled to the half step. and I assume that the driver
would never know it was not on that axis, so it would not
automatically add (or subtract) those microsteps. So, if the axis
were to be pulled to the nearest 1/2 step, and the driver didn't know
it moved, then the other 79 pins would fall on the half step.

I am sure there are applications where 5 thou is huge, and others
where is it nothing. I would also assume that some might have many
hundreds of axis stops.

Interesting problem. I would be interested in any empirical data.

Dave