RE: [CAD_CAM_EDM_DRO] Clarification for microstepping requirement

Eric:

It's not how many positions you have(in this case, every .000025"
instead of every .00025"), but rather how smoothly you get from one
position to the next. While you CAN stop in between the "full" steps,
your position will NOT be guaranteed to be so many 1/10ths of a full
step. Rather, it is that while you are traveling, going from full step
to full step, do you get there "all-at-once" or gradually(well, of
course, you DO get there gradually, but I am referring to what the drive
is telling the motor to do.

It's kind of like a dimmer on a light. If "OFF" is one full step
position, and "ON" is the next full step position, do you "switch the
lights on" or do you dim them up gradually and smoothly.

From what I understand, the dimming up, as opposed to the switching on,
can make your light bulb filaments last longer as there is less stress
imposed by a gradual change in applied voltage.

The situation with the steppers is that at certain speeds you can have
nasty resonances cause by the "switching" of the motor voltages, and
that by gradually changing the voltages(micro-stepping) you are much
less likely to have those problems.


Andy Wander
Verrex Corporation

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of ERIC QUARNSTROM
Sent: Monday, December 12, 2005 4:20 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Clarification for microstepping requirement

Hey all:

I read the great FAQ's on this site regarding steppers and how they work
and microstepping. Very inciteful and I think I even understand how they
do it.
What I can't quite figure out is why it is required. In one of the FAQ's
it says the primary purpose for microstepping is to eliminate the
jerkyness between steps. However, when I do the math on my proposed set
up I come up with a movement of the axis per step that is so small I
can't consider it to be 'jerky'. Therefore I am afraid I either didn't
understand what I read well enough or I'm missing something. My math is
below and I welcome comments.

System statistics:
Lead screw with 10 TPI
1:2 gearing between motor and lead screw motor with 200 steps/revolution

My math:
Every turn of the lead screw gear produces .1 inches of travel.
Every turn of the motor gear produces .05 inches of travel Motor has 200
steps per turn of the motor so every one step would produce .05/200
inches of travel

In summary .00025 inches of travel per full step seems like a very small
amount of movement. So why would I need to divide that by 10 for a
microstepping drive?

Thanks in advance,
Eric Q.



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