RE: [CAD_CAM_EDM_DRO] Re: Clarification for microstepping requirement

The other thing with microstepping, and I'm happy to be corrected here, is
that microstepping is done by varying the duty cycle of two coils. The
frequency of the signial is often fixed and typically around 20-25KHz. This
means that a 5KHz step signal results in a MAXIMUM of 4 microsteps per step.
At 10KHz, or 1KHz with a step multiplier set to 10x, you can only half step.

This actually works out well as I understand it. Many older, half stepping,
drives would transition to full stepping above a certain speed, so I assume
that microstepping drives don't deliver any more top end speed. My 3977
drives actually drive and unloaded motor faster in full step mode than in
any of the microstepping modes. I acknowledge that this may change when the
motors are loaded though.


PK


-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of jeffalanp
Sent: Tuesday, 13 December 2005 7:45 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Clarification for microstepping requirement

Hi,
With your [do you get there "all-at-once" or gradually] senario,
don't forget, that with the "all-at-once" FULL step mode, you
actually OVERSHOOT the FULL STEP point. After reaching the maximum
point at overshoot, you start moving back towards the full step
point, but again, because of momentum, you overshoot again, though
not so much. This oscillation around the full step point can take a
while to die down, and while doing so, transfer its vibrational
energy directly to your machine.

So, instead of a FULL step, move a smaller step (1/8th, 1/10, or
1/16th for example). Your acceleration to get to the closer point is
less, so your overshoot is less, so less ringing and vibration, and
less time to wait for vibrations to disipate so you can actually move
faster in many cases, and power is not wasted trying to bring the
motor to the FULL step point.

Jeff


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Andy Wander" <awander@v...>
wrote:

>
> 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.
>
>
>
> This communication including any attachments, are intended
> for the exclusive use of the addressee(s) and contains
> confidential or copyrighted materials. Duplication,
> distribution or reproduction is strictly prohibited by law
> without written permission of Verrex
>

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