Re: [CAD_CAM_EDM_DRO] Re: Why is the push to such high step rates (Grex and Arc100)?

turbulatordude wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:
>
>
>>It isn't. I believe Mariss is absolutely correct that any finer
>>division of the motor's
>>inherent steps below about 10 is pointless, unless the motor has an
>>
>>
>encoder.
>
>
>>There definitely are closed-loop microstepping systems, where they
>>
>>
>need fine
>
>
>>microstep resolution to keep the system from dithering under mechanical
>>load.
>>
>>Without an encoder, there is no way to control motor position even to a
>>single
>>full step. Friction and torque applied to the motor will cause the
>>position to
>>be offset from the nominal step position. And yet, they keep making
>>
>>
>these
>
>
>>systems.
>>
>>Jon
>>
>>
>
>It is that last sentance. If sounds like they are not all that good.
>
>When I have done the math, it often comes up that it really doen't matter.
>
>
>

wOW! This is just wierd! I absolutely have NO recollection of writing
"that last
sentence". It doesn't really flow with what I was trying to express.
And, in my
next message, I spoke about some systems with very high resolution, just
to say
they exist. I definitely don't NEED, or take advantage of, that
resolution, and it
does NOTHING to improve accuracy.

Basically, a step motor has a given level of positioning accuracy, and
microstepping
drives do nothing to improve that accuracy. They do make slow movement
a little
smoother, and extend the range of velocities that can be achieved
without resonance
and missed step issues. If you need actual positioning resolution finer
than one step
on the motor, you need either a closed-loop drive or a servo motor.

Jon