Re: re:RE: More about motors?

Jon,

I hope it's not a flame war! My first paragraph stands, correct.

"There IS no INHERANT difference between the ACCURACY attained by
steppers vs. servos. In fact, a case could be made (strongly) that
with a stepper system you ALWAYS know the limits of your accuracy,
while with servos the accuracy can be "all over the place", depending
on system stability, etc."

I purposely stayed away from microstepping because of its'
limitations! The further you go from MY statement(s) the easier it is
to make your point! A similar issue "could" be raised by me to
compare a "high end" stepper system, to a poorly designed servo setup!
Typical steppers are manufactured with a 3% OR 5% ACCURACY. This is
NON-cumulative. So the stepper position is repeatable, as you say,
and can be "corrected" into whatever level of ACCURACY is desired.

So lets end this. I can design a stepper system with a high degree of
ACCURACY. I can design a SERVO system with a high degree of ACCURACY.
I can ALSO design EITHER with a low degree of accuracy! The ACCURACY
is NOT INHERANT in EITHER system!

And in the low-cost market, until VERY recently, the "NORM" for
servos was poor compared to steppers. It "looked good on paper" but
the feedback loop corrected poorly, and servos were often "rounding
corners" on square toolpaths!

So, to re-state, the paragraph above IS correct as written. And the
examples given in my post support it.

Ballendo

P.S. I KEEP saying that the situation IS changing! That servo's ARE
becoming more reliable and useful! Compared to steppers. But you
CAN'T just SAY servos are better. Or steppers are better. The TOTAL
of the SYSTEM DESIGN WILL answer the question. Not the servo, or the
stepper.


Jon E wrote:

>>I can't let this MYTH be perpetuated any longer!
>>
>>Steppers run in an open-loop configuration (no encoders or other
>>position feedback system) are as accurate as the steppers and other
>>components are.<big snip>