Re: [CAD_CAM_EDM_DRO] Steppers vs Sevrvos?

In a message dated 06-Aug-01 19:36:02 Central Daylight Time,
cnc@... writes:

> What are the +'s of Servos over Stepper motors and vice versa?
>
>

Steve! Try as I might, to come up with an "adult response" to this valid
question, I find it difficult! So, forgive, if I am frank: Servos require
more discipline, and much, much more smarts than I will surely EVER have!
Steppers can be applied with amazing success with no more than "reasonable
care and workmanship", and will "do the job" very, very well for many, many
CNC applications. Stepper-systems, done well, are less expensive, less
complicated, and easier to comprehend, for a learning-challenged old
[deleted] like myself.

At least "theoretically", a properly-configured servo system "always knows
what movement has (not) taken place, so, "lost steps" are not an issue. The
servo system is "close loop", meaning there is a shaft-encoder to "feed back"
the position information to the controller (computer, etc.), so, if something
should "snag", the machine will "keep on trying" to get where it was headed
before commencing further moves in the program. However, a stepper-system is
"open loop" - meaning that the signal (power) goes only from the controller
to the steppers, and there is no "closed loop" to return the "information" to
the controller, so, it never "knows" what movement has (not) taken place.
So, were there a "snag", etc., the program would have skipped steps, but
would keep on doing its thing, as if no problem had occurred (since it "never
knew"). Thus, an expensive part, and often the machine itself would be
damaged, if not totalled, due to an "everyday kinda snag".

HOWEVER... Many, many earlier CNC machines, and the little ones I build are
"steppers-only, open-loop", and, as they operate "within known confines",
they are perfectly reliable. To know which, when just simply takes years of
"doin' it"!!!

Lotsa luck!

Next question?

Jan Rowland, Troll


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