Re: Steppers versus Servos

Arne Chr. Jorgensen wrote:

> From: "Arne Chr. Jorgensen" <instel@...>
>
> Okay,
>
> Ron wrote "Re: Digest Number 315" :
>
> >I think this servo vs steppers is getting a bit nuts-
>
> It sounds like people are getting tired of this. I am sorry if I have caused
> such trouble.
>

Arne,

Yes, I suppose we have massaged this subject about enough.

I for one found the discussion very helpful though. Never feel sorry about sharing
information. That's what we're here for.

A Synopsis of what I learned here and elsewhere is as follows:

-If one really feels the need for full-time encoder feedback a servo is more economical
and higher performance.

-Some commercial step systems due use encoders- but primarily for
lost step detection rather than real time control.

-There are many steps systems out there that are robust and do not loose
steps in normal operation. The units can be more reliable than brush
type servos.

-Steppers are easy to use and very good for small precise incremental
motions. Following error can be virtually non exsistant. They are not
as good for very high speeds.

After playing with the one of the 8 1500 in oz steppers and drives and a
lot of calculations and head scratching I have decided to bite the bullet
and stay servo. Inertia and load matching was good but-

-I'm pushing 837 lbs on the x axis.

- I spent a year and a half of spare time designing and building a structure
that can handle much higher loads and accelerations than these steppers/drives
can provide.

-I would have to pass through stepper resonance often in the
cutting cycles I desire. Avoiding those step rates would severely
compromise the utility of this particular machine.

-This is a commercial operation (on a shoestring budget). A devastating
slipped step crash might affect the dinner table later.

-I already have a $1500+ Tech80 servo board with 1 millisecond path
update and 250 microsecond servo update capability. And EMC.

I think I will try to sell these units or trade them for servo amps at Groban
or Mannmade here in Chicago.

So again thanks to all for the discussion!
--
Leslie M.Watts
Illinois Tool Works
Corporate Advanced Technology group
(847) 657-4559
http://www.netcom.com/~leswatts/leswp.html