Re: Stepper vs. Servo

Tom,

I'd say you've got it! One thing I will comment on is the statement
about "windows-based" controls... This depends entirely on the
methods used. I'd stick to the part about steppers needing
a "regular" pulse rate, and not demonise one class of system since
there are many different ways to implement the pulse train.

Secondly, it is easy to forget that servos can miss "steps" too!
While the resulting part may LOOK okay, it can actually be WAY off
spec! Since the servos just "catch up" when whatever overload is
overcome, the part may "seem" okay when in fact it isn't. This is not
much of a concern for well maintained, professionally designed
machine tools but needs careful consideration by "amateur" designers.

Hope this helps.

Ballendo

P.S. As you mention, the "appropriate" accel/decel values will be
different for steppers vs. servos.

--- In CAD_CAM_EDM_DRO@y..., "Tom Eldredge" <harmonyt@r...> wrote:
> Mariss,
>
> Thank you for your good post on stepper vs servo. I will add a
comment in
> the form of a question, since I my experience is so limited. In my
two
> years of working on a controller using a stepper driven BP machine
as my
> test bed, I learned that acceleration and deceleration are real
touchy with
> steppers. I have found that servos are much more forgiving in this
area.
> Is this your observation? Also, when making moves with a stepper
wherein
> the x and y axi are very close in frequency, but not exactly, such
as when
> one makes a move at 43 degrees, DEPENDING ON HOW the pulses are
generated,
> the steppers may have more difficulty in following an irregular
pulse rate
> if there is one. This would seem like it would be an issue with
controls
> which are windows based.
>
> I do not know how many of the various low end controllers would
> demonstrate this characteristic, so I don't know how much of an
issue it is
> for most users.
>
> I know you are a hardware guy, but maybe it is worth commenting
on. Lost
> steps are a pain in the neck, and starting and stopping with
appropriate
> levels of acceleration and deceleration are also issues that I
consider when
> thinking of the servo /stepper question.
>
> Anyone, please feel free to correct me, which I hope you do if I am
off
> track.
>
> Thanks for all of your valuable input,
>
> Tom Eldredge