Re: Stepper vs. Servo control

I think this can be an interesting discussion because I think that the
solution of this problem problem is simple, If you have a lot of masses
to move then you have to use servo, if you have a smaller machine it is
much more simple to use steppermotors. Low priced amplifiers already
exists. I think about Dan Mauch's stepper and servoamplifiers.
I think the main problem is the controllersoftware. Myself I would
like to have a software that could run on an old 386 or 486 machine
and that the speed could reach about 200 ipm with a resolution at
about 0.01mm. With this solution you could get a realy low-cost system.
Ernst



-----Original Message-----
From: CG <cnk@...>
To: CAD_CAM_EDM_DRO <CAD_CAM_EDM_DRO@onelist.com>
Date: 22. september 1999 05:42
Subject: [CAD_CAM_EDM_DRO] Stepper vs. Servo control

>From: "CG" <cnk@...>
>
>
>I've been following the latest discussion about low-cost servo amplifiers,
>which got me thinking about step/direction servo systems such as Dan

Mauch's

>(the Servolite?):
>
>If all moves in a CNC system are in the end very small linear

point-to-point

>moves, due to interpolation, contouring, etc., then what is the difference
>between a system that uses step and direction output to a step/direction
>servo driver such as the one Dan Mauch sells (Servolite?), vs. the more
>common motion controller/servo amp setup. Assume the resolutions, motors,
>and encoders are the same, electrical noise isn't a problem, and we're
>talking about a tacho-less system. It seems to me the main difference

would

>be in the PID filter, and probably something to do with "feedforward".
>Whether you keep track of "commanded" position in the PC, on the motion
>controller board, or out at the step/direction driver doesn't seem to me
>like it should make much difference.
>
>I'm asking because software like IndexerLPT can generate over 100,000
>steps/sec on a slow Pentium, doing all of the interpolation for several
>axes, with unlimited lookahead. If you wanted machine resolution to, say,
>.00025", and designed with 10X that for the encoder/electronics resolution
>(.000025"), that's 40,000 steps/inch. That would allow you to run at up to
>2.5 inches/second (150 ipm) which sounds like plenty for what most of us
>want to do. Cut the electronic resolution down, and the bottleneck would

be

>somewhere else. The lookahead, in my view, is what would save this system.
>Being able to anticipate and plan out all accelerations and decelerations

in

>advance would, I hope, remove some of the burden on the PID control system.
>
>It seems very attractive to me to be able to eliminate the need for motion
>control boards (ServoToGo and the like), and talk directly to

step/direction

>servo drivers. Status and E-stop concerns could be easily reported to the
>PC with a few more bits. The PC would have to expect that the motors were
>where they were commanded to be (or on their way there) unless the status
>flags indicated a problem.
>
>Any comments on this approach? Any reviews on current step/direction servo
>drivers and their limitations? Am I just crazy too?
>
>Carlos Guillermo
>
>
>
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