Re: Servo systems (was: re:cleaning, lovejoy, black box tach....)

--- In CAD_CAM_EDM_DRO@egroups.com, Jeff Barlow <jeff@b...> wrote:

> Plus, I'm still hung up on the idea that instantaneous position is

the

> thing we really want to control, rather than velocity. We do want to
> maintain a more or less constant feed rate, and there are clear

limits

> to the accelerations we can tolerate, but as long as the cutter is
> always in the right place at the right time the part should come

out the

> right shape.
>
> The real issue here, I think, is maintaining coordinated motion.
> Intuitively, I seems to me that if one has fine enough position
> feedback, that should be sufficient.
>
> Ok, anyone care to straighten me out on this?
>
> Jeff

Hi,

Actually position is what you want to control.

Using its electronic wisdom, the computer calculates the rate of
acceleration, velocity and distance based on the constraints and
parameters you have entered. It outputs the fruit of its computation
as continuously varying position with time. It is the job of a PID
servo to "fly in formation" with this computer generated moving
target.

If the target accelerates, the servo will too. If the target moves
fast, the servo will also. If the target reverses direction, so will
the servo. If the target stops, you know the rest.

All the while the servo is only maintaining position; a zero
difference in distance between itself and the target. It neither
knows or cares about velocity or acceleration; so long as it keeps
position, all the rest comes out in the wash.

Mariss