Re: [CAD_CAM_EDM_DRO] Re: How bout this idea??

It's been about 10 years since I last did servo stuff, but here's what I
recall. By including a velocity tach loop, the system will break static
friction at the lowest possible error voltage -- less windup and jerk. Also,
a tach places the motor into a velocity mode -- more predictable. All this
yields smoother acceleration, better tracking, and the loop is more stable
than without tach feedback.

In the servo systems I worked on, we just ran the motor command voltage into
the PLUS input of the motor amp (like a big power op-amp), and the tach
feedback into the MINUS input of the motor amp. For DSP systems, we did the
digital equivalent via the control loop algorithm (say, on a Delta Tau
PMAC). The Gecko 3xx closes the loop around the servo motor via a tach
encoder, using it for position feedback. Makes them interchangeable with
steppers, but like others have said, with better performance (for many
reasons). I don't think there's any way to use both tach velocity and table
position feedback on a 3xx, but I'm sure Mariss can give a good description
of the 3xx's capabilities.

Having only a linear encoder on the table for feedback would lead to
infinite loop gain during back-lash and like stated before, the result is
oscillation/instability, position error and poor performance.

Regards,

Paul R. Hvidston, N6MGN
ACKSYS Engineering
Upland, CA

----- Original Message -----
From: <wanliker@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, March 13, 2002 8:54 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: How bout this idea??


> In a message dated 3/13/2002 9:52:50 PM Mountain Standard Time,
> paul_hvidston@... writes:
>
>
> > I'd want a tach on the motor shaft as well.
> >
> Why would this be necessary, and how would you incorporate it into the
> software/system?
> bill
>