Honeywell KFC225 servos - operation Q

On Wed, 09 Mar 2005 08:33:05 +0000, Peter wrote:
....
However, superimposed onto the DC control signal (-10V to +10V or so)
I saw a sinewave ripple, around 500Hz IIRC. The amplitude was only
about 100mV P-P.

The question is whether this is intentional, whether e.g. the servo
uses the presence of this ripple as a confirmation that the computer
unit is still (partially) functioning. It would be quite a clever
trick, but it does mean that it isn't possible to fit a good filter
onto the servo input.

It could very well be intentional - I once worked with a servo system
where they intentionally superimposed a triangle wave on the control V -
they called it "dither". It kept the hydraulic actuator from sticking in
place, so it could move smoothly.

Hope This Helps!
Rich

Rich Grise wrote:


It could very well be intentional - I once worked with a servo system
where they intentionally superimposed a triangle wave on the control V -
they called it "dither". It kept the hydraulic actuator from sticking in
place, so it could move smoothly.

Dither lets it respond more quickly. It's a common mechanical actuator
trick.

I'm sure this frequency is way beyond the bandwith of the motor
drivers.
Sounds like the switching freq on he KFC power supply.

Dithering would be a couple of orders of maginitude lower freq.

I don't think it will negatively affect anything. Could even come
from some sort of ground loop.

Bill Hale