Servos Noisy In Minus Direction

[tmday7]

Hello,
I have a 1996 Acer knee mill with Centroid CNC10 v2.64 i got about a month ago that i have been working on. It mainly needed some mechanical work which i have completed.
Just finished replacing encoders with UsDigital E5s 500CPR. Now iam trying to tune the SEM servos.
With the original Lucas Ledex encoders, servos where real noisy(Buzz not ringing) in both Plus and Minus directions. Using the UsDigital encoders servos are nice and quiet in the plus direction but make a buzzing sound in minus direction. If i jog in .001" increments in minus direction the buzz gets loud and stays like this until i jog back in the plus direction. Sometimes control will shut off servo if left idling like this for to long and reports that Axis was Idling to high.
Thought about getting a higher CPR head and disk but have experienced in the past with other machines that some servo motor,encoder and drives combo dont like the higher resolution, is this so with the Centroid DC30IO? That said i dont get why this problem would only be in one direction.

Any help much appreciated
Troy

[cnckeith]

dc servos naturally make a bit of noise when holding position.
that being said if the axis is free (sloppy) the motor will 'hunt" in between a few encoder pulses which makes noise..if you put your hand on the motor pulley while it is doing this and the noise goes away..there is not enough damping in the system (too loose)
also, i've seen dc motor brushes make noise in one direction and no noise in the other which is a mechanical issue as well.