Servo holding torque

[Instance]

I've just converted a CNC from steppers to AC servos. With the maximum value of KI (in the PID loop), there still isn't enough 'holding torque', like there was with the steppers. Increasing KI *considerably* does give a good result, but then there are oscillations that can't be damped out. The maximum value of KI that's stable still allows about .01" of play.

Does this mean I just need a bigger servo motor?

[sizala]

friend, plz give us more information about your servo size.. which frame , which W(450watt, or 750w..like that).. and any link about the motors and the drivers... i m sure that i can help you.. i m using Panasonic 750watt motors and panasonic drive too.. there ar lots of settings in the driver that can effect the holding torque and the holding style of the motor...
and if i dont reply here then feel free to send me private msg...

best of luck

[mike_Kilroy]

also give info on the cnc (control) being used. what is the type command going to the servo +/-10v speed command? +/-10v torque command? step/dir? digital?

[Instance]

I have a Galil motion controller connected to Pacific Scientific PC834 drives via the analog motor command -/+10V. Mechanically, its Pacific Scientific R24 AC servo motors (NEMA23 size) connector to THK KR46 actuators.

I was able to get better stiffness by increasing KP further after I wrote that post (which allows higher KI too). I think I answered my own question by swapping motors though. Ultimately you need a larger servo to get a really stiff axis with a servo for a usable CNC.