Control Approaches to the Suppression of Machining Chatter Using Active Magnetic Bearings

Several control approaches to the active suppression of machining chatter, a self-excited vibration that limits metal removal rate, are examined using a specially constructed turning experiment. The experiment employs a magnetic bearing for actuation and mimics the dynamics of a flexible rotor. Control forces are applied and vibration measurements taken at a location along this structure that is not collocated with the tool. Three control approaches are considered: speed-independent control, speed-specified control, and speed-interval control. Experimental results with these are compared to those obtained using proportional-integral-derivative (PID) control, a standard approach in the magnetic bearing industry today. Significant improvements over PID in machining stability lobes are obtained and the capability to highly tailor the cutting tool compliance so as to inhibit the onset of chatter is demonstrated. Cutting tests are also presented which demonstrate the significant improvements in chatter-free chip width that may be obtained with advanced control methods