| Machine tool chatter is a dynamics instability of the cutting process, which greatly impedes the implementation of high metal removal rates. Active Magnetic Bearings are promising for improving the cutting process stability because of their capability to actively control the machine tool's dynamic stiffness and damping. This dissertation investigates the application of robust control methods to active magnetic bearings so as to suppress the occurrence of chatter.; An experimental test apparatus was developed to examine chatter suppression. The system includes a flexible test rig driven by a magnetic bearing, a dSPACE real-time digital control system, and a lathe speed regulation system. The non-collocation of the sensor/actuator with the cutting tool and the inherent time-delay feedback of the cutting process both make active chatter suppression with this test rig a challenging problem.; Several important ancillary advances in chatter control system technology are made in this research. First, a feedback linearization scheme is employed to cancel the nonlinearity of the magnetic bearing in the control loop. This allows the magnetic bearing to be accurately treated as a source of force commands in spite of the large journal displacement that may be necessary for the active suppression of chatter. Second, a new technique for cutting process system identification is developed. This approach greatly simplifies the task by "breaking" the coupling effect due to the delay feedback of the cutting process.; Robust controllers were developed using three stability criteria proposed herein: speed independent stability, speed specified stability, and speed interval stability. Experimental results are presented which demonstrate that a significant increase in chatter-free metal removal rates may be achieved in comparison to standard magnetic bearing control methods. |
