Modeling and Control of an Active Magnetic Bearing Spindle System
Magnetically levitated spindles have been considered for high-speed high-precision machining. These systems eliminate contact between the spindle and housing by replacing traditional bearings with rings of electromagnets which levitate the spindle in their center. Levitated spindles may be spun much faster than conventional ones; and with greater precision and longer median time to failure. Furthermore, the close coupling between the spindle dynamics and the cutting process allows for monitoring of cutting force which can be used to infer tool wear and part quality. Magnetic levitation systems are inherently unstable and require some form of feedback control. Challenges for the control system include robust stability, precise positioning of the spindle, and rejection of disturbances caused by rotor imbalance and the cutting process. This work presents the system identification and modeling of an Active Magnetic Bearing Spindle (AMBS) system and the design of a stabilizing controller. An internal model principle type control scheme, the plug-in resonator, is presented for the rejection of imbalance disturbances and reference tracking. The control system is implemented on the AMBS and experimental results are presented.