Active suppression of milling chatter with LMI-based robust controller and electromagnetic actuator

Milling chatter occurs as undesired vibration in the cutting process, imposing negative effects on the tool's life, the quality of surface finishes and the limitation of machining efficiency. In this paper, a discrete output feedback robust controller based on linear matrix inequality (LMI) is developed for the chatter suppression, with an electromagnetic actuator applying the needed active control force. Considering the model of electromagnetic actuator and the actual mounting position in the milling system, active milling chatter control system is modeled and discretized for the controller's design. In addition, uncertainties of model parameters, such as modal parameters, axial cutting depth, are also considered. Then the LMI-based robust controller is designed, with which the performance of active chatter suppression can be guaranteed even the mentioned uncertainties exist in the actual milling system. Simulation results show that the chatter-free boundary of milling process is significantly enlarged with the designed robust controller. An experimental prototype for active milling chatter suppression is also presented, and milling chatter experiments are also performed with the developed spindle system, and the results show that surface finishes and chatter-free boundary are improved significantly.