Metal cutting has a troublesome obstacle in achieving perfect surface finishing while increasing productivity and in high speed machining, named chatter. It also has a deteriorating effect on the machine tool life and safety of the machining operation. Chatter is an unstable self-excited vibration which may happen due to a variety of reasons. Regenerative effect is the most dominant reason of chatter occurrence, which has been studied in this dissertation. In this thesis active control methods for chatter vibration by means of piezoelectric actuator are presented. possibility of improvement in stability lobes by means of changing different structural parameters are investigated. stability lobes diagram is one of the standard methods for chatter evaluation. It specifies the boundary of stable and unstable machining conditions. APiezoelectric sensor and a piezoelectric actuator have been used with the aim to active control of chatter vibration. Both analytical solution and numerical optimization methods are used for active vibration control. Performance of a PID controller in increasing the minimum points in stability lobes is investigated. A PD controller is designed analytically for moving stability lobes in order to stable machining condition. A genetic algorithm optimization has been used to design optimum active controller for chatter vibration suppression. As mentioned, generation of stability lobes which specifies the boundary of stable and unstable machining conditions involves a point by point, complex and time consuming calculations, which makes it impossible to present an inverse evaluation. This means that no closed form and analytical calculation to specify how far a machining condition is from the boundary of instability based on the controlled structural specifications of the machine tool can be presented for using in controller designing. To overcome this problem a genetic algorithm in controller designing has been used. The main idea is changing structural properties by active controller and in turn moving stability lobes in horizontal and vertical directions with the aim to make the machining working point far from unstable boundary, by considering minimum energy consumption. A comprehensive transfer function for the controller is considered. Performance of the designed mechatronic system on chatter suppression has been evaluated in both frequency and time domain and satisfactory.. Key Words: Chatter, Stability lobe, Piezoelectric, Active control, Genetic Algorithm.
