| Self-excited vibration, so called chatter, is known to cause detrimental effects on the machined surface finish and to decrease the machining efficiency. Because of the small amplitude, high frequency properties of chatter, it requires active vibration control providing a force to the cutting system to overcome the chatter effect. To provide such a force, the piezoactuator has been introduced into the cutting system as an important controllable positioning device for ultra-precision machining. With the application of piezoactuator, a much more accurate model is required for achieving the ultra-precision control. In this thesis, rather than using the commonly accepted linear Merchant model, the relationship of cutting force and chip thickness variations is explored as a nonlinear hysteresis model. Furthermore, the piezoactuator itself also exhibits hysteretic behavior. Thereafter, the turning system investigated in this thesis is described as a class of uncertain systems with hysteresis and time delay. The novelty of this thesis is that the hysteresis model is for the first time incorporated into the chatter suppression design for metal cutting systems, but notoriously, it severely complicates the task of controller design and analysis. In this thesis, in order for ultra-precision machining, several robust adaptive control schemes are proposed in different circumstances with such complicated turning systems. The simulation results show significant reduction of chatter by the proposed adaptive controllers in all the circumstances. |
