Design And Analysis On The Robust Control Of A X-Y Ballscrew Mechanism

This thesis presents the design and analysis on the robust control of a X-Y ballscrew mechanism. In this research, a practical and robust controller for positioning control is discussed. The Continuous Motion Nominal Characteristic Trajectory Following (CM NCTF) controller is investigated in this research for tracking motion of an AC driven X-Y ballscrew mechanism. The CM NCTF controller has a simple control structure and straightforward design procedure that does not require an exact model parameter of a plant. In order to enhance the accuracy of the control system, a suitable input signal is designed to make sure the X-Y ballscrew mechanism attenuate smoothly in the deceleration motion. The CM NCTF controller consists of a Nominal Characteristic Trajectory (NCT) and a Proportional and Integral (PI) compensator. The NCT is constructed using the open-loop experimental responses while the PI compensator is designed based on a practical stability limit obtained experimentally. The CM NCTF controller has been evaluated in tracking motion performance. In order to examine the adaptability of the controller to the change of the input, experiments with various inputs is carried out. Besides that, the robustness of the controller is validated through the change of the load of the system. In order to examine the usefulness of the CM NCTF controller, a PI-D controller that has a similar control structure is designed and compared. The tracking performance of the CM NCTF controller is evaluated in maximum peak error Emax, percentage of error Epercent, and root mean square of error Erms. Emax is the difference between the output peak and the reference input, and Epercent is the percentage of the peak error with respect to the reference input. The experimental results proved that the CM NCTF controller has demonstrated better positioning response than the conventional NCTF controller and the PI-D controller by showing a two times smaller motion error. The robustness of the CM NCTF controller is clarified using X-axis, which has heavier load than the Y-axis. The experimental results have again proved that the CM NCTF controller demonstrates better tracking performance than the conventional NCTF controller and the PI-D controller in X-axis. As a conclusion, the CM NCTF controller has better positioning performance as compared to the conventional NCTF controller and PI-D controller. In future, the contour motion for X-axis and Y-axis will be done to evaluate accuracy of the controller. Besides that, the robustness performance in term of change of disturbance force will be considered