Robust control and characterization of nonlinear microdynamics in a ball-screw driven slide system

Ball-screw driven slide systems are largely used in industry for motion control applications. Their performance using standard PID control algorithm is not satisfactory in submicrometer motion control due to nonlinear friction effects.; In this research, controllers based on a bristle-type nonlinear contact model are developed and implemented for submicrometer motion. For submicrometer positioning, a PD control scheme with a nonlinear friction estimate algorithm is developed. The proposed scheme showed superior performance compared with a conventional PID controller. For tracking, the proposed controller in conjunction with disturbance observer performed well even when the friction estimate was not perfectly tuned and the system parameter was allowed to vary. For tracking, a disturbance observer was added to reject external disturbances and to improve robustness. The experimental results indicate that the proposed controller has consistent performance in positioning with less than 1.5% of steady-state error in the submicrometer range. For tracking performance, the proposed controller shows good and robust tracking with respect to parameter variation.; To improve the robustness of the controller, a sliding mode control suitable for compensation of nonlinear microdynamic friction and parameter changes in a ball-screw driven slide system was discussed. In this work, an algorithm that effectively calculates variable switching gain based on the observation of parameter variation and friction disturbance is proposed. To verify the effectiveness of the proposed algorithm, a comparison with the conventional slide mode control is presented and experimentally verified. It is shown from the result of this work that a variable switching gain is critically important in compensating for varying nonlinear friction in the sub-micrometer motion range for ball-screw driven systems.; A means of increasing structural damping in a ball-screw driven slide system is examined by piezoelectric element. The possibility of dissipating mechanical vibration by passive electrical shunts is examined as passive damping improvement, and it shows about 5 dB of reduction of vibration amplitude. Then, the active vibration damping by velocity signal feedback is examined using the piezoelectric element as a force transducer. The active damping provides the reduction of vibration amplitude about 12 dB. In addition, the use of piezoelectric actuator for micropositioning shows good step response for commands between 100 nm and 300 nm.