Development and control of an ultraprecision magnetic suspension stage

Advanced tool actuation technologies that deliver ultra precision positioning accuracy with high stiffness and high bandwidth are critically important to modern fabrication processes such as micro/nano fabrication. In this dissertation, the research on development and control of an ultra precision magnetic suspension stage (MSS) for precision engineering is presented. The research consists of development of the stage system, development of robust nonlinear control algorithms for ultra precision motion control, and development of robust disturbance rejection algorithms to improve dynamic stiffness. Preliminary characterization of micro grooving using the developed MSS is also performed in this research.; The current developed MSS utilizes an electromagnetic actuation scheme and a laser interferometric sensing system with nanometric resolutions. A general framework for ultra precision motion control of magnetic suspension actuation systems in multiple degrees of freedom is developed. It encompasses the development of nonlinear electromagnetic force model for six-degree-of-freedom actuation, and the design of the necessary control architecture. Feedback linearization is adopted in the nonlinear control architecture, while H_∞ robust control synthesis technique is adopted in the design of linear compensators upon the linearized system. Experiments results have illustrated the desired characteristics of the developed system in terms of stabilization, positioning, tracking, and contouring. Inter-axial coupling error reduction by MIMO design is also addressed.; Improved dynamic stiffness is critically important to ultra precision machining and micro/nano fabrication where ultra precision tracking at high bandwidths in face of significant external forces is required. For rejection of wide band disturbances, two approaches, namely, a disturbance compensation algorithm based on the inverse plant dynamics and a chattering free sliding mode (CFSM) disturbance rejection algorithm, are developed. The CFSM scheme utilizes a continuous approximation of the switching function to eliminate chattering and a novel derivative control term to elevate the bandwidth of disturbance rejection. Experimental results have shown that the dynamic stiffness is effectively increased with the developed scheme. To reject narrow band disturbances, a control structure that combines the internal model principle and frequency estimation algorithms based on the adaptive notch filtering theories is developed.