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This paper proposes a new six degrees-of-freedom (6-DOF) electromagnetic precision positioner, made of a hybrid mechanism utilizing both a magnetic driving force and the uplifting force of the fluid, for which a new structure, the electromagnetic actuator, and an effective controller have been developed. The concept of the mechanism design involves not only the magnetic driving mechanism, but also the fluid buoyancy and damping properties, which help to counterbalance the weight of the platen so as to achieve a very low steady-state power consumption. The four goals of the new system design include the following: 1) to have a large range of motion (at the mm level); 2) to achieve precision positioning; 3) to design a compact but low-cost mechanism; and 4) to achieve low power consumption. In this system, there are a total of eight permanent magnets (PMs) attached to the movable carrier, and eight electromagnetic coils appropriately mounted on a fixed base. After exploring the characteristics of the magnetic forces between PMs and electromagnetic coils, the general 6-DOF dynamic model of this system is derived and analyzed. Then, because of the naturally unstable behavior and uncertainties of the underlying system, a robust adaptive sliding-mode controller is proposed to guarantee system stability for both regulation and tracking tasks. Finally, extensive experiments have been conducted to demonstrate the performance of the proposed system. The experimental results show that the range of motion is 3 mm × 3 mm × 4 mm, and the tracking error in each axis is kept to within 10 μm, which reaches the limit of our optical sensors. These experimental results demonstrate satisfactory performance of the positioner in terms of theoretical analysis and experimental results.
Date of Publication: June 2011