Magnetic Levitation Guiding System of a Ropeless Elevator for Semiconductor Wafer Vertical Transport: Experimental Evaluation

Abstract

A novel design of a magnetic levitation (maglev) ropeless elevator for semiconductor wafer vertical transport is newly presented. To satisfy high cleanliness during vertical transport of the wafer, linear motor lifting and maglev guiding are desirable instead of the conventional rope lifting and wheel-based guiding method. Owing to the physically noncontact maglev guiding, particle-free and high-speed operation can be achieved with remarkable ride quality. In this paper, practical challenges for wafer transport, such as the eccentricity of the mass center from the actuating axis, severe acceleration/deceleration conditions as well as periodic large disturbances from normal forces of the linear motor, resonance of the elevator, and manufacturing tolerance of the guide rail, are further considered to satisfy the ride performance in wafer transport by designing a robust feedback controller with a loop shaping technique. A full-scale maglev ropeless elevator was constructed to experimentally validate the effectiveness of the proposed method. The experimental results demonstrated excellent magnetic levitation guiding performance in 5 degrees of freedom, with a maximum airgap fluctuation of 227 µm under harsh lifting conditions (V max = 2600 mm/s).