Contoller design and implementation of 6-DOF magnetically levitated positioner with high-precision

This paper presents the controller design and implementation of a high-precision 6-degree-of-freedom (6-DOF) magnetically levitated (maglev) positioner. This high-precision positioning system consists of a novel concentrated-field magnet matrix and a triangular single-moving part that carries three 3-phase permanent-magnet linear-levitation-motor armatures. Since only a single levitated moving part, namely the platen, generates all required fine and coarse motions, this positioning system is reliable and low-cost. Three planar levitation motors based on the Lorentz-force law not only generate the vertical force to levitate the triangular platen but control the platen's position and orientation in the horizontal plane. All 6-DOF motions are controlled by magnetic forces only. The platen is regarded a pure mass system, and the spring and damping coefficients are neglected except for the vertical directions. Single-input single-output (SISO) digital lead-lag controllers are designed and implemented on a digital signal processor (DSP). This 6-DOF fully magnetically levitated positioner has a total mass of 5.91 kg and currently exhibits a 120 mm x 120 mm travel range. This positioner is highly suitable for semiconductor-manufacturing applications such as wafer steppers, Several experimental motion profiles are presented to demonstrate the maglev stage's capability of accurately tracking any planar and 3-D paths.