Design and control of a MAGLEV platform for positioning in arbitrary orientations

Abstract

This paper presents the design, control and evaluation of a magnetically levitated six degree of freedom (DoF) positioning platform for robot-based inline measurements on freeform surfaces. The positioning system employs eight voice coil actuators (VCAs) for actuation and is capable of maintaining a constant free-floating position of the mover with respect to its supporting frame in arbitrary orientations of the entire system. Based on a balanced design, low crosstalk between the DoFs is obtained and six decentralized model-based PID controllers are designed and implemented. By using the position signals of six optical proximity sensors with sub-micrometer resolution as feedback, the prototype system achieves a closed-loop control bandwidth higher than 100 Hz for each DoF. The translational and rotational positioning ranges are about ±180μm and ±2 mrad, respectively. Steady-state rms positioning errors between 142 and 262nm for the translational DoFs are achieved. Motion experiments show the successful operation of the positioning system in arbitrary orientations, keeping positioning errors below 5 μm/40 μrad.