Abstract: Aiming at the problem that the existing massive transfer motion positioning platform does not have the ability of adjusting within a small axial distance, a composite configuration motion positioning platform (MPP) based on axially translational single-degree-of-freedom Lorentz force magnetic bearings is proposed. In order to improve the bandwidth and accuracy of the platform's axial suspension control, a multi-channel magnetic bearing consisting of an L-shaped permanent magnet and an tilted magnetized permanent magnets is designed. A mathematical model of the magnetic flux density in the air gap region is established through the equivalent surface current method, and the structural parameters affecting the magnitude and uniformity of the magnetic flux density are obtained. The structural parameters are screened by sensitivity analysis and optimized. After optimization, the air gap magnetic density intensity of the bearing is 478.20 mT, and the axial fluctuation rate of the air gap magnetic density is 10.6%, which is 48.02% and 1.8% higher than the 323.07 mT and 10.8% of the original scheme, respectively. Based on the optimization result, a massive transfer device and a Lorentz force magnetic bearing are developed, and magnetic density measurement verification and chip transfer effect testing are conducted. The results show that the optimized scheme has an average magnetic density intensity of 476.75 mT in the bearing air gap, an axial fluctuation rate of 11.1% in the air gap magnetic density, and a current stiffness of 88.6 N/A, which is consistent with the design results. The use of bearing axial active take up of chips in transfer can reduce transfer bad spots generated by chips not completely off, which is of great significance for improving the efficiency and yield of massive transfer.

Key words: massive transfer, Mini/Micro LED, motion positioning platform, Lorentz magnetic bearings, optimized design