Experimental Verification of a Magnetic Levitation Transport System for the OLED Display Evaporation Process Under Vacuum

Abstract

The manufacturing process of OLED displays requires a high accuracy and a highly clean transport system because during the evaporation process, organic materials are inherently sensitive to contamination and uniform deposition of an organic layer is important. Roller-based transfer systems are not suitable for OLED evaporation processes because the roller-based system has a poor driving performance due to nonlinear factors such as friction and generates a large amount of dust. On the other hand, the magnetic levitation transport system has the advantage of not generating any dust, and it is possible to achieve high-precision control. In this letter, a magnetic levitation transport system for the OLED evaporation process is introduced. In particular, experimental verification of the developed system under vacuum is addressed. In terms of levitation control performance, the maximum fluctuation of the levitation airgap at a standstill is 15.3 $\mu$ m $_{pp}$ , and in low-speed and high-speed operation modes, it is 95.0 and 282.3 $\mu$ m $_{pp}$ , respectively. In terms of propulsion control performance, the maximum position error based on ISO-230-22006 standard is 1.5 $\mu$ m, and the maximum speed error at constant speed of 30 mm/s is 0.43 $\%$ . To achieve such a highly precise control, especially under vacuum, novel control algorithms such as intelligent section control are applied to minimize abrupt changes in the activation of electromagnets as the carrier moves, and command shaping algorithms are applied to prevent excitation of the resonance mode of the system while at a higher control bandwidth. Moreover, to verify long-term reliability, a 12-hour continuous operation test is conducted.