A Study on a High Precision Magnetic Levitation Transport System for Carrying Organic Light-Emitting Diode Displays
High precision magnetic levitation control methodologies during the manufacture of Organic light-emitting diode (OLED) displays are designed, manipulated, and experimentally validated in this thesis. OLED displays have many advantages over conventional display technologies including thinner, lighter, lower power consumption, higher resolutions, and greater brightness. However, OLED displays require tighter environmental conditions of the manufacturing processes without the introduction of vibration and contamination. For this reason, magnetic levitation is used to transport the displays attached on the carrier during the manufacturing process. This thesis addresses several critical problems related to implement the levitation control performance of the carrier's motion during the manufacturing process.
Attractive magnetic levitation requires measurement of the airgap between the carrier and the levitation electromagnets. An algorithm for modeling the gap sensor installation errors was developed and subsequently used for controller development. A levitation controller only was initiated as the stationary point for optimal state feedback controller-observer compensator developed in this study. This optimal state feedback controller-observer compensator allows the carrier to be passed from support fixtures without the introduction of vibration. This controller was designed, and its levitation control performance confirmed with both simulation and experimental validation. To implement the levitation control performance of the carrier's motion, a second order notch filter and a first order low pass filter are designed to minimize the mechanical resonance and noise from the gap sensor, respectively. To reduce the sudden change of the levitation forces owing to the discrete allocation of the levitation electromagnets, a section control algorithm is developed; the sum of the levitation forces is equal to the weight of the carrier and the sum of the moment along the propulsion axis is equal to zero.
Using the developed control strategies, the peak to peak variation of the carrier’s motion at a standstill was 50 µm. This same motion at low-speed 30 mm/s was 250 µm. While at high speed 300 mm/s was 430 µm. The relative improvement in the levitation control performance of optimal state feedback controller-observer compensator over the levitation controller only was a peak to peak attenuation of 50 µm at low-speed and 270 µm at high-speed. Most significantly while using optimal state feedback controller-observer compensator could be passed from support fixture to support fixture, i.e., through the deadzone, without mechanical contact or other manufacturing processes, inhibiting vibration.
Having comparative simulation and experimental validation, the proposed control strategies were validated to improve the levitation control performance of the carrier under uncertain disturbance and sensor installation error, and it is expected to manufacture OLED displays with high productivity and low defect rate.