Disturbance Rejection Control for Active Vibration Suppression of Overhead Hoist Transport Vehicles in Semiconductor Fabs

Abstract

In modern semiconductor fabrication plants, automated overhead hoist transport (OHT) vehicles transport wafers in front opening unified pods (FOUPs). Even in a cleanroom environment, small particles excited by the mechanical vibration of the FOUP can still damage the chips if such particles land on the critical area of the wafers. To minimize the vibration excitation force transferred to the FOUP, this research focuses on controlling the vibration displacement level of an OHT hand unit interface between the OHT vehicle and the FOUP. However, since the OHT vehicle and the FOUP keep traveling, the target system is floating and there exists no external anchoring point for a controlling force source. In addition, no sensor attachments are permitted on mass-production FOUPs, which makes this vibration level suppression problem more challenging. In this research, a custom testbed is designed to replicate the acceleration profile of the OHT vehicle under its travel motion. Then, system modeling and identification is conducted using simulation and experiment to verify the fabricated testbed design. Finally, a disturbance observer-based controller (DOBC) is developed and implemented on a custom active vibration suppression actuator with inertia force-based counterbalancing to reduce peak vibration amplitude from 870 μm to 230 μm.