Rotor speed control strategy to avoid resonance frequencies of turbo-molecular pump

Abstract

A novel design of composite turbo-molecular pump (CTMP) is proposed. The major configuration of CTMP is composed by a coarse pump, a turbo-molecular pump (TMP) and a magnetic gear unit (MGU) capable of speed amplification. The modal analysis and the study on rotor/bearing dynamics are undertaken at first to estimate the resonance frequencies of the TMP blade rotor itself solely and the interactive dynamics of blade rotor/radial active magnetic bearing (BR/RAMB) subsystem. Secondly, an economical and efficient method by adjusting the angular acceleration speed of BR, namely RDPS, is proposed to ensure the natural frequencies of BR/RAMB sub-system are not driven by the rotor speed all the time. Besides, a speed route of rotor during the take-off cycle of TMP is proposed to satisfy the requirements of system stiffness and prevention of system resonance being driven. Finally, a position conversion method is introduced to solve the problem of distinct locations of gap sensors and the actual gap between rotor and the auxiliary bearings such that the measurement feedback to the controller, RDPS, becomes applicable to formulate the correct actions for providing enough gap margin to prevent collision of rotor against bearings. To sum up, the CTMP possesses the merit of reduction of electrical energy consumption by 17%, compared with the conventional TMP unit. By intensive computer simulations, the RDPS indeed manifests its outstanding performance to efficiently skip or bypass the natural frequencies of the closed-loop system within a very short time period and guarantee the system stability.