Design of Motor Rotor Support Structure and Rotor Dynamics Study Based on Ultrasonic Levitation Technology
|Course||Mechanical Design and Theory|
|Keywords||ultrasonic levitation piezoelectric transducer squeeze film rotor|
The ultrasonic levitation is a technology which uses high frequency vibration toachieve suspending support. Because of its advantages of Non-contact,little frictionand wearness, requiring no lubrication and simple structure, there are broad prospectsfor the application field of High-speed rotating machinery, precision gyroscope andflywheel energy storage. This paper is based on the project of the National NaturalScience Foundation "Ultrasonic Supporting High-speed Motor (item number:50977037)", proposes constructing ultrasonic levitation support structure for themotor rotor, to study on the dynamic characteristics of the rotor supported by theultrasonic suspension. The paper studies the mechanism of near-field acousticlevitation through theoretical analysis, finite element calculations and experimentaltesting, for cone supporting the rotor both ends and vertical layout of the structure ofscheme, a two-way conical ultrasonic suspension support structure is designed andmanufactured, and a preliminary experiment of the operation of the motor rotor iscarried out. The main contents of this paper are given as follows:1. The relevant theory of the piezoelectric material is introduced,and thefundamental vibration mode of piezoelectric vibrator is analyzed. Electromechanicalequivalent method is employed to analyze the resonance characteristics ofpiezoelectric vibrator, and moreover, the performance parameters related to the energyconversion process are discussed. On this basis, the mechanical and electricalequivalent model of the piezoelectric ultrasonic transducer is created. There areinfluence factors of the transducer effective radiated power, including the vibrationmode of transducer, the materials of components, the vibration speed ratio of frontcover and rear cover. Such work will help lay the foundation for further study.2. The acoustic radiation force model and the gas squeeze film suspension modelfor ultrasonic suspension support are built, further to understand the mechanism of near-field acoustic levitation. Using the methods of experimental testing andtheoretical analysis, the relationship between the levitation gap and carrying capacityis obtained. Calculation results and the scope of the two models are compared, and thegas squeeze film suspension model is more suitable for the calculation of levitationforce in the conditions of small suspension gap by comparison. According to transientanalysis results of gas squeeze film model, the change of dynamic pressure within thelevitation gap is observed,and the time average of the levitation force is calculatedthrough the cycle average processing. Through the analytical derivation and numericalcalculation, it is found that equivalent squeeze number and vibration amplitude ratioexert great influence on the ultrasonic levitation ability, and the relationship betweenultrasonic vibration and the mechanical effect of stiffness and damping in the gap gasfilm is obtained, which provids a theoretical basis for structure design andperformance analysis of ultrasonic levitation supporting device.3. The resonance frequency and vibration mode of piezoelectric transducer withconical radiating surface is measured by experiments and analyzed by finite elementmethod. The performance of the conical-type ultrasonic levitation support structure isanalyzed and tested, during this process the relationship between the levitation forceand levitation gap is gained. Through theoretical analysis it is realised that the criticalspeed and vibration mode of the motor rotor is affected by the change of levitationgap in the ultrasonic levitation condition. a two-way ultrasonic suspension supportstructure is designed and manufactured, and the rotation state of motor rotor isinvestigated under the conditions of ultrasonic levitation support. The relationship oflevitation gap and the maximum speed of the motor rotor is tested, it is found thatthe stiffness of the gas film can be enhanced by reducing the suspended gap,andsimultaneously the maximum speed of the rotor is increased.