【作者】 刘磊；

【导师】 杨志刚；

【作者基本信息】 吉林大学 ， 机械设计及理论， 2012， 硕士

【摘要】 超声波悬浮技术是一种利用高频振动实现物体悬浮支撑的技术，由于其具有非接触、摩擦和磨损小、无需润滑、结构简单等优点，因此在高速旋转机械、精密陀螺、飞轮储能等领域具有广泛的应用前景。本文结合国家自然科学基金项目“超声波支承高速电机（项目编号：50977037）”，构造用于支承电机转子的超声波悬浮支撑结构，并研究转子在超声波悬浮支撑条件下的动力学特性。本文通过理论解析、有限元计算以及实验测试等方法对超声波近场悬浮机理进行了研究，针对转子两端受锥面支撑并且竖直布置的结构方案，设计制作了锥型双向支承的超声波悬浮支撑结构，并对电机转子的运行情况进行了初步的试验研究。本文主要研究内容如下:1.介绍压电材料的相关理论，分析压电振子的基本振动模式，通过机电等效方法分析压电振子的谐振特性，讨论了与能量转换过程相关的性能参数。在此基础上建立压电式超声换能器的机电等效模型，讨论影响换能器有效发射功率的因素，包括换能器的振动模态、各组成部分的材料、前后盖板的振速比等，为下一步的研究奠定基础。2.为进一步了解超声波近场悬浮作用的机理，建立了超声波悬浮支撑的声辐射力模型和气体挤压膜悬浮模型。采用理论分析和实验测试的方法得到悬浮间隙与承载能力的关系，并对两种模型的计算结果进行了比较，通过比较发现气体挤压膜悬浮模型更适合小悬浮间隙条件下悬浮力的计算。通过对气体挤压膜悬浮模型进行瞬态分析，获得悬浮间隙内的动压力变化情况，并经过周期平均处理得到悬浮力时间平均值；通过解析推导和数值计算获得了等效挤压数以及振动幅值比对超声波悬浮能力的影响规律，分析间隙气膜刚度、阻尼等力学效果与超声波振动之间的关系，为超声波悬浮支撑结构的设计与性能分析提供理论依据。3.通过实验和有限元方法测量和分析了圆锥辐射面压电换能器的谐振频率和振动模态。对圆锥型超声波悬浮支撑结构的性能进行分析和测试，获得了悬浮力与悬浮间隙之间的关系。从理论上分析了在超声波悬浮支撑条件下，悬浮间隙变化对于电机转子临界转速与振动模态的影响情况，设计制作了用于支承电机转子的超声波悬浮支撑结构，研究电机转子在超声波悬浮支撑条件下的运行情况，测试悬浮间隙与电机转子最高转速的关系，经研究发现通过减小悬浮间隙，能够增强间隙气膜的刚度支撑效果，并提高转子的最高转速。更多还原

【Abstract】 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.更多还原