| Rotating machinery is widely used in the world of manufacturing.Among them,large rotor systems are mainly used in some large-scale machinery and equipment,such as aero engines,air compressors,etc.;However,in some sophisticated industries,small or micro-rotary machines are needed to work,such as instrumentation,medical systems,etc.At the same time,small rotary machines have higher requirements for the stability and convenience of working operations.It is an indispensable support component for rotating machinery systems.The degree of performance of the bearing will directly affect the working state of the rotor system.Most of the bearings used in the machine are ordinary rolling bearings and plain bearings.The advantage is that the structure is simple and the application is convenient.The disadvantage is that the working stability is not high;At present,some new types of bearings have been developed,such as air bearings,magnetic bearings,etc.,but have complex structures and are limited by materials;Among them,ultrasonic bearings can avoid these disadvantages well and become the main target of research and development by scholars at home and abroad.However,since its gas levitation force is not very large,it is mainly applied to small rotor systems.From this point of view,this paper also conducts an in-depth study on the working mechanism of ultrasonic bearings.The specific research content of this paper is as follows:(1)A new type of ultrasonic extrusion bearing is designed,the main components of which are piezoelectric ultrasonic transducers and rotor bushings.The piezoelectric ultrasonic transducer is composed of a piezoelectric ceramic adhered to a thin metal cylinder of a metal aluminum.The main working principle is to use the inverse piezoelectric effect of piezoelectric ceramic to drive the deformation of the metal aluminum thin-walled cylinder repeatedly.According to the near-field ultrasonic suspension mechanism,gas extrusion occurs in the extremely small air gap between the cylinder and the sleeve.The membrane,which produces a film levitation force,suspends the rotor system,thereby reducing friction and vibration.(2)Modal analysis of the piezoelectric ultrasonic transducer to determine its resonant frequency;The Reynolds equation is established according to the mechanism of ultrasonic suspension gas;The finite difference method is used to solve the equation numerically,and the suspension force of the gas extruded film of the ultrasonic bearing is obtained.And the influence of different parameters on the strong force of the suspension pressure of the gas extrusion film was analyzed and the conclusion was drawn.(3)Exploring the working condition when the bearing capacity of the ultrasonic bearing was less than the rotor load.When the rotor load is greater than the bearing capacity of the bearing,the outer surface of the sleeve will be in local contact friction with the inner surface of the thin wall,which lead to a gas squeeze film levitation force and surface contact force between the rotating stators,that is,a mixed friction state.The rotor system of the ultrasonic bearing in the mixed friction state is mechanically modeled and solved,and the system dynamic response curve is obtained.The influence law of different parameters on its working state is analyzed.(4)When the ultrasonic bearing is in the mixed friction,there is local friction between the rotating stators,so it is necessary to analyze the thermal field.The thermal field distribution of ultrasonic bearings under different rotor loads is studied.Moreover,in each load,the force analysis of the rotor system is performed,and the value of the surface contact force between the rotating stators is derived.Combined with the ultrasonic suspension gas film force,the local friction heat generation of the ultrasonic bearing under the mixed friction work is comprehensively considered;It is fully discussed at three different rotor speed frequencies:low speed,medium speed and high speed;Change the influence parameters of the ultrasonic bearing and explore its thermal field change when the ultrasonic bearing is in the mixed friction state.(5)The ultrasonic bearing-rotor system test bench was designed,and its dynamic response and heat generation were experimentally verified.Carry out experimental operations using a single variable principle;Finally,the dynamic response results of the ultrasonic bearing-rotor system under different influencing parameters and the thermal field distribution are obtained.The theoretical simulation results are further verified,and the working mechanism of the ultrasonic bearing in the mixed friction state is obtained. |
PDF Full Text Request