Theoretical Analysis And Experimental Study On Non-contact Bearing And Ultrasonic Motor Based On Near-field Acoustic Levitation

As the important support and power components of mechanical equipment,bearing and motor play an irreplaceable key role.With the rapid development of science and technology and modern industry,traditional bearings and motors can no longer meet the requirements of precision machinery and equipment for parts with high precision,small structure,large driving torque and no electromagnetic interference.Acoustic levitation is a kind of non-contact suspension technology which uses the radiation force in high energy density s ound field to suspend objects.The non-contact bearing and ultrasonic motor based on near-field acoustic levitation overcomes some problems of traditional non-contact bearings(hydrostatic bearing,hydrodynamic bearing,magnetic bearing)and contact ultrasonic motor,and expands the application fields of bearings and motors.However,the research and development time in this field is relatively short,especially the domestic research started relatively late,and the research is less.There is a lack of necessary cognition and understanding on the driving mechanism of bearings and motors.At the same time,most of the proposed bearing and motor structures are relatively complex,and they have not yet been applied in practical engineering.In the view of the a bove problems,a new type of non-contact bearing and ultrasonic motor were proposed in this paper based on the principle of near-field acoustic levitation.The levitation load-carrying characteristics and rotation characteristics of squeeze film air bearin g and the ultrasonic motor were analyzed theoretically and experimentally,and the working mechanism of the squeeze film air bearing and the non-contact ultrasonic motor was reveled.The contents,methods and achievements of this paper are as follows:A new type of squeeze film air bearing with flexure pivot-tilting pads based on the principle of near-field acoustic levitation was proposed.An analytical model for the levitation load-carrying characteristics of the squeeze film air bearing with flexure pivot-tilting pads was established.The bearing vibration characteristics and levitation load-carrying characteristics test rig was designed and built.The resonance frequency,vibration amplitude,vibration mode,and rotor levitation characteristics of the be aring were tested and analyzed by using the test rig.Based on the finite element method,the modal analysis and stress analysis of the bearing were carried out,and the influence of the structural mode shape on the squeeze film thickness was considered.Combined with the experimental results,the working mode at resonance frequency was determined,and the correctness of the finite element model was verified.By testing and analyzing the change process of the rotor levitation height in the experiment,the levitation load-carrying characteristics of the squeeze film air bearing with flexure pivot-tilting pads were verified.The finite difference method and Newton-Raphson iteration method were used to solve the analysis model of levitation load-carrying characteristics,and the force analysis model of the pad was established to analyze the swing process of the pad.The results of the model were in good agreement with the corresponding experimental results,which verifies the effectiveness of the analytical mode l.The variation of pressure distribution,levitation load-carrying capacity,pad position and other parameters with time was studied,and the influence of structure parameters and operating conditions on the levitation load-carrying characteristics was analyzed.The levitation load-carrying mechanism of the squeeze film air bearing with flexure pivot-tilting pads was analyzed theoretically.The influence of material properties on the bearing performance is further studied theoretically and experimentally.The results show that the time-averaged pressure greater than the ambient pressure in the period provides the levitation force for the bearing,and the material properties ha d the obvious influence on the levitation load-carrying capacity of the bearing.An analytical model of the rotating characteristics of the squeeze film air bearing with flexure pivot-tilting pads under coupled working mode was established.The bearing rotational characteristics test rig was designed and manufactured,and the influence of acoustic radiation force on the bearing rotational characteristics under different working modes was tested.The rationality of the model was verified by comparing with the solution results of the nonlinear model of rotor motion.The influence of bearing installation mode,structural parameters and driving signal on bearing levitation load-carrying characteristics and rotational characteristics under different working modes was predicted by using the analytical model.The results show that the bearing levitation force in coupled working mode was proved by the gas film force produced by dynamic pressure effect and the acoustic radiation force generated by the squeeze film effect.The acoustic radiation force had a certain inhibitory effect on the vibration of the rotor,which reveals the working mechanism of squeeze film air bearing under coupled working mode.The theoretical analysis model of squeeze film air bearing with elastic hinge considering static and dynamic deformation was established.Based on the finite element method,the harmonic response of the bearing was analyzed by ANSYS software,and the rationality of the finite element simulation model was verified by the existing experimental results.The static deformation and dynamic deformation cause d by DC bias voltage and AC voltage were fitted respectively and coupled to the gas film expression.The working mechanism of squeeze film air bearing with elastic hinge was analyzed theoretically.The influence of the static and dynamic deformation of the structure on the rotational characteristics of the bearing was analyzed by the theoretical model,and the influence of the acoustic radiation force on the bearing stability was studied.Compared with the traditional aerodynamic bearings,the characteristi cs of squeeze film air bearing were summarized and analyzed.The results show that the static and dynamic deformation of the structure can promote the stability of the rotor system under certain conditions.Compared with the traditional aerodynamic bearing,the squeeze film air bearing had obvious advantages.A new type of non-contact ultrasonic motor based on the principle of near-field acoustic levitation was proposed.The analytical models of coupled squeeze film control equation,rotor motion equation and stator disk balance equation were established.The vibration and rotation characteristics of the motor were tested by the test rig,and the correctness of the analysis model was verified.T he working mode of the motor was determined by experimental test and finite element analysis.The driving mechanism of non-contact ultrasonic motor was revealed from two aspects of theoretical analysis and experimental test.The results show that the tilting and asymmetric structural modes of the stator disk cause the motor to produce driving torque,and the driving frequency had a significant effect on the rotating characteristics.In conclusion,based on the principle of near-field acoustic levitation,a new type of squeeze film air bearing with flexure pivot-tilting pads and ultrasonic motor were proposed in this paper,which were systematically studied by combining theoretical analysis experimental test methods.At the same time,the deep theoretical analysis of a kind of squeeze film air bearing with elastic hinge w as carried out.The analysis models of levitation load-carrying and rotation characteristics of squeeze film air bearing with flexure pivot-tilting pads were established.The modal analysis and stress analysis of the bearing were carried out by using finit e element method.The test rigs of the bearing vibration characteristics,levitation load-carrying characteristics and rotation characteristics were built respectively.The theoretical analysis model of squeeze film air bearing with elastic hinge consideri ng the static and dynamic deformation of the structure was established,and the harmonic response of the bearing was analyzed based on the finite element method.The correctness of the theoretical analysis model and finite element simulation model of the s queeze film air bearing was verified by the experimental results,and the working mechanism of the levitation load-carrying characteristics and the operation characteristics under coupled working mode were revealed.The theoretical and experimental results show that the time-averaged pressure greater than the ambient pressure in the period provides the support levitation force for squeeze film air bearing,and the acoustic radiation force produced by squeeze film effect had a certain inhibitory effect on th e motion of the rotor,and the stability of the rotor system can be enhanced under certain conditions.The theoretical model of a new non-contact ultrasonic motor was established.The modal analysis of the ultrasonic motor was carried out by using the fini te element method.The validity of the theoretical analysis model and finite element simulation model was verified by the vibration and rotation characteristics test rigs of the motor,and the driving mechanism of the non-contact ultrasonic motor was revealed.The research results of this paper can provide some guidance for the design,experimental test and theoretical analysis of squeeze film air bearing and non-contact ultrasonic motor,and lay a foundation for further promoting the squeeze film air beari ng and non-contact ultrasonic motor to practical engineering application.