| When the lateral dimensions of the transducer,horn,and tool head in the longitudinal ultrasonic vibration system are close to or greater than a quarter of the longitudinal wavelength,they are called large-scale vibrators.Due to the Poisson effect,the large-scale vibrating body will produce severe lateral vibration.The existence of lateral vibration will affect the performance and reliability of the system,shorten the service life of the system,and may even directly lead to the failure of the system in severe cases.Therefore,how to effectively suppress harmful lateral vibrations in a large-scale longitudinal ultrasonic vibration system and improve the uniformity of amplitude distribution and amplitude gain of the system's radiation surface has always been a difficult problem in the field of power ultrasound.Ultrasound workers have also conducted a lot of research on this problem.Most of the current research focuses on two aspects.One is to study the vibration analysis method of large-scale ultrasonic vibrating body and the other is to study the vibration control method of large-scale ultrasonic vibrating body.In the research of vibration analysis methods,apparent elasticity theory has been widely used.Especially when analyzing the relatively regular shape of non-slotted vibrating body,the apparent elasticity method can obtain satisfactory results.However,for large-scale vibrating bodies with relatively complex shapes and with many slots/holes processed on them,the analysis and calculation process will be very complicated,and even large errors will occur.Therefore,it is necessary to provide a new and more effective support theory for the analysis and design of large-scale and complex-structured vibrating bodies with multiple slots/holes.For vibration control,the methods often used at present include machining slots/holes on the vibrating body,attaching elastic parts and machining fine seams,etc.These methods can improve the performance of large-scale ultrasonic vibration systems to a certain extent,but they are very dependent on the developers' practical experience and simulation calculations,and lack effective theoretical basis.Therefore,in order to better meet the application of large-scale ultrasonic vibration systems in actual engineering,it is necessary to explore new and more effective coupled vibration control methods.The essential cause of harmful lateral vibration in a large-scale vibrating body is the propagation effect of elastic waves and the coupling vibration of the vibrating body.Therefore,the effective means to control the lateral vibration is to control the elastic wave behavior in the vibrating body.The near-period phononic theory provides an effective way to artificially control the propagation of elastic waves in a vibrating body.In this paper,combining the band gap characteristics of the near-period phononic crystal structure with the demand for suppression of harmful vibrations in large-scale ultrasonic vibration systems,a novel and effective vibration control method is studied.The large-scale sandwich longitudinal vibration piezoelectric ceramic composite transducer,the large-scale wedge-shaped horn,and the large-scale ultrasonic plastic welding tool head of the ultrasonic vibration system are designed into a near-period phononic crystal structure with a lateral band gap.The lateral band gap realizes the effective suppression and attenuation of harmful elastic waves in the system,and while improving the reliability of the system,it also prolongs its service life,thereby realizing the purpose of optimizing the large-scale ultrasonic vibration system.A new method to improve the uniformity of the amplitude distribution is studied by using the defects(point defects,line defects,homogeneous dislocation junctions,heterogeneous dislocation junctions)of the near-period phononic crystal structure.The large-scale sandwich type longitudinal vibration piezoelectric ceramic composite transducer,the large-scale wedge-shaped horn,and the large-scale ultrasonic plastic welding tool head of the ultrasonic vibration system are designed into a near-period phononic crystal structure with defect characteristics.The Anderson localization characteristics and wave-guide characteristics of defects are used to control the amplitude and phase of the displacement field,so as to achieve the purpose of improving the uniformity of the amplitude distribution of the radiation surface of the large-scale ultrasonic vibration system.The chute type two-dimensional longitudinal-torsion composite mode ultrasonic vibration has attracted much attention due to its processing advantages on hard and brittle composite materials such as ceramics and carbon fiber,but it has the problems of low energy conversion efficiency and small output torsion component.Therefore,how to optimize the mode conversion longitudinal-torsional composite vibration structure and improve the longitudinal-torsional ability has become an urgent problem to be solved.Based on the above problems,the paper puts forward the research of ultrasonic vibration system based on near-period phononic crystal structure.The main research contents are as follows:1?The theory of apparent elasticity is used to analyze the coupled vibration of a large-scale sandwich longitudinal piezoelectric ceramic composite transducer.According to the analysis results,on the front cover of the transducer,a near-period phononic crystal structure based on a two-dimensional square lattice with a abnormal radius point defect is designed.The radial band gap of the designed structure is used to suppress the harmful radial vibration of the piezoelectric ceramic composite transducer.And the Anderson localization effect of the point defect is used to control the intensity and phase of the local sound field to further improve the uniformity of the amplitude distribution of the radiation end face of the transducer.Analyze the influence of the radius and height of the air cylindrical hole of the point defect,and the shape of the defect scatter on the longitudinal resonance frequency and amplitude distribution uniformity of the transducer in order to find the structural parameters that enable the transducer to obtain the best performance.This design can provide theoretical and experimental basis for the optimal design of large-scale sandwich longitudinal piezoelectric ceramic composite transducer.2?The theory of apparent elasticity is used to analyze the coupled vibration of the large-scale wedge-shaped horn.Aiming at the problem of uneven displacement amplitude distribution and small amplification factor of the large-scale wedge-shaped horn,a near-period phononic crystal heterogeneous dislocation junction based on different filling coefficients is constructed on the large-scale wedge-shaped horn in this design.The directional band gap of the dislocation knot can be used to suppress the lateral vibration in the length direction of the horn.And the position of the local conduction mode can be adjusted by changing the size of the lateral dislocation distance?x,so as to achieve the purpose of improving the uniformity of the amplitude distribution and increasing the amplification factor of the large-scale wedge-shaped horn.The finite element software is used to study the influence of the structural parameters of the heterogeneous dislocation structure on the longitudinal resonance frequency,the uniformity of the longitudinal displacement distribution,and the amplification factor of the horn vibration system,which provides a new method to further promote the engineering application of the large-scale wedge-shaped horns.3?The theory of apparent elasticity is used to analyze the coupled vibration of large-scale two-dimensional and three-dimensional tool heads.According to the analysis results,two structures are constructed on the large-scale two-dimensional long strip tool head,which are the homogeneous dislocation junction structure based on the straight air scatter slots and the homogeneous dislocation junction structure based on the oblique air scatter slots.The two structures are used to optimize the two-dimensional ultrasonic vibration system,and the optimization effects of the two scatter slots are simulated and compared to find the best air slot structure parameters.The air scatter slots based on the near-period phononic crystal structure are constructed in the X and Y directions of the large-scale three-dimensional tool head to suppress the coupling vibration of the tool head with two large lateral sizes.The fan-shaped slopes and composite horns are used to increase the amplitude gain of the radiation surface of the three-dimensional vibration system.In order to verify the accuracy of the theoretical and numerical simulation results,the electrical impedance and vibration displacement distribution of the plastic welding vibration system were tested through an impedance analyzer and the full-field scanning laser vibration measurement system.The experimental test results verify the effectiveness of the optimization and provide a favorable basis for further research on the suppression of lateral vibration of large-scale tool heads.4?The periodic fan-shaped hole structure is used to solve the problems of small torsion component and low longitudinal-torsion efficiency in the current chute type longitudinal-torsion composite mode ultrasonic vibration system.Through finite element simulation to study the influence of the structural parameters of the fan-shaped hole on the resonance frequency,torsion amplitude,rotation angle and shear stress of the longitudinal-torsion composite mode ultrasonic vibration system in order to find the structural parameters of the fan-shaped holes that can make the system obtain the best performance.Finally,calculate the improvement range of the fan-shaped hole structure to the system performance. |
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