Vibration Transducer Research Articles

카메라 영상을 이용한 진동변위 측정

Vibration measurements using image processing have been studied by many researchers as it can remotely measure vibration displacements at multiple points simultaneously. It is difficult, however, to obtain accurate displacement from the measured image signals because the resolution of image data is dependent on camera performance and normally lower than that of vibration transducer directly measured. This paper suggests the enhanced technique for vibration displacement measurement by applying the expected value of edge probability distribution to the varying pixel points in the image. The method can both increase the resolution limit of camera image and decrease the measurement errors. The working performance of the proposed technique is verified applying to the vibration measurement of a rotating machine.

Study on Ultrasonic Assisted Laser under Liquid Processing Platform

On the basis of laser-ultrasonic machining and water assisted laser combined machining methods a composite processing method of ultrasonic assisted laser under liquid is proposed. As the key of new technology, its experimental device of combined processing is designed. The device mainly consists of laser processing machine, ultrasonic vibration system (ultrasonic generator and transducer), tank and the water circulation system, fixture of specimen. By Using of finite element method nature frequency of tank with two fixtures of specimen is solved under the condition of combined processing. Analysis results show that the main device parts would work reliably under the vibration of transducer. Physical experiment under liquid proved this platform in water could transmit ultrasonic vibration to specimen and the new combined processing is promising.

A tool for controlling accelerometers. Secondary calibration data

Vibration monitoring requires acceleration transducers capable of providing data with high precision. Accelerometers are the most frequently used vibration transducers. Their calibration plays an important role in measuring vibrations and is a key component in ensuring the integrity of the vibration measurement. For managing secondary calibration data of accelerometers, a database computer system was implemented. The implementation of this software has been an important step forward in providing a wide range of analysis and display tools. This paper reviews the main concepts involving accelerometer secondary calibration and describes the tool developed and the methods used in its development.

Wind Turbine Condition and Power Quality Monitoring by the Approach of Fast Individual Harmonic Extraction

Increasing deployment of wind turbines requires efficient condition monitoring to ensure the safety and availability of these machines. Grid code also requests the operator to enhance the monitoring of the quality of the power generated by the wind turbine. Most commercially available wind turbine condition monitoring systems are supported by a number of vibration transducers. They consequently are complex in hardware, expensive in price, but inefficient in computation and particularly lack of power quality monitoring ability. In view of this, an innovative electrical signal analysis-based wind turbine condition and power quality monitoring technique is developed in this paper by the approach of individual harmonic extraction. The proposed technique has been verified in the lab by applying to detecting both the mechanical and electrical faults emulated on a specially designed wind turbine condition monitoring test rig. Experiments show that the proposed technique is not only sensitive to the faults, but alert to the degradation of power quality.

Role of Key Comparisons in Assurance of the Uniformity of Measurements in the Field of Vibration Measurements

A hardware implementation of a technique of calibration of a reference vibration transducer that corresponds to the protocol of key comparisons and makes it possible for holders of secondary references to assure the uniformity of measurements in the field of vibration measurement is described.

A rectangle-type linear ultrasonic motor using longitudinal vibration transducers with four driving feet

To make full use of the vibrational energy of a longitudinal transducer, a rectangle-type linear ultrasonic motor with four driving feet is proposed in this paper. This new motor consists of four longitudinal vibration transducers which are arranged in a rectangle and form an enclosed construction. Lead zirconate titanate ceramics are embedded into the middle of the transducer and fastened by a wedge-caulking mechanism. Each transducer includes an exponentially shaped horn located on each end. The horns of the vertical transducers intersect at the base of the horizontal transducers' horns; the tip ends of the horizontal transducers' horns are used as the driving feet. Longitudinal vibrations are superimposed in the motor and generate elliptical movements at the tip ends of the horns. The working principle of the proposed motor is analyzed. The resonance frequencies of two working modes are tuned to be close to each other by adjusting the structural parameters. Transient analysis is developed to gain the vibration characteristics of the motor. A prototype motor is fabricated and measured. The vibration test results verify the feasibility of the proposed design. Typical output of the prototype is a no-load speed of 928 mm/s and maximum thrust force of 60 N at a voltage of 200 Vrms.

Condition monitoring of gearboxes using synchronously averaged electric motor signals

Due to their prevalence in rotating machinery, the condition monitoring of gearboxes is extremely important in the minimization of potentially dangerous and expensive failures. Traditionally, gearbox condition monitoring has been conducted using measurements obtained from casing-mounted vibration transducers such as accelerometers. A well-established technique for analyzing such signals is the synchronous signal average, where vibration signals are synchronized to a measured angular position and then averaged from rotation to rotation. Driven, in part, by improvements in control methodologies based upon methods of estimating rotor speed and torque, induction machines are used increasingly in industry to drive rotating machinery. As a result, attempts have been made to diagnose defects using measured terminal currents and voltages. In this paper, the application of the synchronous signal averaging methodology to electric drive signals, by synchronizing stator current signals with a shaft position estimated from current and voltage measurements is proposed. Initially, a test-rig is introduced based on an induction motor driving a two-stage reduction gearbox which is loaded by a DC motor. It is shown that a defect seeded into the gearbox may be located using signals acquired from casing-mounted accelerometers and shaft mounted encoders. Using simple models of an induction motor and a gearbox, it is shown that it should be possible to observe gearbox defects in the measured stator current signal. A robust method of extracting the average speed of a machine from the current frequency spectrum, based on the location of sidebands of the power supply frequency due to rotor eccentricity, is presented. The synchronous signal averaging method is applied to the resulting estimations of rotor position and torsional vibration. Experimental results show that the method is extremely adept at locating gear tooth defects. Further results, considering different loads and different gears in the gearbox suggest some potential advantages and limitations of the method and provide some motivation for future investigations.

영화관 의자용 음향진동자극 시트의 개발

The global movie industry is continuing rapid growth through application of the latest technology. 3D movies are being produced and shown for a more effective viewing experience. Special chairs for audiences are being experimentally manufactured and installed for the greatest viewing effect. This special chair has a structure that applies vibrating stimuli to specific parts of the body by attaching vibration transducers to theater chairs and synchronizing it with each scene of the movie. In a previous study, it has been confirmed that we can analyze the vibration transfer characteristics of sponge seats through the application of an experimental modal analysis method and obtain design variables easily. In this paper, we examine the major design parameters needed in the development of a foaming sponge seat in which auxiliary springs are inserted to improve the vibration transfer effect of a chair seat. Through analyzing several prototypes by applying experimentation as well as the experimental modal analysis method, it was confirmed that the effect of vibration transfer can be improved through the use of an auxiliary member.

Diagnostic concordance between MRI and electrovibratography of the temporomandibular joint of subjects with disc displacement disorders

The aim of this study is to evaluate the diagnostic concordance of MRI and electrovibratography (EVG) of the temporomandibular joint (TMJ) in the diagnosis of articular disc displacement with reduction (ADDwR) and articular disc displacement without reduction (ADDw/oR). 50 patients (12 males, 38 females; mean age 37.46 ± 15.64 years) with a hypothesis of disc displacement were selected. For each patient an MRI of the TMJ was performed. MRIs were evaluated sorting the 100 TMJs by kind of pathology (no pathology, ADDwR, ADDw/oR, and joint hypermobility). Afterwards, the patients had an EVG exam. The EVG exams were performed with vibration transducers over each TMJ, enabling simultaneous, bilateral recording of vibrations emanating from joint sounds during the opening and closing movements. The presence of a sound peak was compared with the MRI diagnosis of ADDwR, while a multipeak aspect was compared with ADDw/oR diagnosis using Cohen's kappa test. The presence of a peak-shaped track has high specificity for ADDwR (90.27%). The Cohen's kappa calculated for the ADDwR was 0.5615 (good-moderate). The presence of a multipeak-shaped track has low specificity (65.22%) and sensitivity (70.42%). The Cohen's kappa calculated for the ADDw/oR was 0.2992 (poor). The present study recommends the use of EVG to support the clinical diagnosis of a disc displacement with reduction when MRI is not available or when subjects cannot be investigated by MRI.

Computer Simulation and Modelling of Standing Wave Ultrasonic Motor Using a Single Flexural Vibration Transducer

This paper presents a standing wave rotary piezoelectric ultrasonic using a single flexural vibration transducer. The motor consists of three main parts, stator, rotor and housing unit. The stator is a single piezoceramic flexural vibration transducer. The rotor is made up of the motor driving wheel and the shaft. A computer simulation and modelling using finite element analysis for the proposed motor is discussed and used in the motor design development process. Finite element analysis has been used to evaluate the motor structure by performing an algebraic solution of a set of equations, describing an ideal model structure, with a finite number of variables. The established simulation and modelling for ultrasonic motor using finite element analysis enabled to select, the material of the flexural transducer, defining the operating parameters for the motor, determining the principles of motion and proposing an innovative technique to control the direction of motion, by controlling the phase between the two modes of vibrations. This enabled to create two directions of motion from a single vibration bar. A prototype of the proposed motor was fabricated and its characteristics measured. This showed that operating parameters of the fabricated prototype are: frequency equal to 40.7 KHz, voltage: 50: 100 volt and current: 50: 100 m-amperes. This is showed a close agreement with FEA. Typical output of the prototype is no-load speed of 120 rpm, a resolution on the order of micrometers and a dynamic response <100 µsec. The motor is able to carry a load equal to 2.8 Newton.

Vibration-based condition monitoring of rotating machines using a machine composite spectrum

Vibration-based condition monitoring (VCM) requires vibration measurement on each bearing pedestal using a number of vibration transducers and then signals processing for all the measured vibration data to identify fault(s), if any, in a rotating machine. Such a large vibration data set makes the diagnosis process complex generally for a large rotating machine supported through a number of bearing pedestals. Hence a new method is used to construct a single composite spectrum using all the measured vibration data set. This composite spectrum is expected to represent the dynamics of the complete machine assembly and can make fault diagnosis process relatively easier and more straightforward. The paper presents the concept of the proposed composite spectrum which was applied to a laboratory test rig with different simulated faults; healthy and three faulty cases named misalignment, crack shaft, and shaft rub. A comparison between the composite spectrum with and without the coherence has been investigated for the simulated faults in the rig. It has been observed that the coherent composite spectrum provides much better diagnosis compared to the non-coherent composite spectrum.

Transient Elastography Is a Useful Noninvasive Tool for the Evaluation of Fibrosis in Paediatric Chronic Liver Disease

Outcome of liver disease in children is mainly determined by severity and progression of liver fibrosis. Liver biopsy is the accepted standard for evaluating fibrosis but is limited by the need for sedation in children, sampling error, and risks including bleeding. The aim of the present study was to compare tools for noninvasive assessment of liver fibrosis in a paediatric cohort. Children undergoing liver biopsy for chronic liver disease were recruited and underwent transient elastography (TE). Liver biopsies were scored by a hepatohistopathologist from F0 (no fibrosis) to F4 (cirrhosis). TE was compared with biopsy score. During the study period, 104 children (62 boys) were enrolled (median age 13.6 years). Diagnosis was autoimmune liver disease in 27; nonalcoholic fatty liver disease in 37; posttransplant in 16; hepatitis B/C in 8; Wilson disease in 5; and the remainder, miscellaneous. TE was successful in all but 7 patients and was a good discriminator of significant fibrosis (≥ F2) (P < 0.001), severe fibrosis (≥ F3) (P < 0.001), and cirrhosis (F4) (P = 0.003). The area under the receiver operating characteristic curve for the prediction of ≥ F2, ≥ F3, and F4 using TE was 0.78, 0.79, and 0.96, respectively. TE performed best in children with autoimmune liver disease and in those posttransplant. The present study demonstrates that TE is a reliable tool in distinguishing different stages of liver fibrosis in paediatric patients. Thus, TE may serve as a useful adjunct to liver biopsy for diagnostic purposes providing a reliable method of noninvasively monitoring liver disease progression in children.

Micro Hole Elliptical Supersonic Boring Quality Research

In this paper a method of ultrasonic elliptical vibration cutting has been applied to precision boring of micro hole due to its superior performances such as low cutting force, high quality surface finish and long tool life. A transducer with the longitudinal excitation is carried out to machining(boring) micro hole of 1Cr18Ni9Ti workpiece. The cutting force and surface quality are studied in detail.The workpiece with surface roughness of Rz 0.4μm is achieved.The results showed that the ultrasonic elliptical vibration transducer can be applied rationally in micro hole precision boring.

Case Studies of LDV-Aided Dynamic Testing

The laser Doppler vibrometer is a non-contact sensing technique developed based on the Doppler effect of a laser beam emerging from a subject surface. As a vibration transducer, the laser Doppler vibrometer offers many advantages over the conventional contact vibration sensors. It allows remote, non-intrusive measurement of structural vibration and it is very useful in scenarios when traditional contacting measurement is inconvenient. In this paper, four laser-based structural dynamic studies were presented and some results were briefly reported, which include laboratory dynamic testing of a bolted steel beam, a scaled-down high-rise building model, and a prestressed concrete reaction wall, and field vibration measurement of a viaduct bridge. Through these demonstrating cases, it is anticipated to help civil engineers get familiar with the laser-based sensing technology and to extend their selections for effective measurement approaches during experimental research.

The Engineering Acoustics Technical Committee

Engineering Acoustics Technical Committee (EATC) encompasses the theory and practice of creating tools for investigating acoustical phenomena and applying knowledge of acoustics to practical utility. This includes the design and modeling of acoustical and vibrational transducers, arrays, and transduction systems in all media and frequency ranges; instrumentation, metrology, and calibration; measurement and computational techniques as they relate to acoustical phenomena and their utility; and the engineering of materials and devices. EATC’s recently sponsored special sessions attracted members from all areas and is an enabler for overlapping interests: single crystal piezoelectrics, transducer design, vector sensors, materials for high power sonar, micromachined silicon mics, multimedia, 3‐D audio, pro-audio, parametric sources, speakers, transduction, projection, materials processing and manufacturing, piezocomposites, sensor fusion, signal processing hardware, data communication, condition-based monitoring of machinery and processes, solid‐state sensors and actuators, hearing aids and ear impedance, thermoacoustic refrigerators and engines, wind turbines, energy harvesting, computer modeling methods, acoustic barriers & noise control, array applications, metamaterials, systems for underwater vehicles, mufflers & silencers, borehole acoustics, flow noise mitigation methods, and non-destructive testing with ultrasound & non-contact methods.

FEM Modeling of Vibro-Impact Response of Metal Plates Excited by a High-Power Ultrasonic Transducer

When thin metal plates are excited by a high-power ultrasonic transducer, superharmonic and high-order subharmonic vibration phenomena of the plates are observed in our experiments. However, the nonlinear mechanism in the system is still not fully understood. In this paper, a finite element model is established based on the experimental conditions and numerical simulations are performed to explore the generation mechanism of the nonlinear vibration. By comparing the waveforms and frequency spectra of the vibration velocity of the plate to these of the contact force between the ultrasonic horn tip and the plates, it can be found that waveform distortion of the contact force is the main reason for generating the superharmonic vibration, while the intermittent contact-impact between the horn tip and the plate is the reason for subharmonic vibration in the plate. The FEM simulation results can explain reasonably the observed experimental phenomena, which are useful to help to improve the effects of the nonlinear phenomena occurred in ultrasonic processing.

Theoretical modeling of guided wave propagation in a sandwich plate subjected to transient surface excitations

A fast and efficient two-dimensional (2D) semi-analytical model based on global matrix method is developed to study the general characteristics of guided wave propagation in a honeycomb composite sandwich structure (HCSS) subjected to time-dependent transient surface excitations. The HCSS used in this study has an extremely lightweight and thick nomex honeycomb core, which is sandwiched between two thin graphite woven composite skins. The homogenized material properties of the skin and the core are considered to be elastic and quasi-isotropic in nature. Far-field time history of surface displacements are calculated for vertical and horizontal tone-burst surface excitations that are representative of thickness and radial mode of vibrations of piezoelectric transducers, respectively. Results are compared with those obtained from Finite element modeling (FEM) in LS-DYNA showing good agreement. Wavelet transform is then performed on the time-domain signal to obtain the group velocities of the propagating modes for their accurate identification on the basis of the theoretical dispersion curve. It is found that the response signal is dominated by the first anti-symmetric mode for a vertical excitation, whereas, the signal characteristics are multimodal in nature with dominating higher order symmetric and anti-symmetric modes for a horizontal excitation. The model is expected to be helpful for appropriate guided wave mode tuning and rapid analysis of data for experimental detection of disbonds in these novel structures.

Radially Composite Ultrasonic Transducers of Piezoelectric Ceramic and Metal Circular Rings

A new type of radially composite ultrasonic transducers in radial vibration is presented and studied. The composite transducer is composed of a radially polarized piezoelectric ceramic ring and a metal ring. The radial vibrations of the radially polarized piezoelectric ring and the metal ring are analyzed and their electro-mechanical equivalent circuits are obtained. Based on the mechanical boundary conditions between the piezoelectric ring and the metal ring, the six-port electro-mechanical equivalent circuit of the radially composite ultrasonic transducer is obtained and the frequency equation is given. The theoretical relationship between the resonance/anti-resonance frequency and the effective electro-mechanical coupling coefficient with the geometrical dimensions of the composite transducer is analyzed. At the same time, the radial vibration of the composite transducer is simulated by using Finite Element Method. The vibrational modal shape and the harmonic response are given numerically. At last, some radially composite ultrasonic transducers are designed and manufactured; their resonance/anti-resonance frequencies are measured. It is shown that the analytical resonance/anti-resonance frequencies are in good agreement with the numerically simulated and experimental results. It is expected that this type of radially composite ultrasonic transducers can be used in large scale ultrasonic liquid processing, such as ultrasonic extraction, ultrasonic sonochemistry and other applications where large radiation surface and ultrasonic power are needed.

Study on the Wave Deformation of a Traveling Wave Piezoelectric Stator Using Composite Transducer

In a previous study, the authors have presented and developed a cylindrical traveling wave piezoelectric motor using a composite transducer. This study focuses the research on the wave deformation problems in the proposed stator. Firstly, the standing wave excited by the longitudinal vibration of the transducer is analyzed, and the vibration amplitudes of particles on the driving teeth are extracted to present the objective wave shape. Then, the wave deformation of the standing wave excited by the bending vibration of the transducer is analyzed. Finally, the longitudinal and bending PZT are excited together to gain a flexural traveling wave in the stator, and the vibration amplitude distributions in radial and circumferential directions are gained. Study result indicates that there are obvious deformations on the two standing waves, which cause the motion trajectories of the surface particles are inconsistent.

A u-shaped linear ultrasonic motor using longitudinal vibration transducers with double feet

A U-shaped linear ultrasonic motor using longitudinal vibration transducers with double feet was proposed in this paper. The proposed motor contains a horizontal transducer and two vertical transducers. The horizontal transducer includes two exponential shape horns located at the leading ends, and each vertical transducer contains one exponential shape horn. The horns of the horizontal transducer and the vertical transducer intersect at the tip ends where the driving feet are located. Longitudinal vibrations are superimposed in the motor and generate elliptical motions at the driving feet. The two vibration modes of the motor are discussed, and the motion trajectories of driving feet are deduced. By adjusting the structural parameters, the resonance frequencies of two vibration modes were degenerated. A prototype motor was fabricated and measured. Typical output of the prototype is no-load speed of 854 mm/s and maximum thrust force of 40 N at a voltage of 200 V(rms).