Vibration Transducer Research Articles

Ultrasonic metal welding with a vibration source using longitudinal and torsional vibration transducers

Conventional ultrasonic metal welding for joining dissimilar metals uses a linear vibration locus, although this method suffers from problems such as low overall weld strength. Our previous studies have shown that ultrasonic welding with a planar vibration locus improves the weld strength. However, the vibration source in our previous studies had problems in longitudinal-torsional vibration controllability and small welding tip. Therefore, the study of the optimal shape of the vibration locus was difficult. Furthermore, improvement of weld strength cannot be expected. We have developed a new ultrasonic vibration source that can control the longitudinal-torsional vibration and can connect to a large welding tip. In this study, we clarified the longitudinal-torsional vibration controllability of the developed ultrasonic vibration source. Moreover, we clarified that using the planar locus of the developed vibration source produced a higher weld strength than our previous studies, and clarified the optimal shape of the vibration locus.

Experimental facilities for modal testing

PurposeThe experimental modal analysis requires good knowledge of various engineering fields, such as mechanical vibrations, transducers used in vibration measurement, transducers and system calibration methods, data acquisition systems, digital signal processing and system identification. Test facilities constitute a key factor for improving the quality of the estimated modal model. This paper aims to describe the experimental facilities at the Institute of Aeronautics and Space (IAE) Modal Testing Laboratory in terms of associated instrumentation and data acquisition system, metrological aspects and computational resources. The discussion is completed with a practical application showing a ground vibration testing (GVT) of an unmanned aerial vehicle (UAV).Design/methodology/approachThe experimental facilities were evaluated in a typical GVT, using three shakers in both vertical and horizontal excitations and 88 response measurement points. The global excitation method was used to excite all desired modes. The reliability of the experimental modal model was validated by an auto modal assurance criterion matrix for the measured modes of the structure.FindingsThe experimental facilities were successfully used for validating the dynamical characteristics of the UAV under testing.Originality/valueThe modal test facilities of the Modal Testing Laboratory at the IAE, the main research center of the Brazilian Air Force, are described in this paper.

Experimental study on monitoring the bolt group looseness in a clamping support structure model

In this article, bolt group looseness monitoring in a clamping support structure model, which is under environmental random excitation, is experimentally investigated. The bolt group has 12 bolts, providing an essential clamping force to fix cargo during transportation. Seven kinds of bolt group looseness degree developed gradually are simulated in experiment. From an economic point of view, vibration transducer of accelerometer is used for monitoring. Time series analysis of Auto-Regressive with eXogenous model with input known and Auto-Regressive–Auto-Regressive with eXogenous model with input unknown are constructed, and the statistical indices of the model residual error are defined as the damage characteristic parameter indicating the bolt group looseness degree. The experimental analysis shows the effectiveness of the proposed method in monitoring the bolt group looseness at early stage, while the variation of structural resonance frequency can only be used to monitor large bolt group looseness degree. The experimental analysis also shows that under a stationary, broadband random excitation, the Auto-Regressive–Auto-Regressive with eXogenous model has the same bolt group looseness monitoring capability with the Auto-Regressive with eXogenous model.

Study on Sensor Vibration Reduction Installation Structure with Damping Material of Ground Reflection Pressure Measurement

In blast field test, strong mechanical shock and vibration affect the output of blast pressure sensors. To avoid this phenomenon, a pressure sensor vibration reduction installation structure was designed for the measurements of ground reflection pressure. The damping material was used in the installation structure. And certain blast field test had been carried out. The data from the field blast test was compared to transducers with vibration reduction and transducers without vibration reduction. The results show that the obvious effect of the vibration reduction can eliminate vibration interference. And it is suitable for the measurements of shock wave over-pressure in blast field test.

Physics of direct-contact ultrasonic cloth drying process

Existing methods of drying fabrics involve energy-intensive thermal evaporation of moisture from clothes. Drying fabrics using high-frequency vibrations of piezoelectric transducers can substantially reduce drying time and energy consumption. In this method, vibrational energy generates instability on the liquid-air interface and mechanically ejects water from a wet fabric. Here, for the first time, the physics of the ultrasonic fabric drying process in direct-contact mode is studied. The kinematic and thermal responses of water droplets and fabrics on piezoelectric crystal transducers and metal mesh–based transducers are studied. The results suggest that on piezoelectric crystal transducers, the response of a droplet subjected to ultrasonic excitation is dictated by the relative magnitude of the surface tension and the ultrasonic excitation forces. The drying process for a fabric on the studied transducers consists of two regimes—vibrational and thermal. When the water content is high, the vibrational forces can eject bulk water rapidly. But the more strongly bound water within the smaller fabric pores evaporates by the thermal energy generated as a result of the viscous losses. This study finds that a metal mesh–based transducer is more suitable for dewatering fabrics, as it facilitates the ejection of water from the fabric–transducer interface to the opposite side of the mesh. A demonstration unit developed consumes 10–20% of the water latent heat energy at water contents greater than 20%.

Gear Fault Diagnosis Using Dual Channel Data Fusion and EEMD Method

When a gear fault is presented, the ensemble empirical decomposition (EEMD) method has been widely used in the detection of gear fault and has given good results. However, under signals from two vibration transducers which are installed in different directions, the vibration data from every sensor becomes necessary to obtain much more precise results. This paper suggests a new feature frequency extraction approach for gear malfunctions diagnosis using the full vector spectrum (FCS) and EEMD method. The approach embodies model building of multi-sensor data fusion and main intrinsic mode functions(IMFs) analysing of merged data from two vibration sensors. By using EEMD the data from single channel can be decomposed into a number of IMFs. To alleviate the diversity problem of EEMD decomposition results occurring in two channels, full vector spectrum (FVS) is introduced. With full vector spectrum, information obtained from each sensor can be merged a piece of vibration evidence in frequency domain, and then we use Hilbert transform to calculate the envelope spectrum of each IMF to evaluate the fault feature frequency. In this work, simulated signal and gear experiment were conducted to validate this strategy. The results have proven that the proposed method can enhance the effectiveness of feature frequency extraction in diagnosing gear faults.

Flaw Detection with a Point-focusing Electromagnetic Acoustic Transducer and Local Vibration around the Slit

Flaw Detection with a Point-focusing Electromagnetic Acoustic Transducer and Local Vibration around the Slit

Good practices in railway vibration prediction using empirical and hybrid models

Empirical and semi-empirical (hybrid) models are commonly used in the prediction of vibratory impact of future railway lines. This paper focuses on the potential impact that a number of details can have on the accuracy of this type of vibration predictions, particularly when experimental assessment of vibration transmission characteristics is carried out. These aspects include different alternatives for installation of vibration transducers, use of different artificial vibration sources, ground borne noise estimation from vibration levels and also the role of some particular surface characteristics in the test site. A number of good practices concerning these aspects are summed up and suggested as a conclusion to help in improving the quality of future vibration predictions based on this sort of models.

An I-shape linear piezoelectric actuator using resonant type longitudinal vibration transducers

Resonant type longitudinal vibration transducers are used in this work to construct a linear piezoelectric actuator with four driving feet. Totally three longitudinal transducers are integrated in I-shape to form the proposed actuator, which contains one vertical transducer and two horizontal transducers. These three transducers vibrate under longitudinal modes with certain temporal sequence, whose vibrations are superimposed in the actuator to generate elliptical motions on the four driving feet. The three transducers are tuned to be suitable dimensions, under which they have very close 1st longitudinal resonance frequencies; the working frequency of the piezoelectric actuator is designed to be about 31.3kHz. The vibration coupling problem between the longitudinal transducers are studied by calculating the motion trajectories of the four feet. It is found that the temporal shift of the longitudinal vibrations can be used to tune the movement trajectories; the four feet can get nearly the same vertical displacements under a phase shift of 105°. At last, the vibration characteristics and mechanical output performances of a prototype are measured. The working frequency of the prototype, the maximum speed, and the maximum thrust force are measured to be 33.15kHz, 1563mm/s, and 158.2N, respectively.

Effect of vibration of flexible transducer on shear resistance of scaling in tunnel drainage

Through a series of laboratory tests, an investigation was conducted into the reduction of shear resistance of scale in tunnel drainage through the use of wave energy. A flexible transducer was used to generate vibration and emitted it through a polyvinylidene fluoride polymer film as various frequencies. Tests were conducted using specially designed and fabricated equipment. The results of the study showed a significant decrease in shear resistance when sonication was applied. The degree of reduction varied by frequency. Using the test results, we discuss the potential development of a new maintenance system method for drainage.

Effect of Split or Partial Electrodes on the Forced Vibrations of Bar-Type Piezoceramic Transducers

The effect of a nonuniform electric load on the admittance and dynamic electromechanical coupling coefficient (EMCC) of energy converters is analyzed using, as examples, well-known problems of the forced vibrations of narrow piezoceramic plates with partial or split electrodes. It is shown that the antiphase excitation of vibrations can be effective to extract harmonics and to increase the operating frequencies of resonators. The presence of unelectroded sections can result in some increase in the EMCCof the principal resonance. If some electrodes are short-circuited, then odd and even longitudinal modes can be excited, which are absent when the electrodes are not split. The calculation of the stress state and admittance is in good agreement with experiments

Twenty-Eight Orders of Parametric Resonance in a Microelectromechanical Device for Multi-band Vibration Energy Harvesting.

This paper contends to be the first to report the experimental observation of up to 28 orders of parametric resonance, which has thus far only been envisioned in the theoretical realm. While theory has long predicted the onset of n orders of parametric resonance, previously reported experimental observations have been limited up to about the first 5 orders. This is due to the rapid narrowing nature of the frequency bandwidth of the higher instability intervals, making practical accessibility increasingly more difficult. Here, the authors have experimentally confirmed up to 28 orders of parametric resonance in a micromachined membrane resonator when electrically undamped. While the implication of this finding spans across the vibration dynamics and transducer application spectrum, the particular significance of this work is to broaden the accumulative operational frequency bandwidth of vibration energy harvesting for enabling self-powered microsystems. Up to 5 orders were recorded when driven at 1.0 g of acceleration across a matched load of 70 kΩ. With a natural frequency of 980 Hz, the fundamental mode direct resonance had a −3 dB bandwidth of 55 Hz, in contrast to the 314 Hz for the first order parametric resonance; furthermore, the half power bands of all 5 orders accumulated to 478 Hz.

On the identification of the angular position of gears for the diagnostics of planetary gearboxes

Generally, in planetary gearbox diagnostics, vibration transducers are placed on the gearbox case near the ring gear. The relative angular position of the planet gears with respect to the transducer is a useful information for the evaluation of vibration signals related to planet/sun gears. This angular position is usually unknown, or it is known with a large tolerance causing serious difficulties in both gears and bearing diagnostics. In fact, noise and spurious component from healthy planets could overhang the informative content about incipient faults. The present work seeks to propose two alternative methods for the identification of the angular position of the planet gears with respect to the transducer. The first one is based on the study of how the power flows inside the Time Synchronous Average of the ring gear, whilst the second method is based on a modified statistical parameter such as the Crest Factor. The effectiveness of these methods is assessed on the basis of actual vibration signals acquired from a faulty planetary gearbox. The knowledge of the exact angular position of the planet gears allows the diagnostics of both gears and bearings, as proven by extensive experimental activities reported in the paper.

Development of wireless vibration transducer based on MEMS accelerometer

When monitoring the vibration of heavy rotating machinery, one often has problems with cables of vibration transducers, as those cables are usually long, heavy and prone to damage. This paper is focused on the development of a wireless vibration transducer, based on the MEMS accelerometer, which is free of those problems. Owing to the schematics proposed, developed sensor’s power consumption is low, at that analog filtering of vibration acceleration signal is provided. In the paper, spectral analysis based method of frequency response correction is also proposed. That method can be used for measurement of the vibration RMS and power spectra, while using an MCU with low computational power for data processing. The results of the tests conducted show that the transducer developed is well-behaved and that its precision is comparable to one of industrial piezoelectric transducers. So, the transducer developed can be used instead of the industrial transducers mentioned; at that, moving of the machine condition detection process from the high–level system to the transducer level allows one to decrease network traffic and simplify monitoring system as a whole.

Experimental Investigation to Predict Tool Wear and Vibration Displacement in Turning – A Base for Tool Condition Monitoring

AbstractIn the present work investigation primarily focuses on identifying the presence of cutting tool vibrations during face turning process. For this purpose an online non-contact vibration transducer i. e. laser Doppler Vibrometer is used as part of a novel approach. The revisions in the values of cutting forces, vibrations and acoustic optic emission signals with cutting tool wear are recorded and analyzed. This paper presents a mathematical model in an attempt to understand tool lifeunder vibratory cutting conditions. Tool wear and cutting force data are collected in the dry machiningof AISI 1040 steel at different vibrationinduced test conditions. Identifying the correlation among tool wear, cutting forces and displacement due to vibration is a critical task in the present study. These results are used to predict the evolution of displacement and tool wear in the experiment. Specifically, the research tasks include: to provide an appropriate experimental data to prove the mathematical model of tool wear based on the influence of cutting tool vibrations in turning.The modeling is focused on demonstrating the scientific relationship between the process variables such as vibration displacement, vibration amplitude, feedrate, depth of cut and spindle speed while getting into account machine dynamics effect and the effects such as surface roughness and tool wear generated in the operation. Present work also concentrates on the improvement in machinability during vibration assisted turning with different cutting tools. The effect of work piece displacement due to vibration on the tool wear is critically analyzed. Finally, tool wear is established on the basis of the maximum displacement that can be tolerated in a process for an effective tool condition monitoring system.

Probe Oscillation Shear Elastography (PROSE): A High Frame-Rate Method for Two-Dimensional Ultrasound Shear Wave Elastography.

Ultrasound shear wave elastography (SWE) utilizes the propagation of induced shear waves to characterize the shear modulus of soft tissue. Many methods rely on an acoustic radiation force (ARF) "push beam" to generate shear waves. However, specialized hardware is required to generate the push beams, and the thermal stress that is placed upon the ultrasound system, transducer, and tissue by the push beams currently limits the frame-rate to about 1 Hz. These constraints have limited the implementation of ARF to high-end clinical systems. This paper presents Probe Oscillation Shear Elastography (PROSE) as an alternative method to measure tissue elasticity. PROSE generates shear waves using a harmonic mechanical vibration of an ultrasound transducer, while simultaneously detecting motion with the same transducer under pulse-echo mode. Motion of the transducer during detection produces a "strain-like" compression artifact that is coupled with the observed shear waves. A novel symmetric sampling scheme is proposed such that pulse-echo detection events are acquired when the ultrasound transducer returns to the same physical position, allowing the shear waves to be decoupled from the compression artifact. Full field-of-view (FOV) two-dimensional (2D) shear wave speed images were obtained by applying a local frequency estimation (LFE) technique, capable of generating a 2D map from a single frame of shear wave motion. The shear wave imaging frame rate of PROSE is comparable to the vibration frequency, which can be an order of magnitude higher than ARF based techniques. PROSE was able to produce smooth and accurate shear wave images from three homogeneous phantoms with different moduli, with an effective frame rate of 300 Hz. An inclusion phantom study showed that increased vibration frequencies improved the accuracy of inclusion imaging, and allowed targets as small as 6.5 mm to be resolved with good contrast (contrast-to-noise ratio ≥ 19 dB) between the target and background.

Interferometer with bismuth silicon oxide crystal for vibration measurement

We present a small-amplitude, high-frequency vibration measurement system. This system is based on the reflective holographic grating in a crystal of bismuth silicon oxide without applying an external electric field. A quarter-wave plate is applied in the reference beam path, with a polarizer after the crystal, to fulfill the quadrature condition when no electric field is applied to the crystal. A reflection configuration is used to obtain a good overlapping of the interference beams, which increases the beam coupling. The factors that affect the diffraction efficiency, including the signal-to-reference-beam intensity ratio and the recording angle, has been investigated. The experimental results coincide with the theoretical results, and the optimal conditions are obtained. The results of comparisons of our system with the vibrometer TEMPO show that the nanometer vibrations of a piezoelectric transducer can be reliably detected.

Feasibility study on the rotary ultrasonic elliptical machining for countersinking of carbon fiber–reinforced plastics

Carbon fiber–reinforced plastics have been widely applied in aerospace industry as aircraft structural components due to their excellent mechanical and physical properties. The countersinking process of the carbon fiber–reinforced plastic hole is indispensable for the assembly of countersunk head screw. In conventional countersinking process of carbon fiber–reinforced plastics, it is prone to produce the delamination, fiber pullout, poor surface levelness and dimensional accuracy of countersunk hole. As a new technology, the rotary ultrasonic elliptical machining for countersinking of carbon fiber–reinforced plastics is employed, which is a non-traditional process that can effectively improve the surface levelness, surface integrity and machining accuracy of carbon fiber–reinforced plastic countersunk hole. This article reported a feasibility study on the rotary ultrasonic elliptical machining for countersinking of carbon fiber–reinforced plastics without coolant for the first time. The processing principle of rotary ultrasonic elliptical machining for countersinking was illustrated according to the countersinking models and the equations of motion locus. Based on the principle analysis, the surface levelness, tool blades’ path and countersunk hole surface morphology in rotary ultrasonic elliptical machining of the separated and unseparated types were analyzed compared to that in conventional countersinking. In addition, the rotary ultrasonic elliptical vibration transducer was designed and fabricated, as well as the experimental platform was set up. The experimental results demonstrated that the rotary ultrasonic elliptical machining achieved much better results than that in conventional countersinking, such as lower thrust force, torque, cutting temperature, better surface levelness, hole dimensional accuracy, surface integrity and chip-removal effect. The experimental results also verified the feasibility of rotary ultrasonic elliptical machining for countersinking of carbon fiber–reinforced plastics.

Vibration Detection of the Electrical Motors using Strain Gauges

This paper presents some aspects regarding to vibration measurement using strain gauge sensors. Mechanical faults, usages, or electrical faults, can be detected through noises and/or vibrations which have different amplitude and frequency against the normal sound of the induction motor. Different vibration transducers can be used for noise and vibration measurements with fault detection purpose. The conditioning circuit of the vibration transducers can be resistive type also and in this case the vibration is converted into a variation of resistance (strain gauges). From resistance variation of the strain gauges a voltage variation can be obtained with proper conditioning circuit. This voltage is measured and analyzed to obtain the vibration components. The amplitude and frequency of the vibration are changing when the functioning conditions of the machine are changing. It is important to determine the harmonic spectra of the vibration for different faults and to compare with the spectra corresponding to the normal functioning of the electrical motor. Two virtual instruments were developed in LabView and LabWindows/CVI to measure and analyze the vibration. Using the virtual instruments the acquired signal was analyzed and the vibration characteristics and spectra were studied in different cases. It is shown through simulations and measurements for a small electrical motor that the weak base influences the amplitude of frequency components of the harmonics spectra.

Radial Vibration of a Regular Polygon Composite Piezoelectric Ultrasonic Transducer

Radial Vibration of a Regular Polygon Composite Piezoelectric Ultrasonic Transducer