Frequency Vibration Signal Research Articles

Measurements and evaluation of measurements of vibrations in steel milling process

The technologists often experience the oscillation existing only during the working period in the milling process. The reason for that is a self-induced oscillation of the tool against the workpiece as there is agenerated cutting power between the tool and the workpiece. The cutting force largely depends on the angle of cutter, the rotational frequency of the spindle and the depth of cut. The oscillations endanger the cutting edges and are very unpleasant for the operators due to the loud noise they make. The basic reason of oscillation is the dynamic interaction between the cutting process and the construction of the device. This report draws from the research on machining of materials by milling and provides the analysis of vibration signal in the direction of cutter rotation at three pre-selected places. The report brings the descriptions of the time course of acceleration and dominant frequency of vibration signal in dependence on the rotational frequency of the spindle which is anoperating parameter of milling and on the depth of cut.

Bearing fault detection utilizing group delay and the Hilbert-Huang transform

Vibration signals measured from a mechanical system are useful to detect system faults. Signal processing has been used to extract fault information in bearing systems. However, a wide vibration signal frequency band often affects the ability to obtain the effective fault features. In addition, a few oscillation components are not useful at the entire frequency band in a vibration signal. By contrast, useful fatigue information can be embedded in the noise oscillation components. Thus, a method to estimate which frequency band contains fault information utilizing group delay was proposed in this paper. Group delay as a measure of phase distortion can indicate the phase structure relationship in the frequency domain between original (with noise) and denoising signals. We used the empirical mode decomposition of a Hilbert-Huang transform to sift the useful intrinsic mode functions based on the results of group delay after determining the valuable frequency band. Finally, envelope analysis and the energy distribution after the Hilbert transform were used to complete the fault diagnosis. The practical bearing fault data, which were divided into inner and outer race faults, were used to verify the efficiency and quality of the proposed method.

A piezoresistive micro-accelerometer with high frequency response and low transverse effect

With the purpose of measuring vibration signals in high-speed machinery, this paper developed a piezoresistive micro-accelerometer with multi-beam structure by combining four tiny sensing beams with four suspension beams. The eight-beam (EB) structure was designed to improve the trade-off between the sensitivity and the natural frequency of piezoresistive accelerometer. Besides, the piezoresistor configuration in the sensing beams reduces the cross interference from the undesirable direction significantly. The natural frequency of the structure and the stress on the sensing beams are theoretically calculated, and then verified through finite element method (FEM). The proposed sensor is fabricated on the n-type single crystal silicon wafer and packaged for experiment. The results demonstrate that the developed device possesses a suitable characteristic in sensitivity, natural frequency and transverse effect, which allows its usage in the measuring high frequency vibration signals.

Electromagnetic Energy Harvester for Low Frequency Vibrations Using MEMS

This paper proposes design and analysis of electromagnetic energy harvester using MEMS technology. The energy harvester is intended to harvest energy from low frequency ambient vibrations that is less than 100Hz. The design would consist of a cantilever which is the simplest MEMS structure which can further be used to power the amplifiers. These amplifiers can be used to amplify the low amplitude and low frequency vibration signals. The work intends to explore the opportunities in harnessing vibrations induced by the live loads, such as laden Lorries & Buses on bridges, to harvest energy in the form of generated voltage. A cantilever based electromagnetic energy harvester can be employed to capture these miniscule level of vibrations and convert them into electrical energy. The Faraday's law of electromagnetic induction is the fundament idea utilized to design the cantilever beam simulated with dimensions of 2500x500μm. The material plays a vital role in sensitivity and hence NdFeB is selected as magnetic material whereas Aluminum as the conducting coil electrode material. The voltage of 2.34mV is generated using single cantilever beam energy harvester. An array of six such cantilevers generates a voltage of 3.27mV. The simulation results confirm that the low ambient vibrations can be effectively utilized to generate useful energy.

Fault Diagnosis with Mult-Signal Test for Reciprocating Compressor

High frequency vibration signal, cylinder-inside pressure and ultrasonic wave are monitored under working condition of a reciprocating compressor. High frequency vibration signal and ultrasonic wave are processed using high frequency band-pass filtering, and then enveloped. The pressure signal is filtered with a low-pass digital filter. The fault causes of the machine can be determined by the enveloped waveform of vibration signal and ultrasonic wave, as well as the pressure curve comprehensively. We can confirm the truth that this fault diagnosis method is accurate and reliable for reciprocating compressors through a number of the results of fault diagnosis.

Planetary Gearbox Fault Diagnosis under Time-variant Conditions Based on Iterative Generalized Synchrosqueezing Transform

The synchrosqueezing transform can effectively improve the readability of time-frequency representation of mono-component and constant frequency signals, but blurs still occur to the time-frequency representation when analyzing multi-component and time-variant frequency signals. In order to address the time-frequency blur issue, an improved synchrosqueezing transform based on iterative generalized demodulation is proposed. The signal is decomposed into mono-components of constant frequency, via iterative generalized demodulation and filtering. The instantaneous frequency and time-frequency representation of such mono-component are accurately estimated by synchrosqueezing transform. The time-frequency representation of original signal is obtained by superposing the reconstructed time-frequency representations of all the mono-components. This proposed method effectively improves the time-frequency readability of synchrosqueezing transform when analyzing time-variant frequency signals, and generalizes the synchrosqueezing transform to multi-component signals as well. Using this method, the vibration signal frequency contents and their time-varying characteristics of a wind turbine planetary gearbox under time-variant conditions are effectively identified, and the gear fault is diagnosed.

Research for the Crack Dynamic Monitoring of Marine Diesel Engine

crankshaft is one of the most important parts and crankshaft fatigue fracture is a major failure. In order to alert fatigue fracture of crankshaft to prevent accidents, diesel engine crankshaft dynamic monitoring based on the actual situations of diesel engines, significance of dynamic balance for marine diesel engine crankshaft system is discussed and as well vibration monitoring and field dynamic balance system for diesel engine crankshaft system is constructed. The least square method is applied to fit fundamental frequency vibration signals of crankshaft system and the field dynamic balance strategy is designed on the basis of the influence coefficient method. The feasibility of the dynamic balance system is tested through experiments in the paper.

Mechanism of a Hair Cell Bioinspired Sensor with Ultrasensitivity to Weak and Low Frequency Vibration Signals

Although significant progresses have been made in sensor technology, it is still a challenging task to develop ultrasensitive sensors to monitor very weak and low frequency vibration signal for early warning of natural disasters and efficient structural health monitoring of infrastructures. It has been reported from previous experiments that some fishes have acute sensitivities to extremely low frequency linear acceleration due to the otolith organs of the inner ear. In this paper, based on the experimental results and qualitative mechanism of the infrasound sensitivity of some fishes conducted by other researchers, a bioinspired gating spring model with negative stiffness is established to simulate the mechanical-electricity transduction of the hair cell in fish ear. Then, numerical analyses of the mechanical model subject to static and dynamic loading are conducted, respectively. It is shown that the gating model has adaptive amplification capability to weak and low frequency excitation compared with the corresponding linear model. This mechanism can be used for the design of bioinspired ultrasensitive sensors for monitoring weak and low frequency vibration signal.

Cause Analysis and Diagnosis of Unbalanced Vibration of Rotor

The paper starts from from the rotor unbalance fault, and analyze the reasons of unbalanced rotor are improper design, material defects, process and assemble error, process problem; Summarizes the frequency spectrum characteristics of rotor unbalance, its features, frequency components of speed have protruding peak on spectrum diagram of detection in radial direction;Puts forward the diagnosis methods of Unbalanced vibration, the first step is to analyze vibration signal frequency components, then analyze its characteristics of vibration in the direction of the change of amplitude and phase. Proved by examples, this paper summarizes the rotor unbalance analysis and diagnosis method is simple and practical, and has reference significance for other vibration problem.

Study on a Novel Piezoelectric Accelerometer with Switch Characteristic

A novel piezoelectric accelerometer with switch characteristic was introduced. The accelerometer is composed of top head, cross elastic beam, base core, insulation cylinder, mass block, piezoelectric elements, and the base etc. The accelerometers structure and operating principle were presented and its mathematic model was established. Test results show that the accelerometer can filter out high frequency vibration signal, which the out signal is smooth compared with the conventional piezoelectric accelerometer, furthermore with good linearity. It can be used in the smart fuze to take the place of conventional piezoelectric accelerometer in order to recognize the target accurately.

Study of Novel Sound Detection TCM Pulse State Sensing Mode

This paper investigates a kind of Chinese Traditional Medicine (TCM) pulse state diagnosis sensor which is based on sound detection. This method has many advantages and is in line with the TCM pulse state multi-attribute characteristics. First the sound measurement method was designed. Then the verification experiment of electret microphone was studied. The experiment results shown some electret microphones are available for low frequency and low energy vibration signal which is similar to TCM pulse state signal measurement. Eventually it comes to the conclusion that this pulse acquisition mode is available method and can effectively reveal the different kinds of pulse signal characteristic differences. Boys and girls TCM pulse state signal were detected separately. It shows that Different gender has different pulse state and the pulse shape is also different.

Study on the Field Dynamic Balance of Diesel Engine Crankshaft

Abstract：Based on the actual situations of diesel engines, significance of dynamic balance for marine diesel engine crankshaft system is discussed and as well vibration monitoring and field dynamic balance system for diesel engine crankshaft system is constructed. The least square method is applied to fit fundamental frequency vibration signals of crankshaft system and the field dynamic balance strategy is designed on the basis of the influence coefficient method. The feasibility of the dynamic balance system is tested through experiments in the paper.

VCM의 제어 및 제진 장치 응용에 관한 연구

The degradation of durability and increase of fatigue on the ship are mainly caused by vibration of the engine and rotating machineries. The damper to minimize the influence from vibration is usually attached between the machineries and its base. General damper applied on the vessel is passive damper which is designed to attenuate specified frequency signals, i.e, high frequency vibration signals. But it is hard to anticipate its performance for low frequency signals. In this research, active vibration isolator using VCM is developed to suppress wide band vibration signals. Routh-Huritz`s stable condition, ultimate sensitivity method and parameter tuning are applied to derive PID parameters and 2 and 4 phase choppers are also adapted to drive VCM. Simulation and experiments are executed to confirm the effectiveness of the proposed control schemes.

Inexpensive Pipelines Health Evaluation Techniques Based on Resonance Determination, Numerical Simulation and Experimental Testing

In this paper, a non-destructive, reliable, and inexpensive vibration-based technique for evaluating Carbon steel pipes structure integrity. The proposed techniques allow a quick assessment of pipes structures at final pipe manufacturing stages and/or just before installation. A finite element modelling (FEM) using ABAQUS software was developed to determine the resonance mode of healthy Carbon steel pipe and a series of experiments were conducted to verify the outcomes of the modelling work. Consequently, the effects of quantified seeded faults, i.e., a 1 mm, 2 mm, 3 mm, and 4 mm diameter holes in the pipe wall on these resonance modes were determined using modelling work. A number of common used vibration analysis techniques were applied to detect and to evaluate the severity of those quantified faults. The amplitudes and frequencies of vibration signals were measured and compared. There were found to be in good agreement with the modelling work and provide important information on pipe construction condition and fault severity.

Wavelet based Neuro-Detector for low frequencies of vibration signals in electric motors

This study presents a Wavelet based Neuro-Detector approach employed to detect the aging indications of an electric motor. Analysis of the aging indications, which can be seen in the low frequency region, is performed using vibration signals. More specifically, two vibration signals are observed for healthy and faulty (aged) cases which are measured from the same electric motor. Multi Resolution Wavelet Analysis (MRWA) is applied in order to obtain low and high frequency bands of the vibration signals. Thus for detecting the aging properties in the spectra, the Power Spectral Density (PSD) of the subband for the healthy case is used to train an Auto Associative Neural Network (AANN). The PSD amplitudes, which are computed for the faulty case, are applied to input nodes of the trained network for the re-calling process of AANN. Consequently, the simulation results show that some spectral properties defined in low frequency region are determined through the error response of AANN. Hence, some specific frequencies of the bearing damage related to the aging process are detected and identified.

Characterization of Regime Transition in Fluidized Beds at High Velocities by Analysis of Vibration Signals

Vibration measurement, as a reliable nonintrusive technique, was used to investigate the hydrodynamics of a gas–solid fluidized bed. The extensive experiments were carried out on a laboratory scale fluidized bed, operated under ambient conditions and various particle sizes of sand, aspect ratios, and superficial gas velocities. Pressure fluctuations and vibration signals were recorded at sample frequencies of 400 Hz and 65.6 kHz, respectively. The signals were processed using various techniques such as the standard deviation, Kolmogorov entropy, average cycle frequency, and power spectral density function. The results showed that the vibration technique is able to predict the regime transition from bubbling to turbulent fluidization conditions. It was shown that the transition from bubbling to turbulent can be determined from the variation of the standard deviation, Kolmogorov entropy, and average cycle frequency of vibration signals. However, the velocity can be determined only from the standard deviation of the pressure fluctuation. Other methods of analysis, applied to pressure fluctuations, predicted the transition between the macrostructure and the finer structure of the fluidized bed system, but not the transition velocity from bubbling to turbulent.

A Study of MRife Algorithm and CSB Algorithm on Frequency Online Estimation

Online estimation of instantaneous frequencies is a method to treat information signals by following a set of certain algorithm for the purpose of extracting the sine wave signal frequency that is overwhelmed in the noise. Among several algorithms available nowadays, two are selected here-one is the modification of Rife (MRife) algorithm based on frequency-domain analysis; and the other is the correlation series based (CSB) algorithm. With simulation methods, the estimation error, stabilization time and computation load of these two algorithms are analyzed and compared respectively. Finally, these two algorithms are applied to estimate the vibration signal frequency of the diesel engine’s base under normal operating conditions. From the results, we come to the conclusion that MRife algorithm and CSB algorithm both have their specific advantages, whereas MRife algorithm is more applicable in the view of estimation error.

Monitoring changes in the speckle field from an optical fibre exposed to low frequency acoustical vibrations

Some preliminary investigations are described of speckle fields produced from light propagation in a multimode optical fibre exposed to low frequency (100 Hz) acoustic vibrations. Measurements are presented that have been made with a photodiode detector and a CCD array, the results obtained with the latter being analysed using space domain chromatic techniques. Optimum operating conditions are considered for providing good sensitivity and repeatability for detecting low frequency vibration signals (not precise parameter measurements) with an ultimate objective of monitoring fault development from the vibration of a mechanical plant.

Vibration Signal Denoising Based on Partial Differential Equation

By studying on partial differential equation(PDE) with its application in picture denoising, a new kind of method based on PDE is proposed for vibration signal denoising, in view of the shortcomings in the traditional filter denoising method. PDE denoising model based on Gauss core function is analyzed in detail, and its discretization processing of the method is also introduced. Experiments in contrast with the traditional denoising method show that the method can effectively eliminate the noise disturbance, keep the edge property and interior continuity, and also avoid signal distortion after denoising. Because of the smooth property of PDE denoising method, its denoising effect is influenced by PDE iterations series and the smooth property factors of vibration signal, so this method has a better effect for low frequency vibration signal denoising.

DETECTING HOLLOW HEART OF POTATO TUBERS USING IMPACT SOUND

An acoustical sorting system was developed to detect hollow heart (cavity) of potato tubers (Spun-ta variety). The system includes a microphone and digital signal processing hardware. It was found that upon impact with a steel plate, potato tubers with no hollow heart emit sound with higher signal magnitudes than with hollow one. Linear discrimi-nate analysis was used to classify potato tubers using three features extracted from the micro-phone signal. One of the discriminate features is the integrated absolute value of microphone output signal. The other two features are the number of data points in the digitized microphone signal after impact that have a slope and signal magnitude below preset threshold levels. The classification accuracy of this system is approximately 98%. The internal quality of potato tubers can be detected by acoustic impact method. The resonant frequency of potato tubers after dropping was found from acquired signal. The hollow heart existence of po-tato tubers can be evaluated by the resonant fre-quency of vibration signal of dropping tubers. This technology of acoustics to evaluate the hollow heart existence is more reliable and accurate spe-cially for export.