Every component characteristic in the closed loop of resonant sensors is analyzed. Based on the component characteristics, the relation between the excitation force and the displacement of the resonator is confirmed. And the closed loop differential equation of resonant sensors is build. The phase drift of the closed loop control system is brought into the differential equation. By solving the differential equation with phase error of the closed loop control system, the relation between phase drift and the difference between the resonant frequency of the closed loop and the natural frequency of the resonator is gained. It is found that the measure error between the resonator natural frequency and the resonant frequency of the closed loop is proportional to tangent of the phase drift of the closed loop control system. The proportion coefficient is negative -3dB bandwidth of the resonator.
At present, the sensitivity phase of low-frequency accelerometer is commonly calibrated by time synchronization (TS), which needs to strictly align its input excitation acceleration signal and output signal in the time domain. However, TS is very difficult to be implemented and has severely restricted the improvement of the measurement accuracy. A novel calibration method that combines the monocular vision method and time-spatial synchronization technique is investigated to achieve the high-accuracy sensitivity phase calibration. The sensitivity phase is accurately calibrated by determining the aligned spatial position between the excitation acceleration signal and the output signal with the monocular vision method. The sensitivity magnitude can also be simultaneously calibrated. Experimental results show that the calibrated sensitivity phase and magnitude by the investigated method agree well with those by the laser interferometry in the range from 0.3 Hz to 2 Hz. The calibration accuracy of the investigated method is especially superior to that of the laser interferometry in the range from 0.01 Hz to 0.3 Hz.
This paper presents a piezoelectric multilayered microcantilever structure as a micro-electro-mechanical system (MEMS) transducer. The proposed micro-transducer is designed for novel audio directional loudspeaker for mobile communication devices. To obtain optimum design parameters and predict the cantilever performance before actual fabrication, the mechanical and electro-mechanical performance was simulated by the finite element method and further validated with theoretical calculation. Finally the fabrication process steps are proposed.
The paper describes a method to estimate the power consumption of miniature audio directional transducer using KZK equation according to a larger transducer with the same structure and the same material. A theoretical analysis of sound propagation and sound power for concave-convex cylindrical transducers is presented, which are made by PVDF film of 28 μm with two-sided silver ink of 10 μm at each side. Experimental investigations using 270×240 mm 2 and 50 ×50 mm 2 transducers are performed. Experiments and theoretical estimation of power consumption of smaller transducer of 50 ×50 mm 2 used in mobile media devices are presented according to the experimental results of 270×240 mm 2 transducer. And the theoretical results agree with the experimental result and meet the power requirement (≪5W) of mobile media devices.
The low-frequency triaxial vibration sensors have been gradually applied in many engineering fields of vibration monitoring because they can measure the multidirection vibrations simultaneously. The accurate axial and transverse sensitivities, determined by the calibration method, are the prerequisite for ensuring their measurement accuracy. Currently, the laser interferometry (LI) which is based on a single component or a tricomponent linear shaker is usually applied to calibrate these sensitivities. However, the former has to require the multiple reinstallations of the sensor and the latter cannot avoid the motion coupling caused by the shaker, these inevitably increase the calibration uncertainty. In this article, we investigate a monocular vision (MV)-based two-component shaker calibration method, which determines the axial sensitivity based on the time-spatial synchronization and transverse sensitivity at the elliptical orbit excitation. The MV method is used to measure this excitation, and a plane sensitivity model is presented to describe these sensitivities. This investigated method can simultaneously reduce the uncertainties caused by the reinstallations and motion coupling to improve the calibration accuracy. Experimental results compared with the LI and Earth's gravitation method demonstrate that the investigated method obtains the satisfactory accuracies both in axial sensitivity magnitude and phase as well as transverse sensitivity magnitude and direction calibration.
The long-stroke shaker is essentially required for the calibration of low-frequency vibration transducers, whose performance parameters have significant impact on the calibration accuracy. The accurate measurement of these parameters is the prerequisite to establish a reliable vibration metrology and traceability system. Currently, an optical collimator or a reference accelerometer is applied to get the static parameter, the laser interferometry or triaxial sensor-based method is used to obtain the dynamic parameters. However, the former relies on an extra device which increases the complexity and cost of calibration system, and the latter is always difficult to accomplish the accurate and efficient measurement of these parameters. In this study, a binocular vision-based long-stroke shaker performance measurement method is investigated, which has ability to determine the static and dynamic parameters simultaneously during the calibration. This vision method obtains the shaker's bending by measuring the inclinations at the different positions of its guideway, and achieves the amplitude characteristic, distortion, repeatability as well as transverse ratio measurements by accurately acquiring the spatial displacements at different frequencies. Comparison experiments with the two commonly used inclination estimation methods, and the laser interferometry and sensor-based method demonstrate that the investigated method is able to get the satisfactory accuracies both for the static and dynamic parameters of long-stroke shaker in vibration calibration.
In recent years, low frequency vibration measurement is being widely concerned in many applications, because low frequency vibration usually introduces a strong influence. The low frequency vibration is commonly measured by the laser interferometry, requiring a complicated system and a high cost laser interferometer, and its flexibility in field vibration measurement is poor; or the method using vibration transducer, requiring a transducer with known sensitivity, and its measurement precision is not high. In this paper, we propose a novel method based on single camera, which achieves low frequency vibration measurement via collecting and processing sufficient frame sequence images. The proposed method is compared with the heterodyne interferometry by measuring the vibration displacements of a long-stroke shaker simultaneously. Experimental results show the proposed method realizes <1% vibration displacement measurement precision at frequencies between 0.05 Hz-5 Hz.
In this paper, the shortcomings and their causes of the conventional homodyne time interval analysis (TIA) method is described with respect to its software algorithm and hardware implementation, based on which a simplified TIA method is proposed with the help of virtual instrument technology. Equipped with an ordinary Michelson interferometer and dual channel synchronous data acquisition card, the primary vibration calibration system using the simplified method can perform measurements of complex sensitivity of accelerometers accurately, meeting the uncertainty requirements laid down in pertaining ISO standard. The validity and accuracy of the simplified TIA method is verified by simulation and comparison experiments with its performance analyzed. This simplified method is recommended to apply in national metrology institute of developing countries and industrial primary vibration calibration labs for its simplified algorithm and low requirements on hardware.
A tri-axial primary vibration calibration system has been set up at National Institute of Metrology for simultaneous calibration of motion transducers. The system is driven by three electrodynamics exciters that are mounted along the three orthogonal axes. The cross-coupling unit based on air bearing is developed for force transferring and motion guiding. Spatial orbit vibration is composited from sine vibration components of the three orthogonal axes. Relationship of shapes and orientations of spatial orbits and amplitudes and phases of sine vibration components is discussed. Multi-exciter vibration control for both cross-coupling compensation and amplitudes and phases control of sine vibration components is investigated. The tri-axial measuring system can simultaneously measure the three orthogonal vibration quantities based on the band-pass sampling method. The experiments show that a variety of spatial orbits can be generated by efficiently reducing the cross-coupling of the tri-axial vibration exciter and the magnitude and the phase shift of sensitivities of a tri-axis accelerometer can be determined.
Noise is always inevitably appeared in images, which directly affects the performance of machine vision applications. Currently, the commonly used denoising methods can be divided into three strategies: the filtering-based, model-based, and deep learning-based methods. However, they are always difficult to get the considerable accuracy and efficiency simultaneously. In this study, a novel denoising method based on autocorrelation function is investigated, which improve the image quality by utilizing the independence of useful periodic information and noise. Simulations and experiments compared with the current denoising methods confirm that the investigated method has a good comprehensive effect on noise reduction and efficiency improvement.
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