Search

The application of automation technology realizes the transformation of people’s production and life-style, and also promotes the transformation of the system form of the network environment. The application of automation in the current network industry is increasing, especially the use of advanced methods and technologies for automatic control. The purpose of this paper is to realize the research on the network measurement and control system in the field of automation technology to promote the ecological development of the network automation process. This paper proposes the use of neural network technology in automation technology to guide the construction of computer network measurement and control systems, which is helpful to analyze and solve the objective problems of system imbalance and improper command output in system automation. The automatic network control system is constructed and optimized by referring to the principles and laws of the neural networks, and the automation of the measurement and control system in the network field is realized. In the test of the system, the results show that when the experimental parameter setting is the input flow value of the flowmeter 2.05 sccm, the output frequency of the inverter in the system jumps between 25 and 40 Hz respectively. The specific parameters of the experiment set the output frequency of the inverter to 50 Hz, and the input flow value of the flowmeter jumps between 2.05 sccm and 4.00 sccm. Therefore, analyzing the measurement and control system of network automation is undoubtedly crucial to the current road in the field of network automation.

In this study, a 1550 nm coherent high-spectral-resolution lidar (CHSRL) is developed to measure the optical properties of aerosols and atmospheric wind profiles in the atmospheric boundary layer. To determine the optical properties, a coherent frequency discriminator based on the fast Fourier transform is designed in the CHSRL to separate the Mie and the Rayleigh–Brillouin backscatter spectra to fulfill the needs of high-spectral measurements. The atmospheric wind velocity is retrieved using the simultaneously measured Doppler shift. This non-optical frequency discriminator is a feasible and low-cost solution compared to a narrow-bandwidth optical filter, such as a Fabry–Perot interferometer or an atomic filter. However, shot, amplifier spontaneous emission, and detector noise interfere with the Rayleigh–Brillouin spectrum. Therefore, a spectrum correction algorithm is proposed to recover the interfered Rayleigh–Brillouin spectrum, and the measurement results of the spectral line agree well with those modeled with Tenti S6 at different central frequencies. Finally, field observations for comparison are conducted with the co-located CHSRL, Raman lidar, and coherent Doppler wind lidar. The comparison results indicate that the correlation coefficient of the aerosol backscatter coefficient is 0.84. The correlation coefficient and standard deviation of wind velocity are 0.98 and 0.13 m · s−1, respectively.

Fringe projection profilometry is a widely used three-dimensional (3D) optical measurement technique. However, it is quite challenging to quickly obtain the 3D information of objects. Minimizing the number of patterns for phase unwrapping is an efficient way to address the above problem, and many methods have been proposed. This paper reports a period-wise phase unwrapping method with only two gray level coding patterns. Due to a hybrid coding strategy implemented, the number of patterns used in the proposed method reduces by one in comparison with conventional gray level method when generating the same number of codewords. A robust decoding scheme is also developed to determine the fringe order, and its accuracy is guaranteed by using the self-correcting method to remove the phase errors. Some experiments have been conducted, and their results confirm that the success of the proposed method.

The phase-coding method for absolute phase measurement possesses a strong robustness because its codewords are encoded into phase domain rather than intensity. However, a misalignment problem arise...

An in-situ laser Doppler current probe (LDCP) for the simultaneous measurements of the micro-scale subsurface current speed and the characterizations of micron particles is dedicated in this paper. The LDCP performs as an extension sensor for the state-of-the-art laser Doppler anemometry (LDA). The all-fiber LDCP utilized a compact dual wavelength (491 nm and 532 nm) diode pumped solid state laser as the light source to achieve the simultaneous measurements of the two components of the current speed. Besides its ability for the measurements of the current speed, the LDCP is also capable of obtaining the equivalent spherical size distribution of the suspended particles within small size range. The micro-scale measurement volume formed by two intersecting coherent laser beams makes it possible to accurately estimate the size distribution of the micron suspended particles with high temporal and spatial resolution. With its deployment during the field campaign at Yellow Sea, the LDCP has been experimentally demonstrated as an effective instrument to capture the micro-scale subsurface ocean current speed. The algorithm for retrieving the size distribution of the small suspended particles (2∼7.5µm) has been developed and validated. The combined LDCP system could be applied to the continuous long-term observations of plankton community structure, ocean water optical parameter over a wide range, and useful to elucidate the processes and interactions of the carbon cycles in the upper ocean.

Phase-coding methods have been widely used for three-dimensional (3-D) shape measurement, which use sinusoidal phase-shifting patterns to recover wrapped phase and the stair phase-coding patterns to determine the fringe order. However, due to the system nonlinearity, random noises, and image blurring, the total number of codewords that can be used is limited. In order to increase the number of codewords, this article presents a two-digit phase-coding (TDPC) strategy, in which each fringe of the sinusoidal phase-shifting patterns corresponds to a two-digit codeword encoded in the phase-coding patterns. In this way, more codewords can be generated without increasing additional patterns. Experiments of the cup and sculptures have been carried out, and the results confirm that the TDPC method can recover the 3-D shape of objects more robustly. Meanwhile, the precision experiment of a standard ball proves the high accuracy of the proposed method.

The calibration of camera systems employing zoom lenses raises several challenges, as changes in lens control settings introduce various imaging conditions, especially different degrees of defocus. This article presents a Fourier-based defocus calibration method to calibrate a camera attached with an electronically focus-tunable lens (ETL). Different from the traditional method which requires changing the scale of the calibration object for sharp images, the proposed method is more concerned with the frequency characteristics of the captured images than the gray distributions. According to the invariance of the fundamental frequencies before and after defocusing the images, coordinates of feature points can be extracted accurately, even in different degrees of defocus. Therefore, one normal size target can also be qualified for zoom system calibration. Then polynomial approximation is used to account for the variation of the intrinsic and distortion parameters across the zoom range. Extensive simulations and experiments were implemented to demonstrate the proposed idea’s robustness against defocus, flexibility, and accuracy.

Typhoid toxin is secreted by the typhoid fever-causing bacterial pathogen Salmonella enterica serovar Typhi and has tropism for immune cells and brain endothelial cells. Here, we generated a camelid single-domain antibody (VHH) library from typhoid toxoid-immunized alpacas and identified 41 VHHs selected on the glycan receptor-binding PltB and nuclease CdtB.

In this paper, nitrogen-doped graphene hydrogel (NGH) has been synthesised by chemically reducing aqueous graphene oxide (GO) solution in the presence of carbamide.Its nitrogen content reac...

In this work, novel hollow coral-shaped Co3O4 nanostructures are synthesized via a precursor conversion method for the first time, and the detailed process of precursor conversion is revealed. l -ascorbic acid as the structure-directing agent and the origin of oxalate (C2O42−) contributes to the formation of the precursors, providing a low-cost and facile method for preparing Co3O4. Hollow coral-shaped Co3O4 nanostructures are obtained by calcining cobalt oxalate precursors in air. The special Co3O4 nanostructures exhibit noticeable pseudocapacitive properties with a capacitance of 626.5 F g-1 at 5 mV s-1 and show superior stability (capacity retention of 99%) and outstanding Coulombic efficiency (˜100%) within 5000 charge–discharge cycles at 10 A g-1. Furthermore, the asymmetric supercapacitor Co3O4//G fabricated by Co3O4 cathode and graphene hydrogel anode delivers a specific capacitance of 115 F g-1 (47.9 mA h g-1) at 1 A g-1 and attains the maximum energy density of 35.93 Wh kg-1 at the power density of 801.6 W kg-1. The excellent durability of Co3O4//G is demonstrated by the retention of 85.1% of initial capacitance after 5000 cycles at 5 A g-1. The novel and feasible route proposed in the work is expected to be applied prospectively and widely in preparing Co3O4 pseudo-capacitance material, which owns great application value in supercapacitors, as well as in batteries.

Conventional camera calibrations with circular patterns always require sharp target images and thus fail if the images are blurred. In this paper, we present an effective calibration approach using three circular gratings, which can be employed in defocus scene. Rather than using the concentric circles as the targets, the proposed method utilizes circular gratings generated by phase-shifting methods. The intrinsic parameters of the camera can be obtained with the images of circular points, and it works even if the camera is out-of-focus. Numerical simulation and real data experiments have been carried out to validate the method. And the results show that our method can calibrate the camera effectively even under severe defocus. Moreover, the entire process requires no metric measurement of the test pattern, which is very flexible to implement and suitable for people who are not familiar with computer vision.

Co2(OH)3Cl was synthesized by a facile solvothermal method with different solvent ratios of water/glycol (Vwater:Vglycol). The Co2(OH)3Cl prepared at the ratio of 1:2 showed uniform cubic nanostructure and provided the highest specific capacitance of 321.79 F g−1 at 0.5 A g−1. The capacitance retention and the Coulombic efficiency were both kept at 100% without obvious decay after continuous 10,000 charge-discharge cycles, demonstrating the durability and eximious stability of the Co2(OH)3Cl when utilized as the supercapacitor electrode material.

Fringe projection profilometry has been proverbially utilized for measuring the shapes of objects. A common challenge in those systems is to accurately obtain a smooth absolute phase. Many new methods have been proposed to address this challenge. In this paper, we discuss a technique based on variant shifting phases. This approach embeds codewords into the shifting phase and only needs four patterns. However, reliable measurement results are difficult to achieve with a large number of codewords because of the phase errors. To address this shortcoming, we present a robust coding method that embeds a specific code sequence into the shifting phase and can generate more than 36 periods. The fringe order is determined using unique three-adjacent-codes combining the current period and its neighbors. An error correction algorithm is also proposed to optimize the codewords. The proposed method is experimentally verified using an established measurement system. The result shows that the proposed method is robust and efficient.

Nuclear mass measurements by means of Schottky mass spectrometry critically rely on an accurate determination of revolution frequencies of the circulating ions in a storage ring. Such a harmonic retrieval problem is conventionally tackled via the periodogram of the Schottky data, where the ion peaks are identified and their spectral locations are obtained by fittings. However, the discrete frequency grid of the periodogram has unfortunately hampered a fine resolution of two closely spaced harmonics. We thereby propose a method based on the state space representation in the frequency domain to overcome this limit. Moreover, its frequency-selective merit has allowed the method to focus only on a narrow band and thus greatly reduced the computational cost while still retaining superb accuracy. With the real Schottky data from an isochronous-Schottky beam time at the experimental cooler-storage ring in Lanzhou, the accuracy of the retrieved harmonics is demonstrated to be around 1 ppm, as limited by the anisochronism effect of the ion optics.

Binary coding methods have been widely used for phase unwrapping. However, traditional temporal binary coding methods require a sequence of binary patterns to encode the fringe order information. This paper presents a spatial binary coding (SBC) method that encodes the fringe order into only one binary pattern. Each stripe of the sinusoidal phase-shifting patterns is corresponding to an N -bit codeword of the binary pattern. A robust stripe-wise decoding scheme is also developed to extract the N -bit codeword, then fringe order can be determined, and stripe-wise phase unwrapping can be performed. Experiment results confirm that the SBC method can correctly recover the absolute phase of measured objects with only one additional binary pattern.

Hollow NiO nanostructures were fabricated by calcining Ni(OH)2 precursors built on the basis of Cu2O templates. The structures and morphology of the products were characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. As the temperature rose from 250 to 550 °C, the products showed stable cubic structures with the lengths about 600 nm of a side at first, then some products deformed into cylinders and debris is generated, and the NiO nanostructures collapsed at 550 °C. Electrochemical test results from cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charging–discharging demonstrated that the sample synthesized at 450 °C showed better electrochemical properties. The hollow NiO nanostructures obtained at 450 °C delivered a capacitance of 1200 F g−1 at 1 A g−1 and displayed good rate capability with a large capacitance of 1010 F g−1 at 5 A g−1. After improving the cycle stability, it will exhibit a more admirable prospect of application.

Stereo cameras have been widely used for three-dimensional (3D) imaging, and their performances are highly depended on the calibration accuracy. This paper presents a marked-crossed fringe pattern for the calibration of stereo cameras. Some coded markers are also encoded into the crossed fringe pattern, and the feature points are encoded into the carried phase. Two wrapped phase maps are recovered by using the Fourier transform, and the markers are extracted and decoded for absolute phase unwrapping. Referring to the absolute phase values, the one-to-one mapping between the world points and the image points can be established to calibrate the stereo cameras. Compared with the traditional method, the proposed method adopts global coding, which can flexibly select any part of the feature points for calibration and obtain high-precision camera parameters. Simulations and experiments show the effectiveness of the method.

Conventional two-wavelength algorithms have been broadly used for three-dimensional shape measurement. However, the maximum unambiguous range of phase unwrapping depends on the least-common multiple of two wavelengths, and thus coprime wavelengths are commonly selected. The recently proposed spatial-shifting two-wavelength (SSTW) algorithm can achieve the maximum unambiguous range with two non-coprime wavelengths, but this algorithm tends to fail for some wavelength selections. To address this problem, this paper presents a general look-up-table-based SSTW (LUT-SSTW) algorithm with arbitrary wavelength selection. The paper also analyzes the phase unwrapping robustness in terms of phase errors and provides guidance for wavelength selection. In addition, an improved LUT-SSTW algorithm is developed to enhance the phase unwrapping robustness, and further relax wavelength selection. Some experiments have been conducted, and their results verify the efficiency of the proposed method.

A recently proposed absolute phase unwrapping method using geometric constraints of the structured light system significantly improves the measurement speed and the robustness. The most important step of this method is to create a minimum phase map as the phase unwrapping reference. Current method usually selects the closest plane as the minimum phase map. However, we found that the position of the minimum phase map is direction-determined and it may induce a fatal error to phase unwrapping under certain circumstances. This letter analyzes the direction-determined phase increasing phenomenon and presents a direction-determined phase unwrapping technique, which includes a new establishment method for the minimum phase map and corresponding phase unwrapping procedures.

Conventional camera calibration methods always require well-focused target images for accurate feature detection. This requirement brings many challenges for long-range vision systems, due to the difficulty of fabricating an equivalent size target to the sensing field-of-view (FOV). This paper presents an out-of-focus color camera calibration method with one normal-sized color-coded pattern as the calibration target. The red, green and blue (RGB) channels of the color pattern are encoded with three phase-shift circular grating (PCG) arrays. The PCG centers used as feature points are extracted by ellipse fitting of the 2π-phase points. Experiments demonstrate that the proposed method can achieve accurate calibration results even under severe defocus.

Absolute phase information is required when multiple separated objects are being measured. The recent proposed phase-coding method can effectively achieve absolute phase retrieval by embedding the fringe order information in phase domain. However, it suffers from the limitation of codewords and the requirement of more coding patterns. To overcome these problems, this paper proposed several improved phase-coding methods to solve the absolute phase with fewer patterns. The four-frame and five-frame method are suitable when the fringes are sparse, since they can respectively encode N ∕ 2 and N fringe periods(generally N ≤ 16 ). If really dense fringe patterns with more than N periods are required, the improved two-step phase-coding algorithm can be adopted since it can encode about N 2 ∕ 2 fringe periods. Experiments were conducted and the results verify the success of the proposed methods.

Stereo cameras have been widely used for three-dimensional (3D) photogrammetry, and stereo calibration is a crucial process to estimate the intrinsic and extrinsic parameters. This paper proposes a stereo calibration method with absolute phase target by using horizontal and vertical phase-shifting fringes. The one-to-one mapping from the world points to the image points that can be recovered by referring to the absolute phase and then used to calibrate the stereo cameras. Compared with traditional methods that only use feature points within the overlapping field-of-view (FOV), the proposed method can use all feature points within the overlapping and non-overlapping FOVs. Besides, since phase is more robust against camera defocusing than intensity, the target images can be captured regardless of the depth-of-field (DOF). With the advantages of whole-field capability and defocusing tolerability, the target placement becomes very flexible. Both simulations and experiment results demonstrate the robustness and accuracy of the proposed method.

Narrow laser echo signal processing plays a decisive role for digital lidar ranging system, especially, in time-of-flight (TOF) measurement accuracy and signal-to-noise ratio (SNR). It will achieve more precise resolution for time measurement with high-speed analog-to-digital converter (ADC), but it also means more expensive. Therefore, a method using transmission pulse spacing modulation, is proposed to realize high-frequency sampling with low-speed analog-to-digital converter, and then the resolution of time-measurement depends on the relationship between the modulation spacing of driving pulse and the sampling period. Consequently, the resolution can be raised to 625 ps, which is suitable for high precise time measurement. Besides, since the power of echo signal is inversely proportional to the square of the distance according to the radar function, the echo signal is weak and may be contaminated by the environment and electronic noise for the long-range lidar. Data accumulation is used to improve the SNR for the echo signal. Both simulation and experimental results show the desirability of this method.

Digital fringe projection (DFP) method has been widely used in three-dimensional (3D) shape measurement. Lots of studies have been conducted to enhance the measurement accuracy and speed by modulating the patterns. However, it is still hard to acquire enough number of 3D results to ensure the continuity of dynamic 3D shape measurement when phase shifting profilometry and temporal phase unwrapping algorithm is adopted. Besides, object motion can introduce phase error and thus measurement error for phase shifting profilometry. To this end, a dynamic 3D reconstruction framework based on modified three-wavelength phase unwrapping algorithm and phase error compensation method is proposed to solve this problem. By redefining the order of fringe patterns projected by the digital light processing (DLP) projector, the number of required patterns for 3D reconstruction can be reduced and the speed of dynamic 3D shape measurement can be improved. And using phase error compensation method based on Hilbert transform, the accuracy of 3D reconstruction can also be improved. Experiments were carried out to demonstrated the effectiveness of the proposed framework. And the modified algorithm successfully improved the speed of dynamic 3D shape measurement by 1 ∕ 3 .

Non-contact optical measurement methods have been widely used in the fields of three-dimensional (3D) machine vision and photogrammetry attributed to their advantages of high precision, high speed and low cost. The calibration results directly affect the accuracy of the vision measurement system. Most of the existing calibration methods with two-dimensional (2D) targets need all of the feature points to be captured by the camera, otherwise it would be difficult to distinguish them due to the usage of identical feature points. This paper presents an active calibration target that consists of phase-shifting wedge gratings (PWGs) with three different periods and globally coded on the basis of rotation invariant local binary pattern (LBP) coding. Feature points are the intersections of several straight lines fitted by the 0 and π phase points. The sub-pixel coordinates can be accurately obtained with the phase-shifting method and the windowed linear fitting. Each feature point has its corresponding label to determine its specific position, therefore the one-to-one correspondence between the image coordinates and world coordinates can be obtained even the images are partially captured, and this characteristic can expand the flexibility in both monocular and multi-camera calibrations. In addition, owing to the phase-shifting method, calibration can be accomplished when the camera is defocused. Simulations and experiments further prove the flexibility and robustness of the proposed method.

Clear and focused pattern images are essential prerequisites for accurate feature detection in traditional camera calibration methods, which introduce numerous limitations in various areas, such as long-distance photogrammetry. A feature detection method robust against defocusing is proposed for extracting the centers or corners of a planar square periodic target. A Fourier transform is employed to calculate two wrapped phase maps from the periodic target images, which are then used to accurately extract the feature points. The calibration procedure is divided into two stages to obtain more accurate results. A rough calibration is performed to calculate the rotation angles between the target and the camera. If the tilt angle is larger than 12°, the corresponding images are removed. Subsequently, the remaining images are used for precise calibration. The simulations and the experiments demonstrate that the proposed method can accurately calibrate a camera with a planar square periodic pattern, even in the case of severe defocusing.

Absolute phase retrieval is important for three-dimensional (3D) shape measurement in fringe projection technique. Numerous phase unwrapping methods have been proposed for addressing this issue, and gray-level is one such technique employed to determine fringe orders for wrapped phase. However, the codeword detection can fail due to random noise or cameras/projectors defocus. We propose an improved method to determine the codewords in this paper. Specifically, three sinusoidal fringe patterns are used to obtain the wrapped phase and three n-ary gray-level (nGL) patterns are employed to obtain the fringe order. Two opposite masks can be calculated through wrapped phase binarization. The masks and the nGL patterns are roughly used to obtain codewords. After half-period correction, the codeword is accurately reconstructed, and the fringe order is also determined. Simulations and experiments demonstrated the robustness and effectiveness of the proposed algorithm to measure isolated objects with complex surfaces.