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Issue 8 ， 2021
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Construction and error source analysis of seawater absorbance measurement system
Abstract：Seawater absorbance sensor is an important equipment for marine environment research. In order to analyze and study the working principle and error source of this equipment， a seawater absorbance measurement system equipped with 645 nm light source was constructed. Firstly， in accordance with the Lambert-Beer law， error transfer principle and structure of the absorbance sensor， the working principle and error source of the seawater absorbance measurement system were analyzed. Then， repeatability tests and absorbance measurement experiments were used to verify the stability and absorbance detection of the system. The results of repeatability tests show that the error can be controlled within ±0.008 3 m-1 by using the calibration-before-measurement method， in which the error caused by the light source and photoelectric sensor is approximately ±0.006 7 m-1， and the error caused by the sample cell processing is approximately ±0.001 6 m-1. The results of the absorbance measurement experiment are as follows： there is a negative measurement error of absorption coefficient from -0.019 44 m-1 to -0.017 08 m-1 for ultrapure water； the absorption coefficient of tap water is 0.005 68/m higher than that of ultrapure water； 3% concentration of sodium chloride solute can increase the absorptivity by 0.097 56 m-1， which is 17.2 times of the increase caused by impurities in tap water； the solute in seawater can increase the absorptivity by 0.726 32 m-1， which is 7.4 times of that induced by 3% concentration of sodium chloride solute. The results given above show that： the measurement error caused by the modules in the seawater absorbance measurement system in this paper is small， which meets the requirements of absorbance measurement experiment； the seawater absorbance measurement system presented here can detect the influence of solute on absorbance， but there is a negative measurement error in the absorbance measurement data.Keywords：optical oceanography;optical remote sensing;ocean colour sensing;absorbance- 284
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Published：2021-09-01 -
Review of monomeric large-size and high precision holographic planar grating manufacturing technology
Abstract：Monomeric large-size planar gratings with high accuracy are a key optical element in semiconductor lithography tooling， inertial confinement fusion， and other applications. However， such gratings are extremely difficult to fabricate. The technologies used for manufacturing high-accuracy monomeric large-size planar gratings are reviewed in this paper. The main manufacturing technologies are introduced， and their advantages as well as disadvantages are discussed. The research progress and the existing challenges associated with single large-aperture interference lithography and stepping interference lithography are discussed. The research progress with regard to scanning beam interference lithography （SBIL）， which is the most promising manufacturing technology for monomeric large-size planar gratings， is reviewed as a highlight. Finally， the development trend of SBIL technology is summarized.Keywords：planar grating manufacturing;scanning beam interference lithography;stripe lock;grid pitch /direction/phase control- 274
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Published：2021-09-01 -
On-orbit geometric calibration and accuracy verification of Jilin1-KF01A WF camera
Abstract：To realize the high-precision geometric positioning of Jilin1-KF01A WF camera， a rigorous geometric model which is an ultra-multi-chip TDI CCD mechanical staggered push-broom imaging system was established， and the on-orbit geometric calibration based on the look-angle model was proposed and verified. This model had an added constraint of geometric positioning consistency of the nearby TDI CCD. The rigorous geometric model was realized using the principle of push-broom satellite imaging system. Then， by decomposing the calibration coefficients into calibration parameters of the interior orientation parameters and the exterior orientation model and combining the imaging characteristics of the large-width and ultra-multi-chip TDI CCD mechanical staggered push-broom imaging system， a step-by step iterative method with constraint of geometric positioning consistency of the nearby TDI CCD was adopted to solve the calibration coefficients. Finally， the on-orbit geometric calibration of Jilin1-KF01A WF camera was performed using the control data to identify the interior and exterior orientation parameters. Experimental results indicate that the proposed calibration model and method are reasonable and effective. The calibration precision of the interior orientation elements is better than 0.3 pixel， and the ultra-multi-chip TDI CCD mechanical staggered push-broom imaging system generates seamlessly stitched images. Moreover， the band-to-band registration accuracy is better than 0.3 pixel. Panchromatic image and the multi-spectral image had the same geometric positioning accuracy. The positioning accuracy without ground control points （GCPs） improves to 20 m （CE90） and the positioning accuracy with GCPs is better than 2 m， which satisfies the 1∶10 000 topographic maps requirements.Keywords：optical remote sensing;Jilin1-KF01A satellite;sub-meter resolution wide view camera;rigorous geometric model;on-orbit geometric calibration- 251
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Published：2021-09-01 -
Effects of ambient temperature and irradiance on performance of half-cut and shingled photovoltaic modules
Abstract：Aiming at new photovoltaic （PV） module technologies， half-cell modules and shingled modules， we systematically analyzed the influence of irradiance and temperature on the electrical stability of PV modules. In accordance with the IEC61215 and IEC61823 standards， we tested the effects of temperature and radiance on the electrical stability of conventional， half-cell， and shingled modules in a simulated indoor environment and a real outdoor environment at a photovoltaic power station. The absolute values of the relative temperature coefficients of the main electrical parameters of shingled and half-cell modules are significantly lower than those of conventional modules under the AM1.5 irradiance condition. This indicates that shingled and half-cell modules have higher thermal stability. Moreover， thermal stability is positively correlated with irradiance. The light utilization efficiency of these two types of modules is greater than that of conventional modules in the incidence angle range of 0–80°； this shows that such modules are less affected by the incidence angle. After accumulative irradiance in an outdoor environment， the light-induced degradation of half-cell and shingled modules is weaker than that of conventional modules； thus， half-cell and shingled modules possess higher stability against long-term irradiance. Half-cell and shingled modules exhibit greater performance stability than conventional modules do in terms of heat， incidence angle， and long-term irradiance. This is mainly due to their stronger thermomechanical stress resistance， which is caused by the small cell area， the smaller Joule heat generated by the circuit， and the weakened hot-spot effect due to the parallel connection of some solar cells inside PV modules.Keywords：photovoltaic module;temperature coefficient;irradiance;light utilization efficiency;light induced degradation- 143
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Published：2021-09-01 -
Polarized laser confocal technique for subsurface damage of lapped quartz glass
Abstract：Subsurface damage is generated during the lapping process of quartz glass. The detection of subsurface damage has been a research focus in the lapping process optimization of quartz glass. This study proposes a nondestructive detection method to detect the subsurface damage of lapped quartz glass. By combining the polarized laser scattering method with the confocal scattering microscopy method，a polarized laser confocal nondestructive detection method for the subsurface damage of lapped quartz glass was proposed， and a nondestructive detection system was developed. In addition， the subsurface damage of lapped quartz glass was detected， and the cross-sectional microscopic destructive method was used to verify the nondestructive detection results. The comparison results of nondestructive detection and destructive detection indicate that the relative error of subsurface damage depth is less than 5%， and the subsurface crack configuration is consistent with that of the destructive detection method. The polarized laser confocal nondestructive detection method can quantitatively detect the subsurface damage of lapped quartz glass. Thus， the study provides an effective detection method for the optimization of quartz glass processing.Keywords：confocal imaging;subsurface damage;polarized laser scattering;cross-sectional microscopy method;quartz glass- 205
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Published：2021-09-01 -
Design of Fourier single-pixel imaging system for high-temperature components
Abstract：For visual measurement at high temperature， it is challenging to reduce the radiation emitted by high-temperature components and the influence of hot gas flow on image quality， which has a significant impact in fields such as aerospace or automotive manufacturing. Owing to the complicated optical imaging environment at high temperature， in this paper， a new method of image acquisition for high-temperature components based on Fourier single-pixel imaging is proposed， and a single pixel imaging system for high-temperature components is established. First， the working principle and reconstruction algorithm of Fourier single-pixel imaging are analyzed. Then， according to the thermal radiation characteristics of the high-temperature object， the influence of the object on the single-pixel imaging and the imaging spectral range are analyzed. Finally， a verification experiment is carried out for single-pixel imaging in a high-temperature environment. Experimental results indicate that only 30% of the sampled data can be used to image the target at high temperature， and the strong interference of the radiated light of the object itself is ignored. The experimental results show that the image features obtained by the proposed method are clearer than those obtained via traditional CCD/CMOS imaging and edge detection. This study provides a potential development direction for the application of single-pixel imaging in the industrial field of high-temperature components.Keywords：single-pixel imaging;high temperature;thermal radiation;light interference- 158
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Published：2021-09-01 -
Visual three-dimensional measurement of aircraft flutter in hypersonic wind tunnel tests
Abstract：The measurement of model flutter data in hypersonic wind tunnel tests is crucial for the safety design of aircraft. However， contact sensors yield a low measurement accuracy and are inconvenient to use. Therefore， this study adopts the non-contact 3D vision measurement technology to measure the vibration of key points on the surface of a model during the test process for the model flutter analysis. The existing measurement systems can only be placed outside the window glass of the test section. Owing to the limitation of the size of the window glass and the influence of the image distortion caused by the glass， the measurement accuracy cannot meet the requirements for the flutter measurement of a hypersonic wind tunnel test model. Placing the measuring system in the test section is an effective approach to solve the above-mentioned problems. However， in the test process， the air pressure in the test section alternates sharply between vacuum and normal pressure， with strong vibration； thus， the existing visual 3D measurement systems cannot be placed in the test section. In this study， through the design of the sealing device and the air floating shock absorber of the visual measurement system， the visual 3D measurement equipment， for the first time， is placed on the platform in the test section of a 1 m hypersonic wind tunnel， and a self-calibration algorithm based on the simultaneous solution of the key points of the model and the system parameters is proposed to eliminate the measurement error caused by the environmental vibration in the test section. The results indicate that in the measurement range of 1 m×1 m×1 m， the camera resolution is 1 000×1 000 pixels，and the measurement accuracy of the system can be greater than 0.1 mm，thereby meeting the requirements for the flutter measurement of a hypersonic wind tunnel test model.Keywords：visual measurement;hypersonic wind tunnel;flutter test;vibration damping device;self-calibration- 214
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Published：2021-09-01 -
Design of micro-structure film for improving viewing brightness of vehicle head-up display
Abstract：Vehicle head-up displays can directly display information required by a driver to view the direction of the driver's sight line as a virtual image， which effectively reduces traffic accidents caused by sight deviation from the driving direction. Current head up display products have some virtual images outside the eyebox area， which leads to problems of low brightness in this area and low light efficiency of the system. We take the scattering angle of single row pixels in the source image as the design unit and design an optical microstructure film to control the direction of the projection light， so that the projection light is more concentrated in the eyebox area. The test results indicate that the average brightness of the eyebox area increased by 31.7%. This method can effectively improve the viewing brightness and system lighting efficiency of the head up display and reduce both light pollution in a cab and the stray light outside the eyebox area.Keywords：head-up display;microstructure;eyebox;system lighting efficiency- 131
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Published：2021-09-01 -
Automatic focusing of Cassegrain telescope based on environmental temperature feedback
Abstract：To adjust the combined focal length deviation of an optical system caused by the changes in environmental temperature in real time during telescope equipment detection， this study established the relationship between the temperature and variation in the imaging focus position. Through theoretical calculations， the relationship between the focal length change of a Cassegrain telescope system and temperature change was obtained. Then， a temperature experiment was conducted using a walk-in programmable high and low temperature box. The change in the focal position per unit temperature of the system was obtained. A second calibration was conducted in the actual working environment. The defocus of the telescope equipment considered in this study was -0.14 mm/℃. By combining theoretical and experimental results， a telescope automatic focusing device based on environmental temperature feedback was designed. Finally， the device was applied to an equipment field observation experiment. We obtained the imaging signal-to-noise ratio of the telescope system before and after the automatic focusing device was applied. The results demonstrated that the defocus corresponded to the temperature change. After the focusing device was incorporated， the mean square error of the resulting image was reduced from 5.056 to 0.729， and the imaging signal-to-noise ratio was increased from 41.09 to 49.50. The automatic focusing technology of environmental temperature feedback helps the telescope system to better capture the observation target， suppress background noise， improve the accuracy of signal acquisition and parameter measurement， and enhance the adaptability of external field detection to environmental temperature changes.Keywords：telescope;combined focal length;environmental temperature;automatic focusing- 136
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Published：2021-09-01
Modern Applied Optics
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Ultra-precision manufacture of X-ray focusing mirror
Abstract：An X-ray focusing mirror is used to collect X-ray radiation in the universe， and is the core component of an X-ray astronomical satellite observation payload. In this study， process exploration and equipment research and development are conducted on the entire process chain （including electroless nickel-phosphorus alloy plating， mold ultra-precision machining， mold coating， electroforming nickel matrix， and demodulator） using the electroforming replication method of a nickel substrate， and finally， the batch ultra-precision manufacturing of X-ray focusing mirrors is completed. The results indicate that the surface roughness of the focusing lens mold processing precision is less than 0.5 nm RMS， surface shape precision is better than 0.5 m， and lens Angle resolution is 33.5″（half-power diameter）， thus validating the reliability of the process. The study findings are expected to provide important technical support for China's space X-ray observation， break the foreign monopoly， and significantly improve China's astronomical observation ability in the field of high-energy celestial bodies.Keywords：X-ray optics;Wolter focusing telescope;glancing incidence;electroforming replication;Ultraprecision machining- 937
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Published：2021-09-01 -
Interval discretization method for workspace of parallel robot
Abstract：The traditional point discretization method （PDM） for the workspace determination of parallel robots has some drawbacks such as low accuracy and missing points. In view of these， considering a 3-RPR planar parallel robot as the research object， an interval discretization method （IDM） with high accuracy and no point omission is proposed based on the interval mathematics theory. Firstly， an expression for the analytic inverse solution of the robot is derived. Then， the position/orientation workspace is obtained using the IDM. Subsequently， the efficiency， accuracy， and error sensitivity of the IDM and PDM are compared. The results indicate the following： （i） with the improvement of calculation accuracy， the efficiency advantage of the IDM becomes increasingly evident； （ii） the calculation error of the IDM and PDM are 0.002% and 0.272%， respectively； and （iii） the sensitivities of the IDM and PDM to the errors of structural size of the robot are 0.394 and 0.396， respectively. The research methods and conclusions provide theoretical guidance for topology optimization and trajectory planning of parallel robots.Keywords：parallel robot;workspace;interval discretization method;point discretization method;numerical behavior- 131
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Published：2021-09-01 -
Fast picking strategy and electrical properties measurement of carbon nanotubes
Abstract：Carbon nanotubes’ pick-up is important to large-scale manufacturing and repairing electronic nano device. In this paper， a micro-nano operating system was built in a scanning electron microscope. A cutting pick-up circuit was proposed by collaboration of tungsten needle and AFM with carbon nanotubes under different magnifications. The energized cutting method was used to realize the rapid picking of carbon nanotubes. Under the situation of containing the contact state of tungsten needle and carbon nanotubes， the point contact circuit model and the line contact circuit model of carbon nanotubes and AFM were established， and the influence of contact pose on electrical properties was analyzed. In addition， the contact length of carbon nanotubes and AFM changing under the condition of the line contact circuit model in order to study the influence of contact length on contact resistance. The results show that the operation strategy can effectively improve the success rate of carbon nanotubes’ pick-up and control the operation time in approximately 8 min； under the low voltage of 0-1 V and the line contact state between carbon nanotubes and gold surface， the contact resistance between carbon nanotubes and tungsten needle or gold surface is ohmic contact， and the contact resistance is inversely proportional to the contact length， while in the point contact state， the contact resistance is non-ohmic contact which indicates that the contact state has effect on the electrical properties between carbon nanotubes and metal. The strategy of carbon nanotubes’ pick-up and the results of electrical properties measurement provide guidance for carbon nanotubes’ pick-up， properties measurement and assembly.Keywords：micro-nano operation;carbon nanotubes;power on cutting;electrical performance- 113
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Published：2021-09-01 -
Design and analysis of bi-flexible mounting structure for large optical lens
Abstract：A new bi-flexible mounting structure is presented for the large lenses used in wide-field survey telescopes. Using this bi-flexible structure， the position and surface precision of the lens can be guaranteed， and the influence of barrel elastic deformation can be considerably reduced. First， the limitations of existing mounting structures for large optical lenses and the structure scheme are elaborated upon. Moreover， the mechanical principle and advantages of the proposed bi-flexible structure are discussed. Thereafter， according to the structural components and structural properties of the bi-flexible structure， a mechanical model of this structure is established based on Euler beam theory. Then， assuming the lens to be a rigid body， an integrated stiffness model of the mounting structure， which includes axial， transverse， and rotary stiffnesses， is derived based on the force equilibrium and considering compatible deformation conditions. Finally， a 640 mm test lens is used as an example for experimental verification. The influence of the barrel on the lens surface precision for three types of mounting structures are simulated. In the worst case， as the barrel undergoes the maximum elastic deformation， the lens surface precision is reduced to 50 nm； this indicates that the bi-flexible mounting structure performs better than the other two types of structures. In addition， the optical measurement results show that the minimum root mean square error is 0.05λ， which further verifies the advantages of the proposed bi-flexible mounting structure.Keywords：Optical lens;bi-flexible;mounting structure;surface precision;numerical simulation- 318
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Published：2021-09-01 -
Design and experiment： u-shaped transmitting coil wireless power transfer system for micro gastrointestinal capsule robot
Abstract：Power cables cannot be used to power micro gastrointestinal capsule robots or other implantable medical equipment， and wireless power transfer systems exhibit poor performance. To address these limitations， this paper proposes a U-shaped transmitting coil wireless power transfer （WPT） system. In contrast to the traditional solenoid-paired transmitting coil， the proposed transmitter coil comprises a magnetic core， which was added after incorporating a few structural improvements. The core can tremendously improve the power transfer efficiency （PTE） and received power. In this study， a theoretical model of the proposed system is established and analyzed via a finite element simulation. To verify the effectiveness of the proposed design， a U-shaped transmitting coil WPT system platform is built， and experimental tests on the PTE of the system and the received power of the receiving coil are conducted. The experimental results demonstrate that the maximum received power of the proposed system is 3780.75 mW and its PTE is 14.13%， which satisfy the power requirements of the robot.Keywords：micro gastrointestinal capsule robot;wireless power transfer;inductive coupling;transmitting coil;power transfer efficiency- 114
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Published：2021-09-01 -
Ultra-precision machining technology of off-axis paraboloid surface based on PMAC time-based control
Abstract：In order to achieve ultra-precision diamond turning of non-rotationally symmetrical， irregular， and complex surfaces such as off-axis paraboloid surfaces， this paper proposes a method for the machining of off-axis paraboloid surfaces using time-based control of a PMAC. This study converts the coordinates of a workpiece based on the translation and rotation equations and then calculates the control parameters based on the time-based control principle. Finally， machining experiments are performed by analyzing the tool motion process. The experimental results show that off-axis paraboloid surfaces with a form error of 2 µm and roughness of Ra 0.02 are successfully machined at a spindle speed of 100 r/min， cutting depth 0.005 mm， and feedrate of 1 mm/min. This method applies to not only the machining of off-axis paraboloid surfaces but also the ultra-precision machining of other rotationally symmetrical and irregular free-form surfaces.Keywords：off-axis paraboloid;fast servo tool;PMAC;time based control- 191
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Published：2021-09-01 -
Design and verification of anti-resonance frequency controller for two stage drive vibration isolation system
Abstract：Existing vibration isolators cannot isolate inertial force interferences of a platform base under a frequency sweep between 0 Hz and platform natural frequency. To solve this problem， a dual-stage actuation active vibration isolation system for an adjustable anti-resonance frequency controller is proposed in this study. The mathematical model of the adjustable anti-resonance frequency controller and parameter design of the dual-stage actuation active vibration isolation system are examined. First， a mathematical model for the designed dual-stage actuation active vibration isolation system is established. Then， based on the anti-resonance frequency characteristics of the system， an adjustable anti resonance frequency controller and its design parameters are proposed. Thereafter， the vibration isolation performance of the adjustable antiresonance frequency control is analyzed. Finally， the effectiveness of the proposed system is verified experimentally. The experiment results show that the closed-loop transmissibility of the proposed controller is less than -15 dB from zero to the first anti-resonance frequency. Furthermore， it is less than -30 dB around the added anti-resonance frequency， which is adjusted between 0 Hz and the first anti-resonance frequency by changing the parameters of the proposed controller. With the proposed controller， the disturbance amplitude of the payload decays from 4 to 0.5 mm/s with a reduction of 87.5% for an impulse disturbance applied to the platform base. The dual-stage actuation active vibration isolation system combined with the adjustable anti-resonance frequency controller can adjust the anti-resonance frequency point in real time by tracking the frequency sweep interference. Our proposed system isolates vibrations effectively and can be applied to the frequency sweep applications with ultra-low vibration requirements， such as semiconductor manufacturing industry.Keywords：dual-stage actuation;active vibration isolation;adjustable anti-resonance frequency controller- 126
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Published：2021-09-01 -
A fast and robust method for detecting elliptical character of cooperative targets in industrial complex background
Abstract：A robust ellipse detection method is proposed herein to meet the demands for recognizing typical cooperative targets in industrial complex backgrounds. First， edge segments are derived from discrete edge points of a preprocessed image by applying an edge tracing algorithm， which is followed by steps of segmentation， filtering， and grouping. Next， a Pascal’s theorem based matching method for arcs of adjacency quadrants and a relationship matrix based arc clustering method are proposed herein to realize fast clustering according to the elliptic matching quality. Then， a non-iterative least square fitting method is used to obtain the parameters of ellipses， and the final result is achieved by eliminating false ellipses based on their parameters. The proposed method performs well in terms of the detection efficiency and robustness owing to the application of a stricter elliptical matching constraint， and a more effective arc clustering method reduces the computational complexity of the parameter fitting step by eliminating non-elliptical datasets. The ellipse fitting efficiency increases， and a more exact and reliable result is acquired. Test results show that the proposed detection method is insensitive to interference factors such as distance， illumination， target’s orientation， and noise. The detection time for the proposed method is less than that for reference algorithms for the test image； the detection time is 183.2 ms for a 640×480 pixel image. The method shows great potential for industrial measuring instruments to search for collaboration targets in complex backgrounds.Keywords：industrial measurement;object identification;ellipse detection;pascal’s theorem;least square method- 155
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Published：2021-09-01 -
Zero-mode waveguide device with microlens for enhancing fluorescence signal intensity
Abstract：In this study， an improved zero-mode waveguide device is designed and developed. This device is used to enhance fluorescence signal intensity and eliminate fluorescence crosstalk. The device is fabricated using micro/nanofabrication technologies. It reduces the divergence angle of fluorescence through a combination of a microlens and nanopores； the constructive interference of fluorescence enhances the intensity of the detection signal. Specifically， electron beam lithography is used to prepare a nanohole array with a controllable diameter， and a microlens array with an adjustable angle is fabricated by combining ultraviolet lithography and reactive ion etching. ImageJ is used to read the fluorescence gray value for signal comparison. Compared with a standard zero-film waveguide device， the improved device increases the fluorescence signal intensity by 14.5 times and the signal-to-noise ratio by 9 times. As determined through SEM characterization， the nanopore diameter of the device is （100.3 ± 4.9） nm， and the inclination angle of the microlens is （21.1 ± 0.7）°. The improved zero-mode waveguide device can effectively mitigate fluorescence crosstalk while enhancing fluorescence signal intensity. Related research provides a feasible solution to the problems of weak fluorescence detection and fluorescence crosstalk.Keywords：zero mode waveguides;nanopore;microlens;fluorescence signal detection- 238
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Published：2021-09-01
Micro/Nano Technology and Fine Mechanics
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End-to-end image dehazing under separated features and collaborative network
Abstract：Hand-designed features limit the performance of traditional dehazing methods， and existing networks encounter problems such as incomplete dehazing and significant loss of detail. Therefore， a model of end-to-end dehazing with separated features and a collaborative network is proposed herein. First， the traditional atmospheric scattering model is transformed to separate the multiplicative and additive features. Second， according to the influence of two features on the final dehazing result， a parallelly driven dehazing architecture is designed based on multiplicative and additive feature extraction frameworks. Further， spatial information and detailed features of different depths are fully considered in the multiplicative feature extraction network， and feature reuse and information compensation are realized using dense cascading to obtain precise and rich target features. Additionally， an additive feature extraction network is built to acquire biased and additive features according to the residual cross-connection structure. Finally， separated features are substituted into the restoration model to obtain a haze-free image. Experiment results show that the proposed network offers a significant dehazing effect， natural colors of restored images， outstanding detail retention， and superior scores of various metrics.Keywords：image dehazing;convolutional neural network;atmospheric scattering model;feature separation;image restoration- 491
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Published：2021-09-01 -
Detection method of wheel hub weld defects based on the improved YOLOv3
Abstract：This study proposes a method for intelligent detection of wheel weld defects， against manual detection， by improving an existing deep learning target detection algorithm， called “You only look once” version 3 （YOLOv3）. The improved algorithm is called YOLOv3-MC. First， an industrial camera was used to capture the images of the wheel hub weld defects， which were then annotated and developed into a data set. The data set was then expanded using a data enhancement method. Second， the detection accuracy of the algorithm was improved using the Mish activation function instead of the Leaky ReLU activation function in the YOLOv3 backbone network. Furthermore， the loss function of the algorithm was modified， and the positioning accuracy of the detection algorithm was improved using the method of complete intersection over union （CIoU）. Finally， the batter model was trained with a training set. The detection experiment was implemented using a validation set and test set. The experimental results yielded a mean average precision （mAP） of 98.94% for the validation set in the optimal model of YOLOv3-MC. The F1 score value of the model was 0.99； the average Intersection over Union （AvgIoU） of the model was 80.92%； the detection speed was 76.59 frames per second （fps）； the model size was 234 MB； and the detection accuracy rate of the optimal model on the test set reached 99.29%. Compared to the traditional machine vision detection method， this method offers an improved detection accuracy and meets the real-time online detection needs of the welding seam during wheel manufacturing.Keywords：weld defect detection;YOLOv3-MC;mish activation function;loss function- 358
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Published：2021-09-01 -
Text detection with kernel-sharing dilated convolutions and attention-guided FPN
Abstract：High-resolution images have characteristic large differences in feature scales. To overcome the difficulty in capturing fine-grained features and the poor fusion of multi-scale features， a text detection method for complex scenes with kernel-sharing dilated convolutions and an attention-guided feature pyramid network （KDA-FPN） is proposed. An intersection over minimum （IOM） strategy is proposed to improve the mask overlap phenomenon （caused by the large change of the text aspect ratio） and detection effect. Firstly， the model uses ResNet50 as the backbone network to capture multi-scale features using the FPN structure. It then uses hole convolution to expand the feature receptive field， improve the multi-scale capture capability of feature information， deeply mine the fine-grained features of text， and reduce it by sharing the core. The model parameter quantity reduces the calculation cost. Concurrently， the context attention module （CxAM） is adopted to capture the semantic information relationship between multiple receptive fields， while the content attention module （CnAM） is applied to accurately locate the target position information to enhance the multi-scale fusion ability and improve the quality of the feature map. Finally， the candidate frames predicted by the same text area are arranged according to their sizes. To suppress the mask overlap of the detection result and achieve accurate text detection， the use of the intersection area ratio of the area between the largest area and adjacent text box to the area of smaller box， as the candidate box screening index， is proposed. The comparative experimental results based on the ICDAR2013 and ICDAR2015 Total-Text datasets show that the accuracy and recall rate of this model are 95.3 and 90.4， respectively， for horizontal scene text detection； 87.1 and 84.2， respectively， for the inclined text detection； and 69.6 and 57.3， respectively， for arbitrary shape text detection. The proposed algorithm effectively overcomes the influence of image resolution， text shape， length， and other factors， resulting in enhanced detection accuracy and highly accurate text boundaries.Keywords：text detection;attention structure;kernel-sharing dilated convolutions;feature pyramid network- 173
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Published：2021-09-01 -
Distortion analysis and reconstruction of OCT image in sector scan mode
Abstract：In order to solve the problem of image distortion in sector scan mode by optical coherence tomography （OCT）， this study investigates the causes， provides a quantitative analysis， and proposes a rectification and reconstruction algorithm for the OCT images in sector scan mode. First， based on the maximization of interclass variance （OTSU） algorithm， a preprocessing of denoise and enhancement was applied to the original image， thereby facilitating the reduction of the influence of background noise on image reconstruction. Thereafter， a mapping relationship between the original OCT image and the reconstructed image was established， thus， achieving the rectification of the distorted OCT image. Here， we took advantage of the OCT system to make a glass sample from the images in sector scan mode and measured the thickness and width of the glass sample after rectifying the images. On comparing the measured values with the actual ones， we found that the measured thickness error ranges between -0.012 mm and 0.053 mm， and the measured width error ranges from -0.107 mm to 0.045 mm. Furthermore， taking the eyes of pigs in vitro as the sample， we made a comparison between the measurement results in the rectangular scan mode to that in the sector scan mode and found that the measured thickness error of corneas range between -0.022 mm and 0.014 mm， and the measured width error of irises range from -0.121 mm to -0.015 mm. Thus， the proposed method reduces the background noise of OCT images and corrects the image distortion effectively. This is of great significance for the application of OCT in sector scan mode， especially， in the field of medical diagnosis and surgical navigation.Keywords：OCT;sector scan mode;image distortion;image reconstruction;the maximization of interclass variance algorithm- 137
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Published：2021-09-01 -
Adaptive radon single-pixel imaging method
Abstract：Single-pixel imaging requires a large amount of sampling. In this study， an adaptive Radon single-pixel imaging method is proposed for the target region that only occupies a part of the scene. This method uses single-pixel detectors to position and image the target region. We used the target positioning method， coding sampling， and reconstruction algorithms to reduce the number of single-pixel imaging samples. Based on the fundamental principle of Radon transformation， the projection information of an image in horizontal and vertical directions was used to obtain the size and position of the target region in the scene. This method established the adaptive Radon-Hadamard single-pixel imaging model. Only single-pixel sampling was performed on the target region and filtered back-projection technology was used to reconstruct the target region. The results show that the proposed adaptive Radon single-pixel imaging method can achieve imaging of the target region in a scene. The number of samples was much lower than the resolution of the reconstructed image and the structural similarity index of the reconstructed image was greater than 95%， which effectively improved the imaging efficiency of single-pixel imaging method.Keywords：single-pixel imaging;Radon transform;target region;sampling number- 170
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Published：2021-09-01 -
Deep manifold reconstruction belief network for hyperspectral remote sensing image classification
Abstract：Traditional deep learning methods extract only deep abstract information from hyperspectral images while failing to fully reveal the local geometric structure relationship between samples. This limits the improvement of classification performance. To address this problem， the present study proposes a new feature extraction network called a deep manifold reconstruction belief network. First， deep abstract features are extracted based on the deep belief network to enhance the identification ability of abstract features. Then， intraclass and interclass graphs are constructed based on the neighborhood points of sample data and reconstruction points of similar neighbors in each neighborhood under the graph embedding framework. Under this framework， intraclass neighbors and their reconstruction points are compressed. By contrast， interclass neighbors and their reconstruction points are separated in low-dimensional space to improve the separability of different types of data and the accuracy of feature classification. Deep discriminant feature extraction is then realized based on the reconstructed points. Experimental results on the KSC and MUUFL Gulfport hyperspectral datasets showed that the overall classification accuracy of the proposed algorithm was 94.71% and 86.38%， respectively. Compared with other algorithms， the proposed algorithm effectively improves the ability of land cover classification and is more conducive to practical applications.Keywords：hyperspectral remote sensing;land cover classification;feature extraction;deep belief network;manifold learning- 353
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Published：2021-09-01 -
Adaptive brightness correction of dim-lightening color images
Abstract：To improve the imaging performance in dim-lighting scenes， we propose adaptive brightness correction of dim-lighting color images. First， frame-averaging and Gamma correction are performed on a sequence of images. Second， the processed images are grouped before the following parallel processing steps are performed. In one of these steps， the images are converted into the YUV color space， and then， based on blind source separation （BSS）， noise is removed from Y-channel components group by group； in another step， the best BSS-denoised Y-channel component is selected by matching with the frame-averaged Y-channel. Third， the best Y-channel component is adjusted based on the peel growth curve and then recombined with the averaged U-channel and V-channel components. Finally， the recombined image is converted back to the RGB color space. Experiment results show that the proposed image enhancement algorithm could increase the brightness of the low-luminosity image by 3.5-54.4 times and increase the information entropy by 1.3-2.9 times. The proposed algorithm outperforms the classical image enhancement algorithms in terms of noise reduction， brightness balancing， and color information restoration.Keywords：dim-lightening;Gamma correction;color space;blind source separation;peel growth curve- 533
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Published：2021-09-01
Information Sciences
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