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RSS2021 Vol. 45, No. 5
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2021, 45(5): 541-547.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.001
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Abstract:
In order to solve the problem of easy deformation and large deformation of 6061 aluminum alloy in the laser welding process, ultrasonic assisted laser welding experiment was carried out with 1mm thick 6061 aluminum alloy sheet as the research object to explore the inhibition effect of ultrasonic on welding deformation of 6061 aluminum alloy. The influence of ultrasonic power on welding deformation was analyzed by single factor test method. Five factors and five levels orthogonal test including ultrasonic power, laser power, welding speed, defocusing amount, and shielding gas flow wer designed. The influence degree of ultrasonic power and conventional welding parameters on welding deformation was analyzed, and the process parameters combination which can obtain the minimum deformation were obtained. The results show that the welding deformation decreases with the increase of ultrasonic power, and the bending deformation and angular deformation of the specimen are reduced by 51.27% and 51.46% respectively when the ultrasonic power is 800W.At the same time, when the laser power is 1000W, the welding speed is 5m/min, the defocusing amount is + 1mm, the shielding gas flow rate is 15L/min, and the ultrasonic power is 800W, the minimum deformation of the specimen can be obtained, and the bending deformation is 0.42mm, and the angular deformation is 0.26mm. This study provides a certain technological and theoretical reference for the application of ultrasonic assisted welding in controlling welding deformation of thin plates.
In order to solve the problem of easy deformation and large deformation of 6061 aluminum alloy in the laser welding process, ultrasonic assisted laser welding experiment was carried out with 1mm thick 6061 aluminum alloy sheet as the research object to explore the inhibition effect of ultrasonic on welding deformation of 6061 aluminum alloy. The influence of ultrasonic power on welding deformation was analyzed by single factor test method. Five factors and five levels orthogonal test including ultrasonic power, laser power, welding speed, defocusing amount, and shielding gas flow wer designed. The influence degree of ultrasonic power and conventional welding parameters on welding deformation was analyzed, and the process parameters combination which can obtain the minimum deformation were obtained. The results show that the welding deformation decreases with the increase of ultrasonic power, and the bending deformation and angular deformation of the specimen are reduced by 51.27% and 51.46% respectively when the ultrasonic power is 800W.At the same time, when the laser power is 1000W, the welding speed is 5m/min, the defocusing amount is + 1mm, the shielding gas flow rate is 15L/min, and the ultrasonic power is 800W, the minimum deformation of the specimen can be obtained, and the bending deformation is 0.42mm, and the angular deformation is 0.26mm. This study provides a certain technological and theoretical reference for the application of ultrasonic assisted welding in controlling welding deformation of thin plates.
2021, 45(5): 548-553.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.002
Abstract:
In order to solve the problem of laser ablation due to the long time laser stop at the single point caused by the excessive density of the data point set in laser galvanometer processing, the original data point set was processed by thinning, curve point set segmentation, and triangular dichotomy Bezier curve fitting data processing, which was converted into an entity composed of a few line and curve. When laser marking, the curve was adaptively interpolated according to the output resolution and curve curvature to solve the problem of too dense or too sparse data points caused by different magnification. By marking the original and processed data with different marking magnification, the results show that the fitted data eliminates the laser ablation phenomenon caused by over-density of the data under the guaranteed 2μm accuracy of the original data. It also has a smoother marking effect at high magnification, as well as a higher marking efficiency and quality. It provides a reference for high density laser processing and has a good application prospect in the field of high quality laser processing such as laser precision etching.
In order to solve the problem of laser ablation due to the long time laser stop at the single point caused by the excessive density of the data point set in laser galvanometer processing, the original data point set was processed by thinning, curve point set segmentation, and triangular dichotomy Bezier curve fitting data processing, which was converted into an entity composed of a few line and curve. When laser marking, the curve was adaptively interpolated according to the output resolution and curve curvature to solve the problem of too dense or too sparse data points caused by different magnification. By marking the original and processed data with different marking magnification, the results show that the fitted data eliminates the laser ablation phenomenon caused by over-density of the data under the guaranteed 2μm accuracy of the original data. It also has a smoother marking effect at high magnification, as well as a higher marking efficiency and quality. It provides a reference for high density laser processing and has a good application prospect in the field of high quality laser processing such as laser precision etching.
2021, 45(5): 554-560.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.003
Abstract:
In order to improve the accuracy and efficiency of power line extraction and reconstruction based on unmanned aerial vehicle (UAV)-borne light detection and ranging (LiDAR) point cloud, a comprehensive power line point cloud extraction and reconstruction method was adopted, in which a step-by-step extraction of power line point clouds, segmented k-means clustering sampling, and a combination of straight line and parabola fitting were combined together. Based on the preprocessing and filtering of the power line corridor point cloud, the power line corridor was segmented and roughly extracted according to the distribution characteristics of the power line point cloud in the elevation direction. Then, the roughly extracted power line points were projected onto the horizontal plane and extracted finely by Hough transform. Subsequently, the single-line separation of the power line was completed by performing segmented k-means cluster sampling on the extracted power line points. Finally, a model combining a straight line and a parabola was used to fit and reconstruct the power line. The measured data was selected to test, and the algorithm was evaluated by the integrity rate of power line extraction and the accuracy and efficiency of reconstruction. The experimental results show that the comprehensive integrity rate of extracting power line points using this algorithm is above 96%, and the result is helpful for efficiently extracting and reconstructing single file single power line point cloud.
In order to improve the accuracy and efficiency of power line extraction and reconstruction based on unmanned aerial vehicle (UAV)-borne light detection and ranging (LiDAR) point cloud, a comprehensive power line point cloud extraction and reconstruction method was adopted, in which a step-by-step extraction of power line point clouds, segmented k-means clustering sampling, and a combination of straight line and parabola fitting were combined together. Based on the preprocessing and filtering of the power line corridor point cloud, the power line corridor was segmented and roughly extracted according to the distribution characteristics of the power line point cloud in the elevation direction. Then, the roughly extracted power line points were projected onto the horizontal plane and extracted finely by Hough transform. Subsequently, the single-line separation of the power line was completed by performing segmented k-means cluster sampling on the extracted power line points. Finally, a model combining a straight line and a parabola was used to fit and reconstruct the power line. The measured data was selected to test, and the algorithm was evaluated by the integrity rate of power line extraction and the accuracy and efficiency of reconstruction. The experimental results show that the comprehensive integrity rate of extracting power line points using this algorithm is above 96%, and the result is helpful for efficiently extracting and reconstructing single file single power line point cloud.
2021, 45(5): 561-565.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.004
Abstract:
In order to avoid damage avalanche photodiode(APD)during the the receiver and transmitter axis testing process of ZY-satellite laser altimeter, a new test method suitable for vacuum environment was proposed. The test system was established through the collimator and laser beam analyzer, and the optical cable connector was sealed through the cabin, a 1064nm continuous light source outside the tank was connected to a designed fiber-optic homogenizer, which was fixed on the focal plane of receiver to produce a uniformly illumination beam and get the optical axis of the receiver. The optical axis of the transmitter was got by multi-stage attenuation. The results show that the method eliminates the risk of APD damage in vacuum environment, and the measure accuracy is better than 6.47μrad, which meets the requirements of laser altimeter. The method has the advantages of compact structure and high precision. It provided a new idea for vacuum test of high energy laser rangefinder and has a wide application prospects.
In order to avoid damage avalanche photodiode(APD)during the the receiver and transmitter axis testing process of ZY-satellite laser altimeter, a new test method suitable for vacuum environment was proposed. The test system was established through the collimator and laser beam analyzer, and the optical cable connector was sealed through the cabin, a 1064nm continuous light source outside the tank was connected to a designed fiber-optic homogenizer, which was fixed on the focal plane of receiver to produce a uniformly illumination beam and get the optical axis of the receiver. The optical axis of the transmitter was got by multi-stage attenuation. The results show that the method eliminates the risk of APD damage in vacuum environment, and the measure accuracy is better than 6.47μrad, which meets the requirements of laser altimeter. The method has the advantages of compact structure and high precision. It provided a new idea for vacuum test of high energy laser rangefinder and has a wide application prospects.
2021, 45(5): 566-570.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.005
Abstract:
In order to obtain high power and high quality ultrashort pulse light source, the chirp compensation fiber design of self-similar pulse was studied for the first time using strong linear chirp generated by the dispersion decreasing fiber (DDF). Firstly, the ultra-short pulse output with half height full width of 52.6fs and peak power of 684.5W was obtained by using dispersion compensation fiber. On this basis, the design of dispersion increasing compensation fiber was studied, and the effects of dispersion-linear-increased fiber and dispersion-exponential-increased fiber on the compression of self-similar pulses were emphatically discussed. When the dispersion increasing coefficient was respectively set to 1km-1, 5km-1, 10km-1, the shortest output pulse width, peak power and the required compensated fiber length were obtained by numerical simulation. The results show that the dispersion increasing fiber can shorten the length of the compensated fiber greatly, which is beneficial to reduce the loss caused by pulse compression, and finally obtain high power ultrashort pulse output with half height full width of 61.8fs and 64.4fs. This result is helpful to the design of self-similar pulse compression fiber.
In order to obtain high power and high quality ultrashort pulse light source, the chirp compensation fiber design of self-similar pulse was studied for the first time using strong linear chirp generated by the dispersion decreasing fiber (DDF). Firstly, the ultra-short pulse output with half height full width of 52.6fs and peak power of 684.5W was obtained by using dispersion compensation fiber. On this basis, the design of dispersion increasing compensation fiber was studied, and the effects of dispersion-linear-increased fiber and dispersion-exponential-increased fiber on the compression of self-similar pulses were emphatically discussed. When the dispersion increasing coefficient was respectively set to 1km-1, 5km-1, 10km-1, the shortest output pulse width, peak power and the required compensated fiber length were obtained by numerical simulation. The results show that the dispersion increasing fiber can shorten the length of the compensated fiber greatly, which is beneficial to reduce the loss caused by pulse compression, and finally obtain high power ultrashort pulse output with half height full width of 61.8fs and 64.4fs. This result is helpful to the design of self-similar pulse compression fiber.
2021, 45(5): 571-575.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.006
Abstract:
In order to improve the extraction efficiency of the boundary point extraction method based on the maximum Angle of adjacent points, a hierarchical fast and accurate boundary point extraction method was proposed. R in the neighborhood at any sampling point set was firstly retrieved, followed by the crude extraction of boundary point according to the distance from the center of gravity point coordinates to the sampling point in the R neighborhood point set. The crude extract of boundary points and their neighborhood points were then projected to the tangent plane, and the maximum angle between adjacent vectors was calculated through the adjacent points and sampling points in the direction of the vector, the final accurate boundary point was then extracted based on the maximum angle. Through theoretical analysis and point cloud data experiment, the feasibility of the algorithm was verified. The results show that this algorithm can respectively shorten the running time by 22.11% and the accuracy by 5.23% compared with the traditional method, and can respectively shorten the running time by 10.99% and improve the accuracy by 7.17% compared with other hierarchical extraction methods. This study provides a reference for boundary extraction in point cloud 3-D reconstruction.
In order to improve the extraction efficiency of the boundary point extraction method based on the maximum Angle of adjacent points, a hierarchical fast and accurate boundary point extraction method was proposed. R in the neighborhood at any sampling point set was firstly retrieved, followed by the crude extraction of boundary point according to the distance from the center of gravity point coordinates to the sampling point in the R neighborhood point set. The crude extract of boundary points and their neighborhood points were then projected to the tangent plane, and the maximum angle between adjacent vectors was calculated through the adjacent points and sampling points in the direction of the vector, the final accurate boundary point was then extracted based on the maximum angle. Through theoretical analysis and point cloud data experiment, the feasibility of the algorithm was verified. The results show that this algorithm can respectively shorten the running time by 22.11% and the accuracy by 5.23% compared with the traditional method, and can respectively shorten the running time by 10.99% and improve the accuracy by 7.17% compared with other hierarchical extraction methods. This study provides a reference for boundary extraction in point cloud 3-D reconstruction.
2021, 45(5): 576-584.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.007
Abstract:
In order to achieve the research of high-efficiency laser wireless energy transmission system, a closed-loop control simulation model of laser wireless energy transmission system was established based on Simulink. In this model, the maximum power point tracking of laser photovoltaic array, the construction of voltage reduction circuit, and the intelligent charging control of lithium battery were realized. Combining the output characteristics of the laser photovoltaic array and the characteristics of the lithium battery multi-stage constant current charging method, a new type of lithium battery multi-stage constant current charging method based on the laser power density closed-loop signal control was proposed. The simulation results show that this method can not only realize the multi-stage constant current charging effect of traditional lithium batteries, but also save about 62.9% of the light energy and increase the conversion efficiency of the system by 62.96%. The study is helpful for the research of high efficiency laser wireless energy transmission system.
In order to achieve the research of high-efficiency laser wireless energy transmission system, a closed-loop control simulation model of laser wireless energy transmission system was established based on Simulink. In this model, the maximum power point tracking of laser photovoltaic array, the construction of voltage reduction circuit, and the intelligent charging control of lithium battery were realized. Combining the output characteristics of the laser photovoltaic array and the characteristics of the lithium battery multi-stage constant current charging method, a new type of lithium battery multi-stage constant current charging method based on the laser power density closed-loop signal control was proposed. The simulation results show that this method can not only realize the multi-stage constant current charging effect of traditional lithium batteries, but also save about 62.9% of the light energy and increase the conversion efficiency of the system by 62.96%. The study is helpful for the research of high efficiency laser wireless energy transmission system.
2021, 45(5): 585-589.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.008
Abstract:
In order to develop a new MAX phase composite coating on the surface of TC4 titanium alloy, a Ti-Al-N composite coating containing Ti2AlN MAX phase was synthesized on the surface of TC4 titanium alloy by laser cladding. The structure characteristics and hardness distribution of the coating were analyzed, and the in-situ synthesis mechanism of the composite coating was studied. The results indicate that the coating and the substrate after powder cladding with different ratios of amount of substance show a good metallurgical bond. The coating is mainly composed of TiAl matrix, Ti2AlN MAX phase, and TiN dendrites. The average hardness of the coating is about twice that of the substrate. The coating thickness is between 1mm~1.6mm. Adding a small amount of Al powder can promote the reaction of TiN and TiAl in the molten pool, thereby significantly increasing the content of Ti2AlN MAX phase in the coating. The research results are of great significance to the preparation of MAX phase composite coatings by laser cladding technology based on the clarification of the MAX phase in-situ synthesis mechanism.
In order to develop a new MAX phase composite coating on the surface of TC4 titanium alloy, a Ti-Al-N composite coating containing Ti2AlN MAX phase was synthesized on the surface of TC4 titanium alloy by laser cladding. The structure characteristics and hardness distribution of the coating were analyzed, and the in-situ synthesis mechanism of the composite coating was studied. The results indicate that the coating and the substrate after powder cladding with different ratios of amount of substance show a good metallurgical bond. The coating is mainly composed of TiAl matrix, Ti2AlN MAX phase, and TiN dendrites. The average hardness of the coating is about twice that of the substrate. The coating thickness is between 1mm~1.6mm. Adding a small amount of Al powder can promote the reaction of TiN and TiAl in the molten pool, thereby significantly increasing the content of Ti2AlN MAX phase in the coating. The research results are of great significance to the preparation of MAX phase composite coatings by laser cladding technology based on the clarification of the MAX phase in-situ synthesis mechanism.
2021, 45(5): 590-595.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.009
Abstract:
In order to meet the technical requirements for the penetration and width of SUS301L stainless steel laser lap welding for subway roof, the influence of welding parameters on the penetration and width was analyzed using numerical simulation technology. The design of parameters were optimized through orthogonal test which obtained the process parameters of laser welding SUS301L stainless steel sheet. The results show that the optimal parameters of laser welding of SUS301L stainless steel sheet is that the laser welding power of 1050W, welding speed of 36mm/s, defocusing amount of 1mm, the flow rate of shielding gas of 25L/min. With the optimal parameters, the width and penetration are respectively 1216.4μm and 407.4μm. The good consistency between the simulation results and the experiment results shows that the correctness of the simulation model can be established in this paper, which can provide reference for the construction of the later process database. Under the optimal welding parameters, the surface of the weld is silvery, continuous and complete, the weld area is isomer and column crystals, and the average shear strength of the weld is 2559.96kN.
In order to meet the technical requirements for the penetration and width of SUS301L stainless steel laser lap welding for subway roof, the influence of welding parameters on the penetration and width was analyzed using numerical simulation technology. The design of parameters were optimized through orthogonal test which obtained the process parameters of laser welding SUS301L stainless steel sheet. The results show that the optimal parameters of laser welding of SUS301L stainless steel sheet is that the laser welding power of 1050W, welding speed of 36mm/s, defocusing amount of 1mm, the flow rate of shielding gas of 25L/min. With the optimal parameters, the width and penetration are respectively 1216.4μm and 407.4μm. The good consistency between the simulation results and the experiment results shows that the correctness of the simulation model can be established in this paper, which can provide reference for the construction of the later process database. Under the optimal welding parameters, the surface of the weld is silvery, continuous and complete, the weld area is isomer and column crystals, and the average shear strength of the weld is 2559.96kN.
2021, 45(5): 596-600.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.010
Abstract:
In order to measure the diameter of the optical microfibers (OMs), the liquid immersion intensity detection method was used. Firstly, the structure of OM-liquid cylindrical waveguide was analyzed theoretically, and the relationship between the additional loss and the shape parameters of the whole OM was obtained. Then, an experimental system was set up to test two groups of OMs with different diameters. The experimental results show that when the diameter was 2.7μm, the minimum resolution of diameter measurement is about 3nm and the diameter offsets of four OMs are 40nm, 30nm, 80nm and 20nm, respectively. When the diameter is 4μm, the minimum resolution of diameter measurement is about 12nm and the diameter offsets of four OMs are 60nm, 90nm, 10nm and 30nm, respectively. At the same time, the results showe well diameter consistency and verified the feasibility of liquid immersion intensity detection method. This research provided technical support for the further development of OMs.
In order to measure the diameter of the optical microfibers (OMs), the liquid immersion intensity detection method was used. Firstly, the structure of OM-liquid cylindrical waveguide was analyzed theoretically, and the relationship between the additional loss and the shape parameters of the whole OM was obtained. Then, an experimental system was set up to test two groups of OMs with different diameters. The experimental results show that when the diameter was 2.7μm, the minimum resolution of diameter measurement is about 3nm and the diameter offsets of four OMs are 40nm, 30nm, 80nm and 20nm, respectively. When the diameter is 4μm, the minimum resolution of diameter measurement is about 12nm and the diameter offsets of four OMs are 60nm, 90nm, 10nm and 30nm, respectively. At the same time, the results showe well diameter consistency and verified the feasibility of liquid immersion intensity detection method. This research provided technical support for the further development of OMs.
2021, 45(5): 601-606.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.011
Abstract:
In order to solve the problem of excessive noise point clouds in the photon counting lidar detection data, a single photon point cloud denoising method based on a combination of improved density-based spatial clustering of applications with noise (DBSCAN) algorithm and statistical filtering algorithm was adopted. The actual flight data of multiple altimeter beam experimental lidar provided by National Aeronautics and Space Administration was experimental data. First, the point cloud density was obtained through the k-dimensional tree for rough denoising, and then the improved DBSCAN algorithm and statistical filtering algorithm were used for fine denoising. The theoretical analysis and experimental verification has achieved good results. The results show that the target point cloud recognition rate in the experimental area is above 85%, and the performance is better than the classic radius filtering algorithm. This result is helpful for photon data denoising.
In order to solve the problem of excessive noise point clouds in the photon counting lidar detection data, a single photon point cloud denoising method based on a combination of improved density-based spatial clustering of applications with noise (DBSCAN) algorithm and statistical filtering algorithm was adopted. The actual flight data of multiple altimeter beam experimental lidar provided by National Aeronautics and Space Administration was experimental data. First, the point cloud density was obtained through the k-dimensional tree for rough denoising, and then the improved DBSCAN algorithm and statistical filtering algorithm were used for fine denoising. The theoretical analysis and experimental verification has achieved good results. The results show that the target point cloud recognition rate in the experimental area is above 85%, and the performance is better than the classic radius filtering algorithm. This result is helpful for photon data denoising.
2021, 45(5): 607-613.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.012
Abstract:
In order to accurately reflect the optical signals received by the lidar, it is necessary to correct and calibrate the afterpulse characteristics of the photomultiplier tube. The probability distribution function of the afterpulse was used to analyse and verify the sounding data of the airborne marine lidar with wavelength of 486nm and 532nm, respectively, and the corrected results were compared with the data obtained by Monte Carlo simulation. The results show that the correlation between the calibration data and the Monte Carlo simulation data is as high as 0.9689(486nm) and 0.8648(532nm), respectively. About 98m(486nm) and 33m(532nm) false signals are eliminated based on the corrected data compared with the data before, and the accuracy of measurement of the airborne marine lidar is improved effectively. This research is helpful for the measurement of ocean depth and the study of submarine geomorphy.
In order to accurately reflect the optical signals received by the lidar, it is necessary to correct and calibrate the afterpulse characteristics of the photomultiplier tube. The probability distribution function of the afterpulse was used to analyse and verify the sounding data of the airborne marine lidar with wavelength of 486nm and 532nm, respectively, and the corrected results were compared with the data obtained by Monte Carlo simulation. The results show that the correlation between the calibration data and the Monte Carlo simulation data is as high as 0.9689(486nm) and 0.8648(532nm), respectively. About 98m(486nm) and 33m(532nm) false signals are eliminated based on the corrected data compared with the data before, and the accuracy of measurement of the airborne marine lidar is improved effectively. This research is helpful for the measurement of ocean depth and the study of submarine geomorphy.
2021, 45(5): 614-619.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.013
Abstract:
In order to calibrate the liquid crystal spatial light modulator (LCSLM) with high precision and meet the application requirements of linear phase modulation, a common-path heterodyne interferometer system was proposed to measure the phase modulation characteristics of LCSLM. The measurement principle was analyzed. Then the experimental data of the phase modulation varying with the input gray value of LCSLM was obtained and the linear calibration was carried out. The measurement results of the LCSLM show that the maximum phase modulation of the LCSLM used in the experiment is 2.55π. The phase modulation curve in the range of 20~240 is linearly corrected using the inverse interpolation method, and the corrected theoretical phase modulation curve is very close to the ideal linear curve. The correlation coefficient between the measured phase modulation curve and the ideal linear modulation curve can reach 0.9996. The proposed method can overcome the dependence of traditional measurement methods on image processing. The measurement precision of the proposed method is higher, and the phase modulation valves of LCSLM can be obtained directly through the lock-in amplifier. This research can provide a reference for high-precision wavefront correction and measurement based on LCSLM.
In order to calibrate the liquid crystal spatial light modulator (LCSLM) with high precision and meet the application requirements of linear phase modulation, a common-path heterodyne interferometer system was proposed to measure the phase modulation characteristics of LCSLM. The measurement principle was analyzed. Then the experimental data of the phase modulation varying with the input gray value of LCSLM was obtained and the linear calibration was carried out. The measurement results of the LCSLM show that the maximum phase modulation of the LCSLM used in the experiment is 2.55π. The phase modulation curve in the range of 20~240 is linearly corrected using the inverse interpolation method, and the corrected theoretical phase modulation curve is very close to the ideal linear curve. The correlation coefficient between the measured phase modulation curve and the ideal linear modulation curve can reach 0.9996. The proposed method can overcome the dependence of traditional measurement methods on image processing. The measurement precision of the proposed method is higher, and the phase modulation valves of LCSLM can be obtained directly through the lock-in amplifier. This research can provide a reference for high-precision wavefront correction and measurement based on LCSLM.
2021, 45(5): 620-624.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.014
Abstract:
In order to make the probe end of the robotic arm always be perpendicular to the surface of the tested workpiece during the scanning process, an adaptive detection algorithm for curved surfaces based on normal feature extraction was proposed. The 3-D data of the surface of the test piece was acquired by the optical scanning device. The mapping function used for pose correction was derived by the normal extraction algorithm. Finally, the adaptive planning of the scan path was completed. In MATLAB, stray points were removed from the sample point cloud, and the three-dimensional reconstruction of the test piece was completed through the QUALIFY software. In the experiment, a curved sample block with a size of 150mm×200mm×10mm was optically scanned and path optimized. The test results show that the maximum deviation of the position test accuracy in the x-axis, y-axis, and z-axis directions are 0.5142mm, 0.2645mm, and 1.4265mm respectively. The maximum value of the overall position deviation is 1.1135mm, and the average value is 0.5647mm. After substituting the deviation as a compensation parameter into the planned path of the manipulator, the system realizes the online adjustment of the probe pose during the scanning process. This research is of great significance to the application fields that require the probe to be strictly perpendicular to the tested workpiece in the automated test system.
In order to make the probe end of the robotic arm always be perpendicular to the surface of the tested workpiece during the scanning process, an adaptive detection algorithm for curved surfaces based on normal feature extraction was proposed. The 3-D data of the surface of the test piece was acquired by the optical scanning device. The mapping function used for pose correction was derived by the normal extraction algorithm. Finally, the adaptive planning of the scan path was completed. In MATLAB, stray points were removed from the sample point cloud, and the three-dimensional reconstruction of the test piece was completed through the QUALIFY software. In the experiment, a curved sample block with a size of 150mm×200mm×10mm was optically scanned and path optimized. The test results show that the maximum deviation of the position test accuracy in the x-axis, y-axis, and z-axis directions are 0.5142mm, 0.2645mm, and 1.4265mm respectively. The maximum value of the overall position deviation is 1.1135mm, and the average value is 0.5647mm. After substituting the deviation as a compensation parameter into the planned path of the manipulator, the system realizes the online adjustment of the probe pose during the scanning process. This research is of great significance to the application fields that require the probe to be strictly perpendicular to the tested workpiece in the automated test system.
2021, 45(5): 625-629.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.015
Abstract:
In order to overcome the problem that the image contrast and collection efficiency of on-site fingerprint images are usually quite low due to complicated background color at the crime scene, a portable fingerprint image acquisition system with a smartphone was proposed. In the system, a microprocessor connected to a smartphone through bluetooth can electrically switch light sources of different wavelengths. Multi-spectrum images were acquired to improve the fingerprint image contrast. With the help of the microprocessor, the smartphone can automatically capture fingerprint images under the illumination of different light sources. To ensure that the image quality can meet the requirements of identification process, the images were further enhanced by using multi-spectrum fusion and orientation filtering. Results show that the proposed system can effectively collect, fuse, and enhance multi-spectrum fingerprint images. It takes less than 1s to acquire and process the images when the number of light sources is 4, which satisfies the requirement of on-site image acquisition. As the system has the advantages of low cost, automation, and high portability, it is expected to be widely applied in criminal investigation.
In order to overcome the problem that the image contrast and collection efficiency of on-site fingerprint images are usually quite low due to complicated background color at the crime scene, a portable fingerprint image acquisition system with a smartphone was proposed. In the system, a microprocessor connected to a smartphone through bluetooth can electrically switch light sources of different wavelengths. Multi-spectrum images were acquired to improve the fingerprint image contrast. With the help of the microprocessor, the smartphone can automatically capture fingerprint images under the illumination of different light sources. To ensure that the image quality can meet the requirements of identification process, the images were further enhanced by using multi-spectrum fusion and orientation filtering. Results show that the proposed system can effectively collect, fuse, and enhance multi-spectrum fingerprint images. It takes less than 1s to acquire and process the images when the number of light sources is 4, which satisfies the requirement of on-site image acquisition. As the system has the advantages of low cost, automation, and high portability, it is expected to be widely applied in criminal investigation.
2021, 45(5): 630-635.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.016
Abstract:
In order to solve the problems of low efficiency and high cost in weighing coal gangue loading, a non-contact coal gangue loading volume measurement method based on laser triangulation was proposed. First, the laser stripe information projected by the laser on the surface of the moving carriage full of coal gangue was continuously collected using the CCD camera. The target area of the image was extracted through median filtering method and threshold segmentation method based on Otsu algorithm during the image pre-process at the same time. Then the center line of the laser stripes were extracted using skeleton-based gray barycentric method. Finally, the Riemann integral method is used to calculate the coal gangue loading of the vehicle. The results show that the error of the system results is controlled within 4%, which meets the requirements of system operation, confirming the feasibility and practicability of the measurement method. This research provides a reference for the load measurement of highway transportation management in complex environments.
In order to solve the problems of low efficiency and high cost in weighing coal gangue loading, a non-contact coal gangue loading volume measurement method based on laser triangulation was proposed. First, the laser stripe information projected by the laser on the surface of the moving carriage full of coal gangue was continuously collected using the CCD camera. The target area of the image was extracted through median filtering method and threshold segmentation method based on Otsu algorithm during the image pre-process at the same time. Then the center line of the laser stripes were extracted using skeleton-based gray barycentric method. Finally, the Riemann integral method is used to calculate the coal gangue loading of the vehicle. The results show that the error of the system results is controlled within 4%, which meets the requirements of system operation, confirming the feasibility and practicability of the measurement method. This research provides a reference for the load measurement of highway transportation management in complex environments.
2021, 45(5): 636-641.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.017
Abstract:
In order to study the thermal damage law of carbon fiber reinforced epoxy composite induced by high power laser, the thermal stress of carbon fiber reinforced epoxy composite with multilayer structure was simulated by COMSOL software. Theoretical analysis and experimental verification were carried out. The temporal and spatial distribution and change of the transient temperature field and stress field of composite materials irradiated by laser with different power densities were obtained. The damage area and morphology of carbon fiber/epoxy resin treated with different laser power density were measured, which was consistent with the trend of numerical simulation results. The results show that, when the temperature of the irradiation center of the target surface is 872K, a temperature plateau appears, that is, the latent heat period of phase change and the latent heat period of reverse phase change, and changes with the laser power density. The laser irradiation target material produced a great axial compressive stress on the upper surface of the carbon fiber. When power density is 293W/cm2, the compressive stress difference is about 1.87MPa; when power density is 3453W/cm2, the compressive stress difference is about 1.42MPa. This result provides a theoretical basis for the research on the thermal damage of carbon fiber/epoxy resin composites caused by highpower lasers.
In order to study the thermal damage law of carbon fiber reinforced epoxy composite induced by high power laser, the thermal stress of carbon fiber reinforced epoxy composite with multilayer structure was simulated by COMSOL software. Theoretical analysis and experimental verification were carried out. The temporal and spatial distribution and change of the transient temperature field and stress field of composite materials irradiated by laser with different power densities were obtained. The damage area and morphology of carbon fiber/epoxy resin treated with different laser power density were measured, which was consistent with the trend of numerical simulation results. The results show that, when the temperature of the irradiation center of the target surface is 872K, a temperature plateau appears, that is, the latent heat period of phase change and the latent heat period of reverse phase change, and changes with the laser power density. The laser irradiation target material produced a great axial compressive stress on the upper surface of the carbon fiber. When power density is 293W/cm2, the compressive stress difference is about 1.87MPa; when power density is 3453W/cm2, the compressive stress difference is about 1.42MPa. This result provides a theoretical basis for the research on the thermal damage of carbon fiber/epoxy resin composites caused by highpower lasers.
2021, 45(5): 642-646.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.018
Abstract:
In order to improve the transmission performance of optical devices and promote the development of micro-optical devices and large-scale integrated optical circuits, a new type of 2-D graphene plasma photonic crystal structure was proposed. By periodically arranging the honeycomb-shaped graphene discs, the diameter of two graphene discs in a period was adjusted to open the Dirac point; based on the finite element method, the propagation of the light field was simulated by COMSOL and the photonic band gap was then calculated. Through breaking the time inversion symmetry, the band topology effect was achieved. The results show that the lattice constants of this designed are all on the order of nanometers, which is nearly 30 times smaller than the free space wavelength with the advantages of miniaturization and high integration. The structure can be dynamically modulated in the 15.3THz~15.8THz frequency range. This research provides a reference for the design of robust nano-scale photonic devices, and is expected to be applied to waveguide frequency control, optical switches and other fields.
In order to improve the transmission performance of optical devices and promote the development of micro-optical devices and large-scale integrated optical circuits, a new type of 2-D graphene plasma photonic crystal structure was proposed. By periodically arranging the honeycomb-shaped graphene discs, the diameter of two graphene discs in a period was adjusted to open the Dirac point; based on the finite element method, the propagation of the light field was simulated by COMSOL and the photonic band gap was then calculated. Through breaking the time inversion symmetry, the band topology effect was achieved. The results show that the lattice constants of this designed are all on the order of nanometers, which is nearly 30 times smaller than the free space wavelength with the advantages of miniaturization and high integration. The structure can be dynamically modulated in the 15.3THz~15.8THz frequency range. This research provides a reference for the design of robust nano-scale photonic devices, and is expected to be applied to waveguide frequency control, optical switches and other fields.
2021, 45(5): 647-653.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.019
Abstract:
In the underwater optical wireless communication-direct current bias-optical-orthogonal frequency division multiplexing (UOWC-DCO-OFDM) system, in order to ensure that the optical signal has a low peak-to-average power ratio (PAPR) at the transmitting end and can carry out long-distance low underwater, the method combining the tone reservation-least squares algorithm (TR-LSA) and companding transformation was adopted. At the same time, the optimized neural network was used to estimate the channel of the underwater environment. Based on this method, the channel equalizer was designed at the receiving end to deal with the strong attenuation of the optical signal in the underwater environment. The results show that the PAPR of the UOWC-DCO-OFDM system is reduced by 9dB, and the bit error rate is 10-3 lower when the signal-to-noise ratio is 10dB, which is under the bit error rate standard of wireless optical communication. The system can realize long-distance underwater transmission of optical signals with low bit error rate.
In the underwater optical wireless communication-direct current bias-optical-orthogonal frequency division multiplexing (UOWC-DCO-OFDM) system, in order to ensure that the optical signal has a low peak-to-average power ratio (PAPR) at the transmitting end and can carry out long-distance low underwater, the method combining the tone reservation-least squares algorithm (TR-LSA) and companding transformation was adopted. At the same time, the optimized neural network was used to estimate the channel of the underwater environment. Based on this method, the channel equalizer was designed at the receiving end to deal with the strong attenuation of the optical signal in the underwater environment. The results show that the PAPR of the UOWC-DCO-OFDM system is reduced by 9dB, and the bit error rate is 10-3 lower when the signal-to-noise ratio is 10dB, which is under the bit error rate standard of wireless optical communication. The system can realize long-distance underwater transmission of optical signals with low bit error rate.
2021, 45(5): 654-661.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.020
Abstract:
Laser cleaning is a new type of laser application technology in which the high-powered lasers are used to irradiate the surface of substrates based on the algorithm of interaction between the laser and the substance, destroying the bonding force between the substrate and the stain. So that, the stain can be separated from the surface of a substrate. Recently, with the development of laser technology, the application range of laser cleaning has continued to expand, and the new researches such as particle cleaning, mold cleaning, and transportation cleaning, etc. have been carried out, but there are still some disadvantages, such as expensive equipment, long test time, etc. In order to understand the research status of laser cleaning in recent years, the laser cleaning mechanism, application field, development status and existing problems have been briefly described, and the advantages of the new laser composite cleaning technology have also been mentioned in green manufacturing and its development potential.
Laser cleaning is a new type of laser application technology in which the high-powered lasers are used to irradiate the surface of substrates based on the algorithm of interaction between the laser and the substance, destroying the bonding force between the substrate and the stain. So that, the stain can be separated from the surface of a substrate. Recently, with the development of laser technology, the application range of laser cleaning has continued to expand, and the new researches such as particle cleaning, mold cleaning, and transportation cleaning, etc. have been carried out, but there are still some disadvantages, such as expensive equipment, long test time, etc. In order to understand the research status of laser cleaning in recent years, the laser cleaning mechanism, application field, development status and existing problems have been briefly described, and the advantages of the new laser composite cleaning technology have also been mentioned in green manufacturing and its development potential.
2021, 45(5): 662-669.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.021
Abstract:
In order to improve the bit error rate of the system, reduce the baseline drift and the absorption scattering of the seawater channel and other characteristics on the optical signal, a low density parity check (LDPC)-Reed Solomon(RS) cascaded interleaving code scheme based on the underwater light-emitting diode(LED) optical communication system was adopted. Under the simulated underwater LED optical communication experimental system, the effects of RS code, LDPC code, and interleaved parameters on the bit-error rate performance of the system were analyzed in the code scheme, and the optimized parameters of the cascaded interleaving code scheme were obtained and verified by the experimental simulation. The results show that the gain of 3.8dB, 2dB, and 1.2dB can be obtained with the optimized cascaded interleaving code system, compared with the uncoded system, RS code system, and LDPC code system, respectively, which can effectively improve the bit error rate performance of the system. This study provides a reference for improving the reliability of the underwater wireless optical communication system.
In order to improve the bit error rate of the system, reduce the baseline drift and the absorption scattering of the seawater channel and other characteristics on the optical signal, a low density parity check (LDPC)-Reed Solomon(RS) cascaded interleaving code scheme based on the underwater light-emitting diode(LED) optical communication system was adopted. Under the simulated underwater LED optical communication experimental system, the effects of RS code, LDPC code, and interleaved parameters on the bit-error rate performance of the system were analyzed in the code scheme, and the optimized parameters of the cascaded interleaving code scheme were obtained and verified by the experimental simulation. The results show that the gain of 3.8dB, 2dB, and 1.2dB can be obtained with the optimized cascaded interleaving code system, compared with the uncoded system, RS code system, and LDPC code system, respectively, which can effectively improve the bit error rate performance of the system. This study provides a reference for improving the reliability of the underwater wireless optical communication system.
2021, 45(5): 670-674.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.022
Abstract:
In order to provide more accurate step temperature rise signal in thermocouple time constant testing, optimize the control effect, and improve the accuracy of thermocouple time constant measurement, Tornambe controller was used to feedback control the output power of semiconductor laser. The system was constructed in the Matlab Simulink module, and the simulation was carried out under the same input signal. The control effects of the second-order Tornambe controller and the proportional-integral-differential (PID) were compared in the running process of system. The results show that the time constant of CO1-K thermocouple measured by PID controller is 456.2ms, while that measured by Tornambe controller is 284.6ms. The second-order Tornambe controller can effectively shorten the time of the thermocouple temperature balance. Moreover, it is more convenient to set the parameters of the controller structure, which has strong practical value.
In order to provide more accurate step temperature rise signal in thermocouple time constant testing, optimize the control effect, and improve the accuracy of thermocouple time constant measurement, Tornambe controller was used to feedback control the output power of semiconductor laser. The system was constructed in the Matlab Simulink module, and the simulation was carried out under the same input signal. The control effects of the second-order Tornambe controller and the proportional-integral-differential (PID) were compared in the running process of system. The results show that the time constant of CO1-K thermocouple measured by PID controller is 456.2ms, while that measured by Tornambe controller is 284.6ms. The second-order Tornambe controller can effectively shorten the time of the thermocouple temperature balance. Moreover, it is more convenient to set the parameters of the controller structure, which has strong practical value.
2021, 45(5): 675-680.
doi: 10.7510/jgjs.issn.1001-3806.2021.05.023
Abstract:
In order to avoid the interference of mutual occlusion between sheep in the traditional flock counting task and improve the accuracy of flock counting, the VDNet(VGG-16+DC net) convolutional neural network flock counting method, combining visual geometry group(VGG) 16 and dialated convolution (DC) net, was adopted. VGG-16 with the fully connected layer removed was used at the front end of the network to extract 2-D features, 6 layers of DC with different dilated rates was used to extract more advanced features. DC expanded the receptive field, replaced the pooling operation, and decreased the complexity of the network while kept the resolution unchanged at the same time. The theoretical analysis and experimental verification were carried out. Finally, a convolutional layer with a convolution kernel size of 1×1 was used to output a high-quality density map, and then the number of sheep in the input image was obtained by integrating the pixels of the density map. The results show that the average absolute error of the counting method in this paper is 2.51, the mean square error is 3.74, and the average accuracy is 93%, respectively. This result is helpful for the task of counting sheep.
In order to avoid the interference of mutual occlusion between sheep in the traditional flock counting task and improve the accuracy of flock counting, the VDNet(VGG-16+DC net) convolutional neural network flock counting method, combining visual geometry group(VGG) 16 and dialated convolution (DC) net, was adopted. VGG-16 with the fully connected layer removed was used at the front end of the network to extract 2-D features, 6 layers of DC with different dilated rates was used to extract more advanced features. DC expanded the receptive field, replaced the pooling operation, and decreased the complexity of the network while kept the resolution unchanged at the same time. The theoretical analysis and experimental verification were carried out. Finally, a convolutional layer with a convolution kernel size of 1×1 was used to output a high-quality density map, and then the number of sheep in the input image was obtained by integrating the pixels of the density map. The results show that the average absolute error of the counting method in this paper is 2.51, the mean square error is 3.74, and the average accuracy is 93%, respectively. This result is helpful for the task of counting sheep.
