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RSS2022 Vol. 46, No. 3
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2022, 46(3): 293-300.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.001
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Abstract:
In order to effectively evaluate the three-dimensional spatial distribution of measurement errors of the laser measurement system, a new uncertainty model based on the calculation of the minimum envelope ellipsoid was proposed. Based on the measured or simulated location data, the isolated forest algorithm was introduced to filter out abnormal data in the point cloud. With the valid data, the minimum envelope ellipsoid uncertainty model was established based on the particle swarm optimization and the error ellipsoid theory. By the coordinate system transformation between the measurement field and the single point uncertainty, the minimum envelope ellipsoid model was applied to the spatial uncertainty distribution analysis. Through the test of the measured data of a single point and a 10m-level space scene, the model can efficiently screen the sampling data and perform different levels of minimum envelope ellipsoid calculations according to the requirements. And then the corresponding uncertainty can be obtained. The results show that based on the measurement position data, the model can efficiently and accurately describe the three-dimensional uncertainty range of a single point position, and can effectively reproduce the uncertainty distribution in the measurement space. With the experimental conditions of a measurement distance 4.7m, the effective data after screening 94.2%, and an envelope ratio 97.5%, an ellipsoid with an uncertainty range of three-axis length 4.95μm, 18.39μm, 30.53μm is obtained by the model calculation. The minimum envelope ellipsoid uncertainty model has important value in many aspects, such as theoretical model verification based on actual measurement, equipment state and measurement environment analysis, and measurement layout design.
In order to effectively evaluate the three-dimensional spatial distribution of measurement errors of the laser measurement system, a new uncertainty model based on the calculation of the minimum envelope ellipsoid was proposed. Based on the measured or simulated location data, the isolated forest algorithm was introduced to filter out abnormal data in the point cloud. With the valid data, the minimum envelope ellipsoid uncertainty model was established based on the particle swarm optimization and the error ellipsoid theory. By the coordinate system transformation between the measurement field and the single point uncertainty, the minimum envelope ellipsoid model was applied to the spatial uncertainty distribution analysis. Through the test of the measured data of a single point and a 10m-level space scene, the model can efficiently screen the sampling data and perform different levels of minimum envelope ellipsoid calculations according to the requirements. And then the corresponding uncertainty can be obtained. The results show that based on the measurement position data, the model can efficiently and accurately describe the three-dimensional uncertainty range of a single point position, and can effectively reproduce the uncertainty distribution in the measurement space. With the experimental conditions of a measurement distance 4.7m, the effective data after screening 94.2%, and an envelope ratio 97.5%, an ellipsoid with an uncertainty range of three-axis length 4.95μm, 18.39μm, 30.53μm is obtained by the model calculation. The minimum envelope ellipsoid uncertainty model has important value in many aspects, such as theoretical model verification based on actual measurement, equipment state and measurement environment analysis, and measurement layout design.
2022, 46(3): 301-306.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.002
Abstract:
To study the influence of different laser processing parameters on the surface hydrophobicity of the micro grooves etched by an ultraviolet picosecond laser on the surface of a soaking plate, a Cassie-Baxter model were constructed. By using the method of single factor experiment, the change rate of laser scanning, laser scanning spacing, speckle transverse overlapping times was experimentally verified, respectively. The results show that the hydrophobicity of the surface of micro-grooves can be improved by reducing the ratio of solid-liquid area and the width of the grooves or shortening the distance between the grooves. The main reasons for the surface hydrophobicity of micro-grooves are the internal micro-nano structure and the adsorbed hydrophobic chemical groups during processing. When the laser scanning rate is 125mm/s, the laser scanning interval is 200μm, and the spots overlap twice, the surface of the micro-grooves etched by ultraviolet picosecond laser has the strongest hydrophobicity. This study provides a reference for enhancing the hydrophobic performance of the condensing end of the soaking plate and improving its over all circulation efficiency.
To study the influence of different laser processing parameters on the surface hydrophobicity of the micro grooves etched by an ultraviolet picosecond laser on the surface of a soaking plate, a Cassie-Baxter model were constructed. By using the method of single factor experiment, the change rate of laser scanning, laser scanning spacing, speckle transverse overlapping times was experimentally verified, respectively. The results show that the hydrophobicity of the surface of micro-grooves can be improved by reducing the ratio of solid-liquid area and the width of the grooves or shortening the distance between the grooves. The main reasons for the surface hydrophobicity of micro-grooves are the internal micro-nano structure and the adsorbed hydrophobic chemical groups during processing. When the laser scanning rate is 125mm/s, the laser scanning interval is 200μm, and the spots overlap twice, the surface of the micro-grooves etched by ultraviolet picosecond laser has the strongest hydrophobicity. This study provides a reference for enhancing the hydrophobic performance of the condensing end of the soaking plate and improving its over all circulation efficiency.
2022, 46(3): 307-311.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.003
Abstract:
In recent years, the design of metamaterial devices based on deep learning has made unprecedented development. However, for the reverse design of two-dimensional materials, it is difficult to solve the problems of falling into the local optimal value in a small sample space by using the traditional artificial neural network. Meanwhile, a lot of computational cost will be needed with the increase of the complexity of the structure. To solve these defects, a residual neural network based on AdaBelief optimization algorithm was proposed. The validity of the network was verified by choosing the design of multilayer alternating thin film structure based on graphene. The structure parameters of the multi-resonant perfect absorption spectra of samples were constructed by using the characteristic matrix method. The results show that the network model reaches 97% of prediction accuracy within a shorter training time. Compared with the prediction results of other neural networks, this network shows the advantages of high prediction accuracy and fast convergence rate, and achieves the design goal of perfect absorption metamaterial structure based on graphene.
In recent years, the design of metamaterial devices based on deep learning has made unprecedented development. However, for the reverse design of two-dimensional materials, it is difficult to solve the problems of falling into the local optimal value in a small sample space by using the traditional artificial neural network. Meanwhile, a lot of computational cost will be needed with the increase of the complexity of the structure. To solve these defects, a residual neural network based on AdaBelief optimization algorithm was proposed. The validity of the network was verified by choosing the design of multilayer alternating thin film structure based on graphene. The structure parameters of the multi-resonant perfect absorption spectra of samples were constructed by using the characteristic matrix method. The results show that the network model reaches 97% of prediction accuracy within a shorter training time. Compared with the prediction results of other neural networks, this network shows the advantages of high prediction accuracy and fast convergence rate, and achieves the design goal of perfect absorption metamaterial structure based on graphene.
2022, 46(3): 312-319.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.004
Abstract:
In order to accurately identify the type of weld seam status in laser welding, image processing, correlation analysis, and neural network methods were used. The study of quasi-steady status was added, and the correlation coefficients of the signal features were used as the input of the neural network model. Theoretical analysis and experimental verification were carried out, and the effects of the correlation of optical and visual signals on the steady-status types of laser welding were obtained. The results show that the correlation between keyhole area and plume area is the best way to distinguish the steady-status types. When its correlation coefficient is 0.2~0.3, it is in steady status, 0.4~0.5 corresponds to the quasi-steady status, and 0.6~0.7 corresponds to the unsteady status. The trained neural network model achieves 98.76% prediction accuracy on the test set, which can meet the needs of accurately identifying types of weld seam status. This research provides a reference for preventing laser welding defects in automated production.
In order to accurately identify the type of weld seam status in laser welding, image processing, correlation analysis, and neural network methods were used. The study of quasi-steady status was added, and the correlation coefficients of the signal features were used as the input of the neural network model. Theoretical analysis and experimental verification were carried out, and the effects of the correlation of optical and visual signals on the steady-status types of laser welding were obtained. The results show that the correlation between keyhole area and plume area is the best way to distinguish the steady-status types. When its correlation coefficient is 0.2~0.3, it is in steady status, 0.4~0.5 corresponds to the quasi-steady status, and 0.6~0.7 corresponds to the unsteady status. The trained neural network model achieves 98.76% prediction accuracy on the test set, which can meet the needs of accurately identifying types of weld seam status. This research provides a reference for preventing laser welding defects in automated production.
2022, 46(3): 320-325.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.005
Abstract:
The composite material is susceptible to external low-energy impact which causes invisible damage during service. In order to achieve the purpose of monitoring the health of the composite material, the fiber Bragg grating (FBG) sensor network was pasted and arranged on the surface of the carbon fiber composite material. The intelligent composite material impact location recognition technology based on the back propagation (BP) neural network system was used to obtain the time-domain signal response value of the FBG sensor to predict the impact position of the composite material. The results show that the BP neural network algorithm has the advantages of strong nonlinear approximation ability, high fault tolerance and strong adaptive ability. It can realize the parameterized identification and positioning of composite laminates, and the ratio of the prediction results to the total length of the composite laminates to be tested less than 0.1. The FBG sensing system provides more accurate information for the self-adjustment and self-repair capabilities of intelligent composite materials.
The composite material is susceptible to external low-energy impact which causes invisible damage during service. In order to achieve the purpose of monitoring the health of the composite material, the fiber Bragg grating (FBG) sensor network was pasted and arranged on the surface of the carbon fiber composite material. The intelligent composite material impact location recognition technology based on the back propagation (BP) neural network system was used to obtain the time-domain signal response value of the FBG sensor to predict the impact position of the composite material. The results show that the BP neural network algorithm has the advantages of strong nonlinear approximation ability, high fault tolerance and strong adaptive ability. It can realize the parameterized identification and positioning of composite laminates, and the ratio of the prediction results to the total length of the composite laminates to be tested less than 0.1. The FBG sensing system provides more accurate information for the self-adjustment and self-repair capabilities of intelligent composite materials.
2022, 46(3): 326-336.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.006
Abstract:
Point cloud is a special data form for 3-D image, which is gradually becoming a research hotspot of 3-D image information processing. Point cloud segmentation plays an important role in point cloud processing and has a direct impact on the results of the algorithm. Point clouds segmentation algorithm that based on geometric features of 3-D images are simpler in structure, more stable in operation results, and easy to adjust, which occupy a major position in practical applications. In this work, the point clouds segmentation methods based on geometric features emerged in recent years were sorted out. According to the theoretical basis and application characteristics of each method, the algorithms were classified into three categories: Edge detection based, surface features based, and model fitting based methods. The characteristics, the main problems of different algorithms, and the main factors that affect the efficiency have been analyzed. Finally, the algorithms performance have been compared, and the future development trend is prospected.
Point cloud is a special data form for 3-D image, which is gradually becoming a research hotspot of 3-D image information processing. Point cloud segmentation plays an important role in point cloud processing and has a direct impact on the results of the algorithm. Point clouds segmentation algorithm that based on geometric features of 3-D images are simpler in structure, more stable in operation results, and easy to adjust, which occupy a major position in practical applications. In this work, the point clouds segmentation methods based on geometric features emerged in recent years were sorted out. According to the theoretical basis and application characteristics of each method, the algorithms were classified into three categories: Edge detection based, surface features based, and model fitting based methods. The characteristics, the main problems of different algorithms, and the main factors that affect the efficiency have been analyzed. Finally, the algorithms performance have been compared, and the future development trend is prospected.
2022, 46(3): 337-343.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.007
Abstract:
In order to solve the problem of low temperature and pressure sensitivity of the existing fiber Bragg grating (FBG) sensors, a thin-walled cylindrical liquid temperature and pressure sensor based on FBG was designed. Both the stainless steel 304 and beryllium bronze C17200 with corrosion resistance, good elasticity, and high coefficient of thermal expansion were used to package the sensor. The finite element analysis method was used to simulate the pressure and temperature characteristics of the sensor. The influence of the material and size of the sensitive element on the sensitivity was studied, and the relationship between the reflection wavelength and the pressure and temperature was analyzed. The results show that the sensor encapsulated with beryllium bronze C17200 has higher pressure and temperature sensitivity, which can respectively reach 153.5pm/MPa and 31.7pm/℃ in the operating range of 0MPa~12MPa and -5℃~40℃, which are increased by 51.2 times and 2.8 times respectively on the basis of the bare grating, respectively. It is expected to be applied to high sensitivity measurement of liquid temperature and pressure. The results can provide reference for high sensitivity temperature and pressure measurement of liquid.
In order to solve the problem of low temperature and pressure sensitivity of the existing fiber Bragg grating (FBG) sensors, a thin-walled cylindrical liquid temperature and pressure sensor based on FBG was designed. Both the stainless steel 304 and beryllium bronze C17200 with corrosion resistance, good elasticity, and high coefficient of thermal expansion were used to package the sensor. The finite element analysis method was used to simulate the pressure and temperature characteristics of the sensor. The influence of the material and size of the sensitive element on the sensitivity was studied, and the relationship between the reflection wavelength and the pressure and temperature was analyzed. The results show that the sensor encapsulated with beryllium bronze C17200 has higher pressure and temperature sensitivity, which can respectively reach 153.5pm/MPa and 31.7pm/℃ in the operating range of 0MPa~12MPa and -5℃~40℃, which are increased by 51.2 times and 2.8 times respectively on the basis of the bare grating, respectively. It is expected to be applied to high sensitivity measurement of liquid temperature and pressure. The results can provide reference for high sensitivity temperature and pressure measurement of liquid.
2022, 46(3): 344-354.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.008
Abstract:
In order to reveal the effect of laser cladding process parameters on the forming quality of Fe based TiC composite cladding layer and optimize the laser cladding process parameters, a YAG solid-state laser was used to achieve laser cladding Fe-based TiC composite coating on 60Si2Mn substrate, and a mathematical model was established to study the influence of output current, pulse width, and scanning speed on cladding width, height, molten pool depth, aspect ratio, dilution rate, and hardness based on response surface method. Then the mathematical model was analyzed by variance analysis. And the functional relationship between process parameters and molding quality was obtained. The results show that the output current and pulse width have a positive correlation with the coating width, and the scanning speed is inversely proportional to the coating width; The scanning speed has no significant effect on the height of cladding layer and the depth of molten pool; The ratio of coating width to coating height increases with the increase of output current; The output current has the most significant effect on the coating dilution ratio, followed by the pulse width; High hardness can be obtained with higher output current and scanning speed; The error of the optimized model is less than 5%. The results can be used to predict the forming quality of Fe based ceramic composite coating and optimize the laser processing parameters.
In order to reveal the effect of laser cladding process parameters on the forming quality of Fe based TiC composite cladding layer and optimize the laser cladding process parameters, a YAG solid-state laser was used to achieve laser cladding Fe-based TiC composite coating on 60Si2Mn substrate, and a mathematical model was established to study the influence of output current, pulse width, and scanning speed on cladding width, height, molten pool depth, aspect ratio, dilution rate, and hardness based on response surface method. Then the mathematical model was analyzed by variance analysis. And the functional relationship between process parameters and molding quality was obtained. The results show that the output current and pulse width have a positive correlation with the coating width, and the scanning speed is inversely proportional to the coating width; The scanning speed has no significant effect on the height of cladding layer and the depth of molten pool; The ratio of coating width to coating height increases with the increase of output current; The output current has the most significant effect on the coating dilution ratio, followed by the pulse width; High hardness can be obtained with higher output current and scanning speed; The error of the optimized model is less than 5%. The results can be used to predict the forming quality of Fe based ceramic composite coating and optimize the laser processing parameters.
2022, 46(3): 355-361.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.009
Abstract:
The traditional convolutional neural network method can loss some feature information, which may lead to unsatisfied terrain classification accuracy in the field of hyperspectral. In order to solve the problem, a new hyperspectral images classification method based on the 2-D and the 3-D, named hybrid convolutional neural network, was proposed. This method mainly extracted features from the spatial enhancement aspect and the spectral-spatial aspect. Firstly, a 3-D-2-D convolutional neural network hybrid structure was proposed for enhance spatial information. Secondly, the 3-D convolutional neural network structure was used for joint feature extraction from the aspect of spectral-spatial, and then the spectral-spatial comprehensive separability information was obtained. Finally, the separately obtained information was feature fused and classified. This method was used for classification experiments on hyperspectral data sets and compared with other methods. The results show that the classification accuracy of this method is 99.36% and 99.95% respectively in Indian Pines and Pavia University data set, and its classification accuracy and kappa coefficient are also better than other methods. This method has a competitive advantage in the classification of hyperspectral images.
The traditional convolutional neural network method can loss some feature information, which may lead to unsatisfied terrain classification accuracy in the field of hyperspectral. In order to solve the problem, a new hyperspectral images classification method based on the 2-D and the 3-D, named hybrid convolutional neural network, was proposed. This method mainly extracted features from the spatial enhancement aspect and the spectral-spatial aspect. Firstly, a 3-D-2-D convolutional neural network hybrid structure was proposed for enhance spatial information. Secondly, the 3-D convolutional neural network structure was used for joint feature extraction from the aspect of spectral-spatial, and then the spectral-spatial comprehensive separability information was obtained. Finally, the separately obtained information was feature fused and classified. This method was used for classification experiments on hyperspectral data sets and compared with other methods. The results show that the classification accuracy of this method is 99.36% and 99.95% respectively in Indian Pines and Pavia University data set, and its classification accuracy and kappa coefficient are also better than other methods. This method has a competitive advantage in the classification of hyperspectral images.
2022, 46(3): 362-367.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.010
Abstract:
In order to verify the effect of vacuum environment on the formation of pores in glass laser welding, the comparative test of glass laser welding under atmospheric and vacuum conditions was adopted.Theoretically analyze and experimentally verify of the change of porosity with laser power and the extent of expansion of glass frit to both ends under the two conditions was then carried out. The results show that, the cause of the porosity is not only the residual gas in the glass frit, but also the sublimation and decomposition of unstable components to produce more gas after the power is increased to 45W, which further improves the pores. It is found that the vacuum condition has little effect on the bonding expansion, and there is no obvious difference. The porosity under vacuum condition is significantly greater than that under atmospheric condition. The porosity is larger under vacuum condition, but the enlargement of porosity can't enlarge the expansion width of glass frit. The results further reveal the formation mechanism of pores under laser-assisted glass frit bonding.
In order to verify the effect of vacuum environment on the formation of pores in glass laser welding, the comparative test of glass laser welding under atmospheric and vacuum conditions was adopted.Theoretically analyze and experimentally verify of the change of porosity with laser power and the extent of expansion of glass frit to both ends under the two conditions was then carried out. The results show that, the cause of the porosity is not only the residual gas in the glass frit, but also the sublimation and decomposition of unstable components to produce more gas after the power is increased to 45W, which further improves the pores. It is found that the vacuum condition has little effect on the bonding expansion, and there is no obvious difference. The porosity under vacuum condition is significantly greater than that under atmospheric condition. The porosity is larger under vacuum condition, but the enlargement of porosity can't enlarge the expansion width of glass frit. The results further reveal the formation mechanism of pores under laser-assisted glass frit bonding.
2022, 46(3): 368-373.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.011
Abstract:
In order to improve the luminous efficiency of light-emitting diode (LED), a metal grating was placed on the light emitting surface of LED. The theoretical analysis based on finite difference time domain method shows that the transmittance of metal grating to the wavelength of 460nm is close to 1 after the optimization of the grating, and the light extraction efficiency of LED can be improved. The optimized metal grating can simultaneously excite surface plasmons polariton and the localized surface plasmon at 460nm, which is helpful to improve the internal quantum efficiency of LED. The luminous efficiency of LED with metal grating structure at 460nm is 30 times higher than that of LED with only a thin layer of Ag on light-emitting surface. The research can provide theoretical guidance for the preparation of high luminous efficiency LED in the future.
In order to improve the luminous efficiency of light-emitting diode (LED), a metal grating was placed on the light emitting surface of LED. The theoretical analysis based on finite difference time domain method shows that the transmittance of metal grating to the wavelength of 460nm is close to 1 after the optimization of the grating, and the light extraction efficiency of LED can be improved. The optimized metal grating can simultaneously excite surface plasmons polariton and the localized surface plasmon at 460nm, which is helpful to improve the internal quantum efficiency of LED. The luminous efficiency of LED with metal grating structure at 460nm is 30 times higher than that of LED with only a thin layer of Ag on light-emitting surface. The research can provide theoretical guidance for the preparation of high luminous efficiency LED in the future.
2022, 46(3): 374-378.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.012
Abstract:
In order to obtain the status information of the workpiece stably under the working environment, the method of multi-fiber Bragg grating (FBG) network monitoring was adopted, and the multi-fiber grating sensors were distributed on the tooling of the assembly structure. On the basis of obtaining the real-time strain field data of the sensitive positions, the difference was analyzed. The function relationship between the assembly error and the strain field distribution, and the appropriate correction parameters were given. The results show that when 100N stress is applied to the workpiece, the maximum deformation value in the x-axis direction is 0.86mm, and the maximum value in the y-axis direction is 0.69mm; compared with the standard measurement data obtained by laser scanning, it can be seen that the test on the x-axis. The average error of the deformation value of the sensitive position is better than 4.7%, and the average error of the deformation value of the sensitive position tested on the y-axis is better than 3.9%. It is feasible to use optical fiber sensing to realize intelligent correction of the assembly process, and it has good linearity and repeatability in the entire test range, which can improve the effect of intelligent assembly control.
In order to obtain the status information of the workpiece stably under the working environment, the method of multi-fiber Bragg grating (FBG) network monitoring was adopted, and the multi-fiber grating sensors were distributed on the tooling of the assembly structure. On the basis of obtaining the real-time strain field data of the sensitive positions, the difference was analyzed. The function relationship between the assembly error and the strain field distribution, and the appropriate correction parameters were given. The results show that when 100N stress is applied to the workpiece, the maximum deformation value in the x-axis direction is 0.86mm, and the maximum value in the y-axis direction is 0.69mm; compared with the standard measurement data obtained by laser scanning, it can be seen that the test on the x-axis. The average error of the deformation value of the sensitive position is better than 4.7%, and the average error of the deformation value of the sensitive position tested on the y-axis is better than 3.9%. It is feasible to use optical fiber sensing to realize intelligent correction of the assembly process, and it has good linearity and repeatability in the entire test range, which can improve the effect of intelligent assembly control.
2022, 46(3): 379-384.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.013
Abstract:
In order to research the hole-making characteristics of high volume fraction silicon carbide particle reinforced aluminum matrix (SiCp/Al) composite material thick plates processed by laser, the hole making test of 4mm thick plate was carried out using different laser processing parameters. And the formation mechanism of the recast layer and its surface cracks in the hole made by the ultraviolet picosecond laser was analyzed. The influence of key laser processing parameters (laser power percentage and scanning speed) on the hole recast layer was obtained. The results of the experiment show that there is a recast layer of hundred microns in the picosecond laser processing of SiCp/Al composite thick plates. The thickness of the recast layer does not change monotonously with the increase of laser power, and the thickness is the smallest at 100% laser power with value of 99.5μm; the thickness increases with the increase of the laser scanning speed, and the smallest value is 71.2μm at a scanning speed of 100mm/s with. In addition, the recast layer of the thick plate ultraviolet picosecond laser processed SiCp/Al composite has a "crescent" arc-shaped morphology. At the same time, there are significant horizontal and vertical cracks on the surface of the recast layer. This research provides theoretical guidance for low-damage micro-hole machining of SiCp/Al composites with picosecond laser.
In order to research the hole-making characteristics of high volume fraction silicon carbide particle reinforced aluminum matrix (SiCp/Al) composite material thick plates processed by laser, the hole making test of 4mm thick plate was carried out using different laser processing parameters. And the formation mechanism of the recast layer and its surface cracks in the hole made by the ultraviolet picosecond laser was analyzed. The influence of key laser processing parameters (laser power percentage and scanning speed) on the hole recast layer was obtained. The results of the experiment show that there is a recast layer of hundred microns in the picosecond laser processing of SiCp/Al composite thick plates. The thickness of the recast layer does not change monotonously with the increase of laser power, and the thickness is the smallest at 100% laser power with value of 99.5μm; the thickness increases with the increase of the laser scanning speed, and the smallest value is 71.2μm at a scanning speed of 100mm/s with. In addition, the recast layer of the thick plate ultraviolet picosecond laser processed SiCp/Al composite has a "crescent" arc-shaped morphology. At the same time, there are significant horizontal and vertical cracks on the surface of the recast layer. This research provides theoretical guidance for low-damage micro-hole machining of SiCp/Al composites with picosecond laser.
2022, 46(3): 385-389.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.014
Abstract:
In order to study the influence of the pump light source spectrum and the absorption spectrum of the gain medium on the output efficiency of light-emitting diode(LED) band pump laser, and to improve the output efficiency, the spectral information was introduced into the laser rate equations to establish the rate equations of the LED band pump Nd∶YAG laser. Theoretical analysis and experimental verification of LED band pumped Nd∶YAG laser were carried out. The Nd∶YAG laser was side-pumped by infrared LEDs. Under the pump energy of 9.1mJ, a 1064nm laser output with an output energy of 607μJ was obtained. The slope efficiency of this LED band pump Nd∶YAG laser was 15.5%, and the corresponding optical-to-optical efficiency was 6.67%. The results show that the calculated solution of the rate equations was basically consistent with the experimental output energy, which is helpful for the study of improving the output efficiency of LED band pump laser.
In order to study the influence of the pump light source spectrum and the absorption spectrum of the gain medium on the output efficiency of light-emitting diode(LED) band pump laser, and to improve the output efficiency, the spectral information was introduced into the laser rate equations to establish the rate equations of the LED band pump Nd∶YAG laser. Theoretical analysis and experimental verification of LED band pumped Nd∶YAG laser were carried out. The Nd∶YAG laser was side-pumped by infrared LEDs. Under the pump energy of 9.1mJ, a 1064nm laser output with an output energy of 607μJ was obtained. The slope efficiency of this LED band pump Nd∶YAG laser was 15.5%, and the corresponding optical-to-optical efficiency was 6.67%. The results show that the calculated solution of the rate equations was basically consistent with the experimental output energy, which is helpful for the study of improving the output efficiency of LED band pump laser.
2022, 46(3): 390-396.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.015
Abstract:
In order to solve the problems of low robustness and poor automation of current tower tilt detection methods based on light detection and ranging (LiDAR) point cloud transmission line, a tower tilt detection method based on layered minimum external rectangle and robust estimation was proposed by using the structural characteristics of tower body which was projected into standard rectangle on the level plane. Firstly, the area and proportion changes of the minimum circumscribed rectangle of each layer of point cloud were used to filter the deviation between the middle point of the rectangle and the axis point of the actual tower caused by the tower head and the high and low legs, and the center point of the minimum circumscribed rectangle of each layer of the tower body was determined as the axis point; Secondly, the elevation difference between the four sides of the minimum circumscribed rectangle and the elevation value of the point set was used to fit the axis of the tower; Finally, robust estimation was introduced into spatial line fitting to restrain the influence of other offset points on spatial line fitting by weight iteration. The experimental results show that the method has good adaptability in different tower types and different point cloud densities, and has strong ability to resist gross errors in the case of shortcomings and noise, and the deviation from the measured value is less than 0.90‰, which has strong practical application value.
In order to solve the problems of low robustness and poor automation of current tower tilt detection methods based on light detection and ranging (LiDAR) point cloud transmission line, a tower tilt detection method based on layered minimum external rectangle and robust estimation was proposed by using the structural characteristics of tower body which was projected into standard rectangle on the level plane. Firstly, the area and proportion changes of the minimum circumscribed rectangle of each layer of point cloud were used to filter the deviation between the middle point of the rectangle and the axis point of the actual tower caused by the tower head and the high and low legs, and the center point of the minimum circumscribed rectangle of each layer of the tower body was determined as the axis point; Secondly, the elevation difference between the four sides of the minimum circumscribed rectangle and the elevation value of the point set was used to fit the axis of the tower; Finally, robust estimation was introduced into spatial line fitting to restrain the influence of other offset points on spatial line fitting by weight iteration. The experimental results show that the method has good adaptability in different tower types and different point cloud densities, and has strong ability to resist gross errors in the case of shortcomings and noise, and the deviation from the measured value is less than 0.90‰, which has strong practical application value.
2022, 46(3): 397-401.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.016
Abstract:
In order to enhance the driving efficiency of high-energy pulsed laser and optimize the engineering realization effect of the driving circuit, the theoretical analysis and simulation verification of the discharge characteristics of the pulsed xenon lamp and the pulse-forming network were carried out by means of circuit analysis and simulation, and the correlation data between the influencing factors and the pulse current waveform were obtained. The results show that both the rectangularity of the pulse current waveform and the difficulty of engineering implementation increases with the number of nodes incresaing. The ideal number of nodes is about 5, and the peak amplitude decreases with the decrease of the final chain inductance, and the ideal value of the weighted value is about 0.8. The rising speed decreases with the increase of the leading inductance, and the ideal value range of the weighted value is 1.2~1.4. This research is beneficial to further promote the engineering application and development of the driving circuit of high energy pulse xenon lamp.
In order to enhance the driving efficiency of high-energy pulsed laser and optimize the engineering realization effect of the driving circuit, the theoretical analysis and simulation verification of the discharge characteristics of the pulsed xenon lamp and the pulse-forming network were carried out by means of circuit analysis and simulation, and the correlation data between the influencing factors and the pulse current waveform were obtained. The results show that both the rectangularity of the pulse current waveform and the difficulty of engineering implementation increases with the number of nodes incresaing. The ideal number of nodes is about 5, and the peak amplitude decreases with the decrease of the final chain inductance, and the ideal value of the weighted value is about 0.8. The rising speed decreases with the increase of the leading inductance, and the ideal value range of the weighted value is 1.2~1.4. This research is beneficial to further promote the engineering application and development of the driving circuit of high energy pulse xenon lamp.
2022, 46(3): 402-407.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.017
Abstract:
In order to investigate the process of 266nm ultraviolet solid-state laser cutting of carbon fiber reinforced plastics (CFRP). The experiment on 266nm ultraviolet solid-state laser cutting CFRP were carried out by single factor experiment, orthogonal experiment, and multiple linear regression analysis, respectively. The effects of laser energy and scanning speed on the width of slit and the width of heat-affected zone were obtained. The results show that with the increasing of laser energy, both the width of the slit and the width of the heat-affected zone increase accordingly. With the increasing of scanning speed, both the width of slit and the width of heat-affected zone decrease. In the experiment, the minimum width of heat-affected zone is 82μm, and the minimum width of slit is 50μm. The influence of laser scanning speed on the width of the slit is more significant, whereas the influence of laser energy on the width of the heat-affected zone is more significant. The empirical formula can quantitatively describe the relationship among the width of the slit, the width of the heat-affected zone, and the laser energy and scanning speed. It has a reference significance for the further research and industrial application of 266nm ultraviolet solid-state laser cutting of CFRP.
In order to investigate the process of 266nm ultraviolet solid-state laser cutting of carbon fiber reinforced plastics (CFRP). The experiment on 266nm ultraviolet solid-state laser cutting CFRP were carried out by single factor experiment, orthogonal experiment, and multiple linear regression analysis, respectively. The effects of laser energy and scanning speed on the width of slit and the width of heat-affected zone were obtained. The results show that with the increasing of laser energy, both the width of the slit and the width of the heat-affected zone increase accordingly. With the increasing of scanning speed, both the width of slit and the width of heat-affected zone decrease. In the experiment, the minimum width of heat-affected zone is 82μm, and the minimum width of slit is 50μm. The influence of laser scanning speed on the width of the slit is more significant, whereas the influence of laser energy on the width of the heat-affected zone is more significant. The empirical formula can quantitatively describe the relationship among the width of the slit, the width of the heat-affected zone, and the laser energy and scanning speed. It has a reference significance for the further research and industrial application of 266nm ultraviolet solid-state laser cutting of CFRP.
2022, 46(3): 408-414.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.018
Abstract:
In order to obtain a relatively stable temperature field, the changes in the temperature field of the methane-oxygen premixed flame at different ratios were obtained through experiments, and the influence of the methane mass fraction on the temperature field of the premixed flame was analyzed. With the help of Mckenna burner, digital holographic technology was used to obtain the interference fringe images of the premixed flame temperature field under different methane-oxygen ratios, and the Butterworth low-pass filter was used to reduce the speckle noise of the pre-processed image. The phase distribution information of the temperature field was extracted by the improved four-way least squares unwrapping method. According to the theoretical relationship between the phase and the temperature, the corresponding temperature information data was obtained, and the B-type thermocouple was used for experimental verification. The experimental results show that the temperature measured by this method is basically consistent with the temperature change measured by the thermocouple under the same conditions, which proves the feasibility of the digital holographic technology to measure the temperature field. When the mass fraction ratio of methane to oxygen is 0.9, the temperature change is about 10K. And the temperature field distribution is the most stable one compared with other working conditions. This research provides a theoretical basis for the related research on methane-oxygen premixed gas and the application of Mckenna burners.
In order to obtain a relatively stable temperature field, the changes in the temperature field of the methane-oxygen premixed flame at different ratios were obtained through experiments, and the influence of the methane mass fraction on the temperature field of the premixed flame was analyzed. With the help of Mckenna burner, digital holographic technology was used to obtain the interference fringe images of the premixed flame temperature field under different methane-oxygen ratios, and the Butterworth low-pass filter was used to reduce the speckle noise of the pre-processed image. The phase distribution information of the temperature field was extracted by the improved four-way least squares unwrapping method. According to the theoretical relationship between the phase and the temperature, the corresponding temperature information data was obtained, and the B-type thermocouple was used for experimental verification. The experimental results show that the temperature measured by this method is basically consistent with the temperature change measured by the thermocouple under the same conditions, which proves the feasibility of the digital holographic technology to measure the temperature field. When the mass fraction ratio of methane to oxygen is 0.9, the temperature change is about 10K. And the temperature field distribution is the most stable one compared with other working conditions. This research provides a theoretical basis for the related research on methane-oxygen premixed gas and the application of Mckenna burners.
2022, 46(3): 415-421.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.019
Abstract:
In order to make up for the limitations of manufacturing technology, laser engineered near shaping (LENS) device was integrated on a five-axis linkage computerized numerical control (CNC) machine by applying the technology of adding and subtracting materials, which forms an equipment realizing additive and subtractive machining structurally; UG post-processing builder was used to develop a post-processing machining system of additive and subtractive materials, which realizes parts' hybrid manufacturing functionally. The results show that hybrid manufacturing can achieve one-time forming for complex metal parts, and reduce machining errors and inefficiencies caused by multiple clamping. Compared with additive or subtractive processing mode, the product yield rate is increased more than 20%, processing time is shortened more than 45%, supporting amount is reduced more than 30%, respectively. Especially for parts with a structure of closed internal flow channel, the surface accuracy of the internal flow channel can reach 0.6μm by using hybrid manufacturing method, which effectively extends parts' service life. Hybrid manufacturing technology can realize processing with weak support, no support, no interference, high-precision and high-efficiency. This research provides reference for the process plan, manufacturing mode, and application expansion of laser hybrid manufacturing.
In order to make up for the limitations of manufacturing technology, laser engineered near shaping (LENS) device was integrated on a five-axis linkage computerized numerical control (CNC) machine by applying the technology of adding and subtracting materials, which forms an equipment realizing additive and subtractive machining structurally; UG post-processing builder was used to develop a post-processing machining system of additive and subtractive materials, which realizes parts' hybrid manufacturing functionally. The results show that hybrid manufacturing can achieve one-time forming for complex metal parts, and reduce machining errors and inefficiencies caused by multiple clamping. Compared with additive or subtractive processing mode, the product yield rate is increased more than 20%, processing time is shortened more than 45%, supporting amount is reduced more than 30%, respectively. Especially for parts with a structure of closed internal flow channel, the surface accuracy of the internal flow channel can reach 0.6μm by using hybrid manufacturing method, which effectively extends parts' service life. Hybrid manufacturing technology can realize processing with weak support, no support, no interference, high-precision and high-efficiency. This research provides reference for the process plan, manufacturing mode, and application expansion of laser hybrid manufacturing.
2022, 46(3): 422-426.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.020
Abstract:
In order to obtain the electronic radiation characteristics under the action of a tightly compact-focused laser, the nonlinear Thomson scattering theory and the model for the interaction of linearly polarized compact-focused laser pulse with a single electron were utilized in this study. And the numerical simulation was completed by using MATLAB. The motion characteristics of the electron, as well as the power and energy distribution at different observation angles were analyzed, especially in the direction of maximum radiation. Compared with the plane-wave laser pulse, it is found that the symmetric-bimodal radiation power pulse no longer holds in time for the pulse width was 0.008fs and 0.121fs, respectively; And the radiation energy shows the dramatic oscillation at low radiation frequency of 0~50ω0. The results can provide great value for the electron emission characteristics in intense laser field.
In order to obtain the electronic radiation characteristics under the action of a tightly compact-focused laser, the nonlinear Thomson scattering theory and the model for the interaction of linearly polarized compact-focused laser pulse with a single electron were utilized in this study. And the numerical simulation was completed by using MATLAB. The motion characteristics of the electron, as well as the power and energy distribution at different observation angles were analyzed, especially in the direction of maximum radiation. Compared with the plane-wave laser pulse, it is found that the symmetric-bimodal radiation power pulse no longer holds in time for the pulse width was 0.008fs and 0.121fs, respectively; And the radiation energy shows the dramatic oscillation at low radiation frequency of 0~50ω0. The results can provide great value for the electron emission characteristics in intense laser field.
2022, 46(3): 427-434.
doi: 10.7510/jgjs.issn.1001-3806.2022.03.021
Abstract:
In order to explore the structural characteristics of high spatial and temporal resolution in the process of sand and dust pollution, a typical dust weather process on 2019-10-27~2019-10-28 in Xilin Gol League of Inner Mongolia Autonomous Region was analyzed using coherent Doppler wind light detection and ranging(LiDAR), ground observation station, aerosol optical depth (AOD) data product of medium resolution image spectrometer satellite, European Centre for Medium-Range Forecasts the 5th reanalysis data (ERA5), and hybrid single particle Lagrangian integrated trajectory (HYSPLIT) backward trajectory model. The results show that the dust was affected by the high altitude cold vortex and the Mongolian cyclone, and the cold front passed over the sand source area of the central and western Mongolia and the western Inner Mongolia Autonomous Region during the high temperature period. The thermal superposition dynamic conditions were favorable for the dust to spread with the westerly wind. The surface temperature changes obviously before and after the arrival of dust. Satellite products, HYSPLIT mode combined with wind profile of LiDAR can more accurately determine the source of dust. At 02:00 on 2019-10-28, the mass concentration of ground PM10 reached the maximum 268μg/m3, and the extinction coefficient exceeded 30km-1 and reached the maximum. Radar inversion data was delayed in time. The aerosol extinction coefficient retrieved by LiDAR can reflect the changes of aerosols in the boundary layer atmosphere. The urban underlying surface weakened the dust pollution rapidly, and the grassland underlying surface where the radar located was prone to be affected by vertical wind shear to produce persistent pollution. This research is helpful to application of coherent Doppler wind LiDAR, understand the pollution process and transmission characteristics of sand and dust.
In order to explore the structural characteristics of high spatial and temporal resolution in the process of sand and dust pollution, a typical dust weather process on 2019-10-27~2019-10-28 in Xilin Gol League of Inner Mongolia Autonomous Region was analyzed using coherent Doppler wind light detection and ranging(LiDAR), ground observation station, aerosol optical depth (AOD) data product of medium resolution image spectrometer satellite, European Centre for Medium-Range Forecasts the 5th reanalysis data (ERA5), and hybrid single particle Lagrangian integrated trajectory (HYSPLIT) backward trajectory model. The results show that the dust was affected by the high altitude cold vortex and the Mongolian cyclone, and the cold front passed over the sand source area of the central and western Mongolia and the western Inner Mongolia Autonomous Region during the high temperature period. The thermal superposition dynamic conditions were favorable for the dust to spread with the westerly wind. The surface temperature changes obviously before and after the arrival of dust. Satellite products, HYSPLIT mode combined with wind profile of LiDAR can more accurately determine the source of dust. At 02:00 on 2019-10-28, the mass concentration of ground PM10 reached the maximum 268μg/m3, and the extinction coefficient exceeded 30km-1 and reached the maximum. Radar inversion data was delayed in time. The aerosol extinction coefficient retrieved by LiDAR can reflect the changes of aerosols in the boundary layer atmosphere. The urban underlying surface weakened the dust pollution rapidly, and the grassland underlying surface where the radar located was prone to be affected by vertical wind shear to produce persistent pollution. This research is helpful to application of coherent Doppler wind LiDAR, understand the pollution process and transmission characteristics of sand and dust.
