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RSS2018 Vol. 42, No. 6
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2018, 42(6): 727-732.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.001
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Abstract:
In order to study the detection of horizontal visibility and vertical aerosol extinction coefficient by monitoring pollutants lidar, the extinction coefficients of 301.5nm and 446.6nm in horizontal and vertical directions and wavelength Ångström index were retrieved by the slope method and the Fernald method. The result shows that, in the horizontal direction, the extinction coefficients and visibility of 301.5nm and 446.6nm vary with time consistently. In the vertical direction, the extinction coefficients of 301.5nm and 446.6nm follow the same trend in time and space. The Ångström index has changed with the change of time. But the spatial change trend is the same. The results are helpful to correct the effect of analytical differential absorption lidar on aerosol.
In order to study the detection of horizontal visibility and vertical aerosol extinction coefficient by monitoring pollutants lidar, the extinction coefficients of 301.5nm and 446.6nm in horizontal and vertical directions and wavelength Ångström index were retrieved by the slope method and the Fernald method. The result shows that, in the horizontal direction, the extinction coefficients and visibility of 301.5nm and 446.6nm vary with time consistently. In the vertical direction, the extinction coefficients of 301.5nm and 446.6nm follow the same trend in time and space. The Ångström index has changed with the change of time. But the spatial change trend is the same. The results are helpful to correct the effect of analytical differential absorption lidar on aerosol.
2018, 42(6): 733-738.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.002
Abstract:
In order to solve the problems of the low quality of image, the large amount of data and the slow rate of transmission, an optical compression and encryption method of multiple-color images by using discrete wavelet transform in Fresnel transform domain had been proposed. In the process of encryption, the low-frequency components of each color image were extracted by using the multilevel decomposition characteristics of wavelet transform, and the low frequency components were reorganized to triplet images (R, G and B), respectively. And the triplet images (R, G and B) were sequentially encrypted through the diffraction encryption system in the Fresnel domain. After triplet images were further encrypted, the encryption of multi-color images was realized. The results show that, the method can not only reconstruct the original color image with high quality, but also encrypt 4 color-images at the same time, which increases the capacity of the encrypted color image. The data volume of the encryption is compressed 1/4 after wavelet transform, which is beneficial to the transmission and storage of the data. The algorithm can effectively compress and encrypt multiple-color images at the same time. It not only improves the quality of the decrypted image, but also has high key sensitivity and good robustness.
In order to solve the problems of the low quality of image, the large amount of data and the slow rate of transmission, an optical compression and encryption method of multiple-color images by using discrete wavelet transform in Fresnel transform domain had been proposed. In the process of encryption, the low-frequency components of each color image were extracted by using the multilevel decomposition characteristics of wavelet transform, and the low frequency components were reorganized to triplet images (R, G and B), respectively. And the triplet images (R, G and B) were sequentially encrypted through the diffraction encryption system in the Fresnel domain. After triplet images were further encrypted, the encryption of multi-color images was realized. The results show that, the method can not only reconstruct the original color image with high quality, but also encrypt 4 color-images at the same time, which increases the capacity of the encrypted color image. The data volume of the encryption is compressed 1/4 after wavelet transform, which is beneficial to the transmission and storage of the data. The algorithm can effectively compress and encrypt multiple-color images at the same time. It not only improves the quality of the decrypted image, but also has high key sensitivity and good robustness.
2018, 42(6): 739-744.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.003
Abstract:
In order to solve the problems of slow processing rate of nano composite electrodeposition, easy agglomeration of particles and poor surface quality of deposition layer, the method of building high energy pulsed laser-assisted nano composite electrodeposition was adopted. Laser irradiation was used to produce localized microregion agitation to alleviate the agglomeration of particles, accelerate the electrochemical reaction rate and improve the surface quality of deposition layer. After finite element simulation and experimental verification, the results show that, laser and electrochemical composing can obviously increase the rate of composite deposition, and the impact of laser can increase the binding of grain, and then promote the densification of the coating. At the same time, this impact can also reduce the agglomeration probability of nanoparticles and refine the coating grain. The research results will be helpful to the development of electrochemical machining technology.
In order to solve the problems of slow processing rate of nano composite electrodeposition, easy agglomeration of particles and poor surface quality of deposition layer, the method of building high energy pulsed laser-assisted nano composite electrodeposition was adopted. Laser irradiation was used to produce localized microregion agitation to alleviate the agglomeration of particles, accelerate the electrochemical reaction rate and improve the surface quality of deposition layer. After finite element simulation and experimental verification, the results show that, laser and electrochemical composing can obviously increase the rate of composite deposition, and the impact of laser can increase the binding of grain, and then promote the densification of the coating. At the same time, this impact can also reduce the agglomeration probability of nanoparticles and refine the coating grain. The research results will be helpful to the development of electrochemical machining technology.
2018, 42(6): 745-750.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.004
Abstract:
In order to maintain the molten pool temperature relatively stable in laser cladding process, close-loop control of molten pool temperature was realized by the combination of colorimetric temperature measurement and proportional-integral-differential (PID) control strategy. A set of on-line measurement and control system for molten pool temperature of laser cladding based on dual-channel color CCD was built. Emissivity ε was incorporated into the undetermined coefficient K, and the corresponding relationship between gray ratio and K was established, and the calculating formula for the temperature of the molten pool was derived. Based on Socket communication, the signal transmission between industrial personal computer and robot controller was realized, and the algorithm of temperature controller based on laser power variation was designed. The experimental results show that, the system can measure and control the temperature of molten pool in real time and accurately, the control accuracy within 3%. The system is applied to thin-walled cylinder stacking forming experiment, which can effectively eliminate the temperature accumulation effect during laser cladding forming process. The difference between the outer diameter of the bottom and top part of the forming part is only 0.9mm. The control scheme has the advantages of good real-time performance, low cost and easy integration.
In order to maintain the molten pool temperature relatively stable in laser cladding process, close-loop control of molten pool temperature was realized by the combination of colorimetric temperature measurement and proportional-integral-differential (PID) control strategy. A set of on-line measurement and control system for molten pool temperature of laser cladding based on dual-channel color CCD was built. Emissivity ε was incorporated into the undetermined coefficient K, and the corresponding relationship between gray ratio and K was established, and the calculating formula for the temperature of the molten pool was derived. Based on Socket communication, the signal transmission between industrial personal computer and robot controller was realized, and the algorithm of temperature controller based on laser power variation was designed. The experimental results show that, the system can measure and control the temperature of molten pool in real time and accurately, the control accuracy within 3%. The system is applied to thin-walled cylinder stacking forming experiment, which can effectively eliminate the temperature accumulation effect during laser cladding forming process. The difference between the outer diameter of the bottom and top part of the forming part is only 0.9mm. The control scheme has the advantages of good real-time performance, low cost and easy integration.
2018, 42(6): 751-757.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.005
Abstract:
In order to adapt the visual recognition of workpiece with different postures in production line and realize the localization and grasping of workpiece based on vision robot, the kinematics model and the visual system model of six degree of freedom(6-DOF) workpiece attitude transformation simulation experiment platform were constructed. The measurement of attitude parameters of workpiece was realized by coordinate transformation. 6-DOF attitude transformation experimental platform coordinate system was set up. Kinematics model of six degree of freedom attitude transformation experiment platform based on Denavit-Hartenberg (D-H) method was constructed through 3 sliding pairs and 3 rotational pairs. D-H parameter table, transformation matrix of each joint and total transformation matrix of experimental platform from the base to the end were obtained. Based on the principle of small hole imaging, the internal and external parameter model of attitude transformation experimental platform was constructed. The internal parameter relation matrix between workpiece surface point and image point and the external relation matrix between workpiece coordinate system and camera coordinate system were obtained. The normal vector of workpiece surface in camera coordinate system was obtained from the image of laser ring light strip. And then, the normal vector of workpiece surface in the world coordinate system was obtained through the transformation of coordinate system. Finally, attitude parameters of workpiece were calculated. The results show that average error of roll angle is 0.373°, average error of pitch angle is 0.253° and average error of deflection angle is 0.673°. The measured value of workpiece is basically consistent with the true value, which meets the requirements of workpiece vision measurement under different postures.
In order to adapt the visual recognition of workpiece with different postures in production line and realize the localization and grasping of workpiece based on vision robot, the kinematics model and the visual system model of six degree of freedom(6-DOF) workpiece attitude transformation simulation experiment platform were constructed. The measurement of attitude parameters of workpiece was realized by coordinate transformation. 6-DOF attitude transformation experimental platform coordinate system was set up. Kinematics model of six degree of freedom attitude transformation experiment platform based on Denavit-Hartenberg (D-H) method was constructed through 3 sliding pairs and 3 rotational pairs. D-H parameter table, transformation matrix of each joint and total transformation matrix of experimental platform from the base to the end were obtained. Based on the principle of small hole imaging, the internal and external parameter model of attitude transformation experimental platform was constructed. The internal parameter relation matrix between workpiece surface point and image point and the external relation matrix between workpiece coordinate system and camera coordinate system were obtained. The normal vector of workpiece surface in camera coordinate system was obtained from the image of laser ring light strip. And then, the normal vector of workpiece surface in the world coordinate system was obtained through the transformation of coordinate system. Finally, attitude parameters of workpiece were calculated. The results show that average error of roll angle is 0.373°, average error of pitch angle is 0.253° and average error of deflection angle is 0.673°. The measured value of workpiece is basically consistent with the true value, which meets the requirements of workpiece vision measurement under different postures.
2018, 42(6): 758-763.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.006
Abstract:
In order to solve the problem of high cost of micro mold design and manufacturing in metal foil micro deep drawing process, a die-less laser shock micro-forming method was used. A high repetition frequency laser with pulse width of 5ns and spot diameter of 50μm was shocked on the T2 copper foil with thickness of 20μm, and theoretical analysis and experimental verification were carried out. The results show that, when the confinement layer is not damaged, the pit depth h, the diameter of pit bottom L1 and the inclination of pit wall (L-L1) increase linearly with the increase of single pulse energy E and spot overlapping rate. The order of inner and outer circumference of laser scanning has no effect on the depth of pits. But it will affect the diameter of the bottom of the pit. When scanning the outer circumference firstly, a larger bottom diameter pit will be formed. The shape of the pit is controllable without die. The study is helpful to the further study on die-less laser micro drawing progressive forming.
In order to solve the problem of high cost of micro mold design and manufacturing in metal foil micro deep drawing process, a die-less laser shock micro-forming method was used. A high repetition frequency laser with pulse width of 5ns and spot diameter of 50μm was shocked on the T2 copper foil with thickness of 20μm, and theoretical analysis and experimental verification were carried out. The results show that, when the confinement layer is not damaged, the pit depth h, the diameter of pit bottom L1 and the inclination of pit wall (L-L1) increase linearly with the increase of single pulse energy E and spot overlapping rate. The order of inner and outer circumference of laser scanning has no effect on the depth of pits. But it will affect the diameter of the bottom of the pit. When scanning the outer circumference firstly, a larger bottom diameter pit will be formed. The shape of the pit is controllable without die. The study is helpful to the further study on die-less laser micro drawing progressive forming.
Numerical simulation of phase transition process of laser drilling on GH4037 nickel-based superalloy
2018, 42(6): 764-768.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.007
Abstract:
In order to study the phase transformation process of laser drilling more accurately, based on the theories of fluid heat transfer and fluid mechanics, a phase transition model of laser drilling on GH4037 nickel-based superalloy was established. In the model, the effect of gravity, viscous force, recoil pressure, solid-liquid phase transition and liquid-gas phase transition process were considered, and the temperature field and velocity field of laser drilling phase transition process were obtained by numerical calculation. The results show that, the reaction pressure of the gasification material can accelerate the flow of the molten pool. When the laser power is 2000W and the pulse width is 1.70ms, the maximum evaporation rate of the material can reach 250m/s. This model provides a theoretical basis for further research on laser drilling.
In order to study the phase transformation process of laser drilling more accurately, based on the theories of fluid heat transfer and fluid mechanics, a phase transition model of laser drilling on GH4037 nickel-based superalloy was established. In the model, the effect of gravity, viscous force, recoil pressure, solid-liquid phase transition and liquid-gas phase transition process were considered, and the temperature field and velocity field of laser drilling phase transition process were obtained by numerical calculation. The results show that, the reaction pressure of the gasification material can accelerate the flow of the molten pool. When the laser power is 2000W and the pulse width is 1.70ms, the maximum evaporation rate of the material can reach 250m/s. This model provides a theoretical basis for further research on laser drilling.
2018, 42(6): 769-774.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.008
Abstract:
In order to obtain experimental 3-D point spread function of a digital confocal microscope optical system, a fluorescence microsphere was used to simulate the point light source, a digital confocal microscope optical system was used to collect the slice images of the fluorescent microsphere with different defocuses, and the multi-image averaging method was used to denoise the slice images. Experimental 3-D point spread function of the microscope optical system was constructed. 3-D microscopic image restoration was carried out by experimental point spread function and was compared with that of theoretical point spread function. The results show that both the point spread functions have good restoration effect for image restoration, but experimental 3-D point spread function obtained by correct experimental method is more consistent with optical transmission characteristics of an optical system and has more accurate recovery effect. Experimental 3-D point spread function constructed in the study provides a better choice for the next step of biological microscopic image restoration. It provides an effective method for the construction of 3-D point spread function of digital confocal microscopes.
In order to obtain experimental 3-D point spread function of a digital confocal microscope optical system, a fluorescence microsphere was used to simulate the point light source, a digital confocal microscope optical system was used to collect the slice images of the fluorescent microsphere with different defocuses, and the multi-image averaging method was used to denoise the slice images. Experimental 3-D point spread function of the microscope optical system was constructed. 3-D microscopic image restoration was carried out by experimental point spread function and was compared with that of theoretical point spread function. The results show that both the point spread functions have good restoration effect for image restoration, but experimental 3-D point spread function obtained by correct experimental method is more consistent with optical transmission characteristics of an optical system and has more accurate recovery effect. Experimental 3-D point spread function constructed in the study provides a better choice for the next step of biological microscopic image restoration. It provides an effective method for the construction of 3-D point spread function of digital confocal microscopes.
2018, 42(6): 775-779.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.009
Abstract:
In order to study the damage morphology of carbon fiber epoxy resin irradiated by laser with different pulse widths, automatic zoom measurement technique was used to test the changes of the damage area, damage depth and damage morphology of carbon fiber epoxy resin with laser energy density. The results show that, under the action of millisecond pulsed laser, a certain temperature accumulation will be produced in the center of the damage region of the composite material. The damage region has some thermal effect, melting, pyrolysis and so on. When the laser energy density is 20.5J/cm2, the damage depth of the material reaches 47.3μm, and the height of carbide precipitated on the surface of the material is 157.1μm. The depth of damage and the height of surface carbonization increase with the increase of energy density. There are obvious thermal reaction regions around the spot under the action of nanosecond laser. When the energy density is greater than 47.3J/cm2, the thermal reaction area of the surface is particularly obvious. And the damage area increases obviously with the increase of laser energy density. Because of the short time, the damage is mainly surface damage and the outward pyrolysis gas expedition results in the fracture of fiber structure. The research results provide an experimental basis for laser damage effect on carbon fiber epoxy resin.
In order to study the damage morphology of carbon fiber epoxy resin irradiated by laser with different pulse widths, automatic zoom measurement technique was used to test the changes of the damage area, damage depth and damage morphology of carbon fiber epoxy resin with laser energy density. The results show that, under the action of millisecond pulsed laser, a certain temperature accumulation will be produced in the center of the damage region of the composite material. The damage region has some thermal effect, melting, pyrolysis and so on. When the laser energy density is 20.5J/cm2, the damage depth of the material reaches 47.3μm, and the height of carbide precipitated on the surface of the material is 157.1μm. The depth of damage and the height of surface carbonization increase with the increase of energy density. There are obvious thermal reaction regions around the spot under the action of nanosecond laser. When the energy density is greater than 47.3J/cm2, the thermal reaction area of the surface is particularly obvious. And the damage area increases obviously with the increase of laser energy density. Because of the short time, the damage is mainly surface damage and the outward pyrolysis gas expedition results in the fracture of fiber structure. The research results provide an experimental basis for laser damage effect on carbon fiber epoxy resin.
2018, 42(6): 780-784.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.010
Abstract:
In order to study magneto-optical imaging (MOI) law of weld cracks under the excitation of rotating magnetic field, the method of using rotating magneto magnetic field to stimulate weld cracks and acquiring magneto-optical images of cracks by a magneto-optical sensor was used. Theoretical analysis and experimental verification were carried out. The dynamic magneto-optical images under different excitation intensities of rotating magnetic field were obtained. According to the principle of magneto-optical imaging and the theory of rotating magnetic field, the gray value of the obtained data was compared and analyzed. Experimental results show that, under the power frequency excitation of rotating magnetic field, any frame of magneto-optical images will change with the going of excitation time. Taking original three frames as a cycle, each frame of magneto-optical images converts to next frame magneto-optical image in turn. It returns to the initial state after 885 frames of magneto-optical images. The discovery of this law is beneficial to reduce the effective excitation time and improve the effect of non-destructive testing of weld defects.
In order to study magneto-optical imaging (MOI) law of weld cracks under the excitation of rotating magnetic field, the method of using rotating magneto magnetic field to stimulate weld cracks and acquiring magneto-optical images of cracks by a magneto-optical sensor was used. Theoretical analysis and experimental verification were carried out. The dynamic magneto-optical images under different excitation intensities of rotating magnetic field were obtained. According to the principle of magneto-optical imaging and the theory of rotating magnetic field, the gray value of the obtained data was compared and analyzed. Experimental results show that, under the power frequency excitation of rotating magnetic field, any frame of magneto-optical images will change with the going of excitation time. Taking original three frames as a cycle, each frame of magneto-optical images converts to next frame magneto-optical image in turn. It returns to the initial state after 885 frames of magneto-optical images. The discovery of this law is beneficial to reduce the effective excitation time and improve the effect of non-destructive testing of weld defects.
2018, 42(6): 785-789.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.011
Abstract:
The current side-view imaging alignment method for polarization-maintaining fiber depended on the specific light intensity distribution, and had strict requirements on the position adjustment of the imaging plane. In order to improve the sensitivity of the fixed axis, increase the universality of the method and improve the stability of the fixed axis, a double-beam light source was used to replace the single-beam light source for the side-view imaging of the polarization maintaining fiber. The idea of finding the intensity distribution of the specific morphology by adjusting the image plane was changed. After theoretical analysis, simulation and experimental verification, the results show that, when using double-beam light source for side-view imaging, the light intensity distribution has bimodal pattern, and the sum of the bimodal light intensity values is selected as the eigenvalue to establish the corresponding relationship between the eigenvalue and the deflection angle. The deflection angle can be determined by cross-correlation analysis. This method not only maintains the advantages of wide range of imaging planes of polarization observation by the lens effect tracing(POL), but also has an axis sensitivity of 11.88% better than the single-beam side-view imaging alignment method. This method has good application prospects.
The current side-view imaging alignment method for polarization-maintaining fiber depended on the specific light intensity distribution, and had strict requirements on the position adjustment of the imaging plane. In order to improve the sensitivity of the fixed axis, increase the universality of the method and improve the stability of the fixed axis, a double-beam light source was used to replace the single-beam light source for the side-view imaging of the polarization maintaining fiber. The idea of finding the intensity distribution of the specific morphology by adjusting the image plane was changed. After theoretical analysis, simulation and experimental verification, the results show that, when using double-beam light source for side-view imaging, the light intensity distribution has bimodal pattern, and the sum of the bimodal light intensity values is selected as the eigenvalue to establish the corresponding relationship between the eigenvalue and the deflection angle. The deflection angle can be determined by cross-correlation analysis. This method not only maintains the advantages of wide range of imaging planes of polarization observation by the lens effect tracing(POL), but also has an axis sensitivity of 11.88% better than the single-beam side-view imaging alignment method. This method has good application prospects.
2018, 42(6): 790-795.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.012
Abstract:
Laser drilling can significantly improve cigarette quality, such as total ventilation rate and draw resistance of cigarettes and satisfy consumers' sensory experience. In order to obtain the best combination of laser drilling parameters, the relationship equation between laser drilling parameters and draw resistance was explored by using full factor experiment method on the premise of the fixed absorption index. The results show that pulse width is more significant than the other two factors (power and offset hole size). When the three factors change one unit at the same time, pulse width contributes the most influence on draw resistance, about 10 times that of power and offset hole size. In order to reduce draw resistance, the three main factors should be as large as possible. The interaction between power and offset hole size is more significant than the interaction among other factors. The study provides statistical basis for quality control of draw resistance, and the method of analyzing problems also provides the reference for other similar experiments.
Laser drilling can significantly improve cigarette quality, such as total ventilation rate and draw resistance of cigarettes and satisfy consumers' sensory experience. In order to obtain the best combination of laser drilling parameters, the relationship equation between laser drilling parameters and draw resistance was explored by using full factor experiment method on the premise of the fixed absorption index. The results show that pulse width is more significant than the other two factors (power and offset hole size). When the three factors change one unit at the same time, pulse width contributes the most influence on draw resistance, about 10 times that of power and offset hole size. In order to reduce draw resistance, the three main factors should be as large as possible. The interaction between power and offset hole size is more significant than the interaction among other factors. The study provides statistical basis for quality control of draw resistance, and the method of analyzing problems also provides the reference for other similar experiments.
2018, 42(6): 796-800.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.013
Abstract:
In order to study evolution of C2, emission characteristics of C2 and C+ in graphite plasma were studied through intensified CCD direct imaging method at various air pressures.Graphite plasma was produced by Nd:YAG laser, the launch positions of C2 and C+ were distinguished through a narrow band-pass filter. At low pressure of 10-2Pa and 3Pa, emission peak of C2 is located near the target and the formation of C2 is mainly generated by direct emission of target material. With the increase of gas pressure to 50Pa, another emission peak of C2 appears at the front of plasma plume due to the enhancement of gas phase recombination reaction. This peak position is consistent with the C+ and then becomes the dominant of C2 emission. The formation of C2 mainly comes from the recombination reaction. The emission intensity of C+ is larger than that of C2. With the increase of pressure to 130Pa, gas phase recombination reaction increases and emission intensity of C2 increases at the front of the plasma. After 1.3μs, the emission intensity of C2 is greater than that of C+. The results show that C2 emission peak position and intensity change significantly with the pressure. The result is helpful for the study of the principle of carbon nanomaterials deposited by carbon plasma.
In order to study evolution of C2, emission characteristics of C2 and C+ in graphite plasma were studied through intensified CCD direct imaging method at various air pressures.Graphite plasma was produced by Nd:YAG laser, the launch positions of C2 and C+ were distinguished through a narrow band-pass filter. At low pressure of 10-2Pa and 3Pa, emission peak of C2 is located near the target and the formation of C2 is mainly generated by direct emission of target material. With the increase of gas pressure to 50Pa, another emission peak of C2 appears at the front of plasma plume due to the enhancement of gas phase recombination reaction. This peak position is consistent with the C+ and then becomes the dominant of C2 emission. The formation of C2 mainly comes from the recombination reaction. The emission intensity of C+ is larger than that of C2. With the increase of pressure to 130Pa, gas phase recombination reaction increases and emission intensity of C2 increases at the front of the plasma. After 1.3μs, the emission intensity of C2 is greater than that of C+. The results show that C2 emission peak position and intensity change significantly with the pressure. The result is helpful for the study of the principle of carbon nanomaterials deposited by carbon plasma.
2018, 42(6): 801-805.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.014
Abstract:
In order to study the application of ultrasonic wave induced by line-source pulse laser on surface crack detection of the coated metal plate, finite element simulation method was used to establish the model of metal plate with cracks with and without nickel coating. Rayleigh wave excited by laser and the propagation process of Rayleigh wave were simulated. Through theoretical analysis of waveform at the receiving point, the relationship of coating thickness, crack depth and Rayleigh wave time-frequency domain signal was obtained. The numerical results show that Rayleigh wave velocity varies with the thickness of coating thickness h. When there are cracks on the surface, the arriving time difference Δt between reflection Rayleigh wave and shear Rayleigh wave of the model without coating has linear relationship with crack depth hc. Δt of the model with coating has linear relationship with crack depth hc at different segmentations. The numerical results provide reference for actual measurement of the surface crack depth of metal sheets with coating.
In order to study the application of ultrasonic wave induced by line-source pulse laser on surface crack detection of the coated metal plate, finite element simulation method was used to establish the model of metal plate with cracks with and without nickel coating. Rayleigh wave excited by laser and the propagation process of Rayleigh wave were simulated. Through theoretical analysis of waveform at the receiving point, the relationship of coating thickness, crack depth and Rayleigh wave time-frequency domain signal was obtained. The numerical results show that Rayleigh wave velocity varies with the thickness of coating thickness h. When there are cracks on the surface, the arriving time difference Δt between reflection Rayleigh wave and shear Rayleigh wave of the model without coating has linear relationship with crack depth hc. Δt of the model with coating has linear relationship with crack depth hc at different segmentations. The numerical results provide reference for actual measurement of the surface crack depth of metal sheets with coating.
2018, 42(6): 806-810.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.015
Abstract:
In order to study the feasibility that laser technology was used to distinguish different metallographic structures, two different metallographic structures of pearlite + ferrite and martensite were obtained by different heat treatment methods. The suitable laser pulse energy was chosen, and the relationship between breakdown spectral line strength induced by laser and metallographic group was analyzed and compared. The principal component analysis was used to distinguish the different metallographic structures. The experimental results show that the spectral line intensity of different metallographic structures is different. The spectral line intensity of pearlite + ferrite structure is larger. The difference of spectral line strength with matrix element Fe is larger than that with matrix element alloy Mn. Different metallographic structures show certain distribution characteristics. Principal component analysis method can distinguish the different metallographic structures. The distinguishing result is the best in wavelength range of 280nm~320nm. This study proves that laser technology has the ability to distinguish different metallographic structures.
In order to study the feasibility that laser technology was used to distinguish different metallographic structures, two different metallographic structures of pearlite + ferrite and martensite were obtained by different heat treatment methods. The suitable laser pulse energy was chosen, and the relationship between breakdown spectral line strength induced by laser and metallographic group was analyzed and compared. The principal component analysis was used to distinguish the different metallographic structures. The experimental results show that the spectral line intensity of different metallographic structures is different. The spectral line intensity of pearlite + ferrite structure is larger. The difference of spectral line strength with matrix element Fe is larger than that with matrix element alloy Mn. Different metallographic structures show certain distribution characteristics. Principal component analysis method can distinguish the different metallographic structures. The distinguishing result is the best in wavelength range of 280nm~320nm. This study proves that laser technology has the ability to distinguish different metallographic structures.
2018, 42(6): 811-816.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.016
Abstract:
In order to improve the design feasibility of receiving system for an airborne laser rangefinder, the maximum allowable input noise level was analyzed according to the parameters of the maximum range and signal-to-noise ratio threshold. Noise was closely related to the sensitivity of laser reception. Based on laser ranging equation, the relationship between the minimum detection sensitivity and detection range was analyzed. The characteristics of echo spectrum, the bandwidth of detection module and amplifier were simulated. The magnification of echo signal and the value of output signal of main amplifier were calculated. At the same time, according to Gaussian white noise model and output signal value of main amplifier, the maximum allowable input noise value of laser ranging receiving circuit was calculated. The circuit was designed and tested. The results show that the deviation between laser reception sensitivity and theoretical value is 5.7%. The deviation between the maximum value of extinction ratio method and the theoretical value is only 1.5%. The method of noise analysis has important guiding significance for the design of receiving system of airborne long-range laser range-finders.
In order to improve the design feasibility of receiving system for an airborne laser rangefinder, the maximum allowable input noise level was analyzed according to the parameters of the maximum range and signal-to-noise ratio threshold. Noise was closely related to the sensitivity of laser reception. Based on laser ranging equation, the relationship between the minimum detection sensitivity and detection range was analyzed. The characteristics of echo spectrum, the bandwidth of detection module and amplifier were simulated. The magnification of echo signal and the value of output signal of main amplifier were calculated. At the same time, according to Gaussian white noise model and output signal value of main amplifier, the maximum allowable input noise value of laser ranging receiving circuit was calculated. The circuit was designed and tested. The results show that the deviation between laser reception sensitivity and theoretical value is 5.7%. The deviation between the maximum value of extinction ratio method and the theoretical value is only 1.5%. The method of noise analysis has important guiding significance for the design of receiving system of airborne long-range laser range-finders.
2018, 42(6): 817-821.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.017
Abstract:
In order to realize real-time, high efficiency and high precision measurement of wall thickness of a polyethylene terephthalate (PET) bottle, through theoretical simulation and experimental verification, taking a PET bottle in 3.5mm thick as an example, the optical model for measuring the wall thickness of the PET bottle was set up. According to the principle of ray tracing, the feasibility of applying reflective fiber optic displacement sensor to measure the wall thickness of a PET bottle was proved. The simulation was carried out by LIGHTTOOLS software. Finally, a device based on reflective optical fiber displacement sensor to measure the wall thickness of PET bottle was designed and verified by experiment. The results show that, the measurement range is 3.20mm~3.80mm, the linearity is 15.8% and the sensitivity is 0.8448mV/μm. Compared with the traditional measurement method, the measurement efficiency of the experimental device will be increased more than 30%. The study has reference value for improving the efficiency and accuracy of actual detection.
In order to realize real-time, high efficiency and high precision measurement of wall thickness of a polyethylene terephthalate (PET) bottle, through theoretical simulation and experimental verification, taking a PET bottle in 3.5mm thick as an example, the optical model for measuring the wall thickness of the PET bottle was set up. According to the principle of ray tracing, the feasibility of applying reflective fiber optic displacement sensor to measure the wall thickness of a PET bottle was proved. The simulation was carried out by LIGHTTOOLS software. Finally, a device based on reflective optical fiber displacement sensor to measure the wall thickness of PET bottle was designed and verified by experiment. The results show that, the measurement range is 3.20mm~3.80mm, the linearity is 15.8% and the sensitivity is 0.8448mV/μm. Compared with the traditional measurement method, the measurement efficiency of the experimental device will be increased more than 30%. The study has reference value for improving the efficiency and accuracy of actual detection.
2018, 42(6): 822-826.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.018
Abstract:
In order to realize dynamic scanning of beam in space, matasurface based solid plasma was designed. Phase compensation of 0°~360° was realized by splicing phase curve of array element of dielectric substrate with different thickness. The mapping between matasurface parameter and phase compensation angle was established by numerical interpolation. The results show that the reflecting main beam direction of the metasurface is θ=15°, θ=25° and θ=30° respectively. The calculated results are in agreement with the designed results. Array elements are reconstructed by changing the excitation region of solid plasma, and dynamic scanning of the beam in the space is achieved in the space of θ=15°, θ=25° and θ=30°. The universal design method of reflective matasurface array unit reduces the design difficulty of array unit, and realizes the design of space beam scanning matasurface by the tunable characteristic of solid plasma.
In order to realize dynamic scanning of beam in space, matasurface based solid plasma was designed. Phase compensation of 0°~360° was realized by splicing phase curve of array element of dielectric substrate with different thickness. The mapping between matasurface parameter and phase compensation angle was established by numerical interpolation. The results show that the reflecting main beam direction of the metasurface is θ=15°, θ=25° and θ=30° respectively. The calculated results are in agreement with the designed results. Array elements are reconstructed by changing the excitation region of solid plasma, and dynamic scanning of the beam in the space is achieved in the space of θ=15°, θ=25° and θ=30°. The universal design method of reflective matasurface array unit reduces the design difficulty of array unit, and realizes the design of space beam scanning matasurface by the tunable characteristic of solid plasma.
2018, 42(6): 827-834.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.019
Abstract:
In order to solve the problem that laser transmission was difficult to connect polystyrene and titanium, polystyrene treated with oxygen plasma was used for laser transmission connection with thin titanium treated by laser surface treatment. Mathematical model of laser transmission connection process parameters was established, and interactive influence of process parameters on connection strength was analyzed. The optimized process parameters were obtained. The results show that the bonding strength of polystyrene and thin titanium after treatment increases from 0.5MPa to more than 6.0MPa. Laser transmission connection problem of polystyrene and titanium can effectively be solved. The combination of the optimum process parameters can be obtained by optimizing the process parameters. The research makes the foundation for industrial application of the process.
In order to solve the problem that laser transmission was difficult to connect polystyrene and titanium, polystyrene treated with oxygen plasma was used for laser transmission connection with thin titanium treated by laser surface treatment. Mathematical model of laser transmission connection process parameters was established, and interactive influence of process parameters on connection strength was analyzed. The optimized process parameters were obtained. The results show that the bonding strength of polystyrene and thin titanium after treatment increases from 0.5MPa to more than 6.0MPa. Laser transmission connection problem of polystyrene and titanium can effectively be solved. The combination of the optimum process parameters can be obtained by optimizing the process parameters. The research makes the foundation for industrial application of the process.
2018, 42(6): 835-839.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.020
Abstract:
In order to solve the problems, such as aberration in spectrum beam combining (SBC) of external cavity of fiber lasers and insufficient feedback of light emitting units, separating the collimation and focusing function of a single transmission lens in a beam combining system instead of multiple lenses, an external cavity feedback system for an optical fiber laser was set up. Laser wavelength was locked. Through theoretical analysis and experimental verification, the result shows that, optical-optical efficiency is 91.5%, output line width of feedback is 0.16nm, output power is 29.7W, M2 in beam combining direction is 1.241, and M2 of non beam combining direction is 1.171. Experimental results are in agreement with theoretical analysis. The external cavity feedback scheme can be applied to spectrum beam combining of fiber lasers.
In order to solve the problems, such as aberration in spectrum beam combining (SBC) of external cavity of fiber lasers and insufficient feedback of light emitting units, separating the collimation and focusing function of a single transmission lens in a beam combining system instead of multiple lenses, an external cavity feedback system for an optical fiber laser was set up. Laser wavelength was locked. Through theoretical analysis and experimental verification, the result shows that, optical-optical efficiency is 91.5%, output line width of feedback is 0.16nm, output power is 29.7W, M2 in beam combining direction is 1.241, and M2 of non beam combining direction is 1.171. Experimental results are in agreement with theoretical analysis. The external cavity feedback scheme can be applied to spectrum beam combining of fiber lasers.
2018, 42(6): 840-844.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.021
Abstract:
In order to design micro-bottles with best sensing characteristics, such as high Q value and low mode volume, mode characteristics and refractive index sensing characteristics of quartz capillary micro-bottles were studied by means of finite element numerical analysis. The influence of different surface curvatures on mode characteristics of echo wall of hollow core and liquid core micro-bottles, including quality factor and percentage of core energy, was calculated and analyzed. The variation of resonance wave length with surface curvature in refractive index sensing application was also discussed. The results show that the 2nd tangential order mode is more affected by curvature of inner wall. Q value is up to 108 when curvature square of inner wall Δk22=0.008. The smaller the inner wall surface curvature is, the greater the energy of core percentage is. High sensitivity refractive index can be realized by the smaller curvature of inner wall. This study provides an effective basis for further development and application of high Q value microbottles in sensing field. It has certain theoretical reference value.
In order to design micro-bottles with best sensing characteristics, such as high Q value and low mode volume, mode characteristics and refractive index sensing characteristics of quartz capillary micro-bottles were studied by means of finite element numerical analysis. The influence of different surface curvatures on mode characteristics of echo wall of hollow core and liquid core micro-bottles, including quality factor and percentage of core energy, was calculated and analyzed. The variation of resonance wave length with surface curvature in refractive index sensing application was also discussed. The results show that the 2nd tangential order mode is more affected by curvature of inner wall. Q value is up to 108 when curvature square of inner wall Δk22=0.008. The smaller the inner wall surface curvature is, the greater the energy of core percentage is. High sensitivity refractive index can be realized by the smaller curvature of inner wall. This study provides an effective basis for further development and application of high Q value microbottles in sensing field. It has certain theoretical reference value.
2018, 42(6): 845-848.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.022
Abstract:
In order to improve the surface strength and hardness of the material, laser cladding technology was used to clad the alloy coating on the surface of the material to improve its surface properties. Nickel-based (Ni60) composite coating was prepared by laser cladding on the surface of material under the same laser power at different laser scanning speeds, and the processing parameters for obtaining the ideal cladding layer on the surface of the substrate were obtained. The properties of the cladding layer were detected. The results show that, with the increase of the laser scanning rate, the surface roughness becomes larger, the width, height of cladding layer and the melting depth of the substrate are reduced to a certain extent. The cracks appear to increase. The microhardness of the cladding layer is about 500HV higher than that of the substrate. The laser cladding technique can realize the hardening of substrate surface in a certain range. The results provide a reference for the study of surface strengthening of materials.
In order to improve the surface strength and hardness of the material, laser cladding technology was used to clad the alloy coating on the surface of the material to improve its surface properties. Nickel-based (Ni60) composite coating was prepared by laser cladding on the surface of material under the same laser power at different laser scanning speeds, and the processing parameters for obtaining the ideal cladding layer on the surface of the substrate were obtained. The properties of the cladding layer were detected. The results show that, with the increase of the laser scanning rate, the surface roughness becomes larger, the width, height of cladding layer and the melting depth of the substrate are reduced to a certain extent. The cracks appear to increase. The microhardness of the cladding layer is about 500HV higher than that of the substrate. The laser cladding technique can realize the hardening of substrate surface in a certain range. The results provide a reference for the study of surface strengthening of materials.
2018, 42(6): 849-853.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.023
Abstract:
In order to realize high-speed demodulation of fiber Bragg grating(FBG) temperature sensors, a high-speed demodulation system of FBG temperature sensor based on field-programmable gate array and small spectrometer module was adopted. Near infrared broadband light radiation from an amplified spontaneous emission light source was used to irradiate the FBG temperature sensor. Center wavelength of the reflective light was determined by Gaussian fitting peak-seeking algorithm. Demodulation method of ambient temperature was determined by center wavelength offset. After theoretical analysis and experimental verification, the results show that high-speed temperature measurement with demodulation velocity of 20kHz and temperature sensitivity of 12.49pm/℃ is completed within the range of 30℃~60℃. High-speed demodulation of FBG temperature sensors is realized.
In order to realize high-speed demodulation of fiber Bragg grating(FBG) temperature sensors, a high-speed demodulation system of FBG temperature sensor based on field-programmable gate array and small spectrometer module was adopted. Near infrared broadband light radiation from an amplified spontaneous emission light source was used to irradiate the FBG temperature sensor. Center wavelength of the reflective light was determined by Gaussian fitting peak-seeking algorithm. Demodulation method of ambient temperature was determined by center wavelength offset. After theoretical analysis and experimental verification, the results show that high-speed temperature measurement with demodulation velocity of 20kHz and temperature sensitivity of 12.49pm/℃ is completed within the range of 30℃~60℃. High-speed demodulation of FBG temperature sensors is realized.
2018, 42(6): 854-858.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.024
Abstract:
In order to reduce the influence of background on detection results of infrared small targets and reduce false alarm rate, infrared background suppression algorithm based on guidance filter and fuzzy algorithm was adopted. The infrared image was decomposed into low-pass band and band-pass band by using multi-scale and multi-direction decomposition mechanism of non sampled contour. The guided filter was used to process low-pass sub-band to smooth images, suppress noise and enhance background details. Band-pass sub-band was processed by fuzzy algorithm to seperate the target from the residual background. Background suppression image was obtained by changing subband images through non subsampled contour inversion. The results show that, the method can reduce mean square error to 5~10, and effectively suppress the background and highlight the target. This study provides the support for improving the detection accuracy of infrared small targets in complex background.
In order to reduce the influence of background on detection results of infrared small targets and reduce false alarm rate, infrared background suppression algorithm based on guidance filter and fuzzy algorithm was adopted. The infrared image was decomposed into low-pass band and band-pass band by using multi-scale and multi-direction decomposition mechanism of non sampled contour. The guided filter was used to process low-pass sub-band to smooth images, suppress noise and enhance background details. Band-pass sub-band was processed by fuzzy algorithm to seperate the target from the residual background. Background suppression image was obtained by changing subband images through non subsampled contour inversion. The results show that, the method can reduce mean square error to 5~10, and effectively suppress the background and highlight the target. This study provides the support for improving the detection accuracy of infrared small targets in complex background.
2018, 42(6): 859-861.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.025
Abstract:
In order to solve the deficiency of the traditional evaluation method of beam parameter product on laser beam quality, based on the characteristics of semiconductor laser beam, the effective focal length data of 6 combined beams of fast axis collimator (FAC) with focal length 1100μm, 6 combined beams of FAC with focal length 600μm, and 10 combined beams of FAC with focal length 600μm were obtained. The theoretical analysis and experimental verification were carried out. The results show that the more obvious the change of L// and θ⊥ is, the more obvious the change of beam parameter product of beam quality is. The error between the measured value and the calculated value is generally less than 5%. This result is helpful for evaluating the beam quality of high energy laser.
In order to solve the deficiency of the traditional evaluation method of beam parameter product on laser beam quality, based on the characteristics of semiconductor laser beam, the effective focal length data of 6 combined beams of fast axis collimator (FAC) with focal length 1100μm, 6 combined beams of FAC with focal length 600μm, and 10 combined beams of FAC with focal length 600μm were obtained. The theoretical analysis and experimental verification were carried out. The results show that the more obvious the change of L// and θ⊥ is, the more obvious the change of beam parameter product of beam quality is. The error between the measured value and the calculated value is generally less than 5%. This result is helpful for evaluating the beam quality of high energy laser.
2018, 42(6): 862-867.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.026
Abstract:
In order to study the influence of noise on detection capability of an avalanche photodiode(APD), hyperspectral images were used to calculate radiation power and the causes and characteristics of all kinds of noise in an APD detection system were analyzed. On this basis, the factors affecting the detection capability of the system were summarized. The relationship between signal-to-noise ratio and background light power in daytime and the relationship between multiplier factor and temperature were simulated. The spectral curves of hyperspectral images were used to calculate the power of background after atmospheric turbulence, atmospheric molecules and aerosol, and then the relationship between background radiation and APD noise after atmospheric transmission was obtained. The results show that when the bias voltage is 340V and background light is enhanced from 0.07mW to 0.35mW, the effective value of noise is enhanced from 108mW to 150mW. The effective value of APD noise will be enhanced with the enhancement of the power of natural background light under the same bias voltage. When background light is 0.35mW and bias voltage is enhanced from 320V to 340V, the effective value of noise is enhanced from 23mW to 150mW. Under the same background, the effective value of noise will increase with the increase of the bias voltage, and the growth rate will gradually accelerate. Background power in a specific region can be obtained from hyperspectral images. The influence of background radiation on the APD noise characteristics is also clarified.
In order to study the influence of noise on detection capability of an avalanche photodiode(APD), hyperspectral images were used to calculate radiation power and the causes and characteristics of all kinds of noise in an APD detection system were analyzed. On this basis, the factors affecting the detection capability of the system were summarized. The relationship between signal-to-noise ratio and background light power in daytime and the relationship between multiplier factor and temperature were simulated. The spectral curves of hyperspectral images were used to calculate the power of background after atmospheric turbulence, atmospheric molecules and aerosol, and then the relationship between background radiation and APD noise after atmospheric transmission was obtained. The results show that when the bias voltage is 340V and background light is enhanced from 0.07mW to 0.35mW, the effective value of noise is enhanced from 108mW to 150mW. The effective value of APD noise will be enhanced with the enhancement of the power of natural background light under the same bias voltage. When background light is 0.35mW and bias voltage is enhanced from 320V to 340V, the effective value of noise is enhanced from 23mW to 150mW. Under the same background, the effective value of noise will increase with the increase of the bias voltage, and the growth rate will gradually accelerate. Background power in a specific region can be obtained from hyperspectral images. The influence of background radiation on the APD noise characteristics is also clarified.
2018, 42(6): 868-872.
doi: 10.7510/jgjs.issn.1001-3806.2018.06.027
Abstract:
In order to solve the contradiction between control precision and overshoot in the application of traditional proportional-integration-differential (PID) controller in fine pointer of beam (FPB), and make it applicable to the hardware platform of the existing control system, one composite PID controller was designed. The controller was composed of traditional PID, feed forward compensation and anti-integral saturation algorithm. Without increasing the complexity and the processing time of the controller significantly, the composite controller shortened adjustment time and overshoot, and improved pointing accuracy and dynamic characteristics of FPB system. The structure of the composite controller was analyzed and was compared with traditional PID controller of FPB. The results show that, under the same experimental conditions, the adjusting time of FPB system with composite PID controller is shortened by 11.4% and the maximum overshoot is reduced from 12.7% to 1.8% compared with FPB system with traditional PID controller. In the existing control system platform with limited computing power, the performance of FPB system can be effectively improved by using composite PID controller.
In order to solve the contradiction between control precision and overshoot in the application of traditional proportional-integration-differential (PID) controller in fine pointer of beam (FPB), and make it applicable to the hardware platform of the existing control system, one composite PID controller was designed. The controller was composed of traditional PID, feed forward compensation and anti-integral saturation algorithm. Without increasing the complexity and the processing time of the controller significantly, the composite controller shortened adjustment time and overshoot, and improved pointing accuracy and dynamic characteristics of FPB system. The structure of the composite controller was analyzed and was compared with traditional PID controller of FPB. The results show that, under the same experimental conditions, the adjusting time of FPB system with composite PID controller is shortened by 11.4% and the maximum overshoot is reduced from 12.7% to 1.8% compared with FPB system with traditional PID controller. In the existing control system platform with limited computing power, the performance of FPB system can be effectively improved by using composite PID controller.
