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RSS2021 Vol. 40, No. 2
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2021, 40(2): 165-171.
doi: 10.13433/j.cnki.1003-8728.20200040
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Abstract:
Based on the discrete convolution Fast Fourier Transform (DC-FFT), the frequency response function of three-dimensional thermo-elastic coating head and coating plate contact problem has been derived. The correctness of the semi-analytical solution was verified via numerical simulation method, and the relationship between the contact stress and the coating thickness of coating head and coating plate was further be discussed. The results showed that the contact pressure between the coating thickness and the surface showed a negative growth trendunder the three-dimensional thermo-elastic domain.The contact pressure on the surface decreased slowly after fastwith the increasing of coating thickness. The elastic modulus of the coating and the substrate has a linear increase with the contact pressure, the increase rate in the surface contact pressure has a great influence with the increasing of coating thickness, and the poisson′s ratio among the coating, the substrate and the heat source also has a great influence on the contact pressure.
Based on the discrete convolution Fast Fourier Transform (DC-FFT), the frequency response function of three-dimensional thermo-elastic coating head and coating plate contact problem has been derived. The correctness of the semi-analytical solution was verified via numerical simulation method, and the relationship between the contact stress and the coating thickness of coating head and coating plate was further be discussed. The results showed that the contact pressure between the coating thickness and the surface showed a negative growth trendunder the three-dimensional thermo-elastic domain.The contact pressure on the surface decreased slowly after fastwith the increasing of coating thickness. The elastic modulus of the coating and the substrate has a linear increase with the contact pressure, the increase rate in the surface contact pressure has a great influence with the increasing of coating thickness, and the poisson′s ratio among the coating, the substrate and the heat source also has a great influence on the contact pressure.
2021, 40(2): 172-180.
doi: 10.13433/j.cnki.1003-8728.20200054
Abstract:
In order to further improve the vibration isolation performance of the vehicle seat suspension, a seat suspension system with quasi-zero stiffness is designed by using the negative stiffness structure of the connecting rod spring and the positive stiffness elastic element in parallel. Based on the multi-objective parameter coordination optimization principle, the structural parameters are optimized, and the optimal value for making the seat suspension dynamic stiffness tend to quasi-zero stiffness is obtained. The effectiveness of the seat suspension vibration isolation system is verified by the dynamic response analysis of the seat suspension vibration isolation system and the simulation experiment. The research results show that the seat suspension system with the negative stiffness of the connecting rod spring can effectively improve the vibration isolation effect of the seat, and can reduce the natural frequency of the system itself, and achieve low frequency and ultra low frequency vibration isolation.
In order to further improve the vibration isolation performance of the vehicle seat suspension, a seat suspension system with quasi-zero stiffness is designed by using the negative stiffness structure of the connecting rod spring and the positive stiffness elastic element in parallel. Based on the multi-objective parameter coordination optimization principle, the structural parameters are optimized, and the optimal value for making the seat suspension dynamic stiffness tend to quasi-zero stiffness is obtained. The effectiveness of the seat suspension vibration isolation system is verified by the dynamic response analysis of the seat suspension vibration isolation system and the simulation experiment. The research results show that the seat suspension system with the negative stiffness of the connecting rod spring can effectively improve the vibration isolation effect of the seat, and can reduce the natural frequency of the system itself, and achieve low frequency and ultra low frequency vibration isolation.
2021, 40(2): 181-187.
doi: 10.13433/j.cnki.1003-8728.20200087
Abstract:
The motion characteristics of the fluid boundary layer have an important influence on the change of the energy exchange coefficient of the pipeline. The self-excited oscillation chamber is divided based on the time-averaged division, and the flow velocity change of the boundary layer in the shear layer of the pulse jet is analyzed. The wall heat transfer performance is expressed by the fluid flow velocity and Nusselt number, and the evolution law of shear eddy current in the self-excited oscillation chamber is analyzed. Combined with the finite element model of the self-excited oscillation chamber, the large eddy simulation numerical method is used to analyze the evolution of the eddy current in the intercept layer and its influence on heat transfer. The near-wall flow velocity and Nusselt number of the boundary layer of the hot runner under the ratio of the length of the outlet tube of the self-vibrating chamber to the length of the self-vibrating chamber are calculated. The results show that the shear layer jet generates a backflow vortex after colliding with the wall surface, and continues to move downward along the pipeline, and repeats this process many times during the downstream pipeline′s continued motion, breaking the boundary layer and maintaining the large-scale quasi-sequence vortex. The heat transfer effect of the pipeline is enhanced under the stability of the vortex core of the structure. The results show that the ratio of the length of the outlet tube of the self-vibrating chamber to the length of the self-vibrating cavity can control the development of the pulsating shear layer. As the ratio increases, the strength of the wall turbulence first increases and then decreases. When the ratio is greater than 1.6, the turbulence intensity begins to decrease, and the overall performance coefficient can be increased by 12% to 35.5% when the ratio is in the range of 1.2 to 1.6.
The motion characteristics of the fluid boundary layer have an important influence on the change of the energy exchange coefficient of the pipeline. The self-excited oscillation chamber is divided based on the time-averaged division, and the flow velocity change of the boundary layer in the shear layer of the pulse jet is analyzed. The wall heat transfer performance is expressed by the fluid flow velocity and Nusselt number, and the evolution law of shear eddy current in the self-excited oscillation chamber is analyzed. Combined with the finite element model of the self-excited oscillation chamber, the large eddy simulation numerical method is used to analyze the evolution of the eddy current in the intercept layer and its influence on heat transfer. The near-wall flow velocity and Nusselt number of the boundary layer of the hot runner under the ratio of the length of the outlet tube of the self-vibrating chamber to the length of the self-vibrating chamber are calculated. The results show that the shear layer jet generates a backflow vortex after colliding with the wall surface, and continues to move downward along the pipeline, and repeats this process many times during the downstream pipeline′s continued motion, breaking the boundary layer and maintaining the large-scale quasi-sequence vortex. The heat transfer effect of the pipeline is enhanced under the stability of the vortex core of the structure. The results show that the ratio of the length of the outlet tube of the self-vibrating chamber to the length of the self-vibrating cavity can control the development of the pulsating shear layer. As the ratio increases, the strength of the wall turbulence first increases and then decreases. When the ratio is greater than 1.6, the turbulence intensity begins to decrease, and the overall performance coefficient can be increased by 12% to 35.5% when the ratio is in the range of 1.2 to 1.6.
2021, 40(2): 188-192.
doi: 10.13433/j.cnki.1003-8728.20200036
Abstract:
Industrial robots are widely used in the processing of large and complex parts. In this paper, for the problem of robot milling chatter identification, the variational mode decomposition-continuous wavelet transform (VMD-CWT) method is used to process the vibration signal collected during processing, and the denoising time-frequency spectrums are constructed to characterize the robot vibration states and used as the input of the identification model. The residual convolution network (ResNet) is used to identify the spectrums, and the convergence speed and prediction accuracy of the model are improved by determining the decomposition scale of wavelet transform and introducing input normalization. The prediction accuracy of the optimized model can reach 95.28%.The vibration state identification of the time-frequency spectrum graph is realized offline.
Industrial robots are widely used in the processing of large and complex parts. In this paper, for the problem of robot milling chatter identification, the variational mode decomposition-continuous wavelet transform (VMD-CWT) method is used to process the vibration signal collected during processing, and the denoising time-frequency spectrums are constructed to characterize the robot vibration states and used as the input of the identification model. The residual convolution network (ResNet) is used to identify the spectrums, and the convergence speed and prediction accuracy of the model are improved by determining the decomposition scale of wavelet transform and introducing input normalization. The prediction accuracy of the optimized model can reach 95.28%.The vibration state identification of the time-frequency spectrum graph is realized offline.
2021, 40(2): 193-197.
doi: 10.13433/j.cnki.1003-8728.20200032
Abstract:
Downhole turbogenerator is one of the most common downhole power supply. Solid phase of drilling fluid will affect the performance of downhole turbogenerator. Based on Eulerian multiphase flow model and Fluent software, three-dimensional numerical simulation of the downhole turbogenerator is carried out. The effects of the solid content, particle size and solid density of drilling fluid on the performance of downhole turbine generator are studied. The simulation results show that the pressure drop, torque, input and output power and efficiency of the turbogenerator increasewith the increasing of solid phase content, the pressure drop, torque, input and output power of the turbogenerator increase firstly and stabilizewith the increasing of solid particle size, while the efficiency increases gradually with the increasing of solid particle size, the pressure drop, torque, input and output power and efficiency of the turbogenerator increase linearlywith the increasing of solid density and the increase in efficiency decreases gradually with the increasing of solid particle size.
Downhole turbogenerator is one of the most common downhole power supply. Solid phase of drilling fluid will affect the performance of downhole turbogenerator. Based on Eulerian multiphase flow model and Fluent software, three-dimensional numerical simulation of the downhole turbogenerator is carried out. The effects of the solid content, particle size and solid density of drilling fluid on the performance of downhole turbine generator are studied. The simulation results show that the pressure drop, torque, input and output power and efficiency of the turbogenerator increasewith the increasing of solid phase content, the pressure drop, torque, input and output power of the turbogenerator increase firstly and stabilizewith the increasing of solid particle size, while the efficiency increases gradually with the increasing of solid particle size, the pressure drop, torque, input and output power and efficiency of the turbogenerator increase linearlywith the increasing of solid density and the increase in efficiency decreases gradually with the increasing of solid particle size.
2021, 40(2): 198-203.
doi: 10.13433/j.cnki.1003-8728.20200039
Abstract:
This paperuses the Chirplet integration method totransform the time-varying differential equations into interval linear equations by reconstructing the structural velocity and displacement response when the acceleration response is measured. Then the physical parameters of the time-varyingsystem are identified based on the least squares algorithm. The Chirplet basis function is suitable for processing time-varying signals since it fits the time-varying system′s response in a short interval. Compared with the traditional wavelet, it tracks better the frequency variation of signals. It also improves the time-varying parameter identification efficiency by combining differential equations. The validity and applicability of the method is verified with a 3-DOF time-varying structure model.
This paperuses the Chirplet integration method totransform the time-varying differential equations into interval linear equations by reconstructing the structural velocity and displacement response when the acceleration response is measured. Then the physical parameters of the time-varyingsystem are identified based on the least squares algorithm. The Chirplet basis function is suitable for processing time-varying signals since it fits the time-varying system′s response in a short interval. Compared with the traditional wavelet, it tracks better the frequency variation of signals. It also improves the time-varying parameter identification efficiency by combining differential equations. The validity and applicability of the method is verified with a 3-DOF time-varying structure model.
2021, 40(2): 204-210.
doi: 10.13433/j.cnki.1003-8728.20200042
Abstract:
The mathematical model of gait curves with the same control points for three lower limb joints was proposed, and the shape parameters were used to distinguish different curves. The gait data of a normal group (10 healthy young men) and a validation group (2 healthy and 3 young men with right ankle injuries) were measured and calculated at normal walking speed with the Perception Neuron motion capture system. Therefore, the vertical displacement trajectories of lower limb joints (hip, knee and ankle) and their shape parameters are obtained. The analysis of whether the shape parameters of the validation group belong to the adjustment range of shape parameters of the normal group shows that most of the shape parameters of the injured are beyond the adjustment range, indicating that the parametric judgment is valid and concluding that this method has reference values for identifying abnormal gaits and evaluating rehabilitation effects.
The mathematical model of gait curves with the same control points for three lower limb joints was proposed, and the shape parameters were used to distinguish different curves. The gait data of a normal group (10 healthy young men) and a validation group (2 healthy and 3 young men with right ankle injuries) were measured and calculated at normal walking speed with the Perception Neuron motion capture system. Therefore, the vertical displacement trajectories of lower limb joints (hip, knee and ankle) and their shape parameters are obtained. The analysis of whether the shape parameters of the validation group belong to the adjustment range of shape parameters of the normal group shows that most of the shape parameters of the injured are beyond the adjustment range, indicating that the parametric judgment is valid and concluding that this method has reference values for identifying abnormal gaits and evaluating rehabilitation effects.
2021, 40(2): 211-217.
doi: 10.13433/j.cnki.1003-8728.20200047
Abstract:
In order to improve the working ability of the automated guided vehicle (AGV) on the hard and flat ground with obstacles, a new type of wheel-legged AGV is designed, and the working principle of the AGV in different motion modes is explained. The kinematics analysis of the AGV in walking mode is carried out, and the working space of its foot is obtained. The motion trajectory of the foot is planned based on the maximum working range of the foot. At the same time, the trajectory of the car body is planned, and the overall walking gait of the AGV is planned based on the static stability margin principle. The motion simulation analysis of the AGV is carried out with the ADAMS. The simulation results show that the motion trajectory and walking gait planned by the scheme are feasible.
In order to improve the working ability of the automated guided vehicle (AGV) on the hard and flat ground with obstacles, a new type of wheel-legged AGV is designed, and the working principle of the AGV in different motion modes is explained. The kinematics analysis of the AGV in walking mode is carried out, and the working space of its foot is obtained. The motion trajectory of the foot is planned based on the maximum working range of the foot. At the same time, the trajectory of the car body is planned, and the overall walking gait of the AGV is planned based on the static stability margin principle. The motion simulation analysis of the AGV is carried out with the ADAMS. The simulation results show that the motion trajectory and walking gait planned by the scheme are feasible.
2021, 40(2): 218-222.
doi: 10.13433/j.cnki.1003-8728.20200092
Abstract:
Because the cooling processis too fast, the crease appears in producing hydrophilic aluminum foils due to the mismatch between cooling velocity and technical requirements when the LT1350 coated wire water cooling roller isused. To remove the crease, the air layer is employed and the Fluent software is used to numerically compare the cooling velocity of different structures of the watercoolingroller. This paper compares temperature contours and quantitative values and studies the effects of air thickness. The numerical data show that thecooling velocity of the LT1350 coated wire water cooling roller is too fast owing to the use of complete water layer and that the foil temperature falls down to the water layer when its rotating angle is 45. The air layereffectively raises the foil temperature with the increase of air thickness.The insulation effect increases while the temperature gradientdecreases. The simulation results show that the thickness of the air layer of theLT1350 coated wire water cooling roller should be 4 ~ 6 cm to satisfy the foil cooling requirements.
Because the cooling processis too fast, the crease appears in producing hydrophilic aluminum foils due to the mismatch between cooling velocity and technical requirements when the LT1350 coated wire water cooling roller isused. To remove the crease, the air layer is employed and the Fluent software is used to numerically compare the cooling velocity of different structures of the watercoolingroller. This paper compares temperature contours and quantitative values and studies the effects of air thickness. The numerical data show that thecooling velocity of the LT1350 coated wire water cooling roller is too fast owing to the use of complete water layer and that the foil temperature falls down to the water layer when its rotating angle is 45. The air layereffectively raises the foil temperature with the increase of air thickness.The insulation effect increases while the temperature gradientdecreases. The simulation results show that the thickness of the air layer of theLT1350 coated wire water cooling roller should be 4 ~ 6 cm to satisfy the foil cooling requirements.
2021, 40(2): 223-229.
doi: 10.13433/j.cnki.1003-8728.20200058
Abstract:
Under the inherent characteristics of nonlinear and non-monotonic implicit function with tremendous design variables, the corresponding computational efficiency of topology optimization must be considered. Therefore, the kernel question is to explore efficient and stable solution strategy. The solution methodology based on the proportional-integral-differential (PID) control algorithm is proposed, under the solid isotropic microstructures material penalty (SIMP) model. The structural compliance minimization topology optimization model under the condition of single working condition is established. The iterative format of the design variables of PID algorithm is illustrated, and the filter method of Helmholtz partial differential equation is introduced to suppress the numerical instability problem. Then the proposed method is extended to the multi-loading condition topology optimization problems. Through the comparison of the optimization criteria method (OC) and the moving asymptote method (MMA), the numerical results demonstrated that the PID method exhibits the property of easy implementation, efficient solution, stable convergence and non-gradient information.
Under the inherent characteristics of nonlinear and non-monotonic implicit function with tremendous design variables, the corresponding computational efficiency of topology optimization must be considered. Therefore, the kernel question is to explore efficient and stable solution strategy. The solution methodology based on the proportional-integral-differential (PID) control algorithm is proposed, under the solid isotropic microstructures material penalty (SIMP) model. The structural compliance minimization topology optimization model under the condition of single working condition is established. The iterative format of the design variables of PID algorithm is illustrated, and the filter method of Helmholtz partial differential equation is introduced to suppress the numerical instability problem. Then the proposed method is extended to the multi-loading condition topology optimization problems. Through the comparison of the optimization criteria method (OC) and the moving asymptote method (MMA), the numerical results demonstrated that the PID method exhibits the property of easy implementation, efficient solution, stable convergence and non-gradient information.
2021, 40(2): 230-236.
doi: 10.13433/j.cnki.1003-8728.20200218
Abstract:
In order to solve the problems of slow data transmission, difficulty in obtaining consumer head data, and obtained inaccurate data in the personalized custom design of the head wearable product network. According to the head features, 23 feature points was founded which could been found accurately in users themselves head. According to the feature points, the 3D model for the head is divided into different sections, and the contour curve of the section is extracted and the curve is divided into three types. The Hermite interpolation curve with free parameters is used to describe these three kinds of curves, and the parameterized head model is established with the Grasshopper software. Using the user′s orthogonal photos with patches, the measurement data of the user head is calculated, and the Grasshopper program parameters are modified to obtain the 3D parameterized model for the user's head. By taking photos of three volunteers, the results have been achieved. This method can be effectively used in the personalized design of head wearable products network.
In order to solve the problems of slow data transmission, difficulty in obtaining consumer head data, and obtained inaccurate data in the personalized custom design of the head wearable product network. According to the head features, 23 feature points was founded which could been found accurately in users themselves head. According to the feature points, the 3D model for the head is divided into different sections, and the contour curve of the section is extracted and the curve is divided into three types. The Hermite interpolation curve with free parameters is used to describe these three kinds of curves, and the parameterized head model is established with the Grasshopper software. Using the user′s orthogonal photos with patches, the measurement data of the user head is calculated, and the Grasshopper program parameters are modified to obtain the 3D parameterized model for the user's head. By taking photos of three volunteers, the results have been achieved. This method can be effectively used in the personalized design of head wearable products network.
2021, 40(2): 237-242.
doi: 10.13433/j.cnki.1003-8728.20200033
Abstract:
A turbo generator′s coil strip needs to be strictly tested after milling its both ends. Traditional artificial mechanical inspection methods are inefficient. In this paper, a vision inspection mechanism for turbo generator′s coil strip is designed. Through the power input of the conveying device, the posture correction of the correction module, the image acquisition and the algorithm processing of the inspection module, the automatic inspection of the rotor copper bar is realized, and the safety and efficiency problems of the manual detection are solved. Establishing a mathematical model to calculate the feasibility of the calibration module, ANSYS Workbench is used to simulate the contact deformation of fixture-workpiece system. Experiments is designed to verify the inspection accuracy of the mechanism. The experimental results show that the machine vision inspection mechanism can quickly and accurately correct the position of the rotor copper row and obtain high-precision size information of the coil strip slot.
A turbo generator′s coil strip needs to be strictly tested after milling its both ends. Traditional artificial mechanical inspection methods are inefficient. In this paper, a vision inspection mechanism for turbo generator′s coil strip is designed. Through the power input of the conveying device, the posture correction of the correction module, the image acquisition and the algorithm processing of the inspection module, the automatic inspection of the rotor copper bar is realized, and the safety and efficiency problems of the manual detection are solved. Establishing a mathematical model to calculate the feasibility of the calibration module, ANSYS Workbench is used to simulate the contact deformation of fixture-workpiece system. Experiments is designed to verify the inspection accuracy of the mechanism. The experimental results show that the machine vision inspection mechanism can quickly and accurately correct the position of the rotor copper row and obtain high-precision size information of the coil strip slot.
2021, 40(2): 243-248.
doi: 10.13433/j.cnki.1003-8728.20200035
Abstract:
Acoustic emission technique has the capability to provide efficient real-time knowledge and monitoring of the grinding process. Root mean square of grinding acoustic emission signal AERMS values are used to analyze the process characteristics. The acoustic emission measurement is employed for monitoring the temperature, force and studying the grindingmechanism of engineering ceramics. This paper explores the relations between the temperature, force, acoustic emission and surface roughness via the grinding of engineering ceramics. Some models for the relationship between the grinding acoustic emission signal of engineering ceramics partially stabilized zirconia and alumina and the grinding force, temperature and surface roughness areestablished. The acoustic emission monitoring in the grindingofengineering ceramics is perfected.It can be concluded that acoustic emission provides the clearest results and a common ground to predict the final surface quality and monitoring of process.
Acoustic emission technique has the capability to provide efficient real-time knowledge and monitoring of the grinding process. Root mean square of grinding acoustic emission signal AERMS values are used to analyze the process characteristics. The acoustic emission measurement is employed for monitoring the temperature, force and studying the grindingmechanism of engineering ceramics. This paper explores the relations between the temperature, force, acoustic emission and surface roughness via the grinding of engineering ceramics. Some models for the relationship between the grinding acoustic emission signal of engineering ceramics partially stabilized zirconia and alumina and the grinding force, temperature and surface roughness areestablished. The acoustic emission monitoring in the grindingofengineering ceramics is perfected.It can be concluded that acoustic emission provides the clearest results and a common ground to predict the final surface quality and monitoring of process.
2021, 40(2): 249-256.
doi: 10.13433/j.cnki.1003-8728.20200037
Abstract:
Owing to the complex internal condition of a ball mill in its grinding process, it is difficult to estimate its load state with experience alone. For the complete empirical mode decomposition (CEEMDAN) of adaptive white noise combined with sample entropy and extreme learning machine (ELM), the paper proposes a ball mill load state identification method. Firstly, the eigenmode decomposition of the original signal under different load conditions is carried out withthe CEEMDAN algorithm, and the effective IMF component is filtered with the correlation coefficient method. Then, the sample entropy of the effective IMF component of the vibration signal under three load states is analyzed for different data. The values for length, embedded dimension and similar tolerance determine the optimal parameters for calculating sample entropy. The results show that there are significant differences in the effective IMF component sample entropy of vibration signals under three load states, which can be used to effectively identify the different load states of the ball mill. The effective IMF component sample entropy of each group of signals is taken as the input of ELM and the load states of the ball mill as output, and the load state recognition model is established. The grinding test is used to verify the effectiveness of this method in theball mill load state recognition. The overall recognition rate is as high as 96.81% and increases by 12.41% compared with that of EMD-sample entropy and MEEMD-sample entropy, namely 9.01%.
Owing to the complex internal condition of a ball mill in its grinding process, it is difficult to estimate its load state with experience alone. For the complete empirical mode decomposition (CEEMDAN) of adaptive white noise combined with sample entropy and extreme learning machine (ELM), the paper proposes a ball mill load state identification method. Firstly, the eigenmode decomposition of the original signal under different load conditions is carried out withthe CEEMDAN algorithm, and the effective IMF component is filtered with the correlation coefficient method. Then, the sample entropy of the effective IMF component of the vibration signal under three load states is analyzed for different data. The values for length, embedded dimension and similar tolerance determine the optimal parameters for calculating sample entropy. The results show that there are significant differences in the effective IMF component sample entropy of vibration signals under three load states, which can be used to effectively identify the different load states of the ball mill. The effective IMF component sample entropy of each group of signals is taken as the input of ELM and the load states of the ball mill as output, and the load state recognition model is established. The grinding test is used to verify the effectiveness of this method in theball mill load state recognition. The overall recognition rate is as high as 96.81% and increases by 12.41% compared with that of EMD-sample entropy and MEEMD-sample entropy, namely 9.01%.
2021, 40(2): 257-261.
doi: 10.13433/j.cnki.1003-8728.20200056
Abstract:
According to the distribution of the neighborhood of the sample point projected in its local micro-cut plane, a hole identification method for the scattered point cloud model with uneven sampling density, complex geometry and different hole area is proposed. With the NP neighborhood, the points located in the density transition area are accurately classified; since the neighborhood of the sample points may span multiple faces, the point cloud normal vector estimated by the PCA (Principle analysis) method is inaccurate, resulting in a point error in the sharp position of the model. Judging, by introducing the distance weight, the accuracy of the local micro-cut plane calculation is guaranteed; for the neighborhood point number k is less, there are more noise points in the detection result, and the larger k value will cover the smaller of the model. Holes, through the method of neighborhood support, effectively detect small-area holes in the model. In order to facilitate the automatic repair of holes, the method of dividing spatial grid clustering is used to determine the position and number of holes, which avoids the repeated calculation of the distance between points and accelerates the clustering speed. The experimental results show that the method can effectively detect the holes with different sizes in the model, and the obtained detection results have fewer noise points and clear hole contours.
According to the distribution of the neighborhood of the sample point projected in its local micro-cut plane, a hole identification method for the scattered point cloud model with uneven sampling density, complex geometry and different hole area is proposed. With the NP neighborhood, the points located in the density transition area are accurately classified; since the neighborhood of the sample points may span multiple faces, the point cloud normal vector estimated by the PCA (Principle analysis) method is inaccurate, resulting in a point error in the sharp position of the model. Judging, by introducing the distance weight, the accuracy of the local micro-cut plane calculation is guaranteed; for the neighborhood point number k is less, there are more noise points in the detection result, and the larger k value will cover the smaller of the model. Holes, through the method of neighborhood support, effectively detect small-area holes in the model. In order to facilitate the automatic repair of holes, the method of dividing spatial grid clustering is used to determine the position and number of holes, which avoids the repeated calculation of the distance between points and accelerates the clustering speed. The experimental results show that the method can effectively detect the holes with different sizes in the model, and the obtained detection results have fewer noise points and clear hole contours.
2021, 40(2): 262-269.
doi: 10.13433/j.cnki.1003-8728.20200024
Abstract:
Aiming at the diversity and randomness of the surface defects of the metal sheet and strip, which makes it difficult to quickly locate and accurately identify, a Defect-Target Detection Network (DNN) by using Faster R-CNN with multilevel feature is proposed. This algorithm uses a Multilevel-Feature Fusion Network (MFN) to fuse the feature maps extracted from VGG-16 in Faster R-CNN to obtain fusion feature maps with rich location information and semantic information. The subsequent networks generate the final defect detection results by using the fusion feature maps. The performance of the present algorithm is evaluated by using the surface defect detection data sets of the steel strip and copper sheet. The experimental results show that the present DNN can detect multiple types of defects with different scales quickly and accurately. Comparing with Faster R-CNN, it has better detection accuracy without losing the basic requirement of excessive detection time speed. The average detection time is of 129.65 ms or 153.17 ms and the mean average precision (mAP) is of 86.13% or 92.54%.
Aiming at the diversity and randomness of the surface defects of the metal sheet and strip, which makes it difficult to quickly locate and accurately identify, a Defect-Target Detection Network (DNN) by using Faster R-CNN with multilevel feature is proposed. This algorithm uses a Multilevel-Feature Fusion Network (MFN) to fuse the feature maps extracted from VGG-16 in Faster R-CNN to obtain fusion feature maps with rich location information and semantic information. The subsequent networks generate the final defect detection results by using the fusion feature maps. The performance of the present algorithm is evaluated by using the surface defect detection data sets of the steel strip and copper sheet. The experimental results show that the present DNN can detect multiple types of defects with different scales quickly and accurately. Comparing with Faster R-CNN, it has better detection accuracy without losing the basic requirement of excessive detection time speed. The average detection time is of 129.65 ms or 153.17 ms and the mean average precision (mAP) is of 86.13% or 92.54%.
2021, 40(2): 270-275.
doi: 10.13433/j.cnki.1003-8728.20200038
Abstract:
Based on the fractional sliding mode control method, the new approximation law of sliding mode function is designed to improve the robustness and response speed of the trajectory tracking control system of a multi-joint manipulator. There are various modeling errors in the modeling process of the multi-jointmanipulator and uncertain factors such as external interference in the working process. The neural network is used to approximate various uncertainties, and the adaptive compensation term of the error in the radial basis function neural network adaptive control is proposed. The approximation error of the radial basis function neural network is reduced. The results show that the control algorithm effectively improves the tracking speed and tracking accuracy and reduces the chattering in thecontrolsystem.
Based on the fractional sliding mode control method, the new approximation law of sliding mode function is designed to improve the robustness and response speed of the trajectory tracking control system of a multi-joint manipulator. There are various modeling errors in the modeling process of the multi-jointmanipulator and uncertain factors such as external interference in the working process. The neural network is used to approximate various uncertainties, and the adaptive compensation term of the error in the radial basis function neural network adaptive control is proposed. The approximation error of the radial basis function neural network is reduced. The results show that the control algorithm effectively improves the tracking speed and tracking accuracy and reduces the chattering in thecontrolsystem.
2021, 40(2): 276-280.
doi: 10.13433/j.cnki.1003-8728.20200044
Abstract:
Because the temperature control system of burner is a time-varying, large delay and non-linear control system, it is difficult to establish an accurate mathematical model and control temperature accurately. Fuzzy PID algorithm is often used to control this kind of system. But the fuzzy PID algorithm needs experts to give the fuzzy rules and adjust the parameters, and there are errors in the process of parameter adjustment, so the control performance is often poor. In this paper, the quantization factors Ke, Kec and proportional factor Ku in the particle swarm optimization fuzzy PID algorithm are used to rapid setting parameters, and then the control system is simulated with MATLAB. The results show that the response speed of the system is faster, the overshoot is smaller and the time to reach the steady state is shorter with the fuzzy PID optimized than particle swarm optimization.
Because the temperature control system of burner is a time-varying, large delay and non-linear control system, it is difficult to establish an accurate mathematical model and control temperature accurately. Fuzzy PID algorithm is often used to control this kind of system. But the fuzzy PID algorithm needs experts to give the fuzzy rules and adjust the parameters, and there are errors in the process of parameter adjustment, so the control performance is often poor. In this paper, the quantization factors Ke, Kec and proportional factor Ku in the particle swarm optimization fuzzy PID algorithm are used to rapid setting parameters, and then the control system is simulated with MATLAB. The results show that the response speed of the system is faster, the overshoot is smaller and the time to reach the steady state is shorter with the fuzzy PID optimized than particle swarm optimization.
2021, 40(2): 281-286.
doi: 10.13433/j.cnki.1003-8728.20200041
Abstract:
In order to analyze influences of various factors on ride quality in the process of vehicle straight driving, a vertical dynamics model of high speed maglev vehicle was established based on multi-body dynamics software Simpack. After applying excitation of track harmonic irregularity, the influence of speed, irregularity wavelength and amplitude, weight of carbody and levitation bogies, suspension parameters on ride quality was studied. The simulation results in whole speed range of high speed maglev vehicle show that, different speed corresponds to different range of sensitive wavelength; with the increase of speed, the wavelength causing the dominant frequency of carbody grows, and range of sensitive wavelength expands. Besides, as the vertical irregularity amplitude increases, the vertical Sperling index rises nonlinearly, while its rising rate decreases gradually. What′s more, increasing weight of carbody and decreasing weight of levitation bogies will improve the ride quality. Furthermore, within the range of engineering application parameters, appropriately reducing primary/secondary vertical stiffness and secondary vertical damping, as well as increasing primary vertical damping, can help to improve the ride quality. Among them, the secondary suspension has greatest contribution to the ride quality.
In order to analyze influences of various factors on ride quality in the process of vehicle straight driving, a vertical dynamics model of high speed maglev vehicle was established based on multi-body dynamics software Simpack. After applying excitation of track harmonic irregularity, the influence of speed, irregularity wavelength and amplitude, weight of carbody and levitation bogies, suspension parameters on ride quality was studied. The simulation results in whole speed range of high speed maglev vehicle show that, different speed corresponds to different range of sensitive wavelength; with the increase of speed, the wavelength causing the dominant frequency of carbody grows, and range of sensitive wavelength expands. Besides, as the vertical irregularity amplitude increases, the vertical Sperling index rises nonlinearly, while its rising rate decreases gradually. What′s more, increasing weight of carbody and decreasing weight of levitation bogies will improve the ride quality. Furthermore, within the range of engineering application parameters, appropriately reducing primary/secondary vertical stiffness and secondary vertical damping, as well as increasing primary vertical damping, can help to improve the ride quality. Among them, the secondary suspension has greatest contribution to the ride quality.
2021, 40(2): 287-295.
doi: 10.13433/j.cnki.1003-8728.20200045
Abstract:
Four-wheel-drive pure electric vehicles combine the good vehicle traffic ability and dynamic performance of four-wheel drive with the environmental protection of new energy vehicles, which is conducive to improve the power and vehicle control technology of new energy electric vehicles. For the structure arrangement and torque transmission mode of vehicle power system, a comparative study andclassification on the structure, working characteristics and research hotspots of different types power systems of pure electric vehicles with wheel drive are summarized. The research results show that the distributed electric four-wheel drive technology has more advantages according to the structural arrangement, control accuracy and work efficiency. Among them, the four-wheel hub motor direct drive technology and intelligent distribution drive torque technology will become the research hotspot and development trend of distributed electric four-wheel drive technology.
Four-wheel-drive pure electric vehicles combine the good vehicle traffic ability and dynamic performance of four-wheel drive with the environmental protection of new energy vehicles, which is conducive to improve the power and vehicle control technology of new energy electric vehicles. For the structure arrangement and torque transmission mode of vehicle power system, a comparative study andclassification on the structure, working characteristics and research hotspots of different types power systems of pure electric vehicles with wheel drive are summarized. The research results show that the distributed electric four-wheel drive technology has more advantages according to the structural arrangement, control accuracy and work efficiency. Among them, the four-wheel hub motor direct drive technology and intelligent distribution drive torque technology will become the research hotspot and development trend of distributed electric four-wheel drive technology.
2021, 40(2): 296-304.
doi: 10.13433/j.cnki.1003-8728.20200034
Abstract:
The braking force distribution algorithm is the basis of electric vehicle regenerative braking research. When the electric vehicle is braking on different roads, in order to obtain better braking effect, considering the influence of road adhesion condition, an optimal distribution algorithm of braking force variable ratio is designed for electric vehicles. The vehicle dynamics equation is used to estimate the slip rate and the adhesion coefficient to realize the road condition identification. Then, for the identified road type, the corresponding braking force variable ratio distribution coefficient is selected and the algorithm is implemented. Finally, the effectiveness of the algorithm is verified by co-simulation with dSPACE software. Compared with the algorithm without considering the road adhesion condition, the braking time of electric vehicle using the new algorithm is reduced by at least 6.6%.
The braking force distribution algorithm is the basis of electric vehicle regenerative braking research. When the electric vehicle is braking on different roads, in order to obtain better braking effect, considering the influence of road adhesion condition, an optimal distribution algorithm of braking force variable ratio is designed for electric vehicles. The vehicle dynamics equation is used to estimate the slip rate and the adhesion coefficient to realize the road condition identification. Then, for the identified road type, the corresponding braking force variable ratio distribution coefficient is selected and the algorithm is implemented. Finally, the effectiveness of the algorithm is verified by co-simulation with dSPACE software. Compared with the algorithm without considering the road adhesion condition, the braking time of electric vehicle using the new algorithm is reduced by at least 6.6%.
2021, 40(2): 305-312.
doi: 10.13433/j.cnki.1003-8728.20200053
Abstract:
The layup structure in 4 areas of the suspension control arm of passenger car by using carbon fiber composite is optimized. Firstly, the layer thickness of each angle was regarded as the designing variable to optimize the modal frequency, quality and strain energy under each working condition of control arm. Then the modal frequency was regarded as the target, and the bending stiffness parameter was used as the designing variable to optimize the layup order. Based on the design of experimental of cluster analysis method, the sample points of the approximate model were determined. The Gaussian process regression method was used to establish the approximate model to save the computation cost, and the value of R2 in verification model was above 0.9. After two-step optimization, the performance indexes of the initial designing plan are improved to some extent and the composite materials are reduced by 11.4%. Comparing with the steel control arm, the mass is reduced by 37.1% to meet all the requirements.
The layup structure in 4 areas of the suspension control arm of passenger car by using carbon fiber composite is optimized. Firstly, the layer thickness of each angle was regarded as the designing variable to optimize the modal frequency, quality and strain energy under each working condition of control arm. Then the modal frequency was regarded as the target, and the bending stiffness parameter was used as the designing variable to optimize the layup order. Based on the design of experimental of cluster analysis method, the sample points of the approximate model were determined. The Gaussian process regression method was used to establish the approximate model to save the computation cost, and the value of R2 in verification model was above 0.9. After two-step optimization, the performance indexes of the initial designing plan are improved to some extent and the composite materials are reduced by 11.4%. Comparing with the steel control arm, the mass is reduced by 37.1% to meet all the requirements.
2021, 40(2): 313-320.
doi: 10.13433/j.cnki.1003-8728.20200055
Abstract:
Aiming at the nanofluidics effect of fluid in nano-channels, the wetting contact state and Poiseuille flow behavior of SPC/E water molecules are calculated and simulated respectively with the molecular dynamics methodin micro-channels with different nano-structures to study the sliding drag reduction effect of different wetting states caused by the micro-nano structure change of the microchannel wall surface. The results show that the periodicity of nano-structures increases, which makes the wettability of the wall surface show Matthew effect, thus achieving the purpose of wettability control. Increasing the hydrophilicity of the wall will reduce the density of the main flow region, fluid velocity and slip velocity. In the process of increasing the hydrophobicity of the wall surface, the density of the main flow region increases. The state of the fluid changes from Wenzel to Cassie, and the fluid velocity and slip length decrease first and then increase. In the process of wettability transition, with the increase of the characteristic contact angle, the wall friction coefficient of fluid flow shows a monotonic decreasing trend when the contact states of dynamic and static fluids on the wall are the same. However, when the contact state of static and dynamic fluids on the wall is different, the friction coefficient will fluctuate slightly and irregularly.
Aiming at the nanofluidics effect of fluid in nano-channels, the wetting contact state and Poiseuille flow behavior of SPC/E water molecules are calculated and simulated respectively with the molecular dynamics methodin micro-channels with different nano-structures to study the sliding drag reduction effect of different wetting states caused by the micro-nano structure change of the microchannel wall surface. The results show that the periodicity of nano-structures increases, which makes the wettability of the wall surface show Matthew effect, thus achieving the purpose of wettability control. Increasing the hydrophilicity of the wall will reduce the density of the main flow region, fluid velocity and slip velocity. In the process of increasing the hydrophobicity of the wall surface, the density of the main flow region increases. The state of the fluid changes from Wenzel to Cassie, and the fluid velocity and slip length decrease first and then increase. In the process of wettability transition, with the increase of the characteristic contact angle, the wall friction coefficient of fluid flow shows a monotonic decreasing trend when the contact states of dynamic and static fluids on the wall are the same. However, when the contact state of static and dynamic fluids on the wall is different, the friction coefficient will fluctuate slightly and irregularly.
2021, 40(2): 321-328.
doi: 10.13433/j.cnki.1003-8728.20200043
Abstract:
In this paper, the “Sparrow” MAV (Micro air vehicle) model is analyzed. “Sparrow” is mounted on a typical transmission mechanism, crank slider mechanism, which can be used to realize motion transformation from rotation to translation. So the mechanism plays an important role in applications of flapping wing micro air vehicle. The motion accuracy and driving torque of the crank slider mechanism are directly affected by mechanism components′ dimension error and deformation. Hereby, motion accuracy and driving torque are investigated in turn theoretically, numerically and experimentally. It is found that dimension error of crank affects the motion accuracy mostly, which influences the driving torque up to 79.66%. Deformation of connecting rod not only affects motion accuracy as the largest deformation component, but also influences flapping angle up to 6.88%.
In this paper, the “Sparrow” MAV (Micro air vehicle) model is analyzed. “Sparrow” is mounted on a typical transmission mechanism, crank slider mechanism, which can be used to realize motion transformation from rotation to translation. So the mechanism plays an important role in applications of flapping wing micro air vehicle. The motion accuracy and driving torque of the crank slider mechanism are directly affected by mechanism components′ dimension error and deformation. Hereby, motion accuracy and driving torque are investigated in turn theoretically, numerically and experimentally. It is found that dimension error of crank affects the motion accuracy mostly, which influences the driving torque up to 79.66%. Deformation of connecting rod not only affects motion accuracy as the largest deformation component, but also influences flapping angle up to 6.88%.
