最新刊期
卷 55 ， 期 4 ， 2021
- 摘要：A new parameter-adjustable radial basis function(RBF)neural network control strategy for a double-joint manipulator is proposed to solve the problems of large initial error in the error approximation process and long time to reach the steady state in the trajectory control of the double-joint manipulator. Firstly, the central parameter of the RBF neural network is modified by a gradient descent method, so that the parameter can be adjusted according to the real-time error of the manipulator, and the online optimization of the parameter can be realized. A fuzzy compensator with adjustable input boundary is proposed to reach the goal that the actual trajectory of the manipulator approaches the ideal trajectory better. By measuring the trajectory error and the derivative of the error, the output of the compensator is transferred to the torque control module after fuzzy reasoning, so that the output torque of the manipulator is closer to the ideal value. Additionally, a genetic algorithm is used to optimize the width of the RBF neural network function. Simulation results show that after the control torque of the manipulator is adjusted by using the RBF neural network control method with adjustable parameters, the accuracy of the manipulator control process is improved by 59%, and the steady time of the manipulator trajectory tracking is shortened by 69%.关键词：2-joint manipulator;RBF neural network;genetic algorithm;fuzzy compensator216|4|6更新时间：2025-07-09
- 摘要：The feed system is affected by multi-source and multi-frequency disturbances in the actual milling process of the machine tool, especially the direct-drive feed system due to the zero transmission, the motion accuracy is more significantly affected by external disturbances. The disturbance mechanism, frequency spectrum characteristics and linear motor feed system thrust current spectrum characteristics are investigated. Comprehensively considering the multi-source disturbance of tool-spindle system during the milling process, the milling force model, spindle centrifugal force model, spindle bearing vibration model are established and the corresponding multi-source disturbance spectrum characteristics are analyzed. The displacement fluctuation characteristics of linear motor feed system under multi-source disturbance excitation are characterized, and single-axis feed cutting experiment is completed on VMC0865 machine tool driven by a linear motor. The experimental results show that as the feed speed is 1 500 mm/min, spindle speed is 5 000 r/min, cutting width is 2 mm, and cutting depth is 2 mm, the mean square value of X-axis displacement fluctuation increases from 0.36 μm to 0.81 μm, and the mean square value of thrust current increases from 0.94 A to 1.15 A; the thrust current heightens the harmonic components of the spindle frequency and its multiplication, division and side frequencies; cutting force affects motion accuracy of the feed system, thereby lowers the quality and accuracy of the part processing. The influence of the process on the spectral characteristics of thrust current of linear motor feed system and the influence of different cutting parameters on the spectral characteristics of thrust current are comparatively analyzed. It is obvious that spindle speed is the most significant cutting parameter for spectral characteristics of thrust current.关键词：multi-source disturbances;linear motor;thrust current;processing parameters94|4|1更新时间：2025-07-09
- 摘要：A tool damage visual detection method using local threshold segmentation is proposed to solve the problem that the current tool damage detection systems are difficult to automatically identify the location of tool damage and accurately measure the amount of tool damage from the collected machine tool damage images. Firstly, the tool image is divided into several small pixel blocks after graying, filtering, noise reduction, rotating and positioning correction. Each pixel block is segmented to obtain its segmentation threshold, that is, the local threshold. Then based on the largest local threshold, the tool image is scanned for global pixels. At the same time, combined with morphological operation, tool damage location recognition is realized, and the geometric characteristics of tool damage are accurately measured based on the identified damage information. An off-line detection experiment platform is built to verify the effectiveness of the proposed method. Experimental results show that the proposed tool damage visual detection method using local threshold segmentation solves the difficulty in automatically identifying the tool damage location and accurately measuring the amount of tool damage from the tool damage image. Comparisons with the existing local variance method, the adaptive threshold method and other methods show that the proposed method improves the average accuracy of tool damage geometric feature measurement by at least 19%, and has a great advantage.关键词：tool damage;visual detection;automatic identification;local threshold segmentation86|4|5更新时间：2025-07-09
- 摘要：A deep learning fault diagnosis model with strong anti-noise ability(HAT-MSCNN)is proposed to solve the problem that the existing fault diagnosis model based on deep learning has insufficient resistance to strong noise interference due to the high noise in the operating environment of rotating machinery. Firstly, the frequency spectrum signals of the samples under normal state of the gearbox training set are arranged from large to small, and the kth amplitude value α of the sort is taken as the reference value. The frequency spectrum signals of all samples in the training set with values being lower than the value of α are set to zero, which reduces the interference of low-amplitude frequency components that are easy to be coupled with noise on the diagnosis model, and highlights the contribution of high-amplitude frequency components to the fault diagnosis model and retains the position information where the zero value is located. Then the processed training set is inputted into a multi-scale convolutional neural network composed of multiple moving step size convolution kernels for training, and finally a fault diagnosis model with strong noise immunity is obtained. The harmonic average value F of precisions and recalls is used as an evaluation index of the model, the weighted gradient activation mapping method is used to visualize the classification weights of the model, and the model is verified on the PHM2009 gearbox data set with rich failure modes. The proposed method is compared with the Raw-MSCNN, Frequency-MSCNN, and EEMD-MSCNN models that use vibration signals, frequency signals, and EEMD denoised signals as input respectively, and the HAT-CNN model that uses the signal processed by the proposed training set sample construction method as input. The results show that when the SNR of the test set is -4 dB, the F value of the proposed HAT-MSCNN is 98.6%, which is 6.4% higher than that of the second-place Frequency-MSCNN. When the SNR of the test set with stronger noise interference is -6 dB, the F value of the proposed HAT-MSCNN is 89.1%, which is 10.9% higher than that of Frequency-MSCNN. It proves that the proposed model has the anti-noise capability under strong noise interference.关键词：fault diagnosis;convolutional neural network;noise reduction;gearbox137|4|3更新时间：2025-07-09
- 摘要：A design method of cognitive radar waveform(CRWD-1D-CNN)using one-dimensional convolutional neural network(1D-CNN)in the presence of clutter is proposed to solve the problem that the waveform designed using single-criterion is difficult to satisfy the radar multi-state and multi-task. Firstly, environment variables are set, and a training set and a test set are constructed according to the mutual information(MI)criterion and the signal-to-interference and noise ratio criterion(SINR); Secondly, a 1D-CNN model containing 3 convolutional layers and 2 full connection layers is designed based on the data form and the number of sampling points; Finally, the 1D-CNN model is trained with the training set, and the learning ability of the 1D-CNN is made use of to learn the MI criterion and SINR criteria, then the trained 1D-CNN is used to generate waveform. An index of target final recognition rate and an index of target recognition rate index are proposed to measure the comprehensive performance of radar. Simulation results show that when the waveform designed by CRWD-1D-CNN method is used as radar transmitting signal, the overall performance of the radar is improved by 0.64% and 2.13% on average compared with using the waveforms generated by using MI and SINR criteria. These results prove that the CRWD-1D-CNN method can effectively combine the MI criterion and SINR criterion, and improve the comprehensive performance of radar.关键词：waveform design;mutual information criterion;signal to interference and noise ratio criterion;one-dimensional convolutional neural network58|5|2更新时间：2025-07-09
- 摘要：The concept of metamaterial is introduced into sandwich plates to solve the low frequency vibration reduction problem of thick plate structure, and a type of sandwich type metamaterial plate is proposed and theoretically studied. The structure of the proposed plate is mainly composed of sandwich type periodic base plate and embedded with sandwich type periodic vibrator, so it has the characteristics of light weight, high rigid, thick scale and low broadband vibration band gap. The generation mechanism of low frequency broadband vibration band gap in sandwich type metamaterial plate is studied by using a finite element method(FEM). It is found that the local resonance mode of the sandwich type vibrator and the Lamb wave mode of the sandwich type periodic base plate respectively dominate the system response according to the modal superposition principle. When the main modes of the plate and vibrator are coupled to each other, the vibrator suppresses the main modes of the sandwich periodic base plate to make the waveless propagation mode in the sandwich plate to form vibration band gaps. The equivalent stiffness of the sandwich type vibrator is the main factor affecting the characteristics of the band gap, and when it is a mixed stiffness mode, the position and width of the band gap can be adjusted together to form a low broadband vibration band gap. Simulation results show that the designed sandwich vibrator has the characteristics of serial-parallel stiffness, resulting in two equivalent stiffness modes in the vibrator. The two modes adjust the position and width of the band gap respectively at the same time, and finally widen the complete band gap by 7 times at low frequencies. Experimental results show that this type of plate has a good low broadband vibration damping characteristic. The proposed sandwich superplate integrates the advantages of sandwich plate and meta-material/structure, realizes the unification of mechanical bearing and low-frequency band gap vibration reduction, and provides a new idea and method for low-frequency vibration reduction of thick plate structure.关键词：sandwich plate;metamaterial structure;vibration band gap;low frequency vibration reduction;metamaterial95|6|3更新时间：2025-07-09
- 摘要：Aiming at the difficulty of directly modeling and analyzing assembly errors of complex mechanical products, an assembly unit partitioning method of complex mechanical products for error propagation is proposed. According to the product assembly process information, the assembly relationships among parts and the measurement relationships are taken into account, which obviously affect product assembly quality, then a part-level association network based on complex network is constructed. The method combining fuzzy analytic hierarchy process(FAHP)and expert scoring is introduced to weight the association relationship among parts to obtain a part-level association weighted network. Compared with the traditional method, the objectivity of the association relationship strength is heightened to a certain extent. An improved link communities(LC)algorithm is used for assembly unit partitioning based on the community characteristics of the part-level network. The division of assembly units reveals the hierarchical nature of the parts network and simultaneously digs out overlapping parts belonging to different assembly units, which more accurately coincides with the characteristics of complex product structures. A low-pressure module of a steam turbine is taken as an example to verify the feasibility and effectiveness of this method. The assembly unit in this method can be further extended to an assembly feature-level error propagation network to provide a relatively complete analysis platform for the assembly quality analysis of complex mechanical products.关键词：assembly unit partitioning;error propagation;complex network92|4|5更新时间：2025-07-09
- 摘要：Aiming at the difficulty in identifying the restoring force of a nonlinear oscillator with negative stiffness, a time-domain nonparametric identification method based on restoring force surface is proposed. The numerical processing schemes of displacement differentiation and acceleration integration are compared and analyzed. A method for drawing three-dimensional restoring force surface diagrams of four typical negative stiffness oscillators and extracting stiffness and damping restoring forces by experimental data is given. This approach shows that the identification accuracy of the polynomial stiffness force and the damping force coefficient can reach more than 95% in the numerical simulation of the four negative stiffness vibrators. Frequency sweep experiment is carried out on the multi-stable oscillators at different acceleration levels by building an experimental platform. Following the designing idea, the restoring force surface of the multi-stable state vibrator is constructed. The surface recognition result coincides with the measured restoring force surface, which verifies the effectiveness of the complex force surface method in identifying the negative stiffness nonlinear oscillators, and this method is also applicable to the nonlinear analysis in the fields of energy harvesting and vibration control.218|6|1更新时间：2025-07-09
- 摘要：The film cooling characteristics of the endwall surface of a turbine engine vane are numerically simulated to improve the cooling efficiency of the gas turbine endwall film. Firstly, the endwall film cooling performance with only discrete film holes is studied. Turbulence models are checked by experimental results, and the mesh independence of the models is verified. On this basis, the film cooling characteristics of the discrete film holes at the endwall under five mass flow ratios(1.4%, 2.1%, 2.7%, 3.1%, and 3.8%)and five film hole orientation angles(20°, 25°, 30°, 35°, and 40°)are studied. The heat transfer coefficients of the entire endwall are calculated by using the given experimental endwall heat flux input conditions. Calculation results show that the average adiabatic film cooling efficiency reaches to 0.21 when the mass flow ratio is 1.4% at the same injection angle(40°). A larger mass flow ratio over than 1.4% leads the coolant detach from the endwall surface, and then the film cooling efficiency of the endwall decreases. The total pressure loss of the cascade increases with the increase of the mass flow ratio. The increase of the mass flow ratio strengthens the flow mixing at the outlet of the hole and increases the heat exchange efficiency. Because of the influence of secondary endwall flow and the structure of film holes, the adiabatic film cooling effect is the highest when the film hole injection angle is 20°. Under the same mass flow ratio(1.4%), the average film cooling efficiency of the end wall reaches 0.27. Reducing the injection angle has little effect on the heat exchange efficiency of the endwall surface.关键词：turbine endwall;film cooling;injection angle;numeral research64|5|8更新时间：2025-07-09
- 摘要：Based on the electromagnetic simulation software Ansoft, a high-voltage AC transmission line model with sag is established to investigate the effects of transmission line faults on the nearby electric field and the electric field distribution near the top of objects. Through the changes of various faults, the distortions of electric field near the high-voltage AC transmission line caused by single-phase grounding fault, two-phase grounding short-circuit fault, two-phase short-circuit fault, and three-phase short-circuit fault are compared and analyzed. On this basis, a model containing trees and buildings is constructed to analyze the changes of electric field intensity around trees and buildings after various faults occur. The results show that the electric field characteristics generated by different faults on the transmission line are obviously different. The maximum electric field intensity near the line after the faults does not exceed the maximum electric field intensity before the faults; different faults have different degrees of influrnce on the maximum intensity and amplitude of electric field around the line, and some faults even have “zero points”. The feasibility of using the change of the electric field to diagnose operating state of the high-voltage transmission line is verified. In addition, after faults, the electric field intensity surrounding the tops of trees and buildings greatly increases, especially when a two-phase short-circuit fault occurs, the maximum intensity at the top of trees is close to 3.81 times of the normal value, and the maximum intensity near the top of the buildings is close to 7.15 times of the normal one, which is more likely to cause corona discharge. This study may provide reference for transmission line design, fault diagnosis, and green development of power grid in the future.关键词：transmission line faults;finite element method;electric field distribution;electric field intensity;green grid74|4|1更新时间：2025-07-09
- 摘要：A new quadrature space-frequency index modulation(TDA-QSFIM)scheme which can obtain transmission diversity in MIMO System is proposed to solve the shortcoming that the quadrature space-frequency index modulation(QSFIM)algorithm cannot achieve transmission diversity. Firstly, two modulated symbols are related through a Hadamard matrix and a rotation matrix to construct a diagonal code, and then the transmitted signal codeword on each resource block is obtained by independently selecting the index number in the space-frequency resource block(RB)twice and placing the in-phase and quadrature components of the diagonal code in different positions of the space-frequency code, respectively. According to the rank criterion of space-frequency coding, the proposed transmission algorithm obtains better bit error rate performance because the codeword design of the algorithm on each resource block makes the transmission diversity order of 2. Simulation results show that when the spectral efficiency is 1.78 bit/(s·Hz-1)and BER is 10-5, the TDA-QSFIM algorithm has a performance gain of about 3.5 dB compared with the QSFIM algorithm under independent Rayleigh channel, and when BER is 10-3 the TDA-QSFIM algorithm has a performance gain of about 5 dB over the QSFIM algorithm under the relative Rayleigh channel.关键词：multiple-input multiple-output;orthogonal frequency division multiplexing;diagonal code;transmission diversity38|4|0更新时间：2025-07-09
- 摘要：Aiming at the problems of false detection, missing detection and low detection accuracy in single shot multibox detector(SSD), an improved SSD object detection algorithm is proposed. The conv4_3 convolution layer and the previous two standard convolutions are replaced by dilated convolution to expand the receptive field. The deconvolution is used to fuse the feature maps of different scales, so that the feature maps formed by fusion contain rich context information. The attention model is added to the feature map to effectively extract the features of regions of interest. Simulation results show that the detection accuracy of the improved algorithm is 0.9% higher than that of the original algorithm, and the detection effect is better. To some extent, it solves the problems of false detection and missing detection, and still meets the requirements of real-time.关键词：object detection;single shot multibox detector;dilated convolution;deconvolution;attention mechanism145|4|2更新时间：2025-07-09
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Fabrication Process and Mechanical Performance of Porous Calcium Silicate/Gelatin Composite Scaffold
摘要：To solve the poor mechanical performance and difficulty of fabrication of controllable complex porous bioceramic bone scaffolds by traditional methods, porous calcium silicate/gelatin composite scaffolds with excellent mechanical performance were developed with a two-step process: fabricating the porous calcium silicate scaffolds by digital light processing(DLP); immersing the porous calcium silicate scaffolds into a gelatin melt. The microstructure of composite scaffolds with different gelatin contents was observed by scanning electron microscope. The effects of gelatin contents on the mechanical performance in Z and X-Y directions of the porous calcium silicate/gelatin composite scaffolds were analyzed. The results show that gelatin fills the microscopic pores and coats the surface of the scaffolds. When the gelatin mass fraction gets 5% and 7.5%, the samples are endowed with good pore connectivity, mechanical strength and toughness. However, the composite scaffolds still exhibit mechanical anisotropy. The compressive strength and strain energy density in the Z direction are increased by 0.63-1.67 times to 5.91 MPa and by 0.84-1.77 times to 5.30×104 J/m3, respectively. The compressive strength and strain energy density in the X-Y direction are increased by 1.56-2.07 times to 10.01 MPa and by 1.51-3.33 times to 10.75×104 J/m3, respectively. Thus, the appropriate gelatin content for preparing porous calcium silicate/gelatin composite scaffold is chosen as 5%-7.5%.关键词：calcium silicate ceramics;gelatin;composite scaffold;light curing;mechanical property63|4|3更新时间：2025-07-09 - 摘要：Bisphenol A epoxy resin was used as basic resin, and micron alumina with different morphology and particle size was used as filler to design and prepare composites. By testing and analyzing the mechanical properties and microstructure of the composites, the influences of the morphology, particle size and content of alumina filler on the mechanical properties of the epoxy resin composites were studied, and the influence mechanism was analyzed. The results show that the mechanical properties of the epoxy resin composites increase first and then decrease with the increase of alumina filler content. When the filler is 5 μm spherical alumina particles and the volume fraction of filler is 3.22%, the mechanical properties of the composite are better. The tensile strength and impact strength can reach 77.62 MPa and 13.92 kJ/m2 respectively, which are 30.48% and 44.10% higher than that of pure epoxy resin. It can be observed from the microstructure that the alumina filler in the epoxy resin forms crazes around itself, which can absorb the external stress and improve the toughness of the composite. By observing the distribution of alumina filler in epoxy resin, it can be found that 5 μm spherical alumina particle has better distribution in epoxy resin and better interface with epoxy resin, which makes the composite has better mechanical properties.关键词：alumina filler;epoxy resin composite material;filler morphology;mechanical properties;microstructure96|7|3更新时间：2025-07-09
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