最新刊期
卷 48 ， 期 12 ， 2014
- 摘要：To solve the integrated scheduling for job and tools in computer numerical control(CNC)machining center, a model considering delivery time and parallel processing of working steps is presented. And the minimized total cost of production is taken as the objective to achieve the collaborative optimization. An improved adaptive genetic algorithm is proposed where a job-tool relationship matrix is adopted to guarantee the legality of solutions, and a rational chromosome encoding and adaptive genetic operations are designed to accelerate the convergence rate and improve solving efficiency. The experimental examples are comparatively analyzed to verify correctness of the model. The proposed algorithm enables to maximally reduce processing cost and job tardiness rate and to improve the convergence rate and stability with greatly reduced iterations.关键词：CNC machining center;tool schedule;parallel machining;adaptive genetic algorithm1054|4|2更新时间：2025-07-09
- 摘要：To improve static and dynamic performances of rotary table, the effects of configurations, assembling technology and external load on the static stiffness of a three-row cylindrical roller bearing for rotary table are investigated. A theoretical model of static stiffness of three-row cylindrical bearing for rotary table is proposed considering the clearance, bolt preloads, and reactions of axial and radial rollers with external load. The contacts between the axial rollers and the outer ring are treated as ideal plane contact. And the actual contact forces and their distribution along the axial of radial rollers are obtained by Boussinesq's relationship between force and deformation, the static stiffness in five directions is then sought out by solving the static equivalent equations. It is shown that the maximum error between experimental and theoretical results of natural frequency of the rotary table is less than 3.0%, thus the theoretical model is verified. The reactions between loads acting on the axial rollers and radial rollers are negligible. The bolt preloads, radial clearance and external load exert obvious effects on the static stiffness of rotary table bearing, and the effect of external load decreases with the increasing preloads of bolts and radial clearance.关键词：three-row cylindrical roller bearing;static stiffness;preload;rotary table854|5|2更新时间：2025-07-09
- 摘要：To reveal ablation characteristics and damage mechanism of difficult-to-machine material processed by ultra-fast pulse laser, the ablation threshold, ablation morphology and interaction mechanism of titanium alloy are investigated by picosecond pulse laser. Focusing on the linear dependence of laser energy density on the ablation area, the threshold fluence of ultra-fast pulse laser-induced ablation in titanium alloy is determined. The ablation morphologies of titanium alloy surface under the different laser parameters are observationally analyzed. The interaction mechanism of titanium alloy processed by ultra-fast pulse laser is explained in detail with the theories of avalanche ionization and multiphoton ionization, and the different ablation zones are distinguished according to the ablation morphology and threshold fluence. The results show that the ablation threshold of titanium alloy reaches 0.109 J/cm2; the ablation quality of titanium alloy processed by a picosecond pulse laser of 1 064 nm wavelength gets better than that by 532 nm wavelength, and low repetition rate favors high-quality microstructure; the ablative central area has more uniform material removal, and the ablation crater has regular shape and smooth surface. With increasing pulse number and laser energy, the accumulation of photon energy increases, ablation dimension and morphological characteristics become more obvious, and the ablation boundary becomes more distinct. It indicates that pulse number and accumulation of photon energy are respectively one of the key factors for inducing surface microstructure. The observed ablation zone can be divided into modified region, transition region, redeposition region and ablation region. Multiphoton ionization dominates in the ablation region, while avalanche ionization dominates in the modified, transition and redeposition regions.关键词：ultra-fast pulse laser;titanium alloy;ablation characteristics;interaction mechanism904|5|9更新时间：2025-07-09
- 摘要：To reduce the probability of discharge between workers or vehicles and bare conductors in 110 kV substation, three new types of reinforced insulation jackets are designed and contrasted, including metal diameter expanding jacket, suspended epoxy insulation jacket, and electrically-contacted epoxy insulation jacket. The minimal discharge distance of those three types and its relationship with the diameter of semi-conducting coating and the expanded diameter is estimated theoretically to find the best size of expanded structure and general standard of diameter expanding jacket. Then a model of 110 kV bare conductor installing metal diameter expanding jackets is constructed to figure out the electric field distribution with finite element method. It is found that the metal diameter expanding jacket serves as the best choice, whose minimal discharge distance decreases by 60% compared with bare conductors, and the electrically-contacted epoxy insulation jacket has nearly the same effect in a short service period, while the suspended epoxy insulation jacket has no effect on the minimal discharge distance.关键词：safe distance;reinforced insulation;diameter expanding jacket;minimal discharge distance;finite element method1004|4|2更新时间：2025-07-09
- 摘要：Considering the low power allocation accuracy of paralleled inverters system using traditional double-loop control and the voltage and frequency deviations caused by droop control in micro-grid, the power allocation mechanism and output voltage characteristics of a parallel system are discussed, and a balanced control strategy of power and voltage for inverters parallel operation is proposed based on virtual impedance and instantaneous output voltage/frequency regulation. Virtual impedance is added to existing control loops to improve the characteristics of output impedance, and the power allocation accuracy is enhanced with P-ω, Q-V droop control. A scheme for regulating output voltage magnitude and frequency also participates in the loops to exert secondary regulation on the voltage and frequency deviations from droop control, and the higher output voltage quality remains. The simulation and experiment demonstrate that the proposed balanced control strategy for power and voltage makes the paralleled inverters share the load power better and preserves the rated output voltage and frequency in islanded micro-grid.关键词：micro-grid;paralleled inverters;power sharing;voltage/frequency regulation;balanced control738|5|4更新时间：2025-07-09
- 摘要：An efficient energy-saving routing algorithm with dynamically adaptive power control(ERAPC)is proposed to address the problems that there exist large energy consumption for transmitting partial data packets, no consideration of node's mobility and high control overhead in vector exchange mechanism lying in the energy-efficient routing algorithm based on cross-layer design(ERBC). The ERAPC extends the usage of acknowledgement(ACK)frames to improve the RSSI-based ranging mechanism, to enlarge the range of power control to all data messages and to reduce nodal energy consumption. Until the sender and the receiver move as close as possible, the data messages are sent out to lower the transmit power further; and an efficient new mechanism of exchanging vectors is presented in ERAPC to decrease the control overhead. Simulation results and comparison with the ERBC algorithm show that the energy consumption of each bit in the ERAPC is reduced by at least 27.27% and the control overhead is reduced by at least 11.87%, respectively.关键词：opportunistic networks;routing algorithm;energy-saving;power control;overhead736|4|5更新时间：2025-07-09
- 摘要：A novel mechanism connecting health seekers to appropriate doctors is proposed to improve the efficiency of question resolving in community-based health service systems. Attitudes of doctors answering questions are introduced in the mechanism, and both the professional matching degree between doctors and questions and the doctor's attitudes are associated and considered at the same time. The probabilistic hypergraph and the query likelihood language model are used to model the professional matching degree, and a doctor's attitude is modeled from his historical data. Meanwhile, a regression model is used to trade off between the professional matching degree and the doctor's attitude. Extensive experimental results on several real-world datasets show that the matching precision of the proposed mechanism increases by about 30%, and the efficiency of resolving problems is greatly improved.关键词：community-based health service system;question routing;probabilistic hypergraph;attitude modeling669|4|1更新时间：2025-07-09
- 摘要：A visual tracking method is proposed to solve the problem that the local feature model is prone to be influenced by the deformation and feature mismatch and leads to drifting. The method constrains the Hough local model by using global features. The Hough model is constructed with a set of local features of an object and estimates the stability of each local feature based on the generalized Hough Transform. Then, the model is updated flexibly through modifying the local feature set to adapt to the object appearance variations. Color cues of the local features are used to calculate the global color probability of being foreground or background. Then the global probability is used to adjust the tracking results and constrains the local features of the model in return. Experimental results on several public video sequences show the robustness of the proposed method in tracking objects with deformation and partial occlusion.关键词：visual tracking;local feature;Hough transform;segmentation622|4|1更新时间：2025-07-09
- 摘要：An online learning model oriented to directed scene motion patterns and based on particle filter is proposed to get over the problem that existing pedestrian tracking algorisms have little consideration on the scene motion patterns, to process the priori scene information and to improve the precision of pedestrian tracking. The model describes the local motion characteristic in phase space of the system state vector using a direction-speed motion histogram matrix, and is updated according to weighted voting of each track unit. The particle filter can accelerate the particles evolution to the true posterior distribution through modifying likelihood probability distribution of particle transfer. Experimental results on two pedestrian data sets with different characteristic forms and comparisons with the standard particle filter algorithm show that the average tracking error of the proposed approach is 40% lower than that of the standard particle filter algorithm, while its computation speed approaches the range of 6 to 15 frames a second, and that the proposed approach completely meets the conditions of real-time application.关键词：directed scene motion pattern;particle filter;pedestrian tracking687|4|1更新时间：2025-07-09
- 摘要：A scheduling solution of class priority multiple queue(CPMQ)is proposed to solve the problem that the response time to graphic tasks is not ensured by existing task scheduling systems of GPU under multitask conditions, and the schedule is implemented on an embedded system. Multiple tasks on GPU are firstly classified into three classes of tasks, that is, graphic tasks, real-time graphic tasks and general purpose computing tasks. These three classes of tasks then queued respectively with different queuing policy. Graphic tasks and general purpose computing tasks are queued by their priorities, while real-time graphic tasks are queued by their deadlines. When the multi-class tasks are scheduled, real-time graphic tasks are selected at first, and then graphic tasks and general purpose computing tasks are selected out using a weighted fair queuing algorithm. Experimental results and comparisons with the original scheduling system of ARM's GPU show that CPMQ increases the frame rate of reel time graphic tasks by 5%-20% without significant increase in execution time of general purpose computing tasks and scheduling expense.关键词：graphic processing unit(GPU);multitask;scheduling;queuing873|4|1更新时间：2025-07-09
- 摘要：A novel three-dimensional(3-D)imaging algorithm of interferometric inverse synthetic aperture radar(InISAR)using multichannel joint sparse recovery(MCJSR), named MCJSR-InISAR, is proposed to improve the problem that the super-resolution images recovered by the single channel super-resolution imaging algorithm do not necessarily share the same positions of the scattering centers. The combined range alignment approach is used to correct the envelope delay caused by the target's translational motion, and then the combined phase adjustment approach is employed to complete the phase compensation of translational motion. The range differences between two echo signals received by different antennas are then compensated. Then, MCJSR is used for super-resolution imaging, and the computational efficiency of the proposed algorithm is improved by using the fast Fourier transform(FFT). Finally, a 3-D InISAR imagery of the maneuvering target is obtained by using both the horizontal and the pitching interferometric phase information. The MCJSR-InISAR algorithm can improve the recovery precision of the strong centers in the target scattering field, and preserve effectively the relative phase information between different channels. Experimental results on real-measured data and comparisons with the single channel super-resolution imaging algorithm show that the proposed algorithm decreases the entropy of the resulting image by about 0.17, and reduces the computational complexity by about O(105).关键词：interferometric inverse synthetic aperture radar;joint sparse recovery;three-dimensional imaging;maneuvering target742|4|1更新时间：2025-07-09
- 摘要：A novel envelope alignment algorithm based on splitting sub-apertures is proposed to improve the problem that it is hard for the envelope alignment to be accurately carried out under the condition of low signal to noise ratio(SNR)in inverse synthetic aperture radar(ISAR). The full-aperture is divided into several sub-apertures with same length, and a linear model is built for envelope error of each sub-aperture. The minimum entropy criterion is used to estimate the envelope error of each sub-aperture. Then a high-order polynomial is used to fit the full-aperture envelope errors, and estimations of sub-apertures are used to successfully achieve the final envelope alignment precisely. Simulation results and comparisons with the traditional envelope alignment algorithms show that the proposed method has advantages in envelope alignment, and the entropy of imaging results reduces by about 0.6 when the input SNR is as severe as -5 dB.关键词：inverse synthetic aperture radar;low signal to noise ratio;envelope alignment;sub-aperture;high-order polynomial838|4|7更新时间：2025-07-09
- 摘要：A high rate space-time block coding spatial modulation(STBC-SM)algorithm based on constellation rotation, called CR-STBC-SM, is presented to improve the spectral efficiency of STBC-SM generated by the spatial modulation. The new scheme chooses two antennas from effective antenna combinations, and then a pair of symbols is drawn from the M-PSK/QAM constellation. The symbols are then transmitted in the form of Alamouti code or constellation rotated Alamouti code. The rotation angles are further optimized to maximize the diversity and coding gains of CR-STBC-SM. Moreover, the CR-STBC-SM uses the orthogonality of Alamouti code to get a low-complexity maximum likelihood(ML)decoder. Simulation results and comparison with the STBC-SM scheme show that under the same number of transmit antennas the CR-STBC-SM achieves an extra spectral efficiency of 0.5 b/(s·Hz). Under the spectral efficiency of 4 b/(s·Hz), the performances of both algorithms are very close, but the CR-STBC-SM saves three transmit antennas, that is, the hardware resource is saved by the CR-STBC-SM.关键词：space-time block coding;spatial modulation;constellation rotation;transmit diversity713|4|4更新时间：2025-07-09
- 摘要：To enhance cooling of high temperature casting mold by porous copper foam inserted in cooling channel, an experimental system simulating the cooling process of high temperature casting mold was constructed, where porous copper foam was inserted into the cooling channel. Taking four flow rates, 0.1, 0.2, 0.3 and 0.4 m3/h of cooling water, after 80 s of cooling time, the temperature at the same position of mold with insert gets 16.2, 19.3, 23.5 and 29.4 ℃ lower than that of mold without insert, and the heat flow rate is 414, 581, 659 and 660 W higher, respectively. When the flow rate increases, the temperature at the same position of the mold with insert decreases while the local temperature gradient and the heat flux increase. It is shown that the copper foam inserted in cooling channel of casting mold facilitates rapid cooling and sequential solidification temperature controlling.关键词：copper foam;heat transfer enhancement;casting mold;cooling;temperature751|4|0更新时间：2025-07-09
- 摘要：To reduce the residual stress in thick arc spraying coatings, Stoney formulation, which is the basis of the curvature method, was modified to reliably test the average residual stress. The process was then optimized with improved accuracy and was successfully applied to manufacturing a long stamping die of 2 m for an automobile external sheet metal part. Experimentally analyzing the relationship of the process parameters such as spraying distance, current, scanning path and speed with the residual stress, it is found that residual stress similarly tends to vary as the single layer coating thickness but with different varying proportion; residual stress is most significantly influenced by scanning path; the stress decreases steadily with the increasing spraying distance and scanning speed, and with the reducing spraying current; the residual stress is finally reduced by 27.5% to 63.9% via optimizing the process parameters.关键词：arc spraying;rapid tooling;process;residual stress809|4|0更新时间：2025-07-09
- 摘要：A combined control strategy based on traditional servo control strategies is proposed to solve the dynamic coupling between the light-flexible base and the table, and to overcome the performance deterioration of centrifugal shaker caused by nonlinear factors. A geometry decoupling controller based on the equivalent coupling model is designed to eliminate the dynamic coupling between the light-flexible base and the table. Effects of all nonlinear factors on the system performance are taken into account, and a feedback controller based on robust control and a feed-forward controller based on 2-DOF control are presented to ensure the stability and control accuracy of the system. A load disturbing force compensator is also introduced to counteract the influence of load characteristics variation on system performance. Simulation results show that the bandwidth of the centrifugal shaker is improved to 250 Hz after the feedback and feed-forward adjusting and geometry decoupling, and satisfies the anticipated bandwidth requirement of servo control strategy. When the load disturbing force is compensated, the overshoot and adjustment time of position close-loop in the radical drop section of load characteristics reduce to 50% of that without using compensation, and the close-loop waveform distortion in the random fluctuation section of load characteristics is also improved.关键词：centrifugal shaker;geometry decoupling controller;robust control;2-DOF control strategy771|4|0更新时间：2025-07-09
- 摘要：The air temperature filed around a spiral wire-on-tube condenser of a no-frost refrigerator was investigated experimentally, and then the condenser was optimized accordingly to enhance air-side heat transfer. A wind-broken foam ring was wrapped around downstream part of the condenser to increase airflow in the radial direction, and a wind-broken foam block was set in upstream part of the condenser centerline to reduce airflow in the axial direction, which nearly does not transfer heat. The results show that the condenser outlet temperature decreases by about 0.7 ℃, the compressor operation time ratio drops by 2.02%, and the refrigerator's electricity consumption descends by 2.37% after the optimization. Moreover, both the wind-broken ring and the wind-broken block effectively prevent high-temperature air around the compressor and downstream part of the condenser from flowing to upstream part of the condenser during the outage of compressor, which benefits the heat transfer of the condenser in next operation.关键词：spiral wire-on-tube condenser;air temperature filed;heat transfer enhancement1015|4|0更新时间：2025-07-09
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