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2008 Vol. 34, No. 09

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Bionic design of column structure of machine tool for high specific stiffness
Yang Yongbin, Chen Wuyi, Zhao Dahai
2008, 34(09): 991-994.
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Improving the specific stiffness of moving structure is important for the improvement of the machining accuracy and dynamic performance of high speed machine tools. Based on structural bionic theory, through study on the contribution of biologic skeleton to organism stiffness and the concept that biologic skeleton shows the best load path of organism, the column-s inner structure was redesigned as skeleton to improve the specific stiffness. The static, modal, and transient analyses of original column and bionic column were carried out, and the results are satisfying. The FEA results show that through structural bionic design the column-s mass was decreased, the specific stiffness structural efficiency and the natural frequency were improved, the transient displacement was decreased, and the stability of bionic column was better than that of original column. Through structural bionic design the static and dynamic character of column was ameliorated.
Data analysis of reliability growth test for electronic equipments based on Fiducial inference
Yang Jun, Zhao Yu, Yu Dan
2008, 34(09): 995-998.
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Reliability growth is an important part of reliability engineering, but for the problem that small samples are often occurred during reliability growth test, there is almost no effective method so far. To solve this problem, fiducial inference with restricted parameter space was studied, for non-location-scale families, it was generalized by standardized likelihood, and it was pointed out that evaluation results obtained by fiducial distribution are equal to the corresponding results obtained by frequency statistics. Under the reliability growth model with monotone constraints, reliability evaluation of electronic equipments for reliability growth test was analyzed by fiducial inference with restricted parameter space, and for cases with complete failure time data or interval-censored failure time data during each stage of the reliability growth test, the upper confidence limit of failure rate for electronic equipments was given in detail.
Identification method for the material parameters of Al alloy under the condition of hypervelocity impact
Hu Zhendong, Huang Hai, Jia Guanghui
2008, 34(09): 999-1002.
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In the research of hypervelocity impact, how to identify the metallic material’s parameters under the extreme distortions and high strain rate is a key problem. Steinberg strength model and Gruneisen equation of state were selected to describe the characteristics of Al6061 under the condition of hypervelocity. The SPH algorithm was applied to simulate the hypervelocity impact. The error between the results of experiment and simulation was defined as the optimization objective and 4 parameters in Steinberg strength model were defined as optimization variables. Four parameters were identified automatically by successive response surface method(SRSM). The optimized parameters have a better simulation results than the initial parameters when comparing with the experiments results.
Detection and control of non-linear errors in 5-axis machining
Wang Dan, Chen Zhitong, Chen Wuyi
2008, 34(09): 1003-1006.
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Non-linear error is an important source of the machining error in multi-axis numerical controlled machining and it is unavoidable. A new strategy to deal with the non-linear error was proposed based on the analysis of former work. In the new strategy the tool positions with large non-linear errors were found out by detecting the movements of rotatory axes of the 5-axis machine tool and then the non-linear errors were compensated by linear interpolation. Comparison work between the original data and compensated data was done and the results show that the proposed strategy could notablely reduce the non-linear error. The strategy proposed could deal with non-linear errors of both general type and the special type which occur at singular position of the machine tool. Simulation results indicate the simplicity and feasibility of the strategy.
Principle and application of vibration suction method
Nashun Buhe, Liu Rong, Yang Hao
2008, 34(09): 1007-1011.
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Vibration suction is a kind of suction method for robots which was newly introduced by researchers. A new mathematical model of vibration suction was brought forward and a testing device was designed to measure the air pressure of the inner chamber of the suction cup. Experiments under different vibration parameters including surface, amplitude and frequency were carried out and the results of the experiments confirm the accuracy of the new model. Stable suction condition was studied in order to achieve suction to wall. According to the theory of vibration suction, a new type of vibration suction module was designed. A performance test experiment was carried out for vibration suction module. The test was carried out to measure the failure pull, the failure flexural torque and the failure torque moment. The result of the test proves the reliability of the module to be used as a foot of a wall climbing robot.
Application of improved PCA to thermal wave image processing
Sun Yanchun, Ma Qishuang, Liu Yueming, Yao Hongyu
2008, 34(09): 1012-1015.
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To solve the problems less valid data in thermal infrared imager, uneasy dipartite corrosion area in image and lower the signal to noise ratio which happened in detection of structure parts- hidden corrosion by thermal wave imaging, the improved PCA (principal component analysis) based on the wavelet was presented. The every frame image was transformed by dyadic discrete wavelet and the characteristic of wavelet transform coefficient was analyzed. Low frequency coefficients were analyzed by fast principal component method which quoted Gram-Schmidt orthonormalization procedure in fixed-point algorithm then distilled principal component and reconstructed the low frequency coefficients. To suppress image noise, the high frequency coefficients were equated to zero. The experimental results indicated that the method made best of thermal infrared imager-s dada, improved the contrast of infrared thermal image and reduced noise of infrared thermal image, and that the method-s compute-time was short.
Distortion correction for small-field space image based on star map matching
Zhang Chun, Qin Shiyin, Zhao Danpei, Liu Zunyan
2008, 34(09): 1016-1019.
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Due to the impacts from launching vibrations and complex space environment, it is inevitable to generate some distortions in images by the small-field space imaging, moreover, the distortion model and parameters may also change sometimes. In fact, there would be a few or a sparse stars in a single small-field space image, thus a kind of distortion correction method for space image was presented based on multi-frame star maps matching with Hausdorff distance. The distortion parameters were calculated by considering the stars as control points. Furthermore, the self-adaptation compensation method was given to remove the error from camera optical axis pointing system because of satellite attitude drift. Simulation experiment results show that the proposed correction method is characterized with small calculation quantity and high precision, so as to decrease the influence of image noise and input error efficiently.
8mm band 2-dimensional synthetic aperture microwave radiometer (BHU-2D)
Xue Yong, Miao Jungang, Wan Guolong
2008, 34(09): 1020-1023.
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The imaging principle, system structure and characteristics, calibration approach, several imaging experiments and imaging results of 2-dimensional synthetic aperture microwave radiometer BHU-2D (BeiHang University 2-Dimensional) were presented. BHU-2D operates at 8mm wave band and has 10 receiving channels. The antenna array of BHU-2D is T-shape; receivers- configuration is super heterodyne and has two down converters. I/Q demodulation and correlation of BHU-2D were carried out with digital method and by software; the channel unbalance, correlation bias and aliasing errors were calibrated with radiated point source and background drop inversion algorithm. At present, BHU-2D was accomplished and has been undergoing testing and imaging experiments, and the radiometric brightness distribution images of man-made scenes and the person in lab were obtained.
Carrier synchronization method for digital terrestrial television system
Zhang Chao, Zhang Xiaolin, Zhang Shuai
2008, 34(09): 1024-1027.
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According to the technique characteristic and frame structure of the China national standard for digital television terrestrial broadcasting system, a carrier synchronization scheme based on the pseudo noise (PN) frame header was presented. After the acquisition of PN frame header, the same PN sequence was recovered at the receiver. Based on the sub-sequence correlation result, the frequency offset was first calculated, and then the phase error was corrected according to the correlation peak. This synchronization method suits three types of PN frame header of digital television (DTV) system, and suits both single carrier and multi-carrier structure. The theory of the algorithm was given and the simulation was performed. The result shows that this method has the superiority of fast synchronization, anti-noise and simple hardware design. This synchronization scheme has been used in the DTV receiver.
Solution to switching angles for selective harmonic elimination inverter
Wu Jianwen, Wang Feng
2008, 34(09): 1028-1031.
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Since the solution to switching angles for selective harmonic elimination inverter is difficult, a method of solution to switching angles based on complex optimal method with constrain conditions was presented,and the design method of objective function and constrain conditions was analyzed．This method enlarges the range of initial switching angles,only considering constrain conditions. It is more reliable compared with solving nonlinear transcendental equations,there is no divergence or singular problem. The narrow pulse is eliminated through restricting constrain conditions in the process of solving switching angles. The optimization for switching angles is available though designing objective function and weighted factor．The results of calculation and experiment show that the method of solving switching angles proposed is correctness and validity.
Performance analysis and improvement on acutely defocused scenes
Sun Minglei, Shi Jingxin, Dong Dai, Zong Guanghua
2008, 34(09): 1032-1036.
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Some classic focusing measures such as gradient function, Brenner function and entropy function, et al, show poor performance in computing high frequency energy in acutely defocused images. Their focusing curves away from the focus show serious nonmonotonicity. The Fourier transform method for image series spectrum analysis was conducted. Three reasons for poor performance in far away focus region were proposed. Firstly, defocused image sequences show strong volatility in power of DC(direct current) component. Secondly, DC component of the image spectrum occupies an overwhelming proportion. Thirdly, the traditional measures have weak ability in filtering DC component of image. According to this, two spatial focusing measures were presented. Experiment results show that performance of focusing curves of acutely defocused images was significantly improved, and high focus resolution can be achieved. This method is particularly important in enhancing reliability of automatic micromanipulation based on microscopic vision.
Improvement of remote user authentication schemes using passwords
Hu Ronglei, Liu Jianwei, Zhang Qishan
2008, 34(09): 1037-1040.
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Password authentication scheme is a promising and practical solution to remote user authentication. The security of an authentication scheme using strong graphical passwords basing on hash function was analyzed. The scheme can not resist to stolen-verifier attack. The adversary can pretend to be a server to cheat a legal user to send him authentication message, and then it masquerades as a legal user by creating a valid login message, passes the authentication phase and gains the authority of a legitimate user without knowing user password. An enhanced scheme was proposed in which smart card is used for storing server authentication message. The server and user can authenticate each other. The adversary can personate neither server nor user and can not get useful login message from eavesdropped communication. The enhanced scheme can withstand replay attack, denial-of-service attack, password-guessing attack, forgery attack, password-file compromise attack and inside attack as the former scheme. It can also withstand stolen-verifier attack and smart card loss attack.
Phase structure and magnetic properties of SmCo x-0.4 Ti0.4 ribbons
Zhang Yu, Yao Zan, Jiang Chengbao
2008, 34(09): 1041-1044.
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SmCox-0.4Ti0.4(x=5.0,5.5,6.5 and 7.0) ribbons were prepared by melt-spinning at a wheel speed of 42m/s, followed by annealing at 750℃ for 2 h.The phase structure and magnetic properties were measured for two types of ribbons, the as-spun and the as-spun/annealed. It was found that the phase structure of the as-spun ribbons changed with the Co content increasing. The as-spun samples with x=5.0, 5.5 and 6.5 showed a 1∶ 5 plus 2∶ 17 phase structure. The x=7.0 ribbons presented a single 1∶ 7 phase structure. The specific saturation magnetization and the specific remanence increased almost linearly with the increasing of Co content. The maximum intrinsic coercivity of 1.01 T was obtained in the as-spun ribbons with x=5.0. Both of the two types showed a fine nanograin microstructure, and leaded to the remanence enhancement. The coercivity mechanism of the ribbons was mainly of the nucleation type, and the reversal magnetization nucleation field arised from the high uniaxial magnetocrystalline anisotropy of the hard phases and the nanograin microstructures. The intrinsic coercivities decreased after annealing, except the sample with x= 7.0.
Discussion of a data integration mechanism with data integrality
Yang Yongqiang, Ma Shilong, Jin Wen
2008, 34(09): 1045-1048.
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At present, the enterprise data is often scattered in various independent business systems, therefore the unified data management and integration is not well realized. Based on the analysis of the distributed and heterogeneous data characteristics, a data integration system with data integrality was proposed. The system introduced the mapping mechanism of three data mode (inner mode, local mode and global mode), established the architecture of hierarchical data model. Because of the architecture, the system could shield of heterogeneous data in the distributed and heterogeneous data environment. The system also proposed a data integrity check algorithm on the global mode. This algorithm would ensure the data integrity in the distributed and heterogeneous data environment. So the system could not only share the data resources, but also integrate the distribution of data resources. Finally, an application example in the earthquake data integration platform was described and analyzed, which showes this mechanism has the data integrity capability.
Simulation on bistatic RCS measurement method in anechoic chamber
Li Zhiping, He Guoyu
2008, 34(09): 1049-1052.
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An method was presented to measure bistatic RCS in anechoic chamber. The target was illuminated by compact antenna test range (CATR), and the scattered field was probed in near-field. The transformation from near-field to far-field (N2F) was analyzed by antennas coupling equation, plane wave synthesis and equivalence theorem. Sampling rate, maximum angle and taper function in N2F were formulated to analyze the measurement-s performance. The sampling interval needs to be half wavelength, and undersample will worsen the maximum angle. The maximum angle-s estimation was perfected using the synthetic aperture-s projection. Far-field was determined by localized near-field approximatively, which can be concluded using stationary phase method. A taper function was applied to the near-field data that reduces the error of the scanning truncation. The method was validated through numerical example finally.
Quantitative evaluation on characteristic index of post-stall maneuvers fighter
Zhang Li, Wang Lixin, Fu Yang
2008, 34(09): 1053-1056.
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The post-stall maneuver can effectively improve the fighter-s ability of air-combat and survival. The dynamic equations of high angle of attack with thrust vector using quaternion method were built. According to the purpose of post-stall maneuver -changing nose pointing, and combining maneuverability and agility, the changing law of primary parameter of post-stall maneuver process was analyzed. Four indexes evaluating the post-stall maneuver quality were proposed, including maximal trim angle of attack, the time taken to change from level flying to maneuver angle of attack and the time taken to change from maneuver angle of attack to initial level flying, the time taken to roll around velocity vector and reach 90° angle of bank at maneuver angle of attack, and the period of post-stall air-combat. The simulation and quantitative evaluation research was carried out, and the results show that these indexes brought forward can lead to convincible evaluation of post-stall maneuver.
Decentralized optimal control of coordination target awareness with multiple vehicles
Wu Wenman, Zhou Rui
2008, 34(09): 1057-1060.
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The centralized coordination control of multiple vehicles was difficult to implement since the highly distributed information and computation, the vehicles motion, and the changing information networks topology. The decentralized coordination control was scalable, heterogeneous, reconfigurable, and robust. The structure of coordination control system for multiple vehicles with the characteristics of decentralized control and centralized control was proposed. The mission management system and the method of decentralized optimal coordination control based on minimal communications were investigated. As an example of coordinated target tracking with multiple passive sensor vehicles, the algorithms of decentralized information fusion were developed. The decentralized optimal control of coordination target awareness with multiple passive sensor vehicles was implemented to maximize the information utility gained by each sensor vehicle under the different constraints of control, communication and safety. The simulation results demonstrate that the performance of coordination target tracking with communication is obviously better than the one of non-coordination without communication.
Tetrahedron-based constructing 3D_streamlines in visualization
Yang Guang, Cheng Shiming
2008, 34(09): 1061-1064.
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Streamline is an important technique in computational fluid dynamics for vector visualization. This algorithm is based on tetrahedron cells. Firstly, hexahedron cells in data field of point cloud were divided into tetrahedron cells. Tetrahedron relations between the adjacent tetrahedron were stored, and then the point of streamline in data filed was located into the tetrahedron cell gradually by looking up the tabulation of adjacent tetrahedron relations. Then according to the deflexion angle of the velocity vector on streamline and the radius of inscribed sphere in the tetrahedron cell, integration step was adaptively determined to improve the precision and efficiency of streamline-tracking. Finally, the points of streamline were obtained by Runge-Kutta numerical integration method, and three-dimension streamline was constructed with the point location and integration step. As a result of avoiding Jacobian matrix inverse transform that is used in the traditional streamline-tracking algorithm, this method reduces the error of matrix conversion and improves efficiency and precision of streamline construction.
Directional adaptive diamond search for motion estimation
Li Rong, Zhang Qishan, Yang Dongkai
2008, 34(09): 1065-1069.
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Based on the research of motion vector distribution, a novel directional adaptive diamond search (DADS) algorithm was proposed. This algorithm adopted three strategies: the initial search point prediction strategy, the early search termination strategy, and the directional adaptive diamond search strategy. The initial search point prediction strategy made the predicted motion vectors close to true values and avoided them falling into the local optimal. The early search termination strategy detected the matching macroblock according to two fixed thresholds, and terminated the current search immediately. The directional adaptive diamond search strategy adopted the small diamond search pattern (SDSP) and four novel directional adaptive diamond search patterns (DADSP), and the search patterns were utilized adaptively based on the type of motion activity. Experimental results show that the proposed algorithm not only significantly reduces the average search points, but also improves the search accuracy to a certain extent, and it excels other traditional fast block matching algorithms in speed and veracity.
Error-predictable adaptive dead reckoning algorithm
Zhou Zhong, Wei Sheng, Zhang Guofeng, Wu Wei
2008, 34(09): 1070-1075.
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A dead reckoning algorithm was presented which is suitable for first-person shooting games. Avatars- moving directions change frequently and their traces consist of continuous broken lines. According to the features, first order derivative polynomial and linear convergence algorithms were selected for position extrapolation and convergence respectively. Avatar-s moving state was used to predict extrapolation error and adjust convergence procedure dynamically. Extrapolation policy was changed with the distance between avatar and its observer in order to reduce state update packets. Experiment results show that the position extrapolation algorithm can reduce state update packets and deviation of reckoning trace in first-person shooting game.
Gust load alleviation control of aircraft with large ratio flying wing configuration
Gao Jie, Wang Lixin, Zhou Kun
2008, 34(09): 1076-1079.
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The configuration of flying wing aircraft with large aspect ratio is advantageous on the characteristic of aerodynamics and stealth, but due to lack of conventional elevator and rudder, gust load alleviation control method for the aircraft with conventional configuration is not suitable anymore. The characteristics of representative arrangement of control surfaces on an aircraft with flying wing configuration were discussed; also the specialty with configuration of flying wing in gust alleviation system was analyzed, when applying the method of direct lift force control. To improve a flying wing aircraft-s response to atmospheric turbulence, a control law of the control system was designed, using the method of poles configuration of invariable characteristic structure. At last, both the aircraft-s open-loop and closed-loop responses to atmospheric turbulence were calculated, analyzed and compared; meanwhile, the aircraft-s ride quality was given and compared to some criterion. Results show that the control law given by the method can improve the aircraft response to atmospheric turbulence effectively.
Low hysteresis brush seal numerical simulations
Wang Zhili, Liang Xiaofeng, Song Fei, Huang Qiwu
2008, 34(09): 1080-1083.
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In order to establish the calculation model of low hysteresis, an anisotropic porous model contained with the bristles bending deflections was employed based on the physical structure of low hysteresis brush seal. The effect of the bristles in the seal was considered a resistance force and was added into the N-S equation as a source term. The model was established on the basis of the finite volume method and the SIMPLE method. The pressure field,velocity vectors distribution and leakage were calculated and analysised. Based on the calculation date, the influence by the main parameters included structure and working condition was investigated. Compared with the common brush seal and low hysteresis brush seal, it is obvious that the low hysteresis brush seal can decrease the pressure between the bristle and the back ring and increase the bristle-s adaptability. In the working state it is beneficial to the seal system.
Time management of RTI based on negotiation group
Lü Fang, Fang Zhou, Zhong Wei, Sheng Wu
2008, 34(09): 1084-1087.
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Aimed at the problems existed in the time management of run-time infrastructure(RTI) at the present time, a method of time management of RTI based on negotiation group was brought forward and applied in the time management service of BH RTI 2.3, which was conducted to solve the problems such as low time advance speed and high network bandwidth engross. This method divided the node in the simulation system into different coordination groups and set the coordinator, which attained global time synchronization through the coordination of local synchronization. The experiment outcome indicates this method preponderates over other methods in both time advance speed and network bandwidth engross on even ground.
Simulation analysis of plastic deformation and residual stress distribution of radial ring rolling
Zhao Xiaoci, Zhang Yidu, Zhang Hongwei
2008, 34(09): 1088-1091.
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To eliminate the residual stress formed during the process of ring rolling, the radial ring rolling was simulated by elas-plastics large deformation finite element analysis. Al alloy rings with rectangular cross-section were adopted as workpieces and total depressing amounts of mandrel with different feed velocities were identical. Magnitude and distribution of plastic deformation in different feed velocity of mandrel were studied. The simulated results show that the fishtail shape coefficient is high when the feed velocity is relatively low and will be reduced with increase of feed velocity. According to the mechanism that inconsistent plastic deformation is the cause of residual stress, the corresponding residual stress distribution of radial ring rolling was analyzed. The research provides foundation for the residual stress relief study.
Multi-phase trajectory collaborative optimization for a hypersonic vehicle
Zhou Hao, Chen Wanchun, Yin Xingliang
2008, 34(09): 1092-1095.
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A approach was proposed to solve multi-phase trajectory optimization problem. The approach allowed the trajectory for hypersonic vehicle in vertical plane dividing into several phase, then obtained the multi-phase trajectory optimal value by collaborative optimization method. Only the transitional phase, gliding phase and descending phase were investigated. The expectation was that the terminal velocity maximum in transitional phase, the range maximum in gliding phase and the flight time minimum in descending phase. The three phase was regarded as three discipline, and the attack angle and initial condition were as input and terminal condition as output for every discipline. The collaborative optimization software coplatform was developed to solve the multi-phase trajectory problem. The result is identical with the one obtained by all in one method or globle sensitivity equation(GSE) method. It also shows the collaborative optimization method is effective to solve the multi-phase trajectory problem.
Double gimbal control moment gyroscopes singularity analysis
Lu Songtao, Wang Lei, Zhao Yushan
2008, 34(09): 1096-1100.
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Aimed at analyzing the singularity of double gimbal control moment gyroscopes(DGCMGs), a gimbal reference frame, an ε-δ definition of apparent and concealed singular points, three sorts of singular points, system momentum taylor series expanded formula at singular point and a determination of null motions were proposed. The relation between singularity of the system and parallelism of each gyroscope angular momentum was discussed. It was strictly proved that the DGCMGs with constant velocity and equal angular momentum and without limit of configuration, has the property that inside singular points must be concealed singular ones. The views above were examined through the numerical simulation of minimal apparent singular points of three orthogonal configuration’s 20° latitude circle.
Measures of effectiveness for blinking jamming under airborne self-protection operations
Gao Bin, Han Ke
2008, 34(09): 1101-1104.
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According to blinking jamming on analysis and modeling about operation procedure of blinking jamming, the measures of effectiveness for blinking jamming against angle guided missiles using radar seekers were evaluated by relational index. Firstly, the basic principle of blinking jamming was obtained, and then the operation process with blinking jamming was analyzed and modeled. With the reference standard of miss distance, the synthetic root mean square deviation was derived. Finally, the kill probability for covered airplanes by self-protection EW(electronic warfare) systems was introduced as the effectiveness index. The simulation results show that the influences between jammer power, covered airplanes velocity, airplanes RCS, mean blinking cycle and kill probability, dual airplanes formation parameter.
Application of unified hardening model under complex loading
Hou Wei, Yao Yangping
2008, 34(09): 1105-1108.
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The overconsolidated clay model, a simple and applied model, can describe many characteristics of overconsolidated clays well, including stress-strain relationships, stress dilatancy, strain hardening and softening, and path dependency behaviour. Compared with the Cam-clay model, the overconsolidated model only requires one additional soil parameter which is the slope of the Hvorslev envelope. Based on the specialy mobilezed plane(SMP) criterion and the corresponding transformed stress tensors, the model can be applied conveniently to three-dimensional complex stress state. By using the loading criteria, the model can be used to describe that the hardening degree, the shear modulus and the overconsolidated degree increase, and the void ratio decreases with increasing cyclic times under the complex loading. The comparisons between predicted results and test data from the cyclic loading and true triaxial tests show that the model can rationally exhibit the soil behaviors under the complex loading.
Novel technique to manufacture short millimeter wave band corrugated horn antenna
Bai Bing, Miao Jungang, Cui Yanjun
2008, 34(09): 1109-1112.
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In short-millimeter band quasi-optical network, it is a difficult problem to design and manufacture corrugated horn antennas acting as Gaussian feeds because of the accuracy of classical manufacture methods. The dimension design methods for corrugated horns were presented in term of the expected Gaussian beam parameters. The mode-matching (MM) method was carried out to numerically predict the performance of corrugated horns comprising large numbers of corrugation ridges and slots. A novel method was proposed to overcome the manufacture difficulties in short millimeter-wave band. The solution is to make the horn in a number of separate sections (either slot or ridge ring) and join them together with appropriate configuration. Two corrugated horns working respectively at 5mm and 3mm bands were realized in this technique. Finally, the performance of the two antennas was measured and the results were compared with the numerical data.
Video vehicle detection algorithm based on edge symmetry
Gao Lei, Li Chao, Zhu Chengjun, Xiong Zhang
2008, 34(09): 1113-1116.
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The existing vehicle detection algorithms are subject to many environmental influences, such as different lighting conditions, shadows. To solve these problems, a novel vehicle detection algorithm was proposed. Different from traditional methods, which use motion features to detect vehicles, the proposed method used edge and symmetry features to locate possible vehicles. First, the color-image was preprocessed with grayscaling, smoothing. The vertical gradient components of the image were found using the vertical mask of Sobel operator. Then the candidate areas with sufficient amount of edges were determined by calculating the gradient of edges. After finding possible vehicle candidates, the proposed method measured the prominent vertical symmetry of candidate areas and verified all possible candidates, as symmetry is an important feature of vehicle. The proposed method also figured out the vertical axis of symmetry and the width of the candidate vehicle. Three important restrictions obtained from above steps, including edges, symmetry and width, were used to validate the candidate vehicles. The experimental results show that the proposed algorithm is effective, reliable and robust.

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