Abstract:The structure of a novel 5-DOF industrial manipulator was analyzed. The homogeneous transformation matrix of the manipulator was obtained by establishing a series of D-H frames. Based on Paul’s inverse transformation, an analytical method that could direct the solution of inverse kinematics problems of series manipulators was proposed, and the closed-form solution of inverse kinematics was derived. Computational simulation results indicated that the algorithm was efficient and real-time. The enveloping surface of the local joints’ workspace was specified using envelop theory. Working dexterity of the manipulator was discussed. The dexterous workspace of the manipulator on which the structure design and motion control were based was established via geometrically overlaying the enveloping surfaces of local joints’ workspace.

Abstract:To solve the problem of search performance in traditional distributed search engine, a non-centralized high parallelization search model was proposed and the traditional model was improved in the index structure and search algorithm. In the model, the index was classified according to document theme, bitmap structure was employed for longer inverted record list, and parallel search algorithm (multi max score heap, MMSH) was achieved in index node by using multi-threading technology. Experimental results show that the improved search model with index classification and bitmap strategy of the inverted list structure can enhance the search pertinence in Merge layer, reduce CPU and memory cost. In the case that the inverted list can not be completely stored in memory, MMSH algorithm can implement highly parallel search and its query efficiency is higher than the classical term-at-a-time algorithm, which shortens the average search time and improves the system throughput. Index classification, bitmap structure and parallel query algorithm can avoid query blindness and improve the performance of distributed search engines.

Abstract:The effects of pitch ratio and blade area ratio on the tip leakage vortex (TLV) were studied in a ducted propeller. Furthermore, the relationship among the TLV, tip loading and tip leakage flow (TLF) of different blades was discussed. The flow field of the ducted propeller with several different blades was numerically simulated and analyzed and the results showed that as the pitch ratio increased, the tip leakage vortex moved away from the suction side of the blade, and the core cavitation number decreased. As the blade area ratio grew, the vortex core trajectory did not alter, and the vortex core cavitation number rose. The TLV was influenced by TLF through flow shearing, while the TLF was controlled by the tip loading, the velocity of TLF at the position with heavier loading was higher.

Abstract:To increase polishing efficiency and improve surface quality of silicon, electrochemical measurements were used to study the influence of polarization potential on passivation of silicon wafer, based on which tribo-electrochemical tests were done to investigate the effect of polarization potential on friction and material removal. Results show that the passivation film with better corrosion inhibition effect can be obtained under anode polarization potential of 1 V in alkaline CeO₂ polishing liquid. A higher polarization would destroy the passivation film, while a lower polarization would suppress the formation of it. Moreover, the passivation film on silicon wafer can increase surface friction coefficient as well as material removal rate.

Abstract:A fast line segment detection method, unite-and-divide (UND) approach, is investigated, which includes two phases, namely the union of spectra in the frequency domain and the division of the sinogram in Radon space respectively. In the union phase, for a given image, its sinogram is obtained by parallel 2D multilayer Fourier transform, Cartesian-to-polar mapping and 1D inverse Fourier transform. In the division phase, every peaks and edges of butterfly wings in its neighborhood in sinogram are firstly specified, with each neighborhood area corresponding to a window in image space, and then, by applying edge-analyzing to each sinogram of each windowed separately, the endpoints of line segments are extracted. Our experiments are conducted on benchmark images, the results reveal that the UND method yields high accuracy, low computational cost and is more robust to noise.

Abstract:It is a viable form of drag reduction for airship to use airship envelope with micron-scale grooves. In this paper, the k-ω SST turbulence model is used to analyze the V-shaped micro-riblets. The velocity and pressure field are obtained using this model. Both the drag reduction mechanism for micro-grooves and the influence of different groove size are analyzed by the streamline pattern and the drag reduction rate. The results show that the streamline pattern is an important reason for drag reduction ability, and the grooves with appropriate size can reduce the drag between fluid and wall.

Abstract:The springback of CNC bending reduces accuracy of tube bending, which leads to the wrinkle during subsequent hydro-forming, and to avoid the defect during hydro-forming, springback compensation is necessary. In this paper, theoretical model of tube plastic bending and strain hardening model of materials were set up firstly, and then the value of springback angle was derived. Meanwhile, several groups of experiments were carried out, and linear fit formula between springback angle and bending angle based on mathematical statistics was also obtained. Finally, the hydro-forming experiments show that the wrinkle can be avoided by springback compensation during CNC bending, and the dimensional accuracy of hydro-formed sub-frame is acceptable.

Abstract:Aiming at the case of the state vector with quaternion constraint in some nonlinear systems, a quaternion constrained cubature Kalman filter algorithm is presented. Based on a minimum constrained cost function, this algorithm uses three-degree spherical-radial cubature rule to approximate the posterior mean and covariance, and gives the QCCKF recursive formula. It can estimate the state effectively, and extends the applications of the cubature Kalman filter (CKF). By simulating for the spacecraft attitude estimation system, simulation results show that the proposed algorithm is superior to CKF and unscented quaternion estimator(USQUE) in precision, satisfies the quaternion constraint, and solves the problem that the nonlinear system has quaternion constraint, which show the validation of the proposed method.

Abstract:In conventional feedback filter, the feedback from some unobservable system states will lead to the divergence of navigation errors. Further the measurement equation of global positioning system/strapdown inertial navigation system (GPS/SINS) is nonlinear, and it increases the complexity of the filter. To solve these problems, a linear measurement equation was derived in this paper. As a complement to this measurement model, a composed adaptive revising filtering method based on the observability of states was presented as well. The eigenvalues and eigenvectors analysis method of error covariance matrix was chosen to analyze the observability of system states as a result of the comparison of three popular observability analysis methods. The feedback factors were thus designed according to the analyzed results. As a consequence, errors from the original data of SINS and GPS receiver can be corrected. Simulation results demonstrate that our proposed method is effective and can improve the estimate accuracy of the system in incomplete observable condition.

Abstract:Considering the large contrast changing of surface targets and sea-sky background and the obvious difference of field depth, an improved image segmentation algorithm based on self-adaptive Mean-Shift is proposed. Spatial bandwidths are adaptively computed according to the estimation of gray distribution around the reference point; then the gray-level bandwidths are adaptively computed with a novel Bayesian theory in the corresponding windows; and finally adaptive segmentation is obtained. In the experiment, both the close and distant target frames, as well as target frames of different contrast, are extracted respectively from the surface vehicle video sequence. Compared with the traditional segmentation algorithm, experimental results prove that the proposed algorithm can effectively complete segmentation of surface target images.

Abstract:A modular adaptive controller is proposed for the nonlinear attitude tracking of micro-spacecraft in the presence of uncertain inertial tensor, external disturbances and saturation constraints, which combines the theory of system immersion and manifold invariance (I&I) and constrained backstepping. Firstly, the spacecraft attitude is globally represented by modified Rodrigues parameters. Then the backstepping controller is derived to implement any operating constraints and obtain the derivatives of virtual control easily by introducing command filters and modified tracking errors. To improve the robustness of baseline controller, the nonlinear estimator is constructed based on I&I to estimate and compensate the time-varying total disturbances on line. Because the I&I approach allows for prescribed uniformly stable dynamics to be assigned to the estimation error, the resulting modular adaptive controller is easier to tune compared to classical adaptive backstepping. And its performance does not suffer from unpredictable dynamical behavior of the estimation laws. The closed-loop input-to-state stability and boundedness of the estimation error are guaranteed by Lyapunov direct method. Comparative simulations state that the proposed controller is successful in achieving high attitude performance and precise estimation of disturbance.

Abstract:To improve accuracy and reduce processing error, the elliptical bevel gearing by additive manufacturing is measured, and the causes of error are analyzed. Space spherical coordinate system, additive manufacturing coordinate system, layers model, theoretical error model and error detection model of ellipse elliptical bevel gear are established by the meshing theory of space transmission and the theory of additive manufacturing. The pre-process of elliptical bevel gearing is analyzed, the process of additive manufacturing is researched and the additive manufacturing method of this gear is obtained. The gears are detected by digital microscope system and coordinate measuring machine, to analyze the surface precision and gear pitch error. The analysis results show that the error of ellipse bevel gear is a little big by the use of material manufacturing method. Optimizing STL model, reducing the diameter of metal powder, decreasing the effect on the processing layer by laser radius and thermal effect, will contribute to raise additive manufacturing precision.

Abstract:Against the problem of huge computation of high-resolution DOA estimation algorithm using acoustic vector sensor array, a fast high-resolution DOA estimation algorithm was proposed based on the combination processing of pressure and particle velocity. The algorithm selected the electronic rotation vector of the reference element as the desired signal and MSWF(multi-stage Wiener filter) was used to estimate the signal subspace, which greatly reduced the amount of computation because it did not need to calculate the cross-covariance matrix of acoustic vector sensor array and Eigen value decomposition. The algorithm is based on the principle of coherency between pressure and particle velocity, which can suppress interference well in isotropic noise field. Theoretical analysis and computer simulations show that the algorithm has good performance of DOA estimation while it greatly reduces the amount of computation.

Abstract:In this paper, the whole cavitation collapse process was divided into cavitation moving phase and cavitation collapse shock phase based on the physical phenomenon of cavitation collapse process, potential flow method and Nonlinear Doubly Asymptotic Approximation(NDAA) were respectively used to calculate the two stages to make a mechanical analysis of the whole process to study the effect of theload of cavitation collapse on the sailing body movement. A new method was established to calculate the load of cavitation collapse, and a whole calculation method on the load of cavitation collapse was established. By comparing the results of numerical calculation with the experiment, the reasonability of the method was validated. Based on it, the law of the load of the cavitation collapse and the shape of the cavitation were obtained. Finally, the effect of elastic vibration on the cavitation collapse was researched, and the elastic vibration had a little effect on the peak value and periods of the collapse load.

Abstract:This paper proposes a robust object tracking algorithm under the Mean-shift framework based on the online update strategy of multi-feature template. At first, to solve the drift problem caused by cluttered backgrounds, the illumination invariant color features and the rotation invariant LBP texture feature were extracted and were combined together with the BWH algorithm. Secondly, in addition to the traditional convergence condition of Mean-shift algorithm, a histogram similarity checking step was presented against the local optima problem. Besides, occlusion detection algorithm based on spatial distribution of the histogram difference was proposed to enhance the precision of the template update. Experimental results showed that the proposed tracking algorithm is robust and accurate against cluttered dynamical background, occlusion and the object deformation.

Abstract:A finite volume method (FVM) is developed for elastic analysis of three-dimensional (3D) anisotropic linear elastic solids with continuously variable material properties. The method employs tetrahedral elements so that it owns adaptability to problems with irregular domain. A staggered unstructured FVM is used for spatial terms. The displacement, velocity and acceleration are defined on the cell vertex while the stress and material properties which are uniform in the cell are defined on the cell center. An Euler scheme is employed for time dependent terms. The numerical results of the FVM agree well with the results of other numerical methods, and the FVM consumes much less computational time and memory, which is able to predict the 3D anisotropic linear elastic problems accurately and efficiently.

Abstract:The paper aims to improve the H∞ control performance of a class of systems. It is concentrated on H∞ preview control for stochastic Ito system with state-dependent noise. Associating game theory and dynamic programming, we present the solvable condition and explicit controller of the stochastic H∞ preview control via decoupling the coupled ordinary and partial differential equations and utilizing the characteristic curve.

Abstract:The research on deterministic small-world network model is an important branch of complex network modeling. This paper analyzes the small-world property of the minimal Cayley graph and proposes a deterministic small-world network model based on minimal Cayley graph. The model constructs a class of small-world networks with high symmetry by selecting a minimal Cayley graph, and appropriately expands its generating set. Compared with the existing models, this model can be used flexibly to get small-world networks with const degree or variable degree, which is adaptable for the disign and analysis of the real networks such as communication network and P2P overlay network.

Abstract:To get better performance of interference hyperspectral image compression, according to the imaging principle ofinterference hyperspectral image, we propose an adaptive direction prediction wavelet transform forLWT (Lifting Wavelet Transformation),to get the best predicted values through adaptive direction in the LWT on the frame direction, and change the order of the traditional wavelet transform.The experiment results prove that the proposed method can get higher SNR at the same bpppb compared with the traditional method, and can get smaller MSE in the recovered spectral curve.

Abstract:To improve the efficiency of micro-EDM, we designed a pulse power supply which can actively match pulse parameters for micro-EDM. By using the processing method of equal energy, we conducted the comparison experiments of processing efficiency in different pulse parameters, designed the structure, function and control strategy of this pulse power supply, and carried out a machining experiment. The results show that the highest machining efficiency can be obtained by selecting the appropriate pulse width and pulse interval, making the electrode capacitance charge and discharge for only one time, and the pulse parameter of the pulse power supply can automatically adjust to electrode voltage and capacitance. When machining the micro holes, the power supply has good processing continuity, high processing efficiency and quality, and when used for micro machining, the power supply can obviously improve the processing efficiency and get good processing quality compared to the traditional power supply.

Abstract:To improve the method of collecting of forest habitat factors such as forest temperature, humidity and light intensity, an automatic collection system of forest habitat factors was completed with the use of embedded technology and wireless sensor network technology. This system used the LPC2148 embedded chip as main control chip, MySQL as the system database AecGIS Server as GIS platform, to obtain forest temperature, humidity and light intensity by the collection device composed of BH1750FVI light sensor and SHT11 temperature and humidity sensor, to establish communication with the host computer by nRF905 wireless communication module so as to store data and real-time display of the dynamic changes of the forest habitat factors in a web page. The test results showed that the data packet numbering mechanism and time synchronization mechanism used into the communication protocol of sensor nodes could alleviate network congestion and reduce the loss rate of the data packets. When the emission frequency of the wireless communication module was set to 433 MHz, the transmission rate and emission power were set to 9 600 bps and 10 dBm, the error rate of frames could be effectively controlled within the range of less than 50 meters.