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Table of Content

    10 March 2017, Volume 28 Issue 05
    Hybrid Kinematics Mechanisms and Its Kinematic Analysis Oriented to Multi 3D Printing
    ZHOU Hui, , DING Rui, , QIN Youlei, , CAO Yi,
    2017, 28(05):  505-511. 
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    In order to solve the bottleneck problems of multi 3D printing equipment, a fully-decoupled five degree of freedom (5-DOF) HKM was presented as the actuator of 3D printing. HKM consisted of 3-CPaRR parallel module and RRo serial module, and the parallel module consisted of three identical CPaRR limb chains, it might realize three-dimensional translations, the serial module RRo was used to adjust the print head posture, improve 3D printing process step phenomenon and interference problems. Screw theory was applied to analyze the kinematic characteristics of mechanisms and to calculate the degrees of freedom of 3CPaRR&RRo which were verified via the ADAMS software. The kinematic matrix of the hybrid mechanisms was carried out by using the D-H convention. The expression of the forward kinematics was deduced to obtain the Jacobian matrix and velocity equations, and the analysis of singularity was carried out. Moreover, simulation model was built with ADAMS, the velocities of the end-effectors of mechanisms were drawn. Thus, the validity of the theoretical analyses was proved.
    Discussion of Low Cycle Fatigue Life Prediction Models for Magnesium Alloys
    CHEN Ling, , ZHANG Xianming, LIU Fei, OUYANG Ping, JIA Yanyan
    2017, 28(05):  512-518. 
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    Through low cycle fatigue experiments of the cast magnesium alloy AZ91D and the wrought magnesium alloy AZ31B at room temperature under stress control, the fatigue life prediction was conducted by the Basquin model, the SWT model and the strain energy-life model. Then, regarding the low cycle fatigue damage of magnesium alloys as an irreversible dissipation process that might be described by the entropy according to the irreversible thermodynamics theory of continuum damage mechanics, and using the mean strain increment per cycle to reflect the effects of the mean stress, a new model for the low cycle fatigue life prediction of magnesium alloys was developed. By this model, the low cycle fatigue life prediction of magnesium alloys was carried out through the experiments mentioned above. Results show that the predicted results are in good agreement with the experimental results. And compared with the other life prediction models, the new model for the low cycle fatigue life prediction of magnesium alloys has a better effectiveness.
    Analysis and Experimental Study of Amplitude Attenuation Characteristics of Vibration Broaching Systems
    MENG Zhen, NI Jing, WU Chuanyu
    2017, 28(05):  518-524. 
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    In order to investigate the major factors of amplitude attenuation during vibration broaching processes, a novel dynamic model of excitation system was established by considering the dynamic characteristics of dual-valve system, the broaching forces affected by the multi cutter tooth and workpiece size parameters. Then, the output waveforms of electro-hydraulic exciter with nonlinear disturbance were studied by the results of numerical simulations and system experiments, which may provide some theoretical references and laboratory evidence for optimizing parameters of the exciter system. The results show that the vibration amplitudes of exciter are mainly limited by the excited frequency. The peak values of waveform are reduced by dynamic broaching forces, which mainly affects the movement characteristics of cylinder piston. Because of that, the displacement amplitudes may tend to zero.
    Adaptive Measurement of Free-form Surfaces Based on CMM Double Parameter Directions
    HE Xueming, LI Yongping, WU Meiping, ZHANG Rong
    2017, 28(05):  525-531. 
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    A kind of adaptive measuring method for free-form surfaces was put forward based on double parameter directions of CMM. At first, a measurable area was generated by boundary points of the surfaces. Then, a few uniform initial scan lines and uniform initial measuring points of each line topology were automatically generated by the measurable area. A B-spline curves were generated by fitting the initial points that automatically measured by the CMM in the U parameter direction and the locations of next point were adaptively predicted by the end curve curvatures. A B-spline surface was fitted by the initial scan lines point cloud, then the next line positions were adaptively determined by the border maximum curvatures of the surfaces in the V parameter direction, and the scanning lines of U parameter direction were measured adaptively, until measurements were completed. Distribution density of the measuring points was determined by the curvature variation characteristics of the measured surfaces. The larger the curvature of the surfaces, the greater the distribution density of the measuring points and the smaller the curvatures of the surfaces, the smaller the distribution density of the measuring points, which guarantees the important feature points not leaking and avoid the data redundancy. The results of measurement experiments for theoretical curves and surfaces show that the measurement precision may reach μm level. The feasibility of the method was verified by an example of a part measurements.
    Bearing Fault Diagnosis Based on DTCWT and DBN
    ZHANG Shuqing, HU Yongtao, JIANG Anqi, LI Junfeng, SU Xinshuang, JIANG Wanlu
    2017, 28(05):  532-536,543. 
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    Based on DTCWT and DBN, a new method of bearing fault diagnosis was proposed. Experiments on bearing vibration signals decomposition show that the signals may be well decomposed into different frequency bands by DTCWT. Then, power entropy of different frequency bands were taken as the fault features and input to the model for classification and the traditional classifiers were taken as the comparison. Results show that the method may identify different fault types accurately, which expands the applications of DBN.
    Stability Analysis of 2D Electro-hydraulic Pressure Servo Valve Based on Squeeze Oil Film Theory
    ZUO Xiqing , RUAN Jian, SUN Jian, LI Sheng, LIU Guowen
    2017, 28(05):  537-543. 
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    A new kind of 2D electro-hydraulic pressure servo valve (EPSV) was designed for aircraft hydraulic braking system herein. Using LVDT to form a closed loop position feedback, servo spiral mechanism was taken as pilot valve, the pressures were accurately controlled through mutual movements among 2D pilot valve, spring and master valve. Based on the squeeze oil film theory, the valve structures were designed to increase the system damping ratio and improve system stability. A mathematical model of the valve and the squeeze oil film theory were built, the relationship among positive opening amounts of the master valve, spring deflections and the output pressures of master valve was simulated to ensure its current-pressure characteristics. Three kinds of conditions, initial system, decreasing open loop gains and increasing system damping ratios, were comparatively analyzed by software MATLAB, simulation results show that: it is necessary to design the valve based on the squeeze oil film theory, the valves stability is improved much after increasing its damping ratios.
    Effects of Shock Absorber Damping on Fatigue Lifes of Torsion Beams
    ZHOU Bing, LI Ning, WU Xiaojian, JIANG Gaosong
    2017, 28(05):  544-549. 
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    In order to study the effects of shock absorber damping on the fatigue lifes of the torsion beams, the finite element model and rigid flexible coupling model were set up. The road load spectrum collected by experiments on strengthened test pavement was used as the input excitation of the vehicle model, and documents of the fatigue analysis could be gotten by the simulation , then the fatigue analyses of torsion beams could be conducted by modal stress recovery, the accuracy of the results could be proved by the bench text of durability. Finally, the contours of fatigue lifes and the minimum fatigue life cycle with different damping coefficients would be obtained ,and the effects of the shock absorber damping on fatigue lifes of the torsion beams might be known.
    Condition Assessment for Rolling Bearings Based on SOM
    ZHANG Quande, CHEN Guo, LIN Tong, OUYANG Wenli, TENG Chunyu, WANG Hongwei
    2017, 28(05):  550-558. 
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    Aiming at the problems that single feature fault diagnosis accuracy was not too high, a rolling bearing condition assessment method was proposed based on SOM  herein. Firstly, the multi-dimensional features were extracted from the original vibration signals and preprocessed by PCA, a fusion model was established by training SOM network and weight vectors of competitive neuron were obtained. Secondly, the fusion index, which was the minimum Euclidean distance between every sample values to the competitive neuron weighting vector, was achieved. Finally, the conditions of rolling bearings were classified by comparing the minimum Euclidean distances among the detected samples and the normal samples. The proposed method herein was applied to condition assessment of the rolling bearings, and the test results show that the fusion index is more sensitive and robust than that of original single feature during the stages of early faults; meanwhile, the fusion index may reflect the states of rolling bearings more accurately.
    Chaotic Prediction and Control of Hydraulic Cylinder Nonlinear Stiffness Constraint System
    LIU Bin, LI Peng, LIU Fei, LIU Haoran, JIANG Jiahao
    2017, 28(05):  559-564,582. 
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    For the chaos of nonlinear stiffness constraint system of a hydraulic cylinder, a kind of dynamic control model of hydraulic cylinder nonlinear stiffness constraint system was established. The critical conditions of chaos in nonlinear stiffness constraint system of the hydraulic cylinder in the sense of Smales horseshoe transformation were obtained by Melnikov method. Through simulation analyses, it is found that when the linear control parameters are changed, the critical conditions for the occurrence of chaos in the system will also change. At the same time, the stability of the system may be improved when the linear control parameters are increased.
    Fault Frequency Extracting Methods Based on LCD and LTSA
    WANG Fei, FANG Liqing, LYU Yan
    2017, 28(05):  565-569,575. 
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    As the fault vibration signal characteristics presented non-stationary and the fault frequencies were hard to extracted, a new feature extraction method was proposed .This approach combined LCD and LTSA which was one of the typical manifold learning methods to extracting fault frequencies. Firstly, the vibration signals were decomposed into multiple intrinsic scale components in multidimensional feature vectors using LCD. Secondly, LTSA method was applied to compress the high-dimensional vectors into low-dimensional vectors, the low-dimensional vectors were used to reconstruct and the new fault signals were obtained. Finally, the new fault signal's spectrum were analysed and the fault characteristic frequencies were acquired. The rolling bearing fault experimental results show that this new technique may extract the inner and outer ring fault frequencies, it verifies the effectiveness of this new approach.

    Study on Laser Cutting Quality of Zirconia Ceramic Based on Vapor-melt Ratio
    WU Di, WANG Xuyue
    2017, 28(05):  570-575. 
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    A laser precision cutting method was used based on vapor-melt ratios controlled, the in-fluences of vapor-melt ratio and thickness on the cutting quality were studied systematically, that is the effects on kerf quality, kerf surface striation formation and roughness. Through observing on samples of different vapor-melt ratios(0.099, 0.160, 0.184, 0.202), which shows that high vapor-melt ratio may improve the kerf quality, enlarge the length of smooth zone of kerf surface and the striation wavelength, decrease the kerf surface roughness. Meanwhile the observations on samples of different thicknesses (0.8mm, 1.0mm, 1.5mm, 3.0mm) show that with the increasing of thicknesses, the vapor-melt ratio reduced, the kerf quality and roughness also decrease, the surface striation also presents different morphologies. When the thicknesses are as 0.8mm and 1.0mm respectively, the surface presents smoothly periodic striation; When the thickness is as 1.5mm, the surface presents two zones, which are smooth zone and rough zone; When the thickness as 3.0mm, the surface presents three zones, which are smooth zone, rough zone and scaled stack zone. The researches of vapor-melt ratios and thicknesses may lead a deeper comprehension on the mechanism of laser cutting, provide theoretical and experimental basis for improving the laser cutting quality of zirconia ceramic.
    Static Calculation and Load Sharing Characteristics Analysis of Double Parallel over Constrained Lifting Mechanisms of Schnabel Car
    ZHAO Yanzhi, JIAO Leihao, WANG Xiangnan, REN Yubo, WEI Hongliang, YU Yuebin
    2017, 28(05):  576-582. 
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    To research the constraint forces and load sharing characteristics of double parallel over constrained lifting mechanisms of schnabel car, a stiffness model of schnabel beam was established based on Timoshenko beam theory. The static calculation was done by simultaneous equations solution of elastic deformation coordination equations and static force balance equations, and the mapping relationships among the bearing capacities and stiffnesses of the mechanisms were obtained. Then, the unbalanced load coefficients of the lifting mechanisms were defined, and the influence rule of load sharing characteristics produced by structure stiffness changes and partial loads were analysed and obtained. The rigid-flexible coupled simulation model of double parallel over constrained lifting mechanisms was built in RecurDyn and the simulation results verified the correctness of theoretical analyses.
    Task Assignment Strategy for Serial Coupling Product Design Based on MWTM
    TIAN Qihua, MEI Yueyuan, LIU Yong, DU Yixian
    2017, 28(05):  583-588. 
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    The task assignment strategy for serial coupling product design, which involved the rework of tasks, was very complex. To solve the problem, the MWTM was introduced to quantify the coupling relations among the tasks in rework amounts. Based on the task assignment derivative matrix, a model of the task assignment for serial coupling product design was built. This model was solved by genetic algorithm and so the optimal task assignment strategy of product design might be obtained for different design requirements. Taking the development of an electric car as an example, validity and feasibility of this model were proved.
    Study on Composite IMC of an Electro Hydraulic Drive Unit of Parallel Stable Platform
    ZHANG Lijie, WANG Lihang, LI Shaohua, LI Yongquan,
    2017, 28(05):  589-596. 
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    According to the requirements of motion control of a hydraulic driven ship stable platform, a composite IMC scheme was proposed based on velocity feed-forward structure. The mathematical model of the control object was obtained by the method of mechanism modeling and parameter identification, which was based on the single channel hydraulic drive unit of the ship stable platform. Simulation and experimental studies of the proposed control method were carried out,and the results show that, with the proposed control method, the tracking performance may be improved, as well as the anti-interference and robustness of the system.
    Complexity Computation Approach of Design Cognition Using Deterministic Information Theory
    XU Jiang, WANG Xiuyue, WANG Yi, GUO Feng
    2017, 28(05):  596-602. 
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    Aiming at the cognition compuatation problems for fuzzy front end of innovation design, the information on design cognition was presented by the oral data and the complexity analysis and computation method were proposed through information processing. Firstly, the complexity of design cognition behaviors from four sides including the process, content, team and approach of design was elaborated. By structurally representing the data and information in the form of linkography, the description on design cognition was made through combination with DIT. Furthermore, the T-code parse algorithm was illustrated on the basis of the definition on the new link-matrix. The analyses of cognition complexity, the information amount and the information entropy were carried out for different stages of design reasoning, the concept distribution and the key concepts. Finally, by taking functional backpack design as an example, the layout characteristics of the design concept and the design processes of convergence and divergence were compared, the effectiveness and feasibility of the method were proved.
    Effects of Ultrasonic Vibration on Drawing Height and Fracture Quality at Corners of Micro-square Cup
    ZHA Changli, CHEN Wei
    2017, 28(05):  603-606. 
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    A SUS304 sheet metal forming experiment set-up was designed to investigate the drawing formability of micro-square cup based on ultrasonic vibrations. Effects of the drawing height and fracture quality at the corners of the micro-square cup were researched with various sample thicknesses, molds and vibration amplitudes. And the normalized ratio coefficient λwas introduced to analysis the sensitivity of three kinds of mold to the ultrasonic vibration in drawing. Results show that using vibration following the deep drawing processes the height is increased from 0.19mm to 0.24mm, from 0.30mm to 0.44mm, and from 0.79mm to 1.10mm for thickness of 40μm, 100μm and 200μm, respectively. The fractures at the corners of the micro-square cup present tears and irregulars in the absence of ultrasonic vibration conditions, and with the increasing of vibration amplitudes, the fractures become flatter. It is observed that the more sensitivity of No.2 mold to ultrasonic vibration is stronger than that of the other two types.
    Dynamic Mechanics Behavior and Constitutive Model of TC4-DT Titanium Alloy Materials
    AI Jianguang, JIANG Feng, YAN Lan
    2017, 28(05):  607-616. 
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    The dynamic mechanics behavior experiments of TC4-DT titanium alloy materials were carried out using high temperature Hopkinson bar with synchro assembly system SHPB apparatus under different strain rates (930~9700s-1) and at room temperature and under different temperature (20~800℃) at high strain rate(5000s-1)respectively.The stress-strain curves of TC4-DT titanium materials were obtained at high temperatures and high strain rates. The TC4-DT materials have the strain rate plasticity effect and have the critical strain rate value, above this value, the strain rate sensitivity increases obviously. The softening effect is weakened with the increase of heating temperature of the materials. The experimental data were  fitted Power-Law and Johnson-Cook two kinds of thermal visco-plastic constitutive equation respectively; and the two kinds of dynamic constitutive model parameters were obtained. the two kinds of fitting curves and the experimental data obtained were compared and analyzed. The results show that the two model predictions have a good agreement with the experimental data. Futher,the fitting precision of the two curves were compared and results show that the fitting errors of the two models are not very different, but the precision of the Power-Law model is slightly better than that of Johnson-Cook model.
    Engine Economic Performance Simulation by Single Valve Working Mode with Variable Lift
    XU Jiangtao, CHANG Siqin, LIU Liang, FAN Xinyu
    2017, 28(05):  617-623. 
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    A working mode of single intake valve with variable lift was put forward based on the fully flexible EMVT technology. Based on EMVT power consumption, the engine was modeled and simulated. The results show that, in the low speed engine conditions by single valve with variable lift mode, the air charging rates may be enhanced, the pumping loss and EMVT driving power may be reduced, so the aims of improving the fuel economy of the engine are achieved. And with the decreasing engine speeds and loadings, the improvement rates assume the increasing trend, such as in engine speed 1000r/min, load 40.0% condition and single valve with 2mm lift, the fuel consumption may be decreased 12.2% compared to the prototype.
    Optimization of Battery Equalization Strategies Based on Dynamic Fuzzy Threshold
    LIU Zhengyu, MA Yadong, SUN Qing, TANG Wei
    2017, 28(05):  624-629. 
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    A fixed terminal voltage threshold simply took as power battery equalization control indicators, which might lead to equalization judgment errors and equalization circuit on-off frequently. To solve above problems, based on the impact analyses of lithium battery polarization voltages, Ohm internal resistance, charge-discharge current on the terminal voltage characteristics, a dynamic fuzzy threshold equilibrium method was proposed. First of all, based on the fuzzy algorithm, terminal voltage thresholds were dynamically setted, then equalization control operations were carried out. Experimental results show that compared with the threshold voltage of the traditional equilibrium strategies, this method may effectively reduce monomer battery terminal voltage differences,obviously shorten the equilibrium time.