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Table of Content

    25 April 2018, Volume 29 Issue 08
    Design and Kinematics of a SCARA Parallel Mechanism with Motion Decoupling and Low Coupling Degree
    SHEN Huiping;XU Ke;YANG Tingli
    2018, 29(08):  883-892. 
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    A new type of motion-decoupling SCARA(selective compliance assembly robot arm) parallel mechanism(PM) with low coupling degree(κ=1) was presented according to topology design theory of parallel mechanism based position and orientation characteristics(POC) equations. Algebraic equations of closed-form direct position were deduced by kinematic modeling based on single-open-chain(SOC), and then solutions for direct position of this PM were solved. Equations of inverse positions were also derived. Finally, workspace, rotation ability and singularity of the PM were analyzed based on the inverse kinematics.
    Influences of Fit Clearances on Steady-state Fluid Forces of Relief Valves
    QU Daohai;ZHOU Yunshan;LUO Wei;LIU Yunfeng;FU Bing
    2018, 29(08):  893-899. 
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    Aiming to solve the pressure regulating precision of electro-hydraulic proportional relief valves affected by steady-state fluid forces, a flow force mathematical model of converged flow spool valves was built. The valve model considering fit clearances was established based on CFD, and a test rig was set up to validate the correctness of the model. Then the influences of different fit clearances on steady-state fluid forces of spool valves were studied. The results show that the spool valve model considering fit clearances has a good coincidence with test results. While relief valve is working, the valve opening is close to fit clearance extremely. As pressure increases, valve opening becomes smaller, and jet angle gets close to 20°. As the clearance increases, valve opening turns smaller, jet angle becomes bigger. In a certain ranges, steady-state fluid forces increase with the increase of clearances, and fit clearances have a small influence on steady-state fluid forces when clearances reach the critical values.
    I.C. Engine Fault Diagnosis Based on Discrete Generalized S-transformation and TD-2DPCA
    ZHANG Shixiong;CAI Yanping;SHI Linsuo;WANG Xu
    2018, 29(08):  899-905. 
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    For the problems of fault diagnosis of I.C. engines, a method was proposed, which is consisted of discrete generalized S-transformation and TD-2DPCA. First of all, vibration spectrum images of cylinder head vibration signals were generated by discrete generalized S transform. Secondly, image matrix was bidirectional compressed by TD-2DPCA to reduce sizes of feature coefficient matrix effectively. Lastly, these feature matrixes obtained from image projects were served as enters of nearest neighbor classifier, which was used to achieve fault types' division. The method was applied to diagnosis example of the vibration signals of valve mechanism eight operating modes, comparisons of different time-frequency characterizations and feature extraction methods were carried out. The results show that the proposed method provides a new way for fault diagnosis of I.C. engines.
    Investigation on a Negative Magnetophoretic-inertial Combined Sortor for Non-magnetic Microparticles
    DU Jiayou1;GUO Wangcheng2;WANG Ruijin2;ZHU Zefei1,2
    2018, 29(08):  906-915,922. 
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    In order to sort non-magnetic micro-particles with a very close diameter, lateral migration of negative magnetophoretic coupled inertial sorter might be numerically calculated for 3 kinds of non-magnetic particles of 3μm,4μm,5μm in different magnetic fields for different microchannel parameters, different inlet velocities and velocity ratios of two inlets. The numerical results show that, greater lateral migration of non-magnetic particles are induced by more powerful magnetic field and bigger particle diameters. Separation efficiency of non-magnetic particles promotes when lower inlet velocity and greater inlet-velocity ratio. Moreover, smaller Ha/Hb and larger extension proportion in sorter are beneficial to particle separation. Partial numerical results verified by laser induced fluorescence experiments may prove the validity of numerical model.
    Simulation and Experimental Study of High Pressure and Large Flow Quick Opening Valves
    WANG Jie;ZHANG Jianzhuo;LIU Lingwei;
    2018, 29(08):  916-922. 
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    In order to solve the problems of large flow quick opening valves for large-tonnage high-speed hydraulic impact testers, a new structure of high pressure large flow quick open valve was put forward. An opening process mathematical model of the valve was established, and the opening processes of valve core were simulated by MATLAB Simulink. Sealing sleeve structure was optimized according to the simulation results. Dynamic response curves were simulated by AMESim model. On the basis of simulation results, the quick opening valves were processed. By the test results,the flow rate of valve is as 48 254L/min when the import and export differential pressures is 15MPa. Theoretical analysis and experimental results are consistent,and the structure of valve is feasible.
    Cylinder Head Vibration Signals Separation of Internal Combustion Engines Based on VMD and RobustICA
    YAO Jiachi1,2;XIANG Yang1,2;QIAN Sichong1,2;ZHANG Guanjun1,2
    2018, 29(08):  923-929,936. 
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    In order to solve the problems that the combustion signals and the piston slap signals in cylinder head vibration signals were difficult to separate in the time-frequency domain, the VMD and RobustICA methods were utilized to separate the independent source signals. The single channel cylinder head vibration signals of an internal combustion engine were measured by tests. Firstly, the measured signals were carried out the pretreatments, such as eliminations of trend items and move average. The VMD algorithm was employed to decompose the vibration signals. Then the RobustICA algorithm was applied to extract the independent components. The CMF method was adopted to combine the obtained independent components which were similar in time domain and frequency domain. Finally, the spectrum analysis, the continuous wavelet transform, the coherence function method and the drag test were utilized to further identify the separation results. The research results show that this method may effectively separate the combustion signals and the piston slap signals from cylinder head vibration signals under different test conditions.
    Flow Characteristics of Spherical Blade Hydraulic Pumps
    YU Yaxin1;JIANG Jianyu1;JIN Bo2,3;CHEN Xing2;FENG Yixiong2,3
    2018, 29(08):  930-936. 
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    A new type of spherical vane hydraulic pump was discussed herein. Firstly, structural characteristics and working principles of the spherical pumps were discussed. Secondly, a formula for calculating displacement of a hydraulic pump with spherical blades was obtained by spherical coordinates, and the accuracy of theoretical analysis was verified by Pro/E volume measurement method. Finally, flows and output characteristics of the pumps were analyzed. The influences of swash plate angle and the number of blades on flow pulsation with spherical vanes were discussed. The results show that when the number of blades increases, the flow pulsations of the vane pumps decrease obviously.
    Nonlinear Characteristic of Single Stage Gear System under Condition of Multiple Factors
    PENG Yumin;MA Chao;LUAN Zhongquan;XU Xiaoli
    2018, 29(08):  937-942. 
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    A nonlinear vibration model of three-degree-of-freedom spur gears coupled with transverse and torsion was established by mass centralized method, considering meshing stiffness, gear backlashes and bearing clearances. Parameter influences on the nonlinear vibration characteristics of the gear system were studied. The results show that, with the increase of frequency, the system enters chaos from periodic motion through a catastrophic way, then from the chaos to periodic motions. In periodic motions, the system changes from period 2 to period 4 through a period-doubling bifurcation, then from period 4 to period 2, and then from period 2 to period 1 through a inverse period-doubling bifurcation. For the different input frequencies, the changes of backlash make the system show different bifurcation characteristics. For some specific frequencies, the changes of the backlash only increase the amplitudes of the system response and do not change its dynamic characteristics.
    Fault Feature Extraction of Rolling Bearings Based on Noises Reduced by Full Vector Spectrum ITD-ICA Blind Source Separation
    LIU Jiahui;DONG Xinmin;LI Jianfei
    2018, 29(08):  943-948. 
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    The advantages of blind source separation and full vector spectrum technology were combined, and a method of signal noise ratio(SNR) of blind source separation for two channels was presented. Firstly, the ITD and ICA method were combined to reduce noises. The vibration signals of two channels were decomposed by ITD. The proper rotation components(PRC) were decomposed by correlation coefficient criterion restructuring as the inputs of ICA matrix. FastICA was used to realize the separation of fault signals and noise signals. Secondly, the full vector spectrum technology was used to carry out the full vector information fusion of the two channel fault signals and full vector spectrum analysis was completed after reducing noises. The comparison of experiments of rolling bearing fault analyses indicates the effectiveness of the method.
    Condition Monitoring Method for Wind Turbine Main Bearings Based on DBN
    WANG Hongbin1;WANG Hong1;HE Qun2;WANG Yueling1;ZHOU Zhen1
    2018, 29(08):  948-953. 
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    A condition monitoring method of wind turbine main bearings was proposed based on DBN. To reduce the modeling difficulties and decrease the training time, a correlation coefficient method was firstly applied to select the modeling variables. Further, a DBN temperature model of the normal behaviors of the main bearings was established and the main bearing temperature was predicted. This model overcomes the shortcomings of traditional neural network that randomly initializes the network weights and easily to fall into the local minimum thus may effectively improve the prediction accuracy of main bearing temperature. Then exponentially weighted moving average was used to analyze the residual errors of main bearing temperature and the failure threshold was determined by kernel density estimation method. Lastly, the main bearing failure was simulated based on the measured SCADA data. The experimental results show that the proposed method may effectively realize the abnormal condition monitoring of the main bearings than that of the traditional prediction methods.
    Acoustic Performance of Tunable Helmholtz Resonator
    AN Jun;LYU Haifeng;GENG Yanzhang;HAN Yannan
    2018, 29(08):  954-957,964. 
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    Traditional Helmholtz resonators belonged to passive silencer structures, and its acoustic performances were determined as long as its structures were determined. However, frequency often changed in actual noise environment. In response to this situation, a tunable frequency Helmholtz resonator was proposed. Piezoelectric ceramics which was instead of rigid backplane of the Helmholtz resonator changed the volume of chamber by adjusting the voltage applied to the piezoelectric ceramics, thereby distorted the silencer frequency. Experiments show that the piezoelectric ceramic in the applications of 400V voltage may produce 0.515mm displacement. Resonant frequency of the Helmholtz resonator is shifted by 80Hz at different voltages, and a control program is designed to meet the frequency changing noise environments.
    Car Dumper Hydraulic System Fault Diagnosis Based on Multi-block MPCA
    E Dongchen 1,2;ZHANG Lijie1,2
    2018, 29(08):  958-964. 
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    The monitoring methods were used separately to detect the faults in car dumper hydraulic systems based on physical model and statistical model. The monitoring variables were divided into some blocks according to the working mechanism in each stages of car dumper hydraulic systems, which makes the causal relationship of variables in each blocks more explicit. Then a MPCA model was built based on variables in each blocks. The multi-block MPCA model and all variables MPCA model were applied to leakage fault monitoring. The results show that the multi-block MPCA model is more sensitive to small leakage and has a higher fault detection rate.
    Performance Simulation for Scroll Expanders
    PENG Bin1,2;LI Yaohong1,2;ZHAO Shengxian1,2
    2018, 29(08):  965-970,978. 
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    In order to investigate performance characteristics of scroll expanders, the changes of the working chamber volumes for equal cross-section and variable cross-setion scroll expanders with respect to the orbiting angles were derived based on the geometric models. A mathematical model was established based on energy and mass balance. Temperatures, pressures, and masses of working chambers were investigated by solving the mathematical model. The relation among the geometric parameters and performance was revealed through quantitative analysis on mathematical model of the scroll expanders. The results provide the foundation for the scroll expander selections and the performance optimizations.
    In Situ Observation and Lubrication Mechanism of Powder Lubrication Interfaces
    KONG Junchao1;WANG Wei1;WANG Wei2;LIU Kun2;WANG Chao2
    2018, 29(08):  971-978. 
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    Loose graphite powder was used to lubricate plane contact tribopairs. A good powder layer with good anti-friction ability was observed under the effects of axial load and shear. Damage forms of powder layers were dynamically observed by optical microscope with CCD digital camera. The influences of surface roughness, load, slip velocity, powder quantity on the damage forms and processes of powder layers were analyzed. Image segmentation was used to calculate real contact area ratio. The results show that damage forms of the powder layers include five stages: complete period, partial area destruction, diffusion of partial area destruction, powder adhesion and complete destruction. The necessary conditions for adhesion stage existence are overload and a certain roughness. The increase of the powder amount and slip velocity may intensify the adhesion.
    PDMS Particle Fabrications by Laser-induced Forward Transfer within Water
    MAI Wenhao;DENG Yu;GUO Zhongning;HONG Wensheng
    2018, 29(08):  979-982. 
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    PDWS was characterized with low surface energy and high viscosity, which made it difficult to form a sphere particles in air. PDMS particles were fabricated within water by laser-induced forward transfer processes. The effects of laser energy and spot sizes on mean diameters of PDMS particles were experimentally investigated, and it turned out that the spot size plays a positive role on enlarge the particles while the pulse energy influences it negatively, and the fabricated PDMS particles have diameter range of 20~100μm and great surface quality. With high speed camera, the particle formation processes were observed, and it resulted from a jet generated by laser induced thermal cavitation.
    Optimized Interpolation Algorithm for Robotic Belt Grinding Processes
    ZHANG Tie;ZHANG Bin
    2018, 29(08):  983-990. 
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    In order to solve the problems of excessive cutting when using robot program generated by classical Taylor interpolation algorithm to grind surfaces where curvature changed greatly, the researches of path interpolation algorithm for robot surface grinding on off-line programming system was carried out. Through comparing various interpolation methods, an optimized Taylor interpolation algorithm was proposed. In the region where the curvature of processing path changed greatly, cutting locations become dense to decrease chord error; where the processing paths were smooth, cutting locations become sparse to ensure processing efficiency. Comparative experiments between the algorithm and the classic interpolation algorithm prove the algorithm may increase machining quality.
    Invasive 3D Real-time Supervision System for Digital Workshop
    ZHANG Tao;TANG Dunbing;ZHANG Zequn;WEI Xin
    2018, 29(08):  990-999. 
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    In order to meet the increasing requirements of supervision systems in the processes of digital transformations, a 3D real-time supervision system, which was oriented to digital workshops, was studied, and the requirement frames, architectures, and operation modes of the supervision system were established. Besides, key technologies of realizing the supervision system were studied. For example, the E-R-T model of the real-time database of the supervision system was established, the 3D scene model optimization technology of the supervision systems was studied, the translation and rotation realization method of the supervision system was expounded, and the interventional display method was put forward based on the real-time question-answer mechanism. The system was successfully applied to the desktop simulation platforms of digital workshops, and the operation effectiveness is good.