Table of Content

25 May 2018, Volume 29 Issue 10

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Fuzzy Risk Assessment of Aeroengine Life-limited Parts Based on Improved Entropy TOPSIS Method

LI Yuanbin1， 2;SUN Youchao1;LI Longbiao1

2018, 29(10):  1135-1140. 

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The TOPSIS method was improved by information entropy weights as attribute weights， failure modes of aeroengine life-limited parts were taken as assessment objects， and risk indicators were blurred.This new method for risk assessment of life-limited parts was proposed.Three factors with severity， occurrence and detection difficulty of failure mode were made to be main risk indicators.Triangular fuzzy number decision matrix was established and standardized.In the case of fault data for small sample， decision information of relevant experts and engineers was integrated to calculate entropy weights of risk indicators， and then the entropy weights were used as weighted vectors to amend the normative decision matrix.The TOPSIS was utilized to evaluate.Five failure modes were evaluated with positive and negative ideal solutions， Euclidean distances and relative proximity data.The fuzzy risk assessment method based on improved entropy TOPSIS may achieve the accurate sorting of assessment objects， and it is more efficient to analyze than the hazard matrix mapping method.The method may provide a reliable basis for risk reduction and development of preventive measures in failure mode and effect analysis（FMEA） method.

Steady-state Tribological Performance of Sliding Friction on Textured Surface

LI Wanzhong1，2;XU Yingqiang1;SUN Jian1;LIU Kai'an1;WU Zhenghai1

2018, 29(10):  1141-1146. 

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Based on steady-state sliding frictional model，the influences of normal loading，sliding speed， initial surface texture and material on steady-state frictional coefficient were researched quantitatively with ball-disk friction pair.Rules of steady-state frictional coefficients under different operating condition were obtained.The results show that steady-state frictional coefficients of sliding friction are positively correlated with wear rates.Steady-state frictional coefficients of different surfaces in morphology descending order are circumferential texture， untextured and radial textures.Regardless of the initial surface， frictional coefficient decreases first and then increases with the increase of revolving speed.With the increase of normal loading， it presents an upward trend.Deeper or wider textured surfaces have higher frictional coefficients and larger instantaneous fluctuation.Moreover， frictional coefficients also associate with the selection of friction pair materials.

DTM Analysis for Free Vibrations of Rotating Functionally Graded Material Timoshenko Beams on Elastic Foundations

TENG Zhaochun;CHANG Bo;FU Xiaohua

2018, 29(10):  1147-1152. 

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Free vibrations of a rotating FGM beam on elastic foundation was investigated based on Timoshenko beam theory.Firstly， the physical neutral surface position for the FGM Timoshenko beam was determined， and two motion governing differential equations of the transverse free vibrations of the rotating beam on elastic foundation were derived by using generalized Hamilton principle.Secondly，DTM was used to transform the differential equations and the boundary conditions.At the same time， the dimensionless natural frequencies of transverse free vibrations of rotating FGM Timoshenko beam on elastic foundation with clamped-clamped， clamped-simply supported and clamped-free three boundary conditions were solved， then the governing differential equation was degenerated and the good agreement among the results of this paper and those available in the literatures validated the presented approach.Finally， the effects of different boundary conditions， different rotating speeds， different elastic modulus and different gradient indexs on the free vibration frequencies of FGM Timoshenko beam were discussed.The results show that the dimensionless natural frequencies of FGM Timoshenko beam increase with the growth of the dimensionless rotating speeds and the dimensionless elastic foundation modulus.Under a certain dimensionless rotating speeds and dimensionless elastic foundation modulus，the dimensionless natural frequencies decrease along with the growth of the FGM gradient indexes.

Eye-on-Hand Calibration Method Based on Specular Reflection

ZHANG Xu1;JIA Junhui1;ZHANG Gang2

2018, 29(10):  1153-1158,1165. 

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For the Eye-on-Hand calibration problems of eye-on-hand robots， a Eye-on-Hand calibration method was proposed based on specular reflection.Images were captured through specular reflection， and a linear solution algorithm was used to determine the pose relationship between ends of the robot and camera coordinate system according to the image theory.In contrast to the conventional calibration method， this method only needed to change the attitudes of plane mirrors 3 times，and might simultaneously get the camera??s internal parameters and pose relationship of the Eye-on-Hand vision systems.It will eliminate robot motion errors caused by the robot's motion parameters in traditional calibration methods.Finally，compared with the Halcon Eye-on-Hand calibration algorithm， the correctness and feasibility of the proposed method were verified.

Nonlinear Dynamics Behaviors of Two-way Cartridge Valves

ZHANG Yongshun1,2;JIANG Wanlu1;SU Xiao1;LEI Yafei1

2018, 29(10):  1159-1165. 

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In order to study the nonlinear vibration problems of the valve spools in the direction control circuit of two-way cartridge valves during the opening processes with pressure fluctuations，considering the pipeline volume effects，a nonlinear dynamics model of valve spools was established，and the numerical simulation was carried out by MATLAB/Simulink.Firstly，according to the model oil source pressure fluctuations existing or not，the opening characteristics of valve spools were studied by means of time domain diagram and phase diagram.Furthermore， in the conditions of oil source pressure fluctuations， the influences of different pressure grades of oil source on the valve spool were analyzed.Finally， for different pipe lengths， the influences of pipe length on the dynamics behaviors of valve spools were studied.The results show that the vibration behaviors of valve spools may be caused by the pressure fluctuations of oil source.In the same pressure fluctuations of oil source， the vibration behaviors of valve spools are weakened with the increase of oil source pressures，which is not easy to collide.Increasing the pipe lengths between pump outlet and valve group， the nonlinear vibration behaviors of valve spools are easily occured，accompanied by paroxysmal vibration beharior.The research provides a theoretical basis for the instability mechanism of large cartridge valve.

Applications of Windowed Interpolation FFT Algorithm in Rolling Bearing Fault Diagnosis

LI Xinyi1;XIE Zhijiang1;LUO Jiufei2

2018, 29(10):  1166-1172. 

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According to the characteristics of rolling bearing fault signals with strong noises and nonlinearities， in order to obtain accurate characteristic defect frequencies（CDF） of rolling element bearings， a new algorithm was proposed for rolling bearing fault diagnosis by Hanning windowing interpolation fast Fourier transformation（FFT） based on MED and TEO.Firstly， the proposed algorithm used MED to denoise fault signals.Secondly，TEO was used to calculate energy of vibration signals.Then， FFT was used to get demodulation spectrum.Thirdly， the windowed demodulation spectrum was presented by Hanning window.Finally， the precise CDF was obtained by using the three spectrum line interpolations.The experimental results show that the proposed algorithm has higher accuracy to identify CDF for the most parts compared with traditional TEO demodulate method based on fewer data?points.

Optimal Design and Performance Analysis of a 3-DOF Reconfigurable Parallel Mechanism

ZOU Qi;QU Haibo;GUO Sheng

2018, 29(10):  1172-1178. 

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A novel planar 3 degrees-of-freedom reconfigurable parallel mechanism with infinite symmetric positions was proposed.The inverse kinematics analysis and direct kinematics analysis were carried out by using loop-closure equation.Then by means of Monte-Carlo method， linkage optimization was presented by genetic algorithm with an objective function consisting of all the factor-workspace，condition numbers of the Jacobian matrix and fluctuation.Afterwards，the constant orientation workspaces were obtained by using a discrete boundary searching algorithm.The singularity of the mechanism was analyzed by the Jacobian matrix and how the reconfigurable mechanism to get rid of the singularity region was discussed.The rotation capability was verified with a newly presented evaluation index and the reachable workspaces under partial joints' stoppages were carried out.The results show the superiorities of the novel reconfigurable parallel mechanism.

Elastodynamics Analysis of a Spherical 2-DOF Redundantly Actuated Parallel Robot

LI Yongquan1，2;SHE Yazhong2，3;WAN Yixin 1，2;ZHANG Lijie2，3

2018, 29(10):  1179-1185. 

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The elastodynamics model of a spherical 2-DOF redundantly actuated parallel robot was established.Firstly，the six space curved rods of the robot system were divided into six substructures，considering the space curved rod bending， tensile and torsion deformations，the elastodynamics model of each substructure was derived based on finite element method.Then，according to the constraint characteristics of the joint rotations，elastodynamics models of every branches were established，and according to the deformation coordination constraints between each branch and the output shaft， the system's elastodynamic model was obtained by assembling the three branches.Finally，based on the comparison of the inherent frequencies which were gained by the theoretical calculation and finite element simulation when the robot was in the initial positions，the correctness of the natural frequencies was verified.By comparing the dynamic responses of spherical 2-DOF redundant and non-redundant actuated parallel robots，it is verified that the output maximum elastic displacement of the output may be significantly reduced by introducing redundant actuation.The research results provide a reliable basis for the structure optimization design and the vibration research of the parallel robots with spatial curved rods.

Research on Acoustic Characteristics of High Intensity Helmholtz Sound Source

QIAO Zhenghui;DONG Wei;CHENG Mei;ZHOU Shuqing

2018, 29(10):  1186-1192. 

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To research the acoustic characteristics of Helmholtz sound source （HSS）， a HSS combined a loudspeaker with a HR was designed and fabricated.With the changes of signal frequencies， the response characteristics of HSS， including equivalent acoustic impedances， terminal voltages， output sound pressures and electro-acoustic efficiencies， were preliminarily explored through numerical simulations and experiments.Results show that the acoustic characteristics of HSS are related to the interactions between loudspeaker and HR， and the equivalent acoustic impedance characteristics of HSS are dominated by HR.The resonances of both loudspeaker and HR may strengthen sound radiation and thus improve electro-acoustic efficiency of HSS.Under selected experimental conditions， the maximum output sound pressure of HSS may be 22 times of that generated by loudspeaker， thereby the electro-acoustic efficiency reaches up to 113%.

Resource Abnormal Management Method of Unsteady Processes of Cloud Manufacturing Services

DONG Yuanfa;WU Zhengjia;DU Xuan;ZHA Jing;YUAN Qingsong

2018, 29(10):  1193-1200. 

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To reduce the uncertainty caused by dynamic changes of cloud manufacturing resources in cloud manufacturing service processes，a management framework of unsteady cloud manufacturing service processes was constructed，and the associated and constrained relationships of cloud manufacturing services and cloud manufacturing resources were defined.Then classified definitions for abnormalities of manufacturing resources were presented，a response mechanism and a propagation algorithm for monophyletic and multiple abnormalities of manufacturing resources were built， and a prototype system was developed for management and control of the unsteady cloud manufacturing service processes.And finally， the method herein was verified in the cloud service processes of prototype trial in a piano manufacturing company.Results show that the proposed method may respond to the abnormal events of resources that affect the service time in a timely manner， and has a good feasibility.

Real-time Intelligent Monitoring for Manufacturing Processes with Big Data Based on Deep Belief Networks

ZHOU Haofei1;LIU Yumin2

2018, 29(10):  1201-1207,1213. 

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Aimed at the problems that process monitoring method based on shallow learning model was difficult to fulfill the requirements of real-time intelligent monitoring for manufacturing processes with big data，a real-time intelligent monitoring method was proposed herein based on deep belief network.Firstly，a quality spectrum for manufacturing processes with big data was established using gray scale images to represent operation states of manufacturing processes with big data.Secondly，the deep belief network was established to recognize the quality spectrum for manufacturing processes with big data.Then， the process quality-spectrum in the “monitoring window” was recognized by the deep belief networks from off-line training to realize real-time intelligent monitoring for manufacturing processes with big data.Finally， the proposed monitoring method was applied to monitor the operation states of an injection molding manufacturing processes with big data.Results indicate that the proposed monitoring method has a better recognition performance compared with the BP neural networks based on principal component analysis and the support vector machines based on principal component analysis， which demonstrates that the proposed monitoring method is efficient.

Applications of Flow Graph to Fault Diagnosis of Planetary Gearboxes

YU Jun1，2;YU Deshui1

2018, 29(10):  1208-1213. 

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Aimed at the problems of complex diagnosis processes of planetary gearboxes and low accuracy of diagnosis results， a fault diagnosis method of planetary gearboxes was proposed based on flow graph.In this method， a construction algorithm of flow graph was utilized to intuitively represent the fault diagnosis knowledges of planetary gearboxes.Then， a reduction algorithm of flow graph was applied to removing unnecessary condition attribute nodes.The consequent relationship among attributes was represented in the simplest manner.Finally， a classification decision algorithm of flow graph was employed to determine fault types of test samples.The simulation and experimental results confirm the accuracy and intuitiveness of this method， which provide a novel way for fault diagnosis of planetary gearboxes.

New Device for Large Structure Block Docking and Multi-cylinder Synchronization Control Method

CHENG Siming;ZHANG Qing

2018, 29(10):  1214-1219,1226. 

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Aiming at the demands of large structure three-dimensional heavy load docking in marine engineering， a new device for heavy load docking and a multi-cylinder coupling synchronous control method were presented in order to realize the mechatronics.Coupling control method was that signals inputting to the controller consisted of both its own errors and the errors between the adjacent two hydraulic cylinders.And the coupler was designed，using the fuzzy PID algorithm mode to obtain the coupling coefficients，since the algorithm might deal with the non-linear characteristics of the hydraulic system.Through AMESim and MATLAB co-simulation，and the conclusions coming from comparison of simulation results and the master-slave synchronization control mode show that this method eliminates the displacement hysteresis caused by master-slave control，which avoids the fluctuation caused by the system acceleration and deceleration， and the synchronization control precision is improved.

Simultaneous Obstacle-avoidance Motion Planning Approach for Dual Arm Robots Based on Improved RRT Algorithm

CHEN Bozhi;LU Liang;LEI Xinyu;ZHAO Ping

2018, 29(10):  1220-1226. 

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A new obstacle avoidance approach was proposed based on improved RRT algorithm.Motion planning for the main arm was conducted and obtained to avoid existing static obstacles in working environments.Then the main arm was regarded as dynamic obstacles to obtain a feasible motion trajectory of the second robot arm.To improve the search efficiency of the algorithm， strategies of nodes-pruning as well as setting of target area were adopted， where the algorithm was terminated if the distance between manipulator's end positions and goal points within prescribed tolerances.Based on MATLAB program modeling experiments， simulation experiments were studied in ADAMS to demonstrate effectiveness and feasibility of the algorithm.

Vacuum Hot-pressing Sintering Processes for a Powder Metallurgy Ti-22Al-25Nb Alloy

YANG Yue1;JIA Jianbo1;LIU Wenchao1;XU Yan1;CHEN Chen1;LIU Xingang1;LUO Junting1， 2

2018, 29(10):  1227-1233,1239. 

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A powder metallurgy （P/M） Ti-22Al-25Nb alloy with dense microstructure and uniform composition was prepared by using vacuum hot-pressing sintering method.The original powders were determined to be Ti-22Al-25Nb （at.%） pre-alloyed powders which obtained by aerosol method.The densification process of the Ti-22Al-25Nb （at.%） pre-alloyed powders was simulated numerically by using the finite element software MSC.Marc.The effects of temperature and pressure on the densification processes of the Ti-22Al-25Nb powders were analyzed.The evolution of relative densities varying with temperature and pressure was revealed herein.In addition， the optimized sintering parameters were obtained to guild the following hot-pressing sintering experiments.The dense P/M Ti-22Al-25Nb alloy with uniform composition was fabricated by hot-pressing sintering experiments.It may be observed that the alloy which is sintered at 1 050 ℃/35 MPa/1 h demonstrates the optimal mechanics properties at room temperature and 650 ℃， respectively.

Natural Characteristic Calculation and Verification of FRCS

ZHOU Zhengxue1　LI Hui1　XUE Pengcheng1　WU Huaishuai1　CHEN Shuyao2

2018, 29(10):  1234-1239. 

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Natural characteristics of FRCS under cantilever boundary were calculated and verified by experiments.Firstly， a theoretical model of FRCS was established by considering the structural characteristics.Then， the natural frequency and mode shape of FRCS were obtained by Rayleigh-Ritz method.Finally， T300 fiber/epoxy composite shell was taken as a study object， and the natural frequency and mode shape were measured by experimental tests.The results show that the errors of the natural frequencies from calculations and experiments are within the range of 2.2%~9.3%， the calculation results of the mode shapes are also consistent with the experimental ones， thus the correctness of proposed method was verified.

Heat Transfer Model of Ring Forgings with Cracks Based on Transient Heat Transfer

ZHANG Yuncun1;TIAN Mengqi2;LI Yabin3

2018, 29(10):  1240-1247. 

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A heat transfer model for cracked forgings based on heat transfer theory was proposed to solve the crack problems in hot forgings.Firstly， the model was based on the heat transfer characteristics of micro bodies， and the differential equation of heat conduction was derived， which satisfied the thermal balance relationship of micro elements.The heat transfer coefficient and thermal conductivity were corrected by taking instantaneous heat flux as an intermediary variable.Secondly，the set of natural convection boundary conditions， internal and external environment of ring forgings crack finite space boundary conditions were distinguished， and then the boundary conditions of hot forging ring heat transfer models with crack were established， and the separation variable method was used to solve the heat transfer model.Finally， the finite element software was used to simulate the heat transfer model of annular forgings with different size cracks， and the validity and feasibility of the heat transfer model was verified.