Table of Content

10 April 2015, Volume 26 Issue 7

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Jacobian Matrix Establishment of 2(2-UPR+SPR) Serial-parallel Manipulator

Hu Bo, Song Chunxiao, Zhang Qingling, Yu Jingjing,

2015, 26(7):  853-858. 

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The Jocobian of a novel 2(2-UPR+SPR) serial-parallel manipulator was established.First, a 2(2-UPR+SPR) serial-parallel manipulator formed by two 2-UPR+SPR mechanisms was presented. This manipulator could provide advantages of both serial and parallel manipulators. Second, the velocity decoupling and velocity constraint equations for single 2-UPR+SPR were analyzed based on the geometric constraints in the mechanism. Finally, the velocity transfer relation for the 2(2-UPR+SPR) serial-parallel manipulator was analyzed. Based on the velocity decoupling and constraint characteristics of single 2-UPR+SPR mechanism, the integral forward and inverse Jacobian matrix for 2(2-UPR+SPR) serial-parallel manipulator were established. The results show that the established Jacobian matrices contain kinematics, coupling and constraint information of each 2-UPR+SPR mechanism. The methodology for establishing the integral Jacobian matrix of the 2(2-UPR+SPR) serial-parallel manipulator herein is also fitable for other serial-parallel manipulators.

Analysis of Pressure Fluctuation in UHV Breaker Hydraulic Pipeline Based on AMESim

Lai Qiwei, Wu Shijing, Zhang Zenglei, Hu Jicai

2015, 26(7):  859-863. 

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With the purpose of settling the impact of hydraulic shock in hydraulic operating system of UHV breaker, energy accumulator and its hydraulic pipeline system served as the research objects. Based on the analysis of pressure fluctuation mechanism，principles of selecting sub-model of pipeline were established. With the simulation of comprehensive model of the hydraulic system using software AMESim, characteristics of pressure fluctuation in the hydraulic pipeline was obtained. Meanwhile，impacts of length and diameter of pipeline on pressure fluctuation were analyzed. The results show that the existing pressure fluctuation amplitude is large, which is not conducive to the stable operation of the system. After combinatorial optimization of length and diameter of pipeline, pressure fluctuation is reduced by over 50%. The adopted research methods have certain theoretical guidance and practical value to optimal design of pipeline system in UHV breaker.

Topology Optimization Using FS-FEM for Complex Three-dimensional Models

He Zhicheng, Chen Shaowei, Li Guangyao, Zhang Guiyong

2015, 26(7):  864-870. 

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The FS-FEM was proposed recently based on tetrahedral mesh, and showed great property in solid mechanics, such as providing very good gradient solutions. The topology optimization design of the continuum structures under static load was formulated in the scheme of FS-FEM. As the face-based smoothing domains were the sub-units of assembling stiffness matrix in the discretized system of smoothed Galerkin weak form, thus the relative density of face-based smoothing domains were served as design variables. In this formulation, the minimization compliance was considered as an objective function, and the mathematic of the topology optimization model was developed using the solid isotropic material with penalization (SIMP) interpolation scheme. The topology optimization problem was then solved by the optimality criteria method. Finally, the feasibility and efficiency of the proposed method were illustrated with several 3D examples that were widely used in the topology optimization design.

Analysis of Load Carrying Capacity of Parallel Mechanism

Yuan Feihu, Zhao Tieshi, Zhao Yanzhi, Weng Dacheng

2015, 26(7):  871-877. 

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The explicit method was used to calculate the maximum extreme of the maximum external load. To get the minimum extreme of the maximum external load, a scaling foctor method was presented based on Lagrange function. Taking into account the effects of components' gravities and inertial forces,the concept of equivalent driving force was presented.Based on this concept, the static carrying capacity and dynamic carrying capacity of parallel mechanism used as motion simulation platform was discussed. The calculation process was put forward based on scaling foctor method. Using a six DOF mechanism as an example, the effects of mechasim poses on carrying capacity and carrying performance indexes was analyzed. A reference to guide and evaluate the design and performance of heavy load parallel mechanism is put forward.

Model Parameter Identification for a Lower E-type Membrane of Six-axis Force Sensor Based on CIWO-EKF

Zhu Wenchao, Xu Dezhang

2015, 26(7):  878-886. 

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The measurement accuracy of a sensor which worked on the environment of the dynamic load could be seriously affected by the pollution of noise signals and the EKF could not gain the optimal system noise matrix. A new EKF based on CIWO was proposed. The nonlinear state-space model was established based on the relationship between the deflection and the strain. The idea of the grass breeding was introduced to achieve the Gauss sampling of system interference matrix consisted of first six-order vibration mode informations and to produce the initial feasible solutions. After combining chaotic search technology with invasive weed optimization (IWO), the global search of the new algorithm was executed by the IWO. Then the chaotic sequences executed the local search to the individual which had the higher fitness value than average and guided the population approaching to the optimal solution. The search process can be avoided to fall into local optimum. Finally, the improved invasive weed optimization algorithm was introduced to optimize the system's noise matrix in EKF. The simulation results indicate that the new algorithm can enhance the measurement accuracy of six-axis force sensor effectively and maintain better robustness and real-time performance.
 

A Feature-based Cutting Force Fast Prediction and Evaluation for Complex Aircraft Structure Parts

Zhou Xin, Li Yingguang, Liu Hao, Liu Changqing

2015, 26(7):  886-891. 

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A feature-based cutting force prediction method was proposed herein, which focused on the problem of flank milling force prediction. Partial shape, dimension, and cutting parameter information were represented based on features, which provided sufficient support for cutting force prediction and evaluation. Analytical approach was adopted to construct cutting force model and correlation coefficient was obtained for the cutting force model by experiments.The proposed method was implemented based on commercial CAM software platform. Experimental results show that the average error of cutting force prediction is 8.73%, which means that the quick and accurate cutting force prediction can be achieved for individual specified features of aircraft structural parts by using the proposed method on CAM platform.

Theoretical Analysis and Test on Static Characteristics of Bolt Joints under Tangential Load

Hui Ye, Huang Yumei, Li Yan

2015, 26(7):  892-898. 

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To observe the static performance of bolt joints accurately, an analytic mathematical model of bolt unit interfacing was established based on joint interfaces basic characteristic parameters. A multi-stage equivalent load analyzing algorithm was proposed to solve non-linear implicit integration equations quickly and correctly when tangential load was applied to the joints, not considering the coupling relation among loads. Torsional and tangent loading tests were conducted using self-designed bolt joint tangent loading device. The results of the tests and analyses indicate that when tangential load does not exceed the maximum static friction, the results reveal a linear relation between joint interface tangential deformation and external load. The consistence between the analysis and test results validates the correctness of analytic model, which provides theoretical and test evidence for investigating static performance of mechanical interface, and the analyzing algorithm makes it easy to apply the joint interface research fruits to engineering practice.

Modal Simulation and Experiment Based on MRF Damping Turning Tool

Zhang Yongliang, Pan Jianjian, Hong Ming, Zhang Wei

2015, 26(7):  898-902. 

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Chatter occurred between the work-piece and tool during the turning process, a magneto-rheological damping tool was designed and developed based on the MRF squeeze mode. To study the dynamic change of the damping characteristics for different excitation currents, the parameters of MRF in the software was defined through entity definition. The modal analysis of damping device was simulated with ANSYS Workbench. Also the transient excitation modal testing platform was built for the modal experiments. The first four modal data of the simulation and experiments were presented. Results show that with the increase of the excitation current, the modal values increase so as the stiffness values.

Periodic Self-evolution of an Aircraft Engine Assembly Workshop under Static Knowledgeable Manufacturing Environment

Jiang Tianhua, Yan Hongsen, Wang Zheng

2015, 26(7):  903-911. 

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For an aircraft engine assembly workshop under static knowledgeable manufacturing environment, the self-evolution problem of knowledgeable manufacturing systems was studied. Rolling horizon method was adopted to implement the assembly workshop's periodic self-evolution. On the basis of the characteristics of the problem, a mathematical model of the static sub-problem at each decision moment was established. A rolling rule was proposed based on the initial decision scheme, and a two-phase algorithm was given to solve the self-evolution problem. For the mathematical model, a BiGA was proposed. Finally, simulation results demonstrate that the proposed model and algorithms are effective and feasible. The influences of the sizes of rolling window and rolling step on the production performance were also analyzed.

Research on Algorithm of S_shape Acceleration and Deceleration Time Based on Newton Iterative Method

Yang Liangliang, Xu Shoujin, Shi Weimin, Ge Hongwei,

2015, 26(7):  912-916,942. 

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Due to S_shape acceleration and deceleration control involved solving multiple high-order equation or inequality, and the final solution was non negative, so that it was difficult to calculate.Therefore nonlinear equations of five independent variables of  S_shape acceleration and deceleration control were decomposed into two nonlinear equations of two independent variables and a linear equation according to time optimal principle and the constraints of speed, acceleration. The final solutions were obtained by Newton iterative method and the iterative correction method then the velocity curve and interpolation algorithm were found. The simulation and experiments were presented to prove that the algorithm is simplicity, stable operation and the ability to meet the requirements of high speed and high precision of computer numerical control.

Applying Modified Colonial Competitive Algorithm to Solve Minimal Hitting Set Problems

Zhu Chuanjun, Cao Jing, Zhang Chaoyong, Lian Kunlei

2015, 26(7):  917-923. 

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A CCA was developed and modified to solve the problem of minimal candidates set. The minimal candidate set was a minimal hitting set. The modified CCA improved performance in initialization, assimilation and rebirth of original CCA by introducing a third type of country, independent country, to the population of countries maintained by CCA. Implementation details of the proposed CCA and modified colonial competitive algorithm(MCCA) were elaborated using an illustrative example. The performance of the algorithms was analyzed, and the results by the MCCA were compared with DMDSE-Tree algorithm. When 90% of the minimal hitting sets are obtained, the MCCA has better efficiency. Finally, the experimental results of certain system verify the effectiveness of the algorithm,which proves that this method can be applied in solving the minimal hitting set of combinatorial optimization problems for selection of equipment effectively.

Cutting Database System of Large Machine Tool Parts Based on Hybrid Reasoning Method

Chen Weike, Fan Weiwei, Li Zhongqun

2015, 26(7):  923-928. 

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According to the demand analyses of large machine tool parts cutting database system, the parameters of main attributes and their mutual relationships were determined in the system. The geometrical and the dimensional feature definition of large machine tool parts were presented. Based on hybrid reasoning technology which combined case-based and rule-based reasoning, a cutting database system was established. The priority of attributes was defined for fast retrieval. Local similarities of specific attributes were determined during case-based reasoning. Combining dynamics optimization technique with instance matching the optimal parameters were found. Then, the ability of the system of solving practical problems is enhanced.

Life Estimation for Transient Temperature and Stress Field of Heavy-duty Gas Turbine Rotor

Ou Wenhao, Yuan Qi, Shi Qingxin

2015, 26(7):  929-935. 

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Taking a specific heavy-duty gas turbine of F class as study object, based on the monitoring data of actual operation, curves denoting temperature changes over time of measuring points in the F class heavy-duty gas turbine unit were extracted at cold starting and hot starting conditions. In these two starting conditions, the heat transfer boundary conditions were calculated throughout, the finite element method was used to analyze the transient temperature field and stress field of the gas turbine rotor in different starting conditions. Based on the results, the low-cycle fatigue life loss was assessed. The calculation results show that maximum thermal elastic stress generally appears at the bottom fillet on the outlet side of the turbine's first stage disc and rounded area on the middle part of the compressor's third stage disc; airflow parameter change speed has enormous influences on the rotor's stress distribution and the life loss of cold starting is up to 0.02%, greater than the corresponding value of the hot starting. The conclusion provides an important reference for the optimization of wheel structure design and the unit operating procedures.

Terminal Sliding Mode Control of a Free-floating Flexible Space Robot

Yu Xiaoyan, Chen Li

2015, 26(7):  936-942. 

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A Terminal sliding mode control was proposed for a free-floating space robot.To discuss such an under-actuated flexible-link flexible-joint space robot, a free-floating space robot with one flexible link and two flexible revolute joints was presented. The dynamical Lagrange equation was established by the momentum conservation. And a singularly perturbed model was formulated and used for designing a reduced-order controller, where the system was decoupled into two subsystems (a flexible space manipulator subsystem and a flexible-joint fast subsystem).A composite controller which consisted of two control components was proposed. A Terminal sliding mode controller was proposed to control the flexible space manipulator subsystem.A flexible-joint fast controller was designed to stabilize the flexible-joint fast subsystem around the equilibrium trajectory set up by the flexible space manipulator subsystem under the effects of the Terminal sliding mode controller. A numerical simulation was carried out, which confirmed the proposed controller is feasible and effective.The virtue of this control scheme is that the base linear position, the base linear velocity, the base linear acceleration need not be measured.In addition, it is ensured that the tracking errors of the manipulator joints converge to zero in finite time.

Experimental Investigation of Flow Characteristics of Right-Angle Turn with Different Tool Included Cavity Using PIV Technique

Hu Jianjun, Kong Xiangdong, Hou Guannan, Yu Bin, Quan lingxiao,

2015, 26(7):  943-948. 

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This paper aimed to investigate the flow field characteristics of right-angle turn channel with different tool included cavities in the typical hydraulic manifold block. A low-speed visualization test rig was developed and the flow field of right-angle turn channel with six kinds tool included cavities was measured using 2D-PIV technique. It is found that two vortices appear in the tool included cavity and the inner corner of outlet section respectively. The vortex in the tool included cavity increases with increasing of the cavity length, the vortex in the inner corner of outlet section has nothing to do with the length of cavity. Then, the effects of length and position of the tool included cavity on flow characteristics of right-angle turn channel were analyzed and found that the arrangement of the tool included cavity opposite to the outlet direction is more advantageous. This study provides design reference for the structure improvement of flow passage in the hydraulic manifold block.

Surface Hardened Mechanism of Grinding Conditions in Small Depth of Cut

Zhang Xiuming, Yu Yongtao, Bai Bin, Xiu Shichao

2015, 26(7):  949-954. 

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Grinding hardening technology was the technology that made the surface layer of the work-piece hardened by using grinding force and grinding heat. Grinding surface hardening process in small depth cut was usually generated by mechanical force and accompanied with thermal strain and phase transition occurred. Based on the theory of plastic deformation caused by dislocation motion, in-depth analyzed the hardening mechanism of mechanical action by grinding force and material thermal phase transformation in small depth cut. Test shows that using larger grinding depth and smaller workpiece feed speed in the grinding can increase the surface microscopic residual stress and promote the effect of the specimen surface hardening layer formation.

Natural Frequencies and Modal Shape Characteristics of a Flexible Manipulator with Elastic Joints

Liu Yufei, Li Wei, Yang Xuefeng, Xu Han

2015, 26(7):  954-959. 

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To investigate the effect mechanism of elastic joint on the natural frequencies and modal shapes of flexible manipulators, an elastic restraint model of the flexible manipulator was established. Based on the elastic restraint model, frequency equation and modal shape function of the flexible manipulator with elastic joint (FMEJ) were subsequently derived. Numerical method was conducted to investigate the first three natural frequencies and modal shapes of the FMEJ. The results demonstrate that the elasticity of the joint has considerable effect on the natural frequencies and modal shapes, and assuming the joint as an ideal fixed restraint a noticeable error will present. According to the sensitivity analysis, the linear restraints have a more considerable effect on the natural frequencies than torsional restraints, especially for the higher frequencies. The effect of torsional restraints on the modal shapes is more considerable, with the torsional restraint increases, the modal shapes change which is obvious for the higher modal shapes. Experiment was conducted to verify the elastic restraint model and the results indicate that the constructed model can characterize the elastic restraints of the joint, and approach to the actual situation which has a smaller error.

Tool Wear in ZrO2 Bioceramic Milling Processes

Wu Haibing, Zuo Dunwen, Sun Quanping, Xu Feng

2015, 26(7):  960-964,993. 

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In order to study the diamond tool wear and its effects on the cutting process in conventional milling of full-sintered ZrO2, long distance milling experiments of ZrO2 bioceramic were carried out. The propagation of  tool wear zone with cutting time and the variation of cutting forces with tool wear process were analyzed. The relation between tool wear and material removal model was discussed by analyses of the influences of tool wear on the micrograph of machined surface. At last, the tool wear mechanism was investigated. The research fruits show that the tool wear extended from cutting edge to flank face with the cutting process in conventional milling of ZrO2, while the material removal model changes from ductile-brittle removal to all-brittle one. The tool wear model is composed of chipping, peeling and graphitic wear.

Accurate Control of a Robot Hydraulic Actuator with Uncertain Friction

Sun Guangbin, Wang Hong, Wang Lin, Li Bin, Ji Li, Wang Fuwang

2015, 26(7):  965-971. 

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This paper presented the design of H∞ robust controller to improve the position control of a hydraulic system. First, the hydraulic system model was established by the analysis of the hydraulic and mechanical dynamics. The Dahl friction model was adopted. Then the H∞ robust controller was designed around the nominal parameter values based on mixed sensitivity. The weighting functions were chosen as optimized objectives. Finally, by simulation and experiments, it is proved this control method can effectively suppress the friction error's effects on the position tracking control, especially the effects of the friction model uncertainty in reversing of velocity. The tracking errors are reduced significantly. Both of the steady and transient performance of the robust controller is superior to the conventional PID controller. Therefore the method was validated.

Residual Stress Fields and Fatigue Life of Cold Expansion Hole in Titanium Alloy TC4

Ge Ende, Su Honghua, Cheng Yuanqing, Fu Yucan, Xu Jiuhua, Xiao Ruiheng

2015, 26(7):  971-976. 

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A 3D finite element simulation was used to study the stress distribution and effects of expansion degrees around the cold expanded hole in TC4 plate. Tangential residual stress distribution under different expansion degrees were obtained in the smallest cross section. The relation of expansion degree to residual stress and fatigue life was discussed. In order to get the fatigue life of different expanded degrees, the experiments of split sleeve cold expansion were carried out. It is found that residual stress can reduce stress concentration and optimize the stress distribution in the smallest cross section under tensile loading, also remarkably retard the crack propagation rate for cold expanded holes. The results show that 4% expansion degree is the optimal cold expanded degrees for TC4 plate in simulation and experiments.

Forming Limit Vision Measurement and Formability of Cu/Al Clad Metals

Sun Tao, Liang Jin, Guo Xiang, Li Leigang, Ren Maodong

2015, 26(7):  977-981. 

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To measure the forming limit strain of Cu/Al clad metal made by explosive welding technique, a new optical measurement method based on the digital image correlation (DIC) method and binocular stereovision was proposed and implemented. The FEM results were used to verify the strain measurement accuracy of the DIC method. Based on the limit strain of Cu/Al clad metals by DIC method, the influences of heat treatment and contact status on forming limit were analyzed. Also, the interfacial and fracture structures were analyzed with SEM.The results demonstrate that the relative error of major strain between DIC method and FEM mothod is 0.1% when Cu/Al clad metals are broken, and the strain distributions agree finite element simulation results well. The forming limit of the clad with Al in the inner layer is higher than the clad with Cu in the inner layer. The formability of the annealed clad is superior to the not annealed one. The clad is broken at both sides with interface fracture.

Robustness Optimization Design of Bumper Structure Based on Protection of Pedestrian Lower Leg

Qian Lijun, Song Jia, Gu Xianguang

2015, 26(7):  982-987. 

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In order to improve lower leg protection of bumper structure, this paper presented a systematic method combining experimental design, radial basis function approximation modeling technology, the global optimization algorithm and 6-Sigma quality design based on Monte Carlo simulation, which was applied to optimize the bumper structure. Due to taking the uncertainty of design variables into consideration, the optimization results are more reliable and robust than that of the deterministic optimization method. Therefore, to some extent, this paper proposed a robustness optimization design method for solving complex engineering problems, and further application of this method can improve the design quality of products greatly.

Ride Comfort Analysis of a Tracked Omnidirectional Mobile Platform

Zhang Yunan, Huang Tao, Zhang Fang, Tian Peng

2015, 26(7):  988-993. 

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For the existing problems of a Mecanum wheeled omnidirectional mobile platform such as bad road adaptability, the structure of the omnidirectional mobile track was proposed, and a tracked omnidirectional mobile platform was developed.The ride comfort of the platform was studied, the virtual prototypes of the tracked and Mecanum-wheeled platforms were established respectively, and simulations of the longitudinal and lateral motions of the both prototypes were mainly accomplished on the grade B~F uneven roads; the ride comfort of the longitudinal and lateral motions of the both prototypes was analysed, and the influence law among the ride comfort of the longitudinal and lateral motions of the platform and the grade of the uneven roads was obtained. The ride comfort tests were accomplished on a dirt road that was equivalent to a grade C road, and the test results can validate the correctness of the simulation results. Therefore, the tracked omnidirectional mobile platform can improve the road adaptability of the Mecanum-wheeled platform.