Frontiers of Mechanical Engineering

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Fault diagnosis of spur gearbox based on random forest and wavelet packet decomposition
Diego CABRERA,Fernando SANCHO,René-Vinicio SÁNCHEZ,Grover ZURITA,Mariela CERRADA,Chuan LI,Rafael E. VÁSQUEZ
Front. Mech. Eng.    2015, 10 (3): 277-286.   https://doi.org/10.1007/s11465-015-0348-8
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This paper addresses the development of a random forest classifier for the multi-class fault diagnosis in spur gearboxes. The vibration signal’s condition parameters are first extracted by applying the wavelet packet decomposition with multiple mother wavelets, and the coefficients’ energy content for terminal nodes is used as the input feature for the classification problem. Then, a study through the parameters’ space to find the best values for the number of trees and the number of random features is performed. In this way, the best set of mother wavelets for the application is identified and the best features are selected through the internal ranking of the random forest classifier. The results show that the proposed method reached 98.68% in classification accuracy, and high efficiency and robustness in the models.

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Remote calibration system for frequency based on in-place benchmark
Xiaobin HONG, Guixiong LIU, Zhuokui WU, Xipeng DU,
Front. Mech. Eng.    2010, 5 (3): 316-321.   https://doi.org/10.1007/s11465-010-0021-1
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According to the deficiencies of remote calibration mode based on material object reference, a new model of a remote calibration system for frequency based on in-place benchmark is introduced, which is made of a calibration subsystem on the spot and a remote management subsystem. The key technology of some key problems for the remote calibration system is particularly discussed, including the time and frequency benchmark receiving module based on global positioning system (GPS), frequency comparison based on a phase method, frequency division based on dual high-frequency phase locked loop (PLL), and remote calibration based on the web. The results show that the system possesses some characteristics, such as high precision, good versatility, and no limitation of time and place.
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EEG controlled neuromuscular electrical stimulation of the upper limb for stroke patients
Hock Guan TAN, Cheng Yap SHEE, Keng He KONG, Cuntai GUAN, Wei Tech ANG
Front Mech Eng    2011, 6 (1): 71-81.   https://doi.org/10.1007/s11465-011-0207-1
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This paper describes the Brain Computer Interface (BCI) system and the experiments to allow post-acute (<3 months) stroke patients to use electroencephalogram (EEG) to trigger neuromuscular electrical stimulation (NMES)-assisted extension of the wrist/fingers, which are essential pre-requisites for useful hand function. EEG was recorded while subjects performed motor imagery of their paretic limb, and then analyzed to determine the optimal frequency range within the mu-rhythm, with the greatest attenuation. Aided by visual feedback, subjects then trained to regulate their mu-rhythm EEG to operate the BCI to trigger NMES of the wrist/finger. 6 post-acute stroke patients successfully completed the training, with 4 able to learn to control and use the BCI to initiate NMES. This result is consistent with the reported BCI literacy rate of healthy subjects. Thereafter, without the loss of generality, the controller of the NMES is developed and is based on a model of the upper limb muscle (biceps/triceps) groups to determine the intensity of NMES required to flex or extend the forearm by a specific angle. The muscle model is based on a phenomenological approach, with parameters that are easily measured and conveniently implemented.

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Review on the progress of ultra-precision machining technologies
Julong YUAN, Binghai LYU, Wei HANG, Qianfa DENG
Front. Mech. Eng.    2017, 12 (2): 158-180.   https://doi.org/10.1007/s11465-017-0455-9
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Ultra-precision machining technologies are the essential methods, to obtain the highest form accuracy and surface quality. As more research findings are published, such technologies now involve complicated systems engineering and been widely used in the production of components in various aerospace, national defense, optics, mechanics, electronics, and other high-tech applications. The conception, applications and history of ultra-precision machining are introduced in this article, and the developments of ultra-precision machining technologies, especially ultra-precision grinding, ultra-precision cutting and polishing are also reviewed. The current state and problems of this field in China are analyzed. Finally, the development trends of this field and the coping strategies employed in China to keep up with the trends are discussed.

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Response surface regression analysis on FeCrBSi particle in-flight properties by plasma spray
Runbo MA,Lihong DONG,Haidou WANG,Shuying CHEN,Zhiguo XING
Front. Mech. Eng.    2016, 11 (3): 250-257.   https://doi.org/10.1007/s11465-016-0401-2
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This work discusses the interactive effects between every two of argon flow rate, voltage, and spray distance on in-flight particles by plasma spray and constructs models that can be used in predicting and analyzing average velocity and temperature. Results of the response surface methodology show that the interactive effects between voltage and spray distance on particle in-flight properties are significant. For a given argon flow rate, particle velocity and temperature response surface are obviously bending, and a saddle point exists. With an increase in spray distance, the interactive effects between voltage and argon flow rate on particle in-flight properties appear gradually and then weaken. With an increase in voltage, the interactive effects between spray distance and argon flow rate on particle in-flight properties change from appearing to strengthening and then to weakening.

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A comprehensive analysis of a 3-P (Pa) S spatial parallel manipulator
Yuzhe LIU,Liping WANG,Jun WU,Jinsong WANG
Front. Mech. Eng.    2015, 10 (1): 7-19.   https://doi.org/10.1007/s11465-015-0324-3
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In this paper, a novel 3-degree of freedom (3-DOF) spatial parallel kinematic machine (PKM) is analyzed. The manipulator owns three main motions (two rotations and one translation) and three concomitant motions (one rotation and two translations). At first, the structure of this spatial PKM is simplified according to the characteristic of each limb. Secondly, the kinematics model of this spatial PKM is set up. In addition, the relationship between the main motions and concomitant motions is studied. The workspaces respectively based on the outputs and inputs are derived and analyzed. Furthermore, the velocity model is put forward. Two indexes based on the velocity model are employed to investigate the performance of this spatial PKM. At last, the output error model can be obtained and simulated. The comprehensive kinematics analysis in this paper is greatly useful for the future applications of this spatial PKM.

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Self-propelled automatic chassis of Lunokhod-1: History of creation in episodes
Mikhail MALENKOV
Front. Mech. Eng.    2016, 11 (1): 60-86.   https://doi.org/10.1007/s11465-016-0370-5
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This report reviews the most important episodes in the history of designing the self-propelled automatic chassis of the first mobile extraterrestrial vehicle in the world, Lunokhod-1. The review considers the issues in designing moon rovers, their essential features, and the particular construction properties of their systems, mechanisms, units, and assemblies. It presents the results of exploiting the chassis of Lunokhod-1 and Lunokhod-2. Analysis of the approaches utilized and engineering solutions reveals their value as well as the consequences of certain defects.

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Comprehensive analysis of the influence of structural and dynamic parameters on the accuracy of nano-precision positioning stages
Chengyuan LIANG, Fang YUAN, Xuedong CHEN, Wei JIANG, Lizhan ZENG, Xin LUO
Front. Mech. Eng.    2019, 14 (3): 255-272.   https://doi.org/10.1007/s11465-019-0538-x
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Nano-precision positioning stages are characterized by rigid-flexible coupling systems. The complex dynamic characteristics of mechanical structure of a stage, which are determined by structural and dynamic parameters, exert a serious influence on the accuracy of its motion and measurement. Systematic evaluation of such influence is essential for the design and improvement of stages. A systematic approach to modeling the dynamic accuracy of a nano-precision positioning stage is developed in this work by integrating a multi-rigid-body dynamic model of the mechanical system and measurement system models. The influence of structural and dynamic parameters, including aerostatic bearing configurations, motion plane errors, foundation vibrations, and positions of the acting points of driving forces, on dynamic accuracy is investigated by adopting the H-type configured stage as an example. The approach is programmed and integrated into a software framework that supports the dynamic design of nano-precision positioning stages. The software framework is then applied to the design of a nano-precision positioning stage used in a packaging lithography machine.

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Planet position errors in planetary transmission: Effect on load sharing and transmission error
Miguel IGLESIAS, Alfonso FERNáNDEZ, Ana DE-JUAN, Ramón SANCIBRIáN, Pablo GARCíA
Front Mech Eng    2013, 8 (1): 80-87.   https://doi.org/10.1007/s11465-013-0362-7
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In this paper an advanced model of spur gear transmissions developed by the authors is used to study the influence of carrier planet pin hole position errors on the behaviour of the transmission. The model, initially conceived for external gear modeling, has been extended with internal meshing features, and thus increasing its capabilities to include planetary transmission modeling. The new features are presented, along with the summary of the model general approach. The parameters and characteristics of the planetary transmission used in the paper are introduced. The influence of carrier planet pin hole position errors on the planet load sharing is studied, and several static cases are given as examples in order to show the ability of the model. Tangential and radial planet pin hole position errors are considered independently, and the effect of the load level is also taken into account. It is also given attention to the effect on the transmission error of the transmission. Two different configurations for the planetary transmission are used, attending to the fixed or floating condition of the sun, and the differences in terms of load sharing ratio are shown.

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Three-dimensional numerical simulation for plastic injection-compression molding
Yun ZHANG, Wenjie YU, Junjie LIANG, Jianlin LANG, Dequn LI
Front. Mech. Eng.    2018, 13 (1): 74-84.   https://doi.org/10.1007/s11465-018-0490-1
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Compared with conventional injection molding, injection-compression molding can mold optical parts with higher precision and lower flow residual stress. However, the melt flow process in a closed cavity becomes more complex because of the moving cavity boundary during compression and the nonlinear problems caused by non-Newtonian polymer melt. In this study, a 3D simulation method was developed for injection-compression molding. In this method, arbitrary Lagrangian-Eulerian was introduced to model the moving-boundary flow problem in the compression stage. The non-Newtonian characteristics and compressibility of the polymer melt were considered. The melt flow and pressure distribution in the cavity were investigated by using the proposed simulation method and compared with those of injection molding. Results reveal that the fountain flow effect becomes significant when the cavity thickness increases during compression. The back flow also plays an important role in the flow pattern and redistribution of cavity pressure. The discrepancy in pressures at different points along the flow path is complicated rather than monotonically decreased in injection molding.

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Additive manufacturing: technology, applications and research needs
Nannan GUO, Ming C. LEU
Front Mech Eng    2013, 8 (3): 215-243.   https://doi.org/10.1007/s11465-013-0248-8
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Additive manufacturing (AM) technology has been researched and developed for more than 20 years. Rather than removing materials, AM processes make three-dimensional parts directly from CAD models by adding materials layer by layer, offering the beneficial ability to build parts with geometric and material complexities that could not be produced by subtractive manufacturing processes. Through intensive research over the past two decades, significant progress has been made in the development and commercialization of new and innovative AM processes, as well as numerous practical applications in aerospace, automotive, biomedical, energy and other fields. This paper reviews the main processes, materials and applications of the current AM technology and presents future research needs for this technology.

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Smart manufacturing systems for Industry 4.0: Conceptual framework, scenarios, and future perspectives
Pai ZHENG, Honghui WANG, Zhiqian SANG, Ray Y. ZHONG, Yongkui LIU, Chao LIU, Khamdi MUBAROK, Shiqiang YU, Xun XU
Front. Mech. Eng.    2018, 13 (2): 137-150.   https://doi.org/10.1007/s11465-018-0499-5
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Information and communication technology is undergoing rapid development, and many disruptive technologies, such as cloud computing, Internet of Things, big data, and artificial intelligence, have emerged. These technologies are permeating the manufacturing industry and enable the fusion of physical and virtual worlds through cyber-physical systems (CPS), which mark the advent of the fourth stage of industrial production (i.e., Industry 4.0). The widespread application of CPS in manufacturing environments renders manufacturing systems increasingly smart. To advance research on the implementation of Industry 4.0, this study examines smart manufacturing systems for Industry 4.0. First, a conceptual framework of smart manufacturing systems for Industry 4.0 is presented. Second, demonstrative scenarios that pertain to smart design, smart machining, smart control, smart monitoring, and smart scheduling, are presented. Key technologies and their possible applications to Industry 4.0 smart manufacturing systems are reviewed based on these demonstrative scenarios. Finally, challenges and future perspectives are identified and discussed.

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Progress in terahertz nondestructive testing: A review
Shuncong ZHONG
Front. Mech. Eng.    2019, 14 (3): 273-281.   https://doi.org/10.1007/s11465-018-0495-9
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Terahertz (THz) waves, whose frequencies range between microwave and infrared, are part of the electromagnetic spectrum. A gap exists in THz literature because investigating THz waves is difficult due to the weak characteristics of the waves and the lack of suitable THz sources and detectors. Recently, THz nondestructive testing (NDT) technology has become an interesting topic. This review outlines several typical THz devices and systems and engineering applications of THz NDT techniques in composite materials, thermal barrier coatings, car paint films, marine protective coatings, and pharmaceutical tablet coatings. THz imaging has higher resolution but lower penetration than ultrasound imaging. This review presents the significance and advantages provided by the emerging THz NDT technique.

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Connected morphable components-based multiscale topology optimization
Jiadong DENG, Claus B. W. PEDERSEN, Wei CHEN
Front. Mech. Eng.    2019, 14 (2): 129-140.   https://doi.org/10.1007/s11465-019-0532-3
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The advances of manufacturing techniques, such as additive manufacturing, have provided unprecedented opportunities for producing multiscale structures with intricate latticed/cellular material microstructures to meet the increasing demands for parts with customized functionalities. However, there are still difficulties for the state-of-the-art multiscale topology optimization (TO) methods to achieve manufacturable multiscale designs with cellular materials, partially due to the disconnectivity issue when tiling material microstructures. This paper attempts to address the disconnectivity issue by extending component-based TO methodology to multiscale structural design. An effective linkage scheme to guarantee smooth transitions between neighboring material microstructures (unit cells) is devised and investigated. Associated with the advantages of components-based TO, the number of design variables is greatly reduced in multiscale TO design. Homogenization is employed to calculate the effective material properties of the porous materials and to correlate the macro/structural scale with the micro/material scale. Sensitivities of the objective function with respect to the geometrical parameters of each component in each material microstructure have been derived using the adjoint method. Numerical examples demonstrate that multiscale structures with well-connected material microstructures or graded/layered material microstructures are realized.

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Creative design inspired by biological knowledge: Technologies and methods
Runhua TAN, Wei LIU, Guozhong CAO, Yuan SHI
Front. Mech. Eng.    2019, 14 (1): 1-14.   https://doi.org/10.1007/s11465-018-0511-0
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Biological knowledge is becoming an important source of inspiration for developing creative solutions to engineering design problems and even has a huge potential in formulating ideas that can help firms compete successfully in a dynamic market. To identify the technologies and methods that can facilitate the development of biologically inspired creative designs, this research briefly reviews the existing biological-knowledge-based theories and methods and examines the application of biological-knowledge-inspired designs in various fields. Afterward, this research thoroughly examines the four dimensions of key technologies that underlie the biologically inspired design (BID) process. This research then discusses the future development trends of the BID process before presenting the conclusions.

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Model-based nonlinear control of hydraulic servo systems: Challenges, developments and perspectives
Jianyong YAO
Front. Mech. Eng.    2018, 13 (2): 179-210.   https://doi.org/10.1007/s11465-018-0464-3
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Hydraulic servo system plays a significant role in industries, and usually acts as a core point in control and power transmission. Although linear theory-based control methods have been well established, advanced controller design methods for hydraulic servo system to achieve high performance is still an unending pursuit along with the development of modern industry. Essential nonlinearity is a unique feature and makes model-based nonlinear control more attractive, due to benefit from prior knowledge of the servo valve controlled hydraulic system. In this paper, a discussion for challenges in model-based nonlinear control, latest developments and brief perspectives of hydraulic servo systems are presented: Modelling uncertainty in hydraulic system is a major challenge, which includes parametric uncertainty and time-varying disturbance; some specific requirements also arise ad hoc difficulties such as nonlinear friction during low velocity tracking, severe disturbance, periodic disturbance, etc.; to handle various challenges, nonlinear solutions including parameter adaptation, nonlinear robust control, state and disturbance observation, backstepping design and so on, are proposed and integrated, theoretical analysis and lots of applications reveal their powerful capability to solve pertinent problems; and at the end, some perspectives and associated research topics (measurement noise, constraints, inner valve dynamics, input nonlinearity, etc.) in nonlinear hydraulic servo control are briefly explored and discussed.

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Damage mechanism and evaluation model of compressor impeller remanufacturing blanks: A review
Haiyang LU, Yanle LI, Fangyi LI, Xingyi ZHANG, Chuanwei ZHANG, Jiyu DU, Zhen LI, Xueju RAN, Jianfeng LI, Weiqiang WANG
Front. Mech. Eng.    2019, 14 (4): 402-411.   https://doi.org/10.1007/s11465-019-0548-8
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The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program “Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing” are reviewed in this work. Large centrifugal compressor impeller blanks were used as the study object. The materials of the blanks were FV520B and KMN. The mechanism and evaluation model of ultra-high cycle fatigue, erosion wear, and corrosion damage were studied via theoretical calculation, finite element simulation, and experimentation. For ultra-high cycle fatigue damage, the characteristics of ultra-high cycle fatigue of the impeller material were clarified, and prediction models of ultra-high cycle fatigue strength were established. A residual life evaluation technique based on the “b-HV-N” (where b was the nonlinear parameter, HV was the Vickers hardness, and N was the fatigue life) double criterion method was proposed. For erosion wear, the flow field of gas-solid two-phase flow inside the impeller was simulated, and the erosion wear law was clarified. Two models for erosion rate and erosion depth calculation were established. For corrosion damage, the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated. KISCC (critical stress intensity factor) and da/dt (crack growth rate, where a is the total crack length and t is time) varied with H2S concentration and temperature, and their variation laws were revealed. Through this research, the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multi-strength field and cross-scale were solved. The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.

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Modeling and optimization of an enhanced battery thermal management system in electric vehicles
Mao LI, Yuanzhi LIU, Xiaobang WANG, Jie ZHANG
Front. Mech. Eng.    2019, 14 (1): 65-75.   https://doi.org/10.1007/s11465-018-0520-z
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This paper models and optimizes an air-based battery thermal management system (BTMS) in a battery module with 36 battery lithium-ion cells. A design of experiments is performed to study the effects of three key parameters (i.e., mass flow rate of cooling air, heat flux from the battery cell to the cooling air, and passage spacing size) on the battery thermal performance. Three metrics are used to evaluate the BTMS thermal performance, including (i) the maximum temperature in the battery module, (ii) the temperature uniformity in the battery module, and (iii) the pressure drop. It is found that (i) increasing the total mass flow rate may result in a more non-uniform distribution of the passage mass flow rate among passages, and (ii) a large passage spacing size may worsen the temperature uniformity on the battery walls. Optimization is also performed to optimize the passage spacing size. Results show that the maximum temperature difference of the cooling air in passages is reduced from 23.9 to 2.1 K by 91.2%, and the maximum temperature difference among the battery cells is reduced from 25.7 to 6.4 K by 75.1%.

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Current research, key performances and future development of search and rescue robots
LIU Jinguo, WANG Yuechao, LI Bin, MA Shugen
Front. Mech. Eng.    2007, 2 (4): 404-416.   https://doi.org/10.1007/s11465-007-0070-2
Abstract   PDF (861KB)
Frequent natural disasters and man-made catastrophes have threatened the safety of citizens and have attracted much more attention. The rescue mission under disaster environment is very complicated and dangerous for a rescue team. Search and rescue (SAR) robots can not only improve the efficiency of rescue operations but also reduce the casualty of rescuers. Robots can help rescue teams and even replace rescuers to perform dangerous missions. Search and rescue robots will play a more and more important role in the rescue operations. A survey of the research status of search and rescue robots in Japan, USA, China and other countries has been provided. According to current research, experiences and the lessons learned from applications, the five key performances of a search and rescue robot are survivability, mobility, sensing, communicability and operability. Multi-technique fusion and multi-agent intelligent network are considered to be requirements for the future development of the search and rescue robot. Disaster prevention, disaster reduction and disaster rescue are the important parts of national public safety. They are also crucial for the safety of citizens and their estates. Search and rescue robotic technique is an urgent needed, strategic and core technique for national development. It will be important and strategic for national economy and safety.
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Novel piezoelectric pump with &#8220;E&#8221;-shaped valve found from sub-experiments
Jianhui ZHANG, Jun HUANG, Xiaoqi HU, Qixiao XI,
Front. Mech. Eng.    2010, 5 (2): 212-218.   https://doi.org/10.1007/s11465-010-0009-x
Abstract   PDF (248KB)
Increasing the driving frequency of a piezoelectric vibrator can resolve the bottleneck of low flow in a valve piezoelectric pump. However, a piezoelectric pump of a traditional valve body presents the hysteretic nature of the valve, and macroscopic performance is up-frequency to flow-sharply. This research is to settle the bottleneck mentioned above. First, through the sub-experiment on various parameters of the plate valve of a piezoelectric pump, the reasons why a valve body itself can influence &#8220;up-frequency to flow-sharply&#8221;, which causes the hysteretic nature of the valve, were discovered. Second, an &#8220;E&#8221;-shaped valve and piezoelectric pump with an &#8220;E&#8221;-shaped valve (PPEV) were invented. Finally, the efficiency of PPEV has been proved helpful to reduce hysteretic nature in experiments. Under the similar conditions, compared with traditional pumps, the driving frequency of novel PPEV can be more than 10 times high, and the flow rate also can be several times high.
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Geometrically constrained isogeometric parameterized level-set based topology optimization via trimmed elements
Yingjun WANG,David J. BENSON
Front. Mech. Eng.    2016, 11 (4): 328-343.   https://doi.org/10.1007/s11465-016-0403-0
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In this paper, an approach based on the fast point-in-polygon (PIP) algorithm and trimmed elements is proposed for isogeometric topology optimization (TO) with arbitrary geometric constraints. The isogeometric parameterized level-set-based TO method, which directly uses the non-uniform rational basis splines (NURBS) for both level set function (LSF) parameterization and objective function calculation, provides higher accuracy and efficiency than previous methods. The integration of trimmed elements is completed by the efficient quadrature rule that can design the quadrature points and weights for arbitrary geometric shape. Numerical examples demonstrate the efficiency and flexibility of the method.

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Creep-fatigue crack growth behavior in GH4169 superalloy
Dianyin HU, Xiyuan WANG, Jianxing MAO, Rongqiao WANG
Front. Mech. Eng.    2019, 14 (3): 369-376.   https://doi.org/10.1007/s11465-018-0489-7
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This study aims to examine the crack growth behavior of turbine disc GH4169 superalloy under creep-fatigue loading. Crack growth experiments were performed on compact tension specimens using trapezoidal waveform with dwell time at the maximum load at 650 °C. The crack growth rate of GH4169 superalloy significantly increased with dwell time. The grain boundaries oxidize during the dwell process, thereby inducing an intergranular creep-fatigue fracture mode. In addition, testing data under the same dwell time showed scattering at the crack growth rate. Consequently, a modified model based on the Saxena equation was proposed by introducing a distribution factor for the crack growth rate. Microstructural observation confirmed that the small grain size and high volume fraction of the d phase led to a fast creep-fatigue crack growth rate at 650 °C, thus indicating that two factors, namely, fine grain and presence of the d phase at the grain boundary, increased the amount of weakened interface at high temperature, in which intergranular cracks may form and propagate.

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Analysis of planetary gear transmission in non-stationary operations
Fakher CHAARI, Mohamed Slim ABBES, Fernando Viadero RUEDA, Alfonso Fernandez del RINCON, Mohamed HADDAR
Front Mech Eng    2013, 8 (1): 88-94.   https://doi.org/10.1007/s11465-013-0361-8
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Planetary gearboxes operate usually in non-stationary conditions generated mainly by variable loads applied to these transmissions. In order to understand the dynamic behavior of planetary gearboxes in such conditions, a mathematic model is developed including driving unit, transmission and load. The variability of load induces a variable speed of the transmission which is taken into account when characterizing the main dynamic parameter of the transmission which is the mesh stiffness function. This function is not periodic following the variability of the transmission speed. The computation of the dynamic response shows an intimate relation between the vibration amplitude level and the load value. As the load increase the vibration level increase. A combined amplitude and frequency modulation is observed which is well characterized using Short Time Fourier transform more suited than the spectral analysis.

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Branch-pipe-routing approach for ships using improved genetic algorithm
Haiteng SUI,Wentie NIU
Front. Mech. Eng.    2016, 11 (3): 316-323.   https://doi.org/10.1007/s11465-016-0384-z
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Branch-pipe routing plays fundamental and critical roles in ship-pipe design. The branch-pipe-routing problem is a complex combinatorial optimization problem and is thus difficult to solve when depending only on human experts. A modified genetic-algorithm-based approach is proposed in this paper to solve this problem. The simplified layout space is first divided into three-dimensional (3D) grids to build its mathematical model. Branch pipes in layout space are regarded as a combination of several two-point pipes, and the pipe route between two connection points is generated using an improved maze algorithm. The coding of branch pipes is then defined, and the genetic operators are devised, especially the complete crossover strategy that greatly accelerates the convergence speed. Finally, simulation tests demonstrate the performance of proposed method.

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Real-time task processing method based on edge computing for spinning CPS
Shiyong YIN, Jinsong BAO, Jie LI, Jie ZHANG
Front. Mech. Eng.    2019, 14 (3): 320-331.   https://doi.org/10.1007/s11465-019-0542-1
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Spinning production is a typical continuous manufacturing process characterized by high speed and uncertain dynamics. Each manufacturing unit in spinning production produces various real-time tasks, which may affect production efficiency and yarn quality if not processed in time. This paper presents an edge computing-based method that is different from traditional centralized cloud computation because its decentralization characteristics meet the high-speed and high-response requirements of yarn production. Edge computing nodes, real-time tasks, and edge computing resources are defined. A system model is established, and a real-time task processing method is proposed for the edge computing scenario. Experimental results indicate that the proposed real-time task processing method based on edge computing can effectively solve the delay problem of real-time task processing in spinning cyber-physical systems, save bandwidth, and enhance the security of task transmission.

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Operation analysis of a Chebyshev-Pantograph leg mechanism for a single DOF biped robot
Conghui LIANG, Marco CECCARELLI, Yukio TAKEDA
Front Mech Eng    2012, 7 (4): 357-370.   https://doi.org/10.1007/s11465-012-0340-5
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In this paper, operation analysis of a Chebyshev-Pantograph leg mechanism is presented for a single degree of freedom (DOF) biped robot. The proposed leg mechanism is composed of a Chebyshev four-bar linkage and a pantograph mechanism. In contrast to general fully actuated anthropomorphic leg mechanisms, the proposed leg mechanism has peculiar features like compactness, low-cost, and easy-operation. Kinematic equations of the proposed leg mechanism are formulated for a computer oriented simulation. Simulation results show the operation performance of the proposed leg mechanism with suitable characteristics. A parametric study has been carried out to evaluate the operation performance as function of design parameters. A prototype of a single DOF biped robot equipped with two proposed leg mechanisms has been built at LARM (Laboratory of Robotics and Mechatronics). Experimental test shows practical feasible walking ability of the prototype, as well as drawbacks are discussed for the mechanical design.

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Semi-active vibration control using piezoelectric actuators in smart structures
Jinhao QIU, Hongli JI, Kongjun ZHU
Front Mech Eng Chin    2009, 4 (3): 242-251.   https://doi.org/10.1007/s11465-009-0068-z
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The piezoelectric materials, as the most widely used functional materials in smart structures, have many outstanding advantages for sensors and actuators, especially in vibration control, because of their excellent mechanical-electrical coupling characteristics and frequency response characteristics. Semi-active vibration control based on state switching and pulse switching has been receiving much attention over the past decade because of several advantages. Compared with standard passive piezoelectric damping, these new semi-passive techniques offer higher robustness. Compared with active damping systems, their implementation does not require any sophisticated signal processing systems or any bulky power amplifier. In this review article, the principles of the semi-active control methods based on switched shunt circuit, including state-switched method, synchronized switch damping techniques, and active control theory-based switching techniques, and their recent developments are introduced. Moreover, the future directions of research in semi-active control are also summarized.

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Inverse Kinematics Analysis of General 6R Serial Robot Mechanism Based on Groebner Base
WANG Yan, HANG Lu-bin, YANG Ting-li
Front. Mech. Eng.    2006, 1 (1): 115-124.   https://doi.org/10.1007/s11465-005-0022-7
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This study presents a solution for the inverse kinematics problem in serial 6R manipulator. Using only seven equations composed of Duffy s four kinematical equations containing three angles and three corresponding angles  identical equations instead of the traditional 14 equations, the authors reduced the inverse kinematics problem in the general 6R manipulator to a univariate polynomial with a minimum degree based on the Groebner Base method. From that, they concluded that the maximum number of the solutions is 16, generally. Also, the mathematics mechanization method can be extended to solve other mechanism problems involving nonlinear equations symbolically.
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Stability and coupling dynamic behavior of nonlinear journal active electromagnetic bearing rotor system
LU Yanjun, HEI Di, WANG Yuan, DAI Rong, LU Yanjun, LIU Heng, YU Lie
Front. Mech. Eng.    2008, 3 (2): 193-199.   https://doi.org/10.1007/s11465-008-0023-4
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The stability and coupling dynamic behavior of a journal active electromagnetic bearing rotor system are analyzed. The gyroscopic effect is considered in the rotor model. The system equations are formulated by combining equations for rotor motion and decentralized proportional integral differential (PID) controllers. A method combining the predictor-corrector mechanism and the Netwon-Raphson method is presented to calculate the critical speed at the corresponding Hopf bifurcation point of the system. For periodic motions, a continuation method combining the predictor-corrector mechanism and shooting method is presented. Nonlinear unbalanced periodic motions and their stability margins are obtained using the shooting method and established continuation method for periodic motions. With the change of control parameters, the system local stability and bifurcation behaviors are obtained using the Floquet theory. The numerical examples show that the schemes not only significantly save computing cost, but also have high precision.
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A brief review on key technologies in the battery management system of electric vehicles
Kailong LIU, Kang LI, Qiao PENG, Cheng ZHANG
Front. Mech. Eng.    2019, 14 (1): 47-64.   https://doi.org/10.1007/s11465-018-0516-8
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Batteries have been widely applied in many high-power applications, such as electric vehicles (EVs) and hybrid electric vehicles, where a suitable battery management system (BMS) is vital in ensuring safe and reliable operation of batteries. This paper aims to give a brief review on several key technologies of BMS, including battery modelling, state estimation and battery charging. First, popular battery types used in EVs are surveyed, followed by the introduction of key technologies used in BMS. Various battery models, including the electric model, thermal model and coupled electro-thermal model are reviewed. Then, battery state estimations for the state of charge, state of health and internal temperature are comprehensively surveyed. Finally, several key and traditional battery charging approaches with associated optimization methods are discussed.

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