Jun 2006, Volume 1 Issue 2

  • Select all
  • XIONG You-lun, YIN Zhou-ping
    After introducing the concepts of digital manufacturing technology, the discipline framework of digital manufacturing is presented in the paper by discussing its basic concept, theory foundation, key technology and scientific problems in detail. As the core of the advanced manufacturing technology, digital manufacturing is gradually becoming the main manufacturing technology of the twenty-first century. Firstly, the main features of digital manufacturing are indicated and its key supporting technologies are investigated by grouping them into four levels related to product development, numerical control, production management, and enterprise collaboration, respectively. Moreover, the existing problems in the research on the multi-discipline theory foundation of digital manufacturing such as manufacturing informatics, computational manufacturing, and manufacturing intelligence, are also indicated. Then, the core scientific problems of digital manufacturing are discussed in depth, which focuses on digitization of manufacturing information, modeling of manufacturing constraints, high-speed and high-precision numerical control theory, and Internet-based collaboration and integration. Lastly, the development trends and application perspectives of digital manufacturing are concluded.
  • Shi-kui CHEN, Michael Yu WANG
    We propose a level set method-based framework for the conceptual design of compliant mechanisms. In this method, the compliant mechanism design problem is recast as an infinite dimensional optimization problem, where the design variable is the geometric shape of the compliant mechanism and the goal is to find a suitable shape in the admissible design space so that the objective functional can reach a minimum. The geometric shape of the compliant mechanism is represented as the zero level set of a one-higher dimensional level set function, and the dynamic variations of the shape are governed by the Hamilton-Jacobi partial differential equation. The application of level set methods endows the optimization process with the particular quality that topological changes of the boundary, such as merging or splitting, can be handled in a natural fashion. By making a connection between the velocity field in the Hamilton-Jacobi partial differential equation with the shape gradient of the objective functional, we go further to transform the optimization problem into that of finding a steady-state solution of the partial differential equation. Besides the above-mentioned methodological issues, some numerical examples together with prototypes are presented to validate the performance of the method.
  • JIAO Jing-pin, FEI Ren-yuan, HE Cun-fu, WU Bin
    It is important to analyze the propagation characteristics of guided waves in acoustic leak location in pipelines. In this paper, the acoustic leak signal is analyzed in the time-frequency domain. Based on the relation of time-frequency distribution of the acoustic leak signal and the dispersion curves of guided waves, the mode components of acoustic leak signals were obtained. The research can provide a guideline for the mode selection in pipeline leak location, and help improve the accuracy of leak location.
  • QIN Fei, YAN Dong-mei
    In the framework of the linearized magnetoelastic theory, the perturbed magnetic fields caused by mechanical stress and deformation were investigated theoretically. Governing equations and boundary conditions to determine the perturbed fields were derived. The effect of mechanical deformation on the magnetic fields was taken into account by coupling structural displacement into the perturbed magnetic field continuous conditions on the boundary of the structure. As an example, the perturbed field of a half-plane magnetized structure caused by a point force was calculated by the Fourier transform method. The results show that the calculated magnetic intensity component normal to the boundary of the structure reaches its maximum at the point force acted while the component tangent to the boundary inverses its direction sharply. The magnetic induction of the perturbed field is proportional to the applied force. Magnitude analysis proved that since the applied magnetic field has a relative weak intensity such as the Earth s magnetic field, influence of the magnetic field on deformation of the structure can be neglected.
  • WANG Li, LU Bing-heng, DING Yu-cheng, QIU Zhi-hui, LIU Hong-zhong
    A novel nano-scale alignment technique based on moiré signal for room-temperature imprint lithography in the submicron realm is proposed. The moiré signals generated by two pairs of quadruple gratings on mold and wafer are optically projected onto two photo-detector arrays, then the detected moiré signals are used to estimate the alignment errors in the x and y directions. The experiment results indicate that complex differential moiré signal is sensitive to relative displacement of the mold and wafer, and the alignment accuracy obtained in the x and γ directions and in θ are ±20 nm , ±25 nm and ±1 μrad (3σ), respectively. They can meet the requirements of alignment accuracy for submicron imprint lithography.
  • YANG Ping
    Large amounts of data in the SCADA systems  databases of thermal power plants have been used for monitoring, control and over-limit alarm, but not for fault diagnosis. Additional tests are often required from the technology support center of manufacturing companies to diagnose faults for large-scale equipment, although these tests are often expensive and involve some risks to equipment. Aimed at difficulties in fault diagnosis for boilers in thermal power plants, a hybrid-intelligence data-mining system based only on acquired data in SCADA systems is structured to extract hidden diagnosis information directly from the SCADA systems  databases in thermal power plants. This makes it possible to eliminate additional tests for fault diagnosis. In the system, a focusing quantization algorithm is proposed to discretize all variables in the preparation set to improve resolution near the change between normal value to abnormal value. A reduction algorithm based on rough set theory is designed to find minimum reducts from all discrete variables in the preparation set to represent diagnosis rules succinctly. The diagnosis rules mining from SCADA systems  database are expressed directly by variables in the database, making it easy for engineers to understand and use in industry applications. A boiler fault diagnosis system is designed and realized by the proposed approach, its running results in a thermal power plant of Guangdong Province show that the system can satisfy fault diagnosis requirement of large-scale boilers and its accuracy rangers from 91% to 98% in different months.
  • LIU Ya-xiong, Sekou Sing-are, LI Di-chen, LU Bing-heng
    To eliminate the motion artifacts of CT images caused by patient motions and other related errors, two kinds of correctors (A type and U type) are proposed to monitor the scanning process and correct the motion artifacts of the original images via reverse geometrical transformation such as reverse scaling, moving, rotating and offsetting. The results confirm that the correction method with any of the correctors can improve the accuracy and reliability of CT images, which facilitates in eliminating or decreasing the motion artifacts and correcting other static errors and image processing errors. This provides a foundation for the 3D reconstruction and accurate fabrication of the customized implants.
  • ZHANG Jian-min, FAN Yu, JIA Dong-yun, ZOU Qiu-ling, WU Ying
    Aimed at enhancing the research status of parallel machine tools, this paper introduces the structure of a 6-SPS parallel machine tool and explains the application significance of the kinematic simulation of the manufacturing pro
  • XIANG Jia-wei, CHEN Xue-feng, HE Zheng-jia, HE Yu-min
    The model-based forward and inverse problems in the diagnosis of structural crack faults were studied. The forward problem is to solve the natural frequencies through a cracked structural model and the inverse problem is to quantitatively determine the crack parameters using the experimental testing frequencies. Then, the one-dimensional crack element of B-spline wavelet on the interval (BSWI) was built to solve the forward problem. Contour plots of normalized crack location versus normalized crack size were plotted by using the first three natural frequencies as the inputs. The intersection of the three curves predicted the normalized crack location and size. The experimental study verified the validity of the wavelet-based crack element in solving crack singular problems to overcome the disadvantages of the traditional finite element method (FEM), such as low efficiency, insufficient accuracy, slow convergence to correct solutions, etc. At the same time, it had adequate identification precision. The new method can be applied to prognosis and quantitative diagnosis of incipient crack.
  • PAN Cun-yun, WEN Xi-sen, YANG Kun-yu, XU Xiao-jun, LIU Min, YAO Qi-shui
    A new kind of transmission-type spherical gear called ring involute spherical gear mechanism  is introduced. Compared to the famous TRALLFA spherical gear, this new spherical gear has an involute tooth profile, and a ring tooth that is distributed continuously on the surface of the sphere. This allows the gear to overcome two disadvantages of the TRALLFA spherical gear: the drive principle error and the manufacturing difficulty. The new transmission and the formation principle of the tooth s surface of the new spherical gear mechanism are first introduced, then another mechanism, called disk rack, is introduced, which is derived from the spherical gear mechanism when one of the spherical gear s tooth number reaches infinity. To make the research more convenient, every part of the new spherical gear mechanism is named. In the following sections, some problems are discussed, such as the assembly form, the construction characteristics, the correct meshing condition, the continuum transmission condition and so on. Furthermore, the paper deduces the surface formula of the conjugate teeth profiles, which proves that the conjugate teeth profiles is also one of the ringed involute spherical gear. In order to analyze the relationship between two coordinate systems, which is attached respectively to the diving spherical gear and the driven spherical gear, the orientation cosine matrix method is utilized. By series rotational transformation, the kinematics model and inverse kinematics model are deduced. Using the method for calculating the transmission ratio of planet gear train, the relationship of the two oscillating angle between output axis and the bracket is established. Based on the research, the kinematics graphic simulation of spherical gear mechanism and disk rack are made respectively. The results prove correctness of the kinematics model.
  • WAN Zhen-ping, LIU Ya-jun, TANG Yong, YE Bang-yan
    With more and more applications of glass in advanced fields of science, the demand for glass machining precision has increased greatly. More and more attention is being paid to glass cutting because precise glass parts with various shapes can be obtained at high efficiency and low cost. To improve the machining precision of part surfaces and to facilitate tool design and cutting parameter selection, the initiation and propagation laws of glass cracks in specimens subjected to normal loading by symmetric wedges were investigated. Research results show that initiation and propagation laws are the same with interior symmetric wedge angles of 30o-120o, while the laws are different with interior symmetric wedge angles equal to or more than "e150o. The relationship between medial crack length and normal loading was also investigated when specimens were indented by symmetrical wedges with interior angles of 30o-120o.
  • JIANG Hong-kai, WANG Zhong-sheng, HE Zheng-jia
    Weak fault features of mechanical signals are usually immersed in noisy signals. A new wavelet method based on lifting scheme to match weak fault characteristics is proposed. In this method, an initial set of finite biorthogonal filters is modified by a lifting and dual lifting procedure alternately, and different lifting operators and dual lifting operators are obtained. The properties of the initial wavelet is improved, and the new wavelet with particular properties is designed. Simulation and engineering results confirm that the proposed method is better than other wavelet methods for extracting weak fault feature. Modulus maxima of the detail signal in every operation cycle are extracted, the position and time that weak signal singularity occurs are clearly found, and slight rub-impact fault caused by axis misalignment and rotor imbalance of a heavy oil catalytic cracking set are desirably extracted. extracted.
  • CHEN Hong, LI He, WEN Bang-chun, ZHANG Xiao-wei
    A dynamic model of a dual-disk vertical over-hung rotor-bearing system is developed, taking into account nonlinear oil-film force. Its dynamic behaviors are investigated by numerical Runge-Kutta method. Its bifurcation and chaos characteristics are analyzed with crack fault and without crack fault. By analyzing the bifurcation plot, Poincare section plots and amplitude spectra, we found that the crack greatly influences the dynamic characteristics of the rotor-bearing system. Because of the strong effect of the nonlinear oil-film force and crack to the system, 1/2 times, 1/3 times frequency components appear in the response spectrum map. The results may bring up theoretical references for fault diagnosis of rotor-bearing systems.
  • HE Zhong-yun, LU Bing-heng, WANG Yi-qing, HONG Jun, TANG Yi-ping
    A creative robot wrist consisting of link mechanisms and a novel robot motion control method based on the cross-sectional vector contours of an STL-formatted model was proposed. By using the wrist and the control method, an industrial robot with five degrees of freedom for rapid tooling using metal arc spraying and electric brush plating techniques was developed. The wrist of the robot including a specially designed link mechanism can maintain the position of the spraying point on the surface of the master pattern whatever the orientation of the gun. Therefore, the kinematic nonlinear coupling between the position mechanism and orientation mechanism in a traditional robot can be avoided. The only input of the control system is the STL-formatted 3D CAD model of the pattern. Without the need of any manual programming, the metal arc spraying and brush plating (if necessary) processes can be performed automatically and efficiently after receiving the 3D CAD data of the pattern. Using this robot system in new car development and trial production, the cost and lead-time can be reduced substantially as compared with the conventional tool making method.
  • LI Jie, ZHAO Xin
    For most time-domain identification methods, a complete measurement for unique identification results is required for structural responses. However, the number of transducers is commonly far less than the number of structural degrees of freedom (DOFs) in practical applications, and thus make the time-domain identification methods rarely feasible for practical systems. A super-element approach is proposed in this study to identify the structural parameters of a large-scale structure in the time domain. The most interesting feature of the proposed super-element approach is its divide-and-conquer ability, which can be applied to identify large-scale structures using a relatively small number of transducers. The super-element model used for time domain identification is first discussed in this study. Then a parameterization procedure based on the sensitivities of response forces is introduced to establish the identification equations of super-elements. Some principles are suggested on effective decomposing of the whole structure into super-elements for identification purposes. Numerical simulations are conducted at the end of this study. The numerical results show that all structural parameters can be identified using a relatively small number of transducers, and the computational time can also be greatly shortened.
  • LIU Yan-bo, WU Jian-zhong, ZHANG Xuan
    Hydraulic synchronized continuous slippage technique, which integrates mechanical, electrical and hydraulic control, is introduced in this paper for the practical requirements of some construction projects. The core of this technique (the stability of the load transfer) is illustrated in detail. Three speed control strategies to transfer the load excessive, lower and same speed are presented to accomplish the smoothness and stability in the process of slippage. An optimization of the speed control strategy (same speed) is deduced from the modeling analysis and its validity and maneuverability are tested by practical application, which provides evidence for similar engineering in theory and practice.
  • MA Lv-zhong, GUO Zong-he, YANG Qi-zhi, YIN Xiao-qin, HAN Ya-li, SHEN Hui-ping
    This paper analyzes the precision of the dissymmetrical parallel mechanism of 3-RRRP(4R) with three translational degrees of freedom (DOF). The parallel mechanism has weakly-coupled, decoupled and real-time characteristics, thus error compensation can be done using control software. Based on topology structure analysis, the inverse and forward solutions are analyzed and the precision is studied using complete differential method. The influencing factors of the manipulator s precision are studied carefully and the means to enhance the precision are also discussed. It is found that the position errors of the moving platform have nonlinear relation with the position of the mechanism. The δθ'3 error has the biggest influence on the nonlinear errors of the position. Otherwise, the original errors of the mechanism are the main reason leading to more errors. Thus enhancing machining and assembling precision is an important method to enhance the precision of the mechanism.
  • XIE Hong, HE Yi-gang, ZENG Guan-da
    This paper presents the hybrid model identification for a class of nonlinear circuits and systems via a combination of the block-pulse function transform with the Volterra series. After discussing the method to establish the hybrid model and introducing the hybrid model identification, a set of relative formulas are derived for calculating the hybrid model and computing the Volterra series solution of nonlinear dynamic circuits and systems. In order to significantly reduce the computation cost for fault location, the paper presents a new fault diagnosis method based on multiple preset models that can be realized online. An example of identification simulation and fault diagnosis are given. Results show that the method has high accuracy and efficiency for fault location of nonlinear dynamic circuits and systems.
  • WANG Wei, CHEN Wei-ping
    Electrostatic-alloy bonding of silicon wafer with glass deposited by Au to form Si/Au-glass water, and bonding of Si/Au-glass with silicon wafer were researched during fabrication of pressure sensors. The silicon wafer and glass wafer with an Au film resistor were bonded by electrostatic bonding, and then Si-Au alloy bonding was formed by annealing at 400vH for 2 h. The air sealability of the cavity after bonding was finally tested using the N2 filling method. The results indicate that large bond strength was obtained at the bonding interface. This process was used in fabricating a pressure sensor with a sandwich structure. The results indicate that the sensor presented better performances and that the bonding techniques can be used in MEMS packaging.
  • CHEN De-yun, YANG Cong-jing, ZHENG Gui-bin, YU Xiao-yang, SUN Li-juan
    Sensor sensitivity field in electrical capacitance tomography is affected by the distribution of multiphase medium, which is the peculiarity of soft field. This brings great difficulty for image reconstruction. To improve the quality of image reconstruction, it is important to analyze the distribution of the sensitivity field. In this article, using the finite element method, we expound a kind of novel plotting pattern to field, which is the distribution of sensitivity field through computer simulation. From experiments and results of sensitivity field analysis, a novel method of image reconstruction based on genetic algorithms is presented. The finite element model is correct and simulation result is fine by adopting unequal interval plotting patterns. At the same time, the result of image reconstruction has high precision.