检索结果-南通市图书馆

Structure and kinematic analysis of a novel 2.DOF translational parallel robot

在线全文

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2007年第10期17卷 1213-1219页

作者： Chen Tao1, Wu Chao2.and Liu Xinjun2.1. School of Application Science and Technology, Harbin University of Science and Technology, Harbin 150080, china 2. department of {2. instruments, tsinghua University, beijing 1.0084, china) School of Application Science and Technology Harbin University of Science and Technology Harbin 150080 China department of precision {2. Tsinghua University Beijing 100084 China

This paper addresses the analysis of a novel parallel robot with 2.translational degrees of freedom (DOFs). The robot can position a rigid body in a plane with constant orientation. The kinematic structure of the robot is first described in detail. Some kinematic problems, such as the inverse and forward kinematics, velocity, and singularity are then analyzed. The working and assembly modes are discussed. Since it is the most important index to design a robot, the workspace of the robot is studied systematically in this paper. Based on the analysis of reachable workspace and singularity, a kind of workspace concept characterizing the region that the end-effector of the robot can reach in practice is defined. The results of this paper will be very useful for the design and application of the robot.

关键词： parallel robot degree of freedom kinematics workspace.

Variation properties of ionospheric eclipse factor and ionospheric influence factor

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2005年第6期15卷 573-576页

作者： ZHAO Chunmei 1,2.*, YUAN Yunbin1, OU Jikun1 and CHEN Jinping3(1. Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, china 2. Graduate School of Chinese Academy of Sciences, beijing 100039, china 3. department of precision Instrument and mechanology, tsinghua University, beijing 1.0084, china) Institute of Geodesy and Geophysics Chinese Academy of Sciences Wuhan 430077 China Graduate School Chinese Academy of Sciences Beijing 100039 China department of precision Instrument and {2. Tsinghua University Beijing 100084 China

The concepts and calculation methods of ionospheric eclipse factor (IEF) and ionospheric influence factor (IFF) are further illustrated. The temporal and spacial variation properties of IEF and IFF are studied, which shows that the properties are influenced by the geographic position and season. The possibility of improving the precision of using GPS data to determine ionospheric delay based on the above variation properties is also analysed.

关键词： GPS Ionospheric eclipse factor Ionospheric influence factor

Density-functional formula for strongly correlated systems

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2005年第5期15卷 395-401页

作者： WANG Huaiyu1*, HAN Rushan2.and CHEN Nanxian1(1. department of Physics, tsinghua University,{2., china 2. department of Physics, Peking University, beijing 100871, china) Dept. of Phys. Tsinghua Univ. Beijing 100084 China Dept. of Phys. Peking Univ. Beijing 100871 China

Density functional method is applied for strongly correlated systems. Based on the assumption that the systems are composed of electrons in singly-occupied orbitals and those in doubly-occupied orbitals, a set of self-consistent equations are obtained by standard variation procedure. The equations consist of two parts. One part is to solve the wave functions of the electrons in singly-occupied orbitals and the other is to solve the wave functions of the electrons in doubly-occupied orbitals. The physical meanings of the terms appearing in the equations are discussed.

关键词： density-functional theory strongly correlated systems doubly-occupied orbital two-particle wave function self-consistent equations.

RESEARCH OF MICRO ELECTRO DISCHARGE MACHINING EQUIPMENT AND PROCESS TECHNIQUES

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Mechanical Engineering 2002年第2期15卷 177-181页

作者： Li Yong Guo Min Li Fang Zhou Zhaoying department of precision {2. and mechanology, tsinghua University, beijing 1.0084, china department of precision {2. and mechanology Tsinghua University 北京 100084

Micro electro discharge machining (micro EDM) is a feasible way tomanufacture micro structures and has potential application in advanced industrial fields. For therealization of micro EDM, it is necessary to pay careful attention to its equipment design and thedevelopment of process techniques. The present status of research and development of micro EDMequipment and process techniques is overviewed. A micro electro discharge machine incorporated withan inchworm type of micro feed mechanism is introduced, and a micro electro discharge machine fordrilling micro holes suitable to industrial use is also introduced. Some of the machiningexperiments carried out on the micro EDM prototypes are shown and the feasibility of the micro EDMtechnology to practical use is discussed.

关键词： Micro electro discharge machining Inchworm mechanism Friction drivemechanism Micro electrode Micro hole Micro structure

Step kinematic calibration of a 3-DOF planar parallel kinematic machine tool

在线全文

学校读者我要写书评

暂无评论

Science china(Technological Sciences) 2008年第12期51卷 2155-2167页

作者： CHANG Peng,WANG JinSong,LI TieMin,LIU XinJun & GUAN LiWen department of precision {2. and mechanology,tsinghua University,beijing 1.0084,china department of precision {2. and mechanology Tsinghua University Beijing China

This paper presents a novel step kinematic calibration method for a 3 degree-of-freedom(DOF) planar parallel kinematic machine tool,based on the minimal linear combinations(MLCs) of error *** method using mapping of linear combinations of parameters in error transfer multi-parameters coupling system changes the modeling,identification and error compensation of geometric parameters in the general kinematic calibration into those of linear combinations of *** using the four theorems of the MLCs,the sets of the MLCs that are respectively related to the relative precision and absolute precision are *** simple and feasible measurement methods in practice are given,and identification analysis of the set of the MLCs for each measurement is carried *** to the identification analysis results,a step calibration including step measurement,step identification and step error compensation is determined by taking into account both measurement costs and *** experiment shows that the proposed method has the following merits:(1) the parameter errors that cannot influence precision are completely avoided;(2. it reflects the mapping of linear combinations of parameters more accurately and enhances the precision of identification;and(3) the method is robust,efficient and effective,so that the errors in position and orientation are kept at the same order of the measurement *** to these merits,the present method is attractive for the 3-DOF planar parallel kinematic machine tool and can be also applied to other parallel kinematic machine tools with weakly nonlinear kinematics.

关键词： parallel kinematic machine tools kinematic calibration parameter identification minimal linear combinations

A novel extended Kalman filter for a class of nonlinear systems

在线全文

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2006年第9期16卷 912-918页

作者： DONG Zhe and YOU Zheng (department of precision Instrument and {2., tsinghua University, beijing 1.0084, china) department of precision Instrument and {2. Tsinghua University Beijing 100084 China

Estimation of the state variables of nonlinear systems is one of the fundamental and significant problems in control and signal processing. A new extended Kalman filtering approach for a class of nonlinear discrete-time systems in engineering is presented in this paper. In contrast to the celebrated extended Kalman filter (EKF), there is no linearization operation in the design procedure of the filter, and the parameters of the filter are obtained through minimizing a proper upper bound of the mean-square estimation error. Simulation results show that this filter can provide higher estimation precision than that provided by the EKF.

关键词： nonlinear systems state estimation Kalman filtering.

Parameter estimation for whole-body kinetic model of FDG metabolism

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2006年第11期16卷 1164-1170页

作者： CUI Yunfeng~1, BAI Jing~1**, CHEN Yingmao~2.and TIAN Jiahe~2.1. department of Biomedical Engineering, tsinghua University,{2., china 2. department of Nuclear Medicine, General Hospital of PLA, beijing 100853, china) department of Biomedical Engineering Tsinghua University Beijing 100084 China department of Nuclear Medicine General Hospital of PLA Beijing 100853 China

Based on the radioactive tracer [ ~ 18 F]2.fluoro-2.deoxy-D-glucose （FDG）, positron emission tomography （PET）, and compartment model, the tracer kinetic study has become an important method to investigate the glucose metabolic kinetics in human body. In this work, the kinetic parameters of three-compartment and four-parameter model for the FDG metabolism in the tissues of myocardium, lung, liver, stomach, spleen, pancreas, and marrow were estimated through some dynamic FDG-PET experiments. Together with published brain and skeletal muscle parameters, a relatively complete whole-body model was presented. In the liver model, the dual blood supply from the hepatic artery and the portal vein to the liver was considered for parameter estimation, and the more accurate results were obtained using the dual-input rather than the single arterial-input. The established whole-body model provides the functional information of FDG metabolism in human body. It can be used to further investigate the glucose metabolism, and also be used for the simulation and visualization of FDG metabolic process in human body.

关键词： compartment model FDG PET parameter estimation.

Study on simulation and experiment of array micro Faraday cup ion detector for FAIMS

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science china(Technological Sciences) 2010年第12期53卷 3225-3231页

作者： TANG Fei, WANG XiaoHao, ZHANG Liang & YAN ZiLin State Key Laboratory of precision Measurement Technology and instruments, {2. of precision instruments and mechanology, tsinghua University, beijing 1.0084, china State Key Laboratory of precision Measurement Technology and instruments Department of Precision Instruments and Mechanology Tsinghua University Beijing China

An array micro Faraday cup ion detector for FAIMS (High-field Asymmetric Waveform Ion Mobility Spectrometry) was introduced, with which the size of the FAIMS system was reduced. With simple structure, good stability, low noise, large measurements range, this detector can work under the condition of atmospheric pressure. The array micro Faraday cup was composed of gate electrode, sensitive electrode and shielding electrode. The sensitive electrode was made of tens of crossing silicon columns with diameter of 2.0 μm. It was fabricated through typical MEMS technology, which was compatible completely with plane FAIMS. It was shown from FLUENT simulation result that the resistance to gas motion was low and the flow field distribution was helpful for full absorption of the ion in this array design. Through electricity simulation, the method to reduce interference on the detection signal of the micro Faraday cup was given out. Connecting with KEITHLEY 2.7 ampere meter, the noise level of the array micro Faraday cup was lower than 0.5 pA. The output signal of the acetone sample measured by experiment was about 2.0 pA. Through contrast experiment, the design parameter of the micro Faraday cup was obtained primarily. This array micro Faraday cup can meet the requirements of the FAIMS system.

关键词： FAIMS MEMS Faraday cup ion detector low current

Research on Theoretical Model of Linear Frequency Modulation Interferometry

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Lasers 2000年第3期9卷 28-34页

作者： CHEN Yan ZHAO Yang (State Key Laboratory of precision Measurement Technology and instruments, {2. of precision instruments,tsinghua University, beijing 1.0084,china) 清华大学精密测试技术及仪器国家重点实验室北京 100084

In this paper, the principle of linear frequency-modulation (LFM) with an external microcavity laser is analyzed mathematically and a method to establish the math model of LFM heterodyne interference is presented. The expression of LFM heterodyne interference is deduced by an illustration of a triangular frequency modulation. At present, one application of the LFM technique is non-guide absolute distance measurement. Experimental results of a system for absolute distance measurement based on a microchip solid laser and LFM technique are given. Based on the precisely theoretical model some effective approaches to improve the performance of LFM and decrease the measuring error are discussed.

关键词： linear frequency modulation heterodyne interference absolute distance measurement