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An approach to error elimination for multi-axis CNC machining and robot manipulation

Science China(Technological Sciences) 2007年第5期50卷 560-574页

作者： XIONG CaiHua School of Mechanical Science and Engineering Huazhong University of Science and Technology Wuhan 430074 China

The geometrical accuracy of a machined feature on a workpiece during machining processes is mainly affected by the kinematic chain errors of multi-axis CNC ma- chines and robots, locating precision of fixtures, and datum errors on the work- piece. It is necessary to find a way to minimize the feature errors on the workpiece. In this paper, the kinematic chain errors are transformed into the displacements of the workpiece. The relationship between the kinematic chain errors and the dis- placements of the position and orientation of the workpiece is developed. A map- ping model between the displacements of workpieces and the datum errors, and adjustments of fixtures is established. The suitable sets of unit basis twists for each of the commonly encountered types of feature and the corresponding locating di- rections are analyzed, and an error elimination (EE) method of the machined feature is formulated. A case study is given to verify the EE method.

关键词： error elimination, multi-axis machine, robot manipulation, kinematic chain, twist

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Subchronic toxicological effects of aquatic nitrobenzene on Medaka and Chinese rare minnow

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Science China Chemistry 2007年第5期50卷 707-717页

作者： ZHOU QunFang1, FU JianJie1,2, MENG HaiZhen1,2, ZHU XueYan1,2, JIANG GuiBin1, ZHANG JianBin1, LIU JieMin2 & SHI GuoQing2 1 State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China 2 Department of Chemistry, School of Applied Science, University of Science and Technology Beijing, Beijing 100083, China State Key Laboratory of Environmental Chemistry and Ecotoxicology Research Center for Eco-environmental Sciences Chinese Academy of Sciences Beijing China Department of Chemistry School of Applied Science University of Science and Technology Beijing Beijing China

Based on the simulative exposure experiments of nitrobenzene to two small experimental fishes, Medaka (Oryzias latipes) and Chinese Rare Minnow (Gobiocypris rarus), it was found that nitrobenzene could decrease in a linear way in the static aquatic system. Both fishes could accumulate dose-related levels of nitrobenzene quickly and eliminate the compound rapidly when they were transferred to clean water. The Chinese rare minnow showed more sensitivity to the acute toxicity exposure of nitrobenzene than Medaka. Typical molecular biomarkers in oxidative defense system including superoxide dismu- tase (SOD), catalase (CAT) showed the chemical induced alterations. The changes of acetylcholi- nesterase (AChE) activities indicated that nitrobenzene might affect the normal neural function. Nitro- benzene exposure could also lead to obvious damaging effects on the target organs, such as gill and liver by hitopathological studies.

关键词： nitrobenzene, Medaka, Chinese rare minnow, bioaccumulation, elimination, molecular biomarkers, histopathological effects

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Mathematical stencil and its application in finite difference approximation to the Poisson equation

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Science China Mathematics 2005年第10期48卷 1421-1429页

作者： FENG Hui~1 ZHANG Baolin~(1,2) & LIU Yang~1 1. Department of Mathematics,Wuhan University,Wuhan 430072,China 2. Laboratory of Computational Physics,Institute of Applied Physics and Computational Mathematics,Beijing 100088. China Department of Mathematics Wuhan University Wuhan China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing China

The concept of mathematical stencil and the strategy of stencil elimination for solving the finite difference equation is presented, and then a new type of the iteration algorithm is established for the Poisson equation. The new algorithm has not only the obvious property of parallelism, but also faster convergence rate than that of the classical Jacobi iteration. Numerical experiments show that the time for the new algorithm is less than that of Jacobi and Gauss-Seidel methods to obtain the same precision, and the computational velocity increases obviously when the new iterative method, instead of Jacobi method, is applied to polish operation in multi-grid method, furthermore, the polynomial acceleration method is still applicable to the new iterative method.

关键词： mathematical stencil, stencil elimination, Poisson equation, finite difference, iterative algorithm,parallelism.

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