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A NURBS Fitting Optimization Method for High⁃Speed Five⁃Axis NC Machining Path Based on Curvature Smoothing Preset Point constraint

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Transactions of Nanjing University of Aeronautics and Astronautics 2021年第3期38卷 404-414页

作者： YANG Gaojie XU Xiang SHI Zhongquan YE Wenhua College of Mechanical and Electrical Engineering Nanjing University of Aeronautics and AstronauticsNanjing 210016P.R.China Jiangsu Key Laboratory of Precision and Micro-manufacturing Technology Nanjing University of Aeronautics and AstronauticsNanjing 210016P.R.China College of Mechanical and Electrical Engineering Hohai UniversityChangzhou 213022P.R.China

Existing curve fitting algorithms of NC machining path mainly focus on the control of fitting error,but ignore the problem that the original discrete cutter position points are not enough in the high curvature area of the tool *** may cause a sudden change in the drive force of the feed axis,resulting in a large fluctuation in the feed *** paper proposes a new non-uniform rational B-spline(NURBS)curve fitting optimization method based on curvature smoothing preset point ***,the short line segments generated by the CAM software are optimally divided into different segment regions,and then the curvature of the short line segments in each region is adjusted to make it ***,a set of characteristic points reflecting the change of the curvature of the fitted curve is constructed as the control apex of the fitted curve,and the curve is fitted using the NURBS curve fitting optimization method based on the curvature smoothing preset point ***,the curve fitting error and curve volatility are analyzed with an example,which verifies that the method can significantly improve the curvature smoothness of the high-curvature tool path,reduce the fitting error,and improve the feed speed.

关键词： curvature smoothing NC machining path NURBS curve fitting weighted constraint

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Gravity change observed in a local gravity network and its implication to seasonal precipitation in Dali county, Yunnan province, China

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Earthquake Science 2014年第1期27卷 79-88页

作者： Xin Zhou Wenke Sun Hui Li Shuhei Okubo Shaoan Sun Lelin Xing Dongzhi Liu Chongyang Shen Laboratory of Computational Geodynamics University of Chinese Academy of Sciences Institute of Seismology China Earthquake Administration Earthquake Research Institute The University of Tokyo

This study investigates data-processing methods and examines the precipitation effect on gravity measurements at the Dali gravity network, established in 2005. High-quality gravity data were collected during four measurement campaigns. To use the gravity data validly, some geophysical corrections must be considered carefully. We first discuss data-processing methods using weighted least- squares adjustment with the constraint of the absolute gravity datum. Results indicate that the gravity precision can be improved if all absolute gravity data are used as constraints and if calibration functions of relative gravi- meters are modeled within the observation function. Using this data-processing scheme, the mean point gravity pre- cision is better than 12 μgal. After determining the best data-processing scheme, we then process the gravity data obtained in the four measurement campaigns, and obtain gravity changes in three time periods. Results show that the gravity has a remarkable change of more than 50 pgal in the first time period from Apr-May of 2005 to Aug-Sept of 2007. To interpret the large gravity change, a mean water mass change （0.6 m in height） is assumed in the ETOPO1 topographic model. Calculations of the precipitation effect on gravity show that it can reach the same order of the observed gravity change. It is regarded as a main source of the remarkable gravity change in the Dali gravity network, suggesting that the precipitation effect on gravity mea- surements must be considered carefully.

关键词： Gravity network Gravity change Gravity datum weighted constraint Precipitationeffect

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