Settlements of foundation and track of TM65 m and its effect on antenna pointing
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摘要: 天马望远镜（简称TM65 m）所建地区属于软土层，为保证望远镜高指向精度，需要坚实的基础支撑高精度的方位轨道平面。2012年7月~2015年7月，基于精密水准测量系统，采用闭合法对基础沉降及轨道面精度共进行了11次测量。测量数据表明基础沉降逐渐趋于均匀沉降，轨道面均方根误差为0.47 mm。测量结果显示天线的基础沉降和轨道面高程随方位角的变化具有相关性，说明基础沉降直接影响了轨道面的精度。采用实验、仿真和理论相结合的方法分析轨道面不平度引起的天线方位轴在东西和南北方向的误差。首先，线性插值测量的轨道不平度数据，提取某方位角对应的天线方位滚轮6支点的高程，然后将高程差作为约束边界条件施加到有限元模型上，最终仿真分析获得不同方位角下方位轴的倾斜量。同时，利用安装在天线座架上的电子倾斜仪对轨道面不平度进行测量，建立了倾斜仪x和y向输出数据与方位轴倾斜及对应方位角的关系模型，经拟合计算得到方位轴的倾斜量随方位角的变化关系曲线。仿真和理论分析结果具有很好的一致性，轨道面不平度对指向精度的影响在4内，分析结果为天线指向模型修正提供了依据。Abstract: The area built TianMa telescope (in brief, TM65 m hereafter) belongs to soft soil layer. Consequently, in order to keep the high level pointing accuracy, it is necessary to build steady foundation to support the high accurate azimuth track. Based on the closed method, the accuracy of foundation settlements and track was measured by the precise leveling survey system for total 11 times from July 2012 to July 2015. The results show that the foundation tends to even settlement and the root mean square error of the track surface is 0.47 mm. At the same time, the results also show that there are relevant between foundation settlements and track heights with variation of the azimuth angle, which illustrates that the foundation settlements directly affect on the track accuracy. In addition, the methods of experiment, simulation and theory were combined to analyze the azimuth axis errors induced by the track unevenness in the eas-west and sout-north direction. Firstly, the measured track data were linear interpolated and, at some azimuth angle, the heights of some 6 supporting points of azimuth wheels were extracted. Then, the constrained boundary conditions of height differences were applied to the finite element model. Finally, the azimuth axis tilts at different azimuth angles were obtained by simulating. Simultaneously, the track unevenness was measured by inclinometer. The relationship between the azimuth axis tilt and corresponding azimuth angle and the x and y data measured by inclinometer was established and the curve of the variation of the azimuth axis tilt with the azimuth angle was achieved. The simulation results show a good agreement with the theoretical analysis and the effect of track unevenness on the pointing accuracy is within 4 arcsec, which provides basis for the pointing model modification.
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Key words:
- antenna structure /
- foundation settlement /
- track surface accuracy /
- pointing accuracy
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