Settlements of foundation and track of TM65 m and its effect on antenna pointing

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.