| This paper is based on the project of ground-based laser emission telescope,which is implemented by Nanjing Astronomical Instrument Co.,Ltd.of CAS.The application background of the optical-telescope is the horizontal frame and the direct drive of DC motor.In this paper,automatic guiding-star of laser-tip,pointing control and satellite tracking method are studied and implemented by programming.The main work of this paper includes two aspects.One is the development of telescope control software,the other is the laser-image processing.The telescope control software is mainly responsible for pointing control and satellite tracking,including functions such as acquiring theoretical position,realizing tracking algorithm,correcting pointing error,human-computer interaction and network communication.Laser-image processing is mainly used for laser-tip detection and calibration,including CCD correction,noise reduction,edge detection,laser-tip and star-image recognition,coordinate calculation and other functions.Based on the study of telescope software control technology of Nanjing Astronomical Instrument Co.,Ltd.of CAS,the author independently completed the algorithm design and software development of the telescope control system,focusing on the following contents:In the aspect of pointing control,the frame model is selected to correct the pointing error.First,measure the zero deviation of code disk.Then obtain multiple sets of pointing error data from efficient sky,including azimuth axis,altitude axis,azimuth error and altitude error.Use Matlab to fit the measured error data with the least square method,and obtain the correction coefficient.In the control program,the real-time correction is carried out.At the significance level of ?=0.05,the residual analysis is carried out to eliminate those points with excessive deviation to improve the fitting accuracy.The validity of the model is verified by calculating RMS error,correlation coefficient and p value of F test.After testing,the pointing accuracy of the modified model is better than 5".In the aspect of satellite tracking,firstly,the ephemeris forecast software is used to process TLE data,and generate the satellite prediction guidance file of the local station,with the data rate of 1 point per second.Secondly,for the satellite passing through the north direction,its azimuth prediction value will jump at 360°(0°).In order to ensure the continuity of the process of tracking satellites with telescope,it is necessary to preprocess the satellite forecast guidance file.Reduce the azimuth value greater than 180° by 360° to make the azimuth prediction value continuous.In the process of tracking,we need to know the theoretical position of the satellite at current time,so we need to interpolate the forecast data.Matlab program is written to calculate and analyze Lagrange polynomial interpolation and Newton polynomial interpolation,The results show that the two interpolation methods achieve the highest accuracy when the order is 2,and the interpolation error is less than 0.01".And compare with the position of interpolation point,when the order is low,the middle position and the two ends position have little influence on the interpolation accuracy.But when high order,the end position interpolation will produce the Runge phenomenon.Because of the high sampling frequency,the polynomial coefficient solution method is used in the tracking system design.Every four points are used as a set of interpolation data,and the augmented matrix is constructed to obtain the unique solution of the coefficient.Through the test and calculation,the interpolation error of the third-order polynomial is less than 0.01",which fully meets the needs of satellite tracking accuracy.Matlab/Simulink is used to build the simulation model of servo system,and the PID of position loop is analyzed and corrected.The experiment shows that the PID algorithm with input feedforward can improve the tracking accuracy.In the satellite tracking program,a multimedia timer with 2ms interval is used to trigger the tracking subprogram.To improve the accuracy,the current time is read in real time in the tracking subprogram,and the theoretical position of satellite prediction at the current time is interpolated using the four adjacent points in the prediction guide file.Then compare with the actual satellite position fed back by the servo system,and adjust tracking speed by incremental PID.The experimental result show that the RMS of the tracking error of the two axes is less than 0.5".In the aspect of laser-tip automatic guide system,due to such factors as long distance and severe atmospheric extinction,the laser-tip cannot present a standard wedge shape,so the existing methods cannot accurately calibrate the light-tip in real time.The algorithm based on Hough detection proposed in this paper can realize the real-time calculation and calibration of laser-tip coordinates,and has a high fault tolerance rate.It can be detected normally under the condition of uneven background brightness and changing environment,improving the efficiency of laser ranging and the accuracy of light beam pointing to the target.At the same time,reduce the workload of manual adjustment of laser.The deviation is less than 2 pixels according to the picture taken in real time.In the laser-tip automatic guide system,the stability and accuracy of the algorithm are also verified.In the algorithm implementation,the image quality is improved by the methods of CCD dark field correction and flat field correction,multi-image overlay,Gauss filter and image enhancement.In this paper,the algorithm principle and image processing effect of the spatial domain method and the frequency domain method are compared,and the spatial domain method is selected for programming.The method of Otsu is used to extract foreground,Sobel operator to detect edge,then the intersection line is fitted based on Hough transform.Considering the influence of background interference,low laser power leading to image of light-tip dimmed,threshold selection deviation and other factors,image processing program select several effective lines for screening.Finally,the laser-tip position is calibrated.The algorithm can detect the laser-tip and calculate the coordinates of the laser-tip accurately in case of unclear visual recognition.The center of mass coordinates of satellite stars can calculated by centroid algorithm.Through the deviation between laser-tip and center of mass,the telescope can be controlled to eliminate the deviation.The laser beam from the telescope will be aimed at the satellite accurately when the laser-tip point to the center of mass.Therefore,it can achieve the scientific goal of automatic guiding star with laser-tip and no need of human judgment and processing. |
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