Research On Single Detector Coarse-Fine Composite Control Technology In Space Laser Communication

The premise of space laser communication is the precise alignment of the beacon beam,so the tracking technology of the composite axis is the key.The dual-detector servo system technology is mature,the tracking accuracy is high,and it is widely used.Compared with the dual-detector type system,the single-detection type composite axis servo system reduces one optical branch and has the advantages of lightness and miniaturization.However,due to the difficulties of the system such as coupling,the application is subject to many restrictions.This paper combines the national background project to study the coupling problem of the single-detection type composite axis servo system.It is believed that the coupling problem of the single-detection type composite axis servo system is mainly because the same detector cannot simultaneously meet the large field of view and large dynamic range of the spindle subsystem.As well as the small field of view,small dynamic range,and high frame rate of the sub-axis subsystem.At this time the main axis subsystem lacks a data source to form a main axis closed loop,ensuring that the target is stable within the sub-axis field of view.A decoupling control scheme based on a typical single-detector composite shaft structure is proposed.The method of coarse tracking and compensation for fine tracking deflection is used to solve the coupling problem.During coarse and fine tracking,the CCD tracking camera and the fine tracking system form a closed loop.The CCD passes high frame rate image information to the image processing unit.After image processing and overall control processing,the PZT driver controls the galvanometer to perform angular deflection to ensure the target spot.At the center of the camera's field of view,the working condition of the PZT driver is detected in real time by the position sensor inside the PZT piezoelectric ceramic driver.After processing such as amplification,filtering,and combined with the information obtained by the CCD detection,it is transmitted to the spindle system as a control input.In order to form the main axis closed loop,ensure that the target is stable within the field of view of the sub-axis.In order to solve the different requirements of the main and sub-axis for the detector,a CCD detector with "window opening" function is adopted,and the system's requirements for the detector in different working stages are achieved by setting CCD parameters online.At the same time,the target prediction is added into the system,and the target prediction algorithm is modeled and simulated by Matlab/Simulink to verify the feasibility,so as to ensure that the target is stable in the fine tracking field of view when the field of view is switched,and the tracking stability is maintained.Finally,an experimental system was established to verify the tracking performance and indicators.The experimental results show that the root mean square error of the coarse tracking azimuth and pitch tracking errors under the ±5°@0.1Hz disturbance are 296 ?rad and 255 ?rad,respectively.The overall tracking error of the system is controlled at about 1 pixel,the RMS error of the tracking pixel of the image is 0.182,and the RMS error of the pitch tracking pixel is 0.165.Based on the actual conditions,the system pixel angular resolution is 16?rad,so the overall tracking accuracy of the system is excellent.At 3?rad,accurate tracking of beacon light can be achieved,the system is stable,and decoupling is realized.