| With the continuous improvement of communication technology and the information transmission between terminals is becoming more and more abundant. Due to the limitation of communication bandwidth, in the field of military, microwave technology is unable to meet the requirements. Optical fiber is becoming popular, in some areas, due to the topography, terrain and other reasons it is unsuited to lay fiber optic cable, then we need a reliable wireless communication technology to solve this problem. Based on these conditions, laser communication technology-came into being. Compared with traditional communication technologies, the free space laser communication has the advantages of large communication capacity, high security, well mobility, strong anti electromagnetic interference ability, construction and maintenance funds and so on. Laser communication technology is considered as the best solution for the future to achieve high speed and large capacity communication in the future.The fast establishment and stable maintenance of laser link is the guarantee and premise of realizing high speed and high reliability laser communication. This need the capture, tracking, targeting (Tracking, and, Pointing, Acquisition, ATP) system to realize. In the process of laser communication, such as star to star, ship to shore, the ATP process is affected by the action distance, atmospheric turbulence and other environmental factors.In order to ensure the continuous and reliable communication link to maintain and achieve higher tracking accuracy, the space laser communication system uses composite axis structure including one level coarse tracking and second level fine tracking. The fine tracking system has the advantages of high frequency, high response speed, small dynamic lag error and so on, making up the shortages of the main shaft system, and the disadvantages of small working range are compensated by the main shaft system. To obtain a higher control bandwidth The second level control system usually used Fast Steering Mirror (FSM).PID control is the most widely used FSM control mode, its structure is simple, is easy to adjust the parameters to get a good control effect. However, with the continuous improvement requirements of control system’s quality, the conventional PID control’s shortcoming such as need accurate mathematical model and improper to nonlinear control process. The practical system has the characteristics of the structure and parameters’ uncertainty, the pure delay, nonlinear coupling, time-varying, and various external disturbances, the conventional PID control can’t get ideal control effect.In order to meet the high accuracy requirement of ATP, this paper proposes the adaptive PID and fuzzy PID control algorithm. The two FSM control algorithms are able to overcome the disadvantages of the traditional PID control system, such as couldn’t adjust the parameters, used in nonlinear systems. We analysis two kinds of control algorithms, built the simulation model and converted it into CCS program, and the DSP2812 is used as the core of the desktop tracking experiments, transformed the system model into VHDL file in FPGA, and verified the two control algorithms in hardware layer.The experimental results show that when the disturbance is large, the anti disturbance performance of the system is greatly improved when used the adaptive PID controller. When using fuzzy PID controller, it still has good robustness when the object is changed. Two control algorithms are applied to achieve the tracking accuracy of 2 micro-radian. As the object of the research and design of the controlled object, fast mirror is used to suppress the influence of various disturbances in the process of ATP. The research and implementation of high precision and fast control algorithm can provide theoretical support and practical experience for high precision tracking in laser communication. It can provide reference for the development of laser communication and tracking technology. |
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