Research On Servo Technology Of Airborne Laser Communication System Based On Internal Model Control

As a means of communication with long distance,high precision and fast rate,laser communication system has a wide range of applications in aerospace fields such as vehicle-borne,shipborne and airborne.Among them,the acquisition,pointing and tracking(APT)system provides the basis for ensuring the steady communication of laser communication system,so how to improve the tracking performance of APT system has become an area of intense research interest.This paper takes the airborne laser communication system as the research background,and conducts an in-depth study on the model of the servo control system,the disturbance error and the tracking technology of the composite axis in the APT system.In this paper,the structure of the airborne laser communication system is analyzed,and the working principle and workflow of the system are introduced.In order to make the system have better tracking effect,the coarse and fine composite axis tracking system with two detectors is adopted,in which the coarse tracking system takes the two axes and two frames of the airborne laser communication platform as the control object,and the fine tracking system takes the fast steering mirror as the control object,and a mathematical model of coarse tracking system and fine tracking system is established by analyzing the links of the system.For the coarse tracking system in the process of tracking or steering periodic motion targets,it is easy to be affected by nonlinear perturbations such as platform vibration,target attitude perturbation,and object model parameter uptake,etc.we propose a repetitive compensation two-degree-of-freedom internal model control method,in which repetitive control can compensate for errors and reduce periodic perturbations,and two-degree-of-freedom internal model control can improve the anti-interference performance of the system.In order to realize the miniaturization design of the fine tracking system servo structure,the combination of four-quadrant detector and fast steering mirror is used as the fine tracking system servo architecture,and the integrated design of tracking and communication is completed by the four-quadrant detector,which can effectively reduce the size,weight and power consumption of the system.And this paper also applies the internal model control effectively to the fine tracking system to correct the fast steering mirror and improve the robustness of the fine tracking system.Finally,the experiments are built to complete the testing of the system tracking index as well as the communication performance.The experimental results show that the tracking residuals of the azimuth and pitch axes are 186.7 μrad and 210.6 μrad,respectively,when the coarse tracking system adopts the two-degree-of-freedom internal model control method with repetitive compensation under the interference of 5°@0.25 Hz,taking the azimuth axis as an example,the coarse tracking accuracy is improved by about 16%compared with the internal model control,and about 44% compared with the PID control.At this time,the coarse tracking error is stabilized in the field of view of the fine tracking four-quadrant detector,and when the fine tracking system adopts internal model control,the fine tracking error is less than 8 μrad,which can achieve precise tracking of the target and stable communication of the system.