Compound axis servomechanism (CAS) is the most popular form of structure used in the large aperture telescope (LAT) system in the last few decades. In the control system of the CAS, the sub-axis which is driven by a fast-steering mirror (FSM) plays a decisive role in observation target tracking. In this paper, the kinetic dynamic of fast observation target (FOT) is analyzed by the time-frequency spectrum method. A sub-axis controller base on the FOT’s kinetic dynamic is proposed to improve the tracking performance of the CAS system. Traditional double-loop control is applied in sub-axis control. The inner loop is designed to provide a large bandwidth to cope with the FOT. As for the outer loop, a new control approach that is PIPI double integrations control is introduced to achieve a better tracking performance for the FOT. Additionally, the relationship between time delay and bandwidth of the LAT system is analyzed to demonstrate that the time delay is the main restriction to further improve the bandwidth of a CCD-based sub-axis controller. The theory and the simulation result indicate the proposed approach can improve the tracking performance of the LAT system to a certain extent, but still not sufficient when it comes to the FOT.
With the widening of the application scenarios for target observation, the traditional ground-based fixed LAT system has been unable to meet the requirement of high precision tracking ,the LAT need to be installed on different motion platforms. In this case, a series of photoelectric tracking systems based on motion platforms have been derived. The combination of LAT and moving platform brings a new problem--Disturbance such as braking, vibrating, and shaking of the platform will cause the deflection and shaking of the LAT imaging screen, which will have a great impact on the LAT tracking. In this paper, a method to determine the change of the attitude angle θ of the target in the field of view caused by the movement of a moving platform is proposed to suppressed overcome the disturbance introduced caused by the application of LAT in moving platform carrier. According to the angular position data of the target tracking point acquired by the CCD system and the attitude information of the motion platform in the geodetic coordinate system provided by the inertial navigation system, the attitude angle of the target can be calculated by applying the proposed attitude estimation algorithm. This method not only, provides a specific estimation process of target attitude angle, but also offers principle information for tracking state decision, image processing, and fiducial direction calculation.
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