| The stabilized platform is an equipment which can keep its orientation under the external disturbance, or can run regularly according to a given torque relative to the inertia space.Since wave fluctuations can cause a moving ship swaying at sea, the camera mounted on ship may be unstable due to this swaying and often miss the targets. Hence, in order to obtaing high-quality image it requires the mounted platform maintains stable. This stabilization can be achieved through the azimuth, the pitching and the roll drive systems. Based on the above situation we have an issue to study. It comes from a project:Sea Security Command System on Olympic Sailing Competition (No. GAYY2008001), which is signed with Qingdao Technological University and Qingdao Municipal Public Security Bureau. All our researches are based on this project. There are many problems associated with the platform stabilization, here only the aspects of measurement and control system are stressed.The main researches of this thesis are as follows:(1) The kinematical features of the two and three axis stabilized platforms are analyzed and compared. Meanwhile, the designing idea of three-axis camera stabilized platform contained the roll framework is also realized. According to the structure characteristics of the three-axis stabilized platform, its corresponding kinematic and dynamic coupling equations are deduced; (2) The classic lead-lag control and the variable structure control (VSC) methods are adopted to correct the platform system. The comparative simulation results show that the VSC method possesses the virtue of fast response fast, strong robustness with respect to the parameter change and external disturbance. In addition, its control performance is superior to the lead-lag control method; (3) The factors of controling precision are analyzed and several methods are proposed to improve the precision. Especially, in view of the noise existed in the gyroscopes measurement signal, a time series model is developed on the dynamic output data sample series. To say it in detail, it follows from the comparison between the Kalman filter algorithm and Sage-Husa adaptive filter algorithm that the last one is more suitable for the stabilization problem. Furthermore, some improvements are done on the Sage-Husa algorithm which result in more running efficiency; (4) A control-system-design method based on FPGA is put forward, which leads to successful applications.The main innovation is showed as follows:(1) Principle defect of two-axis stabilized platform is analyzed, and points out that the two-axis stabilized system can only achieve the point of the shaft stability, and can't eliminate the disturbance of view axis rotation direction. In order to solve the problem, three-axis camera stabilized platform should be set up; (2) Sage-Husa adaptive filter algorithm was improved started form classic Kalman filter according to the criterion of spread of filter, this improvement may reduce calculation and enhance real-time of the system; (3) The VSC method based on friction compensation is put forward and applied to the correction of stable platform. VSC can change trajectory according to the state of the system in dynamic process and forces system to follow a prescribed "sliding mode" state. And this point just fits application background of the system platform; (4) Digital control circuits is designed based on high-speed controller FPGA, and the device could make rapid response to the movement of target, and adjust error as quick as possible. |
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