| In the process of navigation, ships will have the movement of rolling, pitching, heading, rising and falling because of the influences of storms or other environmental conditions. However, equipments are usually fixed firmly on ships. The movement will change the direction of equipments. Stabilization and tracking platform is used to isolate the ship movement and achieve high-performance tracking movement, which is of great strategic significance and illustrate a good prospect of application. The existing studies were aimed at the stabilization and tracking platform with series structure. In this paper, the stabilization and tracking platform with parallel structure was studied systematically for the first time. The study was carried out from the aspects of principles, features, optimization and control etc... The main contents are as follows:In chapter 1, on the basis of referring to domestic and international associated documents, structures and the current application situation of the existing stabilization and tracking platform were summarized, characteristics and application of parallel mechanism were briefly introduced, and the current research conditions of configuration, workspace, performance indices, dimensional optimization, control strategies and other aspects of parallel mechanism were summed up. The related study background and significance of the subject were expounded, and the main study work was proposed.In chapter 2, the kinematics and dynamics models of parallel stabilization and tracking platform were built. Firstly, the constitution of stabilization and tracking system with parallel platform was introduced, and the structure of a new 4TPS-1PS parallel platform was designed. The model of platform's actuating link was built considering the characteristics of electricity, mechanism and gas. The control command formulas of stabilization and tracking were deduced. The kinematics model of the parallel platform was built, and a real-time analytic forward kinematics solution and numerical forward kinematics solution based on Newton-Raphson method were presented. The dynamics model of the parallel stabilization and tracking platform with static base plate was built. The similarities and differences between dynamics models of the platform with moving or static base plate were analyzed. Furthermore the dynamics model of the platform with moving base plate was built. The influences of ships' disturbance on the cylinders' forces were simulated and analyzed.In chapter 3, the operating characteristics of parallel stabilization and tracking platform were studied. The pneumatic resistance of the servo electric cylinder was simulated, and the speed-output force curve of the servo electric cylinder was plotted out. The concept of full reachable workspace was expounded, and the full reachable rotation workspace was used to evaluate the workspace of parallel 4TPS-1PS platform. The theoretical rotation limits of the parallel platform were analyzed by geometry method, and a rapid solution of full reachable rotation workspace was put forward. The full reachable rotation workspace of the parallel platform prototype was calculated and plotted out. Rapid solutions of the parallel platform's speed and output force were put forward. It was concluded that the parallel stabilization and tracking platform's workspace had the characteristics of large range and symmetry, and the output speed and generalized force had the merits of large amplitude and little change with the parallel platform's pose.In chapter 4, performance indices and dimensional optimization of the parallel stabilization and tracking platform were studied. The expressions of weighted global condition number, installed power of parallel platform and other performance indices were deduced. The relations between performance indices and structure parameters were analyzed. The parallel stabilization and tracking platform was optimized by using Genetic algorithm (GA), and taking the installed power of the parallel platform as the direct optimized goal and the other performance indices as constraints. The simulation results showed that the installed power of the parallel platform with optimized structure parameters was greatly reduced and the requirements of other performance indices were met.In chapter 5, control strategies of the parallel stabilization and tracking platform were studied. Firstly, the PID control strategy with pose open loop was analyzed. Then a pose servo control strategy was presented, in which the platform was taken as a whole, and controlled directly with pose servo, while the cylinders were no longer controlled with position servo singly. The robust pose servo controller was designed by using the sliding mode variable structure control theory. The simulation results showed that the coupled errors caused by the inconsistencies of four cylinders' dynamic performances were almost eliminated, and the precise coordination between four cylinders was realized. Addressing the characteristics and the need of stabilization and tracking, the calculating disturbance force compensation was introduced to improve the control strategy. The simulation results showed that the influences of ships' disturbance, external disturbance and dynamic model errors were effectively eliminated, and high isolation degree and tracking precision were achieved by using this control strategy. Furthermore, the strategy was robust.In chapter 6, experimental studies of stabilization and tracking were carried out. The parallel stabilization and tracking platform experimental device was developed, and the hardware and the software of the control system were designed. The parallel six degree-of-freedom hydraulic servo platform was used to simulate the ship's movement for doing the stabilization and tracking control experiments in the laboratory. Functional tests of the parallel platform were firstly carried out to validate the correctness and rationality of the hardware and software design. Based on this, the experimental studies of tracking, stabilization and stabilization and tracking control were made by using the control strategy designed in chapter 5. Meanwhile, the accuracies and performances of the parallel platform were tested and the effectiveness of the control strategy was verified.In chapter 7, the major work of the study was summarized, and the conclusions and innovations of the study were elaborated. And the future study of the parallel stabilization and tracking platform was also prospected.
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