Analysis Of Singular Configuration And Research Of Its Solving Method Of The Hydraulic STEWART Platform Of Flight Simulator

Hydraulic Stewart platform is the typical parallel manipulator, which has been successfully applied to the motion system of large aircraft flight simulator and has become its important components due to the capacity of realizing 6-DOF movement and the merits of high rigidity, large load capacity, relatively simple structure, high precision and relatively easy to control, etc. However, the major drawbacks of hydraulic Stewart platform are that there are singular configurations in special condition and the workspace is very limited in comparison with serial manipulator. Based on the singular configuration analysis of Stewart platform and aiming at the problem of existing singular configuration, for the different requirements of task workspace, the dissertation take specific and systematic study on the respects of nonsingular structure design, the safety protection of hydraulic Stewart platform with singular structure and eliminating singular configuration using redundant mechanism. Finally, it achieved the purpose of solving the problem of singular configuration and satisfying the requirement of workspace at the same time.Hydraulic Stewart Platform is a multi-variable and non-linear complex system in nature. The kinematics and dynamics study of hydraulic Stewart platform is the research basis of other related characteristics and control strategies. The dissertation analyzed the kinematics and dynamics of hydraulic Stewart platform. It established multi-body dynamics model of Stewart platform using Kane method, derived mathematical model of asymmetric servo valve control of asymmetric hydraulic cylinder. On the base of that, it established entire dynamics model of the whole hydraulic Stewart platform. After that, it analyzed the coupling characteristic between DOF using the established entire dynamics model and verified the correctness of analytic results through experiments.Due to the spatial structure of six branches, it makes the singular configuration judgment of Stewart platform very complex. To analyze if there exist singular configuration in the task workspace and reachable workspace of a Stewart platform, based on the singularity study of parallel manipulator by predecessors, the dissertation analyzed the relevant characteristics of Stewart platform at the Hunt singular configuration and the relevant experiments was taken. Then, using Jacobian matrix of the mechanism and solved the matrix through programming, it achieved the analytical expression of singular locus equation of the Stewart platform which contains arbitrary three posture variables and represented the singular locus of Stewart platform in three-dimensional space. After that, it analyzed the singular configuration of an electric Stewart platform in task workspace and reachable workspace with the proposed singular locus analysis method and verified the conclusion through experiments.For a certain demand of the task workspace, there exists nonsingular Stewart platform to meet the requirements, so it needs to study a method to design Stewart platform with nonsingular structure. The dissertation established a homotopy algorithm to solve forward position kinematics of Stewart platform. On this base, After analyzing the structural parameters, combined with the extreme pose analysis method of Stewart platform, considering the structural parameters of the Stewart platform, the static force applied on legs, the maximum condition number and configuration bifurcation behavior of the mechanism, it designed Stewart platform with nonsingular structure. Then, it analyzed and verified the designed Stewart platform through simulations and experiments and found out that there does not exist singular configuration in the reachable workspace of the designed Stewart platform which is determined by the legs.For the hydraulic Stewart platform which has singular configuration in the reachable workspace due to the workspace requirement of task, the dissertation proposed concept of singular zone and nonsingular zone. Using the legs length and combined with the extreme poses analysis method, it established a criterion to judge if the Stewart platform entered into the singular zone. Then, it designed hydraulic protection device of hydraulic Stewart platform. Using the proposed criterion and hardware devices, it realized the protection of hydraulic Stewart platform when entered into the singular zone because of the system being out of control.As for the redundant parallel manipulator having function of eliminating singular configuration, the dissertation increased three redundant legs on the base of the original non-redundant hydraulic Stewart platform and designed redundant hydraulic Stewart platform with "6+3" style structure. Then, it analyzed kinematics, dynamics, and established multi-body dynamic model of redundant hydraulic Stewart platform and optimized redundant driving force. After that, it compared the relevant characteristics of non-redundant hydraulic Stewart platform with redundant hydraulic Stewart platform and found out that redundant hydraulic Stewart platform can further improve the performances of the system. It analyzed the principle and function of eliminating singular configuration of redundant hydraulic Stewart platform, and simulating with the established virtual prototype to verify the effect in solving Hunt singular configuration. Finally, with the designed redundant hydraulic Stewart platform, it eliminated the existed singular configuration in the reachable workspace of the original non-redundant one.