Research On Key Technologies Of Design And Control Of Parallel Weave Compensation System With Six DOFs

Parallel wave compensation system with six DOFs is an important equipment in offshore replenishment, which is especially useful for the tasks need accurate location, such as the stacking of the containers and the filling of the torpedoes and missiles. It can control the positions and orientations of the cargos, as well as reduce the impact of wave induced ship motion. So far, few research has been done on parallel wave compensation system and the relative technologies are not sophisticated. The design and control both lack of theoretical supports. Based on these situations, this thesis explores some key problems in the design and control of parallel wave compensation system. The results can direct the manufacture of parallel wave compensation system.In fact, parallel wave compensation system is a cable-driven parallel mechanism with moving base. According to the practical environment and functional requirements of parallel wave compensation system, four design criteria of the cable-driven parallel mechanism are established. Based on the criteria, this thesis studies the determination of wrench feasible workspace, the design of singularity-free mechanism and the anti-pendulation and vibration characteristics respectively. In order to solve the problems of uncertain parameters and unknown disturbances faced by the control of parallel wave compensation system, this thesis studies the sliding mode control method, the identification of inertial parameters and the tension distribution optimization algorithm.The details of the contents are as follow.1) The structural scheme of six-DOF wave compensation system based on cable-driven parallel mechanism is proposed. The principles of relative motion compensation and pendulation reduction are analyzed, which prove that this scheme can completely compensate the six-DOF relative motion between the ships and eliminate the pendulation of the cargos. The design criteria of cable-driven parallel mechanism are made, which constitute the basement of the following research.2) In order to cover the shortage of the existing methods of workspace determination, a new method of determining the wrench feasible workspace based on the boundary search is proposed, which tests the wrench feasible condition of a single pose through high-dimensional projection and searches the boundary of the workspace using the depth-first algorithm. It can not only obtain the intuitive expression of the workspace but also reduce the computational burden. The relations between the wrench feasible workspace and the configuration parameters are analyzed, which provide the evidences for the design of configuration parameters.3) The types and characteristics of singularities of cable-driven parallel mechanism are analyzed and the elimination methods of the architecture singularity and the configuration singularity are studied. A method of singularity test is proposed, which uses interval evaluation and the branch-and-prune algorithm to detect the existence of singularity in task space and provides a new way to avoid singularities.4) The methods of eliminating pendulation and suppressing vibration that induced by the moving base are investigated. The concept and determination method of anti-pendulation workspace are proposed to weigh the anti-pendulation capability and the relations between the anti-pendulation capability and the configuration parameters are analyzed to show the direction of enhancing the anti-pendulation capability. The conclusions are demonstrated by experiments of scaled mechanisms. Then the vibration equations of cable-driven parallel mechanism are derived and the natural frequencies and the impact factors are analyzed.5) The main problems faced by the control of parallel wave compensation system are uncertain parameters and unknown disturbances. To solve these problems, a sliding mode control method with boundary layer and an identification method of inertial parameters are proposed. For the cable-driven parallel mechanisms with redundant configurations, a tension distribution optimization method based on the alternating projection is proposed, which can obtain the continuous optimal tension distribution in presence of feasible solutions and the best approximate distribution without presence of feasible solutions. The effect of the above methods is verified by co-simulations of Matlab and Adams. The simulation results are compared with those of conventional computed torque control. It is proved that the control method proposed in this thesis is robust to uncertain parameters and unknown disturbances and can enhance the accuracy of wave compensation control.