Optimization of low impact docking mechanism based on integrated joint design and task-oriented force ellipsoid index

Low impact docking mechanism (LIDM) is a key fundamental equipment for space missions that is used to capture and connect vehicles. Its strict requirements for mass and volume makes a major challenge to achieve larger workspace and load capacity (the docking direction is maximum). Essentially, it is a Gough–Stewart platform (SP), and the main design difficulties are configuration design and dimension optimization. The paper proposed a new integrated joint and SP classification, which guide the configuration design. Meanwhile, a unified kinematics model is established by the vector method, and the force Jacobian matrix is obtained by the principle of virtual work. The key to dimension optimization is to seek a reasonable evaluation index. A proposed general evaluation index, task-oriented force ellipsoid (TOFE), is applicable to both isotropic and anisotropic design demands. It normalizes the input and output, transforms an anisotropic problem into an isotropic problem, and uses the smallest hypersphere radius as the characterization. Then, using non-dominated sorting genetic algorithm (NSGA-II) obtain the Pareto front of the workspace and load capacity. Moreover, the influence of dimension parameters on output performance was revealed. Finally, the dimension optimization of the LIDM is completed, and its load capacity is improved by 13.51%.