Research On Multi-link Embracing Space Capture Mechanism

Space on-orbit capture technology is a cutting-edge space technology and its main tool is space capture mechanism.Space capture mechanism can perform on-orbit capture,repair and reuse on expired spacecrafts in space to reduce economic losses,or drag them to the grave orbit to release space resources.Research on space capture mechanism is of great significance to the development of our country’s aerospace industry.In response to the difficulty of capturing space non-cooperative targets on orbit,a multi-link embracing space capture mechanism is proposed in this paper.The 4URU parallel mechanism with 5-DOF(degree of freedom)is used as the body of the capture mechanism,and the foldable spatial 8R lingkage with 3-DOF is used as the moving platform of the parallel mechanism.Combining the two mechanisms together to form the configuration of the space capture mechanism.The obtained space capture mechanism has the characteristics of multiple capturing DOF and large-scale fold deformation.The internal space enclosed by the 4URU parallel mechanism and the foldable spatial 8R linkage is used to capture space non-cooperative target as a whole.It can be adapted to capture targets of different sizes,and it can lock the target after capturing to prevent it from escaping,which can improve the capture ability greatly.The main research contents are as follows:(1)The configuration design of the parallel mechanism is carried out and the branch chain configuration of the parallel mechanism with 3T2 R of 5-DOF is synthesized.The branch chain form is analyzed as URU configuration and the number of branch chain is determined as four.The single-loop fold-and-expand mechanism of moving platform is selected.After analysing the motion characteristics of Bennett mechanism,symmetrical Bricard mechanism and the foldable spatial 8R linkage,the foldable spatial 8R linkage is selected as the moving platform of the mechanism.Therefore,the overall configuration of the capture mechanism is determined as the form of 4URU parallel mechanism plus a foldable spatial 8R linkage and the capture strategy of the space capture mechanism is provided.(2)The kinematics analysis is carried out for the space capture mechanism.The decoupling of the mechanism is completed by solving the kinematics conversion relationship between the foldable spatial 8R linkage and the 4URU parallel mechanism,and then the kinematics analyses of the foldable spatial 8R linkage and parapllel mechanism are carried out respectively to obtain their motion characteristics.The analyses of envelope space,capture stability,capture capacity and capture simulation of the mechanism are performed,which theoretically verify the rationality of the configuration.(3)The simulation analysis on the foldable spatial 8R linkage is carried out and the relationship curve between the driving joint and the passive joint is measured to verify the correctness of the theoretical analysis.The simulation analysis of the capture process is performed on the mechanism.The processes of capturing cylindrical target and spherical target are simulated respectively.The angular displacement of joint and change curve of contact force are measured and analyzed,which verify the rationality of the design and provide input parameters for structural design and prototype development.(4)The design of mechanical structure and control system,strength check of parts and manufacture of prototype are carred out on the capture mechanism.Finally,a 1:20scaled prototype is developed,and the capture experiments on ground are performed to capture typical geometric shapes such as cylinder and sphere,which verify the correctness of the design.