Abstract: Multiple 3-R(SRS)RP multi-loop mechanisms are used as modules to integrate a manipulator for obtaining high rigidity, high intensity, high mobility, and large workspace, thereby satisfying the requirements of space on-orbit tasks. Based on the configuration of the multi-loop mechanism, a whole structure design scheme of the space manipulator, including structural designs of SRS compound hinge, multi-loop mechanism module, and multi-loop mechanism system, is proposed. The SRS compound hinge is designed on the basis of an improved spherical joint mechanism. Two spherical and one additional revolute joints are combined, and all the motion axes intersect at one point, thereby improving the motion accuracy and simplifying kinematics model. Then, one connection method between platforms of different modules is developed for constructing the space manipulator system. Each module of the system is designed by planning its connecting links. Thus, the axes of the revolute joints on moving and base platforms are coincident, thereby meeting the requirements of folding and bending motion process. This design strategy eliminates the structural interference of coupling kinematic chains. In addition, the inverse-kinematics models of the multi-loop mechanism module and system are established thus inverse-kinematics analyzing. Based on the kinematics model and analysis, the numerical analysis of the workspace of multi-modular manipulators is conducted. It turns out that the three-modular manipulator achieves a large reachable workspace and bending angle, which provides theoretical basis for manufacture of the prototype.

Key words: 3-R(SRS)RP multi-loop mechanism, structural design, inverse-kinematics analysis, workspace