Design of Three-Phalange Underactuated End Tool for the Chinese Space Station

Abstract

Creating an effective terminal operation tool for in-orbit space station services is challenging, especially when dealing with limited spaces and intricate manipulations. Debate has long surrounded the use of anthropomorphic hand tools in orbit, primarily due to concerns about dexterity and adaptability. To overcome these hurdles, we have designed a unique underactuated three-joint end tool finger. This finger can adapt to irregular objects without complex parallel linkages, making it simpler and more efficient for use in confined spaces. The grasping mechanism is composed of two steps: an initial parallel pinch to stabilize the grip followed by an indirect adaptive grasping phase. By optimizing the arrangement and connections of its components, we have significantly enhanced the finger’s adaptive capabilities. Through kinematics and force analysis, along with performance evaluations, we have validated the finger’s primary functionalities. Notably, the contact force between the object and the middle phalange can reach 30 N, marking improvement over existing research. To assess the finger’s performance, we analyzed its dexterity and workspace, finding that it requires only one motor to manipulate its three phalanges and to adapt to shapes and sizes ranging 30–60 mm in diameter. Despite the small space constraints, our finger exhibits exceptional dexterity, achieving a score of 0.9 after size optimizations. These results demonstrate its potential as an effective solution for in-orbit service operations.