Abstract:

Single-loop mechanisms can realize various kinds of motion and have wide applications. Closed chains are often put in the open-chain mechanisms as partial structure to improve the dynamic performance and increase the structure stiffness, which are widely used in engineering practice. A spatial single-loop RPSC mechanism which can realize vertical Darboux motion is introduced and its constraint and motion properties are analyzed based on screw theory. A special class of actuation singularity can be found by analyzing the constraints of this RPSC mechanism after the actuated joint is locked. A more intuitionistic geometric interpretation of this kind of singular configuration is given with the comparison of a similar planar mechanism. The key characteristics of the RPS limb in the mechanism are summarized, on the basis of which a class of more general single-loop mechanisms with similar properties are proposed.

Key words: actuation singularity, dead point, screw theory, vertical Darboux motion, spatial single-loop mechanism