A novel discontinuously movable six-revolute mechanism

摘要

A novel discontinuously movable mechanism (DMM), namely the (RR)RR(RR) six-bar DMM is proposed to shed light on the discontinuous mobility in special mechanisms via the group-based approach. This mechanism includes two (RR) subchains with adjacent R axes perpendicularly intersecting and one set of three adjacent revolute R pairs with parallel axes. Its discontinuous mobility has a bifurcation towards two distinct working modes with one-dof finite mobility. One mode is a rotation around the common axis of two coaxial revolute pairs and the other mode is a planar motion of a 4R linkage with parallel R axes. The special mobility is explained by using the Lie group algebraic properties of the displacement set. In addition, the same spatial arrangement of the R axes can be linked in a different way such that another chain with a quite different mobility is constituted but its infinitesimal mobility is not altered.