Mobility, Singularity and Configuration Analysis of a Bennett-Based Reconfigurable 8R Linkage

In this paper, a reconfigurable spatial 8R linkage is discussed. By adding coaxial joints to the links of a Bennett linkage, the mechanism is allowed to switch between a series of Bennett linkages with the same rod-length ratio and continuous different twist angles. Two types of revolute joints, which are θ-joint and a-joint, have been defined. Kinematic model of the mechanism is established based on the screw theory, whereby a singularity and mobility criterion in intuitive form is proposed and applied. Due to the 2 DoFs of the reconfigurable 8R linkage, the mechanism is able to both fold around its diagonal and change the twist angles of the θ-joint axes. The relationship of the two DoFs is developed, which explains the decoupled folding and twisting action of the mechanism. Simulations and prototype testing have been performed to validate the analysis. In the end, a series of derivative mechanisms, which have the same movement but different kinematic pairs, are presented.