Workspace and singularity analysis of a double parallel manipulator

A double parallel manipulator (DPM) is composed of two parallel mechanisms with a central axis. The device is expected to have large workspace by reducing interference between links and to avoid singularity by constraining its motion. To prove this, workspace and singularity are analyzed. The workspace of the device is decoupled into a positional and an orientational workspace, each of which is computed and compared with that of a Stewart platform. The singularities occurring outside the workspace are analytically found at the configurations where a Jacobian matrix becomes rank deficient. To ascertain the analytical results, they are geometrically examined at the configurations where the duty for resisting forces and moments is not properly shared by a central axis and linear actuators due to losing static equilibrium. The geometrical results are coincident to the analytical results, which proves the DPM is free from the singularity problem.