A new 3-DOF mechanism for quasi-direct-drive robot manipulators

A new spacial mechanism is described which can provide the basic 3 degrees of freedom (DOF) of a manipulator. All three motors are mounted fixed to the base support structure to greatly reduce the arm inertia. Motion is transmitted via a differential and a spacial 5-bar linkage. The differential converts the motions of two of the motors into a 2 DOF input link of the 5-bar linkage. For the mechanism to move freely, the three passive joints of the 5-bar linkage must provide 12 constraints. The mechanism can be made very stiff resulting in a high speed-high accuracy arm. The kinematics are remarkably easy to analyze, and the mechanism can be made with singularities confined to the workspace boundaries.