Marine Propulsor based on a Three-Degree-of-Freedom Actuated Spherical Joint

We have designed and manufactured an innovative spherical joint mechanism with three actuated degrees of freedom, aimed at re-examining sculling as a potential propulsion technology with high efficiency and maneuverability. In addition, the mechanism might also enable propellers with directional thrusting capability. A parallel architecture was chosen for this type of mechanism in order to enable rigidity as well high actuation frequencies and amplitudes. Indeed, as the motors are fixed, inertial forces are lower than for a serial robot. The resulting spherical parallel mechanism (SPM) with coaxial shafts was designed and manufactured with the following specifications:  Fixed center of rotation (spherical joint)  Working frequency ~ 2.5 Hz under charge  Unlimited rotation about main axis  Arbitrary motion within a cone of ± 60° The equations for the inverse kinematics of the mechanism have been established and can yield the trajectories of each actuator for any desired motion applied to the oar or blade.