Development of a redundant anthropomorphic hydraulically actuated manipulator with a roll-pitch-yaw spherical wrist

The demand for redundant hydraulic manipulators that can implement complex heavy-duty tasks in unstructured areas is increasing;however,current manipulator layouts that remarkably differ from human arms make intuitive kinematic operation challenging to achieve.This study proposes a seven-degree-of-freedom(7-DOF)redundant anthropomorphic hydraulically actuated manipulator with a novel roll-pitch-yaw spherical wrist.A hybrid series-parallel mechanism is presented to achieve the spherical wrist design,which consists of two parallel linear hydraulic cylinders to drive the yaw/pitch 2-DOF wrist plate connected serially to the roll structure.Designed as a 1R£RRR-1S£U mechanism(“R”,“P”,“S”,and“U”denote revolute,prismatic,spherical,and universal joints,respectively;the underlined letter indicates the active joint),the 2-DOF parallel structure is partially decoupled to obtain simple forward/inverse kinematic solutions in which a closed-loop subchain“R£RR”is included.The 7-DOF manipulator is then designed,and its third joint axis goes through the spherical center to obtain closed-form inverse kinematic computation.The analytical inverse kinematic solution is drawn by constructing self-motion manifolds.Finally,a physical prototype is developed,and the kinematic analysis is validated via numerical simulation and test results.