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 1RPRRR-1SPU 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 “RPRR” 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.

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With the electronization process of mobile hydraulics moving forward, the basic demand of power limitation control is increasingly fulfilled by electronic pump controllers to replace hydro-mechanical regulators. However, the nonlinear power controller introduces additional dynamics and potential oscillations into the electrohydraulic system. In this paper, the dynamic performance of the electrohydraulic system is analyzed using the linearized mathematical model and root locus tool, considering the factors of pump dynamic, actuator dimension, power setting point, and so on. A pump-based virtual leakage compensator is designed to reduce oscillations due to low damping excited by the power controller. The stability and parameter selection are then discussed to obtain optimal dynamic behavior. Using the traditional power controller as a comparison, the boom lifting motion test of a 2-ton excavator was carried out to validate the proposed compensator. The test result indicates that the proposed controller with optimized parameters has the ability to suppress pressure fluctuations and velocity oscillations.