Aiming at the tough requirements for safety and maintainability in mobile hydraulic systems, in this paper, an active fault-tolerant control (FTC) system is proposed against the valve faults of an independent metering valve. Not only moderate faults of activated valves, but also significant faults and un-activated valve faults are considered. Without additional hardware redundancy, analytical redundancy is derived by the coordinate control of other fault-free valves. Accordingly, an FTC system in parallel with a normal controller is designed based on the pressure feedback. It consists of a set of reconfigurable controllers and a decision mechanism. The control signals, control loops and operating modes can all be precisely reconfigured to adaptively match unmodeled fault dynamics. A bumpless transfer controller based on a latent tracking loop is designed to smooth the switching between the normal controller and FTC. Consequently, random valve faults can be tolerated with minor degradations in motion tracking and energy-saving performance. The feasibility of the FTC system is evaluated by a 2-ton excavator.

Human–robot shared control provides a promising opportunity to improve operational safety and efficiency for a teleoperated hydraulic manipulator system that works in unstructured environments, such as rescue response and underwater exploration. However, the poor dynamic of the heavy-duty manipulator (e.g., oscillation tendency and response delay) brings a challenging problem on intent prediction and effective assistance. To overcome this problem, a blended shared control method is proposed via locally weighted intent prediction. First, a task learning method from demonstration is presented by task-based action primitives with the Bayesian nonparametric clustering to extract subgoals of the remote arm trajectory, especially a locally weighted chattering cancellation method is proposed to reduce unintended action primitives due to velocity fluctuations. A dynamic intent prediction method is presented based on the empirical and real-time motion information by introducing an iterative transition matrix and a locally weighted dynamic angle, respectively. A prediction-based arbitration rule is finally established to blend the controllers of the human and robot seamlessly. Comparative tests in two typical scenes were carried out on a teleoperated hydraulic manipulator system. The results validate the proposed shared control method with fewer collision accidents and reduced task completion time, and subjective feelings on operation are also improved.

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.

Due to the complex control software based on electronic sensors, an independent metering control system (IMCS) has a higher risk of failures than a traditional electro-hydraulic (EH) system. Considering the tough requirements of safety and reliability in mobile applications, this paper innovatively proposes an active sensor-fault-tolerant controller (SFTC) for IMCSs. It is a model-free controller without any additional sensors. All the faults of the inlet, outlet, and supply pressure sensors are tolerated via analytical redundancy rather than hardware redundancy. The core of the analytical redundancy is to reconfigure the control loops of the normal controller by utilizing the cross-couplings among multi variables. To guarantee the switching stability from the normal controller to the SFTC, a bumpless transfer strategy based on latent tracking is designed, such that the abrupt output jump of the SFTC is suppressed and a smooth switching is obtained when the fault occurs. The feasibility of the SFTC system was evaluated by implementing the system on the 2-ton excavator. The experimental results of boom motions verify the effectiveness of the controller under abrupt and random sensor faults.

With the compact circuit layout and small size, hydraulic manifolds sometimes cause high pressure loss. The purpose of this paper is to investigate the pressure loss under different circumstances with various geometry features and present solutions to reduce pressure loss. The pressure loss performance is evaluated by both experimental and numerical methods. Verified by the experiments, the numerical simulations are qualified to depict the correct trend of the pressure drop. After the basic analysis of traditional passages, three novel forms are proposed, which are very hard to be manufactured by a common method. Furthermore, the geometrical features are selected optimally by means of full factorial experiments to balance the pressure loss and space requirement. Moreover, taking advantage of 3D printing, it is possible to build the passages in novel forms which are beyond the capacity of conventional manufacturing. Results show that the pressure loss can be reduced considerably by adopting a smooth transition, where the reduction can reach up to 50%.