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.

This paper proposes a decoupling compensation method for damping improvement of the electrohydraulic control system with multiple actuators. The low damping property of hydraulic systems has been a remarkably troublesome issue for a few decades. Previously, this issue with one actuator has been addressed effectively by state feedback and signal compensation, e.g., dynamic pressure feedback. However, the poor damping with multiple actuators is still intractable and pendent due to the complex coupling effect of different loads. A decoupling compensator based on pump/valve combined control is proposed for a typical electrohydraulic system with multiple actuators for mobile machinery. Using decoupling control of different load branches, the coupling hydraulic circuit with multiple cylinders is transformed into multiple separate single-cylinder circuits with dynamic compensation. The dynamic characteristics of different actuators are then improved synchronously without mutual interference, while the steady performance remains the same without loss of controllability. Compound motion tests on a 2-ton hydraulic excavator were carried out. The results showed that the proposed compensator reduced velocity and pressure oscillations under different working conditions, so the dynamic performance is improved for the multiactuator system.

Rate control is the most used operation method for master–slave hydraulic manipulators. However, the trajectory from the master controlled by the operator cannot completely meet the dynamic limitations and flow restriction of the hydraulic manipulator. Continuous large errors and oscillation will occur due to flow restrictions and high-order dynamics beyond the dynamic boundaries that significantly limits the velocity tracking performance of a hydraulic manipulator. In this article, we propose a flow-limited rate control scheme for the master–slave hydraulic manipulators. The variable velocity mapping is developed, adjusting the velocities to meet the pump and valves’ flow limits. An adaptive robust rate controller of hydraulic manipulators is designed. An adaptive boundary estimator is introduced to estimate the hydraulic manipulator acceleration boundaries, and a variable structure controller is used to plan the velocities to meet dynamic limits. The proposed control scheme is tested on a hydraulic manipulator. The results show that the control scheme reduced velocity error and avoid the manipulator vibration, so the performance is improved for the hydraulic manipulator.