Multiple degrees-of-freedom (multi-DOF) hydraulic manipulators are usually recognized as hard-to-control systems to achieve dynamic trajectory tracking because of strong nonlinearities, uncertainties, and complex couplings within the dynamics. In practice, when the end-effector of the multi-DOF hydraulic manipulator is tracking a given trajectory continuously, some joints may experience frequent stop-and-go or low-speed motions due to its kinematics. In such situations, dynamic friction becomes one of the main factors that affect the control performance. Inadequate compensation for the dynamic friction can result in undesired crawling or oscillatory behaviors of the manipulator. However, it is challenging to make effective compensation of the dynamic friction in control design due to its complicated and nonlinear properties. In this article, motion control of a multi-DOF hydraulic manipulator with extra consideration on the nonlinear friction for dynamic trajectory tracking is proposed. First, to make a more precise compensation of the nonlinear friction force, an improved LuGre model ensuring continuity and differentiability is developed, along with the method for obtaining nominal values of internal friction state based on desired trajectories. Then, a model-based adaptive robust motion controller is developed for the multi-DOF hydraulic manipulator. The nonlinearities and uncertainties of the high-order dynamics are well addressed in the closed-loop system, and the transient and asymptotic tracking performance can be guaranteed in theory. Finally, experimental validation was conducted, and the comparison with existing methods showed the improved tracking performance.

To improve tracking and synchronization control precision of electro-hydraulic shaking tables system, this paper presents a novel adaptive reaching law sliding mode controller (ARLSMC) for double shaking tables system with parameter uncertainty and disturbance. The ARLSMC combined a sliding mode controller based on a novel adaptive reaching law to improve dynamic performance with an adaptive controller to estimate the uncertain parameters online in order to reduce the system chattering. Besides, the proposed ARLSMC is introduced into the cross-coupled controller of double shaking tables. The stability of the control system is analyzed applying Lyapunov theory, and it is proven that both the tracking errors and synchronization error can converge to zero in finite time. The co-simulation model is built using MATLAB/Simulink and Adams for verification of the proposed control strategy. Various simulation tests are performed and simulation results demonstrate that the proposed method has a fast dynamic response performance, high control precision, and strong robustness.

Industrial robots are gradually being employed in machining processes, particularly the cutting process, owing to their flexibility, mobility, and economic efficiency. However, it is difficult to make the manufacturing process intelligent owing to the complexity of robot machining process information handling and programming. In this paper, the architecture of a STEP-NC compliant closed-loop robot machining system was designed, including its function model and information stream. A methodology based on STEP-NC was established to enable the analysis of high-level information directly and automatically generating robot program according to the actual machining conditions. The STEP-NC Application Activity Model (AAM) and Application Reference Model (ARM) of closed-loop robot machining system is built to integrate the machining process data, monitoring and inspection data, mechanical equipment data, machining status data and inspection result data within a unified data flow, making it possible to realize intelligent manufacturing and adaptively adjusting the robot machining process. The proposed closed-loop robot machining system was implemented based on an open STEP-NC interpreter that interprets the high-level information in STEP-NC directly to reduce machining robot programming time. An industrial camera was integrated with the robot for rawpiece positioning, then the STEP-NC interpreter can generate robot path rapidly according to the parameters of manufacturing features and position of rawpiece. The STEP-NC interpreter can generate a robot control program or communicate with a software controller using an application program interface, so it can be integrated with both existing industrial robot controllers and future open robot controllers. Finally, case studies are conducted for the functional verification of the proposed STEP-NC compliant closed-loop robot machining system.

The docking principle based on flux pinning is detailed and flux pinned docking mechanism is designed. In order to perform the space docking experiment on earth readily and cheaply, the simulated docking experimental platform with a flux pinned docking mechanism is first designed and established. By performing the single docking experiment on the simulated docking experimental platform, the dynamic docking time response of flux pinned docking mechanism is directly extracted by using the high speed camera and the real time tracking software TEMA. The analytical result of docking time response can assess whether the collision between two spacecraft modules of flux pinned docking mechanism happens or not. Furthermore, the docking frequency response can be extracted based on Fast Fourier Transformation. Based on the docking frequency response and the half power method, the dynamic connection characteristics (connection stiffness, damping ratio, and damping coefficient) of flux pinned docking mechanism can be calculated and analyzed, which estimates its performance. Based on the single docking experiment, the multiple docking experiments can be carried out to validate the reusable feasibility and to acquire connection characteristics of every time docking. The experimental demonstration system is designed and established in order to support future space docking for CubeSat sized spacecraft based on flux pinning and to accumulate some useful experimental datum.

Human-in-the-loop optimization (HILO) has been used to identify subject-specific assistive strategies and improve the performance of wearable exoskeletons. However, there is still a gap in research on HILO regarding knee exoskeleton flexion assistance. We present a HILO methodology that optimizes the flexion torque delivered by the knee exoskeleton. The cooperation mechanism of flexor and antagonist muscles assisted by the exoskeleton is first analyzed through the dynamic model. Furthermore, the online rapid metabolic evaluation function, including the electromyographic (EMG) signals of the semitendinosus (SEM) and vastus medial (VM), is designed based on the cooperative working mechanism of the antagonist muscle. The upper and lower controllers are designed respectively to realize the construction of the HILO closed-loop control system. Finally, we experimentally demonstrate the effectiveness of the HILO methodology proposed in this letter through EMG and metabolic indicators. In particular, for the knee joint, the time required to identify assistance strategies is significantly reduced by our protocol. This research will contribute to the design of fast convergence HILO methods from the perspective of human natural driving.