Various quasi-zero stiffness (QZS) systems have been developed and applied in the vibration control domain in recent years. However, most QZS systems are usually unstable against external disturbances, and their QZS ranges are very limited. To address these issues, this study develops a highly stable QZS vibration isolation system integrated with magnetorheological fluids (MRFs). The MRFs endow the vibration isolation system with stiffness variability in vertical and lateral directions to against external disturbances, which innovatively solves the unstable problem of QZS systems. Meanwhile, the stiffness variability also makes the system adaptable to vibrations with different frequencies, so the system can deliver the best vibration isolation performance in response to various excitations. The system consists of a vertical isolation unit and a lateral isolation unit. By paralleling a nonlinear positive stiffness QZS component with a nonlinear negative stiffness QZS component in the vertical isolation unit, a large QZS range in the vertical direction and smaller stiffness are realised, thus improving the vibration isolation performance. In this study, the vibration isolation system is designed and prototyped; its QZS characteristics and adjustable stiffness features in both the vertical and lateral directions are experimentally verified; the frequency responses of the system are obtained experimentally; and the stability and the vibration isolation performance of the system are also evaluated by experiments with the designed control algorithms. This study provides a solution to overcome the unstable problem of QZS systems and extend the limited QZS range, whilst realising QZS characteristics in both vertical and lateral directions, thus broadening the application of QZS systems.

The stability analysis is studied for $H_{\infty } $ controlled networked active quarter-vehicle suspension systems with a resilient event-triggered scheme (RETS) under periodic denial-of-service (DoS) jamming attacks in this article. For the networked suspension system, the system-state signals are measured by sensors and transmitted to the cloud controller through a wireless network and then the control signal is transferred to the actuator to control it. An event-triggered scheme (ETS) is designed to reduce the workload of data transmission, which is effective to select some most useful information to transmit and discard some redundant data. DoS attacks can block the data transmission when it is active, so a resilient event-triggered $H_{\infty } $ control method is built based on the Lyapunov stability theory. The exponential stability of the controlled suspension system, as well as the $H_{\infty } $ performance, is analyzed in this article. Some simulation results show that the proposed control method is effective to improve driving comfort and driving safety and reduce the workload of data transmission under periodic DoS attacks.

Karst water may break into coal tunnels through the rock fissures and cause severe coal mine disasters. The direct current resistivity (DCR) is sensitive to underground water and can be used to detect fissures during the coal mining process. However, the three-dimensional (3-D) measurement of the DCR is still a challenging task and has not been applied to the practical coal mining dynamic process. To bridge this research gap, this study proposes a new 3-D cross-borehole method by monitoring the DCR at multiple points to analyze the geoelectrical field evolution in the underground coal mining process. Based on the forward and inversion theoretical analysis, a DCR observation system is developed for a real unground coal mine to evaluate the cross-borehole points. The 3-D resistivity distributions at different positions in the coal mining process are calculated. The analysis result demonstrates obvious resistivity changes with the evolution of the Karst water zone during the coal mining, and the location and movement of the Karst water can be well estimated. As a result, the proposed 3-D cross-borehole method is very effective for monitoring the DCR and is able to accurately detect the underground water.

Overshoot and long settling time are two common problems of the positioning control for robotic arms. To solve the positioning control problems, an innovative variable stiffness and variable damping (VSVD) magnetorheological (MR) actuation system for robotic arms was designed, prototyped and evaluated in this paper. The system can reduce the overshoot and settling time of the robotic arm with less energy consumption by controlling the stiffness and damping of its VSVD unit. A robotic arm with the VSVD actuation system was developed and prototyped. In order to evaluate the performance of the system, a step route and a customised route were designed for the robotic arm system to trace. Under these two routes, the positioning control performances of the VSVD robotic arm were evaluated numerically and experimentally with the control modes of uncontrolled, VD, VS and VSVD, respectively. Both the numerical and experimental results demonstrated that the VSVD control mode works best in general with less overshoot, settling time and energy consumption, indicating that the proposed VSVD actuation system can serve as a good candidate to solve the positioning control problems of robotic arms.

The velocity sensitive characteristic of the conventional linear magnetorheological (MR) damper is undesirable in the application of impact protection. It will induce large damping forces when the damper suffers high velocity impacts, whilst comprising the energy dissipation efficiency of the damper and posing a serious threat to occupants and mechanical structures. This work reports a new MR impact damper (NMRID) with low velocity sensitivity. Unlike the conventional MR impact damper (CMRID) in which MR fluids (MRFs) flow from one chamber to the other through a small annular gap between the piston and cylinder, the NMRID has a whole annular gap between the shaft and cylinder that is filled with MRFs, and the MRFs work in a pure shear mode without any liquid flow. In this work, a NMRID and a CMRID were prototyped. The velocity sensitivities of these two impact dampers were compared via numerical analysis and experimental impact tests. The analysis and test results indicate that NMRID possesses a much lower velocity sensitivity than the CMRID; the dynamic range of the NMRID decreases less than CMRID with the increase of nominal impact velocity. Then, to demonstrate the controllability of NMRID, impact tests with a bang–bang control were implemented, and the peak force of NMRID was successfully controlled around a target force under different levels of nominal impact velocity. This research proves that the designed NMRID is less sensitive to velocity than the CMRID and the NMRID has good controllability, demonstrating that the NMRID can serve as a better candidate than CMRID in applications with high impact velocity.