Evolutionary pressures have pushed humans to become efficient walkers, but inefficient divers. People consume more energy to travel the same distance underwater than on land. In diverse overground locomotion, emerging exoskeletons have reduced the metabolic cost of humans. Can we also improve the energy economy in underwater locomotion via exoskeletons? Here, we propose an underwater exoskeleton to assist scuba diving using flutter kick, by applying assistive knee extension torque during the strike phase of the diving kick cycle. When divers wore the powered exoskeleton, the average net air cost across six experienced divers was reduced by 22.7$\pm$10.0%, and the peak quadriceps activation was decreased by 20.9$\pm$7.5%, compared with normal diving without the exoskeleton. The average gastrocnemius activation also decreased by 20.6$\pm$5.3%, suggesting that the divers sufficiently utilized the exoskeleton assistance. These results indicate that applying exoskeleton assistance is conducive to improving the endurance of human underwater diving and enhancing our ability to explore the underwater world. Our study extends the application boundary of wearable robots, and provides a reference for the design and assessment of future underwater assistive devices, with the potential to strengthen the connection between humans and the ocean.

Wearable robotic devices interact with human by applying assistive force in parallel with muscle-tendon systems. Designing actuations in mimicking the natural activation patterns of human muscles is a promising way to optimize the performance of wearable robots. In this paper, we propose a bio-inspired cable-driven actuation system capable of providing anisometric contractions (including concentric and eccentric contraction) assistance or nearly acting as a transparent device in an efficient manner. A novel clutch-spring mechanism is employed to accomplish switches between assistive modes and the transparent mode. Corresponding control strategies coordinating with the mechanical design were presented and described in detail. Multiple evaluations were conducted on a test bench to characterize the system performance. The closed-loop bandwidth of the system running concentric assistance control was 18.2 Hz. The R-squared values of linear fitting under eccentric assistance control were above 0.99. The engagement time of the proposed clutch was about 90 ms. Applying the actuation to an ankle exoskeleton, multiple walking experiments with electromyography measurement were performed on five subjects to show its application potential in existing wearable robots. Experimental results revealed that the proposed design could reduce soleus muscle activity by 27.32% compared with normal walking. This study highlights the importance of functional bionic design in human-assistance-related devices and introduces a general actuation system that could be directly applied to existing cable-driven wearable robots.

In this paper, we present a low-damping active knee prosthesis (LDKP) with low noise and high backdrivability. The proposed prosthesis is driven by a motor and then decelerated by a four-stage synchronous belt. High backdrivability given by this structure accelerates the prosthetic response. A control system containing several sensors are embedded in the proposed prosthesis to recognize different modes and provide corresponding strategies. Preliminary experiments were carried out on a transfemoral amputee subject, demonstrating the features of low noise, high backdrivability and ability to reproduce natural walking gaits.

Wearable robotic devices often need electrical energy. An interesting idea is to collect mechanical energy during walking and convert it into electrical energy to recharge these devices directly. In this article, we built a light-weight robotic prosthesis (1.3 kg) with the feature of self-charging. During stance phase, the prosthetic ankle joint with damping, is driven by human dynamics. The rotated ankle joint backdrives the motor, and the motor works as a generator according to the electromagnetic induction theory. Five subjects participated in experiments to verify the feasibility and five speeds walking were studied (0.7, 0.9, 1.1, and 1.3 m/s treadmill speeds and one self-selected outdoor walking speed). Experimental results demonstrate that the electrical regenerative energy per step is 1.53 ± 0.29 J on average. Meanwhile, an average consumed energy per step of the robotic prosthesis is 4.64 ± 0.15 J, which means 33 ± 5% energy can be returned to the active prosthesis (battery, 24 V, 2.6 Ah).