Recently, vacuum-based jamming mechanisms have been actively researched for safe human-robot interaction. However, most layer jamming mechanisms provide restricted motion in one direction such that their application in wearable robots is significantly limited. In this article, we propose a novel, soft, multi-degree of freedom (multi-DoF) layer jamming mechanism that employs a sliding linkage-based layer jamming mechanism (SLLJ). SLLJ allows movement not only in linear direction but also in the pitch and yaw directions along with a large resisting force, small thickness, and lightweight compared to conventional layer jamming mechanisms. We designed and fabricated SLLJ components, namely sliding linkage-based layers, soft pins, end holders, and enclosure. In addition, we conducted experimental validation and analysis of its linear tensile resisting force and bending torque in the yaw direction. The proposed SLLJ exhibited maximum resisting force of 264.8 N, compared to 284.1 N of the conventional layer jamming mechanism. Various shapes of SLLJ can be fabricated easily and adapted to a wide range of wearable assistant robots for rehabilitation and injury prevention, which require multi-DoF motions with variable stiffness and substantial resisting force.

The prosthetic arms generally face several challenges: most critically, they are not lightweight to the users and do not provide full degrees of freedom (DoF) for the arms. In order to address this problem, we propose a novel bio-inspired lightweight and high-DoF wrist for prosthetic arms. The proposed robotic wrist is lightweight, albeit more dexterous by simplifying the human wrist structure into a two-row ellipsoid joint and implementing novel ligament routing. The two-row ellipsoid structure effectively reduces the weight of the full-DoF wrist within sufficient ranges of motion (RoM) required for its mobility. A novel routing-by-ligament tunnel allows for the employment of stiffer ligaments in a compact structure, thereby securing the full DoF of the wrist without compromising its load capacity. We conducted a musculoskeletal simulation to show that the bioinspired wrist helps to increase the energy efficiency of the entire upper limb. Our experimental results demonstrated that the proposed wrist greatly reduces the weight of the entire prosthetic arm while improving its range of motion, tensile stiffness, and control performance.

Interest in the field of human-centered robotics continues to grow, particularly in utilizing pneumatic artificial muscles (PAMs) for close human–robot collaborations. Addressing the limited control performance of PAMs, we proposed a hybrid actuation scheme that combines PAMs (macro) and a low-inertia DC motor (mini). While the scheme has shown significantly improved control performance and robot safety, a small DC motor has difficulties in handling the large stored energies of the PAMs, particularly for large changes in initial load due to PAM failure. In order to further improve robot safety, we develop a new hybrid actuation scheme with PAMs (macro) and a particle brake (mini). This design allows for a higher torque-to-weight ratio and inherently stable energy dissipation. Addressing optimal mini actuation selection between a motor and a brake, and a control strategy for PAMs and a brake, we conducted comparative studies of hybrid actuations with (1) a DC motor and (2) a brake for concept validation. Experimental comparisons show that the hybrid actuation with PAMs and a brake provides higher energy efficiency for control bandwidths under 2 Hz, and more effective reduction of large impact forces due to the brake’s high torque capacity and passive energy dissipation.

A lumbar-degenerative flat back is a condition caused by a decline in back muscle strength with aging. The symptoms of this condition include severe lower back pain and spinal disorders, which restrict people from performing activities of daily living (ADL). Recently, various wearable robots have been developed to assist the weakened muscles. However, despite their effectiveness, the wearables require either bulky and rigid structures (active wearables) or tend to constrain users’ motion (passive wearables). In addition, the complex biomechanics of the human spine have not been sufficiently investigated during the design process. To address these issues, we propose a human-inspired spine assistive robot with a routed twisted string actuator (RTSA, active element) and a flat-back alleviation mechanism (FAM, passive element). This innovative RTSA conforms to the complex human spine curvature while minimizing friction and assists the ADL with its unique prioritizing characteristics. The human spine-inspired FAM, on the other hand, was designed to prevent spinal disorder injury while performing ADL. The experimental results showed that the proposed system successfully reduced the electromyography signals while performing ADL. Furthermore, the spinal disorder injury during trunk motion could be prevented by reducing the lumbopelvic ratio of the users.