Supernumerary Robotic Limbs (SRLs) have become an effective method for assisting post-stroke patients in their daily life activities. However, conventional SRLs are constrained by functionality, wearability, and portability limitations, which are attributed to the presence of bulky robot actuators, gears, complex design, and high power consumption. This paper presents twisted string actuated (TSAs) flexure robot joints (FRJs) for a supernumerary robotic arm (SRA). This design aims for a compact, lightweight, energy-efficient, affordable, wearable, and portable SRL. The Twisted string actuation replaces the bulky actuator and gearbox in the robot joint. The FRJ joint design and modelling is proposed for the TSA-actuated Flexure Robot Joint (FRJ) and verified through experimental validation. A prototype of the 3 Degrees of Freedom SRL was developed, weighing 2.5 kg and possessing a payload capacity of 0.15 kg. The TSA-driven FRJ can produce 3 Nm joint torque at the cost of 32.5 mNm maximum motor torque, and the full SRL’s power consumption is 40 watts. In addition, a demonstration of bimanual tasks is presented using the proposed SRL to check its feasibility. Furthermore, the proposed SRL has merits compared with the existing SRLs in the literature.

Twisted string actuation through a conduit enhances flexibility, one of the most important features of twisted string actuators (TSAs). It allows remote transmission of power along an arbitrary curved surface, such as the human body, while avoiding interference with the natural movement of the wearer. However, TSAs on guided sliding surfaces or inside conduits have not been extensively investigated. This study experimentally investigates TSAs inside a conduit and its undesirable behaviors, namely, pullback and chatter, and their causes. In addition, this paper proposes a pre-twist method to overcome undesirable behaviors by introducing a certain amount of advanced twists as an initial condition to compensate for any opposite directional twist. This study also investigated the relationship between the required amount of pre-twist and string parameters (radius, length, and stroke) and external conditions (deflection angle and external load). Furthermore, an online required pre-twist estimation method is proposed to minimize the performance loss due to the present pre-twist. The feasibility is experimentally proved using a comparison study.

A bio-inspired novel CAT-leap parkour rolling mechanism (CPRM) is designed and developed for mobile robots. It was inspired by cat-leap jumping and monkey rolling motion. It enhanced the mobility of the mobile robot. Using CPRM, the robot can climb and cross unknown obstacles as well as perform locomotion. This mechanism protects the robot from unexpected impact forces on the robot during climbing and landing. It also can cross obstacles having double robot height. We developed a CPRM with a six-wheeled triangle-shaped mobile robot having two cat-leap arms for parkour rolling motion, allows a soft landing. We would like to share our experience working with CPRM mechanism and design from the inception to the realization, which includes design and iterations, prototype development, feasibility, functioning steps, advantages, and future applications.