Upper-Limb Exoskeleton Assisting Shoulder Extension for Climbing

Abstract

Humans are not good at climbing due to physical limitations while being compared to some other closed species. Artificial environments are designed to support daily activities of humans to avoid climbing. Enhancing the ability to climb fighting against gravity will be very helpful in unavoidable scenarios such as exploration, adventure, and rescue missions in geographic and unstructured environments. To evaluate the feasibility of applying wearable robots to assist climbing, the primary study in this paper focuses effects of shoulder assisting moment on the reduction of muscle activities during pulling up. The upper-limb exoskeleton prototype was designed and built. For each shoulder joint, there is one passive degree of freedom for the abduction-adduction motion and another actuated degree of freedom for the flexion-extension motion. The exoskeleton's body is hung on the human body through straps like a backpack and the upper arm limbs are attached to the human arms. For lightweight, the structural links were fabricated from octagonal carbon fiber tubes connected by the joints printed from carbon-fiber reinforced nylon. To support pulling up, the T-Motor AK70-10 brushless DC motors for the left and right shoulders were programmed to behave like torsion springs having a desired stiffness with the equilibrium reference set at the angle when the upper arm limbs lie horizontally. The shoulder extension assisting moment from the motor is proportional to the shoulder flexion angle measured from the equilibrium whenever the body is lower than the reference level. During pullup experiments with different assistive levels, the muscle activities of teres major (TM) and triceps brachii (TB) were observed on a healthy male volunteer to evaluate the human climbing effort.