Flexos: A Portable, SEA-Based Shoulder Exoskeleton with Hyper-redundant Kinematics for Weight Lifting Assistance

In this paper, we present Flexos, a fully portable shoulder exoskeleton developed for logistic and industrial tasks. The device presents a simplified design with only a single, series elastic actuated joint employing an active torque control that assists the user in performing weight-lifting tasks. The device is lightweight and can be easily worn as a backpack. Ergonomic-shaped human-robot interfaces have been custom designed and 3D printed in order to achieve maximum comfort for the wearer. The exoskeleton has a hyper-redundant kinematic chain - a flexible link-connecting the backpack to the main series elastic actuator, which exerts torque on the upper arm. The SEA output torque is set by a closed-loop controller, whose aim is to compensate for gravity torque due to the human arm and weights lifted by the user. The device allows covering almost all the shoulder range of motion - 89.2% flexion/extension, and 88.4% internal/external rotation. Seven healthy participants were involved in a pilot study to assess the reduction of muscular activity - sEMG - in five targeted muscles during static and dynamic weight-lifting tasks. The assistance provided by the exoskeleton resulted in an average (-31.6% static, -24.6% dynamic) reduction of muscular effort.