Towards Reducing Risk of Injury in Nursing: Design and Analysis of a New Passive Exoskeleton for Torso Twist Assist

Nursing is among the most physically challenging occupations and involves intensive lifting activities often including twisting of torso while performing tasks such as patient handling. Frequent and repetitive twisting of the body is known to induce large demands on the musculature, which may lead to MSD with direct and indirect costs to the hospital governance. One solution proposed through this article includes an exoskeleton specifically designed to assist in twisting movements of the trunk. This involves a double-actuator fully passive system that assists in rotation of the torso with the help of mechanical springs and cable modules. Our study provides a conceptual design of the mechanism, and a preliminary analysis using the concepts of kinematics, dynamics, usability, wearability, and freedom of movement. Results show that the mechanism could offer freedom of rotation for the wearer’s torso up to 52, 25 and 22 degrees (with stationary hip joint) along the transverse, sagittal and coronal planes, respectively. Moreover, similar force generation (up to 80N) was obtained in both actuators for same rotation on transverse plane in both directions for a combination of spring stiffness (0.5 – 1 N/mm) and damping (0.1 - 0.5 N-sec/mm) parameters. Our proposed design could also be integrated to the current exoskeletons in the form of a module and could be beneficial in more general work settings.