Hybrid occupational exoskeleton for bimanual multijoint assistance
F. Missiroli, N. Lotti, E. Tricomi, C. Bokranz, R. Alicea, M. Xiloyannis, J. Krzywinski, S. Crea, N. Vitiello, and L. Masia,
"Rigid, Soft, Passive, and Active: a Hybrid Occupational Exoskeleton for bimanual multijoint assistance”.
IIEEE Robotics and Automation Letters, doi: 10.1109/LRA.2022.3142447. PDF
Occupational Exoskeletons (OEs) are being developed with the aim to make work safer by reducing the effort required of the back muscles during lifting, or the effort of the shoulder muscles during tasks of overhead manipulation. However their assistance is restricted to the shoulder flexion-extension, with no supporting action for more distal joints such as the elbow articulation.
In our work we propose a new combination of devices which derive from the current concept of assistive industrial exoskeletons for overhead tasks with the ultimate goal to feature upper-limb OEs with elbow gravitational support. Our assumption was that the more distal joint such as the elbow can be assisted through an exosuit powered by DC motors placed on the torso through wire ropes routed via Bowden cables.
Figure 1: Hybrid bimanual exoskeleton developed to assist the elbow and shoulder joints; on the top-left the front view of the wearable device with positioning of the principal components, on the bottom-right back view of the suit with attention drawn to the actuation stage and control stage.
The device, is a fully embedded system comprising of two modular and interconnected layers that can be worn independently: a new prototype of actuated soft wearable elbow exosuit that supports flexion, and a passive occupational exoskeleton assisting the shoulders in overhead static and dynamic tasks (i.e. MATE, COMAU, Turin, Italy).
The sensing network for motion detection of the exosuit comprises four IMUs, communicating the arm postures via bluetooth low energy to the controller stage.
To control the active layer of the hybrid device we estimate a reference torque from a biomechanical model of the user, accounting for the 3D kinematics of the joints. This is then tracked by an admittance controller comparing the estimated torque with the torque delivered by the exosuit to the human joint. The error torque is then converted into a motor velocity command.
The device, successfully reduces muscular activation on the shoulders as well as the elbows: a reduction of 32% of the biceps activation during elbow flexion has been reported and provided by the actuated layer and an average reduction of 31% of the deltoids activation during shoulder abduction.
Moreover, the co-contraction index of the main muscles involved in the elbow and shoulder motion, presents no difference wearing the device respect to the no assistance condition, for this we can speculate that the hybrid exoskeleton does not hinder the user movements.