Development and Experimental Validation of a Passive Exoskeletal Vest.

Passive upper limb exoskeletons are often designed to relieve muscle fatigue of manufacturing workers. Existing exoskeletons often provide partial assistance, and their assistive torque is only affected by elastic elements and mechanisms, which, however, are not sufficient because of the changing load of the shoulder joint due to the motion of the elbow and the weight of various tools. To improve the assistive effect without affecting the free movement of the arm, a passive exoskeletal vest has been designed. This exoskeleton has two operating states which can be switched using a unique ratchet bar mechanism. The upper arm can be locked at any vertical position when engaged. The assistive torque is determined by the load. The arm also can move freely without any resistance when separated. Seven subjects participated in the evaluation experiment, who performed static tasks, precision tasks, and dynamic tasks. The experimental data demonstrate that (1) the exoskeleton can effectively reduce the activation level of related muscles at a variety of tasks. (2) The accuracy and stability of the arm during heavy work are not affected. (3) The exoskeleton has a minimal restriction on the range of motion of the arm. (4) the comfort and portability achieved a high score of 8 (1-10) from subjective measures. The experimental results further revealed that the designed exoskeletal vest could effectively relieve the shoulder burden, where it does not impede or restrain the arms movements.