Operational and Biomechanical Evaluation of a Wrist Exoskeleton Prototype for Assisting Meat-Cutting Tasks

Abstract

Although a growing number of exoskeletons have been developed for occupational applications, wrist exoskeletons remain relatively rare. However, in the meat processing industry, elbow and hand-wrist musculoskeletal disorders are particularly common. The aim of this article was to assess the potential effectiveness and risks of a 670 g wrist exoskeleton prototype designed to assist operators during meat-cutting tasks. Six professional butchers performed three standardized tasks reproducing meat-cutting gestures in foam, in three randomized experimental conditions: 1) without exoskeleton, 2) wearing the exoskeleton passive, with brakes off, and 3) using it with brakes activated, locked in a static position. Cutting forces were recorded using an instrumented table, joint angles using an optoelectronic motion capture system, muscle activity using surface electromyographic (EMG), and user experience was assessed using questionnaires. The cutting inaccuracy was defined as the area between the prescribed task and the actual cut on the foam surface. Joint torques were estimated by inverse dynamics with and without taking the exoskeleton’s mass into account, to isolate its effect. Linear mixed-effects statistical models were fitted. With the exoskeleton active during tasks, EMG activity was decreased of up to 18.7% (p < 0.01 to p < 0.001) in the wrist flexors and increased of up to 61.7% (not significant to p < 0.05) in the upper trapezius. Shoulder elevation joint torques were increased of up to 39.7% (p < 0.001), mainly due to the exoskeleton mass. The proposed multicriteria exoskeleton evaluation has provided guidance for following prototyping stages. Too heavy wrist exoskeletons could increase the risk of shoulder tendinitis for such tasks.