Design optimization for improved usability in a passive upper limb exoskeleton for industrial use based on Pneumatic Artificial Muscles

In the industrial field, overhead works are one of the leading causes of Work-related Musculoskeletal Disorders (WMSDs). These disorders not only pose a significant health risk to workers but, also, negatively impact industrial productivity. It has been observed that, in Europe, absenteeism rates in industries caused by WMSDs, exceed those due to the influenza virus. Both these aspects, in view of the advancements of Industry 4.0, represent an issue to which a solution must be found to ensure greater workers safety. A promising solution to mitigate these risks is provided by exoskeletons for industrial use, which are electromechanical devices worn by operators and designed around the shape and function of the human body. Their purpose is to assist workers by enhancing operational capacity and reducing physical effort. Since these devices must be worn in direct contact with the user, their development leads to significant challenges. Specifically, they must guarantee, first and foremost, the safety and comfort of the user, while simultaneously assisting movement without restricting it but rather supporting the worker during occupational tasks. In this scenario, passive exoskeletons for upper limbs come into play. In particular, the prototype analysed in this master’s thesis is a passive exoskeleton for industrial applications, which employs two Pneumatic Artificial Muscles, specifically two McKibben Muscles (MKMs), as energy storage elements. The particularity in the functioning of MKMs is linked to their ability to generate tensile forces when pressurized, which closely resemble the behavior of natural muscles. The exoskeleton under consideration operates by generating a support torque that counteracts the gravitational one; the latter is generated by both the load of the user's arm and by the presence of any additional tool in its hands. This mechanism leads to a reduction in load magnitude at the shoulder joint level and, consequently, to a lower incidence of injuries. First, an evaluation has been conducted to assess the progress and the significant advancements made in exoskeleton technology over the past few decades, and then, the principles governing the operation of PAMs have been explained. Subsequently, the focus shifted to the core objective of the thesis, namely, to optimize and improve usability and efficiency of a former exoskeleton prototype. To this end, the prototype has been analysed, highlighting the adjustments made to the components with the aim of improving and optimizing the structure's usability. The structural behavior of the exoskeleton, both in terms of stresses and displacements, has been tested, using Finite Element Methods, to evaluate its performance under typical working conditions. Ultimately, supplementary analyses have been conducted to estimate the entity of the loads exerted on the subject during the functioning of the device.