Reduction of Compression in Upper Body Wearable Robot using Passive Actuator and Moment Arm Structure

Abstract

As many occupations such as car mechanics, orchardists, and laparoscopic surgeons require prolonged and repetitive use of their upper body, the prevalence of musculoskeletal disorder in shoulder is particularly high among these professionals. However, a weight compensation of upper extremity can reduce the burden borne by the shoulder. There have been several researches on wearable solutions with rigid structures that reduce the upper limb fatigue, but a user can further benefit with minimal intrusion of workspace and safer interaction when the soft counterpart is applied. As tendon actuation is one of the popular choices among soft wearable robots, the intrinsic issue of axial compression due to the size of the moment arm needs to be addressed. In this paper, a method to reduce the tension-induced compression in upper body soft wearable device is proposed. Unlike the constant moment arm modelling assumed in the previous upper limb wearable device, the added structure on the shoulder increases the moment arm, thus significantly decreasing the tension and compression on anchored region while generating the equal amount of torque. The proposed quasi-zero stiffness mechanism generates a steady tension force which produces resulting sinusoidal torque when coupled with the new moment arm structure.