A Hybrid Variable-Stiffness Soft Back Support Device

Back support devices(BSDs) have the potential to mitigate overexertion in industrial tasks and also to provide assistance to people with weak back muscle strength in daily activity. While state-of-the-art active BSDs can offer a high assistive force, they are bulky and heavy, making them uncomfortable for daily use. On the contrary, passive BSDs are compact but need manual adjustment to be versatile. This work presents a hybrid soft BSD that can provide task-oriented assistance by tuning the stiffness (0.58 N/mm, 0.92 N/mm, and 1.7 N/mm) and slack length (0 mm to 67 mm) in a compact design. The tunable stiffness allows for selecting a task-specific force profile, and the slack tuning will ensure that the device enables unhindered movement when assistance is not required. Compared with rigid devices, the device's compliance can potentially increase human comfort. We propose an analytical model that facilitates device design and estimates the device performance. Furthermore, the device's tuning capabilities are evaluated in human squatting and stooping experiments, showing that the desired force profile is correctly applied.

I. Introduction

Back injuries are among the most prevalent injuries [1], and the medical cost related to back injuries in the US was more than 365 billion in the year 2019 [2]. Back support devices (BSDs) have the potential to mitigate overexertion, which is a cause of the majority of back injuries [3]. Besides overexertion, BSDs could also compensate for reduced trunk muscle strength in the elderly population to assist in daily life activities [4]. BSDs can be classified according to actuation and rigidity, and each category has its advantages and disadvantages.