Soft Semi-active Back Support Device with Adaptive Force Profiles using Variable-elastic Actuation and Weight Feedback

TL;DR

This paper introduces a soft, lightweight back support device combining passive and active elements with adaptive force profiles, capable of assisting with object lifting by adjusting stiffness and force levels based on user feedback.

Contribution

It presents a novel soft BSD integrating variable-stiffness passive components and an active artificial muscle for adaptive assistance, validated through bench and on-body tests.

Findings

Device can switch stiffness and force levels effectively.

Reduces back muscle activity during lifting tasks.

Demonstrates weight-adaptive assistance using biofeedback.

Abstract

Portable active back support devices (BSDs) offer tunable assistance but are often bulky and heavy, limiting their usability. In contrast, passive BSDs are lightweight and compact but lack the ability to adapt their assistance to different back movements. We present a soft, lightweight, and compact BSD that combines a variable-stiffness passive element and an active element (an artificial muscle) in parallel. The device provides tunable assistance through discrete changes in stiffness values and active force levels. We validate the device's tuning capabilities through bench testing and on-body characterization. Further, we use the device's tuning capabilities to provide weight-adaptive object lifting and lowering assistance. We detect the weight handled by the user based on forearm force myography and upper-back inertial measurement unit data. Furthermore, electromyography analyses in five participants performing symmetric object lifting and lowering tasks showed reductions in back extensor activity. Preliminary results in one participant also indicated reduced muscle activity during asymmetric lifting.