A Passive Lifting Assist Exoskeleton with Multiple Working Modes: Theoretical Evaluation and Design Concepts

A belt-type passive exoskeleton equipped with multiple working modes has been designed to support the back muscles during manual lifting tasks. Our concept is to develop a wearable assistive device that can provide motion-based assistance like the existing passive devices in the down phase of lifting, but in the up phase, can supply more load-based power. To achieve this goal, we designed two purely mechanical control mechanisms that can preload the load-based assist force and release it when the wearer intends to erect the trunk. This paper presents mathematical proof using a linked segment model and moment balance equations in the sagittal plane. Simulation proof is also provided based on a simple musculoskeletal model which executed sagittal plane lifting with a 20kg load in hands in stoop posture under three different conditions (no assist, classic mode, enhanced mode). The subsequent results suggest that the device substantially reduces the muscle force and lumbar moment by 27.7-43.5%, and in the enhanced mode, the efficacy is better than the classic mode. No such a quasi-passive back-support exoskeleton was found at the time of writing. This design concept is promising to help reduce the risk of back injuries in heavy load lifting and works that need workers to keep a forward bending and static holding postures such as vehicle assembly.