Personal Mobility With Synchronous Trunk-Knee Passive Exoskeleton: optimizing Human-Robot Energy Transfer

In this article, we present a personal mobility device for lower-body impaired users through a lightweight exoskeleton on wheels. On its core, a novel passive exoskeleton provides postural transition leveraging natural body postures with support to the trunk on sit-to-stand/stand-to-sit (STS) transitions by a single gas spring as an energy storage unit. We propose a direction-dependent coupling of knees and hip joints through a double-pulley wire system, transferring energy from the torso motion toward balancing the moment load at the knee joint actuator. Herewith, the exoskeleton maximizes energy transfer and the naturalness of the users movement. We introduce an embodied user interface for hands-free navigation through a torso pressure sensing with minimal trunk rotations, resulting on average 19 degrees +/- 13 degrees on six unimpaired users. We evaluate the design for STS assistance on 11 unimpaired users observing motions and muscle activity during the transitions. Results comparing assisted and unassisted STS transitions validate a significant reduction (up to 68%, p < 0.01) at the involved muscle groups. Moreover, we show its feasibility through natural torso leaning movements of +12 degrees +/- 6.5 degrees and -13.7 degrees +/- 6.1 degrees for standing and sitting, respectively. Passive postural transition assistance warrants further work on increasing its applicability and broadening the user population.

Automated summary

This article introduces a lightweight exoskeleton wheelchair as a personal mobility device for lower-body impaired users. The exoskeleton utilizes a novel passive mechanism using a gas spring as an energy storage unit to provide postural transition support during sit-to-stand/stand-to-sit transitions. A direction-dependent coupling of knees and hip joints is achieved through a double-pulley wire system, maximizing energy transfer and natural movement. The device features an embodied user interface for hands-free navigation using torso pressure sensing. Evaluation on unimpaired users shows significant reduction in muscle activity during assisted sit-to-stand/stand-to-sit transitions. Natural torso leaning movements are also demonstrated. Further research is needed to enhance the applicability and expand the user population of the passive postural transition assistance.