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 user’s movement. We introduce an embodied user interface for hands-free navigation through a torso pressure sensing with minimal trunk rotations, resulting on average
$\text{19}^{\circ } \pm \text{13}^{\circ }$
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%,
$p< \text{0.01}$
) at the involved muscle groups. Moreover, we show its feasibility through natural torso leaning movements of
$+\text{12}^{\circ }\pm \text{6.5}^{\circ }$
and
$- \text{13.7}^{\circ } \pm \text{6.1}^{\circ }$
for standing and sitting, respectively. Passive postural transition assistance warrants further work on increasing its applicability and broadening the user population.