Shared control in exoskeletons

Abstract

Currently, lower-body exoskeletons for
paraplegics are investigated as an alternative to wheelchairs
and as an exercise method with medical benefits. Literature
provides little examples for users to influence the
length or frequency of steps taken by the exoskeleton,
complicating stability and practical usability. This study
proposes a novel control paradigm that allows users to
influence step parameters of the exoskeleton, through a
bi-directional haptic interface that also provides feedback.
The exoskeleton handles the cyclic walking pattern while
the patient is enabled to correct for disturbances. I adapted
an existing lower-body exoskeleton trajectory generator to
allow real-time adaptation of step length and swing time.
To demonstrate a proof-of-concept of the control paradigm,
I implemented the controller for a virtual 2D exoskeleton,
to be controlled by an existing bi-manual haptic control
interface. A human-in-the-loop experiment was performed
with the goal to compare the benefits of user control
over either step length or swing time with a situation
with no human control. In the experiment perturbations
of increasing magnitude were applied to a 2D virtual
exoskeleton, participants could increase or decrease either
step length or swing time during swing to correct for these
disturbances. The number of successful step taken before
the perturbations resulted in a fall were measured. The
swing time group succeeded in making the exoskeleton
walk stably significantly longer then when there was no
human input, proving that the proposed control paradigm
is feasible and beneficial for stability.