Can lower-limb exoskeletons support sit-to-stand motions in frail elderly without crutches? A study combining optimal control and motion capture

With the global geriatric population expected to reach 1.5 billion by 2050, different assistive technologies have been developed to tackle age-associated
movement impairments. Lower-limb robotic exoskeletons have the potential to support frail older adults while promoting activities of daily living, but the need
for crutches may be challenging for this population. Crutches aid safety and stability, but moving in an exoskeleton with them can be unnatural to human
movements, and coordination can be difficult. Frail older adults may not have the sufficient arm strength to use them, or prolonged usage can lead to upper limb
joint deterioration. The research presented in this paper makes a contribution to a more detailed study of crutch-less exoskeleton use, analyzing in particular the
most challenging motion, sit-to-stand (STS). It combines motion capture and optimal control approaches to evaluate and compare the STS dynamics with
the TWIN exoskeleton with and without crutches. The results show trajectories that are significantly faster than the exoskeleton’s default trajectory, and identify
the motor torques needed for full and partial STS assistance. ... mehrWith the TWIN exoskeleton’s existing motors being able to support 112 Nm (hips) and 88 Nm
(knees) total, assuming an ideal contribution from the device and user, the older adult would need to contribute a total of 8 Nm (hips) and 50 Nm (knees). For
TWIN to provide full STS assistance, it would require new motors that can exert at least 121 Nm (hips) and 140 Nm (knees) total. The presented optimal control
approaches can be replicated on other exoskeletons to determine the torques required with their mass distributions. Future improvements are discussed and
the results presented lay groundwork for eliminating crutches when moving with an exoskeleton.