4.7 Article

Self-Aligning Mechanism Improves Comfort and Performance With a Powered Knee Exoskeleton

Publisher

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TNSRE.2021.3064463

Keywords

Exoskeletons; Wearable robots; Predictive models; Legged locomotion; Task analysis; Thigh; Strain; Human-robot misalignment; exoskeleton comfort; rehabilitation robotics; wearable robotics

Funding

  1. National Institute for Occupational Safety and Health [T42/CCT810426]
  2. US Department of Defense [W81XWH-16-1-0701]

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Misalignments between powered exoskeleton joints and the user's anatomical joints are inevitable, but self-aligning mechanisms have been shown to improve user comfort and performance. Experimental evidence demonstrates up to 15.3% increased comfort and 38% improved performance when using a self-aligning mechanism in a powered knee exoskeleton. Additionally, spurious forces and torques were reduced by up to 97% with the self-aligning mechanism unlocked.
Misalignments between powered exoskeleton joints and the user's anatomical joints are inevitable due to difficulty locating the anatomical joint axis, non-constant location of the anatomical joint axis, and soft-tissue deformations. Self-aligning mechanisms have been proposed to prevent spurious forces and torques on the user's limb due to misalignments. Several exoskeletons have been developed with self-aligning mechanisms based on theoretical models. However, there is no experimental evidence demonstrating the efficacy of self-aligning mechanisms in lower-limb exoskeletons. Here we show that a lightweight and compact self-aligning mechanism improves the user's comfort and performance while using a powered knee exoskeleton. Experiments were conducted with 14 able-bodied subjects with the self-aligning mechanism locked and unlocked. Our results demonstrate up to 15.3% increased comfort and 38% improved performance when the self-aligning mechanism was unlocked. Not surprisingly, the spurious forces and torques were reduced by up to 97% when the self-aligning mechanism was unlocked. This study demonstrates the efficacy of self-aligning mechanisms in improving comfort and performance for sit-to-stand and position tracking tasks with a powered knee exoskeleton.

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