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

• Published in: IEEE transactions on neural systems and rehabilitation engineering Vol. 29; pp. 629 - 640
• Main Authors: Sarkisian, Sergei V., Ishmael, Marshall K., Lenzi, Tommaso
• Format: Journal Article
• Language: English
• Published: United States IEEE 2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Comfort; Exoskeleton; exoskeleton comfort; Exoskeletons; Human-robot misalignment; Joints (anatomy); Knee; Legged locomotion; Predictive models; rehabilitation robotics; Self alignment; Strain; Task analysis; Thigh; Torque; wearable robotics; Wearable robots
• ISSN: 1534-4320; 1558-0210; 1558-0210
• DOI: 10.1109/TNSRE.2021.3064463

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.