Enhancing Comfort and Repeatability of Humanrobot Attachment Systems: Comparison of a Compliant Orthosis for BLUE SABINO

The human-robot attachments (HRA) connecting humans to exoskeleton robots should facilitate user independence, efficient donning/doffing, maintain user-robotkinematic alignment using interfaces that are sufficiently rigid, comfortable to wear, and (with the aid of the exoskeleton) accommodate dexterous human motion. This report presents a proof-of-concept comparison of an innovative self-aligning, sizeadjustable HRA system designed for the upper arm. A novel discretely contracting orthosis adjusted by a dial ratcheting cable mechanism was fabricated from flexible and semi-rigid plastics to improve support and rigidity. Experiments comparing this new design to an existing rigid HRA design for the BLUE SABINO are conducted to characterize suitability in terms of ability to maintain kinematic alignment and to distribute interaction forces evenly on the user's arm. Piezoelectric force-sensitive-resistor sensors embedded in an elastic sleeve are used to measure human/orthosis interface forces at 8 Locations distributed on the circumference of the arm interface. Kinematic alignment was assessed for $5^{\text {th }}$ percentile female to $95^{\text {th }}$-percentile male sizes using 3D-printed mock arm cross sections. Laser alignment experiments found that the proposed device reduced arm center to orthosis center misalignment magnitude by up to 11.5 mm for $5^{\text {th }}$ percentile male arm circumference vs. the existing design. Force measurements are inconclusive but indicate the potential to alter force distribution while being adequately adjustable and usable with repeatable settings.