Compact and Foldable Hip Exoskeleton With High Torque Density Actuator for Walking and Stair-Climbing Assistance in Young and Older Adults

Exoskeletons hold great potential to enhance human locomotion performance, but their development is often hindered by bulky, heavy, and obtrusive actuator and mechanism designs. Here, we present a compact and lightweight hip exoskeleton endowed with a custom high torque density actuator and two foldable mechanisms, namely foldable waist belt with self-alignment mechanism and foldable thigh brace with self-adjusting linear slider mechanism. Our model of actuator electromagnetic design considered four design parameters, including end winding length, stator teeth number, rotor pole pair number, and gear ratio that are tailored for portable exoskeletons. Two foldable mechanism enhanced exoskeleton adaptability and user comfort. Benchtop experimental results demonstrated that our actuator can provide an 18 N <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\cdot$</tex-math></inline-formula> m peak torque with a packaging factor improvement of 27% in contrast with state-of-the-art actuators used in exoskeletons. The volume of our exoskeleton was reduced by 55% and the weight was reduced from 3.7 to 2.7 kg compared to our prior design. Preliminary human experiments demonstrated the feasibility of our exoskeleton to reduce metabolic rate during walking and stair climbing for young and older adults.