Biomechanical design of an agile, electricity-powered lower-limb exoskeleton for weight-bearing assistance

Abstract

This paper proposes the design of an electricity-powered lower-limb exoskeleton called “Human Universal Mobility Assistance (HUMA)”. HUMA was developed as a research platform with the objective of providing its wearer with weight-bearing assistance for human strength/endurance augmentation. It has 12 degrees of active/spring passive/free passive freedom to assist human locomotion. The artificial leg has two electricity-powered degrees of freedom (DoFs) for hip/knee flexions/extensions, passive spring-installed two DoFs for ankle inversion/eversion and plantarflexion/dorsiflexion, and two free, passive DoFs for hip roll/yaw movements. HUMA has mechanical structures for active artificial hip and knee joints; the hip actuator is not directly connected to the robot’s leg system, but a universal joint is installed between the actuator and the leg system to allow a free coaxial hip yaw/roll DoF for the wearer. Therefore, the hip-actuating torque is transferred solely for hip flexion/extension. Its active artificial knee is structured by a four bar-based polycentric linkage, and is power=driven by an actuator in the middle of the robot’s thigh segment through the other four bar-based power transmission linkage. This powered knee structure yields several advantages related to (1) human–robot knee alignment during leg motion, (2) the expansion of the zone of voluntary knee stability, (3) the angle-dependent variable knee torque/velocity amplification ratio, and (4) a reduction in the total moment of artificial leg inertia. The exoskeleton was tested for dynamic gait by using assistive torques determined by a control algorithm. Experiments were conducted on the robot while it walked at 5 km/h (≈1.39 m/s) with/without a 20 kg load, as well as for a 10-km/h (≈2.78 m/s) run.