Transformable Wheelchair–Exoskeleton Hybrid Robot for Assisting Human Locomotion

Abstract

This paper presents a novel wheelchair–exoskeleton hybrid robot that can transform between sitting and walking modes. The lower-limb exoskeleton uses planetary-geared motors to support the hip and knee joints. Meanwhile, the ankle joints are passive. The left and right wheel modules can be retracted to the lower legs of the exoskeleton to prepare for walking or stepping over obstacles. The chair legs are designed to form a stable sitting posture to avoid falling while traveling on smooth surfaces with low energy consumption. Skateboard hub motors are used as the front driving wheels along with the rear caster wheels. The turning radius trajectory as the result of differential driving was observed in several scenarios. For assisting sit-to-stand motion, the desired joint velocities are commanded by the user while the damping of the motors is set. For stand-to-sit motion, the equilibrium of each joint is set to correspond to the standing posture, while stiffness is adjusted on the basis of assistive levels. The joint torques supported by the exoskeleton were recorded during motion, and leg muscle activities were studied via surface electromyography for further improvement.