Magnetic Pantographic Exoskeleton Illustrated With a Biomimetic Ankle-Foot Simulator for 3-DOF Noncontact Actuation/Measurements

This article presents a 3-DOF planar magnetic pantographic exoskeleton (Mag-PGE) with embedded sensors for manipulating/measuring the motion and force/torque (F/T) of an ankle joint in the sagittal plane. A biomimetic ankle-foot simulator (AFS) is designed to facilitate investigation and help visualize its potential uses for in-bed acute stroke rehabilitation where the affected leg muscles are often passive. Unlike a conventional motor in which the rotor is supported by mechanical bearings on the stator, the (stator and rotor) of the Mag-PGE are separately attached to the (shank and foot) sharing the ankle joint of the human leg such that it enables the foot to flex in the sagittal plane, imposing no mechanical constraints on the ankle joint. A Mag-PGE/AFS model with closed-form solutions to the rotor magnetic field and motor F/T is provided; both forward and inverse problems are considered. The methods to design, train, and calibrate embedded sensors utilizing the rotor magnetic field to measure the rotor/foot motion are numerically and experimentally evaluated. As illustrated with an AFS, the model along with the embedded measurements plays a pivotal role in computing the forward and inverse solutions to the 3-DOF motor force-current model.