A Multifunctional Ankle Exoskeleton for Mobility Enhancement of Gait-Impaired Individuals and Seniors

This letter proposes a multifunctional ankle exoskeleton to safely expand the mobility. By applying torque to the ankle in dorsiflexion and plantarflexion, the exoskeleton prevents foot drop and foot slip and helps the ankle to push off the ground. The exoskeleton includes a remote center-of-motion (RCM) mechanism, a linear actuation module, and fastening modules. The RCM mechanism, which has two degrees of freedom, is designed to be aligned with the talocrural and subtalar axes of the ankle. A key feature of the RCM mechanism is a three-dimensional combination of two four-bar linkage mechanisms that have the linear motion and rotational motion, respectively. Only the talocrural axis is actively actuated for dorsiflexion and plantarflexion of the ankle, whereas the subtalar axis is passively released to allow the unconstrained motion by the user. The active axis is driven by a linear actuation mechanism comprising a ball-screw and a brushless dc motor. The device can be separated into fastening modules and actuation module and weighs only 869 g/leg without the battery. The results of ground and treadmill tests indicate that the peak torque and average positive mechanical power delivered by the exoskeleton are approximately 20 N·m and 6.21 W, respectively.