Fuzzy Enhanced Adaptive Admittance Control of a Wearable Walking Exoskeleton With Step Trajectory Shaping

The generation of motor adaptation in response to mechanical perturbation during human walking is seldom considered in an exoskeleton system. Reshaping step trajectory over consecutive gait cycles for a walking exoskeleton is investigated in this article. Step adjustment of a walking exoskeleton can adapt to human walking intention by shaping step trajectory. This work develops an admittance adaptive fuzzy control strategy for a walking exoskeleton robot to provide assistance for human lower limb movement. Considering human walking intention and utilizing an admittance model, it shapes a reference trajectory to ensure that the walking exoskeleton follows it according to the human–robot force produced by its wearer. Considering a nonlinear and dynamic model with uncertainties, this work designs an integral-type Lyapunov function controller to track a reference trajectory. A disturbance observer is integrated into the controller design to compensate for uncertain disturbance in order to achieve an effective tracking performance. Finally, this work conducts experiments on two healthy subjects with the proposed method on a walking exoskeleton to validate its effectiveness. The results show that it can be applied to walking exoskeletons to enhance human mobility.

I. Introduction

As an important branch in the field of robotics, exoskeleton robots are indispensable in enhancing human mobility and gaining much interest from academia and industry. They have been developed by many research institutions and companies. Many of them have already been deployed in military applications and medical fields [1]. In addition, through the realization of an assisted exoskeleton, we can improve the performance of its human wearer and enhance the human strength to help the wearer perform a variety of tasks [2], e.g., climbing stairs and carrying heavy loads while marching at a high speed [3]–[6]. However, many walking exoskeletons take no human–robot interaction strategies into consideration. They ignore that the step of a walking exoskeleton needs to adapt to the ground in some scenarios. For example, when there is a small puddle on the walking ground, it needs to adjust the step length to go over such puddle.