Design of a 2DoF Ankle Exoskeleton with a Polycentric Structure and a Bi-Directional Tendon-Driven Actuator Controlled Using a PID Neural Network

Taehoon Lee,Inwoo Kim,Yoon Su Baek

doi:10.3390/act10010009

Abstract

Lower limb exoskeleton robots help with walking movements through mechanical force, by identifying the wearer’s walking intention. When the exoskeleton robot is lightweight and comfortable to wear, the stability of walking increases, and energy can be used efficiently. However, because it is difficult to implement the complex anatomical movements of the human body, most are designed simply. Due to this, misalignment between the human and robot movement causes the wearer to feel uncomfortable, and the stability of walking is reduced. In this paper, we developed a two degrees of freedom (2DoF) ankle exoskeleton robot with a subtalar joint and a talocrural joint, applying a four-bar linkage to realize the anatomical movement of a simple 1DoF structure mainly used for ankles. However, bidirectional tendon-driven actuators (BTDAs) do not consider the difference in a length change of both cables due to dorsiflexion (DF) and plantar flexion (PF) during walking, causing misalignment. To solve this problem, a BTDA was developed by considering the length change of both cables. Cable-driven actuators and exoskeleton robot systems create uncertainty. Accordingly, adaptive control was performed with a proportional-integral-differential neural network (PIDNN) controller to minimize system uncertainty.

Highlights

An exoskeleton can help the wearer to maintain posture or perform agile movements, by performing the role of assisting or supporting the forces by understanding the intention of the wearer for the desired movements
By measuring the rotational change of the talocrural joint and subtalar joint during walking, and calculating the length change of both cables according to dorsiflexion and plantar flexion, we developed a bi-directional tendon-driven actuator (BTDA) that can account for differences in the length changes of both cables
A 2DoF ankle exoskeleton robot that matched the actual axis of the ankle was designed, and a polycentric structure was applied to minimize misalignment in the talocrural joint according to the movement of the ankle

Summary

Introduction

An exoskeleton can help the wearer to maintain posture or perform agile movements, by performing the role of assisting or supporting the forces by understanding the intention of the wearer for the desired movements. It can play a role in preventing external shocks that may occur, in advance. Many robots to help patients, including wearable robots to help with daily life and rehabilitation robots to recover muscle strength, have been developed [4,5,6] These robots support daily life by assisting the wearer’s muscle strength and performing rehabilitation training. Research has already shown that walking ability can be improved by wearing an exoskeleton robot for gait rehabilitation [7]

Methods

Results

Discussion

Conclusion