Ergonomic dual four-bar linkage knee exoskeleton for stair ascent assistance

Sarin Kittisares; Tohru Ide; Hiroyuki Nabae; Koichi Suzumori

doi:10.3389/frobt.2023.1285520

Ergonomic dual four-bar linkage knee exoskeleton for stair ascent assistance

Front Robot AI. 2023 Dec 6:10:1285520. doi: 10.3389/frobt.2023.1285520. eCollection 2023.

Authors

Sarin Kittisares¹, Tohru Ide¹, Hiroyuki Nabae¹, Koichi Suzumori¹

Affiliation

¹ Suzumori Laboratory, Department of Mechanical Engineering, School of Engineering, Tokyo Institute of Technology, Tokyo, Japan.

Abstract

Introduction: Robotic exoskeletons are emerging technologies that have demonstrated their effectiveness in assisting with Activities of Daily Living. However, kinematic disparities between human and robotic joints can result in misalignment between humans and exoskeletons, leading to discomfort and potential user injuries. Methods: In this paper, we present an ergonomic knee exoskeleton based on a dual four-bar linkage mechanism powered by hydraulic artificial muscles for stair ascent assistance. The device comprises two asymmetric four-bar linkage mechanisms on the medial and lateral sides to accommodate the internal rotation of the knee and address the kinematic discrepancies between these sides. A genetic algorithm was employed to optimize the parameters of the four-bar linkage mechanism to minimize misalignment between human and exoskeleton knee joints. The proposed device was evaluated through two experiments. The first experiment measured the reduction in undesired load due to misalignment, while the second experiment evaluated the device's effectiveness in assisting stair ascent in a healthy subject. Results: The experimental results indicate that the proposed device has a significantly reduced undesired load compared to the traditional revolute joint, decreasing from 14.15 N and 18.32 N to 1.88 N and 1.07 N on the medial and lateral sides, respectively. Moreover, a substantial reduction in muscle activities during stair ascent was observed, with a 55.94% reduction in surface electromyography signal. Discussion: The reduced undesired load of the proposed dual four-bar linkage mechanism highlights the importance of the adopted asymmetrical design for reduced misalignment and increased comfort. Moreover, the proposed device was effective at reducing the effort required during stair ascent.

Keywords: exoskeleton; hydraulic artificial muscle; knee joint mechanism; physical human-robot interaction; stair ascent; wearable robot.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported by the JSPS KAKENHI Grant-in-Aid for Scientific Research(A) grant number JP18H03760.