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

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

Sarin Kittisares  1 , Tohru Ide  1 , Hiroyuki Nabae  1 , Koichi Suzumori  1
Affiliations

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

Sarin Kittisares et al. Front Robot AI. .

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.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
A diagram of a crossed four-bar linkage mechanism.
FIGURE 2
FIGURE 2
The optimal four-bar linkage configuration of the medial side at 0° and 120° knee angles. The trajectories of the human tibia and the proposed mechanism is shown in blue and orange, respectively.
FIGURE 3
FIGURE 3
The optimal four-bar linkage configuration of the lateral side at 0° and 120° knee angles. The trajectories of the human tibia and the proposed mechanism is shown in blue and orange, respectively.
FIGURE 4
FIGURE 4
A photograph of the HAM used in this study.
FIGURE 5
FIGURE 5
Photograph of the proposed device for the right leg on the lateral and medial sides.
FIGURE 6
FIGURE 6
Experiment setup of the undesired load experiment. The subject was seated with their leg hanging above the ground. The pressure sensor was inserted under the lower shank brace on the anterior side of the leg.
FIGURE 7
FIGURE 7
The proposed device worn by the participant.
FIGURE 8
FIGURE 8
The participant performing stair ascent with the assistance of the proposed device.
FIGURE 9
FIGURE 9
Experimental and theoretical force-contraction relationship of the HAM used in this paper.
FIGURE 10
FIGURE 10
The linear model of the HAM used in the design process.
FIGURE 11
FIGURE 11
EMG signal on the Rectus femoris of the subject during stair ascent.
FIGURE 12
FIGURE 12
Theoretical output torque of the proposed device.
See this image and copyright information in PMC

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