Journal of Bionic Engineering (2025) 22:1231–1248https://doi.org/10.1007/s42235-025-00678-9

AES-SEA and Bionic Knee Based Lower Limb Exoskeleton Design and LQR-virtual Tunnel Control

Yi Long1,2 · Zhibin Cai1  · Hexiao Guo3

1 Faculty of Robot Science and Engineering, Northeastern University, Shenyang 110000, China 

2 Foshan Graduate School of Innovation, Northeastern University, Foshan 528312, China 

3 College of Information Science and Engineering, Northeastern University, Shenyang 110819, China

Abstract 

The lower limb assisted exoskeleton is a prominent area of research within the field of exoskeleton technology. However, several challenges remain, including the development of flexible actuators, high battery consumption, the risk of joint misalignment, and limited assistive capabilities. This paper proposes a compact flexible actuator incorporating two elastic elements named Adjustable Energy Storage Series Elastic Actuator (AES-SEA), which combining an adjustable energy storage device with a series elastic actuator for application in exoskeleton hip joints. This design aims to enhance energy efficiency and improve assistive effects. Subsequently, we introduce a novel knee joint bionic structure based on a pulley-groove configuration and a four-link mechanism, designed to replicate human knee joint motion and prevent joint misalignment. Additionally, we propose an innovative controller that integrates concepts from Linear Quadratic Regulator (LQR) control and virtual tunnel for level walking assistance. This controller modulates the assisted reference trajectory using the virtual tunnel concept, enabling different levels of assistance both inside and outside the tunnel by adjusting the parameters Q and R. This approach enhances the assisting force while ensuring the safety of human-computer interaction. Finally, metabolic experiments were conducted to evaluate the effectiveness of the exoskeleton assistance. 

Keywords Bioinspired joint · Energy storage · Human-exoskeleton Interaction · Lower limb exoskeleton · LQR control · Series elastic actuation (SEA)