Unidirectional variable stiffness hydraulic actuator for load-carrying knee exoskeleton

Abstract

This article presents the design and experimental testing of a unidirectional variable stiffness hydraulic actuator for loadcarrying knee exoskeleton. The proposed actuator is designed for mimicking the high-efficiency passive behavior of biological knee and providing actively assistance in locomotion. The adjustable passive compliance of exoskeletal knee is achieved through a variable ratio lever mechanism with linear elastic element. A compact customized electrohydraulic system is also designed to accommodate application demands. Preliminary experimental results show the prototype has good performances in terms of stiffness regulation and joint torque control. The actuator is also implemented in an exoskeleton knee joint, resulting in anticipant human-like passive compliance behavior.

Knee Joint Biomechanics in Physiological Conditions and How Pathologies Can Affect It: A Systematic Review

“…The swing phase consists of two subphases: initial (toe off to knee maximum flexion) and terminal swing (knee maximum flexion to heel strike) [16,17]. The main function of the knee in the swing phase is assisting flexion-extension for toe clearance, foot placement, and taking over the load in the next step [19,20]. Zheng [21] reported that the knee biomechanics is affected mainly by walking speed.…”

“…During walking, running, and stair climbing, a high stiffness in the weight acceptance phase and a low stiffness in the swing phase can be observed. For walking, Zhu et al [20] and Wang [12] found that the knee quasistiffness was around 3.0 and 2.27 Nm/deg in the stand phase. Sridar et al [34] indicated E: first peak knee extension moment; F: first peak knee flexion moment; G: second peak knee extension moment; H: second peak knee flexion moment.…”

“…The moment-angle (stiffness) curves of the knee joint for normal walking, running, stair climbing, and sit-to-stand. (a) Normal walking[20,34]. (b) Running[35,36].…”

Development and Control of an Electro-Hydraulic Actuator System for an Exoskeleton Robot

“…That is, for the wearer to bend the knee, a controller opens solenoid valves and the wearer has to bend the knee joint of the robot. This makes the wearer feel tired and has the disadvantage of the slow response [12][13][14]. Such conventional hydraulic systems are complicated because of solenoid valves and have problems such as leakages.…”

Design and simulation of leg exoskeleton cycling-actuated wheelchair

“…Borisoff et al proposed a concept that combines the characteristics of the wheelchair with an exoskeleton using the wheelchair for the movement and the exoskeleton for the rehabilitation. 17 The exoskeleton design has become a research hot spot with solutions that now provide specific advantages in strength enhancement 18,19 and rehabilitation tasks [20][21][22][23] for humans. For example, the Honda exoskeleton was designed to support the wearer's body weight, which reduces strain on the articulations in the knees, ankles, and hips.…”