Abstract
Abstract. Misalignment between the instantaneous center of rotation (ICR) of human joint and the ICR of wearable robotic exoskeleton widely exists among most of exoskeletons widely used in rehabilitation, which results in discomfort, even endangers human safety. In order to alleviate it, this study focuses on the solution of misalignment in knee joint of lower limb exoskeletons, and proposes a compliant five-bar parallel mechanism, which offers two mobility in sagittal plane, as well as the torsional springs mounted on this mechanism, have the potential to automatically adjust the ICR of output link connected to thigh with respect to the basis link connected to shank. To reach this goal, we build the stiffness model of the mechanism and optimize its variables. And the self-alignment of the compliant five-bar parallel mechanism is verified via experimental investigations.
Highlights
Wearable robotic exoskeletons have been researched for several years, and they are widely applied in various fields ranging from rehabilitation of patients (Hesse et al, 1995) to performance assistance (Zoss et al, 2006)
The majority of exoskeleton rotary joints are typically modeled as hinges, due to the limitation of the unicentric feature, these mechanisms have a drawback of causing misalignment, in other words, causing inconsistency between human limbs and exoskeleton during movement, even though their initial positions are carefully aligned
Human joints cannot be assumed as simple kinematic pairs, since human skeletal structure consists of bones, ligaments and cartilage, and this intricate structure results in complicated kinematics of joints
Summary
Wearable robotic exoskeletons have been researched for several years, and they are widely applied in various fields ranging from rehabilitation of patients (Hesse et al, 1995) to performance assistance (Zoss et al, 2006). Motions of two links of this mechanism are mutual coupling, such that the trajectory of the joint is determined in advance, and during the movements, this design cannot solve the changing misalignment in the real time. Referring to a trajectory of the ICR of knee joint, Sakai et al (2015) proposed a device with the combination of sliding channel and wire-pulley, and its rotational center could keep pace with that of human femur This design determined the trajectory of its motions based on a specific motion data, which in turn make itself fail to fit other individuals. Some studies achieved self-alignment by using amounts of sensors and control system in exoskeleton (Krut et al, 2010; Zoss et al, 2016) Those solutions compensate the misalignment by observing the macroscopic deviation, and guide the position or the torque of the human joints.
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