Design Of A Planar Compliant Exoskeleton Mechanism For Self-aligning Human Lower Extremity Movement

Motion misalignment between exoskeletons and human limbs commonly exists in the use of exoskeleton robots,which will cause discomfort even hurt users.In order to ensure the safety and flexibility of the human-exoskeleton interaction,a compliant and underactuated planar five-bar mechanism is proposed in this paper,which is focused on the lower extremity exoskeleton knee joint.The stiffness characteristics of the mechanism is analyzed via stiffness mapping and virtual work principle.Based on the actual using conditions,the ideal stiffness is designed and the structure size is optimized by GAs.Finally,SimMechanics and prototype experiments were used to verify the mechanism,and the motion self-aligning performance of exoskeleton was evaluated and analyzed.The main contents of this paper are as follows:Firstly,the planar compliant five-bar mechanism provides two DOF in the sagittal plane.Compliant parts,installed at joints,will deform responding to the human-exoskeleton interaction force,which adjusts the movement and deformation of exoskeleton knee joint.Such that the output of the mechanism is in accord with the movements of human knee joint,which promotes the alignment of exoskeletons and users’ limbs,and alleviates the misalignment between human and exoskeleton.Secondly,the stiffness mapping theory of parallel mechanism is used to decompose the mechanism into two chains for kinematic analysis,and the stiffness model is established based on virtual work principle.Based on the motion trajectory samples of knee joint axis and the five-bar mechanism workspace,the boundaries of the mechanism variables was designed.Given the wearing and using conditions,the stiffness characteristics of the mechanism are optimized via GAs,and the ideal variables of the mechanism and the parameters of the compliant parts are obtained.Finally,the proposed exoskeleton system is modeled by SimMechanics,and its abilities to attenuate displacement and reduce interaction force are simulated.The performance of motion self-aligning of the compliant five-bar mechanism is verified by experiments.In addition,aiming to reduce the complex of the structure,a new generation of design is proposed and analyzed in this paper.