Research On Quasi-passive Power-assisted Lower-limb Exoskeleton Driven By Tendon-sheath Actuation System

In recent years,the number of patients with lower-limb motion dysfunction caused by aging,diseases,competitive sports,car accidents,natural disasters and daily exercise has been increasing.The lower-limb exoskeleton for assistance walking and rehabilitation training has wide application prospects which can improve patients exercise capacity,ensure their life quality,reduce their economic pressure and alleviate the shortage of medical resources.Some results on the study of the lower-limb exoskeleton has been achieved by the domestic and foreign advanced scientific research institutions,but research limitations in lightweight structure,low energy consumption,driving technology,sensor technology,coordination control and effect evaluation have delayed the engineering application of the exoskeleton.Built on the above research background and the advantages of human lower-limb movement mechanism and the passive bipedal walking theory,a quasi-passive power-assisted lower-limb exoskeleton driven by tendon-sheath actuation system is developed.The main research contents of this paper are as follows:Based on the studies in human anatomy,kinematics and motion measurement,the characteristics and relationships of the lower-limb joint motion,walking cycle and the foot movement are analyzed.The concept of the whole walking cycle includes five basic walking patterns is proposed,which provides the theoretical basis for the walking phase estimation through the planter force and the subsequent analysis and simplification of dynamic models.Models of the rimless wheel and the simplest bipedal walking which indicate the passive bipedal walking theory are analyzed,the Poincare regression mapping method is adopted to analyze the existence and the influence of motion limit cycles,low energy consumption characteristics of the passive bipedal walking theory are illustrated in perspectives of the model parameter configuration,action of gravity,gait transition and energy compensation type,which brings inspiration and guidance to design a power-assisted lower-limb exoskeleton which is more humanoid in the motion and DOF configuration and more reasonable in mass distribution,and which also has the joint driving style with low energy consumption.A quasi-passive power-assisted lower-limb exoskeleton prototype driven by tendon-sheath actuation system is established and the design of the main structure and control system is following principles of its own dynamics characteristics,increasing the passive compliant driving DOFs,reducing the active driving DOFs and the quantity of sensors.The active hip joint is driven by tendon-sheath actuation system to accomplish the external placement of the joint drive motor and the far-end compliant driving,and finally,the walking assistance is achieved by controlling the joint torque output;The passive compliant joint design is implemented by mechanical spring components to adjust the COM of the exoskeleton and comply the movement trend with the energy storage and release,aims to reduce the energy consumption and improve the mechanism performance;The impulse module along the thigh lever is used as the trigger signal for the man-machine initiative movement as pedal,plantar flexion,knee flexion and the thigh flexion to aid the accomplishment of the gait conversion and achievement of the lower limb strength training;Model analysis and experiments about force and displacement transmission characteristics of the compliant single-tendon-sheath and double-tendon-sheath actuation system are accomplished,the effects of pretension,total curvature,the radius of the roller and the friction coefficient on the friction torque and the transmission efficiency are analyzed,moreover,the parameter identification experiment of the system internal impedance torque is conducted to compensate the friction torque;The sensor system includes the orthogonal encoder,the plantar force sensor,the human-machine interaction force sensor and the sEMG sensor is installed for the motion identification of the man-machine system and the assistance effect evaluation of the exoskeleton.The positive kinematics equation of the single exoskeleton leg model is built,and the operational space and workspace analysis of joint variables are carried out,the workspace is solved by geometry method and Monte Carlo method respectively.The inverse kinematics solutions of forward kinematics equations,the Jacobin matrix,the kinematic redundancy and the motion singularity are analyzed.The dynamics model analysis of early single stance phase and late double stance phase of the lower-limb exoskeleton has been conducted,the Lagrange dynamics equations are given and the torque of each joint in the walking process is calculated.The man-machine exoskeleton system dynamics model is analyzed and the influence factors of the joint drive torque are determined,which provides the basic idea to make the assistance control strategy.The control strategy of man-machine exoskeleton system is analyzed and the hierarchical intelligent control method based on the model and the calculated torque is adopted to power-assisted motion control of the exoskeleton active joint.First of all,judge the exoskeleton joint motion and experimenter's walking intention through the perceptual layer;Secondly,deliver the perceptual layer information to the decision-making layer,based on that,the exoskeleton joint ideal output torque,human-machine control torque,single leg gravity compensation torque and system internal impedance torque is calculated,the impulse module release state is determined,and finally the ideal motor output torque is confirmed;Finally,the value of ideal motor output torque is delivered to the executive layer,through the servo motor to realize the active control of exoskeleton joint.In order to validate the effectiveness of exoskeleton control strategy,the wearing walking tests and exoskeleton assisted effective evaluation are conducted.