Development And Performance Study Of Ankle-Joint Walking Assistance Device

Exoskeleton robots have been used in many fields,such as weight-bearing,assisted walking,rehabilitation training and so on.For lower extremity exoskeletons,there are some devices that can apply auxiliary torque to lower extremity joints to enhance the walking ability of healthy people or help disabled people walk.Although rigid exoskeleton can provide greater torque,it generally has more complicated mechanical structure and larger mass,which increases energy consumption.As a substitute for rigid exoskeleton,a flexible wearable device is developed in this paper.This device includes nylon tape and textile parts,which have smaller hardness,but will not produce a lot of elongation or contraction under the action of force.These flexible components are light in weight and reliable in combination with human joints.The device will not affect the natural gait of normal walking,and will cause less harm to human body.It is well known that ankle joint movement requires greater muscle strength than other lower limb joint movements,so providing additional force for ankle joint movement can assist walking more effectively.The main research work of this paper is as follows:(1)Firstly,the range of motion,dynamic model and muscle contraction model of human lower limbs during walking are introduced based on Lagrange method.OpenSim is used to simulate the kinematic characteristics and moment changes of lower extremity joints.After parallel active actuators are connected to the muscles controlling ankle plantarflexion,the changes of muscle metabolism rate are compared.which proves the feasibility of walking augmentation device in principle.(2)The structure and static model of pneumatic artificial muscle(PAM)are studied.Abaqus is used to simulate and analyze the characteristics of PAM.The effects of design parameters,such as diameter,length,initial braid angle and input pressure,on the output characteristics of PAM are studied.A PAM made of flexible materials is designed and fabricated.An experimental platform for pneumatic control is built and the static and dynamic characteristics of PAM are tested by experiments.(3)The structural scheme of ankle-joint wearable exoskeleton is proposed,and a reasonable control system is designed.The PAM is controlled by direct-acting solenoid valves,which have the functions of inflating,exhausting and maintaining.The working condition of solenoid valves are controlled by relays,and the control signals are sent by Arduino.At the same time,Arduino reads the signals of each sensor,including force sensor,pressure sensor and inertial sensor,and transmits the data to the upper computer through serial communication.The program of the upper computer is written by Matlab,which can control the state of the relays and display and save the data of each sensor.(4)The experimental study of wearable walking assistance device is carried out.By installing IMUs on the foot and leg respectively,the change of ankle angle in gait cycle can be detected.According to the measurement results,the gait characteristics can be analyzed and the actuation stage of the PAMs can be determined.After assembling the device,a reasonable control method is determined to control the actuation of PAMs in the definite gait stage to provide force for the plantarflexion of ankle joint.The force produced by the device is measured by the walking experiment,and the result proves that the device can achieve the effect of providing force for walking.