Study Of An Ankle Exoskeleton By Using Power Modulation To Assists Push-off

The research on exoskeleton has gradually developed towards light weight and miniaturization.It can improve the comfort of wearing the exoskeleton and enhance the exoskeleton boosting effect by reducing the weight and volume of the exoskeleton and reducing the unnecessary interaction of the exoskeleton with human movements.In order to reduce the weight of the exoskeleton and make it more lightweight and compact,this thesis will use a peak power amplification mechanism similar to the working principle of the muscle-tendon to reduce the power requirement of the exoskeleton on the driving part,thus the driving part of the exoskeleton can use a small motor with low power and light weight,and to reduce the overall weight of the exoskeleton.The main contents of this thesis are as follows:(1)This thesis analyzes the working principle of peak power amplification ankle exoskeleton.The ankle plantar-flexion,which can produce peak power,about only 15 percent of the entire gait cycle time,provides the main energy for the human body to move forward during walking.Therefore,the ankle exoskeleton generally only assists the ankle joint at push-off phase.According to the characteristics of the ankle joint power and the characteristics of the exoskeleton assistance,this thesis uses a peak power amplification method for the exoskeleton.When the exoskeleton is not at pushoff phase,the motor stores energy to the energy storage element.During the ankle plantar-flexion period,the energy storage element releases energy and outputs a peak power to assists the ankle joint,which is like to the ankle joint plantar-flexion power,thereby reducing the power requirement of the exoskeleton for the driving part.The exoskeleton can use a small power,light weight and small motor.(2)Based on the working principle of the exoskeleton to research the structure and hardware parameters.The structure design mainly includes the driving part with a clutch,the energy storage structure part and the wearing part.The engagement and disengagement of the clutch part is realized by a servo with a cam and a return spring.This thesis optimizes and improves the overall structure of the exoskeleton through the analysis of the interaction between the exoskeleton and the human body.Besides,this thesis proposed to use variable stiffness energy storage element coil spring to improve the energy storage capacity of the energy storage element in terms of peak power amplification of exoskeleton.Therefore,the exoskeleton can produce a relatively stable assist torque and higher assist power during the assist process.(3)The exoskeleton control in this thesis mainly includes two parts.The upper layer control is based on the IMU to identify gait phase to determine the timing of the assist of the exoskeleton.The lower layer control mainly includes motor control and clutch control.The engagement and disengagement of the clutch is controlled based on the instruction sent by the upper control.(4)The effectiveness evaluation experiment of exoskeleton.Based on the system characteristics of this exoskeleton,peak power amplification experiments were conducted to analyze the peak power amplification effect of the actual work of the exoskeleton;and biomechanical experiments of the human lower extremity wearing the exoskeleton.Experiments have shown that the peak power generated by this exoskeleton is 35.22 w,and the peak power of the ankle joint can be reduced by 11.25 percent when the human is walking.