Study Of Human Ankle Joint Dynamic During Upright Standing Push-recovery With Small-disturbance

When subjecting to external disturbance,human being maintain upright stance balance via central nervous system(CNS).Under small external disturbance,the Ankle Joint Strategy of human plays a key role in keeping upright balance for human being.From the biomechanical point of view,this thesis concentrates on revealing the dynamic characteristics and internal control mechanism of human ankle joint strategy via experimental study on 8 subjects under push-recovery task.The main work done in this thesis can be summarized as follows:(1)In the case where human subjecting to external disturbance,the process that human being swinging around the ankle is simplified as a first-order inverted pendulum model.During the sway phase,the oscillation of the center of pressure(COP)follows the oscillation process of the center of mass(COM).Human ankle joint adjusts the position of COM to maintain body balance via controlling COP.Also,the torque and stiffness calculation equations of human ankle joint are derived in this thesis.(2)Design the human push-recovery experimental platform.During experimental process,a sandbag is used to be the external disturbance.Through adjusting the heights of the sandbag,different external forces can be applied to the back of each subject.During the data process,the electromyography(EMG)of the tibialis anterior(TA),gastrocnemius(GAS)and soleus(SOL)are selected to analyze the muscle activation of human ankle joint.By using 3D printing technology,the encoder is fixed on the experimental leather shoes,and the encoder data is collected using the STM32 development board to form a simple device for measuring the angle of the ankle joint.The human foot pressure is recorded by the fore measurement insole.Based on the measured foot pressure,the human ankle torque is then calculated.To allow using multiple devices to measure simultaneously,a multi-threaded Window program is designed under the Visual C++ environment.(3)Dynamic characteristics of ankle joint under small-disturbance and muscle reflex control mechanism analysis.Firstly,the EMG of TA,GAS and SOL is processed into muscle activation.Then,the human ankle torque is calculated by the human foot pressure.By analyzing the experimental data,it is found that there is no significant change in the muscle activation level of the aforementioned three muscles.Moreover,the SOL activation level and the ankle joint rotation angle are highly linear with the ankle torque.Besides,the muscle reflex can well predict the muscle activation.This thesis investigates and analyzes the dynamic characteristics of human ankle joint under human push-recovery experiment.The experimental results show that the ankle joint is similar to the torsion spring,and the stiffness is stabilized in a certain range by muscle reflection to resist disturbance.The data and conclusions obtained in this paper can provide human biomimetic parameters for the design of the bipedal robot with muscle reflexes.