The Design And Experiment Study Of Flexible Knee Joint Assistive Device With Variable Stiffness

With the development of society and science,the appearance of man-machine integration technology provides a method to improve the ability and efficiency of human movement,and the auxiliary devices such as exoskeleton and flexible power suit have been widely studied.Exoskeleton can enhance the human body’s mobility and reduce the load,and it has great development prospects in the military and medical fields.However,exoskeleton is difficult to be widely used in daily life because of its large volume and mass,which requires energy supply and low matching degree with human body.Flexible assistive devices have the characteristics of strong flexibility and high comfort,which can make up for the deficiency of exoskeleton.In this paper,a knee joint aid with variable stiffness based on flexible woven fabric and bionic variable stiffness principle is designed,in order to reduce exercise consumption and improve human exercise ability by adjusting and optimizing knee joint stiffness.The research contents include the following aspects:1.By using the kinematics and dynamics analysis method of the knee joint in a gait cycle,the relationship between the knee joint stiffness and the metabolic cost of human movement in the gait cycle is given through the kinematics parameters such as step frequency,pace and stride length,as well as the dynamic parameters such as the moment and deflection angle of the knee joint.The changes of knee joint stiffness and metabolic cost at different speeds are studied,and the influence mechanism of variable stiffness knee joint flexible assistive devices on human movement economy is expounded.2.Analyze the mechanism of stiffness change of shark’s skin and trunk,analyze the feasibility of using this mechanism for accessories,and use it to design flexible woven fabric components with fiber angle to control stiffness,study the working principle of components,and finally use this mechanism to realize the stiffness change of knee joint flexible accessories.3.Establish the structural model of flexible textile,study and analyze the selected materials and fabric fiber structure,give the selection standard and method,and analyze the material mechanics and micromechanics,study the influence law of fiber angle in fabric microstructure on fabric stiffness,and use COMSOL simulation experiment method to study the stress-strain relationship under different angles between the stress direction and the warp knitting direction of woven fabric,and obtain the stiffness change law at different angles.Based on the assumption of uniform boundary conditions and the characteristics of representative voxels,the relationship between fiber angle and fabric elongation is determined,and finally the relationship between fiber angle and stiffness of woven fabric is determined.4.Design and make the woven fabric materials with different stiffness required for the experiment,and install them on the experimental AIDS.After wearing them,walk,and use the high-speed POD power meter to measure the pace frequency,running power and other data in the process,and then calculate the knee joint stiffness and metabolic cost.According to the stiffness of human knee joint when wearing different parameters of assistive devices,the relationship between fiber angle and metabolism of woven fabric of flexible assistive devices with variable stiffness is obtained,which can be used to evaluate human sports economy.5.Finally,the method of changing the joint stiffness of assistive devices after wearing by adjusting the angle of fabric fibers is verified,and the optimization mechanism and its feasibility for human sports economy are expounded.