Design Of Flexible Variable Gearing Skeletal Muscle-like Actuator And Investigation On Its Mechanical Characteristics

Biological skeletal muscle is a flexible automatic transmission system,which can adjust its morphological changes according to external load conditions,and then adjust its speed output.Therefore,it is the simplest and most efficient biological actuator.Skeletal muscle can enable humans and animals to achieve flexible,adaptable and efficient movement by running different inherent mechanical characteristics modes.Therefore,with the development of manufacturing technology and intelligent materials,various flexible skeletal muscle-like actuators have emerged one after another,and become a research hotspot in the field of flexible actuators.However,it is still a challenge to develop flexible actuators with flexible variable transmission mechanism and integration of inherent mechanical characteristics.This paper aims to realize artificial skeletal muscle with flexible automatic transmission system,high stress-strain and integrated inherent mechanical properties.Firstly,we should understand the structure and movement principle of biological skeletal muscle,and then guide bionic design.A bio-inspired design strategy based on human skeletal muscle is proposed systematically.Hill's three factors muscle model as the design basis,the design and development of skeletal muscle-like flexible actuator meeting the requirements of flexible automatic transmission and biomechanical characteristics are realized.In addition,through in-depth study of key issues such as force transfer and material system of the flexible actuator,the performance of the actuator with large stress-strain is realized.The main research contents of this paper are as follows:1.Design of skeletal muscle-like actuator and research on variable gearing characteristics.Inspired by the macroscopic structure of biological skeletal muscle,a highly imitating skeletal muscle is proposed,which is called Himi SK flexible actuator.The actuator is composed of active contractile unit and passive flexible matrix.The contractile unit acts as muscle-like fiber and the flexible matrix acts as connective tissue.Isotonic contraction experiments under different air pressures and loads were established.The results show that the designed muscle-like actuator itself is a flexible transmission system,which can realize variable gearing through its own shape change.That is to say,the speed output can be adjusted automatically by adapting to external load conditions through flexible deformation,without relying on sensors and controllers.2.Analysis on the mechanism and influencing factors of flexible transmission system of skeletal muscle-like actuator.Develop finite element analysis method to deeply analyze how the actuator adjusts the speed output through its own shape change under different loads;At the same time,based on the finite element analysis method,the important factors affecting the displacement/velocity and varaible gearing ratio of the actuator are analyzed.The analysis results show that the material properties of flexible matrix and the number of contrctile units are the factors that directly affect the displacement/velocity of the actuator,and the arrangement angle of contractile units(pennate angle)and the number of contractile units affect the gearing ratio of the actuator.The gearing ratio of flexible actuator is beneficial to the generation of force-velocity characteristics of actuator.Furthermore,it provides design criteria for the study of contraction characteristics and mechanical characteristics of skeletal muscle-like actuator.3.Study on intrinsic mechanical characteristics of skeletal muscle-like actuator.Taking human semimembranosus as bionic object,combined with the structural composition of semimembranosus,the arrangement angle of muscle fibers and the simplified shape of muscle outer contour,a highly imitating human semimembranosus actuator was developed.At the same time,guided by Hill's three-element model,the imitation semimembranosus actuator consists of three components: contractile unit,flexible matrix and reinforcing bands at both ends.The contractile unit is used as active contractile element,the flexible matrix is used as series elastic element,and the reinforcing belts at both ends are used as parallel elastic elements.Isotonic contraction and isometric contraction experiments are established,and interference experiments are carried out on flexible actuators.The experimental results show that the force-velocity and force-length characteristics similar to those of human skeletal muscle can be achieved simultaneously in a single flexible actuator.In response to external disturbances,it has inherent self-stability and robustness,which come from the adaptive deformation of bionic structure and flexible matrix materials.4.Optimization of material system of skeletal muscle actuator.Based on the study of semimembranosus-like actuator,different material systems are optimized.According to the comparison of stress-strain,output force and output velocity of different material systems,the optimal material system is obtained.Combining the optimal material system,the force transfer characteristics of skeletal muscle and the design criteria of the actuator,the tendon actuator with large-scale parallel structure of contraction units was developed.The stress produced is similar to that of biological muscle(0.32 MPa),which can lift more than 220 times of its weight,and the strain is 11.7%.The integration of contrction characteristics and inherent mechanical characteristics with high power density and high stress-strain is realized,and it is applied to the application of joint rotation and swing.It has wide application potential in the field of artificial limbs and flexible robots.