Study On Skeletal Muscle-Like Soft Actuator With Drive And Transmission Integration

The complex,hierarchical y layered skeletal muscle system that enables the body to achieve diverse and efficient movements is dominated by flexible materials.The drive of the system is entirely caused by soft tissue(muscles,tendons,etc.).Human skeletal muscles can be considered as"perfect soft actuator"with coMPatibility and deformability,and can efficiently achieve fast,powerful movements and very complex movement patterns.Studies have shown that the human skeletal muscle is both a drive unit and a transmission unit,and has a stepless shifting function.It is a flexible power system that integrates driving,shifting and transmission.CoMParing with the mechanical system which adopts complex mechanism combination and control to realize automatic transmission in engineering,it has the advantages of simplicity,direct,economy and high efficiency.Based on this inspiration,this paper aims to develop a skeletal muscle-like soft actuator with the characteristics of drive and transmission integration similar to biological skeletal muscle.After analyzing the basic structural composition of skeletal muscle,muscle fiber configuration and spatial structure,and the principle of variable transmission biology,the design of skeletal muscle-like soft actuator is proposed.The simulation analysis is used to predict the dynamic response characteristics of the soft actuator.Samples are manufactured and the automatic transmission function is checked by performance test.The influencing factors and inherent laws of its inherent variable transmission mechanism are revealed.A highly anthropomorphic Semimembranosus muscle actuator is developed and coMPared with the mechanical properties of the biological muscle.The specific research work and main conclusions are as follows:(1)The basic structural composition of skeletal muscle and macroscopic muscle fiber structure,as well as the three-dimensional morphological changes of muscle fiber movement to realize the dynamic principle of variable transmission,and the design of bionic structure of skeletal muscle-like soft actuator is proposed.It consists of a driving unit that simulates"muscle fibers"and a flexible matrix that mimics"peripheral connective tissue."The driving unit is embedded and encapsulated in the flexible matrix according to the structure of the skeletal muscle pinnate angle,so that the spatial deformation of the flexible matrix can be driven by the driving unit,and the coordinated movement of the skeletal muscle can be realized simply and easily.The dynamic response characteristics of the soft actuator are simulated by nonlinear finite element ABAQUS/CAE.It is found that the internal driving units show a tendency of axial shortening and radial expansion accoMPanied by rotation,similar to that observed in skeletal muscle.And the greater the internal pressure,the more obvious the trend of change.The amount of deformation in the vertical direction of the soft actuator increases as the air pressure rises,and reaches the maximum deformation of 17.5 mm at 0.20MPa.It shows that the pressure has a certain influence on the dynamic response of the actuator.(2)A skeletal muscle-like soft actuator with the same size and structure as the simulation model is fabricated by casting process,and two coMParative actuators are made.The actuation performance test is performed by driving the actuator with compressed air of different steady pressure values and applying loads of different masses from low to high.At a pressure of 0.4MPa,the skeletal muscle-like soft actuator can lift about 25 times its own weight.When the load is constant,the shrinkage of the actuator is proportional to the pressure,and when the load is zero,the test results and simulation results of the actuator shrinkage varying with the pressure are similar.When the pressure is constant,the shrinkage of the actuator is inversely proportional to the load force,so that the maximum output force of the actuator is proportional to the pressure.During the whole contraction period,the output force of the actuator gradually increases to the rated load and remains unchanged,and when the output force remains unchanged,the contraction speed of the actuator will appear a stable and unchanged stage.The analysis of this stage shows that the actuator has a variable transmission mechanism similar to that of the biological skeletal muscle.That is to say,it can operate at high speed under low load and produce more output force under high load to overcome the contraction of external load.(3)By processing and analyzing the test data,the assumption that the transmission ratio of the soft actuator varies in a load-dependent manner is verified.The transmission ratio decreases with the increase of load,that is to say,the actuator will benefit the output of force under high load and output higher speed under low load.Moreover,the higher the pressure,the higher the change of transmission ratio and the wider the range of variable transmission.The variable transmission mechanism of the soft actuator is automatic,not from any control mechanism,and does not need sensory information and feedback control.By coMParing the soft actuator with the two coMParative samples,it is found that the cooperative driving of the pinnate angle and the flexible matrix is important for the actuator,because the flexible matrix and the pinnate angle will greatly increase the ability and range of its variable transmission.According to the experimental data of these three kinds of actuators,an empirical formula of the functional relationship between their transmission ratio and system load and pressure is obtained:AGR(28)-aP~b F(10)cP~d.This equation better expresses the dynamic characteristics of the actuator and guides its design and operation.(4)Based on the biomechanical model of skeletal muscle and the structural characteristics of human Semimembranosus muscle,a highly anthropomorphic Semimembranosus muscle actuator design is proposed.The main feature is that the double-row of driving units are arranged obliquely and packaged together with a vent tube in a flexible matrix.The shape of the flexible matrix is similar to that of the human semimembranosus muscle,which can highly imitate the shape of semimembranosus muscle and the arrangement of muscle fibers.Through the mechanical test experiments of isotonic contraction and isometric contraction,and based on the biomechanical equation of skeletal muscle,the mechanical properties of soft actuator are further quantified.It is found that coMPared with the skeletal muscles of cats,frogs,rats and humans,the semimembranosus muscle-like actuator has similar structural and mechanical characteristics of biological muscles,namely the force-velocity and force-length curve relationships,achieving the goal of highly anthropomorphic bionic skeletal muscle development.A simple application of a semimembranosus muscle-like actuator is proposed.A 1:1 ratio of the average size of the adult skeletal model is selected,and the human semimembranosus muscle is replaced with this actuator to achieve the knee flexion movement of the human body.