Research On Bionic Soft Manipulator With Variable Stiffness Of Artificial Muscle Driven By Electric Heating

The traditional rigid manipulator has the disadvantages of large rigidity,complex control,high requirements for operating environment,poor environmental adaptability and insufficient human-computer interaction.The emergence of soft manipulator greatly makes up for the shortcomings of rigid manipulator.Based on the design improvement of the existing technology,a gecko like soft manipulator with variable stiffness and electrothermal driving artificial muscle is developed in this paper.The main body of the manipulator is composed of a tough silicone rubber base and three identical soft fingers.The fingers of the soft manipulator are layered structure and realize corresponding functions respectively,mainly including the adhesive film with mushroom microstructure in the lower layer,the thermoplastic polyurethane elastic film with variable stiffness in the middle layer and the artificial muscle with driving function in the upper layer.The three-layer structure is formed by adhesive combination.According to the function of each layer of finger structure and the relevant performance test of manipulator body,the results are as follows:1)The mold with mushroom microstructure was prepared by soft lithography,and the film with microstructure was obtained after curing and demoulding by pouring.Designed and manufactured with a diameter of 10 μm 、20 μm、30 μm and 40 μm the mushroom like microstructure film samples of showed good morphology under light microscope and electron microscope.In the experiment of the relationship between maximum adhesion force and preload,they basically show a positive correlation.The experimental results show that the diameter is 20 μm The adhesion effect of M microstructure film sample is the best under 0.8N preload.Test 20 μm the relationship between adhesion force and time,adhesion force and film deformation,and film deformation and time.In the experiment,the maximum adhesion force and deformation of film samples accord with the experimental law.In the contact angle experiment,the experimental results of each group of film samples are higher than the blank control group without structure,and the hydrophobicity of the film is greatly improved,which has a certain effect on improving the self-cleaning,antifouling and waterproof of the film.2)Thermoplastic polyurethane elastomer films with melting point of 60 ℃ were prepared by hot pressing,and samples for dynamic thermomechanical analysis and tensile experiments were prepared.In the dynamic thermomechanical analysis experiment,the data of three parameters of sample storage modulus,loss modulus and loss angle with temperature are obtained.The storage modulus is 44.8405 MPa at the initial temperature of 19.89 ℃ and reaches the minimum value of 0.42171 MPa at the end;The loss modulus is 2.0324 MPa at19.89 ℃,and reaches the minimum value of 0.1268 MPa at the end of heating.The experiment shows that the stiffness of thermoplastic polyurethane elastomer film decreases when the temperature increases and increases when the temperature decreases.In the tensile experiment,the stress-strain curves of six groups of samples at different temperatures are obtained,and the scatter diagram of the relationship between the elastic modulus and temperature is drawn.The elastic modulus of the material decreases with the increase of temperature.Finally,after reaching the melting point of 60 ℃,the elastic modulus is 0.00055 MPa and does not change.The experimental results show that the selected material meets the functional requirements of variable stiffness in the working process of soft manipulator.3)The finger structure is designed by different drawing software,and the finger mold is made by 3D printing.The prepared composite material is poured into the mold,cured at room temperature and demoulded to obtain the artificial muscle of the driving layer.In the experiment of exploring the relationship between the content of graphene and the heat transfer performance of artificial muscle,seven groups of samples with different content of graphene were prepared,and the temperature changes of each group of samples were recorded during the heating process.The experimental results show that the temperature rise rate and maximum temperature of the samples are positively correlated with the content of graphene,and the higher the content,the more obvious the temperature rise effect.Then the thermal conductivity and thermal diffusion coefficient of each group of samples were measured.Both of whom increased to a certain extent with the increase of graphene content.The experimental results also show that the addition of graphene can increase the heat transfer ability of artificial muscle and improve the working efficiency of soft manipulator.4)The prepared three-layer structure is cut and glued,and the complete finger is obtained after curing.Apply 24.92 V voltage to the finger for bending test.The finger begins to expand and bend at 50 s,and the bending effect is obvious and basically reaches the maximum degree at 75 s.Under the support of DC power supply,the grasping ability of the assembled software manipulator is tested,and the three objects with different shapes,sizes and quality are grasped respectively.The experimental results show that after a certain time,the three fingers of the software manipulator begin to expand and bend,which can adapt to the external contour of different objects and grasp the experimental object,stay away from the desktop for a certain time,and the deformation of the fingers recovers after cooling to release the object,Each layer of finger structure plays its own role and works together,and the experimental results are in line with expectations.