The Study On Grasping Forces Planning And Structural Optimization Design Of Pneumatic Soft Manipulator

As a new type of structure that can be used for object gra sping,the soft manipulator is inspired by the biological system organization in nature with softness and body compliance.It can overcome the shortcomings of traditional rigid manipulator,such as large contact force,complex control strategy and high cost.It is especially suitable for the application field of automatic grabbing of flexible and easily damaged objects.In this paper,a kind of three-finger pneumatic soft manipulator is designed,around which structural design and production,material constitution,bending deformation theory of air chamber,grasping force planning and structural optimization design are studied.The main research contents are as follows:(1)Based on the fast pneumatic grid structure,a single pneumatic soft manipulator is designed,the thickness,width,height and length gradient coefficient of the air chamber are taken as the design variables,and the three tentacle pneumatic soft manipulator is designed according to the geometric dimension relationsh ip when grasping the object.Using the layered casting method to create the physical objects of the soft tentacles,and building an experimental platform for measuring the bending deformation of the soft tentacles and the output force of the soft tentacle end contact.The standard tensile specimen of the matrix material is made and the uniaxial tensile test is carried out.The constitutive parameter s of the test data are fitted,and Ogden second-order constitutive model is determined as the analytical constitutive model of the material.(2)Using the piecewise constant curvature theory to analyze the bending behavior of the soft tentacle single-cell,the theoretical model of a single air chamber under small strain is established by using the principle of virtual work,and the model is modified in a large strain range,the accuracy of the theoretical model is verified by comparing with the experimental results.The sensitivity analysis of the structural parameters which affect the bending angle of the air chamber is carried out,and the height of the air chamber has the greatest influence.The bending deformation model of the soft tentacles is constructed which based on the D-H method,the results are in good agreement with the experimental results.The working space of the soft manipulator is analyzed with Monte Carlo method,which provides the basis for the next research on the grasping forces planning of the soft manipulator.(3)The contact forces planning theory for precision grasping of soft tentacles including contact model,force spiral balance and force closure conditions is established.The contact forces planning goals with maximizing contact force stability coefficient and minimizing contact force vector 2-norm is proposed,and the multi-objective optimization mathematical model of contact force is established.The contact force of three precision grasping cases is solved by multi-objective particle swarm optimization algorithm,the corresponding Pareto optimal frontier is obtained.A finite element model for solving the positive output force of the soft tentacle end contact is established,and the accuracy of the finite element model is verified by comparing with the experimental results,the output force characteristics of the soft tentacles fingertip are obtained by curve fitting method.(4)The structural optimization objectives with maximizing the specific contact force,maximum positive contact force and minimizing the end state angle are proposed and established,the height,wall thickness and gradient coefficient of the air chamber are selected as the optimization variables,and a multi-objective optimization model is constructed.Based on the optimized Latin hypercube test design method,50 sample points were selected,and the finite element calculation of sample points is carried out and the main effect analysis of parameter influence is carried out.The third-order response surface models of specific contact force,positive contact force and end state angle are constructed,which solved by multi-objective particle swarm optimization,the optimal solution with end state angle less than 65 ° is selected,and the accuracy of the optimization results is verified.Comparing the specific contact force and positive contact force before and after optimization,the optimized structure improves the comprehensive grasping performance of the soft manipulator.