Design Method Of Flexure-jointed Linkages Using Combined Flexible Beams With Large Deflection

Flexure-jointed linkages(FJLs)transfer the motion and force through the large deflection of flexible members.Compared with traditional rigid mechanisms,FJLs have the advantages of easy manufacture and assembly,less friction and light weight,and have many application prospects in bionics and medical treatment.However,the movement of FJLs is always accompanied by a complex deflection process,which makes its modeling,analysis,and design much more difficult than rigid mechanisms.In particular,the FJL with a large range of movement involves the solution of complex problems such as nonlinearity,coupling of motion and force.Accurate modeling is very difficult,and there is a lack of effective methods to guide optimal design.In order to overcome the shortcomings in the current design method of the FJLs with large deflection,this dissertation systematically studies the design method of one-DOF FJL which can approximately reproduce the desired motion path.The main research achievements are as follows:A flexible element of the combined flexible beam(CFB)composed of several beams with constant curvature is proposed,which enriches the structural form of flexible joints.For this kind of flexible element,a modeling method for the force-displacement model and strain energy of planar bending CFB is proposed.With the help of the elliptic integral solution,the force-displacement model of a flexible beam with constant curvature and large deflection is derived.Based on this,the force-displacement model of planar bending CFB is established according to the deformation superposition principle.The strain energy model of CFB is derived according to the solution parameters of bending deflection of CFB and the principle of energy superposition.The simulation and experimental results show that the derived models can not only accurately predict the bending deflection and strain energy stored in CFB under end loads,and the maximum deviations are less than 0.7% and 2.5%,respectively,but also ensure the solving accuracy and avoid introducing too many intermediate variables.Based on the above work,a modeling method of kinematics and strain energy of FJLs with CFB is proposed.In this method,the closed loops in the mechanism are disassembled into rigid-flexible coupling serial chains and equivalent to CFB through force analysis.The force-displacement model of CFB is used to quickly establish the kinematics of FJLs,which effectively reduces the difficulty of kinematics modeling.According to the strain energy model of CFB,the strain energy stored in FJL is quickly established.The simulation results show that the kinematics and strain energy model of the FJL can accurately predict its output path and the strain energy stored in the mechanism under any configuration,and the maximum relative deviations are less than 0.35% and 2.3%,respectively.The derived models reveal the influence law of structural parameters on the output path and strain energy of the FJL,which provides an important basis for its optimal design.In the optimal design of FJLs,a design method for the structure and dimension parameters of single-degree-of-freedom FJLs that can approximately reproduce the desired motion path is proposed.Starting from the rigid mechanism that meets the desired motion path and taking the CFBs as the flexible elements to replace the passive joints in the rigid linkage,this design method considers the material failure and geometric constraints and minimizes the path deviation and strain energy between the FJL and the rigid linkage.Multi-objective genetic algorithm is used to optimize the design variables.Taking planar six-bar and spatial five-bar FJLs as examples,the design process of the two mechanisms is illustrated.The physical prototypes of compliant quadruped robot and bionic flapping-wing aircraft are built.The feasibility of the design method is verified by the movement ability and lift test experiments of two prototypes respectively.The outcomes of this dissertation have important theoretical significance and practical value for enriching and developing the design theory and method of FJLs with the expected motion path and promoting the design and application of the FJLs with a new structure.