Research On Topology Optimization Method Of Compliant Constant Force Mechanism

Compliant mechanisms have the advantages of high precision,assembly-free and frictionfree.In the fields of materials science,biomedical and microelectromechanical systems(MEMS),which require high-precision micro/nano manipulation,compliant mechanisms are highly valued.Due to the fragility of the manipulated object,micro/nano manipulation requires precise control of the force during the manipulation process.The constant force mechanism is a kind of mechanism that can output stable constant force without the help of external sensors,so it is beginning to draw increasing attention from researchers.Topology optimization,as an important design method for compliant mechanisms,has not been studied deeply enough.Based on this background,this diseration studies the topology optimization method of the compliant constant force mechanism.The main research works are as follows:(1)Based on the geometrical nonlinear topology optimization method,a topology optimization model of the compliant constant force mechanism is established.The output characteristics of the constant force mechanism are studied and the related performance indexes are quantified.The output stability of the constant force mechanism relative to the reference constant force is used to establish the objective function.An adaptive selection strategy of the reference constant force is proposed.Considering the geometrical nonlinear effects brought by the large deformation of the constant force mechanism,an additive hyperelasticity technique is given,and the strain energy difference method is used to extract the sensitivity information of the elements.Finally,the effectiveness of the proposed method is verified by numerical examples,and the performance of the optimized compliant constant force mechanism is verified by experiments.(2)A material adaptive interpolation method is proposed for dealing the numerical instability in the nonlinear optimization process of the compliant constant force mechanism.Based on the power-law penalty strategy,a material parameter is introduced to adjust the overall deformation resistance capability of the intermediate density elements to avoid excessive deformation.An adaptive adjustment strategy of the material parameter is given to minimize the finite element analysis error brought by the material adaptive interpolation method.Finally,the effectiveness of the proposed method in improving the convergence of the nonlinear optimization of the compliant constant force mechanism and the improvement of the optimization efficiency are demonstrated by several numerical examples of the constant force mechanism.(3)To control the maximum stress during the nonlinear topology optimization of the compliant constant force mechanism,the relationship between the global stress gradient and the material density of the hyperelastic material is studied.A global stress gradient model of the hyperelastic material is established for the topology opitimzation.The mathematical relationship between elemental stress and density is given by combining the constitutive equation of the hyperelastic material.The global stress expression is constructed by the P-norm method,and the global stress gradient model of the hyperelastic material is established based on the relative density of the elements.The topology optimization model of the compliant constant force mechanism with stress constraint is constructed.The effectiveness for maximum stress control in the optimization of constant force mechanism is verified by several numerical examples,and an experimental comparison is given to further verify the effectiveness of the model.(4)An adjustable constant force microgripper design with a two-stage configuration is proposed for the application of the constant force mechanism in micro/nano manipulation.An adjustable constant force mechanism design is proposed,which combines a positive stiffness mechanism and a constant force maechanism.The adjustable constant force mechanism is used as the first-stage acutator.Based on the geometrically nonlinear topology optimization method,a microgripper with parallel grasping capability is designed as the second-stage manipulator.In order to realize parallel grasping,the parasitic movement and the deflection of jaw is limited by adding constraint functions to the optimization model.The motion and output characteristics of the adjustable constant force microgripper is verified by simulation analysis.Finally,the adjustable constant force microgripper was tested by zebrafish cell manipulation experiments.The research work in this disertation provides a topology optimization method for designin compliant constant force mechanisms.It further improves the theory of optimal design of the compliant constant force mechanism,and provides new ideas for the application of compliant constant force mechanism in the field of micro/nano manipulation.