Design And Application Of Nonlinear Stiffness Compliant Elements

In recent years,compliant mechanism has been widely used in precision engineering,flexible intelligent structure and human-computer interaction due to its advantages of integrated design and processing,no friction,energy storage and high transmission efficiency.With the rapid development of medical robots,compliant mechanisms play an important role in medical surgical robots,rehabilitation robots and other directions.Typical application scenarios include force sensing surgical instruments and compliant actuators.In view of the lack of force sensing in surgical instruments,a force sensing biopsy instrument design method based on compliant elements is proposed in this paper;At the same time,in view of the problem that most of the existing compliant actuators adopt the constant stiffness compliant elements,which leads to the limited task adaptability and control performance,the analysis and design method of nonlinear compliant elements are studied based on the flexible beam deformation theory,and the nonlinear compliant elements with a given stiffness shape for compliant actuators are developed.The specific research contents are as follows:Firstly,the advantages and disadvantages of the existing flexible mechanism stiffness analysis methods are introduced and summarized.The flexible curved beam stiffness model which can describe the nonlinear stiffness is established by combining the chain algorithm and the pseudo rigid body 2R model.The simulation is carried out by using the finite element analysis method.The results show that the stiffness model has good accuracy and has certain practical value.Secondly,based on the nonlinear stiffness curved beam stiffness description model given above,aiming at the lack of force sensing function of current clinical biopsy forceps,the design scheme of flexible biopsy forceps with force sensing function is proposed,and the stiffness analysis method of flexible curved beam of flexible biopsy forceps is given,so as to obtain the coupling mapping relationship between its deformation and biopsy force,Thus,the force information of biopsy forceps can be calculated indirectly,that is,the force sensing biopsy operation can be realized.The accuracy of the stiffness analysis model and the feasibility of force sensing function are proved by simulation and prototype experiment.Finally,according to the requirement of compliant actuator for nonlinear stiffness design,this paper adopts three chain curved beam torsion compliant element configuration,and its end is hinged to simplify the stress situation.The theoretical analysis is carried out by using the nonlinear stiffness curved beam stiffness description model proposed above and verified by finite element simulation.The mechanism of nonlinear stiffness,that is,the geometric nonlinearity of the mechanism,is given.Furthermore,a general design method for torsional compliant elements with discrete stiffness characteristics is given.Taking a compliant element with three discrete stiffness characteristics as an example,its geometric parameters are designed theoretically.The feasibility of the proposed design method is verified by prototype experiments.This study provides a new idea for the design of compliant mechanisms with given stiffness characteristics.