Dynamic Analysis And Synthesis Of Compliant Mechanisms

Compliant mechanisms gain their motion from the relative flexibility of their members. Compared with conventional rigid-body mechanisms, compliant mechanisms have many advantages such as part-count reduction, reduced assembly time, simplified manufacturing processes, increased precision, reduced wear, and reduced weight. At present, compliant mechanisms have attracted much attention and become the focus of mechanisms research. They have been developed rapidly in recent years due to their advantages as required in modern machinery. Most of these works are focused on the structural and kinematic analysis and design of compliant mechanisms. However, the study of the dynamics of compliant mechanisms is lacking. With the increasing requirements of task and application, the dynamic analysis to improving the dynamic characteristics and design of compliant mechanism is a new hot topic in mechanism research. The study of the dynamic analysis of compliant mechanisms has great theoretical significance and practical value.By taking the planar compliant mechanisms as subject investigated, the dynamics and synthesis of the compliant mechanisms are studied in aspects of dynamic modeling, dynamic analysis, optimal design and experiment verification in this dissertation.Firstly, the dynamic models of compliant mechanisms with flexure hinges are created. The stiffness of four flexure hinges are deduced respectively, and the effect of design parameters on stiffness of flexure hinge is studied. By taking the compliant parallel-guiding mechanism and compliant slider-crank mechanism as subject investigated, the dynamic model of compliant mechanisms with flexure hinges is created based on the Lagrange equation.Secondly, the dynamic models of compliant mechanisms with compliant links are developed. Considering the large deflection of compliant links, the numerical method and the finite element method are utilized respectively to generate the dynamic models of compliant mechanisms with compliant links. The difference and application of these models are discussed.Thirdly, the dynamic characteristics of compliant mechanisms are investigated. Based on the proposed dynamic models of the compliant mechanisms, the natural frequency is calculated. By using direct differential method for sensitivity analysis, the effect of design parameters on dynamic characteristics is discussed. The compliant link's dynamic stress and strain are calculated,the value and position of maximal stress were derived. Based on the cumulative damage resulted from the alternate dynamic stress, the fatigue lives of the compliant links are predicted. A new method is obtained for calculating the driving torque, it shows that the flexure hinges have impact on the driving characteristics of compliant mechanisms.Fourthly, optimal design of compliant mechanisms is investigated. Based on the characteristics analysis, the material selection is studied. The stiffness of flexure hinge is taken as optimal design objective. The natural frequency and driving torque are taken as constraints. The optimal design of compliant mechanism with flexure hinges is performed. Then, the total compliant links mass and the total strain energy are taken as optimal design objective, respectively. The natural frequency and dynamic stresses are taken as constraints. The optimal design of compliant mechanism with compliant links is performed.Finally, the experimental study of compliant mechanism is performed. The compliant parallel-guiding mechanism is developed. The experimental studies of natural frequency and strain are performed. The comparison between the experiment results and the theoretical results verifies the validity of the experiment system and theoretical models.