Research On Several Key Issues For Kinematic Design Of Planar Mechanisms With Stochastic Parameters

Stochastic uncertainty analysis of mechanism is the art of formulating a mathematical model within which one can ask and get answer to the question:"What is the motion law that a mechanism complies with when given that one or more of its material properties or geometric dimensions and properties are of a random or incompletely known nature, and/or that the actions on the structure in some respects have random or incompletely known properties?". And stochastic uncertainty design is a decision problem added to the stochastic uncertainty analysis. Being capable of completing the prescriptive motion (movement) accurately and duly is one of the major objectives of mechanisms design. Parameter uncertainty of the mechanical structures that compose the mechanisms is inherent in most engineering problems, and loads that are applied to the mechanisms are also random. Thus, the random mechanism systems with random structural parameters subjected to random loads are appeared. Therefore, the research on the kinematic design of the mechanism systems with stochastic uncertainty parameters is of the highest importance for design purposes.Reliability-based design and robust design are very advanced ideas. They have extensive application prospects on account of significance in improving product quality and making performance more stable. Therefore, these two theories can be applied to deal with stochastic uncertainty parameters in kinematic design of mechanisms. Reliability theory is used to deal with uncertainties in reliability-based design, and robust design attempts to make the structure abilities insensitive to variations of design variables. In practical engineering, the aforementioned methods are very effective to improve engineering design with the consideration of the uncertainties. Unfortunately, these methods usually have been used separately in different design stages for different purposes. Therefore, it is essential to combine the reliability-based optimization theory, the reliability sensitivity analysis technique and the robust design method and to develop a reliability-based robust design approach of mechanisms.In this dissertation, based on summarizing the theory of kinematic design of planar mechanisms with stochastic parameters in the world, a brilliant concept for kinematic design of planar linkages is proposed. In this new system, the theory of robust design, reliability design and reliability-based robust design are widely used. The main productions obtained from this paper are following as:This dissertation is divided into 6 Chapters and the main productions obtained from this paper are following as:Chapter 1:Introduction. We explicate the engineering background, the aim and meaning of the research; introduce the rise, the concept, the development of reliability-based design theory; narrate briefly advances in reliability-based optimization method and the tendency of the reliability-based optimization approach development, and set forth the significant meaning of the study on the theory & method of robust design.Chapter 2:Mathematics background and basic theory of reliability. First, mathematics theories and methods used by this dissertation are briefly introduced, and then the details of reliability-based theory and reliability-based optimization methods are described in Chapter 2.Chapter 3:Kinematic accuracy analysis for planar linkage mechanism. In Chapter 3, comprehensively considering the parameters uncertainty of the mechanical structures and input, the kinematic accuracy model is formed.Chapter 4:Reliability-based optimization design of mechanisms with arbitrary distribution parameters. A practical and effective numerical method of reliability-based optimization design of mechanisms with arbitrary distribution parameters is proposed in Chapter 3. Techniques from the perturbation method, the Edgeworth series, the reliability-based design theory and the optimization technique are employed to present an approach for the reliability-based optimization of mechanisms with arbitrary distribution parameters on the condition of first four moments of original random variables known. The theoretical formulae of reliability-based optimization method of mechanisms with arbitrary distribution parameters are obtained. The approach is applied to develop the reliability-based optimization design theory with arbitrary distribution parameters.Chapter 5:Reliability-based robust design of mechanisms. In Chapter 5, firstly, by composing the reliability-based design theory and sensitivity analysis method, a useful and efficient approach of reliability sensitivity is presented, change laws of the reliability sensitivity are given, the influences of design parametric changes on reliability of mechanisms are studied and theoretic foundation are provided for reliability-based design of mechanisms. Secondly, on the basis of the reliability-based optimization design theory, the reliability sensitivity analysis technique and the robust design method, the reliability-based robust design is discussed and a practical and effective numerical approach of reliability-based robust design of mechanisms is presented. The theoretical formula for reliability-based robust design of mechanisms is obtained. The reliability sensitivity is added to the reliability-based optimization design model and the reliability-based robust design is described as a multi-objection optimization, in which the maximum of the capability of the mechanisms and the minimum of the reliability sensitivity with respect to the mean value of design variables are taken as objective functions, while including a series of reliability constrains and geometry constrains etc..The reliability-based robust design method of mechanisms is proposed and the application field of reliability-based robust design is developed well in Chapter 5. The reliability-based robust design of mechanisms attempts to make the kinematic accuracy reliability variations of mechanisms are insensitive to variations in design variables in the stage of design, which can minimize the effect of variations without eliminating the causes. When the reliability-based robust design approach is applied to mechanisms design, which is very useful and effective to improve quality and reliability of mechanisms.Chapter 6:Conclusions and prospects. We draw the main conclusions of this dissertation and discuss the outlooks of reliability theory and robust design method, and their applications in the kinematic design of mechanisms with stochastic parameters.