The Energy Characteristic State Models For Mechanical System Conceptual Design

A new modeling methodology for scheme design of mechanical systems based on the energy and structure characteristic state is developed in the thesis. The models for conceptual design processes of a product mainly include in the kinematic scheme design, configuration and the structural scheme design. The goal of the research is to solve the modeling problems and to support these conceptual design processes of mechanical systems by computer aided. This research is also supported by National Natural Science Foundation of China under Grant No.50075012 and No.51075051 and National Science and Technology Major Project of China under Grant No.2009ZX04014-034.The energy characteristic state modeling method for a basic energy unit (BEU) is firstly proposed. The BEUs, which are the functional carriers to transform the energy states, are defined. Then the energy characteristic state vector of the BEU is expressed by means of kinematic characteristic state sub-vector and dynamical characteristic state sub-vector. Meanwhile, in order to describe the energy state of the moving frame, its energy state is regarded as the initial energy state of the BEU. Therefore, the energy characteristic state equation with non-zero initial energy state of the BEU is built, which describes the output energy characteristic states of the BEU by the initial energy characteristic state and the output responses on input energy characteristic states.This thesis researches on modeling methods for the kinematic scheme design of mechanical systems by means of BEUs combination and its energy characteristic state models. The connecting constraint models for combination of BEUs are set up by researching on combining patterns and the constraints characteristics of BEUs. The models describe the constraints between connected links or between kinematic pairs by introducing connecting constraint matrix. Then, the models for kinematic conceptual design of mechanical systems are explored using the energy characteristic models and connecting constraint models of BEUs. The systematic models describe not only the processes of general combination patterns of BEUs with fixed frames, but specially the superposed combination of BEUs with moving frames.A structure characteristic state modeling method for structure layout conceptual design of a mechanical system is proposed. This thesis, based on the invariant feature of the fixed positions of the supporting elements in a mechanical system and reflecting the system structure configurations to some extent, presents that the structure characteristic state is a special stable state. Thus, a structure characteristic state equation describing the structure characteristic for the input and output of BEU is constructed using state space theory, which maps the kinematic characteristics to the structure characteristics of BEUs. And then the models, describing the direction and location characteristics of BEUs, links and kinematic pairs, are established by analyzing their characteristic relations. At last, the structure characteristic models of expressing the system characterization of its structure and layout characteristics are explored based on the method of units combination.The static and dynamic performances of supporting parts in a mechanical system directly affect the overall system performances. This thesis presents a structure scheme configuration design method for complex mechanical parts based on the function constraint models and the performances, and establishes components configuration design model based on energy characteristic state and the orientation characteristic of all BEUs in the system. This design method classifies parts structure configuration design into physical model and structural model design, in which physical model design of parts introduces loads and its positions, shapes and sizes constraints. Using the structural topology optimization technology to realize the concept configuration design of parts satisfying their performances, parts structure scheme configurations are finally obtained.Finally, through an example the thesis verifies the effectiveness and systematization of the proposed modeling methods for the scheme design of a mechanical system.