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A General Approach to Design Automation

This thesis developed a domain independent “shell system for routine mechanical design”. This shell is used to produce domain specific design systems by simply placing domain- related knowledge into it. A general “design model”, which is an informal description of the mechanisms behind the design process, has been implemented. The design model is established based on the “characteristics and mechanisms common in routine mechanical design activities”. By examining particular design examples, it is concluded that the routine design activities have: 1) a “common design procedure” from specification recognition to detailed design; 2) “common mechanisms” to determine parameters and the like; and 3) “common knowledge formats” to express design knowledge. Only “detailed design knowledge” is specific to each domain, but can be represented in common knowledge formats. The “model” and its implementation, the shell system, describe the design process in four stages: specification development, synthesis, analysis and non-functional considerations. The synthesis achieves rough structural configurations by following the “configuration decomposition approach” which is derived from the well-developed configuration decomposition patterns in the routine design, and which uses function-to-configuration, configuration decomposition and function-checking relations. In the analysis stage, configuration parameters are determined by design relations which are represented by “design slices” written in the form of “basic description elements”. The analysis knowledge is organized in a multilevel structure from lower levels of basic description elements, design slices, to upper levels of “design procedures” and “knowledgeable configuration units”. Design slices are classified as “solving slices” and “checking slices” responsible respectively for determining parameters and ensuring that checking criteria among parameters are met. A design procedure is a pile of design slices and determines a set of parameters since design relations are used in groups. The uppermost level consists of knowledgeable configuration units. They organize design procedures, parameter sets and configuration decomposition patterns under a configuration. The reasoning process in analysis is decentralized through a number of “interpreters” which handle various tasks such as choosing a design procedure. The non-functional design aspects are considered in the design relations and are incorporated into the analysis. The shell system provides general design knowledge representation formats and general reasoning mechanisms. It is implemented on a SUN workstation using KEE which provides object-oriented programming and rule reasoning facilities. Connection between design components is dealt with using partial configurations and constraints which define the relationships between configurations and partial configurations involved in a connection. The iteration process caused by dependency among parameters is handled using the failure design procedures, that is, if a checking relation is not satisfied, a failure design procedure is called to modify some parameters at the early design stage. The geometry aspect is implemented parametrically based on an existing feature-based modelling system (IPDM). Two specific design systems: a cam system and a bolted flange system, have been developed based on the shell. Both accept given specifications, and output configurations with parameters and graphic display. The development process of these two systems is simple and efficient; and design results are satisfactory. These examples illustrated the versatility and effectiveness of the developed approach to routine mechanical engineering design activities. The major feature of this work is the explicit descriptive style in representing the design knowledge. The domain independent shell approach enhanced by this feature greatly simplifies the development of domain specific knowledge bases. / Thesis / Master of Engineering (ME)
Date09 1900
CreatorsChen, Shuejun
ContributorsElMaraghy, Hoda, Mechanical Engineering
Source SetsMcMaster University
Detected LanguageEnglish

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