Research On Methods For Conceptual Design Of Mechanical Products

Conceptual design is regarded as the most important stage in the product development. Decisions made at this stage have significant influence on factors such as performance, reliability, safety and environmental impact of a product. More importantly, a poor design concept can never be compensated for by a good detailed design. With the supports from NSFC (Grant No. 50275013, 50275019), customer needs transformation, product feature modeling, concept generation, knowledge-based reasoning, concept evaluation and development of prototyping system in conceptual design are studied. Some examples are provided to demonstrate the proposed methods.The main work and creative points are described as follows.1. A functional flow based method for conceptual feature modeling is presented. Firstly, the hierarchical relation and mapping logic among function, behavior and structure are discussed. Then product features are formally represented and organized in functional, behavioral and structural domains. In these domains, the features are modeled in terms of input and output flows with functional basis, bond graph and directed graph, respectively. Functional flow is constructed to link the three features. The Function-Behavior-structure (FBS) feature mapping model is built based on the functional flow. The design concepts are subsequently obtained by the decomposition of functional feature and hierarchical mapping. In the end, a case study for the functional solving of transmission system is given to demonstrate the proposed method.2. An energy-interaction based method for concept generation is presented. The single behavior of basic element is represented in terms of input and output energy flows, in which the characteristics of type, dimension, direction and constraint of energy ports are extracted effectively. By linking the single behaviors according to the causal relation between them with the directed graph, the causal behavioral link (CBL) and behavioral topology matrix are constructed to represent the interaction between basic elements intechnical system. The model for concept generation is established based on the energy interaction, which includes concept variant and concept creation. The former is implemented by extending the CBL-based design template under the constraints; the latter is implemented by combining the basic elements based on the generated CBL by positive reasoning. In the end, a case study of the concept generation of high-speed single needle lockstitch straight button holing sewing machine is given to demonstrate the proposed method.3. A state-space based method for concept reasoning and a fuzzy distance measurement based method for concept evaluation are presented. Firstly, a framework for knowledge acquisition in conceptual design is established, which includes knowledge elicitation and knowledge representation. The design knowledge is elicited based on the FBS model, and represented with a hybrid paradigm of object and production rules. Then a state-space based exhaustive solving strategy is proposed to reason out the concepts automatically from the desired design specifications. The tree of state space is generated by searching basic elements orderly from the base under design specifications, in which a design concept is described by one branch. The importance weights of different criteria and the ratings of various alternatives under different criteria are assessed in linguistic terms represented by fuzzy numbers. Fuzzy value of each of the alternatives is computed using standard fuzzy arithmetic. Concept of fuzzy distance measure is introduced to decide the final ranking of alternatives. To avoid the combination explosion, an A* algorithm-based heuristic solving strategy is subsequently proposed by defining the heuristic evaluation function as a fuzzy multi-criteria decision-making. The satisfied solutions are obtained in a reasonable time by directing the search path with evaluation values. In the end, two case studies for the design of auto gate's driving device and hoist device are given to demonstrate the proposed methods.