PROMPT: An Innovative Design Tool

We describe a system, Prompt, used to design physical systems. Prompt employs a multi-level approach to design. When simple constraint propagation over prototypes [Adda fails, Prompt can significantly modify prototypes by reasoning about their structure and physics. Prompt derives the behavior of a prototype from its structure using knowledge of physics stored in a Graph of Models. It then uses heuristics called Modification operators to control the process of modifying the prototypes. In this paper we describe how our system works in the domain of structural design. We describe the kinds of analysis Prompt performs on beams and how it makes innovative changes to prototypes. ems [Srir85, M.itc85, Mitt86b] configure their designs from a fixed finite library of atomic components. The design process in such systems is best thought of as hierarchical refinement. These systems start with a rough schematic that is successively refined at each step. Each stage of the refinement process generates constraints which are used to guide the partial design; successive refinements are performed and in the final stage, the atomic components and their parameter values are chosen so as to satisfy these constraints. Such design systems use functional models [Joha85] of prototypes and therefore cannot reason about, or modify, the structure or behavior of the atomic components. It is often the case that the constraints generated by such a process cannot be satisfied by any combination of parameters of the components in the library. For example, it is evident that weight and torsional stiffness requirements conflict in the design of beams. If the system’s entire library of beams consists of a solid, circular beam parameterized by the radius and the length of the beam, it is easy to conceive of a design specification that cannot be met by varying parameters over the library. The solution to such design problems lies in modifying one or more prototypes in the library. In order to modify a prototype, the system must first be able to derive the behavior of the prototype from its structure and the underlying physics. e system must then use the results of this analysis to appropriately modify the prototype. There are two major difficulties with developing a system that works in this manner. First, analysis is expensive. Analysis requires representing large engineering domains and prototypes can be analyzed along many different dimensions. Second, mapping the results of analysis to structural changes requires sophisticated reasoning about complex equations. In its full generality the Analyze-Modify loop is very powerful but inefficient. Prompt is a design system that is capable of analyzing and modifying the prototypes in its library. Prompt introduces two mechanisms to help alleviate the difficulties of the Analyze-Modify loop. Graphs of odeb , are helpful in reasoning about large engineering domains. I[Adda87, Penb87] h of Models paradigm in detail. consist of three parts; a set of prec the application of the operator, a set of heuristics that help focus the analysis of the prototype, and a set of heuristics that control the mapping from the results of the analysis to the structural changes. In our example above, the second part of a Modification operator directs Prompt to analyze the prototype of the solid circular beam with respect to stress distribution. The analysis is carried out using the Graph of Models paradigm. The third part of the operator directs Prompt to redistribute the mass of the rod, thus inventing the concept of a tube. ore powerful than pure parameterization and powerful than general reasoning from first principles, dification Operators offer an intermediate level of reasoning about structural changes. The rest of this paper describes the main ideas in Prompt by working through our example. Beam design is an interesting domain for various reasons. First, the theory is well understood, thus providing a firm foundation for analysis from the first principles. Second, the domain is of some importance in robot design. Emtlly, the domain includes interesting aspects of reasoning about shape and mathematical equations. 2 Cmastraimt Satisfaetkm The first stage in Prompt is similar to existing design systems. Hierarchical decompositions and the atomic components are stored in structures called Prototypes [Adda85]. Prototypes are similar to the frame-like representation structures used in other systems [SrirSS, tc85]. A component prototype contains the constraints on its interactions Mu-thy and Addanki 637 From: AAAI-87 Proceedings. Copyright ©1987, AAAI (www.aaai.org). All rights reserved.