Computer-Aided Creative Mechanism Design

Existing knowledge-based CADICAM systems do not support creativity since they are based on fixed vocabularies which contain a set of pre-defined functional and design features, and use these to define a library of standard solutions which the designer can use to compose designs automatically. However, the essence of creative design is to create new features and adapt them to new problems. Our system FAMING (Functional Analysis of Mechanisms Invents New Geometries, in Chinese, it means invention) attempts to support creative design by envisioning the qualitative behavior of an existing mechanism in different given environments and identifying interesting behaviors which fulfill part of required functions. The shapes which implement the corresponding functions are associated by a technique, called causal inversion, and can be indexed and added to new designs. The composition technique we have developed maintains the achieved individual functions and elaborates al1 parts together by solving the compositional constraints discovered by a qualitative envisionment. In fact, the compositional approach makes designing efficient by overcoming the complexity of a search made by incremental modification. All the ideas exploited in this thesis are implemented, and the plausibility of the representation and approach are demonstrated, by the design of kinematic pairs such as an escapement used in the mechanical clock. As an example of creative design, a new, simpler forward-reverse mechanism (mechanism that transforms an oscillating motion into a rotation which advances in one direction and, in a period of rest, reverses the motion to a lesser degree) is designed by composing two ratchets and adapting them to the new environment. This domain was chosen for study because the shape interactions dominate the function of kinematic pairs and simultaneous consideration of object shape interactions is beyond the capacity of human beings. We think that the same technique c m be extended to future applications of more sophisticated shape designs, such as cams, gearboxes, and finally kinematic chains for an entire mechanism. Our approach of causal inversion and composition is directly related to the assembly of machines with different kinds of interrelated parts, and can be applied to more general areas of design.