Conceptual Synthesis of Mechanisms from Qualitative Speci cations of Behaviour

This paper describes a novel method for the synthesis of mechanisms from their qualitative behavioural speci cations. The technique has been implemented in the context of automated design of mechanisms in Technics Lego. We introduce a new kinematic abstraction called a unity machine which is a machine with a single degree of freedom. Unity machines are the mechanical analogues of functions in programming languages. Unity machines are the key abstraction that allow for compositional synthesis of mechanisms from a basis set, guided by functional speci cations. Geometric constraints accumulated during unity machine synthesis are satis ed by a qualitative kinematics analyzer based on Kramer's [Kramer] geometric engine. This allows us to cleanly integrate detailed dimensional synthesis by feature-oriented re nement with the abstract unity machine synthesis. Three steps in the design process { unity machine construction, qualitative kinematic analysis, and re nement { are illustrated in the context of the design of an autonomous tripod walker. This work was supported by NSF-IRI-8907271 and the Xerox Design Research Institute. The Legoites are listed in reverse alphabetical order. The rst Legoites who worked on an early version of the Lego synthesis program were Scott Benson and Robert Wisniewski. Their help and participation in the Cornell Design Project is gratefully acknowledged.