A constraint solver to define correctly dimensioned and overdimensioned parts

• Authors: M. Luisa Martínez;Jesús Félez
• Venue: Computer-Aided Design
• Year: 2005

Creating mechanical parts through conceptual design implies the use of constraints. When developing conceptual design-based CAD programs, two independent modules must be created: on the one hand, the sketcher module, which must define the model's geometrical constraints and interpret the user's intention through a system of rules. On the other, the calculation module which must resolve the final geometry and eventually dimension the mechanical part. This paper presents a new approach to the constraint-based solvers. The proposed approach establishes the complete two-dimensional geometry and constraints of a sketch and relates it with the complete dimensioning of the sketch. The developed methodology gives as result a complete and consistent dimensioning of the sketch following the rules established by a standard like ISO, determining also if the system is over-constrained and detecting the redundant dimensions. The methodology establishes the most suitable dimensioning but, it is also possible to obtain other alternatives of full sets of dimensions. First, the geometric constraints considered are described, and the use of each one justified, together with the numerical methods used to resolve the set of non-linear constraints obtained. A procedure has also been developed for choosing the set of independent constraints of the system, by introducing the priority factor concept, which lets the overriding constraints in the system be decided, and then the algorithms developed for automatically assigning the constraints are presented. Also described are the criteria followed that lead to an automatic generation of dimensions, as well as to equivalent and alternative dimensioning. Finally, a series of examples are presented to show the possibilities of the developed methodology.