Tolerance Synthesis by Constraint Propagation

Optimizing the manufacturing cost is critical in tolerance synthesis. Decreasing the tolerance range will improve performance but will also increase the manufacturing costs. It is desirable to optimize the tolerance range under such constraints of product design as the relationship between the dimensions of entities of a component and the functional requirement of the design. We propose a constraint-based reasoning mechanism to synthesize a new set of tolerances to satisfy the functional requirements of a product and minimizing the manufacturing cost during the tolerance propagation in interval constraint networks by genetic algorithm. A hierarchical interval constraint network and interval propagation techniques for automatic tolerance synthesis are presented in this paper. The nodes in interval constraint networks represent the entities, the attributes, and the functional requirements of the mechanical parameters or the constraint functions. The arcs represent the relationships between the entities, the attributes, the functional requirements and the constraint functions. In tolerance synthesis, given the functional requirement tolerances, the goal is to synthesize a new set of entity tolerances. Backward propagation technique is developed for tolerance synthesis. In backward propagation, the minimization of the manufacturing cost is developed based on genetic algorithm. The goal of the proposed investigation is to develop a constraint-based reasoning technique for tolerance design, which plays an important role in the relationship between performances and manufacturing cost of a product. Such technique should be able to satisfy all the constraints in the tolerance design and minimize the manufacturing cost.