Robust Fixture Layout Design for a Product Family Assembled in a Multistage Reconfigurable Line

Reconfigurable assembly systems enable a family of products to be assembled in a single multistage system by adjusting and reconfigurabling fixtures according to each product. The sharing of fixtures among different products impacts their robustness to fixture variation and process disturbances due to frequent reconfiguration. This paper proposes a methodology to achieve robustness of the fixture layout design through an optimal distribution of the locators for a product family. This objective is accomplished by: (1) the use of a multistage assembly process model for the product family, and (2) minimizing the combined sensitivity of the products to fixture variation. The optimization considers the feasibility of the locator layout by taking into account the constraints imposed by the different products and the processes (assembly sequence, datum scheme and reconfigurable tools workspace). The high dimension design space makes the problem challenging from the optimization point of view. A case study where three products are assembled in four stages is presented. The sensitivity of the optimal layout was benchmarked against the ones obtained using dedicated assembly lines for each product. This comparison proves that the proposed approach does not significantly sacrifice robustness while allowing the assembly of three products in a single reconfigurable line.