SMT Feeder Slot Assignment for Predetermined Component Placement Paths

Surface Mount Technology (SMT) is a popular method of Printed Circuit Board (PCB) assembly in which high speed automated assembly machines are capable of placing in excess of 40,000 components per hour. In order to achieve these impressive assembly rates, complex placement machines must be programmed efficiently. Intrinsic to the configuration of these machines and the assembly process are some well established Operations Research problems. This paper addresses the feeder sequencing problem for an assembly machine with a sliding feeder rack in conjunction with a X-Y positioning table and a turret placement mechanism. This problem is a Quadratic Assignment Problem, and is proven to be - complete.1 Two different heuristic methods are proposed, each with unique characteristics that have the potential to be beneficial to an assembly operation dependent upon the restrictions of the planning task. One method is to assign feeder slots based on the transition between component types that naturally occur in the board placement path. The second method begins with an initial slot assignment and identifies exchanges between pairs of slots that generate improvements in the objective function. Minimizing the feeder travel distance over an assembly is the goal of each heuristic. A comparative analysis between the two heuristics is performed. Examples are presented and the attributes of each method are discussed. Arguments are presented to support “near-optimal” solutions to the problem. Given the complexities of the system, proper planning of the assembly process can take advantage of the independent control of each mechanism to create a natural relaxation of specific constraints.