PCB assembly scheduling with alternative nozzle types for one component type

The placement machine is the bottleneck of a printed circuit board (PCB) assembly line. The type of machine considered in this paper is the beam-type placement machine that can simultaneously pick up several components from feeders. It is assumed that the number of nozzle types (NTs) is less than the number of heads on the beam. The objective of the PCB assembly scheduling for a single placement machine is to minimize the cycle time based on the average machine operation time instead of the travelling distance. To minimize the cycle time, the number of turns and the number of pickups should be minimized. The PCB assembly scheduling is hierarchically decomposed into four problems: the nozzle assignment problem, the head allocation problem, the component type (CT) grouping problem and the pickup clustering problem, which are optimized successively and iteratively. First, the nozzle assignment problem considering alternative NTs for one CT is dealt with by the proposed genetic algorithm. For a given nozzle assignment solution, the head allocation problem is solved by a previously greedy heuristic to minimize the number of turns.Then, the CT grouping problem and the pickup clustering problem are solved by a proposed greedy heuristic and a modified agglomerative hierarchical clustering approach, respectively, to minimize the number of pickups. Numerical experiments are carried out to examine the performances of these proposed heuristic approaches. The importance of considering alternative NTs for one CT for the cycle time is also confirmed.