Real-time scheduling for multi headed placement machine

This paper proposes a methodology for real-time scheduling to sequence the pickup and placement of component on multi headed placement machines in printed circuit board (PCB) assembly. The latest technology of surface mount device (SMD) placement machines have a smart feeder carrier that automatically identifies the exact location of each component type on the feeder slot, detects component´s missing from the component feeders (and continues working with other component types) and allows a component to be reloaded during a pick and place operation without stopping the operation. Assuming that the components on the feeder carrier may be misplaced or some of the required components are missing, we generate an initial schedule using a greedy constructive heuristic by only considering the available placement points. The initial solution can immediately be used to assemble components for the first PCB. While the placement machine is assembling components, we employ the CPU free time (whilst the robot arm is moving) to improve the initial schedule by using a randomised hill climbing search technique. Thus, the subsequent PCB´s will use the improved schedule. Our experimental result on two data sets show that we gain 58.79% and 76.69% (respectively) improvement on assembly cycle time over the initial schedule.