The assembly of electronic products has brought huge challenges to the production and operation scheduling due to the large number of components, the wide variety of electronic components, and the short life cycle of electronic products. Many types, small quantities, and variable quantities have become the mainstream production mode of electronic manufacturing. . In this mode, the switching time between multiple varieties occupies an increasing proportion of the entire assembly time.

It consists of a high-speed placement machine and a multi-function placement machine. In fact, the entire PCB assembly line also includes feeders, screen printers, dispensers, reflow and curing ovens, and closing machines. These devices are connected in series to form a PCB assembly line, but these auxiliary devices are also It does not constitute a bottleneck process for the entire pipeline and is therefore omitted during modeling. Each placement machine can accommodate 20 feeding slots, and each component occupies one feeding slot on the placement machine. In general, the number of component types required for a single-type PCB circuit board does not exceed the capacity of the feeder, but the total number of component types required for a multi-type PCB usually exceeds the capacity of the feeder.

The components required for different types of PCB circuit boards in the mounting process are placed on these supply chutes, and the pick-and-place device removes the components from the feed chute and mounts them to the specified position on the PCB. According to survey data on empirical research objects, the average time for a high-speed placement machine to mount one component is 0.06s, and the average switching time for one supply slot is 180s. Multifunction SMT machine has two worktables, but only one workbench works, another workbench is only used for placing large or special-shaped components, each worktable accommodates 10 feed chutes, and it takes 0.18s to place an average component. The average switch time for one feeder is 220s. When switching between different types of PCBs, the placement machine needs a certain preparation switching time, which is usually about 6 times the time for switching a component feeding slot, ie, 1200 s. This shows that the switching time plays a decisive role in the assembly of electronic products.

 In a multi-variety, small-batch environment, PCBs are usually grouped first, and PCBs with similar characteristics are grouped into groups. In this way, the assembly between PCBs of different varieties within the same group does not require replacement of feeders, nor does it require Switching time; but when there is a need to change feeders between two sets of PCBs, the switching time between them needs to be considered. According to this, the PCB production scheduling problem is divided into two levels: the first level of scheduling problem is called "board level" scheduling problem, that is to determine the production order of each PCB within a PCB group; the second level of scheduling problem is called For the "group level" scheduling problem, the production order between PCB organizations is determined.