For printing machines setup times account for a significant portion of the overall production time. They depend heavily on the sequence of jobs. In cooperation with Herlitz PBS AG we have developed a detailed model of the setup process. Based on this model a code has been developed that solves their scheduling problem: Given several non identical machines and a set of jobs, find an optimal assignment of the jobs to the machines and a sequence on each machine so that the last job is completed as early as possible. Current work concentrates on evaluating the code at Herlitz and extending it for further applications.
At Herlitz PBS AG, Berlin, gift wrap has to be printed on two non-identical printing machines. The gift wrap is printed in up to six colors on various kinds of materials in various widths. The colors may differ considerably from one gift wrap to the next. The machines differ in speed and capabilities, not all jobs can be processed on both machines. Setup times for the machines are quite large in comparison to printing time. They depend strongly on whether material, width, or colors have to be changed, so in particular on the sequence of the jobs.
