How Hexaly solves scheduling problems with changeover times for Ouest-France
Ouest-France is a daily French newspaper that emphasizes both local and national news. The paper is produced in 50 different editions covering many departments in the West of France. With 2.5 million daily readers, it is the most-read francophone newspaper globally. Each edition of Ouest-France includes specific pages for its region, department, and municipalities concerned by the edition. In this context, Ouest-France asked Hexaly for a consulting mission to optimize printing schedules in its plants. The underlying problem is related to production scheduling with changeover times.
Printing schedule optimization problem
Ouest-France prints 750,000 newspapers on six rotary presses on three sites every night. The optimization problem is to schedule printing editions on these presses. The printing process is constrained by the content’s finalization time, depending on the news and sports results, and by the delivery time to subscribers’ homes before 7:30 AM. Printing schedules differ every night because the setup time between two consecutive editions printed on the same machine changes. Indeed, the number of pages in each edition, the number of pages to be changed, and the characteristics of the press affect the setup time, also called “changeover time” in the production scheduling literature. We summarize the problem’s main decisions, constraints, and objectives below:
Input data
- 6 rotary printing presses, with their characteristics (printing time and speed), located on 3 geographical sites.
- 50 newspaper editions of 4 types (Ouest-France, Presse Océan, Courrier de l’Ouest, Maine Libre), resulting in 750,000 copies to be printed each evening.
Decisions
On each printing press, decide which editions are printed and in which order.
Constraints
- All editions must be printed on one rotary press.
- Some editions must be printed on a subset of rotary presses, possibly on a given press.
Objectives
- Minimize lateness of editions’ delivery: editions should arrive at the delivery site before a specific date to deliver to subscribers on time.
- Minimize the preparation time between two editions on the same press.
- Minimize the distance traveled by the editions between the printing and delivery sites.
- Balance the workload between presses: the number of editions and quantities printed and the total printing times should be similar.
Why Hexaly?
Thanks to the unique modeling features offered by Hexaly, namely list variables, Ouest-France‘s production scheduling problem was straightforward to model. Then, the state-of-the-art optimization algorithms inside Hexaly allow solving the problem in minutes of running time, despite the six objectives to optimize in lexicographic order.
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