Multi-Site Scheduling

1. Multi-Site Scheduling Yang-Ja Jang Factory Automation Lab. 1999/10/07

2. Contents • Introduction • Multi-Site Scheduling System (MUST) • Planning and Scheduling in a multi-site environment • Conclusion

3. Introduction • Trends • PPC in a multi-site environment becomes more and more important • suppliers and customers tend to work more closely in order to avoid stockouts and unnecessary inventories • coordinated/requirements planning systems are clearly superior to uncoordinated/demand replenishment systems • Present • sequential structure of the decision process • decisions at the operational level are taken independently in each site • ability of each site to effectively achieve in due time the planned production quantities is crucial

4. Introduction - cont’d • Multi-site scheduling problem • manufacturing a product in a site may require a number of components from other sites • transportation time between sites has to be taken into account Site 1 Site 3 Site 2 Site 4 Site 5 Site 6

5. Introduction - cont’d • Some specific features of multi-site scheduling caused by the distribution of the production • complex interdependencies between production processes in different plants • temporal relations between intermediate and final products • same item can be manufactured in different plants • transport of parts between different plants needs transportation capacities • cumulative and not precise information is used on the global level

6. Introduction - cont’d • Objective of multi-site scheduling • support the distribution planning on the global level • support schedulers in distributed production plants in a coordinated way • global schedule must be translated into detailed schedules as part of the local scheduling process • early detection of capacity problems and the coordination of the scheduling activities of the production sites

7. A Multi-Site Scheduling System(MUST) Proc. Artificial Intelligence and Manufacturing, 1998 Jürgen Sauer Dept. of Computer Science, Univ. of Oldenburg, Germany

8. Introduction • On the global level, products must be distributed to plants where the intermediates have to be produced • On the local level, the intermediates have to be scheduled within the local production sites • Scheduling system must cover • predictive scheduling: the creation of a schedule of the activities over a longer period • reactive scheduling: adaptation of an existing schedule due to actual events in the scheduling environment • interactive scheduling: decisions made by human scheduler e.g. change priorities, set operations on specific schedule positions...

9. Requirements of Multi-Site Scheduling • In global scheduling generalized data are used instead of precise data • Local scheduling systems for individual plants that accomplish the local realization of global requirements should be integrated • Coordination of decentralized scheduling activities for all plants within one enterprise is necessary • The uncertainty about the actual “situation” in individual plants has to be regarded • Different goals have to be regarded on the different levels

10. Multi-Site Scheduling Hierarchy Logistics Dept. Global Scheduling System G1 G2 G3 G4 G5 Global Level Events orders 1 2 3 4 5 6 Events Schedules Events Schedules Local Scheduling System Local Scheduling System M1 M2 M3 M4 M5 M1 M2 M3 M4 M5 Local Level 1 2 3 4 5 6 1 2 3 4 5 6 Events Schedules Events Schedules Shop-Floor Data Collection Shop-Floor Data Collection

11. Multi-Site Scheduling Hierarchy • Global scheduler • Solution of the global scheduling problem should be as robust as possible i.e. it should give enough flexibility for a local scheduler to react to local disturbances without affecting the other sites • uses buffer times for local production • tries to optimize load balancing on the machine groups • preserves as much as possible of the existing global schedule in order to minimize the subsequent effort on the local level • Local scheduler • Goals of local schedulers such as optimizing machine utilization, set-up times and meeting due dates of intermediates are often in contrast to each other • handles possible disturbances caused by unexpected events

12. Components of MUST • Global predictive scheduling • generates global level schedule with an initial distribution of internal orders to local production sites • Global reactive scheduling • If problems cannot be solved on the local level or the modified local schedule influences other local schedules, it redistributes internal orders to local plants and adapt the global schedule • Local predictive scheduling • draws up detailed local production schedules based on the global schedule • Local reactive scheduling • tries to remedy local disturbances locally by interactive repair

13. Components of MUST • Communication and coordination • global to local • global schedule consisting information on internal orders, affiliated intermediate product, machine groups to use, time windows that must be met, and required quantities of intermediate products • unexpected events that effect the local level • local to global • local realization of the global requirements with information on internal orders • appearance of failure events • suggestions for possible local rescheduling

14. MUST Architecture Global Scheduling System User Interface Communication with Logistics Dept. Global Interactive Scheduling Global Predictive Scheduling Global Reactive Scheduling Database Communication with Sites Local Scheduling System Local Scheduling System ••• User Interface Communication User Interface Communication Local Interactive Scheduling Local Interactive Scheduling Local Predictive Scheduling Local Reactive Scheduling Local Predictive Scheduling Local Reactive Scheduling Local Database Plant 1 Shop Floor Data Collection Local Database Plant N Shop Floor Data Collection

15. Problem Definition R: resources P: products O: actual orders HC: hard constraints SC: soft constraints

16. Solution Approaches

17. Communication Global Blackboard (logistics->global) -events new_order, cancel_order, change_order change_Mgr (local->global) -events breakdown(Mgrp) -confirm (local realization) (global->local) -global schedule -events new_order, cancel_order change_order (shop floor->local) -events breakdown, delay -confirm (shop floor realization) Local Blackboard n

18. Conclusion • Multi-site scheduling system must support all the scheduling and coordination tasks of a distributed production environment • Scheduling subsystems must provide user with interactive as well as predictive and reactive scheduling and with communication facilities for data exchange

19. Planning and Scheduling in a multi-site environment PP&C, Vol. 10, No. 1, 19-28 W. Roux*, S. Dauzere-Peres** and J. B. Lasserre* *LAAS, France **Ecole des Mines de Nantes, France

20. Introduction • In multi-site production environment, sequential structure of the PPC frustrates production planners, schedulers and operators • When not sufficient capacity • Rescheduling one job in a work center often merely shifts the capacity problem to another site • Overtime and extra shifts may not be the most cost-effective solution to the problem • Capacity planning should provide feedback to lot-sizing steps • lot sizing scheduling

21. Notation and Definition

22. Notation and Definition

23. Planning Model

24. Notation from the scheduling level

25. Capacity constraints of scheduling level

26. Integrated Model

27. Methodology • Two-level decomposition Planning Module Sequence Site 1 Production Plan Site 2 Site s Scheduling Module

28. Local Search Technique in Scheduling • Find an initial solution • Repeat the following until max iterations without improvement on the makespan • Explore the neighborhood to find the best non-tabu move • Make the move • Compute the makespan of the new solution • Update the tabu list • Restore the best solution and stop

29. Parallel Computing for Scheduling • LANDA (Local Area Network for Distributed Application) • LANDA uses an ethernet network of workstations as a parallel virtual machine • Evaluation of Speedup

30. Computational experiments • Data: SITE 1 (final site) SITE 2 SITE 2 SITE 2 SITE 2

31. Computational experiments • Cost • Time

32. Conclusion • Multi-site scheduling system must take the complex interdependencies between different production sites into account • Exact scheduling constraints are incorporated into the model so as to achieve at least one feasible schedule • Parallel computing yields significant computational savings and permits to solve of large size problems

33. Further Research • Research has to be done on other communication possibilities, e.g. based on protocols like contract nets, on a multi-agent realization of the system, on object-oriented techniques and on a design support system • Various industry scenarios have to be testified and validated in multi-site environment

34. References • Sauer, J.: "Knowledge-Based Scheduling Techniques in Industry", in: Jain, L.C., Johnson, R.P., Takefuji, Y., Zadeh, L.A.(Eds.): Knowledge-Based Intelligent Techniques in Industry, S. 53 - 84, 1999. • Sauer, J.: "A Multi-Site Scheduling System", in: AAAI's Special Interest Group in Manufacturing Workshop on Artificial Intelligence and Manufacturing: State of the Art and State of Practice, Albuquerque, S. 161 - 168, AAAI Press, Menlo Park, 1998. • Sauer, J.: "Knowledge-Based Systems Techniques and Applications in Scheduling", to appear in: Leondes, T.L. (Ed.): Knowledge-Based Systems Techniques and Applications, Academic Press, San Diego, 1999. • Sauer, J., Suelmann, G., Appelrath, H.-J.: "Multi-Site Scheduling with Fuzzy Concepts", in: International Journal of Approximate Reasoning IJAR, 19 (1998), S. 145-160, Elsevier Science, 1998 • W. Roux, S. Dauzere-Peres and J. B. Lasserre: “Planning and scheduling in a multi-site environment”, Production Planning and Control, Vol. 10, No. 1, 19-28, 1999