Planning and Scheduling Two Worlds in One System Roman Barták Charles University in Prague (Visopt B.V.)

Roman Barták 2PLANET Information Day, May 26, 2003 Talk Outline Bridging the terminology gap Planning vs. scheduling Planning vs. scheduling Bridging the technology gap Example problems Example problems Visopt ShopFloor System From modeling to solving From modeling to solving Integrating planning into scheduling Integrating planning into scheduling

Roman Barták 3PLANET Information Day, May 26, 2003 Terminology gap Do we understand each other?

Roman Barták 4PLANET Information Day, May 26, 2003 Planning and scheduling in practice marketing planning what is the company strategy? what is the company strategy? long-horizon planning what and when should be produced? what and when should be produced? production planning how to produce given items? how to produce given items? operation scheduling what is the exact sequencing of operations? what is the exact sequencing of operations?

Roman Barták 5PLANET Information Day, May 26, 2003 Planning task “The planning task is to find out a sequence of actions that will transfer the initial state of the world into a state where the desired goal is satisfied“

Roman Barták 6PLANET Information Day, May 26, 2003 Planning task at example A B C D A D Plan Pick(C) Release(C,table) Pick(B) Release(B,D) Pick(C) Release(C,B) B C Initial world A D B C Final world

Roman Barták 7PLANET Information Day, May 26, 2003 Planning task at glance Input: an initial state of the world an initial state of the world a description of actions changing the world a description of actions changing the world a desired state of the world a desired state of the worldOutput: a structure of actions a structure of actionsFeatures: Activities are not know in advance Activities are not know in advance No time and resources No time and resources

Roman Barták 8PLANET Information Day, May 26, 2003 Scheduling task “The scheduling task is to allocate known activities to available resources and time respecting capacity, precedence (and other) constraints“

Roman Barták 9PLANET Information Day, May 26, 2003 Scheduling task at example

Roman Barták 10PLANET Information Day, May 26, 2003 Scheduling task at glance Input: a set of activities with precedences a set of activities with precedences a set of available resources a set of available resourcesOutput: allocation of activities to resources allocation of activities to resourcesFeatures: Activities are known in advance Activities are known in advance Time and resources are restricted Time and resources are restricted

Roman Barták 11PLANET Information Day, May 26, 2003 Technology gap Can we integrate?

Roman Barták 12PLANET Information Day, May 26, 2003 Traditional „integration“ 1.Do planning first i.e. decide about necessary activities 2.Do scheduling next i.e. allocate activities to time and resources activities failure Actually, planning and scheduling is done separately there.

Roman Barták 13PLANET Information Day, May 26, 2003 Do we need to integrate more? Sometimes more tighten integration of planning and scheduling is necessary. When? If there are too frequent backtracks from scheduling to planning. If there are too frequent backtracks from scheduling to planning. Improving the planner may help. If existence of the activity depends on allocation of other activities. If existence of the activity depends on allocation of other activities. Foregoing planning of activities cannot be done there.

Roman Barták 14PLANET Information Day, May 26, 2003 Process-dependent activities re-heatingre-cycling AB setup by-product transition final product heat process heat process process long duration re-heat

Roman Barták 15PLANET Information Day, May 26, 2003 Visopt ShopFloor Integration in practice

Roman Barták 16PLANET Information Day, May 26, 2003 factory description Visopt ShopFloor at glance customer demands (orders) plan/schedule a generic scheduling engine beyond traditional scheduling

Roman Barták 17PLANET Information Day, May 26, 2003 Transition scheme scheduling resources with complex behaviour a state transition scheme with min/max batches batch counters force given state (cleaning) after a given number of batches force given state (cleaning) after a given number of batches AAABCC CCAAA CCBAAA load heat unload clean cool clean produce A (3-4) produce B (1-2) produce C (2-4) loadheatunloadloadheatunloadcoolclean

Roman Barták 18PLANET Information Day, May 26, 2003Dependencies batches consume and produce items dependency delay moved quantity items are moved between resources supplier consumer supplier-consumer dependencies describe relations between batches (resources) describe relations between batches (resources) N-to-N relations Alternative recipes Recycling

Roman Barták 19PLANET Information Day, May 26, 2003Demands Production in the factory must be evoked somehow! This is realised via external demands. In Visopt ShopFloor the demands are described as orders of items: item (product) quantity delivery time alternative product? variable quantity? delivery delay?

Roman Barták 20PLANET Information Day, May 26, 2003Optimisation What do the users need to optimise? minimise makespan minimise number of set-ups minimise lateness minimise earliness maximise resource utilisation... minimise makespan minimise number of set-ups minimise lateness minimise earliness maximise resource utilisation... So what is the common objective? more satisfied demands expensive set-ups penalty for delays storing cost fix expenses Always ask why does the user need a given objective! minimise costmaximise profit In Visopt ShopFloor we minimise cost (= maximise profit): income for delivered items (negative cost) penalty for late deliveries costs of production / moving / storing M O N E Y

Roman Barták 21PLANET Information Day, May 26, 2003 The task Input factory description resources resources dependencies dependencies initial situation demandsOutput plan how to satisfy the demands? schedule how to realise the plan?

Roman Barták 22PLANET Information Day, May 26, 2003endstart K-1 K K+1 Slot representation Resource-centric model a resource schedule = a sequence of batches a resource schedule = a sequence of batches realised via a sequence of slots (slot = space for batch) realised via a sequence of slots (slot = space for batch) time shift Slot variables describe parameters of batch to be filled in the slot describe parameters of batch to be filled in the slot slots can slide in time slots cannot swap the position state state state =a batch type that can be filled into the slot startend duration serial serial =a position in the state sequence times times =start, end, duration connected via constraints +serial

Roman Barták 23PLANET Information Day, May 26, 2003Dependencies When the batch is known (located to a slot), ask for missing suppliers/consumers! Dependency generator (realisation of a simple planner)  Scheduling = deciding about batches in slots Using information about dependencies in the batch K-1 K-1K

Roman Barták 24PLANET Information Day, May 26, 2003 (Pseudo) Demo

Roman Barták 25PLANET Information Day, May 26, 2003 Conclusions

Roman Barták 26PLANET Information Day, May 26, 2003 A message of the talk Planning and scheduling are different areas with different solving technologies. But they can be integrated into a single solver!

Planning and Scheduling Two Worlds in One System Roman Barták Charles University in Prague (Visopt B.V.)