industrial applications of constraint based scheduling helmut simonis parc technologies ltd ic-parc,...

Industrial Applications of Constraint Based Scheduling

Industrial Applications of Constraint Based Scheduling

Helmut SimonisParc Technologies Ltd

IC-Parc, Imperial College London

Helmut SimonisParc Technologies Ltd

IC-Parc, Imperial College London

Based on joint work withY. Cloner, A. Aggoun (COSYTEC)

© 2003 Parc Technologies © 2003 Parc Technologies LimitedLimited

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Overview

• Global constraints• Scheduling with global constraints• Brief history• Operational examples


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Constraint Programming - in a nutshellConstraint Programming - in a nutshell

• Declarative description of problems with– Variables which range over (finite) sets of values– Constraints over subsets of variables which restrict possible value

combinations– A solution is a value assignment which satisfies all constraints

• Constraint propagation/reasoning– Removing inconsistent values for variables– Detect failure if constraint can not be satisfied– Interaction of constraints via shared variables– Incomplete

• Search– User controlled assignment of values to variables– Each step triggers constraint propagation


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Need for global constraintsNeed for global constraints

Y in {2,3}

Z in {1,3}

U in {1,2,3,4}

X in {2,3}

Y

X

Z

U

1

2

3

4

local reasoning, no action global reasoning, detect implications by bi-partite matching


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Global constraints

• Work on sets of variables– Global conditions, not local constraints

• Semantic methods– Operations Research– Spatial algorithms– Graph theory– Network flows

• Building blocks (high-level constraint primitives)– Multi-purpose– As general as possible– Usable with other constraints– Very strong propagation – Acceptable algorithmic complexity


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Temporal RelationsTemporal Relations

• Some task must start after others have finished

• Easy to model with inequality constraints

• Much better reasoning possible when considered together with resource constraints precedence constraint


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Cumulative (Disjunctive) ResourcesCumulative (Disjunctive) Resources

End

Limit

start

duration

resource

time

resource

Cumulative constraint


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Machine Choice (Speed)Machine Choice (Speed)

M1

M2

M3

M4

M5

M6

time

machine

start

machineduration 1

Diffn (2D)


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Machine CalendarsMachine Calendars

M1

M2

M3

M4

M5

M6

time

machine

start

machineduration 1

Diffn (2D) with calendar rules

Interruptions

non-interruptible task


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Consumable ResourcesConsumable Resources

Storage

Max capacity

Min capacity


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Storage AssignmentStorage Assignment

produce

store

consume

Diffn (2D)


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Storage Assignment with CapacityStorage Assignment with Capacity

produce

store

consume

Diffn (3D)


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Sequence Dependent SetupSequence Dependent Setup

cycle with distance matrix

forbidden sequence

variable time


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Brief history of CP-based schedulingBrief history of CP-based scheduling• Alice (Lauriere), 1978• CHIP (Dincbas, Van Hentenryck, Simonis), 1987• First commercial CP scheduling application (HIT, ICL),

1989• Cumulative resources (Aggoun, Beldiceanu), 1993• Disjunctive resources (Nuijten, Caseau, LePape), 1994• Machine choices (Beldiceanu, Contejean), 1994• Sequence dependent setup (Beldiceanu, Contejean),

1994• Alldifferent (Regin), 1994• Pre-emptive scheduling constraint (Baptiste, LePape),

1998• LP/CP hybrids (Wallace, Rodosek, El Sakkout), 1998


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PLANE (Dassault)PLANE (Dassault)

• Assembly line scheduling– developed by Dassault Aviation for Mirage 2000 Jet/ Falcon

business jet

• Two user system– production planning 3-5 years– commercial what-if sales aid

• Optimization– requirement to balance schedule– minimize changes in production rate– minimize storage costs

• Benefits and status– replaces 2 week manual planning– operational since Apr 94– now used in US for business jets


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FORWARD (TECHNIP, COSYTEC)FORWARD (TECHNIP, COSYTEC)

• Oil refinery production scheduling– Incorporates ELF FORWARD LP tool

• Schedules daily production– Crude arrival -> processing -> delivery– Design, optimize and simulate

• Crude mix optimization– Ship unloading, storage – Pipeline transport

• Product blending– Explanation facilities– Handling of over-constrained problems

• Status– Operational at FINA, ISAB, BP,…


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ORDO-VAP (VCA, COSYTEC)ORDO-VAP (VCA, COSYTEC)

• Production scheduling for glass factory– integrated with Ingres Information system– manual and automatic scheduling

• Constraints– multi-stage manufacturing– consumer/producer– varying production rates, setup– balance manpower utilization– minimize downtime

• Status– 2 phases– operational since March 96– replaced manual operation


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MOSES (Dalgety, COSYTEC)MOSES (Dalgety, COSYTEC)

• Production scheduling for animal feed production– Feed in different sizes/ for different species– Contamination human health risk– Strict regulations imposed by customers

• Constraints– Avoid contamination risks– Machine setup times– Machine choice (quality/speed)– Limited storage of finished products– Very short lead times (8-48 hours)– Factory structure given as data

• Status– operational since Nov 96– installed in 5 mills


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Bandwidth on demand (Schlumberger, IC-Parc, PTL)Bandwidth on demand (Schlumberger, IC-Parc, PTL)

• Provide on-demand, high QoS bandwidth for limited time period

• Use cases– Well logging– Video conference

• Runs on MPLS-TE, diffserv• Temporal extension of general routing

problem– Hard QoS limits– Overall bandwidth limits– Uses hybrid (CP/MIP/local search) algorithm

• Delivered on Schlumberger’s Dexa.net– Self-provisioned by customer


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ConclusionConclusion

• Constraints are a mature technology for scheduling

• Easy to combine different constraints in one system, flexible for modeling complex systems

• Most useful for hard problems, medium size (hundreds of tasks, dozens of resources)

• Large variety of solutions in different application fields using commercial, off-the-shelf tools

industrial applications of constraint based scheduling helmut simonis parc technologies ltd ic-parc,...

Documents

parc technologies limited

d slide

capacity slide

inequality constraints

interaction of constraints

global constraints work

global constraints y

aggoun cosytec slide