Transcript Planning and Scheduling Two Worlds in One System

Planning and Scheduling
Two Worlds in One System
Roman Barták
Charles University in Prague
(Visopt B.V.)
[email protected]
http://ktiml.mff.cuni.cz/~bartak
Talk Outline
Bridging the terminology gap

Planning vs. scheduling
Bridging the technology gap

Example problems
Visopt ShopFloor System
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From modeling to solving
Integrating planning into scheduling
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Terminology gap
Do we understand each other?
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Planning and scheduling in practice
marketing planning

what is the company strategy?
long-horizon planning

what and when should be produced?
production planning

how to produce given items?
operation scheduling
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what is the exact sequencing of operations?
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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“
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Planning task at example
Final world C
C
A
B
D
B
A
Initial world
D
C
Plan
Pick(C)
Release(C,table)
Pick(B)
Release(B,D)
Pick(C)
Release(C,B)
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B
A
D
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Planning task at glance
Input:

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an initial state of the world
a description of actions changing the world
a desired state of the world
Output:
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a structure of actions
Features:
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Activities are not know in advance
No time and resources
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Scheduling task
“The scheduling task is to
allocate known activities to
available resources and time
respecting capacity, precedence
(and other) constraints“
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Scheduling task at example
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Scheduling task at glance
Input:
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a set of activities with precedences
a set of available resources
Output:
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allocation of activities to resources
Features:
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Activities are known in advance
Time and resources are restricted
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Technology gap
Can we integrate?
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Traditional „integration“
i.e. decide about necessary
activities
failure
activities
1. Do planning first
2. Do scheduling next
i.e. allocate activities to time
and resources
Actually, planning and scheduling is done separately there.
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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.
Improving the planner may help.

If existence of the activity depends on
allocation of other activities.
Foregoing planning of activities cannot be done there.
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Process-dependent activities
re-heating
heat
heat
re-heat
process
process
process
long duration
re-cycling
by-product
A
setup
B
transition
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final product
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Visopt ShopFloor
Integration in practice
www.visopt.com
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Visopt ShopFloor at glance
a generic scheduling engine beyond traditional scheduling
factory description
customer demands
(orders)
plan/schedule
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Transition scheme
scheduling resources with complex behaviour
a state transition scheme with min/max batches
produce A (3-4)
A A A B C C
produce B (1-2)
C C
produce C (2-4)
A A A
C C B A A A
batch counters
 force given state (cleaning)
after a given number of batches
load
clean
cool
heat
clean
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load
heat
unload
load
heat
unload
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cool
unload
clean
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Dependencies
batches consume and produce items
moved quantity
supplier
consumer
dependency delay
items are moved between resources
supplier-consumer dependencies
 describe relations between batches (resources)
Alternative recipes
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N-to-N relations
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Recycling
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Demands
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)
• alternative product?
quantity
• variable quantity?
• delivery delay?
delivery time
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Optimisation
What do the users need to optimise?
Always ask why does the user need a given objective!
minimise makespan
minimise number of set-ups
minimise lateness
minimise earliness
maximise resource utilisation
...
more satisfied demands
expensive set-ups
penalty for delays
storing cost
fix expenses
So what is the common objective?
MONEY
In Visopt ShopFloor we minimise cost (= maximise profit):
• income for delivered items (negative cost)
• penalty for late deliveries
• costs of production / moving / storing
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The task
Input
factory description
 resources
 dependencies
initial situation
demands
Output
plan
how to satisfy the demands?
schedule
how to realise the plan?
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Slot representation
Resource-centric model

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a resource schedule = a sequence of batches
realised via a sequence of slots (slot = space for batch)
slots can slide in time
slots cannot swap the
position
time shift
Slot variables
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describe parameters of batch to be filled in the slot
state = a batch type that can be filled
into the slot
K-1
K
state +serial
end start
times = start, end, duration
end start
duration
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K+1
serial = a position in the state
sequence
connected via constraints
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Dependencies
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
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K-1
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K
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(Pseudo) Demo
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Conclusions
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A message of the talk
Planning and scheduling are
different areas with different
solving technologies.
But they can be integrated into a
single solver!
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PLANET Information Day, May 26, 2003
Roman Barták
Planning and Scheduling
Two Worlds in One System
Roman Barták
Charles University in Prague
(Visopt B.V.)
[email protected]
http://ktiml.mff.cuni.cz/~bartak