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When Theory CrashedWhen Theory Crashedinto Realityinto Reality
Yossi RissinYossi RissinChief Executive Officer, Visopt B.VChief Executive Officer, Visopt B.V
Roman BartákRoman BartákChief Scientist, Visopt B.V.Chief Scientist, Visopt B.V.
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What is the talk about?
Planningvs.scheduling
PracticeTheory
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Planners from VenusPlanners from VenusResearchers from MarsResearchers from Mars
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A theoretical factory
O M machinesO N jobs
- each job consists of Oi operations with the precedence relation (dedicated machines for operations)
O Job Shop Scheduling (JCC)- Flow Shop Scheduling
- Open Shop Scheduling
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JSS in Practice?
„I have never seen a Job Shop Scheduling Problem in practice“
Wim Nuiten, ILOG
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The Human Factor
(Planners & plant personnel are motivated by:)O Pride. No disclosure of mistakes, problems
and weaknesses.O Position in the organisation. Position is
protected by being nice to superiors, serving many masters at once, gaining professional respect.
O Future security. No disclosure of knowledge, development of organisation dependency.
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The Human Factor
(Planners & plant personnel are characterised by:)O Politics. Internal politics and power plays
are key factor in decision taking.O Inconsistency. A human being is tend to
inconsistency and easily affected by mood, environment and psychology pressure.
O Unexpected. Human behaviour can be determined and can be foreseen just by statistical methods (big numbers, long periods, distributions, etc.)
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The Ideal Scheduling Projects
O Fully automatic factory based on robots and AGV’s- Engineering oriented- No one to argue with- No one knows better- More visibility, less surprises and fluctuations
O New factory, not operating yet- Very stable, no fluctuations- No previous “know-how”- No old rules and procedures- No bad habits- No day-to-day-reality to confront the theory
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Points Of View
O Planners- The planner’s world consists of products and their
flow- “how can I produce this product now, and this one and that
one…”- “How can I satisfy Mr. X from sales and Mr. Y from the plant
and the customer at the same time, without getting into new troubles…”
O Academy- The engineer/researcher world consists of resources
and their usage- “How can I use the resources to get max X and min Y…”- “How can I get, using objective metrics, a plan that for the
long term, will improve the plant efficiency…”
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Not Invented Here
O “We are different…”- Means, what you know is useless here
O “Outsiders cannot understand it, it takes a lot of time…”- Means, you have to listen to us or to spend part of
your life here
O “Methods that suite others cannot implemented here…”- Means, your experience and knowledge are
impressive, but you have to start from scratch
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Visopt View
O Visual Modelling Language
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Inside Visopt
O Complex resources loadload
heatheat unloadunload
cleanclean
coolcool
O General item flow
N-to-N relationsAlternative recipes Recycling
clean load heat unload load heat unload cool clean
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Quality IssuesQuality Issues
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Theoretical Objectives
O Minimise makespan
O Minimise lateness (tardiness)
O Minimise earliness
O Minimise the number of set-ups
O Maximise resource utilisation
O ...
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Quality Definition
O Quality metrics by the user/planner - “It should looks like the schedules I am doing…”- “Good plan should resemble those I use to make
manually…”- “In order to produce good plan you have to follow my
rules, know-how, procedures…”- Good plan is a one that can be ‘sold’ to production
people easily
O Most of times there are no history records of the manual plans to analyse their efficiency!
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Visopt View
O Understand the reason by asking Why!
minimise makespan
minimise lateness
minimise earliness
minimise number of set-ups
maximise resource utilisation
...
minimise makespan
minimise lateness
minimise earliness
minimise number of set-ups
maximise resource utilisation
...
more satisfied demands
penalty for delays
storing cost
expensive set-ups
fix expenses
So what is the common objective?
M O N E YM O N E Y
In Visopt we minimise costminimise cost (= maximise profitmaximise profit).
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Bridging the GapBridging the Gap
Lessons learned
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The Common Language
O The planner tells a “story” – how to produce a given product or product family, but cannot follow what was understood- Tables and fields say nothing to the planner
and not resemble his world
O Visual modelling is the key – same, simple language for the user and the computer – the ability to draw the user story
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Best Is Worse
O “The Worst Enemy Of The Good Is The Best”- A very good plan (based on objective metrics)
delivered after three hours is not relevant anymore – the factory is not the one it was few hours ago
O The art of real-life scheduling is to deliver a plan which is good enough and fast enough:- Good enough – the user cannot improve it in
reasonable time- Fast enough – depends on the plant dynamics. One
hour can be too late for one plant and very fast to another
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The Cure Is The Pain
O Most manual planning methods that are considered as “know-how” are not relevant to automated scheduling…
O What is considered as the “solid true” (Cure), is many times simplifications of reality to enable the manual scheduling (The pain)
O Extract the real knowledge from the overall know-how with the help of plant experts- Always ask Why, for everything, and never accept an
answer such as “this is the way to do it”- If there is no solid reason behind the “fact” – ignore it
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Scheduling Is Knowledge Handling
O Scheduling is not mathematics, but first of all a knowledge handling process- Capturing the real knowledge- Mapping the knowledge so the user can verify
and update it- Process it concerning its elusive nature- Understand and overcome the accurate
mathematical metrics when dealing with knowledge
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What is the real difference?
O 2 slides per hour talkO only three words are
different on these slides
O 78 slides per hour talk
Based on „real-life“ data (PACT 96)!
PractitionerPractitioner ResearcherResearcher
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Thank you!Thank you!Yossi RissinYossi [email protected]@visopt.com
Roman BartákRoman Bartá[email protected]@visopt.com
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