Computeraided Equipment Selection in Assembly Line Design

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Computer-aided Equipment Selection in Assembly
Line Design

• Pierre De Lit
• CAD/CAM Department
• Université libre de Bruxelles

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What will we talk about?

• Introduction
• The PROMETHEE II method
• Selection of assembly methods
• Equipment selection
• Conclusions

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What will we talk about?

• Introduction
• The PROMETHEE II method
• Selection of assembly methods
• Equipment selection
• Conclusions

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The aim is to design hybrid assembly lines

• Different kinds of stations
• Manual
• Dedicated/Robotic

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The user can follow a quick or a detailed solving
approach
Quick solving
Detailed solving
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What will we talk about?

• Introduction
• The PROMETHEE II method
• Selection of assembly methods
• Equipment selection
• Conclusions

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PROMETHEE is a multicriteria decision-aid method

• PROMETHEE is a method
• allowing the designer to choose the best
  alternative...
• Decision-aid
• by taking different criteria of different kind
  into account
• Multicriteria

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Choosing a new car is a multicriteria problem

• Criteria
• Price (FB)
• Consumption (l/100km)
• Comfort
• Power
• ...

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According to the criterion, solutions are better
or worse
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A preference function is defined for each
criterion
Criterion Power
Ppower(a,b)
Preference threshold 20
2 20
Indifference threshold 2
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The indifference threshold should depend on
relative variations

• Example
• d f(a) - f(b) 10 CV - 5 CV 5 CV
• d f(a) - f(b) 150 CV - 145 CV 5 CV
• Influence of d should be stronger in the first
  case
• Compute the preference function with respect to
  the relative variation between the evaluations

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Intermediate evaluation functions are used for
qualitative criteria
Example comfort
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A PROMETHEE II ranking is computed for each
solution

• Multicriteria preference index p(a,b)

• Multicriteria solution flow

• PROMETHEE II complete ranking

f f - f- net flow
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The PROMETHEE II method has three main features

• Establishes a complete ranking of the different
  alternatives
• By comparing the relative difference of
  performance of all the solutions criteria by
  criteria
• By taking user preferences into account, by mean
  of criteria weights

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What will we talk about?

• Introduction
• The PROMETHEE II method
• Selection of assembly methods
• Equipment selection
• Conclusions

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Quick solving approach
Quick solving
SELEQ (Pre-selection of assembly equipment)
RP (Resource planning)
Detailed logical layout
List offunctional groups
Equipment DB
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Each operation is decomposed into three primitive
actions

• Feeding
• Picking from the storage, positionning and
  orienting before transfer
• Handling
• Transfer to final position and orientation
• Insertion
• Bringing together with other components

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Three possible methods are considered for each
sub-operation

• Manual method
• The most flexible
• Robotic method
• Partially flexible
• Dedicated or automated method
• The most specific

The solutions are ranked with PROMETHEE II
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Common criteria have been classified into four
categories

• General criteria of the line
• cycle time, payback period
• Geometrical features of each part
• dimensions, symmetry, etc.
• Non-geometrical criteria for each part
• fragility, slipperyness, hotness, etc.
• Generic criteria for the operation
• number of part variants, repetitions, etc.

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Some criteria are specific to each sub-operation

• Specific criteria for feeding
• Part is packed, risk of overlapping, etc.
• Specific criteria for handling
• presence of handling surface, need for optical
  magnification, etc.
• Specific criteria for insertion
• resistance to insertion, limited view, etc.

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The principal window presents the operations and
their modes
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The influence of an answer to one question can be
checked
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The influence of each type of criterion can be
measured
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The influence of the criteria themselves can be
approciated
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The weights can be modified and their influence
easily seen
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The operating mode evaluation influences the line
balancing
- Tc - Prec constraints
Operating modes
Preference constraints
LB
WS1
WS2
WS3
WS4
(manual)
(manual)
(dedicated)
(robotic/ dedicated)
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The line balancing influences the operating mode
evaluation
First layout
WS 2
Robotic
Second layout
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What will we talk about?

• Introduction
• The PROMETHEE method
• Selection of assembly methods
• Equipment selection
• Conclusions

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Detailed solving approach
Rough logical layout
LB (Line balancing)
Operating times
Detailed solving
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The equipment are stored in the database
according to a tree
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The aim of the equipment selection is to create
functional groups

• Functional group potential set of equipment used
  for the line design with
• cost
• time (possible to deal with masked times)
• availability
• room occupied
• Several functional groups can be created for one
  operation

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A functional group creation occurs in three steps
Select a general category
Some combinationsare not allowed (ex RMR)
Select a technical category
Parameters describe the needs - screwing torque -
riveting force - number of axes of a robot -
feeding autonomy
Select the equipment
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The equipment used is finally chosen by a
resource planner
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The equipment selection results from a compromise
(PROMETHEE)
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What will we talk about?

• Introduction
• The PROMETHEE method
• Selection of assembly methods
• Equipment selection
• Conclusions

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Let us conclude

• New method for equipment selection in three main
  stages
• Operating method selection
• Construction of functional groups
• Selection of the equipment by a resource planner
• Tool is simple to use and interactive
• Designer preferences can be set transparently
• Results are easy to trace