Title: CHAPTER SIX
1CHAPTER SIX
- Computational Facility Layout
2The Facility Layout Problem
- Given the activity relationship as well as the
space of the department, how to construct plan
the layout of the facility - The basis of the layout planning is the closeness
ratings or material flow intensities - minimize the flow times distance
- Maximize the closeness (adjacency)
- For most practical real world instances, the
computational complexity has results in various
heuristics - What is heuristic?
- Construction Heuristic
- Improvement Heuristic
3Heuristic and Optimality
- Consider the knapsack problem
- Z max 5 x1 7 x2 11 x3 12 x4 17 x5
- Subject to 2 x1 3 x2 4 x3 5 x4 7
x5 lt 10 - Heuristic An intuitive problem solving
method/procedure - Constructive
- Heuristic 1, Pick sequentially the ones with the
best benefit - Heuristic 2, Pick sequentially the ones with the
best benefit per unit - Greedy Improvement
- Exchange two items in a solution
- Meta-Heuristic Simulated Annealing, Genetic
Algorithm - Optimal Solution
- Mathematical Programming and Optimization
- Linear Programming, Integer Programming,
Nonlinear Programming
4A Simple Facility Layout Problem
- Suppose we have 10 identical sized departments
and the flow intensity between these 10
department is fij - Find the best arrangement of the 10 department
along an aisle so that the total travel (flow
intensity times distance) is minimized - A Quadratic Assignment Model is necessary to
Optimally solve the problem
1 2 3 4 5 6 7 8 9 10
Position
Department
5A Quadratic Assignment Model
- Decision Variables
- X(i,j) -- 1 Department I will be located at
position j - 0 Otherwise
- Constraints
- Each one position can hold exactly one department
- SUM( i in 110) x(i,j) 1
- Each department has to be assigned exactly one
position - SUM( j in 110) x(i,j) 1
- Objective
- SUM(I, j, m, n, all in 1..10 ) x(i,j)
x(m,n)f(i,m)d(j,n) - This is an integer quadratic assignment problem.
6Pair-Wise Exchange Heuristic
From\To 1 2 3 4
1 -- 10 15 20
2 -- 10 5
3 -- 5
4 --
- Phase I Construct Phase Initial Solution
(1,2,3,4) - Phase II Improvement Pair Wise Exchange
- a) Exchange two departments
- b) If results in better solution, accept go to
a) - otherwise stop
7Pair Wise Exchange Heuristic
8Pair Wise Exchange Heuristic
9Pair Wise Exchange Heuristic
10Pair Wise Exchange Heuristic
11Pair-Wise Exchange Heuristic
- Limitations
- No guarantee of optimality,
- The final solution depends on the initial layout
- Leads to suboptimal solution
- Does not consider size and shape of departments
- Additional work has to be re-arrange the
department if shaper are not equal
12Graph Based Method
- Graph based method dates back to the later 1960s
and early 1970s. - The method starts with an adjacency relationship
chart - Then, we assign weight to the adjacency
relationships between departments - A graph, called adjacency graph is constructed
- Node to represent department
- Arc to represent adjacency, weight on arc
represents the adjacency score - Goal To find a graph with maximum sum of arc
weights - However, not all the adjacency relations can be
implemented in such a graph, that is the graph
may not be planar.
13A Planar Graph
- Planar graph A graph is a planar if it can be
drawn so that each edge intersects no other edges
and passes through no other vertices - Intuitively, a planar graph is a graph where
there is no intersection of arcs (flow of
material) - To find a maximum weight planar graph
14Procedure to Find Maximum Weight Adjacent Planar
Graph
- Step 1 Select a department pair with largest
weight - Step 2 Select a third department based on the
sum of the weights with the two departments
selected. - Step 3 Select next unselected department to
enter by evaluating the sum of weights and place
the department on the face of the graph. - Here, a face of a graph is a bounded region of a
graph - Step 4 Continuing the Step 3 until all
departments are selected - Step 5 Construct a block layout from the planar
graph
15From Graph to Block Design
- Let us blow air into each node in the planar
graph - Nodes explode
- Interior faces becomes a dot
- The edge in primal graph becomes the boundary
between departments - Dual Graph
- Nodes in dual ? faces in primal
- Edge in dual if two faces connects in the
primal graph - The faces in dual represents the department
- Draw Block Design
16Limitation of Graph Based Method
- Limitations
- The adjacency score does not account for
distance, nor does it account for distance other
than adjacent department - Although size is considered in this method, the
specific dimension is not, the length between
adjacent departments are also not considered. - We are attempting to construct graphs, called
planar graphs, whose arcs do not intersect. - The final layout is very sensitive to the
assignment of weights in the relationship chart.
17Graph-based Method
18Graph-based Method
19Graph-based Method
20Graph-based Method
21Graph-based Method
22Graph-based Method
23Computer Relative Allocation of Facility
Techniques (CRAFT)
- Discrete or Continuous Representation
- Discrete Representation
- A two-dimension array with numbers
- Each cell represents a unit area numbers
represent the department occupied the cell
24A Sample Problem
25Valid Discrete Representation
- Valid Representation
- Contiguous If an activity is represented by more
than one unit, every unit of the must share at
least one edge with at least one other unit - Connectedness The perimeter of an activity must
be a single closed loop - No Enclosed Void No activity shape shall contain
an enclosed void
3
3 3
3 3
3 3
3
3 3
3 3 3
3 3
3 3 3
26Computer Relative Allocation of Facility
Techniques -- CRAFT (1963)
- Algorithm
- 1) Any Incumbent Layout
- Describe a tentative layout in blocks
- Determine centroids of each department
- Cost S distance (in the from-to matrix) X
unit cost - Distance can be Euclidian or Rectilinear
- 2) Improvement make pair wise or three way
exchanges - equal area only
- adjacent (generally)
- 3) If better solution exists Choose the best, go
to 1) - Otherwise Stop
27CRAFT
28CRAFT
29CRAFT
30CRAFT
31CRAFT
32CRAFT
- In the original design, exchange has to be
departments of equal area or adjacent
departments.
33Shape Consideration
- Shape Consideration
- Shaper Ratio Rule The ratio of a feasible shape
should be with specified limits - Corner Counter The number of corners for a
feasible shaper may not exceed specified maximum
34Excel Add-ins for facility Planning
- The Excel Add-In
- Written by Prof. Paul Jensen (UT-Austin)
- Contains an implementation of CRAFT and can be
downloaded at - http//www.me.utexas.edu/jensen/ORMM/frontpage/je
nsen.lib/index_omie.htmlormm - Sequence
- Create a Plant
- Define the Facility
- Optimum Sequence
- Craft Method
- Fixed Point
- Optimize
35Mixed Integer Program
- The work begins latterly in the 1990s by
Montreuil - The departments are assumed to be rectangular
within a rectangular plant. - Plant
- Length Bx, Width By
- Shape consideration
- Area,
- The (minimum, maximum) width of a department
- The (minimum, maximum) length of a department
- Decisions Where to put the Departments
(Centroid) and the shape (length,width) of the
department - Objective flow_intensity cost distance
36MIP(Mixed Integer Program)
37MIP(Mixed Integer Program )
38MIP model setup
39MIP model setup II
- Constraint (6.13) ensures the upper corner of j
is less than the lower corner of i if z_ij(x) 1
. i.e., to the east of i. Note if z_ij(x) 0,
(6.13) is redundant.
- Constraint (6.14) ensures to the north-south
relationship
- Constraint (6.15) ensures that no two
departments overlap by forcing a separation at
least in the east-west or north-south direction.
40MIP Models
- Benefit of MIP Model
- Department shapes as well as their area can be
modeled through individually specified lower and
upper limits !!! - It might be able to control length-width ratio as
well - (xi xi ) lt R (yi-yi) or
- (yi yi ) lt R (xi-xi)
- Heuristically, we can combine CRAFT with MIP.
- Get a initial layout using CRAFT, use MIP to find
the best rectangular layout design - Solving the problem exactly (optimal solution) is
hard - 810 are the typical size solvable in a
reasonable amount of time
41Commercial Facility Layout Packages
- In the Instructors Opinion, there is no
commercial package that will suit all the needs,
partly due to the difficult of the problem, but
more due to the fact that Facility Layout is a
combination of Science and Art. - There has been a trend to combine optimization
techniques with interactive graphic procedures,
especially people have an unique pattern
reorganization capability than computers. - We encourage the reader to use the web to keep
abreast of new developments, resort to
professional publications, which periodically
publish survey of software packages for
facilities planning, and new techniques
42References
- Literature Presentation topics
- General Survey
- Meller, R.D. and K. Gau, The Facility Layout
Problem Recent and Emerging Trends and
Perspective, Journal of Manufacturing Systems,
155, 351-366,1996 - Kusiak, A. and S. S. Heragu, The Facility Layout
Problem, European Journal of Operational
Research, v29, 229-251, 1987 - Mixed Integer Programming
- Montreuil, B., A Modeling Framework for
Integrating Layout Design and Flow Network
Design, Proceedings of the Material Handling
Research Colloquium, Hebron, KY, 1990 - Assignment Problem and the Location of Economic
Activities, Econometrica,
43Reference
- Reference (Continue)
- Graph Based Approach
- Hassan, M. M. D and G. L. Hogg, On Constructing
a Block Layout by Graph Theory, International
Journal of production Research, 296, 1263-1278,
1991 - Irvine, S. A. and I. R. Melchert, A New Approach
to the Block Layout Problem, International
Journal of Production Research, 358, 2359-2376,
1997 - Computerized Layout Design
- Bozer, Y.A., R.D. Meller and S.J. Erlebacher, An
Improvement Type Layout Algorithm for Single and
Multiple Floor Facilities, Management Science,
407, 451-467 1994 - Tate, D.M. and A. E. Smith, Unequal Area
Facility Layout Using Genetic Search, IIE
Transactions, 274, 465-472, 1995 - Your Contribution In The Future !!
44Assignments
- Using Excel Add-ins as well as graph based method
to solve the following problems - 6.8, 6.9, 6.10, 6.11 6.14, 6.15, 6.19, 6.20
- Compare the results and see if they make sense or
not. - Work in group, select one of the papers and
present it in class at the end of the quarter.
45Thanks
46BLOCPLAN
- Set up all departments in bands (2or3)
- Continuous areas not blocks
- Use From to or a relationship chart
- Uses two way exchanges
47BLOCPLAN
48BLOCPLAN
49BLOCPLAN
50MIP(Mixed Integer Program)
- Generally a construction type model
- Requires some knowledge of linear and integer
programming - Solutions to these types of problems are
difficult - We will examine the general formulation
51LOGIC
- Layout Optimization with Guillotine Induced Cuts
- Slice the area to partition the plant between
departments - Supersedes BLOCPLAN, because all BLOCPLANS are
LOGIC plans - Improved by pair wise exchange or simulated
annealing
52LOGIC
53LOGIC
54LOGIC
55LOGIC
56LOGIC
57LOGIC
58LOGIC