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Facilities Planning
Lecture 7-8:
Layout Planning
Algorithmic Approaches
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Quadratic Assignment
Problem
Departments are to be assigned topredetermined locations (sites) in the floorplan.
Each department is treated as a unit square,so that any department can be assigned toany site.
This is a quadratic assignment problem,since the cost of assigning a department toa particular location depends on the
locations of the other departments.
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...
Mathematical Formulation
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Quadratic Assignment
Problem
Optimal solution procedures aredifficult to solve for realistic sizeproblems. Therefore, two types of
heuristic procedures are considered.
Construction Procedure
Improvement Procedures
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Evaluation of Facility Designs
Which layout is best?
Is layout A better than Layout B?
Several Common Methods for Block Layouts
Distance Based Scoring
Requires flow and distance
Adjacency Based Scoring
Requires subjective AEIOU relationships
Multi-Objective Scoring
Many methods available
Weighted factor scoring
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Distance Based Scoring
Volume-Distance product
Distance usually measured rectilinearly, between centroids
Assumes that the material flow system has already beenspecified
Assumes that the variable flow cost is proportional to distance
Distance often depends on the aisle layout and material handlingequipment
Can also add a cost term ($/dx) to convert to $
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How should you measure
distance?
Most common is rectilinear distancebetween centroids
d(X, P) = |x - a| + |y - b|
Absolute difference in x direction PLUS absolutedifference in y direction
P = (a, b)
X = (x, y)
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Finding Centroids (x*, y*)
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Fun with Centroids!
Centroid-to-centroid distances can beminimized easily, but may produceunrealistic facilities!
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Layout Evaluation: Distance-
based scoring Example
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Example Each dept. is 100 x 100
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Can you find a better
arrangement?
Keep same department and facilityshapes.
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Adjacency-Based Scoring
Score arbitrarily-definedif areas are adjacent
Requires definition of adjacent
Share a common border
Centroids within certain distance
Can penalize if X relationship areas are adjacent
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Example - Revisited
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Multi-Objective (weighted
Factor) Scoring
Useful in group evaluation situations
Must decide on weights
While totally subjective, allows for faircomparisons
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Algorithmic Approaches
SLP is informal
Does not provide a formal procedure or algorithmfor critical steps.
Algorithm: a precise rule (or set of rules) specifying
how to solve some problem
Has an objective function
Amenable to computer implementation
Types of input
Qualitative flow data (i.e. relationship chart)
Quantitative data (i.e. from-to chart, flow-between)
Both
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Algorithmic Approaches:
Classification of algorithms
Based on objectivefunction
Distance based
Adjacency based
Format of layoutrepresentation
Discrete representation
Continuous representation
Primary function
Improvement
Construction
Algorithms mustaddress two issues:
The order ofplacement of
departments in therelationship diagram(or unit block plan)
The relative
locations of thedepartments
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Classification of algorithms
Based on objective function
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Distance-based Algorithms:
Objective function
Minimizeflow * distance
Called a distance-based objective
Distance is measured rectilinearly from the department centroid
Input is a from-to chart
fij= amount of flow (or, number of trips or unit loads) betweendepartments i and j
cij= cost of moving a unit load between departments i and j
d
ij
= distance between departments i and j
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Adjacency-based Algorithms:
Objective function
Maximizeadjacency
Input is an activity relationship chart
Sum of all adjacent relationship values
Easy to use and intuitive
But disregards distance between non-adjacent departments
Means you can generate layouts with similar scores but vastlydifferent travel distances
otherwise
adjacentarejandisdepartmentifxij
,0,1
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Adjacency-based Algorithms ...
Normalized adjacency score
Or
Efficiency Rating
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Classification of algorithms
Based on format of layoutrepresentation
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Layout Representation Format
Discrete
The area of each department is rounded off to the nearestinteger number of grids.
A smaller grid size yields a finer resolution and gives moreflexibility in department shapes, but
Results in a larger number of grids which complicatescomputations. Why?
Continuous
Does not use a grid
More flexible but more difficult to use
Usually limited to rectangular building and departments
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Graphical Representation
Points and lines representation is notconvenient for analysis
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Graphical Representation
(cont.)
Most procedures employ a unit areasquare representation as an approximation
Space available and space required for eachactivity are expressed as an integer multiple of
the unit area.
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Graphical Representation
(cont.)
Unit Square Area approximation can also berepresented by a two dimensional array ormatrix of numbers
Easy to manipulate (e.g., determine adjacency)but difficult to visually interpret
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Examples of Split and Unsplit
departments
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Factory CAD/Flow/Plan
AutoCAD based add-on
Has multiple applications
CAD: drawing templates
FLOW: evaluation of material flow; manual SLPtype manipulation
PLAN: layout alternative generation
FactoryPLAN
Uses Spiral-type algorithm to generatealternative layout options
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Graphical Representation
FactoryCAD
Overlay to
AutoCAD
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Classification of algorithms
Based on Primary function:
Improvement based
Construction based
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Classification of Algorithms:
Primary functions
Improvement-based
Start with an initial layout and try to improve it throughincremental changes
Example
Pair-wise exchange
CRAFT (Computerized Relative Allocation of FacilitiesTechnique)
Construction-based
Develop from scratch' and progressively build layout
Example
ALDEP (Automated Layout Design Program)
CORELAP (Computerized Relationship Layout Planning)
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Improvement-based:
Pairwise Exchange Method (i)
Compute the total cost of existing layout based on
initial from-to chart and distance matrix (c = f *d)
Exchange two departments
Recompute the total cost
Consider all pairwise interchanges and evaluate thecost of each
Perform the one that yields the greatest reduction intotal cost
Continue until no further improvement is obtained
Not guaranteed to find the optimal solution but willbe locally optimal.
The method assumes departments areas are equal
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Improvement-based:
Pairwise Exchange Method (ii)
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Improvement-based:
Pairwise Exchange Method (iii)
TCABCD = 5(15)+8(35)+10(50)+5(20)+3(35)+2(15)=1090
TCBACD = 5(15)+8(20)+10(35)+5(35)+3(50)+2(15)=940
TCCBAD = 5(20)+8(35)+10(15)+5(15)+3(35)+2(50)=810
TCDBCA= 5(35)+8(15)+10(50)+5(20)+3(15)+2(35)=1010
TCACBD = 5(35)+8(15)+10(50)+5(20)+3(15)+2(35)=1010
TCADCB= 5(50)+8(35)+10(15)+5(15)+3(35)+2(20)=900
TCABDC= 5(15)+8(50)+10(35)+5(35)+3(20)+2(15)=1090
C-B-A-D
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Improvement-based:
Pairwise Exchange Method (iv)
Remarks:
Not guaranteed to yield the optimal layout(heuristic)
It is possible to cycle back
Symmetric layout arrangements are possible
Only considers departments with equal sizes
(different size -> CRAFT)
BE CAREFUL! on constructing from-to chart
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Improvement Algorithms
Too many degrees of freedom to devise a good
method for modifying the block plan.
Most all improvement algorithms limit the kinds ofchanges that are permitted.
Basic procedure
CHOOSE a pair (or triple) of activities
ESTIMATE the effect of exchanging them
EXCHANGE if the effect is to reduce the total cost
CHECK to be sure the new layout is better
Repeat Until no more improvements are possible.
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Improvement Algorithms
To CHOOSE a pair of activities
Activities that have the same area, or
Activities that share a common boundary.
There are many possibilities for EXCHANGE when
the areas are not equal.
Generally, the shape ratio and corner count rules areviolated, therefore, manual adjustment is sometimesrequired.
ESTIMATE the value of the exchange by comparingthe cost if the two centroids are switched.
However, this estimate will not necessarily be correct forunequal area activities.
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CRAFT
Computerized Relative Allocation
of Facilities Technique
Download from:
http://www.me.utexas.edu/~jensen/ORMM/frontpage/jensen.lib/index_omie.html
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CRAFT (Computerized Relative
Allocation of Facilities Technique)
Perhaps the most famous improvement algorithm
First computer-aided layout algorithm (1963)developed based on the study of Armour & Buffa(1933)
Improvement-type layout algorithm
Inputs
Existing block layout, Flow matrix (from-to)
Distance metric used is the rectilinear distance betweendepartment centroids.
Cost per unit distance matrix (optional)
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CRAFT
The main objective behind CRAFT is to minimize
total transportation cost:
Where Transportation cost = flow * distance * unit cost
Requires the assumptions that:
Move costs are independent of the equipment utilization.
Move costs are linearly related to the length of the move.
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Steps in CRAFT1. Determine department centroids.
2. Calculate rectilinear distance between centroids.3. Calculate transportation cost for the initial layout by multiplying
From-To (flow) chart,
Unit cost matrix, and
From-To (distance) matrix
4. Improve the layout by performing all-possible two or three-wayexchanges
Consider department exchanges of either equal area departmentsordepartments sharing a common border.
Determine transportation cost of each departmental interchange.
Select and implement the departmental interchange that offers thegreatest reduction in transportation cost.
5. Repeat the procedure for the new layout until no interchange is ableto reduce the transportation cost.
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Example 1: CRAFT
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Example 1: Possible Swaps
CRAFT does not actually swap and re-calc centroids
Swaps centroids and looks for best improvement
Iteration #1 - Possible Swaps
A-B Cost = 2650, C-D Cost = 2650, A-C Cost = 2270 *
Iteration #2 - Possible Swaps
C-B Cost =1950, C-A (already did this), A-D Cost=1950
Break tie abitrarily and select A-D swap, actual Cost=1870
Iteration #3 Possible Swaps
C-B Cost =2270, A-D (already did this one), A-C Cost =2500
No improvement found
STOP
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Example 1: Improved Layout
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Example 2:
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Example 2: CRAFT
Initial Layout1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 181 A A A A A A A A A A G G G G G G G G
2 A A G G
3 A A A A A A A A A A G G G G
4 B B B B B C C C C C E E G G G G G G5 B B C C E E E E E E E E
6 B B C C C C C E E E E E E E E
7 B B B B B D D D D F F F F F F F E E
8 D D D D D D D F F F
9 D D F F F F F F
10 D D D D D D D D H H H H H F F F F F
Dummy Department
Receiving D. Shipping D.
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New Layout
after exchanging E and F
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1 A A A A A A A A A A G G G G G G G G
2 A A G G
3 A A A A A A A A A A G G G G
4 B B B B B C C C C C F F G G G G G G
5 B B C C F F F F F F F F
6 B B C C C C C F F F F F F F
7 B B B B B D D D D E E E E E E F F8 D D D D D D D E E F F
9 D D E E E E E E F F
10 D D D D D D D D H H H H H E E F F F
Receiving D.Shipping
D.
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Example 2: Contd.
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Final LayoutAfter
exchangingB and C
Receiving D.Shipping D.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1 A A A A A A A A A A G G G G G G G G2 A A G G
3 A A A A A A A A A A G G G G
4 C C C B B B B B B B F F G G G G G G
5 C C C B B F F F F F F F F6 C C B B B B B B F F F F F F F
7 C C C C B D D D D E E E E E E F F
8 D D D D D D D E E F F
9 D D E E E E E E F F10 D D D D D D D D H H H H H E E F F F
M l Adj t t CRAFT
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Manual Adjustment on CRAFT
Output
50
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CRAFT Facts
A heuristic solution procedure for the more
generalize quadratic assignment problem
CRAFT only exchanges departments that are
Adjacent (share at least one common edge)
Have equal areas
Adjacency is a necessary but not sufficient criteriafor swapping departments
CRAFT simplistically assumes cost is linearly
related to distance;
1=1$ means 100=$100
In real life, you have fixed cost of investment in MH
0=$100 1=$101 100=$200
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Limitations in Exchanging
Exchange dept.#2 with dept. # 1,3,and 4
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CRAFT Facts...
Quality of final solution depends on the initial layout
CRAFT is a path-oriented method so the final layout isdependent on the initial layout.
Therefore, a number of different initial layouts should beused as input to the CRAFT procedure.
CRAFT allows the use of dummy departments torepresent fixed areas in the layout.
Final solution may be locally optimal, not globallyoptimal
Many derivatives have emerged
MCRAFT, BLOCPLAN, MULTIPLE, etc.
Mixed Integer Programming Models
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MICRO-CRAFT (MCRAFT)
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MICRO-CRAFT (MCRAFT)
PC version of CRAFT allowing non-adjacent exchanges
Can exchange any two departments whether they areadjacent or not
Shifts other departments automatically if the exchangeddepartments are not adjacent and equal sized
Uses bands and assigns grid within band to a department
MCRAFT requires the user to specify
Facility dimensions (rectangular width X length)
Number of bands
Layout vector or fill sequence
Computes grid size, number of rows and columns
Procedure
Starts from top-left corner of building
Sweeps bands in a serpentine fashion
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MCRAFT Micro CRAFT
Horizontal sweep patterns are used to
place departments (similar to ALDEP)
and move departments while two non-adjacentunequal-size departments are being exchanged
Layout is specified by a sequence of departments
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MCRAFT1. After the band width is set, MCRAFT requires a vector (the
order) of the departments as an initial layout.
Based on this vector, it locates the departments following theserpentine flow directions
2. A swap/exchange selection procedure similar to that of
CRAFT is implemented.
Not necessarily limited to adjacent or equal-size departments!!
3. If any improving exchange is selected, then the two
departments are swapped using a shifting procedure of theother departments.
4. REPEAT 3 and 4 until no improvement can be made.
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MCRAFT Example initial
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MCRAFT Example, initial
layout
MCRAFT Example final
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MCRAFT Example final
layout
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MCRAFT - Comments
Smoother shapes compared to CRAFT
Facility shape is a restriction
Allows multi-floor layout planning
Uses a From-To chart for input flow data
Band widths are equal
A department may occupy two bands
Unless departments are already arranged in bants, it will notcapture the initial layout properly.
More exchange alternatives. The number of alternativesincrease exponentially with the number of departments
Fixed departments may cause problems
Fixed department may move
MCRAFTs primary strength is also its primary weakness
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BLOCKPLAN
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BLOCPLAN
Like MicroCRAFT, arranges departments in bands
Uses a relationship chart as well as a from-to chart
Can be used only one at a time
Objective function: Measures layout cost using
distance based, or
adjacency-based, or
REL-DIST
Number of bands determined by the program
Usually two or three bands
Band widths may vary
Departments contained in only one band
departments are rectangular
Uses continuous layout representation
Can do both construction and improvement
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Example 6.1
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Flow-Between and Relationship Chart
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Example
E=0.63REL-DIST = 2887
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Example Contd.
E=0.63
REL-DIST = 2708
A=10, E=5, I=2, O=1, U=0, X= -10
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MULTIPLE
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MULTIPLE / LayOPT
MULTI-floor Plant Layout Evaluation
Can also be used for single floors
Similar to CRAFT
Identical Objective function
Not restricted to rectangular shapes
Discrete representation
Improvement-type algorithm
Uses From-To chart
Uses two-way exchanges
Sweep patterns are used to place departments in layout
Sweep pattern is based on space filling curve (SFC) concept
Many alternative SFCs can be created
Layout is specified by a sequence of departments
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MULTIPLE...
Pairwise exchange is performed on the sequence
position of departments
Like MicroCRAFT and BLOCPLAN (and unlike CRAFT),MULTIPLE can exchange non-adjacent departments
Not restricted to equal size departments
Layout vector denotes order of departmentplacement
Fill sequence is determined by Space Filing Curve(SFC)
Can exchange departments by changing their position inlayout vector
SFC can bypass fixed departments or areas
SFC can move around a fixed department
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Example
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Department shapes
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Department shapes
Ratio of its longer side to its shorter side
Divide the area of smallest enclosingrectangle (SER) to the area of department.
Divide its perimeter into its area
Ideal shape: S*=P/A=4( )/A
Normalized shape factor: s/s*
Reasonable shapes 1.0< F < 1.4
A
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Layout Construction Algorithms
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Construction Algorithms
For i = 1 to n
SELECT an activity to be placedPLACE the selected activity in the layout
End For
Selection rules
Choose the next activity having the largest number of A(E, I, etc.) relationships with the activities already in thelayout. Break ties randomly.
Supplement above procedure with TCR for choosing firstdepartment and breaking ties.
Consider flow cost chart and user specified placementpriorities.
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Construction Algorithms
Placement Rules
Contiguity Rule
If an activity is represented by more than one unit areasquare, every unit area square representing the activity mustshare at least one edge with at least one other unit areasquare representing the activity.
Connectedness Rule
The perimeter of an activity must be a single closed loop thatis always in contact with some edge of some unit areasquare representing the activity.
The followings are infeasible shapes for activities.
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Construction Algorithms
Placement Rules (cont.)
Five basic shapes for an activity representedby 4 unit area squares.
Determining possible shapes becomes nontrivial
for activities with more than 5 unit area squares,and some of the shapes have bizarreconfigurations.
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Construction Algorithms
Placement Rules (cont.)
Therefore, additional rules are often used.
Enclosed Voids Rule
No activity shape shall contain an enclosed void.
Shape Ratio Rule
The ratio of a feasible shapes greatest length to its greatestwidth shall be constrained to lie between specified limits.
Corner Count Rule
The number of corners for a feasible shape may not exceed aspecified maximum.
Given an activitys shape there are a large number ofalternative placements for it in a layout, including differentlocations and mirror images and rotations.
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Construction Algorithms
Bounded placement procedures
Accept a specified facility configuration and fit the activitiesinto the facility.
May not be able to enforce all of the activity shape rules.
E.g., ALDEP
Free placement procedures
Create a layout without regard to the resulting facilityconfiguration.
May produce layouts requiring considerable adjustment toconform to conventional building configurations.
E.g., CORELAP
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ALDEP
Automated Layout DEsign
Program
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ALDEP
Automated Layout DEsign Program by Seehof and
Evans (1967)
Construction algorithm
Same basic data input requirements and objectives
as CORELAP
Relationship chart
Department areas
Additionally, sweep width
Block Size, Minimum acceptable closeness rating (MACR)
Arbitrarily selects first department
Allows fixed departments
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ALDEP- Layout Construction
First department selected randomly
Next department selected based on relationshipwith first
If more than one with same relationship, choice is random
If no departments with minimally acceptable closeness
relationship (MACR) exist, choice is random
Place first department in the upper left corner andextend downward.
Develop layout using serpentine space filling curve.
Additional departments begin where the previousone ended
Sweep width < area of smallest department
Why?
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Sweep Width
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Sweep Pattern
Can accommodate a variety of building shapes andirregularities.
Scoring Mechanism: Adjacency Score
ALDEP rates the layouts by determining an adjacencyscore by assigning values to the relationships amongadjacent departments.
A = 64, E = 16, I = 4, O = 1, U = 0, X = -1024
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ALDEP-Example
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ALDEP - Layout
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Example
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Scoring Procedure
AdjacentDepartments Relationship Value Rating4-2 and 2-4 E 16 324-1 and 1-4 I 4 8
2-1 and 1-2 E 16 321-6 and 6-1 U 0 06-5 and 5-6 A 64 128
6-7 and 7-6 E 16 325-7 and 7-5 I 4 87-3 and 3-7 U 0 0
Total 240
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Example:
Excel example:
ALDEP
http://../2008/ALDEP.xlshttp://../2008/ALDEP.xlshttp://../2008/ALDEP.xls8/6/2019 FP II Single
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CORELAP
COmputerized RElationshipLAyout Planning
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CORELAP
COmputerized RElationshipLAyout Planning by Lee andMoore (1967)
Construction algorithm Inputssimilar to ALDEP
Relationship chart
Number of departments
Area of each department
Weight of REL chart entries
Calculates a total closeness
rating (TCR) from therelationship chart
Department with highest TCRis placed in the center
Tie-breaker is area size
Next department chosen bythe relationship with firstdepartment
Start with A relationships
If no As, then Es, Is, etc.
Calculate the placementrating
Based on relationshipweights
Sum of weights ofadjacent departments
Tie breaker is boundarylength
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Algorithm:
Compute Total Closeness Rating (TCR)
A=6 E=5 I=4 O=3 U=2 X=1
Highest TCR placed into center of layout(rect. shape)
Search for next dept to enter as one with A,then E, etc and use TCRs to break ties(Highest TCR, Largest Area, Lowest Dept.
Number (random))
Use placing rating methodto decide placement
1st
8
1
2 3
7 6
5
4
2nd
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CORELAP - Example
3 enters first
4 enters next (A with 3)
2 enters (both 1 & 2 have E but 2 has higher TCR)
1 enters next (has A with 2)
5 enters last
Order of entry 3-4-2-1-5
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CORELAP - Layout Concept
Get rect. shaped depts
(generally) andirregular borders
Highest TCR goes in
center to increaseadjacency
Same layout each time
Scoring uses smalleris better
Details in book.
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Placement decision:
Placing rating: sum of the weighted closenessrating btw the department to enter the layout andits neighbors.
Place to the highest placing rating.
In case of tie, compare boundry lengths of thetied locations.
Calculate layout score
Sum (Numerical closeness rating X lenght of shortestpath)
Use shortest rectilinear path between departments
NOT rectilinear distance btw departments
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Example:
Excel example:
CORELAP Original
CORELAP
http://../2008/CORELAP-original.xlshttp://../2008/CORELAP.xlshttp://../2008/CORELAP-original.xlshttp://../2008/CORELAP.xlshttp://../2008/CORELAP.xlshttp://../2008/CORELAP-original.xls8/6/2019 FP II Single
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Notes on ALDEP and CORELAP
Construct initial block diagrams
They are arbitrary and use subjectiveinformation
They are useful in that they help the
designer generate layout ideas
Do not treat scores as ratio values
200 pts is not twice as good as 100 pts
Many other factors to consider in any reallayout project
Codes for these programs are almost non-
existent
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What algorithm to choose ?
Whats the task?
Construction
Improvement
What are theconstraints?
Shape
Fixed departments
What is the
objective function ?
Distance-based
Adjacency-based
All computerizedoutputs still need to
be massaged
Dynamic Layout Analysis -
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y y y
Simulation
Many languages available
Arena most widely used for general purpose
AutoMOD most widely used for MH systems
Existing Hot Dog Line
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Example AutoMOD
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Computerized Layout Planning
Does not provide an absolute bestmodel for finding the optimal layout.
Does provide algorithms for evaluatinga large number of alternative layouts.
It is important to understand theunderlying assumptions and scoringmodels of each procedure in order tocorrectly interpret the results.
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Homework
Chapter 6
6.7, 6.12, 6.13
6.18, 6.23,
6.25, 6.27, 6.29
6.31,
6.38, 6.40
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LOGIC
Layout Optimization with Guillotine Induced
Cuts.
Inputs are
from-to chart,
total area,
dept areas
Distance-based objective function
Improvement algorithm, can be used forconstruction too
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LOGIC: Algorithm
Divides building into smaller and smaller
sections by successive horizontal or verticalcuts.
Stops when each section is a single
department
Constructs a tree to keep track of cuts andsubsections
Choice of cuts made using search strategy:
Such as simulated annealing
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Cut-Tree for ExampleA,B,C,D,E,F,G,H
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Example ...
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Selling Your Plan
Lecture 10 (Chp.11 & Chp.12):
Evaluation and Selection process
Preparion, Presention, Implemention,and Maintenance
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Selling Your Plan
The Layout
Try to illustrate howthe design works
2-D or 3-D CADDrawing
May need large plots
Include flow lines
Show analysis results
Show multiplealternatives
Simulation model ifpossible
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Selling Your Plan
The Written Report
Make it easy to read and
understand
Avoid detailed calculations inbody of report, use summarytables, plots etc.
Label all Figures and Tableswith a sequential number andadd a caption
Be organized and neat, useconsistent headers, sub-headers, 1.0, 1.1, 1.1.1
Dont teach FP, SELL yourdesign!
Writing IS re-writing!
Letter of Transmittal
Cover Page
Executive Summary (1-page only)
Table of Contents
Introduction (Problem description,be specific)
Current System (if applicable)
Operation and Analysis
Critique
Proposed System
Design Methodology
Operations and Analysis
Results/List of Features
Cost Justification
Plan of Implementation (optional)
Conclusions (rephrase and restateintro) and Recommendations
Appendices (with supporting data,
reference them in order)
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Selling Your PlanThe Oral Presentation
Be brief and direct
Be confident, well-dressed
Use quality visuals and avoid gimmicks
Match speech to sequence of slides
Be open to questions at any time
Stay on point!
What is the problem?
What should be done?
How should it be done?
Why should your design be implemented?
List features
REHEARSE, REHEARSE, REHEARSE!
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Evaluation & Selection
Economic Justification
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Objectives of this Section
Discuss the importance of proper economic
justification (EJ).
Present a basic 7-step approach.
Understand some of the difficulties related
to FP/MH investments.
Review some useful techniques
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Evaluation
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Evaluation
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Why is EJ Important?
Stockholders have money.
They dont want to give it to you
Interest Lost
Opportunity Cost unless you offer a greater rate ofreturn Youd like to determine that rate
What if you make a mistake?
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A 7-Step Process
Specify the alternatives
Define the planning horizon
Estimate the cash flows
Specify the interest rate
Compare the alternatives
Perform sensitivity analysis
Select the best alternative
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1. Specify the alternatives
Many possible solutions usually exist.
Define a mutually exclusive set offeasible alternatives.
Avoid size gates.
Get the big picture.
Design the whole, justify the whole, andimplement the pieces.
Dont forget the Do-Nothing alternative.
Some Rules of Thumb
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. Think long term, (5-10 years)but not too long. Dont confuse PH w ithequipment or depr. life. Use the same PH for all
alternatives. Some companies have standardPHs.
2. Define Planning Horizon
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3. Estimate Cash Flows
Most difficult aspect
Yearly estimates of costs and benefits
Comprised of direct, indirect, and intangiblefactors.
Must be based only on future costs andbenefits only.
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Categories of Costs/Benefits
Direct Market Consequences
items which have an established market price, such as:
Increased Sales
Labor (direct, indirect)
Energy, Materials, Space
Indirect Market Consequences
items not directly priced in the marketplace but a value isassignable.
Safety, Inventory, Speed of service
Intangibles
items which cannot be assigned a value
Flexibility/expandability
Effect on future business practices
Effect on market share
www.grossassociates.com/cal
http://www.grossassociates.com/calculator.cfmhttp://www.grossassociates.com/calculator.cfm8/6/2019 FP II Single
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culator.cfm
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Indirect and Intangible Items
Higher morale
Better customer service
Reduced supervision
Reduced training
Less clutter
Reduced product loss
Reduced product damage
Experience with newtechnology
Increased flexibility
Less resistance to change
Less paperwork
Improved mgmt productivity
Faster deliveries
Better quality of life
Improved reliability
Ease of design change
Improved relationships
Reduced handling
Less expediting
Reduced inspection
Reduced scrap
Reduced rework
Reduced setup time
Better quality
Reduced transportation
Increased safety
Better scheduling andworkflow
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What Are They Worth?
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Some Common Effects
Can be tricky to
evaluate:1. Increased Throughout
2. Decreased Labor
3. Improved Quality
4. Improved Safety
5. Decreased Inventory
6. Space Savings
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Increased ThroughputDemand > Capacity
Each additional unitproduced can be sold
Value each added unit asthe profit gained
Watch for added expensesdownstream.
Added capacity needed,
Integer effects
Returns increase
Fieldsupport/maintenance
Etc.
Demand < Capacity
Each added unit cant besold
Can deliver units faster
Can meet demand withfewer production hours
Value of time saved is theresult of labor saved,energy saved.
Look for other creative
uses for excess timeavailable.
Training? Selling?Maintenance?
Decreased Labor
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(Automation)
Will excess employees be laid off?
Labor $ saved
Will they displace the hiring of temps?
Lower hiring expense?
Can we use them to increase sales?
Increased revenue
Can we eliminate a shift?
Savings of labor, energy, managementoverhead
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Improved Quality
Fewer rejects
increased throughput (just did that one!)
Happier customers
Increased demand (can you meet it?)
How will it affect future growth?
Fewer returns
Lower demand for:
Customer service
Return processing
Field repair
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Improved Safety
Cost Avoidance
Medical costs
Lost Time
Replacement Worker Costs
Lost productivity
Workers Comp
Reduced Turnover
Hiring expense
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Lower Inventory Levels
Interest earned on capital
Storage Space Savings
Energy
Insurance
Protection
Lease
Savings in loss due to damage, pilferage
Negative effects
Slower response?
Higher costs charged by vendors (storage)?
Lost sales?
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Space Savings
What is each square foot worth?
Dont value it using allocated overhead.
Concentrate on actual present savings:
Energy
Insurance
Protection
Lower lease cost (if leasing space)
Potential sale or lease of excess space (if own space)
Future cost avoidance:
May delay need for expansion
Must analyze (predict) future growth
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Activity Based Costing
A better way to understand and control indirect costs.
It assigns costs to products or customers based on theactivitiesinvolved and the resources they consume.
Overhead is traced to a product rather than spread across allproducts based on direct labor hours.
Products and customers consume activities which in turn,consume resources.
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4. Specify the Interest Rate
Hurdle rate
Return on investment
Minimum attractive rate of return (MARR)
Interest rate used in DCF calculations
Should reflect opportunity cost of alternativeuses for capital
Most American companies use MARR of 10-20%
Japanese firms use 5-10%
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5. Compare the Options
Many different methods exist
Companies have preferred ones
Most popular are:
Net Present Worth (NPW)
Internal Rate of Return (IRR)
Compute After Tax with inflation
Easy to use, but incorrectAssumes i=0%Fails to consider cash flowsbeyond PP
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Is Payback Any Good?Yr A B
0 -$1000 -$2000
1 250 1000
2 250 10003 500 0
4 1000 -200
a) What is the payback period for each?
b) Which do you think is best?
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Finding Present Values
Example of Investment
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Alternatives
Two mutually-exclusive alternatives are compared
against a do-nothing option (NPW=0)
i=13%
Select the option that Maximizes NPW
Exercise - Should we
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invest?
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Using Spreadsheets Illustrated here with MS-Excel
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6. Supplemental Analysis
What if some of your data is wrong?
How much error will impact the decision to invest?
Breakeven Analysis
requires least amount of information
Is true value above or below breakeven?
Sensitivity Analysis
requires more information
Whats the range of possible values?
Risk Analysis
requires the most information
What are the possible values and their probabilities?
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7. Select Preferred Option
Obtain support from users of the system
Speak the language of the listener
Dont oversell technical aspects
The decision makers perspective is broad
This proposal is just one of many
Selling is the name of the game
Show well-being to the firm!
THE GOLDEN RULE . . .
Those with gold make the rules.
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Facilities Planning
Lecture 11:Warehousing & Distribution
Systems
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Why to have a Warehouse
To better match supply with customer demand
Allows us to respond quickly to customer demand
Allows for buffering against surges in demand or supply
To consolidate product to reduce transportation
costs and to improve customer service
To provide value added processing
Assembly may occur Dell
LL Bean Monogramming
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Missions of a Warehouse
To effectively ship product in any configuration to
the next step in the supply chain without damagingor altering the products basic form
Improving order picking operations
Utilization of cross-docking
Increasing productivity
Effectively utilizing energy, labor, space resources
Old rule of thumb: When warehouse 80% full, more space isneeded.
Increasing value-added services
Warehouse Management
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System (WMS)
Software that tracks and manages
warehouse activities
Records receipts of inventory into thesystem and registers shipments out
Manages the stock locations and recordswhere goods are placed
Helps generate orders for replenishment
Can help with assigning items to locations inthe warehouse
Warehouse Management Systems(WMS)
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Operations of a WarehouseOperations of a Warehouse
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Inbound Processes
Receiving
Put-away
Outbound Order-Picking
Checking, Packing, Shipping
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Typical Warehouse Functions
REpackaging
Cross-Docking
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Receiving and Shipping
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Receiving and Shipping
Consider handling, storing, and control
requirements to provide the propercombination of space, equipment, andpeople.
Receiving and shipping functions interfacewith the outside environment.
Receiving:
Accounts for about 10% of operating costs in a
facility
Shipping:
Accounts for around 15% of total costs
Receiving and Shipping:
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Facility Requirements
Receiving
Stage and spot carriers
Waiting
Maneuvering
Unloading
Dockboards
Receiving area
Staging area
Office area
Shipping
Staging area (mayinclude accumulate andpack)
Office area
Stage and spot carriers
Dockboards
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Receiving and Shipping:
Desirable Attributes.
Directed flow paths (avoid double handling)
Continuous flow of effort (try to scheduleinbound shipments)
Concentrated area that minimizes material
handling
Efficient material handling (try to influence unitload configuration)
Provide safe operations
Minimize damage
Provide good housekeeping
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Receiving principles1. Dont receive
2. Prereceive (Advance shipping notes)3. Cross-dock cross-dockable material
4. Put away directly to primary or reserve locations
5. Stage in storage locations6. Complete all necessary steps for efficient load
decomposition and movement at receiving
Prepackage in issue increments
Apply necessary labeling and tags
Cube and weigh for storage and transport planning
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Receiving principles...7. Sort inbound materials for efficient putaway
8. Combine putaways and retrievals whenpossible
9. Balance the use of resources at receivingby scheduling carriers and shifting time-consuming receipts to off-peak hours
10. Minimize or eliminate walking by flowinginbound material past workstations.
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Shipping principles1. Select cost and space effective handling units
2. Minimize product damage
Unitize and secure loose items in cartoons or totes
Unitize and secure loose cases on pallets
Unitize and secure loose pallets in outbound trailers
3. Eliminate shipping and direct-load outboundtrailers4. Use storage racks to minimize floor space
requirements for shipping staging
5. Route on-site drivers through the site andminimize paperwork and time
6. Use small-parcel shipping
Receiving and Shipping:
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Space Planning
What is to be receiving and shipped?
What, how much, when
Receiving and shipping analysis chart
Number and type of docks
Estimate with simulation, queuing analysis
Configuration
Carrier approaches, traffic flow and waiting area
Apron depth, bay width
An indivual with proper equipment can load and unload 7500lb/hr.
Space requirements for receiving and shipping area:
Personnel Convenience, Offices, Material Handling EquipmentMaintenance, Trash Disposal, Pallet and Packing Material Storage,Truckers Longue, Staging Area, Equipment Maneuvering
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Equipment Planning
Equipment required for a proper interface
between the carriers and the docks.
Dock levelers
Portable ramp
Permanent ramp
Yard ramp
Scissor lift
Bumper pads
Dock shelters
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Storage & warehousing
Storage & warehousing
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Storage Function
Activity of storing raw materials, supplies,and in process material.
Warehousing Function
Activity of storing finished goods.
Accounts for around 15% of warehouse
operating expenses
Storage and Warehousing
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Basic Functions
Receiving
Identification andsorting
Dispatching to storage
Placing in storage
Storage
Removing from storage
Order accumulation
Packing
Shipping
Record keeping
Additional Functions
Inbound inspection
Parts preparation
Kitting
Item packaging
Storage and Warehousing
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Goal:
Maximize resourceutilization whilesatisfying customerrequirements, or
Maximize customerservice subject toresource constraints
Resources:
Space
Equipment
Personnel
Objectives:
Maximize spaceutilization
Maximize equipmentutilization
Maximize laborutilization
Maximize accessibilityof all materials
Maximize protection ofall materials
Storage and Warehousing SPACEPLANNING: Storage Analysis Chart
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Storage Location Methods
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Dedicated Storage
Each stock keeping unit (SKU) is
assigned a spot
Easy to find and manage
Pick times may be longer
Need overflow areas
Must plan space for maximumon hand
Storage locations can bearbitrarily determined, such aspart number sequence, or theycan be determined based on theSKU's activity level and inventory
level.
Number of storage locations isthe sum of the maximuminventory level for each SKU.
Randomize Storage
SKUs are stored in any
available location
Retrievals are first-in, first-out (FIFO).
Allows for better spaceutilization
Requires good controlsystem
Closest-open-locationrule often used
Space is planned for
average amount of eachSKU
Safety Stock +(Replenishment Qty)
Example
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Can be a substantial difference inwarehouse space requirements!
Example
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Randomize Storage:Dedicated Storage:
Dedicated Storage
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Maximize Throughput
Assign SKUs to storage locations based on the ratio oftheir activity to the number of locations assigned to theSKU.
NOTE: Activity is the number of storages/retrievals perunit time not the quantity of material moved.
Inverse of cube per order
Hit rate
SKU with the highest ranking is assigned to thepreferred openings (i.e., closest to the I/O point).
The Cube-per-Order Index forDedicated Storage
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Smallest value gets best locations
Inverse is the hit rate for a particular location
Logic is that items that have lots of transactionsAND do not take up much space should get thebest locations
Items that either do not have many transaction ORones that take up lots of space should go in theworst locations
Example
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Multiple I/O Points
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Rank order locations using weighted-average dx
Total Dx. for theSlotting
Assignment
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Assignment
Multiply distance
for each cell timethe expectednumber of hits per
time (1/COI).
Storage Layout Planning
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Supermarket Storage
Combination of random and assigned storage.
Class-Based Storage
Hybrid configuration which assigns SKUs to classesbased on their activity-to-space ratios, but usesrandomized storage within the classes.
As 80% of S/R need 20% of space
Bs 15% of S/R need 30% of space
Cs 5% of S/R but need 50% of space
Yields some of the throughput benefits of dedicatedstorage and the space benefits of randomized storage.
If materials enter and leave WH from one I/O pt.
Material Shipped/Received inDifferent Amounts
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Calculate Shipping/Receiving Ratio
S/R = (Trips To Shipping)/(Trips fromReceiving)
S/R1 locate nearer to shipping
S/R=1 does not matter
Proposed Layout
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Storage and Warehousing
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Layout Planning
Objectives
To utilize spaceeffectively
To provide efficientmaterials handling
To minimize storagecost while providing therequired levels ofservice
To provide maximumflexibility
To provide goodhousekeeping
Principles
Popularity
Similarity
Size
Characteristics
Space Utilization
Storage and Warehousing:Layout Principles
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Popularity
Size
Provide a variety ofstorage location sizesto accommodate a
variety of products.
Utilize adjustable racksor shelves if productand unit load sizes areuncertain or changeperiodically.
Similarity
Items that are receivedand shipped togethershould be storedtogether.
Characteristics
Perishable materials
Oddly shaped items
Crushable items
Hazardous materials
Security of items frompilferage
Compatibility betweenitems
Storage and WarehousingPrinciples: Popularity
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Entrance
and Exit
Fast
Moving
Medium
Moving
SlowMoving
Receive Main Aisle Ship
H
G
F
A
D
C
B
E
Product
Quantity pe
Receipt
Trips to
Receive
Average
Customer
Order Siz
Trips to
Ship
A 40 pallets 40 1.0 pallet 40
B 100 pallets 100 0.4 pallets 250C 800 cartons 200 2.0 cartons 400
D 30 pallets 30 0.7 pallets 43
E 10 pallets 10 0.1 pallets 100
F 200 cartons 67 3.0 cartons 67
G 1000 cartons 250 8.0 cartons 125
H 1000 cartons 250 4.0 cartons 250
Storage and Warehousing: LayoutPrinciples: Space Utilization
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Conservation of Space
Maximizingconcentration
Maximizing cubeutilization
Minimizinghoneycombing
Limitations of Space
Clear height
Stacking height
Floor loading
Columns
Materials Accessibility
Each storage face hasaisle access
Majority of items storedalong the long axis ofthe area
Aisles should not beplaced along wallswithout doors
Avoid locked stock by
using a two-bin system
Storage and Warehousing:Space Utilization
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Loss of Cube
Utilization
Aisle Example
Storage and Warehousing:Space Utilization ...
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Loss of Cube Utilization
Honeycombing
Wasted space that results because a partial row or stack cannot beutilized because adding materials would result in blocked storage.
Space Standard
Volume requirement per unit load stored to include allocatedspace for aisles and honeycombing.
Storage Models
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Determine best design for each storage subsystem
Unit loads stored and retrieved with lift trucks
Four conventional storage methods analyzed
Block stacking
stacked on top of each other
stored on floor in storage lanes
Deep lane storage
Single-deep rack
Double-deep rack
Tradeoff between density of storage and accessibility
Have different types of space losses due to rack design and
honeycombing
Minimize average amount of floor space required
Storage and Warehousing
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Equipment Planning
Storage Equipment Types
Bulk Storage
includes block and tight-blocking stacking
Portable Racks or Stackable Racks
Pallet Rack
Cantilever Racks -- provide long uninterrupted spans
Drive-In or Drive-Through Racks
Flow-Through Rack
Bin Racks or Shelving
Sliding Racks
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Order Picking
Order Picking
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A classical problem inwarehousing anddistribution is the orderpicking problem.
Picking several
different items tocompose an order.
Could be a customerorder, delivery for a
retail store, kit formanufacturing orassembly, etc.
Order Picking...
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Processing customer orders (typically done
by the computerized warehousemanagement system of the facility):
checking that the requested material is availableto ship;
if necessary, coordinating order fulfillment withother facilities of the distribution network;
producing the pick lists to guide the orderpicking and the necessary shipping
documentation;
scheduling the order picking and the shippingactivity.
Order Picking ...
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The set of physicalactivities involved in
collecting from the storagearea the materialsnecessary for the fulfillmentof the various customerorders.
~55% of warehouseoperating costs
Activity % Order Picking Time
Traveling 50%
Searching 20%
Pick 15%
Paperwork and OtherActivities 15%
Pick Lists
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Order Picking Objectives
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Productivity (pick rate)
Piece pick operations measure the pick rate in line items
picked per hour
Case pick operations measure cases per hour and line itemsper hour.
Pallet pick operations measure is pallets picked per hour.
Productivity gains are usually in the form of reducing the travel
time.
Cycle Time
Amount of time it takes to get an order from order entry to theshipping dock
Immediate release of orders to the warehouse for picking andmethods that provide concurrent picking of items within largeorders are ways to reduce cycle times.
...
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Accuracy
Does the customer get what they ordered? Affected bymany factors,
product numbering scheme,
design of product labels,
packaging,
picking documents,
location numbering scheme,
storage equipment,
lighting conditions, and
picking method used.
Technology can aid picking accuracy (pick-to-light,scanners)
Principles of Order Picking
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1. Apply Paretos Law
2. Use a clear easy-to-read Picking doc.3. Use a pre-routed, pre-posted picking doc
4. Maintain an effective stock-location system5. Eliminate and combine tasks if possible
Traveling and extracting
Traveling and documenting
Picking and sorting
Picking, sorting, and packing
Principles of Order Picking
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6. Batch orders
Procedure Pickers per Order Line Items perPick
Periods per Shift
Discrete Single Single Single
Zone Multiple Single SingleBatch Multiple Single Single
Wave Single Single Multiple
Zone-Batch Multiple Multiple Single
Zone-Wave Multiple Single Multiple
Zone-Batch-Wave
Multiple Multiple Multiple
Principles of Order Picking
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7. Establish separate forward and reserve picking areas8. Assign popular items to easily accessible locations
9. Distribute picking activity so as to reduce congestion10. Assign items that are likely to be requested together to the
same or nearby locations11. The order picker should be responsible for order accuracy
12. Avoid counting13. Require pick confirmation14. Design picking vehicles to minimize sorting time and errors
and to enhance pickers comfort
15. Eliminate paperwork from the order picking activity
Single Order Picking
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Product is stored in fixed locationson static shelving or pallet rack.
An order picker picks one orderat a time following a route upand down each aisle until theentire order is picked.
The order picker will usually usesome type of picking cart.
The design of the picking flowshould be such that the orderpicker ends up fairly close to theoriginal starting point.
The picking document shouldhave the picks sorted in thesame sequence as the pickingflow.
Works well in operations witha small total number of ordersand a high number of picksper order.
Operations with low picks perorder will find the travel timeexcessive
Operations with large numbersof orders will find that the
congestion from many pickersworking in the same areasslows down the processing.
Batch Picking
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Multiple orders are groupedinto small batches.
An order picker will pick allorders within the batch inone pass using aconsolidated pick list.
Usually the picker will use amulti-tiered picking cartmaintaining a separate tote orcarton on the cart for eachorder.
Batch sizes usually run from 4to 12 orders per batch
depending on the averagepicks per order in that specificoperation.
In operations with low picks perorder, batch picking can greatlyreduce travel time by allowing the
picker to make additional pickswhile in the same area.
Accuracy can suffer if you do notprevent mixing of orders.
In very busy operations, batchpicking is often used inconjunction with zone picking andautomated material handlingequipment.
In order to get maximumproductivity in batch pickoperations, orders must beaccumulated in the system untilthere are enough similar picks tocreate the batches.
Zone Picking
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The order picking version of theassembly line.
Picking area is broken up intoindividual pick zones.
Order pickers are assigned aspecific zone, and pick itemswithin that zone.
Orders can be moved from onezone to the next as the pickingfrom the previous zone iscompleted (also known as "pick-and-pass"). Or, items can beconsolidated and sorted.
Balance the number of picks fromzone to zone to maintainconsistent flow.
Creating fast pick areas close tothe conveyor is essential inachieving high productivity inzone picking.
Most effective in large operationswith high total numbers of SKUs,high total numbers of orders, andlow to moderate picks per order.
Separate zones also provide forspecialization of picking
techniques such as havingautomated material handlingsystems in one zone and manualhandling in the next.
Wave Picking
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Selected groups of orders are scheduled
for picking at specific time of the day
Usually have multiple pick periodsthroughout a shift.
Useful to coordinate picking, replenishment,and shipping functions
Can be combined in all other methods to
create hybrid picking schemes
Zone-batch-wave picking
Comparison
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Order Picking Problems
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Batching
Group orders into pick lists
Based on priority or item similarity between orders
Sequencing
Sequence items in the pick list
Based on item locations to minimize expected traveldistance in picking tour (total pick time)
Picking tour is a specification of the sequence in whichitems in a specific order will be picked
This problem is prevalent where items must be picked
from both sides of an aisle and the picker cannot reachitems on both sides without changing position
Wide aisles are common to allow two-way traffic, turningaround in the aisle, or product storage with fork lifts
Pick Sequencing
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How picker traverses aisles the route they take
Often difficult to describe a pick routing or sequenceto picker
Easy to tell picker which location is next picked
Difficult to tell picker exact route to take to next pick
Traveling Salesman Problem (TSP)/VRP
S-Shaped strategy
Largest Gap strategy
Bin numbering strategy
The Pick SequencingProblem
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Given a picking list, sequence the visits to thepicking locations so that the overall traveling effort(time) is minimized.
Remarks
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The TSP problem is an NP-complete problem: It can besolved optimally for smallinstances, but in general, it willbe solved through heuristics.
There is a vast literature onTSP and the development of
heuristic algorithms for it (e.g.,Lawler, Lenstra, Rinnooy Kanand Shmoys, The TravelingSalesman Problem: A guidedtour of combinatorial
optimization, John Wiley andSons, 1985).
When the no subtour constraintis removed, the remainingformulation defines a Linear
Assignment Problem (LAP) (whichis an easy one; e.g., theHungarian Algorithm) => Solvingthe corresponding LAP canprovide lower bounds forassessing the sub-optimality of the
solutions provided by the appliedheuristics.
In the considered applicationcontext, the distances cij shouldbe computed based on the
appropriate distance metric; i.e.,rectilinear, Tchebychev, shortestpath
S-Shaped Pick Sequencing
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Any aisle containing at least one item to be picked is traversedentirely
An exception is made for last aisle if number of visited aisles is odd
Aisles where nothing has to be picked are skipped.
Thus aisles are visited in the shape of an S.
The picker thus enters an aisle from one end and leaves the aisle fromthe other end, starting at the left side of the warehouse.
After picking the last item, the order picker returns to the front end of theaisle.
This strategy is used frequently, because it is very simple to use andto understand.
S-shape strategy efficient when
Large number of SKUs per order
When it is time consuming to enter and leave aisles i.e. high bay orderpicking trucks
S-shaped Pick Sequence
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Largest Gap Strategy
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All aisles except first and last are exited on same side entered
How far to go into aisle?
picker enters an aisle as far as the largest gap within an aisle
Gap = distance between any two adjacent picks, distance between thefirst pick and the front aisle, or distance between the last pick and theback aisle
The largest gap is the part of the aisle that is not visited by theorder picker.
If the largest gap is between two adjacent picks, the picker performsa return route from both ends of the aisle.
Otherwise, a return route from either the front or back aisle is used.
The largest gap within an aisle is therefore the portion of the aislethat the picker does not traverse.
Largest Gap strategy works well when
The number of picks per aisle (pick density per aisle) is low
The additional time to change aisles is short.
Largest Gap Pick Sequence
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S-Shape Heuristic The order picking route starts at the depot
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The order picking route starts at the depot.
It goes to the front of the main aisle closest to thedepot, that contains at least one item (1).
This main aisle is traversed up to and including
the block farthest from the depot, that contains atleast one item (2).
If the current block contains at least one item: Goto the left most aisle containing items or go to theright most aisle containing items, whichever is theclosest (3);
go from one aisle to the next and traverse any
aisle containing items entirely; after picking thelast item, return to the front of the block (4).
If this block contains no items: Traverse the aisleof this block, that is closest to the currentposition.
Repeat this procedure for all blocks until theblock closest to the depot has been considered(5).
Finally, return to the depot.
Largest Gap heuristic
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the order picking route starts at the depot; it goes to the frontof the main aisle closest to the depot, that contains at leastone item; traverses this main aisle up to and including theblock farthest from the depot that contains at least one item
(1).
On traversing the cross aisle (the rear aisle), each aisle isentered as far as the largest gap and left from the sameside that it was entered (2).
A gap represents the distance between any two adjacentitems, or between a cross aisle and the nearest item. Thus,the largest gap is the part of the aisle that is not traversed.
The last aisle of the block is traversed entirely, by which we
arrive in the next cross aisle (3).
This cross aisle is traversed, while visiting the aisles of theblocks on both sides of the cross aisle up to the largest gap.First the aisles on one side of the cross aisle are visited (4)and thereafter the aisles on the other side (5).
One aisle is again traversed entirely to reach the next crossaisle (6). This may be either the left or the right most aislecontaining items, depending on which of the two gives theshortest travel distance within the cross aisle.
This process is repeated for all blocks containing items.
If a block does not contain items, then the aisle of this block,that is closest to the current position is traversed entirely.After considering the last block, return to the depot (7).
Aisle-by-Aisle Heuristic
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This heuristic is described inVaughan and Petersen (1999).Basically,
Every main aisle is visited once.
The order pickers starts at thedepot and goes to the left mostaisle containing items. All items inthis main aisle are picked and
A cross aisle is chosen to proceedto the next main aisle.
Again all items in this main aisleare picked and the order pickersproceeds to the next main aisle.
The aisle-by-aisle heuristic
determines which cross aisles touse to go from one aisle to thenext in such a way that thedistances traveled are minimized.
Interactive Warehouse
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http://www.roodbergen.com/warehouse/
Crossdocking
http://www.roodbergen.com/warehouse/http://www.roodbergen.com/warehouse/http://www.roodbergen.com/warehouse/http://www.roodbergen.com/warehouse/http://www.roodbergen.com/warehouse/8/6/2019 FP II Single
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Eliminates the inventory-holding function of awarehouse
Allows it to serve itsconsolidation and shippingfunctions
Transfer incoming shipmentsdirectly to outgoing trailerswithout storing them
Arriving goods from thevendor already have acustomer assigned
Workers only move theshipment from the inboundtrailer to an outbound trailerbound for the appropriatedestination.
Eliminates expensivefunctions of inventory holdingand order picking but requires
information systeminfrastructure in modernsupply chains.
Shipments typically spend lessthan 24 hours at the facility,
sometimes less than an hour=> Just-In-Time for distribution
Examples
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Home Depot operates a pre-distribution crossdock in Philadelphiaserving more than 100 stores in the Northeast area.
Wal-Mart uses
traditional warehousing for staple stock - i.e., items that customers areexpected to find in the same place in every Wal-Mart (e.g., toothpaste,shampoo, etc.)
crossdocking for direct ship - i.e., items that Wal-Mart buyers have gotten
a great deal on and are pushing out to the stores
Costco uses pallet-based post-distribution crossdocking
Computer firms like Dell consolidate the major computer componentsin merge in transit centers.
JIT manufacturers consolidate inbound supplies in a nearby
warehouse
LTL and package carriers (UPS, FedEx) crossdock to consolidatefreight
Optimizing the CrossdockPerformance
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The major operational cost for crossdock is the labor.
Hence, the system performance is optimized by seeking to
maximize the throughput of the crossdock operations byestablishing an efficient freight flow.
Factors affecting the freight flow:
Long term decisions:
Number of doors and shape of the building
Employed material handling systems
parking facilities
Medium term decisions:
Crossdock layout, i.e., the characterization of the various doors asstrip or stack doors, and the assignment of specific destinations to
the stack doors
Short term decisions
Inbound Trailer Scheduling
Doors and Parking
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Number of stack doors:
determined by the volume of freight moved to each customer,
and any potential delivery schedules
Number of strip doors:
since trailer unloading is a faster job than trailer loading, acommon rule of thumb is to have twice as many stack doors asstrip doors, so that you balance the incoming with the outgoing
flow.
In general the larger the number of doors in the crossdock, thelarger the distances that must be traveled.
The parking lot should provide parking space for two trailersper door, so any flow surges can be accommodated withoutconsiderable problems.
Shape
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Corners are bad! Specifically:
Internal corners take away door locations (about 8 doorsper corner)
External corners take away storage space in front of thedoor (w/2 doors worth of floor space)
But min corners increases travel distance and congestionat centrally located doors
Suggested building shapes:
I for small crossdocks (up to 150 doors)
T for medium size crossdocks (between 150-250 doors)
X or H for the largest crossdocks (above 250 doors)
Frequently, the building shape is constrained
Crossdock Layout
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In general, centrally located doors should bereserved for the unloading activity and fordestination with large outgoing flows.
On the other hand, if the freight on eachinbound trailer is destined to a small andstable set of customers, then the facility canbe decongested by establishing distinct hubs
serving clusters of destinations that tend tohave their freight on the same incomingtrailers.
Crossdock Layout ...
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Two extensively used heuristics are:
the block heuristic:
Assign first the unloading activity to the best doors (i.e. thedoors having the smallest average distances to all otherdoors).
Subsequently, assign the remaining doors to outbound
destinations, prioritizing them in decreasing order of theirflow intensities
the alternating heuristic:
The door assignment alternates between a strip door and a
stack door to the destination with the next highest flow
The alternating heuristic produces solutions that are typically10% better than the solutions produced by the blockheuristic.
I-shape CrossdockRoadway Express crossdock in Chicago Heights, IL
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T-shape CrossdockAmerican Freightways crossdock in Atlanta
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H-shape CrossdockCentral Freight crossdock in Dallas; the largest LTL dock in the world -550doors
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Order Picking Equipment
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Static shelving
Recommended