facility layout nearness diagram

8/12/2019 Facility Layout Nearness diagram

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Facility layout

Activity relationship analysis


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REL chart

Flow analysis tends to relate various activities on somequantitative basis (refer Travel chart).

Typically, the relationship is expressed as a function oftransport cost or material handling cost.

There might be other qualitative aspectsof layout design thatmight be important.

The activity relationship chart (REL chart) was developed tofacilitate the consideration of qualitative factorsanalytically!

The REL chart replaces the numbers in the Travel chart by aqualitative closeness rating.


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REL chart

All pairs of relationships are evaluated, and a closeness rating(A, E, I, O, U,andX) is assigned to each pair.

When evaluating activity relationships forNactivities, thereareN(N-1)/2such evaluations.

With the exception of Urating, the reason for the assignedrating is indicated using a numeric code.

Closeness ratings represent an ordered preference forcloseness.

Specifically,AandXratings are considered to be most

important ratings. Hence, any layout must satisfyAandXratings.

Thus,AandX > E > I > O > U, where >means moreimportant or higher ranking than.


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REL chart

A: Absolutely necessary

E: Especially important

I: Important

O: Ordinary closeness OKU: Unimportant

X: Undesirable


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REL chart

Assignment of the closeness rating is subjective.

Rule of thumb:

Very fewAandXrelationships should be assigned. (no morethan 5% of the closeness ratings to be anAandX).

No more than 10% should be anE.

No more than 15% to be anI.

No more than 20% to be an O.

Which means that about 50% of the relationships should be U.


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Hierarchical approach

Block plans, or block layouts are developed first bydetermining the sizes, shapes and relative locations ofdepartments or other designated activities.

Next, detailed layouts are designed for each department.

Thus different REL charts are needed for designing blockplans and detailed layouts.

The process of constructing an activity relationship chart canbe complicated by the presence of multiple relationships thatwill influence the design of the layout.


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REL chart example


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REL chart REL diagram

From REL chart, we construct activity relationship diagram(REL diagram).

The purpose is to depict spatially the relationships of theactivities.

The basic premise is that geographic proximity can be used tosatisfy particular relationships.

For example, when the activity relationships reflect themagnitudes of material flows, pairs of activities having thegreatest pair wise flow are located next to each other.

Similarly, pairs of activities having anArating are locatedadjacently.


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Activity relationship diagram


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Activity relationship diagram


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Graph based process

Each activity is represented by a circle, node or vertex.

Activities that must be adjacent are denoted by connecting the

respective nodes or vertices with lines, links or edges.

The resulting representation of the activities and relationshipsis the activity relationship diagram or graph.

Agraph is planarif it can be drawn so that its vertices are

points in the space and each edge can be drawn such that it

intersects no other edges and passes through no other vertices.

A requirement for the existence of a layout satisfying the

activity relationships depicted in the graph is that the graph be

planar.


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Graph based process

Regions defined by a graph are referred to as faces; with theunbounded outside region is the exterior face.

Two faces are said to be adjacent if they share a common edge.

An additional aspect of a graph is its dual. To construct the dual of a planar graph, place a dual node in

each face of the primal graph.

Whenever two faces are adjacent in primal, connect thecorresponding dual nodes by an edge such that it crosses the

edge that divides the primal faces.

If the REL diagram is a planar graph, its dual graph will beplanar.


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Graph based process

It is not a simple matter to establish the planarity of a graph fora reasonably large layout problem.

Computer codes do exist for establishing the same though.

More importantly, upper bound exists on the number of pairs

of adjacent activities. If there areNactivities, no more than 3N-6pairs of activities

can be adjacent.

That is, if the graph of adjacency relationships has more than

3N-6edges, it cannot be planar. However, this is an upper bound. Examples can be constructed

such that non-planarity results with less number of adjacentactivities considered.


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Graph based process

If at least half of the relationships are Uratings, then for

planarity to exist, the upper bound places the following

limitations on the number of activities:

Hence if more than 10 departments are involved, planarity

will not exist if allA, E, I,and Orelationships must besatisfied via adjacency.

102

)1(5.063 NNNN


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Graph based process

Therefore, for large problems, if adjacency is the basis ofsatisfying closeness requirements, it might be that onlyA, orAand E, relationships can be satisfied.

If the distribution of closeness rating is 5% A, 10%E, 15%I,

and 20% O, then as many as 118 departments can beaccommodated if onlyArelationships must be satisfied viaadjacency.

However, ifAandErelationships are to be satisfied viaadjacency, no more than 38 departments can be

accommodated.

Similarly, to includeA, E, andIrelationships, only 18departments can be fit.


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Graph based process

In summary,

The graph based approach provides a structured approach for

developing the REL diagram.

Graph based approach is widely used in activity-based blocklayouts.

It emphasizes the importance of constructing a planar graph of

the REL chart if the block diagram is to be constructed to

satisfy the relationships.


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Graph based process

Limitations

Interpretation of closeness to mean adjacency. This, at times,

results in peculiar shapes of departments to satisfy adjacency

requirements.

There is no well-defined algorithm to draw a planar graph.

Planarity requirement is a limitation: Just because a set of

requirements can not be satisfied via a planar graph does not

mean that a block layout cannot be developed. It only means

that it is not possible to satisfy all relationships with adjacency.


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Relationship diagram process


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Designing a layout

After the block layout is ready, estimate is made of the space

requirements.

This includes space required for machines, equipments,

products.

Estimation of human resources needed is made based on the

number of machines operated and production rate.

Then, space relationship diagrams are made.


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Sample: Space relationship table


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Example: Alternate block diagram


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Example: Alternate block diagram


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Use of computers in layout design

Many Systematic Layout Planning (SLP) commercial softwarepackages available.

Examples:

CRAFT (Computerized Relative Allocation of Facilities

Technique) CORELAP (COmputerized RElationship LAyout Planning)

ALDEP (Automated Layout DEsign Program)

PLANET (Plant Layout Analysis aNd Evaluation Technique)

Originally developed in late 60s, many of these packages arestill around.. with latest additions to the features!


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Layout design

It has to be noted that if the favorable factors dont lend

themselves for quantification, it is very difficult to calculate

the utility of a layout using a computer software.

How do you measure flexibility of a layout against another?

So some form of quantifiable function is used in most of the

algorithms.


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Adjacency-based rating

The layout score is computed as:

where,

Xiis the number of adjacencies in class i, and

wiis the weighting factor for class i.

Typical weights:A (64), E(16), I(4), O(1), U(0) and X(-1024)

Larger the score, better is the layout.

6

1i

iiXws


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Distance-based scoring

The scoring model for mactivities:

Cijis the cost per unit distance of flow between activities iand

j. (same as i-to-jandj-to-i)

Dijis the distance between activities iandj.

1

1 1

m

i

m

ij

ijijDcs


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Pair-wise switching algorithm

Cost of the default layout =

50+2*100+2*20+30+50+10+2*20+100+50 = Rs. 570

Cost of new layout = 50+100+20+2*30+50+10+2*20+100+50= Rs. 480

facility layout nearness diagram

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