Computation Section
Subunit Facility Layout
 -Optimum Sequence

The sequential layout is defined by the department width and the sequence used to layout the departments along the aisles of the facility. The optimum sequence method of solution starts with an arbitrary initial sequential solution and tries to improve the layout by switching two departments in the sequence. At each step, the method computes the cost changes for all possible switches of two departments and chooses the most effective pair. The two departments are switched in the sequence and the method repeats. The process stops when no switch results in a reduced cost. To illustrate we start with the departments sequenced in order of department index as below.


Clicking the Solve button presents the dialog below. The top button stops at each iteration to show the new layout. The second button stops when there is no further improvement.


Starting from the initial sequence, the program finds the best switch and presents its conclusion below.


Clicking Yes causes the change in layout. Notice that departments 9 and 10 are switched in sequence and in location.


The next best switch is departments 1 and 3. Notice that the change in sequence affects the relative locations of the departments switched. When the departments are of different size, the locations of all departments between are also adjusted.


We restarted the process with the initial sequence and chose the Do Not Stop option. The process stopped with no further improvement after one additional switch of departments 6 and 7. The result is shown below.


To the right of the layout appears a summary of the switches made during the process.


Above the layout there are several additional buttons. The Random Layout button generates a random sequence of departments and places them on the layout. Since the switch heuristic does not guarantee optimality, it is useful to start at several different solutions and select the best.

The Evaluate button evaluates the current sequence placed in column G of the worksheet. The user can manually change the sequence. The Switch button allows the user to force the program to switch two departments. The Change Facility button allows the user to change features of the facility, such as length, width or department width, or change the solution options. The Show Flows button draws lines between centroids to show the flows. We discuss the Opt. Form and Optimize buttons later.

  For the example we generated a random sequence using the Random Layout button and performed the switch procedure until no improvement was possible. The resulting layout is shown below with the summary results. Note that this layout is much different that the one previously discovered. Its cost is slightly larger than before.

We initiated the layout with a department width of 4 with the resultant sequential layout as below.


After a sequence of switches we obtain the final layout shown with its summary below.


Clicking the Show Flows button shows the flow lines between departmental centroids. The thickness of a line shows the relative magnitude of the flow-cost between two of the departments. Four different thickness are used with a thin line indicating a relative small flow-cost between two departments and a thick line indicating a large flow-cost.


The sequential layout can be easily automatically generated. The sequential layout method quickly finds good layouts for alternative facility designs. The Traditional Craft method is an alternative. It is described on the next page.

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Operations Management / Industrial Engineering
by Paul A. Jensen
Copyright 2004 - All rights reserved