ANEMIA DE CÉLULAS FALCIFORMES

of all of the principal functions that our design must perform and also some of the key features it must have. The list should be of a manageable size, and all of the entries should be at the same level of detail to help ensure consistency. Then, across from each of the functions or features, we list each of the different means of realizing the function or feature that we can think of. We strongly encourage separating functions from key features, for several reasons. First, we know that our design must be fully functional to satisfy our client’s requirements. By putting all the functions together on the morph chart, we know we have addressed them all. The second reason we encourage separating functions from features is that a morph chart can quickly become rather large, and we may lose track of or confuse functions with key features. If we separate function from features at the outset, we can easily create two “design space” models in two separate charts, if necessary.

If we listed all the functions for the beverage container problem and arrayed the means corresponding to each to the right of each entry, we’d get the morph chart shown in Figure 7.1. We see that some functions have more means than others, for example, the function Contain Beverage has four means, while Resist Forces has only two. When we see a very small number of means this suggests that either we have a small design space (i.e., limited choices) or we have not fully explored the available design space.

We start building conceptual designs from the morph chart by noting that any feasible design must be functionally complete: every function, listed in the leftmost column must be achieved by that design. So we assemble designs by choosing one means from each row, and combine them into a functional design concept or scheme. Thus, we see in Figure 7.2a that one feasible design for the new juice container is a heat-sealed bag with a tear corner, thick walls, and a distinctive label, and another is a bottle with a twist top, made of a flexible material and with a distinctive shape.

MEANS FUNCTION

1 2 3 4 5 6

Contain Liquid Can Bottle Bag Box

Fill and Seal Container Fill and Heat

Seal Sealed Cap Glue ContainerMaterial Twist Top Bottle Cap Empty Container Pull Tab Inserted Straw Twist Top Tear

Corner ContainerUnfold Zipper Resist Forces Thick Walls Flexible

Materials Identify Product Shape of

Container DistinctiveLabel Color

Figure 7.1 A morphological (“morph”) chart for the juice container design problem with functions listed in the leftmost column. The means by which each can be implemented are arrayed along a row to each entry's right.

The design generation method we have just described makes the morph chart into a spreadsheet with which we can “calculate” the number of potential designs. How many potential designs are there in that morph chart, that is, just how big is our design space? The answer reflects the combinatorics that result from combining a single means in a given row with each of the remaining means in all of the other rows. Thus, for the beverage container morph chart of Figure 7.1, the number of design alternatives could be as large as 4 5  6  2  3 ¼ 720.

While it seems that the design space for this simple example has suddenly become very large, it is important to recognize that not all of the combinations allowed by our combinatorial arithmetic are valid combinations, that is, not all of these 720 combinations are feasible designs. For example, we can see (Figure 7.2b) that we can’t really design a bag with a zipper or a can with an unfolding corner!

MEANS FUNCTIONS

1 2 3 4 5 6

Contain Liquid Can Bottle Bag Box

Fill and Seal Container Fill and Heat

Seal Sealed Cap Glue ContainerMaterial Twist Top Bottle Cap Empty Container Pull Tab Inserted

Straw Twist Top CornerTear ContainerUnfold Zipper Resist Forces Thick Walls Flexible

Materials Identify Product Shape of

Container DistinctiveLabel Color

(a) MEANS

FUNCTIONS

1 2 3 4 5 6

Contain Liquid Can Bottle Bag Box

Fill and Seal Container Fill and Heat

Seal Sealed Cap Glue ContainerMaterial Twist Top Bottle Cap Empty Container Pull Tab Inserted

Straw Twist Top CornerTear ContainerUnfold Zipper Resist Forces Thick Walls Flexible

Materials Identify Product Shape of

Container DistinctiveLabel Color

(b)

Figure 7.2 The morphological (“morph”) chart for the juice container design problem (Figure 7.1) is used to show (a) two feasible design alternatives whose means are dark and light shaded, and (b) two infeasible combinations whose means are also dark and light shaded.

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Thus, our morphological chart provides both a tool to develop a design space and create design alternatives, and it provides an approach to prune that design space by identifying and excluding infeasible, incompatible alternatives. We exclude infeasible alternatives by, again, applying interface constraints, as well as physical principles and plain common sense.

We can use the morph chart to include key features as well as functions. In the juice container, for example, we might include a set of entries related to the materials we want to use, in which case we could distinguish between glass, plastic, Mylar, and cardboard. These features can help us understand our design space and conceptualize alternative designs, as well as generating more infeasible designs such as a glass bag.

There is a lot we can learn from our morph chart. Consider our problem with not having many means for Resisting Forces. The heart of this problem is that we need to consider resisting forces in more detail, distinguishing between Resisting Temperature and Resisting Shocks. At the same time, this may take us more deeply into particular designs than is appropriate at the conceptual stage. Once we have selected a concept, such as a bottle, we can increase its resistance to forces by thickening the walls, adopting appropriate structural elements, or wrapping it in a protective plastic. This shows us that it is important that we list functions (and features) at the same level of detail when we build a morph chart. Otherwise, we will find ourselves developing highly detailed designs at the conceptual stage, or still creating concepts even after we have settled on a scheme. Similarly, when doing a complex design task (e.g., designing a building), we don’t want to worry about means for identifying exits or for opening doors while developing different concepts for moving between floors (e.g., elevators, escalators, and stairways).

We can also use morph charts to expand the design space for large, complex systems by listing principal subsystems in a starting column and then identifying various means of implementing each of those subsystems. For example, if we were designing a vehicle, we would need a subsystem Provide Power, which would have corresponding means like Gasoline, Diesel, Battery, Steam, and LNG. Each of these power sources is itself a subsystem that needs further detailed design, but we see we can use the morph chart idea to develop an array of subsystems to expand our range of design choices for a complex design. We might even choose to create a morph chart for some of these subsystems to help us appreciate the design choices implicit in our concepts and schemes.