CAPITULO III. TRATAMIENTO DE LA ANEMIA EN EL EMBARAZO
2.6. CUADRO HEMÁTICO
Asked what a bookcase does, a child might answer, “It doesn’t do anything, it just sits there.” An engineer, however, would say that the bookcase does at least two things: It resists the force of gravity exactly to support the weight of the books, and it enables the organization of those books with dividers or by its shelf lengths. Thus, this bookcase doesn’t “just sit there.” Understanding functionality is essential to successful design. There are consequences, often tragic, for failing to understand and design for all of a design’s
functions: recall the Hyatt Regency failure we discussed in Chapter 1. We will now explore how we talk about what designs do and then describe ways to establish functions.
6.1.1 Functions: Input Is Transformed into Output
We begin with our dictionary definition from Chapter 1:function n: those things a designed device or system is supposed to do.
For our work as designers, it is helpful to take a systems view and relate doing something to transforming an input into an output. Of course, this is also reminiscent of elementary calculus in which we write y¼ f(x) to denote how the function f(x) transforms the input of the independent variable x into an output of a dependent variable y. For most of our purposes, engineering functions involve the transformation or transfer or flow of energy, materials, or information. We frequently view such transformations through the prisms of the conservation and balance principles that we detail when we discuss physical modeling in Chapter 9.
We see energy in mechanical, thermal, fluid, or electrical forms, and we see energy transformed as it is stored, transmitted, converted, or dissipated. We also view energy transformation or transfer to include forces transmitted or used to support (conservation of momentum or balance of forces), current flows (conservation of charge), and so on. We must account for all of the energy going into and coming out of a device or a system. This does not mean that the device or system is an ideal one in which energy is conserved. Rather, it means that energy can’t simply disappear, even when it is dissipated.
Similarly, materials flow occurs in a variety of ways: moving or flowing through some conveyance (like a pipe), being transferred or located in a container, being separated into constituents, or added to, mixed in with, or located within one or more materials. Thus, cement, aggregate, and water are mixed to create concrete, which is then typically moved (while being mixed), poured, finished, and allowed to set and harden.
Finally, information flow includes the transfer of data in any of several forms: tables and charts on paper, data transmitted over the Internet or by wireless, and electrical or mechanical signals transmitted to sense or measure behavior or control response. The transformation of information occurs when, for example, a room temperature measured by a thermometer is transmitted to a wall thermostat that then instructs a heater or an air conditioner to change what it is doing. We might even think of the energy that is required to turn data into information and information into knowledge.
6.1.2 Expressing Functions
Given that functions are the things that a designed device must do, the statement of a function typically couples an action verb to a noun or object: lift a book, support a shelf, transmit a current, measure a temperature, or switch on a light.
The object in a verb–noun formulation function may start off with a specific reference to a particular design idea, but it is usually best to look for more generality. For example, while one bookcase function is “support books,” bookcase shelves often support trophies, art, or even piles of homework. Thus, a more general, more useful statement of the function to be performed is to “resist forces due to gravity,” which can in
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turn be associated with any objects weighing less than some predetermined weight (i.e., force): support a given number of kilograms (or pounds). When describing functions, then, we should use a verb–noun combination that best describes the most general case.
Similarly, we also should avoid tying a function to a particular solution. If we were designing a cigarette lighter, for example, we should avoid “applying flame to tobacco” because it eliminates car lighters that use electrical resistance in a wire. That specific formulation also eliminates using the lighter to ignite paper, wood, or charcoal briquettes. We can also categorize functions as being either basic or secondary functions. A basic function is the specific, overall function that must be performed, and secondary functions are (1) other functions needed to perform the basic function or (2) those that result from doing the basic function. Secondary functions maybe categorized further as either required or unwanted functions. Required secondary functions are those needed for the basic function. For example, the basic function of an overhead projector is to project images. This requires several secondary functions, including converting energy, generating light and focusing images. The projector also produces unwanted secondary functions such as generating heat and generating noise. Of course, such undesirable by-products may also spawn new required functions, for example, quieting noise or dissipating generated heat. This last example also suggests that we should try to anticipate all secondary functions, lest they turn into undesirable unanticipated side effects that may significantly affect how a new design is perceived and accepted.