Page 43 - Modern Control Systems

Section 1.4 Engineering Design 17
work to assist in construction projects, crop monitoring, and continuous weather
monitoring. In a military setting, UAVs can perform intelligence, surveilUmce, and
reconnaissance missions [74]. Smart unmanned aircraft will require significant
deployment of advanced control systems throughout the airframe.

1.4 ENGINEERING DESIGN

Engineering design is the central task of the engineer. It is a complex process in
which both creativity and analysis play major roles.

Design is the process of conceiving or inventing the forms, parts, and details of a
system to achieve a specified purpose.

Design activity can be thought of as planning for the emergence of a particu-
lar product or system. Design is an innovative act whereby the engineer creatively
uses knowledge and materials to specify the shape, function, and material content
of a system. The design steps are (1) to determine a need arising from the values
of various groups, covering the spectrum from public policy makers to the con-
sumer; (2) to specify in detail what the solution to that need must be and to em-
body these values; (3) to develop and evaluate various alternative solutions to
meet these specifications; and (4) to decide which one is to be designed in detail
and fabricated.
An important factor in realistic design is the limitation of time. Design takes
place under imposed schedules, and we eventually settle for a design that may be less
than ideal but considered "good enough." In many cases, time is the only competitive
advantage.
A major challenge for the designer is writing the specifications for the technical
product. Specifications are statements that explicitly state what the device or prod-
uct is to be and do. The design of technical systems aims to provide appropriate de-
sign specifications and rests on four characteristics: complexity, trade-offs, design
gaps, and risk.
Complexity of design results from the wide range of tools, issues, and knowledge
to be used in the process. The large number of factors to be considered illustrates the
complexity of the design specification activity, not only in assigning these factors
their relative importance in a particular design, but also in giving them substance
either in numerical or written form, or both.
The concept of trade-off involves the need to resolve conflicting design goals, all
of which are desirable. The design process requires an efficient compromise between
desirable but conflicting criteria.
In making a technical device, we generally find that the final product does not
appear as originally visualized. For example, our image of the problem we are solving
does not appear in written description and ultimately in the specifications. Such
design gaps are intrinsic in the progression from an abstract idea to its realization.
This inability to be absolutely sure about predictions of the performance of
a technological object leads to major uncertainties about the actual effects of the