15
Controls and Controlling
Actions
How do the operators avoid the occasional mistake, confusion, or accidental bumping against the wrong
control? Or misaim? They dont. Fortunately, airplanes and power plants are pretty robust. A few errors
every hour is not importantusually.
D.A. Norman (2002)
INTRODUCTION
Machines communicate information about their status to their operators through displays. Operators
communicate how they want the machines status to change by manipulating controls. There are
many kinds of physical devices available for use as controls, including push buttons, toggle
switches, joysticks, and knobs. They can be operated using the hands, feet, and, in some cases,
eye and head movements. Sound-sensitive controls that respond to human speech are used for
machines that restrict the operators ability to divert his or her gaze to a control panel. In cars, for
example, interactive voice navigation systems can respond to voice commands and give driving
directions, without the driver ever having to look away from the road (Chengalur et al., 2004).
Different kinds of controls require different types of actions. This means that a control that
works well in one situation may not necessarily be the best in another situati on. Moreover, rapid
changes in technology insure that there will always be new probl ems to overcome in control design.
For example, handh eld devices such as PDAs pose unique problems for data entry (and display)
because they a re so small. Users may benet from novel controls (e.g., special pressure-sensitive
controls; Paepcke et al., 2004). The job of the human factors engineer is to use ergonomic data to
determine the particular controls and layout of the panel that will optimize both operator and system
performance.
Effective controls have several characteristics. First, they are easily operated by their users.
Second, their sizes and shapes are determined by biomechanic and anthropometric factors (see
Chapter 16), as well as by population stereotypes for the mapping of the control settings to system
states (see Chapter 13). Third, they are appropriate for the controlling action they were designed to
facilitate, they can accommodate the muscle force required to move them, and respond with
necessary speed and accuracy (Bullinger et al., 1997).
Usually, several controls are arranged together on a panel. A good control panel will insure that
the operator can easily determine the identities and functions of each control. Also, the operat or
must be able to reach all the controls and apply the forces necessary for their operation. In this
chapter, we will discuss the featu res of controls and control panels that make them usable, and how
human factors engineers can contribute to their design.
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