Human Factors in Simple and Complex Systems, Second Edition, 2nd Edition

15

Controls and Controlling

Actions

How do the operators avoid the occasional mistake, confusion, or accidental bumping against the wrong

control? Or misaim? They don’t. Fortunately, airplanes and power plants are pretty robust. A few errors

every hour is not important—usually.

—D.A. Norman (2002)

INTRODUCTION

Machines communicate information about their status to their operators through displays. Operators

communicate how they want the machine’s 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 operator’s 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 benefit 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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