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1.11 Operator Interface

Many mechatronic systems require interaction with a human operator. The interaction can range from an ON/OFF switch to a fully-animated, multiscreen display. Other systems don't require any operator interface at all because they are themselves controlled by computer systems located in other parts of a larger system. Many of the computers in an automobile, for example, have no explicit operator interface and are buried deep within engine controls, braking systems, and so on. Some of them, however, do use an operator interface — in this case, the highly specialized operator interface used by the driver. The accelerator pedal serves as a command for power, the brake pedal for deceleration. Both are currently hybrid controls. They operate physical components directly and also give command signals to control computers. As cars become even more computer controlled, most of the direct connections will probably disappear. On many airplanes, they already have disappeared. Most large commercial and military aircraft in production at the turn of the century have "fly-by-wire" control systems in which the pilot's controls are linked only to computers — there is no direct physical link between the pilot and the control surfaces.

The automobile and airplane examples point out the most important property of operator interfaces: done well they facilitate proper system operation; done poorly they can lead to severe safety problems, particularly during unusual operating modes.

Operator interfaces, even those for fully computer-controlled systems, can be based on unique physical devices (such as the gas pedal on a car) or can use a computer-driven display. The design of the interface is a highly specialized activity and can consume a large portion of the implementation resources for a computer control system. Psychology, human-factors engineering, cultural factors, and various other considerations all play a part. Computer-based graphic displays cause particular problems for software portability because GUI (graphical user interface) software tends to be highly nonportable (see chapter 13 on Java for an exception to this).

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