Page 137 - MATLAB an introduction with applications

122 ——— MATLAB: An Introduction with Applications

(a) Man-made control systems
(b) Natural, including biological-control systems
(c) Control systems whose components are both man-made and natural.
An electric switch is a man-made control system controlling the electricity-flow. The simple act of pointing
at an object with a finger requires a biological control system consisting chiefly of eyes, the arm, hand and
finger and the brain of a person, where the input is precise-direction of the object with respect to some
reference and the output is the actual pointed direction with respect to the same reference. The control
system consisting of a person driving an automobile has components, which are clearly both man-made
and biological. The driver wants to keep the automobile in the appropriate lane of the roadway. The driver
accomplishes this by constantly watching the direction of the automobile with respect to the direction of
road. Figure 3.2 is an alternate way of showing the basic entities in a general control system.

Objectives Results
Control system

Fig. 3.2 Components of a control system
In the steering control of an automobile for example, the direction of two front wheels can be regarded as
the result or controlled output variable and the direction of the steering wheel as the actuating signal or
objective. The control-system in this case is composed of the steering mechanism and the dynamics of the
entire automobile. As another example, consider the idle-speed control of an automobile engine, where it is
necessary to maintain the engine idle speed at a relatively low-value (for fuel economy) regardless of the
applied engine loads (like airconditioning, power steering, etc.). Without the idle-speed control, any sudden
engine-load application would cause a drop in engine speed that might cause the engine to stall. In this
case, throttle angle and load-torque are the inputs (objectives) and the engine-speed is the output. The
engine is the controlled process of the system. A few more applications of control-systems can be found
in the print wheel control of an electronic type writer, the thermostatically controlled heater or furnace which
automatically regulates the temperature of a room or enclosure, and the sun tracking control of solar collector
dish.
Control system applications are found in robotics, space-vehicle systems, aircraft autopilots and controls,
ship and marine control systems, intercontinental missile guidance systems, automatic control systems for
hydrofoils, surface-effect ships, and high-speed rail systems including the magnetic levitation systems.

3.3 EXAMPLES OF CONTROL SYSTEMS

Control systems find numerous and widespread applications from everyday to extraordinary in science,
industry and home. Here are a few examples:
(a) Home heating and air-conditioning systems controlled by a thermostat
(b) The cruise (speed) control of an automobile
(c) Manual control:
(i) Opening or closing of a window for regulating air temperature or air quality
(ii) Activation of a light switch to regulate the illumination in a room
(iii) Human controlling the speed of an automobile by regulating the gas supply to the engine

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