Chapter 1 – Introduction to Control Systems

Control theory is a relatively new field in engineering when compared with core topics, such as statics, dynamics, thermodynamics, etc. Early examples of control systems were developed actually before the science was fully understood. For example the fly-ball governor developed by James Watt to control overspeed of his steam engine was developed out of necessity, long before the science of controls came into being. Figure 1.1 shows an example of this controller. The fly-balls are mounted on a shaft that turns and is driven by the engine through the pulley shown. As the engine speeds up, the fly-balls are flung outward by their centrifugal force. This outward movement pulls the lever arm down, which raises its other end. This is tied to the steam inlet valve, which closes as the flyball weights move further outward. So if the engine tries to run away, the inlet steam valve will close, shutting off the fluid driving the engine.