ABSTRACT
Control by a person over his or her immediate environment is necessary for survival and to fulfill all his physical needs and desires. The advancement of civilization and standards of living accompanying it have been strongly affected by the type and quality of tools and machines employed to enable necessary work activities to be accomplished. Throughout history until the last two centuries, machines were driven by water, wind, human, and animal power. Control by the human was of the most basic types: either one in which the human supplied all of the force, energy, and direction of movement as in using hand tools, or one in which the human directed forces as in plowing with animal power or steering a sailing vessel. All feedback was through human perception of the controlled activity and environmental conditions. Machines powered by external and internal combustion engines and by electricity extended the concept of control to include the production of mechanical energy and the operation of a great variety of machines and processes. Feedback from the process could now occur by direct observation as in sawing a board with a power saw or through displays through which the machine provides representative information (quantitative, qualitative, digital, analog, or graphic) about what is taking place or has taken place in the process.
