1.4.  HUMAN CONTROL SYSTEMS

The relation between the behavior of living creatures and the functioning of feedback control systems has recently gained wide attention. Wiener [1] implied that all systems, living and mechanical, are both information and feedback control systems. He suggested that the most promising techniques for studying both systems are information theory and feedback control theory.

Several characteristics of feedback control systems can be linked to human behavior. Feedback control systems can “think” in the sense that they can replace, to some extent, human operations. These devices do not have the privilege of freedom in their thinking process and are constrained by the designer to some predetermined function. Adaptive feedback control systems which are capable of modifying their functioning in order to achieve optimum performance in a varying environment, have gained wide attention. These systems are a step closer to the adaptive capability of human behavior [2].

The human body is, indeed, a very complex and highly perfected adaptive feedback control system. Consider, for example, the human actions required to steer an automobile. The driver’s objective is to keep the automobile traveling in the center of a chosen lane on the road. Changes in the direction of the road are compensated for by the driver turning the steering wheel. His objective is to keep the differences between the output (the car’s actual position on the road) and the input (the car’s desired position on the road) as close to zero as possible.

Figure 1.11 illustrates the block diagram of the feedback control system involved in steering an automobile. The error detector in this case is the brain. This in turn activates the driver’s muscles, which control the steering wheel. Power amplification is provided by the automobile’s steering mechanism, which controls the position of the front wheels. The feedback element represents the human’s sensors (visual and tactile). Of course, this description is very crude—any attempt to construct a mathematical model of the process should somehow account for the adaptability of the human being and the effects of learning, fatigue, motivation, and familiarity with the road.

Figure 1.11 Steering of an automobile—a feedback control system involving a human.