ABSTRACT
Positioning systems in general have their most basic form, and also the most complex, in the human being. The brain serves as the summing network that accepts the command for a desired motion or position, the musculatory system serves as the power source or prime mover to cause motion to take place, and the sensory system, such as the eyes, determines the present position. In general, these three things-the brain, the muscles, and the eyes-are analogues to the three basic parts of any positioning system. The brain accepts the command, or reference as it is sometimes called, and compares it to the feedback to answer the question, ‘‘How do we get to where we want to be?’’ The eyes are the feedback device, sometimes called a measuring system, which answers the question, ‘‘Where are we?’’ The difference between the command or the desired position and the actual position (determined from the feedback device) is referred to as the position error. It is this error that makes the prime mover cause motion to take place, resulting in the actual position equaling the desired position and the position error being reduced to zero.
