The practical realization of final-value systems with limiting constraints

In certain applications, the desired function of a control system is to control some variable accurately only at one instant of time. Examples of this can be found in homing missile guidance systems or aircraft landing systems. In the latter case, it is desired to have the vertical component of velocity be small at the instant of touchdown. Complicating features of such systems are the constraints imposed by physical limitations, such as the limited vertical acceleration capability of airplanes, and the noise or inaccuracy of measurements of the controlled variable. The optimum configuration for such systems has been derived, and this form can be used as the basis for the design of actual systems. The theoretical derivation of the optimum system idealized the actual situation, and a number of problems must be considered when the physical system is designed. Such problems as the closed-loop realization, the number of measurements of the system response, and the manner in which these measurements are utilized are discussed in this paper.