Optimization of nonlinear control systems by means of nonlinear feedbacks

The first portion of this paper is devoted to the logical selection of a category of nonlinear systems - systems having: 1. controllers with any number of time lags or leads, and usually operating in their saturated region (velocity saturation, force saturation, etc.), and 2. loads consisting of combinations of nonlinear masses, nonlinear dampers, and nonlinear springs. (Nonlinearities which involve explicit functions of time, such as mass and inertia of a controlled rocket motor missile, introduce special considerations not included here.) In the second part of the paper, characteristics of an intentionally nonlinear element added to the feedback are considered. In the final part, the nonlinear element is shaped to provide optimum response in the saturated region of operation.