A new technique for the design of automatic-control systems with nearly optimum transient response has been developed. The fundamental concept in the new method is that the control or forcing of the output member must be performed in such a manner that the error or deviation and its derivatives should be reduced to zero in three steps for third and higher-order systems. These three steps consist of a single period of maximum corrective action which forces the controlled variable in the direction of decreasing error or deviation, a single period of maximum corrective action in the opposite sense to decelerate the controlled variable, and finally a force-free period at the end of which the error and its derivatives simultaneously go to zero. In the practical embodiment of this mode of control a proportional control action exists during the final phase. During this proportional control period, the controller corrects any errors introduced by the instrumentation during the initial phases. In addition to the superior transient performance, a predictor-control system has the advantage that its response is not affected by variations in gain, if the gain is sufficiently large, and that the allowable gain in the proportional region is considerably in excess of that permitted in conventional linear-type systems. As a result, the steady-state accuracy which can be obtained is not dependent on a critical gain setting and the system response and accuracy are not degraded by the incorporation of variable gain elements.

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