The Principle of a Servo-Type Mechanism Requiring Variable Elements
Rudolf F. Drenick · Proceedings of the IRE · 1953
The subject of this article is the theoretical synthesis of a mechanism which has some essential features in common with conventional servomechanisms and some with analog computers. It operates on a feedback principle; that is, at one point of the system an input is compared with a signal fed back from the outputs of the device, and an error signal is derived from this comparison. The basic distinction lies in the fact that this one error signal is used in this mechanism to control two outputs which are subject to a constraint. This is accomplished by a suitable variation in the gains of the system.