A method for evaluating nonlinear servomechanisms

A method is presented for determining a valid mathematical description of a class of nonlinear servomechanisms from measurements of the servo response to a set of input signals. In the sense used here, a valid mathematical description means a description that predicts the response of the servomechanism to a given class of inputs with a desired degree of accuracy. The set of input signals may consist of either sinusoids or Gaussian random signals. The response of the servomechanism is measured as a function of the amplitude and frequency composition of the input. The types of servomechanisms treated are conventional, single-loop feedback systems having a zero energy-storage nonlinear element, which may be located anywhere in the forward part of the loop. The evaluation procedure determines the transfer functions of the linear elements on both sides of the nonlinear element and the response function of the nonlinear element. The characteristics of the nonlinear and linear element must be such that only a small amount of nonlinear distortion exists at the input to the nonlinear element.