Abstract
This paper concerns the so-called “filtered nonlinear servos,” i.e., servos where the signal undergoes a filtering effect from a linear part of the device. “Hereditary phenomena,” such as Coulomb friction, gear backlash, and so on, are dealt with. A general stability criterion is derived, and it is shown how the Nyquist criterion appears as a particular case. The criterion indicates whether or not a servo is liable to hunt, but it is still necessary to state whether or not the possible hunting will have a limited amplitude. An approach to this problem is sketched and it is shown how the first results may be considered as quantitatively valid for quasi-linear systems. Some conclusions previously derived by assuming the transfer functions to be analytic appear as a limiting case of the present results.
