Adaptive control systems

Claim 1

A magnetostrictive actuator comprising: a generally cylindrical housing having an open end and a closed end; a rod of magnetostrictive material having two ends, said rod retained within said housing, one of said ends retained by the closed end of said housing; a transverse wall at the open end of said housing which defines a cavity between said wall and said rod; spring means for applying an adjustable axial compressive stress to an other of said ends of said rod; an electromagnet incorporated in said housing and magnetically coupled to said rod; means for generating a control current within said electromagnet, said control current and said electromagnet comprising a means for inducing a corresponding magnetic field within said rod; and an actuating member, extending through said transverse wall and in contact with said rod, an axial position of said actuating member, relative to the housing, responsive to the length of said rod wherein said actuating member is connected to control a process in response to an externally-generated demand signal, and said means for generating a control current includes a control system comprising: an estimator for providing a model of the response of said process to external influences; a control designer, responsive to said estimator, for comparing the model provided by said estimator with a stored model and for generating feedback control signals as a result of such comparison; two switched filters for applying to the control current positive and negative feedback signals, resptively; and a variable structure controller for controlling switching between said two filters in response to said demand signal.