A fuzzy logic based flight control system for “Ocean Voyager” autonomous underwater vehicle

A new variable structure fuzzy logic based flight control system (FCS) for the “Ocean Voyager” autonomous underwater vehicle is presented. This FCS is composed of three independently operating setpoint-based fuzzy logic controllers (FLCs) which regulate the heading, pitch, and depth of the vehicle. Each FLC contains a set of rules of the form: “IF <situation> THEN <action>.” Rules which are most satisfied during the current state of the vehicle are reflected to the greatest degree in the controller output. Control action is realized through rudder and stern plan deflection. Planes are mounted on the tail of the vehicle in a cruciform fashion. Previously, the control rules of “Ocean Voyager” FCS formed a static, nonlinear mapping between inputs and outputs. This format is typical of many FLCs used today. The new variable structure controller dynamically scales the nonlinear mapping formed by the rules during different stages of a step response. This format combines the minimum time characteristics of bang-bang control, with the smooth robust convergence of linear control. Testing of this FCS has been done using a six degree of freedom, nonlinear, dynamic model of the “Ocean Voyager”. Variable structure heading, pitch and depth controllers have shown increased performance over previous control strategies. Dynamic control of an AW is a complex, highly nonlinear problem. This work presents a simple approach. By which robust, minimum time control of the “Ocean Voyager” may be executed