Cross Track Error and Proportional Turning Rate Guidance of Marine Vehicles

The problem of turning rate guidance and control of marine vehicles is considered. Feedback with feed- forward rudder control is used to deliver a specified turning rate for the vehicle, while a guidance law is employed to create the necessary sequence of turning rate commands which would allow conver- gence to a desired geographical path. Two different guidance schemes are presented and analyzed, namely, cross track error and proportional turning rate guidance. Stability conditions are computed ex- plicitly, while nonlinear analysis techniques illustrate the significance of design parameters on the final system response that cannot be inferred from linearized stability results. naval and commercial operations have unique mission re- quirements and dynamic response characteristics. In partic- ular, they are required to be highly maneuverable and very responsive as they operate in obstacle-avoi dance and object- recognition scenarios. The need, therefore, arises to main- tain accurate path-keeping in confined spaces and shallow waters under the influence of steady- and time-varying ex- ternal forces. The primary vehicle guidance system is based on heading or turning rate commands that are generated based on a specified geographical sequence of desired way points. Speed commands can be generated by incorporating temporal attributes to the way points. These guidance com- mands are then passed to the vehicle controller which at- tempts to deliver the commanded heading and/or heading rate of change by an appropriate use of the vehicle control surfaces (Healey et al 1990). Unlike open sea operations, for vehicle missions in coastal areas and confined waters, the way point sequence must be very dense so that satisfactory path accuracy is maintained. One efficient way of maneu- vering through a given way point sequence is by using a line-of-sight guidance law which commands a heading angle that is directly related to the line-of-sight angle between the vehicle position and a desired destination point. The vehicle controller is then an orientation control law which delivers the commanded heading. Previous studies (Papoulias 1991, 1992), have demonstrated that this scheme is guaranteed stable only if the way point separation is above some critical value. This conclusion is true regardless of the particular form of the line-of-sight guidance or the heading control law used. Similar results hold for vertical plane guidance (Pa-