MODELING AND CONTROL OF AN ODYSSEY III AUV THROUGH SYSTEM IDENTIFICATION TESTS

摘要

We address the issue of dynamic modeling and control of the Blue-fin Odyssey III class vehicle "Caribou", operated by the MIT Sea Grant AUV Laboratory. Focus is on demonstrating a simple forward design procedure for the flight control system, which can be carried out quickly and routinely to maximize vehicle effectiveness. In many situations, the control loops are tuned heuristically in the field; frequent retuning is necessitated by the inevitable changes in vehicle components, layout, and geometry. Our paradigm here is that 1) a prototype controller is developed, based on an initial model, 2) this controller is then used to perform a very compact set of runs designed to identify the vehicle dynamic response, and 3) a revised, precision controller based on this improved model is implemented for the ultimate mission. We first developed a hydrodynamic model of the vehicle from theory and benchtop laboratory tests; no data from prior field tests with this vehicle was used. Body added mass approximations were included as well as lift and hydrostatic forces and moments. Inertial properties were approximated by assuming the vehicle density was that of water. Caribou's tail-cone assembly consists of a double-gimbaled thrust-vectoring duct, with significant positioning dynamics and a non-traditional hydrodynamics. We carefully tested this tailcone's response behavior through laboratory tests, and created a low-order model. Using the tailcone model and the vehicle's initial hydrodynamic model, we developed a conservative controller design from basic principles. The control system consisted of a heading controller, pitch controller, and depth controller; the pitch control loop was nested inside the depth control loop. This control system was successfully tested in the field: the vehicle was controllable within several degrees of heading and approximately one-half meter of depth, on the first-pass design. System identification tests were then completed with the preliminary controller to gain a better understanding of the complete hydrodynamics of the vehicle, and in order to develop a precision controller based on the improved model. The resulting data provided a full-system linear model of the vehicle, and led to a successful controller redesign, with significantly improved performance.