Study on motion control of vehicle for sea bottom survey

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In this study, an underwater vehicle named DELTA after its Δ-shape wing has been developed, what we call, an ROV (Remotely Operated Vehicle) in the field of offshore engineering. For the purpose of wide area survey of sea bottom, DELTA control system should be designed such that it can be operated both as a towed vehicle for fast movement and as a self-propulsive vehicle for good maneuverability. In general, the shape required for the two vehicles are quite different from each other form the viewpoint of hydrodynamics, that is, a streamlined shape for self-propulsive vehicle and a blunt shape for self-propulsive vehicle. Therefore it is very interesting to design the DELTA control system which works very well as the two functional vehicles.DELTA has three actuators consisting of right thruster, left thruster, weight shifter, and four sensors mode with higher speed, a control purpose is to keep the depth at the specified level against towing speed variations and mother ship oscillations … More . We tried H∝ feedback control for using the weight shift mechanism against towing speed variations.On the other hand, in the self-propulsive mode, a control purpose to facilitate precise and good maneuverability against the towing cable effect. We obtained successful experimental results for linear running a water tank using LQG multivariable feedback control with integral action. It was shown that equalized thrusters and differential thruster could control longitudinal behavior and lateral-directional behavior respectively. However in the case of nonlinear running, for example, collision avoidance the LQG control system will not work very well because of large parameter variations due to rapid speed variation and strong water current. In addition, there is another problem that the towing cable disturbs DELTA's attitude when DELTA is going around. These problems should be solved by robust controllers, in particular, gain-scheduling controllers. The latter problem also seems to be formulated as a nonholonomic control system which is a hot issue in the fields of robotics and nonlinear control. Less