Abstract
In the first paper, a simple altitude control system for an autonomous vehicle, based on distance observation by four ultrasonic fan beams to different directions, was studied. And it was assured that the proposed system could control the vehicle to keep the predetermined altitude for most cases.In this report, further study is made to clarify practical feasibility of the proposed system, and the following results are obtained.(1) By using a variable directional ultrasonic beam to measure the minimum distance to the obstacle, the guidance logic can be simplified and the vehicle can avoid obstacles of the same size as the turning radius of the vehicle.(2) For a vehicle with variable cruising speed, its attitude can be controlled well only by changing the control parameters in proportion to the thrust power.(3) Angular velocity saturation of rudder motion causes oscillation of the attitude control, which can be suppressed by applying an optimal control algorithm based on the linear quadratic problem formulation.(4) A three dimensional mathematical model is formulated, and the controllability of the vehicle attitude around each of three axes is investigated. By changing the vehicle attitude in 3 axes at the same time, it is assured that attitude in each axis can be controlled independently without serious interferences for the applied model.
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