自主水下載具之觀測性操控路徑規劃

Observability-Based Maneuvering Planner for AUV

觀測性為線性系統的初始狀態以及系統輸出之間之關係。本文使用線性時變方程式描寫自主式水下載具之運動，藉由監控觀測性，系統控制器可以即時更新較佳的輸入，使系統輸出估測更為準確與可靠。載具之不可觀測狀態代表狀態空間中無法藉由感測器量測來改善估測值之模態，本研究使用以卡曼濾波器為基礎所衍生之間接式即時定位與地圖建立的方法，藉由估測慣性導航儀誤差狀態，回授修正來提高自主式水下載具導航的精確度。當導航誤差增大時，啟動穩態迴轉或蛇行路徑來改變觀測性矩陣中之各模態的配置，以減少導航誤差。本文藉由數值模擬，將此法使用於配置前視聲納的自主式水下載具上，其結果顯示在水下載具運動過程中，藉由觀測路徑選擇改變加速度和載具與環境特徵之相對距離，可以調整觀測性，進而提高載具水下定位精度。 Observability is a property in linear system which relates the initial state and the system output. This work uses a linear time-varying equation to describe the motion of an autonomous underwater vehicle (AUV) that enables the utilization of observability analysis during the AUV maneuver. Through the observability analysis, the unobservable mode which indicates the state direction without information from sensor observation in state space is identified. Then an observability-based maneuver planner is developed to prevent the state error from growing up. The maneuver planer here involves a covariance threshold of heading and an observability-based maneuver patterns that involve heading maneuvers such as steady turn and S-shape motions. An AUV which implemented the maneuver planner is simulated to explore a 2-D environment by a forward-looking sonar. The vehicle explores in a set path and the covariance is tracked all the time. Once the covariance is greater than the threshold, the observability-based maneuver is executed. Simulation results show that variations of the accelerations of vehicle and the relative position between feature and vehicle are different between straight-line motion and heading turning and S-shape motions. The difference of variations of the projected length of unobservable mode on state space can also be shown. This indicates the unobservable mode can be controlled through maneuvering and will affect the accuracy of vehicle state.