回坞是指自主水下航行器(AUV)完成任务后返回水下支持平台的过程,是实现AUV自主回收的关键步骤。本文中提出一种基于路径跟踪的AUV回坞控制算法。考虑AUV的机动能力,采用Dubins曲线规划一条连接AUV初始点和回收点的回坞路径,由两段半径为AUV最小转弯半径的圆弧和一段直线构成,在起点、终点处分别与AUV初始航向和回收器入口方向相切。设计AUV非线性全局路径跟踪控制,建立以沿路径运动的参考点为原点的Serret-Frenet坐标系,描述路径跟踪误差并建立误差的动态模型,从而克服传统方法的奇异性问题,然后将航向角看作路径跟踪误差的控制输入,设计航向角指令和路径参数的变化率,使路径跟踪误差全局渐近稳定,从而实现AUV对回坞路径的跟踪。仿真结果验证了本文所提出的回坞控制算法的有效性。
Homing is the process that an autonomous underwater vehicle(AUV) returns to its underwater supporting station after mission,and it is the key operation in the AUV′s autonomous retrieval.The AUV homing control algorithm based on path following is proposed in this paper.The homing path is planned with the Dubins curve to connect the AUV starting point and the docking point using one straight line and two arcs with radius equal to the AUV minimum turning radius determined by the AUV′s maneuvering capability.The tangent vectors of the homing path at the start-point and end-point are along the AUV′s initial heading and the docking entrance direction respectively.The nonlinear dynamic model of the path following errors is derived in the Serret-Frenet coordinate originating at the reference point moving on the path,overcoming the singularity problem in the classic methods.The command yaw angle is designed as the control input of the path following errors,which are proved to be globally asymptotically stable while properly choosing the rate of the path curve parameter.The simulation studies demonstrate the effectiveness of the proposed homing path planning and following controller.