Avoiding collisions is a crucial ability for unmanned vehicles. In this paper, we present the constant avoidance angle algorithm, a reactive method for collision avoidance. It can be used to avoid both static and moving obstacles by making the vehicle keep an avoidance angle between itself and the obstacle edge. Unlike many other algorithms, it requires neither knowledge of the complete obstacle shape nor that the vehicle follows a desired speed trajectory. Instead, safe vehicle headings are provided at the current vehicle speed. Thus, the speed can be used as an input to the algorithm, which provides flexibility and makes the approach suitable for a wide range of vehicles, including vehicles with a limited speed envelope or high acceleration cost. We demonstrate this by applying the algorithm to a marine vehicle described by a full kinematic and dynamic model in three degrees of freedom. We specifically consider vehicles with underactuated sway dynamics, where the vehicle velocity contains a component that cannot be directly controlled. Such dynamics can be highly detrimental to the performance of collision avoidance algorithms and need to be included in the design and analysis of control systems for such vehicles. In this paper, we compensate for the underactuation by including these dynamics in the underlying analysis and control design. We provide a mathematical analysis of sparse obstacle scenarios, where we derive conditions under which safe avoidance is guaranteed, even for underactuated vehicles. We furthermore show how the modular nature of the algorithm enables it to be combined both with a target reaching and a path following guidance law. Finally, we validate the results both through numerical simulations and through full-scale experiments aboard the R/V Gunnerus.

中文翻译：

---

使用恒定回避角算法的欠驱动船舶的避碰

对于无人驾驶车辆而言，避免碰撞是至关重要的能力。在本文中，我们提出了恒定回避角算法，这是一种避免碰撞的反应性方法。通过使车辆保持自身与障碍物边缘之间的避让角，可用于避免静态障碍物和移动障碍物。与许多其他算法不同，它既不需要了解完整的障碍物形状，也不需要车辆遵循所需的速度轨迹。而是以当前的车速提供安全的车辆行驶方向。因此，速度可以用作算法的输入，从而提供了灵活性，并使该方法适用于广泛的车辆，包括速度范围有限或加速成本较高的车辆。我们通过将算法应用到由三个自由度的完整运动学和动力学模型描述的船舶上来证明这一点。我们专门考虑具有不足的摇摆动力学的车辆，其中车速包含无法直接控制的分量。这样的动力学可能对避免碰撞算法的性能非常有害，并且需要被包括在这种车辆的控制系统的设计和分析中。在本文中，我们通过将这些动态因素包括在基础分析和控制设计中来补偿欠驱动。我们提供了稀疏障碍场景的数学分析，在这种情况下，我们得出了即使在驾驶不足的情况下也可以确保安全避开的条件。我们进一步展示了算法的模块化本质如何使它能够与目标到达和遵循制导律的路径相结合。最后，我们通过数值模拟和R / V Gunnerus上的全面实验来验证结果。