Zhang Haijie, Zhao Jianguo
Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523, United States of America.
Bioinspir Biomim. 2017 Jan 31;12(2):025001. doi: 10.1088/1748-3190/aa53c4.
Marvelous vision based dynamic behaviors of insects and birds such as perching, landing, and obstacle avoidance have inspired scientists to propose the idea of time-to-contact, which is defined as the time for a moving observer to contact an object or surface if the current velocity is maintained. Since with only a vision sensor, time-to-contact can be directly estimated from consecutive images, it is widely used for a variety of robots to fulfill various tasks such as obstacle avoidance, docking, chasing, perching and landing. However, most of existing methods to estimate the time-to-contact need to extract and track features during the control process, which is time-consuming and cannot be applied to robots with limited computation power. In this paper, we adopt a featureless estimation method, extend this method to more general settings with angular velocities, and improve the estimation results using Kalman filtering. Further, we design an error based controller with gain scheduling strategy to control the motion of mobile robots. Experiments for both estimation and control are conducted using a customized mobile robot platform with low-cost embedded systems. Onboard experimental results demonstrate the effectiveness of the proposed approach, with the robot being controlled to successfully dock in front of a vertical wall. The estimation and control methods presented in this paper can be applied to computation-constrained miniature robots for agile locomotion such as landing, docking, or navigation.
昆虫和鸟类基于视觉的奇妙动态行为，如栖息、着陆和避障，激发科学家提出了接触时间的概念，其定义为移动的观察者以当前速度保持不变时与物体或表面接触所需的时间。由于仅使用视觉传感器，接触时间可以从连续图像中直接估计出来，因此它被广泛应用于各种机器人以完成诸如避障、对接、追逐、栖息和着陆等各种任务。然而，大多数现有的估计接触时间的方法在控制过程中需要提取和跟踪特征，这既耗时又无法应用于计算能力有限的机器人。在本文中，我们采用一种无特征估计方法，将该方法扩展到更一般的具有角速度的设置，并使用卡尔曼滤波改进估计结果。此外，我们设计了一种基于误差的控制器，并采用增益调度策略来控制移动机器人的运动。使用具有低成本嵌入式系统的定制移动机器人平台进行了估计和控制实验。车载实验结果证明了所提方法的有效性，该机器人被控制成功对接在垂直墙壁前。本文提出的估计和控制方法可应用于计算受限的微型机器人，以实现诸如着陆、对接或导航等敏捷运动。
