玉米除草机器人视觉导航系统设计与试验

    Design and experiment of the visual navigation system for a maize weeding robot

    • 摘要: 玉米苗带准确检测与精准跟踪是玉米除草机器人实现自主作业的重要基础。针对玉米除草机器人苗带检测,该研究提出了基于感兴趣区域更新的玉米苗带实时识别及导航线提取方法,首先利用单目相机采集机器人前向玉米苗带,将苗带图像进行归一化和超绿处理,采用改进自适应响应阈值SUSAN(small univalue segment assimilating nucleus)角点法以及冗余离群特征点剔除法获得玉米苗特征点,以改进的顺序聚类算法对视频帧进行玉米苗带聚类处理,再利用最小二乘法拟合出各玉米苗带,最后基于机器人航向偏差和其相对玉米苗带的横向偏差实时调整感兴趣区域和更新导航线;同时,针对除草机器人苗带行线跟踪,提出以运动学为模型的PID(proportion integration differentiation)转向角决策方法,建立了导航跟踪控制模型;并在Visual Studio平台下,利用OpenCV库开发了导航控制系统。试验结果表明,玉米除草机器人导航线提取准确率为96.8%,每帧图像平均处理时间为87.39 ms,具有较好的实时性和抗干扰性;在模拟环境下,玉米苗带直线和曲线跟踪平均误差≤1.42 cm,标准误差≤0.41 cm;在农田环境下,不同速度导航跟踪平均误差≤1.51 cm,标准误差≤0.44 cm。研究结果可为玉米除草机器人田间自主作业提供关键技术支撑。

       

      Abstract: Maize weeding robots play a significant role in the green production of modern agriculture. A high production efficiency can also be gained to reduce the labor costs, particularly with no chemical pollution. The autonomous operation of maize weeding robot can depend mainly on the accurate detection and tracking of maize seedling belt. In this study, an updated real-time recognition was proposed to extract the navigation line between the maize seedling belts using Region of Interest (ROI), in order to facilitate the seedling belt detection of maize weeding robot. A monocular camera was used to capture the maize seedling belt in front of the robot. Images preprocessing was firstly implemented to effectively segment the seedling zone and background using optimal threshold selection, according to the large gap between the green area of seedlings and weeds. Secondly, the feature points of seedling belt were accurately extracted using an improved adaptive response threshold Small univalue segment assimilating nucleus (SUSAN) corner method. The redundant outliers of feature points were then removed to reduce the amount of clustering calculation for the better real-time performance. Thirdly, the regional hierarchical clustering was incorporated into the sequential cluster, in order to improve the speed of clustering. The maize seedlings were also performed on the regional sequential clustering with clustering process. Moreover, the least square method (LSM) was used to fit each maize seedling belt. Finally, the ROI was adjusted to update the navigation line in real time, according to the heading deviation of the robot and the lateral deviation relative to the maize seedling belt. Meanwhile, the kinematics model was utilized to optimize the steering angle under the PID controller. The optimal steering angle was obtained to avoid the pressure and damage from the wheel skid using the seedling belt row tracking of the weeding robot. The navigation control system was developed using OpenCV library on the Visual Studio platform. A real-time detection of maize navigation line was realized for the synchronous interaction between the navigation line deviation under the STM32 control terminal, and the manual control of weeding robot navigation. A continuous video was randomly captured from the collected maize seedling belt data set as a test, in order to verify the accuracy of the real-time navigation line extraction. Results show the accuracy rate of navigation line extraction was 96.8% with the average processing time of 87.39 ms, indicating the excellent real-time and anti-interference. The average tracking error of maize seedlings with the straight lines and curves was less than or equal to 1.42cm, while the standard tracking error was less than or equal to 0.41cm in the simulated environment. In the farmland, the average tracking error of navigation at different speeds was less than or equal to 1.51cm, and the standard error was less than or equal to 0.44cm, indicating the accurate operating of the weeding robots in the maize seedling belt rows. In summary, the seedling belt extraction and navigation tracking control of weeding robot was precisely realized by the navigation control system of maize weeding robot. The fast and accurate identification of seedling band can be suitable for the strong adaptability and stability of navigation tracking control system, fully meeting the navigation requirements of maize weeding robot operation. The finding can provide the technical support for the subsequent research of weeding robots.

       

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