Abstract
The application of mobile robots is an important link in the development of intelligent greenhouses. In view of the complex environment of a greenhouse, achieving precise positioning and navigation by robots has become the primary problem to be solved. Simultaneous localization and mapping (SLAM) technology is a hot spot in solving the positioning and navigation in an unknown indoor environment in recent years. Among them, the SLAM based on a two-dimensional (2D) Lidar can only collect the environmental information at the level of Lidar, while the SLAM based on a 3D Lidar demands a high computation cost; hence, it has higher requirements for the industrial computers. In this study, the robot navigation control system initially filtered the information of a 3D greenhouse environment collected by a 3D Lidar and fused the information into 2D information, and then, based on the robot odometers and inertial measurement unit information, the system has achieved a timely positioning and construction of the greenhouse environment by a robot using a 2D Lidar SLAM algorithm in Cartographer. This method not only ensures the accuracy of a greenhouse environmental map but also reduces the performance requirements on the industrial computer. In terms of path planning, the Dijkstra algorithm was used to plan the global navigation path of the robot while the Dynamic Window Approach (DWA) algorithm was used to plan the local navigation path of the robot. Through the positioning test, the average position deviation of the robot from the target positioning point is less than 8 cm with a standard deviation (SD) of less than 3 cm; the average course deviation is less than 3° with an SD of less than 1° at the moving speed of 0.4 m/s. The robot moves at the speed of 0.2, 0.4, and 0.6 m/s, respectively; the average lateral deviation between the actual movement path and the target movement path is less than 10 cm, and the SD is less than 6 cm; the average course deviation is <3°, and the SD is <1.5°. Both the positioning accuracy and the navigation accuracy of the robot can meet the requirements of mobile navigation and positioning in the greenhouse environment.
Highlights
With the development of mechanization and automation, agriculture has undergone an accelerated upgrading toward information and intelligent agriculture in the world
The proposed autonomous navigation system for the greenhouse mobile robot was designed based on 3D Lidar and 2D Lidar Simultaneous localization and mapping (SLAM)
The hardware part was mainly composed of 3D Lidar, an inertial measurement unit (IMU), an odometer, and an encoder
Summary
With the development of mechanization and automation, agriculture has undergone an accelerated upgrading toward information and intelligent agriculture in the world. With the development of high technology and with the incremental labor cost, the application of robots in agriculture has become more and more extensive. Robots enjoy a large application market in picking, plant protection, inspection, and other aspects of greenhouses (Uyeh et al, 2019). In terms of the autonomous navigation of robots, the navigation solutions based on Global Navigation Satellite System (GNSS) have been fully applied in the field operations environment (Pérez Ruiz and Upadhyaya, 2012). As there are many obstructions in greenhouses to cause the loss of satellite signals, the greenhouse environment is not suitable for mobile robots. Path planning and movement, which are safe, fast, and effective, have become the primary difficulties in the application of greenhouse mobile robots
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