Agricultural robot positioning system based on laser sensing

In order to solve the positioning problem of global navigation satellite system (GNSS) based robots and autonomous agricultural machinery, which is low accuracy or even unable to locate under the environment of weak or no satellite signals such as hangars and greenhouses. This research proposes an agricultural robot positioning system based on laser sensing. The system is designed by using two-dimensional laser scanner and laser receiver, which obtains the point cloud of the laser receiver on the robot through the scanning laser emitted by the two-dimensional laser scanner , and the laser receiver inductively scans by the laser scanner, the location of mobile laser receiver (i.e. agricultural robot) is obtained by fusing the time difference of laser scanning induction and the point cloud characteristics of mobile laser receiver. The agricultural robot positioning system based on laser sensing consists of mobile laser receiver, processor, fixed laser receiver and two-dimensional laser scanner. The mobile laser receiver and processor are installed on the robot, and the fixed laser receiver and two-dimensional laser radar are fixed at the known geodetic coordinate position. According to the position relationship between the laser scanner coordinate system and the known geodetic coordinate system. The laser scanner scanning at a certain period to obtain a known number of fixed-order point cloud data. The fixed laser receiver senses the periodic irradiation of the laser scanner to generate the base station laser signal, and the serial number of the fixed laser receiver shell in the point cloud is known. The mobile laser receiver senses the periodic irradiation of the laser radar to generate the mobile laser signal during the movement of the robot. According to the trigger time difference between the fixed laser signal and the mobile laser signal, the angle between the laser rays that are irradiated to the mobile laser receiver and the laser rays that are irradiated to the fixed laser receiver can be obtained in a scanning period of the laser scanner. And the scattered point set of the mobile laser receiver in the laser radar point cloud can be found, and the center coordinate of the mobile laser receiver can be obtained by combining the point cloud feature matching algorithm. The robot positioning can be calculated by combined with the geodetic coordinates of the laser scanner and the position relationship between the laser scanner coordinate system and the geodetic coordinate system, the central coordinates of the mobile laser receiver under the geodetic coordinate system. The geodetic coordinates of the robot are calculated by the positioning algorithm based on laser sensing, and the geodetic coordinates of the robot without GNSS signal are supplemented without changing the positioning solution and control algorithm of the existing robot unmanned system. For example, when the robot leaves the hangar, it switches to the GNSS positioning system for positioning and navigation in the area with both the positioning signals of the robot positioning system based on laser perception and the GNSS signal. When entering the hangar, switch to the robot positioning system based on laser sensing for positioning and navigation in the area cover with both the positioning signal of the robot positioning system based on laser perception and the GNSS signal. The verification test is carried out with the reference of total station which shows that within the scanning range of laser radar, when the robot is at a speed of 0.8 m/s, the absolute average value of the maximum deviation of the positioning error in a straight line is 4.1 cm, and the maximum root mean square error is 1.5 cm; when the robot driving on a curve, the absolute average value of the maximum deviation of positioning error is 6.2 cm , and the maximum root mean square error is 2.6 cm. The result shows that this method can achieve accurate robot positioning and meets the positioning accuracy requirements for automatic navigation of agricultural robots in agricultural machinery warehouses and other environments.