# BDS/IMU Integrated Auto-Navigation System of Orchard Spraying Robot
## 2 Materials and Methods  
### Overall Design of the System  
The automatic navigation system of the spraying robot, as shown in Figure 1, consists of four parts; namely a positioning unit, a controller, an actuator, and a feedback unit. Among these parts, the BDS receiver and IMU form a positioning unit, which is used to obtain the position and attitude information of the spraying robot in real-time. The controller part is composed of an industrial computer and single chip microcomputer, and the former provides sufficient computing power for the navigation control algorithm, the later provides reliable control for real-time transmission. The actuator part adopts a high-precision servo motor to drive the master wheel through the reducer, and the master wheel outputs power to the track, which controls the track with high precision and high torque to realize the motion control of the spraying robot. The feedback unit detects the servo motor speed through a single chip microcomputer, then transmits it to the industrial computer and forms a closed-loop control.  
According to the technical parameters of orchard spraying, a dual-motor independent drive crawler chassis was designed with a crawler center distance of 0.62 m and a crawler length of 2.2 m. Figure 2 shows the industrial computer, BDS positioning antenna and receiver (F-V111, Qianxun Weizhi Internet Inc., Shanghai, China), IMU (100D2, Beijing Sanchi Inertial Technology Co., Ltd., Beijing, China), servo motor, motor driver (KYDBL4875-2E, Jinan Keya Electron and Technology Inc., Jinan, China), single chip microcomputer development board, and encoder installed on the spraying robot. The positioning accuracy of the FV-111 BDS receiver reaches the centimeter level, with both horizontal and vertical static positioning errors below 1.5 cm. The 100D2 has a built-in three-axis accelerometer, a three-axis gyroscope, and a three-axis magnetometer, of which the three-axis accelerometer has a measurement range of \(\pm\)2 g, the zero bias of 5 mg, and the noise density of 110 \(\mathrm{\SIUnitSymbolMicro g}/\sqrt{\mathrm{Hz}}\); the three-axis gyroscope has a measurement range of \(\pm\)1000 \(\mathrm{\SIUnitSymbolDegree}/\mathrm{s}/\sqrt{\mathrm{Hz}}\), the zero bias of 50 \(\mathrm{\SIUnitSymbolDegree}/\mathrm{h}\), and the noise density of 0.005 \(\mathrm{\SIUnitSymbolDegree}/\mathrm{s}/\sqrt{\mathrm{Hz}}\). The system obtains the position and attitude information through the combination of the BDS receiver and IMU, and the industrial computer is utilized as the control terminal of the spraying robot for information acquisition and decision calculation, which was transmitted to the single chip microcomputer. The single chip microcomputer  
Figure 1: The design of the automatic navigation system of the spraying robot.  
outputted speed and direction signals to the motor drivers, which controlled the rotation of the servo motors, and receives the encoder information to feedback to the industrial computer.  
Error Kalman Filter Integrated Navigation Algorithm Based on the Measurement of Position and Heading Angle  
The integrated navigation system consists of an independent BDS receiver and an IMU, applying a loosely integrated navigation mode, which can provide high-precision positioning information and good stability.