# Research on 2D Laser Automatic Navigation Control for Standardized Orchard
## 2 Materials and Methods  
### System Composition  
The orchard vehicle automatic test platform based on the electric agricultural vehicle (model: SH-GL) was mainly composed of 2D laser, automatic steering system and front wheel rotation angle detection system. The structure of the test platform is shown in Figure 1. The laser was installed at the center of the front of the vehicle, the height was 0.6 m from the ground and data were transmitted to the main controller PC through the network port. The automatic steering system was composed of 86 BYGH2503 stepper motor, DLD6-20B electromagnetic clutch and chain transmission. Based on Stm32F103 which communicates with the main controller PC through the USB serial port, it realizes automatic steering through Proportion Integration Differentiation (PID) control. The front wheel angle system was based on Wittower-RE38 encoder and communicates with the Stm32F103 through AD conversion. A tracking device was fixed at the center axis of the test platform and made the ink outlet of the device as close to the ground as possible. The white ink was placed in the tracking device, and the actual walking path of the test platform was recorded by the ink droplet trajectory.  
Figure 1: Test platform composition: (**A**) 2D laser; (**B**) Stm32F103; (**C**): automatic travel switches; (**D**) main controller PC; (**E**) tracking device; (**F**) 121 power supply; (**G**) steering system; (**H**) front wheel angle system.  
The 2D laser was UST-20 LXLiDAR manufactured by HOYUKO. Its specific parameters are shown in Table 1. As shown in Figure 2, the navigation control terminal PC was the core of the control system. This study was based on Windows 10 Visual Studio 2015 for data processing and software algorithm design.  
In order to test the performance of the front wheel angle system, a bench test was designed. The front wheel was set up, the test platform was in no-load state and the pulse control signal was applied to control the front wheel of the test platform to rotate \(30^{\circ}\) to the left and right (the maximum rotation angle of the test platform was \([-30^{\circ},30^{\circ}]\)). The result is shown in Figure 3. The fitting degree \(R^{2}\) of the regression equation of the left and right turn response curves of the test platform was 0.9938 and 0.9918, respectively, indicating that the system obtains the rotation angle as linear.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Description** & **Parameter** \\ \hline Light source & Semiconductor laser (905 nm) \\  & 0.06 (m)–8 (m) \\ Measuring range & Maximum detection distance 60 (m) \\ Ranging accuracy & 40 (mm) \\ Angular resolution & 0.25\({}^{\circ}\) \\ Maximum scanning range & 270\({}^{\circ}\) \\ Scanning period & 25 (ms) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specifications of the laser range sensor.  
Figure 3: Test platform left and right steering step response curve results.  
Figure 2: The principle of system.  
In order to test the performance of the automatic steering control system, the sine wave steering tracking test was designed. Place the test platform on the open concrete pavement, apply a sine wave signal with frequency of 0.5 \(\pi\)Hz and an angular amplitude of 10\({}^{\circ}\). Finally, record front wheel angle data. The test results are shown in Figure 4. The electric steering control system can track the control signal well, with slight oscillation near the peak \(\pm\)10\({}^{\circ}\), the large tracking error was 0.86\({}^{\circ}\) and the average absolute tracking error was 0.304\({}^{\circ}\), indicating that the automatic steering control system has better performance.