# The Full-Field Path Tracking of Agricultural Machinery Based on PSO-Enhanced Fuzzy Standley Model
## 4 Results and Discussion
### Combine Harvester Field Test  
In order to further verify the fitness of the PSO-FSM algorithm, a field test was performed based on a wheeled combine harvester C230 (provided by [PERSON], Moline city, IL, USA) as shown in Figure 14. In the design of the autonomous navigation system of C230, the same dual-antenna RTK position system was employed as the wheeled mobile  
Figure 12: Path tracking result of different algorithms. (**a**) Lateral error of path tracking for straight line; (**b**) Lateral error of path tracking for curve path segment. Figure 13: Full-field path tracking trajectory of PSO-FSM. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Algorithm** &
\begin{tabular}{c} **Guiding Distance** \\ **(m)** \\ \end{tabular} & **Maximum Error (cm)** & **MAE (cm)** & **RMSE (cm)** \\ \hline SM & 12 & 32 & 7.4 & 11.4 \\ \hline PSO-FSM & 5 & 3 & 1.6 & 2.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Full-field path tracking error of the mobile vehicle. vehicle, and steering angle sensor, electric steering wheel were installed to set up the close-loop control of self-driving. Electric control ignition, electric control shift, electric control accelerator and electric control clutch were designed to realize unmanned combine harvester. The C230 harvester has an operating width of 5 m and a turning radius of about 8 m. Its navigation system configuration and operation during harvesting operation is consistent with that of the mobile vehicle experiment, and the path planning scheme shown in Figure 7 is employed for the full-field path tracking test. The whole control system includes an electric steering wheel, angle sensor, electric throttle and control unit related to grain unloading and threshing. The electric steering wheel is Shanghai Lianshi EMS2 steering drive unit, whose working current goes up to 10 A. The advantages of EMS2 include high torque, high precision, IP65 dustproof and waterproof, which is suitable for the harsh operating environment of a combine harvester. The angle sensor is DWQCAB-V-CH from Beijing Tianhaike Company, with a linearity of 0.02%FS and angular resolution of 0.022\({}^{\circ}\). The angle sensor is installed directly above the steering vertical axis of the harvester and is directly connected to the center steering vertical axis. Because of the large operating width of C230, the average operating speeds for a straight line and automatic turn are about 0.8 m/s and 0.6 m/s, respectively, which is almost the same as manual driving operating. Limited by the large turning radius and reliability of manual-automatic gear switching, only the straight line harvesting operation and automatic turning at the outer circle path were performed in the field test. The result of the unmanned operation of the combine harvester in the farmland is shown in Figure 15, where both the straight line and curved path tracking errors are smaller than 0.5 m if the path tracking algorithm is stable. However, the maximum lateral tracking error of the harvester is 0.63 m due to the harsh field soil environment, such as side slip resulting from field ridge. However, the tracking accuracy is acceptable for the C230 automatic navigation because of its large operation width. Compared with the mobile vehicle test result, we can conclude that the harsh soil condition and state delay of the steering control system have a complicated effect on the parameter tuning of SM, especially for bigger and heavier combine harvesters. Because heading information is only employed to correct the positioning error in this test, the lever-arm error coming from pitch and roll is not compensated, which can be seen from the field ridge-induced tracking error. Furthermore, the lever-arm of the GNSS antenna installed in C230 is obtained manually by measuring tape, and more precise lever-arm and high-frequency attitude information  
Figure 14: Reconstruction of the electric control system for the combine harvester. would improve the dual-antenna RTK position, which needs further verification and is also part of our future work.