# Utilization of Quasi-Zenith Satellite System for Navigation of a Robot Combine Harvester
## 2 Materials and Methods  
### Research Platform  
The platform used in this study was a combine harvester (AG1100, Yanmar Co., Ltd., Osaka, Japan) equipped with navigation sensors as shown in Figure 1. The combine harvester is equipped with a real-time kinematic global navigation satellite system (RTK-GNSS) receiver (SPS855, Trimble, Sunnyvale, CA, USA) to obtain the reference measurements. An IMU (VN100, VectorNav, Dallas, USA) provides the attitude measurement of the robot combine harvester. The CLAS and MADOCA positioning augmentations are provided by a QZS receiver (MI-3008-GM4-QZS, Magellan Systems, Amagasaki, Hyogo, Japan). A GPS splitter (ALDCBS1 \(\times\) 2, GPS NETWORKING, Pueblo, CO, USA) was used to divide the GNSS signal during the dynamic experiments. Specifications of the combine harvester are shown in Table 1. During harvesting, it usually works in the medium gear with at a speed of 2.0 m/s. It has and engine output of 80.9 kW. This is the largest combine harvester produced in Japan, because the size of the fields is no longer than 100 m by 30 m in the main island of Japan.  
The combine harvester is controlled by a PC sending commands via a CAN (Controller Area Network) bus. A PC is connected to the CAN bus via a communication card, and there is an Electronic Control Unit (ECU) inside the combine harvester that conducts the communication work and can shield the combine harvester from incorrect CAN messages. Furthermore, the RTK-GNSS receiver, the QZS receiver and the IMU are connected to the PC through the serial port using the RS-232 protocol. Moreover, the combine harvester can work in both \"manual mode\" and \"automatic mode\". In automatic mode, it can only be controlled by a computer. The safety of the system is also improved, since when there is no command sent every 200 ms, the combine harvester will automatically stop [1].  
The combine harvester used in this research uses the fulltime drive system (FDS). In 1998, Yanmar Co., Ltd., Japan established the FDS with steering wheel by combining the forced differential transmission with the conical steering link [11]. By using the FDS with steering wheel, the combine harvester has an advantage in its movement for straight forward-backward movements. During these movements, each crawler of the combine harvester runs at the same speed. Additionally, the FDS is utilized for turning in 3 different ways as shown in Figure 2. During a gentle turning, the speed of the outside crawler remains the same but the speed of the inside crawler decreases as shown in Figure 2a. During a normal turn; similar to a gentle turn, the outside crawler speed remains but the inner crawler stops in order to decrease the turning radius as shown in Figure 2b. For a sharp turn, the steering angle reaches its maximum value, then the inner crawler runs in the opposite direction of the outside crawler as shown in Figure 2c [1].  
\begin{table}
\begin{tabular}{c c} \hline Length (mm) & 6150 \\ Width (mm) & 2350 \\ Height (mm) & 2760 \\ Engine output (kW) & 80.9 \\ Crawler size (mm) & 500 \(\times\) 1780 \\  & Low: 0–1.0 \\ Speed (m/s) & Medium: 0–2.0 \\  & High: 0–2.81 \\ \hline \end{tabular}
\end{table}
Table 1: Specifications of the AG1100 combine harvester.  
Figure 1: Platform of the study—AG1100 equipped with navigation sensor.