Agriculture Reference
In-Depth Information
RTK-GPS
IMU
FIGURE 2.2
Real-time kinematic GPS (RTK-GPS) and inertial measurement unit (IMU)
as navigation sensors.
a command from the control center and send information data through a wireless
local area network or packet communication. The robot vehicles such as a robot
tractor and a robot combine harvester can perform their designated tasks and work
simultaneously with each other. The operator at the control center can analyze the
data sent by the robot vehicles in real time and can immediately send the necessary
information to the farmers, retailers, producer's cooperation, etc. Furthermore, using
GIS, the operator can monitor the real-time status of the robot vehicles while they
are performing their tasks.
2.3 NAVIGATION SENSORS
To perform an autonomous navigation of the robot vehicles and vehicles, navigation
sensors are indispensable (Tillett, 1991). Many types of navigation sensors have been
proposed in the past, such as GPS (O'Connor
et al., 1995, 1996; Bell, 1999), machine
vision (Pilarski
et al., 2002; Han
et al., 2004; Rovira-Más
et al., 2005; Subramanian
et al., 2006), radar (Reina
et al., 2011), laser (Barawid
et al., 2007), and ultrasonic
sensors. However, GPS has been used lately for an autoguidance system in actual
farming. In particular, RTK-GPS is becoming popular as a navigation sensor
because farmers are pursuing guidance with higher accuracy (Rovira-Más et al.,
2010). Predetermined work paths called a navigation map can be made by obtaining
two points,
A
and
B
, by the RTK-GPS. These
A
and
B
points are used as the reference
points to create the navigation map using commercial software. The RTK-GPS is
used to obtain the vehicle position with respect to UTM coordinates, and an inertial
measurement unit (IMU) is used to obtain the vehicle posture (roll, pitch, and yaw
angles). Then, the IMU drift error is normally corrected based on a Kalman filter or
other statistics-based methods. These navigation sensors enable the robot to follow
the predetermined points in the navigation map. Figure 2.2 shows the RTK-GPS
and the IMU. Generally, the RTK-GPS has an accuracy of ±2 cm, whereas the IMU
composed of fiber optics gyroscope has an accuracy of 0.2°.
2.4 AUTONOMOUS NAVIGATION CONTROL
A navigation system is basically composed of a “mission planner” and “autonomous
operation” as shown in Figure 2.3. The mission planner has two functions for cre-
ating both travel paths of the robot tractor, and maneuvers of the robot to prop-
erly achieve the field management such as a hitch function and an engine speed set
during autonomous operation. On the other hand, the autonomous operation can be
used in guided situations. The autonomous operation has functions of following the
