Agriculture Reference
In-Depth Information
Fig. 4.5
Display of an user interface to an automatic guidance system. The lightbar (
top
) indicates
cross-track errors. The signals from two different GNSS satellite systems can be used simultane-
ously in order to improve availability. Site-specifi c section control of implements (
e.g.
sprayer) is
possible (Courtesy of Trimble Agric. Div., Westminster, USA, altered)
absolute accuracy of the GPS technology is independent of the working width
(see above).
The basic components needed for manual lightbar- or automatic guidance are:
• a GPS receiver
• a user interface for displaying cross-track errors and for user input,
e.g.
the
working-width or the location of the fi rst guidance line
• algorithms for path-planning that compute cross-track errors relative to a guid-
ance line.
In addition to these items, automatic guidance always requires to install
•
an actuator for vehicle steering and a detector for manual override.
In hilly fi elds or when very precise guidance is needed, additional components
for automatic guidance can be useful,
e.g.
components for terrain compensation
(Sect.
4.4
) and a steering angle sensor. The still dominant practice is to
retrofi t
farm
machines with the guidance components. For this, a hydraulically- or electrically
driven servo-motor is connected to the steering wheel in the cab. Its friction roller
runs against the rim of the steering wheel and thus turns it. In many cases, the retro-
fi tted components including the actuator for steering and the manual override for it
can be moved from one tractor to another. So one set of components can be used for
guiding in successive farming operations with different machines.
