Agriculture Reference
In-Depth Information
Fig. 4.4
Manual guiding assisted by lightbar indications (From John Deere & Co., altered)
combination with differential GPS on carrier phase signals and dual frequencies, the
cross-track-error is on the average only 22 cm (Bombien
2005
). And what is impor-
tant when operating with modern present-day farm machinery: this average cross-
track-error in
absolute values
does not depend on the working width, which is the
case with conventional navigating. Compared to conventional manual steering with-
out using GPS and with a working width of 6 m, the cross-track-error is halved.
Based on a working width of 24 m, the cross-track-error is reduced to a quarter. And
guidance at night is much facilitated.
An
automatic guidance system
(Fig.
4.5
) is similar to a lightbar system except
that now the signals that come from the computer algorithms do not induce the
driver any more to steer, instead these signals go to electric- and hydraulic steering
actuators. To engage the automatic system, the driver pushes a button. This allows
the system to take control and hence to lead the vehicle along the closest guidance
line. And manual control is simply resumed by turning the steering wheel.
In principle, automatic guidance systems can also be used for the headland turns.
However, presently many farmers still use it only for the passes across the fi eld and
steer manually at the headlands. Hence most of the time, they are relieved from
steering and can concentrate on supervising and adjusting the remote-controlled
implements. Shortly before the machine arrives at the headlands, a sound reminds
the driver. After having completed the manual turning, the driver again pushes the
button for automatic control. With real time kinematic GPS, the
cross-track-error
is as low as 2-5 cm (Bombien
2005
; Reckleben
2011
). So compared to manual
lightbar steering based on differential GPS with carrier phased signals plus dual
frequencies, the cross-track error is reduced to about one sixth. In case conventional
manual steering without any GPS and without tramlines is the basis of comparison,
the cross-track-error for a working width of 6 or 24 m goes down to 1/12th and
1/24th respectively. Because again - contrary to conventional steering - the
