Agriculture Reference
In-Depth Information
buildings or a mask angle (Sect. 3.7 ) . If both systems are combined for a fused
navigation control, it is possible to bridge short-term disruptions of GPS signals by
a control via inertial sensing.
4.4.2
Drawn- and Mounted Implements
The implement is the actual device doing the fi eld work. But on a side-slope, it is
possible for the tractor to follow the desired line, but have the implement widely off
the path. This results mainly from side forces that act on the implement and drag it
downhill. And crabbing of the tractor along a side-slope can have an effect too. The
downhill drift on the implement occurs with towed machines as well as with those
that are mounted on the three-point-hitch of the tractor. However, towed implements
are particularly susceptible.
Corrections for this downhill drift can be made based on GPS signals from an
antenna that is located on the implement itself. However, relying solely on signals
that come from the implement without having an antenna on the tractor is not recom-
mended. The reason for this is that then the driver would have to spend much effort
for keeping the heading of the tractor in the vicinity of the path. Hence the signals
from the GPS-implement-antenna are used in combination with the respective signals
for the tractor.
The systems for correcting the downhill drift rely on either passive- or active
steering of the implement. Passive guidance corrections of the implement are based
on compensations via the heading of the tractor by steering somewhat away from
the path in order to make up for the drift of the implement. Instead, a ctive guidance
corrections are made by steering devices on the implement itself. The result is that
with active guidance both the tractor and the implement follow the desired path,
whereas with passive steering this holds only for the implement, while the tractor is
on a line that is slightly offset (Fig. 4.10 ).
This offset-position of the tractor can be a problem on steeper slopes, which
cause more offset-distance. This can make driving and operating in inter-row strips
impossible, e.g. of potatoes, beets, vegetables and maize. Active guidance does
away with these problems, but in return requires steering tools on the implement.
These steering tools vary as much as the implements do. Common devices used for
this are
steerable tires
laterally movable hitches
steerable frames
steerable coulters (Fig. 4.11 ).
The assumption that implements on a three point hitch do not drift downwards
does not hold well. The position of these implements is approximately parallel to
the rear axle of the tractor. This means that the implement “tails out” when the atti-
tude of the tractor changes. Tractors tend to a crab-attitude with a corresponding
Search WWH ::




Custom Search