Agriculture Reference
In-Depth Information
a dynamically updated “as-applied” history of where the product has been applied
to the field. The task computer uses a GPS (global positioning system) receiver to
determine the location of each of the boom's sections, and decide if each boom sec-
tion should be on or off. If the area under the boom has not yet been sprayed and is
an acceptable spray location (within the defined boundaries), the section is turned
on. If the area has already been sprayed or is outside the field boundaries, the sec-
tion is turned off. Both map-based and sensor based systems will be explained in
more detail in the next section (Section 10.4) in the context of variable rate chemical
application.
Section control systems can be biased to reduce either overlap or underlap. A
system biased to reduce overlap requires a greater portion of unsprayed area within a
given section for that section to be turned on. Conversely, a system biased to reduce
underlap will require a greater sprayed area within a given section to turn the spe-
cific section off. With adjustable biasing and the increased on/off control resolution
of section control, an operator can optimize field spraying, saving both time and pes-
ticide. Luck et al. (2010) found that the implementation of automated section control
in row crop spraying at a resolution of seven sections reduced overapplication result-
ing from overlap from 12.4% in a manually control five section system to only 6.4%.
Boom section control can lead to substantial dynamic variation in nozzle pres-
sures and flow rates as sections are turned on and off (Sharda et al., 2010). The nozzle
pressure varied between 6.7% and 20.0%, which equated to an increase of 3.7% to
10.6% in nozzle flow rate during boom and nozzle section control with controller
compensation. The nozzle pressure variations resulted in nozzle off-rate between
-36.6% and +10.7% for 70° point row boom control tests when exiting and reen-
tering point rows. Thus, even with controller flow compensation, overapplication
resulted when exiting point rows, whereas underapplication occurred during reentry
(Sharda et al., 2011a). Even with the integration of rate control with section control,
the variation in application rate remains an issue because of the slower response of a
rate control system (in the order of seconds) as compared to that of a section control
system (in the order of milliseconds). A feedforward control system based on the
measurement of boom pressure and flow rate, knowledge or boom section states, and
a boom model can be a potential solution to reduce this deviation in application rate.
10.3.5 B
OOM
/T
OWER
C
ONTROL
Boom or tower (
tower
refers to structures of sprayers used in specialty crops such as
single- and multihead air-blast sprayers and tower sprayers) control refers to control-
ling the position and orientation of the mechanical structures to which the atom-
izers are mounted. A goal of boom/tower control is to achieve appropriate position
and orientation of spray nozzle(s) with respect to the target plants or pests. Much
work has been done to investigate the effect of sprayer boom movement on field-
crop spraying applications. Spray distribution uniformity is influenced by the vehicle
steering system, vehicle speed, amount of carrier water or air, tire pressure, and
ground unevenness, all of which can be linked to boom or tower dynamics and noz-
zle movement and position relative to the target plant or pest (Chaplin and Wu, 1989;
Langenakens et al., 1995; Clijmans et al., 2000; Miller et al., 2004). Langenakens
