Sprutbommens rörelser : en sprutteknisk felkälla
This study, which is mainly of literary sources, has been performed to fulfil the requirements of the Swedish University of Agricultural Sciences for the degree of Master of Science. Uniform spray distribution is of vital importance for successful results of a chemical control measure. Different studies show that spray distribution can be seriously affected by sprayerboom movements. The objectives of this study have been, firstly, to describe these movements and their influence on the results of a chemical control measure and, secondly, to describe technical methods to reduce these movements and to describe the performances of these methods. Boom movements are caused mainly by the rolling and yawing movements of the sprayer. This implies that the size of these movements increases at an increased distance from the mounting point of the boom. It also implies that the mechanical strains on the boom and its suspension increase progressively with increased boomlength. Likewise slender boomstructures and looseness in the boomsection joints can severely affect the positioning of the boom. Improved positioning of the boom can be achieved by designing the boomsuspension so that it allows a certain degree of freedom for the sprayer to move relative to the boom. Possibilities then exist for either isolation from, or compensation for, the disruptive movements of the sprayer. The method of isolation represents a passive suspension system, in which "internal" disruptive energy is absorbed by damping devices. The method of compensation represents an active suspension system, in which external restoring energy is supplied by e.g. a hydraulic cylinder. In order to obtain the optimal boom positioning with these methods the boom should be a self-supporting structure and as stiff as possible in both directions. When in operation the boomsection joints should either be locked tightly or be provided with damping devices. Up to now the horizontal boom movements have not received any well justified attention. These movements have shown themselves to affect spray distribution as much as, or even more than, the vertical movements, especially if the boom is equipped with fan spray nozzeles. Therefore it is essential that both the vertical and the horizontal boom movements are reduced. The ability of a passive suspension system to keep the boom in its correct spraying position is however restricted in some situations e.g. when spraying across a side slope (fig 27) or when spraying along furrows (fig 29). Then it has to be corrected, either manually or by means of an active system. The performance of a passive suspension that is effective only in the vertical plane will be disrupted by internal random frictional forces due to the horizontal movements of the sprayer. The performance of an ideal passive suspension that does not have this disruptive internal friction will very much depend on the physical properties of its mechanical components, which implies that this system has an optimal performance only under specific conditions. An active suspension does not have these disadvantages, but on the other hand it requires rather sensitive and expensive equipment. Independent research results show pronounced reduction of boom movements with passive suspension systems. Active suspension systems are not yet commonly used in commercial applications. Results from trials with these systems have not been available. From the fact that the boom movements increase at an increased distance from the mounting point of the boom and that downward movements affect spray distribution more than upward movements do, the conclusion can be drawn that the ends of the boom should be set somewhat higher than the centre section. Considering available standard deviation values of vertical boom displacement and also considering the risk of spray drift etc, the extended sections of the boom should be raised approximately 0,5—l,0 cm per metre distance from the boom mounting point. According to various authors, a sprayer exceeding l0-l2 m working width should be equipped with a boom suspension system designed to reduce boom movements. A conclusion can be drawn from this study is that an active suspension system probably would be justified for working widths exceeding 18 meters. Among other possibilities and advantages the following should be attained by applying corrective measures for improved boom positioning: - Reduced application rate. - Increased work rate. - Reduced potential for drift of spray. - Increased penetration of crop canopy. - Reduced mechanical strain on the boom and the boom suspension. The general awareness of these factors could be essentially increased if a test of sprayerboom movements were included in official sprayer tests. The test in question can probably be made on a stationary test rig which shakes the sprayer in all three directions.
spray distribution; boom movements; boom suspension
Rapport - Sveriges lantbruksuniversitet, Institutionen för lantbruksteknik
Publisher: Institutionen för lantbruksteknik, Sveriges lantbruksuniversitet
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