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Agricultural sprayers are used to apply chemical treatments (pesticides and fertilizer) to crops. A sprayer distributes the chemical by employing many nozzles spaced evenly along a boom structure oriented perpendicular to the direction of travel to cover large areas with each machine pass. To maximize spray efficacy, the nozzles must be held a specific distance from the target to be sprayed. With diversification of crop types grown in Western Canada, foliar application of chemical treatments at multiple points during the plants life cycles are now required. This multi-growth-stage application process requires a machine with a large range of vertical adjustment; thus permitting the nozzles to be maintained the correct distance from the target (crop) as it grows. Suspended boom sprayers provide the range of adjustment required. The suspended boom structure consists of three controlled sections which are positioned via use of hydraulic actuators. To reduce the effect of terrain inputs through the carrying frame on the booms orientation, most suspended boom sprayers incorporate a passive suspension system to limit coupling between the carrying frame and boom. By doing this however, a negative effect is created. During typical operation, the operator will use the actuator to reorient one section thereby maintaining the desired distance from the boom to the target; the opposing section will deviate from its desired position due to coupling of the boom sections through the passive suspension system. The quantification of this problem was the basis for this research. A computer simulation model of the boom structure, passive suspension system, hydraulic actuator, and on/off type directional valve was created. Comparisons to experimental data showed the model was applicable for predicting trends in boom performance related to manipulation of actuator velocity profiles. Standardized changes in the actuated sections orientation were used to establish the existing performance baseline and quantify the problem. Alternative commercially available directional valves (proportional and pulse width modulated) were then simulated and used in conjunction with the boom model to determine if boom performance improvements may be realized by defining the actuators acceleration rate during orientation changes. The proportional valve was able to limit the acceleration and deceleration of the actuated section to reduce the coupling effect and improve the non-actuated sections performance. However, the performance of the actuated section degraded more significantly in all trials regardless of input profile. The performance degradation resulted as slower acceleration and deceleration of the actuator required an increased amount of time for the desired orientation of the actuated section to be reached. It was also concluded that performance of the dynamic orientation of the boom structure was equivalent for orientation changes driven wither by pulse width modulation of an on/off valve or a true proportional valve. The boom structures large inertia and low natural frequency acted as a suitable filter for the flow and pressure pulsations introduced by pulse width modulation. |
