| The variable-rate spraying system is the vital component in the precision agriculture,the core is that difference information of pest and weed disease in the small area of farmland is gained by utilizing the technologies of GPS,geographical information technology,real-time sensor,and the good atomization characteristics of spray work according to target is precisely and quickly done by pressure control mode, flow control mode,reagent injection control mode.Spray flow was controlled by a new way that PLC controls electric proportional valve for flow regulation after the advantages and disadvantages of many variable spraying systems and variable spraying technology of domestic and overseas were analyzed.Variable-rate spraying systems and related measurement and control software were designed,controlling of spray flow and collecting of dynamic data were realized,and finally the characteristic of spray flow control was researched by experiment.Research results as following:1) Adjustment range of spray flow was measured,the maximum adjustable ratio was 7(configuration:N11053 nozzle),and the minimum adjustable ratio was 3.2 (configuration:N6014 nozzle).2) The flow adjustment characteristic of electric proportional valve was researched and algorithm of flow rate control was designed.(1) Electric proportional valve actuators in condition of two different nozzles have the parabolic properties of flow-rate adjustment,larger dead area and saturation region of flow rate adjustment were appeared,hysteretic characteristics were obviously showed,and the hysteretic characteristic of system with the type of N11053 nozzle was more obvious than N6014 nozzle which showed the hysteretic characteristic is more obvious when adjustment range of spray flow-rate was wider.(2) The best adjustment range of system with N11053 nozzle is from 3 L/min to 5 L/min and the best adjustment range of system with N6014 nozzle is from 1.5 L/min to 2.1 L/min.3) The changes of quantitative spray precision of variable-rate spraying system with the changes of flow-rate was researched. (1) Flow-rate fluctuation was smaller at the situation of smallest target spray flow-rate(0.7 L/min) and biggest target spray flow-rate(4.5 L/min),than in other situations,when increasing or decreasing spray flow-rate.(2) Quantitative spray error decreased while increasing spray flow-rate and the result was just opposite when decreasing spray flow-rate,which showed the precision of increasing spray flow-rate was higher than the precision of decreasing spray flow-rate.4) Transient characteristics of variable-rate spraying system was researched.(1) The delay time of variable-rate spraying increased from 0.3s to 1.5s while increasing amplitude of decreasing spray flow-rate;but it was not the same situation while increasing amplitude of increasing spray flow-rate.(2) The overshoot phenomenon of flow-rate appeared when increasing spray flow-rate with the amplitude of over 0.35L/min,but it was not appeared when decreasing spray flow-rate with any amplitude.(3) The delay time of variable-rate spraying was shortened from 1s to 0.8s when decreasing spray flow-rate from 0.6L/min to 4.5L/min by the combined control with electric proportional valve and on-off valve,but it also increased the overshoot of 0.07L/min(1.5%of the target spray flow-rate).
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