| The traditional way to spray is to manage a certain area of land by regarding it as an area in which plant diseases and insect pests are generally consistant. In fact, influence of growing conditions and production are different. Particularly, plant diseases and insect pests often appear in a small area, then spread gradually. If spraying evenly, it is possible to cause pesticide pollution. On the contrary, vatiable rate application can spray according to specific circumstance of plant diseases and insect pests. It is one of effective ways to reduce pesticide application.According to the analysis and summary of variable rate spraying technology at home and abroad. A method was introduced to make spray quantity under control which use the single chip processor and PWM technology as technical support. With this method spraying flow can be adjusted by controlling the working frequency of electric diaphragm pump. In this paper a new variable rate sprayer system was designed as well as the spray characteristics were analysed.The main work in this paper are as follows:(1)Based on analysis of the variable rate spray methods and variable rate control principle,a variable spray control system was created which consist of single chip processor driver circuit、measuring instrument、adjusting button and electric diaphragm pump.(2)The hardware designing and software programming were completed in this paper.The hardware system was consist of control module、power module、driver module and duty cycle adjusting module.The control module was composed of MSP430SCM、 crystal circuit and reset circuit. It can generate a square wave signal and transmit the signal to driver module which consists of IR2103and MOSFET.With the support of power module. the driver module can drive diaphragm work and the duty cycle adjusting module can adjust the duty cycle of square wave signal, so the average voltage of diaphragm can be adjusted accordingly.In this way, spray flow can be easily controlled.(3)According to system test requirement,spray distribution test system、droplets size test system and spray speed-field test system were set up while a basic test method was determined. The frequence of square wave signal was8kHz in this test. The adjustable range of duty cycle is been set at40%-100%. In this paper,40%、50%、60%、70%、80%、90%、100%was chosen as research object and measure flow control characteristic、spray distribution、droplets size、spray angle and spray speed-field respectively.(4)Experimental data were been analysed in detail while spray characteristics under each condition was detailedly discussed. The results show that, the interrelationship between spray flow and duty cycle of this variable-rate spray control system can be expressed by a quafric curve (the correlation degree is0.98). The adjustable range of flow was1.71. With increase of duty cycle, spray distribution become more and more large. This kind of distribution can be regarded as normal distribution. If duty cycle increase, droplets size will decrease. When the duty cycle increase from40%-100%, Dv0.5will decrease by32.386μm and the variable range basicly locate in a relative reasonable range. Moreover, the spray angle slowly increase with the growth of duty cycle. The minimal value is41.53°while the maximum value is61.78°. With the growth of spray flow, speed of droplets increase accordingly and a obvious speed-field was formed. The basic rule is that the spray speed is gradually decrease from up to downd and the fastest spray is always near the nozzle. The speed growth of droplets near the axis was lager than the two sides.The experiments show that working performance of this variable rate spray system is stable and reliable, good maneuverability, high spray quality. The system is highly compatible with knapsack sprayer and can be effectively applied to agricultural production. |
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