| The serious lag in plant protection machinery and agricultural chemical application skills in our country has hindered the effective control of crop pests,and caused many negative effects,such as low utilization rate of agricultural chemicals,excess pesticide residue,environmental pollution,pesticide hazard,operator toxicosis.All of these have resulted in many bonehead damages and other bad effects.In order to optimize application technology of agricultural chemicals,control pesticide drift,improve effective utility rate of pesticides,and diminish environmental pollution,it is extremely far-reaching significant to improve the test performance of instrumentation of plant protection machinery for spraying application,and study the atomization characteristic after the liquid sprayed out of nozzles. So some researches were carried on in this area by the author.The main achievements and conclusions in this study were presented here:1.An atomization nozzle test-bed was built up,and two sets of spray flow control devices, intermittent and continuous spray flow control system based on Pulse-width Modulation (PWM),were designed and developed.â‘ A switching-mode solenoid valve was actuated by a square electrical signal with tunable duty cycle and tunable frequency within 20 Hz.The intermittent variable spray flow based on PWM was achieved.â‘¡An electromagnetic proportional regulating valve was driven by a square electrical signal with 24kHz frequency and adjustable duty cycle,then the continuous variable spray flow based on PWM technology was achieved.The results showed that the expected assumptions about these two sets of spray flow control systems were reached. Compared with the conventional spray flow control method based on pressure,the flow regulating ranges of these two spray flow control methods based on PWM technology were all widen.The flow regulating ranges of intermittent spray based on PWM were 4.17,4.00 and 2.70 for the flat-fan nozzle,hollow-cone nozzle,and solid-cone nozzle, respectively;and those of continuous spray based on PWM were 7.14,3.57 and 3.70 for the flat-fan nozzle,hollow-cone nozzle and solid-cone nozzle,respectively. 2.A measurement method of spray angle based on image processing was put forward, aiming at the limitation of the former measurement methods,which often cause big errors of spray angle detection.The same spray was shot twice,then two images of the spray were obtained.After these two images were registered,fused,a sharp and high quality image was achieved.When the quality of the resulting image was evaluated with Expectation Maximum algorithm(EM),the spray image edges were extracted. Then the irregular edges of atomization image were fitted to regression lines using the least square fitting function in MATLAB toolbox.Two intersected straight lines most approximative to the edges were obtained.The angle between these two fitted lines was just the wanted atomization angle.According to the definition and the principle of least square fit,the error sum of squares is the least.3.A method based on EM algorithm to evaluate the quality of the fused image quantitatively was developed.The image edge intensity was modeled using a mixture Rayleigh probability density functions(pdfs).The parameters and weights of mixture terms in the mixture model can be calculated using the EM iterative algorithm.The term with the smallest parameter corresponds to the weak edges,or the low-frequency background fluctuation.The term with the largest parameter corresponds to the strong edges.Then the smallest variance parameter can be used to estimate the variance of the image noise,and the largest parameter can be used to measure the image blurring. Compared with other image quality evaluation methods,the advantages of this method are that the detail information about the formation of the image needn't be used and the smaller noise can also be estimated exactly.4.The communication between configuration software without VBA and MATLAB was solved.In the control system of the nozzle measurement test-bed,because of the good man-machine interface and many other merits,the configuration software used in industrial control was selected to be the master control interface and run on the stage.In order to make up the deficiencies of the configuration on computation abilities, MATLAB with the powerful abilities of engineering calculation and image processing was selected as the calculating and processing tool,and run background.Thus it had complementary advantages.The configuration software "Centurystar" without VBA was selected in system development because of the project costs.So the communication between configuration without VBA and MATLAB became the key issue.A new method was proposed,by which the configuration without VBA can communicate with MATLAB taking advantage of Activeâ…©technology,namely taking the VBA editor in Excel macro as a bridge.Four solutions for the communication were compared: Activeâ…©technology,DDE technology,MATLAB engine technology,and MATLAB compiler technology.Based on the advantages and disadvantages of the four methods, different method can be selected in the actual development according to the practical situation.In the nozzle test control system,the requested portability is not so high. Activeâ…©technology was selected because of its simplicity,short developing cycle,and before or after MATLAB was invoked,it shouldn't be open.So comparatively,less computer memory is needed.5.The characteristics of intermittent spray based on PWM technology were studied.For the PWM intermittent spray,the diameter and the velocity of spray droplets were measured using Particle Dynamical Analyzer(PDA),the most advanced and high precision method currently.Using of the software developed by the author and statistical method in MATLAB,the effects of the pulse intermittent variable spray control on spray characteristics were studied in this part.The results indicated that the spray distribution centralized a little bit toward center area,the spray angle became smaller slightly,and the spray droplet diameter became bigger slightly.All these effects are very small.Comparatively,the effects of intermittent spray flow control on spray distribution,spray angle,and spray droplet size spectra were the serious for solid-cone nozzle,but were minor for flat-fan nozzle.Compared with conventional spray flow control method based on pressure,the influences of intermittent flow control on spray distribution,spray angle and spray droplet size spectra for flat-fan nozzle could be neglected.Under the intermittent spray flow control manner,the droplet velocity and the spray kinetic energy were decreased with decreasing flow slightly.The trends of kinetic energy median diameter(KEMD) and volume median diameter appeared similar. It indicated that KEMD was related to spray droplet size,rather than velocity.6.The characteristics of continuous spray based on PWM technology were studied.In the same way,the spray characteristic parameters of PWM continuous spray control were measured,calculated and analyzed.The results showed that the spray distributions and angles of all the nozzles tested in the experiments were influenced greatly by PWM continuous spray flow control.When the flow rate decreased,the spray distribution centralized toward the center area seriously,and the spray angle became smaller significantly,but the spray droplet diameter became smaller slightly.The effect of PWM continuous spray flow control on spray droplet size was very slight,it almost could be neglected.The spray droplet velocity and the spray kinetic energy both decreased with the decreasing flow.Especially when the duty cycle was less than 75%, the decrement of spray droplet velocity is significant.Same as the volume median diameter(VMD) trend,spray cloud kinetic energy median diameter(KEMD) decreased as the flow decreased.It indicated that the spray cloud KEMD was related to spray droplet size,rather than velocity.7.Comparing among PWM pulse intermittent spray,PWM continuous spray,and pressure-based spray manner,it could be found that the flow regulating range of pressure-based spray was the most narrow,the effects of the pressure-based spray on spray characteristics was the most significant.When the pressure was raised to increase spray flow,the spray distribution and dispersion deformed seriously,the spray droplet size spectra moved toward small droplets heavily.But the utility efficiency of the system energy was very low.Relatively,the influence of PWM intermittent spray flow control on spray characteristic was minor.For flat-fan nozzle,the influences of PWM intermittent spray on spray distribution,spray angle,and spray droplet size spectra could even been ignored.The spray cloud dynamic property could be improved slightly. Therefore,in terms of agricultural application aiming at improving chemical coverage and deposition rate,the intermittent variable spray method based on PWM control technology should be the first choice.However,the flow regulating range of PWM continuous spray flow control is the widest.It could reach the range of 7:1.Although PWM continuous spray flow control has some effects on spray angle and dispersion, this kind variable spray wouldn't make the droplet size spectra changed.So when the transverse width needs to be considered in spatially variable application,PWM continuous flow control can be the alternative method.8.A method based on PWM intermittent spray technology to improve spray deposition was investigated.The results of four group comparative experiments showed that pulsed intermittent sprays from enlarged nozzles operating at elevated liquid pressure could make the flow rate controlled,and produce suitable smaller droplets diameter spectra,and meanwhile the speed of spray droplets could be increased.Therefore,the spray deposition can be improved.Because the basic approach to improve spray deposition is keeping the suitable smaller spray droplet spectra and improving spray droplet speed.
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