【作者】 邓巍；

【导师】 丁为民；

【作者基本信息】 南京农业大学 ， 农业机械化工程， 2007， 博士

【摘要】 我国植保机械和农药使用技术严重落后,已严重妨碍了农作物病虫害的防治,带来了诸如农药有效利用率低、农产品中农药残留超标、环境污染、作物药害、操作者中毒等负面影响,造成了不应有的损失以及其它许多不良后果。因此,提高植保施药机械测试设备的测试性能、研究液体从喷嘴喷射出后的雾化特性和提高喷雾沉积率的方法,对于优化农用化学制品的应用技术、控制有害物质的飘移、提高农药有效利用率、减小环境污染都有极其深远的意义。作者做了一些相关领域的研究工作,现将本研究中所做的工作和研究结论归纳如下:1.建立了雾化喷头试验台;设计并建立了基于脉宽调制(PWM)控制技术的脉动间歇式和连续式两套喷雾流量控制装置。①用频率在20Hz以内可调、占空比可调的方波电信号驱动开关式电磁阀,实现了基于脉宽调制(PWM)技术的间歇式变量喷雾。②用频率为24KHz、占空比可调的脉冲方波电信号驱动电磁比例调节阀,实现了基于脉宽调制(PWM)技术的连续式变量喷雾。试验结果表明,这两套喷雾流量控制装置达到了预期设想,与传统基于压力式流量控制方法相比,喷雾流量调节范围都有一定程度的提高。PWM间歇式喷雾流量控制范围为:平口扇形喷嘴、中空锥形喷嘴、实心锥形喷嘴的流量调节范围分别为4.17、4.00、2.70;PWM连续式喷雾流量控制范围为:平口扇形、中空锥形、实心锥形喷嘴的流量调节范围分别为7.14、3.57、3.7 0。2.针对以往喷雾角测定方法误差较大等局限性,提出了一种基于图像处理的喷雾角测定方法。对同一次喷雾连续拍摄两次,得到一次喷雾的两张图像,对其进行图像配准、图像融合,以得到图像质量较高的图像,并用EM算法评价估计图像质量之后,提取喷雾图像射流边界,利用MATLAB工具箱中的最小二乘直线拟合函数,对不规则的喷雾图像边界进行最小二乘线性拟合,得到了最接近实际射流边界的两条相交直线,二直线的夹角即为喷雾角。根据最小二乘拟合的定义和原理,用此方法求得的喷雾夹角误差平方和最小。3.提出一种基于EM算法的图像融合质量评价方法。用混合瑞利概率密度函数对边缘强度分布建模,用EM算法迭代估算出混合瑞利密度函数中各项的参数和权重。混合模型中最小参数项对应于弱边缘,或是低频背景波动;最大参数项对应于强边界。可用混合项中的最小参数项估计噪声,用最大参数项度量图像的模糊度。与其它方法相比,该方法的优点是,不需要知道图像构造等细节信息,且对较小噪声也能较精确地估计出。4.实现了基于ActiveX技术的无VBA组态软件和MATLAB间的通信。在喷头测试试验台的控制系统中,工控组态软件因其良好的人机界面等诸多优点被选为主控界面,运行在前台,为了弥补组态计算能力差的不足,选用具有强大工程计算和图像图形处理能力的MATLAB软件作为计算处理工具,运行在后台,以实现优势互补。因工程造价问题,选用了无VBA的组态软件“世纪星”,因此无VBA组态软件和MATLAB间的通信问题成为关键。提出了无VBA组态软件如何利用ActiveX技术与MATLAB通信的新思路和方法,即以Excel宏的VBA编辑器作为桥梁。并探讨比较了四种方法:Act iveX技术、DDE技术、MATLAB引擎技术、MATLAB编译器技术,根据这四种方法的优缺点,在实际开发中可根据实际情况选用不同的方法。在喷头测试试验台的控制系统中对M文件的可移植性要求不是很高,ActiveX技术因使用时简单、开发周期短、调用MATLAB前后不必开启MATLAB、占用内存少等优点而被选用。5。研究了基于PWM控制技术的间歇式变量喷雾的雾化特性。对于PWM间歇式喷雾,用现阶段最先进的、精度较高的粒子动态测量分析仪(PDA)测量了喷雾流场中液滴的速度和粒径,用自行编写的软件和MATLAB科学计算统计方法,研究并分析了间歇式变量喷雾控制对喷雾特性的影响。研究结果表明,随着流量的减小,雾量分布有集中到中央区域的趋势、喷雾角稍有减小、雾滴粒径稍有增大,但间歇式流量控制对雾量分布方式、喷雾角、雾滴粒径的影响程度都较小,相对而言,对实心锥形喷嘴的影响较严重,对平口扇形喷嘴的影响较轻。与传统的基于压力的流量控制方法相比,基本可以认为间歇式流量控制对平口扇形喷嘴的雾量分布方式、喷雾角、粒径谱的影响可忽略不计。对于间歇式流量控制,当流量减小时,喷雾液滴速度和比能也稍有减小。动能中值直径(KEMD)与喷雾液滴粒径变化趋势相同,说明间歇喷雾动能中值直径与喷雾液滴粒径紧密相关,而与液滴速度无关。6.研究了基于PWM控制技术的连续式变量喷雾的雾化特性。以同样的方法,测量、计算并分析了PWM连续式变量喷雾的雾化特性参数。研究结果表明,雾量分布方式和喷雾角受PWM连续式流量控制的影响较严重,随着流量的减小,所测试的所有喷嘴的雾量分布方式都显著集中到中央区域,喷雾角显著减小,雾滴粒径稍有减小。PWM连续流量控制对喷雾液滴粒径的影响较小,一般可以忽略不计。随着喷雾流量的减小,液滴速度和比动能都会减小,尤其是在占空比在75%以后,液滴速度减小的幅度较大。流量减小时,喷雾云动能中值直径(KEMD)减小,与体积中值直径(VMD)的变化趋势相同,说明喷雾云动能中值直径与粒径相关,与液滴速度无关。7.比较了PWM间歇式喷雾、PWM连续式喷雾、基于压力的喷雾方式,发现:基于压力的喷雾方式的喷雾流量调节范围最小,对喷雾特性的影响程度最大,当增大压力以提高流量时,雾量分布方式及分散度严重变形,粒径谱向小粒径方向移动幅度很大,但系统对能量的利用率很低。相比较而言,PWM脉动间歇式喷雾流量控制对喷雾特性的影响最小,对于平口扇形喷嘴,一般可以忽略间歇喷雾对喷雾分布方式、喷雾角、粒径谱的影响,喷雾云动态性能可稍被改善。因此对于以纵向调节为目的农业变量喷施而言,基于PWM控制技术的间歇式变量喷雾应该是首选。然而,PWM连续式喷雾流量控制方法的流量调节范围最大,对于平口扇形喷嘴,其流量调节范围可达7:1。虽然此种流量控制方法对喷雾分散特性(即喷雾角和分布方式)有一定的影响,但对喷雾液滴粒径谱的影响较小。若考虑喷施时的横向宽度变化要求时,PWM连续式流量控制不失为一种可供选择的方法。8.探讨了一种基于PWM间歇式喷雾技术的、提高喷雾沉积率的方法。四组比较试验结果表明,使较大喷嘴在提高工作压力的情况下间歇喷雾,系统调节喷雾占空比、压力和喷嘴大小,可在保证流量得到控制的同时,产生合适的粒径谱,雾滴速度也可得到提高,这样可以提高喷施沉积率。因为提高喷施沉积性能的根本出发点是保持合适的较小粒径谱和提高雾滴速度。更多还原

【Abstract】 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.①A 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.②An 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 ActiveⅩtechnology,namely taking the VBA editor in Excel macro as a bridge.Four solutions for the communication were compared: ActiveⅩtechnology,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. ActiveⅩtechnology 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.更多还原