Variable-rate Sprayer Research Articles

Evaluation of a Laser Scanning Sensor in Detection of Complex-Shaped Targets for Variable-Rate Sprayer Development

<abstract> Sensors that can accurately measure canopy structures are prerequisites for development of advanced variable-rate sprayers. A 270° radial range laser sensor was evaluated for its accuracy in measuring the dimensions of target surfaces with complex shapes and sizes. An algorithm for data acquisition and three-dimensional (3-D) canopy image construction were designed and processed with an embedded computer. Test targets included three beach balls at three heights, a rectangular box, a cylinder, two artificial trees, and three field-grown ornamental trees. Other variables included 2, 3, 4, and 5 m detection distances and sensor travel speeds of 3.2, 4.8, 6.4, and 8.0 km h^-1. The laser sensor measurements of the test targets were statistically similar with the actual measurements. The average root mean square error (RMSE) and coefficient of variation (CV) varied slightly with detection distance and travel speed. Among all the dimension measurements in the ranges of 0.58 to 2.54 m in the X direction, 0.58 to 2.54 m in the Y direction, and 0.58 to 2.94 m in the Z direction, the highest average RMSE of 68 mm occurred in the Z direction and the highest average CV of 8.6% occurred in the Y direction. Similarity of paired images from the laser sensor and a camera was greater than 0.85 for all targets. These tests confirmed the capability of the laser sensor and the algorithm to accurately measure complex-shaped targets, offering potential for integration of the sensor and algorithm into sprayers that would make real-time adjustment of spray outputs to match plant structures and travel speeds.

Constant pressure control for variable-rate spray using closed-loop proportion integration differentiation regulation

Traditional sprayers adopt large-area uniform pesticide application, resulting in a low effective utilisation of pesticide and a harmful effect to the natural environment. Variable-rate spray is the key point to precision chemical application. However, it is inevitable that the spray pressure sharply fluctuates during variable-rate spray, which will definitely influence the spray characteristics, such as spray droplet sizes, spray angles, spray droplet velocities, etc., and reduce the efficiency of pesticide applications. Therefore, the research on how to keep the spray pressure constant during the process of variable- rate spray has practical significance to precision pesticide applications. In order to achieve the stability of spray pressure for variable- rate spray, a sprayer with constant-pressure control was set up using a closed-loop proportion integration differentiation (PID) controller of constant-pressure water-supply, which employed the techniques of single-phase alternating current (AC) chopper variablevoltage control and PID feedback regulation. Using hollow-cone nozzles, the spray volume was changed by adjusting spray pressure, frequency, and duty cycle of electromagnetic valve switching. The spray features concerning the spray angle and the spray volume distribution were studied in laboratory. The conclusions are as follows: i) for a given input spray pressure, the closed-loop controller with AC chopper and PID feedback regulation can effectively control the pressure fluctuations during the variable-rate spray through varying the frequency and the duty cycle; ii) the spray angle was slightly affected by the flow-rate change through adjusting the frequency and the duty cycle of electromagnetic valves or changing the number of open nozzles. The spray angle changes were controlled within the range of the maximum deviation 0.87° from mean value and the minimum deviation 0.03° from mean value; iii) when the spray pressure was set as 0.3 Mpa, the peak radial position of the spray volume distribution basically unchanged and the spray volume and the peak values of the spray distribution gradually increased with the increasing duty cycle. When the setting pressure was increased, the spray volume increased and the peak radial position of the spray distribution gradually expanded toward outside, however the peak value of the spray distribution decreased a little.

Effects of Operating Parameters for Dynamic PWM Variable Spray System on Spray Distribution Uniformity

Abstract: A dynamic PWM (Pulse Width Modulation) variable spray experiment platform was built up to study the spray distribution characteristics of PWM spray progress. The homogeneity of single nozzle dynamic spraying was evaluated based on this platform under different experiment condition. Carmine solution concentration-absorbance technology was adopted to get the CV (Coefficient of Variation) value of percent area spray coverage. RSM (Response Surface Methodology) with three variables including frequency, duty cycle of PWM control signal and forward velocity of spray was employed to study the effects of these three factors on dynamic spray distribution uniformity. Compared with previous common study of static spraying, the research on this paper can evaluate the actual spray distribution uniformity of dynamic spraying more accurately. Moreover, the platform and the research method can provide references for the settings of PWM variable-rate spray operation parameters in practical plant protection work.

Development of a Variable Rate Spray Controller for an Unmanned Aerial Application

Development of a Variable Rate Spray Controller for an Unmanned Aerial Application

Embedded Computer-Controlled Premixing Inline Injection System for Air-Assisted Variable-Rate Sprayers

Improvements to reduce chemical waste and environmental pollution for variable-rate sprayers used in orchards and ornamental nurseries require inline injection techniques. A microprocessor controlled premixing inline injection system implementing a ceramic piston chemical metering pump and two small transition tanks was developed for air-assisted variable-rate sprayers. Unlike conventional direct inline injection systems that inject chemical concentrates into the delivery lines, this system first dispensed specific amounts of water and chemical concentrates into an injection chamber and then agitated the mixture in a transition (or premixing) tank. The mixture was then transferred into a second transition (or buffer) tank for discharge from the spray pump. This process was repeated when the buffer tank neared empty. The mixture in the buffer tank was maintained at a constant concentration that allowed the sprayer to discharge a wide dynamic range of variable-rate outputs with a consistent concentration for every nozzle. A touch screen monitor with an embedded computer allowed operators to interface with the injection system. The metering pump accuracy was verified with three simulated pesticides (water, prime oil, and milk). Mixture uniformity consistency was tested with six different viscous simulated pesticides (sucrose solutions) at viscosities ranging from 0.9 to 31.3 mPa-s. Test results confirmed that the metering pump accurately dispensed the simulated pesticides at different pump speeds, and the premixing inline injection system provided consistent concentrations of spray mixtures at the spray pump outlet. The new system avoided lag time, inconsistent spray mixture concentrations and inaccurate metering of chemical concentrates at low flow rates associated with conventional direct inline injection systems, and can further improve spray application efficiencies for variable-rate precision sprayers.

Prototype Variable Rate Sprayer for Spot-Application of Agrochemicals in Wild Blueberry

Abstract. Wild blueberry growers apply herbicides uniformly to control weeds within fields. The repeated and excessive use of herbicides in bare spots and blueberry plant areas that exist within fields has resulted in an increased cost of production and environmental contamination. A prototype variable rate (VR) sprayer was developed for spot-application (SA) of herbicides to the weeds. The boom was divided into 16 sections (0.76 m per section). The VR control system consisted of eight digital color cameras mounted on a separate boom in front of the tractor, a 20-channel MidTech Legacy 6000 controller, and two 8-channel VR controllers (VRCs) interfaced to a Pocket PC (PPC) via wireless Bluetooth®. Cameras were connected via USB cables to a computer. The cameras were capable of taking the images in real-time. Custom software was developed for processing the images to detect weeds in real-time. The triggering signals were sent to the VRC to open the specific nozzles where the weeds had been detected. The VR sprayer performed well and adequately sprayed propyzamide on red sorrel (Rumex acetosella L.) and flumioxazin on moss (Polytrichum commune) within the selected wild blueberry fields. Results of T-test from experiment 1 suggested that the percent area coverage of water sensitive papers in target and non-target areas after the flumioxazin application was significant indicating SA technique using VR sprayer accurately applied the flumioxazin on targets. SA from experiment 2 resulted in a 69% reduction in propyzamide use with 25 cm before and after target buffer and 28% cover of red sorrel.

Study of Pressure Characteristics in PWM Controlled Variable Rate Spraying System

In PWM controlled variable rate spraying system, spraying quantities were regulated by fast switching solenoid valves. However, hydraulic impacts were generated by these fast switching solenoid valves in pipe system, which affected stabilities of spraying quantities and atomization characteristics. In order to study pressure changing regularities when solenoid valves operated, then to design a pressure controller to improve spraying qualities in PWM controlled variable rate spraying system, Fluent was used to simulate pressure characteristics in the pipe system and pressure curves were drawn under the following 3 working conditions, solenoid valve opening, closing, and switching continuously with 5 Hz frequency and 50% duty ratio. Related experiments were carried out to test real pressure signals in the pipe based on a PWM controlled variable rate spraying system. Relative errors between simulation results and experiment results were below 10%. Thus, this simulation model of PWM controlled variable rate spraying system in Fluent was reliable to simulate pressure characteristics in the pipe in other common working conditions, and which contributed to design pressure controller and to optimize the whole PWM controlled variable rate spraying system.

Development of Digital Flow Control System for Multi-Channel Variable-Rate Sprayers

Abstract. Precision modulation of nozzle flow rates is a critical step for variable-rate spray applications in orchards and ornamental nurseries. An automatic flow rate control system activated with microprocessors and pulse width modulation (PWM) controlled solenoid valves was developed to control flow rates of multi-channel nozzles independently for variable-rate sprayers. The system consists of a data acquisition module, a data processing module, and a flow rate control module. An embedded computer along with a touch screen was used to process control algorithms and allowed communication between the sprayer operator and the control system. The flow rate control module was designed with multi-channel driver circuits for activating the solenoid valves and driver protection circuits for avoiding surge voltages due to frequent on/off actions of the solenoid valves. Laboratory tests were conducted to verify the accuracy of the control system with three nozzles (0.530 to 1.703 L min -1 ) at four different operating pressures (138 to 345 kPa) and ten duty cycles (10% to 100%). The microcontroller-controlled circuit precisely produced PWM signals with desired pulse widths to match the duty cycles, and linear spray outputs were achieved accurately with the duty cycles of the PWM-controlled solenoid valves. With the protection circuit for the solenoid valve drivers, the longevity of the solenoid valves increased from 350 to 2,426 h. The system offers flexibility in choosing the number of connection channels needed for the number of nozzles individually or in a group on sprayers. Accordingly, together with canopy structures and travel speeds from laser scanning or other sensors, this compact control system is capable of performing variable flow rate functions for multiple nozzles separately.

Advanced Technologies for the Improvement of Spray Application Techniques in Spanish Viticulture: An Overview

Spraying techniques have been undergoing continuous evolution in recent decades. This paper presents part of the research work carried out in Spain in the field of sensors for characterizing vineyard canopies and monitoring spray drift in order to improve vineyard spraying and make it more sustainable. Some methods and geostatistical procedures for mapping vineyard parameters are proposed, and the development of a variable rate sprayer is described. All these technologies are interesting in terms of adjusting the amount of pesticides applied to the target canopy.

Spatial distribution visualization of PWM continuous variable-rate spray

Abstract: Pesticide application is a dynamic spatial distribution process, in which spray liquid should be able to cover the targets with desired thickness and uniformity. Therefore, it is important to study the 2-D and 3-D (dimensional) spray distribution to evaluate spraying quality. The curve-surface generation methods in Excel were used to establish 1-D, 2-D, and 3-D graphics of variable-rate spray distribution in order to characterize the space distribution of the variable-rate spray. The 1-D, 2-D, and 3-D distribution graphs of Pulse-Width Modulation (PWM)-based continuous variable-rate spray were developed to provide a tool to analyze the distribution characteristics of the spray. The 1-D graph showed that the spray distribution concentrated toward the center of the spray field with the decreased flow-rate. The 2-D graph showed that the spray distribution always spread as the shape of Normal Probability Distribution with the change of the flow-rate. The 3-D graph showed that the spray distribution tended to be uniform when the sprayer travelled forward at the appropriate speed. This study indicated that the visualization method could be directly used for analysis and comparison of different variable-rate spray distributions from different experimental conditions and measuring methods. Keywords: spray distribution, pulse width modulation (PWM), variable-rate spray, distribution visualization DOI: 10.3965/j.ijabe.20130604.001 Citation: Deng W, Huang Y B, Zhao C J, Wang X, Liu J L. Spatial distribution visualization of PWM continuous variable-rate spray. Int J Agric & Biol Eng, 2013; 6(4): 1－8.

Spray Deposition inside Tree Canopies from a Newly Developed Variable-Rate Air-Assisted Sprayer

Abstract. Conventional spray applications in orchards and ornamental nurseries are not target-oriented, resulting in significant waste of pesticides and contamination of the environment. To address this problem, a variable-rate air-assisted sprayer implementing laser scanning technology was developed to apply appropriate amounts of pesticides based on tree canopy characteristics including tree height, width, volume, foliage density, and occurrence. The new sprayer performance was evaluated in an apple orchard by quantifying spray deposition inside canopies at three different growth stages (leafing, half-foliage, and full-foliage) with three sprayer treatments: the new variable-rate sprayer (S 1 ), the same sprayer without the variable-rate function (S 2 ), and a conventional air-blast sprayer (S 3 ). Their spray coverage and deposits inside canopies were measured and compared with water-sensitive papers and nylon screens. The three sprayer treatments provided fairly consistent spray coverage and deposits in the spray direction (or canopy depth direction) at the leafing stage. The variations in spray coverage and deposits in the spray direction increased considerably for S 2 and S 3 at the half-foliage and full-foliage stages. S 1 produced better uniformity in spray coverage and deposits across the tree height direction than S 2 and S 3 at all growth stages. Compared to constant-rate sprayers, the new variable-rate sprayer only consumed 27% to 53% of the spray mixture while still achieving adequate spray coverage inside the canopies. In addition, the spray deposition from the new sprayer was very consistent regardless of the canopy growth stage. Therefore, the new sprayer increased spray efficiency and improved spray accuracy by greatly lowering the possibility of overspray, resulting in reduced spray costs and potential reduction of environmental pollution.

Spray Drift and Off-Target Loss Reductions with a Precision Air-Assisted Sprayer

Abstract. Spray drift and off-target losses are inherent problems of conventional air-assisted sprayers; consequently, their low efficiencies cause environmental pollution and public anxiety. A new drift reduction technology incorporating laser scanning capabilities with a variable-rate air-assisted sprayer was developed to address these problems. This new sprayer, the same sprayer with the variable-rate function disabled, and a conventional constant-rate air-blast sprayer were tested for comparison of spray drift and off-target losses in an apple orchard. Tests were conducted at three different growth stages: trees just beginning to leaf (leafing), half foliage, and full foliage. Spray deposits from spray drift and off-target losses were collected within tree rows at ground level, above and behind the sprayed trees, in the spaces between trees, and from 3.2 m tall poles at 5, 15, and 35 m from the tree rows. Compared to the constant-rate sprayers, the laser-guided variable-rate sprayer reduced average spray losses on the ground by 68% to 90% and around tree canopies by 70% to 92%, reduced airborne spray drift by 70% to 100%, and most importantly, reduced the spray volume by 47% to 73%, while spray deposition quality inside the canopy for these sprayers was comparable. These results demonstrate that the variable-rate sprayer incorporating the innovative laser scanning technology reduced spray drift and off-target losses of pesticides, was environmentally sustainable, and was economically beneficial to growers.

Spot-application of fungicide for wild blueberry using an automated prototype variable rate sprayer

Wild blueberry producers apply fungicide uniformly without considering significant bare spots in the field. The wrong or over use of fungicide in bare spots results in an increased cost of production and threatens the environment. An automated prototype variable rate (VR) sprayer was used for spot-application (SA) of Chlorothalonil (Bravo®) fungicide in a wild blueberry field. Eighteen 6.1 m wide test tracks were selected in the field and bare spots were mapped using a real-time kinematics-global positioning system (RTK-GPS). Six plots were selected randomly for three different application rates. Water sensitive papers (WSP) were placed in foliage and bare spots in SA and uniform-application (UA) tracks. The percent area coverage (PAC) of WSP with both SA and UA in foliage and bare spot areas were calculated. Plant growth parameters were measured from all 108 randomly selected plots in SA, UA and control (CN) tracks for comparison. Plant images were taken over six selected plots in each of the 18 tracks. Images were analyzed using custom developed software to calculate the percentage of green pixels (PGP) for determining the effect of Bravo® on plant health. Fruit yield parameters were also measured from selected plots for comparison. Non-significance of the t test for SA versus UA plant targets’ PAC indicated that there was no significant bias in the SA with saving (9.90–51.22 %) and SA was accurate. Bravo® did not show any significant difference on plant growth parameters among SA, UA and CN. However, PGP, floral bud and harvestable yield of SA and UA were significantly increased over CN. Therefore, a VR sprayer could be used for SA of fungicides in wild blueberry cropping system to reduce chemical usage and maintain crop productivity.

Variable rate sprayer. Part 2 – Vineyard prototype: Design, implementation, and validation

The structural characteristics of the canopy are a key consideration for improving the efficiency of the spray application process for tree crops. However, obtaining accurate data in an easy, practical, and efficient way is an important problem to be solved. This paper describes the technical characteristics of a sprayer prototype developed for vineyards, following the principles and previous laboratory tests described in the complementary paper Variable rate sprayer. Part 1 – Orchard prototype: design, implementation and validation. This prototype can modify the sprayed volume application rate according to the target geometry by using an algorithm based on the canopy volume inspired by the tree row volume (TRV) model. Variations in canopy width along the row crop are electronically measured using several ultrasonic sensors placed on the sprayer and used to modify the emitted flow rate from the nozzles in real time; the objective during this process is to maintain the sprayed volume per unit canopy volume (Lm−3). Field trials carried out at different crop stages for Merlot and Cabernet Sauvignon vines (Vitis vinifera) indicated a good relationship between the applied volume and canopy characteristics. The potential pesticide savings were estimated to be 21.9% relative to the costs of a conventional application. This conclusion is in accordance with the results of similar research on automated spraying systems.

Variable rate sprayer. Part 1 – Orchard prototype: Design, implementation and validation

Discussions in recent decades about dosage models for applying plant protection products in orchards have failed to reach a compromise solution. Furthermore, canopies are spatially variable, and a uniform dose may not be adequate for the entire orchard. Spraying at an adequate volume application rate on a site-specific basis would help reduce the amount of agrochemicals used in the framework of precision horticulture and precision fructiculture.An orchard sprayer prototype running a variable-rate algorithm to adapt the volume application rate to the canopy volume in orchards on a real-time and continuous basis was designed, implemented, and validated. An equivalent prototype was designed for vineyards and described in a companion paper (‘Variable rate sprayer. Part 2 – Vineyard prototype: Design, implementation and validation’). The orchard prototype was divided into three parts: the canopy characterization system (using a LiDAR sensor), the controller executing a variable-rate algorithm, and the actuators. The controller determines the intended flow rate by using an application coefficient (required liquid volume per unit canopy volume) to convert canopy volume into a flow rate. The sprayed flow rates are adjusted via electromagnetic variable-rate valves. The goal of the prototype was to keep the actual application coefficients as close as possible to the objective.Strong relationships were observed between the intended and the sprayed flow rates (R2=0.935) and between the canopy cross-sectional areas and the sprayed flow rates (R2=0.926). In addition, when spraying in variable-rate mode, the prototype achieved significantly closer application coefficient values to the objective than those obtained in conventional spraying application mode.

Weed Image Edge Detection Based on Order Morphology Transformation

Weed recognition is one of the key parts of variable rate spray system, and is the important part of precision agriculture. This paper applied the order morphology to weed recognition, and constructs the edge detection operations that fit to weed image. The corresponding simulation is also done, the result show that the operation that this paper proposed is very suit for weed edge detection.

Development of a Variable-Rate Sprayer for Nursery Liner Applications

Sensor-guided application technologies are needed to achieve constant spray deposition for the rapid growth of nursery liner trees during a growing season. An experimental real-time variable-rate sprayer was developed to adjust spray outputs automatically based on the liner canopy size. The developed sprayer consisted of two vertical booms, an ultrasonic sensor detecting system coupled with a spray flow rate controlled unit, a microcontroller, and a spray delivery system. Two booms were integrated with five opposing pairs of equally spaced spray nozzles. The sensors were mounted 0.35 m ahead of the spray nozzles to ensure sufficient time for signal processing. The accuracy of the sprayer in triggering spray against detected targets moving at 3.2 km h-1 was evaluated by use of a high-speed camera. An outdoor laboratory plot consisting of six different-sized tree species was used to test the sprayer performance consistency. Test results revealed that the spray nozzles were triggered from 4.5 to 12.5 cm ahead of detected targets. Seventy-five percent of test runs for detecting canopy volume of the six tree species produced significant (p < 0.05) Pearson correlation coefficients from 0.43 to 0.88 when the sprayer travel speed was from 3.2 to 6.4 km h-1. While the sprayer applied variable output rates from 0 to 20.4 L min-1 at travel speeds from 3.2 to 8.0 km h-1, the mean spray coverage inside canopies of six tree species was 12.0% to 14.7% and the mean spray deposit was 0.72 to 0.90 L cm-2. Effects of travel speed on both mean spray deposit and coverage were insignificant. Therefore, the newly developed sprayer offered a possibility to achieve uniform spray deposition and coverage for nursery liner applications despite variations in liner canopy size and sprayer travel speed.

Development of a Variable-Rate Sprayer with Laser Scanning Sensor to Synchronize Spray Outputs to Tree Structures

Efficient and effective precision spray equipment and strategies are in high demand to reduce pesticide use in tree crop production. An experimental variable-rate air-assisted sprayer implemented with a high-speed laser scanning sensor was developed to control the spray output of individual nozzles in real time. The sprayer consisted of a laser scanning sensor control system and an air and liquid delivery system. Each nozzle in the delivery system, coupled with a pulse width modulated (PWM) solenoid valve, achieved variable-rate delivery based on occurrence, height, and width of the target tree and its foliage density. Other components of the sensor control system included a unique algorithm for variable-rate control that instantaneously processed measurements of the canopy surfaces. To determine system delay time, a high-speed video camera was used to record the time period between sensor detection of the canopy and nozzle activation. Spray deposition uniformity inside canopies was verified by quantifying spray coverage inside four ornamental nursery trees of different sizes and canopy densities at 3.2 and 6.4 km h-1 travel speeds. Test results demonstrated that differences in spray coverage inside the canopies of these four trees in the spraying direction were not statistically significant, even though these trees had different structures, canopy volumes, and foliage densities. The canopy volume and foliage density measured with the algorithm developed for the laser sensor-controlled detection system exhibited little variation between the two travel speeds. Design criteria for the sensor-controlled system in the experimental sprayer were acceptable for variable-rate application, having great potential for spray volume and drift reduction, and thus reducing environmental impact.

Research On The Performance Of The Ultrasonic Measurement System Of The Tree Canopy Volume

Abstract Variable-rate spraying technology can change the application rate by the target information. And the tree canopy volume was a very important target information. An ultrasonic measurement method of canopy volume was presented, and an ultrasonic measurement system of canopy volume was developed. The average of Wheaton and Albrigo manual measurement values was defined as the manual measurement values in this paper.150 peach trees having different canopy volumes were selected to as the experimental objects. Experiment results indicated that the ultrasonic measurement system had high stability (R2=0.968, Std. Error of the Estimate was 0.061719), the manual measurement method had high stability(R2=0.973, Std. Error of the Estimate was 0.060214), and the manual measurement values and the ultrasonic measurement values were in a good agreement(R2=0.968, Std. Error of the Estimate was 0.065314), that is the ultrasonic measurement system had high precision.

Nozzle Flow Model of High Pressure Variable-Rate Spraying Based on PWM Technology

Nozzle flow model for high pressure variable-rate spraying is indispensable when orchard sprayer is controlling liquid flow based on Pulse Width Modulation (PWM) technology. Three flow models for Teejet AITXA 8002, 8003 and 8004 nozzles are obtained by using nozzle flow model test system which is established in this paper. The results from equation hypothesis test and test for lack of fit of flow model shows that those three flow models work well. Nozzle flow model validation trials show that the relative errors of model flow and actual flow are small, while the maximum relative error is 6.50%; the flows characteristics of different nozzles with the same type are almost the same.