ELECTROSTATIC TREATMENT OF AGRICULTURAL CROPS WITH AN UNMANNED ELECTRIC DEVICE

One of the options for improving the efficiency of the machine and tractor unit in the field is the use of course indi -cators, thrusters, hydraulic autopilots and other equipment. However, these devices do not exclude environmental pollution by exhaust gases and the presence of significant operating costs for fuel and lubricants. In this regard, the paper proposes an electric-powered unmanned device (EPUD), which can perform the tasks with high accuracy (deviations from the set course average 16 cm) due to autonomous movement on GPS/GLONASS satellite radio navigation signals on agricultural lands. For the effective application of liquid agents to agricultural crops, a device is proposed that provides an electric charge of the introduced fine aerosol, which is installed on the EPUD and reduces the electrical energy consumed by 23.5% compared to existing analogues. All this, combined, will reduce operating costs up to 10%, as well as improve the environmental performance of crop spraying. Based on the conducted stud ies of the EPUD, its design was developed and a prototype with a software and hardware part was created. A device for the electric charge of the introduced aerosol, which makes it possible to increase the uniformity of the aerosol application on the plant, has been developed and investigated. The effectiveness of the developed technical solution had been proved by laboratory and field tests.

given course employing radio navigation signals makes it possible to ensure the autonomy of its operation, and therefore, to eliminate errors associated with the physical and professional capabilities of the operator. For the effective operation of the EPUD, the introduction of pesticides is proposed by using a fine aerosol (the diameter of the drops does not exceed 210 microns), which, in comparison with traditional full-volume spraying with the same consumption of pesticides (fertilizers) per unit area, covers the entire surface of the treated crop evenly and will also increase the productivity of the plant.

Purpose of the research
Reduction of operating costs for the application of liquid fertilizers and pesticides through the development and implementation of an unmanned electric unit with an electric charging device for the introduced fine aerosol. Research objectives are -to develop a design and create a prototype EPUD with software and hardware that allows autonomous movement on the field; -to develop and research a device for an electric charge of the introduced aerosol; -to conduct laboratory and field tests of the developed EPUD with the device of electric charge of the introduced fine aerosol.

METHODS
The EPUD is a universal, self-contained electric chassis with a device for applying liquid fertilizers and pesticides in an electrostatic field (Fig. 1). The engine of the device is represented by a solid rectangular frame with   The control system controls and controls the traction drive system as a whole (wheel speed, engine torque, breaker currents, and the route of the set course). The control system of the EPUD consists of two main parts: the power circuit and the information block. The power circuit includes a battery pack, a renewable energy source (solar panel), a motor controller, and a BDCM. The information block includes the navigation system and the drive control system, respectively. Nowadays the most common method of applying liquid preparations is full-volume spraying (dispersion >500 microns). Its main drawback is the runoff of the drug from the plants resulted from excessive wetting, which leads to an increase in the cost of production and soil contamination. To eliminate this drawback, it is proposed to apply liquid fertilizers and pesticides with a fine aerosol (the diameter of the drops does not exceed 210 microns), which, in comparison with full-volume spraying, with the same consumption of pesticides (fertilizers) per unit area, covers the entire surface of the treated crop evenly. In closed ground conditions, a high efficiency of using a dispersion of <210 microns for processing agricultural crops are observed, when in open ground conditions a significant disadvantage is the uneven deposition of aerosol on the treated surface of the plant. One of the ways to eliminate this drawback is to give the aerosol particles an electric charge. In an electrically charged aerosol, additional forces of interaction of particles arise -electrostatic scattering and mirror image, which contributes to the equalization of the concentration by volume while increasing the deposition rate [11]. The principle of electrostatic spraying is as follows (Fig. 3): air is pumped into the container with the working fluid using a vortex fan, the generator from the working fluid forms a fine aerosol. Under the influence of vortex flows, the aerosol is directed to the nozzles, at the ends of which electrodes are installed, passing through which the aerosol acquires a charge and enters the processing zone of agricultural crops. Nowadays it is known to use electric charging of liquid-air droplets by applying a constant high potential to the electrode (electrostatic induction) [1,12]. However, this method of electric charging has its drawback -the low efficiency of charge accumulation by sprayed drops, which ultimately requires an increase in the electric potential at the electrode, which affects the uniformity of the T distribution of the applied drug to the plant. The sequence of operation of the system is as follows. The boundaries of the processed field are set, then the EPUD starts moving as the system continuously receives radio navigation signals from satellites, based on which the current position of the EPUD is determined. Also, based on these signals, the control program calculates the amount of deviation from the specified trajectory. In this case, signals are generated, which in the form of a voltage are transmitted to the electric drive (an electric DC motor) of each wheel with an operating voltage of 48 V. Due to the difference in the speed of rotation of the wheels, the EPUD rotates at the required angle, i.e., it provides a manoeuvre for approaching the current trajectory of the EPUD to the necessary one, which corresponds to the principle of parallel operation of the unit on the field [13,14]. The mismatch between the actual position of the EPUD and the specified trajectory is determined by the current coordinate and the calculated trajectory of the unit. We assume that the radius of the return of the EPUD to a given course when it deviates will be equal to the value of the deviation A, which is determined by the distance of the perpendicular from the geometric centre of the unit to the line of the given path.
For theoretical research and justification of the design and technical parameters of the device, it is necessary to draw up a kinematic scheme of the movement of the EPUD in the field (Fig. 4). When drawing up the kinematic scheme of the movement of the EPUD, the following assumptions are made: the centre of mass of the device is located in the geometric centre of the body; both wheels of each side rotate at the same speed and always touch the support surface In the rectilinear motion of an EPUD moving on a given course, the speed (the speed of the centre of mass) is equal to the speed of all its wheels: where V 1 is the speed of the left side of the EPUD, m/s; V 2 -speed of the starboard side of the EPUD, m/s; V dev -the speed of the EPUD, m/s. According to the theory of cars and tractors [15], the radius of the side turn R turn will be determined by the following expression: where B is the transverse wheelbase, m. The speed of the device R dev is accepted according to the agrotechnical requirements. When the EPUD deviates from the set course, it is assumed that the speed of the left (lagging) side V 1 is const and the turning radius R1 is equal to the deviation value A, which is determined by the current coordinate and the calculated trajectory of the device. Accordingly, to return to the required trajectory, it is necessary to determine the speed of the right (running) side V 2 ( Fig. 4): where A is the value of the deviation of the EPUD from the set course (return radius), m Based on the kinematic scheme, a mathematical model of the EPUD movement is compiled, the main element of which is the wheel motor, which is a direct drive based on a brushless DC motor. A brushless DC motor in a mathematical model is described by the equations [16,17]: where -dynamic drive force, Н; F1… F4 -active forces (developed by each EPUD), H; Fс1… Fс4 -longitudinal forces (friction forces), H; Flf1… Flf4 -lateral forces, H.
Since each wheel of the EPUD is equipped with its own drive, the longitudinal forces (friction forces) Fc will be defined as the rolling friction forces of the driving wheel [18] dt dV m R N k F c ⋅ = (6) where k -the value of the longitudinal drift, m; N -reaction force of the reference surface, H; R -wheel radius, m. The lateral forces are determined by: where φ -coefficient of adhesion of tires to the bearing surface; λ -dynamic wheel load factor; G dev -gravity (weight) of the device, H. The study proposes a method for improving the efficiency of electric charging of aerosol droplets, which consists of using a resonant transformer and periodically interrupting the operation of the resonant transformer generator. Fig. 5 shows a block diagram of the proposed device for electric charging of liquid-air droplets. The device for electric charging of liquid-air droplets consists of a power source 1, an electronic key 2 that provides a break in the supply circuit with a low frequency, a multivibrator 3 with a high-frequency oscillating circuit L 1 C 1 , and the inductance L 1 is a low-voltage winding of the resonant transformer 4, the inductance L 2 is a high-voltage winding of the resonant transformer 4 and forms a second oscillating circuit L 2 C 2 with the capacitor C 2 , to which the diode 5 and the electrode 6, which is a cylinder, are connected in series and is installed behind the sprayer 7. The principle of operation of the proposed device for electric charging of a liquid-air mixture is described as follows. A multivibrator 3 with an oscillating circuit L 1 C 1 generates a carrier (modulated) signal ω 1, and an electronic key 2 that breaks the supply network with a low frequency generates a modelling signal ω 2 . Next, the resulting amplitude-modulated voltage is increased by a resonant transformer 4, rectified by a diode 5, and fed to electrode 6. Fig. 6 shows the time dependence of the potential on the electrode surface. The proposed device makes it possible to increase the efficiency of electric charging of liquid-air droplets by applying a potential to the electrode that changes over time.

RESEARCH RESULTS
Based on the theoretical descriptions of the EPUD and the device for electric charging of liquid-air droplets, their comprehensive study was carried out in the object-visual modelling environment Matlab (Simulink), according to which the experimental design of the BPEA and the device for electric charging of liquid-air droplets were created (Fig. 7).  The technical characteristics of the EPUD and the device for electric charging of liquid-air droplets are presented in Table 1.  Fig. 9. In automatic mode, the electric device was controlled by the GPS/GLONASS navigation satellite control system, and the manual mode meant remote control by the operator on the course indicator. One of the above statements is the low power consumption of a device that charges drops with an alternating electrostatic voltage, compared to a device that charges drops with a constant electrostatic voltage. Fig. 10 shows the dependence of the power consumption of the aerosol electric charging device on the supply voltage obtained during the research. When setting the value of the interrupt frequency ω2, the pulse duration t was selected in such a way that with the end of the damped oscillations, the next oscillations began. According to the obtained research results, the power consumption P decreases with an increase in the interrupt frequency ω2. However, at an interrupt frequency of more than ω2=100 Hz, a deterioration in the process of electric charging of liquid-air droplets is observed (carrier frequency ω1=52 kHz). Thus, the electric charging of droplets with an alternating electrostatic voltage of negative polarity allows you to reduce the electrical energy consumed. One of the parameters that make it possible to evaluate the effectiveness of spraying plants in an electrostatic field is the specific deposition density of electrically charged droplets N spd, which was determined by the inertial method in the absence of wind. Liquid-air drops were deposited on slides coated with a mixture of boric ointment and transformer oil in a ratio of 2.5:1. The glasses were placed at the level of the leaves directly on the path of the EPUD passage.
According to the obtained values of Nspd at different velocities of the VEPUD, the average value of the specific deposition density Nspd was determined. During the experiments, the speed VEPUD of the EPUD movement (from 5 m/s to 12 m/s) and the voltage U (from 1 kW to 4 kW) applied to the electrode changed. At the same time, the specific charge of liquid-air droplets was determined (the ratio of the charge of the droplets to its mass) by the following formula: where U k -the potential of the metal vessel in which the sprayed droplets accumulated, relative to the ground, B; С -electric capacity of a metal vessel relative to the ground, F С в -input electric capacity of the measuring device, F;m -the mass of the liquid worked to the bottom in the metal vessel, kg. Based on the obtained values of the specific charge of liquid-air droplets, the dependence shown in Fig. 11 is constructed. According to the obtained dependence of the specific charge of the drops q уд on the voltage at the electrode U at different speeds of movement of the EPUD V EPUD , it can be seen that with an increase in the speed of movement of the EPUD V EPUD , and, consequently, with an increase in the flow rate of the liquid Q, the specific charge of the drops q уд decreases, which is associated with an increase in the number of droplets passing through the electrostatic field. When studying the efficiency of droplet deposition on slide glasses according to the above method, two methods of electric charging of droplets were also compared: -with a constant electrostatic voltage; -with variable (in amplitude) electrostatic voltage (Fig.  12). As can be seen from the obtained research results, when applying a potential variable in amplitude (variable electrostatic voltage) U=3 kW to the electrode, the maximum value of the average specific density of electrically charged droplets that worked to the. bottom is observed, N aspd .=284 pcs / cm 2 (Fig. 12), which is defined as the sum of the specific deposition densities obtained at different speeds of the EPUD movement, divided by the number i of the EPUD movement speeds (N aspd =∑N sp.i /i). The decrease in the average specific density of deposition of electrically charged droplets with a further increase in voltage is associated with a decrease in the diameter of the droplets due to their additional crushing in the electrostatic field, as a result, the droplets become sensitive to a small movement of air masses.

DISCUSSION
Field tests have shown that the deviation of the electric device from the course in the automatic control mode is on average 16.6 cm. This accuracy is sufficient for the application of liquid fertilizers and pesticides [15,19,20]. As it can be seen from the presented dependencies, the use of electric charging of liquid-air droplets with variable electrostatic voltage reduces the electrical energy consumed by 23.5% compared to applying a constant amplitude potential (voltage) to the electrode. In addition, the fine aerosol envelops all processed objects more effectively in the area of direct processing. This method leads to the most economical and efficient method of process-ing agricultural crops with liquid fertilizers and pesticides compared to processing without electric charging or with treatment with constant electrostatic voltage and it can be used in precision farming systems [11,21,22]. The conducted studies have shown that when applied to the electrode with a variable amplitude potential (variable electrostatic voltage) U=3 kW, the maximum value of the average specific deposition density of electrically charged droplets N spd = 284 pcs/cm2 is observed. In the course of the research, it was found that the greatest efficiency of plant treatment by electric charging of sprayed drops with a variable electrostatic voltage of negative polarity was observed at the voltage at the electrode U=3 kW and the speed of movement of the EPUD VEPUD = 9 km/h. The value of the specific density of deposition of electrically charged droplets was N sp = 311 pcs/cm 2 .

CONCLUSIONS
A device for electric charging of fine aerosol intended for spraying agricultural crops has been developed and investigated, which, along with well-known analogues, reduces the consumption of electrical energy by periodically interrupting the power supply circuit of the device.The absence of exhaust gases and runoff of liquid fertilizers and pesticides from plants to the soil makes it possible to get a more environmentally friendly final product and reduce the cost of its production. 450 thousand rubles were spent on the development of a prototype of the proposed technical solution. With this budget, the EPUD is equipped with batteries with a capacity of 20 Ah, which allows having a power reserve up to 45 km on a single charge with the ability to process up to 2.2 hectares per hour. According to technical and economic calculations, the developed technical solution in comparison with traditional methods of plant processing makes it possible to reduce operating costs by up to 10 %. The payback period will be about 2 years, taking into account the processing of more than 300 hectares per year.