Pengjun Wang，Yongsheng Chen，Dongxia Sun，Aibing Wu，Yanjie Hao,Mingjiang Chen

(1.Nanjing Institute of Agricultural Mechanization,Ministry of Agriculture and Rural Affairs,Nanjing,210014,China;2.Binzhou Agricultural Machinery Research Institute,Binzhou,256600,China)

Abstract: In order to ensure that the amount of organic fertilizer applied in the field is accurately controllable and meets the needs of field crop growth,a solid organic fertilizer application control system based on BP neural network algorithm is designed.The supporting equipment of the system adopts a solid organic fertilizer spreader with chain plate and fertilizer baffle to control the amount of fertilizer.The control system is developed based on supervisory control and data acquisition (SCADA),and the human-computer interaction is realized by the touch screen.The basic data of the control system is provided by the actual demand for basic fertilizer in farmland and input into the system through the input box.According to the speed of the vehicle,the momentum BP neural network algorithm is used to first control the opening size of the fertilizer blocking device and provide an input value for the rotating speed control of the fertilizer chain plates.Finally,the elastic BP neural network algorithm is used to control the rotating speed of the fertilizer chain plates.The experimental results show that the control system can change the opening size of the fertilizer blocking device and the speed of the chain plate of the fertilizer spreader in real time according to the set basic fertilizer demand and the traveling speed of the vehicle,and the control deviation of the fertilizer amount is less than 9%.

Keywords:solid organic fertilizer spreader;precision agriculture;SCADA;BP neural network

0 Introduction

As a kind of organic fertilizer spreading equipment,the solid organic fertilizer spreader has the characteristics of high spreading efficiency,good uniformity,and labor saving[1-3].At present,the existing solid organic fertilizer spreaders at home and abroad can manually adjust the fertilizer blocking device and control the speed of the chain plate,but they cannot realize quantitative spreading according to the traveling speed,which saves costs[4-10].Foreign research on the control system of organic fertilizer spreader mainly focuses on liquid organic fertilizer,which is imported through prescription maps and combined with the fertilizer distribution mechanism to realize the on-demand supply of liquid organic fertilizer[11].Domestic scholar Weinan Yang and other researchers used FPGA as the core control system to control the solid organic fertilizer spreading through the T-S fuzzy algorithm.However,the cost of the control equipment is high,which is not conducive to mass promotion[12].Thus,it is necessary to develop a control system for solid organic fertilizer spreader that is inexpensive and integrates visualization and intelligence.

The control system of the solid organic fertilizer spreading device designed in this paper takes SCADA as the control core,which includes the vehicle speed monitoring system,the chain plate speed and the opening size monitoring system of the fertilizer blocking device.It can be combined with the BP neural network control algorithm.According to the change of vehicle speed,the speed of the fertilizer chain plates and the opening of the fertilizer blocking device can be automatically adjusted in real time to achieve precise fertilizer spreading.

1 System composition and working principle

The basic structure of the solid organic fertilizer spreader is shown in Figure 1,including fertilizer chain plates,fertilizer boxes,fertilizer blocking device,andfertilizer spreading disc.Power is provided by the tractor.When spreading fertilizer,the fertilizer chain plate and the fertilizer retaining plate are controlled by hydraulic pressure,and the fertilizer spreading disc is directly driven and outputted by the tractor PTO.

Fig.1 Basic structure of solid organic fertilizer spreader1.Revolution speed transducer 2.Fertilizer chain plates 3.Fertilizer boxes 4.Fertilizer blocking device 5.Displacement transducer 6.Fertilizer spreading disc

The control system consists ofa touch screen,SCADA,hydraulic solenoid valve,revolution speed transducer,displacement transducer,and Beidou navigation system.The Beidou navigation system is used to monitor the walking speed of the fertilizer spreader.Displacement transducer is used to monitor the opening of the fertilizer blocking device.The revolution speed transducer is used to monitor the speed of the fertilizer chain plates.When the system is working,according to the input actual fertilizer demand,combined with the travel speed of the fertilizer spreader.By using a relay to open and close the hydraulic solenoid valve and the hydraulic solenoid return valve,the opening of the fertilizer blocking device and the speed of the fertilizer chain plates can be adjusted to achieve the purpose of precise fertilizer operation.During the operation of the fertilizer spreader,adjust the solenoid valve opening by controlling the on and off of the hydraulic flow solenoid valve relay，and finally realize the control of the rotation speed of the fertilizer chain plates.By connecting hydraulic solenoid valve to both rising and falling control,the precision of the rising and falling of the fertilizer blocking device is improved by controlling the opening and closing time.By opening the corresponding hydraulic solenoid valve in real-time,the hydraulic circuit is unblocked,and ensured the normal operation of the hydraulic system.

2 Design control system

2.1 Design hardware of control system

The control system hardware includes one TPC6000-A102 industrial panel computer,one Kunlun Coast KL-N4118 eight-way analog quantity acquisition module,two Kunlun Coast KL-N4214 relay output modules,one CZ716 tachometer acquisition revolution speed transducer,one Sabang pull wire displacement transducer.SCADA system adopts force control software.All of the sensors selected in the system with 4 mA to 20 mA data output mode can support Modbus communication protocol.The hardware system structure is shown as in Figure 2.

Fig.2 Hardware system structure diagram

As shown in Figure 2,a displacement transducer is installed on the fertilizer blocking device and installs a revolution speed transducer on the rotation axis of the chain plate to collect the operation information of the fertilizer spreader.Both sensors transmit data to the fertilizer spreader through the 4 mA to 20 mA output to the data acquisition module.The data acquisition module communicates through 485 protocol,and the speed data of Beidou navigation is also transmitted to SCADA through 485 protocol.After processing the data,the actual amount of fertilizer per mu is displayed in SCADA.

2.2 Design software of control system

2.2.1 Design interface of touch screen

This article adopts the TPC6000-A102 industrial tablet computer and installs the force control software in the computer to directly complete the touch screen display design.The program does not need to be downloaded through the Ethernet port or USB device.The touch screen human-computer interaction interface directly adopts the power-on interface.There are six parts displayed on the screen,including the input text box for the amount of fertilizer,the text box for displaying the amount of fertilizer in real-time,the text box for displaying the speed of the vehicle,the automatic fertilizer control button,and the manual control button for the fertilizer locking device.The user can input the amount of organic fertilizer spreading in the field based on experience to provide basic data for subsequent vehicle fertilizer application control.The input range of the fertilizer spreading amount is 225-2 250 kg/hm2.The display text box of the fertilizer spreading amount is based on the fixed 6-meter spreading width,the traveling speed of the vehicle,and the real-time data returned by the displacement transducer and the revolution speed transducer.The current fertilizer spreading amount is comprehensively calculated and displayed in the text box.The manual control buttons of the fertilizer blocking device and the chain plate are mainly used when the vehicle discharges the remaining organic fertilizer out of the fertilizer tank after the operation is completed.The power-on display screen of the touch screen is shown in Figure 3.

Fig.3 Monitoring interface diagram

2.2.2 SCADA system

SCADA means supervisory control and data acquisition[13-15].This article uses the SCADA system of force concontrol software to complete the programming.When we enter the system,firstly we can enter the main interface,and then we can set the demand per hectare.Finally after the setting is completed,we can select automatic spreading.The system workflow is shown in Figure 4.The specific process is as follows:the system receives the input fertilizer demand,then collects navigation data;the BP neural network system controls the opening size of the fertilizer blocking device and the revolution speed of the chain plate,collecting data at the same time.By controlling the opening and closing of the solenoid valve and the opening and closing time,the hydraulic system can complete the opening of the fertilizer blocking device.By controlling the energization time of the solenoid valve,the hydraulic flow rate control is realized,and the speed of the chain plate is finally controlled.The actual amount of solid organic fertilizer applied is calculated from the opening of the fertilizer blocking device,the speed of the fertilizer chain plate,and the speed of the vehicle according to formula (1).

Fig.4 Control flow chart

In the SCADA system,we need to process the collected data to get the actual amount of fertilizer spread.The average amount of fertilizer spread per mu is related to therevolution speed of the chain plate,the opening size of the fertilizer blocking device,and the speed of the vehicle.The formula for calculating the amount of fertilizer is as follows

(1)

WhereWis the amount of fertilizer spread per acre,kg/hm2;Ris the radius of the fertilizer sprocket,m;kis the revolution speed of the fertilizer sprocket,r/min;Dis the width of the fertilizer chain plate,m;His the opening size of the fertilizer blocking device,m;ρ is the bulk density of solid organic fertilizer,kg/m3;vis the traveling speed of the vehicle,km/h;Bis the spreading width,m.

3 Design of BP neural network algorithm

The main influencing factors during the operation of the solid organic fertilizer spreader are the demand for spreading fertilizer and the speed of the vehicle.The speed of the vehicle will be affected by the viscosity of the ground,the condition of the gravel,and uneven ground.Different vehicle speeds and fertilizer requirements correspond to different openings of the fertilizer blocking device and the speed of fertilizer chain plates.

The opening of the fertilizer blocking device is input to the momentum neural network algorithm through the actual vehicle speed and the actual amount of fertilizer.The required value of the opening degree of the fertilizer blocking device is calculated by this algorithm.Use the opening value of the fertilizer blocking device obtained in the previous step as well as the vehicle speed and the amount of fertilizer as the input of the elastic neural network algorithm.It is used to meet the control needs of solid organic fertilizer spreading process.

3.1 BP neural network neuron model

The neuron model in this article uses a two-fold neuron superposition model.The input of the first neuron is the amount of fertilizer required and the speed of the vehicle.The output of the first neuron is the opening size of the fertilizer blocking device.Since the opening size of the fertilizer blocking device is controlled by hydraulic pressure,it is easy to produce an overcorrection during the control process.Therefore we use the momentum BP neural network algorithm.The algorithm can use a larger learning rate without causing the divergence of the learning process.Therefore,the opening size of the fertilizer blocking device can be quickly obtained,which provides a calculation basis for the speed of the fertilizer chain plates output by the second neuron.The second neuron input is the opening size of the fertilizer blocking device,vehicle speed and the amount of the fertilizer.The output is the speed of the fertilizer chain plates.Since the opening size of the fertilizer blocking device may have a large number,the slope tends to zero.We use elastic BP neural network algorithm.This algorithm is used to eliminate the adverse effects of gradient amplitude.The algorithm can converge quickly.Through the calculation of this algorithm,the speed value of the fertilizer chain plates is finally obtained quickly.Suppose the opening size of the fertilizer blocking device isa1,the revolution speed of the chain plate isa2,fis the transfer function between input and output,wis the appropriate weight,p1is the fertilizer demand,p2is the vehicle speed,and the network output can be expressed as

a1=f(wp1+wp2)

(2)

a2=f(wp1+wp2+wa1)

(3)

According to the relationship between the above input and output,a neuron model is established,as shown in Figure 5.

Fig.5 Neuron model

3.2 Momentum BP neural network algorithm

In this paper,the opening control of thefertilizer blocking device adopts the momentum BP neural network algorithm[16-17].The input of the algorithm uses vehicle speed and the amount of fertilizer.The change in input volume is small.It is easy to produce over correction during the control process.We use momentum BP neural network algorithm to reduce the amount of correction.The algorithm can keep the correction direction toward the direction of convergence.And also provide input for the output of the second neuron model.The learning speed of the algorithm is very high.According to the requirements of the above two aspects.While ensuring the stability of the algorithm,we use the momentum BP neural network algorithm to converge faster.The algorithm has a shorter learning time.Through this algorithm,we have realized the fast control of the opening size of fertilizer blocking device.The opening of the fertilizer blocking device is controlled according to the set application amount of fertilizer and vehicle speed.

As shown in equation

(4)

Whereη(0<η<1)is the momentum factor,andnis the number of learning times；Δx(n)is the nth amplitude correction value of the weight.

It can be seen that the algorithm always reduces the correction amount so that the convergence direction is along the correction direction,the momentum convergence rate is faster,and the learning time is shorter.

3.3 Elastic BP neural network algorithm

In this paper,therotating speed of the fertilizer chain plates control adopts an elastic algorithm[18-20].The vehicle speed,the amount of fertilizer and the opening size of the fertilizer blocking device are the input to the algorithm.The fertilizer demand and fertilizer door opening values in the input variables will appear large numbers.The gradient amplitude in the algorithm operation will have an adverse effect.Therefore,we use the elastic BP neural network algorithm to output the rotating speed of the fertilizer chain plates.In this algorithm,the weights are constantly modified on the same gradient.So as to overcome the adverse effects of gradient amplitude deviation.As formula (5)

Δx(n+1)=Δx(n+1)×sign[g(n)]

(5)

Where Δx(n)is the amplitude correction of the nth iteration of the weight;g(n)is the nth time iteration gradient.

4 Test of system operation

4.1 Test location and content

The test site is located in the corn planting area of Wudi County,Binzhou City,Shandong Province.The test site is 13.33 hm2fields.

The system was tested in the application of granular organic fertilizer in April 2019,and in September 2019 powdered organic fertilizer was tested with the control system during the fertilizer application process.

4.2 Analysis of test results

Through thesolid organic fertilizer spreader experiment,it is concluded that the opening size of the fertilizer blocking device and the revolution speed of chain plate can be adjusted in real-time during the fertilizer spreading process.When the vehicle speed stabilizes,the state of the fertilizer blocking device and chain plate is stable.

When carrying out the fertilization test,we input the organic fertilizer requirement per mu into the system.Upload the vehicle speed monitored by the navigation to the momentum BP neural network control system to control the fertilizer blocking device to open to a suitable position.The opening of the fertilizer blocking device and the vehicle speed and the organic fertilizer requirement are input into the flexible BP neural network control system to control the speed of the chain plate.Finally,precise control of the amount of fertilizer is achieved.

After completion,the input organic fertilizer demand is compared.The particle organic fertilizer application test in April 2019 is shown in Table 1,and the powder organic fertilizer test in September 2019 is shown in Table 2.

Tab.1 Field test results of granular organic fertilizer

According to the test results in Table 1 and Table 2,in the field test,when the average spreading amount is less than 1 800 kg/hm2,there is a positive error,which means that there is more spreading.When it exceeds 1 800 kg/hm2,the height of the fertilizer blocking device will exceed fertilizer conveying height,which means that there is less spreading and that the control error fluctuates stably within the required spreading amount,satisfying the design requirements.Comprehensive relative error data in the table,it is concluded that the relative error between the amount of the system set spreading and the amount of actual spreading is less than 9%.The control system has a good control effect and meets the design requirements.

Tab.2 Field test results of powdery organic fertilizer

5 Conclusions

In this paper,a solid organic fertilizer spreading device control system based on BP neural network is designed to achieve precise control and stable operation of the solid organic fertilizer spreading amount.The following conclusions are drawn.

1)Use the touch screen computer to complete the human-computer interaction and interface design,including the control interface.The background can be written into the BP neural network algorithm script.The operation is simple,and the amount of fertilizer can be displayed in real-time.

2)The design of the BP neural network control system is completed.The output obtained from the first stage is put asthe second input.The momentum BP neural network algorithm control system is used to accurately control the opening of the fertilizer blocking device.The flexible BP neural network algorithm control system is adopted to realize the precise control of the speed of the fertilizer chain plates.

3)The test results show that the system can accurately adjust the opening size of the fertilizer blocking device and the revolution speed of the chain plate according to the actual vehicle speed and the demand for spreading fertilizer.Thus,through experiments,the amount of fertilization meets the set requirements.When the data becomes stable,the system automatically stops the adjustment.The solid organic fertilizer spreader realizes stable spreading.