Abstract
The research aims to design and build a set of intelligent control and precision sowing simulation system for wheat. the researchers attempt to drive feed shaft by DC motor replacing pure mechanical wheel-driven seeding mode, to make up the leakage of seeds and random seeding quantity during sowing. The variation of the motor speed is achieved by adjusting the duty ratio of PWM (pulse width modulation), and the PWM is controlled by stc89c52 MCU timer interrupt method. All the information will be processed in the host control system. After processing the information is real-time displayed by liquid crystal and sent out to the slave control system used to drive the feed shaft by PWM dynamically, to realize intelligent control and achieve drill operation speed change, seeding quantity and spacing in the rows stable. The DC motor used to drive feed shaft is with rated voltage of 12V, and the power is taken from the battery of the tractor. The seed-metering device is designed by the researchers. Simulation tests show that the application of the wheat intelligent control and precision seeding system can meet the requirements of precision sowing.
Keywords
Introduction
Precision seeding partly is sowing seeds to land according to the precise particle number of seeds and seeds and lines distance, to ensure even distribution and harvest and reduce seeding waste. It is the development direction of sowing technology today. Mechanical seeder uses wheels to drive feed shaft is widely used in wheat seeding at present. Because the wheels have to drive feed shaft, it is easy slippage to cause uneven seeding or even the leakage of seeds [1], and they are not able to set sowing amount and planting space according to their own wishes. they need to change these values by manually adjusting the chain or the replacement of seed-metering device [2, 3]. At present domestic wheat seeder of intelligent control and precision seeding study stay at monitoring the leakage of seeds and seed and fertilizer residual amount and fault alarming etc in the process of sowing [4–7].
In 2004, Lou Xiuhua used five-wheel device to meter seeding machine speed, using stepper motor by intelligent control methods to drive the feed shaft, shaft speed can be calculated and determined by sowing quantity and other parameters [8]. Five-wheel devices with high price are not conducive to the promotion of seeding machine. In 2009, Tang Yaohua installed hall sensors on the tractor front wheel to meter speed, using stepper motor to drive the feed shaft [9]. Hall sensor accuracy is too low, which is not conducive to the acquisition of real-time speed. In 2012, Li Jie studied in the condition of fixing thousand grain weight of wheat, using encoder to collection the real-time information of wheat planter, by setting seed spacing and sowing quantity to intelligently and real-time regulate stepper motor rotation speed to drive the feed shaft of wheat seeder [10]. Fixed thousand grain weight of wheat condition is too harsh to sowing. Intelligence is the focus of current research. In the present study, the researchers design a set of precision seeding and intelligent control multi-row wheat seeder simulation system based on intelligent sowing. The system sets the thousand grain weight of wheat and sowing amount information through the key, seed spacing change correspondingly. In the process of planting tractor speed change, the control chip control DC motor drives the feed shaft speed change through PWM, so that the seeding quantity and seed spacing are fixed. All the information is displayed by LCD screen. This system greatly makes up the shortages which existed before the sowing machine was invented [11].
The overall design scheme
The system composition and working principle
The simulation system consists of mechanical part and control part. The core of mechanical system is independently designed to complete multi-row seeding function through seed-metering device. The control system structure is shown in Fig. 1, including: planter simulation speed, host speed acquisition and parameters setting, slave receive information from host and motor control [12].
Working principle: The planter simulation speed is connected with the rotary encoder. The rotary encoder is used to the acquisition of working speed, using the button to set the seeding quantity and thousand grain weight of wheat information. All the information will be sent to the host control system, after processing the information including seeding quantity, thousand grain weight of wheat, planter working speed, seed spacing will be real-time displayed through the LCD screen. It is convenient to man-machine conversation. At the same time the host control system sends planter working speed and seed spacing to the slave system through the Bluetooth wireless transmission function. The slave system dynamically regulates DC motor speed through the PWM control according to the information received from the host control system. Achieving operating speed of sowing machine change, sowing amount and seed spacing stable.
The theoretical calculation of relevant parameters
By calculating the researchers get the relationship between thousand grain weight of wheat(G1), seeding quantity(G2) and seed spacing(D) satisfying the following formula: . From here we can see that seed spacing is determined by thousand grain weight of wheat and seeding quantity. At the same time, by calculating the researchers get the relationship between planter speed(V1), seed spacing(D) and feed shaft speed(V2) satisfying the following formula: . From the formula we can see that feed shaft speed is determined by planter speed and seed spacing.
The design of mechanical system
The design of mechanical system mainly comprises seed-metering device. This system designed seed-metering device is shown in Fig. 2. This seed-metering device has evenly distributed holes in the core in accordance with the corresponding size of wheat grain in the annular wheel. Each circle groove can accommodate a seed and complete the function of precision sowing [13]. In each column of the seed-metering device evenly interval distributed 5 or 6 circle grooves, By this method increasing the distance between sowing wheat grains and letting the overall distribution of sowing more uniform. The planter can complete 11 rows sowing at the same time. wheat can along the corresponding tube below fall to the ground achieving the goal of multi-row precision sowing. The inner core of seed-metering device rotates a circle sowing 187 seeds [14–17].
The design of control system
The hardware circuit design of control system
Planter simulation speed
The acquisition of planter real-time speed is achieved by means of the encoder. Planter real-time speed is not allowed under the laboratory conditions. So the planter simulation speed is adopted. In the process of planting, the acquisition of sowing machine operating speed is through the encoder fixed on the wheel calculating pulse number. Here the researchers connected and fixed the encoder by coupling with a small DC motor used to simulate planter wheel rotation in the process of sowing. The control circuit is as illustrated by Fig. 3. The working principle is by slowly rotating the potentiometer to change the input analog voltage of analog-digital conversion chip PCF8591P. PCF8591P chip transmits the collected analog voltage by I2C bus to control chip STC89C52 after AD conversion. Then the control chip STC89C52 carries on corresponding calculation [18]. Using the timer interrupt, the results will be used to control the duty ratio of PWM wave. PWM signal drives DC motor through the drive circuit, achieving the goal that by rotating potentiometer gradually change the small DC motor speed to simulate the operating speed of seeding machine.
Host speed acquisition and parameters setting
The MK60DN512ZVLQ10 chip uses ARM micro controller Cortex-M4 kernel. The control circuit is shown in Fig. 4. The host system uses the LCD screen display parameters setting by buttons and after system processing. Thousand grain weight of wheat is determined by actual measurement; seeding quantity is set up by the button. After parameters setting the control chip automatically calculates seed spacing according to the corresponding relationship getting before and display by the LCD. Through the timer interrupt encoder gets pulses so as to measure speed, sampling frequency is 5 times per second, which is 5 times per second to calculate the real-time speed and display by liquid crystal. Through the blue tooth wireless transmission module the collected real-time speed and seed spacing information is sent from host to slave control system for further processing.
Slave receive information from host and motor control
The slave control circuit is shown in Fig. 5, using the same MK60DN512ZVLQ10 chip as the host. Through the blue tooth wireless transmission module the real-time speed and seed spacing information is received from host. Then calculates the theory feed shaft rotating speed according to the parameters relationship getting before. Using PWM the control chip dynamically regulates the speed of DC motor, making it the same as the theory feed shaft rotating speed. To satisfy the speed of planter changes, the seeding quantity and seed spacing stable. The voltage used to drive DC motor is 12V and the control system adopts the voltage of 5V or 3.3V. In order to prevent the over voltage strike and current backflow, the researchers installed two pieces of optical coupler 6N137. Optical coupler input end and output end is connected through the “light” coupling. With good electrical insulation properties, it is suitable for occasions with a requirement of high speed of data transmission.
The control system software flow chart
Process control system is shown in Fig. 6.
The system starts to run after initialization. As the program running on rotary encoder measures speed by getting real-time.
The operator can at any time by pressing a button to set thousand grain weight of wheat and seeding quantity. After real-time processing system the corresponding parameters will be displayed by liquid crystal, at the same time seed spacing and planter working speed information will be sent via blue tooth to the slave control system. The slave receives information and control feed shaft through the PWM speed real-time adjustment of DC motor to realize the quantitative and fixed seed spacing.
Simulation test
The speed calibration of DC motor drives feed shaft through PWM
Pulse width modulation (PWM) is in the premise of fixing PWM square wave cycle, through software method to adjust the micro controller PWM control register to adjust the PWM duty ratio. Different duties are corresponding with different DC motor speed. When PWM wave frequency is set too low, vibration of the motor is more powerful. In order to eliminate the vibration, improve the motor PWM frequency is needed. The frequency setting is 10000 Hz used in the program. Because the DC motor driver chip needs PWM minimum pulse width is 30us, so if the duty ratio is lower than 30% feed shaft will stop. Otherwise you can replace the motor driver chip or adjust the PWM frequency to achieve. In order to achieve the actual rotation speed of the feed shaft accurately according to the theory rotation speed, the speed calibration of the motor drive feed shaft using PWM control system is made. Through the experiment with encoder can measure the corresponding relationship between the rotation speed of feed shaft and duty ratio, getting the data are shown in Table 1.
Curve fitting bases on the obtained data, the results are shown in Fig. 7.
The figure shows that the fitting curve is approximate to a straight line, that is feed shaft speed: . X is the duty ratio with the range of 30–100. So according to different seed spacing (D) there are suitable corresponding range of planter speed (V1). After recording the relationship between them to the program, the slave of control system receives the information of V1 and D and get the corresponding duty ratio by calculation. Control chip adjusts the DC motor speed with the duty ratio to achieve the goal that planter speed change, the feed shaft speed corresponding change, and the seeding quantity and seed spacing are fixed.
The feed shaft speed test
The test is conducted in the case of 1.6 cm seed spacing.By the calculating formula obtained before can get the suitable planter speed have a range for 1.56 km/h–12.38 km/h. According to different planter speed can get the theoretical feed shaft speed and the actual rotation speed. the corresponding data are shown in Table 2.
According to Table 2 making curve fitting, the result is shown in Fig. 8. That the control chip through the PWM to intelligent control feed shaft speed can achieve good results.
Conclusions
This system is able to set the seeding quantity and thousand grain weight of wheat parameters by buttons. The encoder serves to set the planter operating speed. The control chip automatically calculates seed spacing and the corresponding feed shaft speed, to ensure planter speed change, seeding quantity and seed spacing stable. Based on the test discussed above, it is safe to draw conclusions as follows: Seeding quantity and thousand grain weight of wheat parameters can be used to calculate seed spacing because different spacing have their corresponding optimum planter operating speed. There exists minor deviation of the actual rotation speed from the theoretical feed shaft speed due to vibrations, which needs to meet the sowing requirements. The future sowing machine tends to be more intelligence-based. The simulation carries on preliminary inquiry and needs for further optimization design.
Footnotes
Acknowledgments
The authors want to acknowledge the financial support of Shandong province agricultural equipment research and development innovation project (2015YZ103, 1 million yuan); At the same time the authors acknowledge the financial support of Shandong province agricultural major application technology innovation project (200,000 yuan); In addition, Shandong Agricultural University the modern agricultural intelligent equipment research and development project should also be acknowledged for there financial support (60,000 yuan).