Design of monitoring system for wheat precision seeding-fertilizing machine based on variable distance photoelectric sensor

Precision seeding has become the main developing direction of the modern seeding technology, and the quality of seeding machine's operation will directly affect the growth and yield of wheat. Facing complex field moisture, machine vibration, noise and other unfavorable factors as well as the fully closed environment of seeds' tubes and fertilizer's tubes, only using audio-visual method is difficult to know the running status of seeder in real time. When the seeds' tubes and fertilizer's tubes are plugged or the seeds and fertilizer are lacked, it will cause the question of seedling absence in large areas, and result in yield reduction. Therefore, researching and developing the monitoring system of seeding-fertilizing machine has important significance and benefits both in producing and economy. In the early research stage of the laboratory, an electronically controlled wide wheat fertilization precision seeder was designed to achieve wide precision seeding. In order to realize the real-time monitoring of the process of wheat precision seeding-fertilizing machine and ensure the operation quality, a monitoring system with variable distance photoelectric sensor, which can realize the function of wheat precision seeding-fertilizing machine, was designed based on the previous research. The monitoring system takes the STM32 MCU (micro control unit) hardware detection system as the lower computer, and transmits the information by Modbus communication protocol to man-machine interface of MCGS (Monitor and Control Generated System) touch screen displaying real-time operation status. The lower computer uses a reflective photocell as a monitoring sensor, and determines the malfunction type by combining the information of seeds' and fertilizer's flow and shaft rotation measured by master system's rotary encoder and transferred by Modbus communication. The monitoring sensors of wheat and fertilizer were adopt OH-1021 reflective photoelectric sensor which transmitting terminal and receiving terminal distributed on the same side. When there are particles blocking infrared light, the sensors output low level; when there are no particles, the sensors output high level. The sensor output experiences a high-low-high level change process when the infrared light is reflected while the particles flow through the photoelectric sensor. It is easier to determine the operating status of the fertilizing according to the fertilizer shaft speed and the output of fertilizer sensor data collected by MCU, since the fertilizing sensor was installed under the row fertilizer device. But the seed tube with sensor was installed above the seeding device, in which the wheat particles were full and flowing slowly. The initial detection distance of the seed sensor is set as 5 mm, which is the sum of the short diameter (3 mm) of single wheat particle and the tube thickness (2 mm). In normal operation, the wheat particles reflect the infrared light when flowing through the position of seed sensor, and the sensor output experiences a high-low-high level change process. The MCU determines the operating status of the seeding according to the sensor output and seed shaft speed. During the monitoring of seeding, the type of malfunction cannot be distinguished when the infrared light is located on the gap between 2 particles on the wall of the seed tube. The MCU controls the conduction of the triode via changing the IO (Input /Output) port output by activating the variable pitch task function, and thereby controls the detection distance of the sensor. When the output of the MCU is high, the triode is turned on, then voltage of the sensor is increased, resulting in the increase of detection distance, and therefore the type of malfunctions is determined by further understanding on the seed-reserve in the seed tube. The circuit simulation test results of the lower computer's seeds' tube show that the detection distance of the photoelectric sensor of the seeds' tube is changed by 4-7 mm under the amplifier circuit; monitoring system prototype test results show that the accuracy of fault alarm at least reaches 92.5%, and the response time of lacking seeds and fertilization, blockage and leakage is less than or equal to 0.2, 0.3 and 0.3 s, respectively. The monitoring system realizes high-precision real-time monitoring of wheat seeding and it can improve the quality of wheat seeding.