Seeding monitor system for planter based on polyvinylidence fluoride piezoelectric film

Abstract: During the process of seeding, once the fault cannot be identified, there will be a large area of missed planting and loss of agricultural production. It is very important to improve the reliability of the seed monitoring system. In this paper, a seed monitoring system was developed based on a PVDF piezoelectric film sensor. The system is simple, with strong applicability. The sensor with the cantilever structure has little effect on the seed coefficient of variation. The system can work in harsh environments. According to the sensor output signal and the forward speed of the machine, the amount of seeding, the speed of seeding, seeding acreage, leakage rate, and other performance indicators can be gained. An alarm will be given once there is the phenomenon of a missing seed or blocking. According to the alarm signal, the tractor driver stops to check the planter.A PVDF piezoelectric film sensor is installed in the seeding tube under the seed-metering device. During the process of seeding, seeds sideswipe the PVDF piezoelectric film one by one. The stricks of seeds make deformations of the piezoelectric film. At the same time, the piezoelectric polarization is generated inside the film. Positive and negative charges are gathered on the upper and lower surfaces of the piezoelectric film respectively. The charges generate a voltage signal. When the seed-metering device fails, the piezoelectric sensor will not be subject to stricks of seeds, and the voltage signal disappears. Therefore, the voltage signals generated by the piezoelectric sensor can be used to determine whether there is a missed planting phenomenon. In order to avoid rebounds of the seed on the sensor, the sensor is installed in a 30? angle with the vertical direction. The piezoelectric film sensor is soft, thin, and highly sensitive. The sensor is near to the seed-metering device, the collision of seed and the sensor is rapid, so the phenomenon of blocking is prevented at the installation position for the sensor.The system hardware is composed of a monitor and an alarm circuit. The central processors of the monitor and alarm are two single-chip microcomputers, and the type is STC89C52. The signals of the PVDF sensor and the hall sensor are collected by the monitor circuit. The alarm circuit is mainly used for processing the human-computer interaction. Two single-chip microcomputers communicate by a wireless data transmission module NRF24L012. The information of seeding performance gathered by the monitor is transmitted to the alarm through the wireless transmission. The alarm circuit displays the alarm signals.The system was applied for both a bench test and a field test. When the amounts of seeding are 5, 8.75 and 10 seeds per second, the system accuracy for amount of seeding is 95.3%, 96%, and 92.5% respectively, the system accuracy for missed planting is 90.4%, 91%, and 90.2% respectively. A large amount of seeds does not affect the system's accuracy. When the planter forward speed is 3, 4 and 5 km/h, the system accuracy for the amount of seeding is 95.2%, 93.8%, and 90.4% respectively, the system accuracy for missed planting is 93.3%, 93.1%, and 89.7% respectively. The system has a strong ability of anti-interference. Equipment vibrations do not affect the accuracy of the system. This system can effectively monitor seeding performance, and help to improve sowing quality.