油菜精量排种器种子流传感装置设计与试验

Design and experiment on seed flow sensing device for rapeseed precision metering device

针对油菜精量播种过程中缺乏小粒径种子流传感而导致播量监测困难的问题,设计了一种油菜精量排种器种子流传感装置。运用高速摄影技术及碰撞动力学模型,记录并分析油菜种子与聚偏氟乙烯压电薄膜的碰撞轨迹,为传感装置的导管、压电薄膜倾角、出种口位置等关键结构参数提供依据。基于油菜种子与压电薄膜的碰撞信号特征分析,设计了沉槽基板-压电薄膜感应结构,将碰撞信号的衰减时间从9缩短至1 ms,提高了对高频种子流检测的时间分辨率,同时能够有效抵抗机械振动带来的干扰影响。对微弱碰撞信号进行放大、半波整流、电压比较、单稳态触发转化为单脉冲信号,通过单片机定时计数采集处理,实现油菜种子流排种频率与排种总量的实时检测,并利用无线收发模块定时发送给监测显示终端,实现播量数据的实时显示与保存。油菜精量排种器台架及数粒仪高频排种试验表明:在排种频率8.1~32.9 Hz范围内,检测准确率不低于99.5%。田间播种试验表明传感装置能够实时检测精量排种器的排种频率与排种总量,在无排种时计数为零,正常播种状态时检测准确率不低于99.1%,机械振动及粉尘对传感装置没有影响。该传感装置为油菜精量播种过程播量监测、漏播检测以及补种提供有效支撑。

Precision seeding plays an important role in intelligent agricultural machinery development due to its advantages of saving seeds, reducing labor intensity, improving operation efficiency and increasing farmers＇ income. In the planting process, seed metering device is in a closed status and sowing quantity affects crop yield directly, and thus sowing quantity monitoring become one of the development trends in intelligent precision seeding. In recent years, various methods for precision seeding such as photoelectric sensor detection, high-speed photography, and capacitance sensing have been proposed to improve seeding performance for the corn, rice, soybean and other large seeds. Few studies have focused on the sensing method of small seeds such as rapeseed because of its small size, light weight and high frequency seeding. Thus, the development and application of monitoring technology about precision sowing for small seeds are limited. In this study, a seed flow sensing device for rapeseed precision metering device was designed and tested. Specifically, collision trajectory between rapeseed and PVDF （polyvinylidene fluoride） piezoelectric film was recorded and analyzed using high-speed photography and collision dynamics. These data provided a quantitative reference for the design of key structures in terms of the height of catheter, sloping angle of piezoelectric film, position of seed-output, etc. The sensing structure of sinking groove substrate and piezoelectric film was designed based on the analysis of characteristics of impact signal between rapeseed and piezoelectric film. The structure could limit the free oscillation amplitude of the piezoelectric film that could weaken the peak voltage of the free oscillation effectively. The decay time of impact signal was reduced from 9 to 1 ms, which improved the time resolution for high frequency seed flow detection and effectively eliminated the interference caused by mechanical vibration. The signal conditioning circuit turned weak signal into single pulse signal by signal amplification, half wave rectification, voltage comparison, and mono-stable triggering. Then, the real-time detection of seeding frequency and seeding quantity of rapeseed flow was obtained through the timing and counting function of the MCU （STC12C2052AD）. Finally, these data were transmitted at a fixed time interval （1 s） by 2.4 GHz wireless transmission module to the monitoring display terminal, and the real-time display and storage of detection data （including the seeding frequency and the total seeding amount） were realized. Bench experiment consisted of two tests. One was carried out on the pneumatic precision metering device for rapeseed bench test. During the test, a seeding plate （40 holes） was set at a suitable speed such as 12, 18, and 24 r/min （seeding frequency was 8, 12, and 16 Hz）, and the sensing device was installed under the metering device. After a period of seeding time, the detection seeding quantity, seeding time and actual seeding quantity were recorded by observing monitoring display terminal and by manual counting the seeds in the seeds collecting bag. Another test about high-rate seeding was carried out using microcomputer automatic counting instrument. During the test, seeding frequency was set as about 20, 24, 28, and 32 Hz, respectively by adjusting the vibration level, and then the detection of seeding quantity, the seeding time and the actual seeding quantity were obtained using a similar method of the first test. Tests of rapeseed precision metering device bench and high-rate seeding with counting instrument showed that the detection accuracy was not less than 99.5% by comparing detection seeding quantity and actual seeding quantity in the seeding frequency ranging from 8.1 to 32.9 Hz. In addition, the field experiment was carried out on precision joint planter of 2BYM8 for rapeseed driven by a LOVOL M704-BA tractor. The results indicated that the sensing device based on the composite sensing structure of sinking groove substrate and piezoelectric film sensing composite structure can detect the seed flow seeding frequency and seeding quantity, with the counting number being zero without seeding and the detection accuracy being not less than 99.1% under normal seeding. Besides, the mechanical vibration and dust had no effect on the sensing device. The piezoelectric rapeseed flow sensing device presented may facilitate metering quantity monitoring, loss sowing detection and reseeding.