The Basic Characteristics Of Grain Impact Sensor Utilizing Two Crossed PVDF Films

China is the largest producer and consumer of food in the world.With the rapid development of agricultural mechanization,both productivity and efficiency of cereals have increased significantly.When harvesting using the modern machines,the measurement of grain loss is of great importance for improving operation quality and increasing economic returns.Numbers of scholars are researching on the grain impact sensors with high sensitivity,fast response,high detection frequency and strong anti-interference.In recent years,PVDF(Polyvinylidene Fluoride)piezoelectric film has received much attention for its excellent characteristic.Besides,the structure of array type is adopted for designing grain impact sensors.This kind of grain impact sensors provide larger capacity for counting grains and give more details about grain location.Thus,this paper proposes a novel grain impact sensor with two crossed PVDF films,which can response simultaneously and independently to the collisions.By analyzing the grain collisions,the number and location of grains can be easily obtained.In addition,an effective method is proposed to analyze the response performance considering the interaction of two crossed PVDF films,multiple collision continuously and collision of two grains.The main research contents and results are as follows:(1)A grain impact sensor utilizing two crossed PVDF films was designed,and its working principle was explained.The relationship between the size and the response of the sensor unit was analyzed,using finite element simulation software,based on such relationship,the size and structure of sensor were optimized.Then a prototype grain sensor was manufactured.(2)A test bench with control system,and data acquisition system were developed.Either single or double particles falling freely at different heights and different angles will be acquired through the test bench.Signals of sensor display on the computer.(3)The response theory is analyzed in terms of vibration and energy,and then the response characteristics of the sensor are researched from collision tests.Besides,the factors that affect the sensor response are analyzed.The results show that the sensor has good repeatability of the response,but the response consistency between different locations is poor.The main reason is that the manual pressing and bonding between the sensing units lead to poor consistency of sensor characteristic.Besides,the response of upper layer is generally significant,but some positions in the lower layer have small response,the proportion of insignificant signals is under 13.89%.When the grain collision is captured by one grain sensor,the vibrations may also affect the accuracy of the nearby sensors.The average interference-to-noise ratio of adjacent units in the upper layer is 21.90 dB,and the lower layer is 10.05 dB.The minimum speed of collisions that the sensor can detect is 1528.8 per second.For the collision at different heights,the square sum of the responses at the upper andlower layers is approximately linear,and the difference of the response time is no more than 3.7×10-3 s.(4)The collision recognition and counting method based on the multi-sensor fusion theory is studied,and the data fusion architecture of feature level is developed.It is demonstrated from the experiment that the continuous collision and simultaneous collision of multiple particles can be counted and distinguished successfully.