Study On Detection Method And System Of The Powder Bulk Density Of The Screw Feed

In the chemical industry,food processing,powder metallurgy,agricultural materials and other industrial and agricultural production,the screw feeder is widely used in powder quantitative dosing or packaging.During the feeding process,the bulk density of the powder in the spiral conveying pipe varies with the working conditions.To obtain the bulk density of the powder in the spiral conveying pipe has a very important value and significance on improving the accuracy of quantitative feeding and dosing efficiency.According to the actual structure of the screw feeding device,this paper proposes a method to detect the bulk density of the powder in the spiral conveying pipe based on the capacitance method.The detecting method and system of the bulk density of screw feed are studied.The main contents and results are as follows:Firstly,the structure model of the powder bulk density capacitive sensor is designed.The mechanism of powder bulk density detection is analyzed.The mathematical relationship between the bulk density and the output capacitance of the sensor is deduced.The influencing factors of the powder bulk density are analyzed.Secondly,the simulation model of sensor is established by using finite element method,and the performance of sensor output is analyzed based on COMSOL Multiphysics simulation software.The influence of the presence or absence of the shield,the presence or absence of the radial electrode,the angle of the electrode plate,the radius of the shield,the embedding depth of the radial electrode,the thickness of the electrode plate and the position of the screw shaft on the output performance of the sensor are discussed.The sensor structure parameters are optimized based on performance simulation,which provides a theoretical basis for sensor development.Then,the weak capacitance detection circuit of the powder bulk density capacitance sensor based on the MS3110 chip is designed.The powder bulk density detection system based on MSP430F149 microcontroller is built.The detection system software is designed.The entire system of hardware and software are debugged.The absolute error of weak capacitance detection is ±0.0018pF,and the relative error is ±0.36%.Finally,the calibration device of the powder bulk density capacitance sensor is designed.Powder bulk density sensor calibration test,output performance test and system performance test is carried out by using the wheat flour as the screw feeding powder.The bulk density of the capacitance sensor is calculated by the calibration test of the powder bulk density sensor.The linearity between the output capacitance and the input bulk density of the powder bulk density sensor is±2.388%,and the detection sensitivity is about 3.131.The absolute error of the sensor is±0.0173pF and the relative error is±0.66%by the output performance test of the powder bulk density sensor.The absolute error between the detection value and the actual value of the detection system is +0.0188 g/cm3 and the relative error is ±3.11%by the performance test of the powder bulk density detection system.