| Straw is an important biomass resource in the process of agricultural production,and it has various utilization values.As the main equipment of straw collection,baler is widely used.In plain areas such as Huang-Huai-Hai and the middle and lower reaches of the Yangtze River,affected by the fragmentation characteristics of plots,square balers,especially small square balers,occupy a major market share.Moisture content is an important index in straw harvesting,transportation,storage and utilization.The water content of straw during storage affects its quality to a certain extent,and also affects the subsequent comprehensive utilization.However,at present,there is a lack of on-line detection of moisture content in balers in China,and the existing research in the field of grain harvesters has some problems,such as low detection accuracy and insufficient generalization ability of models,which are difficult to apply to complex field working environment.Based on this,this paper summarizes the existing agricultural materials moisture content detection methods on the basis of research results,based on the capacitance method detection principle,research and development of a square baler based on straw bales moisture content on-line detection device.Specific research contents are as follows:(1)Through the analysis of the structure and working principle of the baler,it is determined that the electrode plate of the capacitance sensor adopts the plane structure;The detection principle of planar plate capacitor and the factors affecting the detection accuracy of capacitor are analyzed.The installation scheme of pressure sensor and temperature sensor is defined.On this basis,the design scheme of on-line detection device for moisture content of bales is determined.(2)In order to avoid the influence of edge effect on the detection sensitivity of capacitor plate,three-dimensional electric field simulation analysis of capacitor plate is carried out.Through response surface optimization test,the optimum structural dimensions of capacitor plate are determined as follows: plate length 148.6 mm,plate width 47.7 mm,plate thickness 1mm and plate spacing 5.1 mm.(3)An on-line moisture content detection device based on STM32F103 single chip microcomputer is developed,which integrates capacitance detection module,pressure detection module and temperature detection module to collect all kinds of data synchronously;Based on Matlab,the moisture content monitoring system of upper computer is developed,which realizes the functions of data transmission of lower computer,moisture content calculation and display of upper computer.(4)Taking rice straw as the experimental object,the moisture content detection model based on BP neural network algorithm was established.The model verification results show that the determination coefficient R2 is 0.986,the root mean square error RMSE is 0.008998,and the relative prediction deviation RPD is 5.99.The model has high detection accuracy and stability.(5)According to the requirement of on-line test of moisture content of bales,a square baler test-bed is designed.A 3k W motor and a reducer are selected to provide power for the test-bed,and the maximum thrust of piston push rod is 12250 N.(6)The performance test of the on-line detection device for moisture content of bales in square baler was carried out.The device was used to detect the moisture content of rice straw in the range of 13.1% ～ 28.04% under the pressure of 109 N ～ 671 N and the ambient temperature of15.8 ～ 19.6 ℃ in the baling chamber.The experimental results show that the relative error of water cut prediction is-6.51% ～ 8.66%,the absolute error is-1.63% ～ 1.72%,and the coefficient of fitting curve between the actual water cut and the predicted water cut is 0.949.This shows that the moisture content detection device has good accuracy and stability,and can basically meet the actual production needs. |
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