Abstract:Considering the problem that the indoor measurement of soil physical or mechanical properties is time-consuming in laborious, and the function of instruments in the field measurement is single, a measuring device for farmland soil physical and mechanical characteristics was designed. The device can measure soil moisture content, firmness, cohesion and internal friction angle, and the measurement results can be displayed and stored in the mobile APP. It realized walking control based on self-propelled mobile platform. An STM32 single chip microcomputer was used as the core controller, an FDR sensor was used to obtain the soil moisture content, and the soil firmness and shear strength parameters, including cohesion and internal friction angle were measured through the cone penetration component. In addition, the measurement principles of the cone penetration component and the soil moisture content detection component of the device were analyzed, the hardware circuit and software of the device measurement control system were designed, and the input and output responses of cylindrical pressure sensor, thin film pressure sensor and soil moisture sensor were determined by sensor calibration test, respectively. Totally 71 soil samples were selected, and the mathematical measuring models of soil cohesion and internal friction angle were established by the least square method based on the sample moisture content and sample friction coefficient data obtained based on the conical force balance relationship. The model fitting coefficient R2 was 0.932 and 0.956, respectively. Field measurement experiments were carried out to measure soil moisture content, firmness, cohesion and internal friction angle. The results showed that compared with AYD-2 type soil firmness meter, oven drying method and ZJ-D type direct shear instrument, the average relative errors of soil firmness, soil moisture content, cohesion and internal friction angle measured by the measuring device of farmland soil physical and mechanical properties were 3.34%, 5.06%, 10.40% and 8.20%, respectively. The research result can provide a reference for the development of a fast and integrated measurement device for multiple physical and mechanical properties of farmland soil.
