Analysis and experiment of tillage depth and width stability for plowing and rotary tillage combined machine

Abstract: The plowing and rotary tillage combined machine developed in this study is a duplex-operation scarification machine designed with the combination of plough mechanism and rotary tillage mechanism in the front. Such a design allows the cultivator to accomplish multiple tasks simultaneously, such as plow tillage, rotary tillage, straw chopping for mulching, soil pulverization, soil covering, and surface leveling. To investigate the stability of the plowing and rotary tillage combined machine, the factors such as cultivator tillage stability were examined from 3 different aspects: traction, force analysis in the horizontal plane, and vibration analysis. The center of mass of the machine could be determined on the longitudinal vertical plane of the machine, where the traction line passing through the instantaneous center of rotation intersected with the vertical line passing through the center of mass. The traction angle (15°-30°), i.e., the angle between traction line and horizontal line , was a crucial factor affecting tillage stability. The forces acting on the machine on the horizontal plane during operation were analyzed to obtain the plow tilt angle (23°-30°) from the equilibrium equations of the plough, rotary blade, and traction forces on the horizontal plane; the plow tilt angle affected tillage stability by directly impacting the force balance on the horizontal plane. From an analysis of the vibrational excitation during machine operation, it was determined that alternating load in rotary blade operations was the main source of machine vibration excitation. The lift angle of the rotary blade (54°-85°) affected the alternating load, therefore influencing tillage stability. The traction angle, plow tilt angle, and lift angle of the rotary blade were used as the experimental variables, and the stability coefficient under tillage depth-based working conditions and the stability coefficient under tillage width-based working conditions were used as the experimental indicators in a 3-factor/2-level quadratic orthogonal rotating combinatorial test to determine the optimal parameter combination of the influencing factors. Subsequently, the regression equations with the stability coefficient as the objective functions as well as the response surface for the stability coefficient could be obtained by analyzing the test results using the Design-Expert software. The variance analysis showed that among the 3 variables in the test, the plow tilt angle had the greatest influence on the tillage depth and tillage width stability coefficients, while the lift angle of the rotary blade had the least influence on the coefficients. The response surface analysis showed that with a fixed lift angle of the rotary blade of 69.5°, an optimal tillage depth stability coefficient of 91.7% could be obtained with traction angle and plow tilt angle of 23.7° and 26.8°, respectively. An optimal tillage width stability coefficient of 93.2% could be achieved with traction angle and plow tilt angle of 25.2° and 27.3°, respectively. The optimal parameter combination was traction angle of 17.3°, plow tilt angle of 27.8°, and rotary blade's lift angle of 72.6°. This optimal combination could achieve the working condition tillage depth stability coefficient of 91.8% and the tillage width stability coefficient of 93.4%, respectively. The validation experiments showed that with the optimal parameter combination of the influencing factors, the working condition tillage depth stability coefficient and the tillage width stability coefficient were 91.5% and 93.1%, respectively; these results were consistent with the ones obtained via software analysis. Other tillage performance indicators of the machine, such as tillage depth, tillage width, surface leveling degree, pulverization rate, and straw coverage rate which were respectively 1.87, 1.98, 21.20, 90.30% and 90.70%, all met the agronomic requirements.