Experiment on three-axis working resistances of rotary blade and working parameters optimization

Abstract: Small type rotary tillers are widely used in southern China. During the operation of rotary tiller, rotary blades will be subjected to three-axis working resistances. The forward resistance is the major source of power consumption, and meanwhile, the vertical resistance and lateral resistance will influence moving stationarity of whole machine and wear of blade respectively. So far, current research focuses on the relation model between forward resistance and working parameters, but little research has been done on vertical resistance and lateral resistance. There are many factors that could affect three-axis working resistances, such as the state of soil, geometry of rotary blade, operational parameters and position of blade in soil. In order to explore the relationships between working resistances and these factors, taking C-type rotary blade for the research object, single blade cutting resistance experiments were carried out in the soil bin. The experimental soil came from the orchard in Guangdong Province, and was red, clayey and wet. Considering the accuracy of experimental data and operability of process, bend angle of blade, working width, tilling depth, forward speed and phase angle were identified as the main experimental factors, resistance per unit working width of blade was identified as experimental index, and the orthogonal experiment with 7 factors and 3 levels was designed. Levels of each factor could be changed easily. Bend angle of blade and working width could be set in punch machine. Tilling depth could be controlled through the way of moving up and down the support frame on test vehicle. Forward speed could be quickly regulated by traction motor. Rotary blade would be installed on the cutter head, which had a center hole and curved groove, and phase angle could easily be controlled by adjusting fixed location of blade in the curved groove. The soil in the bin had 3 layers: uppermost layer, middle layer and lowest layer; the moisture content was 14.3%, 20.6%, and 29.8% respectively for the 3 soil layers, and the soil compactness was 105, 310, and 531 kPa respectively. Custom three-dimensional force sensor was adopted to measure resistances, with measure range of 2 kN. USB-4711 portable data acquisition card was used, with sampling rate of 100 Ks/s. The three-axis resistances detection system for cutter of agricultural machinery was designed based on Labview2012. By range analysis, significance test, k value analysis and linear regression modeling, the results showed that the primary and secondary order of the factors that affected forward resistance was tilling depth, working width, phase angle, bend angle and forward speed. Among them, working width and tilling depth had similar effect degree, bend angle and phase angle also had similar effect degree, and working width, and tilling depth had significant effect on the index. The optimal combination was bend angle of 120°, working width of 80 mm, tilling depth of 80 mm, phase angle of 60° and forward speed of 0.3 m/s. The primary and secondary order of the factors that affected vertical resistance was bend angle, tilling depth, phase angle, working width and forward speed. Bend angle, working width, tilling depth, and phase angle had similar effect degree, and also had significant effect on the index. The optimal combination was bend angle of 100°, working width of 80 mm, tilling depth of 80 mm, phase angle of 120°, and forward speed of 0.3 m/s. The primary and secondary order of the factors that affected lateral resistance was phase angle, tilling depth, bend angle, working width and forward speed. Tilling depth, phase angle and bend angle had similar effect degree, but they had no significant effect. The optimal combination was bend angle of 100°, working width of 80 mm, tilling depth of 80 mm, phase angle of 60°, and forward speed of 0.5 m/s. Making discussion about these results, and comprehensively considering the operation efficiency and energy saving, it is finally found that the best operating mode is bend angle of 120°, working width of 80 mm, tilling depth of 80 mm, and forward speed of 0.5 m/s in practice. The results of contrasting test in fields showed that torque and amplitude of walking rotary tiller were decreased by 12% and 21% respectively when working in the best operating mode. Although the mass wear of rotary blade increased, the wear per unit working width of blade was decreased by 16%. This study can provide the reference for saving energy, improving stationarity of rotary tiller and reducing blade wear.