Development of the sliding cutter for the shortened stem of tumorous stem mustard

Brassica juncea var. tumida (tumorous stem mustard, TSM) is one of the most important vegetable crops of the Brassica genus of the Cruciferae family. However, the low level of mechanized harvesting cannot fully meet the large-scale production in the TSM industry. There is a high demand to shorten the stem cutting for the better integration of agricultural machinery and agronomy in the process of mechanized harvesting of TSM. In this study, a sliding-cut TSM harvester was proposed to optimize the operating parameters of its sliding cutter. Firstly, the structure and working principle were elaborated for the TSM harvester and root-cutting device, according to the agronomic requirements of the TSM harvesting. The sliding cutting was analyzed to compare the current shortened stem reciprocating and rotary cutting of TSM. The shape and structural parameters were determined to ensure the working strength of the sliding cutter. The installation of the sliding cutter was clarified, according to the force analysis. The contact parameters were calibrated between purple soil and slide cutter in the southwestern region. A soil-sliding cutter interaction model was established using EDEM software. A simulation was then implemented to analyze the impact of different operating speeds and cutter angles on the working resistance of the sliding cutter. The results showed that the angle between the sliding cutter and the working resistance was negatively correlated at the same speed, whereas, the working resistance of the sliding cutter was positively correlated with the working speed at the same sliding cutter angle. The soil tank test was conducted to verify the reliability of the parameter setting in the discrete element model, indicating the better performance of the sliding cutter. The cutting test was also carried out to optimize the test parameters, with the cutting resistance as the evaluation index, and with the operating speed, the angle of the cutter, as well as the cutting distance as the influencing factors. The results showed that the operating speed of the sliding cutter was positively correlated with the cutting resistance, whereas, the cutting distance was negatively correlated with the cutting resistance. The cutting resistance first decreased and then increased, when the tool angle was from 60° to 120°. The influencing factor of cutting resistance was ranked in the order of importance: operating speed, tool angle, and cutting distance. Furthermore, the operating speed of the sliding cutter was 0.1 m/s, the included angle of the cutter was 65°, and the cutting distance was 20 mm after optimized rounding. The values of cutting force in three repeated tests were 141.24, 156.32 and 150.65 N, respectively, where the errors were 9.8%, 21.53%, and 17.12%, respectively, compared with the theoretical of 128.63 N. Those values were 44.30%, 38.35% and 40.59% lower than the average cutting force in the Box-Behnken test. The optimal parameters of sliding knife operation were also verified. The findings can provide a strong reference for the mechanized harvesting of TSM, indicating the important engineering application.