Development of a variable-diameter threshing drum for rice combine harvester using MBD - DEM coupling simulation

According to different feeding rates, the threshing gap of rice combine harvester needs to be flexibly adjusted to prevent blockage. The research shows that the threshing performance of adjusting threshing gap by changing the drum diameter is better than that by changing the concave grid position, but there are few researches on the variable-diameter threshing drum. The objective of this paper was to specifically develop a variable-diameter threshing drum and a monitoring method for rice combine harvester to improve the threshing performance. The adjusting part of the variable-diameter threshing drum was consisted of two sets of the side and the middle adjustment mechanism, which were driven by hollow hydraulic cylinder. The three states (becoming larger, smaller and stationary) of drum diameter could be realized by the designed hydraulic actuating system. The mathematical model among the feeding rate, the threshing gap and the piston rod load force of hydraulic cylinder was deduced, and the MBD - DEM coupling simulation was carried out. Finally, a field experiment was carried out. As a result, the angle of guide rail was determined 30 degrees. When the piston rod of hydraulic cylinder moved +/- 8.66 mm, the threshing gap would be adjusted +/- 5 mm. The field experiment showed that the feeding rate and the threshing gap had obvious influence on the piston rod load force, which was basically consistent with the results of the mathematical model and the coupling simulation. Therefore, the method of monitoring the piston rod load force is feasible and provides the basis for the research of an adaptive control system for combine harvester.