Investigation of propelling mechanism of a levelling machine for a seedling bed based on vibration modes

This paper deals with a levelling machine for a seedling bed of a rice plant, which is a labor saving device in agricultural work. In order to make the seedling bed flat, the levelling machine vibrates by rotary motion of an eccentric rotor and presses the ground by the base plate of the machine. It is found that at a specific rotating speed, the machine can propel by itself, although the operators usually pull the machine using leads to move. The purpose of this study is to investigate the operational propelling mechanism of the levelling machine experimentally. The experimental result shows that propelling speed increases significantly under the condition that the rotational frequency of the eccentric weight is slightly higher than the natural frequency of an in-phase torsional mode of the plate. In this condition, a phase difference between the rear and front edges of the plate occurs, synthesizing the rigid mode and the torsional mode with a certain phase difference. In addition, the rear edge of the plate moves over an oval orbit which major axis is inclined to the propelling direction, and strongly kicks the ground surface after the front edge lifts up, then the plate is pushed to the slant upper part. Because the front edge is stuck on the surface at which phase the front edge lands and the rear edge hangs in the air, the plate turns around the front edge. As a result, the rear edge lands forward from the prior position. Because this motion of the plate occurs in turns, the machine can propel by itself effectively.