Abstract: A lightweight paddy field weeder consisting driving-weeding compound components was designed based on the paddy production condition in China. The weeder is powered by a gasoline engine and the weeding rolls are driven to operate by a power transmission assembly composed of reduction gear and switch bevel gear system. A rotary harrow weeding roll with lower soil penetrating impact and better capacity to prevent sinking is designed using finite element method with fluid-structure interaction simulation. Depth of paddy mud (A), thickness of water layer (B) and rotary velocity (C) of the weeding roll are selected as the factors in the full scale field test to explore their effects on the average torsion of the principal axis, on the weeding rate and the injury rate of paddy seedlings. Variance analysis of the resting results show that the sequence of the factors affecting the average torsion and weeding rate are both B>A>C. the effect of the factors on the injury rate is insignificant. Lower average torsion and higher weeding rate can be achieved with larger depth of paddy mud. The average torsion decreases and the weeding rate increases as the water layer thickness increases. As the rotary velocity increases, the average torsion increases first and then decreases and the weeding rate increases. The optimum performance of the weeder can be obtained when the depth of paddy mud is 300 mm, the water layer is 60 mm and the weeding roll velocity is 160 r/min. Under such condition, the average torsion is 20.84 N?m, the weeding rate is 93.2% and the seedling injury rate is 1.2.

Key words: paddy weeder, paddy soil, fluid-structure interaction, rotary harrow weeding roll, full scale test