Design and test of 3GY-1920 wide-swath type weeding-cultivating machine for paddy

Abstract: In order to improve the mechanical weeding efficiency and reduce the injury rate of seedling caused by frequent swerve at the end of the field, a wide-swath machine, named 3GY-1920 type wide-swath weeder, was designed for intertillage and weeding in paddy field. This weeding machine driven by the paddy tractor mounted relevant components including the wide-swath adjustable frame, the hydraulic control system, the weeding unit and profiling mechanisms. To match triple working widths of ride style high-speed rice transplanter, this weeder was equipped with 19 weeding rolls. The working width was designed to be 5.4 m according to line spacing of rice seeding, which was normally 0.3 m. As the transplanter could not follow one path line in 3 different processes, the whole frame was divided into 3 parts including the left-side frame, the right-side frame and the bearing frame. A hydraulic system, including oil pump, different types of electromagnetic valves, hand valve, 4 hydraulic cylinders, relief valve, throttle valves and so on, were equipped to control the 4 single-rod double-acting hydraulic cylinders, which could adjust the frames to fold or unfold for transportation or weeding, and the real-time motion of rolls on the side frames. The weeding roll was designed as the spiral cutter weeding roll referring to the existing rollers and the bearing capacity and shearing strength of paddy. And the different parameters for weeding rolls such as the working resistance and the capacity to damage soil were tested with the explicit finite element software ANSYS/LSDYNA. The weeding roll was composed of 6 cutters; every cutter was sharpened and rotated around the axis by 720° and welded into the reel. A spring type profiling mechanism was also designed and applied to ensure the stable working depth. The installation height and working depth of weeding machine were adjusted before weeding so as to avoid injuring the plants due to the difference of the size of the rice seedlings. When the weeding machine moved forward at a certain speed, the weeding rolls were rotated by the force of soil resistance, elastic force of spring, and forward stress of traction. And the spiral cutters on the roll moved downward into and out of the soil for shearing weeds and stirring soils to cover weeds at the same time. An all-factor experiment on the weeding rate and injury rate of seedlings was conducted to test the performance of this weeding machine. Depth of the weeding and travel speed were selected as 2 factors in this experiment. Results showed that the operating efficiency of this weeding machine was 0.6-1.8 hm2/h, the average weeding rate was 82%, and the average seedling injury rate was 4.8%. With the increment of travel velocity, the weeding rate rose and then fell, and the injury rate kept rising. With the increase of working depth, the weeding rate continued to rise, and the seedling injury rate went up at first and then declined. The weeder showed the optimal operation effect when the weeder's speed was 0.6 m/s, and the roll's working depth was maintained at 6 cm. Under the parameter combination, the average weeding rate was 87.2% and no seedlings were damaged. A yield test was also performed to compare the differences between 2 weeding methods (mechanical weeding and chemical weeding). Results were as follows: The average yield of rice under mechanical weeding was 686.56 g/m2 while that under chemical weeding was 659.83 g/m2. The average number of useful spikes per hole in the testing zone was 13.25 under the condition of mechanical weeding and 9.36 using chemical method of weed control. The average number of holes per square meter was 19.71 and 21.68 based on mechanical and chemical weeding respectively. The result suggests that the mechanical weeding may hurt the seedlings compared to chemical weeding method, however, its weeding and inter-cultivation function can promote the tilling of plants and improve the yield of rice.