Objective  In order to solve the problem of low automation and high difficulty of mechanical intra-row weeding in paddy field, a pneumatic paddy intra-row weeding device was developed based on the recognition and positioning technology of machine vision.

Method  The mechanism of pneumatic intra-row weeding device was designed by applying the principle of mechanical design, discrete element dynamics (DEM) simulation method and field test. Firstly, the structure of pneumatic intra-row weeding device was designed, and the geometric parameters of the mechanism were calculated using the kinematic equations. The feasibility of the mechanism was determined from kinematic simulation by the motion analysis module of Pro/E. Then, the interaction between weeding blade and paddy soil was simulated and the simulation results were confirmed through test. Finally, the field test was carried out to evaluate the working performance of the whole machine, and the working parameters affecting weeding rate and seeding injury rate were analyzed using a three-factor and five-level quadratic rotation orthogonal test.

Result  The connecting rod length of the pneumatic intra-row weeding device was 35.00 mm and the oscillating rod length was 72.24 mm. The horizontal distance from the weeding part to the rotary center was 84 mm and the vertical distance was 191 mm. The DEM simulation results showed the better structure was the blending blade claw in 10°, which contact resistance was relatively low with an average value of 3.12 N when contacting with soil and the soil was disturbed to a great extent at this angle with affected area of 149.69 cm². The field test results showed the device achieved the optimum working performance with the average weeding rate of 83.91% and seedling injury rate of 3.63% when the machine forward speed was 0.25 m/s, the cylinder protruding speed was 0.45 m/s and the weeding depth was 2.5 cm.

Conclusion  The pneumatic paddy intra-row weeding device satisfies the requirements of above 80% weeding rate and below 4% seedling injury rate. It could meet the requirements of intra-row weeding and seedling avoiding in paddy field.