Rice seedling segmentation is a fundamental process of extracting the guidance line for automated rice transplanters with a visual navigation system, which can provide crop row information to ensure the transplanter plants seedlings along the crop row without damaging seedlings. However, obtaining accurate rice seedling segmentation in paddy fields is still a challenging task. In this paper, a rice seedling segmentation method in paddy fields is proposed. The method mainly consists of two steps: image graying and threshold segmentation. In the procedure of image graying, the RGB (Red Green Blue) seedling image is first converted into the YCrCb color space and a Cg component is constructed. A color-index 2Cg-Cb-Cr is then constructed for image graying based on the excess green index (2G-R-B), which can reduce the influence of illumination variation on the equality of image graying. For the second step, an improved Otsu method is proposed to segment rice seedlings. With respect to the improved Otsu method in this research, the background variance of within class variance is weighted by a probability parameter to ensure that the method works well for both bimodal and near-unimodal histogram images, and the search range of gray levels is constrained to reduce the time to search the segmentation threshold. Experimental results indicate that the proposed method achieves better segmentation results and reduces the computational cost compared with the traditional Otsu method and other improved Otsu methods.

In order to realize automatic steering controls of rice transplanters in paddy fields, an automatic steering control algorithm is essential. In this study, combining the fuzzy control with the proportional-integral-derivative (PID) control and the kinematics model, a compound fuzzy PID controller was proposed to adjust the real time data of the PID parameters for the automatic steering control. The Kubota SPU-68C rice transplanter was then modified with the new controller. Next, an automatic steering control experimental with the modified transplanter was carried out under two conditions of linear tracking and headland turning in verifying the automatic steering effect of the transplanter in different steering angle situations. The results showed that the deviation with the new controller and the modified transplanter was acceptable, with maximum deviation in linear tracking of 7.5 cm, the maximum headland turning a deviation of 11.5 cm, and the average a deviation of less than 5 cm. In conclusion, within the allowable deviation range of the field operation of the rice transplanter, the proposed algorithm successfully realized automatic steering controls of the transplanter under different steering angles.

Multi-grain hole-forming sowing and uniform hole spacing are important agronomic requirements for precise hole-direct seeding of rice.This paper designs a kind of impeller type seed guiding device. The main structural parameters of the impeller seed guide device were analyzed by constructing the kinematics model of the rice seed in the impeller seed guide process. The experiment analysis were carried out with the long-grain rice variety Chuangliangyou 4418 as the seeding object. The optimal structural parameter combination of seeding-guiding device was determined as inner impeller radius 56 mm, blade offset angle 11° and seeding angle 36°. On this basis, the seeding performance test of different seed guiding devices of internal suction seed-metering device was carried out by using rice seeds with different external dimensions. The test results show that the impeller has better cavitation and hole spacing uniformity than the seed guide tube. The average hole diameter is not higher than 21.7 mm, the qualified rate of hole diameter is not lower than 96.1%, and the coefficient of variation of hole spacing is not higher than 10.1%. Compared with the seed guide tube, which is increased by 32%, 16% and 34% respectively, and the average hole distance is about 200 mm in theory.