基于触感引导的小型水田行进底盘自动对行方法

为了解决小型水田底盘因路径偏差导致的稻苗碾压损伤问题，该研究提出一种基于触感引导的自动对行方法。采用自制的感测器获取稻株定位历程触感数据，通过数据的分割阈值设定、区域谷值提取、横向距离标定获得感测器与稻株的横向距离。根据水稻机械化移栽行距规整性，利用行距与定位数据几何关系校验稻株定位数据，解算获得稻列方向相邻稻株中点位置，实现对行目标点坐标提取。基于时变坐标系跟踪方法，控制转向电机实时校正路径偏差，实现小型水田底盘自动对行。田间性能试验表明：当行进速度为0.5m/s时，自动对行绝对误差平均值为3.11cm、绝对误差标准差为1.10 cm、绝对误差最大值为4.75 cm，研究成果为水田环境作业底盘自动导航提供了新思路和借鉴。

Design and experiment of the tactile guidance system for the automatic alignment of small paddy moving chassis

Chassis alignment can mainly include the satellite navigation, visual guidance, and manual remote control in the small paddy. However, some problems have led to the damage to rice seedlings in the alignment process, such as the low navigation accuracy, large background interference, and multiple line of sight obstacles. In this study, a tactile-guided system was proposed for the automatic alignment of small paddy chassis. Firstly, a self-developed tactile sensor was used to acquire the tactile data, in which a flexible bending sensor was used as the core element for the tactile data acquisition. The bending sensor was placed between several carbon fiber sheets, in order to improve the own bending stiffness and also to suppress the own oscillation. Secondly, the data was processed to obtain the localization coordinates of the rice plant. The positive relationship between the degree of bending of the sensor and the output voltage was utilized to obtain the information on the position of the rice plant. Three steps were included the data segmentation threshold setting, region valley extraction, and lateral distance calibration. The valid unit of tactile sensing was extracted to set a segmentation threshold. The useless data was filtered out in the non-contact area, and the interference data from the own slight vibration. The data in the sensing unit was further processed to extract the voltage valley value in the sensing area, in order to achieve the initial extraction of the location point of the rice plant. The localization point data was converted into the lateral distance between the rice plant and the sensor by the sensor mapping. Thirdly, the positioning points of rice plants were calibrated, according to the regularity that the sum of the lateral distance measured by the left sensor and the lateral distance measured by the right sensor was equal to the rice row distance. As such, the pseudo-localization points of rice plants were eliminated to improve the reliability of rice plant positioning. Finally, a tracking mode with time-varying coordinate system was proposed to establish the dynamic coordinate system. A calculation was realized on the lateral distance between the center point of the rice line and the center of gravity of the body (target point transverse coordinate). The vertical coordinate was the longitudinal distance between the sensor and the center of the rear wheel axle of the paddy chassis. The coordinates of the aligned target point were real-time transmitted to the electronic control unit during the whole alignment process. The steering servo motor was controlled to correct the path deviation in real time, according to the correspondence between the steering mechanism and the steering angle of the paddy field chassis, in order to realize the automatic alignment of the small paddy field chassis. The field performance test showed that the automatic alignment was better than the manual remote alignment, when the driving speed was 0.5 m/s. The average absolute error of the automatic alignment was 3.11 cm, the standard deviation of the absolute error was 1.10 cm, and the maximum absolute error was 4.75 cm, when the driving speed was 0.5 m/s. The performance of automatic alignment decreased slightly with the increase of driving speed. Anyway, the performance can fully meet the requirements of chassis alignment in paddy fields. The finding can provide a new idea and reference for the automatic chassis navigation in paddy field environment.