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Successful use of an auto-guided agricultural machine in paddy fields depends on the ability to generate a full-coverage path consisting of inner and outer-work paths adapted to various field shapes in the presence of an enclosing field boundary. To enhance the performance of a coverage path planner (CPP) developed in our previous study, this article describes the development of a complete CPP for a fully autonomous tillage tractor that provides automatic generation of both inner and outer-work paths, and boundary corner turning methods applicable to polygonal-shaped paddy fields with various corner angles. Computer simulation of the developed turning manoeuvres was conducted using a 3D tractor-driving simulator by analysing the trajectories of a virtual tractor on ground under varying corner angle conditions. A field evaluation was performed with a 60-kW auto-guided tillage tractor equipped with the developed CPP in three different shapes of paddy fields. The results of the computer simulation confirmed that the designed boundary corner turning methods could provide an acceptable level of tracking performance with lateral deviations <70 mm when following boundary corner turning paths. In the field tests, the autonomous tillage tractor successfully followed the whole paths with lateral and heading root-mean-squared errors ranging from 32 to 101 mm and 0.6°–2.2°, respectively, and demonstrated superior tillage performance by reducing the skipped areas of 1.7% (triangle), 0.9% (quadrilateral), and 1.0% (pentagon) of the total area as compared with that of 8.5% obtained with the previously developed system. • A complete coverage path planner for a fully autonomous tractor was designed. • The planner automatically provides inner and outer-work paths in polygonal paddy fields. • The outer-work path with a boundary corner can cover the corner effectively. • Application of the path planner to various shapes of paddy fields was satisfactory. [ABSTRACT FROM AUTHOR]

• A novel path planner for the entry and exit operations of a fully autonomous tractor was developed. • An occupancy grid map with virtual obstacles was designed and A* algorithm was applied on it. • Two path smoothing processes were used to reduce redundant turning and control waypoints. • Application of the entry-exit path planner to the paddy field was satisfactory. A field boundary with a single entrance as well as the entry and exit paths of the tractor based on the entrance location are key design requirements that must be considered when planning an effective path for an autonomous tractor operating in a paddy field to avoid collisions with the embankments that hold floodwater. In creating a complete in-field coverage path, an entry-exit path planner that generates paths to/from the start/end points of the auto-traveled path is needed to achieve effective field operations for a fully autonomous tractor. In this study, a novel path planner for the entry and exit operations of an autonomous tractor was developed using the A* algorithm to enable the tractor located at the entrance to automatically go to the start point of an agricultural task and return to the entrance after completing the agricultural task. An occupancy grid map with virtual obstacles was designed and the A* algorithm was applied to it to create a path for the tractor to reach its destination via the entry-exit path accurately in terms of positioning and heading. Two path-smoothing processes, a line-of-sight path smoother (LOPS) and a collinear-node path smoother (CNS), were performed to reduce redundant turning and control waypoints derived by the A* algorithm. The feasibility of using the developed algorithms was investigated via computer simulations followed by field tests with a 60-kW autonomous tractor. The simulation results confirm that the entry and exit paths generated by the proposed planner effectively guided the tractor to reach the given target points in terms of location and direction under the various entry, start, and end conditions by reducing the lateral and heading errors compared with those obtained without using the proposed search space and smoothers. For validation testing in two real paddy fields, the entry-exit paths were successfully generated in response to different entrance locations and the tractor followed the entry path and started the operation at the start point of the work path with a lateral deviation of ≤8.5 cm. In addition, the tractor navigated the exit path automatically and reached the destination with a lateral deviation of <12 cm and a heading error of <22° to the entrance and the operator was then able to drive the tractor to exit the field easily without backward navigation. [ABSTRACT FROM AUTHOR]

Successful adoption of auto-steering agricultural vehicles in Korean paddy fields depends on the ability to accurately follow a full path, including straight and curved paths for agricultural tasks and headland turning in each row, in the presence of sliding caused by wet ground conditions in relatively small fields. To improve the performance of an autonomous tillage tractor originally developed in our previous study, this article describes a simulation study, conducted using a 3D computer simulator, that accounts for the slippery motion of a virtual tractor on ground with varying adherence properties, In addition, this study performed field evaluation of an auto-guided tillage tractor equipped with a slip estimation-based path-tracking algorithm that is robust to slippage in paddy fields. The test platform was built with a 60-kW tractor equipped with an RTK-GPS (real-time kinematic-global positioning system) and IMU (inertial measurement unit) system, a navigation controller that could estimate the sideslips of the tractor in real-time, and a three-point hitch dynamometer that could measure tillage drafts. The results of the computer simulation confirmed that the slip estimation-based path-tracking algorithm was superior in guiding the tractor along curved paths on the ground with relatively low coefficients of cornering stiffness by reducing the lateral deviations as compared with those obtained with the conventional look-ahead distance method. In field tests run in an arable field, the autonomous tillage tractor equipped with the slip observer algorithm demonstrated improved performance as compared to the previously developed system by reducing the RMSE (root mean square error) for lateral deviation on curved paths from 29 cm to 15 cm. Highlights • A computer simulator that can account for slippery motion of vehicle is developed. • The system includes an anti-sliding controller for autonomous path tracking. • Application of the tested tractor to full-path tillage operation is satisfactory. [ABSTRACT FROM AUTHOR]