Path-tracking simulation and field tests for an auto-guidance tillage tractor for a paddy field

• A computer simulator capable of virtually testing the motion of a tractor is developed.
• Key control parameters of path tracking algorithms are optimized via computer simulation.
• Field validation tests are conducted in a paddy field using a prototype auto guided tractor.

The application of an auto-guided tractor to rice cultivation in Korean paddy fields may be limited by tire slippage and headland turning due to wet soil conditions and the use of small-sized fields < 1 ha. This study examines the development of a computer simulator capable of virtually testing the motion of a tractor based on a look-ahead distance method in a real-time 3D graphic environment. The tractor motion was simulated based on the dynamic model of a vehicle that considered the effects of tire slippage and side force imparted by soil. The validity of the computer simulation was confirmed by a paved road test, thereby providing tracking trajectories similar to those obtained from the road test. However, an oscillation in the steering angle, ranging from −8 to +5 deg., occurred when the tractor traveled on straight paths. This oscillation might be related to the limitations of the electric motor in controlling the tractor’s hydraulic steering system due to the non-linear response of the hydraulic actuator to the rotation of the steering wheel by motor torque. In an arable field (90 m × 25 m), the auto-guided tractor followed the predefined path including C-shape headland turning with acceptable tracking, showing RMS lateral errors ranging from 3.8 to 12.8 cm on the straight paths. However, RMS lateral errors obtained on the curved paths increased to 100 cm when the tractor traveled in a wet sub-field with moisture content > 30%, thereby requiring more accurate estimation of sliding parameters.