Automated rerailing of a road-rail shunting vehicle on road-level tracks using 2D-Lidar

Road-rail vehicles are emerging increasingly in small flat yards for shunting wagons. While numerous research works suggest automation of the shunting operation to improve its efficiency, the rerailing procedure of such vehicle, i.e., switching between road and rail mode, remains manually executed. Hence, we present a simple but novel method for a road-rail vehicle with skid-steer drive to rerail automatically on road-level tracks (e.g., level-crossing). The vehicle uses two 2D-Lidar sensors to scan the floor for (rail) in order to estimate its lateral displacement and angular orientation towards the track centre. A simplified model and a PID-type controller for the yaw rate were deployed while keeping the linear velocity constant for the vehicle to align itself at the centre of and parallel to the track. Upon reaching the goal, the rail wheels are descended and the rerailing is completed. Test runs were conducted from a random initial pose near the track centre while limiting the travel range in x-direction to 2.5 m, yet allowing a change of direction each time the vehicle reaches this limit. In 97% of the test runs, the vehicle rerailed successfully in 47 s on average (12 s of which was needed for lowering the rail wheels) with three changes of direction or less. In the remaining 3% of cases it took more attempts. Automated rerailing could be used not only as assistance function for the shunting personnel, but also as important feature of an autonomous shunting robot that is able to access both road and rail domains.