Spline-based Trajectory Generation for Autonomous Truck-Trailer Vehicles in Low Speed Highway Scenarios

Abstract

Trajectory generators are designed to create reference paths that are parametrized by time as well as by velocity or acceleration. In the literature, it has been noted that often path planners are the last step in the planning module of autonomous truck-trailer vehicles, which results in a collision-free track. A trajectory generator can improve this path by making it smoother, which improves passenger comfort and decreases stress on the engine. The available trajectory generators are in their majority based on large number of optimizations, which limits their real-time applicability. This research aims to create a computationally efficient parametric method for trajectory generation that leads to a continuous motion of the vehicle. Using cubic splines, a unique method of parametrization is applied such that a custom velocity profile is defined along the trajectory. Together with choosing appropriate boundary conditions for each path segment, a trajectory is generated that proves continuous reference tangent angle and yaw rate, while following a velocity profile that is continuous in acceleration. This leads to a continuous longitudinal and lateral motion of the truck-trailer vehicle. While continuity conditions are achieved, simulations results showed high reference yaw rate peaks, which could be difficult to track under non-ideal circumstances. An alternative generator was designed based on quintic splines, such that yaw rate peaks can be limited. However, this minimization leads to oscillations of the reference trajectory. A trade-off needs to be defined to balance between minimizing peak yaw rates and oscillations. Closed-loop simulations using a kinematic truck-trailer model show that tracking the generated trajectory lead to continuous steering wheel and velocity input signals. Furthermore, the trajectory was smoothly tracked without the use of an optimal controller. Eventually all research goals have been achieved. Further studies could analyse the performance of the proposed trajectory generator using a dynamic truck-trailer model such that effects of wheel slip and load transfer can be investigated. It is also of interest to analyse the trailer behaviour when tracking the trajectory.