Systematic Model Based Path Tracking Control of Actively Steered Implements in Simulation and Experiment

Precise tractor and implement path tracking control based on Global Navigation Satellite Systems (GNSS) became fundamental for automation of field work. Actively steered implements, e.g. with steered wheels, became the latest development to increase implement path tracking precision. Controlling the resulting tractor implement multiple input multiple output (MIMO) systems is a challenge due to numerous implement and actuator types as well as disturbances and uncertainties resulting from slopes and varying soil. Despite that controller setup for the farmer is required to be intuitive. This work uses a systematic approach supporting various steering actuators by combining linear-quadratic regulator (LQR) control and subsequent output feedback approximation. This approach limits parameter adjustments during setup to a very small set of intuitive parameters. The controller is applied to an unsteered implement as well as an implement with actively steered drawbar and/or actively steered wheels. An experimental tractor implement setup with numerous actuators is newly presented. Using this hardware straight line tracking on level ground was performed in experiments. Simulations using a non-linear kinematic plant model were performed in addition. The plant model was able to resemble experimental results for the given scenarios. The controller was found to provide the centimeter level precision required. On slippery slopes additional measures, e.g. integral control or disturbance feedforward, have to be taken. Varying tractor longitudinal velocity between 1 m/sec and 4.5 m/sec showed little influence on the controller's performance.