Self-tuning regulator for a tractor with varying speed and hitch forces

Due to the changes in the soil, speed and hitch forces, the dynamics of a farm tractor are constantly changing making the design of an autonomous lane-tracking controller a very complex task. To be able to react to those changes, this paper presents a new adaptive system based on a self-tuning regulator made up of a recursive least-squares parameter identification algorithm for the plant combined with a minimum-degree pole placement (MDPP) method for changing the parameters of a digital RST controller in real time. The MDPP is computed by solving the Diophantine equation for the desired closed-loop reference model. The results presented show how the system is able to adapt the control parameters for different speeds and changes in the hitch cornering stiffness. As future work, this method could also be applied and assessed as a general controller, covering different sizes and different types of steering systems for off-road vehicles.