Robust Leader–Follower Control for Cooperative Harvesting Operation of a Tractor-Trailer and a Combine Harvester Considering Confined Space

The cooperative grain unloading of a tractor-trailer and a combine harvester is a key means to improve the efficiency of crop harvesting operations. In view of the problem, this paper proposes a robust leader-follower control method for a tractor-trailer to track a combine harvester in a confined farmland environment for the cooperative harvesting operation. Firstly, considering the model uncertainties, the kinematic and dynamic models of the autonomous tractor-trailer system are established. Subsequently, based on the relative kinematics and nonlinear transformations, a second-order Euler-Lagrange error dynamic model for cooperative harvesting system of a tractor-trailer and a combine harvester is proposed. The effective combination of sliding mode control (SMC) and radial basis function (RBF) neural network compensates for model uncertainties in the control system, and achieves the robust leader-follower control of a tractor-trailer and a combine harvester. Considering the confined operation environment due to irregular farmland boundaries or obstacles, an obstacle avoidance strategy is proposed based on an improved artificial potential field (APF) method to ensure that the tractor-trailer can also pass smoothly even in confined working space. The results demonstrate that the proposed robust leader-follower control method can successfully achieve the cooperative control of a tractor-trailer and a combine harvester in crop harvesting operations. Moreover, in confined farmland environments, the proposed obstacle avoidance strategy can ensure that the tractor-trailer successfully avoids both dynamic and static obstacles while tracking the combine harvester, and the required obstacle avoidance space is smaller.