Nonlinear control design for row guidance system of an automated asparagus harvesting robot

In this paper, a row guidance system based on nonlinear control strategy is proposed for an automated asparagus harvesting robot. The control system is developed using a two-layer structure to reject both internal and external disturbances. At the low level, two independent speed control loops are designed for the two drive motors to stabilize the motor speeds by rejecting the internal disturbance; at the high level, a nonlinear controller is suggested using integrator backstepping method to produce reference speeds for the motors. The nonlinear control law is determined based on a control Lyapunov function, and can guarantee the global asymptotic stability of the controlled system. An accurate kinematic simulation model of the prototype is built to evaluate performance of the proposed control regime. The tracking error consisting of the lateral offset and orientation error is computed from the modeled pseudo-measurements of the front and rear side distances. The tracking performance was verified by simulation studies with different initial poses considering measuring noise and variation of the tracking trajectory.