Path tracking of mobile robots for greenhouse spraying controlled by sliding mode variable structure

Abstract: In order to solve the bad effects of the complex unstructured environment of intensive planting, ground obstacles and spatial disorders on the trajectory tracking control precision of the spraying mobile robot working in greenhouse environment, a sliding mode control scheme was proposed to guarantee system robustness to uncertain parameters and external disturbances. Meanwhile, a novel weighed integral gain reaching law was introduced to solve the inherent chattering problem of sliding mode control, which can be freely controlled with the introduced law. Moreover, the asymptotical stability of the closed loop system was proved by Lyapunov function. The simulation and experimental results showed that adopting the proposed control method, the angular velocity of driving motor for mobile robot can reach the desired value in 0.015 s and the output signal of controller was smooth with the maximal amplitude of 0.02 V. Since the weighed integral gain reaching law included the absolute value of integral for switching function, when switching function approached zero, the gain of switching term converged to zero, while when the state of the system was not on the sliding mode surface, the integral weighted coefficient was negative which can effectively avoid switching gain increasing, smooth control was achieved. The straight-line walking test showed that the mobile robot can successfully eliminate lateral deviation, and can make the actual trajectory near to the desired route in the shortest time. So, it can avoid serious overlap and missing spraying phenomena in the work area. The research results provide a reference for precision spraying the greenhouse crops.