Sliding Mode Control And Application For Underactuated Robot Systems

Underactuated systems are a class of control systems characterized by the presence of more degrees of freedom than control inputs, and are very common in the field of control research. Due to the particular characteristics of underactuated systems, in control processes, underactuated areas are self-stabilized while actuated systems are controller-stabilized. Ongoing development of such systems has brought about new challenges to control theory, and comprise an important research direction in the field of control theory. Given the diversity of underactuated systems, and aside from the partial feedback linearization method, there is a lack of a uniform solution to the control issue present in underactuated systems. Here we investigate three types of underactuated systems utilizing controllers designed for position and velocity tracking control:a deformable linear object robot operating system, a two-wheeled self-balance vehicle (UW-Car), and an underactuated acrobot arm system.We adopt sliding mode control for stable control of underactuated systems. A sliding mode controller is designed for dynamic model of underactuated system in general form. In order to enhance the robustness of the sliding mode controller, this thesis proposes a type of disturbance observer incorporating a sliding mode control for a class of underactuated systems. By estimating and compensating for the disturbance by using a disturbance observer, the system is approximated as a standard model without perturbation and inference, and a sliding mode controller is thereby designed. This method is particularly suitable for large external disturbance environments or environments whose upper bounds are difficult to estimate.We propose a sliding mode controller to dampen the vibration in the end of deformable linera object in this thesis. We obtain the dynamic model of a deformable linera object formulated by using finite element method. Based on this model, by using local linearization, linear transformation of variables and Schur decomposition of matrices, actuated and underactuated parts of the deformable linera object dynamic model are separated. Based on the decoupled dynamic model, a sliding mode controller is designed to force the underactuated state variables to converge to sliding mode hypersurface and actuated state variables satisfy the siding mode condition, and cause vibration at the end of the deformable linera object to dampen quickly. To solve the input saturation problem, an adaptive sliding mode control law is designed to suppress the damping at the end of deformable linera object. By designing a proper adaptive law, the adaptive sliding mode controller can both eliminate the effect of input saturation no the performance of the system and dampen the vibration at the end of a deformable linera object quickly. MATLAB simulations used to verify the theory analysis. The results show that the sliding mode controller can manage the vibration suppression at the end of a deformable linera object, and the adaptive sliding mode controller can suppress the vibration at the end of deformable linera object with input saturation.The two-wheeled self-balance vehicle (UW-Car) is a characteristic example of underactuated system. Sliding mode controllers are designed for velocity control and optimal braking control of two wheeled vehicle UW-Car. Through mechanical structure analysis, the Lagrangian dynamics method is used to obtain the dynamic model of the UW-Car. Based on this model, the equilibrium point of the UW-Car while undergoing motion is calculated and the UW-Car’s velocity tracking control is realized through terminal sliding mode controller. Taking speed reduction and braking as the UW-Car’s primary research direction, we propose an optimal braking control method to achieve the shortest braking distance. A switching controller with optimal parameters calculated by genetic algorithm is designed. From comparisons between MATLAB simulation results and experiments, we arrive at the conclusion that the dynamic model of UW-Car is accurate and that the sliding mode controller for velocity tracking control and optimal braking control is effective.The thesis presents a type of disturbance observer incorporating a sliding mode control applying to underactuated arm acrobot. Based on the dynamic mode of acrobot with disturbance, the disturbance observer is designed to estimate and compensate for the disturbance, and sliding mode controller is designed for the stable control of acrobot system. In large external disturbance environments, compare to simulation results of traditional sliding mode controller, the sliding mode controller with disturbance observer achieves greater effectiveness. Acrobot is the simplest underactuated system. By applying the controller to acrobot, the method can be gradually extended to more complex underactuated systems.