Sliding Mode Controller Design For Inverted Pendulum Balancing Mobile Robot

In recent years,impressive advancements in the field of robotics resulting from the progress in hardware and computing technologies have been harnessed for the development of unconventional transportation systems.One of them is the two-wheeled balancing mobile robot(2WBMR).2WBMR possesses movement and balance capabilities similar to human beings.However,such a control system faces many challenges in positioning and disturbance rejecting,because the plant is not only unstable and nonlinear but also non-minimum phase and underactuated.This thesis attempts to establish the nonlinear model of 2WBMR,and studies the positioning and disturbance rejection problems based on the sliding mode control(SMC)method.The main contents and contributions are summarized as follows.1.First,an attempt is made to build the nonlinear 2WBMR model using Simulink in MATLAB.The model was constructed using various Simulink blocks.The merit of the model is that it is easy to understand and adaptable to systems with wide-ranging parameters.2.Subsequently,a control strategy combining the SMC with an optimal linear quadratic regulator(LQR)is proposed for the system.The SMC is a nonlinear control method,which can guarantee the robustness of the control system.In this thesis,the state feedback is introduced to the SMC,and the LQR method is used to choose parameters according to pole assignment and quadratic minimization.The 2WMBR system is linearized for analyzing the control system properties.The proposed controller will be applied to the nonlinear 2WBMR system.To overcome chattering in the SMC,a new reaching law using the sigmoid-like function is proposed.Then,the resulting controller is applied to the 2WBMR system for output regulation.It is shown that the proposed SMC with LQR performs better than the LQR in positioning.3.After this,an integral sliding mode control(ISMC)is presented as an extension to the conventional SMC for disturbance rejection.In the ISMC,the controller is designed using the linear model of the system and applied to the nonlinear system.The performance of the nonlinear system of the 2WBMR is evaluated by using the step disturbance for ISMC,SMC,and LQR.In simulations,it is observed that the ISMC is superior to both SMC with LQR and LQR in disturbance rejection.4.Furthermore,a linear matrix inequality(LMI)based SMC is developed for the 2WBMR system.It is shown that the LMI-based SMC has superior positioning performance to the ISMC,conventional SMC and LQR.Even though the ISMC is found suitable for step disturbances,it is less suitable for sinusoidal disturbances.The LMI-based SMC showed reasonably good performance for both step and sinusoidal disturbances.In conclusion,this thesis builds the nonlinear model of the 2WBMR using Simulink,and proposes three design methods.The purpose of developing different design methods is to identify the most suitable controller.It is found the LMI-based SMC is the most suitable controller followed by the ISMC and then the SMC with LQR.