Robotic systems are widely used in industry,agriculture,military and other fields due to the advantages of fastness,accuracy and efficiency.Robotic system is a nonlinear system with strong coupling,uncertainties and subject to various disturbances in practice,e.g.,unmodeled dynamics,linkage mass,measurement noises,joint friction,load change,and external environmental disturbances.Disturbances in a robotic system can degrade the position tracking performance and even undermine its stability.Therefore,it is necessary to design effective control methods to compensate the disturbances.Disturbance observer is a valid way to compensate disturbances in a robotic system.In this thesis,the control methods based on disturbance observer are studied for the robotic system subject to the exogenous disturbance,matched disturbance and mismatched disturbance,so as both disturbance attenuation and position tracking performance are achieved simultaneously for robotic system.The main contributions of this thesis are summarized as follows:1)For nonlinear robotic system subject to the exogenous disturbance,exogenous disturbance attenuation and position tracking problems are studied.A composite control approach is proposed which consists of backstepping controller and nonlinear disturbance observer.Firstly,a backstepping controller is designed to achieve position tracking performance under the assumption that there is no disturbance.Secondly,a nonlinear disturbance observer is constructed to estimate the exogenous disturbance.Finally,the composite controller is derived integrating with the nonlinear disturbance observer and the backstepping controller previously designed,so that both disturbance attenuation and position tracking performance are achieved simultaneously for a multi-input-multi-output nonlinear robotic system.Stability and position tracking performance of the overall system are studied via a Lyapunov function analysis.The effectiveness of the proposed approach is verified by the experiments on the Phantom Omni robots.The experimental results show that with the proposed approach the exogenous disturbance in robotic system can be much effectively depressed while better achieving position tracking than the backstepping controller without disturbance observer.2)For nonlinear robotic system subject to the exogenous disturbance with unknown parameters,disturbance estimation and position tracking problems are studied.The external disturbance is generated by an exogenous system with unknown parameters.A composite control approach is proposed which consists of backstepping controller,nonlinear two-step disturbance observer and disturbance estimator.Firstly,a backstepping controller is designed to achieve position tracking performance under the assumption that there is no exogenous disturbance.Secondly,a nonlinear two-step disturbance observer and a disturbance estimator are constructed to estimate the exogenous disturbance.Finally,the composite controller is derived integrating with the nonlinear two-step disturbance observer,disturbance estimator and the backstepping controller previously designed,so that both disturbance attenuation and position tracking performance are achieved simultaneously for robotic system.Stability and position tracking performance of the overall system are studied via a Lyapunov function analysis.The simulation results show that with the proposed approach the exogenous disturbance with unknown parameters in robotic system can be much effectively depressed while better achieving position tracking than the backstepping controller without disturbance observer.3)For nonlinear coupled robotic system subject to matched and mismatched disturbances,an adaptive disturbance observer-based exponential sliding mode controller is designed to achieve disturbance attenuation and position tracking.Firstly,matched disturbance,mismatched disturbance,and its derivative are defined as the lumped disturbance in robotic system.Secondly,a nonlinear disturbance observer is constructed to estimate the lumped disturbance,and an adaptive law is proposed to estimate the bound of the lumped disturbance.Finally,an exponential sliding mode controller is derived by combining the nonlinear disturbance observer and exponential convergence law,so that both disturbance attenuation and position tracking performance are achieved simultaneously for robotic system.Stability and tracking performance of the robotic system is analyzed via Lyapunov function approach.The simulation results show that with the proposed approach both matched and mismatched disturbances in robotic system can be much effectively depressed while better achieving position tracking than the traditional sliding mode controller. |