Font Size: a A A

Disturbance Observer Based Robust Sliding Mode Control For A Two Degree-of-Freedom Serial Flexible Link Robot

Posted on:2018-04-09Degree:MasterType:Thesis
Country:ChinaCandidate:L Y HanFull Text:PDF
GTID:2348330536987549Subject:Detection Technology and Automation
Abstract/Summary:PDF Full Text Request
With the improvement of robotics,robots with lightweight,high speed,low energy consumption,high load capacity and high precision have become the demand of social development.Hence,flexible link(a typical rigid-flexible coupled multi-body system)has emerged.A robot system with flexible link has some typical characteristics such as multi-input and multi-output(MIMO),nonlinearity,strong coupling and natural instability.Flexible link is a complicated control objective with flexible structure and the complex characteristics of movement.As a low cost experimental platform of modularized structure,flexible link with two degrees of freedom can be used to verify many kinds of control methods,which in turn provides convenience in research and design of the algorithms for robotic arms.In this thesis,based on an experimental platform developed by QUANSER in Canada,robust sliding mode control methods are developed and also applied to the position tracking control of a robot with 2DOF flexible link in the existence of modeling uncertainties and unknown external disturbances.Main aspects of this research are shown as follows:Firstly,the linear and nonlinear mathematical models of the 2DOF flexible link are established on the basis of its structure and characteristics of movement and also by referring to some relative literatures as well as the experimental instruction manual.Secondly,ignoring modeling error of the system and considering only the unknown external disturbances which are treated as an equivalent input disturbance(EID),a sliding mode disturbance observer-based position tracking controller is designed for the position tracking control of the linear model of the 2DOF flexible link robot.The sliding mode disturbance observer is used to estimate unknown external disturbances and then counteract them.Due to simple structure,the controller is easy to be realized.MATLAB numerical simulation results illustrate that the tracking performance and robustness of the 2DOF flexible link robot system can be guaranteed by the proposed sliding mode disturbance observer-based position tracking controller.And the effectiveness of the designed controller is demonstrated by experimental results.Next,based on the linear model,an observer-based robust method,which considers the unknown external disturbances and unknown states,is designed and then applied to each subsystem of the 2DOF flexible link robot for position tracking control.The observer consists of a state observer and a disturbance observer,where the state observer is designed to estimate unknown states and the disturbance observer is mainly used to predict unknown external disturbances generated by uncertain external systems.The stability of each subsystem is proved according to the Lyapunov function.Simulation and experimental results also indicate that each subsystem of 2DOF flexible link robot has good performance on position tracking with the designed observers above-mentioned.Following,to deal with 2DOF flexible link robot system with modeling uncertainties and unknown external disturbances,a nonlinear disturbance observer-based reaching law sliding mode controller is designed and also employed to the position tracking control of the 2DOF flexible link robot system.The nonlinear disturbance observer designed above can be used to estimate the compound disturbances which include the modeling uncertainties and unknown external disturbances.The developed reaching law sliding mode controller can realize good position tracking control of the 2DOF flexible link robot.Stability of the whole closed-loop system is proved by picking reasonable Lyapunov function.Results of numerical simulation conducted show that the proposed controller can also ensure the stability of the position tracking control of the 2DOF flexible link robot system in the existence of the compound disturbances.Experimental results also verify that the 2DOF flexible link robot has good performance on position tracking with the above designed controllers.Finally,a backstepping sliding mode control method is designed based on a second order nonlinear disturbance observer.The proposed nonlinear disturbance observer is mainly used to estimate the composite disturbances composed of modeling uncertainties and external disturbances.The developed backstepping sliding mode control scheme can realize satisfactory position tracking for the 2DOF flexible link robot.In the meantime,the stability of the whole closed-loop system is proved by using the Lyapunov method.Then,numerical simulation results show that the proposed control scheme can ensure the precision of the 2DOF flexible link robot in tracking desired position under the influence of compound disturbances.Real-time simulation results show that the designed backstepping sliding mode controller based on the nonlinear disturbance observer can guarantee a good performance of the whole closed-loop system in position tracking control.
Keywords/Search Tags:2DOF flexible link robot, linear system, nonlinear system, equivalent input disturbance, disturbance observer, sliding mode control
PDF Full Text Request
Related items