Research On The Trajectory Tracking Control Of A 6-DOF Manipulator Based On Fully-Actuated System Models

As the most widely used type of robot in the industrial field and an important component of complex robots,multi-degree-of-freedom manipulators require highprecision control as the foundation of their application.Since trajectory tracking control of manipulators is widely used in applications such as assembly,spraying,palletizing,and sorting,this paper studies the trajectory tracking problem of a sixdegree-of-freedom manipulator based on a high-order fully-actuated system model,combined with a nonlinear disturbance observer(NDO)and a feature structure configuration method.The specific research contents are as follows:Firstly,this paper establishes a kinematic model and a nominal dynamic model of an actual six-degree-of-freedom manipulator using an improved DenavitHartenberg(D-H)parameter method and Lagrange dynamics equations.The accuracy of the established models is verified by utilizing the robot toolbox in Matlab and relevant properties of the dynamic model.Subsequently,a trajectory tracking controller was designed for a six-degree-offreedom(6-DOF)manipulator,which is subject to internal and external uncertainties,including internal modeling errors,joint friction,and external disturbances.The controller was based on a second-order fully-actuated system model and the nonlinear disturbance observer(NDO).Specifically,an NDO was designed to estimate the IEU and compensate for their effects on the system via a compensating controller.Then,a direct parameterization method was used to design the trajectory tracking controller,which gives the degrees of freedom in the form of explicit free parameters during the controller design process.By optimizing these free parameters,different system performances,such as fast response and disturbance rejection,can be conveniently controlled.Moreover,a switch control strategy was used to dynamically adjust the controller parameters to solve the problem of excessive output peaks of the controller.Finally,to avoid the possibly negative impact of control of the motors on the trajectory tracking accuracy of the six-degree-of-freedom manipulator,the motor’s dynamic model is incorporated into the second-order fully-actuated system model.This leads to a third-order fully-actuated system model with voltage signals as inputs.The NDO and direct parameterization method are then utilized to design the trajectory tracking controller.Firstly,NDO is designed based on the second-order state feedback signal estimated by tracking-differentiator(T-D)to compensate for the IEU of the system.Then,based on the T-D,the direct parameterization method is employed to design the trajectory tracking controller,and the SCS is used to limit the controller’s output peak value.Finally,simulations are conducted using the chosen six-degree-of-freedom manipulator to validate the effectiveness of the proposed theory,which demonstrates the good signal construction ability of T-D,the accurate disturbance observation ability of NDO,and the effectiveness of the trajectory tracking controller.