Research On Trajectory Tracking Control Of Flexible Joint Manipulator With Uncertainty

In recent years,with the intelligent development of robots,flexible joint manipulators have attracted more and more attention due to their advantages of lightweight,high safety,strong adaptability,and low energy consumption.However,while the flexibility of joints brings many application advantages to the manipulator,it also causes the dynamics model and control of the manipulator to become more complex,especially when the system is affected by modeling uncertainties and external disturbances.Therefore,in this paper,the following research on position tracking control of flexible joint manipulators is conducted to address the uncertainty problem:Firstly,considering the matched disturbance on the motor-side of the flexible joint manipulator,a robust controller is designed by using the linear sliding mode control method,so that the manipulator can overcome the disturbance and track the desired signal.However,it has large chattering and low control precision.Therefore,a new fractional-order terminal sliding mode controller is designed by introducing fractional-order calculus operator into the design of sliding mode surface.The simulation results show that this method can not only overcome the influence of disturbance,but also significantly improve the control accuracy and controller chattering.Secondly,in view of the mismatched disturbance on the link-side of the flexible joint manipulator,the singular perturbation method is used to decompose the flexible joint manipulator system into two fast and slow subsystems.After decomposition,the mismatched disturbance in the original system is transformed into a part of the matched disturbance in the slow subsystem.Since the traditional singular perturbation method is only applicable to the case of small joint flexibility,a flexibility compensation controller is designed to increase the equivalent stiffness of the joint,so that the singular perturbation method can be used to decompose the system when the joint flexibility is large.In order to deal with the disturbance in the slow subsystem,a new multi-dimensional finite-time disturbance observer is designed to estimate the disturbance term,and the estimated disturbance information is compensated in the slow subsystem control law.The final flexible joint manipulator control law is obtained by combining the fast and slow subsystem control laws and the flexible compensation control law.Simulation results verify that the control method has excellent control performance regardless of the joint stiffness when there is mismatched disturbance on the link-side of the flexible joint manipulator.Finally,to effectively control the flexible joint manipulator with limited input torque and uncertain joint stiffness parameters,an auxiliary system is designed to suppress the influence of control input constrains.On this basis,the dynamic surface control method is adopted,and the first-order low-pass filter is introduced to avoid the repeated derivation of the virtual control signal.The joint stiffness and the upper bound of the disturbance are estimated by the adaptive technology.The simulation results show that the proposed control method can overcome motor-side disturbance and track the desired signal under the condition of uncertain joint stiffness and limited control constrains.