Montion Control Of Cable Driven Parallel Robot Based On Nonlinear Disturbance Observer

With the advantages of large operating space,low manufacturing cost,simple structure and easy configuration reconfiguration,cable-driven parallel robots have been widely used in many fields such as space exploration,aerospace,biological medicine,storage handling and high-speed photograph.However,its highly nonlinear dynamic behavior,actuation redundancy,and low-stiff cables have severely restricted the improvement of robot trajectory tracking accuracy.Therefore,a robust control method based on nonlinear disturbance observer is proposed for the trajectory tracking problem of cable-driven parallel robot in this paper.The effectiveness of the proposed control scheme is verified by using the experimental platform of planar four-cable-driven parallel robot.The main work of this paper includes:According to the kinematic characteristics of the planar four-cable drive parallel robot,a dynamic model is established using Newton's second law,and the forward and inverse kinematics are analyzed.Drive the relation between the cable length,speed,and acceleration of the planar four-cable drive parallel robot and the position,speed,and acceleration of the end-effector.The function expression between accelerations,the forward solution method is established by Newton-Raphson numerical iteration method,and the validity of the forward and inverse solution model is proved by numerical examples.A robust control method based on a nonlinear disturbance observer is proposed to improve the tracking accuracy of a cable-driven parallel robot.The method consists of a robust error sign integral controller(RISE)and a nonlinear disturbance observer(NDO).The RISE controller,as a robust nonlinear continuous controller,can ensure the robustness of the semi-closed loop system to parameter uncertainties and external disturbances.The nonlinear disturbance observer is used as feedforward compensation to deal with the nonlinear friction and vibration disturbance.It is determined that the RISE controller is used to compensate the bounded disturbance of the system,and the nonlinear friction and vibration disturbance are realized by NDO,which improves the tracking accuracy of the cable-driven parallel robot to the reference trajectory under the condition of uncertain operating parameters.A simulation example is used to verify the effectiveness of the cable-driven parallel robot control method based on the nonlinear disturbance observer.Based on the dynamic model of the planar four-cable-driven parallel robot,the control architecture of the planar four-cable-driven parallel robot was constructed,and the dSPACE software and hardware were used to control the robot motion in real time.The least square method was used to identify the dynamics model of the planar four-cable driven parallel robot,and the control parameters of RISE+NDO control algorithm were clarified.Through trajectory tracking experiments,the trajectory tracking effects of RISE+NDO and feedforward P/PI cascade control algorithm are compared and analyzed,and the effectiveness of the proposed algorithm is verified.