Composite UDE Of Steel Box Girder Sand Blast Derusting Cantilever Type Stewart Parallel Mechanism Predetermined Time Sliding Mode Control

Road and bridge infrastructure occupies a vital position in modern transportation construction,large steel components are one of the more common components in road and bridge infrastructure,is one of the key supporting components to bear the load,with the improvement of its quality and safety requirements,the requirements for the sand blast derusting construction process on the surface of large steel components are also increasing.Whether the surface anti-corrosion and rust removal of large steel components can meet the requirements of micron-level roughness is related to its anti-corrosion performance and service life,so it is very important for high-quality sand blast derusting operations on the surface of large steel components.At present,the sand blast derusting operation of steel box girder of bridge is manual operation,which not only has low working efficiency,high safety risks,but also endangers the health of workers.The existing sand blast derusting operation equipment,such as gantry derusting equipment structure is huge,poor mobility,climbing wall derusting equipment low stiffness,weak bearing capacity,and difficult to deal with complex curved surface,so it is difficult to be used for sand blast derusting operation on the surface of large steel members such as bridge steel box girder.Based on the Stewart parallel mechanism,this research group independently developed a steel box girder sand blast derusting parallel robot,which is composed of cantilever Stewart parallel mechanism,lifting mechanism and mobile platform,etc.It has the advantages of high stiffness,strong bearing capacity and good mobile performance,and can realize arbitrary movement,free lifting,six-degree of freedom position and pose accurate movement operation.This paper focuses on the high performance control of the cantilever Stewart parallel mechanism.The cantilever Stewart parallel mechanism has a complex structure,and its mechanism system has uncertainties such as modeling errors,joint friction,and external random disturbances such as sand-jet reaction force.In this paper,on the basis of the research and establishment of the dynamic model of the cantilever Stewart parallel mechanism,The Uncertainty and Disturbance Estimator is designed to estimate and compensate the existing uncertainties and disturbances.Further,a compound UDE predetermined time sliding mode control method is proposed to improve its robustness and convergence performance.The main work completed in this paper is as follows:(1)The kinematics and dynamics of the cantilever Stewart parallel mechanism are analyzed.The kinematics of the mechanism was analyzed by analytical method,and the inverse kinematics solution and the Jacobian transformation matrix from the end of the mechanism to the active joints were obtained.The expected motion path of the parallel operation mechanism was determined according to the process requirements of sand blast derusting and the actual prototype parameters.The Lagrange method was used to establish the dynamics model of the cantilever Stewart parallel mechanism,and the correctness of the inverse kinematics and the dynamics model was verified by simulation experiments.(2)An uncertainty and disturbance estimator for parallel mechanism systems is designed.In view of the uncertainties of the mechanism system such as modeling errors,joint friction,and external random disturbances such as the reaction force of the sandjet,a filter based uncertainty and disturbance estimator was designed to accurately estimate the disturbance under the condition of unknown upper bound of disturbance amplitude and low sampling frequency,and feedforward compensation was carried out to reduce the subsequent design of sliding mode control gain.Sliding mode control buffeting is reduced.(3)A sliding mode control method for composite UDE predetermined time of sand blast derusting cantilever Stewart parallel mechanism is proposed.Design a predetermined time convergence non-singular terminal sliding mode controller to take advantage of sliding mode control robustness and adjustable predetermined time parameters,so that the tracking error of the cantilever Stewart parallel mechanism can stably converge to the neighborhood of the origin at a predetermined time according to the actual operation requirements,so as to improve the robustness and convergence performance of the sand blast derusting cantilever Stewart parallel mechanism,and realize its high-performance trajectory tracking control.The Lyapunov function is constructed to theoretically prove the stability of the proposed control method.The effectiveness of the proposed control method is verified by comparing with the predetermined time sliding mode control of uncomposite UDE and the non-singular terminal sliding mode control of undesigned predetermined time composite UDE.(4)Completed the construction of sliding mode control system and prototype experimental platform construction of steel box girder sand blast derusting parallel robot composite UDE.Using the distributed structure of "upper computer(IPC-610L)+ lower computer(CK3M)",the hardware system is built and the upper computer software is designed,and the effectiveness of the proposed control method is further verified through prototype experiments based on the cantilever Stewart parallel mechanism system.