| At present,in road and bridge construction,the surface of large steel components such as steel box girder sandblasting and derusting by mostly human,which has low efficiency,high safety hidden danger and easy to harm the health of the operator.Most of the existing sand blasting and derusting equipment has a low degree of automation.A few foreign sandblasting robots,such as Blastman,adopt series mechanism design,which has some defects such as low stiffness,weak bearing capacity,poor mobility,and it is difficult to handle the sandblasting derusting operation of large steel members with U-shaped ribbed complex curved surface such as steel box girder.Based on the Stewart parallel structure,this research group independently developed a steel box girder sandblasting and derusting parallel robot.It is composed of a parallel operating mechanism,a lifting mechanism and a mobile platform.It has the advantages of high rigidity,strong carrying capacity,and good mobility.It can realize arbitrary movement,free lifting,six-degree-of-freedom position and precise movement operation.This article focuses on the control of its parallel operating mechanism.Due to the complex structure of the parallel operating mechanism and the influence of the jet reaction force on the terminal moving platform,there are currently two difficulties in achieving its high-performance trajectory tracking control:(1)since the actual gas pressure used in sandblasting is 6 to 8 times the atmospheric pressure,it is necessary to overcome the strong interference of the reaction force of the spray gun jet;(2)uncertainty problems such as modeling errors and random interference in the mechanism need to be solved.For this reason,this article first researches and proposes a jet reaction force calculation and compensation method,and on this basis,studies and proposes a backstepping adaptive sliding mode control method with jet reaction force compensation.The main tasks completed in this paper are as follows.(1)Complete the kinematics and dynamics analysis of the parallel operating mechanism.Use the analytical method to analyze the kinematics of the mechanism,and obtain the inverse kinematics solution and the Jacobian transformation matrix from the end of the mechanism to the active joints.Determine the expected motion trajectory of the parallel operating mechanism according to the requirements of sandblasting and derusting technology and the actual prototype parameters.The dynamics model of the parallel manipulator was established by Lagrange method,and the correctness of the inverse kinematics solution and dynamics model was verified by simulation.(2)A calculation and compensation method for jet reaction force is proposed.According to the conservation of momentum and the flow characteristics of the sandblasting flow field,the magnitude of the jet reaction force is calculated.Through vector transformation,it is converted into terminal generalized force compensation amount.Finally,by means of Jacobian matrix,the torque compensation of the jet reaction force on the active joint driving motor is obtained.(3)A backstepping adaptive sliding mode control method for parallel sandblasting and derusting robot is proposed.On the basis of the jet reaction force compensation,aiming at the modeling error and random disturbance and other uncertain problems in the system.Considering that the backstepping design method is easy to use Lyapunov theorem theory to analyze the stability of closed-loop control system,this paper adopts the backstepping method.Firstly,the desired dynamic and static performance of the closed-loop system is achieved by designing the virtual control quantity.Then a recursive sliding mode control law is introduced to improve the robustness of the system against uncertain factors.Furthermore,the Lyapunov adaptive law is designed to estimate the upper bound of the uncertainty information to avoid the high selection of sliding mode switching gain,so as to suppress the chattering effect of sliding mode control.Simulation results show that: compared with the backstepping adaptive sliding mode control without jet counterforce compensation,the proposed control method has better trajectory tracking performance;compared with the backstepping sliding mode control with jet counterforce compensation,the output torque of the active joint drive motor is less chattering.(4)The construction of the backstepping adaptive sliding mode control system with jet counterforce compensation and the construction of the experimental platform for the parallel robot of steel box girder sand-blasting derusting was completed.The hardware system was built with the distributed structure of "host computer(IPC-610L)& lower computer(CK3M)" and the upper computer software was designed to carry out the control experiment of end trajectory tracking.The necessity of the jet reaction force compensation and the effectiveness of the proposed backstepping adaptive sliding mode control method is further verified. |
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