Adaptive Backstepping Sliding Mode Control For Sand Blast Derusting Parallel Mechanism Against Unmatched Interference

At present,long-span steel structure bridges are mostly used in bridge construction in our country.In the construction process of the steel box girder bridge,the corrosion of the steel box girder surface by the external environment will affect the service life of the steel structure and then affect the whole bridge body,so the sandblasting and rust removal work on its surface is essential.Most of the existing sand blast derusting equipment are inefficient,and the sandblasting quality highly depends on the proficiency of the operators.In view of the shortcomings of current semiautomatic sand blast derusting equipment,such as wall-climbing robots,etc.,it is difficult to solve the problem of sand blast derusting of long-span steel box girders with complex curved surfaces such as U-shaped ribs,our research group has developed a parallel sandblasting derusting robot for steel box girders based on Stewart parallel mechanism,which is composed of parallel operating mechanism,lifting mechanism and mobile platform.It has the advantages of high stiffness,strong load-bearing capacity and good mobility,and can realize arbitrary movement,free rise and fall,accurate six-degree-of-freedom posture operation and so on.This paper mainly studies the antimismatched interference control of its parallel mechanism.Because the end of the parallel mechanism of sand blast derusting is disturbed by the jet reaction force produced during sandblasting,this reaction force acts directly on the sand blast derusting and the on-line construction of the platform,which brings additional acceleration in the operation of the mechanism,which causes the mechanism to deflect in a very short time,resulting in a sudden change in the pose and velocity of the mechanism,and is not in the same channel as the control input,which is a kind of unmatched interference from the point of view of control.It is difficult to solve the problem of mismatched interference only by using traditional sliding mode control method.Therefore,aiming at the sand blast derusting parallel robot,in order to realize the highperformance trajectory tracking control of its parallel mechanism,this paper first designs an extended state observer to estimate and compensate the jet reaction.An adaptive backstepping sliding mode control method based on extended state observer is proposed.The main work of this paper is as follows:(1)Complete the kinematics analysis of the parallel mechanism for sand blast derusting,and the dynamics analysis considering the unmatching interference of the jet reaction force.Using the length constraint and geometric relationship of the parallel mechanism,the kinematics analysis of the Stewart six-degree-of-freedom motion platform is carried out by analytical method,and the relationship between the terminal pose parameters and the pose parameters of each active joint is obtained,and the Jacobian matrix is established;according to the sandblasting Determine the expected trajectory of the parallel mechanism based on the rust process requirements and actual prototype parameters;use the Lagrange method to establish the dynamic model of the parallel mechanism,and introduce non-matching disturbance items in the pose-velocity channel to obtain the dynamic state equation including non-matching disturbance items.Simulation experiments verify its correctness.(2)An on-line estimation method of unmatched interference based on extended state observer is proposed.Aiming at the jet reaction force of the sandblasting derusting parallel mechanism,by adding an unmeasured auxiliary state variable with mismatched disturbance,the dynamic equation of the unmatched disturbed parallel mechanism is reconstructed into the state equation of disturbance and control quantity in the same channel,and an extended state observer is designed to realize the on-line estimation of mismatched interference.(3)An adaptive backstepping sliding mode control method for sand blast derusting parallel mechanism is proposed.An adaptive switching gain sliding mode control algorithm based on the dynamic model of parallel mechanism is designed by backstepping method.in the process of backstepping design,the intermediate virtual control quantity is designed based on the estimated value of unmatched interference to compensate the unmatched interference of the parallel mechanism system.Through its sliding mode control function.Furthermore,the effects of uncertain factors such as modeling errors of parallel mechanisms,external random disturbances and fast time-varying terms and other error terms exceeding the observer bandwidth in mismatched disturbances are further suppressed,so as to enhance the robustness of the system and improve its tracking performance.the sliding mode control chattering is suppressed by designing an adaptive law to dynamically adjust the switching gain of sliding mode control.Through the results of simulation:compared with the without unmatched disturbance estimation adaptive backstepping sliding mode control and with mismatched disturbance estimation but no adaptive backstepping sliding mode control,the adaptive backstepping sliding mode control method proposed in this paper has better trajectory tracking performance,and the output torque chattering of electric cylinder driven motor is smaller.(4)The experimental platform of adaptive backstepping sliding mode control for sand blast derusting parallel mechanism with unmatched interference online estimation is completed.The hardware system is built by using the distributed structure of "upper computer(IPC-610L)+ lower computer(CK3M)".The upper computer software and control algorithm are designed,and the parallel mechanism motion control experiment is carried out to further verify the necessity of mismatched interference estimation and compensation and the effectiveness of the proposed adaptive backstepping sliding mode control method.