Adaptive Sliding Mode Control Of Hybrid Mechanism For Automobile Electro-coating Conveying Based On Time-delay Estimation

With the rapid development of modern automobile coating technology,the automobile electro-coating is more and more demanding for conveying system.Due to the structure of cantilever beam,the load-bearing capacity and flexibility of the existing automobile electro-coating conveying equipments need to be further improved.The hybrid mechanism is a kind of mechanical structure which combines the series and parallel mechanism with the advantages of high rigidity,high load and good dynamic characteristics.Besides,it can realize multi-degree of freedom and multi-mode movement.Therefore,a novel hybrid mechanism for automobile electro-coating conveying has been developed based on the advantages of hybrid mechanism.The novel hybrid mechanism for automobile electro-coating conveying based on hybrid mechanism combines the advantages of serial mechanism and parallel mechanism.However,its hybrid structure has strong coupling effect between the joints of the mechanism,and the dynamic characteristics of the mechanism are significant when the mechanism is in high-speed motion.So,it is necessary to study the dynamic control of the mechanism.Good dynamic control of the conveying mechanism depends on its precise dynamic model,while the structure of the closed chain and kinematic constraints in the mechanism lead to the complexity of its dynamic model.Traditional modeling methods are difficult to establish mathematical models that can fully reflect their dynamic characteristics and realize real-time control.Therefore,the time-delay estimation technique is used to obtain the system model online in this paper.In addition,the conveyor system is seriously affected by the existing complex uncertainty factors like friction,external interference and the time delay estimation error generated when the time-delay estimation technique is used to obtain the model.For the above problems,the sliding mode control is applied to the conveying mechanism to improve the control of the mechanism considering its good robustness to the uncertainty.In order to ensure stability and robustness of the system,the selection of switching gain is usually larger than the upper bound of uncertainty in sliding mode control.In practical engineering,the selection of switching gain is required to be as large as possible due to the unknown upper bound.But,excessive switching gain will cause chattering which will weaken the control performance.To solve these problems,a new adaptive law which can adjust not only the magnitude of the switching gain but also the speed of the switching gain is designed.Then an adaptive sliding mode control strategy based on time-delay estimation is proposed to make hybrid mechanism for automobile electro-coating conveying achieve better tracking performance and smaller chattering at the same time.At first,this paper has an overview of the development of the existing automobile electro-coating conveying equipments,the present situation of the research on the hybrid mechanism as well as its motion control method and the development of time-delay estimation.Secondly,based on the kinematic analysis,the inverse model of kinematics is established,the jacobian matrix is deduced and the desired trajectory of the mechanism is determined.After that,the Lagrange method is adopted to establish the dynamic model for simulation and the time-delay estimation is used to obtain the dynamic model online for the controller design.On this basis,in order to improve the robustness of the system to various uncertain factors,a sliding mode controller based on time-delay estimation is designed.The correctness and effectiveness are verified by MATLAB simulation.Further,in order to solve the problem of chattering caused by sliding mode control,a new adaptive law is designed for switching gain of sliding mode control.Thus,an adaptive sliding mode control based on time-delay estimation is further proposed.Compared with a conventional adaptive law based time-delay estimation sliding mode control without considering the speed of switching gain,the simulation results show that the proposed adaptive sliding mode control based on time-delay estimation may achieve better tracking performance and smaller chattering at the same time.Finally,the control system and the experimental platform of the adaptive sliding mode control based on time-delay estimation of the hybrid mechanism for conveying are established which provide the conditions to carry out motion control experiment.The experimental results further validate the feasibility and correctness of the proposed adaptive sliding mode controller based on time-delay estimation.