Study On Dynamic Modeling And Second Order Sliding Mode Control Of A Novel Hybrid Mechanism For Automobile Electro-Coating Conveying

Currently, the existing automobile electro-coating conveying systems, such as the suspended conveyor and the swing-rod conveyor, can not solve the problem of air bag on car roof. Rodip and Vario Shuttle, can eliminate the air bag on car roof. But they are the cantilever beam structures which have the low flexibility and the poor ability to withstand heavy payload.Therefore, supported by National Natural Science Foundation of China(Grant No. 51375210), a novel hybrid mechanism for automobile electro-coating conveying has been developed by using the advantages of hybrid mechanism, such as high rigidity, high capacity, good dynamic performance and convenience to achieve multiple degrees of freedom. This mechanism can not only eliminate the air bag on car roof in the process of electrophoresis, but also has the advantages of strong payload, high flexibility and wide applicability.For the novel hybrid mechanism for automobile electro-coating conveying, the mechanism has high nonlinearity and strong coupling due to its hybrid structure. When the mechanism is running in high speed, the dynamic characteristics of this mechanism will make a comparatively great impact on the control accuracy. Therefore, in order to ensure that the conveying mechanism is stable, reliable and accurate in various working conditions and coating processes,it is necessary to study the dynamic control of the mechanism to improve the control performance. The control effect of dynamic control depends on the established dynamic model.Because the conveying mechanism is a complex multi-chain mechanism, it is more suitable to describe the mechanism movement from the whole. Then, a method of combining screw theory and the principle of virtual work is proposed to establish dynamic model of the mechanism,which regards the whole system as a body from the point of view of virtual energy. Moreover,it is hardly to realize the high performance control of hybrid mechanism by the traditional method for dynamics control in practical application because of the influence of uncertainties, such as parameter variation, internal friction and external disturbance. Sliding mode control is not sensitive to external disturbance and system parameter variation, easy to implement, and has strong robustness. But the control performance of sliding mode control is influenced by the chattering caused by the discontinuous switching characteristic. To solve the above problems, a second order sliding mode control method based on Super-Twisting algorithm is presented in this paper, which not only meets the requirement of the system robustness, but also eliminates the chattering. At the same time, in order to further improve the system convergence speed, a second order nonsingular fast terminal sliding mode control method is proposed by introducingthe nonsingular fast terminal sliding surface on the basis of the second order sliding mode control method based on Super-Twisting algorithm. This paper may lay the groundwork for the practical application of the novel hybrid mechanism for automobile electro-coating conveying in the automotive coating industry.At first, the general development and application situation of automobile electro-coating conveying equipments and hybrid mechanism are overviewed in this paper. The research status of the related theory of the hybrid mechanism is expounded systematically from three aspects of kinematics analysis, dynamic modeling and control method. Secondly, the mathematical basis of the screw theory and the working principle and features of the novel hybrid mechanism for automobile electro-coating conveying are introduced. Considering that the conveying mechanism is a complex multi-chain mechanism and is more suitable to describe the mechanism movement from the whole. The kinematical analysis of the mechanism is carried out by using screw theory. Thirdly, the dynamic model with screw form is formulated by utilizing screw theory and the principle of virtual work, and the simulation results verify the reliability of the established dynamic model. Then, in order to solve the chattering problem inherent in the traditional sliding mode control, a second order sliding mode control method based on Super-Twisting algorithm is proposed. The simulation results show that the method not only makes the system have stronger robustness and higher steady-state accuracy, but also eliminates the chattering. To furthermore improve the speediness, a second order nonsingular fast terminal sliding mode control algorithm is proposed by introducing the nonsingular fast terminal sliding surface. The MATLAB/Simulink simulation results show that the control algorithm not only maintains all the advantages of the second order sliding mode control method based on Super-Twisting algorithm, but also improves the convergence speed. Finally, according to the control requirement of the conveying mechanism, the experimental platform is established. The motion control experiments are completed based on the experimental platform. The experiment results further verify the feasibility and effectiveness of the second order nonsingular fast terminal sliding mode control algorithm proposed in this paper for the novel conveying mechanism.