Improved Integral Suboptimal Second-Order Sliding Mode Control Of A Novel Hybrid Conveying Mechanism For Automobile Electro-Coating

A novel hybrid conveying mechanism for automobile electro-coating is developed by our research group,which can remedy the drawbacks of the existing conveying mechanisms,such as low carrying capacity and flexibility.In this paper,we research on the control methods to further improve the flexibility of the conveying mechanism under the situation of conveying different weights and considering the resistance of the electrophoretic fluid.The system of the novel hybrid conveying mechanism for automobile electro-coating has the characteristics of nonlinearity and strong coupling.The complexity of dynamic modeling is caused by the closed-chain structure and kinematic constraints.Besides,the variation of the loaded vehicle model and the change of the electrophoretic fluid resistance will impact the system model.In addition,the system has a variety of uncertainties,such as coupling dynamics,friction,and external disturbances.The sliding mode control is used to improve the flexibility of the conveying mechanism,which has the advantages of fast response,insensitivity to external disturbance and system parameters variation.However,high-frequency chattering problem exists in the conventional sliding mode control,which will influence the control performance of the system.To solve the chattering problem,an integral suboptimal second-order sliding mode control algorithm is proposed.To further improve the flexibility of the conveying mechanism under the situation of greater uncertainties,an improved integral suboptimal second-order sliding mode control algorithm based on the switching control of finite state machine is further improved to realize the high performance control of the system.At first,this article introduces the research background of the novel hybrid conveying mechanism for automobile electro-coating,and analyzes the control method to enhance the flexibility of the conveyor system.And secondly,the change of the loading automobile model and the change of electrophoretic fluid resistance as the system uncertainty are considered.By calculating and analyzing the dynamic carrying capacity of the conveying mechanism and the maximum resistance of the electrophoretic fluid,the uncertainty boundary of the conveying mechanism control system is obtained.Then,the inverse kinematic model,the Jacobi matrix and the desired trajectory of the conveying mechanism are derived.After that,the Lagrange method is adopted to establish the conveying mechanism dynamic model.The dynamic simulation is completed by MATLAB,and the simulation results verify the reliability of the dynamic model.In order to realize the flexible control of the conveying mechanism under variable load conditions,a kind of suboptimal second-order sliding mode controller is studied and designed based on the established dynamic model,and the stability and robustness of the control algorithm are theoretically proved.Based on this,in order to make the control quantity more accurate and enhance the flexible control effect of the conveying mechanism in the complex disturbance environment,the switching control of the finite state machine is studied to design an improved integral suboptimal second-order sliding mode controller.And the stability of the algorithm is proved.Under the same load,when the system has external disturbance,friction force and electrophoretic fluid resistance,MATLAB simulation analysis is performed on the integral suboptimal second-order sliding mode controller and the improved integral suboptimal second-order sliding mode controller.The results show that compared with the integral suboptimal second-order sliding mode controller,the active joints of the conveying mechanism have higher trajectory tracking accuracy and better robust performance under the improved integral suboptimal second-order sliding mode controller.Through analyzing the MATLAB simulation results of the condition that the integrated suboptimal sliding mode controller includes the electrophoretic fluid resistance in the model and the electrophoretic fluid resistance is not included,the improved integral suboptimal second-order sliding mode controller presented in this paper has strong robustness to change electrophoretic fluid resistance and can maintain good trajectory tracking performance.Through the analysis of the MATLAB simulation results of improved integral suboptimal second-order sliding mode controller under different loads,each active joint can maintain a high trajectory tracking accuracy.The controller meets the need for flexible control of the system.Finally,the control system and the experimental platform are established which provide the conditions to carry out the motion control experiment of the novel hybrid conveying mechanism for automobile electro-coating.The experimental results further validate the feasibility and effectiveness of the proposed improved integral suboptimal second-order sliding mode controller.