Sliding Mode Control Integrated With Disturbance Observer Of A Novel Hybrid Mechanism For Automobile Electro-coating Conveying

In the process of modern automobile manufacturing, the electro-coating conveying system works throughout the whole process of the production line, is the artery. Traditional suspension conveyor system exists some problems, such as the auto body pollution, the air in the canopy and the cavity. The pendulum chain conveyor resolved the pollution problem of auto body, however,cannot eliminate the roof air bag. Although swing rod conveyor resolved the pollution problem of auto body, but unable to eradicate the bubble of roof. International advanced Ro Dip conveyor and multi-shuttle conveyor are cantilever beam structure, which has poor capacity under heavy and large load, and the flexible level is not high. In this paper, therefore, a novel hybrid mechanism for automobile electro-coating conveying is developed to meet the higher demands of automobile coating production line for flexibility, environmental protection and automation level.Hybrid mechanism is a multivarible, highly nonlinear and coupling control system, the control effect of existing control method based on dynamic model is related to the accuracy of the hybrid mechanism dynamics model. The closed chain structure and kinematic constraints of Hybrid mechanism make the dynamic model is more complicated. In addition, the parameter uncertainties and modeling errors caused by the physical parameters measurement error, the friction and external disturbances existed in the practical engineering system make it difficult to establish accurate dynamic model. Therefore, the traditional PID control is difficult to achieve high performance tracking control. And the sliding mode control have good adaptability and robustness can be used to the control of hybrid mechanism due to the advantages of rapid response, is not sensitive to external disturbance and system parameter changes, without online identification of system, simple physical implementation etc. However, the large switch gain will induce larger system chattering while the parameter uncertainties, modeling errors, friction and external unknown disturbances is serious, which lead to the wear of physical system. To overcome the problems existing in sliding mode control and make the system obtain the better tracking performance and stronger robustness, For a novel hybrid mechanism for automobile electro-coating conveying with modeling errors, parameter uncertainties, friction and external unknown disturbances, a kind of nonlinear disturbance observer is introduced and a control method which integrated sliding mode control with disturbance observer is proposed.In this paper, firstly the development of automobile electro-coating conveying system, and the research status of hybrid mechanism are introduced. Secondly, the inverse kinematics model,the Jacobi matrix and the forward kinematics model are built and analyzed, and the simulation results of inverse kinematics for the mechanism by MATLAB shows that the kinematics analysisis correct. Thirdly, the dynamic model is formulated by using the Lagrange method, and the simulation results verify the reliability of the model. Considering parameter uncertainties,modeling errors, friction and external unknown disturbances exist in mechanism, a sliding mode control scheme integrated with disturbance observer is proposed to eliminate their adverse effects and improve the control performance. The sliding mode controller is designed according to the control requirements, and the disturbance observer is designed to estimate the parameter uncertainties, modeling errors, friction and external unknown disturbances, and the estimate value is used as disturbance compensation, which is integrated with sliding mode controller. The stability of the proposed control algorithm is proved by using the Lyapunov method, and the method is compared with single sliding mode control by MATLAB simulation. The simulation results proved that the proposed method can not only make the system obtain the better tracking performance and stronger robustness, but also weaken the chattering, the simulation of sliding mode control and sliding mode control integrated with disturbance observer is compared.Therefore, the high performance tracking control of automobile electro-coating conveying mechanism can be achieved. After that, the hardware design of the mechanism is established by using the distribute control of “PC+UMAC”. The control system software design of the mechanism is established by developing the program of slave computer based on Pewin32 Pro and designing the human machine interface based on VS2013 and MFC. Finally, the validity and effectiveness of the control algorithm is verified by the experiment for the designed sliding mode control with disturbance observer based on the control system.