Nonsingular Fast Terminal Sliding Mode Control With Sliding Mode Observer Of A Novel Hybrid Conveying Mechanism

The existing automobile electro-coating conveying equipments mainly include Varioshuttle conveyor and RoDip conveyor,but their performances need to be further improved due to the high requirements of manufacturing and installation technology,high costs of mechanism operation and maintenance,inadequate bearing capacity and low degree of flexibility caused by cantilever beam structure.Hybrid mechanism combines the advantages of both serial and parallel mechanisms,which is featured with high stiffness,high precision,high bearing capacity,large workspace and flexible motion.It can realize multi-degree-of-freedom and multi-mode motion.Hence,a novel bilaterally symmetrical type of automobile electro-coating conveying mechanism is developed based on the hybrid mechanism by our research group.The high performance motion control for the hybrid conveying mechanism is focused in this paper by taking advantages of the novel hybrid mechanical structure.The novel hybrid conveying mechanism is a complex system with high nonlinearity,strong coupling and multi-variable characteristics.Compared to kinematic control,dynamic control for the hybrid mechanism is capable to achieve better control performances by taking the dynamic characteristics and the couplings into account.Therefore,the dynamic control method is adopted in this paper.The closed-chain structure and kinematic constraints of the parallel conveyor mechanism make the dynamic model more complex,which makes it difficult to establish the accurate dynamic model.In addition,uncertainties such as modeling error,friction and external interference exist in the hybrid conveying mechanism.Thus it is difficult to achieve high-performance control.Considering that sliding mode control has the advantages of rapid response,insensitivity to various uncertainties,e.g.,modeling error,friction,external disturbance,and strong robustness,a terminal sliding mode control is introduced in this paper to improve the control performance of the novel hybrid conveying mechanism.However,the convergence rate of the system state by using the terminal sliding mode control is slow when it is far from the equilibrium state,and the terminal sliding mode control encounters the physically unrealizable problem owing to singularity.Therefore,a novel non-singular fast terminal sliding mode control method for the novel hybrid conveying mechanism is proposed to improve the convergence rate and tracking accuracy of the terminal sliding mode control system and to solve the singularity problem of the controller.Unfortunately,the upper boundary of the uncertainty in the control system is unknown in practical engineering applications,the selection of switching gain for the non-singular fast terminal sliding mode control is required to be as large as possible to overcome the uncertainty in the most serious situation of the system.The system performance will be affected by the exaggerated switching gain which will bring chattering and saturation to the non-singular fast terminal sliding mode control system.Given that the estimation errors of sliding mode observer for estimating uncertainties,including modeling error,friction,and external disturbance,can be convergent in finite time,and the sliding mode observer can still guarantee high estimating accuracy under the complex industrial environments.Therefore,a sliding mode observer intergrated non-singular fast terminal sliding mode control method for the novel hybrid mechanism is presented in this paper by combining the non-singular fast terminal sliding mode control method with sliding mode observer.The presented control method could improve the robustness of the conveying mechanism control system and avoid using exaggreted switching gain of the non-singular terminal sliding mode control by compensating the adverse effect of uncertainties on the control performance of the mechanism with the feedforward of sliding mode observer.Then the high performance control of the novel hybrid conveying mechanism could be realized.Firstly,the developments of automobile electro-coating conveying equipment and hybrid mechanisms are introduced,and the research status of motion control of hybrid mechanism is analyzed in detail.The kinematics analysis and inverse kinematics equation of the novel hybrid conveying mechanism are established,and the Jacobian matrix of the hybrid conveying mechanism is obtained.Afterwards,the kinematics simulation is carried out by MATLAB software.Secondly,on the basis of kinematics analysis,the dynamic model of the hybrid conveying mechanism is established by Lagrange method.The correctness of the dynamic model is verified by simulation analysis with MATLAB.Then,a non-singular fast terminal sliding mode controller is designed to improve the performance of the control system of the hybrid conveying mechanism based on the dynamic model.The problem of slow convergence rate existing in the terminal sliding mode control method when the system state is far from the equilibrium state and the singularity problem existing in the design of controller,which may make the output signal of the controller infinitely large,are sloved by using the designed non-singular fast terminal sliding mode controller.By comparing to terminal sliding mode control,the superiority of the designed controller is verified through simulation.Furthermore,the control method combining the non-singular fast terminal sliding mode control method with sliding mode observer is proposed to solve the chattering problem and the actuator saturation problem caused by high switching gain of the non-singular fast terminal sliding mode control.Lyapunov analysis is conducted to demonstrate the stability of the proposed control method.The comparative simulation results verify the correctness and effectiveness of the proposed control method by comparing to the non-singular fast terminal sliding mode control method.Finally,the construction of the sliding mode observer intergrated non-singular fast terminal sliding mode control system and the experimental platform of the novel hybrid conveying mechanism are completed.On this basis,the motion control experiments are carried out and the experimental results further verify the effectiveness and superoritiy of the designed control method.