Study On PD With Sliding Mode Control Of A Novel Hybrid Mechanism For Automobile Electro-coating Conveying

The conventional automobile electro-coating conveying systems,such as RoDip and Vario Shuttle,which adopt the cantilever structures,have the poor ability to withstand heavy and large payload and the low flexibility.In response to these problems,a novel hybrid mechanism for automobile electro-coating conveying has been developed based on the hybrid mechanism,supported by National Natural Science Foundation of China(Grant No.51375210).The hybrid mechanism has the characteristics of the serial mechanism and the parallel mechanism,which has the advantages of wide applicability and high capacity.Parallel mechanism is the main body of hybrid mechanism,which consists of multiple motion branches.Due to the highly nonlinear,strong coupling,time-varying parameters and unknown disturbances of the hybrid mechanism,it is difficult to obtain the high performance.In order to ensure the conveying mechanism running smoothly and reliablly,it is necessary to study its control algorithm.In the existing control algorithm,sliding mode control(SMC)is insensitive to external interference,and it has strong robustness.But the equivalent control of SMC depends on the accuracy of the system dynamic model.However,it is difficult to establish an accurate dynamic model,due to the uncertainties such as uncertain parameters,unknown extern disturbances and model errors.The switching gains of SMC are often chosen to be large enough to solve the the problem of uncertainties,but such large switching gains may cause chattering phenomenon and effect the control performance of system.It means that there is a trade-off between modeling and performance.That is one of the disadvantages of applying SMC.On the other hand,most robots are equipped with proportional-derivative(PD)or proportionalintegral-derivative(PID)controllers,owing to the simple structure,the clear physical meaning of each control gain and the easy implementation.However,PD control is difficult to achieve high control performance with uncertainties,nonlinearity and multivariable.To solve the above problems,a PD with SMC(PD-SMC)control method is presented in this paper,which not only takes the advantages and avoids the drawbacks of both SMC and PD control,but also makes the system obtain the better tracking performance.At the same time,in order to further improve the system robustness and eliminate the chattering,a linearization PD-SMC controller(TDE-PD-SMC)based on its dynamic model,which is linearized by Time-delayed estimation(TDE),is designed to improve its performance of motion control.Anther problem is that so much parameters of the TDE-PD-SMC need to be chosen.A set of matrix inequality about controller parameter is obtained when the stability proof of controller by Lyapunov method,which provides the basis for the selection of controller parameters.So that workload of control parameters selection can be reduced.Compared with other nonlinear PD algorithms which need special method to adjust their parameters,the TDE-PD-SMC has a higher practical value of engineering.Firstly,the development of automobile electro-coating conveying equipments and the motion control research status of hybrid mechanism are summarized.Secondly,the inverse kinematics,the forward kinematics,the Jacobi matrix are derivated and the dynamic model is aslo built.The kinematic model and dynamic model of the conveying mechanism are simulated by MATLAB.The simulation results show the correctness of kinematics analysis and the reliability of dynamic model.Thirdly,in order to solve the problem that the performance of SMC depends on the accurate dynamic model,a PD-SMC is designed for the conveying mechanism.Further,in order to further overcome the negative effects of the nonlinearity on the PD sliding mode control,the TDE-PD-SMC is designed.The simulation results show that the TDE-PD-SMC not only has higher tracking accuracy and stronger robustness,but also reduces the chattering of the SMC.Finally,the experimental platform of the control system of the conveying mechanism is established by adopting the distributed structure of "PC and UMAC".At the same time,the debugging and troubleshooting plans of the conveying mechanism are given.The motion control experiments are completed based on the experimental platform.The experiment results verify the feasibility and effectiveness of the PD-SMC controller further.