Global Robust Super-twisting Sliding Mode Control With Two-layered Adaptive Law For A Conveying Hybrid Robot

With the cantilever beam structure,the existing conveying robots for automobile electro-coating have the defects of weak carrying capacity and low flexibility level.To remedy the defects,our research group combined the advantages of serial robots and parallel robots,and developed a conveying hybrid robot for automobile electro-coating,which is characterized by the flexible operation,large working space,high flexibility level and strong carrying capacity.The developed conveying hybrid robot can realize the Multi-mode movement of walking,lifting and turning.The hybrid robot is a complex nonlinear system with multiple inputs and outputs,which has various uncertainties,including modeling errors,frictions and external interferences.In this paper,a dynamic sliding mode control(SMC)method is mainly studied to improve the robust performance against uncertainties in the hybrid robot system.At present,some difficulties still exist in the dynamic SMC study of hybrid robots,such as the lack of the robustness in the approaching phase of the dynamic SMC,and the fact that the dynamic SMC control system is prone to serious chattering in the sliding stage due to the conservative selection of the switching gains when the upper bound information of the uncertainties is unknown.Hence,in this paper,a global robust sliding surface is designed to eliminate the approaching phase,and a global robust super-twisting sliding mode control(STW)method with two-layered adaptive law is further explored to quickly obtain low switching gains in the sliding phase.The main works accomplished in this paper are as follows:(1)Kinematic analysis and dynamics analysis of the conveying hybrid robot are performed.Based on the kinematic analysis conducted by the analytic method,the forward kinematics solution,the inverse kinematics solution and the Jacobian matrix of the hybrid robot are deduced.Based on the dynamic analysis performed by the Lagrange method,the standard dynamic model and the dynamic model including uncertainties of the hybrid robot are established.The correctness of the models is verified by MATLAB simulation.(2)A global robust STW method for the conveying hybrid robot is proposed.For the problem of the non-robustness in the approaching phase of the dynamic SMC,based on a global robust sliding surface,a global robust STW controller is designed to eliminate the approaching phase,and then the global robustness of the control system is ensured.Next,the theoretical proof of the stability is accomplished and the MATLAB simulation is carried out.The results show that,compared with the STW,the global robust STW system has global robustness.(3)A global robust STW with two-layered adaptive law for the conveying hybrid robot is further proposed.In the sliding phase of the global robust STW,serious chattering of the control system is easily caused via the conservative selection of the switching gains due to the unknown upper bound information of the uncertainties.To solve the problem,the equivalent control is reconstructed and a two-layered adaptive law is designed to quickly obtain the low switching gains in the SMC sliding phase.As a result,a global robust STW controller with two-layered adaptive law is built to suppress the chattering effectively while the global robustness is ensured.Next,the theoretical proof of the stability is accomplished and the MATLAB simulation is carried out.The results show that the global robust STW system with two-layered adaptive law can efficiently reduce the chattering under the premise of ensuring the global robustness compared with the unreconstructed global robust STW with adaptive law.(4)The experimental platform of the global robust STW system with two-layered adaptive law for the conveying hybrid robot is constructed and the experimental verification is carried out on the prototype.The distributed structure of “host computer + slave computer” is selected,and the hardware design,as well as the software development,of the global robust STW system with two-layered adaptive law for the conveying hybrid robot is performed.On this basis,the comparative experiment between the proposed global robust STW system with two-layered adaptive law and the unreconstructed global robust STW with adaptive law is finished.The experimental results further verify the effectiveness and superiority of the proposed global robust STW method with two-layered adaptive for the conveying hybrid robot.