| In industrial applications,gantry numerical control machine tools(GNCMT)is widely applied for manufacturing large and heavy workpieces to meet the requirement of large-scale machining.For the high-performance motion control of GNCMT,the gantry stage is generally driven coordinately by two motors.The control task of the dual-drive system is nor only to make the gantry stage track the desired motion trajectory as much as possible for tracking function,bu also to ensure the coordinated motion between the two servo motors for synchronization function.Due to the complex dynamical behaviour in the dual-drive system,such as nonlinearity and coupling dynamcs,it's difficult to apply the classical three-loop control strategy to meet the engineering design requirements of the dual-drive control system.In addition,the servo systems inevitably suffer from modeling errors and unknown external disturbances,which have a significant impact on the control accuracy and system stability.Therefore,the high-performance synchronization motion control of the GNCMT has always been a key technology for advanced CNC machine tools and a major practical problem to be investigated.Taking the gantry stage with dual-drive system as the research object,this paper aims to improve the tracking and synchronization performance of the dual-motor driving system,and carries out in-depth study of synchronous motion control algorithm with the help of classical control theory based on transfer function and modern control theory based on state equation,striving to provide necessary theory and methods for the analysis and design of the dual-drive control system.The main contents and contributions of this paper are as follows:1)Firstly,the detailed movement of the gantry stage is analized,with the multi-input and multi-output(MIMO)model of the dual-drive system established,including the model of the AC servo motor,the dynamic model of the rack and pinion transmission system and the three-degree-of-freedom(3DOF)coupling dynamic model of the gantry stage.Then,the classical “three-loop” control structure of AC servo drive system and its engineering design method is briefly investigated,followed by the parallel synchronization control strategy which is widely used in industrial applications.Finally,the control performance indexes of the dual-drive system are introduced,including tracking performance index,disturbancerejection performance index,and synchronization performance index.2)A novel control strategy synthesized by internal model principle and sliding mode technology is proposed for the high-performance motion control of servo motor systems.Firstly,in order to overcome the drawback that the standard internal model control(IMC)must make a compromise between the servo and regulatory requirements when using the IMC rules for the control parameter tuning,an enhanced IMC scheme based on a 2-degree-of-freedom(2DOF-IMC)structure is designed for both the desired set-point tracking and good disturbance rejection of the closed-loop system.To solve the control problems of various uncertainties in the servo system,a robust control strategy synthesized by the 2DOFIMC and sliding mode control(SMC)is proposed.In this control strategy,on the one hand,the linear feedback control gains in the SMC system can be tuned by the IMC rules;on the other hand,the sliding mode equation of the IMC system can be established and the SMC technology can be used to improve the robust performance of the IMC system.Furthermore,the stability of the proposed controller is guaranteed via Lyapunov theory.Finally,the effectiveness of the proposed strategy is verified by simulations based on MALTAB/Simulink platform.3)A robust synchronization control strategy based on IMC and SMC is proposed for the the dual-drive system in the gantry stage.Firstly,in order to apply the IMC rules to design the synchronization controller of the dual-drive system easily and efficiently,the model of the gantry stage with dual-drive system is firstly simplified thorough linearization and orderreduction.Then,the linear feedback controller parameters in the parallel synchronization control strategy are designed based on the control parameter tuning method of the signle servo axis.However,the parallel control strategy ignores the strong coupling dynamics in the dual drive system and the synchronization control accuracy depends on the tracking control performance of a single servo axis.Thus,it's difficult to solve the synchronization control problem of the gantry stage.To overcome this drawback,a cross-coupling synchronization control strategy based on 2DOF-IMC is proposed.This control strategy designs an additional rotary motion controller to attenuate the coupling effects.As a result,the synchronization control accuracy can be improved.Based on this strategy,a robust control law synthesized by the SMC tenonlogy is introduced to further improve the control performance of the IMC system in the presence of various uncertainties.Finally,the simulation platform of the dualdrive control system is established based on MALTAB/Simulink software and compared simulations are performed.The simulation results show that when the robust control law based on SMC is introduced into the cross-coupling synchronization control strategy based on 2DOF-IMC,both the tracking accuracy and the synchronization accuracy of the dualdrive system can be improved significantly.4)To handle the control problems of the dual-drive system in the presence of strong disturbances,an active disturbance rejection synchronization control strategy based on extended state observer(ESO)is proposed.In this strategy,all the unknown disturbances and model errors in the dual-drive system are treated as the total disturbance or the augmented system state,and an extended state observer is constructed for on-line disturbance estimation and compensation,so that the total disturbance is suppressed and the disturbance-rejection performance of the system is improved.However,the ESO with limited bandwidth cannot completely eliminate the influence of the disturbance on the system performance in a limited time,thus limiting the control accuracy of the system to a certain extent.To further improve the control performance of the observer and feedback control system with finite bandwidth,as well as the tracking accuracy and synchronization accuracy of the dual-drive system,a novel synchronization control strategy synthesized by 2DOF-IMC,SMC and ESO is proposed,and the dynamic characteristics of its tracking error and synchronization error are analyzed based on the Lyapunov theory.Finally,the effectiveness of the proposed activedisturbance-rejection robust synchronization control strategy is verified by simulations.5)The experimental platform of the gantry stage with dual-drive system based on EtherCAT network is designed.In order to illustrate the rationality and effectiveness of the simplified model,a series of system identification experiments were firstly carried out on this platform.Based on the identified model,a linear feedback synchronization controller based on IMC principle,a robust synchronization controller based on SMC technology and an active-disturbance-rejection synchronizaiton controller based on ESO are designed,and then the comparing experiments of various synchronization control strategies are performed.The experimental results demonstrate the practicability,efficiency and effectiveness of the proposed strategy. |
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