Modeling And Precision Synchronization Control Of Direct-drive Motion Stages With Redundant Actuation And Coupled Rigid-flexible Dynamics

For direct-drive motion stages with redundant actuation,an innovative synchronization con-trol philosophy is proposed in this dissertation,which focuses on not only synchronized motion performance,but also simultaneous regulation of internal forces between the redundant drive axes.Specifically,systematic and novel methods for modeling of the coupled rigid-flexible dynamics,and synchronization control of this kind of stages are studied and proposed respectively.The dissertation analyzes the structural characteristics of the high-performance-oriented re-dundant direct drive systems.It should be noted that there are subtle but fundamental differences between the synchronization control of dual motors studied here and the coordinated motion control of two-axes machines for contour following tasks.Dynamics of individual axes in the synchroniza-tion control are completely coupled,which is in contrast to the essentially decoupled axis dynamics of the coordinated motion controls.Large internal forces and unknown complex coupling nonlin-earities exist due to the high-rigid physical constraint and the consequent closed-chain structure between the redundant axes,which significantly restricts the possible further enhancement of the control performance.Thus,motion tracking with strong disturbance rejection capability and avoid-ing excessive internal forces are both keys to smooth operation of these systems with fast response and high precision.However,existing control approaches mainly focus on pure motion compensa-tion and synchronization,and the problem of internal force regulation has been essentially ignored.That is why existing control schemes can not meet the requirements of higher performance con-trol design.With this in mind,after deeply studying the dynamic model of redundant direct-drive stages,this dissertation proposes a simple yet effective synchronization control scheme based on thrust allocation to suppress the influence of excessive internal forces first.Further more,a multi-variable synchronization control scheme is proposed then to control the internal forces and motion synchronization at the same time and achieves further improved performance.Firstly,the dissertation explores the modeling method of the coupled rigid-flexible dynamics based on the physical connection rigidity and the guide ball bearing flexibility.The proposed phys-ical modeling method gives a complete kinematic description and dynamic relationship for each moving part of the closed-chain structure.The resulting multi-order coupling model is of impor-tance for the analysis of the limits of control performance.Also,further studying of the coupling dynamics for the control oriented parametric model is useful for future controller design.Secondly,a precision synchronization control scheme with thrust allocation strategy is studied,which consists of two levels,and is of low order and easy for implementation.In level ?,the adaptive robust control(ARC)theory is applied for motion tracking with guaranteed robust transient and steady-state per-formance.In level ?,a thrust allocation algorithm is proposed based on the steady-state constraint condition to regulate the internal forces.The proposed controller can achieve both the goals of ensuring the accuracy of motion tracking and avoiding excessive internal force.Lastly,a multiple-input-multiple-output(MIMO)precision synchronization control method which simultaneously controls internal force and motion performance is investigated.On the basis of the obtained coupled multi-order rigid-flexible dynamics,a compensation control oriented parametric MIMO coupling model is established,which includes the nonlinear uncertainties and coupling nonlinearities.Us-ing the effective model compensation and high-performance robust feedback technologies of ARC,and the desired compensation(DC)which only relies on the reference trajectory information and online parameter adaptation,the proposed MIMO DCARC controller can ensure both the steady state and transient performance of the internal force regulating and motion tracking,and further improve the overall control performance.Identification results validate the effectiveness of the proposed modeling method.Control experimental results also show that,in comparison with tra-ditional approaches,both of the proposed schemes can achieve decreased internal forces,lower energy consumption,and higher motion performances.The proposed modeling and control meth-ods are effective in solving the control problems described above.The dissertation consists of the following five chapters:In Chapter 1,the background and development of the dual-drive systems studied here are intro-duced,after which the main problems in the control and application are summarized.Afterwards,a comprehensive literature survey is given,including the modeling and analysis of redundant dual-drive stage,the precision control theory of linear motor and the synchronization control of dual motors respectively.After that,an innovative synchronization control philosophy is put forward which focuses on not only synchronized motion performance,but also simultaneous regulation of internal forces between the redundant drive axes.A brief introduction of the work to be done in this dissertation is subsequently given.In Chapter 2,a complete description of the translation and rotation kinematics of the cross-beam is given based on the elastic analysis of the recirculating ball bearing of linear motion guides.With the study of the force and motion relationship among the various components,a physical rigid-flexible coupling dynamic model based on physical connection rigidity and guide bearing flexibility is established.After that,the high-order linear dynamics and the flexible modes characteristics in-fluenced by the bearing stiffness of the guide rail are analyzed.Identification experimental results validate the effectiveness of the model.The frequency range of the flexible modes caused by the high-order rotation dynamics is also analyzed.In addition,according to the existing control strategy based on motion synchronization,an adaptive robust synchronization controller with cross-coupled synchronization error model is designed as a representative.Results of comparative experiments with different controller gains show that the control performance is significantly restricted by the coupling rotational dynamics,which is useful for the following control design.In the Chapter 3,an two-level adaptive robust synchronization control with thrust allocation is proposed.The method applies ARC theory in the motion tracking control level to ensure the track-ing performance of the system in presence of uncertainties,while uses a thrust allocation algorithm in the other level to avoid excessive internal forces between axes.The overall controller is also easy for realization in practice.For the unknown or variation of load distribution,an adaptive al-location factor is introduced via a physical model based recursive least squares estimation(RLSE)algorithm.For a kind of task situations with known load motion,a compensation algorithm is intro-duced into the allocation.The experimental comparisons with the existing synchronization control algorithm verify the control performance and practical value of the proposed control algorithms.In Chapter 4,an MIMO adaptive robust synchronization scheme is proposed which consid-ers the rotational dynamics directly in the controller design.Firstly,a parametric multi-variable coupled model is obtained which is feasible for the compensation control and online parameter adaptation.A synchronization control method which simultaneously controls the internal force and motion performance is proposed subsequently.Considering the the measurement noise in prac-tice,the desired compensation technique is applied and an MIMO DCARC controller is designed.Finally,comparative experiments are carried out on a dual-drive gantry stage.Compared with the deterministic robust control(DRC)algorithm,the proposed DCARC behaves much better and shows its high performance essence.It is verified that the MIMO synchronization control method proposed in this chapter further enhances the performance of dual-drive systems.In Chapter 5,the research progress of this dissertation is summarized.The conclusions and innovations are highlighted.A brief prospect for future work is made.