| Machine tool cutting is the most commonly used mechanical manufacturing method in industrial production,and ball screw is widely used in the feed system of machine tools because of its high rigidity and transmission efficiency.The tracking accuracy of the machine tool feed motion directly affects the surface quality of the parts processing,but in the process of high speed cutting,the vibration mode of the feed system will be excited,and the vibration mode will change with the vareitions of the table position and the part mass.System vibration limits the bandwidth of the control system,resulting in instability of the system and reducing the tracking accuracy of the machine tool during cutting process.In addition,external disturbances such as cutting force and nonlinear friction in the cutting process will also affect the tracking accuracy,and the high frequency disturbances will also excite the system resonance.At the same ti me,the feedback signal of the system sensors will have random interferences and noises.To summarize,the main goals of the research are to design servo controllers for the above problems,which can suppress the vibration of the system and achieve high tracking precision,high servo bandwidth and high robustness to the time-varying vibration mode,external disturbances and random noises.In order to study the servo control method for ball screw drive system,it is necessary to establish relevant control models for system dynamics characteristics.A rigid body control model is established for the low frequency state of the system.A flexible control model which can express the first order vibration mode is established for the high frequency state of the system.A flexible control model with uncertain parameters is established for the uncertainty of the system parameters and a LPV model is established to reflect the dynamic time-varying characteristics of the system.The parameters of the control model are identified on the high-speed ball screw drive experiment system built for the project.The friction model of the feed system is identified by genetic algorithm,and the moment of inertia and damping are identified by using the friction model and the least squares estimation method.The sine sweep frequency test method is used to identify the flexible control model of the system,and the experiments are carried out under various positions and different masses to study the time-varying dynamic characteristics of the system.The servo controller is designed for the rigid body control model.First,an adaptive sliding mode controller based on an extended state observer is proposed,the sliding mode control law is designed by using the state variables and external disturbances observed by the extended state observer to ensure the tracking accuracy and robustness for the disturbances of system.Second,the vibration compensation method is designed for the vibration suppression in the actual operation process.The P-PI controller with feedforward and active disturbance rejection control are designed.The simulation and contrast tracking experiments verify that the adaptive sliding mode controller based on the extended state observer has higher tracking precision and is more robust to the change of worktable quality and disturbances.A generalized extended state observer is designed for the system flexible control model.The parameter uncertainties,external disturbances and nonlinear dynamics of the system are regarded as the matched and mismatched perturbations.The system state variables and perturbations are observed by the generalized extended state observer,and a tracking controller designed based on the linear quadratic regulator theory is combined with the generalized extended state observer which can effectively compensate the perturbations of the system.In order to further increase the vibration suppression performance of the controller,a notch filter is designed.Finally,the effectiveness of the generalized extended state observer and the control method is verified by simulation and tracking experiments.Compared with the controller designed for the rigid body model,the controller designed for the flexible body model has a higher system bandwidth.In order to further improve the tracking precision of the feed system,based on the system flexible control model,and considering the matched and mismatched perturbations existing simultaneously,a integral sliding mode controller combined with generalized extended state observer is designd to compensate the matched and mismatched perturbations effectively,and a optimize design method for the coefficient matrix in integral sliding mode controlle law is proposed,which solves the complex characteristic of the parameter tuning with the traditional sliding mode control law.Simulation and tracking experiments show that this method can improve tracking accuracy and bandwidth when the system has parameter uncertainties,external disturbances and vibration.Considering the time-varying vibration mode of the ball screw drive system,a parallel structure controller is designed to achieve the control objectives.The controller consists of two parts: 1)the tracking controller is a linear quadratic regulator controller with a reference trajectory designed for the linear time-invariant(LTI)flexible control model,which is used to achieve precise tracking for the reference trajectory;2)the vibration suppression controller is interpolated with a series of local ?-synthesis controller,and each?-synthesis controller is used to suppress the flexible mode of the system in a certain load mass and table position.Then,based on the robust controller Youla parameterization,a gain-scheduling controller can be interpolated to effectively suppress the time-varying flexible mode of the system.The tracking experiments on a large stroke indicate that compared with the P-PI controller with feedforward and only using the tracking controller,the parallel structure controller has better vibration suppression characteristics and is more robust to the time-varying Characteristics and external disturbances of the system. |
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