Active Negative Stiffness Micro-vibration Isolation Technology With Infinite Stiffness And Zero Stiffness Composite

Active micro-vibration isolation technology with excellent low-frequency performance has been one of the core technologies to suppress micro-vibration within the lithography.The micro-vibration directly affects the positioning accuracy of the ultra-precision motion platform in the lithography machine and the stability of the metrology frame,and finally restricts the improvement of the critical dimension and the alignment precision.Two types of disturbance sources that cause micro-vibrations are base vibration and direct disturbance.The traditional micro-vibration isolation technique based on zero-stiffness principle can effectively isolate the base vibration,but it will weaken the system's resistance to direct disturbance.Therefore,when the effects of base vibration and direct disturbance are in the same magnitude order,the traditional method must weigh the influence of the two,and thus cannot effectively suppress the micro-vibration inside the lithography machine.The base vibration isolation and direct disturbance suppression are difficult to balance,and this problem has become the main technical bottlenecks to improve the performance of active micro-vibration isolation in the lithography machine.Purpose of this paper is to balance the base vibration isolation and the direct disturbance suppression in the micro-vibration isolation of lithography machine.Firstly,we propose an optimization method of feedback quantity configuration based on the disturbance rms response to obtain the optimal configuration of feedback quantity and the optimal value of feedback coefficient.Secondly,we propose an active negative stiffness micro-vibration isolation method with infinite stiffness and zero stiffness composite to balance the base vibration isolation and direct disturbance suppression.Thirdly,a disturbance self-sensing method for the actuator applied in force feedback active microvibration isolation is proposed,which directly measures and compensates the disturbance force in real time to suppress the direct disturbance.The main contents and results of this thesis are as follows:Aiming at the optimization problem of feedback quantity allocation for multi-factor disturbance,an optimization method of feedback quantity allocation based on disturbance rms response is proposed.The performance of vibration isolation with the single or combination of the direct feedback quantities is analyzed in SDOF active vibration isolation model.In this method,the disturbance rms response is used as a single index to evaluate the vibration level.And the functional relationship is built up to quantitatively analyze the effect of the feedback quantity allocation and each disturbance on the vibration.In the relationship,the feedback coefficients and the disturbances PSD are used as the independent variables,and the disturbances rms response are used as dependent variables.The optimal allocation of feedback quantities and the optimal value of feedback coefficients are determined by this method,and the influences of the base vibration and direct disturbance are also clarified by this method.Aiming at the problem that base vibration isolation and direct disturbance suppression are difficult to balance,an active negative stiffness isolation method with infinite stiffness and zero stiffness composite is proposed in this thesis.This method realizes the infinite stiffness and zero stiffness composite control by the absolute displacement feedback.In this method,the equivalent stiffness between the isolated device and the reference point or the base is infinite or zero respectively,which means the isolated device rigidly connected with the reference point and completely isolated from the base.The results show that the method can effectively reduce the vibration of the isolated device.Aiming at the problem that the disturbance force measurement of the flexible device is not accurate,a disturbance self-sensing method for active micro-vibration isolation actuator for force feedback is proposed.The method can directly measure and compensate the disturbance force by the actuator.Uniformity of the magnetic field distribution is improved by optimizing the drive coil structure of the actuator.Self-sensing circuit with active Kelvin bridge is designed to realize the linear extraction of self-sensing voltage.The results show that the method can realize the disturbance force self-sensing.Finally,the experimental platform is created,and the theoretical method and simulation results presented in this paper are experimentally verified.The results show that the error between the vibration velocity rms value computed by the root mean square response method and the measured value is less than 7.7%,and the feasibility of the method is verified.Under the random excitation condition,the vibration velocity rms of the vibration isolation device is 21.7% lower than that of the passive condition,and 8.4% lower than the zero stiffness principle.The self-sensing sensitivity coefficient of the actuator is better than 2.0 mV·s/N.Self-sensing of the disturbance force is realized.