Study And Experimental Verification Of Stiffness Adjustment Method Of Split Type Vibration Isolator

Ultra precision equipment vibration isolation technology has been applied to many high-tech areas,represented by lithography IC manufacturing,represented by a variety of new super resolution microscopy system of ultra-precision measurement field,represented by numerical control machine tool field of ultra-precision machining precision vibration isolation system are needed to provide security equipment works smoothly.However,because the vibration of the environment is generally the vibration of low frequency and small amplitude,the vibration isolation system needs to have low natural frequency to effectively isolate the low frequency.However,the lower natural frequency will lead to the reduction of the system stiffness and the deterioration of the load capacity of the system.The use of positive and negative stiffness in parallel to form quasi-zero stiffness can effectively avoid the above problems,so that the system has both large static stiffness and low dynamic stiffness.In this paper,according to the performance index of split lithography machine vibration isolator,a kind of adjustable quasi-zero stiffness ultra-low frequency vibration isolator based on positive and negative stiffness in parallel is proposed and designed into a 6-DOF vibration isolation system.The control strategy of the vibration isolation system is designed and verified by experiments.The main research work is as follows:The static stiffness of the system is increased and the dynamic stiffness is reduced by the parallel parallel method of positive stiffness and negative stiffness.A parallel structure of air spring and magnetic negative stiffness unit is designed to change the stiffness in the vertical direction.The structure of the inverted pendulum and the structure of the parallel spring are designed to adjust the horizontal stiffness.Finally,the whole vibration isolator is designed in detail.The stiffness of the vibration isolator is calculated theoretically,and the adjustment range of horizontal stiffness and vertical stiffness is analyzed respectively,which lays a foundation for the subsequent control.Then the six free dynamics model of vibration isolation system is established according to the calculated stiffness of each mechanism.In order to improve the control accuracy,the independent control mode was subsequently selected.Therefore,the six modes of the vibration isolation system were decoupled to obtain six independent equations of motion.The transformation matrix of the sensor from the physical axis to the logical axis and the actuator from the logical axis to the physical axis are established for the vibration isolation system.A control strategy of position PID control,absolute speed feedback and ground speed feedforward is proposed.The difference between relative velocity feedback and absolute velocity feedback is compared to explain the reason of increasing ground velocity feedforward after choosing absolute velocity feedback.The absolute speed sensor has the function of spread spectrum and filter so that it can meet the performance requirements of the experiment at the frequency of0.3Hz-1KHz.The output energy of the actuators of the voice-coil motor is tested,which is almost the same as the simulation results.Finally,an experimental platform was built for testing.Firstly,the stiffness adjustment test was carried out,which could meet the performance requirements under different loads.Then the vibration isolation performance of the vibration isolation system was tested,and the transfer function of the vibration isolation system was measured under the condition of no active control.The passive vibration isolation performance was tested again with the addition of active control.The transfer function from ground to load was measured.