| In the field of ultra-precision instruments and equipment, large air spring micro vibration isolation slab is the core equipment. In order to isolate the environmental vibration, vibration isolation slab needs to combine lower natural frequency and larger damping ratio. The most common solution is to use the passive vibration isolation system which is composed of air spring and additional damping device. But as the ground micro vibration frequency is close to the natural frequency of air spring vibration isolation system, and the damping force of passive damping device is very limited by interfering with the ground vibration, passive vibration isolation does not apply to the ground micro vibration isolation. Therefore, how to further reduce the natural frequency while meeting the requirements of large load, and how to further increase the system damping ratio by interfering with the ground vibration are leading studies in the field of micro vibration isolation for large precision instruments and equipment.According to the problems above mentioned, this paper presents a micro vibration isolation method for large precision instruments and equipment based on the lorentz force actuator which is controled by active negative stiffness control method. The active negative stiffness vibration isolation device based on active negative stiffness control method which is paralleled with the air spring can further reduce the natural frequency of the vibration isolation system. A micro vibration isolation method for large precision instruments and equipment based on the lorentz force actuator which is controled by active damping control method is proposed. This method can further improve the system damping characteristics. Theoretical studies and experimental results were proceeded on above aspects in this thesis, and the main investigation work and achievements are described as follows:1. In order to solve the problem that it is difficult to reduce the natural frequency of large vibration isolation slab by passive control method, a micro vibration isolation method for large precision instruments and equipment based on the lorentz force actuator which is controled by active negative stiffness control method is proposed. First, the lorentz force actuator can be equivalent to negative stiffness elastic element by an active control method by analysing the characteristics of force and displacement. Then, a positive and negative stiffness parallel single degree of freedom model is established by analysing the relationship between the elastic stiffness and the stability of the system. The stiffness of independent degrees of freedom must be greater than zero. The vibration transmissibility is derived and simulated. It confirmed the result that the method can effectively reduce the natural frequency of the system and expand vibration attenuation band.2. In order to solve the problem that the passive damping device is difficult to effectively isolate ground micro vibration, a micro vibration isolation method for large precision instruments and equipment based on the lorentz force actuator which is controled by active damping control method is proposed. First, the lorentz force actuator can be equivalent to an active damper by control the output force of lorentz force actuator which is inversely proportional to the velocity of the load. Then, an active damping and passive damping parallel single degree of freedom model based on active damping control method is established by analysing the passive damping characteristics of the air spring vibration isolation system. The vibration transmissibility and damping ratio are simulated. It confirmed the result that the method can further increase the system damping ratio. Finally, the the lorentz force of the actuator output force is optimized by LQR method.3. Due to the problem that vibration coupling between different degrees of freedom is not conducive to the application of active negative stiffness control method and active damping control method, six degrees of freedom vibration model of large air spring vibration isolation slab was established, and the model is simplified. Coupling natural frequencies and coupling degree of the model are derived and simulated. An active decoupling method is used to decouple the freedom degrees of translational and rotational. Active decoupling control model of large air spring vibration isolation slab is derived and simulated. The results show that the active decoupling method can effectively reduce the coupling degree of the system. And the active decoupling method provides the basis for the active negative stiffness control method and active damping control method to applied to the large air spring vibration isolation slab.4. The active control methods and simulation results which are presented in this paper are verified by experiments. On the large air spring vibration isolation slab, impulse response experiment is conducted and analyzed in three axial of the slab respectively by passive control method and active negative stiffness control method. Experimental results show that the natural frequency of vibration isolation slab in short axis direction, long axis direction and vertical direction by passive control method is 0.53 Hz, 0.50 Hz and 0.66 Hz. By active negative stiffness control method, it is 0.47 Hz, 0.47 Hz and 0.59 Hz in short axis direction, long axis direction and vertical direction. It confirmed the result that the active negative stiffness control method can effectively reduce the natural frequency of the system. On the large air spring vibration isolation slab, impulse response experiment is conducted and the damping ratio is analyzed in three axial of the slab respectively by passive control method and active damping control method. Experimental results show that damping ratio in short axis direction, long axis direction and vertical direction by passive control method is 13.76%, 14.32% and 14.10%. By active damping control method, it is 14.38%, 15.74% and 15.50% in short axis direction, long axis direction and vertical direction. It confirmed the result that the active damping control method can effectively increase the damping ratio of the system. Finally, ground random vibration response experiment is conducted in three axial of the slab by active negative stiffness control method and active damping control method. In accordance with international general evaluation methods, the result by passive control method is compared with the result by active negative stiffness control method and active damping control method. Experimental results show that the vibration velocity in short axis direction, long axis direction and vertical direction by passive control method is 4.07μm/s, 4.28μm/s and 3.69μm/s. By active damping control method, it is 2.84μm/s, 2.39μm/s and 1.85μm/s. It confirmed the result that active negative stiffness control method and active damping control method can effectively reduce the vibration velocity of the large air spring vibration isolation slab. |
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