Model Analysis And Experimental Study Of Absolute Gravity Instrument Vibration Isolation Platform

The absolute gravimeter isolation platform provide a reference point for measuring the freefall displacement using laser interferometry in absolute gravimeter. Its main task is to eliminate or suppress the effects of micro-vibration on measurement reference point. And the precision of isolation platform directly affects measurement accuracy in absolute gravity meter.By using cycle method, bartlatt law, the maximum entropy method, and the feature vector method, analyzing the power spectrum of micro-vibration signal collected through the ultra-broadband seismometer (CTS-1F1201) shows that the high frequency energy of micro-vibration is concentrated in the band from5Hz to20Hz, and low frequency energy from0.1Hz to0.4Hz, which provides a important technical indicator for the design of absolute gravimeter isolation platform. Passive vibration isolation technology can only suppress the high-frequency interference well, except the low frequency interference due to its own disadvantage. Currently, since the external energy and feedback control technology is used in the active isolation system, the active isolation system can achieve better isolation effect in a relatively wide band range, as well in the low frequency band. For absolute gravimeter isolation platform, this article begins from the kinetic equation of passive single-stage, two-stage isolation system and active single-stage, two-stage isolation system respectively, builds a mathematical model, simulates and analyzes the effect of system parameters on the performance of isolation system. The influence of damping and natural angular frequency on the isolation system performance is analyzed for passive isolation system, while the effect of displacement, velocity feedback and acceleration feedback is discussed for active isolation system. And the results shows that good isolation has been achieved during the0.1Hz-20Hz band by using active isolation technology.In addition, the paper designs the hardware for the control system of isolation platform, and introduces the working principle and design ideas of high-precision capacitive displacement sensor. The minimum application system is based S3C2440microprocessor. And the electromagnetic actuator, which is composed of compensation coil and magnetic cylinder, is also designed based on the principle that current-carrying conductor in a magnetic field will be forced (Ampere force). Meanwhile, the paper introduces and improves the traditional PID algorithm for the actual problems, then applies to active isolation system. And the desired effect is achieved through simulation.Finally, the experiment and the carried-out experimental results are described.