Research On Vibration Reduction Technology Of Absolute Gravimeter With Reference Prism

Vibration suppression of reference prism is an important way to solve the vibration interference problem of high precision absolute gravity measurement of free-falling body.Accurate measurement of the vibration signal of the reference prism of the absolute gravimeter is a solution to improve the measurement accuracy of the absolute gravimeter.In this regard,this paper analyzes the advantages and disadvantages of different methods according to different forms of absolute gravimeter measurement methods,including hardware vibration isolation technology and synchronous vibration measurement technology.A device is designed to measure the vibration acceleration of reference prism directly on the gravity acceleration measurement optical path.The relationship between the output signal of the pendulum vibration measuring sensor and the vibration quantity of the reference prism was studied from three different angles:mechanical swing ring,electromagnetic energy exchange and force balance feedback,and the corresponding transfer function was derived.The reference prism vibration measurement experimental device, electromagnetic transducer vibration measurement device and force balance feedback vibration measurement device were designed and the vibration measurement experiment was carried out.The amplitude-frequency characteristics of the ground vibration acceleration reflected by the output voltage of different experimental devices in the frequency band of 50 s～160 Hz were obtained by using the sinusoidal calibration method.The normalized transfer function of the output voltage reflecting the ground vibration acceleration was obtained by using the nonlinear fitting method.The method of measuring vibration of reference prism by electromagnetic transducer is discussed,and the influence of force balance feedback on vibration measurement and vibration damping performance of reference prism is analyzed.Experimental measurements show that the damping of the reference prism vibration measurement device system is 2.27,and the natural frequency of the mechanical pendulum is ω₀=3.73rad/s,that is,the natural vibration frequency f₀=0.59 Hz.Therefore,the experimental device exhibits vibration attenuation effect at a high frequency band higher than 0.59 Hz,and has damping effect.Compared with the vibration measurement experiment of electromagnetic transducer,the former shows the characteristics of low-pass filter and the latter shows the characteristics of high-pass filter.Compared with the force balance feedback vibration measurement experiment,the former has better suppression effect on the ground vibration and stronger vibration reduction effect,while the latter has stronger tracking effect on the ground vibration in the wide band and better gain stability.The gain G_amp=13042 is obtained through the shaking table experiment.On the basis of good coincidence between the laboratory measurement data and the theoretical data,the vibration experiment of the vertical vibration pendulum is carried out in the Beijing National Observatory.The results show that the two groups of experimental curves coincide with the amplitudefrequency characteristic curves drawn by the theoretical model formula,which verifies the reliability of the reference prism vibration measurement device in practice.The reference prism vibration measurement method proposed in this paper can not only directly obtain the vibration acceleration of the reference prism,but also compensate the measurement error caused by vibration interference of the absolute gravimeter through the algorithm,but also has certain vibration damping ability,and further attenuates the high-frequency vibration of the reference prism.