An Ultra-Low-Frequency Active Vertical Vibration Isolator With Horizontal Constraints for Absolute Gravimetry

Absolute gravimeters have been widely used as an important instrument in geological exploration and geophysics. To achieve a required measurement precision, it is necessary to integrate a vertical vibration isolator with ultra-low resonance frequency into the gravimeter. In this paper, an active vibration isolator designed on the basis of a BM-10 passive vibration isolation platform is presented. In the isolator, a seismometer placed next to the payload on the same plate outputs a voltage signal proportional to the payload’s velocity. According to this signal, a feedback circuit based on a PID controller controls two identical voice coil actuators to drive the platform synchronously. In this way, the vibration of the payload is suppressed. The BM-10 platform has 6-DOF passive vibration isolation originally, but its horizontal vibration isolation is proved unnecessary or even harmful in absolute gravimetry. Hence, two linear bushings are applied as a horizontal constraint to ensure that the payload only moves vertically in a straight line. Experiments show the resonance period of the isolator reaches approximately 88 s. In addition, the active vibration isolator has shown a much better performance for vibrations at low frequency than the passive isolator. In the future, the vibration isolator will be improved and then be integrated in the NIM-AGRb-1 atom-interferometry absolute gravimeter for the evaluation of its performance.