Ultra-low-frequency vertical vibration isolator based on a two-stage beam structure for absolute gravimetry

To reduce seismic and environmental vibration noise, ultra-low-frequency verticalvibration isolation systems play an important role in absolute gravimetry. For this purpose, an isolator based on a two-stage beam structure is proposed and demonstrated. The isolator has a simpler and more robust structure than the present ultra-low-frequency vertical activevibration isolators. In the system, two beams are connected to a frame using flexural pivots. The upper beam is suspended from the frame with a normal hex spring and the lower beam is suspended from the upper one using a zero-length spring. The pivot of the upper beam is not vertically above the pivot of the lower beam. With this special design, the attachment points of the zero-length spring to the beams can be moved to adjust the effective stiffness. A photoelectricdetector is used todetect the angle between the two beams, and a voice coil actuator attached to the upper beam is controlled by a feedback circuit to keep the angle at a fixed value. The system can achieve a natural period of 100 s by carefully moving the attachment points of the zero-length spring to the beams and tuning the feedback parameters. The system has been used as an inertial reference in the T-1 absolute gravimeter. The experiment results demonstrate that the system has significantvibration isolation performance that holds promise in applications such as absolute gravimeters.

Source: Review of Scientific Instruments - October 3, 2016 Category: Physics Authors: G. Wang, K. Wu, H. Hu, G. Li and L. J. Wang Source Type: research