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 vertical vibration 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 active vibration 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 photoelectric detector is used to detect 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 significant vibration isolation performance that holds promise in applications such as absolute gravimeters.
Department of Precision Instruments, Tsinghua University, Beijing 100084, China.
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G
Wang
Department of Precision Instruments, Tsinghua University, Beijing 100084, China.
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Wu
Department of Precision Instruments, Tsinghua University, Beijing 100084, China.
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Hu
Department of Precision Instruments, Tsinghua University, Beijing 100084, China.
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G
Li
Department of Precision Instruments, Tsinghua University, Beijing 100084, China.
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Wang