5:00 PM - 5:15 PM
[SGD23-04] Performance evaluation of a test mass launch system including a reaction reduction mechanism for a rise-and-fall AG
Keywords:absolute gravimeter, launch system, reaction reduction mechanism, gravity, prediction of volcanic eruption, estimating a subsurface density structure
We adopt a rise-and-fall method to realize the downsizing of the absolute gravimeters. The measurement of gravity acceleration is based on the reconstruction of the orbit of the test mass thrown up or dropped in vacuum chamber. This method has some advantages. The simple free-fall method has several problems such as bulky mechanism to lift up the test mass, repeated measurements, and long time to take for the preparation. Hence, we developed the launch equipment that has no need for lifting up the test mass and can measure repeatedly. In addition the finite speed of light effect and drag effect are offset. As a result, systematic error becomes small. The equipment can throw up the test mass by 3mm in height simply by applying the signal to a piezoelectric element which is incorporated in the displacement enlarging mechanism. And the reaction reduction system is attached for the purpose of improvement of the measurement accuracy. When the test mass is thrown up, the floor recoil affects the interferometer and generates a systematic error. Specifically, we put the same piezoelectric element and the displacement enlarging mechanism on the other side of the baseplate to which the launch system is attached. These displacement enlarging mechanisms move symmetrically by applying the same signal to the piezos. When the test mass is thrown up, the counter mass fixed by springs is launched downwards at the same time to compensate the recoil effect. Moreover, to avoid the vibration occurrence by movement of displacement enlarging mechanism, we applied the signal of which acceleration is as continuous as possible. We could observe the reaction as much as 20% of peak acceleration without its mechanism. The result of gravity measurement in February and development status will be reported.