Patent ID: 8677828
Filing Date: 2014-03-25
Classification: G01H

Abstract:
1. A vibration detecting device detecting a period of vibration of an object and an external force, comprising: a piezoelectric plate; a first excitation electrode and a second excitation electrode provided on one surface and another surface of the piezoelectric plate respectively to vibrate the piezoelectric plate; an oscillator circuit electrically connected to the first excitation electrode; a plate-shaped member provided in a vessel and having one end supported in a cantilever manner; a movable electrode for variable capacitance formation provided at another end of the plate-shaped member and electrically connected to the is second excitation electrode; a fixed electrode provided in the vessel to face the movable electrode, connected to the oscillator circuit, and forming variable capacitance when capacitance between the fixed electrode and the movable electrode is varied due to bending of the plate-shaped member; and a frequency information detecting part detecting a signal being frequency information corresponding to an oscillation frequency of the oscillator circuit, wherein an oscillation loop is formed from the oscillator circuit back to the oscillator circuit through the first excitation electrode, the second excitation electrode, the movable electrode, and the fixed electrode, and wherein vibration of the vessel produces a first state where the plate-shaped member bends toward the fixed electrode to approach the fixed electrode and a second state where the plate-shaped member is more apart from the fixed electrode than in the first state, and the frequency information is used for finding a period of the vibration by utilizing a fact that an oscillation frequency corresponding to the first state and an oscillation frequency corresponding to the second state alternately appear.