Measuring and testing – Vibration – Sensing apparatus
Reexamination Certificate
1999-10-28
2001-10-16
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
Sensing apparatus
C356S484000, C356S519000
Reexamination Certificate
active
06301968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration measurement method and apparatus and in particular, to a vibration measurement method and apparatus capable of detecting a very small displacement, speed, and periodicity.
This vibration measurement method and apparatus can be applied to an experiment analysis such as an automobile production technology. More specifically, engine vibration analysis, body transmission and vibration analysis, analysis of noise in the cabin, and muffler vibration analysis. The present invention can also be applied to various other fields. Since the present invention can accurately measure a very small vibration with a non-contact state, it can be applied to an instrument damage such as a drill. Furthermore, the present invention can be applied to vibration of a plant using a motor, leak of a water pipe and a gas pipe. Furthermore, sweetness of a large size fruit such as watermelon can be checked according to the vibration caused by knocking. Here, the vibrating object to be measured includes a vast area from the engine to the watermelon.
2. Description of the Related Art
Conventionally, when measuring a vibration of an object to be measured, firstly, a laser beam oscillated from a laser resonator is applied through a lens to the surface of the vibrating object. The beam is scattered on the surface and a part of the scattered beam returns to the resonator and mixed with the oscillated beam, so that the Doppler speed component becomes a beat wave. By analyzing this beat wave, vibration periodicity, speed change, and displacement are calculated.
However, in the aforementioned conventional example, when a vibrating plane has displaced by half of the laser oscillation wavelength &lgr;, a chopping wave is generated. Accordingly, it is difficult to measure a displacement smaller than &lgr;/2 and the speed change.
Furthermore, in the conventional example, there is a problem that when the vibrating object displaces by a very small displacement, it is impossible to calculate vibration by replacing the Doppler frequency with a vibration plane moving speed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a vibration measurement method and apparatus capable of accurately measuring a vibration of a vibrating object independently of the displacement amount of the vibrating object.
The vibration measurement method according to the present invention comprises steps of: applying a laser beam of a first wavelength to an object to be measured; generating a beat wave from a laser beam of a second wavelength different from the first wavelength and a return beam reflected by the object to be measured; and outputting the generated beat wave as a vibration information of the object to be measured.
Here, the first wavelength and the second wavelength may not be fixed to certain values. For example, the first wavelength and the second wavelength may be successively changed while maintaining a constant difference between the first wavelength and the second wavelength. Moreover, it is also possible to successively change the difference between the first wavelength and the second wavelength.
Here, the laser beam of the first length is applied to an object to be measured, and while receiving a return beam from the object, a laser beam of the second length is applied, so as to generate a beat wave of a frequency according to this wavelength difference. The return beam from the object to be measured has a wavelength changed by the Doppler effect according to the object displacement speed. Accordingly, it is possible to obtain a waveform of the Doppler frequency Fd overlapped by the beat frequency caused by the wavelength difference. Consequently, if the beat wave Fb generated in the beat wave generation step is deleted by the beat frequency component Fa generated by the wavelength difference, it is possible to obtain the Doppler frequency caused by the object displacement speed. For example, if a frequency change of the beat wave of frequency Fb or the frequency change of the frequency Fb deleted by the affect of the frequency component Fa caused by the wavelength difference is converted into a voltage change, it is possible to obtain a speed change waveform of the object to be measured.
Moreover, it is possible to store as a reference beat wave, a beat wave generated by the beat wave generation step when the object to be measured is in a normal state, so that the reference beat wave can be used for inspection of the object. That is, if a beat wave generated by the beat wave generation step is different from the reference wave, it can be decided that the object has a defect. Thus, the vibration information output step outputs as vibration information a beat wave itself, the beat wave which has been subjected to a frequency-voltage conversion into a speed change waveform, the speed change waveform which has been integrated into a displacement data, the speed change waveform which has been subjected to a frequency analysis to generate a vibration frequency spectrum of the object to be measured, and the like.
In order to generate a frequency difference between an oscillated beam and a return beam, it is possible to modulate a drive current of the laser resonator. Moreover, it is also possible to vibrate the laser source itself so as to generate a frequency difference between the oscillated laser beam and the return beam. Furthermore, it is possible to use a surface acoustic wave element to change the wavelength of the laser beam applied to an object to be measured and receive a return beam reflected from the object, so as to obtain a wavelength difference between the oscillated beam and the return beam.
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Maruyama Tetsuro
Ohno Akiyoshi
McGinn & Gibb PLLC
Miller Rose M.
Suzuki Motor Corporation
Williams Hezron
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