Measuring and testing – Vibration – Sensing apparatus
Reexamination Certificate
1999-05-21
2001-05-01
Kwok, Helen C. (Department: 2856)
Measuring and testing
Vibration
Sensing apparatus
C310S321000
Reexamination Certificate
active
06223601
ABSTRACT:
BACKGROUND OF THE INVENTION
Vibration sensors of a resonator array type have been proposed in which: a plurality of resonators having different lengths (that is, different resonant frequencies) are arranged in the form of an array, and allowed to resonate selectively in response to a vibration wave such as a sound wave with specific frequencies for the respective resonators, and the resonance levels of the respective resonators are converted to electric signals so that intensities of the vibration wave for respective frequency bands are detected. (For example, W. Benecke et al., “A Frequency-Selective, Piezoresistive Silicon Vibration Sensor, Digest of Technical Papers of TRANSDUCERS” 85, pp. 105-108 (1985), or E. Peeters et al., “Vibration Signature Analysis Sensors for Predictive Diagnostics,” Proceedings of SPIE '97, vol. 3224, pp-220-230 (1997)).
BRIEF SUMMARY OF THE INVENTION
In a conventional vibration sensor, a piezoresistor is formed at the base of a resonator, and changes in the resistance value of the piezoresistor, which occur due to vibrations (resonance) of the resonator, are detected by a Wheatstone bridge, etc. so that an electric output signal is taken out of the resonator. In particular, in the sensor disclosed in the latter document, the output signal is obtained while the Wheatstone bridge output from each resonator is being switched by a multiplexer.
In the vibration sensor of this type, there is a demand for controlling the gain (detection sensitivity) of a specific frequency band of an inputted vibration wave. In a conventional vibration sensor, in order to obtain such a detection sensitivity controlling function, it is necessary to provide a circuit construction which can subject the electric output signal obtained from each resonator to an amplifying process or a damping process at a succeeding step. This results in a problem of a large circuit scale as a whole.
When a resonator is supported as a cantilever beam, a strain in the resonator is the greatest at the foot thereof, and decreases toward the tip thereof. In the case when a piezoresistor is formed at the foot of each resonator at which the strain is the greatest, since the length of each resonator is different, the magnitude of strain at the foot of each resonator is different even if the amplitude at the tip of each resonator is the same. This is because even if the amplitude is the same, a shorter resonator has a greater strain, while a longer resonator has a smaller strain. The resulting problem is that even if the tip vibrates with the same amplitude, the level of an electric output signal differs depending on each of the resonators.
In accordance with the present invention, a detector such as a piezoresistor, installed in each of the resonators, is adjusted in its position so that it is possible to provide a vibration wave detecting method and a vibration wave detector which achieve a detection sensitivity controlling function by using a simple circuit construction.
Moreover, in accordance with the present invention, a detector such as a piezoresistor, installed in each of the resonators, is adjusted in its position so that it is possible to provide a vibration wave detecting method and a vibration wave detector which can easily make the levels of electric output signals in the resonators equal to each other.
Referring to one example of the present invention, the following description will briefly discuss the principle of the present invention. In the present invention, a plurality of resonators having respectively different resonant frequencies are arranged in the form of an array. In response to an inputted vibration wave, the respective resonators selectively react with resonant frequencies that the resonators own, and the intensities of respective frequency components in the vibration wave are detected as electric output signals by using piezoresistors installed in the respective resonators. In this case, taking it into account that the magnitude of a strain is different depending on portions of each resonator (in the case of a cantilevered resonator, greater on the foot and smaller at the tip thereof), the installation position of the piezoresistor is adjusted for each resonator in order to obtain an output signal having a desired level from the piezoresistor. In this manner, by adjusting the installation position of the piezoresistor in each resonator, it becomes possible to set a detection gain for each resonator. Moreover, this arrangement makes it possible to freely control the output gain of each resonator easily without the need for installing an amplifier at the succeeding step; thus, it becomes possible to obtain a desired frequency characteristic, and to realize a vibration wave sensor having a detection sensitivity controlling function by using a simpler arrangement as compared with a conventional sensor. Furthermore, it is possible to make the levels of electric output signals at the respective resonators equal to each other by adjusting the installation position of the piezoresistor in each of the resonators.
As described above, in accordance with the distribution of the sizes of strains in the respective resonators, the installation position of the piezoresistor in each of the resonators is adjusted so as to realize a detection sensitivity controlling function. Moreover, when each piezoresistor is installed at a position where the magnitudes of strains in the respective resonators are equal to each other, it becomes possible to obtain a flat frequency characteristic by making the levels of electric output signals of the respective resonators equal to each other.
Here, the piezoresistors of the respective resonators are parallel-connected and a voltage is applied to one end of the parallel circuit so as to take out the sum of the electric outputs of the respective resonators from the other end of the parallel circuit; thus, it is possible to simplify line connections.
Moreover, when a sound wave is used as the vibration wave to be detected, it is possible to realize an acoustic sensor having a detection sensitivity controlling function.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
REFERENCES:
patent: 5856722 (1999-01-01), Haronian et al.
patent: 6012334 (2000-01-01), Ando et al.
patent: 6079274 (2000-06-01), Ando et al.
W. Benecke et al. “A Frequency-Selective, Piezoresistive Silicon Vibration Sensor” Digest of Technical Papers of Transducers, pp. 105-108, 1985.
E. Peeters et al. “Vibration Signature Analysis Sensors for Predictive Diagnostics” Proceedings of SPIE, vol. 3224, pp. 220-230, 1997.
Harada Muneo
Ikeuchi Naoki
Barnes & Thornburg
Kwok Helen C.
Sumitomo Metal Industries Limited
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