Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-08-12
2001-05-22
Moller, Richard A. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S660000
Reexamination Certificate
active
06234022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bearing rigidity evaluation apparatus for evaluating bearing rigidity of a bearing such as a double row bearing, a duplex bearing, or the like, to which a preload is applied.
2. Description of the Related Art
Heretofore, a double row bearing or a duplex bearing to which a preload is applied needs to have high rigidity in terms of performance of a machine equipped with the bearing. However, if the amount of the preload increases so that rigidity becomes too high, the excessive preload causes lowering of bearing performance (such as increase of frictional moment, abnormal heating, fatigue life, and so on). Accordingly, the value of bearing rigidity needs to be controlled in a predetermined range while being related to the amount of the preload.
The following apparatus is known as an apparatus for measuring the value of rigidity of a bearing. Japanese Patent Unexamined Publication No. Hei.5-10835 discloses a method in which a vibration signal generated from a rotating bearing is subjected to frequency analysis to thereby obtain both a contact angle of a rolling body and a resonance frequency of the bearing so as to obtain both the bearing rigidity and the amount of preload on the basis of the contact angle and the resonance frequency. Further, Japanese Patent Examined Publication No. Hei.2-61700 discloses a method in which vibrations given to a bearing box or a shaft by a vibrating machine is detected by a velocity or acceleration sensor and amplified by an amplifier, and an output signal of the amplifier is analyzed by a frequency analyzer to detect a resonance frequency of a bearing. The relation between the detected resonance frequency and the amount of preload is obtained in advance by calculation such as a finite-element method, or the like, so that the amount of preload can be detected on the basis of the resonance frequency.
Both the methods described in Japanese Patent Examined Publication No. Hei.2-61700 and Japanese Patent Unexamined Publication No.5-10835, however, utilize resonance. Accordingly, in the case where the value of rigidity of a duplex bearing is to be measured, when the rigidity of the bearing is relatively low, there is no problem. On the other hand, the rigidity of the bearing is high, a vibration mode due to the bearing as a structural body and a vibration mode due to a bearing spring are coupled with each other, so that it is difficult to detect rigidity caused by the bearing spring.
Further, even in the case of a bearing as a single body, the same problem as described above arises in accordance with local vibration modes of a low-rigidity portion-including bearing such as a flanged bearing and elastic vibration modes of inner and outer races. Accordingly, in a bearing requiring high rigidity, bearing rigidity is hardly detected on the basis of the resonance frequency by use of a vibration model having inner and outer races as mass points as described in Japanese Patent Unexamined Publication No. Hei.5-10835. Further, when external vibrations in a measurement frequency band are detected, S/N ratio with respect to the external vibrations also becomes a subject of discussion.
SUMMARY OF THE INVENTION
In view of the aforementioned problem, it is an object of the present invention to provide a bearing rigidity evaluation apparatus in which bearing rigidity of a bearing to which a preload is applied can be obtained accurately.
To attain the above object, there is provided a bearing rigidity evaluation apparatus for evaluating bearing rigidity of a bearing such as a double row bearing, a duplex bearing, or the like, to which a preload is applied, comprising: a vibrating machine for giving vibrations with a predetermined frequency axially to an inner race of the bearing or to a shaft fitted to the inner race; at least one pair of outer race vibration detecting means respectively provided in positions symmetrical to each other with respect to a point of center of the bearing for detecting vibrations of an outer race of the bearing; an inner race vibration detecting means for detecting vibrations in an axial center position of either one of the inner race and the shaft fitted to the inner race; an addition means for adding output signals of the at least one pair of outer race vibration detecting means; a transfer function computing unit for calculating a resonance frequency (natural frequency) of the bearing by obtaining a transfer function between the outer race and either one of the inner race and the shaft to thereby eliminate an in-phase component signal contained in an output signal of the inner race vibration detecting means and an output signal of the addition means; and a rigidity transformation computing unit for obtaining the bearing rigidity on the basis of the resonance frequency (natural frequency) calculated by the transfer function computing unit.
In the above bearing rigidity evaluation apparatus, vibrations having a predetermined frequency are given axially to an inner race of the bearing or to a shaft fitted to the inner race to thereby excite the bearing to vibrate. Vibration modes of the excited bearing include: a vibration mode caused by a bearing spring in a frequency band of a vibrating force (a vibration mode in an axial direction of the bearing); an elastic bending mode of the outer race coupled with the vibration mode caused by the bearing spring; a vibration mode uncoupled with the vibration mode caused by the bearing spring; and external vibrations mixed from the outside. Vibrations of the excited bearing are detected by the inner race vibration detecting means and the outer race vibration detecting means. In this occasion, when vibrations detected by at least one pair of outer race vibration detecting means are added up in time sequence by an adding means, conical vibration components are erased. The vibration mode uncoupled with the bearing spring and the external vibrations mixed with the detection system are detected as components of the same phase and the same amplitude in the inner and outer races. Accordingly, when a transfer function between the inner and outer races is obtained on the basis of vibrations of the outer race after erasing of the conical vibration components and vibrations of the inner race or of the shaft fitted to the inner race, which are detected by the inner race vibration detecting means, in-phase components (the uncoupled vibration mode or the external vibrations mixed with detecting system) contained in the respective vibrations are erased so that a resonance frequency (natural frequency) of the bearing is obtained. Further, bearing rigidity is obtained on the basis of the calculated resonance frequency (natural frequency). Accordingly, bearing rigidity of a bearing to which a preload is applied can be obtained accurately.
Preferably, configuration is made so that a transfer function is obtained after low-frequency components contained in vibrations detected by the inner race vibration detecting means and in vibrations added up by the adding means, respectively, are removed by filter means. By this configuration, vibration components as a cause of noise are removed, so that S/N ratio can be improved.
Preferably, configuration is made so that a preload applied to the bearing is calculated on the basis of both the obtained bearing rigidity and a contact angle of the bearing. By this configuration, the preload applied to the bearing can be obtained accurately, so that quality assurance accuracy with respect to the amount of preload applied to the bearing can be improved.
REFERENCES:
patent: 5109700 (1992-05-01), Hicho
patent: 5263372 (1993-11-01), Matsuzaki et al.
patent: 5477730 (1995-12-01), Carter
patent: 5517858 (1996-05-01), Matsuzaki et al.
patent: 5533400 (1996-07-01), Gasch et al.
patent: 5618993 (1997-04-01), Matsumoto et al.
patent: 5686669 (1997-11-01), Hernandez et al.
patent: 2-61700 (1990-12-01), None
patent: 5-10835 (1993-01-01), None
patent: 10-96672 (1998-04-01), None
Moller Richard A.
NSK Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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