Stress wave sensor

Details Stress wave sensor Stress wave sensor

2000-08-11

2004-02-03

Williams, Hezron (Department: 2856)

Measuring and testing

Vibration

Resonance, frequency, or amplitude study

C073S582000, C073S599000, C702S056000

Reexamination Certificate

active

06684700

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally directed to sensors and particularly to sensors used in stress wave analysis.
2. Description of Related Art
Stress wave analysis is an ultrasonic instrumentation technique which is used for measurement of friction and shock in mechanical devices. Stress waves are in the form of high frequency structure borne sounds caused by friction between moving parts. The analysis of the stress waves involves the detection and amplification of the high frequency sounds. In addition to the high frequency sounds, other noises and vibration signals are also present, which are not directly related to the stress waves. However, these other signals can interfere with proper analysis of any stress waves emitted by a mechanical device and should be eliminated.
Past attempts at stress wave analysis have incorporated specially selected piezoelectric accelerometers as stress wave sensors. However, these transducers are not specifically designed to detect stress waves, and suffer important shortcomings relative to Analog Signal. Conditioning (“ASC”) and Digital Signal Processing (“DSP”) elements of stress wave analysis instrumentation, such as those shown in FIG.
1
.
An accelerometer, when used as a stress wave sensor, is often selected to have maximum repeatability of its primary resonant frequency between 30 Khz and 40 Khz, and its sensitivity at the primary resonant frequency. When secondary resonances are also present in the sensor's frequency response, they are often very difficult, if not impossible, to eliminate or control, with the same precision as the primary resonance as shown in FIG.
2
. Efforts to adjust or control these secondary resonances may also cause unintended and undesirable changes in the sensitivity of the primary resonance.
Accordingly, what is needed in the art is a sensor having characteristics that receives stress wave signals while discarding background noises and vibrations. It is therefore to the effective resolution of the shortcomings of the prior art that the present invention is directed.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a sensor having characteristics designed specifically for detecting stress waves for use in a stress wave analysis system. In order to eliminate vibration, audible noise and acoustic emission sources that are not directly related to friction and mechanical impact events in operating machinery, it is preferred, to detect stress waves in a narrow frequency range, such as, but not limited to, 35 Khz to 40 KHz. At this frequency range, stress waves from friction and impact sources typically propagate through machine structures at detectable amplitudes. Thus, in order to maximize the signal to noise ratio of stress waves, relative to background noise and vibration, the sensor of the present invention is designed and calibrated with a frequency response and damping characteristics that are specifically tailored for stress wave analysis.
The sensor of the present invention preferably satisfies the following three criteria:
(a) has a resonant gain of approximately 30 db, at its primary resonant frequency, to assure adequate selective amplification of stress waves;
(b) provide a total energy content of the Resonant Energy Integral within a specified tolerance band (i.e. +/−10% of a standard value) and which can be measurable using standard test equipment and fixtures to produce calibration data that is traceable to recognized standards; and
(c) have its resonant output decay to half amplitude in five cycles or less, and be down to no more than twenty (20%) percent of the initial response in the number of cycles that correspond to the corner frequency of the band pass filter.
Accordingly, it is an object of the present invention to provide a sensor having a frequency response and damping characteristics specifically designed for stress wave analysis.


REFERENCES:
patent: 3554012 (1971-01-01), Sohoel
patent: 3842663 (1974-10-01), Harting et al.
patent: 3924456 (1975-12-01), Vahaviolos
patent: 4207771 (1980-06-01), Carlos et al.
patent: 4429578 (1984-02-01), Darrel et al.
patent: 4530240 (1985-07-01), Board et al.
patent: 5004985 (1991-04-01), Holroyd et al.
patent: 5005142 (1991-04-01), Lipchak et al.
patent: 5043736 (1991-08-01), Darnell et al.
patent: 5101162 (1992-03-01), Webster et al.
patent: 5115671 (1992-05-01), Hicho
patent: 5210704 (1993-05-01), Husseiny
patent: 5239468 (1993-08-01), Sewersky et al.
patent: 5309379 (1994-05-01), Rawlings et al.
patent: 5333240 (1994-07-01), Matsumoto et al.
patent: 5365787 (1994-11-01), Hernandez et al.
patent: RE34975 (1995-06-01), Orban et al.
patent: 5566092 (1996-10-01), Wang et al.
patent: 5581016 (1996-12-01), Gonzalez et al.
patent: 5602761 (1997-02-01), Spoerre et al.
patent: 5608845 (1997-03-01), Ohtsuka et al.
patent: 5659136 (1997-08-01), Koch et al.
patent: 5734087 (1998-03-01), Yamashita
patent: 5852793 (1998-12-01), Board et al.
patent: 5875420 (1999-02-01), Piety et al.
patent: 5952587 (1999-09-01), Rhodes et al.
patent: 6076405 (2000-06-01), Schoess
Xu et al., “An ANS Based Helicopter Transmission Diagnostic System,” IEEE, 8/97.
Yen, “Health Monitoring of Vibration Signatures,” IEEE, date unknown—(Since date unknown cited in an abundance of caution).
Yen et al., “Health Monitoring of Vibration Signatures in Rotorcraft Wings,” IEEE, date unknown—(Since date unknown cited in an abundance of caution).
Marciano et al., “Mechanical System Condition Monitor (MSCM) System Design,” IEEE, 8/90.

Affiliated with

Also associated with

Rating

Stress wave sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Stress wave sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Stress wave sensor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3318652