Method and apparatus for measuring change in state of object to be measured using flexural and torsional vibrations

• US 5,777,228 A
• Filed: 02/25/1997
• Issued: 07/07/1998
• Est. Priority Date: 05/11/1995
• Status: Expired due to Fees

• Current Assignee: All Nippon Airways Co., Ltd., Iwatsu Electric Company Limited
• Original Assignee: All Nippon Airways Co., Ltd., Iwatsu Electric Company Limited
• Inventors: Yamamoto, Shigeharu, Tsuboi, Kiyoshi
• Primary Examiner(s): Oda, Christine K.
• Application Number:
  US08/805,299
• Time in Patent Office: 497 Days
• Field of Search: 364/506, 364/507, 364/512, 364/563, 73/579, 73/583, 73/602
• US Class Current: 73/579
• CPC Class Codes: G01N 2291/269 Various geometry objects
• CPC Class Codes: G01N 2291/2693 Rotor or turbine parts
• CPC Class Codes: G01N 29/12 by measuring frequency or resonance of acoustic waves measuring frequency or resonant frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04, G01H13/00; acoustic resonators G10K11/04; vibration or shock testing of structures G01M7/00
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01N 29/38 by time filtering, e.g. using time gates
• CPC Class Codes: G01N 29/42 by frequency filtering or by tuning to resonant frequency
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14

Abstract

A method and apparatus for detecting a change in the state of a part of an object to be measured that has a section having a first plate part and a second plate part which has a plate surface opposite to a plate surface of the first plate part with a gap between the plate surfaces and is integral with the first plate part or is connected to the first plate part. The method includes, and the apparatus has device for, applying vibrations to the object to be measured at a site at the section to generate flexural, torsional and stationary vibration waves in the object, subjecting the stationary vibration waves generated in the object to be measured to a spectral analysis, calculating the frequency difference of spectra divided into two by high order torsional vibrations generated at the section out of the group of spectra by the stationary vibration waves, and detecting a change in thickness between the first plate part and the second plate part or a defect formed in the first plate part or the second plate part based on the calculated frequency difference.

Claims

1. A method of detecting a change in the state of a part of an object to be measured that has a section comprising a first plate part and a second plate part which has a plate surface opposite to a plate surface of said first plate part with a gap between said plate surfaces and is integral with said first plate part or is connected to said first plate part, comprising the steps of

applying vibrations to said object to be measured at a site at said section to generate flexural, torsional and stationary vibration waves in said object,

subjecting the stationary vibration waves generated in said object to be measured to a spectral analysis,

calculating the frequency difference of spectra divided into two by high order torsional vibrations generated at said section out of the group of spectra by said stationary vibration waves, and

detecting a change in thickness between said first plate part and said second plate part or a defect formed in said first plate part or said second plate part based on the calculated frequency difference.

2. An apparatus for detecting a change in the state of a part of an object to be measured that has a section comprising a first plate part and a second plate part which has a plate surface opposite to a plate surface of said first plate part with a gap between said plate surfaces and is integral with said first plate part or is connected to said first plate part, comprising

a vibration application means for applying vibrations to said object to be measured at a site at said section where flexural, torsional and stationary vibration waves are generated,

a pick-up means for picking up vibrations of said object to be measured and converting said vibrations into electric signals,

a spectral analysis means for receiving the signals from the pick-up means and subjecting the stationary vibration waves generated in said object to be measured to a spectral analysis,

a frequency difference calculation means for calculating the frequency difference of spectra divided into two by high order torsional vibrations generated at said section out of the group of spectra by said stationary vibration waves obtained by said spectral analysis means, and

a detection means for detecting quantitatively a change in thickness between said first plate part and said second plate part or a defect formed in said first plate part or said second plate part based on the frequency difference calculated by said frequency difference calculation means.

3. The apparatus for detecting a change in the state of a part of an object to be measured as claimed in claim 2, wherein said vibration application means is a means for applying vibrations to said object to be measured by impacting.

4. The apparatus for detecting a change in the state of a part of an object to be measured as claimed in claim 2, wherein said vibration application means is a means for impacting said object to be measured, and a gate means for taking out natural vibrations of said object to be measured after a prescribed time after the application of vibrations is provided between said pick-up means and said frequency displacement detection means.