Defect detecting method and apparatus

• US 5,144,838 A
• Filed: 06/07/1991
• Issued: 09/08/1992
• Est. Priority Date: 10/04/1989
• Status: Expired due to Fees

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company), Iwatsu Electric Company Limited
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company), Iwatsu Electric Company Limited
• Inventors: Tsuboi, Kiyoshi
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): Finley, Rose M.
• Application Number:
  US07/711,908
• Time in Patent Office: 459 Days
• Field of Search: 73/579, 73/582, 73/583, 73/602, 73/592, 73/645, 73/646, 73/658, 73/659, 364/508
• US Class Current: 73/579
• CPC Class Codes: G01M 7/025 Measuring arrangements
• CPC Class Codes: G01N 2291/014 Resonance or resonant frequency
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 29/045 by imparting shocks to the workpiece and detecting the vibrations or the acoustic waves caused by the shocks measuring resonant frequency G01H13/00; measuring strength properties by application of mechanical stress G01N3/00
• 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

Abstract

A defect detecting method for detecting whether or not an object to be measured has a defect comprises the steps of vibrating the object to be measured, picking up the vibration, and detecting that a spectrum of the characteristic vibration of the object to be measured is separated into two portions. Also, a defect detecting apparatus comprises a vibrator vibrating an object to be measured, a detector for picking up an vibration of the object to be measured and for converting the vibration into an electric signal, and a signal processor for receiving the electric signal from the detector, for analyzing a spectrum of a characteristic vibration of the object to be measured, and for determining whether the defect is present or absent depending on whether a spectrum of a defect of the object to be measured is present or absent.

Claims

1. A defect detecting method for detecting defects in an object, comprising the steps of:

applying a vibration to said object until a first predetermined time;

recording a vibration wave form from said object after said first predetermined time;

determining a first time after a peak value of said vibration waveform and a second time after said first time,

applying to said vibration wave form, an emphasizing window which emphasizes said vibration wave form from between said first time and said second time, thereby defining an emphasized vibration wave form;

transforming the emphasized vibration wave form to frequency domain to form a transformed vibration spectrum, wherein said transformed vibration spectrum has all peaks corresponding to each vibrational order of said object in a limited frequency range;

retransforming a limited frequency range containing all peaks corresponding to a selected vibrational order to time domain, thereby forming a wave form in time series of said selected vibrational order;

determining an envelope of the wave form in times series of said selected order, wherein oscillations in said envelope indicate defects in said object.

2. A method according to claim 1, wherein:

a frequency of oscillation in the envelope of the wave form in time series of said selected vibrational order corresponds to a size of defects in said object.

3. A method according to claim 1, further comprising:

signal processing of said transformed vibration spectrum which sharpens peaks therein.

4. A method according to claim 3, wherein:

said signal processing step does not change Q values of said peaks.

5. A defect detecting device for detecting defects in an object, comprising:

first applying means for applying a vibration to said object until a first predetermined time;

recording means for recording a vibration wave form from said object after said first predetermined time;

first determining means for determining a first time after a peak value of said vibration waveform and a second time after said first time,

second applying means for applying to said vibration wave form, an emphasizing window which emphasizes said vibration wave form from between said first time and said second time, thereby defining an emphasized vibration wave form;

transforming means for transforming the emphasized vibration wave form to frequency domain to form a transformed vibration spectrum, wherein said transformed vibration spectrum has all peaks corresponding to each vibrational order of said object in a limited frequency range;

retransforming means for retransforming a limited frequency range containing all peaks corresponding to a selected vibrational order to time domain, thereby forming a wave form in time series of said selected vibrational order;

second determining means for determining an envelope of the wave form in times series of said selected vibrational order, wherein oscillations in said envelope indicate defects in said object.

6. An apparatus according to claim 5, wherein:

a frequency of oscillation in the envelope of the wave form in time series of said selected vibrational order corresponds to a size of defects in said object.

7. An apparatus according to claim 5, further comprising:

signal processing means for signal processing of said transformed vibration spectrum which sharpens peaks therein.

8. An apparatus according to claim 9, wherein:

said signal processing means does not change the Q values of said peaks.

9. An apparatus according to claim 5, wherein:

said recording means includes one of a microphone and a displacement meter.