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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
First Claim
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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.

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