Infrared NDI for detecting shallow irregularities
First Claim
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1. A method of non-destructive inspection (NDI) of a structure, the method comprising:
- identifying an irregularity on a surface of the structure;
determining a null value representing a difference between respective response functions of a first non-imaging thermal sensor and a second non-imaging thermal sensor;
measuring the temperature of a first portion of a surface of a structure proximate the irregularity with the first non-imaging thermal sensor;
measuring the temperature of a second portion of the surface of the structure proximate the irregularity with the second non-imaging thermal sensor, wherein measuring the temperatures of the first and second portions each comprise halting measurement of the temperature of the respective portion once the temperature that is measured has fallen by a predefined decrement;
determining a normalized difference signal by determining a difference signal representing any difference in temperature between the first and second portions as measured by the first and second non-imaging thermal sensors, respectively, and defining the normalized difference signal to represent any departure of the difference signal from the null value;
repeatedly measuring different first and second portions of the surface of the structure proximate the irregularity and repeatedly determining the normalized difference signal for each of the different first and second portions of the surface of the structure that are measured; and
emitting an alert signal based upon the normalized difference signal if the temperature of the first portion is different from the temperature of the second portion by at least a temperature difference threshold for any of the different first and second portions of the surface of the structure that are measured.
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Abstract
First and second thermal sensors measure the respective temperatures of portions of a surface of a structure such as an aircraft component. An alert signal is emitted if the temperatures of the surface portions are substantially different. An energy source causes heat flow within the structure. Subsurface irregularities such as disbanded areas between composite layers and foreign materials obstruct heat flow within the structure and cause proximate surface portions to exhibit different temperatures. A non-alert signal may be emitted if the temperatures of proximate surface portions are essentially the same.
56 Citations
23 Claims
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1. A method of non-destructive inspection (NDI) of a structure, the method comprising:
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identifying an irregularity on a surface of the structure; determining a null value representing a difference between respective response functions of a first non-imaging thermal sensor and a second non-imaging thermal sensor; measuring the temperature of a first portion of a surface of a structure proximate the irregularity with the first non-imaging thermal sensor; measuring the temperature of a second portion of the surface of the structure proximate the irregularity with the second non-imaging thermal sensor, wherein measuring the temperatures of the first and second portions each comprise halting measurement of the temperature of the respective portion once the temperature that is measured has fallen by a predefined decrement; determining a normalized difference signal by determining a difference signal representing any difference in temperature between the first and second portions as measured by the first and second non-imaging thermal sensors, respectively, and defining the normalized difference signal to represent any departure of the difference signal from the null value; repeatedly measuring different first and second portions of the surface of the structure proximate the irregularity and repeatedly determining the normalized difference signal for each of the different first and second portions of the surface of the structure that are measured; and emitting an alert signal based upon the normalized difference signal if the temperature of the first portion is different from the temperature of the second portion by at least a temperature difference threshold for any of the different first and second portions of the surface of the structure that are measured. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An inspection device comprising:
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a first non-imaging radiometer having a first field of view along a first axis, the first radiometer capable of generating a first signal indicative of the temperature of a first surface when the first surface is disposed in the first field of view; a second non-imaging radiometer disposed proximate the first radiometer and having a second field of view along a second axis, the second axis different from the first axis, the second radiometer capable of generating a second signal indicative of the temperature of a second surface when the second surface is disposed in the second field of view; an indicator element; a comparator disposed in electronic communication with the first radiometer, the second radiometer, and the indicator element, the comparator capable of determining a difference between the first signal and the second signal; a circuit for determining a null value representing a difference between respective response functions of the first and second non-imaging thermal sensors and for determining a normalized difference signal based upon any departure of the difference between the first and second signals from the null value and causing the indicator element to indicate, based upon the normalized difference signal, whether the temperature indicated by the first signal is different from the temperature indicated by the second signal by at least a temperature difference threshold; a level adjust device configured to control a sensitivity of the inspection device by adjustably establishing the temperature difference threshold; and a shut-down function configured to halt measurement of the temperature of the respective portion of the surface of the structure once the temperature that is measured has fallen by a predefined decrement. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A method of inspecting the skin of a structure below the surface of the skin, the method comprising:
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determining a null value representing a difference between respective response functions of a pair of infrared radiometers; heating the skin of the structure through an outward surface of the skin to cause heating of the surface; concurrently measuring the respective temperatures of proximate portions of the heated surface using the pair of infrared radiometers and halting measurement of the temperature of the respective portion once the temperature that is measured has fallen by a predefined decrement; comparing the measured temperatures to determine a normalized difference signal by determining a difference signal representing any difference in temperature between the proximate portions of the heated surface as measured by the pair of radiometers and defining the normalized difference signal to represent any departure of the difference signal from the null value; determining the presence of an irregularity within the skin below the surface based upon the normalized difference signal if the respective temperatures of the proximate portions differ by at least a temperature difference threshold; and controlling a sensitivity with which an inspection is conducted by adjustably establishing the temperature difference threshold. - View Dependent Claims (17, 18)
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19. A method of inspecting a layered composite aircraft structure, the method comprising:
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determining a null value representing a difference between respective response functions of a pair of thermal radiometers; heating a surface of a layered composite aircraft structure; determining whether a temperature difference is present by concurrently measuring the respective temperatures of proximate portions of the heated surface using the pair of thermal radiometers, wherein concurrently measuring the respective temperatures of proximate portions of the heated surface comprises halting measurement of the temperature of the respective portion once the temperature that is measured has fallen by a predefined decrement; determining a normalized difference signal by determining a difference signal representing the temperature difference and defining the normalized difference signal to represent any departure of the difference signal from the null value; returning the aircraft structure to flying service based upon the normalized difference signal if the temperatures differ by less than the temperature difference threshold; and performing further inspection of the layered composite aircraft structure based upon the normalized difference signal if the temperatures differ by at least the temperature difference threshold. - View Dependent Claims (20, 21, 22, 23)
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Specification