Infrared inspection system and method employing emissivity indications

• US 5,294,198 A
• Filed: 10/01/1991
• Issued: 03/15/1994
• Est. Priority Date: 10/01/1991
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Cincinnati Electronics Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Cincinnati Electronics Corporation (L3Harris Technologies, Inc.)
• Inventors: Schlagheck, Jerry G.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): GUTIERREZ, DIEGO F
• Application Number:
  US07/769,430
• Time in Patent Office: 896 Days
• Field of Search: 374/4, 374/5, 374/6, 374/7, 374/126, 374/128, 374/124, 374/137, 364/557, 250/332
• US Class Current: 374/4
• CPC Class Codes: G01N 25/72 Investigating presence of flaws

Abstract

A unit having differing thermal emissivities at differing regions thereof is monitored with an infrared camera for deriving a signal having magnitudes representing infrared emission from multiple pixels in the camera field of view. A computer responsive to the signal (a) stores data representing emissivity and standard temperature of the unit at each of the pixels, (b) combines indications of the infrared emission from each pixel and the stored data representing emissivity of each pixel to derive an indication of monitored temperature of each pixel, (c) compares the stored data representing standard temperature of each pixel and the indications of monitored temperature of each pixel, and (d) derives an indication of the deviation between the magnitude of the standard temperature and monitored temperature at each pixel. In response to the indication of the deviation at each pixel, a property of the unit related to the deviations at the pixels is derived.

Claims

1. Apparatus for analyzing a unit in the form of a device or a structure having differing thermal emissivities at differing regions thereof comprising an infrared camera for monitoring infrared emission from the unit and for deriving a signal having magnitudes representing the infrared emission from multiple pixels in a field of view of the camera, a computer responsive to the signal including:

means storing data representing emissivity and standard temperature of the unit at each of the pixels, the stored emissivity and standard temperature data for some of the pixels of the unit differing from the stored emissivity and standard temperature indication of others of the pixels of the unit, means for;

(a) combining indications of the infrared emission from the pixels and the stored data representing emissivity of the pixels to derive an indication of monitored temperature of the pixels, (b) comparing the stored data representing standard temperature of each pixel and the indications of monitored temperature of the pixels, and (c) deriving an indication of the deviation between the magnitude of the standard temperature and monitored temperature at the pixels; and

means responsive to the indication of the deviation at each pixel for indicating a property of the unit, the property being related to the deviations at the pixels.

2. The apparatus of claim 1 wherein the means for indicating includes a two-dimensional display for displaying an image of the deviation at each pixel, the image spatially corresponding with an image of the unit.

3. The apparatus of claim 2 wherein the means for indicating responds to a deviation in excess of a predetermined value at any pixel for signaling that the unit is unacceptable for its intended purposes.

4. The apparatus of claim 1 wherein the signal is derived for each pixel of a single analyzed unit at plural times, the computer deriving the deviation indication for each pixel at each of the plural times, the property indicating means for the single analyzed unit responding to the deviation indication for each pixel at each of the plural times.

5. A method of analyzing a unit in the form of a device or a structure having differing thermal emissivities at differing regions thereof comprising monitoring infrared emission from the unit with an infrared camera so the camera derives a signal having magnitudes representing the infrared emission from multiple pixels in a field of view of the camera, supplying the signal to a computer storing data representing emissivity and standard temperature of the unit at each of the pixels, the stored emissivity and standard temperature data for some of the pixels of the unit differing from the stored emissivity and standard temperature indication of others of the pixels of the unit, the computer responding to the signal and the stored data by (a) combining indications of the infrared emission from the pixels and the stored data representing emissivity of the pixels to derive an indication of monitored temperature of the pixels, (b) comparing the stored data representing standard temperature of each pixel and the indications of monitored temperature of the pixels, and (c) deriving an indication of the deviation between the magnitude of the standard temperature and monitored temperature at the pixels;

responding to the indication of the deviation at the pixels for indicating a property of the unit that is related to the deviations at the pixels.

6. The method of claim 5 wherein the pixels for which the deviation magnitudes are derived are first pixels, the unit having a standard pixel with known radiation emissivity, the standard pixel being spatially displaced from

7. The method of claim 6 wherein the method is performed to derive the data representing the standard temperature for the first pixels by performing said steps of claim 6 on Q units having second pixels corresponding to said first pixels and further pixels having the known emissivity and corresponding with said standard pixels, where Q is at least several, deriving indications of the detected intensities from the corresponding second pixels and the further pixels of the Q units, the computer combining the derived indications of the detected intensities from the corresponding second pixels and the further pixels of the Q units to derive the data representing the standard temperature of the first pixels.

8. The method of claim 7 wherein the computer derives the data representing the standard temperature for the first pixels in response to ##EQU8## where:

I_T1 =intensity of radiation from the second pixels at the first temperature

I_T2 =intensity of radiation from the second pixels at the second temperature

I_STDT1 =intensity of radiation rom the further pixels at the first temperature

I_STDT2 =intensity of radiation from the further pixels at the second temperature

1/3_STD =the known radiation emissivity

Q=the number of the at least several units

q=is successively each of 1, 2 . . . Q

B=average value of B for the Q units

C=average value of C for the Q units

S_B =standard deviation of B for the Q units

S_C =standard deviation of C for the Q units.

9. The method of claim 8 wherein the steps of claim 5 are performed on the first pixels of a monitored unit and on the standard pixel of the monitored unit, the computer deriving the indication of the temperature of the first pixels in response to ##EQU9## I_T1(test) =intensity of radiation from the first pixels of the monitored unit at the first temperature

I_T2(test) =intensity of radiation from the first pixels of the monitored unit at the second temperature

I_STDT1(test) =intensity of radiation from the standard pixel of the monitored unit at the first temperature

I_STDT2(test) =intensity of radiation from the standard pixel of the monitored unit at the second temperature.

10. The method of claim 7 wherein the computer derives indications of (a) the standard temperature for the first pixels in response to B·

r(B,C) and (b) the monitored temperature for the first pixels in response to B_test ·

r_tested (B,C), and (c) the deviations between the indications of standard temperature for the first pixels and the monitored temperatures for the first pixels of the monitored

11. The method of claim 7 wherein the computer derives the data representing the standard temperatures for the first pixels by (a) determining first and second measures of the average infrared intensity from the second pixels of the O units at said first and second temperatures, (b) determining a third measure of the deviations of the infrared intensity from the second pixels of each of the O units at the first temperature from the first measure, (c) determining a fourth measure of the deviations of the infrared intensity from the second pixels of each of the O units at the second temperature from the second measure, (d) non-linearly combining the third and fourth measures for each of the O units to derive a first resultant, (e) linearly combining the first resultant, (f) determining first and second indications of the spread of values of the detected intensities from the first pixels at the first and second temperatures, respectively, and (g) combining the second resultant with the first and second indication of the spread of values.

12. The method of claim 7 wherein the computer obtains the standard temperature data for the first pixels from a statistical function of (a) the known emissivity and (b) the detected intensities at the further pixels and at the second pixels of the O units while the O units are at the first and second temperatures.

13. The method of claim 12 wherein the computer combines a value derived from the statistical function with a measure of the detected intensity for the first pixel to provide the indication of the standard temperature for the first pixels.

14. The method of claim 13 wherein the computer derives the statistical function value by determining the average values and the standard deviations of the intensities from the second pixels of the O units at the first and second temperatures, and combining the determined average values and standard deviations.

15. The method of claim 6 wherein the unit includes plural components and the method is performed to detect the expected lifetime of the unit, each of the components occupying a plurality of said first pixels and having known pixel locations on the unit, further comprising using the camera to monitor the intensity of infrared radiation emitted from the first pixels forming the components while the components are stimulated to a higher temperature than ambient temperature of the unit, the computer responding to the radiation indications for the first pixels of each particular component and an indication of the particular component radiation emissivity to derive an indication of expected operating temperature of each particular component, responding to the indication of expected operating temperature of each particular component and a stored value relating expected operating temperature of each particular component to the lifetime of the particular component to derive a second indication representing the expected lifetime of each particular component, and combining the second indications for all of the components to derive the indication of the unit expected lifetime, the temperature indication of each particular component being derived by combining the indications of (a) the monitored radiation intensity from all of the first pixels occupied by the particular component and (b) the radiation emissivity of the first pixels occupied by the particular component.

16. The method of claim 5 wherein the unit includes plural components and the method is performed to detect the expected lifetime of the unit, each of the components occupying a plurality of said pixels and having known pixel locations on the unit, further comprising using the camera to monitor the intensity of infrared radiation emitted from the pixels forming the components while the components are stimulated to a higher temperature than ambient temperature of the unit, the computer responding to the radiation indications for the pixels of each particular component and an indication of the particular component radiation emissivity to derive an indication of expected operating temperature of each particular component, responding to the indication of expected operating temperature of each particular component and a stored value relating expected operating temperature of each particular component to the lifetime of the particular component to derive a second indication representing the expected lifetime of each particular component, and combining the second indications for all of the components to derive the indication of the unit expected lifetime, the temperature indication of each particular component being derived by combining the indications of (a) the monitored radiation intensity from all of the pixels occupied by the particular component and (b) the radiation emissivity of the pixels occupied by the particular component.

17. The method of claim 16 wherein the intensity of the infrared radiation for the pixels is monitored while the unit is at first and second displaced temperatures, and further including monitoring the intensity of infrared radiation emitted from a standard pixel of the unit while the unit is at the first and second temperatures, the standard pixel having known radiation emissivity, and combining indications of the monitored intensity of the infrared radiation of the pixels and the standard pixel while the unit is at the first and second temperatures with an indication of the emissivity of the standard pixel to provide an indication of the temperature of each pixel.

18. The method of claim 5 wherein the indicated property is an indication of worthiness of the unit for its intended use.

19. The method of claim 5 wherein the camera monitors the emission at plural times while the unit is being transiently stimulated.