METHOD FOR DETECTING THERMAL CHANGES ON A SURFACE

• US 3,854,336 A
• Filed: 01/26/1972
• Issued: 12/17/1974
• Est. Priority Date: 01/26/1972
• Status: Expired due to Term

• Current Assignee: Malcolm M. Bibby
• Original Assignee: Malcolm M. Bibby
• Inventors: Bibby, Malcolm M.
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Corr, Denis E.
• Application Number:
  US05/221,010
• Time in Patent Office: 1,056 Days
• Field of Search: 73/351,146,355R 250/83.3H,340
• US Class Current: 374/124
• CPC Class Codes: G01J 2005/066 Differential arrangement, i.e. sensitive/not sensitive
• CPC Class Codes: G01J 5/0022 for sensing the radiation of moving bodies
• CPC Class Codes: G01J 5/0066 for hot spots detection
• CPC Class Codes: G01J 5/04 Casings
• CPC Class Codes: G01J 5/047 Mobile mounting; Scanning arrangements
• CPC Class Codes: G01J 5/48 Thermography; Techniques using wholly visual means
• CPC Class Codes: G01K 13/08 in rotary movement
• CPC Class Codes: G01K 3/10 in respect of time, e.g. reacting only to a quick change of temperature
• CPC Class Codes: G01N 25/72 Investigating presence of flaws
• CPC Class Codes: G01N 33/26 Oils; Viscous liquids; Paints; Inks G01N33/22 takes precedence

Abstract

A sensitive method for detecting minute changes in apparently repetitive infrared signals in which infrared signals from repeated surface scans are processed by subtracting the signals representative of a scanning interval from signals representative of a subsequent scanning interval and differences resulting from a series of such subtractions are summed.

Claims

1. In a method for detecting by infrared scanning thermal changes on a surface of a pneumatic object subject to imposition of load and the generation of heat when in service wherein the object is heated, signals are generated proportional to surface temperature variation and the surface is subjected to repeated scans, the improvement which comprises generating reference values of signals representative of a scanning interval over a surface of the object, subtracting said reference values from values of signals representative of a subsequent scanning interval over the same surface area, making the subtractions between a series of scanning intervals and summing the resulting differences.

2. Method of claim 1 in which the magnitude of the signals proportional to surface temperature variation over a scanning interval is maintained at substantially constant value.

3. The process of claim 1 in which each scanning interval is a plurality of scans and the values of said generated signals are averaged over the interval.

4. The process of claim 1 in which each scanning interval is a plurality of scans, the values of said generated signals are averaged over the interval, the values of signals subtracted representative of a scanning interval are values of a reference scanning interval subject to modification by the averaged values of each subsequent scanning interval according to a weighting factor and the differences are summed according to a second weighting factor.

5. The process of claim 4 in which the object scanned is a pneumatic tire and the rms value of the output signal waveform is maintained substantially constant.

6. The process of claim 1 in which the object scanned is a pneumatic tire being tested by rotation under load on a test wheel, the signals generated proportional to surface temperature variation are analog voltage signals representative of surface temperature variation on the tire surface the magnitude of which is maintained at substantially constant value, the beginning of each revolution of the tire is determined and sampling of the voltage signals is initiated at predetermined frequency whereby the voltage signals are identified with particular areas of the tire surface, the analog voltage signals are converted to digital signals, the values of the digital signals are averaged over a scanning interval of a plurality of scans, the averaged digital values are converted to reference values for subtraction from averaged digital values of a subsequent scanning interval according to the relationship An An 1 + 1/m (In - An 1) the subtractions are made between said reference values and the averaged digital values of a scanning interval subsequent to the interval represented by the reference data, summing of the resulting differences is done according to a weighting factor which is the inverse of a powder of 2 and, both the averaged values of the digital signals of said subsequent scanning interval and the sum of previous differences with respect to the segments of the tire are displayed.

7. Apparatus for detecting by infrared scanning thermal changes on a surface of a pneumatic object subject to imposition of load and the generation of heat when in service comprising a. means for heating the object, b. means for detecting infrared emission, c. means for generating signals proportional to surface temperature variation coupled to said means for detecting infrared emission, d. averaging means for averaging said signals proportional to surface temperature variation over a scanning interval comprising a plurality of scans to produce reference values of signals representative of a scanning interval, e. first storage means for storing said reference values of signals representative of a scanning interVal, f. second storage means operatively connected to said first storage means for storing subsequent values of signals proportional to surface temperature variation representative of a subsequent scanning interval over the same surface area, and g. subtraction means operatively connected to said first and second storage means for obtaining difference in values between said reference values and said subsequent values.

8. Apparatus of claim 7 which includes means for maintaining the magnitude of the signals proportional to surface temperature variation over a scanning interval at substantially constant value.

9. Apparatus of claim 7 which includes means for summing successive differences between the average values of succeeding scanning intervals and the value of a reference scanning interval.

10. Apparatus of claim 9 which includes means for displaying the average signals of the current scanning interval and means for displaying the accumulated differences.

11. Apparatus of claim 7 for scanning a pneumatic tire which includes means for moving the infrared detecting means over the surface of a tire being tested by rotation under load to select the position corresponding to the desired scan number, means for sensing the beginning of each revolution and means for sensing a plurality of segments of the tire.

12. Apparatus of claim 11 which includes means for detecting when the signals exceed a predetermined limit and means for automatically terminating the test when the predetermined limit is exceeded.

13. Apparatus of claim 9 for scanning a pneumatic tire which includes means for moving the infrared detecting means over the surface of a tire being tested by rotation under load to select the position corresponding to the desired scan band number on the tire, means for sensing the beginning of each revolution of the tire and means for sensing a plurality of segments of the tire with reference to the beginning of each revolution.

14. Apparatus of claim 13 which includes means for detecting when the signals exceed a predetermined limit and means for automatically terminating the test when the predetermined limit is exceeded.

15. Apparatus of claim 13 which includes means for printing out the location on the surface at which the predetermined limit is exceeded.

16. Apparatus of claim 14 which includes means for printing out the location on the surface at which the predetermined limit is exceeded.

17. Apparatus of claim 7 for scanning a pneumatic tire which includes means for maintaining the magnitude of the signals proportional to surface temperature variation over a scanning interval at substantially constant value, means for averaging the values of signals over a scanning interval comprising a plurality of scans, means for summing differences between the average value of succeeding scanning intervals and the value of a reference scan, means for moving the infrared detecting means over the surface of a tire being tested by rotation under load to select the position corresponding to the desired scan band number, means for sensing the beginning of each revolution, means for sensing a plurality of segments of the tire with respect to the beginning of each revolution, means for displaying the average value of signals of the current scanning interval, means for displaying the accumulated differences, means for detecting when a value of the signals exceeds a predetermined limit and means for automatically terminating the test when the predetermined limit is exceeded.

18. Apparatus for detecting thermal changes on the surface of a tire being tested by rotation under load on a test wheel which comprises two radiometers for converting thermal flux to analog voltage signals representative of surface temperature variations, mountable to scan both sides of the tire, means for moving the radiometers for viewing adjacent concentric bands from bead to tread, means for moving the radiometers parallel to the axis oF the test wheel on which the tire is mounted for following the contours of the tire, means for sensing the beginning of each revolution of the tire, means to initiate sampling of said voltage signals at predetermined frequency so as to correlate the signals with particular segments of the tire, means for maintaining the magnitude of the analog voltage signals from each radiometer at substantially constant value, means for converting said analog voltage signals to digital signals, means for averaging the values of said digital signals over a scanning interval of a plurality of scans, means for storing the averaged digital values, means for converting said averaged digital values to reference values for subtraction from averaged digital values of a subsequent scanning interval according to the relationship An An 1 + 1/m (In - An 1) means for storing the reference values, means for obtaining differences between said reference values and the averaged digital values of a scanning interval subsequent with respect to the interval represented by the reference data, means for summing said differences according to a weighting factor which is the inverse of a power of 2, means for displaying both the averaged values of the digital signals of the subsequent scanning interval and the sum of previous differences with respect to segments of the tire, means for detecting when a value of said sum of differences exceeds a predetermined limit, means for automatically terminating the test when the predetermined limit is exceeded and means for printing out the location on the tire surface at which the predetermined limit is exceeded.