Digital image system and method for determining surface reflective and refractive characteristics of objects

• US 5,477,332 A
• Filed: 04/05/1995
• Issued: 12/19/1995
• Est. Priority Date: 12/17/1992
• Status: Expired due to Term

• Current Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Original Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Inventors: Blackmon, James B. Jr., Stone, Kenneth W.
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US08/417,647
• Time in Patent Office: 258 Days
• Field of Search: 356/371, 356/372, 356/375, 356/376, 356/394, 356/398, 356/128, 356/124, 356/361, 356/237, 356/239, 356/445, 356/429, 356/430, 250/559, 250/561, 250/562, 250/571, 250/572, 348/125, 348/128
• US Class Current: 356/613
• CPC Class Codes: G01B 11/255 for measuring radius of curvature measuring diameter G01B11/08
• CPC Class Codes: G01N 21/55 Specular reflectivity

Abstract

A computer controlled system for determining various physical surface characteristics of an object includes a light source array, positioned to illuminate a surface for evaluation, in which individual lights in the array illuminate the object on a mutually exclusive basis, a radiometer, positioned to receive light from the object, producing image data relative to positions of the light pixels and a computer apparatus that, among other functions in the system, interprets the image data and determines at least the surface waviness, radius of curvature and cant angle of the surface.

Claims

1. A system for determining physical surface characteristics of an object, for any of concave, convex and flat shaped objects, including at least the characteristics of radius of curvature, cant angle and surface waviness of said selected surface region of a concave object, said object being positioned for inspection of a selected surface region thereon, comprising:

a plurality of radiation sources, each of said radiation sources for individually illuminating said selected region of said object surface with radiation;

said radiation sources being spaced in position from one another over a predetermined area both laterally and longitudnally and being spaced from said selected surface region;

energizing means for energizing each of said radiation sources in a predetermined sequence on a mutually exclusive basis to expose said selected surface region to an interval of incident radiation from each of said radiation sources in turn, whereby said surface region is exposed to a series of radiation pulses;

radiation detection means located at another fixed position spaced from said selected surface region;

said radiation detection means positioned to receive and detect radiation from multiple positions within said selected surface region and produce spacial position information of the multiple spacial positions within said selected region from which radiation emanates and intensity information of the intensity of the received radiation from each such spacial position, whereby radiation produced by any individual light source results in emanation of radiation from multiple locations within said selected surface region and all radiation emanations from different locations on said surface region produced by energization of each radiation source are detected in sequence;

data file means for temporarily storing said information detected by said radiation detection means;

composite data file means for storing spacial location information, reflection information corresponding to each spacial location and radiation source identification of the radiation source producing said reflected radiation, whereby information in said composite data file means is selected for each spacial location;

comparing means for determining the existance of any overlap in spatial position between each reflection produced responsive to energization of any one of said radiation sources with the spatial position of the reflection subsequently produced by any of said other radiation sources and, responsive to each such overlap determination, identifying the maximal one of said radiation sources producing the greater intensity reflection at each such spacial location, and storing the identification of said maximal light source, said spacial location corresponding thereto and said corresponding intensity in said composite file means and, in the absence of any such overlap at a given spacial location, for also storing in said composite file means the spacial location, corresponding intensity information, and the identification of the radiation source producing such radiation for each spacial location at which no such overlap in radiation occurs;

first calculating means for calculating a surface slope value for each of said spatial positions in said composite data file to produce surface slope value information for each spacial location as a function of the distance of such spacial location from a predetermined reference point on said surface region, whereby a series of measured surface slope values are produced;

second calculating means for calculating a least mean squares line from all said surface slope values, said least mean squares line being representative of best estimate line slope and intercept values as a function of the distance from said predetermined reference point on said surface region;

said second calculating means including;

slope angle calculating means for calculating the slope angle of said least means square line based on said series of measured surface slope values to define a least means square line slope angle; and

intercept calculating means for calculating the intercept of said least means square line along an axis vertical to said reference position based on said series of measured slope values to provide a cant angle for the surface;

inverting means for inverting least means square line slope angle to produce a radius of curvature value for said surface region;

third calculating means for subtracting from the measured surface slope value obtained for a position at a given distance from said reference position from the respective best estimate slope value at the corresponding position from said reference position for each of the measured slope values in said series to produce a series of surface slope error values; and

fourth calculating means for calculating the standard deviation for said series of surface slope error values to provide a surface waviness figure for said surface region.

2. The invention as defined in claim 1, wherein said comparing means, further comprises:

means for inspecting in sequence each set of information placed in said data file means for each spacial location with the corresponding information in said composite data file means for said spacial location and replacing said information in said composite data file means with corresponding information for said respective spacial position found in said data file means only in the event the intensity information for said respective spacial position in the data file means is greater than the corresponding intensity information found in said composite file, whereby, following completion of sequential energization of said radiation sources by said energization means, said composite data file means includes the maximum intensity information obtained for each spacial location.

3. The invention as defined in claim 2, further comprising:

means for placing information produced by said radiation detection means into said data file means; and

means for replacing information placed in said data file means following energization of a selected one of said radiation sources with information produced by said radiation detection means responsive to energization of the next selected radiation source, whereby said data file means contains only information derived from the most recently energized radiation source.

4. The invention as defined in claim 2, further comprising:

means overwriting the information placed in said data file means following energization of a selected one of said radiation sources with subsequent information produced by said radiation detection means following energization of the next selected radiation source, whereby said data file means contains only information derived from the last most recently energized radiation source.

5. The invention as defined in claim 2, wherein said radiation detection means comprises a modified video camera.

6. The invention as defined in claim 5, wherein said video camera includes an aperature through which to receive radiation images, and wherein said aperature is of a diameter not exceeding one millimeter.

7. The invention as defined in claim 6, wherein said radiation sources comprise light sources;

and wherein said aperature of said video camera and said light sources are each of a diameter of 1 millimeter.

8. The invention as defined in claim 1, wherein said energizing means initiates energization of each radiation source only after the lapse of a quiescent interval during which none of said radiation sources is energized, whereby energization of a radiation source is always preceded by a quiescent interval;

and wherein said radiation detection means is also positioned to receive and detect radiation reflected from said selected surface region and produce spacial position information of the spacial positions within said selected region from which radiation is reflected and intensity information of the intensity of the received radiation from each such spacial position in the absence of energization of any of said radiation sources, whereby all radiation reflections from different locations on said surface region produced by ambient radiation sources, other than said first radiation sources, are detected to produce ambient light information for each said spacial position; and

, further comprising;

means for subtracting the intensity levels in said ambient light information from the intensity levels at the corresponding spacial positions stored in said data file means following energization of the next selected radiation source in said sequence to produce corrected intensity level information in said data file means in respect of said next selected radiation source.

9. The invention as defined in claim 1, wherein said radiation detection means comprises:

radiometer means; and

, further including;

digitizer means;

said digitizer being coupled to said radiometer means for at least providing information from said radiometer means in digital form.

10. The invention as defined in claim 1, wherein said radiation source means comprises light sources.

11. The invention as defined in claim 1 wherein said radiation source means comprises light sources for producing radially directed light.

12. The invention as defined in claim 11, wherein said light sources comprise lamps.

13. The invention as defined in claim 1, wherein said radiation source means comprises light sources for producing light;

and further comprising;

beam splitter means, said beam splitter means being located between said radiometer means and said object and being within the field of view of said radiometer means; and

wherein said light sources are positioned to direct light to said beam splitter, wherein said beam splitter diverts said light, incident on said beam splitter means, to said object, whereby radiation emanating from said object comprises light reflected from said object; and

wherein light emanating from said object proceeds through said beam splitter to said radiometer means.

14. The invention as defined in claim 1, further including:

means for determining from said least means square line the average slope value existing at said reference position of said surface region to produce a reference position slope value;

whereby a cant angle of said surface region is derived.

15. The invention as defined in claim 1, further comprising:

display monitor means for visually displaying data in said composite data file means.

16. The invention as defined in claim 1, wherein said radiation sources are arranged in a planar array.

17. The invention as defined in claim 1, wherein said object is of a concave geometry having a radius of curvature and wherein said radiation sources are located a distance from said object approximately equal to said radius of curvature of said object.

18. The invention as defined in claim 1, wherein said radiation sources emit radiation of essentially equal intensity.

19. The invention as defined in claim 18, wherein said radiation sources comprise point light sources.

20. The invention as defined in claim 19, wherein said point light sources comprise a diameter no greater than one millimeter.

21. The invention as defined in claim 1, wherein said radiation sources emit radiation of essentially equal intensity and wherein said radiation sources are arranged in a planar array.

22. The invention as defined in claim 21, wherein said planar array comprises radiation sources arranged in rows and columns.

23. The invention as defined in claim 1, further comprising:

frame means for holding said radiation sources in fixed position, said frame means being positionable for permitting said radiation sources to be positioned at any of a variety of positions relative to said object under inspection.

24. A system for determining surface characteristics of a selected surface region of an object, including at least the characteristics of slope error at various positions along the surface, surface waviness, cant angle and radius of curvature of said selected surface region, comprising:

a plurality of sources of electromagnetic radiation, each of said sources for illuminating said selected surface region in entirety on a mutually exclusive basis, said sources being spaced from one another, laterally and longitudnally, over a predetermined area and spaced from said selected surface region by known distances;

radiometer means for receiving radiation from said selected surface region to produce received radiation data of the radiation emanating from all portions of said selected surface region, including position information and corresponding intensity information, for each spot within said selected surface region from which radiation emanates, whereby multiple radiation emanating spots are detected;

said radiometer means being spaced from said selected surface region by a known distance;

computer means for controlling said radiation sources and for receiving and processing said data from said radiometer means;

said computer means including;

first program means for initiating energization of said radiation sources in sequence, whereby each of said sources in turn illuminates said selected surface region and said radiometer means produces data resulting from each such illumination;

second program means for calculating the surface slope angle for each said spot as a function of distance from a reference position along each of two mutually orthogonal axes centered at said reference position to produce a series of measured slope angles and related distances from said reference position along each of said axes;

third program means for calculating a least means square line along each of said axes based on said series of measured slope values to provide at least corresponding best estimate slope values at the respective distances from said reference position, said least means square lines being representative of best estimate slope values as a function of distance from said reference position along their respective axis;

each said least means square line including a line slope and an intercept with a vertical axis at said reference position, with said intercept defining the cant angle of said surface region;

fourth program means for determining the deviation between the measured slope angle of each spot in said series and the corresponding best estimate slope value for the respective spot from said means squares line to provide a series of slope error figures along the respective axis; and

fifth program means for inverting said slope of said least means square line to provide a radius of curvature figure for said selected surface region.

25. The system as defined in claim 24, wherein said computer means further includes:

sixth program means for identifying the one of said radiation sources that produces the greatest intensity of radiation received at said radiometer means for each said spot; and

wherein said second means, in producing said series of measured slope values, calculates said slope angle for each said spot based at least in part upon the spacial relationship between said selected surface region and the one of said radiation sources identified by said seventh means for said spot and between said radiometer means and said spot.

26. A method for determining physical characteristics of concave, convex and flat shaped objects from which electromagnetic radiation can emanate, comprising:

positioning said object in a position spaced from a plurality of substantially identical electromagnetic radiation sources;

illuminating the object with electromagnetic radiation from each of said plurality of electromagnetic radiation sources with each of said radiation sources providing radiation of essentially the same intensity one at a time in sequence;

receiving, at another location spaced from said object, radiation emanating from different locations on said object in response to radiation produced by each of said radiation sources and identifying all such locations and the radiation source that was producing radiation at the time such radiation is received, whereby radiation emanating from a particular location on said object when one of said radiation sources is producing radiation may overlap with radiation resulting at that same location when another of said radiation sources is producing radiation;

determining whether radiation produced by any one of said radiation sources overlaps with radiation produced at that same location by any of the other of said radiation sources and in the event of such overlap identifying which of said plurality of radiation sources resulted in the greatest intensity of radiation from said overlap location;

calculating the slope of the surface of the object at each location thereon from which radiation emanated, based on the relative positions between the radiation source that resulted in the greatest intensity of radiation at that location and the relative position between said object and the location at which said radiation is received to obtain a plurality of slope values for different locations on the surface of said object.

27. The method of claim 26, further including:

calculating the slope for a least means square line based on the relative positions between the radiation source that resulted in the greatest intensity of radiation at each location from which radiation emanated and the relative position between said object and the location at which said radiation is received; and

inverting the value of said least means square line slope to provide the radius of curvature of said object.

28. The method of claim 27, further including the step of:

calculating a vertical axis intercept of said least means square line to define the least means square line through the range represented by said slope values and to obtain the cant angle for said object.

29. The method of claim 28, further including the step of:

calculating the deviation between the slope value for each location in said plurality of slope values with the value of the slope calculated for that same location by said least means square line to produce a series of slope angle deviations.

30. The method of claim 29, further including the step of:

calculating the standard deviation of said series of slope angle deviations to provide a waviness figure for said object.