Laser alignment system

• US 4,889,425 A
• Filed: 11/02/1987
• Issued: 12/26/1989
• Est. Priority Date: 11/02/1987
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Edwards, Frank E., Wilcken, Stephen W.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Wallace, Linda J.
• Application Number:
  US07/115,202
• Time in Patent Office: 785 Days
• Field of Search: 356/141, 356/152, 356/149, 356/153-155, 356/250, 356/400, 356/32, 33/263, 33/266, 33/276, 33/278-280, 33/286, 33/288, 33/264, 33/281, 250/578, 358/107
• US Class Current: 356/141.3
• CPC Class Codes: G01B 11/16 for measuring the deformation in a solid, e.g. optical strain gauge
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes

Abstract

A system for monitoring changes in shape of a structure employs a laser source attached to the structure and a set of beam splitters mounted at various locations on the structure and arranged to route portions of a laser beam produced by the laser source into various video cameras also mounted on the structure. Each video camera includes a photodetector array and produces an output signal indicating the intensity of light detected by each photodetector of the array, thereby indicating the beam intensity distribution in a corresponding plane of interest. The video output signal of each camera is digitized and stored as an intensity data array in the memory of a digital computer. The computer calculates from the intensity data array the position of the centroid of the beam with respect to a reference point on the plane of interest using a least squares fit of the intensity data to a two-dimensional Gaussian intensity distribution. Any deviation of the calculated beam centroid position from the reference point indicates a change in jig shape in the plane of interest. The reference point in each plane of interest is determined by a least squares fit of the computed beam centroids in several planes to a line.

Claims

1. An apparatus for monitoring change in shape of a structure comprising:

light source means for generating a light beam, said light source means being rigidly attached to said structure;

photodetecting means rigidly attached to said structure and positioned such that said light beam is directed onto said photodetecting means, said photodetecting means producing data representing a light intensity distribution of said light beam directed onto said photodetecting means; and

means receiving the data for calculating values of parameters of a function modeling beam intensity distribution of the light beam, such that the calculated parameter values optimize a fit with respect to predetermined criteria of the intensity distribution modeled by the function to the intensity distribution represented by the data, wherein at least one of the parameters represents a position of said light beam on said photodetector, and for ascertaining change in shape of the structure by comparing a position of the beam defined by a calculated value of said at least one parameter to a reference position.

2. The apparatus in accordance with claim 1 wherein said photodetecting means comprises a video camera.

3. The apparatus in accordance with claim 1 wherein said light source means comprises a laser.

4. An apparatus for monitoring change in shape of a structure comprising:

light source means for generating a light beam, said light source means being rigidly attached to said structure;

a plurality of photodetecting means, each comprising a photodetector array rigidly attached to said structure at locations spaced apart thereon;

a plurality of beam splitters attached to said structure and positioned to direct portions of said light beam along separate paths relative to said structure onto photodetector arrays of separate ones of said photodetecting means, said paths respectively representing relative orientation between parts of said structure intended to have fixed relationship,

said photodetecting means producing data representing a light intensity distributing of the portions of said light beam directed onto said photodetector arrays; and

processing means receiving the data produced by said photodetecting means for calculating values of parameters of a function modeling beam intensity distribution of the light beam, such that the calculating parameter values optimize a fit with respect to predetermined criteria of the intensity distribution modeled by the function to the intensity distribution represented by the data produced by said photodetecting means, wherein at least one of the parameters represents a position of said light beam on the photodetecting means, for determining a reference position of said light beam on at least one of said photodetecting means in accordance with the calculated parameters, and for ascertaining change in shape of the structure by comparing a position of the beam defined by a calculated value of at least one of said parameters to said reference position.

5. The apparatus in accordance with claim 4 wherein at least one of said plurality of photodetecting means comprises a video camera.

6. The apparatus in accordance with claim 4 wherein said light source means comprises a laser.

7. The apparatus in accordance with claim 4 further comprising a plurality of pipes for conveying therein said light beam from said light source to ones of said beam splitters and for conveying positions of said light beam between ones of said beam splitters and said photodetecting means.

8. An apparatus for monitoring change in shape of a structure comprising:

a light source means for generating a light beam, said light source means being rigidly attached to said structure;

a plurality of photodetecting means, each comprising a photodetector array rigidly attached to said structure at locations spaced apart thereon;

a plurality of beam splitters attached to said structure and positioned to direct portions of said light beam along separate paths relative to said structure onto photodetector arrays of separate ones of said photodetecting means, said paths respectively representing relative orientation between parts of said structure intended to have fixed relationship,

said photodetecting means producing data representing a light intensity distribution of the portions of said light beam directed onto said photodetector arrays;

output means for determining from said data the movement of photodetector arrays of ones of said photodetecting means with respect to said light beam for thereby ascertaining the relative movement between parts of said structure; and

at least one weight attached to at least one of said beam splitters, said weight having a mass sufficient to prove it substantial movement of said at least one beam splitter in response to vibration of said structure.

9. A method for monitoring change in shape of a structure comprising the steps of:

generating a light beam at a fixed position on said structure;

intercepting said light beam at a multiplicity of points in fixed array relation to a second position on said structure;

producing analog data at said multiplicity of points representing a light intensity distribution of said light beam;

digitizing said analog data to produce digitized data representing said light intensity distribution;

storing the digitized data;

calculating values of parameters of a function modeling beam intensity distribution of the light beam, such that the calculated parameter values provide a best fit with respect to predetermined criteria of the intensity distribution modeled by the function to the intensity distribution represented by the stored digitized data, wherein at least one of the parameters represents a position of said light beam on said photodetector; and

ascertaining change in shape of the structure by comparing a position of the beam defined by a calculated value of said at least one parameter to a reference position.

10. The method in accordance with claim 9 wherein said light beam is a laser beam.

11. A method for monitoring change in shape of a tool structure comprising the steps of:

generating a light beam in fixed relationship to a first location on said structure;

splitting said light beam into separate portions and directing said portions of said light beam along separate paths relative to said structure toward a plurality of second locations on said structure;

intercepting said separate portions of said light beam at said second locations, each portion being intercepted at a separate multiplicity of points in fixed array toward which a said light beam portion is directed;

producing signal data at each said multiplicity of points representing a light intensity distribution of a light beam portion at a said second location;

calculating values of parameters of a function modeling beam intensity distribution of the light beam, such that the calculated parameter values provide a best fit with respect to predetermined criteria of the intensity distribution modeled by the function to the intensity distribution represented by the stored digitized data, wherein at least one of the parameters represents a position of said light beam on said photodetector; and

ascertaining change in shape of the structure by comparing a position of the beam defined by a calculated value of said at least one parameter to a reference position.

12. An apparatus for monitoring change in shape of a structure comprising:

photodetecting means comprising a planar surface attached to said structure, said surface having orthogonal x and y axes and producing an output signal representing an intensity of light I(x,y) at each of a plurality of points at coordinates (x,y) on said surface referenced to the x,y axes of said surface;

light source means for generating a light beam, said light source means being rigidly attached to said structure with said light beam directed onto said surface, said light beam having an intensity distribution on said surface substantially in accordance with an intensity distribution function I,(x,y) having as variables coordinates x and y of points on said surface and having as constants the radius r at which intensity distribution function I'"'"'(x,y) has diminished by a predetermined factor from a point (h,k) of peak light intensity I_o on said surface; and

means for determining from said output signal said intensity of light I(x,y) at a plurality of points (x,y), and determining a combination of values of I_o, r, h, and k which substantially minimizes a weighted sum of squares of the light intensity I(x,y) represented by said output signal less, a computed value of said intensity distribution function I'"'"'(x,y) for said plurality of points (x,y) and for monitoring change in shape of said structure by monitoring deviation of determined values of h and k from reference values.

13. The apparatus in accordance with claim 12 wherein said intensity distribution function is

14. The apparatus in accordance with claim 12 wherein said surface of said photodetecting means comprises an array of photodetectors, each photodetector controlling a magnitude of a separate portion of said photodetector means output signal in accordance with an intensity of light striking a said photodetector.

15. The apparatus in accordance with claim 12 wherein said light beam is a laser beam.

16. The apparatus in accordance with claim 12 wherein said structure is subject to vibration and wherein said apparatus further comprises a weight attached to said photodetecting means of mass sufficient to prevent substantial movement of said photodetecting means in response to the vibration of said structure.

17. An apparatus for monitoring change in shape of a structure comprising:

light source means rigidly attached to said structure for generating a light beam;

a plurality of photodetecting means rigidly attached to said structure, each comprising a planar surface having orthogonal x and y axes and producing an output signal representing an intensity of light I(x,y) at each of a plurality of points at coordinates (x,y) on said surface referenced to the x,y axes of said surface;

beam splitting means rigidly attached to said structure for directing portions of said light beam onto separate ones of said surfaces, each portion of said light beam having an intensity distribution on the surface onto which it is directed substantially in accordance which an intensity distribution function I'"'"'(x,y) having as variables coordinates x and y of points on the corresponding surface and having as constants the radius r at which intensity distribution function I'"'"'(x,y) has diminished by a predetermined factor from a point (h,k) of peak light intensity I_o on said surface; and

means for determining from the output signal produced by each of said photodetecting means the intensity of light I(x,y) at said plurality of points (x,y) on the surface of said each photodetecting means, for determining for each surface a combination of values of I_o and r and of said coordinates h and k which substantially minimizes a weighted sum of squares of the light intensity 1(x,y) represented by said output signal less a computed value of said intensity distribution function for a plurality of points (x,y) of said surface, for determining from said combination of values of coordinates h and k for a plurality of said surfaces parameters defining an estimated path of said light beam, for determining from said parameters the coordinates of a reference point on each of said surfaces, and for monitoring a change in shape of said structure by comparing the determined coordinates of said reference point of each surface to the determined h and k coordinates for said each surface.

18. The apparatus in accordance with claim 17 wherein said intensity distribution function is

19. A method for monitoring change in shape of a structure comprising the steps of:

attaching to said structure light source means for generating a light beam;

attaching to said structure a plurality of photodetecting means, each having a planar surface and producing an output signal representing an intensity of light I(x,y) at a plurality of points at coordinates (x,y) on said surface referenced to x,y axes of said surface;

directing portions of said light beam onto separate ones of said surfaces, each portion of said light beam having an intensity distribution on the surface onto which it is directed substantially in accordance with an intensity distribution function I'"'"'(x,y) having as variables coordinates x and y of points on the corresponding surface and having as constants the radius r at which intensity distribution function I'"'"'(x,y) has diminished by a factor of e^-2 from a point of peak light intensity I_o on said surface, which point of peak light intensity I_o is located at coordinates h and k on the corresponding surface.

determining from the output signal produced by ones of said photodetecting means said intensity of light I(x,y) at ones of said plurality of points (x,y) on surfaces of said ones of said photodetecting means;

determining for ones of said surfaces a combination of values of I_o, r, h, and k which substantially minimizes a weighted sum of the squares of I(x,y) less computed values for the intensity distribution function I'"'"'(x,y) for said plurality of points (x,y); and

ascertaining change in shape of said structure from determined values of h and k for said ones of said surfaces.

20. The method in accordance with claim 19 wherein said intensity distribution function is

21. The method in accordance with claim 19 wherein the step of ascertaining change in shape of said structure from determined values of h and k for said ones of said surfaces comprises the substeps of:

determining from said combination of values of coordinates h and k for a plurality of said surfaces the parameters defining an estimated path of said light beam,

determining from said parameters the coordinates of a reference point on ones of said surfaces, and

comparing the determining coordinates of the reference point of at least one of said surfaces to the determined h and k coordinates for said at least one surface, thereby to ascertain changes in shape of said structure.