Optical measuring apparatus and method

• US 4,708,483 A
• Filed: 06/28/1985
• Issued: 11/24/1987
• Est. Priority Date: 06/28/1985
• Status: Expired due to Fees

• Current Assignee: Radian International, LLC (Aecom Incorporated)
• Original Assignee: Rexnord Corporation
• Inventors: Lorenz, Robert D.
• Primary Examiner(s): Rosenberger, R. A.
• Assistant Examiner(s): Cooper, Crystal D.
• Application Number:
  US06/750,348
• Time in Patent Office: 879 Days
• Field of Search: 356/376, 356/375, 356/1
• US Class Current: 356/602
• CPC Class Codes: G01B 11/026 by measuring distance between sensor and object G01B11/0608 takes precedence
• CPC Class Codes: G01B 11/26 for measuring angles or tapers; for testing the alignment of axes

Abstract

An optical triangulation probe is provided for measuring the distance and inclination of a surface. A light source is utilized for projecting a beam toward the surface to form a light spot on the surface. The image of the light spot is reflected and formed on a light detector means which produces a signal representation of the image intensity distribution of the light spot image and the location of the image on the detector means. Estimating means utilizes the signal representation of the light spot image and a signal representation of a theoretical image to estimate the location of the light spot image on the detector means. The distance of the surface and its inclination as established upon making the estimation due to the known triangulation relationship between the location of the light spot image on the detector means and the location of the light spot on the surface.

Claims

1. In an optical triangulation probe apparatus for measuring the distance of a surface utilizing light reflected from the surface and including a light source projecting a beam of light toward the surface, the combination comprising:

an actual light spot image having a predetermined known image intensity distribution shape and formed from the light reflected from the surface;

detector means for receiving the actual light spot image and producing a plurality of signals representative of the image intensity distribution of the actual light spot image shape and the location of the image on the detector means, the position of the actual light spot on the detector means having a known relationship to the distance of the surface; and

estimating means containing a signal representation of a theoretical reference light spot image intensity shape and the spatial location of the theoretical reference light spot image for receiving the plurality of signals representative of the intensity distribution of the actual light spot image shape and estimating the spatial location of said plurality of signals representative of the intensity distribution of the actual light spot image coinciding with the signal representation of the theoretical reference light spot image shape whereby the surface distance is measured due to the known relationship between the position of the actual light spot image and the distance of the surface.

2. The apparatus according to claim 1 wherein the sizes of the actual light spot image shape and the theoretical light spot image shape are substantially equal.

3. The apparatus according to claim 1 or 2 wherein the actual light spot image shape and the theoretical desired light spot image shape have the same image function.

4. The apparatus according to claim 3 wherein the actual light spot image shape on the detector means is substantially constant in size.

5. In an optical triangulation probe apparatus for measuring the displacement of a surface from a reference position utilizing light reflected from the surface and including a light source projecting a beam of light toward the surface, the combination comprising:

an actual light spot image having a predetermined known image intensity distribution shape and formed from the light reflected from the surface;

detector means for receiving the actual light spot image and producing a signal representation of both the intensity distribution of the image shape of the actual light spot image and the position on the detector means at which the actual light spot image is received;

a data base containing a signal representation of both the intensity distribution of a theoretical desired light spot image shape and a reference spatial location of the theoretical light image shape corresponding to the reference position of said surface; and

estimating means receiving the signal representation of the intensity distribution of the theoretical desired light spot image shape and its spatial location and the signal representation of the intensity distribution of the actual light spot image shape for calculating the cross correlation function of said signal representations at the reference location of the theoretical desired image shape and at additional spatial locations of the theoretical desired light image shape until an estimation of the peak value of the cross correlation function is obtained; and

means for identifying the distance between the reference spatial location at which the initial cross correlation function is calculated and the spatial location at which the peak value of the cross correlation function is calculated, said distance being representative of the displacement of said surface from the reference position.

6. The apparatus according to claim 5 wherein:

the detector means comprises a plurality of juxtaposed photodiodes each receiving a portion of the actual light spot image and producing a signal comprising a part of the signal representation of the image intensity distribution of the actual light spot image, said signal having a width of one photodiode; and

the actual light spot image has an image width in terms of diodes such that the standard deviation of the location estimator due to image noise does not exceed 1.0 diode.

7. The apparatus according to claim 6 wherein the image width of the actual light spot is such that the standard deviation of the location estimator does not exceed 0.1 diode.

8. The apparatus according to claim 6 or 7 wherein the image width of the actual light spot image is in the range of 5 to 20 diodes.

9. The apparatus according to claim 6 wherein the theoretical desired light spot image and the actual light spot image both have shapes such that the cross correlation function of the two image shapes is unimodal in character.

10. The apparatus according to claim 5 or 9 wherein the theoretical desired light spot image and the actual light spot image both have shapes such that the peak value of the cross correlation function of the two image shapes is uniquely identified.

11. The apparatus according to claim 5 wherein both the theoretical desired light spot image and the actual light spot image have Gaussian image shape.

12. The apparatus according to claim 5 further comprising indicating means responsive to the identifying means for indicating the displacement of the surface from its reference position.

13. The apparatus according to claim 5 wherein the beam of light is collimated such that the size of the actual light spot image on the detector means is independent of the position of the surface.

14. The apparatus according to claim 5 or 13 wherein the actual light spot image shape on the detector means is substantially constant in size.

15. The apparatus according to claim 5 wherein the sizes of the actual light spot image shape and the theoretical desired light spot image shape are substantially equal.

16. The apparatus according to claim 5 or 15 wherein the actual light spot image shape and the theoretical desired light spot image shape have the same image shape function.

17. A method utilizing light for locating the position of a surface comprising the steps of:

projecting an actual light spot having a predetermined known image intensity distribution shape onto said surface;

reflecting light from the surface to form an actual image of the light spot on a light detector means at a location on the detector means having a known relationship to the position of the surface;

producing a plurality of signals with the detector means representative of the intensity distribution of the actual light spot image on the light detector means and indicative of the spatial location of the actual image on the detector means;

generating a plurality of signals representative of the intensity distribution of a theoretical desired light spot image shape; and

calculating the cross correlation function of the two light spot image shapes from their representative signals at a spatial reference location of the theoretical desired light spot image shape relative to said actual light spot image spatial location and at additional closer locations of the two image shapes until the peak value of the cross correlation function is calculated to determine the spatial location of the actual light spot image relative to the reference location of the theoretical desired light spot image whereby the position of the surface is established due to the known relationship between the spatial location of the actual light spot image on the light detector means and the position of the surface.

18. The method according to claim 17 further comprising the step of indicating the position of the surface.

19. The method according to claim 17 wherein the cross correlation function calculation is accomplished by calculating a unimodal cross correlation function.

20. The method according to claim 17 or 19 wherein the step of projecting an actual light spot onto the surface is accomplished by projecting a light spot having an image that contributes to the unimodal character of a cross correlation function calculated with the use of the actual image shape.

21. The method according to claim 20 wherein the step of generating a plurality of signals is accomplished by generating a plurality of signals representative of the intensity distribution of a theoretical desired light spot image shape that contributes to the unimodal character of a cross correlation function calculated with the use of the theoretical desired image shape.

22. The method according to claim 17, 18, 19, or 21 wherein the light detector means comprises an array of photodiodes, and the step of calculating the cross correlation function is accomplished by initially making calculations at spatial intervals corresponding to the widths of individual photodiodes and, when calculated cross correlation values approach a peak value, making further calculations at spatial intervals less than the width of each photodiode.

23. The method according to claim 17 wherein the steps of projecting a light spot onto said surface and generating a plurality of signals is accomplished by projecting a light spot onto the surface having a Gaussian image intensity distribution shape and generating a plurality of signals representative of a Gaussian image intensity distribution shape.

24. The method according to claim 17 wherein the steps of projecting a light spot onto said surface and generating a plurality of signals are respectively accomplished by projecting a light spot onto the surface having an image intensity distribution shape function that is recursive in form and generating a plurality of signals representative of an image intensity distribution shape function that is recursive in form.

25. A method utilizing light for locating the position of a surface comprising the steps of:

projecting onto the surface an actual light spot having an image intensity distribution shape that contributes to the unimodal character of a cross correlation function calculated with the use of the image shape;

reflecting light from the surface to form an actual image of the light spot on a light detector means at a location on the detector means having a known relationship to the position of the surface;

producing a plurality of signals with the detector means representative of the intensity distribution of the actual light spot image shape on the detector means and indicative of the spatial location of the actual image on the detector means;

generating a plurality of signals representative of the intensity distribution of a reference light spot image shape; and

calculating a unimodal cross correlation function of the two light spot image shapes from their representative signals at a spatial reference location of the reference light spot image shape relative to the actual light spot image spatial location and at additional closer relative locations of the two image shapes until the peak value of the cross correlation function is calculated;

determining the location of the actual light spot image shape relative to the spatial reference location of the reference light spot image shape using the location of the reference light spot image shape when the peak value of the cross correlation is calculated and the spatial reference location of the reference light spot image shape; and

indicating the position of the surface using the known relationship between the location of the actual light spot image shape as determined and the position of the surface.

26. The method according to claim 25 wherein the step of generating a plurality of signals is accomplished by generating a plurality of signals representative of the intensity distribution of a reference light spot image shape that contributes to the unimodal character of a cross correlation function calculated with the use of the reference image shape.

27. The method according to claim 25 wherein the step of generating a plurality of signals is accomplished by generating a plurality of signals representative of the intensity distribution of a theoretical desired light spot image shape that contributes to the unimodal character of a cross correlation function calculated with the use of the theoretical desired image shape.

28. A method utilizing light for locating the position of a surface comprising the steps of:

projecting onto the surface a light spot having an image intensity distribution shape that contributes to the unique identification of the peak value of a cross correlation function calculated with the use of the function of the light spot image shape;

reflecting light from the surface to form an actual image of the light spot on a light detector means at a location on the detector means having a known relationship to the position of the surface;

producing a plurality of signals with the detector means representative of the intensity distribution of the actual light spot image shape on the detector means and indicating the spatial location of the actual image on the detector means;

generating a plurality of signals representative of the intensity distribution of a reference light spot image shape that contributes to the unique identification of the peak value of a cross correlation function calculated with the use of said representative signals; and

calculating the cross correlation function of the two light spot image shapes from their representative signals at a spatial reference location of the reference light spot image shape relative to the actual light spot image spatial location and at additional closer relative locations of the two image shapes until the peak value of the cross correlation function is calculated to determine the location of the actual light spot image relative to the reference location of the reference light spot image whereby the position of the surface is located due to the known relationship between the spatial location of the actual light spot image on the light detection means and the position of the surface.

29. In an optical probe apparatus for measuring the angle of inclination of a surface and including a light source, the combination comprising:

optical means producing from the light source a plurality of parallel light beams and directing the light beams toward the surface to form a plurality of light spots each corresponding to a light beam;

detector means on which an actual image of each of said light spots is formed by light reflected from the surface for producing a signal representation of the location of each of the actual light spot image shapes on the detector means, the positions of each of the actual light spot images on the detector means having a known relationship to the distance of the surface from the probe and the inclination of the surface such that each ofthe light spots on the surface can be uniquely spatially located; and

estimating means receiving said signal representations for determining from the signal representations the spatial location of the light spots on the surface and the inclination of the surface.

30. The apparatus according to claim 29 wherein the estimating means comprises computer means for calculating the inclination of the surface from the signal representations

31. The apparatus according to claim 29 wherein the estimating means comprises a data base containing a stored signal representation of the relationship between the inclination of the surface and the distance on the detector means between predetermined pairs of actual light spot images, the predetermined pairs of actual light spot images corresponding to those pair of light spots between which it is desired to determine the inclination of the surface, whereby the estimating means can estimate the inclination of the surface by use of the data base.

32. The apparatus according to claim 29 further comprising:

a data base containing a reference signal representation of both the intensity distribution of a reference light spot image shape and a reference spatial location corresponding to the distance of the surface from the probe; and

wherein

the estimating means receives the reference signal representation and calculates the cross correlation function of the reference signal representation and the signal representation of one of the actual light spot images at said reference location and at additional spatial locations of the reference light spot image shape until an estimate of the peak value of the cross correlation function is obtained, the distance between the reference signal representation at its reference location and its location when said peak value is calculated being an estimate of the location of the actual light spot image shape, and therefore the distance of the surface from the probe due to the known relationship between the position of the actual light spot images and the distance of the surface from the probe.

33. The apparatus according to claim 32 wherein:

the reference light spot image shape is a theoretical desired light spot image shape; and

the actual light spot shapes each have a predetermined known image shape.

34. The apparatus accordinf to claim 33 wherein the estimating means calculates the cross correlation function of the theoretical desired signal representation and the signal representation of a second one of the actual light spot image shapes at said reference location and at additional spatial locations of the theoretical desired light spot image shape until an estimate of the peak value of the cross correlation function is obtained with respect to the second actual light spot image shape, the distance between the reference singal representation at its reference location and its location when the peak value related to the second actual light spot image shape is calculated being an estimate of the location of the second actual light spot image shape, the distance between the locations of the second actual light spot image shpae and said one actual light spot image shape on the detector means being an estimate of the inclination of the surface due to the known relationship between the positions of each of the light spot image shapes and the inclination of the surface. PG,43

35. The apparatus according to claim 33 wherein the theoretical desired light spot image shape and the actual light spot image shape both are such that they contribute to a unimodal character of the cross correlation function.

36. The apparatus according to claim 29, 30, 31, 32, 33, 34 or 35, wherein each of said parallel light beams are collimated, such that the size of the actual light spot image on the detector means is independent of the distance of the surface from the probe.

37. The apparatus according to claim 29, 30, 31, 32, 33, 34, or 35, wherein the sizes of the actual light spot image shape and the reference light spot image shape are substantially equal.

38. The apparatus according to claim 29, 30, 31, 32, 33, 34 or 35, wherein the actual light spot image shape and the reference light spot image shape have the same image shape function.

39. The apparatus according to claim 29 further comprising:

an imaging lens having an opticl axis, the optical axis and a first pair of the plurality of beams being positioned such that the pair of beam intersect the optical axis and define a first probing plane, inclination of the surface occurring in the first probing plane; and

the receiving surface of the detector means is aligned in the probing plane.

40. The apparatus according to claim 39 wherein:

a second pair of said plurality of beams define a second different probing plane, inclination of the surface occurring in the second probing plane.

41. A method, utilizing a light source for locating the position and inclination of a surface comprising the steps of:

producing from the light source a plurality of parallel light beams having a predetermined known image intensity distribution shape and directing the light beams toward the surface to form a plurality of light spots each corresponding to a light beam and having said predetermined known image intensity distribution shape;

reflecting light from the surface to form a plurality of actual light spot image shapes each having said predetermined known image intensity distribution shape on a light detector means at locations on the detector means each having a known relationship to the inclination of the surface and to the distance of the surface from a reference position;

producing signal representation with the detector means of the intensity distribution of each of the plurality of actual light spot image shapes and indicative of the spatial location of the actual light spot image shapes on the detector means;

generating a signal representation of the intensity distribution of a theoretical desired light spot image shape;

calculating from their signal representations the cross correlation function of the theoretical desired image shape and the first one of a pair of actual light spot image shapes and the cross correlation function of the theoretical desired image shape and the second one of said pair of actual light spot image shapes at a spatial reference location and at additional closer locations of the theoretical desired light spot image shape relative to the actual light spot image shape spatial locations of each one of the pair of actual light spot image shapes until the peak value of the cross correlation function is calculated for each of the pair of actual light spot image shapes to determine the spatial location of each of the pair of actual light spot image shapes relative to the reference location of the theoretical light spot images whereby the position and inclination of the surface is established due to the known relationship between the locations of the pair of actual light spot image shapes on the light detector means and the position and inclination of the surface.

42. The method according to claim 41 in which, in the steps of calculating the two cross correlation functions, the calculation of the functions is performed simultaneously.

43. The method according to claim 41 wherein;

the step of calculating the two cross correlation functions is accomplished with a pair of actual light spot image shapes which have their corresponding light spots located in a first plate; and

further comprising the step of performing said step of calculating the two cross correlation functions using a second pair of actual light spot image shapes located in a second different plane.

44. The method according to claim 43 wherein the first and second pair of actual light spot image shapes have one common light spot image shape.

45. In an optical probe apparatus for measuring the angle of inclination of a surface and including a light source producing a beam of light, the combination comprising:

optical means positioned in the path of the beam of light for dividing the beam of light into two parallel light beams and directing the two parallel light beams toward the surface to form two actual light spots on the surface and cause light to reflect from the surface;

detector means having a reflected light receiving surface on which an image of each of the two light spots is formed for producing a signal representation of the location of each of the light spot images on the detector means, the positions of the two light spot images on the detector means having a known relationship to the distance of the surface from the probe and the inclination of the surface such that each of the light spots on the surface can be uniquely spatially located; and

means receiving said signal representations for determining from the signal representation the spatial location of the light spots on the surface and the inclination of the surface.