Hidden change distribution grating and use in 3D moire measurement sensors and CMM applications

• US 5,319,445 A
• Filed: 09/08/1992
• Issued: 06/07/1994
• Est. Priority Date: 09/08/1992
• Status: Expired due to Term

• Current Assignee: Opton Co., Ltd.
• Original Assignee: John M. Fitts
• Inventors: Fitts, John M.
• Primary Examiner(s): ROSENBERGER, RICHARD A
• Application Number:
  US07/941,710
• Time in Patent Office: 637 Days
• Field of Search: 356/376, 356/375, 250/237 G, 250/227 G
• US Class Current: 356/604
• CPC Class Codes: G01B 11/254 Projection of a pattern, viewing through a pattern, e.g. moiré
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light

Abstract

A high-speed three-dimensional surface measurement system for use in determining the surface of an object from at least one electronic signal produced by a mini-moire sensor. At least one light source illuminates at least a surface area of the object with at least one fringe pattern. The light source has a hidden change distribution grating or matrix of gratings for producing the fringe pattern. The grating has hidden variations distributed substantially across the grating. The grating has a pseudo-random grating pattern in which a nominal fringe pattern has a small uniform period with the hidden variations distributed statistically across the grating. The hidden variations are so small that at any one point on the grating a noise-like value of the hidden variations is on the order of an overall noise equivalent phase value. A CCD camera receives reflected illumination from the surface area and provides an electronic signal representative of reflected illumination received thereby.

Claims

1. A high-speed three-dimensional surface measurement system for use in determining the surface of an object from at least one electronic signal using a moire process, comprising:

at least first means for illuminating at least a surface area of the object with at least one fringe pattern, said at least first means for illuminating having optical grating means for producing said at least one fringe pattern, said optical grating means consisting of a nominal pattern having a pattern frequency and small statistical variations in the pattern frequency such that phase calculations associated with the variations are unique and hidden in noise of the moire process;

at least one means for receiving reflected illumination from said surface area, said at least one means for receiving reflected illumination providing an electronic signal representative of reflected illumination received thereby; and

means for determining a surface phase of the surface are of the object from the electronic signal by utilizing the phase calculations associated with the variations in the pattern frequency, the surface phase being representative of the surface area of the object.

2. The system according to claim 1, wherein said optical grating means is a pseudo-random grating pattern in which a nominal fringe pattern has a small uniform period with the hidden variations distributed statistically across said optical grating means.

3. The system according to claim 2, wherein said at least one means for receiving has a noise equivalent phase value and wherein said hidden variations are so small that at any one point on the optical grating means a noise-like value of said hidden variations in one the order of said noise equivalent phase value of said at least one means for receiving.

4. The system according to claim 1, wherein energy of the hidden variations is distributed substantially evenly over said optical grating means.

5. The system according to claim 1, wherein energy of the minimal variations is distributed unevenly over said optical grating means.

6. The system according to claim 1, wherein said optical grating means has first and second hidden change distribution gratings oriented at right angles to one another.

7. The system according to claim 1, wherein said optical grating means has first and second polarization sensitive hidden change distribution gratings and wherein said system further comprises means for individually polarizing said first and second polarization sensitive hidden change distribution gratings to thereby separately produce first and second patterns.

8. The system according to claim 7, wherein each of said first and second polarization sensitive hidden change distribution gratings has a respective controllable light source.

9. The system according to claim 1, wherein said optical grating means is a Ronchi grating.

10. The system according to claim 1, wherein said optical grating means has first and second hidden change Ronchi gratings oriented at right angles to one another.

11. The system according to claim 10, wherein said system further comprises mean for rotating said optical grating means through a predetermined angle to insure sufficient triangulation between said at least one first means for illuminating and said at least one means for receiving illumination.

12. The system according to claim 10, wherein said system further comprises means for rotating said at least one means for receiving illumination through a predetermined angle to insure sufficient triangulation between said at least one first means for illuminating and said at least one means for receiving illumination.

13. The system according to claim 1, wherein said optical grating means has first and second polarization sensitive hidden change distribution gratings and wherein said system further comprises means for individually polarizing said first and second polarization sensitive hidden change distribution gratings to thereby produce first and second patterns.

14. The system according to claim 13, wherein each of said first and second polarization sensitive hidden change distribution gratings has a respective controllable light source.

15. The system according to claim 13, wherein said system further comprises means for rotating said optical grating means through a predetermined angle to insure sufficient triangulation between said at least first means for illuminating and said at least one means for receiving illumination.

16. The system according to claim 13 wherein said predetermined angle is in the range of 0°

to 45°

for a pattern of said first and second patterns for use on objects having knife edges.

17. The system according to claim 13, wherein said predetermined angle is in the range of 0°

to 30°

for a pattern of said first and second patterns for use on objects in general.

18. The system according to claim 1, wherein said system further comprises second means for illuminating at least said surface area of the object for providing two dimensional information to said at least one means for receiving reflected illumination.

19. Method for determining the surface of an object using a mini-moire sensor and a moire process, comprising the steps of:

providing an optical grating means consisting of a nominal pattern having a pattern frequency and small statistical variations in the pattern frequency such that phase calculations associated with the variations are unique and hidden in noise of the moire process;

projecting the pattern onto a surface area of an object;

recording an image intensity of the pattern projected on the surface area;

passing the image intensity through a first pass filter to generate a residual phase plus hidden pattern phase;

processing the generated residual phase plus hidden pattern phase in a matched filter that uses a known hidden change phase as a reference to produce a unique autocorrelation function;

providing an N modulus map for substantially every pixel in at least a portion of a field-of-view of the moire sensor; and

determining a surface phase of the surface area of the object phase from the residual phase plus hidden pattern phase, the autocorrelation function and the N modulus map, the surface phase being representative of the surface area of the object.

20. The method according to claim 19, wherein the method further comprises using a second pass filter to remove the hidden change phase from the surface phase.

21. The method according to claim 19, wherein a 2π

modulus N is calculated for substantially every pixel in at least a portion of a field-of-view relative to the object.

22. The method according to claim 19, wherein grating means is a hidden change distribution grating.

23. The method according to claim 19, wherein said optical grating means is a hidden change distribution matrix means.

24. The method according to claim 19, wherein said optical grating means is a hidden change Ronchi grating.

25. A high-speed three-dimensional surface measurement system for determining the surface of an object using a moire process, comprising:

a mini-moire sensor having a hidden change Ronchi grating consisting of a nominal Ronchi pattern having a pattern frequency and small statistical variations in the pattern frequency such that phase calculations associated with the variations are unique and hidden in noise of the moire process;

said mini-moire sensor having means for projecting the pattern onto a surface area of an object;

said mini-moire sensor having means for recording an image intensity of the pattern projected on the surface area;

means for passing the image intensity through a first pass filter to generate a residual phase plus hidden pattern phase;

means for processing the generated residual phase plus hidden pattern phase in a matched filter that uses a known hidden change phase as a reference to produce a unique autocorrelation function;

means for providing an N modulus map for substantially every pixel in at least a portion of a field-of-view of the moire sensor; and

means for determining a surface phase of the surface area of the object phase from the residual phase plus hidden pattern phase, the autocorrelation function and the N modulus map, the surface phase being representative of the surface area of the object.

26. The system according to claim 25, wherein said system further comprises a second pass filter for removing the hidden change phase from the surface phase.

27. An upgrade for a coordinate measuring machine for high-speed surface measurement of the surface of an object using a moire process, the coordinate measuring machine having at least a pan/tilt head, comprising:

a mini-moire sensor attached to the pan/tilt head of the coordinate measuring machine;

said moire sensor having at least first means for illuminating at least a surface area of the object with at least one fringe pattern, said at least first means for illuminating having optical grating means for producing said at least one fringe pattern, said optical grating means consisting of a nominal pattern having a pattern frequency and small statistical variations in the pattern frequency such that phase calculations associated with the variations are unique and hidden in noise of the moire process, and said moire sensor also having a single means for receiving reflected illumination from said surface area, said at least one means for receiving reflected illumination providing an electronic signal representative of reflected illumination received thereby; and

means for determining the three-dimensioned surface configuration of said surface area of the object from said electronic signal by utilizing the phase calculations associated with the variations in the pattern frequency;

wherein said coordinate measuring machine has at least one mode wherein said mini-moire sensor continuously scans the object.

28. The upgrade according to claim 27, wherein said upgrade further comprises a removable rotary table in the coordinate measuring machine and on which the object is supported, and wherein said rotary table eliminates extensive X-axis and Y-axis motions of the coordinate measuring machine.

29. The upgrade according to claim 27, wherein said upgrade further comprises means for providing an operator with a video display of the surface area of the object, said means for providing having a quick look display/operator interface.

30. The method according to claim 27, wherein the method further comprises the steps of:

initially automatically scanning the object with said mini-moire sensor to generate a full X-Y-Z data surface map of the object and storing said full X-Y-Z data surface map; and

generating specific measurements of the object from the determined three-dimensional surface configuration and said stored full X-Y-Z data surface map.

31. A high-speed three-dimensional surface measurement system for use in determining the surface of an object from at least one electronic signal using a moire process, comprising:

mini-moire sensor having at least first means for illuminating at least a surface area of the object with at least one fringe pattern, said at least first means for illuminating having optical grating means for producing said at least one fringe pattern, said optical grating means consisting of a nominal pattern having a pattern frequency and small statistical variations in the pattern frequency such that phase calculations associated with the variations are unique and hidden in noise of the moire process, and also having a single means for receiving reflected illumination from said surface area, said at least one means for receiving reflected illumination providing an electronic signal representative of reflected illumination received thereby;

means for processing said electronic signal by utilizing the phase calculations associated with the variations in the pattern frequency to provide at least a storable X-Y-Z image of the surface area of the object; and

means for moving said mini-moire sensor in order to scan the object.

32. The system according to claim 31, wherein said system further comprises second means for illuminating at least said surface area for providing two dimensional information to said means for receiving reflected illumination.

33. The system according to claim 31, wherein said system further comprises means for producing strobed illumination in said first means for illumination.

34. The system according to claim 31, wherein said single means for receiving reflected illumination is a CCD camera having a CCD array and wherein camera electronics associated with said CCD camera have at least one electronic shutter for freezing an image into the CCD array.

35. The system according to claim 31, wherein said means for processing has:

moire video controller means for interfacing with and controlling at least said mini-moire sensor and for forming X-Y-Z data from the electronic signal from the moire sensor;

moire data processor means for processing the X-Y-Z data derived from the electronic signal from the moire sensor;

data analysis processor means for user analysis of the X-Y-Z data;

moire video network means for connecting the moire data processor means to the moire video controller means; and

data transfer network means for connecting the data analysis processor means to the moire data processor means.