Optics: measuring and testing – Shape or surface configuration – Triangulation
Reexamination Certificate
2000-01-10
2004-02-10
Smith, Zander V. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
Triangulation
C356S605000, C356S512000
Reexamination Certificate
active
06690474
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of surface measurement and, more specifically, to the field of non-contact surface measurement.
BACKGROUND OF THE INVENTION
Dimensional metrology, the measurement of the size and shape of objects, is very important in today's manufacturing environment in which machines perform much of the fabrication and assembly of complex objects composed of many subassemblies. The shape and size of each component in a complex assembly, such as an automobile, must be held to close tolerances to ensure that the components fit together properly.
Ideally such measurements of shape and size are accomplished without physical contact in order to save time in making the measurement. Many non-contact measurement methods make use of available machine vision systems. The measurement of surface contour information is an especially difficult problem in machine vision systems since depth information is often lost or is difficult to interpret. To compensate for the loss of depth information and the difficulty in interpreting the information which is available, many machine vision systems utilize light to create moire patterns on the surface of the object in order to obtain contour information. One disadvantage of the moiré technique is its inflexibility with respect to objects of different sizes. Objects of different sizes may require new corresponding physical setups. Due to this disadvantage, it is difficult to use a moire technique for large-scale objects. Another disadvantage of a moiré technique is that the resolution obtained using the technique may not be high enough for many applications
Interferometric methods have also been used when detailed measurements of the surface are needed. Although interferometric systems provide surface contour information, they are sensitive to vibrations in both the object being measured and the source of illumination being used.
What is needed is a technique which avoids these problems by resolving fringe order ambiguities, mitigating degradation due to speckle effects and attaining high resolution.
SUMMARY OF THE INVENTION
The invention is related to a method for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including the steps of providing two sources of radiation having a spatial distribution of spectral regions, illuminating the surface with radiation from each of the sources to produce a first fringe pattern at a first position on the surface, moving the first fringe pattern to a second position, generating a first wrapped cycle map in response to the first and second positions of the first fringe pattern, estimating fringe numbers in the first fringe pattern, changing the first fringe pattern to generate a second fringe pattern at a first position, moving the second fringe pattern to a second position, generating a second wrapped cycle map in response to the first and second positions of the second fringe pattern, estimating fringe numbers in the second fringe pattern in response to the estimated fringe numbers in the first fringe pattern, and determining three-dimensional position information of the point on the surface in response to the estimated fringe numbers in the second fringe pattern and the second wrapped cycle map.
The invention is further related to a method for synthesizing a wrapped cycle map corresponding to a fringe pattern of a predetermined spacing on a surface including the steps of providing two sources of radiation having a spatial distribution of spectral regions, illuminating the surface with radiation from each of the sources to produce a first fringe pattern at a first position on the surface, moving the first fringe pattern to a second position on the surface, generating a first wrapped cycle map in response to the first and second positions of the first fringe pattern, changing the first fringe pattern to generate a second fringe pattern at a first position, moving the second fringe pattern to a second position, generating a second wrapped cycle map in response to the first and second positions of the second fringe pattern, subtracting the second wrapped cycle map from the first wrapped cycle map, and wrapping the difference between the second wrapped cycle map and the first wrapped cycle map to generate a wrapped cycle map corresponding to the fringe pattern of the predetermined spacing.
The invention further relates to a method for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including the steps of generating a first and a second beam of radiation having a first frequency and being coherent with respect to one another, illuminating the surface with the second beam of radiation, generating a first interference pattern at a first position in response to the first beam of radiation and radiation from the second beam of radiation scattered by the surface, moving the first interference pattern to a second position, generating a first wrapped cycle map in response to the first and second positions of the first interference pattern, estimating intensity cycles in the first interference pattern, changing the first interference pattern to generate a second interference pattern at a first position, moving the second interference pattern to a second position, generating a second wrapped cycle map in response to the first and second positions of the second interference pattern, estimating intensity cycles in the second interference pattern in response to estimated intensity cycles in the first interference pattern, and calculating three-dimensional position information in response to the estimated intensity cycles in the second interference pattern and the second wrapped cycle map.
The invention further relates to a method for determining, on an object having a surface, three-dimensional position information of a point on the surface of the object including the steps of generating a first and a second beam of radiation being coherent with respect to one another, illuminating the surface with the second beam of radiation, generating a first interference pattern in response to the first beam of radiation and radiation from the second beam of radiation scattered by the surface, phase shifting one of the first and second beams of radiation with respect to the other of the first and second beams of radiation to generate a first phase shifted interference pattern, generating a first wrapped cycle map in response to the first interference pattern and the first phase shifted interference pattern, changing the first interference pattern to generate a second interference pattern, phase shifting one of the first and second beams of radiation with respect to the other of the first and second beams of radiation to generate a second phase shifted interference pattern, generating a second wrapped cycle map in response to the second interference pattern and the second phase shifted interference pattern, subtracting the second wrapped cycle map from the first wrapped cycle map, and wrapping the difference between the second wrapped cycle map and the first wrapped cycle map to generate a wrapped cycle map.
The invention also relates to an apparatus for projecting fringes onto a surface of an object including two sources of radiation having a spectral distribution, a collimator in optical communication with the two sources, the collimator generating two substantially collimated beams of broadband radiation, a diffractive grating in optical communication with the collimator, and a lens in optical communication with the diffractive grating, the lens generating two images of radiation having a spatial distribution of spectral regions.
The invention also relates to a method for projecting fringes onto a surface of an object including the steps of providing two sources of radiation separated by a distance and generating radiation having a spectral distribution, collimating the radiation to generate two substantially collimated beams of radiation, delin
Massachusetts Institute of Technology
Smith Zander V.
Testa Hurwitz & Thibeault LLP
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