Method and apparatus for digital morie profilometry calibrated for accurate conversion of phase information into distance measurements in a plurality of directions
First Claim
1. A method for measuring the profile of an object by digital moire interferometry which comprises the following steps:
- calibrating a volume in space in which volume the object is disposed during measurement to provide reference phase information identifying the locations in distance from an origin of a coordinate system of a multiplicity of sets of positions in said volume, each of said sets being in a different one of a multiplicity of parallel planes spaced a known distance from each other in said volume;
obtaining phase information from the profile of said object in said volume at said plurality of positions;
identifying from the phase information obtained from said profile, the ones of said planes on opposite sides of said profile; and
determining from the differences between said phase information from said profile and said sets of phase information for said planes on said opposite sides of said profile absolute distance measurements of the dimensions of said profile, at least through a cross-section thereof.
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Accused Products
Abstract
Projectors and cameras disposed about an object under test obtain digital moire information of overlapping aspects (views) of the object. The system is calibrated using a calibration pattern of straight lines on a flat reference surface and a projected pattern of lines which are perpendicular to the lines of the calibration pattern and contain marker fringes between predetermined lines. Each aspect is calibrated individually by stepping the calibration pattern along the axis of each camera so as to obtain a plurality of tables which relate phase information to distance in each of a plurality of planes spaced successively closer to the camera. The calibration tables define a calibrated volume in space between the cameras and projectors. When the object under test is located in this volume, the video signals from the camera are converted into digital moire information. This information is directly related to the calibration information and is converted with the aid of the calibration information into absolute distance measurements along the perimeters of cross-sections through the object.
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Citations
35 Claims
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1. A method for measuring the profile of an object by digital moire interferometry which comprises the following steps:
- calibrating a volume in space in which volume the object is disposed during measurement to provide reference phase information identifying the locations in distance from an origin of a coordinate system of a multiplicity of sets of positions in said volume, each of said sets being in a different one of a multiplicity of parallel planes spaced a known distance from each other in said volume;
obtaining phase information from the profile of said object in said volume at said plurality of positions;
identifying from the phase information obtained from said profile, the ones of said planes on opposite sides of said profile; and
determining from the differences between said phase information from said profile and said sets of phase information for said planes on said opposite sides of said profile absolute distance measurements of the dimensions of said profile, at least through a cross-section thereof. - View Dependent Claims (2, 3)
- calibrating a volume in space in which volume the object is disposed during measurement to provide reference phase information identifying the locations in distance from an origin of a coordinate system of a multiplicity of sets of positions in said volume, each of said sets being in a different one of a multiplicity of parallel planes spaced a known distance from each other in said volume;
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4. A method for measuring the profile of an object by digital moire interferometry which comprises the following steps:
- calibrating a volume in space in which volume the object is disposed during measurement to provide reference phase information identifying the locations in distance from an origin of a coordinate system of a plurality of sets of positions in said volume, each of said sets being in a different one of a plurality of parallel planes spaced a known distance from each other in said volume;
obtaining phase information from the profile of said object in said volume at said plurality of positions;
identifying from the phase information obtained from said profile, the ones of said planes on opposite sides of said profile;
determining from the differences between said phase information from said profile and said sets of phase information for said planes on said opposite sides of said profile absolute distance measurements of the dimensions of said profile, at least through a cross-section thereof; and
wherein said calibrating step is carried out by illuminating a target having a pattern of lines spaced from each other and paralleling a first of three orthogonal axes;
deriving a plurality of first tables each containing data representing a matrix of values representing distances from phase variations in the intensity of light reflected from said target at said set of positions from each of said plurality of said planes, said set of positions being along a second of said orthogonal axes which is also perpendicular to said lines of said target, said planes being spaced along a third of said orthogonal axes, each of said tables being derived with said target pattern disposed in a different one of said plurality of parallel planes;
projecting a ruling having a plurality of spaced parallel lines upon said target pattern so that the lines of said ruling are perpendicular to the lines of said target;
optically making at least a predetermined one of said ruling lines;
deriving a table containing data representing the difference in the phase of the variations in the intensity of the reflected light from said marked line and from a window spaced at a predetermined position along said first axis, said last named table identifying the positions of each of said planes along said third of said orthogonal axes;
deriving a second plurality of tables each containing data representing a matrix of phase information derived from the variations in the intensity of light reflected from said target pattern with said ruling projected thereon at said set of positions in each of said plurality of planes; and
said step of determining said dimensions comprising the steps of deriving said dimensions of said profile along said second axis from those of said first plurality of tables for planes straddling said profile and from the phase information from said object, and deriving said dimensions along said third of said axes from those of said second plurality of tables for the planes straddling said profile and from the phase information from said object. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
- calibrating a volume in space in which volume the object is disposed during measurement to provide reference phase information identifying the locations in distance from an origin of a coordinate system of a plurality of sets of positions in said volume, each of said sets being in a different one of a plurality of parallel planes spaced a known distance from each other in said volume;
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17. A system for measuring the profile of an object by digital moire interferometry which comprises means for calibrating a volume in space which volume the object is disposed during measurement to provide reference phase information identifying the locations of a multiplicity of sets of positions in said volume, each of said sets being in a different one of a multiplicity of parallel calibration planes spaced from each other in said volume;
- means for obtaining phase information from the profile of said object in said volume at said plurality of positions;
means for identifying from the phase information obtained from said profile, the ones of said calibration planes on opposite sides of said profile; and
means for determining from the differences between said phase information for said calibration planes on said opposite sides of said profile absolute distance measurements of the dimensions of said profile, at least through a cross-section thereof. - View Dependent Claims (18, 19)
- means for obtaining phase information from the profile of said object in said volume at said plurality of positions;
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20. A system for measuring the profile of an object by digital moire interferometry which comprises means for calibrating a volume in space which volume the object is disposed during measurement to provide reference phase information identifying the locations of a plurality of sets of positions in said volume, each of said sets being in a different one of a plurality of parallel calibration planes spaced from each other in said volume;
- means for obtaining phase information from the profile of said object in said volume at said plurality of positions;
means for identifying from the phase information obtained from said profile, the ones of said calibration planes on opposite sides of said profile;
means for determining from the differences between said phase information from said profile and said sets of phase information for said calibration planes on said opposite sides of said profile absolute distance measurements of the dimensions of said profile, at least through a cross-section thereof; and
wherein said calibrating means comprises a target having a pattern of lines spaced from each other and paralleling a first of three orthogonal axes;
means for illuminating said target, means for deriving a plurality of first tables each containing data representing a matrix of distance values derived from the phase variations in the intensity of light reflected from said target at said set of positions from each of said plurality of said planes, said set of positions from each of said plurality of said planes, said set of positions being along a second of said orthogonal axes which is also perpendicular to said lines of said target, said planes being spaced along a third of said orthogonal axes, each of said tables being derived with said target pattern disposed in a different one of said plurality of parallel planes;
means for projecting a ruling having a plurality of spaced parallel lines upon said target pattern so that the lines of said ruling are perpendicular to the lines of said target;
means for optically marking at least a predetermined one of said ruling lines;
means for deriving a table containing data representing the difference in the phase in the intensity of the light reflected from said marked line and at a predetermined position in a window spaced at a predetermined position perpendicular to the projected lines, said last named table identifying the positions of each of said planes along said third of said orthogonal axes;
means for deriving a second plurality of tables each containing data representing a matrix of phase information from light reflected from said target pattern with said ruling projected thereon at said set of positions in each of said plurality of planes; and
said means for determining said dimensions comprising means for deriving said dimensions comprising means for deriving said dimensions of said profile along said second axis from those of said first plurality of tables for planes straddling said profile and from the phase information from said object, said means for deriving said dimensions along said third of said axes from those of said second plurality of tables for the planes straddling said profile and from the phrase information from said object. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
- means for obtaining phase information from the profile of said object in said volume at said plurality of positions;
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33. A method for measuring the profile of an object by digital Moire interferometry which comprises the following steps:
- calibrating a volume in space in which volume the object is disposed during measurement to provide reference phase information identifying the locations and distance from an origin of a coordinate system of a plurality of sets of positions in said volume, each of said sets being in a different one of a plurality of parallel planes spaced a known distance from each other in said volume;
obtaining phase information from the profile of said object in said volume at said plurality of positions;
identifying from the phase information obtained from said profile, the ones of said planes on opposite sides of said profile;
determining from the differences between said phase information from said profile and said sets of phase information from said planes on said opposite sides of said profile absolute distance measurements of the dimensions of said profile, at least to a cross-section thereof; and
wherein said phase information is obtained by detecting the interference fringes between a target at each of said positions and a projected image both of which have spaced lines and one of which has a marked line which provides a marked fringe. - View Dependent Claims (34, 35)
- calibrating a volume in space in which volume the object is disposed during measurement to provide reference phase information identifying the locations and distance from an origin of a coordinate system of a plurality of sets of positions in said volume, each of said sets being in a different one of a plurality of parallel planes spaced a known distance from each other in said volume;
Specification