JP2008170282A - Shape measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring device capable of performing accurate three-dimensional shape measurement by creating a projection pattern so as to prevent influence of the surface shape of a specimen. <P>SOLUTION: This shape measuring device comprises a pattern projection section for projecting a predetermined projection pattern to the specimen, an imaging section for imaging the specimen to which the projection pattern is projected, a shape calculation section for calculating the position of the optical axis direction of a plurality of parts of the specimen corresponding to the projection pattern from an imaged image acquired by the imaging section, a brightness calculation section for performing position matching of the projection pattern projected by the pattern projection section with the imaged image acquired by the imaging section, and calculating the brightness of a point on an image surface of the imaged image, and a pattern correction section for correcting the brightness of the position on the projection pattern with the brightness of the point on the image surface of the imaged image acquired by the brightness calculation section. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for measuring a three-dimensional shape by pattern projection.

  Various techniques for measuring the surface shape of an object such as an industrial product have been proposed, and one of them is an optical three-dimensional shape measuring apparatus. There are various types of optical three-dimensional shape measurement devices and configurations, but a predetermined projection pattern (a striped pattern or a lattice pattern) is projected onto the test object, and the test object is imaged. From the above, there is a method for calculating the height of each image position by calculating the phase of the stripes at each image position (each pixel) and measuring the three-dimensional surface shape of the test object (see Patent Document 1).

  In such an apparatus, for example, a projection pattern composed of a fringe pattern is projected onto the surface of the test object, and a fringe pattern projected onto the test object from an angle different from the projection direction is imaged. The phase distribution of the fringe pattern is calculated from the captured image of the surface, and the three-dimensional shape of the surface of the test object is obtained using the principle of triangulation or the like.

  An example of the configuration is shown in FIG. 4, and the light from the light source 51 is projected onto the surface of the test object 54 through the projection pattern mask 52 having a striped pattern and the projection lens 53. The stripe pattern of the projection pattern mask 52 projected on the surface of the test object 54 is deformed according to the three-dimensional shape of the surface of the test object 54, and the pattern of the surface of the test object 54 thus deformed is projected. The image is picked up by the image pickup device 56 (for example, a CCD sensor) through the image pickup lens 55 from an angle different from the direction, and sent to the arithmetic processing device 57, where the calculation processing of the picked-up image data is performed. The arithmetic processing unit 57 calculates the phase distribution of the fringe pattern from the captured image data of the surface of the test object imaged in this way, and calculates the three-dimensional shape of the test object surface using the triangulation principle or the like. Processing is performed.

JP 2000-9444 A

  By the way, the above-mentioned three-dimensional shape measurement is performed because the scattered light on the test object is used. However, depending on the surface state of the test object and the incident angle of the projection pattern, the scattered light can be obtained sufficiently. Depending on the surface inclination, there is a problem that halation occurs due to the influence of specular reflection light, and a captured image of a projection pattern with an appropriate contrast ratio cannot be obtained. Naturally, when a three-dimensional measurement is performed using a captured image of such a projection pattern, the measurement result has an error.

  The present invention has been made in view of such a problem, and it is possible to generate a projection pattern and perform accurate three-dimensional shape measurement so as not to be affected by the surface shape of the test object. An object of the present invention is to provide a simple measuring device.

  In order to solve the above problems and achieve the object, a shape measuring apparatus according to the present invention images a pattern projection unit that projects a predetermined projection pattern onto a test object, and the test object on which the projection pattern is projected. The image projection unit, the shape calculation unit that calculates the position in the optical axis direction of the plurality of portions of the test object corresponding to the projection pattern from the captured image obtained by the imaging unit, and the pattern projection unit The projection pattern and the captured image obtained by the imaging unit are associated with each other, and the luminance calculation unit that calculates the luminance of a point on the image plane of the captured image is obtained by the luminance calculation unit. And a pattern correction unit that corrects the luminance of the point on the projection pattern according to the luminance of the point on the image plane of the captured image.

  The luminance calculation unit is configured to obtain a point on the projection pattern projected by the pattern projection unit and a captured image obtained by the imaging unit based on the shape measurement result of the test object obtained by the shape calculation unit. It is preferable that the position is associated with a point on the image plane.

  In addition, the pattern correction unit performs luminance correction on the point on the projection pattern performed using the luminance of the point on the projection pattern and the point on the image plane of the captured image obtained by the luminance calculation unit, It is preferable that the bright portion of the luminance is corrected so as to have a two-dimensional spread within the sensitivity range of the imaging unit.

  According to the present invention configured as described above, the luminance of the points on the projection pattern and the points on the image plane of the captured image is calculated, the luminance is corrected for the points on the projection pattern, Based on the principle of triangulation from the captured image of the projected pattern of the contrast ratio, the 3D shape of the test object is obtained, and the contrast ratio of the projected pattern captured by the surface shape of the test object has become extremely large Even in this case, it is possible to perform accurate three-dimensional shape measurement.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 shows a schematic configuration of a three-dimensional shape measuring apparatus according to the present invention. First, the shape measuring apparatus will be described with reference to FIG.

  The shape measuring device projects a light source 1, a projection pattern mask 2 for giving a stripe pattern to the light from the light source 1, and light from the light source 1 that has passed through the projection pattern mask 2 onto the surface of the test object 20. A pattern projection unit including the projection lens (group) 3 and an imaging unit including the imaging device 5 that captures the reflected light from the test object 20 via the imaging lens (group) 4 are configured. .

  In the pattern projection unit, the projection pattern mask 2 is constituted by, for example, a liquid crystal element, and the projection pattern generator 6 can generate a projection pattern (for example, a sinusoidal striped pattern) having an arbitrary pitch and an arbitrary luminance. Thereby, the light from the light source 1 passes through the projection pattern mask 2, is condensed by the projection lens 3, and a desired projection pattern formed by the projection pattern mask 2 is projected onto the surface of the test object 20. it can.

  The imaging unit includes an imaging device 5 (for example, a CCD camera) that captures an image of the test object 20 through the imaging lens 4 with reflected light from the test object 20. The image data of the test object 20 imaged by the imaging device 5 is sent to the arithmetic processing device 7, where the image arithmetic processing described below is performed, and the surface shape of the test object 20 is measured. Note that the pattern projection unit and the imaging unit are integrally fixed by a single frame, and the test object 20 is placed and supported on a support table (not shown).

  The arithmetic processing unit 7 includes a shape calculation unit 8 that calculates the position in the optical axis direction of each part corresponding to the pattern of the test object 20 from the image data of the test object 20 imaged by the imaging device 5, and a pattern projection unit. The positions of the points on the projection pattern mask 2 projected by the above and the points on the captured image plane obtained by the imaging device 5 are correlated, and the brightness of the points on the projection pattern mask 2 and the points on the captured image plane A luminance calculation unit 9 that calculates the luminance of the projection pattern mask 2, a pattern correction unit 10 that corrects the luminance of the projection pattern mask 2, and an image correction unit 11 that corrects the luminance of the captured image obtained by the imaging device 5.

  A method of measuring the surface shape of the test object 20 using the surface shape measuring apparatus configured as described above will be described below with reference to the flowchart of FIG.

  In this measurement, first, the projection pattern generation device 6 generates the projection pattern mask 2 into a first fringe pattern (a sinusoidal coarse fringe pattern having a pitch large enough to measure the shape of the test object 20) (step). S1). The test object 20 is irradiated with light from the light source 1 through the projection pattern mask 2 and the projection lens 3 to project the first fringe pattern on the surface of the test object 20. The light thus projected and reflected from the test object 20 is collected through the imaging lens 4, and the first stripe pattern projected on the test object surface is imaged by the imaging device 5 (step S2).

  The imaging by these imaging devices 5 is performed a plurality of times (for example, phase 1, phase 2, and phase 3 in FIG. 2) by changing the phase of the first fringe pattern formed by the projection pattern mask 2, and a set of imaging Obtain an image group. The image data obtained in this way is sent from the imaging device 5 to the arithmetic processing device 7.

  In general, in the pattern projection method, since there are a plurality of edge patterns or sinusoidal patterns having the same phase, it is necessary to distinguish (unwrap) from adjacent patterns. Here, the first stripe pattern (coarse stripe pattern having a large pitch) and the second stripe pattern (dense stripe pattern) having a smaller pitch than the first stripe pattern described below are projected to facilitate unwrapping. be able to.

  As shown in FIG. 3A, when the image data is sent as described above, the shape calculation unit 8 in the calculation processing device 7 calculates the position of the test object 20 in the optical axis direction (step S3). ). A projection pattern mask projected onto the test object 20 by calculating the position in the optical axis direction of the test object 20 (including a portion that cannot be clearly calculated) from the image data obtained by projecting the first fringe pattern. It is possible to associate the positions of the points on 2 and the points on the image plane of the captured image. Further, for example, the projection pattern mask 2 detects the point P (X, Y) on the screen of the picked-up image that is located in a portion where the position of the test object 20 in the optical axis direction cannot be calculated clearly. A point Q (x, y) on the projection pattern mask 2 that is not projected with a contrast ratio sufficient to 20 can be detected. Note that the correspondence between the points on the projection pattern mask 2 and the points on the image plane of the captured image is also performed by lighting each point on the projection pattern mask 2 and imaging the points on the image plane. be able to.

  Further, in the luminance calculation unit 9 in the arithmetic processing unit 7, the luminance B () of the point Q (x, y) on the projection pattern mask 2 on which the projection pattern mask 2 is not projected onto the test object 20 with a sufficient contrast ratio. The luminance B (X, Y) of the point P (X, Y) on the image plane of the captured image whose position is associated with x, y) and the point Q (x, y) is obtained (step S4). Therefore, the luminance B (x, y) of the point Q (x, y) can be associated with the luminance B (X, Y) of the point P (X, Y).

  Next, in order to measure the accurate shape of the test object 20, a second fringe pattern (a dense fringe pattern having a smaller pitch than the first stripe pattern) is projected onto the test object 20, but FIG. ), It is necessary to correct the luminance of the portion of the projection pattern mask 2 that is not projected onto the test object 20 with a sufficient contrast ratio. Therefore, in the pattern correction unit 10 in the arithmetic processing unit 7, the brightness B () of the point Q (x, y) on the projection pattern mask 2 on which the projection pattern mask 2 is not projected onto the test object 20 with a sufficient contrast ratio. x, y) is used to correct the luminance of the portion of the projection pattern mask 2 that is not projected onto the object 20 with a sufficient contrast ratio (step S5).

  Correction of the luminance of the portion of the projection pattern mask 2 where the projection pattern mask 2 is not projected onto the test object 20 with a sufficient contrast ratio is performed using the following equation (1).

S (x, y) = c [sin (ax + b) / B (x, y)] (1)
Here, S (x, y) is the luminance of the projection pattern mask 2 after correction, a is the pitch of the projection pattern mask 2, b is the phase of the projection pattern mask 2, and c is a luminance coefficient that can be arbitrarily determined. .

  In Equation 1, the brightness of the portion of the projection pattern mask 2 that is not projected onto the test object 20 with a sufficient contrast ratio is the image plane of the captured image where the projection pattern mask 2 is not projected onto the test object 20 with a sufficient contrast ratio. The luminance B (x, y) of the point Q (x, y) on the projection pattern mask 2 associated with the luminance B (X, Y) of the upper point P (X, Y) has an inverse relationship. Therefore, at a point P (X, Y) where the captured image cannot obtain a luminance B (X, Y) sufficient to enable a clear shape measurement of the test object 20, the point P (X, Y) The brightness B (x, y) of the point Q (x, y) on the corresponding projection pattern mask 2 can be corrected to a brightness sufficient to enable accurate shape measurement. The luminance is normalized by the sensitivity of the imaging device 5, so that the luminance B (x, y) can be spread with appropriate nonlinearity within the sensitivity range of the imaging device 5.

  The correction of the brightness of the portion of the projection pattern mask 2 in which the projection pattern mask 2 as described above is not projected on the test object 20 with a sufficient contrast ratio is performed by correcting the point Q (x, y) on the projection pattern mask 2 after the correction. The point Q (x on the projection pattern mask 2 on which the projection pattern mask 2 is not projected on the test object 20 with a sufficient contrast ratio is corrected by correcting the bright part of the brightness B (x, y) to be wide. , Y) and the position of the position P (X, Y) on the image plane of the captured image can be reduced.

  As shown in FIG. 3 (C), as described above, the portion of the projection pattern mask 2 that does not project the projection pattern mask 2 onto the test object 20 with a sufficient contrast ratio is corrected to generate a second fringe pattern ( Step S6). Then, in the same manner as the first fringe pattern, the second fringe pattern projected on the surface of the test object is imaged by the imaging device 5 (step S7).

  Further, as in the case of the first fringe pattern, the imaging device 5 changes the phase of the second fringe pattern and performs imaging a plurality of times (for example, phase 1, phase 2, and phase 3 in FIG. 2) to obtain image data. The image data obtained in this way is sent to the arithmetic processing unit 7, and the luminance C1 (C1) of the captured image obtained by projecting the second fringe pattern onto the test object 20 in the luminance calculation unit 9 in the arithmetic processing unit 7. X, Y) is calculated.

  However, since the second fringe pattern is generated by correcting the luminance of the portion of the projection pattern mask 2 that is not projected onto the test object 20 with a sufficient contrast ratio in the projection pattern mask 2, the second fringe pattern Even if the brightness distribution C1 (X, Y) of the captured image obtained by projecting is used as it is, an accurate shape measurement result of the test object 20 cannot be obtained.

  Therefore, the brightness C1 (X, Y) of the captured image obtained by projecting the second stripe pattern is set to the brightness R (X, Y) of the portion of the captured image corresponding to the brightness S (x, y) of the second stripe pattern. Y) and the brightness T (X, Y) of the captured image other than the portion corresponding to the brightness S (x, y) of the second stripe pattern, and the accurate shape measurement result of the test object 20 can be obtained. In order to obtain this, it is necessary to correct the luminance R (X, Y) again. Accordingly, in the image correction unit 11 in the arithmetic processing unit 7, the point P (on the image plane of the captured image corresponding to the luminance B (x, y) used when the projection pattern mask 2 is corrected (step S5). The luminance R (X, Y) is corrected using the luminance B (X, Y) of X, Y) (step S8).

  Here, since the projection with the second stripe pattern does not change the positional relationship of the projection pattern mask 2, the test object 20, the imaging device 5, etc. at the time of projection with the first stripe pattern, the first stripe pattern is not changed. The correspondence between the position on the projection pattern mask 2 obtained by the projection and the position on the image plane of the captured image can be used as it is.

  Correction of the luminance R (X, Y) of the captured image of a portion corresponding to the luminance S (x, y), which is a part of the luminance C1 (X, Y) of the captured image obtained by projecting the second stripe pattern The brightness C2 (X, Y) of the captured image obtained in this way is calculated using the following equation (2).

  C2 (X, Y) = R (X, Y) × B (X, Y) + T (X, Y) (2)

  Then, the phase value of each image is calculated using the luminance C2 (X, Y) of the captured image, and the shape of the test object 20 is measured using the principle of triangulation (step S9).

  As described above, in the captured image of the projection pattern mask 2 projected onto the test object 20, detailed phase information (accurate shape measurement of the test object 20 is performed on all necessary portions of the projection pattern mask 2. Therefore, the three-dimensional shape of the test object 20 can be accurately measured.

1 is a schematic configuration explanatory diagram showing a configuration of a three-dimensional shape measuring apparatus according to an embodiment of the present invention. It is a flowchart which shows the shape measuring method which concerns on the said invention. In the above-described shape measuring method, (A) is a schematic configuration explanatory diagram showing the correspondence between the projection point Q by the first fringe pattern projection and the position of the imaging point P, and (B) is a schematic configuration explanation showing the generation of the second fringe pattern. FIG. 4C is a schematic configuration explanatory diagram of the luminance distribution by the second stripe pattern projection. It is schematic structure explanatory drawing which shows the structure of the conventional shape measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Projection pattern mask 3 Projection lens 4 Imaging lens 5 Imaging apparatus 6 Projection pattern generation apparatus 7 Arithmetic processing apparatus 8 Shape calculation part 9 Luminance calculation part 10 Pattern correction part 11 Image correction part 20 Test object

Claims (3)

A pattern projection unit that projects a predetermined projection pattern onto the test object;
An imaging unit that images the object on which the projection pattern is projected;
A shape calculation unit that calculates positions in the optical axis direction of a plurality of portions of the test object corresponding to the projection pattern from a captured image obtained by the imaging unit;
A brightness calculation unit that associates positions of the projection pattern projected by the pattern projection unit and a captured image obtained by the imaging unit, and calculates a luminance of a point on an image plane of the captured image;
A pattern correction unit that corrects the luminance of a point on the projection pattern based on the luminance of the point on the image plane of the captured image obtained by the luminance calculation unit;
A shape measuring device comprising:   The luminance calculation unit, based on the shape measurement result of the test object obtained by the shape calculation unit, points on the projection pattern projected by the pattern projection unit and an image of a captured image obtained by the imaging unit The shape measuring apparatus according to claim 1, wherein the position is associated with a point on the surface.   The pattern correction unit performs luminance correction on the points on the projection pattern using the luminances of the points on the projection pattern and the points on the image plane of the captured image obtained by the luminance calculation unit. The shape measuring apparatus according to claim 1, wherein the bright portion is corrected so as to have a two-dimensional spread within a sensitivity range of the imaging unit.

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