JP2008309551A - Method and apparatus for shape measurement and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shape measuring method capable of improving measurement accuracy by reducing the effects of multiple reflection. <P>SOLUTION: The shape measuring method comprises steps (S101-S103) for setting the reduction or quenching of part of a projection pattern multiply reflected at a surface of an object to be inspected and imaged and steps (S104-S105) for projecting the projection pattern reduced or quenched by the pattern projection part in the last steps to the object to be inspected, imaging, at an imaging part, the object to be inspected to which the projection pattern is projected, and measuring the three-dimensional shape of the object to be inspected on the basis of images of the object to be inspected to which the projection pattern reduced or quenched in the last steps is projected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a shape measuring method for measuring a surface shape (three-dimensional shape) of an industrial product, etc., a storage medium storing the shape measuring method, and a shape measuring apparatus.

  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 (striped pattern or lattice pattern) is projected onto the test object, and the test object is imaged. There is a technique that calculates the height of each image position by calculating the fringe phase at each image position (each pixel) and measures the three-dimensional shape of the test object (see, for example, Patent Document 1).

  In such an apparatus, for example, a projection pattern consisting of a fringe pattern is projected onto the surface of a test object (measuring 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 using the surveying principle or the like, and the three-dimensional shape of the surface of the test object is obtained.

An example of the configuration is shown in FIG. 6, and the light from the light source 51 is projected onto the surface of the test object 54 through the projection pattern mask 52 and the projection lens 53 having a stripe pattern. 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 An image is picked up by an image pickup device (for example, a CCD sensor) through an image pickup lens 55 from an angle different from the projection direction, and sent to the arithmetic processing device 57, where the picked-up image data is processed. In the arithmetic processing unit 57, the phase distribution of the fringe pattern is calculated using the imaged image data of the surface of the object thus imaged using the principle of triangulation, etc., and the three-dimensional shape of the surface of the object is calculated. Processing is performed.
JP 2000-9444 A

  However, in such a shape measurement method, when the surface of the test object is a glossy surface such as a metal surface, the pattern image projected on the other surface may cause multiple reflections depending on the shape of the test object. However, there is a possibility that the measurement accuracy is lowered due to reflection in the pattern image of the surface to be originally measured.

  The present invention has been made in view of such problems, and provides a shape measuring method in which the influence of multiple reflections is reduced and measurement accuracy is improved, and a storage medium storing the shape and a shape measuring apparatus. With the goal.

  In order to achieve such an object, a shape measuring method according to the present invention includes a pattern projecting unit that projects a predetermined projection pattern onto a test object, and the test object on which the projection pattern is projected by the pattern projecting unit. A shape measuring method using a shape measuring device that measures a three-dimensional shape of the test object based on an image of the test object imaged by the imaging unit, A first step of performing a setting for dimming or extinguishing a part of the projected pattern to be imaged by multiple reflection on the surface of the specimen; and the dimming or extinction in the first step by the pattern projection unit The projected pattern is projected onto the test object, and the test object on which the projection pattern that has been dimmed or extinguished is imaged by the imaging unit, and the dimming or extinction is performed. Wherein the projection pattern is is projected based on the image of the object, and a second step of measuring the three-dimensional shape of the test object.

  In the above-described invention, the projection pattern has a periodic striped pattern, and the first step generates a plurality of types of the projected patterns having different periods of the striped pattern by the pattern projection unit. A first sub-step of projecting, a second sub-step of imaging the test object onto which the projection pattern is projected, for each of the plurality of types of projection patterns by the imaging unit; and the second sub-step A third sub-step for calculating a position at which the multiple reflection occurs on the surface of the test object based on image information of the test object imaged for each of the plurality of types of the projection patterns; And a fourth substep for performing a setting for dimming or extinguishing a part of the projection pattern based on the position where the multiple reflection occurs calculated in the substep. Arbitrariness.

  In the above-described invention, it is preferable that in the fourth sub-step, the position where the light is reduced or extinguished in the projection pattern is specified by performing ray tracing from the position where the multiple reflection occurs.

  A storage medium according to the present invention stores the shape measuring method according to the above-described invention.

  The shape measuring apparatus according to the present invention includes the storage medium according to the above-described invention.

  According to the present invention, it is possible to improve the measurement accuracy by reducing the influence of multiple reflection.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 shows a schematic configuration of a three-dimensional shape measuring apparatus in which the shape measuring method according to the present embodiment is used. First, the shape measuring apparatus will be described with reference to FIG. In FIG. 1, the shape measuring apparatus M is shown in FIGS. 1 (a) and 1 (b). However, this is the same, and for the sake of convenience of description, the projection pattern mask 2 is striped at equal intervals. A projection pattern PT1 having a pattern is shown in FIG. 1A, and a projection pattern PT2 is formed by quenching (or dimming) a part of a striped pattern (projection pattern PT1) on the projection pattern mask 2. This is shown in FIG.

  The shape measuring device M 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 10. The pattern projection unit MA including the projection lens 3 to be imaged and the imaging optical system MB including the imaging device 7 that captures the reflected light from the test object 10 via the imaging lens 6 are configured.

  In the pattern projection unit MA, the projection pattern mask 2 is composed of a liquid crystal element or the like, receives a control signal from the display control unit 8 electrically connected to the liquid crystal element, and has an arbitrary shape, transmittance, and pitch. A pattern (for example, a periodic striped pattern PT1 whose luminance distribution is a sine wave function) can be formed. As a result, the light from the light source 1 passes through the projection pattern mask 2 and is condensed by the projection lens 3, thereby projecting a desired projection pattern PT1 formed by the projection pattern mask 2 onto the surface of the test object 10. Can be made.

  In the imaging optical system MB, the imaging device 7 is composed of a CCD camera or the like that receives light from the test object 10 and images the test object 10, and can capture an image of the projection pattern PT1 reflected by the test object 10. It is like that. Further, the image data of the test object 10 imaged by the imaging device 7 is sent to the arithmetic processing device 9, where predetermined image calculation processing is performed to calculate the height of the surface of the test object 10, and The three-dimensional shape (surface shape) of the specimen 10 is obtained.

  Next, the shape measuring method of the test object 10 by the shape measuring apparatus M configured as described above will be described below with reference to the flowchart shown in FIG. The shape measuring method (program) is stored in a storage medium in the arithmetic processing unit 9. First, in step S101, as shown in FIG. 1A, the pattern projection unit MA projects a striped projection pattern PT1 (sinusoidal striped pattern) onto the test object 10, and the projection pattern PT1 is projected. The detected object 10 is imaged by the imaging unit MB. At this time, the light from the light source 1 is irradiated onto the test object 10 via the projection pattern mask 2 and the projection lens 3, and the reflected light from the test object 10 forms an image on the image sensor 7 via the imaging lens 6. The image of the test object 10 onto which the projection pattern PT1 is projected is picked up by the image sensor 7 and a measurement image of the test object 10 is acquired.

  The measurement image data of the test object 10 obtained in this way is sent from the image sensor 7 to the arithmetic processing device 9. In the present embodiment, the display control unit 8 and the projection pattern mask 2 project two types of projection patterns PT1 having different fringe periods (pitch), and each projection pattern PT1 in each period (pitch). Then, the image of the test object 10 on which the pattern is projected is captured by the imaging unit MB.

  Further, in this embodiment, in order to obtain the phase of the pattern projected on the test object 10 by the phase shift method, the pattern of three types of projection patterns PT1 whose phases are changed by the display control unit 8 and the projection pattern mask 2 are used. An image of the projected object 10 is captured. At this time, due to the phase connection, the image pickup unit MB can pick up the projection pattern PT1 at each phase by changing the period (pitch) of the striped pattern as required by the display control unit 8 and the projection pattern mask 2. It is performed once, and a set of measurement image data groups is acquired.

  When the measurement image data is sent in this way, in step S102, the arithmetic processing unit 9 performs a predetermined arithmetic process, and based on the image data picked up in step S101, the target is measured using the principle of triangulation. The height of the surface of the specimen 10 is calculated, and the three-dimensional shape (surface shape) of the specimen 10 is measured. At this time, the height of the surface of the test object 10 (two types) is calculated based on two types of projection patterns PT1 having different stripe pattern periods (pitch), and the three-dimensional shape of the test object 10 is calculated. Measure.

  Next, in step S103, a position where multiple reflection occurs on the surface of the test object 10 is calculated and estimated from the surface height of the test object 10 calculated based on the two types of projection patterns PT1.

  Here, consider a case where the reflected light from the test object 10 causes multiple reflection due to irregular reflection or the like. When the surface of the test object 10 is a glossy surface, as shown in FIG. 1A, a part PTa of the projection pattern that causes multiple reflection may be reflected in the image of the test object 10. Considering the reflectance of the surface of the test object 10, it is assumed that the multiple reflected light detected by the imaging unit MB is at most up to double reflected light, and the double reflected light is detected by the imaging unit MB. The manner in which light from the pattern projection unit MA causes double reflection in the test object 10 and reaches the imaging unit MB is indicated by a broken line in FIG. 3, and a case where reflection due to multiple reflection (double reflection) occurs. Can be considered as a case where the light from the pattern projection unit MA is reflected at the point P2 on the surface of the test object 10 and then reflected at the point P1 to reach the imaging unit MB. FIG. 4 shows an example in which the light from the pattern projection unit MA causes double reflection at the test object 10 to cause reflection. The luminance I at the point where such reflection occurs is the amplitude of the luminance of the reflected light from the point P1 to be measured, and the amplitude of the luminance of the reflected light from the point P2 causing multiple reflection (double reflection). Can be expressed by the following conditional expression (1).

  I = a × sin (θ0 + θs + θp1) + b × sin (θ0 + θs + θp2) (1)

  Here, the first term of the conditional expression (1) represents the luminance due to the projection pattern PT1 at the point P1, and the second term represents the luminance due to the reflection from the point P2 to the point P1. Further, θ0 is an initial phase, θs is a phase for the phase shift method, θp1 is a phase based on the three-dimensional coordinates of the point P1, and the first term of the conditional expression (1), that is, the phase at the point P1 is θ0, It can be expressed as the sum of θs and θp1. Furthermore, θp2 is the phase of the point P2 in three-dimensional coordinates, and the second term of the conditional expression (1), that is, the phase at the point P2 can be expressed by the sum of θ0, θs, and θp2.

  As can be seen, the phase difference between the point P1 and the point P2 is θp1−θp2, and when this θp1−θp2 changes, the shape measurement result changes. Since the value of θp1−θp2 varies depending on the period (pitch) of the striped pattern, the presence or absence of reflection can be determined using this. However, since the above formula is established only in the phase change direction of the pattern, the reflection cannot be detected when the direction of the reflection is orthogonal to the phase change direction. Therefore, it is preferable to confirm the two phase change directions orthogonal to each other.

  By the way, for example, when a projection pattern PT1 having a stripe pattern period (pitch) of 5 mm (0.2 lines / mm) is projected on the reference measurement surface, the phase of the reflection is exactly one line (5 mm). If it is deviated only by this, the three-dimensional coordinates of this point (the height of the surface of the test object 10) can be calculated without being deceived. Next, when a projection pattern PT1 having a stripe pattern period (pitch) of 3.3 mm (0.3 lines / mm) is projected, the phase of the reflection is about 1.5 lines (≈5 mm / 3.3 mm). Therefore, the luminance balance between the three phases is lost, and the three-dimensional coordinates are deviated and calculated accordingly.

  The surface height of the test object 10 is set such that the pitch of the stripe pattern in which the phase difference between the point P1 and the point P2 is 2π (360 °) is 1, and the ratio of reflection to the normal projection pattern is 0.1. FIG. 5 is a trial calculation of the Z detection deviation, which is a measurement error of FIG. 5, and a portion with a large data divergence is obtained by comparing shape data (surface height) when the pitch (period) of the striped pattern is changed. From this, it is possible to estimate (calculate) a position where reflection occurs, that is, a position where multiple reflection occurs on the surface of the test object 10. In FIG. 5, the Z detection deviation is shown as a ratio (%) to the distance (phase difference) between the points P2 and P1.

  When the position at which multiple reflection occurs is estimated in this way, in the next step S104, the part that causes reflection (multiple reflection) in the projection pattern PT1 is identified (estimated) by performing ray tracing from the position at which multiple reflection occurs. Then, a setting is made to dimm (or extinguish) that portion. Then, as shown in FIG. 1B, the pattern projection unit MA projects the projection pattern PT2 in which the portion causing the reflection is dimmed (or quenched) onto the test object 10, and the projection pattern PT2 is obtained. The projected object 10 is imaged by the imaging unit MB.

  At this time, the light from the light source 1 is irradiated onto the test object 10 via the projection pattern mask 2 and the projection lens 3, and the reflected light from the test object 10 forms an image on the image sensor 7 via the imaging lens 6. The image of the test object 10 onto which the projection pattern PT2 is projected is picked up by the image sensor 7 and a measurement image of the test object 10 is acquired. The image of the test object 10 onto which the projection pattern PT2 has been projected is one that is not reflected and that is not affected by multiple reflections.

  The measurement image data of the test object 10 obtained in this way is sent from the image sensor 7 to the arithmetic processing device 9. Note that because of the phase connection, the imaging of the projection pattern PT2 by the imaging unit MB is performed a plurality of times by changing the period (pitch) of the striped pattern by the display control unit 8 and the projection pattern mask 2, and a set of measurement image data groups Is acquired.

  When the measurement image data is sent in this way, in step S105, the arithmetic processing unit 9 performs a predetermined arithmetic process, and based on the image data picked up in step S104, the object is measured using the principle of triangulation. The height of the surface of the specimen 10 is calculated, and the three-dimensional shape (surface shape) of the specimen 10 is measured. At this time, it is not possible to measure the three-dimensional shape of the test object 10 for the portion of the projection pattern PT2 that is dimmed (or extinguished) (that is, the portion that causes reflection), but in step S102 Since the three-dimensional shape of the part is measured, complementation is performed using the three-dimensional shape data of the part calculated in step S102.

  Thus, according to the shape measurement method of the present embodiment, based on the image of the test object 10 on which the projection pattern PT2 in which the portion causing the reflection (multiple reflection) is dimmed (or quenched) is projected. In addition, since it includes the step (S105) of measuring the three-dimensional shape of the test object 10, it is possible to reduce the influence of multiple reflections and improve the measurement accuracy.

  Further, by calculating the position at which multiple reflection occurs on the surface of the test object 10 based on the image information of the test object 10 captured for each of two types of projection patterns having different stripe pattern periods (pitch), It is possible to estimate the position where multiple reflection occurs relatively easily.

  At this time, by performing ray tracing from the position where multiple reflection occurs, by specifying the position to be dimmed (or extinguished) in the projection pattern, the portion causing reflection (multiple reflection) is dimmed (or The projection pattern PT2 that has been extinguished can be more reliably formed.

  In the above-described embodiment, a position where multiple reflection occurs on the surface of the test object 10 based on the image information of the test object 10 captured for each of two types of projection patterns having different stripe pattern periods (pitch). The position to be dimmed (or extinguished) in the projection pattern is specified by performing ray tracing from the position where multiple reflection occurs, but is not limited to this, and from the design data of the test object A position to be dimmed (or extinguished) in the projection pattern may be specified by calculating the ray tracing. In this way, it is not necessary to project two types of projection patterns onto the test object, so that the measurement time can be shortened.

  In the present embodiment, the program is stored in the arithmetic processing unit 9, but may be stored in a rewritable storage medium such as a RAM separately from the arithmetic processing unit 9.

It is a schematic block diagram of the shape measuring apparatus used for the shape measuring method which concerns on this invention. It is a flowchart which shows the shape measuring method which concerns on this invention. It is a schematic diagram which shows the mode of multiple reflection. It is a schematic diagram which shows an example of reflection. It is a graph which shows the relationship between the pitch of a striped pattern, and Z detection shift. It is a schematic block diagram of the conventional shape measuring apparatus.

Explanation of symbols

M shape measuring device MA pattern projection unit MB imaging unit PT1 projection pattern PT2 projection pattern 10 test object

Claims (5)

A pattern projection unit that projects a predetermined projection pattern onto the test object; and an imaging unit that images the test object on which the projection pattern is projected by the pattern projection unit, and the image captured by the imaging unit. A shape measuring method using a shape measuring device for measuring a three-dimensional shape of the test object based on an image of the test object,
A first step of performing a setting for dimming or quenching a part of the projected pattern to be imaged by multiple reflection on the surface of the test object;
Projecting the projection pattern that has been dimmed or extinguished in the first step by the pattern projection unit onto the test object, and the test object on which the projection pattern that has been dimmed or quenched has been projected. A second step of measuring a three-dimensional shape of the test object on the basis of an image of the test object on which the projection pattern that has been imaged by the imaging unit and reduced or extinguished is projected. A shape measuring method characterized by comprising: The projection pattern has a periodic stripe pattern,
The first step comprises:
A first sub-step of projecting a plurality of types of the projection patterns having different stripe periods from each other by the pattern projection unit;
A second sub-step of imaging the object on which the projection pattern is projected by the imaging unit for each of the plurality of types of the projection patterns;
A third sub-step for calculating a position where the multiple reflection occurs on the surface of the test object based on image information of the test object imaged for each of the plurality of types of projection patterns in the second sub-step. When,
And a fourth sub-step for performing a setting for dimming or extinguishing a part of the projection pattern based on the position where the multiple reflection occurs calculated in the third sub-step. The shape measuring method according to claim 1.   3. The shape measuring method according to claim 2, wherein, in the fourth sub-step, a position to be dimmed or extinguished is specified in the projection pattern by performing ray tracing from a position where the multiple reflection occurs. .   A storage medium in which the shape measuring method according to any one of claims 1 to 3 is stored.   A shape measuring apparatus comprising the storage medium according to claim 4.

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