JP2008185381A - Shape measuring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shape measuring apparatus capable of accurate three-dimensional shape measurement. <P>SOLUTION: The shape measuring apparatus comprises a projection part 20 for projecting a projection pattern made of slit light S having a prescribed width to an object to be inspected 5; an imaging part 30 for imaging an projection image projected to the object to be inspected every time the slit light S is projected for scanning at regular intervals; an image generating part 41 for multiplying each projection pattern image imaged at the imaging part 30 by three modulation coefficients or more computed according to the scanning location of the slit light S to acquire three modulation images or more, arranging and synthesizing a group of modulation images acquired by the multiplication of the same modulation coefficients in the scanning direction of the slit light S to generate three sinusoidal pattern projection images or more; and a shape measuring part 42 for computing a phase distribution of the object to be inspected 5 on the basis of the three sinusoidal pattern projection images or more to measure the surface shape of the object to be inspected 5 on the basis of the phase distribution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a shape measuring apparatus that measures a three-dimensional shape of a test object such as an industrial product using a light cutting method.

  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 measuring apparatuses and configurations, but a projection pattern made of slit light is projected onto the surface of the test object, and the projection pattern is scanned over the entire surface of the test object. The projection pattern projected on the specimen is imaged, and the height of the specimen surface is calculated for each pixel using the principle of triangulation for each pixel, and the three-dimensional shape of the specimen surface is measured. The shape measuring method by this method is generally called a light cutting method (for example, see Patent Document 1).

Japanese Patent Application Laid-Open No. 5-272927

  As shown in FIG. 5, the slit light S projected on the test object 105 has a predetermined width d. For this reason, when the slit light S is projected onto the edge portion of the test object 105, a part of the slit light S irradiates the test object 105 side, and the remaining part is on the outer surface of the test object 105. There is a case where the side of the support 110 that holds the test object 105 is irradiated. On the other hand, on the imaging surface 132a, two projection patterns PP1 and PP2 are imaged at the same position in the slit base line direction, and it is difficult to perform accurate shape measurement based on such an image. .

  The present invention has been made in view of such problems, and in a shape measuring apparatus that measures a three-dimensional shape of a test object by projecting slit light having a predetermined width onto the test object, the present invention An object of the present invention is to provide a shape measuring apparatus capable of accurately performing shape measurement.

  In order to achieve the above object, a shape measuring apparatus according to the present invention projects a projection pattern made of at least one slit light having a predetermined width and extending linearly onto a test object, and the projection unit projects the projection pattern. A scanning unit that moves the projected pattern relative to the test object and scans the surface of the test object with the projection pattern, and a projection pattern that is projected onto the test object every time the slit light is scanned at a predetermined interval. Multiply three or more modulation coefficients calculated according to the scanning position of the slit light for each of the imaging unit to be imaged and the projection pattern image captured by the imaging unit to obtain three or more modulation images, and the same An image generator for generating three or more sine wave pattern projection images by combining the modulation image groups obtained by multiplying the modulation coefficients in the scanning direction of the slit light, and testing from the three or more sine wave pattern projection images And the calculated phase distribution, and a shape measuring section for measuring the surface shape of the object based on the phase distribution.

  The shape measuring unit calculates height information from each image of the test object imaged by the imaging unit, and measures the surface shape of the test object based on the phase distribution and the height information. Is preferred.

  The imaging unit includes an imaging lens system that forms an image of the test object, and an imaging device that captures an image formed by the imaging lens system, and the imaging surface of the imaging device is the imaging surface. The focal plane on which the imaging plane is formed on the object side via the imaging lens system is arranged so as to project the projection pattern, and is inclined from a plane orthogonal to the optical axis of the imaging lens system. The pattern projection system is preferably arranged so as to coincide with the cut surface.

  According to the shape measuring apparatus according to the present invention as described above, a sine wave pattern projection image is obtained from a projection pattern image captured at every predetermined scanning interval, while the projection pattern made of slit light is scanned on the surface of the test object. The shape of the surface of the test object is measured by calculating the phase distribution from these projection images. Therefore, even if the slit light has a predetermined width and the projection pattern is projected in the situation shown in FIG. 5, the shape measurement can be accurately performed from the phase distribution calculated for the measurement point corresponding to the edge portion. become able to.

  Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 shows a schematic configuration of a shape measuring apparatus according to the present invention. First, the shape measuring apparatus will be described with reference to FIG. The shape measuring apparatus 1 includes a support base 10 for placing and holding the test object 5 on the support surface 10a, and a pattern projection for projecting a slit-like projection pattern onto the test object 5 held on the support base 10. The system 20, an imaging system 30 having an imaging device 32 that images reflected light from the test object 5 via the imaging lens group 31, and the test object 5 based on image data captured by the imaging system 30. And an arithmetic processing unit 40 that performs shape measurement.

  Although the internal configuration of the pattern projection system 20 is not shown, the pattern projection system 20 includes a pattern forming unit that receives illumination light from a light source and shapes it into one slit light S having a predetermined width. The light source is composed of an LED or the like and emits illumination light having a constant luminance. The pattern forming unit is configured to include, for example, a cylindrical lens or a slit plate having a thin strip-shaped notch. When the slit light S extending in the direction orthogonal to the paper surface of FIG. 1 is projected by the pattern projection system 20, the sectional light contour (projection pattern) of the projected cut surface 20a indicated by the slit light S in a straight line in FIG. ) Is projected onto the test object 5.

  In the imaging system 30, an image of a projection pattern projected onto the test object 5 by the imaging lens group 31 is formed on an imaging surface 32a of an imaging device 32 provided with a photoelectric conversion element such as a CCD. The image picked up by the image pickup device 32 is sent to the arithmetic processing device 40, where the image arithmetic processing described below is performed, and the three-dimensional shape measurement of the test object 5 is performed.

  The imaging system 30 is a so-called Scheimpflug optical system, and the main plane 31a of the imaging lens group 31 forms a plane orthogonal to the optical axis 30L of the imaging system 30, while The imaging plane 32a is disposed so as to be inclined with respect to the plane orthogonal to the optical axis, and is in a conjugate relationship with the imaging plane 32a. The focal plane on which the imaging plane 32a forms an image on the object 5 side via the imaging lens group 31. 30f is inclined with respect to the optical axis orthogonal plane and intersects the main plane 31a and the imaging surface 32a on the same axis. The imaging surface 32a and the pattern projection system 20 are arranged so that the focal plane 30f coincides with the projection cut surface 20a. Therefore, in this imaging system 30, the reflected light from the cross-sectional contour line of the projection cut surface 20a coincident with the focal plane 30f, that is, the projection pattern is always in focus regardless of the shape of the projected portion. An image can be taken.

  The pattern projection system 20 and the imaging system 30 are configured to be integrally fixed by one frame. The support table 10 is provided with a scanning device 15 that moves the support table 10 relative to the frame in a direction different from the optical axis direction and the slit base line direction of the pattern projection system 20 and the imaging system 30. Therefore, by projecting the projection pattern onto the test object 5 held on the support table 10 while moving the support table 10 by the scanning device 15, the entire surface of the test object 5 is scanned with this projection pattern. The In order to obtain the same action, a scanning device may be provided so as to move the frame while fixing the support 10. Further, the scanning device 15 is provided with a position detector composed of an encoder or the like for detecting the moving direction of the support 10, that is, the position of the slit light in the scanning direction. It is configured to be output to.

  The arithmetic processing unit 40 generates an image (hereinafter referred to as a sine wave pattern projection image) that is virtually projected on the entire surface of the test object 5 based on the image sent from the imaging system 30. The image generation unit 41 includes a shape measurement unit 42 that measures the shape of the test object 5 based on the sine wave pattern projection image generated by the image generation unit 41.

  A method for measuring the surface shape of the test object 5 using the shape measuring apparatus 1 configured as described above will be described. In this measurement, the slit light S is projected by the pattern projection system 20 while moving the support 10 holding the object 5 by the scanning device 15. The reflected light from the test object 5 is collected through the imaging lens group 31, enters the imaging device 32, and is imaged in the focused state on the imaging surface 32a. The arithmetic processing unit 40 acquires an image formed on the imaging surface 32a every time the slit light is scanned at a predetermined interval based on the detection value of the position detector.

  An image captured by the imaging system 30 in this way is illustrated in FIG. The projection pattern has a predetermined width d and is deformed according to the height of the test object 5 with respect to the reference position (the support surface 10a of the support base 10). As is conventionally known, the height of the measurement point on the surface of the test object 5 can be obtained from the deformation amount δ of the projection pattern by using the principle of triangulation. That is, the deformation amount δ can be handled as height information with respect to the measurement point.

  Then, the image generation unit 41 determines the brightness of the projection pattern image for each image acquired by the arithmetic processing unit 40 at predetermined scanning intervals according to the scanning position of the slit light from which the projection pattern image is captured. The first to third modulation images are obtained by multiplying the first to third modulation coefficients (which are coefficients for changing the luminance), respectively. FIG. 3 shows maps α1, α2, α3 of the first to third modulation coefficients with respect to the scanning position of the slit light. These maps α1, α2, and α3 are sinusoidal curves having the same pitch, and the second map α2 for determining the second modulation coefficient is different in phase from the first map α1 for determining the first modulation coefficient. The third map α3 for determining the third modulation coefficient is shifted in phase by 240 degrees.

  The three modulated images acquired from each image in this way are stored separately in the first to third memories in the arithmetic processing unit 40. In each image, the first modulated image obtained by multiplying the first modulation coefficient is stored in the first memory, and the second modulated image obtained by multiplying the second modulation coefficient is stored in the second memory, respectively. Each third modulated image obtained by multiplying the third modulation coefficient is stored in the third memory.

Then, in the image generation unit 41, the modulated image groups stored in the respective memories are arranged in the scanning direction and synthesized. As a result of this synthesis, three fringe images are obtained as if a sine wave pattern was projected over the entire surface of the test object as was done by the conventional phase shift method. FIG. 4 illustrates the first fringe image Iv ₁ generated by synthesizing the first modulated image group stored in the first memory. A second striped image generated by synthesizing the second modulated image group stored in the second memory with the first striped image Iv ₁ is an image in which the phase of the sine wave pattern is shifted by 120 degrees. The third fringe image generated by synthesizing the third modulated image group stored in the memory is an image in which the phase of the sine wave pattern is shifted by 240 degrees.

  Using the three fringe images obtained in this way, a phase distribution is calculated in the same manner as in the conventional phase shift method, and each measurement point on the surface of the test object 5 is calculated based on the calculated phase distribution. Height is measured. This phase distribution can be calculated using the three luminance values obtained from each of the three fringe images for the same measurement point. In the method of calculating the phase distribution and measuring the height, it is necessary to perform the phase connection process and specify the shape. In this configuration example, since the deformation amount δ of the projection pattern can be obtained as height information in each image used for the synthesis of the fringe image, phase connection is performed based on the phase distribution and the height information. The shape of the test object 5 can be specified without performing a calculation process related to the process.

  Thus, in the shape measuring apparatus 1 of the present configuration example, the projection pattern is an apparatus configuration that takes the aspect of the light cutting method of scanning the entire surface of the object 5 with the projection pattern made of slit light having a predetermined width. Each image acquired at each scanning interval is modulated, and the modulated images are arranged and combined to generate a fringe image as if a sine wave pattern was projected. Then, the phase distribution is calculated based on the fringe image, and the shape of the test object is measured. For this reason, the height can be measured at each measurement point based on the luminance value of the measurement point, so that the shape of the edge portion can be accurately measured while projecting slit light having a predetermined width. Will be able to do. Further, even if there is a portion where the reflectance condition is different on the surface of the test object 5, the shape measurement can be accurately performed for each measurement point in the same manner.

  Further, the focal plane 30f of the imaging system 30 is inclined with respect to a plane orthogonal to the optical axis 30L, and is aligned with the projection cut surface 20a of the slit light S projected by the pattern projection system 20. For this reason, the projection pattern projected on the test object 5 is always imaged in a focused state. For this reason, it is not necessary to increase the depth of focus of the imaging system 30, the numerical aperture of the imaging lens system can be increased, the resolution is improved, and the measurement accuracy is improved.

  Although the embodiment of the shape measuring apparatus according to the present invention has been described so far, the scope of the present invention is not necessarily limited to the above configuration. The generation of the virtual sine wave pattern projection image is not limited to the configuration in which the luminance of the projection pattern image captured by the imaging system 30 is multiplied by the modulation coefficient, and the luminance of the light source of the pattern projection system is set to the support base 10. A modulation device that modulates a sine wave pattern according to the moving position may be provided. In this case, first, the slit light is scanned over the entire surface of the object while being modulated along the sine wave pattern of the first phase, and similarly, the sine wave patterns of the second and third phases are sequentially formed. The slit light may be scanned over the entire surface of the object while being modulated along, and the images obtained during each scan may be combined. Further, the support base 10a is intermittently moved at every scanning interval, and slit light whose brightness is modulated along each of the three phase patterns according to the stop position of the support base 10 is projected, and three projection patterns having different brightness from each other are projected. It is good also as a structure which acquires this image and synthesize | combines the obtained modulated image. Thereby, it becomes possible to measure the shape of the test object 5 by calculating the phase distribution using the shape measuring apparatus configured to scan the slit light over the entire surface of the test object 5. Similarly, the shape of the test object can be accurately measured.

It is a block diagram of the shape measuring apparatus which concerns on this invention. It is explanatory drawing explaining the aspect of the projection pattern image imaged on the imaging surface. It is explanatory drawing about a 1st-3rd modulation coefficient. It is explanatory drawing explaining the 1st fringe image obtained by synthesize | combining the image of the projection pattern multiplied by the 1st modulation coefficient. It is explanatory drawing about the condition where the slit light is irradiating the edge part of a to-be-tested object, (a) is explanatory drawing which shows a shape measuring apparatus typically by the front view in the condition, (b) is the figure It is explanatory drawing which shows the projection pattern image imaged on an imaging surface in a condition.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shape measuring device 5 Test object 10 Support stand 20 Pattern projection system 30 Imaging system 40 Arithmetic processing device 41 Image generation part 42 Shape measuring part

Claims (3)

A projection unit for projecting a projection pattern made of at least one slit light having a predetermined width and extending linearly onto a test object;
A scanning unit that moves the projection pattern projected by the projection unit relative to the test object, and scans the surface of the test object using the projection pattern;
An imaging unit that images the projection pattern projected onto the test object each time the slit light is scanned at a predetermined interval;
Each of the projection pattern images picked up by the image pickup unit is multiplied by three or more modulation coefficients calculated according to the scanning position of the slit light to obtain three or more modulation images, and multiplied by the same modulation coefficient. An image generation unit that generates three or more sinusoidal pattern projection images by combining the modulation image groups acquired in the scanning direction of the slit light and combining them;
A shape measuring unit that calculates a phase distribution of the test object from the three or more sinusoidal pattern projection images and measures a surface shape of the test object based on the phase distribution. A shape measuring device.   The shape measuring unit calculates height information from each image of the test object imaged by the imaging unit, and measures the surface shape of the test object based on the phase distribution and the height information. The shape measuring apparatus according to claim 1, wherein The imaging unit includes an imaging lens system that forms an image of the test object, and an imaging device that captures an image formed by the imaging lens system,
The image pickup surface of the image pickup device is disposed to be inclined from a surface orthogonal to the optical axis of the image pickup lens system, and the image pickup surface is focused on the object side through the image pickup lens system. The shape measuring apparatus according to claim 1, wherein the pattern projection system is arranged such that a surface coincides with a projection cut surface of the projection pattern.

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