JP2010210571A - Image correlation displacement gauge and displacement measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately and rapidly measure both of a parallel moving amount and a rotating amount of an in-plane displacement even if an acquired image is rotated. <P>SOLUTION: An image correlation displacement gauge 100 measures an in-plane displacement from correlation between a reference image S of a speckle pattern obtainable by irradiation of a measurement target 102 at a position to be a reference with an emitted light beam 114 and an acquired image T of a speckle pattern obtainable by irradiation of the measurement target 102 after the in-plane displacement with the emitted light beam 114, and includes a storing part 122 for storing two reference images S; a moving amount processing part 124 for performing correlation calculation of the two reference images S and the acquired image T and determining the parallel moving amount M in the in-plane displacement for each reference image S from the results of the correlation calculation; and a rotation amount processing part 126 determining the rotation amount θ in the in-plane displacement from the distance L between the two reference images S and the difference among the parallel moving amounts M of each of them. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes a reference image of a speckle pattern obtained by irradiating the measurement target at a reference position with the coherent light illumination means, and the measurement target after in-plane displacement (in-plane movement) The present invention relates to an image correlation displacement meter that measures the in-plane displacement and a displacement measurement method, and in particular, obtains a rotation amount of a measurement object from a correlation with an acquired image of a speckle pattern obtained by irradiation of the coherent light onto The present invention relates to an image correlation displacement meter and a displacement measurement method.

  As described in Patent Document 1 and Non-Patent Document 1, as a displacement meter that can detect a two-dimensional displacement with non-contact and high resolution without using a scale, a light beam is projected onto the measurement object, and the measurement object An in-plane displacement meter is known in which a speckle pattern, which is an interference pattern of reflected light from the surface (measurement target surface), is received by an image sensor and a displacement in an in-plane direction (referred to as in-plane displacement) is measured. ing.

JP 2006-184091 A

“Mitsutoyo nano-resolution two-dimensional image encoder Non-contact measurement of minute displacement of structure” Nikkei Advanced Technology No. 69 (2004.9.13)

  A general image has some characteristics in the image, and it is possible to obtain the rotation amount after the in-plane displacement of the measurement object with high accuracy by using them. However, it is difficult to grasp features at a glance with speckle patterns. For this reason, it is difficult to use a technique for obtaining a rotation amount used for a general image for an image of a speckle pattern.

  More specifically, the in-plane direction displacement meter as shown in Patent Document 1 is translated as shown in FIG. 7A if the acquired image after the in-plane displacement is not rotated (θ = 0 deg). The in-plane displacement of only the amount can be obtained with high accuracy. However, as shown in FIG. 7B, when the rotation amount θ is given to the acquired image (for example, θ = 10 deg), the rotation amount is obtained by rotating the reference image after obtaining the parallel movement amount, for example. It is conceivable to obtain θ. In that case, as shown in FIG. 8, the reference image is changed at a very small angle (for example, every 2 deg), and then the correlation calculation is performed with the acquired image, and the rotation angle of the acquired image is determined with the highest correlation peak angle. This is obtained as θ. However, in such a method, since the rotation amount θ of the acquired image is generally unknown, it does not easily converge to obtain the rotation amount θ and requires a huge calculation time. At the same time, with such a method, it is very difficult to accurately measure the rotation amount θ.

  The present invention has been made to solve the above-described problems, and even when the acquired image is rotated, it is possible to measure both the parallel movement amount and the rotation amount of the in-plane displacement with high accuracy and high speed. It is an object to provide an image correlation displacement meter and a displacement measurement method.

  The invention according to claim 1 of the present application includes an illumination unit for coherent light, and a reference image of a speckle pattern obtained by irradiating the measurement object at a reference position with the coherent light, and the measurement after in-plane displacement An image correlation displacement meter that measures the in-plane displacement from a correlation with an acquired image of a speckle pattern obtained by irradiation of the coherent light onto an object, and a storage unit that stores a plurality of the reference images; A correlation calculation between a plurality of reference images and the acquired image is performed, and a movement amount processing unit that calculates a parallel movement amount of the in-plane displacement with respect to each reference image from the result of the correlation calculation; A rotation amount processing unit that obtains a rotation amount of the in-plane displacement from a distance between reference images and a difference in each of the parallel movement amounts. It is intended.

  In the invention according to claim 2 of the present application, the movement amount processing unit obtains the parallel movement amount from a correlation calculation between one reference image of the plurality of reference images and the acquired image, and then the plurality of reference images. The area of the acquired image is limited based on the distance between them, and the acquired image in the limited area is subjected to correlation calculation with another reference image.

  The invention according to claim 3 of the present application is also provided with illumination means for coherent light, and a reference image of a speckle pattern obtained by irradiating the measurement object at a reference position with the coherent light, and after in-plane displacement A displacement measuring method for measuring the in-plane displacement from a correlation with an acquired image of a speckle pattern obtained by irradiating the measurement object with the coherent light, the step of storing a plurality of the reference images; A step of reading a plurality of reference images and performing a correlation operation with the acquired image, a step of obtaining a parallel movement amount of the in-plane displacement from each of the reference images based on a result of the correlation operation, and the plurality of references And a step of obtaining a rotation amount of the in-plane displacement from a distance between images and a difference in each parallel movement amount. Than is.

  According to the present invention, it is possible to measure both the parallel movement amount and the rotation amount of the in-plane displacement with high accuracy and high speed by using a plurality of reference images.

The schematic diagram which shows the structure of the image correlation displacement meter which concerns on 1st Embodiment of this invention. Similarly, a schematic diagram showing the principle of calculating the rotation amount of the image correlation displacement meter The figure which similarly shows the flow of rotation amount calculation of an image correlation displacement meter The figure which similarly shows the relationship between the amount of rotation and the correlation level The schematic diagram which shows the principle of rotation amount calculation of the image correlation displacement meter which concerns on 2nd Embodiment of this invention. The figure which similarly shows the flow of rotation amount calculation of an image correlation displacement meter The figure which shows the relationship with the acquired image at the time of using the conventional in-plane direction displacement meter The figure which shows the correlation calculation method when the same in-plane direction displacement meter is used

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  A first embodiment according to the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram showing the configuration of the image correlation displacement meter according to the first embodiment of the present invention, FIG. 2 is a schematic diagram showing the principle of calculating the rotation amount of the image correlation displacement meter, and FIG. FIG. 4 is a view showing the relationship between the rotation amount and the correlation level.

  First, the configuration of the present embodiment will be described with reference to FIG.

  The image correlation displacement meter 100 includes a coherent light illuminating unit, a light receiving optical system that receives a speckle pattern obtained by the coherent light irradiated on the measurement target surface 104 of the measurement target 102, and a reference image obtained by the light receiving optical system. And a processing system for processing S and the acquired image T.

  The illumination means for coherent light is mainly composed of a laser light source 110 and a collimating lens 112 that converts the laser light emitted from the laser light source 110 into parallel light. Laser light emitted from the laser light source 110 is converted into a projection beam (coherent light) 114 which is parallel light by the collimator lens 112 and is irradiated onto the measurement target surface 104.

  The light receiving optical system includes a lens 116 for condensing an image of a speckle pattern obtained by irradiating the measurement target surface 104 with the projection beam 114, a pinhole 118 serving as a diaphragm, and a lens 116. And a solid-state imaging device 120 that outputs the formed image as electronic data for each pixel.

  The processing system includes a storage unit 122, a movement amount processing unit 124, and a rotation amount processing unit 126. The storage unit 122 stores a plurality (two) of speckle pattern reference images S obtained by irradiating the measurement target 102 with the projection beam 114 at the reference position of the measurement target 102. The movement amount processing unit 124 calls a plurality of (two) reference images S stored in the storage unit 122, and performs a correlation operation between the reference images S and the acquired image T obtained by the solid-state imaging device 120. Can do. The reference image S and the acquired image T are two-dimensional pixel data. For this reason, the correlation calculation between the reference image S and the acquired image T is performed by sequentially changing the position in units of pixels in the acquired image T. The movement amount processing unit 124 recognizes the position showing the highest correlation peak as the position of the image after the in-plane displacement of the reference image S in the acquired image T (referred to as a comparison image) as a result of the correlation calculation, The translation amount M can be obtained from the difference in position between the comparison image and the reference image S. The movement amount processing unit 124 performs this correlation operation on the two reference images S, and obtains the respective parallel movement amounts M with respect to the reference image S. The rotation amount processing unit 126 can obtain the rotation amount θ using the parallel movement amount M and the distance L between the two reference images S. The rotation amount processing unit 126 outputs the parallel movement amount M and the calculated rotation amount θ as an in-plane displacement (M, θ). Note that the parallel movement amount M and the rotation amount θ may be obtained based on any reference image S.

  Next, the principle of calculating the rotation amount of the inter-image correlation displacement meter in the present embodiment will be described with reference to FIG.

  It is assumed that when in-plane displacement occurs after acquisition of the reference images S1 and S2, the location of the reference images S1 and S2 moves to S11 and S21, respectively, with the rotation amount θ1. Then, the comparison images S11 and S21 have an inclination θ1 relative to the acquired image T1. However, when performing the correlation calculation, the correlation calculation is performed with the acquired image T1 without giving the rotation amount θ1 (or Δθ1) to the reference image S1. At this time, even if the correlation calculation is performed without giving the inclination θ1, the reference image S1 has a strong correlation at the position of the comparison image S12 (the correlation peak becomes large). Therefore, for example, the parallel movement amount M1 can be obtained assuming that the center position A of the reference image S1 has moved to the center position C of the comparison image S12. At the same time, the translation amount M2 can be obtained assuming that the center position B of the reference image S2 has moved to the center position D of the comparison image S22. Therefore, as shown in FIG. 2B, when the parallel movement amount M1 from the center position A to the position C is subtracted from each of the center positions C and D, the calculated center position C becomes the center position C1, and the center position D becomes Each moves to the center position D1. The center position A overlaps the center position C1, and the distance between the center position AB (C1D1) between the center position A (C1) and the center position B (D1) is L1. For this reason, since the positions of the center position B, the center position A (C1), and the center position D1 become clear, the angle θ1 can be obtained as the rotation amount. The longer the distance L1 between the central positions AB of the two reference images S1 and S2, the higher the rotation amount θ1 is obtained as a value.

  Next, FIG. 3 shows a flow for calculating the rotation amount of the image correlation displacement meter according to the present embodiment, and the operation thereof will be described.

  First, the measurement target 102 is irradiated with the projection beam 114 at a position serving as a reference for in-plane movement, and the speckle pattern reference images S1 and S2 obtained therefrom are stored in the storage unit 122 (step S2).

  Next, after the in-plane displacement, an acquired image T1 is obtained by irradiating the measurement target 102 with the projection beam 114. Correlation calculation between the obtained acquired image T1 and the reference images S1 and S2 is performed (step S4).

  Next, as a result of correlation calculation between the acquired image T1 and the reference images S1 and S2, the position having the largest correlation peak is set as the position of the comparison images S12 and S22. Then, the distances between the respective center positions AC and BD are calculated as parallel movement amounts M1 and M2 (step S6).

  Next, the rotation amount θ1 is calculated using the obtained parallel movement amounts M1 and M2 and the distance L1 between the reference images S1 and S2 (between the center positions AB) (step S8).

  For this reason, in this embodiment, in order to calculate the rotation amount θ1, it is not necessary to perform correlation calculation using a large number of reference images to which a minute rotation amount is given in advance. Further, the obtained rotation amount θ1 is not limited to the rotation amount assumed in advance.

  That is, even if the acquired image T1 is rotated and based on an image that is difficult to find at first glance like a speckle pattern, the in-plane displacement is parallelized by using the two reference images S1 and S2. It is possible to measure both the movement amount M1 (M2) and the rotation amount θ1 with high accuracy and high speed.

  For example, if the rotation amount θ1 = about 10 deg, the correlation level of the correlation peak is sufficiently high as shown in FIG. 4, and therefore the parallel movement amount M1 (M2) with the same accuracy as when there is no rotation amount (θ1 = 0 deg). ) Can be measured.

  As shown in FIG. 4, the smaller the rotation amount θ1 of the acquired image T1, the higher the correlation level of the correlation peak. For this reason, the smaller the rotation amount θ1 is, the more accurately the rotation amount θ1 can be obtained.

  Next, a second embodiment of the present invention will be described with reference to FIGS.

  In the present embodiment, the configuration itself is the same as that of the first embodiment shown in FIG. However, the processing in the movement amount processing unit 124 is different. In the first embodiment, the correlation calculation of the reference image S is performed on all the pixel data of the acquired image T. However, in the second embodiment, the target area for the correlation calculation of the acquired image T is limited. ing.

  First, the principle of calculating the rotation amount of the image correlation displacement meter according to the present embodiment will be described with reference to FIG.

  When the two reference images S3 and S4 are used, the distance L2 between the center positions EF is determined, and it can be considered that the distance L2 between the center positions GH remains unchanged after the in-plane displacement. For this reason, it is assumed that the locations of the reference images S3 and S4 have moved to S31 and S41, respectively, with the rotation amount θ2. Then, as shown in FIG. 5, when the translation amount M3 of the reference image S3 to the comparison image S32 is obtained, the comparison image S42 (S41) is located at a position separated from the center position G of the comparison image S32 by the distance L2. It can be assumed that there is a center position H. That is, it can be considered that the comparison image S42 for the reference image S4 exists on the circumference SF of the radius L2 with the center position G of the comparison image S32 for the reference image S3 as the center. For this reason, the calculation area on the acquired image T2 for obtaining the translation amount M4 with respect to the reference image S4 can be limited only to the circumference SF. Thus, the calculation time can be shortened by reducing the calculation area of the acquired image T2 with respect to the reference image S4.

  Specifically, the flow of calculating the rotation amount of the image correlation displacement meter according to the present embodiment will be described with reference to FIG.

  First, the measurement target 102 is irradiated with the projection beam 114 at the reference position, and the speckle pattern reference images S3 and S4 obtained therefrom are stored in the storage unit 122 (step S20).

  Next, an acquired image T2 is obtained by irradiating the measurement target 102 with the projection beam 114 after the in-plane displacement. Then, a correlation calculation between the obtained acquired image T2 and the reference image S3 is performed (step S22).

  Next, as a result of correlation calculation between the acquired image T2 and the reference image S3, the position having the largest correlation peak is set as the position of the comparison image S32. Then, the distance between the center position EG of the reference image S3 and the comparison image S32 is calculated as the parallel movement amount M3 (step S24).

  Next, the position p is calculated using the parallel movement amount M3 and the distance L2 between the reference images S3 and S4 (between the center positions EF) (step S26). At this time, the position p is a position obtained by moving the center position F from the center position E by the parallel movement amount M3 obtained with respect to the center position G, and a distance between the reference images S3 and S4 (between the center positions EF). It is a position on the circumference SF having a radius of L2.

  Next, the reference point is sequentially shifted on the circumference SF with the position p as the reference point, and the correlation calculation between the reference pixel S4 and the reference image S4 having the reference point as the center position in the comparison image T2 is performed. Each is executed (step S28). Then, the position where the correlation peak is maximized is determined as the position of the comparison image S42 having the center position H, and the parallel movement amount M4 from the reference image S4 is obtained. At this time, the speckle pattern image from the measuring object 102 may have some errors depending on the measurement system and the moving system. For this reason, the measurement interval on the circumference SF and the width in the radial direction of the circumference SF can be appropriately determined according to the errors.

  Next, the rotation amount θ2 is calculated using the obtained parallel movement amounts M3 and M4 and the distance L2 between the reference images S3 and S4 (between the center positions EF) (step S30).

  In this way, when image correlation is performed, since the position p on the limited circumference SF is used as a reference, the calculation amount is much larger than the correlation calculation performed on all the pixel data of the acquired image T2. Can be reduced. For this reason, the present embodiment can shorten the calculation time for calculating the rotation amount θ2 as compared with the first embodiment, and can achieve higher speed.

  Although the present embodiment has been described with reference to the above embodiment, the present invention is not limited to the above embodiment. That is, it goes without saying that improvements and design changes can be made without departing from the scope of the present invention.

  For example, in the above embodiment, there are two reference images S, but the present invention is not limited to this. Three or more reference images S may be used. In that case, the present invention can be applied by using a plurality of comparison images with respect to the reference image S that remains without leaving the acquired image T after the in-plane displacement. At this time, the arrangement relationship may be such that the regions of the plurality of reference images S overlap each other.

  In the above embodiment, the distance L between the reference images S is defined by the center position of the reference image S, but the present invention is not limited to this. The upper end, lower end, corner, or other position of the reference image S may be used.

  In the above embodiment, in order to limit the area of the acquired image T2, the center position H of the comparison image S42 comes only on the circumference SF of the radius L2 with the center position G of the comparison image S32 as the center. However, the present invention is not limited to this. For example, as shown in FIG. 4, the correlation calculation with the acquired image T may be further limited to a narrow angle range on the circumference SF using the fact that the correlation level is high when the rotation amount M is small. Alternatively, the limitation on the circumference SF may be removed, and the correlation calculation may be limited only to a region having a narrow rotation angle.

DESCRIPTION OF SYMBOLS 100 ... Image correlation displacement meter 102 ... Measurement object 104 ... Measurement object surface 110 ... Laser light source 112 ... Collimating lens 114 ... Light projection beam 116 ... Lens 118 ... Pinhole 120 ... Solid-state image sensor 122 ... Memory | storage part 124 ... Movement amount processing part 126 ... Rotation amount processing section

Claims (3)

A reference image of a speckle pattern obtained by irradiating the measurement target at a reference position with a coherent light illumination means, and obtained by irradiation of the coherent light to the measurement target after in-plane displacement. An image correlation displacement meter that measures the in-plane displacement from a correlation with an acquired image of a speckle pattern,
A storage unit for storing a plurality of the reference images;
A correlation processing between the plurality of reference images and the acquired image, and a movement amount processing unit for obtaining a parallel movement amount of the in-plane displacement from each of the reference images from the result of the correlation calculation;
A rotation amount processing unit for obtaining a rotation amount of the in-plane displacement from a distance between the plurality of reference images and a difference in each of the parallel movement amounts;
An image correlation displacement meter comprising:   The movement amount processing unit obtains the parallel movement amount from a correlation calculation between one reference image of the plurality of reference images and the acquired image, and then determines the acquired image based on a distance between the plurality of reference images. The image correlation displacement meter according to claim 1, wherein the area is limited, and an acquired image of the limited area is subjected to correlation calculation with another reference image. A reference image of a speckle pattern obtained by irradiating the measurement target at a reference position with a coherent light illumination means, and obtained by irradiation of the coherent light to the measurement target after in-plane displacement. A displacement measuring method for measuring the in-plane displacement from a correlation with an acquired image of a speckle pattern,
Storing a plurality of the reference images;
Reading the plurality of reference images and performing a correlation operation with the acquired image;
Obtaining a translation amount of the in-plane displacement from each correlation image from the result of the correlation calculation;
Obtaining the amount of rotation of the in-plane displacement from the distance between the plurality of reference images and the difference in the amount of parallel movement of each,
A displacement measuring method comprising:

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