JP4189925B2 - Surface displacement measuring method and surface displacement measuring apparatus - Google Patents

Description

  The present invention relates to a surface displacement measuring method and a surface displacement measuring device for measuring the amount of displacement of a general structure when the general structure is deformed due to factors such as external force and temperature change.

  For the purpose of developing a heater block that can achieve flatness at a set temperature, the displacement distribution of the heater block is measured with high accuracy, and the shape at high temperature is evaluated and fed back to the design. As a minute displacement measuring method, a speckle interferometry method (for example, see Non-Patent Document 1) is known. Speckle interferometry, for example, uses the fact that the speckle pattern changes before and after deformation to form the speckle interference fringe by taking the absolute value of the difference between the speckle pattern before and after deformation. This is a method of determining the amount of deformation by obtaining the phase difference.

  The phase difference of speckle interference fringes is determined depending on the wavelength of the laser beam, the incident angle of the laser beam, and the amount of change in the position of the scattering point on the object surface before and after deformation (ie, the amount of deformation of the object surface). Therefore, when the phase difference is obtained and the angle between the laser beam and the object normal is obtained from the measurement conditions, the deformation amount of the object surface is on the order of the wavelength of the laser beam, for example, on the order of several nm to several hundred nm. There is an advantage that can be determined by.

  However, if the minute displacement measurement using the speckle interferometry is performed as an out-of-plane displacement measurement, when the heater block is installed horizontally, the measurement from the upper surface of the heater block may not be able to measure with high accuracy due to atmospheric fluctuations. There is. Therefore, the present inventor considered using a digital image correlation method (see, for example, Non-Patent Documents 2 and 3) that is relatively resistant to atmospheric fluctuations as a method of measuring the displacement amount of the surface of the heater block. .

  In the digital image correlation method, a digital image captured by an imaging device using an imaging device such as a CCD (Charge Coupled Device) is image-processed before and after the deformation of the measurement object, and the entire measurement range is measured. This is a method capable of simultaneously measuring both the magnitude and direction of surface deformation. The digital image correlation method is a measurement method that is relatively resistant to disturbance in the measurement space because it does not use interference of a monochromatic light source such as a laser as in the speckle interferometry.

  In the digital image correlation method, the reference subset 10 in the pre-deformation image 10a shown in FIG. 13A is used as a reference while gradually shifting the position from the post-deformation image 10b shown in FIG. 13B. A correlation function between the subset 10 and the deformed image 10b is calculated, and the pixel movement amount is obtained by obtaining the pixel position having the highest correlation from the peak position of the correlation value as shown in FIG.

  However, this peak position does not necessarily obtain the highest correlation. That is, it does not always move accurately by the amount corresponding to the moving pixel in units of one pixel, and it is general that the true peak position of the correlation comes between the pixels on the horizontal axis in FIG. Therefore, in the digital image correlation method, interpolation between pixels is performed to increase measurement accuracy. Conventionally, there is a report that the measurement pixel can be evaluated with an accuracy of 0.1 to ± 0.02 pixel.

  As the method, (1) using the correlation value of the pixel where the highest correlation value was obtained and the correlation value of the pixels located around it, performing curve interpolation and curved surface interpolation through these points, A method for obtaining a maximum value or a minimum value to obtain a peak value between pixels, (2) a numerical value between pixels by linear interpolation or curve interpolation of an intensity distribution between pixels, and using a Newton-Raphson method, There is a method for obtaining the position where the correlation function is minimized.

  Here, by using the digital image correlation method, the pixel movement amount and the actual displacement obtained by continuously moving the displacement amount on the order of several tenths of the displacement amount of one pixel. The relationship with the quantity is shown in FIG. Although the relational expression between the movement amount and the displacement amount of the pixel should be linear in nature, it can be confirmed that it is not linear as shown in FIG. In the conventional digital image correlation method, the amount deviating from the linearity becomes a measurement error. When obtaining a minute displacement of one pixel or less by the digital image correlation method, it is important to reduce this measurement error.

  Note that there is a document that examines a deviation from linearity regarding interpolation between pixels (see Non-Patent Document 4). In this document, as a method for reducing this shift, a method is proposed in which a high-order function is used for interpolation of the intensity distribution between pixels and the Newton-Raphson method is used.

Edited by Pramod, K. Rastogi, “Digital Speckle Pattern Interferometry and Related Techniques”, (UK), John Wiley & Sons, Ltd Press, 2001 By Michael A. Sutton, Stephen R. McNeill, Jeffrey D. Helm, and Yuh J. Chao, “ Photomechanics, Topics in Applied Physics ", (Germany), Springer-Verlag Berlin Heidelberg, 2000, vol. 77, p. . 323-372 Digital image by HA Bruck, SR McNeill, MA Sutton, WH Peters III・ Corration Using Newton-Raphson Method of Differential Collection "Digital Image Correlation Using Newton-Raphson Method of Partial Differential Correction" (USA), Experimental Mechanics, 1989 September, Vol. 29, No. 3, p. 261-267 "Hubert W. Schreier", Joachim R. Brasasch, Michael A. Sutton, "Systematic Errors in Digital Image." Systematic errors in digital image correlation caused by intensity interpolation, (USA), Optical Engineering, November 2000, Vol. 39, No. 11, p. 2915-2921

  However, when the measurement is actually performed using the above-described conventional digital image correlation method, the measurement accuracy depends on the deformation amount per pixel. Therefore, when measuring a minute range at a high magnification, the measurement accuracy itself is improved. However, the measurement range becomes extremely small. In addition, it is necessary to measure a somewhat large range for measurement of a minute displacement distribution such as the thermal expansion of the heater block, and it is indispensable to increase the accuracy of the absolute deformation amount.

  On the other hand, Non-Patent Document 4 uses several types of interpolation methods using images obtained by translating continuously grayscale-distributed images or binarized images every 1/20 of one pixel. The result of the examined simulation is shown. That is, Non-Patent Document 4 performs an ideal analysis under conditions different from actual measurement, calculates on a computer, and evaluates errors by changing the interpolation method. Therefore, in actual measurement, even if this method is used, a deviation always occurs and an error occurs.

  Actual measurement is affected by lens aberration, pixel characteristics of the image sensor, pattern of the surface of the measurement object, etc., so even when the method described in Non-Patent Document 4 is used, lens aberration and imaging are included in the analysis results. Errors due to the characteristics of the pixel of the element are integrated. In particular, it is clear that the error increases as the distance from the center of the captured image increases due to the influence of aberration.

  Since the digital image correlation method is a simple method that simply captures an image of a measurement object using an image sensor, it is a measurement method that is relatively strong against fluctuations in the measurement space. However, the digital image correlation method has a lower measurement accuracy than methods using laser interference such as the speckle interferometry, moire interferometry, and holography. Since the amount of displacement of the surface of the heater block is very small, it is important to increase the measurement accuracy in order to use the digital image correlation method.

  Therefore, in the present invention, when measuring the amount of displacement of the surface when a general structure such as a heater block is deformed due to factors such as external force or temperature change using the digital image correlation method, It is an object of the present invention to provide a surface displacement measuring method and a surface displacement measuring device that can perform highly accurate measurement in consideration of the influence of the characteristics of pixels of an image sensor.

The surface displacement measuring method of the present invention is a surface displacement measuring method for measuring the amount of displacement of the surface of a measurement object by imaging the measurement object with an imaging device, and the imaging device or the measurement object is represented by α ₀ ( α ₀ : Decimal number less than 1 (the same applies hereinafter)) The image is sequentially picked up by the image pickup device while moving by a predetermined amount of movement corresponding to the pixel, and the amount of movement of the pixel on each image is compared by comparing each of the picked up images. A calibration curve creating step for creating a calibration curve from the relationship between the imaging device or the predetermined amount of movement of the measurement object, and images before and after the deformation of the measurement object by the imaging device, respectively, By comparing, the movement amount N ₁ + α ₁ of the pixel on the image before and after the deformation (N ₁ : an integer, a decimal number less than α ₁ : 1; the same shall apply hereinafter) is calculated, and calibration is performed from the calculated movement amount of the pixel. With a curve And a surface displacement amount calculating step of calculating an amount of displacement of the surface of the measuring object.

The surface displacement measuring device of the present invention includes an imaging device that images a measurement object, a control unit that measures a displacement amount of the surface of the measurement object based on an image of the measurement object imaged by the imaging device, and an imaging device or A movable part that can move by a predetermined amount of movement corresponding to α ₀ pixel of the image of the measurement object obtained by imaging the measurement object with the imaging device, and the control unit uses the movable part to move the imaging device or the measurement object to the image. Images are sequentially captured by the imaging device while being moved by a predetermined amount of movement corresponding to the α ₀ pixel, and by comparing each of the captured images, the amount of movement of the pixel on each image and the predetermined movement of the imaging device or measurement object A calibration curve creation step for creating a calibration curve from the relationship with the quantity, and images obtained by the imaging device before and after the deformation of the measurement object, respectively, and comparing the captured images before and after the deformation Modification calculates the moving amount N ₁ + α ₁ pixel on the image before and after the execution of a surface displacement amount calculating step of calculating an amount of displacement of the surface of the measurement object by using a calibration curve from the moving amount of the calculated pixel To do.

According to the present invention, the image pickup device or the measurement object is sequentially picked up by the image pickup device while being moved by a predetermined movement amount corresponding to the α ₀ pixel of the image, and each of the picked-up images is compared with each other. From the relationship between the amount of pixel movement and the predetermined amount of movement of the imaging device or measurement object, the amount of movement of α ₀ pixels or less in the image captured by the imaging device and the actual amount of movement of the imaging device or measurement object A calibration curve showing the relationship between and is created. Since this calibration curve is created from the image pickup device used for actual measurement and the image picked up using the measurement object, errors due to the influence of the lens aberration of the actual image pickup device, the pixel characteristics of the image pickup device, etc. It will be reflected. Then, the imaging device captures images before and after the deformation of the measurement object, and compares the captured images before and after the deformation to calculate the pixel movement amount N ₁ + α ₁ before and after the deformation. The displacement amount of the surface of the measurement object is calculated from the calculated movement amount of the pixel using the created calibration curve.

Further, the calibration curve creation step of the present invention corresponds to the imaging device or the measurement target one by one along two orthogonal axes, and α ₀ (decimal number less than α ₀ : 1) pixel of the image. Images are sequentially picked up by the image pickup device while being moved by a predetermined amount of movement, and each of the picked-up images is compared, so that 1 from the relationship between the amount of movement of the pixels on each image and the predetermined amount of movement of the image pickup device or measurement object. It is desirable to create two calibration curves per axis.

  When imaging is performed while moving the imaging device or the measurement target, the amount of movement captured by the imaging device is very small, and it is difficult to completely match the axial directions of the imaging device and the measurement target. Therefore, when the imaging device or the measurement object is moved and imaged by the imaging device, each of the axes along two orthogonal axes (for example, the x axis and the y axis), that is, the imaging device or the measurement object is x. By moving in the axial direction and then moving in the y-axis direction or vice versa, creating two calibration curves for the x-axis direction and y-axis direction of the image captured by the imaging device per axis Thus, it is possible to create a calibration curve that reflects a measurement error caused by a mismatch in the axial direction between the imaging device and the measurement object.

When measuring a three-dimensional displacement, the calibration curve creation step includes two axes (for example, x-axis and y-axis) orthogonal to the imaging apparatus or measurement object and one axis (for example, z-axis) orthogonal to these. ) And a total of three axes, and each image is sequentially captured by the imaging device while being moved by a predetermined amount of movement corresponding to α ₀ (decimal number less than α ₀ : 1) pixel of the image. It is desirable to create two calibration curves per axis from the relationship between the amount of movement of the pixels on each image and the predetermined amount of movement of the imaging device or measurement object by comparing each image.

  It is possible to create two calibration curves per axis by moving one axis along each of three axes including two orthogonal axes and one orthogonal to them. Therefore, it is possible to measure the three-dimensional displacement of the measurement object reflecting the measurement error caused by the mismatch between the imaging device and the measurement object in the axial direction.

  According to the present invention, a calibration curve reflecting an error due to the influence of the aberration of the lens of the actual imaging device, the characteristics of the pixel of the imaging device, or the like is created using the imaging device and the measurement object used for actual measurement, Using the created calibration curve, the displacement amount of the surface of the measurement object is calculated from the image captured by the imaging device. Thereby, it becomes possible to perform highly accurate measurement of the displacement amount of the surface of the measurement object in consideration of the aberration of the lens, the characteristics of the pixels of the image sensor, and the like.

  Further, when an image is captured by the image capturing apparatus while moving the image capturing apparatus or the measurement object, one axis is moved along two orthogonal axes, that is, the image capturing apparatus or the measurement object is moved in the x-axis direction and then the y-axis direction. Or in the reverse order, and by creating two calibration curves in the x-axis direction and the y-axis direction of the image captured by the imaging device per axis, the axes of the imaging device and the measurement object It is possible to create a calibration curve that reflects the measurement error caused by the direction mismatch. This makes it possible to measure the displacement of the surface of the measurement object with high accuracy, taking into account not only the aberration of the lens and the characteristics of the pixels of the image sensor, but also the measurement error caused by the axial mismatch between the image capture device and the measurement object. Can be performed.

Furthermore, according to the present invention, one axis along each of two axes orthogonal to each other and one axis orthogonal to these, and corresponding to α ₀ (decimal number less than α ₀ : 1) pixel of the image. Create a calibration curve that reflects the measurement error caused by the mismatch in the axial direction between the imaging device and the measurement object by creating two calibration curves per axis while sequentially moving the image by a predetermined amount of movement. can do. As a result, not only the aberration of the lens and the characteristics of the pixels of the image sensor, but also the high three-dimensional displacement of the surface of the measurement object considering the measurement error caused by the axial mismatch between the imaging device and the measurement object. Accurate measurement can be performed.

(Embodiment 1)
FIG. 1 is a schematic configuration diagram of a surface displacement measuring apparatus according to a first embodiment of the present invention.
In FIG. 1, a surface displacement measuring device according to a first embodiment of the present invention includes a CCD camera 2 as an imaging device that images a measuring object 1, a computer 3 to which the CCD camera 2 is connected, and a measuring object. And a stage 4 that holds 1. The CCD camera 2 is arranged in the horizontal direction toward the stage 4.

The stage 4 includes a movable part (not shown) that can move the measurement object 1 by a predetermined movement amount. The movable portion is movable by an amount of movement corresponding to α ₀ (a decimal number less than α ₀ : 1) pixel of an image captured by the CCD camera 2. The moving direction of the stage 4 is in the imaging plane imaged by the CCD camera 2. In the following example, when creating a horizontal calibration curve, the stage 4 is moved linearly in the horizontal direction. When creating a calibration curve in the vertical direction, the stage 4 is moved linearly in the vertical direction.

  The computer 3 controls the movable parts of the CCD camera 2 and the stage 4 and measures the amount of displacement of the surface of the measurement object 1 based on the image of the measurement object 1 captured by the CCD camera 2. is there. Processing performed by the computer 3 will be described below.

First, in a state where the measurement object 1 to be actually measured is held on the stage 4, the computer 3 parallels the stage 4 by a predetermined movement amount (movement amount (1 μm) in the example of FIG. 2) corresponding to α ₀ pixels. Images are sequentially taken by the CCD camera 2 while being moved. This operation is performed up to the required moving distance. Then, the computer 3 compares the captured images with each other, so that the calibration shown in FIG. 2 is performed based on the relationship between the movement amount (pixels) of the pixel on each image and the predetermined movement amount (μm) of the stage 4. Create a curve.

  Note that the procedure for obtaining the movement amount of the pixel on each image by comparing the captured images is the same as the conventional digital image correlation method described with reference to FIGS. Further, in order to increase the accuracy of the movement amount of the pixels on each image, as in the conventional case, (1) the correlation value of the pixel having the highest correlation value and the correlation value of the pixels positioned around it are obtained. Utilizing curve interpolation and curved surface interpolation through these points to find the maximum value and minimum value to obtain the peak value between pixels, (2) Linear interpolation and curve interpolation of the intensity distribution between pixels There is a method of obtaining a position where the correlation function is minimized by using a Newton-Raphson method or the like by digitizing between pixels.

  FIG. 2 is a plot of the amount of movement of the pixels on each image thus obtained on the horizontal axis and the actual amount of movement of the stage 4 on the vertical axis. In FIG. 2, white circles are plotted with the amount of movement in the upper right direction in FIG. 1 as a positive value (positive). On the other hand, the black circle is plotted with the amount of movement in the lower left direction of FIG. 1 as a negative value (negative). A calibration curve is obtained by interpolation based on the plots of these white and black circles. In the example of FIG. 2, the calibration curve CC-P in the positive range and the calibration curve CC-N in the negative range are obtained separately, but the invention is not particularly limited to this. Hereinafter, the obtained calibration curve is defined as f (x).

  In the surface displacement measuring method according to the first embodiment of the present invention, the obtained calibration curve f (x) is used. FIG. 3 is a flowchart showing the processing of the computer 3 for executing the surface displacement measuring method according to the first embodiment of the present invention in comparison with the conventional method.

As shown in FIG. 3, the computer 3 first captures images before and after deformation due to factors such as external force and temperature change of the measurement object 1 by the CCD camera 2, and compares the captured images before and after deformation. Thus, the movement amount N ₁ + α ₁ of the pixel on the image before and after the deformation is calculated. The procedure for obtaining the movement amount of the pixel on the image before and after the deformation by comparing the captured images before and after the deformation is the same as the above-described procedure.

  In the surface displacement measuring method according to the first embodiment of the present invention, the computer 3 uses the calibration curve f (x) obtained above to calculate the surface of the measurement object 1 from the calculated pixel movement amount. The amount of displacement is calculated. Specifically, as shown in FIG. 3, the displacement amount dx = f (x) is obtained by substituting the pixel movement amount x obtained by the digital image correlation method into the calibration curve f (x).

  As shown in FIG. 3, the displacement amount dx thus obtained is a value with higher accuracy than the displacement amount dx ′ = x × ux obtained by multiplying the displacement amount ux per pixel by the conventional method. In order to schematically realize the deformation state of the surface of the measurement object 1, the stage 4 is translated on a straight line, and the surface displacement measurement method and the conventional surface displacement measurement in the first embodiment of the present invention are performed. The results measured by the methods are shown in FIG. Note that CD-P and CD-N in FIG. 4 show the measurement results obtained by the surface displacement measurement method according to the first embodiment of the present invention, and MD shows the measurement results obtained by the conventional surface displacement measurement method.

  In this case, the measurement result should be a linear line with y = x, but as shown in FIG. 4, a conventional method for optically multiplying the length corresponding to one pixel by the amount of movement of the pixel to obtain the amount of displacement. In this case, there is a large deviation from the linear straight line, and an error occurs. On the other hand, in the surface displacement measuring method according to the first embodiment of the present invention using the calibration curve f (x), it can be seen that they are arranged on a linear straight line with very good accuracy.

(Embodiment 2)
FIG. 5 is a schematic configuration diagram of a surface displacement measuring apparatus according to the second embodiment of the present invention. 6 and 7 are diagrams showing the relationship between the moving amount and the moving pixel when the stage is moved in each axial direction. Since the surface displacement measuring device has the same configuration as that of the first embodiment of the present invention shown in FIG. 1, the same reference numerals are given and description thereof is omitted.

The stage 4 includes a movable part (not shown) that can move the measurement object 1 by a predetermined movement amount. The movable portion is movable by an amount of movement corresponding to α ₀ (a decimal number less than α ₀ : 1) pixel of an image captured by the CCD camera 2. The moving direction of the stage 4 is within the imaging plane imaged by the CCD camera 2 and can move linearly in the horizontal direction as the x axis and in the vertical direction as the y axis. Thereby, the measuring object 1 can be moved to a predetermined position.

Next, processing performed by the computer 3 in the second embodiment of the present invention will be described below. First, in a state where the measurement object 1 to be actually measured is held on the stage 4, the computer 3 moves the stage 4 to a predetermined movement amount corresponding to α ₀ pixels in the horizontal direction that is the x-axis direction (in the example of FIG. Images are sequentially taken by the CCD camera 2 while being moved by a moving amount (1 μm). Then, the computer 3 compares the captured images with each other so that the calibration shown in FIG. 6 is performed based on the relationship between the movement amount (pixels) of the pixel on each image and the predetermined movement amount (μm) of the stage 4. Create a curve.

As shown in FIG. 6, if the stage 4 is moved in the x-axis direction, two calibration curves f _xx (X) and f _xy (X) can be created. This is because the axial direction of the pixel of the CCD camera 2 and the axial direction of the stage 4 do not completely coincide.

Subsequently, the CCD image is sequentially captured by the CCD camera 2 while moving the stage 4 by a predetermined amount of movement (in the example of FIG. 7, the amount of movement (1 μm)) corresponding to the α ₀ pixel in the vertical direction that is the y-axis direction. Then, the computer 3 compares the captured images with each other so that the calibration shown in FIG. 7 is obtained from the relationship between the movement amount (pixels) of the pixel on each image and the predetermined movement amount (μm) of the stage 4. Create a curve. As shown in FIG. 7, also in this case, two calibration curves f _yx (Y) and f _yy (Y) can be created.

  Note that the procedure for obtaining the amount of movement of the pixels on each image by comparing the captured images is the same as in the first embodiment.

In the surface displacement measuring method according to the second embodiment of the present invention, a total of four calibration curves f _xx (X), f _xy (X), _fyx (Y), and f _yy (Y) obtained are used. FIG. 8 is a flowchart showing the processing of the computer 3 for executing the surface displacement measuring method in the second embodiment of the present invention in comparison with the conventional method.

As shown in FIG. 8, the computer 3 first captures images before and after deformation due to factors such as an external force of the measurement object 1 and a temperature change by the CCD camera 2, and compares the captured images before and after the deformation. Thus, each direction movement amount (N _1x + α _1x , N _1y + α _1y ) of the pixel on the image before and after the deformation is calculated. The procedure for obtaining the movement amount of the pixel on the image before and after the deformation by comparing the captured images before and after the deformation is the same as the above-described procedure.

In the surface displacement measuring method according to the second embodiment of the present invention, the computer 3 uses the four calibration curves f _xx (X), f _yx (Y), f _xy (X), and f _yy (Y). Using the calculated movement amount of the pixel, the displacement amount of the surface of the measurement object 1 is calculated. Specifically, as shown in FIG. 8, the movement amount X _cam of the pixel in the x direction obtained by the digital image correlation method is expressed as X _cam = X by using two calibration curves f _xx (X) and f _yx (Y). The movement amount Y _cam in the y direction is expressed as f _xx (X) + f _yx (Y), and Y _cam = f _xy (X) + f _yy (by the two calibration curves f _xy (X) and f _yy (Y). Y), and these two equations are solved by simultaneous nonlinear equations to obtain displacement amounts X and Y.

  The displacement obtained in this way is a value with higher accuracy than the displacement obtained by multiplying the displacement per pixel by the conventional method. In order to schematically realize the deformation state of the surface of the measurement object 1, the stage 4 is translated in a straight line, and the surface displacement measurement method and the conventional surface displacement measurement according to the second embodiment of the present invention are performed. The results measured by the methods are shown in FIG.

  In this case, the measurement result should be a linear straight line of y = x. However, as shown in FIG. 9, in the conventional method for obtaining the displacement amount by multiplying the length corresponding to one pixel by the movement amount of the pixel, There is gradually an error from the straight line. On the other hand, in the surface displacement measuring method using the calibration curve obtained according to the second embodiment of the present invention, it can be seen that they are arranged on a linear straight line with very good accuracy.

  As described above, in the second embodiment of the present invention, the stage 4 is sequentially moved in the x-axis direction and the y-axis direction to create two calibration curves in each direction. It is possible to perform highly accurate measurement of the displacement amount of the surface of the measurement object in consideration of the measurement error caused by the mismatch between the axial direction and the axial direction of the stage 4. In the second embodiment of the present invention, when the calibration curve is created, the stage 4 is sequentially moved in the x-axis direction and the y-axis direction, but of course, it may be moved in the reverse order.

(Embodiment 3)
In the first and second embodiments of the present invention, an example has been described in which the measurement object 1 is imaged by the CCD camera 2 from one direction and the in-plane displacement (two-dimensional displacement) is measured. It is also possible to measure the out-of-plane displacement (three-dimensional displacement) by providing the CCD camera 2 and imaging the measurement object 1 from a plurality of directions. Hereinafter, a method for measuring a three-dimensional displacement will be described.

  FIG. 10 is a schematic configuration diagram of a surface displacement measuring apparatus according to the third embodiment of the present invention. In FIG. 10, a surface displacement measuring device according to a third embodiment of the present invention includes a CCD camera 2 as an imaging device that images the measuring object 1, a computer 3 to which the CCD camera 2 is connected, and a measuring object. And a stage 4 that holds 1. The CCD camera 2 is arranged in an oblique direction toward the stage 4.

  The moving direction of the stage 4 includes the horizontal direction serving as the x-axis and the vertical direction serving as the y-axis described in the second embodiment of the present invention, and the depth direction perpendicular to these two axes and serving as the z-axis. Each of them can be moved linearly. As a result, the measurement object 1 can move to a predetermined position outside the imaging surface imaged by the CCD camera 2.

In addition to the processing of the computer 3 in the second embodiment of the present invention, the computer 3 in the third embodiment of the present invention moves the stage 4 in a predetermined direction corresponding to α ₀ pixels in the depth direction that is the z-axis direction. Images are sequentially picked up by the CCD camera 2 while moving by a moving amount. Thereby, the computer 3 can create two calibration curves f _zx (Z) and f _zy (Z) in the z-axis direction. Since the axial direction of the pixel of the CCD camera 2 and the axial direction of the stage 4 do not completely coincide, two calibration curves can be formed in the z-axis direction.

  In the surface displacement measuring method for measuring the three-dimensional displacement, it is necessary to use two CCD cameras 2 in order to measure the displacement in the z-axis direction. Accordingly, since six calibration curves are created for each CCD camera 2, the surface displacement measuring method in the third embodiment of the present invention using two CCD cameras 2 produces a total of twelve calibration curves. Use a calibration curve.

The computer 3 captures images before and after deformation due to factors such as an external force of the measurement object 1 and a temperature change by the two CCD cameras 2. By comparing the images before and after deformation by the imaging, the movement amount of the pixel of the image before and after the deformation for each CCD camera _{2 (N 1x1 + α 1x1,} N 1y1 + α 1y1), (N 1x2 + α 1x2, N _1y2 + _α1y2 ). The procedure for obtaining the movement amount of the pixel on the image before and after the deformation by comparing the captured images before and after the deformation is the same as the above-described procedure.

Then, the computer 3, twelve calibration curve _{f xx1 (X), f xy1} (X), f yx1 (Y), f yy1 (Y), f zx1 (Z), f zy1 (Z), f xx2 ( X), f _xy2 (X), f _yx2 (Y), f _yy2 (Y), f _zx2 (Z), f _zy2 (Z) are used to calculate the surface of the measurement object 1 from the calculated pixel movement amount. The amount of displacement is calculated. Specifically, the moving amount X _cam1 in the x direction of the first unit of the CCD camera 2 pixels obtained by the digital image correlation method, three calibration curves _{f xx1 (X), f yx1} (Y), f zx1 and the _{(Z) X cam1 = f xx1} (X) + f yx1 (Y) + f zx1 (Z), the moving amount Y _cam1 in the y direction, three calibration curves _{f xy1 (X), f yy1} (Y), f the _zy1 (Z) is expressed as _{Y cam1 = f xy1 (X)} + f yy1 (Y) + f zy1 (Z). Further, the movement amount X _{cam2 in} the x direction of the pixel of the second CCD camera 2 obtained by the digital image correlation method is expressed by three calibration curves f _xx2 (X), f _yx2 (Y), and f _zx2 (Z). X _cam2 = f _xx2 (X) + f _yx2 (Y) + f _zx2 (Z) and the movement amount Y _{cam2 in} the y direction are obtained by three calibration curves f _xy2 (X), f _yy2 (Y), f _zy2 (Z ), Y _cam2 = f _xy2 (X) + f _yy2 (Y) + f _zy2 (Z). Using these four nonlinear equations, displacement amounts X, Y, and Z are obtained.

  As described above, in the third embodiment of the present invention, the stage 4 is sequentially moved in the x-axis direction, the y-axis direction, and the z-axis direction to create two calibration curves for each axis. It is possible to measure the displacement amount of the surface of the measurement object with high accuracy in consideration of the measurement error caused by the mismatch between the axial direction of the pixel of the camera 2 and the axial direction of the stage 4. In the third embodiment of the present invention, when the calibration curve is created, the stage 4 is sequentially moved in the x-axis direction, the y-axis direction, and the z-axis direction, but of course, it may be moved in any order.

In the first, second, and third embodiments of the present invention, an example in which the measurement object 1 is moved by a predetermined movement amount corresponding to the α ₀ pixel of the image by the movable unit provided in the stage 4. Although described, the CCD camera 2 may be moved by a predetermined movement amount corresponding to the α ₀ pixel of the image instead of the measurement object 1. In this case, the CCD camera 2 is provided with a movable portion similar to the above. Even with such a configuration, it is possible to obtain the same operations and effects as described above.

  As an example, the surface displacement distribution measured by the surface displacement measuring method according to the second embodiment of the present invention using the calibration curve when the IC chip is mounted on the substrate and driven by passing an electric current. Is shown in FIG. In addition, the result measured by the speckle interferometry is also shown for comparison. The measurement result represents the amount of displacement in the horizontal direction after about 5 seconds obtained by each method after conduction.

  The speckle interferometry is a displacement distribution measuring method only in the laser irradiation direction, and the amount of displacement per speckle interference fringe is a very high-precision measuring method that is about the wavelength of the laser. Although the conventional digital image correlation method captures the tendency of speckle interference fringe distribution, the displacement amount by the conventional digital image correlation method at the position where the displacement amount is particularly large (A in FIG. 11) is measured by speckle. The result is very different. However, in the surface displacement measuring method according to the second embodiment of the present invention using four calibration curves, a very good correlation with the speckle measurement result is obtained as shown in FIG. Using the digital image correlation method and calibration curve, it was confirmed that displacement distribution measurement with higher accuracy than the conventional method is possible.

  Next, as another example, the back side of the flat plate is extruded with a micrometer to be three-dimensionally deformed, and among the three-dimensional displacements measured according to the third embodiment of the present invention, the amount of displacement in the z-axis direction The measurement results are shown in FIG.

  As shown in FIG. 12, the measurement results of the movement amount by the micrometer and the displacement amount in the z-axis direction measured by the surface displacement measurement method according to the third embodiment of the present invention are slightly shifted by 10 μm. However, it can be seen that the other results are highly correlated.

  Since the present invention realizes highly accurate surface displacement measurement based on the digital image correlation method that is resistant to disturbance in the measurement space, it is possible to measure in high and low temperature environments. It is useful for investigation of causes of heat generation due to downsizing and multilayering, malfunction caused by thermal deformation, measurement of deformation distribution of various materials, and measurement of deformation behavior during actual operation. It is also useful for actual measurement of boundary conditions of the finite element method, which is widely used in the design field in recent years.

It is a schematic block diagram of the surface displacement measuring device in the 1st Embodiment of this invention. It is a figure which shows the relationship between the movement amount of the pixel on each image, and the actual movement amount of a stage. It is a flowchart which shows the process of the computer which performs the surface displacement measuring method in the 1st Embodiment of this invention compared with the conventional method. It is a figure which shows the result each measured by the surface displacement measuring method in the 1st Embodiment of this invention, and the conventional surface displacement measuring method. It is a schematic block diagram of the surface displacement measuring device in the 2nd Embodiment of this invention. It is a figure which shows the relationship between the moving amount when moving a stage to a x-axis direction, and a moving pixel. It is a figure which shows the relationship between the movement amount when moving a stage to a y-axis direction, and a moving pixel. It is a flowchart which shows the process of the computer which performs the surface displacement measuring method in the 2nd Embodiment of this invention compared with the conventional method. It is a figure which shows the result each measured by the surface displacement measuring method in the 2nd Embodiment of this invention, and the conventional surface displacement measuring method. It is a schematic block diagram of the surface displacement measuring device in the 3rd Embodiment of this invention. It is a figure which shows the surface displacement distribution measured by the surface displacement measuring method and speckle interferometry in the 2nd Embodiment of this invention. It is a figure which shows the measurement result of the displacement amount of the z-axis direction measured with the surface displacement measuring method in the 3rd Embodiment of this invention. It is explanatory drawing which shows the procedure which calculates | requires the moving amount | distance of a pixel by the digital image correlation method. It is a figure which shows the correlation with the subset used as a reference | standard and the image after a deformation | transformation. It is a figure which shows the relationship between the movement amount of a pixel, and the actual displacement amount.

Explanation of symbols

1 Measurement object 2 CCD camera 3 Computer 4 Stage

Claims (6)

A surface displacement measurement method for imaging a measurement object with an imaging device and measuring a displacement amount of the surface of the measurement object,
The imaging device or the measurement object is sequentially captured by the imaging device while being moved by a predetermined amount of movement corresponding to α ₀ (decimal less than α ₀ : 1) pixel of the image by the movable unit , and each captured image is captured. By comparing each, the image pickup device per axis with respect to each movement direction axis of the movable portion from the relationship between the movement amount of the pixel on each image and the predetermined movement amount of the image pickup device or the measurement object. A calibration curve creating step for creating two calibration curves in the x-axis direction and the y-axis direction perpendicular to the captured image ;
Images before and after the deformation of the measurement object are respectively captured by the imaging device, and by comparing the captured images before and after the deformation, the movement amount N ₁ + α ₁ (N ₁ : integer, alpha _1: calculate less than one decimal), the surface displacement measurement method including a surface displacement amount calculating step of calculating an amount of displacement of the surface of the measurement object by using the calibration curve from the moving amount of the calculated pixel . The calibration curve creating step includes
The imaging apparatus or the measurement object is a predetermined axis corresponding to each of α ₀ (decimal numbers less than α ₀ : 1) pixels of the image along one axis along two axes orthogonal to the moving direction axis of the movable part. By sequentially moving the moving amount by the image pickup device and comparing the picked up images, the relationship between the moving amount of the pixel on each image and the predetermined moving amount of the image pickup device or the measurement object is obtained. 2. Two calibration curves in the x-axis direction and the y-axis direction perpendicular to each other of an image captured by the imaging device are created per one axis with respect to each moving direction axis of the movable part. The surface displacement measuring method as described. In the calibration curve creation step, when measuring a three-dimensional displacement,
The imaging apparatus or the measurement object is placed on one axis along each of three axes including two axes orthogonal to the movement direction axis of the movable part and one axis orthogonal to these two axes, and α of the image ₀ (decimal less than α ₀ : 1) Images are sequentially captured by the imaging device while being moved by a predetermined amount of movement corresponding to a pixel, and each captured image is compared with each other to obtain the amount of movement of the pixel on each image. From the relationship with the predetermined amount of movement of the imaging device or the measurement object , two of the x-axis direction and the y-axis direction orthogonal to the image captured by the imaging device per axis with respect to each movement direction axis of the movable unit. The surface displacement measuring method according to claim 1, wherein two calibration curves are created. An imaging device that images the measurement object, a control unit that measures a displacement amount of the surface of the measurement object based on an image of the measurement object imaged by the imaging device, and the imaging device or the measurement object A movable portion that can move by a predetermined amount of movement corresponding to α ₀ (decimal less than α ₀ : 1) pixel of the image of the measurement object imaged by the imaging device;
The control unit sequentially captures an image with the imaging device while moving the imaging device or the measurement target by a predetermined amount of movement corresponding to α ₀ (decimal number less than α ₀ : 1) pixel of the image by the movable unit. By comparing each captured image, the relationship between the amount of movement of the pixel on each image and the predetermined amount of movement of the imaging device or the measurement object per axis with respect to each moving direction axis of the movable unit A calibration curve creating step for creating two calibration curves in the x-axis direction and the y-axis direction orthogonal to each other of the image captured by the imaging device ;
Images before and after the deformation of the measurement object are respectively captured by the imaging device, and by comparing the captured images before and after the deformation, the movement amount N ₁ + α ₁ (N ₁ : integer, alpha _1: 1 less than decimal) is calculated, in which said performing a surface displacement amount calculating step of calculating an amount of displacement of the surface of the measurement object by using the calibration curve from the moving amount of the calculated pixel Surface displacement measuring device. The calibration curve creating step includes
The imaging apparatus or the measurement object is a predetermined axis corresponding to each of α ₀ (decimal numbers less than α ₀ : 1) pixels of the image along one axis along two axes orthogonal to the moving direction axis of the movable part. By sequentially moving the moving amount by the image pickup device and comparing the picked up images, the relationship between the moving amount of the pixel on each image and the predetermined moving amount of the image pickup device or the measurement object is obtained. 5. Two calibration curves in the x-axis direction and the y-axis direction perpendicular to each other of an image captured by the imaging device are created per one axis with respect to each moving direction axis of the movable part. The surface displacement measuring apparatus as described. In the calibration curve creation step, when measuring a three-dimensional displacement,
The imaging apparatus or the measurement object is set to one axis out of a total of three axes including two axes orthogonal to the moving direction axis of the movable part and one axis orthogonal to these two axes, and α ₀ ( α ₀ : Decimal number less than 1) Images are sequentially captured by the imaging device while being moved by a predetermined movement amount corresponding to a pixel, and each of the captured images is compared with each other, whereby the movement amount of the pixel on each image and the imaging Two calibrations in the x-axis direction and the y-axis direction orthogonal to the image captured by the imaging apparatus per axis with respect to each movement direction axis of the movable part due to the relationship with the predetermined movement amount of the apparatus or measurement object The surface displacement measuring apparatus according to claim 4, wherein a curved line is created.