KR100994590B1 - Apparatus and method for measuring microdeformation using interference of light - Google Patents

Abstract

Disclosed are a micro deformation measuring apparatus and method using optical interference. Micro-strain measurement apparatus using the optical interference according to an embodiment of the present invention, the optical interference optical system for generating a light interference image by irradiating light on the surface of the measurement object; A differential image obtaining unit obtaining a differential image from the generated optical interference image; A single image phase extracting unit extracting phase information from the obtained difference image; A three-dimensional phase obtaining unit obtaining three-dimensional phase information from the extracted phase information; And a 3D deformation information acquisition unit for obtaining deformation information of the surface of the measurement object from the obtained 3D phase information.

Optical Interference, Continuous Image Acquisition, Difference Image, Image Segmentation, Single Interference Image, 3D Phase, Directional Filter, Deformation Information

Description

Apparatus and method for measuring small strain using optical interference {APPARATUS AND METHOD FOR MEASURING MICRODEFORMATION USING INTERFERENCE OF LIGHT}

The present invention relates to an apparatus and a method for measuring micro deformation using optical interference.

Precise phase information resulting from optical interference provides fine strain information from micrometers to nanometers. Therefore, it is generally impossible to measure in a real environment in which external vibration is present, and it is difficult to directly apply it in an industrial field because the measurement is possible only after dust is prevented. Therefore, the microstrain measurement apparatus using the optical interference is mainly configured and utilized in a special environment that can reduce the effects of vibration.

Optical interference technology is widely used in the field of precision measurement. For example, Japanese Patent 5-157514 discloses a method of measuring microscopic deformation of an object using holographic light interference, and US Patent 5,777,741 discloses a method of measuring microvibration of an object using optical interference. Also, US Patent 2005/0105097 discloses a method of extracting strain phase information in a local region using optical interference, and Korean Patent 10-0505019 discloses a method of measuring strain using pattern recognition of two points. , US Patent 2005/0219553 discloses a method of extracting the phase deformation information of the object by using the moire technique.

As described above, there are various methods for measuring the micro deformation of an object using optical interference, and each field has advantages and disadvantages. For example, a method for increasing precision is sensitive to external noise, and particularly has a disadvantage of being sensitive to external vibration.

The present invention has been made to improve the prior art as described above, and an object of the present invention is to improve the performance of the optical interference device that is weak to external vibration to provide phase information with high precision while being resistant to external noise and To provide a way.

Another object of the present invention is to provide an apparatus and method for measuring microscopic deformation of the surface of a measurement object even in the presence of vibration by acquiring a single optical interference image for a very short time and extracting phase information.

The object of the present invention is not limited to the above-mentioned objects, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object and solve the problems of the prior art, the micro-deformation measuring apparatus using the optical interference according to an embodiment of the present invention, the optical interference optical system for generating an optical interference image by irradiating light on the surface of the measurement object; A differential image obtaining unit obtaining a differential image from the generated optical interference image; A single image phase extracting unit extracting phase information from the obtained difference image; A three-dimensional phase obtaining unit obtaining three-dimensional phase information from the extracted phase information; And a 3D deformation information acquisition unit for obtaining deformation information of the surface of the measurement object from the obtained 3D phase information.

In accordance with another aspect of the present invention, there is provided a method for measuring small strain using optical interference, comprising: generating an optical interference image by irradiating light onto a surface of a measurement object; Obtaining a difference image from the generated optical interference image; Extracting phase information from the obtained difference image; Acquiring three-dimensional phase information from the extracted phase information; And acquiring deformation information of the surface of the measurement object from the obtained three-dimensional phase information.

Specific details of other embodiments are included in the detailed description and the accompanying drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and those skilled in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

According to the embodiment of the present invention, the performance of the optical interference device that is weak to external vibration can be improved to provide phase information with high accuracy while being resistant to external noise.

According to the exemplary embodiment of the present invention, by obtaining a single optical interference image for a very short time and extracting phase information, the microscopic deformation of the surface of the measurement object may be measured even in the presence of vibration.

An embodiment of the present invention discloses an apparatus and method for measuring small strain using optical interference that can measure a small strain even in a vibrational field by acquiring a single optical interference image for a very short time and extracting phase information.

That is, the apparatus and method for measuring small strain using optical interference according to an exemplary embodiment of the present invention may continuously obtain an optical interference image of a measuring object that is continuously continuously deformed at an image acquisition speed of a camera, By extracting the interference phase image which is the relative distortion information according to the time difference, and after dividing the image by the similar frequency region with respect to the extracted interference phase image, by extracting the phase information according to the directionality for each of the divided regions and measuring them, The micro deformation information of the object may be extracted.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of an apparatus for measuring small strain using optical interference according to an exemplary embodiment of the present invention.

Referring to FIG. 1, a micro distortion measuring apparatus using optical interference according to an exemplary embodiment of the present invention may include an optical interference optical system 100, a continuous image obtaining unit 120, a differential image obtaining unit 130, and a single image phase extracting unit. 140, a three-dimensional phase acquisition unit 150, and a three-dimensional deformation information acquisition unit 160.

The optical interference optical system 100 emits light onto the surface of the measurement object 106 to generate an optical interference image of the surface of the measurement target. In this case, the light may include light having excellent coherence, for example, a laser beam. The optical interference optical system 100 obtains the generated optical interference image as an electrical image using the camera 115.

That is, the optical interference optical system 100 generates an optical interference image containing the modified phase information on the horizontal (In-Plane) direction of the surface of the optically-interferred measurement object 106 using the switch 109, or vertically ( After generating an optical interference image including deformation information about an out-of-plane direction, the generated optical interference image may be obtained as an electrical image using the camera 115.

In more detail, the optical interference optical system 100 uses two laser beams (a first beam and a second beam) by using a first optical splitter 102 to emit a laser beam emitted from a laser 101 having excellent coherence. Divide by) The split first beam (first beam) illuminates at a certain angle to the surface of the measurement object 106 via the mirrors 103 and 104 for controlling the direction and the lens 105 for diffusing the light. . The divided second beam (second beam) passes through the second light splitter 108 through the mirror 107 which controls the direction and passes through the second beam (the second beam) and the third beam (the third beam). Is divided into

The second beam (second beam) passing through the second light splitter 108 passes through the direction control mirrors 110 and 111 and the light diffusing lens 112, and the irradiation angle of the first beam is measured with the measurement object 106. ) Is irradiated at an angle with respect to the vertical direction of the surface. Accordingly, an optical interference speckle pattern is generated on the surface of the measurement object 106, which contains phase information about deformation in a horizontal (In-Plane) direction, and the generated optical interference speckle pattern is formed by the camera 115. Obtained by

If the second beam split by using the switch 109 is blocked, the third beam reflected (split) by the second light splitter 108 may be mirrored 116, lens 117, or mirror 118. After passing through the lens 119 and reflected by the third light splitter 113, it is incident on the camera 115 by the imaging lens 114.

The optical interference optical system 100 generates an optical interference image through the above process.

The continuous image obtaining unit 120 continuously acquires the optical interference image in real time using the camera 115 provided in the optical interference optical system 100 and stores the obtained optical interference image in a storage device (not shown). do. That is, the continuous image acquisition unit 120 acquires the speckle optical interference image incident on the camera 115 in real time and stores the obtained optical interference image in a storage device.

The difference image acquisition unit 130 obtains a difference image (fringe image) from the optical interference image stored in the storage device. In this case, the difference image obtaining unit 130 subtracts the second optical interference image generated at a second time different from the first time from the first optical interference image generated at the first time among the optical interference images. A time difference image may be acquired. Here, the first time and the second time may be specified by the user.

The short image phase extractor 140 extracts phase information from the obtained difference image. Here, the phase information may include deformation information of the surface of the measurement object 106. In addition, the phase information is information obtained from an optical interference image of a sine wave pattern. Accordingly, the single image phase extractor 140 may obtain, from the difference image, wrapped phase information that repeats at a period of 2π (the phase starts again every 2π), which is a period of light.

In this case, the short image phase extraction unit 140 may divide the difference image according to frequency magnitude characteristics, and extract the phase information from the divided difference image. In addition, the short image phase extraction unit 140 may extract averaged phase information from the divided difference image. A detailed description thereof will be described later with reference to FIG. 2.

The 3D phase acquirer 140 obtains unwrapped phase information from the wrapped phase information extracted by the single image phase extractor 140. Here, the unfolded phase information may include change information about a degree of deformation in a horizontal (in-plane) or vertical (out-of-plane) direction with respect to the surface of the measurement object 106.

The three-dimensional phase acquiring unit 140 deforms information in the horizontal direction (accumulated integral phase) through a test piece, such as a tensile test, in which the upper part of the measurement object 106 is fixed and the lower part is pulled down and the specimen property is examined. Information). In this case, the generated cumulative integrated phase information may include cumulative integral phase information that is further accumulated toward the bottom of the measurement object 106.

The three-dimensional phase acquisition unit 140 expands the phase information by using a least-squares phase unwrapping method using a path-independent method, thereby unfolding the unwrapped phase information as the three-dimensional phase information. Can be obtained.

The 3D deformation information obtaining unit 160 obtains deformation information of the surface of the measurement object 106 from the obtained 3D phase information. In this case, the 3D deformation information obtaining unit 160 may differentiate the accumulated integrated phase information generated by the 3D phase obtaining unit 140 to obtain deformation information (absolute deformation amount) at each position on the surface of the measurement object 106. Can be obtained.

2 is a block diagram of the single image phase extraction unit 140 of FIG. 1.

Referring to FIG. 2, the single image phase extractor 140 may include a differential image storage buffer 210, an image divider 220, a multiple signal processing image generator 230, a multiple frequency converter 240, and a multiple conjugate. The filter processor 250, the multiple reverse frequency converter 260, and the multiple wrapping phase map acquirer 270 are included.

The difference image storage buffer 210 stores the difference image acquired by the difference image acquisition unit (see 130 of FIG. 1).

The image divider 220 divides the difference image stored in the difference image storage buffer 210 according to the frequency magnitude characteristic to generate a divided image. For example, when the image divider 220 has a low frequency characteristic and the right portion 1320 has a high frequency characteristic, as in the difference image as illustrated in FIG. 13, the difference image is performed. Is divided into two regions, that is, the left portion 1310 and the right portion 1320 to generate two divided regions.

In addition, when all of the difference image periods have similar periods, the image divider 220 divides the difference image into one image without dividing the difference image in detail.

The multi-signal processing image generator 230 generates a split image for multi-signal processing to signal-process the image divided by the image splitter 220. In this case, when the user does not want an averaged image of the divided images, the multi-signal processing image generator 230 may use each of the divided images as they are.

However, when the user wants to extract the averaged phase information, the multi-signal processing image generator 230 generates an averaged image for each local region for signal processing for each divided image.

For example, FIG. 4 is an exemplary diagram illustrating an example of a process of generating an averaged image of a divided image according to an exemplary embodiment of the present invention. As shown in FIG. 4, the multi-signal processing image generator 230 extracts the transformed phase information in the X-axis direction from the j-th line in one divided image (Kx * Ny pixels) of the entire image (Nx * Ny pixels). In this case, a process of obtaining an averaged strain phase on the Y axis about 9 lines is performed.

Specifically, the size of the image divided from the entire image (Nx * Ny pixel) array size is Kx * Ny pixels. If the user wants to obtain the deformation phase in the X-axis direction in the j-th row, and wants to extract the average change phase of the surrounding 9-rows, the multi-signal processing image generating unit 230 has a j-4th row. From the data to the j + 4th line data, one divided image (Kx * Ky pixels) for multi-signal processing is generated. The multi-signal processing image generator 230 performs signal processing on the generated divided image (Kx * Ky pixels), and then extracts a phase in the X-axis direction averaged in the Y-axis direction, and then performs image processing. The extracted average phase is used as phase information in the j-th row.

The multi-frequency converter 240 converts the split image (averaged image) generated by the multi-signal processing image generator 230 into a frequency domain.

The multi-conjugated filter processor 250 selects data of a predetermined frequency domain (a frequency domain desired by a user) using a conjugate filter on the divided image converted into the frequency domain. That is, the multi-conjugated filter processing unit 250 may select a divided image of a specific frequency region designated by the conjugate filter from the converted divided image of the frequency domain. A detailed description thereof will be described later with reference to FIG. 3.

The multiple inverse frequency converter 260 converts the data (split image) of the selected frequency domain into a time domain.

The multi-wrapping phase wrap acquisition unit 270 obtains a wrapping phase map as phase information from the data (split image) converted into the time domain.

3 is a block diagram of the multi-conjugated filter processor 250 of FIG. 2.

Referring to FIG. 3, the multi-conjugated filter processor 250 selects a signal from two frequency domains having a conjugate relationship specified by a conjugate filter, and then has a signal having a frequency magnitude component of a band that the user wants to extract. It selects a divided image of the multi-filter selection unit 310, a multi-conjugated filter generator 320, and a multi-conjugated filter applying unit 330.

The multiple filter selector 310 selects a type of filter to be applied to each of the multiple signal processing split images in the frequency domain. Here, the filter may be a low pass filter, a band pass filter, a high frequency pass filter, etc. In general, since the phase information includes a lot of low frequency components, a band pass filter of a low frequency region is frequently used.

The multi-conjugated filter generator 320 generates a conjugated filter having only one of two frequency domains having a conjugated relationship which may include frequency components having a size selected by a user. That is, the multi-conjugated filter generator 320 may generate a conjugate filter by selecting only one of two frequency domains having a conjugate relationship including a frequency component of a desired size in the X-axis and Y-axis directions desired by the user. have. Here, the total size of the conjugate filter buffer may be the same as the size in the frequency domain of each divided image. In addition, the conjugate filter is filled with 1 to select only one of F (w _x , w _y ) or F ^* (w _x , w _y ) from which the DC component (DC) has been removed, and all of them are set to 0 to discard the remaining part. Fill it in (see Equation 2). Here, the filter area of the area selected as 1 is an area including the size and direction of the frequency that the user wants to extract from the fringe image.

The multi-conjugated filter applying unit 330 multiplies the generated conjugate filter with the divided image for multi-signal processing converted into the frequency domain and selects data selected by the conjugate filter portion.

Hereinafter, the signal processing of the short image phase extracting unit according to an embodiment of the present invention will be described in detail with an equation.

Each divided image f (x, y) for processing multiple signals in the time domain may be expressed by Equation 1 below.

Here, d is a DC component of the image, b is a brightness intensity for each (x, y) position, Φ is a phase component to be measured.

The multiple frequency converter 240 of FIG. 2 converts each of the divided images for multiple signal processing in the time domain represented by Equation 1 into divided images in the frequency domain as shown in Equation 2 below.

F (Wx, Wy) = D + B (Wx, Wy) + B ^* (Wx, Wy)

Where D is the DC coefficient in the frequency domain, F is the frequency domain representation for f, B is the frequency domain representation for b, and ^* represents the complex conjugate.

The multi-conjugated filter generator 320 of FIG. 3 selects only one of B (Wx, Wy) or B ^* (Wx, Wy) without DC in Equation 2, and then selects a desired X-axis and Y-axis direction. Generates a conjugate filter C (Wx, Wy) having a size of the frequency component as desired. In this case, the size of the divided image buffer and the size of the filter buffer in the frequency domain are the same.

The multi-conjugated filter applying unit 330 of FIG. 3 multiplies the filter generated by the multi-conjugated filter generator 320 and the multi-segmented image converted into the frequency domain, and selects data of the part selected by the conjugate filter. Do this.

For example, assuming that the period of the signal having the largest frequency among the modified phase components in the X-axis direction to be extracted from the entire image (Nx * Ny pixels) is about z pixels, the size of the filter window is (Nx / z). * ε. Here, epsilon is a real value larger than 1.0, which is set to extract a larger frequency component in order to obtain more detailed information.

The multiple inverse frequency converter 260 of FIG. 2 multiplies a multiple conjugate window filter by a multiconjugated window filter to a data image of a frequency domain divided by the multiple conjugate filter filter 330 in a frequency domain, thereby applying multiple multiples in a frequency domain to which a conjugate filter is applied. A split image for signal processing is obtained, and the obtained split image for multiple signal processing (conjugated filter) is converted into a time domain to obtain a signal as shown in Equation 3 below.

The multi-wrapping phase map acquisition unit 270 applies the following equation 4 to each of the divided images for multi-signal processing as shown in Equation 3, which is converted into the time domain, and uses the following equation as a phase information (image). Acquire.

The wrapping phase map obtained as the phase information is data broken in units of 2π starting from 0 again when the phase exceeds 2π. This is an inherent characteristic of phase information obtained by an interferometer using interference of light having a constant sine pattern. Therefore, the user can compose one complete three-dimensional phase information by joining the phase information broken by 2 [pi].

Accordingly, the 3D phase acquirer 150 of FIG. 1 may obtain unwrapped phase information from the wrapped phase information obtained by the single image phase extractor 140 of FIG. 1. At this time, the 3D phase acquisition unit 150 spreads the phase with respect to the wrapped phase information by using a path-independent least-square phase unwrapping method that has been implemented in many existing studies. Unwrapping) can be performed.

The three-dimensional phase information obtained by the three-dimensional phase acquisition unit 150 may be cumulative three-dimensional deformation information in which a phase is accumulated and added in some cases. For example, the strain of the tensile test piece that is deformed in the horizontal (In-Plane) direction in the tensile tester is cumulative strain phase data in which phases are accumulated and added.

The three-dimensional deformation information obtaining unit 160 of FIG. 1 takes derivatives with respect to the three-dimensional phase information obtained by the three-dimensional phase obtaining unit 150 (phases added by accumulating the phases), and thus, on each surface of the measurement object. The deformation amount can be obtained.

FIG. 5 is a diagram illustrating an example of a fringe image, which is a differential image of measuring a deformation amount in a horizontal (in-plane) direction of a tensile test specimen according to an exemplary embodiment of the present invention. 6 to 8 are diagrams showing an example of a variation amount measured in the X-axis direction averaged 90 pixels on the Y-axis with respect to the image of FIG. 5.

5 is a fringe image obtained by the differential image acquisition unit 130 of FIG. 1, and the X * Y pixel size is 640 * 90 pixels. FIG. 6 is a deformed phase map in the averaged X-axis direction, and FIG. 7 shows three-dimensional phase information unfolded by the least-squares phase unfolding method of the path-independent method with respect to FIG. 6. As shown in FIG. 7, the strain in the horizontal (In-Plane) direction of the tensile test piece is cumulatively added cumulative phase information. FIG. 8 shows the amount of deformation at each position in the tensile test piece obtained by subtracting 21 * 21 windows against FIG. Here, in order to obtain the image of FIG. 6, phase information in the X-axis direction was extracted by covering the filter window in the X * Y direction with a 55 * 1 window in the conjugate filter window in the frequency domain of FIG. 5.

As can be seen from the experimental results of FIGS. 6 to 8, when the deformation amount in a specific direction such as the tensile test piece is most, it can be seen that the method of measuring the average deformation amount of the whole provides phase distortion information with improved signal-to-noise ratio. In this case, however, detailed deformation amount information in each pixel may not be provided.

9 to 11 are diagrams showing an example of the deformation phase change amount extracted by covering 55 * 20 windows from the conjugate filter window X * Y pixels with respect to FIG.

FIG. 9 is a modified phase map in the X-Y-axis two-dimensional direction, FIG. 10 shows 3-dimensional cumulative phase information unfolded by the least-squares phase unfolding method of the path-independent method with respect to FIG. 9, and FIG. 11 is shown in FIG. 10. Show the three-dimensional deformation at each position of the tensile test specimen obtained by subtracting 21 * 21 window.

As can be seen from the experimental results of FIGS. 9 to 11, the conjugate filter window having a simple X * Y window size provides overall deformation information but may have poor local resolution.

FIG. 12 is a diagram showing an example of a deformation amount image at each position of a test piece in which the deformation amount in the average X axis direction of 9 lines, which is an average value of 9 pixels on the Y axis, is measured with respect to FIG. 5.

As can be seen from the test results of FIG. 12, it can be seen that the phase extraction method for the average amount of deformation of surrounding pixels provides an improved amount of deformation compared to the conventional method.

FIG. 13 is a view showing an example of a differential image measured in a tensile test piece beyond a yield region according to an embodiment of the present invention, and FIG. 14 is obtained through multiple segmentation and multiple signal processing of an image according to an embodiment of the present invention. It is a figure which shows an example of one modified phase image.

The right image, which is the second region 1320 of FIG. 13, may be difficult to observe visually because the amount of phase change is too large. Accordingly, in the exemplary embodiment of the present invention, the image of FIG. 13 is divided into a first region 1310, which is a low frequency region, and a second region 1320, which is a high frequency region, and is multiplied with each of the divided regions 1310 and 1320. Signal processing is performed using signal processing, and the modified phase information as shown in FIG. 14 may be obtained by combining the modified phase information extracted through the signal processing.

In FIG. 14, 100 lines of average strain phase information were extracted in the X-axis direction. As can be seen from the results of FIG. 14, it can be seen that the multiple image segmentation and multiple signal processing schemes according to an embodiment of the present invention can effectively extract phase information of a low frequency component and a high frequency component.

15 is a flowchart illustrating a method for measuring small strain using optical interference according to an exemplary embodiment of the present invention. Here, the micro strain measurement method using the optical interference may be implemented by a micro strain measurement apparatus (hereinafter, referred to as a micro strain measurement apparatus) using the optical interference of FIG. 1.

Referring to FIG. 15, in operation S1510, the micro deformation measurement apparatus generates a light interference image by irradiating light onto a surface of a measurement object.

Next, in operation S1520, the microscopic distortion measurement apparatus continuously acquires the optical interference image in real time using a camera, and stores the obtained optical interference image in a storage device.

Next, in operation S1530, the micro distortion measurement apparatus obtains a difference image from the optical interference image stored in the storage device. In this case, the micro deformation measuring apparatus detects the first optical interference image and the second optical interference image corresponding to the second time difference selected based on the selected first time from the optical interference image, and detects the first optical interference image. By subtracting the second optical interference image from the first optical interference image, a time difference image may be obtained. Here, the first and second time may be specified by the user.

Next, in operation S1540, the micro distortion measurement apparatus extracts phase information from the obtained difference image. Here, the phase information may include deformation information of the surface of the measurement object. In addition, the phase information is information obtained from an optical interference image of a sine wave pattern. Accordingly, the microscopic strain measurement apparatus may obtain, from the difference image, wrapped phase information that repeats at a period of 2π (the phase starts again every 2π), which is a period of light.

In this case, the micro distortion measurement apparatus may segment the difference image according to a frequency magnitude characteristic, and extract the phase information from the divided difference image. In addition, the micro distortion measurement apparatus may extract the averaged phase information from the divided difference image. Hereinafter, a description thereof will be made in detail.

First, the micro distortion measurement apparatus stores the obtained difference image in a difference image storage buffer, and divides the stored difference image according to frequency magnitude characteristics. For reference, when the periods of the difference images all have similar periods, the micro distortion measurement apparatus divides the difference image into one image without dividing the difference image in detail.

Subsequently, the micro distortion measurement apparatus generates a split image for multi-signal processing for signal processing the split image, and converts the generated split image into a frequency domain.

Subsequently, the micro distortion measuring apparatus selects data of a predetermined frequency domain using a conjugated filter on the image converted into the frequency domain. That is, the micro strain measuring device generates a conjugate filter that selects only one of two conjugated frequency domains that may include frequency components of a predetermined size (specified by a user), and generates the conjugated filter and the The divided images for multi-signal processing transformed into the frequency domain may be multiplied with each other to select data of a portion selected by the conjugate filter.

Subsequently, the micro strain measurement apparatus converts the data of the selected frequency domain (data of one part of the conjugate) into a time domain, and obtains a wrapping phase map as phase information from the data converted into the time domain.

Next, in operation S1550, the microscopic strain measurement apparatus obtains 3D phase information from the extracted phase information. In this case, the micro-strain measurement device can obtain the unwrapping phase information as the three-dimensional phase information by unfolding the phase information using a least-square phase unwrapping method using a path independent method. Can be. The obtained 3D phase information may also include a lot of accumulated 3D phase information due to its characteristics. For example, the strain phase in the horizontal direction of the tensile test piece may be cumulatively integrated three-dimensional phase information due to its characteristics.

Next, in operation S1560, the micro deformation measurement apparatus obtains deformation information for each local region of the surface of the measurement object from the obtained 3D phase information. In this case, the micro deformation measuring apparatus may acquire the deformation information for each local area of the surface of the measurement object by differentiating the generated accumulated integrated 3D phase information.

Embodiments of the present invention include computer readable media including program instructions for performing various computer implemented operations. The computer readable medium may include program instructions, local data files, local data structures, or the like, alone or in combination. The media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical recording media such as CD-ROMs, DVDs, magnetic-optical media such as floppy disks, and ROM, RAM, flash memory, and the like. Hardware devices specifically configured to store and execute the same program instructions are included. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like.

While specific embodiments of the present invention have been described so far, various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below, but also by the equivalents of the claims.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above-described embodiments, which can be variously modified and modified by those skilled in the art to which the present invention pertains. Modifications are possible. Accordingly, the spirit of the present invention should be understood only by the claims set forth below, and all equivalent or equivalent modifications thereof will belong to the scope of the present invention.

1 is a block diagram of an apparatus for measuring small strain using optical interference according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of the single image phase extractor of FIG. 1.

3 is a block diagram of a multi-conjugated filter processor of FIG. 2.

4 is an exemplary diagram illustrating an example of a process of generating an averaged image of a divided image according to an exemplary embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of a fringe image, which is a differential image of measuring a deformation amount in a horizontal (in-plane) direction of a tensile test specimen according to an exemplary embodiment of the present invention.

6 to 8 are diagrams showing an example of a variation amount measured in the X-axis direction averaged 90 pixels on the Y-axis with respect to the image of FIG. 5.

9 to 11 are diagrams showing an example of the deformation phase change amount extracted by covering 55 * 20 windows from the conjugate filter window X * Y pixels with respect to FIG.

FIG. 12 is a diagram showing an example of a deformation amount image at each position of a test piece in which the deformation amount in the average X axis direction of 9 lines, which is an average value of 9 pixels on the Y axis, is measured with respect to FIG. 5.

13 is a view showing an example of the differential fringe image measured in the tensile test piece beyond the yield region according to an embodiment of the present invention.

14 is a diagram illustrating an example of a modified phase image obtained through multiple division and multiple signal processing of an image according to an embodiment of the present invention.

<Explanation of symbols for main parts of the drawings>

100: optical interference optical system 120: continuous image acquisition unit

130: difference image acquisition unit 140: short image phase extraction unit

150: three-dimensional phase acquisition unit 160: three-dimensional deformation information acquisition unit

210: differential image storage buffer 220: image divider

230: Multiple signal processing image generator 240: Multiple frequency converter

250: a multi-conjugated filter processor 260: a multi inverse frequency converter

270: multiple wrapping phase map acquisition unit 310: multiple filter selection unit

320: multi-conjugated filter generating unit 330: multi-conjugated filter applying unit

Claims (18)

In the micro deformation measurement apparatus using optical interference, An optical interference optical system that generates an optical interference image by irradiating light onto the surface of the measurement object; A differential image obtaining unit obtaining a differential image from the generated optical interference image; A single image phase extracting unit extracting phase information from the obtained difference image; A three-dimensional phase obtaining unit obtaining unwrapping phase information as three-dimensional phase information by unfolding the phase information using a least-square phase unwrapping method of a path independent method; And Three-dimensional deformation information acquisition unit for obtaining the deformation information of the surface of the measurement object by differentiating the three-dimensional phase information Micro deformation measurement apparatus using optical interference, comprising a. The method of claim 1, A continuous image acquisition unit for continuously obtaining the generated optical interference image in real time and storing the obtained optical interference image in a storage device Micro strain measurement device using the optical interference, characterized in that it further comprises. The method of claim 1, The difference image acquisition unit, A time difference image is obtained by subtracting a second optical interference image generated at a second time different from the first time from the first optical interference image generated at a first time among the optical interference images. Micro strain measurement device using optical interference. The method of claim 1, The single image phase extraction unit, And extracting wrapped phase information repeated in the period of light from the obtained differential image. The method of claim 1, The single image phase extraction unit, And dividing the difference image according to frequency magnitude characteristics and extracting the phase information from the divided difference image. The method of claim 1, The single image phase extraction unit, And dividing the difference image according to a frequency magnitude characteristic, and processing the divided difference image to extract phase information averaged in a direction desired by a user. The method of claim 1, The single image phase extraction unit, An image divider for dividing the difference image according to frequency magnitude characteristics to generate a divided image; A multiple frequency converter converting the divided image into a frequency domain; A conjugation filter processing unit for designating any one of two frequency domains having a conjugated relationship by the conjugate filter and selecting a signal of a specific frequency domain from the designated frequency domain from among the divided images of the frequency domain; A multiple reverse frequency converter for converting the signal of the selected frequency domain into a time domain; And Multiple wrapping phase map acquisition unit for obtaining a wrapping phase map from the transformed signal of the time domain Micro deformation measurement apparatus using optical interference, comprising a. The method of claim 7, wherein The multiple conjugate filter processing unit, Designate any one frequency domain from two frequency domains having the conjugate relationship, and adopt a frequency domain excluding a signal of a DC component from the designated frequency domain, and among the signals of the adopted frequency domain, the maximum and And a signal of the specific frequency region in the direction specified by the conjugate filter in consideration of the minimum periodic interval. delete delete In the small strain measuring method implemented by the small strain measuring device, Generating a light interference image by irradiating light onto a surface of a measurement object in the micro deformation measuring apparatus; Acquiring a difference image from the generated optical interference image in the micro distortion measurement apparatus; Extracting phase information from the obtained difference image in the micro distortion measurement apparatus; Spreading the phase information in the micro deformation measuring apparatus using a path-independent least square phase unfolding method; And Acquiring the deformation information of the surface of the measurement object by differentiating the unfolded phase information in the micro deformation measurement apparatus; Micro strain measurement method using light interference, characterized in that it comprises a. The method of claim 11, In the micro distortion measuring apparatus, continuously obtaining the generated optical interference image in real time; And Storing the obtained optical interference image in a storage device in the micro distortion measurement apparatus; Micro strain measurement method using the optical interference, characterized in that it further comprises. The method of claim 11, Acquiring the difference image from the optical interference image, Acquiring a time difference image by subtracting a second optical interference image generated at a second time different from the first time from the first optical interference image generated at a first time among the optical interference images Micro strain measurement method using light interference, characterized in that it comprises a. The method of claim 11, The step of extracting the phase information from the difference image, Dividing the difference image according to a frequency magnitude characteristic; And Extracting the phase information from the divided difference image Micro strain measurement method using light interference, characterized in that it comprises a. The method of claim 11, The step of extracting the phase information from the difference image, Generating a divided image by dividing the difference image according to a frequency magnitude characteristic; Converting the generated divided image into a frequency domain; Designating a frequency domain of one of two frequency domains having a conjugated relationship by a conjugate filter among the divided images of the frequency domain, and selecting a signal of a specific frequency domain from the designated frequency domain; Converting the signal of the selected specific frequency domain into a time domain; And Obtaining a wrapping phase map from the transformed time domain signal Micro strain measurement method using light interference, characterized in that it comprises a. delete delete A computer-readable recording medium for recording a program for executing the method of any one of claims 11 to 15 on a computer.

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