JP2011191282A - Displacement measuring method using moire fringe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a displacement measuring method using moire fringes that secures high accuracy and enables safe, easy, and rapid measurement by image-photographing, from a remote point, a crack, break, joint occurring in a concrete structure, steel structure, earth structure, rock mass, or ground. <P>SOLUTION: In the displacement measuring method using moire fringes for measuring a minute relative displacement between two points using the moire fringes, a lattice having a spatially periodic structure is displayed on each of two plate-like components of a measuring device 10 consisting of the two plate-like components that are installed along a measuring object and stacked mutually, and the movement amount of the moire fringes generated by optical interference between lattices is read, thereby measuring the displacement of the measuring object. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a displacement measuring method using moiré fringes, and more specifically, to concrete structures, steel structures, earth structures, or rocks, cracks, cracks, joints, etc. generated in the ground. The present invention relates to a displacement measuring method in which a minute relative displacement of a measurement target is measured by image photographing from a point separated by using a stripe.

  In concrete structures and steel structures such as tunnels and bridges, the interval between cracks and joints may change over time due to unexpected loads and ground displacement. In addition, in soil structures, cracked rocks, and landslide slopes, cracks may develop or the ground may move as a sign of instability of a particular rock block or the entire slope. In this way, in the construction field, fixed displacement observation of the relative displacement between two points represented by cracks is performed regularly over a long period of time for the purpose of maintaining and managing structures and evaluating the stability of rock and ground. There are many cases to do.

  Conventionally, in measurement that requires high accuracy, automatic measurement has been performed by electronic circuits using sensors such as strain gauges and extensometers, and mechanical measurement devices, but in general, the equipment is expensive and the measurement range is narrow. There are disadvantages such as.

  In simple measurement, the measurement location is marked, and each time on-site measurement is performed manually using a crack scale, crack gauge, etc., but the measurement accuracy and variation depend on the operator. In addition, since measurement cannot be performed unless the measurer is close to the measurement location, there are disadvantages such as danger in the work and low work efficiency depending on the situation in the field.

  In contrast, many methods for measuring displacement based on images taken with a digital camera or the like have been developed in recent years. For example, Japanese Patent Laying-Open No. 2002-340529 (Patent Document 1) discloses a crack displacement measuring method for a structure using a digital camera. Japanese Patent Application Laid-Open No. 11-173839 (Patent Document 2) discloses a deformation state analysis apparatus for a structure or the like and a data analyzer used therefor.

  However, in many of these methods, the basic principle is to directly measure the distance by counting the number of pixels in the image. Therefore, since the actual distance per pixel obtained from the angle of view and the number of pixels of the captured image is the minimum resolution, the number of pixels of a digital camera that is currently commercially available is taken from a close distance of 10 to several tens of centimeters. Even so, the resolution per pixel is limited to about 0.05 to 0.1 mm. For example, since cracks in concrete structures often require measurement on the order of 0.1 mm, it is necessary for the measurer to approach very close to the measurement point using these methods. Moreover, it is difficult to measure a displacement smaller than the actual distance per pixel from the principle.

  A method of measuring displacement from a long distance using moire has also been developed. For example, Japanese Patent Laid-Open No. 10-82614 (Patent Document 3) discloses a micro displacement measuring apparatus using moire fringes.

  JP 2002-340529 A   Japanese Patent Laid-Open No. 11-173839   JP-A-10-82614

  However, in this method, a solid grid is set at an observation point, and a reference grid created separately by software is superimposed to generate a moire fringe image. The displacement is measured from the amount of movement of the moire fringe by comparing the past and current moire fringe images created in this way, so if you do not shoot at the same angle of view and resolution from a completely fixed position, you can measure Difficult to do.

  Therefore, the present invention is based on the background as described above, and the technical problem is that the concrete structure, the steel structure, the earth structure, or the rock, cracks generated in the ground, cracks An object of the present invention is to provide a displacement measurement method using moiré fringes, which secures high accuracy and enables safe, simple and quick measurement by taking an image from a distant point for a joint.

  The invention according to claim 1 is a displacement measuring method using a moire fringe for measuring a minute relative displacement between two points using a moire fringe, which is installed along the measurement object and overlapped with each other. In addition, a grating having a spatially periodic structure is displayed on each of the two plate-like parts of the measuring device comprising two plate-like parts, and the amount of movement of moire fringes caused by optical interference between the gratings The displacement of the measurement object is measured by reading.

  According to a second aspect of the present invention, in the displacement measuring method using the moiré fringes according to the first aspect, the moiré fringes display different grids on each of the two plate-like components of the measuring device. Thus, the amount of movement of moire fringes caused by optical interference between the lattices is displayed at an arbitrary magnification relative to the actual displacement of the measurement target.

  According to a third aspect of the present invention, in the displacement measurement method using moiré fringes according to the second aspect, an image is taken by a photographing device from a point away from the measuring device and is caused by the inclination of the photographing angle by the processing device. Measuring the displacement of the measurement object by geometrically correcting the distortion of the data, reading the movement amount of the moire fringes of the measuring device from the corrected image data by pattern matching, and dividing the movement amount of the moire fringes by the magnification. It is characterized by.

  More specifically, the present invention relates to a measurement device installed on a measurement target, a photographing device such as a digital camera that photographs the measurement device from a remote location, and a geometrically corrected image obtained by geometrically correcting distortion of captured image data. It is composed of a computer that reads the amount of movement of the moire fringes from the data and calculates the displacement of the measurement target, and a processing device including software.

  The measuring device is composed of two plate-like parts, and is fixed and installed in front of a measurement target such as a crack. Each of the two plate-like components displays a lattice having a spatially periodic structure, and moire fringes are generated due to optical interference between the lattices. Specifically, two linear gratings having different parallel intervals (hereinafter referred to as “parallel gratings”) or two linear gratings inclined at the same interval (hereinafter referred to as “inclined gratings”) optically interfere with each other. Thus, using the phenomenon of generating moire fringes composed of bright and dark patterns, the displacement of the measurement target is displayed as the amount of movement of moire fringes at an arbitrary magnification. Here, the magnification of the movement amount of the moire fringes with respect to the displacement of the measurement target can be arbitrarily set using the lattice spacing and the inclination angle as parameters.

  Measurement is performed by photographing an image of a display unit of a measurement device that displays the displacement of the measurement target as a moving amount of moire fringes by such a principle using a photographing device such as a digital camera from a remote location. In measurement from such a distant point, it is difficult to shoot from a direction completely orthogonal to the plane formed by the display unit of the measurement device, so the display unit of the measurement device is caused by the inclination of the shooting angle. It is recorded as image data distorted from an original rectangle to a trapezoid.

  Since the amount of movement of the moire fringes cannot be accurately read from the distorted image data, the image data is geometrically corrected to an original rectangular shape by a processing device including a computer and software. Using the fact that the light and dark pattern formed by moire fringes has a known period, the amount of movement of the moire fringes is read by matching the image data corrected by the processor with the theoretical pattern, and this amount of movement is magnified with respect to the displacement. The displacement of the measurement object is finally obtained by dividing by.

  The final measurement accuracy by this measurement method is various, including the magnification of the measurement device, the brightness at the time of shooting, the sensitivity of the shooting device and the resolution of the shot image, the reading error of the moire movement amount in the processing device, etc. However, if it is a captured image with a resolution that can recognize the light and dark patterns of moire fringes, measurement is possible even if the resolution is not enough to separate and identify the individual line segments that make up the grid. Is possible.

  In addition to this, since the displacement of the measurement object is greatly enlarged as the amount of movement of the moire fringes, the principle is to measure the displacement smaller than the actual distance per pixel of the image, which was impossible with the conventional method. Is possible. Although it varies depending on the various factors described above, measurement with an accuracy of about 1/10 of the actual distance per pixel is sufficiently possible under general conditions. Therefore, for example, when the measurement target is at a high place or a dangerous place, a high resolution, that is, a digital camera having a large number of pixels and a telephoto lens are used. Measurement with an accuracy of about 05 mm is possible.

  According to the present invention, for example, a concrete structure such as a tunnel or a bridge, a steel structure, an earth structure, or a bedrock, cracks, cracks, joints, etc. generated on the ground can be imaged from a remote point. Measurement accuracy and high accuracy can be ensured by eliminating the dependence of measurement accuracy and variation on the measurer.

  In addition, since the moiré displacement is read after geometric correction of the captured image data, and finally the displacement of the measurement target is obtained, measurement is also performed from directions other than the direction completely orthogonal to the plane formed by the display unit of the measurement device. be able to. Furthermore, since the measurement can be performed by taking an image from a point distant from the measuring device, the measurement can be performed safely, easily and quickly even in a high place or a dangerous place.

  It is a block diagram which shows embodiment of this invention.   It is a front view of the upper board and lower board which constitute the measuring device of the present invention.   It is a front view of the state where the upper board and lower board which constitute the measuring device of the present invention were piled up mutually.   It is the figure cut | disconnected between AA of FIG.   It is a figure which shows the principle which expands a displacement amount to arbitrary magnifications by the moire fringe which two linear grating | lattices (parallel grating | lattice) from which a parallel space | interval differs differs.   It is a figure which shows the principle which expands a displacement amount to arbitrary magnifications by the moire fringe which two linear grating | lattices (tilted grating | lattice) of the same space | interval which incline mutually form.   It is a figure which shows an example of the displacement of a measuring apparatus using a parallel grating, and a moire fringe movement.   It is a figure which shows an example which carries out geometric correction of the image | photographed image, and reads a displacement amount by pattern matching.

  FIG. 1 is a block diagram showing an embodiment of the present invention. The present invention relates to a measuring device 10 installed on a measurement object, and a photographing device 12 such as a digital camera for photographing from a point away from a display unit of the measuring device 10. And a processing device 14 composed of a computer, software, and the like that geometrically correct the distortion of the captured image data, read the amount of movement of moire fringes from the corrected image data, and calculate the displacement of the measurement target.

  As shown in FIGS. 2, 3, and 4, the measuring apparatus 10 includes two plate-like components 10 </ b> A and 10 </ b> B (referred to as an upper plate 10 </ b> A and a lower plate 10 </ b> B) that are superposed on each other, and measures cracks and the like. It is fixed and installed along the object (see FIG. 1). The display portions 11A and 11B of the two plate-like components 10A and 10B display lattices 13A and 13B having a spatially periodic structure, and the superimposed lattices 13A and 13B interfere with each other optically. By using the phenomenon of generating moire fringes composed of bright and dark patterns, the displacement of the measurement target is enlarged and displayed as the amount of movement of the moire fringes. FIG. 3 is a front view showing a state in which the components 10A and 10B (the upper plate 13A and the lower plate 13B) are overlapped with each other.

  The generation of moire fringes by the two gratings 13A and 13B is performed by a method using two linear gratings having different parallel intervals (parallel grating, see FIG. 5) and a method using two linear gratings having the same interval inclined to each other (an inclined grating, As shown in FIG. 6, the enlargement magnification of the movement amount of the moire fringes with respect to the displacement amount can be arbitrarily set using the lattice spacing and the inclination angle as parameters.

  In the method using the parallel grating (see FIG. 5), if the distance between the linear gratings is d1 and d2 (> d1), the displacement magnification X and the moire fringe period D can be calculated by the following equations.

Magnification of displacement: X = d1 / (d2-d1)
Moire fringe period: D = d1 × d2 / (d2−d1)

  Here, Table 1 shows the relationship of each parameter with respect to typical magnifications of d2 = 1.0 mm and enlargement magnification X = 9-50. From this table, if the enlargement magnification X = 10, 20, 25, 50, very high processing accuracy is required, so that processing is easier when X = 9, 19, 24, 49, etc.

  Further, in the method using the inclined grating (see FIG. 6), if the interval between the linear gratings is d and the inclination formed by the two gratings is θ, the displacement magnification X and the moire fringe period D are calculated by the following equations. Can do. When θ is small, it can be expressed by the approximate value shown in the final term of each equation.

Magnification of displacement: X = 1 / (2 × SIN (θ / 2)) ≈1 / θ
Moire fringe period: D = d / (2 × SIN (θ / 2)) ≈d / θ

  Here, Table 2 shows the relationship of each parameter with respect to typical magnifications in the range of enlargement magnification X = 5-50.

  In addition to the method using the two linear lattices described here, the method using the orthogonal lattice obtained by synthesizing the two-way linear lattice, the method using two concentric circles, etc. Applicable depending on measurement purpose and required accuracy.

  An example of the structure of the measuring apparatus 10 using such moire fringes is shown in FIGS. As shown in these drawings, the measuring device has a shape in which two plate-like components 10A and 10B each displaying a grid are superimposed on each other. In order to see moire fringes due to two gratings through the upper plate 10A, the upper plate 10A is preferably made of a material that can transmit light, such as glass or synthetic resin, and the lower plate 10B is used to improve the visibility during measurement. It is desirable to use an opaque and bright material such as white.

  An example of the displacement of the measuring apparatus 10 and the movement of moire fringes using a parallel grating (see FIG. 5) is shown in FIG. FIG. 7 shows an example in which the magnification of the measuring apparatus 10 is X = 19.

  Here, since a tunnel wall surface or the like is assumed as a measurement target, it is not always a flat surface. Therefore, if the measurement device 10 is too large, it is difficult to reliably fix and install the measurement device 10. For this reason, in the case of the measuring apparatus 10 shown in FIG. 7, the display range is one moiré fringe period. If this is the case, the measurement range is limited to displacement corresponding to one cycle of ± moire fringes, and in order to solve this, a vernier is provided to extend the measurement range to a plurality of moire fringe cycles.

  In addition, light and dark patterns due to moire fringes are generated regardless of the line width of the straight lines that make up the grid. However, assuming use in measurement, reading errors due to pattern matching are generally smaller when the difference between light and dark is large. it can. For this reason, the line width has a certain thickness, and the visibility is improved when the dark portion is almost filled with the grid. Therefore, in the case of the measuring apparatus 10 shown in FIG. 1/2.

  The measuring device 10 measures a minute relative displacement between two points. Since materials such as concrete, bedrock, and ground have much lower tensile strength than compressive strength, cracks occur perpendicular to the direction in which they are pulled. Accordingly, since the displacement often expands in a direction perpendicular to the crack, the measuring device 10 may be fixed with an adhesive or the like for general measurement.

  However, when a complicated behavior is predicted, a two-direction displacement measuring device using a moire fringe by an orthogonal lattice obtained by synthesizing two-way linear lattices or a moire fringe by two concentric circle groups is effective.

  With such a measuring device 10, the display units 11A and 11B, which display the displacement of the measurement object as a movement amount of moire fringes, are imaged by a photographing device 12 such as a digital camera from a remote location. (Shooting is performed with the imaging device 12 from the display unit 11A side of the upper plate 10A). In measurement from a distant point, it is difficult to take a picture from a direction completely orthogonal to the plane formed by the display units 11A and 11B of the measuring device 10 (upper plate 10A and lower plate 10B). As a result, the display units 11A and 11B of the measuring apparatus 10 (upper plate 10A and lower plate 10B) are recorded as image data distorted from an original rectangle to a trapezoid.

  Since the amount of movement of moire fringes cannot be accurately read from the distorted image data, the image data is geometrically corrected to the original rectangular shape by the processing device 14 including a computer and software. The light and dark pattern formed by the moire fringes has a known period and is matched with the theoretical pattern based on the image data corrected by the processing device 14, thereby reading the movement amount of the moire fringes with high accuracy. The displacement of the measurement object is obtained by dividing the movement amount by the magnification for the displacement. By adopting such a measurement method, it is possible to eliminate the dependence of the measurer on measurement accuracy and variation.

  FIG. 8 shows an example of geometrically correcting a photographed image and reading the displacement amount by pattern matching.

  The final measurement accuracy by this measurement method includes the magnification of the measurement device 10, the brightness at the time of photographing, the sensitivity of the photographing device 12, the resolution of the photographed image, the reading error of the moire movement amount in the processing device 14, and the like. However, if the captured image has a resolution capable of recognizing the light and dark patterns of moire fringes, it is not a resolution that can separate and identify individual line segments constituting the grid. Even measurement is possible.

  In addition to this, since the displacement of the measurement object is greatly enlarged as the amount of movement of the moire fringes, the principle is to measure the displacement smaller than the actual distance per pixel of the image, which was impossible with the conventional method. Is possible. Although it varies depending on the various factors described above, measurement with an accuracy of about 1/10 of the actual distance per pixel is sufficiently possible under general conditions. Therefore, for example, in a high place or a dangerous place where the measurement target is high, a high resolution, that is, a digital camera with a large number of pixels and a telephoto lens are used. Measurement with an accuracy of about 0.05 mm is possible.

  For example, in the case of shooting with a telephoto lens equivalent to a focal length f = 210 mm and a digital camera having a high pixel of 24 million pixels (horizontal 6000 × vertical 4000 pixels) in terms of 35 mm film, the image resolution by the simple calculation shown in the following table Is 0.29 mm / pixel at the shooting distance L = 10 m and 0.57 mm / pixel at the shooting distance L = 20 m.

  On the other hand, the measurement accuracy of the measurement apparatus 10 with the enlargement magnification X = 19 and taking the reading error of 1 pixel into consideration is about 0.02 mm and 0.03 mm, respectively. Maintains sufficient measurement accuracy.

  From the results of the above estimation, for example, when the measurement point is high or dangerous, use a digital camera with a high pixel count and a telephoto lens, etc. from a place away from the measurement device 10 by several tens of meters (meters) or more. However, measurement with sufficient accuracy is possible.

  If the magnification of the measuring device 10 is increased, the measurement accuracy is naturally improved under the same shooting conditions, but the size of the measuring device 10 increases the cost because high processing accuracy is required for manufacturing the measuring device 10. The problem is that it becomes difficult to install in the field and the measurement range becomes narrow, so the magnification ratio X = about 40 to 50 is the practical upper limit from the subject of the present invention and the required accuracy. Seem.

  In addition, since the captured image data is subjected to geometric correction using the processing device 14 including a computer and software, and the moire movement amount is read from the image data by pattern matching, the captured image is digital information such as a digital camera. Is desirable. However, even an image from a film camera or the like can be used by digital conversion.

10 Measuring device 10A Parts (upper plate)
10B parts (lower plate)
12 Imaging device 14 Processing device

Claims (3)

  A displacement measurement method using moiré fringes that uses a moire fringe to measure a minute relative displacement between two points. From two plate-shaped components that are installed along the measurement object and stacked on top of each other Displacement of the object to be measured by displaying a spatially periodic lattice on each of the two plate-like components of the measurement device and reading the amount of movement of moire fringes caused by optical interference between the lattices Displacement measurement method using moiré fringes characterized by measuring.   The moiré fringe displays the different gratings on each of the two plate-like components of the measuring device, thereby changing the amount of movement of the moiré fringes caused by optical interference between the gratings. The displacement measurement method using moiré fringes according to claim 1, wherein the display is performed at an arbitrary magnification.   An image is taken from a point away from the measuring device, and the processing device geometrically corrects distortion of the image data caused by the inclination of the shooting angle, and pattern matching is performed on the movement amount of the moire fringes of the measuring device from the corrected image data. The displacement measuring method using the moire fringes according to claim 2, wherein the displacement of the measurement object is measured by dividing the movement amount of the moire fringes by the enlargement magnification.

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