JP2010249589A - Method and device for measuring strain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a strain measuring method and a strain measuring device for noncontactly and easily measuring wide-range strain distribution in a measuring object such as plastic, rubber, metal, structure, and structural material. <P>SOLUTION: The strain measuring device includes: a laser light projector 1 for radiating a measurement spot 9 of the measuring object 5 with laser light 4; a light receiving part 2 for picking up an image of a laser speckle pattern 3 being reflection light of the laser light 4; an image processing means for seeking the center of gravity point 12 of each speckle of the picked-up image of the laser speckle pattern 3; and a measurement means for measuring the strain of the measuring object 5 by detecting the amount and direction of movement of the center of gravity point 12 of each speckle. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a strain measurement method and a strain measurement apparatus for measuring a strain distribution of a measurement object such as a test piece such as plastic, rubber, metal, and other structures and structural materials in a non-contact manner.

  Conventionally, as a method of measuring the strain of the object to be measured, a measuring method in which a resistance wire strain gauge is attached to the object to be measured, or a laser beam is divided into two light beams by a beam splitter, and the distortion of the object to be measured is measured. There is known an electronic speckle interferometry (ESPI) based on a two-beam method in which an amount of distortion is obtained from a change in a speckle pattern before and after deformation of an object to be measured by overlapping and irradiating with an angle in a direction.

  In the measurement method using a resistance wire strain gauge, it is necessary to attach a resistance wire strain gauge to the object to be measured as a pre-processing of measurement, and it is necessary to pay attention to the direction and strength of attachment to the measurement location, requiring skill of the measurer. . Furthermore, when a measurement object is cracked or broken during measurement, the resistance wire strain gauge may come off, or the resistance wire strain gauge may be damaged or broken. For this reason, the measuring method using a resistance wire strain gauge requires that the resistance wire strain gauge be correctly attached in the strain direction of the object to be measured, and is limited to one-way measurement within the measurement range of the resistance wire strain gauge. It is not suitable for strain measurement with large elongation.

  In electronic speckle interferometry, it is necessary to irradiate laser light to be split into two optical paths by means of a beam splitter, and to irradiate with an angle from two directions in the strain direction of the object to be measured. It becomes complicated, it is necessary to estimate the distortion direction of the measurement location in advance, and to irradiate the laser beam so that it is parallel to the distortion direction. The object to be measured is small, and distortion measurement only in one direction within a narrow range. It was limited.

  Further, the inventor of the present application has proposed a strain measurement method and apparatus that uses a laser speckle pattern to measure a Poisson's ratio in real time without contact with a test piece (see Patent Document 1). A highly accurate displacement measurement method and apparatus for a measurement object using laser reflected light, in which the irradiated laser light is cross light having a focal point between the laser projector and the measurement object, have been proposed (see Patent Document 2). ).

JP 2007-64864 A JP 2008-304190 A

  According to the measurement method using a resistance wire strain gauge, the strain direction of the object to be measured is predicted in advance, the resistance wire strain gauge is attached, the strength and strain amount to be applied are predicted, and the skill of the measurer is required. There is a problem that it is limited to measurement in one direction within the measurement range of the strain gauge and is not suitable for strain measurement of an object to be measured having a large elongation rate.

  According to the electronic speckle interferometry, the laser beam is split into two by a beam splitter, the distortion direction of the measurement location is predicted in advance, and the two split laser beams are overlapped and irradiated to measure in one direction within a narrow range. There is a problem that it is limited and unsuitable for strain measurement of an object to be measured having a large elongation rate, and the optical system becomes precise and complicated.

  In addition, since the strain measurement method and apparatus described in Patent Document 1 automatically tracks the measurement system along the direction of elongation of the test piece, a measurement object whose strain direction is not constant is to be measured. In addition, when measuring strains at a plurality of locations using a plurality of measurement systems, there is a problem that the configuration of the apparatus becomes complicated.

  Accordingly, the present invention provides a strain measurement method and a strain measurement apparatus that can easily measure a wide range of strain distribution of an object to be measured in plastic, rubber, metal, structures, structural materials, and the like, in a non-contact manner. is there.

  In order to solve the above-described problem, the present invention irradiates a measurement spot of a measurement object with laser light, images a laser speckle pattern, which is reflected light of the laser light, in a light receiving unit, and picks up the imaged laser speckle pattern A strain measuring method is provided in which the center of gravity of each speckle is obtained, the amount of movement and the direction of movement of the center of gravity of each speckle is detected, and the strain of the object to be measured is measured.

  In addition, the strain measurement method of the present invention measures the strain of the object to be measured by irradiating a plurality of measurement locations with laser light.

  In addition, the present invention provides a laser projector that irradiates a measurement site of a measurement object with a laser beam, a light receiving unit that images a laser speckle pattern that is a reflected light of the laser beam, and a laser speckle pattern that has been captured. The present invention provides a distortion measuring device comprising an image processing means for obtaining the center of gravity of each speckle and a measuring means for detecting the amount and direction of movement of the center of gravity of each speckle to measure the distortion of the object to be measured. is there.

  In addition, the strain measuring apparatus of the present invention includes a plurality of sets of laser projectors and light receiving units, and irradiates a plurality of measurement locations with laser light.

  In the distortion measuring apparatus of the present invention, the measuring means includes means for measuring the distortion of the object to be measured by adding the moving amount and moving direction of the center of gravity points of different speckles.

  The strain measurement method of the present invention irradiates a measurement site of an object to be measured with laser light, images a laser speckle pattern that is reflected light of the laser light with a light receiving unit, and each speckle of the captured laser speckle pattern. By measuring the center of gravity of each speckle and detecting the amount and direction of movement of the center of gravity of each speckle to measure the distortion of the object to be measured, pre-processing and special signs are required for measuring the distortion. The center of gravity of the speckle that moves in parallel with the amount and direction of distortion of the object to be measured by irradiating the object to be measured with laser light from minute distortion to large deformation without using a complicated optical system. The movement of the point can be continuously measured, and there is an effect that the strain distribution of the object to be measured can be easily measured without contact.

  In addition, the strain measurement method of the present invention has an effect that the entire strain distribution can be measured even in a large measurement object by irradiating a plurality of measurement points with laser light to measure the distortion of the measurement object. is there.

  In addition, the strain measuring apparatus of the present invention includes a laser projector that irradiates a measurement site of a measurement object with a laser beam, a light receiving unit that images a laser speckle pattern that is a reflected light of the laser beam, and an imaged laser. The image processing means for obtaining the center of gravity of each speckle of the speckle pattern, and the measuring means for detecting the movement amount and direction of the center of gravity of each speckle to measure the distortion of the object to be measured. Therefore, when measuring distortion, pre-processing and special labeling are not required, and no complicated optical system is used. It is possible to continuously measure the movement of the center of gravity of the speckle that moves in parallel according to the amount of distortion and the direction of distortion, and to measure the strain distribution of the object to be measured easily and non-contactedly. .

  In addition, the strain measuring apparatus of the present invention includes a plurality of sets of laser projectors and light receiving units, and irradiates a plurality of measurement points with laser light, so that the entire strain distribution can be obtained even for a large object to be measured. There is an effect that can be measured.

  Further, the strain measuring apparatus of the present invention is characterized in that the measuring means includes means for measuring the strain of the measured object by adding the moving amount and moving direction of the center of gravity points of different speckles. Even if the amount of distortion is large and each speckle moves beyond the imaging range, the movement of the center of gravity of the different speckles is added, so the movement of the center of gravity of the speckle can be continuously measured and expanded and contracted. There is an effect that it is possible to measure the distortion of the measurement object having a large rate.

The block diagram which shows one Example of this invention distortion measuring device. The figure which shows the speckle pattern generation | occurrence | production state of the one Example. The block diagram which shows the other Example of this invention distortion measuring device. The figure which shows the speckle pattern generation | occurrence | production state of the Example. The figure which shows a speckle pattern generation and imaging structure.

Embodiments of the present invention will be described based on examples shown in the drawings.
The distortion measuring apparatus according to the present invention includes a laser projector 1 that irradiates a measurement spot 9 of a measurement object 5 with a laser beam 4 and a light receiving unit that images a laser speckle pattern 3 that is a reflected light of the laser beam 4. 2, image processing means for obtaining the center of gravity 12 of each speckle of the captured laser speckle pattern 3, and the amount and direction of movement of the center of gravity 12 of each speckle are detected to measure the distortion of the object 5 to be measured. Measuring means.

FIG. 5 is a diagram showing the configuration of speckle pattern generation and imaging.
As shown in FIG. 5, when the object to be measured 5 is irradiated with the laser beam 4 excellent in straightness, high luminance, monochromatic light, and coherence, the irradiation laser light 4 is generated in a space based on the rough surface of the object to be measured 5. Diffuse reflection causes laser speckle pattern 3 to occur. Since this laser speckle pattern 3 has the property of moving in parallel with two-dimensional distortion and deformation on the surface of the object 5 to be measured, the laser speckle pattern 3 is continuously imaged by the light receiving unit 2, and the image processing apparatus By detecting the moving direction and moving amount of the laser speckle 3 imaged at 6, the distortion direction and the distortion amount of the surface of the object to be measured 5 can be derived, and a non-contact and high response distortion measuring device is obtained. be able to.

  As shown in FIGS. 1 to 4, the non-contact type strain distribution measuring method using the laser speckle pattern of the present invention irradiates the measurement spot 9 of the object 5 with the laser beam 4, and the surface of the object 5 is measured. The laser speckle pattern 3 generated in the space based on the rough surface is continuously imaged by the light receiving unit 2 such as a CCD camera, the center of gravity 12 of each speckle of the laser speckle pattern 3 is obtained, and the distortion of the object to be measured 5 is obtained. Accordingly, the movement of the speckle centroid point 12 and the movement direction of the speckle centroid point 12 are detected simultaneously to measure the strain distribution of the object to be measured. In addition, when the amount of distortion of the DUT 5 is large and each speckle moves and deviates from the imaging range, the movement of the barycentric point 12 of each speckle newly entered and imaged is added. By continuing, it is possible to continuously measure even a large amount of distortion.

  FIG. 1 shows a strain distribution measurement system in a narrow region (measurement location 9) of the object 5 to be measured. In FIG. 1, reference numeral 10 denotes a support base that supports the object to be measured 5, and 8 denotes a load device that applies a point load to the object to be measured 5 from above. When the load device 8 applies a load from above the object to be measured 5 placed on the support base 10, the load is applied to the object to be measured 5 and distortion occurs.

  The laser projector 1 uses visible light having high brightness and directivity in order to draw a stable laser speckle pattern 3 on the object 5 to be measured, and includes a laser element, a cooling circuit, a driving circuit, and a lens. The beam light can be irradiated. The lens of the laser projector 1 is provided so that the beam diameter of the laser beam 4 to be irradiated can be changed, and the region to which the laser beam 4 is irradiated is made variable. Further, the laser light 4 can use cross light as well as straight light or spot light so that minute distortion of the object to be measured 5 can be detected.

  The light receiving unit 2 includes a CCD element and a night vision tube provided in front of the CCD element that blocks external light, and is configured to directly image the laser speckle pattern 3. The light receiving unit 2 has a function of capturing an image of the laser speckle pattern 3 drawn on the object to be measured 5 and outputting the image to the image processing device 6 using an NTSC signal (analog signal).

  The image processing device 6 includes image processing means for inputting the NTSC signal of the speckle pattern 3 captured by the light receiving unit 2 and obtaining the center of gravity 12 of each speckle of the speckle pattern 3. This image processing means is configured to continuously obtain the center of gravity 12 of each speckle, and detects the movement of each speckle by detecting the amount and direction of movement of the center of gravity 12. Can do. A known calculation method can be used for calculating the center of gravity.

  In addition, the image processing apparatus 6 includes a measuring unit that measures the distortion of the DUT 5 based on the movement amount and movement direction of the center of gravity 12 of each speckle detected by the image processing unit. Further, the image processing device 6 outputs the speckle pattern 3 and its center of gravity, and distortion information of the object to be measured 5 to the display device 7. The measuring means can digitize the degree of distortion of the DUT 5 using a Poisson's ratio or the like, and can schematically represent a change in the positional relationship between the center of gravity points.

  FIG. 2 shows the speckle pattern 3 imaged in the embodiment shown in FIG. FIG. 2 shows a state in which a load is applied to the DUT 5. Before the load is applied to the object to be measured 5, the speckle pattern 3 is stationary. However, when a load is applied to the object to be measured 5, the object to be measured 5 is distorted in proportion to the magnitude of the load. A state (arrow in the figure) where the blue pattern 3 moves in parallel with the strain direction is shown.

  As shown in FIG. 1 and FIG. 2, the speckle pattern 3 has a property of moving in parallel with the strain direction on the surface of the object 5 to be measured. The barycentric point 12 (black point in the figure) of the speckle moves. Therefore, the distortion measuring device according to the present invention calculates the amount of movement and the direction of movement of the center of gravity 12 of each speckle in the captured speckle pattern 3 by the image processing device 6 so that the object to be measured 5 against the load can be measured. Strain distribution can be measured.

  FIG. 3 shows a strain distribution measurement system in a wide area (measurement points 9a to 9e) of the object 5 to be measured. In the embodiment shown in FIG. 3, reference numerals 11 a to 11 e are measurement systems constituted by the laser projector 1 and the light receiving unit 2 shown in FIG. 5. The measurement locations 9a to 9e indicate appropriate measurement positions of the object 5 to be measured. In the illustrated embodiment, the measurement systems 11a to 11e emit laser beams 4 at the center and four corners of the object 5 to be measured. Irradiation enables measurement of the strain distribution over a wide area of the DUT 5. By providing the laser projector 1 and the light receiving unit 2 in an integrated manner, it is also possible to move the measurement systems 11a to 11e and measure distortion at arbitrary measurement locations 9a to 9e.

  FIG. 3 shows a method of measuring a wide-range strain of the DUT 5 with respect to the tip load. As shown in FIG. 3, when the load device 8 applies a load from above the object to be measured 5 placed on the support base 10, the load is applied to the object to be measured 5 and distortion occurs.

  FIG. 4 shows a speckle pattern at each measurement location 9a to 9e in FIG. FIG. 4 shows a state in which a load is applied to the DUT 5. Before the load is applied to the object to be measured 5, the speckle pattern 3 at each of the measurement points 9a to 9e is stationary. However, when a load is applied to the object to be measured 5, the object to be measured is proportional to the magnitude of the load. 5 shows a state where distortion occurs and the speckle pattern 3 at each of the measurement points 9a to 9e moves in parallel with the distortion direction.

  The image processing device 6 includes image processing means and measurement means. The image processing means is configured to obtain the speckle centroid points 12 at the measurement points 9a to 9e, and detect the movement and direction of the centroid points 12 to detect the movement of each speckle. It is. The measuring means is based on the position data of the measurement points 9a to 9e on the object to be measured 5 and the amount and direction of movement of the center of gravity 12 of each speckle at the measurement points 9a to 9e detected by the image processing means. The strain distribution in a wide area of the measurement object 5 can be measured.

  In the illustrated embodiment, the image processing device 6 performs time-sharing processing (distortion distribution processing) between the plurality of measurement systems 11a to 11e, displays the positional relationship of the measurement systems 11a to 11e on the display device 7, and The distortion values (left and right and vertical movement amounts) in each measurement system 11a to 11e can be displayed. The image processing apparatus 6 sequentially (time division) processes image information collected from each of the measurement systems 11a to 11e by, for example, a phase-only correlation method, statistical interference, a cross-correlation method, and the like, and obtains a distortion value from the processed image data. Is to ask.

  The image processing apparatus 6 includes a separate computer that is individually provided in each of the measurement systems 11a to 11e to obtain a distortion value, and collects the obtained distortion values of each measurement system at once. The display apparatus 7 includes each measurement system. It is also possible to display the positional relationship and display the distortion value. Thus, by providing the image processing apparatus 6 individually, the strain distribution measurement of the DUT 5 can be obtained at high speed.

  In the above embodiment, the moving amount and moving direction of the centroid 12 are shown as an example of the image processing means, and the accuracy is 1 μm. However, the cross-correlation method, the phase-only correlation method, the statistical interference method, which are existing image processing, are used. Can be used to measure instantaneous distortion and submicron accuracy.

The strain measurement method and apparatus according to the present invention are not limited to the application of a tip load to the object to be measured 5 as shown in the above-described embodiment, but include a wind tunnel test, a fluid test, an extensometer for a tensile tester, a vibration test, and fatigue. The present invention can be applied to various uses such as strain distribution measurement of an object to be measured 5 in a test.
In addition, the strain measurement method and apparatus according to the present invention enables comprehensive strain distribution measurement of the DUT 5 by using a large number of measurement systems 11.

  Further, in the case of simultaneously measuring the strain distribution of a large object 5 such as an aircraft wing, the integrated laser projector 1 and light receiving unit 2 are installed at appropriate positions on the object 5 and simultaneously measured. By doing so, comprehensive distortion measurement can be performed.

DESCRIPTION OF SYMBOLS 1 Laser projector 2 Light-receiving part 3 Speckle pattern 4 Laser light 5 Measured object 6 Image processing apparatus 7 Display apparatus 8 Load apparatus 9 Measurement location 10 Support base 11 Measurement system 12 Center of gravity

Claims (5)

  Laser light is irradiated to the measurement location of the object to be measured, the laser speckle pattern, which is the reflected light of the laser light, is picked up by the light receiving unit, the center of gravity of each speckle of the picked up laser speckle pattern is obtained, and each spec A strain measurement method that measures the strain of the object to be measured by detecting the amount of movement and the direction of movement of the center of gravity of the object.   The strain measurement method according to claim 1, wherein the strain of the object to be measured is measured by irradiating a plurality of measurement locations with laser light.   A laser projector that irradiates a laser beam to a measurement location of the object to be measured, a light receiving unit that images a laser speckle pattern that is a reflected light of the laser beam, and a barycentric point of each speckle of the captured laser speckle pattern A distortion measuring apparatus comprising: an image processing means for obtaining a difference; and a measuring means for detecting the movement amount and direction of the center of gravity of each speckle to measure the distortion of the object to be measured.   The distortion measuring apparatus according to claim 3, comprising a plurality of sets of laser projectors and light receiving units, and irradiating a plurality of measurement locations with laser light.   The distortion measuring apparatus according to claim 3 or 4, wherein the measuring means includes means for measuring the distortion of the object to be measured by adding the moving amount and moving direction of the center of gravity of different speckles.

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