JP2010117326A - Device and method for measuring stress - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stress measuring device and a stress measuring method capable of measuring optical path difference with higher accuracy, by removing a problem of color irregularity of a background color, and by reducing a measurement error caused by a sense generated in each measurer relative to the optical path difference and a measurement error caused by the color irregularity of the background. <P>SOLUTION: This device includes: a background illumination means 1 including a white light source 1a; first and second polarizing plates 2, 3 forming a crossed Nicol state; a sensitive color plate 4 constituted so that a green (G) value becomes minimum in the state of the optical path difference 0 nm; a photographing means 5 for photographing an image transmitted through the members 2, 3, 4; and an analysis means 6 for operating a difference between a background color RGB value acquired from image data of only the background color and an optical path difference standard plate RGB value acquired from image data including an optical path difference standard plate to use the result as a reference RGB value, using a difference between a measured sample RGB value acquired from image data of a measured sample and the reference RGB value as an optical path difference estimated value, and operating by adding a thickness of the measured sample and a photoelastic coefficient of the material to the optical path difference estimated value, to thereby determine a stress value of the measuring sample. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a stress measuring apparatus and a stress measuring method used for measuring a stress of a transparent member such as a glass product.

  Among glass products, for example, products widely used in consumer and industrial applications such as discharge lamps are required not to be destroyed until the required life time even when a load such as pressure and temperature during operation is applied. As explained by Griffith's crack theory, glass products are susceptible to breakage starting from microscopic scratches (cracks) on the surface. It has the feature of breaking from the strongly acting part.

  In general, fracture of glass products is due to the fact that (1) residual stress generated in the glass after production and (2) load during operation, which is a combination of two factors acting during use, exceeded the fracture limit of glass. Occurs when. For this reason, when designing and manufacturing products, it is safe for consumers to predict how much the above two factors will affect destruction and to exclude products that are at risk of destruction by inspection before shipping. It is important to provide a reliable product.

  Inspection and measurement methods using photoelasticity are widely used as methods for visualizing stress in glass and judging the quality of glass products. This method is a method for examining the stress state from the strength and distribution of birefringence by utilizing the fact that when a transparent object is stressed and light is passed through the object, birefringence is generated in the light. An inspection apparatus using this technique is commercially available under the name of a glass strain measuring instrument. In addition, among the photoelastic methods, a sensitive color method for determining a stress state based on a color distribution is widely used.

  In the sensitive color method, a measurer puts a measurement sample to be observed in a stress measuring device and visually observes the distribution state of the sensitive color that appears, whereby the presence or absence of stress and its strength can be examined. The stress intensity is generally calculated by comparing the color state of a color sample called a standard plate with the color state of a measurement sample and calculating the stress value from the optical path difference of birefringence obtained by the color sample.

  For example, as a stress measuring instrument and measuring method using a sensitive color method, a first measurement using a light source, a fixed polarizing plate fixed with respect to the optical axis, a slit whose width and position can be adjusted, and a Babinet compensator Means, a second measuring means using an orthogonal sensitive color plate, a switching means for switching the first and second measuring means, a rotating polarizing plate rotatable with respect to the optical axis, and an eyepiece An edge stress measuring device and a measuring method for a transparent plate-like body provided are known (see Patent Document 1).

  Also, when visualizing the stress state using the sensitive color method, the stress state is visualized by photographing the sensitive color of the measurement sample using a photographer or the like and mapping the RGB color characteristics. Yes.

JP 2003-262553 A

Problems when measuring stress using a conventional stress measuring device include the following.
(1) When the difference between the color samples is small, it is difficult to accurately determine the optical path difference.
(2) Depending on the measurer, the color sense may vary, and the obtained optical path difference may vary depending on the measurer.
(3) Due to the characteristics of the light source and diffusion plate of the stress measurement device, the background color often has uneven color, and the optical path difference obtained differs depending on the measurement position in the field of view, so that an accurate stress state is judged. It is difficult. This problem is caused by aging of the light source and the diffusion plate, and it cannot be solved even if the arrangement of the light source and the diffusion plate is improved, so it is difficult to accurately quantify the stress. . Therefore, even in the case of the same stress, a numerical value is measured as a different stress. On the contrary, when a different stress is applied, the stress may be measured as the same stress, causing a problem. Furthermore, it is also affected by the position of the stress measuring device and the brightness around it. Furthermore, even when data is collected and analyzed with photographic data and visualized, the optical path difference may vary between measurement dates and measurement environments due to problems of background color and color unevenness.

  The problem (3) has not been solved even when the stress state is visualized using a sensitive color method as can be understood from the above description.

  The present invention eliminates the problem of uneven color of the background color, reduces the measurement error caused by the sensation generated for each measurer and the measurement error caused by the uneven color of the background for the optical path difference of the transparent object, and reduces the optical path. An object of the present invention is to provide a stress measuring apparatus and a stress measuring method capable of performing difference measurement with higher accuracy.

  A stress measurement device according to a first aspect of the present invention includes a background illumination unit that includes a white light source and illuminates a measurement sample from the back; a first deflection plate interposed between the background illumination unit and the measurement sample; and a white light source. A background illumination means for illuminating the measurement sample from the back; a first deflection plate interposed between the background illumination means and the measurement sample; and opposed to the first deflection plate with the measurement sample sandwiched therebetween A second deflector that cooperates with the first deflector to create an orthogonal Nicol state; and is configured to minimize the green (G) value in a state where the optical path difference is 0 nm, between the measurement sample and the second deflector An intervening sensitive color plate; photographing means for photographing an image transmitted through the second deflecting plate; and an RGB value of an optical path difference standard plate obtained from image data obtained by photographing an optical path difference standard plate in front of the background illumination means; The difference from the RGB value of the background color obtained from the image data of only the background color Calculate the reference RGB value, and use the difference between the measurement sample RGB value obtained from the image data of the measurement sample and the reference RGB value as the optical path difference estimation value. The optical path difference estimation value includes the thickness of the measurement sample and the photoelastic coefficient of the material. And an analysis means for calculating the stress value of the measurement sample by adding

  In the stress measuring method of the second invention, image data obtained by photographing an image of only the background color is converted to obtain a background color RGB value, and then an optical path difference standard plate is inserted in front of the background illumination means. A first step of obtaining the RGB value of the optical path difference standard plate by converting the image data obtained in this manner, and obtaining in advance the difference between the RGB value of the optical path difference standard plate and the background color data RGB value as a reference RGB value; The measurement sample RGB value is obtained by converting the image data obtained by photographing the measurement sample in front of the means, and the optical path difference estimated value is obtained by comparing the difference between the measurement sample RGB value and the reference RGB value obtained in advance. And a second step of calculating a stress of the measurement sample by adding the thickness of the measurement sample and the photoelastic coefficient of the material to the estimated optical path difference value.

  According to the first invention, the analyzing means calculates a difference between the optical path difference standard plate RGB value obtained from the image data including the optical path difference standard plate and the background color RGB value obtained from the image data of only the background color. The reference RGB value is calculated, and the difference between the measurement sample RGB value obtained from the image data of the measurement sample and the reference RGB value is calculated to obtain an optical path difference estimated value. The optical path difference estimated value includes the thickness of the measured sample and the photoelastic coefficient of the material. And calculating the stress value of the measurement sample by eliminating the problem of uneven color of the background color, reducing the measurement error caused by the uneven color of the background color, and reducing the measurement sample made of a transparent object such as glass. It is possible to provide a stress measuring apparatus that can perform optical path difference measurement with higher accuracy by eliminating measurement errors caused by a sense generated for each measurer with respect to the optical path difference.

  According to the second invention, in the first step, the image data of only the background color is converted to obtain the background color RGB value, and then the optical path difference standard plate is put in front of the background illumination means and photographed. The obtained image data is converted to obtain the RGB value of the optical path difference standard plate, and the difference between the RGB value of the optical path difference plate and the background color data RGB value is obtained in advance as a reference RGB value. The image data obtained by putting the measurement sample into the image is converted to obtain the measurement sample RGB value, the difference between the measurement sample RGB value and the reference RGB value obtained in advance is compared to obtain the optical path difference estimated value, and the optical path difference estimation is performed. By adding the thickness of the measurement sample and the photoelastic coefficient of the material to the value and calculating the stress of the measurement sample, the problem of uneven color of the background color is eliminated and measurement errors due to uneven color of the background are reduced. And transparent objects such as glass The optical path difference Ranaru measurement sample by eliminating the measurement error caused by the sensation occurs every measurer, it is possible to provide a more stress measuring method can be performed in a more accurate optical path difference measurement.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment for carrying out the stress measuring apparatus of the first invention. In the figure, the stress measuring device includes a background illumination means 1, first and second deflecting plates 2, 3, a sensitive color plate 4, an imaging means 5, and an analysis means 6.

  The background illumination means 1 includes a white light source 1a and a diffuser plate 1b, and illuminates the measurement sample 11 with white light from the back. The white light source 1a includes, for example, an annular fluorescent lamp and generates white light. The diffuser plate 1b diffuses white light generated from the white light source 1a in order to illuminate the measurement sample 11 with uniform illuminance.

  The first and second deflecting plates 2 and 3 are also referred to as λ / 4 plates, and are a pair of deflecting plates that are arranged in a front-rear facing relationship in front of the background illumination means 1 to create an orthogonal Nicole state. The measurement sample 11 is arranged between them. If desired, for example, the first deflecting plate 2 can be fixed, and the second deflecting plate 3 can be turned, for example, so that the orthogonal state can be confirmed by fine adjustment.

  The sensitive color plate 4 is formed of a crystal plate that rotates, for example, the deflection surface of transmitted light by an amount depending on the wavelength so as to minimize the green (G) value in a state where the optical path difference is 0 nm. Then, it is disposed between the measurement sample 11 and the second deflection plate 3. Since the green (G) value in the white light transmitted through the sensitive color plate 4 is configured to be minimum in a state where the optical path difference is 0 nm, the green color included in the light transmitted through the second deflection plate 3 Although the (G) value is minimized, the green (G) value increases as the optical path difference increases. Further, when the optical path difference of the green (G) value is 0 nm, only red (R) light and blue (B) light among white light is transmitted, and a so-called sensitive color of red-violet light is obtained. The light color of the transmitted light of the sensitive color plate 4 changes sensitively according to the optical path difference.

  The photographing means 5 is a means for photographing an image produced by the transmitted light that has passed through the first and second deflecting plates 2 and 3 and the sensitive color plate 4, and is a digital type that outputs RGB values of the image, for example, a CCD. A camera or the like is desirable. However, even if it is an analog type photographing means, an RGB value of an image can be output if an A / D converter for converting to an RGB value is attached.

  The analysis means 6 is a characteristic component of the present invention, and performs a predetermined analysis in each of the stress measurement preparation stage and the stress measurement execution stage to cancel out the color unevenness of the background color, and thereby the stress value or / and stress. It is comprised so that intensity distribution can be calculated | required. Moreover, it can comprise so that the result may be displayed on a monitor if desired. The analysis means 6 can be configured using a computer such as a personal computer.

  The measurement sample 11 is a transparent object that allows background light to pass through, and is made of, for example, glass. And when measuring the stress, it arrange | positions on the optical path between the 1st deflection plate 2 and the sensitive color plate 4 of a stress measuring device.

  FIG. 2 is a flowchart showing an analysis procedure in one embodiment for implementing the stress measurement method of the second invention and the analysis means in the first invention. The upper part of the line crossing the middle of the figure shows the first step as a stress measurement preparation stage, and the lower part shows the second step as the stress measurement execution stage. Note that numbers in circles in the figure indicate an example procedure, and are shown in the following in place of numbers surrounded by “”.

The procedure in the preparation stage of the stress measurement (1) preparation stage is as follows.
In “1”, using the photographing unit 5, “background photographing” is described and image data of only the background color is obtained. The image data includes an optical path difference standard plate (hereinafter referred to as an optical path difference standard plate) and a measurement sample 11 that are not placed in the stress measuring device, and only the background illumination means 1 is operated to produce an image of only the background color. This is obtained by photographing with the photographing means 5.
In “2”, image data of only the background color is converted into RGB values over the entire field of view of the photographing unit, and a background color RGB value expressed as “background data” is obtained.
In “3”, the optical path difference standard plate is put into the stress measuring device and is photographed as described as “photographing the standard plate”. In this photographing, the entire region including the optical path difference image and the background color image of the optical path difference standard plate is photographed, and the photographing data is converted into “optical path difference standard plate RGB values”.
In “4”, a difference between the RGB value of the optical path difference standard plate and the background color RGB value of “2” is calculated over the entire field of view to obtain a reference RGB value represented as “RGB difference value” in the drawing.
“5” completes the stress measurement preparation stage.

  Either of the two images may be taken first, but should be performed at the same time so as not to be affected by fluctuations in the background color. In addition, the stress measurement preparation stage can be performed at a desired time. For example, it may be performed once a month or may be performed every measurement.

(2) Stress measurement in the material, which is the execution stage of stress measurement, is as follows.
In “1”, the measurement sample 11 is put into the stress measuring device as “put sample”, and the optical path difference image and the background color image of the measurement sample 11 are taken together by the photographing means 5. To obtain “measurement material image data”. The measurement sample image data is converted over the entire field of view to obtain measurement sample RGB values.
In “2”, the difference between the RGB value of the measurement sample and the background color RGB value obtained in the preparation stage of (1) is calculated over the entire area of the image to obtain the calculation (RGB value).
In “3”, the estimated optical path difference value is obtained by comparing the calculation (RGB value) and the reference RGB value obtained in the preparation stage of (1) over the entire area.
In “4”, the stress value is calculated by adding the thickness of the measurement sample 11 and the photoelastic coefficient of the material to the estimated optical path difference value.
In “5”, as a result of “4”, the stress value of the measurement sample 11 is obtained.

  Thus, the effect of the background color is not offset in the obtained stress value.

  FIG. 3 is a graph showing the relationship between the background color RGB value and the optical path difference in the first and second inventions. The graph of FIG. 3 is a graph showing the relationship between the optical path difference obtained by the sensitive color method and the RGB value of the background color (white), and corresponds to “2” in (1) of FIG. In the figure, the horizontal axis represents the optical path difference (nm) and the vertical axis represents the color value (RGB). Also, the curve G in the figure is a green (G) value at a wavelength of 530 nm, the curve R is a red (R) value, and the curve B is a blue (B) value, both of which are the optical path difference and the magnitude of the color value in the optical path difference. It shows.

  As can be seen from FIG. 3, when the optical path difference is 0, the green (G) value is minimum, the red (R) value is about 195, and the blue (B) value is about 205, which is the maximum. It has a deep reddish purple color with a strong bluish tint. As the optical path difference increases toward the plus (+) side, the red (R) value decreases and the blue (B) value continues to saturate at a large value, increasing the bluishness of the sensitive color (red purple). Go. On the other hand, as the optical path difference increases to the minus (−) side, the red (R) value increases and eventually becomes saturated, and the blue (B) value decreases. It will increase. In short, the stress value and the direction of the stress in the transparent object can be calculated by utilizing the fact that the sign of the red (R) value and the blue (B) value is reversed with the optical path difference of 0 nm as a boundary.

  FIG. 4 is a graph showing the relationship between the reference RGB value and the optical path difference in the first and second inventions. The graph shown in FIG. 4 shows the result of calculating the difference between the background color RGB value shown in FIG. 3 and the standard plate optical path difference RGB value, and corresponds to “4” in (1) of FIG. . In the figure, the horizontal axis represents the optical path difference (nm), and the vertical axis represents the color value-zero optical path difference color value.

  As can be understood from FIG. 4, since the increase / decrease tendency of the color value similar to that of FIG. 3 is obtained, the stress value and its direction can be determined.

  FIG. 5 is a graph for explaining a deviation at the time of mapping the optical path difference standard plate RGB value. In the figure, both the horizontal axis and the vertical axis indicate the optical path difference (nm). Further, in the figure, ■ indicates a measured value, and symbols indicating ranges above and below ■ indicate a range where deviation can occur.

  The RGB value of the optical path difference standard plate corresponds to the prior art in which the uneven color of the background color is ignored. When the optical path difference value on the horizontal axis is taken as the measurement value, the vertical axis is about 10 nm above and below the measurement value. It is shown that the deviation of can occur. Therefore, depending on the position in the entire captured image, a maximum deviation of about 10 nm can occur in the optical path difference.

  FIG. 6 is a graph for explaining a state in which there is no deviation when mapping the reference RGB values of the first and second inventions. In the figure, both the horizontal axis and the vertical axis indicate the optical path difference (nm). Also, ■ in the figure is a measured value.

  As can be understood from FIG. 6, it can be understood that the above deviation does not occur when the stress value and the direction of the measurement sample are calculated using the reference RGB values of the present invention.

  By the way, the optical path difference can be expressed by a calculation formula: (optical path difference) = (photoelastic coefficient) × (stress) × (thickness). Therefore, if this calculation formula is modified, the photoelastic coefficient and thickness of the measurement sample are known from the calculation formula: (stress) = (optical path difference) / (photoelastic coefficient) × (thickness). By measuring and calculating the direction of the difference and the optical path difference, the stress value and the direction of the stress can be obtained.

  Further, the stress value and the direction of the stress as a calculation result can be imaged or digitized and displayed on a monitor or a document.

The block diagram which shows one form for implementing the stress measuring apparatus of 1st invention The flowchart which shows the analysis procedure in the form for implementing the stress measuring method of 2nd invention, and the analysis means in 1st invention The graph which shows the relationship between the background color RGB value and the optical path difference in the first and second inventions The graph which shows the relationship between the reference | standard RGB value and optical path difference in 1st and 2nd invention Optical path difference standard plate Graph explaining the deviation when mapping RGB values The graph explaining the state without a deviation at the time of mapping of the reference RGB values of the first and second inventions

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Background illumination means, 1a ... White light source, 1b ... Diffuser plate, 2 ... 1st deflection plate, 3 ... 2nd deflection plate, 4 ... Sensitive color plate, 5 ... Imaging means, 6 ... Analysis means

Claims (2)

Background illumination means comprising a white light source and illuminating the measurement sample from the back;
A first deflection plate interposed between the background illumination means and the measurement sample;
A second deflecting plate that faces the first deflecting plate across the measurement sample and creates an orthogonal Nicol state in cooperation with the first deflecting plate;
A sensitive color plate configured to minimize the green (G) value in a state where the optical path difference is 0 nm and interposed between the measurement sample and the second deflecting plate;
Photographing means for photographing an image transmitted through the second deflection plate;
The standard RGB by calculating the difference between the RGB value of the optical path difference standard plate obtained from the image data taken with the optical path difference standard plate in front of the background illumination means and the background color RGB value obtained from the image data of only the background color The difference between the measurement sample RGB value obtained from the image data of the measurement sample and the reference RGB value is the optical path difference estimated value, and the optical path difference estimated value is added to the thickness of the measurement sample and the photoelastic coefficient of the material. An analysis means for obtaining a stress value of a measurement sample;
A stress measuring device comprising: Image data obtained by photographing an image of only the background color is converted to obtain a background color RGB value, and then the image data obtained by photographing with an optical path difference standard plate placed in front of the background illumination means is converted. A first step of obtaining an optical path difference standard plate RGB value and obtaining in advance a difference between the optical path difference standard plate RGB value and the background color data RGB value as a reference RGB value;
Next, convert the image data obtained by putting the measurement sample in front of the background illumination means to obtain the measurement sample RGB value, and compare the difference between the measurement sample RGB value and the reference RGB value obtained in advance to compare the optical path difference. A second step of obtaining an estimated value and calculating the stress of the measured sample by adding the thickness of the measured sample and the photoelastic coefficient of the material to the estimated optical path difference;
The stress measuring method characterized by comprising.

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