JP6364921B2 - Tire shape analyzing apparatus and tire shape analyzing method - Google Patents

Description

  The present invention relates to a tire shape analysis device and a tire shape analysis method, and more particularly to a tire shape analysis device and a tire shape analysis method for analyzing distortion of a groove bottom surface of a tire.

  Cracks may occur on the groove bottom surface of the tire. In order to investigate the cause of cracks and the countermeasures, it is necessary to measure the distortion of the groove bottom surface.

  Regarding the measurement of tire distortion, there is a technique for making a cut on the tire groove bottom surface, measuring the opening amount of the cut, and measuring the distortion based on the cut (see, for example, Patent Document 1 and Patent Document 2).

  Further, there is a technique for measuring the cross-sectional shape of the groove based on the photographed image (see, for example, Patent Document 3).

JP 2012-154910 A JP 2012-131352 A JP 2012-154910 A

  When measuring the groove bottom surface distortion of a tire, using the technique described in Patent Document 1 or Patent Document 2 is not preferable because it is necessary to damage the tire. Further, with the technique described in Patent Document 3, it is difficult to measure the groove bottom surface distortion of the tire.

  This invention is made in view of the above, Comprising: It aims at providing the tire shape analysis apparatus and tire shape analysis method which can measure the groove | channel bottom surface distortion of a tire precisely.

In one aspect, the tire shape analysis device includes a photographing unit that photographs a lattice sheet provided in an area including at least a groove portion that is a recessed portion from the surface of the tire, and a non-contact shape measurement method that uses the photographing unit. an analysis unit for analyzing the captured image, based on an analysis result by the analysis unit, the e Bei a calculation unit for calculating a distortion of the surface of the groove, the imaging unit includes first and second camera The inter-camera distance, which is the distance between the first camera and the second camera, is defined as 150 mm ≦ inter-camera distance ≦ 400 mm, and the focal points of the lenses of the first camera and the second camera When the distance is f, a tire-camera distance, which is a distance between a midpoint between the position of the first camera and the position of the second camera and the lattice sheet attached to the tire, 10.5 × f mm ≦ Tire-camera distance ≦ 18.5 × f mm and 0.51 ≦ Camera distance / Tire-camera distance ≦ 1.35 .

In another aspect, the tire shape analysis method includes a step in which the photographing unit photographs a lattice sheet provided in a region including at least a groove portion that is a recessed portion from the surface of the tire, and the analysis unit performs non-contact shape measurement. the method includes the steps of analyzing the image captured by the imaging unit, based on the analysis result by the analysis unit, calculation unit, see it contains and calculating the distortion of the groove surface, the imaging unit An inter-camera distance, which is a distance between the first camera and the second camera, is defined as 150 mm ≦ inter-camera distance ≦ 400 mm; and When the focal length of the lens of the second camera is f, the midpoint between the position of the first camera and the position of the second camera and the lattice sheet affixed to the tire The distance between the tire and the camera, which is the distance, is defined as 10.5 × f mm ≦ the distance between the tire and the camera ≦ 18.5 × f mm and 0.51 ≦ the distance between the camera / the distance between the tire and the camera ≦ 1.35 The

  In one aspect, the tire shape analysis device and the tire shape analysis method can accurately measure the groove bottom surface distortion of the tire.

FIG. 1 is a configuration diagram showing a tire shape analysis system including a tire shape analysis device according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating functions of the tire shape analysis device of the tire shape analysis system. FIG. 3 is a diagram illustrating an example of an image obtained by photographing a lattice sheet. FIG. 4 is a diagram illustrating an example in which phase analysis is performed by the sampling moire method. FIG. 5 is a diagram for explaining the lattice pitch of the lattice sheet. FIG. 6 is a diagram for explaining the radius of curvature of the groove bottom surface of the tire. FIG. 7 is a diagram for explaining the installation position relationship of the camera of the photographing unit with respect to the tire that is the subject of photographing. FIG. 8 is a diagram for explaining the installation position relationship of the camera of the photographing unit with respect to the tire that is the subject of photographing. FIG. 9 is a diagram for explaining the inter-camera distance. FIG. 10 is a diagram for explaining the inter-camera distance. FIG. 11 is a diagram for explaining the position of the groove bottom curved surface. FIG. 12 is a diagram for explaining generation of moire fringes in the sampling moire method. FIG. 13 is a flowchart for explaining the selective sampling moire method. FIG. 14 is a diagram illustrating an example of moire fringes generated for the result of performing the thinning process with five pixels. FIG. 15 is a diagram illustrating an example of an image of a lattice sheet. FIG. 16 is a flowchart illustrating an example of a tire shape analysis method realized by the tire shape analysis apparatus of the present embodiment.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Further, the constituent elements of this embodiment include those that can be replaced while maintaining the identity of the invention and that are obvious for replacement. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

  FIG. 1 is a configuration diagram showing a tire shape analysis system including a tire shape analysis device according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating functions of the tire shape analyzing apparatus of the tire shape analyzing system shown in FIG. In these drawings, FIG. 1 schematically shows the overall configuration of the tire shape analysis system, and FIG. 2 shows the main functions of the tire shape analysis apparatus.

  The tire shape analysis system 1 according to the present embodiment is applied to a system that measures the groove bottom surface distortion of the tire 2. The tire shape analysis system 1 includes a photographing device 3 and a tire shape analysis device 4 (see FIG. 1).

  The tire 2 includes groove portions M1 to M4. The groove portions M <b> 1 to M <b> 4 are portions that are recessed from the surface of the tire 2. In the present embodiment, lattice sheets SS1 to SS4 are attached to an area including the four groove portions M1 to M4. In the present embodiment, lattice sheets SS1, SS2, SS3, and SS4 are attached to the four groove portions M1, M2, M3, and M4, respectively. When the lattice sheets SS1, SS2, SS3, and SS4 are pasted, for example, a spray paste is used as an adhesive. The lattice sheets SS1, SS2, SS3, and SS4 may be attached manually by an operator or using an apparatus or a jig (not shown). The lattice of the lattice sheets SS1, SS2, SS3, and SS4 is, for example, a 1 mm square lattice. In the following description, the lattice sheets SS1, SS2, SS3, and SS4 may be collectively referred to as the lattice sheet SS.

  The photographing apparatus 3 includes a pair of cameras 31a and 31b and a pair of illumination lamps 32a and 32b. The cameras 31a and 31b are photographing units that photograph the tire 2, and are configured by, for example, a CCD (Charge Coupled Device) camera. Strictly speaking, the cameras 31a and 31b photograph a region including the lattice sheet SS attached to the groove, which is a portion recessed from the surface of the tire 2.

  The photographing apparatus 3 has a camera fixing bar 33. The pair of cameras 31 a and 31 b are fixed to the camera fixing bar 33. The pair of cameras 31a and 31b are fixed at different positions on the camera fixing bar 33 so that the tire 2 can be photographed from different directions. These cameras 31a and 31b simultaneously photograph the tire 2 from the left and right directions to generate a tire image (digital image data of the tire 2). In the following description, the two cameras 31a and 31b may be collectively referred to as the camera 31.

  The illumination lamps 32a and 32b are lamps that illuminate the photographing ranges of the cameras 31a and 31b, and are constituted by, for example, halogen lamps. These illumination lamps 32a and 32b may be always-on types or flash-on types.

  The tire shape analysis device 4 is, for example, a PC (Personal Computer) in which a predetermined analysis program is installed, and performs image processing on the image of the tire 2 photographed by the photographing device 3 to perform tire analysis processing.

  As shown in FIG. 2, the tire shape analysis device 4 according to the present embodiment includes an analysis unit 41 that analyzes an image of the tire 2 photographed by the photographing device 3 by a non-contact shape measurement method, and an analysis by the analysis unit 41. And a strain calculating unit 42 for calculating the surface strain of the groove based on the result. The analysis unit 41 includes an image smoothing unit 411, a luminance distribution acquisition unit 412, a thinning processing unit 413, a moire fringe creation unit 414, a phase distribution calculation unit 415, and a three-dimensional shape calculation unit 416.

  The image smoothing unit 411 smoothes the captured image. The luminance distribution acquisition unit 412 obtains an image indicating the luminance distribution from the image smoothed by the image smoothing unit 411. The thinning processing unit 413 performs thinning processing on an image showing a luminance distribution. The thinning processing unit 413 and the moire fringe creation unit 414 create moire fringes by performing linear interpolation on the thinned image. The phase distribution calculation unit 415 calculates the phase distribution of the lattice sheet based on the moire fringes. Based on the calculated phase distribution of the lattice sheet, the three-dimensional shape calculation unit 416 calculates a three-dimensional shape in a region including at least a groove portion that is a recessed portion from the tire surface.

  The distortion calculation unit 42 calculates the distortion of the groove bottom surface based on the three-dimensional shape calculated by the three-dimensional shape calculation unit 416.

  FIG. 3 is a diagram illustrating an example of an image obtained by photographing the lattice sheet SS. The image photographed by the photographing device 3 includes a lattice sheet SS affixed to the groove surface of the tire 2. As shown in FIG. 3, the groove bottom curved surface portion WR can be photographed by the photographing device 3.

  FIG. 4 is a diagram illustrating an example in which phase analysis is performed on the image illustrated in FIG. 3 by a sampling moire method that is an example of a non-contact shape measurement method. By using the sampling moire method, the distortion of the groove bottom surface can be calculated with higher accuracy than other methods. The sampling moire method has a restriction that, for example, a pattern in which gratings are periodically arranged in the same direction as the camera pixel is a target of phase analysis. In the present embodiment, the above restriction can be eliminated by photographing the lattice sheet SS on the surface of the tire 2 from an oblique direction rather than the front.

  As the non-contact shape measurement method, a digital image correlation method, a Fourier transform method, a light section method, or the like may be used, and any method may be used as long as it can calculate the distortion of the groove bottom surface.

[Lattice sheet]
FIG. 5 is a diagram for explaining the lattice pitch of the lattice sheet SS. As shown in FIG. 5, the lattice sheet SS is provided with a large number of rectangular holes, and the distance KP between the center positions of the adjacent holes is the lattice pitch of the lattice sheet SS.

  Here, as a result of the inventor's verification of an appropriate lattice pitch, the following has been found. When the radius of curvature of the groove bottom surface is R, when the lattice pitch is smaller than 0.21 × R, it is difficult to attach the lattice sheet SS so that the lattice does not collapse. Further, when the lattice pitch is larger than 2.40 × R, it is difficult to detect the maximum value of the concentrated strain generated on the groove bottom surface. Therefore, it is desirable that the lattice pitch of the lattice sheet used in the present embodiment satisfies the formula (1).

  0.21 × R ≦ lattice pitch ≦ 2.40 × R (1)

  By using a lattice sheet having such a lattice pitch, the distortion of the groove bottom surface of the tire can be measured with high accuracy. Note that when the lattice pitch is greater than 2.40 × R, the number of locations where the strain gradient is large increases, and it is difficult to specify which is the concentrated portion of the true groove surface strain, which is not preferable.

  Note that the lattice sheet SS is not limited to the case where a large number of rectangular holes are provided, but may be provided with a number of other shapes, for example, triangular holes. The size of the holes may be arbitrary (provided that the lattice pitch KP can be identified visually).

[Curve radius of groove bottom surface]
FIG. 6 is a diagram for explaining the radius of curvature of the groove bottom surface of the tire. As shown in FIG. 6, assuming a circle KR inscribed in the groove bottom surface of the tire 2, the radius r of the circle KR is the radius of curvature of the groove bottom surface of the tire 2.

  7 and 8 are diagrams for explaining the installation position relationship of the camera of the photographing device 3 with respect to the tire 2 that is a photographing target.

  As shown in FIG. 7, the camera 31 is installed at a position where the tire 2 that is a subject of photographing can be photographed. More precisely, the camera 31 is installed at a position where the grooves M1, M2, M3 and M4 provided in the tire 2 can be photographed. The camera 31 is rotatable about the axis J, and the photographing direction Y can be changed. In the present embodiment, the axis J is installed on an extension line of the center line CL that passes through the equator plane of the tire 2. The center line CL is directed from the center point O of the tire 2 through the point P toward the axis J.

  As shown in FIG. 8, the camera 31 includes boundary points A and B between the groove portion M1 and the flat surface of the tire, boundary points C and D between the groove portion M2 and the flat surface of the tire, and a groove portion M3 and the flat surface of the tire. It is necessary to be able to photograph all the boundary points E and F between the groove part M4 and the boundary points G and H between the groove part M4 and the flat surface of the tire.

  Here, the angle formed by the center line CL and the shooting direction Y is defined as the shooting angle of the camera 31. Then, the shooting angle φ of the camera 31 can be defined by the following equation (2).

  −θmax ≦ shooting angle φ (deg) ≦ θmax (2)

In the example shown in FIG. 8, the angle θN (N is a natural number) is
θ1 = An angle (absolute value) formed by (→) AB and (→) PO,
θ2 = An angle (absolute value) formed by (→) BA and (→) PO,
θ3 = (→) An angle (absolute value) formed by CD and (→) PO,
θ4 = An angle (absolute value) formed by (→) DC and (→) PO,
θ5 = An angle (absolute value) formed by (→) EF and (→) PO,
θ6 = An angle (absolute value) formed by (→) FE and (→) PO,
θ7 = An angle (absolute value) formed by (→) GH and (→) PO,
θ8 = An angle (absolute value) formed by (→) HG and (→) PO,
It is. In other words, the angles θ1 to θ8 are angles formed by the vectors heading in the direction connecting the boundary points A to H with the flat portions of the tires of the grooves M1 to M4 provided in the tire and the vectors in the centerline CL direction, respectively. Yes, the angle θmax is the maximum absolute value of the angles θ1 to θ8. Note that (→) PO is a vector in the direction of the center line CL, and “(→)” indicates that the immediately following code is a vector. In consideration of taking a picture with the tire turned over (that is, in FIG. 8, points A and H, points B and G, points C and F, and points D and E are interchanged), Formula (2) was defined.

[Camera distance and tire-camera distance]
9 and 10 are diagrams for explaining the inter-camera distance that is the distance between the camera 31a as the first camera and the camera 31b as the second camera. FIG. 11 is a diagram for explaining the position of the groove bottom curved surface.

  Here, the distance between the camera 31a and the camera 31b along the center line 33C of the camera fixing rod 33 is defined as an inter-camera distance (inter-camera distance L31). Further, at the center line 33C of the camera fixing rod 33, it is affixed to the midpoint between the position where the camera 31a is fixed and the position where the camera 31b is fixed, that is, the midpoint 33M between the camera 31a and the camera 31b and the tire 2. The distance from the surface of the grid sheet SS is defined as a tire-camera distance (tire-camera distance L33).

  When the inventor examined the inter-camera distance L31, when the inter-camera distance L31 <150 mm, the measurement accuracy decreased. When the distance between the cameras L31> 400 mm, depending on the tire-camera distance L33, the lattice of the lattice sheet SS of the photographed image may be greatly bent, making analysis difficult.

  The inventor examined the tire-camera distance L33. Assuming that the focal length f of the lenses of the cameras 31a and 31b is 16 mm, the luminance of one line on the lattice sheet SS is obtained when the tire-camera distance L33 <168 mm. The distribution became a square wave, and the measurement accuracy decreased. In addition, when the distance between the tire and the camera L33> 295 mm, the number of pixels per one grating period decreased, and the measurement accuracy decreased. It should be noted that 168 mm / 16 mm = 10.5, and 295 mm / 16 mm = 18.5.

  Here, the inventors examined the values of the camera-to-camera distance / tire-camera distance corresponding to the camera angle, and the results shown in Table 1 were obtained.

  When the tire-camera distance L33 is fixed to 295 mm and the camera-to-camera distance L31 is changed to 100, 150, 200, 300, 400 mm, the value of the camera-to-camera distance / the tire-camera distance is 0.34, 0. .51, 0.68, 1.01, and 1.35. Further, in the strain output range W shown in FIG. 11, the average strain (groove width direction) of the groove bottom curved surface portion WR is −1.2, −1.4, −1.6, −1.6, − 1.5. In addition, the reference | standard of distortion is the inflation pressure 0 kPa and the contrast inflation pressure 250 kPa.

  Then, when the inter-camera distance L31 is 100 mm, the average distortion (width direction of the groove portion) of the groove bottom curved surface portion WR is −1.2, and there is a large deviation compared to other values. For this reason, if the distance between the cameras is in the range of 150 mm to 400 mm, the deviation of the average distortion is within 0.2%, and the measurement accuracy can be said to be almost unchanged. That is, when the value of the distance between the cameras / the distance between the tire and the camera is smaller than 0.51, the angle φ3 formed between the viewing direction (shooting direction) of the camera 31 and the center line 33C of the camera fixing rod 33 shown in FIG. It is too large and the measurement accuracy decreases. Further, when the value of the distance between the cameras / the distance between the tire and the camera is larger than 1.35, the lattice of the lattice sheet SS of the photographed image is greatly bent, and the measurement accuracy is lowered.

  As a result of the above examination, it has been found that the camera-to-camera distance L31 and the tire-camera distance L33 are desirably set to satisfy all of the expressions (3), (4), and (5).

150 mm ≦ distance between cameras ≦ 400 mm (3)
10.5 × fmm ≦ Tire-camera distance ≦ 18.5 × fmm (4)
0.51 ≦ Camera distance / Tire-camera distance ≦ 1.35 (5)

  By setting the distance between the camera and the distance between the tire and the camera as described above, a good analysis result was obtained.

  Here, the inventor has hypothesized that if the camera line of sight (camera shooting direction) does not change, the measurement accuracy is constant regardless of the distance between the cameras and the distance between the tire and the camera. Then, the inventor measured the distortion of the groove bottom surface with the camera angle (camera distance / tire-camera distance) fixed at 1.19 for verification of the hypothesis. The results are shown in Table 2.

  Referring to Table 2, assuming that the distance between the cameras is 351 mm, the distortion measurement error in the tire width direction is 0. When the distance between the cameras is 250, 240, 230, 220, 210, and 200 mm. The value was 24% to 0.26%, and it was found that the measurement accuracy was unchanged. And if it is the range which satisfy | fills all of Formula (3), Formula (4), and Formula (5), even if it changes the distance between cameras and the distance between tires and cameras, a favorable analysis result may be obtained. I understood.

[Camera selection]
When the inventor examined, when the camera 31 with a focal distance f = 35 mm was used at a camera-tire distance of 187 mm, blurring occurred at both ends of the lattice sheet SS, and it was difficult to analyze the distortion. Therefore, when a lens with an increased F value (aperture value) is used, this time, the amount of light is insufficient, and it is necessary to shoot with a longer exposure time. For this reason, there is a problem that it takes a long time to shoot especially when the camera 31 is calibrated.

  In order to solve these problems, the inventor used a 16 mm lens having a small focal length f in order to focus on both the groove bottom and the groove wall, and good analysis results were obtained.

[Example of non-contact shape method]
In the present embodiment, for example, a sampling moire method is used as a non-contact shape measurement method. The sampling moire method is a method of measuring a shape by sampling a photographed image of a measurement object pasted with a two-dimensional grid every predetermined pixel (every X pixels). As another non-contact shape measurement method, for example, a digital image correlation method or a Fourier transform method may be used. In the present embodiment, a case of using a thinning selection type sampling moire method among sampling moire methods will be described. The thinning selection type sampling moire method is a method of referring to the phase distribution of the thinning number optimal for analysis for each pixel of the captured image in the sampling moire method.

[Generation of moire fringes and calculation of phase distribution by sampling moire method]
In the sampling moire method, for example, a captured image is smoothed in a certain direction (for example, the vertical direction), and the smoothed image is thinned out and linearly interpolated to obtain a moire fringe image, and the phase distribution is used. To search for a corresponding point in the screen between the two cameras.

  Here, an example of generation of moire fringes and calculation of phase distribution in the sampling moire method will be described in more detail with reference to FIG. FIG. 12 is a diagram for explaining generation of moire fringes in the sampling moire method. FIG. 12 is cited and modified from No. 10 (2010) “Evaluation of accuracy of dynamic measurement method of three-dimensional shape / strain distribution using sampling moire method”, Proceedings of the Japan Society of Experimental Force, No. 10 (2010). The example shown in FIG. 12 is an example in which moire fringes are generated by the thinning-out uniform sampling moire method using the thinning number “4”.

  In step S11, the analysis unit 41 obtains an image obtained by smoothing the captured image of the groove bottom surface in the vertical direction (longitudinal direction). The following describes the processing when smoothing in the vertical direction, but the same processing is performed when smoothing in the horizontal direction (lateral direction).

  In step S12, the analysis unit 41 extracts one line from the smoothed image, and obtains an image 90 indicating a luminance distribution.

  In step S13, the analysis unit 41 thins out every four pixels for one image 90, thereby generating four images 91a to 91d. The images 91a to 91d have different pixels for starting thinning. The number of images generated by thinning out the pixels matches the thinning number. For example, when the decimation number is “4”, four images are generated, and when the decimation number is “5”, five images are generated.

  In step S14, for each of the images 91a to 91d, the analysis unit 41 performs linear interpolation using the luminance of the pixels for which the thinned pixels are not set and the luminance of the pixels for which the thinned pixels are set. The processing set by is performed. Thereby, moire fringes 92a to 92d are obtained.

  In step S15, the analysis unit 41 applies the luminance of the moire fringes 92a to 92d to the following equation (6), so that the phase σ of the position corresponding to the pixel position (k) in the phase distribution corresponding to the thinning number is obtained. can get.

  Here, X is a thinning-out number (X is a natural number), and I (k) indicates the luminance of the k-th moire fringe (k is a natural number). In the example shown in FIG. 12, moire fringes 92a, 92b, 92c, and 92d correspond to the first, second, third, and fourth moire fringes, respectively.

  By calculating the phase value corresponding to each pixel position using Equation (6) with reference to the moire fringes 92a to 92d, the phase distribution 93 when the image 90 is thinned by the thinning number “4” is calculated. can do.

  By calculating the phase distribution 93 of the moire fringes with the phase distribution 94 of the reference grating, a phase distribution 95 of the grating sheet having a phase of −π to π can be obtained.

  FIG. 13 is a flowchart for explaining the selective sampling moire method.

  In step S201, the image smoothing unit 411 of the analysis unit 41 obtains an image obtained by smoothing the captured image of the groove bottom surface in the vertical direction (vertical direction). This process is the same as step S11 in FIG.

  In step S202, the luminance distribution acquisition unit 412 of the analysis unit 41 extracts one line from the smoothed image, and obtains an image indicating the luminance distribution. This process is the same as step S12 of FIG.

  In step S203, the thinning processing unit 413 of the analysis unit 41 performs thinning processing with a plurality of types of pixels. In this example, 4 pixel thinning or 5 pixel thinning is selected and performed. Images obtained by performing the thinning process with four pixels are the same as the images 91a to 91d obtained by the process of step S13 described above.

  In step S204, the moiré fringe creation unit 414 of the analysis unit 41 generates moiré fringes for the results obtained by performing the thinning process on 4 pixels and 5 pixels respectively in step S203. The moire fringes generated for the result of performing the thinning process with four pixels in step S203 are the same as the moire fringes 92a to 92d obtained by the process of step S14 described above.

  FIG. 14 is a diagram illustrating an example of moire fringes generated for the result of performing the thinning process with five pixels. FIG. 14 is cited and modified from No. 10 (2010), “Evaluation of accuracy of dynamic measurement method of three-dimensional shape / strain distribution using sampling moire method”, Proceedings of Japan Society for Experimental Force, No. 10 (2010). As shown in FIG. 14, a moiré pattern is obtained by performing a process of setting the luminance of a pixel for which the thinned pixel is not set by linear interpolation using the luminance of the pixel for which the thinned pixel is set. Stripes 92e to 92i are obtained.

  In step S205, the phase distribution calculation unit 415 of the analysis unit 41 generates the moire fringes 92a to 92d generated with respect to the result of the thinning process performed on four pixels and the moire generated on the result of the thinning process performed with five pixels. By applying the luminance of the stripes 92e to 92i to the above equation (6), the phase σ of the position corresponding to the pixel position (k) in the phase distribution corresponding to the thinning number is obtained.

  By calculating the phase value corresponding to each pixel position using Equation (6) while referring to the moire fringes 92a to 92d and the moire fringes 92e to 92i, the image of one line is referred to as “4” and “5”. It is possible to calculate the phase distribution in the case of thinning out by the thinning number. That is, by calculating the phase distribution of the moire fringes 92a to 92d and the moire fringes 92e to 92i with the phase distribution of the reference grating, the phase distribution of the grating sheet having a periodicity of −π to π can be obtained. it can.

  In step S206, the phase distribution calculation unit 415 of the analysis unit 41 refers to the phase distribution of the lattice sheet suitable for shape analysis for each pixel. FIG. 15 is a diagram illustrating an example of an image of the lattice sheet SS. In FIG. 15, for example, in an image obtained by photographing the lattice sheet SS, when one pitch P4 having a lattice pitch corresponds to 4 pixels, the phase distribution of the lattice sheet generated for the result of performing the 4-pixel thinning process is referred to. . Further, in the image obtained by photographing the lattice sheet SS, when another pitch P5 of the lattice pitch corresponds to 5 pixels, the phase distribution of the lattice sheet generated with respect to the result of the 5-pixel thinning process is referred to.

  In step S207, based on the result of referring to the phase distribution of the lattice sheet for each pixel in step S206, the phase distribution calculation unit 415 of the analysis unit 41 determines the phase distribution of the lattice sheet for shape calculation. Thereby, in an image obtained by photographing the lattice sheet SS, an accurate shape analysis result can be obtained regardless of the number of pixels corresponding to one lattice pitch. In other words, for example, if thinning is performed with a fixed number of pixels, analysis accuracy may be lowered in a region where one pitch corresponds to five pixels. On the other hand, by reducing the number of pixels to be thinned out and fixing 4 pixels or 5 pixels as described above, it is possible to avoid a decrease in analysis accuracy for each area where one pitch corresponds to 5 pixels or 4 pixels. can do. In this way, the phase distribution of the thinning number that is optimal for analysis by the analysis unit 41 is selected.

  The phase distribution for shape calculation is determined as follows, for example. That is, for example, for an image 90 showing a luminance distribution obtained by extracting one line from a smoothed image, the number of pixels corresponding to the interval between the darkest pixels is obtained, and the number of pixels is set as the number of thinned pixels. Then, a phase distribution corresponding to the result of performing the thinning process with the number of pixels is set as a phase distribution for shape calculation.

  The process for obtaining the phase distribution as described above is the phase analysis process. By the phase analysis process, the distortion of the groove bottom surface of the tire can be measured with high accuracy.

[Tire shape analysis method]
FIG. 16 is a flowchart illustrating an example of a tire shape analysis method realized by the tire shape analysis device 4 of the present embodiment.

  In FIG. 16, in step S <b> 101, a lattice pattern is attached to a portion including the groove bottom surface of the tire 2. In step S <b> 102, the imaging device 3 that is an imaging unit captures an image of a lattice sheet that is provided in an area that includes at least a groove that is a recessed portion from the surface of the tire. In step S <b> 103, the analysis unit 41 analyzes the image photographed by the photographing device 3. In step S104, based on the analysis result by the analysis unit 41, the strain calculation unit 42 calculates the distortion of the surface of the groove.

  By the above tire shape analysis method, the distortion of the groove bottom surface of the tire can be measured with high accuracy.

DESCRIPTION OF SYMBOLS 1 Tire shape analysis system 2 Tire 3 Image pick-up device 4 Tire shape analysis device 31a, 31b Camera 32a, 32b Illumination lamp 33 Camera fixing rod 41 Analysis part 42 Distortion calculation part 411 Image smoothing part 412 Luminance distribution acquisition part 413 Thinning process part 414 Moire fringe creation unit 415 Phase distribution calculation unit 416 Three-dimensional shape calculation unit

Claims (7)

An imaging unit that images a lattice sheet provided in an area including at least a groove that is a recessed part from the surface of the tire;
With a non-contact shape measurement technique, an analysis unit that analyzes an image photographed by the photographing unit;
Based on the analysis result by the analysis unit, Bei example and a calculation unit that calculates a distortion of the groove surface,
The photographing unit includes first and second cameras,
The inter-camera distance, which is the distance between the first camera and the second camera,
150mm ≦ distance between cameras ≦ 400mm
And
When the focal length of the lenses of the first camera and the second camera is f, the midpoint between the position of the first camera and the position of the second camera and the tire attached to the tire The distance between the tire and the camera, which is the distance to the lattice sheet,
10.5 × f mm ≦ distance between tire and camera ≦ 18.5 × f mm
And
0.51 ≦ Camera distance / Tire-camera distance ≦ 1.35
A tire shape analysis device defined by . The non-contact shape measuring method is a sampling moire method,
The tire shape analysis device according to claim 1, wherein the analysis unit analyzes an image photographed by the photographing unit by the sampling moire method. The tire shape analysis apparatus according to claim 2, wherein the sampling moire method is a selective sampling moire method that refers to a phase distribution of thinning numbers optimal for analysis by the analysis unit for each pixel of a captured image. The lattice sheet is affixed to an area including at least the groove,
The photographing unit photographs a lattice sheet attached to the groove,
The analysis unit analyzes an image of a lattice sheet photographed by the photographing unit,
The tire shape analysis device according to any one of claims 1 to 3, wherein the calculation unit calculates a distortion of a surface of the groove based on an analysis result by the analysis unit. The lattice pitch of the lattice sheet is relative to the curvature radius R of the groove bottom of the tire.
0.21 × R ≦ lattice pitch ≦ 2.40 × R
The tire shape analyzing apparatus according to any one of claims 1 to 4, wherein the tire shape analyzing apparatus is a tire shape analyzing apparatus. The photographing unit
The tire shape analysis device according to any one of claims 1 to 5, wherein a shooting angle that is an angle formed by a shooting direction and a center line of the tire is defined by the following equation.
-Θmax ≤ shooting angle ≤ θmax
However, θmax is the maximum absolute value of the angles formed by the vector in the direction connecting the boundary points of the groove portions provided in the tire and the flat portion of the tire and the vector in the centerline direction. A step of photographing a lattice sheet provided in an area including at least a groove portion that is a portion recessed from the surface of the tire by the photographing unit;
An analyzing unit analyzing an image photographed by the photographing unit by a non-contact shape measuring method;
Based on the analysis result by the analysis unit, calculation unit, see contains and calculating the distortion of the groove surface,
The photographing unit includes first and second cameras,
The inter-camera distance, which is the distance between the first camera and the second camera,
150mm ≦ distance between cameras ≦ 400mm
And
When the focal length of the lenses of the first camera and the second camera is f, the midpoint between the position of the first camera and the position of the second camera and the tire attached to the tire The distance between the tire and the camera, which is the distance to the lattice sheet,
10.5 × f mm ≦ distance between tire and camera ≦ 18.5 × f mm
And
0.51 ≦ Camera distance / Tire-camera distance ≦ 1.35
A tire shape analysis method defined by .