JP2022050282A - System and method for analyzing tire shapes - Google Patents

Abstract

To allow for quantitatively measuring the groove depth in a contact patch of a tire.SOLUTION: A tire shape analysis system 1 comprises: a groove shape measurement unit 40 configured to measure three-dimensional shapes of grooves receding from a surface of a tire under measurement; a total contact area generation unit 42 configured to generate a total contact area representing an area with filled grooves in a contact patch of the tire; and a groove depth measurement unit 44 configured to measure positions and depth of the grooves within the total contact area.SELECTED DRAWING: Figure 1

Description

The present invention relates to a tire shape analysis system and a tire shape analysis method.

Patent Document 1 discloses a technique for measuring a strain generated on a contact patch of a tire. In Patent Document 1, reference points are marked on the land surface and the groove bottom of the tire contact patch, and the tire contact patch is photographed by a plurality of cameras in the first state, and the test road surface is described. A second photographing step of rolling the grounded tire and photographing the ground contact surface of the tire with a plurality of cameras in a second state different from the first state, for each of the land surface and the groove bottom. , Pattern matching is performed between the image taken in the first shooting step and the image taken in the second shooting step, and the two-dimensional or three-dimensional distortion is calculated based on the displacement of the reference point.

Further, Patent Document 2 discloses a technique for measuring a deformed state of a tread surface when a tire touches the ground. In Patent Document 2, a tire tread is imaged by irradiating a tire tread with a laser beam from the side opposite to the tire with the grounding plate having transparency to which the tire touches the ground and the grounding plate. Is shooting. As a result, three-dimensional data representing the deformed shape of the tread portion and the tread groove of the tire tread in the grounded deformed state is acquired.

Japanese Unexamined Patent Publication No. 2017-07690 Japanese Unexamined Patent Publication No. 2009-139268

According to the technique disclosed in Patent Document 1, the groove bottom strain of the ground contact surface of the tire can be measured. Further, according to the technique disclosed in Patent Document 2, three-dimensional data representing the deformed shape of the tread portion and the tread groove can be acquired. However, according to these techniques, there is room for improvement because the groove depth of the contact patch of the tire cannot be quantitatively measured.

The present invention has been made in view of the above, and an object of the present invention is to provide a tire shape analysis system and a tire shape analysis method capable of quantitatively measuring the groove depth of the contact patch of a tire. ..

In order to solve the above-mentioned problems and achieve the object, the tire shape analysis system according to an aspect of the present invention measures the three-dimensional shape of the groove which is a portion recessed from the surface of the tire to be measured. The groove depth for measuring the groove depth at the position of the groove in the total ground contact area, the measurement unit, the total ground contact area creation unit that creates the total ground contact area that is the region filled with the ground contact region of the tire, and the groove depth. It has a measuring unit.

The groove depth measuring unit includes a groove distribution data creating unit that creates groove distribution data indicating the position of the groove in the total ground contact region, and a groove depth that calculates the groove depth at each position indicated by the groove distribution data. It is preferable to have a calculation unit.

The groove depth calculation unit measures the shape of a sheet provided on the main surface of a road surface plate imitating a road surface, and determines the distance from the sheet to the groove bottom of the tire groove in contact with the road surface plate. The groove depth is preferable.

Further having a groove volume calculation unit for approximating the groove depth at each position calculated by the groove depth calculation unit with a minute rectangular parallelepiped and obtaining the total volume of the approximated rectangular parallelepiped as the groove volume in the total ground contact region. Is preferable.

It is preferable that the groove shape measuring unit captures the pattern formed in the groove of the tire with at least two cameras and analyzes the captured image of the cameras to measure the shape of the groove.

It is preferable that the groove shape measuring unit analyzes the pattern pattern on the captured image by using a weighted phase analysis method and measures the shape of the groove.

The groove shape measuring unit preferably divides the imaging range of the groove into two regions including a common region, and the common region preferably has one cycle or more of the pattern pattern.

It is preferable that the groove shape measuring unit repeats the movement of the two cameras and the photographing by the two cameras to photograph all the grooves in the total ground contact area.

When the midpoint position between the two cameras is defined as (X, Y), the movement range X of the two cameras in the tire circumferential direction is −maximum ground contact length / 2 ≦ X ≦ maximum ground contact length / 2. The movement range Y of the two cameras in the tire width direction is preferably −maximum contact width / 2 ≦ Y ≦ maximum contact width / 2.

The tire shape analysis method according to an aspect of the present invention includes a step of measuring the three-dimensional shape of a groove, which is a portion recessed from the surface of the tire to be measured, and a region filled with the ground contact region of the tire. It has a step of creating a total ground contact area and a step of measuring the groove depth at the position of the groove in the total ground contact area.

According to the present invention, the groove depth of the contact patch of the tire can be quantitatively measured.

FIG. 1 is a block diagram showing a configuration of a tire shape analysis system according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a groove shape measuring unit in FIG. FIG. 3 is a block diagram showing the function of the groove shape measuring unit shown in FIG. FIG. 4 is a diagram showing an example of an image obtained by taking a grid sheet. FIG. 5 is a diagram showing an example in which the image shown in FIG. 4 is phase-analyzed by the sampling moire method, which is an example of the non-contact shape measurement method. FIG. 6 is a diagram for explaining the lattice pitch of the lattice sheet. FIG. 7 is a diagram for explaining the radius of curvature of the groove bottom surface of the tire. FIG. 8 is a diagram for explaining the generation of moire fringes in the sampling moire method. FIG. 9 is a flowchart for explaining the selective sampling moire method. FIG. 10 is a diagram showing an example of moire fringes generated for the result of thinning out with 5 pixels. FIG. 11 is a diagram showing an example of an image of a grid sheet. FIG. 12 is a flowchart showing a groove shape measurement process by the groove shape measuring unit. FIG. 13 is a flowchart showing a tire analysis method by the tire shape analysis system according to the present embodiment. FIG. 14 is a diagram showing an example of a power spectrum that can be acquired by performing a two-dimensional Fourier transform on an image captured by the photographing unit. FIG. 15 is a flowchart showing a process of measuring the groove shape using the Fourier transform method. FIG. 16 is a flowchart showing a tire analysis method by the tire shape analysis system according to the present embodiment. FIG. 17 is a diagram showing the positional relationship between the tire to be photographed and the camera. FIG. 18 is an enlarged view showing a part of FIG. 17. FIG. 19 is a diagram showing the positional relationship between the cameras. FIG. 20 is a diagram showing an example of an image of a tire contact patch. FIG. 21 is a diagram showing a total grounding area creation process by the total grounding area creating unit. FIG. 22 is a block diagram showing the function of the total grounding area creation unit. FIG. 23 is a diagram illustrating the movement of the road surface plate and the operation of the trigger device. FIG. 24 is a diagram illustrating the movement of the road surface plate and the operation of the trigger device. FIG. 25 is a flow chart showing the operation of the total grounding area creating unit. FIG. 26 is a diagram showing an example of a specific arrangement of a camera and a lighting lamp when a ground plane image is acquired by a ground plane image acquisition unit. FIG. 27 is a diagram showing an example of a specific arrangement of a camera and a lighting lamp when a ground plane image is acquired by a ground plane image acquisition unit. FIG. 28 is a diagram showing an example of a specific arrangement of a camera and a lighting lamp when a ground plane image is acquired by a ground plane image acquisition unit. FIG. 29 is a diagram illustrating an inclination angle of the lamp with respect to the tire circumferential direction. FIG. 30 is a diagram illustrating an inclination angle of the lamp with respect to the tire circumferential direction. FIG. 31 is a view of the arrangement of the lighting lamps from the direction along the rotation axis of the tire. FIG. 32 is a view of the arrangement of the lighting lamps from a direction perpendicular to the rotation axis of the tire. FIG. 33 is a view of the arrangement of the lighting lamps from the upper surface side of the road surface plate. FIG. 34 is a diagram illustrating an inclination angle of the lamp with respect to the tire width direction. FIG. 35 is a diagram illustrating an inclination angle of the lamp with respect to the tire width direction. FIG. 36 is a diagram showing an example of irradiation of light from a lamp, which enhances the brightness of the chamfer of the sub-groove. FIG. 37 is a diagram showing an example of irradiation of light from a lamp, which enhances the brightness of the chamfer of the sub-groove. FIG. 38 is a diagram showing an example of irradiation of light from a lamp, which enhances the brightness of the chamfer of the sub-groove. FIG. 39 is a diagram showing an example of irradiation of light from a lamp, which enhances the brightness of the chamfer of the sub-groove. FIG. 40 is a diagram showing an example of irradiation of light from a lamp, which enhances the brightness of chamfering of a sub-groove. FIG. 41 is a diagram showing an example of irradiation of light from a lamp, which enhances the brightness of chamfering of a sub-groove. FIG. 42 is a diagram showing an example of camera arrangement. FIG. 43 is a diagram showing an example of camera arrangement. FIG. 44 is a flow chart showing an example of processing by the grounding characteristic analysis unit. FIG. 45 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 46 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 47 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 48 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 49 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 50 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 51 is a diagram showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit. FIG. 52 is a diagram showing an example of GCA. FIG. 53 is an explanatory diagram of the expansion process. FIG. 54 is an explanatory diagram of the shrinkage treatment. FIG. 55 is a diagram showing an example of the groove distribution in the total ground contact area. FIG. 56 is a diagram showing a case where one camera is used. FIG. 57 is a diagram showing a case where three cameras are used. FIG. 58 is a diagram illustrating the height of the road surface plate. FIG. 59 is a diagram showing a configuration for obtaining a height distribution. FIG. 60 is a diagram showing the contents of processing of the groove depth calculation unit. FIG. 61 is a diagram showing the contents of processing of the groove depth calculation unit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description of each embodiment, the same or equivalent components as those of the other embodiments are designated by the same reference numerals, and the description thereof will be simplified or omitted. The present invention is not limited to each embodiment. In addition, the components of each embodiment include those that can be easily replaced by those skilled in the art, or those that are substantially the same. It should be noted that the plurality of modifications described in this embodiment can be arbitrarily combined within the range of those skilled in the art.

FIG. 1 is a block diagram showing a configuration of a tire shape analysis system according to an embodiment of the present invention. As shown in FIG. 1, the tire shape analysis system according to the present embodiment includes a groove shape measuring unit 40, a total ground contact area creating unit 42, a groove depth measuring unit 44, and a groove volume calculating unit 46. The groove depth measuring unit 44 has a groove distribution data creating unit 441 and a groove depth calculating unit 442. Hereinafter, the processing contents of each of these parts will be described.

(Groove shape measuring unit)
FIG. 2 is a configuration diagram showing the groove shape measuring unit 40 in FIG. 1. FIG. 3 is a block diagram showing the function of the groove shape measuring unit 40 shown in FIG. In these figures, FIG. 2 schematically shows the overall configuration of the groove shape measuring unit 40, and FIG. 3 shows the main functions of the groove shape measuring unit 40.

The groove shape measuring unit 40 measures the groove shape of the tire 60. The groove shape measuring unit 40 includes a photographing device 3 and a tire contact patch analysis device 20 (see FIG. 2).

The tire 60 includes grooves M1 to M4. The groove portions M1 to M4 are portions recessed from the surface of the tire 60. In the present embodiment, the lattice sheets SS1 to SS4 are attached to the region including the four groove portions M1 to M4. In the present embodiment, the lattice sheets SS1, SS2, SS3, and SS4 are attached to the four groove portions M1, M2, M3, and M4, respectively. When attaching the lattice sheets SS1, SS2, SS3 and SS4, for example, spray glue is used as an adhesive. The lattice sheets SS1, SS2, SS3 and SS4 may be attached manually by an operator, or may be performed by using a device or 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 grid sheets SS1, SS2, SS3 and SS4 may be collectively referred to as the grid sheet SS.

The photographing apparatus 3 has a pair of cameras 15b and 15c and a pair of lighting lamps 32a and 32b. The cameras 15b and 15c are photographing units for photographing the tire 60, and are configured by, for example, a CCD (Charge Coupled Device) camera. More precisely, the cameras 15b and 15c photograph a region including a grid sheet SS attached to the groove, which is a portion recessed from the surface of the tire 60.

Further, the photographing device 3 has a fixed rod 15 AM. The pair of cameras 15b and 15c are fixed to the fixing rod 15AM. The pair of cameras 15b and 15c are fixed at different positions on the fixing rod 15AM so that the tires 60 can be photographed from different directions. These cameras 15b and 15c simultaneously capture the tire 60 from the left and right directions to generate a tire image (digital image data of the tire 60).

The illumination lamps 32a and 32b are lamps that illuminate the shooting range of the cameras 15b and 15c, and are composed of, for example, halogen lamps. These lighting lamps 32a and 32b may be a constantly lit type or a flash lit type.

The tire contact patch analysis device 20 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 60 taken by the photographing device 3 to perform tire analysis processing.

As shown in FIG. 3, the tire contact patch analysis device 20 according to the present embodiment includes an analysis unit 41 that analyzes an image of the tire 60 taken by the photographing device 3 by a non-contact shape measuring method. 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, a three-dimensional shape calculation unit 416, and an inverse Fourier transform unit. It is equipped with 419.

The image smoothing unit 411 smoothes the captured image. The luminance distribution acquisition unit 412 obtains an image showing 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 creating unit 414 perform linear interpolation on the thinned image to create moire fringes. The phase distribution calculation unit 415 calculates the phase distribution of the grid sheet based on the moire fringes. The three-dimensional shape calculation unit 416 calculates the three-dimensional shape in a region including at least a groove portion which is a portion recessed from the surface of the tire, based on the calculated phase distribution of the grid sheet. The inverse Fourier transform unit 419 performs an inverse Fourier transform process described later.

FIG. 4 is a diagram showing an example of an image obtained by photographing the lattice sheet SS. The image taken by the photographing device 3 includes a grid sheet SS attached to the surface of the groove portion of the tire 60. As shown in FIG. 4, the groove bottom curved surface portion WR can be photographed by the photographing device 3.

FIG. 5 is a diagram showing an example in which the image shown in FIG. 4 is phase-analyzed by the sampling moire method, which is an example of the non-contact shape measurement method. By using the sampling moiré method, the strain on the groove bottom surface can be calculated with higher accuracy than other methods. The sampling moiré method has a limitation that, for example, a pattern in which a grid is periodically arranged in the same direction as a camera pixel is targeted for phase analysis. In the present embodiment, the above limitation can be solved by taking a picture from an oblique direction rather than from the front with respect to the lattice sheet SS on the surface of the tire 60.

As the non-contact shape measuring method, a digital image correlation method, a Fourier transform method, an optical cutting 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. 6 is a diagram for explaining the lattice pitch of the lattice sheet SS. As shown in FIG. 6, 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 was found. When the radius of curvature of the groove bottom surface is R, and 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 occurring on the groove bottom surface. Therefore, it is desirable that the lattice pitch of the lattice sheet used in the present embodiment satisfies the equation (1).

0.21 x R ≤ lattice pitch ≤ 2.40 x R ... (1)

By using a grid sheet having such a grid pitch, it is possible to measure the strain on the groove bottom surface of the tire with high accuracy. When the lattice pitch> 2.40 × R, the number of places where the strain gradient is large increases, and it becomes difficult to identify which is the true concentration part of the groove surface strain, which is not preferable.

The lattice sheet SS is not limited to the case where a large number of rectangular holes are provided, and may be provided with a large number of holes having other shapes such as triangles. Further, the size of the hole may be arbitrary (provided that the distance KP of the lattice pitch can be visually identified).

FIG. 7 is a diagram for explaining the radius of curvature of the groove bottom surface of the tire. As shown in FIG. 7, assuming a circle KR inscribed in the groove bottom surface of the tire 60, the radius R of the circle KR is the radius of curvature of the groove bottom surface of the tire 60.

(Example of non-contact shape measurement method)
In this embodiment, for example, a sampling moire method is used as a non-contact shape measurement method. The sampling moiré method is a method of measuring a shape by sampling a captured image of a measurement object to which a two-dimensional grid is attached at predetermined pixel intervals (X pixel intervals). As another non-contact shape measuring method, for example, a digital image correlation method, a Fourier transform method, or the like may be used. In this embodiment, a case where the thinning selection type sampling moire method is used among the sampling moire methods will be described. The thinning selection type sampling moiré method is a method in the sampling moiré method in which the phase distribution of the thinning number optimal for analysis is referred to for each pixel of the captured image.

(Sampling moiré method)
In the sampling moire method, for example, a captured image is smoothed in a certain direction (for example, in 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. Search for the corresponding points in the screen between the two cameras.

Here, an example of generating moire fringes and calculating the phase distribution in the sampling moire method will be described in more detail with reference to FIG. FIG. 8 is a diagram for explaining the generation of moire fringes in the sampling moire method. FIG. 8 is quoted and modified from Proceedings of the Japanese Society of Experimental Powers, No. 10 (2010) “Accuracy evaluation of dynamic measurement method of 3D shape / strain distribution using sampling moiré method”. The example shown in FIG. 8 is an example in which moire fringes are generated by the thinning 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 (vertical direction). The following describes the process in the case of smoothing in the vertical direction, but the same process is performed in the case of smoothing in the horizontal direction (horizontal direction).

In step S12, the analysis unit 41 extracts one line from the smoothed image to obtain an image 90 showing the luminance distribution.

In step S13, the analysis unit 41 thins out one image 90 every four pixels to generate four images, images 91a to 91d. The pixels of the images 91a to 91d are different from each other. The number of images produced by thinning out the pixels matches the number of thinning out. For example, when the thinning number is "4", four images are generated, and when the thinning number is "5", five images are generated.

In step S14, the analysis unit 41 linearly uses the brightness of the pixels in which the thinned pixels are not set and the brightness of the pixels in which the non-thinned pixels are set for each of the images 91a to 91d. Processing to be set by interpolation is performed. As a result, moire fringes 92a to 92d can be obtained.

In step S15, the analysis unit 41 applies the luminance of the moire fringes 92a to 92d to the following equation (2) to obtain the phase σ of the position corresponding to the pixel position in the phase distribution corresponding to the thinning number.

Here, X is a thinned number (X is a natural number), and I (k) indicates the brightness of the kth moire fringe (k is a natural number). That is, when obtaining the phase σ of the position corresponding to the pixel position in the phase distribution corresponding to the thinning number, the brightness of the position corresponding to the pixel position is quoted from the kth moire fringe and stored in I (k). Then calculate the phase σ. In the example shown in FIG. 8, the 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 the equation (2) with reference to the moire fringes 92a to 92d, the phase distribution 93 when the image 90 is thinned out by the thinning number "4" is calculated. can do.

By calculating the phase distribution 93 of the moiré fringes with the phase distribution 94 of the reference grid, the phase distribution 95 of the lattice sheet having a periodicity from −π to π can be obtained.

FIG. 9 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. 8 described above.

In step S202, the luminance distribution acquisition unit 412 of the analysis unit 41 extracts one line from the smoothed image to obtain an image showing the luminance distribution. This process is the same as step S12 of FIG. 8 described above.

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. The image obtained by performing the thinning process with four pixels is the same as the images 91a to 91d obtained by the process of step S13 described above.

In step S204, the moire fringe creation unit 414 of the analysis unit 41 generates moire fringes, respectively, for the results of the thinning process of 4 pixels and 5 pixels in step S203, respectively. 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. 10 is a diagram showing an example of moire fringes generated for the result of thinning out with 5 pixels. FIG. 10 is quoted and modified from Proceedings of the Japanese Society of Experimental Powers, No. 10 (2010) "Evaluation of accuracy of dynamic measurement method of 3D shape / strain distribution using sampling moiré method". As shown in FIG. 10, by performing a process of setting the luminance of the pixel in which the thinned pixel is not set by linear interpolation using the luminance of the pixel in which the pixel not thinned is set. Moire fringes 92e to 92i can be obtained.

In step S205 of FIG. 9, the brightness of the moire fringes 92a to 92d generated by the phase distribution calculation unit 415 of the analysis unit 41 for the result of the thinning process with 4 pixels, and the result of the thinning process with 5 pixels. By applying the generated moiré fringes 92e to 92i to the above equation (2), the phase σ of the position corresponding to the pixel position in the phase distribution corresponding to the thinning number can be obtained.

By calculating the phase value corresponding to each pixel position using the equation (2) with reference to the moiré fringes 92a to 92d and the moiré fringes 92e to 92i, the one-line images are referred to as "4" and "5". It is possible to calculate the phase distribution when each is thinned out by the thinning number. That is, by calculating the phase distribution of the moiré fringes 92a to 92d and the moiré fringes 92e to 92i with the phase distribution of the reference lattice, it is possible to obtain the phase distribution of the lattice sheet having a periodicity from −π to π. can.

In step S206 of FIG. 9, the phase distribution calculation unit 415 of the analysis unit 41 refers to the phase distribution of the grid sheet suitable for shape analysis for each pixel. FIG. 11 is a diagram showing an example of an image of the grid sheet SS. In FIG. 11, for example, in an image obtained by photographing a grid sheet SS, when one pitch P4 having a grid pitch corresponds to four pixels, the phase distribution of the grid sheet generated for the result of performing the four-pixel thinning process is referred to. .. Further, in the image obtained by photographing the grid sheet SS, when another 1 pitch P5 of the grid pitch corresponds to 5 pixels, the phase distribution of the grid sheet generated for the result of the 5-pixel thinning process is referred to.

In step S207 of FIG. 9, the phase distribution calculation unit 415 of the analysis unit 41 determines the phase distribution of the grid sheet for shape calculation based on the result of referring to the phase distribution of the grid sheet for each pixel in step S206. As a result, accurate shape analysis results can be obtained regardless of the number of pixels in which one pitch of the grid pitch corresponds to the image obtained by capturing the grid sheet SS. That is, for example, if thinning is performed by fixing to 4 pixels, the analysis accuracy may decrease in a region where 1 pitch corresponds to 5 pixels. On the other hand, by thinning out 4 pixels or 5 pixels as described above without fixing the number of pixels to be thinned out, it is possible to avoid a decrease in analysis accuracy in each region where one pitch corresponds to 5 pixels or 4 pixels. can do. In this way, the phase distribution of the thinning number that is most suitable for the 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 the image 90 showing the luminance distribution obtained by extracting one line from the image obtained by smoothing the captured image, the number of pixels corresponding to the distance between the darkest pixels is obtained, and the number of pixels is defined as the number of thinned pixels. Then, the phase distribution corresponding to the result of the thinning process based on the number of pixels is defined as the phase distribution for shape calculation.

FIG. 12 is a flowchart showing a groove shape measurement process by the groove shape measuring unit 40. In FIG. 12, in step S101, a grid pattern is attached to a portion of the tire 60 including the groove bottom surface. In step S102, a grid sheet provided in a region including at least a groove portion which is a portion recessed from the surface of the tire is photographed. In step S103, the captured image is analyzed. From the above, the groove shape of the tire can be measured.

(Digital image correlation method)
The groove shape may be measured using a digital image correlation method. In the digital image correlation method, the pattern matching method is applied to the captured image. For example, one of feature-based matching, region-based matching, or phase-based matching is applied. Next, the corresponding points of the captured images from a plurality of different directions corresponding to the above-mentioned phase distribution are calculated. Then, the three-dimensional shape is calculated based on the corresponding points of the images taken from a plurality of different directions and the line of sight (shooting direction) of each camera. The phase distribution of the captured images acquired by the cameras 15b and 15c based on the corresponding points of the captured images and the line of sight of the camera, that is, the relative positions of the camera 15b, the camera 15c, and the tire 60 (road surface plate 221), is used as the line-of-sight data. By using it, a three-dimensional shape can be obtained.

FIG. 13 is a flowchart showing a tire analysis method by the tire shape analysis system 1 according to the present embodiment. In FIG. 13, in step S601, the surface of the tire forming the random pattern is photographed by at least two cameras. In step S602, the pattern matching method is applied to the images captured by the two cameras. In step S603, the corresponding points of the captured images from a plurality of different directions are calculated. In step S604, the three-dimensional shape is calculated based on the calculated corresponding points (corresponding to the phase distribution) and the line of sight (shooting direction) of each camera.

(Fourier transform method)
The groove shape may be measured using the Fourier transform method. FIG. 14 is a diagram showing an example of a power spectrum that can be acquired by performing a two-dimensional Fourier transform on an image captured by the photographing unit. FIG. 14 shows the power spectra of the vertical frequency and the horizontal frequency. The inverse Fourier transform unit 419 in FIG. 3 extracts the primary harmonic wave WV in the vertical direction and the primary harmonic wave WH in the horizontal direction from the power spectrum shown in FIG.

FIG. 15 is a flowchart showing a process of measuring the groove shape using the Fourier transform method. In FIG. 15, in step S501, the pattern pattern is photographed by at least two cameras. In step S502, the captured image is subjected to a two-dimensional Fourier transform to acquire a power spectrum. In step S503, the first-order harmonic wave WV in the vertical direction and the first-order harmonic wave WH in the horizontal direction are extracted from the acquired power spectrum, and two-dimensional inverse Fourier transform is performed on each of them. In step S504, the wrapping type phase distribution obtained by the two-dimensional inverse Fourier transform is phase-connected and converted into the unwrapping type. In step S505, the three-dimensional shape is calculated based on the phase distribution of the image captured by each camera and the line of sight (shooting direction) of each camera.

(Weighted phase analysis method)
The groove shape may be measured using a weighted phase analysis method. FIG. 16 is a flowchart showing a tire analysis method by the tire shape analysis system 1 according to the present embodiment. In FIG. 16, in step S501, the pattern pattern is photographed by at least two cameras. In step S502a, the captured image is smoothed in the vertical direction and the horizontal direction, respectively. In step S502b, the phase distribution of the grid is obtained for the image smoothed in the vertical direction and the horizontal direction in step S502a. For example, the phase distribution of the lattice is obtained by using the technique described in Japanese Patent No. 5795095. For example, the weighting function W _x (k) in the vertical direction (x direction) and the weighting function W _y (l) in the horizontal direction (y direction) are set as the weighting function W _xy (k, l) in the two-dimensional direction. When expressed, it becomes as shown in equation (3). The phase calculation formula in the vertical direction (x direction) is the formula (4), and the phase calculation formula in the horizontal direction (y direction) is the formula (5). The phase distribution of the lattice is obtained by using the equations (4) and (5).

In step S504, the phase distribution of the wrapping type (wrapped by π and returned to −π) obtained by step S502b is phase-connected and converted into an unwrapping type. In step S505, the three-dimensional shape is calculated based on the phase distribution of the image captured by each camera and the line of sight (shooting direction) of each camera.

(Shooting in multiple shots)
When photographing a groove provided with a pattern, it is preferable to divide the imaging range and photograph it in a plurality of times, instead of photographing the entire groove at one time. For example, it is preferable to divide the shooting range into two and shoot in two shots.

FIG. 17 is a diagram showing the positional relationship between the tire to be photographed and the camera. FIG. 18 is an enlarged view showing a part of FIG. 17. In FIGS. 17 and 18, the left-right direction in the figure is the tire width direction, the depth direction in the figure is the tire circumferential direction, and the road surface plate 221 extends direction. In FIG. 17, the tire 60 is in contact with the upper surface 221U of the road surface plate 221. Cameras 15b1 and 15b2 and cameras 15c1 and 15c2 are provided on the lower surface 221D side of the road surface plate 221. The cameras 15b1 and 15b2 are arranged so as to overlap each other in the depth direction of the figure. The cameras 15c1 and 15c2 are arranged so as to overlap each other in the depth direction of the figure.

In this example, a case where the cameras 15b1 and 15b2 and the cameras 15c1 and 15c2 capture the range H of the tire 60 will be described. The range H includes the groove 62 of the tire 60. FIG. 18 shows an enlarged range H. As shown in FIG. 18, the range H includes two ranges H1 and a range H2. Therefore, the imaging range of the groove 62 is divided into two ranges H1 and H2, and the imaging is performed twice. There is a common region HC in the two ranges H1 and H2. That is, the photographing range of the groove 62 is divided into two areas including a common area. The common region HC is preferably one cycle or more in the tire width direction of the pattern pattern. By dividing the imaging range while providing the common region HC in this way, it is possible to accurately synthesize the groove shape for each imaging region and acquire the shape of the entire groove. If the common region HC is less than one cycle in the tire width direction of the pattern pattern, the accuracy of groove shape synthesis is lowered due to the limitation of the sampling moire method, which is not preferable.

Here, the positional relationship between the cameras will be described. FIG. 19 is a diagram showing the positional relationship between the cameras. In FIG. 19, the camera 15b corresponds to the cameras 15b1 and 15c1 shown in FIG. 17, and the camera 15c corresponds to the cameras 15b2 and 15c2 shown in FIG.

As shown in FIG. 19, the camera 15b and the camera 15c are fixed to the fixed rod 15AM. The distance between the camera 15b and the camera 15c (hereinafter, the distance between the cameras) is preferably, for example, 150 mm or more and 400 mm or less. When the camera is installed on the fixed rod, the distance 15D along the center line 15S of the fixed rod 15AM is the inter-camera distance.

Further, the distance from the midpoint position 15P between the camera 15b and the camera 15c to the lattice sheet SS provided in the groove of the tire to be photographed (hereinafter, the distance between the tire and the camera) is (10.5 × F). ) Mm or more (18.5 × F) mm or less. However, F is the focal length of the lens of the camera.

Further, the ratio of the distance between cameras to the distance between tires and cameras is preferably 0.51 or more and 1.35 or less. When the camera is installed on the fixed rod 15AM, the distance 15E from the grid sheet SS to the center line 15S is the distance between the tire and the camera.

In the example described with reference to FIGS. 17 and 18, the shooting range is divided into two ranges and two shots are taken, but the shooting range is divided into three or more ranges and the shots are taken separately. You may. That is, the shooting range may be divided into at least two ranges and shot separately. In any case, it is divided so as to include a common area, and the common area is preferably one cycle or more in the tire width direction of the pattern pattern.

(Camera movement range)
The cameras 15b and 15c are movable, and it is preferable that all the grooves on the tire contact patch can be photographed. That is, it is preferable to repeatedly move the cameras 15b and 15c and shoot with the cameras 15b and 15c to shoot all the grooves in the total ground contact area. By repeating the movement of the camera and the shooting with respect to the shooting range divided as described above, the groove depth and the groove volume on the entire tire contact patch can be evaluated.

FIG. 20 is a diagram showing an example of an image of a tire contact patch. In FIG. 20, the camera is movable in the tire width direction and the tire circumferential direction, and the movement range HM of the camera is preferably as follows. That is, when the origin (0,0) is the ground contact center 610 of the tire and the midpoint position 15P of the two cameras 15b and 15c is defined as (X, Y), the maximum ground contact length L7 along the tire circumferential direction is obtained. On the other hand, the movement range X in the tire circumferential direction is preferably −L7 / 2 or more and L7 / 2 or less. Further, the moving range Y in the tire width direction with respect to the maximum contact width W7 along the tire width direction is preferably −W7 / 2 or more and W7 / 2 or less. By setting the moving range HM of the camera as described above, it is possible to evaluate the groove depth and the groove volume in the entire tire contact patch.

(Total grounding area creation process)
FIG. 21 is a diagram showing a total grounding area creation process by the total grounding area creating unit 42. FIG. 22 is a block diagram showing the function of the total grounding area creating unit 42. In these figures, FIG. 21 schematically shows the overall configuration of the total grounding area creating unit 42, and FIG. 22 shows the main functions of the total grounding area creating unit 42.

The total ground contact area creating unit 42 is applied to a system that analyzes the ground contact surface 61 by acquiring an image of the ground contact surface 61 of the pneumatic tire 60. The total ground contact area creating unit 42 includes a tire testing machine 2, a photographing device 10, and a tire contact patch analysis device 20.

The tire testing machine 2 is a device that imparts test conditions to the tire 60. In the configuration of FIG. 21, the tire tester 2 has a support device 300, a drive device 5, and a transparent road surface plate 221. The support device 300 is a device that rotatably supports the tire 60, and has a rim 400 on which the tire 60 is mounted. The drive device 5 is a device that applies a driving force to the tire 60 and the road surface plate 221. The drive device 5 includes a motor 6 that drives the tire 60 and the road surface plate 221 and a motor control device 7 that controls the motor 6. The drive device 5 includes gears (not shown) and the like, and drives the road surface plate 221 horizontally.

In the tire testing machine 2, the support device 300 supports the tire 60 mounted on the rim 400, and the tire 60 is pressed against the upper surface 221U which is one main surface of the road surface plate 221 to apply a load to the tire 60. The road surface plate 221 reproduces a flat road surface. The tire 60 pressed against the road surface plate 221 deforms the ground contact surface 61 in the same manner as when traveling on a flat road surface. By driving the road surface plate 221 horizontally, the rolling state of the tire 60 when the vehicle is running is reproduced with the surface of the road surface plate 221 as the road surface, and the dynamic ground contact characteristics can be analyzed. Further, the support device 300 displaces the rim 400 to adjust the positional relationship between the tire 60 and the road surface plate 221 to impart a slip angle or an angle angle to the tire 60. Further, the drive device 5 can drive the motor 6 by the motor control device 7 to rotate the rim 400 by a predetermined angle. Further, the support device 300 and the drive device 5 can change the test conditions by adjusting the load, the rotation speed, the slip angle, the angle angle, and the like.

The road surface plate 221 is a light transmitting plate having a property of transmitting light. The road surface plate 221 does not have to transmit 100% of light, and may have a light transmittance capable of photographing the surface of the tire 60 through the road surface plate 221. The road surface plate 221 is, for example, a flat plate made of acrylic resin or a flat plate made of glass. Since the contact state between the tire 60 and the flat plate is photographed and image analysis is performed, the ground contact state of the tire 60, which is closer to reality, can be analyzed. Regarding the road surface plate 221, specifications such as plate thickness and refraction angle are not specified.

The photographing device 10 includes a camera 15a which is a photographing unit for photographing the tire 60, a lighting lamp 16 which is a light source, and a trigger device 17. The camera 15a is composed of, for example, a CCD (Charge Coupled Device) camera. The camera 15a is fixed in the photographing device 10. The camera 15a photographs the ground contact surface 61 of the tire 60 pressed against the road surface plate 221 by photographing the tire 60 via the road surface plate 221. Specifically, the camera 15a is arranged on the lower surface 221D side, which is the other main surface of the road surface plate 221, in a direction in which the optical axis is orthogonal to the lower surface 221D side, and the tire is provided from the lower surface 221D side via the road surface plate 221. Take a picture of 60. As a result, the camera 15a photographs the tire 60 including at least the ground contact surface 61, and generates digital image data of the tire 60 including the ground contact surface 61.

The illumination lamp 16 is a lamp that illuminates the shooting range of the camera 15a, and is composed of, for example, a halogen lamp. The lighting lamp 16 is a general term for a plurality of lamps 161 to 168 provided as described later. The lighting lamp 16 irradiates the ground contact surface 61 of the tire 60 pressed against the road surface plate 221 with light. The lighting lamp 16 irradiates light from the lower surface 221D side of the road surface plate 221 through the road surface plate 221 or between the upper surface 221U side of the road surface plate 221 and the tire 60. The plurality of lighting lamps 16 are arranged at positions other than the position where the road surface plate 221 moves. As the photographing device 10 moves, the camera 15a in the photographing device 10 and the lighting lamp 16 move together.

The number of these lighting lamps 16 may be different depending on the test conditions of the tire testing machine 2. For example, when the load when pressing the tire 60 against the road surface plate 221 is small, the ground contact area becomes narrow. Therefore, in this case, the number of the illumination lamps 16 may be relatively small, and the number of the illumination lamps 16 may be arranged at two locations diagonal to the moving direction of the road surface plate 221. On the other hand, when the load when pressing the tire 60 against the road surface plate 221 is large, the ground contact area becomes wide, so it is necessary to irradiate the ground contact surface 61 with light from more directions. Therefore, in this case, the lighting lamps 16 are arranged at four or more locations surrounding the ground plane 61. Further, these lighting lamps 16 may be a constantly lit type or a flash lit type.

The trigger device 17 is a device that outputs a trigger signal indicating the timing of shooting by the camera 15a. The trigger device 17 outputs a semiconductor laser and outputs a trigger signal when the reflected light is detected. In this example, a retroreflective sheet 18 is attached to the side surface of the road surface plate 221. The semiconductor laser output by the trigger device 17 is reflected by the retroreflective sheet 18, and the detection unit 171 of the trigger device 17 reflects the reflected light. Is detected, a trigger signal is output. If the relationship between the attachment position of the retroreflective sheet 18 and the position of the camera 15a is fixed, the ground contact surface 61 at the same position of the tire 60 can be photographed even when the imaging is performed a plurality of times.

The tire contact patch 20 is, for example, a PC (Personal Computer) in which a predetermined analysis program is installed, and processes an image of the tire 60 input from the photographing device 10 to analyze the contact patch 61 of the tire 60. I do. The process of analyzing the contact patch 61 of the tire 60 includes a process of calculating the contact patch 61 based on the captured image of the tire 60. The tire contact patch analysis device 20 includes a processing device 30 that performs arithmetic processing such as analysis of the contact patch 61 and data storage, an input unit 21 that allows an operator to perform an input operation to the tire contact patch analysis device 20, and an analysis result. And a display unit 22 for displaying various information. A pointing device such as a keyboard or a mouse is used for the input unit 21, and a display device such as a liquid crystal display is used for the display unit 22. The input unit 21 and the display unit 22 are electrically connected to the processing device 30, whereby the tire contact patch analysis device 20 allows the operator to perform an input operation on the input unit 21 while visually recognizing the display unit 22. Is possible. Further, the camera 15a is connected to the processing device 30 of the tire contact patch analysis device 20, which enables the tire contact patch analysis device 20 to acquire an image taken by the camera 15a.

The processing device 30 included in the tire tread analysis device 20 includes a processing unit 31 having a CPU (Central Processing Unit) and the like, and a storage unit 50 such as a RAM (Random Access Memory). The processing unit 31 and the storage unit 50 configured in this way may be provided in the same housing, may be provided in different housings, or a plurality of storage units 50 may be provided in both forms. It may be provided.

The processing unit 31 included in the processing device 30 functionally includes a grounding surface image acquisition unit 32, a grounding characteristic analysis unit 33, and a marking extraction unit 401. Of these, the contact patch image acquisition unit 32 acquires a photographed image of the contact patch 61 of the tire 60 to be analyzed. The captured image is a digital image of the ground contact surface 61 of the tire 60, which is captured by the camera 15a. Further, the ground contact characteristic analysis unit 33 creates a contact area image showing the contact area of the tire 60 based on the contact patch image acquired by the contact patch image acquisition unit 32. In the following description, it is assumed that all the captured images of the ground plane 61 are composed of 256 gradations, and black is defined as brightness "0" and white is defined as brightness "255".

The ground contact characteristic analysis unit 33 includes a groove extraction unit 34 and a ground contact characteristic calculation unit 35. The groove extraction unit 34 extracts the groove image from the captured image. The grounding characteristic calculation unit 35 subtracts the groove image from the image of the rough grounding region obtained by the binarization process with the predetermined brightness as the threshold value for the captured image. The grounding characteristic calculation unit 35 may, for example, perform a smoothing process on the captured image and then perform a binarization process with the luminance threshold value set to “220” to obtain an image of a rough grounding region. For the smoothing process, for example, a process using a median filter having a region within a radius of 4 pixels from the pixel of interest as a peripheral pixel (hereinafter referred to as a median process) may be used. As will be described later, the groove extraction unit 34 may perform a process of removing the portion corresponding to the marking included in the captured image to extract the groove image. Further, as will be described later, the grounding characteristic calculation unit 35 may perform a process of removing the portion corresponding to the marking included in the captured image to extract a rough grounded area image.

The groove extraction unit 34 includes a chamfered image extraction unit 34A, a groove bottom extraction unit 34B, a main groove bottom extraction unit 34C, and a synthesis unit 34D. The chamfer image extraction unit 34A extracts a chamfer image showing the chamfered portion provided at the edge of the groove of the tire 60 from the captured image. The chamfered image extraction unit 34A extracts a portion having a brightness higher than a predetermined brightness from the captured image as a chamfered image. The groove bottom extraction unit 34B extracts a portion having a brightness lower than a predetermined brightness from the captured image as a groove bottom image showing the bottom of the groove. The main groove bottom extraction unit 34C extracts a low-luminance portion surrounded by a portion having a brightness higher than a predetermined brightness from the captured image as a main groove bottom image showing the bottom of the main groove. The compositing unit 34D combines the chamfered image, the groove bottom image, and the main groove bottom image to obtain a groove image.

(Extracting part at the bottom of the main groove)
The main groove bottom extraction unit 34C includes a smoothing processing unit 341, a first candidate image extraction unit 342, a second candidate image extraction unit 343, and a superposition processing unit 344. The smoothing processing unit 341 smoothes the captured image in the tire circumferential direction. The first candidate image extraction unit 342 extracts the first candidate image that has been binarized by a predetermined first luminance threshold value from the smoothed image smoothed by the smoothing processing unit 341. The second candidate image extraction unit 343 extracts a second candidate image obtained by binarizing the smoothed image smoothed by the smoothing processing unit 341 with a second luminance threshold value lower than the first luminance threshold value. The superposition processing unit 344 obtains a main groove bottom image by superimposing the image of the isolated object included in the first candidate image and not including the ground block and the second candidate image.

Here, the groove of the tire 60 is a general term for the main groove, the sub-groove, and the chamfer provided in the opening of the groove provided on the tread surface of the tire 60. The main groove is a groove having an obligation to display a wear indicator specified in JATTA. Further, the sub-groove is a lateral groove extending in the tire width direction, and opens when the tire touches the ground and functions as a groove.

The analysis program used in the tire contact patch 20 is stored in advance in the storage unit 50, and when analyzing the contact patch 61 of the tire 60, the program stored in the storage unit 50 is stored in the processing unit 31. Each function is executed by calling in and executing the operation according to the program in the processing unit 31.

The total grounding area creation unit 42 according to the present embodiment has the above configuration. Hereinafter, the operation of the total grounding area creating unit 42 will be described. In the total ground contact area creating unit 42, first, the tire 60 is attached to the support device 300 of the tire tester 2, and the ground contact surface 61 is photographed by the camera 15a while rotating the tire 60 while being pressed against the road surface plate 221. .. At that time, the tire 60 is photographed in a state of being irradiated with light by a plurality of lighting lamps 16 from a plurality of directions. Therefore, the camera 15a can take a picture of the tire 60 with a difference in brightness between the ground contact surface 61 and the portion other than the ground contact surface 61. The captured image is acquired by the tire contact patch analysis device 20, and the tire contact patch analysis device 20 analyzes the contact patch 61 based on the acquired image.

For the extraction of the groove portion of the tire 60, a distance sensor that detects the difference in height (depth) by using the triangulation method can also be used. However, in order to detect the groove portion of the entire ground plane 61, it is necessary to scan the detection range of the distance sensor. Therefore, it is difficult to analyze the dynamic ground contact characteristics in a state where the tire 60 is rolling only by using the distance sensor.

(Lighting conditions for shooting)
When acquiring an image of the contact area of the ground contact surface 61 of the tire 60, the lighting lamp 16 may be arranged on the upper surface 221U side of the road surface plate 221 so as to surround the ground contact surface 61 on the upper surface 221U side of the road surface plate 221. preferable. When acquiring an image of the contact area of the ground contact surface 61 of the tire 60, it is preferable to irradiate the tire 60 with light by an illumination lamp 16 arranged so as to surround the contact portion on the upper surface 221U side to acquire the image. ..

(Movement of road plate and operation of trigger device)
23 and 24 are diagrams illustrating the movement of the road surface plate 221 and the operation of the trigger device 17. FIG. 23 shows a state before the road surface plate 221 moves and before the trigger device 17 detects the reflected light by the retroreflective sheet 18. FIG. 24 shows a state after the road surface plate 221 has moved and when the trigger device 17 detects the reflected light by the retroreflective sheet 18.

In FIG. 23, the upper surface 221U of the road surface plate 221 is flat, and the upper surface 221U is a flat road surface for the tire 60 to roll. In FIG. 23, the tire 60 is fixed to the rim 400 of the support device 300 in a state of being in contact with the upper surface 221U of the road surface plate 221. Therefore, the tire 60 rotates with the movement of the road surface plate 221. The total ground contact area creation unit 42 moves the road surface plate 221 in the direction of the arrow Y1. As the road surface plate 221 moves in the direction of the arrow Y1, the tire 60 rotates in the direction of the arrow Y2. In the state shown in FIG. 23, the detection unit 171 of the trigger device 17 does not detect the reflected light by the retroreflective sheet 18. Unless the trigger device 17 detects the light reflected by the retroreflective sheet 18, the road surface plate 221 continues to move in the direction of the arrow Y1. Since the photographing device 10 is fixed to the road surface plate 221, the photographing device 10 also moves with the movement of the road surface plate 221. The moving speed of the road surface plate 221 is, for example, 0.5 km / h. Instead of the road surface plate 221, a rotating drum having a transparent outer peripheral surface may be used.

When the road surface plate 221 moves in the direction of the arrow Y1 and reaches the state shown in FIG. 24, the detection unit 171 of the trigger device 17 detects the reflected light by the retroreflective sheet 18. When the detection unit 171 of the trigger device 17 detects the reflected light, the total grounding region creation unit 42 outputs a signal of a shooting instruction to the camera 15a. As a result, the contact patch 61 of the tire 60 can be photographed. The road surface plate 221 may be transparent as long as the portion 110 corresponding to the shooting range of the camera 15a is transparent, and the portion other than the portion 110 may be opaque. That is, the road surface plate 221 may be entirely transparent, or only the portion 110 corresponding to the photographing range may be transparent.

(Operation of the total grounding area creation unit)
FIG. 25 is a flow chart showing the operation of the total grounding area creating unit 42. When analyzing the tire 60, the total ground contact area creating unit 42 irradiates the tire 60 pressed against the road surface plate 221 with light from the lighting lamp 16 (step S201). Next, the total ground contact area creation unit 42 starts driving the motor 6 by the motor control device 7 (step S202). The total grounding region creation unit 42 determines whether or not the trigger device 17 has detected the reflected light by the retroreflective sheet 18 while the motor 6 is being driven (step S203) (step S204). When the trigger device 17 does not detect the light reflected by the retroreflective sheet 18, the total grounding region creating unit 42 continues to drive the motor 6 (steps S204, No → S203).

When the trigger device 17 detects the reflected light from the retroreflective sheet 18, the total ground contact area creating unit 42 takes a picture of the tire 60 by the camera 15a (step S204, Yes → S205). After that, the total ground contact area creation unit 42 stops driving the motor 6 and irradiating light (step S206).

(Example of specific arrangement and example of captured image)
Next, an example of a specific arrangement of the camera 15a and the lighting lamp 16 will be described. 26 to 28 are views showing an example of a specific arrangement of the camera 15a and the lighting lamp 16 when the ground plane image acquisition unit 32 acquires the ground plane image. FIG. 26 is a view of the arrangement of the lighting lamps 16 from the direction along the rotation axis of the tire 60. FIG. 27 is a view of the arrangement of the lighting lamps 16 from the upper surface 221U side of the road surface plate 221. FIG. 28 is a view of the arrangement of the lighting lamps 16 from a direction perpendicular to the rotation axis of the tire 60. In the following description, the direction along the rotation axis of the tire 60 is referred to as the tire width direction, and the direction perpendicular to the rotation axis is referred to as the tire circumferential direction.

In the photographing by this apparatus, the tire 60 to be analyzed had an air pressure of 230 kPa, a load of 6 kN, a rotation speed of 0.5 km / h, and a slip angle of 0 °. For the camera 15a, the camera gain was set to 3 dB, the F value was set to 4, and the exposure time was set to 1 ms.

Referring to FIGS. 26 to 28, the tire 60 is in contact with the upper surface 221U of the road surface plate 221. A camera 15a is provided on the lower surface 221D side of the road surface plate 221. The camera 15a is arranged so that its optical axis 151 is located on the normal line of the center point of the ground contact surface 61 of the tire 60. By arranging the optical axis 151 of the camera 15a so as to pass through the center point of the ground plane 61, the ground plane 61 can be photographed from the normal direction of the center point of the ground plane 61. As a result, stable analysis accuracy can be ensured. The closer to the edge of the captured image, the greater the effect of lens aberrations, the more the spatial resolution fluctuates, and the more unstable the analysis accuracy becomes. By arranging the camera 15a in this way, the influence of lens aberration can be minimized.

Referring to FIGS. 26 to 28, lamps 161 and 162, 163 and 164 are arranged as one main surface side lamp on the upper surface 221U side of the road surface plate 221. Further, a lamp 165, 166 and a camera 15a are arranged as other main surface side lamps on the 221D side of the road surface plate 221. The lamps 161 and 162 are arranged at positions separated from the tire 60 in the tire circumferential direction. The lamp 161 and the lamp 162 are provided on different sides of the tire 60. The lamp 163 and the lamp 164 are arranged at positions separated from the tire 60 in the tire width direction. The lamp 163 and the lamp 164 are provided on different sides of the tire 60. In this way, the lamps 161 to 164 are arranged so as to surround the ground contact surface 61 of the tire 60. If the tire 60 is not irradiated over all four sides of the contact patch 61, it becomes difficult to outline the contact patch, and the analysis accuracy may decrease. On the other hand, by arranging the lamps 161 to 164 so as to surround the ground contact surface 61 of the tire 60 and irradiating light over all four sides of the ground contact surface 61, the outline of the ground contact shape can be clarified and the analysis accuracy can be improved. Can be improved.

Here, in FIGS. 26 and 28, the height from the center of the light emitting surface of each of the lamps 161 to 164 to the upper surface 221U of the road surface plate 221 is defined as H1 to H4. In FIGS. 26 and 28, the inclination angles of the lamps 161 to 164, that is, the angles formed by the light irradiation direction with respect to the upper surface 221U of the road surface plate 221 are set to θ1 to θ4. In FIG. 27, the distance in the tire circumferential direction from the center of the light emitting surface of each of the lamps 161 and 162 to the center of the tire 60 is defined as the distances D1 and D2. In FIG. 27, the distances in the tire width direction from the center of the light emitting surface of each of the lamps 163 and 164 to the center of the tire 60 are defined as D3 and D4. In FIG. 27, the center of the light emitting surface of each of the lamps 161 and 162 at the position in the tire width direction coincides with the center of the tire.

The heights H1 to H4 are preferably 0 mm or more and 201 mm or less. The lowest value of heights H1 to H4 is 0 mm. This is because the lighting lamp 16 is placed on the road surface plate 221. If the heights H1 to H4 exceed 201 mm, the light from the illumination does not enter the ground plane 61 well, the contour of the ground plane becomes inaccurate, and the analysis accuracy deteriorates, which is not preferable.

The distances D1 and D2 in the tire circumferential direction are preferably larger than half of the maximum contact length of the tire 60 and smaller than 1345 mm. However, it is necessary to prevent each lighting lamp 16 from coming into contact with the tire 60. It is not preferable to make the minimum values of the distances D1 and D2 smaller than half of the maximum contact length of the tire 60. This is to prevent the lighting lamp 16 from coming into contact with the tire 60. If the distances D1 and D2 exceed 1345 mm, the amount of light of the illumination that hits the ground plane 61 is insufficient, the contour of the ground plane 61 becomes inaccurate, and the analysis accuracy is lowered, which is not preferable.

The distances D3 and D4 in the tire width direction are preferably larger than half of the maximum contact width of the tire 60 and smaller than 300 mm. However, it is necessary to prevent each lighting lamp 16 from coming into contact with the tire 60. It is not preferable to make the minimum values of the distances D3 and D4 smaller than half of the maximum contact width of the tire 60. This is to prevent each lighting lamp 16 from coming into contact with the tire 60. If the distances D3 and D4 exceed 300 mm, the amount of light of the illumination that hits the ground plane 61 is insufficient, the contour of the ground plane 61 becomes inaccurate, and the analysis accuracy is lowered, which is not preferable.

The inclination angles θ1 to θ4 of each lighting lamp 16 are preferably Atan (Hn / Dn) /π*180-0.6 ° or more and Atan (Hn/Dn)/π*180+0.6 ° or less (preferably. n = 1 to 4). For θ1 to θ4, it is preferable that each lighting lamp 16 irradiates light toward the center of the ground plane 61. By irradiating the light in this way, the light enters the ground plane 61 well. Therefore, the inclination angles θ1 to θ4 of the lighting lamp 16 are preferably Atan (Hn / Dn) / π * 180 (n = 1 to 4). However, the measurement error of ± 0.6 ° was set as the allowable range.

In this embodiment, H1 = H2 = 30 mm, H3 = H4 = 13 mm, D1 = D2 = 260 mm, D3 = D4 = 230 mm, θ1 = 9.7 °, θ2 = 11.6 °, θ3 = θ4 = 0 °. did.

By arranging the lamps 161 to 164 as described with reference to FIGS. 26 to 28, light is irradiated so as to surround the contact patch 61 of the tire 60, and the contact patch image can be acquired.

Further, referring to FIGS. 26 to 28, lamps 165 and 166 are arranged as other main surface side lamps on the lower surface 221D side of the road surface plate 221. The lamps 165 and 166 are both line illuminations whose longitudinal direction is the tire circumferential direction. The lamps 165 and 166 are arranged at positions separated from each other in the tire width direction of the tire 60. The lamp 165 and the lamp 166 are provided on different sides of the tire 60. That is, the lamps 165 and 166 are widthwise lamps that irradiate the ground plane 61 with light from the outside to the inside in the tire width direction. In this way, the lamps 165 and 166 are arranged so as to irradiate the ground contact surface 61 of the tire 60 with light in the tire width direction. The light from the lamp 165 and the lamp 166 illuminates the edge of the main groove, making it easier to determine the main groove.

Here, in FIG. 28, the heights from the center of the light emitting surface of the lamps 165 and 166 to the lower surface 221D are H5 and H6. In FIG. 28, the inclination angles of the lamps 165 and 166, that is, the angles formed by the light irradiation direction with respect to the lower surface 221D of the road surface plate 221 are set to θ5 and θ6. In FIG. 27, the distances in the tire width direction from the center of the light emitting surface of the lamps 165 and 166 to the center of the tire are defined as D5 and D6. The angles θ5 and θ6 are preferably in the range of 19.4 ° or more and 22.4 ° or less. If the heights H5 and H6 change, the appropriate angles θ5 and θ6 at that time also change. In that case, the images acquired by the camera 15a may be displayed live, and the angles θ5 and θ6 may be adjusted so that the edges of the main groove shine most while checking the displayed contents. In this embodiment, H5 = H6 = 62 mm, D5 = D6 = 215 mm, θ5 = 21.8 °, and θ6 = 20.1 °.

29 and 30 are views illustrating the tilt angle of the ramps 165 and 166 with respect to the tire circumferential direction. In FIG. 29, arrows Y5 and Y6, which are the directions of light from the lamps 165 and 166, are along the tire width direction. If the light from the lamps 165 and 166 travels in the tire width direction, the edge of the main groove extending in the tire circumferential direction can be made to shine with high brightness.

It is preferable that both the longitudinal angle θ15 of the lamp 165 with respect to the tire circumferential direction and the longitudinal angle θ16 of the lamp 166 with respect to the tire circumferential direction shown in FIG. 30 are 0 °. When both the angle θ15 and the angle θ16 are 0 °, the longitudinal direction of the lamp 165 and the longitudinal direction of the lamp 166 become parallel, and the brightness is satisfactorily increased for all the chamfers of the main groove existing in the ground plane 61. Stable analysis accuracy can be ensured. If the angle θ15 and the angle θ16 are 0 ° ± 1 °, there is no problem in increasing the brightness of the chamfer of the main groove. If the angle θ15 and the angle θ16 exceed the range of 0 ° ± 1 °, it is not possible to increase the brightness of all the chamfers of the main groove existing on the ground plane 61. For example, only a part of the chamfers can be increased in brightness. In some cases, it may not be possible and the analysis accuracy may decrease.

Here, when the edge of the sub-groove is chamfered, it is preferable that a lamp that allows light to travel in the tire circumferential direction is provided under the road surface plate. FIG. 31 is a view of the arrangement of the lighting lamps 16 from the direction along the rotation axis of the tire 60. As shown in FIG. 31, it is preferable that lamps 167 and 168 are provided as lamps on the other main surface side on the lower surface 221D side, which is the other main surface of the road surface plate 221. The lamps 167 and 168 are both line illuminations whose longitudinal direction is the tire width direction. The lamps 167 and 168 are arranged at positions apart from each other in the tire circumferential direction of the tire 60. The lamp 167 and the lamp 168 are provided on different sides of the tire 60. That is, the lamp 167 and the lamp 168 are circumferential lamps that irradiate the ground plane 61 with light from the outside to the inside in the tire circumferential direction. In this way, the lamps 167 and 168 are arranged so as to irradiate the ground contact surface 61 of the tire 60 with light in the tire circumferential direction. Lamps 167 and 168 can increase the brightness of the chamfering of the sub-groove. That is, the lamps 167 and 168 irradiate the ground plane 61 with light that enhances the brightness of the edge of the sub-groove.

Further, in FIG. 31, the heights from the center of the light emitting surface of the lamps 167 and 168 to the lower surface 221D are H7 and H8. In FIG. 31, the inclination angles of the lamps 167 and 168, that is, the angles formed by the light irradiation direction with respect to the lower surface 221D of the road surface plate 221 are set to θ7 and θ8. FIG. 32 is a view of the arrangement of the lighting lamps 16 from a direction perpendicular to the rotation axis of the tire 60. FIG. 33 is a view of the arrangement of the lighting lamps 16 from the upper surface 221U side of the road surface plate 221. The angles θ7 and θ8 are preferably 3.5 ° or more and 6.0 ° or less in order to maximize the chamfering of the sub-groove. In this embodiment, H7 = H8 = 30 mm, θ7 = 4.2 °, and θ8 = 4.9 °.

In FIG. 33, the distances in the tire circumferential direction from the center of the light emitting surface of each lamp 167 and 168 to the center of the tire 60 are defined as D7 and D8. The light from the lamps 167 and 168 can increase the brightness of the chamfer of the sub-groove existing on the ground plane 61. In this embodiment, D7 = D8 = 183 mm.

34 and 35 are views illustrating the tilt angle of the ramps 167 and 168 with respect to the tire width direction. In FIG. 34, arrows Y7 and Y8, which are the directions of light from the lamps 167 and 168, are along the tire circumferential direction. If the light from the lamps 167 and 168 travels in the tire circumferential direction, the edge of the sub-groove extending in the tire width direction can be made to shine with high brightness.

It is preferable that both the longitudinal angle θ17 of the lamp 167 with respect to the tire width direction and the longitudinal angle θ18 of the lamp 168 with respect to the tire width direction shown in FIG. 35 are 0 °. When both the angle θ17 and the angle θ18 are 0 °, the longitudinal direction of the lamp 167 and the longitudinal direction of the lamp 168 become parallel, and the brightness is satisfactorily increased for all the chamfers of the sub-grooves existing on the ground plane 61. Stable analysis accuracy can be ensured. If the angle θ17 and the angle θ18 are 0 ° ± 1 °, there is no problem in increasing the brightness. If the angle θ17 and the angle θ18 exceed the range of 0 ° ± 1 °, it is not possible to increase the brightness of all the chamfers of the sub-grooves existing on the ground plane 61. For example, only a part of the chamfers can be increased in brightness. In some cases, it may not be possible and the analysis accuracy may decrease.

36 to 41 are views showing an example of irradiation of light from the lamps 167 and 168, which enhances the brightness of the chamfer of the sub-groove. FIG. 36 shows an example of a captured image when the light from the lamps 167 and 168 is strong. FIG. 36 shows an example of a photographed image when the ground plane 61 is irradiated with light having an illuminance of about 1.3 million lux. FIG. 37 is an enlarged view showing a portion 201 of the sub-groove in FIG. 36. In FIG. 37, the edge E1 of the sub-groove glows white, indicating that the amount of light in the tire circumferential direction is sufficient. FIG. 38 is an enlarged view showing a portion 202 of the sub-groove in FIG. 36. In FIG. 38, the edge E2 of the sub-groove glows white, indicating that the amount of light in the tire circumferential direction is sufficient. As shown in FIGS. 37 and 38, when the light from the lamps 167 and 168 is strong and the edges E1 and E2 of the sub-groove are shining white, the difference between the brightness of the grounded portion and the brightness of the edge of the sub-groove is large. Due to its large size, the edge portion of the sub-groove can be easily separated from the captured image.

FIG. 39 shows an example of a captured image when the light from the lamps 167 and 168 is weak. FIG. 39 shows an example of a photographed image when the ground plane 61 is irradiated with light having an illuminance of about 600,000 lux. FIG. 40 is an enlarged view showing a portion 201'of the sub-groove in FIG. 39. In FIG. 40, the edge E1'of the sub-groove is not so bright, and it can be seen that the amount of light in the tire circumferential direction is insufficient. FIG. 41 is an enlarged view showing a portion 202'of the sub-groove in FIG. 39. In FIG. 41, the edge E2'of the sub-groove is not so bright, and it can be seen that the amount of light in the tire circumferential direction is insufficient. As shown in FIGS. 40 and 41, when the light from the lamps 167 and 168 is weak and the edges E1'and the edge E2'of the sub-groove are not so bright, the brightness of the ground contact portion and the brightness of the edge of the sub-groove The difference is small, and it is difficult to separate the edge portion of the sub-groove from the captured image.

As can be seen from FIGS. 36 to 41, it is preferable to set the light from the lamps 167 and 168 to a high illuminance of about 1.3 million lux and acquire a captured image in which the edge of the sub-groove is shining.

In FIGS. 26 to 35, the illuminance in the tire width direction and the illuminance in the tire circumferential direction according to the lamps 161 to 164 may be the same degree of illuminance, or either illuminance may be increased. For the lamps 165 to 168, it is preferable to make the illuminance in the tire circumferential direction larger than the illuminance in the tire width direction. Otherwise, the chamfer of the sub-groove existing on the ground plane 61 cannot be illuminated, and the analysis accuracy is lowered. The illuminances of the lamps 161 to 164 need to be equal to or higher than the illuminances of the lamps 165 to 168. Otherwise, the contour of the tire ground contact shape cannot be determined and the accuracy is reduced.

42 and 43 are views showing an arrangement example of the camera 15a. FIG. 42 is a view of the camera 15a viewed from a direction along the rotation axis of the tire 60. FIG. 43 is a view of the camera 15a viewed from a direction perpendicular to the rotation axis of the tire 60. As shown in FIGS. 42 and 43, the camera 15a is preferably provided below the ground plane 61. As shown in FIGS. 42 and 43, the camera 15a is preferably provided below the range W1 in the tire circumferential direction of the contact patch 61 and below the range W2 in the tire width direction of the contact patch 61. That is, the camera 15a is provided in a range surrounded by a line extending in a direction perpendicular to the lower surface 221D side of the road surface plate 221 from the contour of the ground plane 61. By arranging the camera 15a in this range, stable analysis accuracy can be ensured. If the camera 15a is taken away from the ground plane 61, the groove wall is an obstacle, the edge of the main groove cannot be observed, and the analysis accuracy is lowered, which is not preferable. In FIGS. 42 and 43, the distance L in the tire radial direction from the lower surface 221D of the road surface plate 221 to the camera 15a is preferably 121 mm or more and 240 mm or less. The distance L in the tire radial direction is, for example, 206 mm. However, the optimum value of the distance L differs depending on the groove width existing on the ground plane 61.

(Processing of grounding characteristic analysis unit)
An example of the processing by the grounding characteristic analysis unit 33 and the image acquired or created by the processing will be described. FIG. 44 is a flow chart showing an example of processing by the grounding characteristic analysis unit 33. FIG. 44 shows an example of processing by the processing unit 31 centered on the grounding characteristic analysis unit 33. 45 to 51 are diagrams showing an example of an image acquired or created by the processing of the grounding characteristic analysis unit 33.

In FIG. 44, first, the contact patch image acquisition unit 32 acquires a photographed image of the contact patch 61 of the tire (step S31). By the process of step S31, for example, the captured image shown in FIG. 45 can be acquired.

Next, the chamfered image extraction unit 34A of the groove extraction unit 34 extracts from the captured image a portion having a brightness higher than a predetermined brightness as a chamfered image showing the chamfered portion of the groove (step S32). By the process of step S32, for example, the chamfered image shown in FIG. 46 can be acquired.

The groove bottom extraction unit 34B of the groove extraction unit 34 extracts a portion having a brightness lower than a predetermined brightness from the captured image as a groove bottom image showing the bottom of the groove (step S33). By the process of step S33, for example, the groove bottom image shown in FIG. 47 can be acquired.

The main groove bottom extraction unit 34C of the groove extraction unit 34 extracts a low-brightness portion surrounded by a portion having a brightness higher than a predetermined brightness as a main groove bottom image showing the bottom of the main groove from the captured image (step S34). ). By the process of step S34, for example, the image of the bottom of the main groove shown in FIG. 48 can be acquired.

The composite unit 34D of the groove extraction unit 34 combines the chamfered image, the groove bottom image, and the main groove bottom image to obtain a groove image (step S35). By the process of step S35, for example, the groove image shown in FIG. 49 can be acquired.

Next, the grounding characteristic calculation unit 35 separates the captured image with the high-luminance portion as white and the medium-luminance portion and the low-luminance portion as black based on a predetermined threshold value to obtain a rough grounding region image (step). S36). By the process of step S36, for example, a rough ground contact area image shown in FIG. 50 is obtained from the captured image shown in FIG. 45. Thereby, for example, it is possible to obtain a rough grounded area image in which the block of the non-grounded surface, the chamfering and marking of the groove are white, and the bottom of the groove and the portion of the grounded block are black.

Further, the grounding characteristic calculation unit 35 subtracts the groove image (FIG. 49) from the rough grounding area image (FIG. 50) to obtain an actual grounding area image (Actual Contact Area, hereinafter abbreviated as ACA) (step). S37). By the process of step S37, for example, the ACA shown in FIG. 51 can be obtained.

Here, "subtracting the groove image from the rough grounded area image" means that the luminance value of the groove is subtracted from the luminance value of the rough grounded area image for each same pixel position. In this embodiment, the processing by the grounding characteristic analysis unit 33 and the images acquired or created by the processing are all composed of 256 gradations, and black is the luminance "255" and white is the luminance "0" except for the captured image. Is defined. However, if the value after subtraction is lower than "0", it is replaced with "0". In this example, after the subtraction process, the shrinkage process is performed once, the expansion process is performed twice, the shrinkage process is performed once, the area occupied by the black object is 100 pixels or less (= replaced with white pixels, the same applies hereinafter), the shrinkage process is performed twice, and so on. The expansion treatment was performed 4 times and the contraction treatment was performed 2 times in this order. After that, the occupied area of 200 pixels or less of the white object was deleted (= replaced with black pixels; the same applies hereinafter), and the occupied area of 200 pixels or less of the black object was deleted to obtain the ACA shown in FIG. 51.

The ACA shown in FIG. 51 is the total area of the block grounded on the road surface. Based on the ACA shown in FIG. 51, for example, a total ground contact area image (Ground Contact Area, hereinafter abbreviated as GCA) shown in FIG. 52 can be obtained.

GCA is the total area of ACA surrounded by an outer ring line when the groove is filled. FIG. 52 is a diagram showing an example of GCA. Regarding the ACA shown in FIG. 51, for example, the order of expansion treatment 5 times, shrinkage treatment 10 times, expansion treatment 12 times, shrinkage treatment 14 times, expansion treatment 17 times, shrinkage treatment 20 times, expansion treatment 109 times, shrinkage treatment 99 times. The GCA of FIG. 52 can be obtained by processing the above.

FIG. 53 is an explanatory diagram of the expansion process. FIG. 54 is an explanatory diagram of the shrinkage process. As shown in FIG. 53, the expansion process is a process of replacing the pixel of interest with a black pixel if there is even one black pixel around the pixel of interest. That is, in the expansion process, each white pixel is set as the center pixel, and one of the eight pixels around it (one pixel each of the upper left, upper, upper right, right, lower right, lower, lower left, and left closest to the center pixel). However, if a black pixel exists, it is a process of replacing the center pixel with a black pixel. On the contrary, the shrinkage processing is a process of replacing the attention pixel with a white pixel if there is even one white pixel around the attention pixel, as shown in FIG. 54, for example, when the attention pixel is a black pixel. That is, in the shrinkage processing, each black pixel is set as the center pixel, and one of the eight pixels around it (one pixel each of the upper left, upper, upper right, right, lower right, lower, lower left, and left closest to the center pixel). However, if a white pixel exists, the central pixel is replaced with a white pixel.

Here, by using the ACA shown in FIG. 51 and the GCA shown in FIG. 52, the groove distribution in the total ground contact region, which is the groove-filled region, can be obtained. That is, by subtracting the luminance value of the image showing ACA of FIG. 51 from the luminance value of the image showing GCA of FIG. 52 for each same pixel position, an image of the groove distribution in the total ground contact region can be obtained. FIG. 55 is a diagram showing an example of the groove distribution in the total ground contact area. After the subtraction process, noise may be removed if necessary. For example, in FIG. 55, after subtracting the luminance value of the image showing ACA of FIG. 51 from the luminance value of the image showing GCA of FIG. 52 for each same pixel position, the shrinkage process, the expansion process three times, and the black object It is acquired by executing in the order of deleting 1000 pixels or less of the occupied area of the object.

(Groove distribution in the total ground contact area)
The groove distribution data creation unit 441 creates groove distribution data. The groove distribution data is the groove distribution in the total ground contact area shown in FIG. 55. Let M (i, j) be the groove distribution in the total ground contact area shown in FIG. 55. Here, i indicates a horizontal direction (tire circumferential direction) position of the image, and j indicates a vertical direction (tire width direction) position of the image. Since i and j of the groove distribution M (i, j) are in pixel units, it is necessary to convert them into length units x and y as described later. Assuming that the groove distribution in the total ground contact area when converted into length units is M (x, y), the groove depth of the tire contact patch can be expressed by the following equation (4).
Groove depth on the tire contact patch = (Z (x, y) -α) x M (x, y) ... (4)

In the equation (4), x is the tire circumferential position, y is the tire width direction position, Z (x, y) is the groove height distribution, α is the road surface plate height, and (Z (x, y). -Α) indicates the groove depth. It is shown that a groove exists at the position where M (x, y) is "1", and there is a groove other than the groove at the position where M (x, y) is "0".

Here, the height distribution Z (x, y) of the groove can be obtained, for example, by using a range finder or a three-dimensional scanner as a measuring device. That is, the height of the groove is measured by measuring the distance at each position of the road surface plate while scanning and moving the measuring device on the lower surface side of the road surface plate, and storing the measurement result of the distance in association with the movement information of the measuring device. The height distribution Z (x, y) is obtained.

It is also possible to measure the groove height distribution Z (x, y) using two cameras. In this case, the three-dimensional coordinates of the groove are calculated for the images taken by the two cameras, for example, in the same manner as the sampling moire method described above. That is, the three-dimensional shape of the groove is calculated based on the phase distribution (unwrapping) of each camera and the line of sight of each camera, and the three-dimensional coordinates are obtained. The three-dimensional coordinates include the above-mentioned tire circumferential position x, tire width direction position y, and coordinates z in the direction perpendicular to the road surface plate 221. The directions of x, y, and z are perpendicular to each other. Further, the directions of x and y are parallel to the upper surface or the lower surface of the road surface plate. Therefore, by defining z at the position (x, y) on the road surface plate as the groove height distribution Z (x, y), the groove height distribution Z (x, y) can be obtained.

By using the formula (4), the groove depth of the tire contact patch can be quantitatively measured. As a result, the development direction of the tire becomes clear, and the development efficiency is improved.

(Conversion from pixel unit to length unit)
Since i and j of the groove distribution M (i, j) described above are in pixel units, they need to be converted into length units. To convert to a unit of length, the ratio of the length to the pixel may be obtained, and the ratio may be multiplied by the values of i and j. For example, by providing a grid sheet or a grid sheet on the upper surface 221U of the transparent road surface plate 221 and measuring it, the ratio of the length to the pixel can be obtained. Here, a grid sheet is defined as a graph paper having squares with relatively thin lines, and a grid paper with thick grids is defined as a grid sheet.

FIG. 56 is a diagram showing a case where one camera is used. As shown in FIG. 56, a square sheet ST1 having squares having known vertical and horizontal lengths is provided on the upper surface 221U of the transparent road surface plate 221. One camera 15a is provided on the lower surface 221D side of the road surface plate 221. With the camera 15a, the spatial resolution can be obtained for each pixel of the image in which the square sheet ST1 is captured. Based on the spatial resolution, the above i and the above j can be converted into length units. Since one camera 15a is used, the camera used when creating the above-mentioned total ground contact area can be used as it is.

In FIG. 56, instead of the square sheet ST1, a grid sheet having squares having known vertical and horizontal lengths may be used. In that case, the image obtained by capturing the grid sheet is analyzed by the camera 15a by the sampling moire method described above. That is, the image obtained by capturing the grid sheet is smoothed in the vertical direction (vertical direction) and the horizontal direction (horizontal direction), respectively, to obtain the phase distribution of the grid. Every time the phase value advances by 2π such as 0, 2π, 4π, ..., The lattice (square) advances by one cycle. Therefore, the in-screen coordinates of the captured image corresponding to the phase values of 0, 2π, 4π, ... (Hereinafter, 2π addition) are examined, and the difference in the in-screen coordinates at the adjacent phase values by 2π is obtained. For example, the difference in the coordinates in the screen is calculated for 0 and 2π, 2π and 4π, respectively. Since the length and width are known, that is, the length of one cycle of the grid along the length and width is known, the value obtained by dividing the length of one cycle of the grid by the difference in the coordinates in the screen is calculated. It can be obtained as the ratio of the length to the pixel. Based on the ratio of the lengths, the above i and the above j are converted into length units. The ratio of the length to the pixel is preferably obtained for each pixel of the captured image. When the ratio of the length to the pixel is obtained for each pixel of the captured image, the difference in the coordinates in the screen is calculated by selecting the phase values adjacent to each other by 2π so that the pixels sandwich the corresponding phase value. For example, if the corresponding phase value of a pixel in the captured image is 7π, the difference in in-screen coordinates between the phase values 6π and 8π is calculated, and the length of one cycle of the grid is divided by the difference. Is calculated as the ratio of the length to the pixel. Further, as the phase values adjacent to each other by 2π, for example, the coordinates in the screen of the captured image corresponding to the phase values of x, x + 2π, x + 4π, ... The ratio of the length to the pixel may be calculated.

FIG. 57 is a diagram showing a case where three cameras are used. As shown in FIG. 57, in this example, a grid sheet ST2 having squares having known vertical and horizontal lengths and three cameras 15a, 15b, and 15c are used. The three cameras 15a, 15b and 15c are provided on the lower surface 221D side of the road surface plate 221. By taking pictures with the cameras 15a, 15b and 15c, an image of the three-dimensional shape (x, y, z) of the grid sheet can be obtained.

The above i and the above j can be converted into length units by reflecting the image of the three-dimensional shape (x, y, z) on the camera 15a used when calculating the total ground contact area and searching for the corresponding points in the screen. ..

Here, regarding the phase distribution of the captured images of the cameras 15a, 15b, and 15c, the phase value has a value peculiar to the position of the surface of the lattice sheet ST2, and therefore, the following processing is performed using this. conduct. That is, any one of the sampling moire method, the Fourier transform method, and the weighted phase analysis method described above is applied to the captured images of the cameras 15a, 15b, and 15c to calculate the phase distribution. Next, the three-dimensional coordinates are calculated for each phase value based on the phase distribution of the images captured by the cameras 15b and 15c and the line of sight of the cameras 15b and 15c. On the other hand, the phase value corresponding to the pixel position (i, j) to be converted is searched for in the length unit from the phase distribution of the image captured by the camera 15a. When the phase value is found, the three-dimensional coordinates (x, y, z) corresponding to the phase value are quoted from the results obtained by the cameras 15b and 15c described above. The pixel positions (i, j) corresponding to the phase value are converted into x, y of the quoted three-dimensional coordinates. By performing this work for other phase values in the same manner, the pixel unit is converted into the length unit. If the phase value cannot be found, it is excluded from the conversion target in length units. The groove distribution M (i, j) is digital data and has a point distribution. In order to make the distribution continuous, the groove distribution in the range of ± 1/2 pixels in the horizontal direction of the image and ± 1/2 pixels in the vertical direction of the image from the point (i, j) has a value of M (i, Set uniformly to j). After that, eight positions (i-1 / 2, j-1 / 2), (i, j-1 / 2), (i + 1/2, j-1 /) around the pixel position (i, j). 2), (i + 1/2, j), (i + 1/2, j + 1/2), (i, j + 1/2), (i-1 / 2, j + 1/2), (i-1 / 2, j) Also, as described above, the pixel unit is converted to the length unit. That is, the numerical value in parentheses as a pixel unit is converted into a length unit.

(Distribution of height of road surface plate)
FIG. 58 is a diagram illustrating the height α of the road surface plate 221. As shown in FIG. 58, the height α of the road surface plate 221 is the distance from the measuring device SK to the upper surface 221U (the surface on which the tire 60 contacts) of the road surface plate 221. The height α can be obtained by the following method.

For example, when a range finder or a three-dimensional scanner is used as a measuring device SK, if the distance from the upper surface 221U to the measuring device SK can be specified, the specified distance becomes the height α. In this case, for example, the stepping motor moves based on the specified distance, and the position of the measuring device SK changes.

It is also possible to measure the height α using two cameras. In this case, the height α is measured as follows. That is, two cameras are provided on the lower surface 221D side of the road surface plate 221 to search for a feature point (for example, the corner of the grounding block of the tire 60) visible on the upper surface 221U of the road surface plate 221 and each camera at the feature point. In-screen coordinates (X, Y) are calculated. At this time, pattern matching is performed on the images taken by the two cameras. As a result, it is calculated which in-screen coordinates of each camera the feature point belongs to. Then, the height α is calculated based on the in-screen coordinates (X, Y) of each camera and the result of the camera calibration. Here, camera calibration is a measurement method for obtaining the line of sight of two cameras. Therefore, the three-dimensional shape is calculated based on the in-screen coordinates (X, Y) of each camera and the line of sight of each camera, the three-dimensional coordinates (x, y, z) are obtained, and the road surface plate of the three-dimensional coordinates is obtained. The coordinates z in the direction perpendicular to 221 can be extracted as the height α.

Here, the actual height α of the road surface plate 221 differs depending on the location. Therefore, the above equation (4) can be corrected by obtaining the distribution R (x, y) of the height α of the road surface plate 221 by the following method.

FIG. 59 is a diagram showing a configuration for obtaining the distribution R (x, y) of the height α. As shown in FIG. 59, the sheet ST is provided on the upper surface 221U side of the road surface plate 221. The sheet ST may be, for example, a flexible patterned sheet or reflective sheet. A measuring device SK is provided on the lower surface 221D side of the road surface plate 221.

The measuring device SK is, for example, a range finder or a three-dimensional scanner. The measuring device SK measures the distance from the measuring device SK to the sheet ST provided on the upper surface 221U side at each position of the road surface plate 221. It should be noted that the two cameras may be used as the measuring device SK, and the distance to the seat ST may be measured for each position of the road surface plate 221 by image processing. For example, the phase distribution of the grid is calculated by photographing the grid sheet provided on the upper surface 221U side of the road surface plate 221 with two cameras and analyzing by the sampling moire method described above. The three-dimensional shape is calculated based on the phase distribution of the grid and the line of sight of each camera, and the three-dimensional coordinates (x, y, z) are obtained. The three-dimensional coordinates include the tire circumferential position x, the tire width direction position y, and the coordinates z in the direction perpendicular to the road surface plate 221. The directions of x, y, and z are perpendicular to each other. Therefore, by defining z at the position (x, y) on the road surface plate as the distribution R (x, y) of the height α, the distribution R (x, y) of the height α can be obtained.

Since the distance to the seat ST for each position of the road surface plate 221 is the distribution R (x, y) of the height α, the height α of the above equation (4) is used as the distribution R of the height α ( By substituting with x, y), the following equation (5) can be obtained.
Groove depth on the tire contact patch = (Z (x, y) -R (x, y)) x M (x, y) ... (5)

By finding the distribution R (x, y) of the height α of the road surface plate 221 and using the equation (5) obtained by correcting the above equation (4), even if the height of the road surface plate varies depending on the location, the tire contact patch. The groove depth on the ground can be measured with high accuracy. For the distribution R (x, y), the numerical value of the height is stored. For M (x, y), "1" or "0" is stored.

(Groove depth calculation unit)
Next, the processing of the groove depth calculation unit 442 will be described. 60 and 61 are diagrams showing the contents of processing of the groove depth calculation unit 442.

As shown in FIG. 60, the groove depth calculation unit 442 approximates the shape of the groove with a minute rectangular parallelepiped. Each rectangular parallelepiped 8 _ij shown in FIG. 60 has a height along the shape of the groove 62. Here, as shown in FIG. 61, the position of each rectangular body 8 _ij , that is, the measurement point is x ₁₁ to x _NM (N and M are natural numbers) and the tire width direction (y direction) with respect to the coordinates in the tire circumferential direction (x direction). The coordinates of are y ₁₁ to y _NM (N and M are natural numbers). Focusing on the positions (x _N-1 , 2, y _N-1 , 2) shown in FIG. 61, the length (minor length) of the bottom surface of the rectangular parallelepiped at that position in the tire circumferential direction is dx _N-1,2 . , The length (minor length) in the tire width direction is dy _N-1,2 .

As shown in FIG. 60, the bottom surface of the rectangular parallelepiped 8 _ij has a length in the tire circumferential direction of dx _ij and a length in the tire width direction of dy _ij . Therefore, the bottom area of the rectangular parallelepiped 8 is dx _ij × dy _ij . The height of the rectangular parallelepiped 8 _ij is Z (x _ij , y _ij ) -R (x _ij , y _ij ). Therefore, the volume of the rectangular parallelepiped 8 _ij is dx _ij x dy _ij x [Z (x _ij , y _ij ) -R (x _ij , y _ij )] obtained by multiplying the base area by the height.

(Groove volume calculation unit)
The processing of the groove volume calculation unit 46 will be described. The groove volume calculation unit 46 obtains the volume of each rectangular parallelepiped 8 _ij along the shape of the groove 62, and obtains the sum of them. Thereby, the volume (volume) of the groove 62 can be calculated. That is, the groove volume of the tire contact patch can be calculated by the following equation (6).

Groove volume on the tire contact patch = ΣΣ ((Z (x _ij , y _ij ) -R (x _ij , y _ij )) x dx _ij x dy _ij x M (x _ij , y _ij ))
… (6)

When M (x _ij , y _ij ) is "1", it means that there is a groove, and when M (x ij, y ij) is "0", it means that there is a groove other than the groove. Further, dx _ij and dy _ij are preferably 1 mm or less. If dx _ij and dy _ij exceed 1 mm, the error with respect to the groove volume of the correct answer becomes large (for example, it exceeds 1%), which is not preferable. dx _ij and dy _ij may be 0.5 mm or less. This makes it possible to reduce the error. However, the processing time becomes long.

The inventor treated the above dx _ij and dy _ij as 1 mm, 0.5 mm, 0.1 mm and 0.05 mm. As a result, the error was 1%, 0.25%, 0.01%, 0.0025%.

As described above, the groove depth at each position of the groove is approximated by a minute rectangular parallelepiped, and the total volume of the approximated rectangular parallelepiped is obtained as the groove volume in the total ground contact region to quantify the groove volume of the tire contact surface. Can be measured.

(Tire shape analysis method)
According to the tire shape analysis system described above, the following tire shape analysis method is realized. That is, a step of measuring the three-dimensional shape of the groove, which is a portion recessed from the surface of the tire to be measured, and a step of creating a total ground contact area, which is a region filled with the ground contact region of the tire. A tire shape analysis method having a step of measuring the groove depth at the position of the groove in the total ground contact region is realized. By this tire shape analysis method, the groove depth of the contact patch of the tire can be quantitatively measured.

1 Tire shape analysis system 2 Tire tester 6 Motor 7 Motor control device 8 Square body 15AM Fixed rods 15a, 15b, 15c Camera 16 Lighting lamp 17 Trigger device 18 Retroreflective sheet 20 Tire tread analysis device 21 Input unit 22 Display unit 30 Processing device 31 Processing unit 32 Ground plane image acquisition unit 33 Ground characteristic analysis unit 34 Groove extraction unit 35 Ground characteristic calculation unit 40 Groove shape measurement unit 41 Analysis unit 42 Total ground area creation unit 44 Groove depth measurement unit 46 Groove volume calculation Unit 50 Storage unit 60 Tire 61 Ground plane 161 to 168 Lamp 171 Detection unit 221 Road surface plate 221D Bottom surface 221U Top surface 300 Support device 341 Smoothing processing unit 342 First candidate image extraction unit 343 Second candidate image extraction unit 344 Overlay processing unit 400 Rim 401 Marking extraction unit 411 Image smoothing unit 412 Brightness distribution acquisition unit 413 Thinning processing unit 414 Moare fringe creation unit 415 Phase distribution calculation unit 416 Three-dimensional shape calculation unit 419 Inverse Fourier conversion unit 441 Groove distribution data creation unit 442 Groove depth Calculation unit SK measuring device

Claims (10)

A groove shape measuring unit that measures the three-dimensional shape of a groove that is recessed from the surface of the tire to be measured, and a groove shape measuring unit.
A total ground contact area creation unit that creates a total ground contact area that is a groove-filled area with respect to the ground contact area of the tire, and a total ground contact area creation unit.
A groove depth measuring unit for measuring the groove depth at the groove position in the total ground contact area, and a groove depth measuring unit.
Tire shape analysis system with. The groove depth measuring unit is
A groove distribution data creation unit that creates groove distribution data indicating the position of the groove in the total ground contact area, and a groove distribution data creation unit.
A groove depth calculation unit that calculates the groove depth at each position indicated by the groove distribution data, and a groove depth calculation unit.
The tire shape analysis system according to claim 1. The groove depth calculation unit is
2. Tire shape analysis system described in. A claim having a groove volume calculation unit for approximating the groove depth at each position calculated by the groove depth calculation unit with a minute rectangular parallelepiped and obtaining the total volume of the approximated rectangular parallelepiped as the groove volume in the total ground contact region. Item 2 or the tire shape analysis system according to claim 3. The groove shape measuring unit is
The tire according to any one of claims 1 to 4, wherein the pattern pattern formed in the groove of the tire is photographed by at least two cameras, and the image captured by the cameras is analyzed to measure the shape of the groove. Shape analysis system. The groove shape measuring unit is
The tire shape analysis system according to claim 5, wherein the pattern pattern is analyzed on the captured image by using a weighted phase analysis method, and the shape of the groove is measured. The groove shape measuring unit is
The imaging range of the groove is divided into two areas including a common area.
The tire shape analysis system according to claim 5 or 6, wherein the common area is one cycle or more of the pattern pattern. The groove shape measuring unit is
The tire shape analysis system according to any one of claims 5 to 7, wherein the movement of the two cameras and the photographing by the two cameras are repeated to photograph all the grooves in the total ground contact area. When the midpoint position between the two cameras is defined as (X, Y),
The movement range X of the two cameras in the tire circumferential direction is
-Maximum grounding length / 2≤X≤Maximum grounding length / 2
The movement range Y of the two cameras in the tire width direction is
-Maximum grounding width / 2≤Y≤Maximum grounding width / 2
The tire shape analysis system according to any one of claims 5 to 8. A step of measuring the three-dimensional shape of a groove which is a portion recessed from the surface of the tire to be measured, a step of creating a total ground contact area which is a region filled with the ground contact region of the tire, and the total of the above. A tire shape analysis method comprising measuring the groove depth at the position of the groove in the ground contact area.

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