JP7518372B2 - Tire shape analysis system and tire shape analysis method - Google Patents

Description

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

Patent Document 1 discloses a technology for measuring distortions occurring on the contact surface of a tire. In Patent Document 1, the method includes a first photographing process in which reference points are marked on the land surface and groove bottom of the tire contact surface and the tire contact surface is photographed in a first state by multiple cameras, and a second photographing process in which the tire is placed in contact with a test road surface and rolled, and the tire contact surface is photographed in a second state different from the first state by multiple cameras. For each of the land surface and groove bottom, pattern matching is performed between the images photographed in the first photographing process and the images photographed in the second photographing process, and two-dimensional or three-dimensional distortion is calculated based on the displacement of the reference points.

Patent Document 2 discloses a technology for measuring the deformation state of the tire tread when the tire touches the ground. In Patent Document 2, a transparent grounding plate material that the tire touches the ground is used, and a laser beam is irradiated onto the tire tread from the opposite side of the grounding plate material to the tire, via the grounding plate material, and an image of the tire tread is taken. This allows for the acquisition of three-dimensional data that represents the deformed shape of the tread portion and tread grooves of the tire tread surface in a deformed state upon contact with the ground.

JP 2017-067690 A JP 2009-139268 A

The technology disclosed in Patent Document 1 makes it possible to measure the groove bottom strain on the tire's contact surface. In addition, the technology disclosed in Patent Document 2 makes it possible to obtain three-dimensional data that represents the deformed shape of the tread portion and tread grooves. However, these technologies cannot quantitatively measure the groove depth on the tire's contact surface, so there is room for improvement.

The present invention has been made in consideration of the above, and its purpose is to provide a tire shape analysis system and a tire shape analysis method that can quantitatively measure the groove depth of the tire's contact surface.

In order to solve the above-mentioned problems and achieve the objective, a tire shape analysis system according to one embodiment of the present invention has a groove shape measurement unit that measures the three-dimensional shape of a groove, which is a portion that is recessed from the surface of the tire being measured, a total contact area creation unit that creates a total contact area, which is an area where the grooves are filled in with the contact area of the tire, and a groove depth measurement unit that measures the groove depth of the position of the groove within the total contact area based on the three-dimensional shape .

It is preferable that the groove depth measurement unit has a groove distribution data creation unit that creates groove distribution data indicating the positions of the grooves within the total contact area, and a groove depth calculation unit that calculates the groove depth at each position indicated by the groove distribution data.

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

It is preferable that the device further includes a groove volume calculation unit that approximates the groove depth at each position calculated by the groove depth calculation unit with a tiny rectangular parallelepiped and determines the groove volume within the total contact area as the sum of the volumes of the approximated rectangular parallelepipeds.

It is preferable that the groove shape measuring unit photographs the pattern formed in the grooves of the tire with at least two cameras and measures the shape of the grooves by analyzing the images captured by the cameras.

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

It is preferable that the groove shape measuring unit divides an imaging range of the groove into two areas including a common area, and that the common area is one period or more of the pattern.

It is preferable that the groove shape measurement unit repeatedly moves the two cameras and takes images using the two cameras to capture images of all grooves within the total contact area.

When the midpoint position between the two cameras is defined as (X, Y), it is preferable that 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, and the movement range Y of the two cameras in the tire width direction is -maximum ground contact width/2≦Y≦maximum ground contact width/2.

A tire shape analysis method according to one aspect of the present invention includes the steps of measuring the three-dimensional shape of a groove, which is a portion recessed from the surface of the tire being measured, creating a total contact area, which is an area where the grooves are filled in relative to the tire's contact area , and measuring the groove depth at the position of the groove within the total contact area based on the three-dimensional shape .

The present invention makes it possible to quantitatively measure the groove depth of a tire's contact surface.

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 diagram showing the configuration of the groove shape measuring unit in FIG. FIG. 3 is a block diagram showing the functions of the groove shape measuring unit shown in FIG. FIG. 4 is a diagram showing an example of an image captured of a lattice sheet. FIG. 5 is a diagram showing an example of phase analysis performed on the image shown in FIG. 4 by a sampling moire method, which is an example of a non-contact shape measurement technique. 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 a tire. FIG. 8 is a diagram for explaining the generation of moire fringes in the sampling moire method. FIG. 9 is a flow chart for explaining the selective sampling moire method. FIG. 10 is a diagram showing an example of moire fringes generated as a result of performing thinning processing at five 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 measuring process performed by the groove shape measuring unit. FIG. 13 is a flowchart showing a tire analysis method performed 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 imaging unit. FIG. 15 is a flow chart showing a process for measuring the groove shape using the Fourier transform method. FIG. 16 is a flowchart showing a tire analysis method performed by the tire shape analysis system according to the present embodiment. FIG. 17 is a diagram showing the positional relationship between the tire, which is the subject of the image capture, and the camera. FIG. 18 is an enlarged view of a portion of FIG. 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 the total contact area creation process performed by the total contact area creation unit. FIG. 22 is a block diagram showing the functions of the total contact area creation unit. FIG. 23 is a diagram illustrating the movement of the road plate and the operation of the trigger device. FIG. 24 is a diagram illustrating the movement of the road plate and the operation of the trigger device. FIG. 25 is a flow chart showing the operation of the total contact area creation unit. FIG. 26 is a diagram showing an example of a specific arrangement of the camera and the illumination lamps when the contact surface image acquisition unit acquires a contact surface image. FIG. 27 is a diagram showing an example of a specific arrangement of the camera and the illumination lamps when the contact surface image acquisition unit acquires a contact surface image. FIG. 28 is a diagram showing an example of a specific arrangement of the camera and the illumination lamps when the contact surface image acquisition unit acquires a contact surface image. FIG. 29 is a diagram illustrating the inclination angle of the ramp with respect to the tire circumferential direction. FIG. 30 is a diagram illustrating the inclination angle of the ramp with respect to the tire circumferential direction. FIG. 31 is a diagram showing the arrangement of the illumination lamps as viewed from a direction along the rotation axis of the tire. FIG. 32 is a diagram showing the arrangement of the illumination lamps as viewed from a direction perpendicular to the rotation axis of the tire. FIG. 33 shows the arrangement of the lighting lamps as viewed from the top side of the road plate. FIG. 34 is a diagram illustrating the inclination angle of the ramp with respect to the tire width direction. FIG. 35 is a diagram illustrating the inclination angle of the ramp with respect to the tire width direction. FIG. 36 is a diagram showing an example of irradiation with light from a lamp to enhance the brightness of the chamfer of the sub-groove. FIG. 37 is a diagram showing an example of irradiation with light from a lamp to enhance the brightness of the chamfer of the sub-groove. FIG. 38 is a diagram showing an example of irradiation with light from a lamp to enhance the brightness of the chamfer of the sub-groove. FIG. 39 is a diagram showing an example of irradiation with light from a lamp to enhance the brightness of the chamfer of the sub-groove. FIG. 40 is a diagram showing an example of irradiation with light from a lamp to enhance the brightness of the chamfer of the sub-groove. FIG. 41 is a diagram showing an example of irradiation with light from a lamp to enhance the brightness of the chamfer of the 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 diagram showing an example of processing by the ground characteristic analysis unit. FIG. 45 is a diagram showing an example of an image acquired or created by the processing of the ground contact characteristic analysis unit. FIG. 46 is a diagram showing an example of an image acquired or created by the processing of the ground contact characteristic analysis unit. FIG. 47 is a diagram showing an example of an image acquired or created by the processing of the ground contact characteristic analysis unit. FIG. 48 is a diagram showing an example of an image acquired or created by the processing of the ground contact characteristic analysis unit. FIG. 49 is a diagram showing an example of an image acquired or created by the processing of the ground contact characteristic analysis unit. FIG. 50 is a diagram showing an example of an image acquired or created by the processing of the ground contact characteristic analysis unit. FIG. 51 is a diagram showing an example of an image acquired or created by the processing of the ground contact characteristic analysis unit. FIG. 52 is a diagram showing an example of a GCA. FIG. 53 is an explanatory diagram of the expansion process. FIG. 54 is an explanatory diagram of the contraction process. FIG. 55 is a diagram showing an example of groove distribution within the total contact area. FIG. 56 is a diagram showing the case where one camera is used. FIG. 57 is a diagram showing a case where three cameras are used. FIG. 58 is a diagram for explaining the height of the road plate. FIG. 59 is a diagram showing a configuration for determining the height distribution. FIG. 60 is a diagram showing the contents of the process of the groove depth calculation unit. FIG. 61 is a diagram showing the contents of the process of the groove depth calculation unit.

The following describes in detail an embodiment of the present invention with reference to the drawings. In the following description of each embodiment, components that are the same as or equivalent to those in other embodiments are given the same reference numerals, and their description is simplified or omitted. The present invention is not limited to each embodiment. Furthermore, the components of each embodiment include those that are easily replaceable by a person skilled in the art, or those that are substantially the same. The multiple modified examples described in this embodiment can be combined in any way that is obvious to a person skilled in the art.

Figure 1 is a block diagram showing the configuration of a tire shape analysis system according to an embodiment of the present invention. As shown in Figure 1, the tire shape analysis system according to this embodiment has a groove shape measurement unit 40, a total contact area creation unit 42, a groove depth measurement unit 44, and a groove volume calculation unit 46. The groove depth measurement unit 44 has a groove distribution data creation unit 441 and a groove depth calculation unit 442. The processing content of each of these units will be described below.

(Groove shape measuring part)
Fig. 2 is a configuration diagram showing the groove shape measuring unit 40 in Fig. 1. Fig. 3 is a block diagram showing the functions of the groove shape measuring unit 40 shown in Fig. 2. In these figures, Fig. 2 shows a schematic diagram of 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 has grooves M1 to M4. The grooves M1 to M4 are recessed from the surface of the tire 60. In this embodiment, lattice sheets SS1 to SS4 are attached to the area including the four grooves M1 to M4. In this embodiment, lattice sheets SS1, SS2, SS3, and SS4 are attached to the four grooves 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 using a device or jig not shown. The lattices of the lattice sheets SS1, SS2, SS3, and SS4 are, for example, 1 mm square lattices. In the following description, lattice sheets SS1, SS2, SS3, and SS4 may be collectively referred to as lattice sheets SS.

The photographing device 3 has a pair of cameras 15b and 15c and a pair of illumination lamps 32a and 32b. The cameras 15b and 15c are photographing units that photograph the tire 60, and are, for example, CCD (Charge Coupled Device) cameras. More precisely, the cameras 15b and 15c photograph an area that includes the lattice sheet SS attached to the groove portion, which is a portion recessed from the surface of the tire 60.

The photographing device 3 also has a fixed rod 15AM. A pair of cameras 15b and 15c are fixed to the fixed rod 15AM. The pair of cameras 15b and 15c are fixed to different positions on the fixed rod 15AM so that they can photograph the tire 60 from different directions. These cameras 15b and 15c simultaneously photograph 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 ranges of the cameras 15b and 15c, and are, for example, halogen lamps. These illumination lamps 32a and 32b may be of a constant lighting type or a flash lighting type.

The tire contact patch analysis device 20 is, for example, a PC (Personal Computer) with a specific analysis program installed, and performs tire analysis processing by performing image processing on the image of the tire 60 captured by the imaging device 3.

As shown in FIG. 3, the tire contact patch analysis device 20 according to this embodiment includes an analysis unit 41 that analyzes the image of the tire 60 captured by the imaging device 3 using a non-contact shape measurement method. The analysis unit 41 includes an image smoothing unit 411, a luminance distribution acquisition unit 412, a thinning processing unit 413, a moiré fringe creation unit 414, a phase distribution calculation unit 415, a three-dimensional shape calculation unit 416, and an inverse Fourier transform unit 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 the image showing the luminance distribution. The thinning processing unit 413 and the moiré fringe creation unit 414 perform linear interpolation on the thinned image to create moiré fringes. The phase distribution calculation unit 415 calculates the phase distribution of the lattice sheet based on the moiré fringes. The three-dimensional shape calculation unit 416 calculates the three-dimensional shape of a region that includes at least a groove portion, which is a portion recessed from the surface of the tire, based on the calculated phase distribution of the lattice sheet. The inverse Fourier transform unit 419 performs inverse Fourier transform processing, which will be described later.

Figure 4 is a diagram showing an example of an image of the lattice sheet SS. The image captured by the imaging device 3 includes the lattice sheet SS attached to the surface of the groove of the tire 60. As shown in Figure 4, the groove bottom curved surface portion WR can be captured by the imaging device 3.

Figure 5 shows an example of phase analysis performed on the image shown in Figure 4 using the sampling moiré method, which is an example of a non-contact shape measurement method. By using the sampling moiré method, the distortion of the groove bottom surface can be calculated with higher accuracy than other methods. The sampling moiré method has a restriction that, for example, the target of phase analysis is a pattern in which a lattice is periodically arranged in the same direction as the camera pixels. In this embodiment, the above restriction can be eliminated by photographing the lattice sheet SS on the surface of the tire 60 from an oblique direction rather than from the front.

In addition, non-contact shape measurement methods may include digital image correlation, Fourier transform, and light section methods, and any method that can calculate the distortion of the groove bottom surface may be used.

(Grid sheet)
6 is a diagram for explaining the lattice pitch of the lattice sheet SS. As shown in Fig. 6, the lattice sheet SS has a large number of rectangular holes, and the distance KP between the centers of adjacent holes is the lattice pitch of the lattice sheet SS.

The inventors verified the appropriate lattice pitch and found the following. When the lattice pitch was smaller than 0.21 x R, where R is the radius of curvature of the groove bottom surface, it was difficult to attach the lattice sheet SS without causing the lattice to collapse. Also, when the lattice pitch was larger than 2.40 x R, it was difficult to detect the maximum value of the concentrated strain occurring on the groove bottom surface. Therefore, it is desirable for the lattice pitch of the lattice sheet used in this embodiment to satisfy formula (1).

0.21×R ≦ grating pitch ≦ 2.40×R … (1)

By using a lattice sheet with such a lattice pitch, the strain on the tire groove bottom surface can be measured with high precision. Note that if the lattice pitch is > 2.40 x R, the number of locations with a large strain gradient increases, making it difficult to identify which areas are the true concentrated areas of groove surface strain, which is not preferred.

The lattice sheet SS is not limited to having a large number of rectangular holes, and may have a large number of holes of other shapes, such as triangular holes. The size of the holes may be arbitrary (however, it is assumed that the lattice pitch distance KP can be identified visually).

Figure 7 is a diagram for explaining the radius of curvature of the groove bottom surface of a tire. As shown in Figure 7, if a circle KR is assumed to be 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 moiré method is used as a non-contact shape measurement method. The sampling moiré method is a method of sampling a captured image of a measurement object to which a two-dimensional grid is attached at predetermined pixel intervals (every X pixels) to measure the shape. Other non-contact shape measurement methods, for example, a digital image correlation method or a Fourier transform method, may be used. In this embodiment, a case where a thinning-out selection type sampling moiré method is used among the sampling moiré methods will be described. The thinning-out selection type sampling moiré method is a method in which, in the sampling moiré method, a phase distribution of the optimal thinning-out number for analysis is referred to for each pixel of the captured image.

(Sampling Moire Method)
In the sampling moiré method, for example, a captured image is smoothed in a certain direction (e.g., the vertical direction), and the smoothed image is thinned and linearly interpolated to obtain a moiré fringe image, and corresponding points on the screen between the two cameras are searched for using the phase distribution.

Now, an example of the generation of moiré fringes and the calculation of phase distribution in the sampling moiré method will be described in more detail with reference to FIG. 8. FIG. 8 is a diagram for explaining the generation of moiré fringes in the sampling moiré method. FIG. 8 has been quoted and modified from "Accuracy Evaluation of Dynamic Measurement Method of Three-Dimensional Shape and Strain Distribution Using Sampling Moiré Method" in Proceedings of the Japan Society for Experimental Mechanics, No. 10 (2010). The example shown in FIG. 8 is an example of generating moiré fringes by the uniform thinning sampling moiré method using a thinning number of "4".

In step S11, the analysis unit 41 obtains an image of the captured image of the groove bottom surface that has been smoothed in the vertical direction (lengthwise direction). The following describes the process when smoothing in the vertical direction, but the process is similar when smoothing in the horizontal direction (lateral direction).

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

In step S13, the analysis unit 41 thins out every four pixels of one image 90, generating four images, images 91a to 91d. Images 91a to 91d each start thinning out at a different pixel. The number of images generated by thinning out pixels matches the thinning number. For example, if the thinning number is "4", four images are generated, and if the thinning number is "5", five images are generated.

In step S14, the analysis unit 41 performs a process of setting the luminance of pixels for which thinned pixels are not set for each of the images 91a to 91d by linear interpolation using the luminance of pixels for which non-thinned pixels are set. This results in moiré fringes 92a to 92d.

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

Here, X is the thinning number (X is a natural number), and I(k) indicates the luminance of the kth moiré fringe (k is a natural number). That is, when calculating the phase σ at a position corresponding to a pixel position in the phase distribution corresponding to the thinning number, the luminance at the position corresponding to that pixel position is taken from the kth moiré fringe and stored in I(k), and then the phase σ is calculated. In the example shown in Figure 8, moiré fringes 92a, 92b, 92c, and 92d correspond to the first, second, third, and fourth moiré fringes, respectively.

By calculating the phase value corresponding to each pixel position using equation (2) while referring to the moiré fringes 92a to 92d, it is possible to calculate the phase distribution 93 when the image 90 is thinned out by a thinning factor of "4".

By calculating the phase distribution 93 of the moiré fringes with the phase distribution 94 of the reference grating, it is possible to obtain the phase distribution 95 of the grating sheet, whose phase has a periodicity ranging from -π to π.

Figure 9 is a flowchart explaining the selective sampling moiré method.

In step S201, the image smoothing unit 411 of the analysis unit 41 obtains an image smoothed in the vertical direction (lengthwise direction) from the captured image of the groove bottom surface. This process is similar to 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 and obtains an image showing the luminance distribution. This process is similar to step S12 in FIG. 8 described above.

In step S203, the thinning processing unit 413 of the analysis unit 41 performs thinning processing using multiple different numbers of pixels. In this example, thinning is performed by selecting 4 pixels or 5 pixels. The images obtained by performing thinning processing using 4 pixels are similar to the images 91a to 91d obtained by the processing in step S13 described above.

In step S204, the moiré fringe creation unit 414 of the analysis unit 41 generates moiré fringes for the results of the thinning process performed in step S203 by 4 pixels and 5 pixels. The moiré fringes generated for the results of the thinning process performed in step S203 by 4 pixels are similar to the moiré fringes 92a to 92d obtained by the process in step S14 described above.

Figure 10 shows an example of moiré fringes generated as a result of thinning out five pixels. Figure 10 has been quoted and modified from "Accuracy Evaluation of Dynamic Measurement Method of Three-Dimensional Shape and Strain Distribution Using Sampling Moiré Method" in Proceedings of the Japan Society for Experimental Mechanics, No. 10 (2010). As shown in Figure 10, moiré fringes 92e to 92i are obtained by performing a process in which the brightness of pixels that do not have thinned out pixels is set by linear interpolation using the brightness of pixels that have not been thinned out pixels.

In step S205 of FIG. 9, the phase distribution calculation unit 415 of the analysis unit 41 applies the luminance of the moiré fringes 92a to 92d generated as a result of performing the thinning process at four pixels, and the luminance of the moiré fringes 92e to 92i generated as a result of performing the thinning process at five pixels, to the above formula (2), thereby obtaining the phase σ at the position corresponding to the pixel position in the phase distribution corresponding to the number of thinnings.

By calculating the phase value corresponding to each pixel position using equation (2) while referring to moiré fringes 92a-92d and moiré fringes 92e-92i, it is possible to calculate the phase distribution when one line of an image is thinned out by thinning factors of "4" and "5". In other words, by calculating the phase distribution of moiré fringes 92a-92d and moiré fringes 92e-92i with the phase distribution of the reference grating, it is possible to obtain the phase distribution of a lattice sheet having a phase periodicity from -π to π.

In step S206 in FIG. 9, the phase distribution calculation unit 415 of the analysis unit 41 refers to the phase distribution of the lattice sheet suitable for shape analysis for each pixel. FIG. 11 is a diagram showing an example of an image of the lattice sheet SS. In FIG. 11, for example, in an image obtained by photographing the lattice sheet SS, if one pitch P4 of the lattice pitch corresponds to four pixels, the phase distribution of the lattice sheet generated as a result of performing a four-pixel thinning process is referenced. Also, in an image obtained by photographing the lattice sheet SS, if another pitch P5 of the lattice pitch corresponds to five pixels, the phase distribution of the lattice sheet generated as a result of performing a five-pixel thinning process is referenced.

In step S207 of FIG. 9, the phase distribution calculation unit 415 of the analysis unit 41 determines the phase distribution of the lattice sheet for shape calculation based on the result of referring to the phase distribution of the lattice sheet for each pixel in step S206. This makes it possible to obtain accurate shape analysis results regardless of the number of pixels equivalent to one pitch of the lattice pitch in an image captured of the lattice sheet SS. In other words, for example, if thinning is performed at a fixed number of four pixels, a decrease in analysis accuracy may occur in areas where one pitch corresponds to five pixels. In contrast, by thinning out four or five pixels as described above without fixing the number of pixels to be thinned out, it is possible to avoid a decrease in analysis accuracy for each area where one pitch corresponds to five or four pixels. In this way, a phase distribution with an optimal number of thinnings is selected for analysis by the analysis unit 41.

The phase distribution for shape calculation is determined, for example, as follows. That is, for image 90 showing the brightness distribution, for example, in which one line is extracted from an image obtained by smoothing the captured image, the number of pixels corresponding to the distance between the darkest pixels is found, and this number of pixels is set as the number of thinned pixels. Then, the phase distribution corresponding to the result of performing the thinning process with this number of pixels is set as the phase distribution for shape calculation.

Figure 12 is a flowchart showing the groove shape measurement process by the groove shape measurement unit 40. In Figure 12, in step S101, a grid pattern is attached to a portion of the tire 60 that includes the groove bottom surface. In step S102, an image of the grid sheet provided in an area that includes at least the groove portion, which is a portion recessed from the tire surface, is taken. In step S103, the captured image is analyzed. In this manner, the tire groove shape 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, a pattern matching method is applied to the captured image. For example, any one of feature-based matching, area-based matching, and phase-based matching is applied. Next, corresponding points of the captured images from a plurality of different directions corresponding to the above-mentioned phase distribution are calculated. Then, a three-dimensional shape is calculated based on the corresponding points of the captured images from a plurality of different directions and the line of sight (photographing direction) of each camera. The three-dimensional shape can be obtained by using the phase distribution of the captured images acquired by each of the cameras 15b and 15c as line of sight data based on the corresponding points of each captured image 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 plate 221).

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

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

Figure 15 is a flow chart showing a process for measuring the groove shape using the Fourier transform method. In Figure 15, in step S501, the pattern is photographed with at least two cameras. In step S502, the photographed image is subjected to a two-dimensional Fourier transform to obtain a power spectrum. In step S503, the first harmonic wave WV in the vertical direction and the first harmonic wave WH in the horizontal direction are extracted from the obtained power spectrum, and each is subjected to a two-dimensional inverse Fourier transform. In step S504, the wrapping type phase distribution obtained by the two-dimensional inverse Fourier transform is phase-connected to convert it into an unwrapping type. In step S505, the three-dimensional shape is calculated based on the phase distribution of the images photographed by each camera and the line of sight (photographing direction) of each camera.

(Weighted Phase Analysis)
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, a pattern pattern is photographed by at least two cameras. In step S502a, the photographed image is smoothed in the vertical direction and the horizontal direction. In step S502b, the phase distribution of the lattice 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 using the technology described in Japanese Patent No. 5795095. For example, when 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 expressed as a weighting function W _xy (k, l) in two-dimensional directions, it becomes as shown in Equation (3). Then, the phase calculation formula in the vertical direction (x direction) is Equation (4), and the phase calculation formula in the horizontal direction (y direction) is Equation (5). The phase distribution of the grating is obtained using equations (4) and (5).

In step S504, the wrapping type phase distribution (wrapping at π and returning to -π) obtained in step S502b is phase-unwrapped to convert it into an unwrapping type. In step S505, the three-dimensional shape is calculated based on the phase distribution of the images captured by each camera and the line of sight (capture direction) of each camera.

(Taken in multiple sessions)
When photographing a groove having a pattern, it is preferable to divide the photographing range and photograph the groove several times, rather than photographing the entire groove in one go. For example, it is preferable to divide the photographing range into two and photograph the groove twice.

Figure 17 is a diagram showing the positional relationship between the tire, which is the subject of the image capture, and the camera. Figure 18 is a diagram showing an enlarged portion of Figure 17. In Figures 17 and 18, the left-right direction of the figure is the tire width direction, and the depth direction of the figure is the tire circumferential direction and the extension direction of the road surface plate 221. In Figure 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. Cameras 15b1 and 15b2 are arranged overlapping in the depth direction of the figure. Cameras 15c1 and 15c2 are arranged overlapping in the depth direction of the figure.

In this example, the 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 view of the range H. As shown in FIG. 18, the range H is made up of two ranges H1 and H2. Therefore, the capture range of the groove 62 is divided into two ranges H1 and H2, and is captured twice. The two ranges H1 and H2 have a common area HC. That is, the capture range of the groove 62 is divided into two areas including a common area. The common area HC is preferably one or more periods in the tire width direction of the pattern pattern. By dividing the capture range while providing the common area HC in this way, the groove shape for each capture area can be synthesized with high accuracy, and the shape of the entire groove can be obtained. Note that if the common area HC is less than one period in the tire width direction of the pattern pattern, the accuracy of synthesis of the groove shape decreases due to the constraints of the sampling moiré method, which is not preferable.

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

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

In addition, it is preferable that the distance from the midpoint position 15P between cameras 15b and 15c to the lattice sheet SS provided in the groove of the tire being photographed (hereinafter referred to as the tire-camera distance) is (10.5 x F) mm or more and (18.5 x F) mm or less, where F is the focal length of the camera lens.

Furthermore, it is preferable that the ratio of the camera distance to the tire-camera distance is 0.51 or more and 1.35 or less. When the camera is installed on the fixed bar 15AM, the tire-camera distance is the distance 15E from the lattice sheet SS to the center line 15S.

In the example described with reference to Figures 17 and 18, the shooting range is divided into two ranges and photographed twice, but it may be divided into three or more ranges and photographed separately. In other words, it is sufficient to divide the shooting range into at least two ranges and photograph them separately. In either case, it is preferable to divide it so as to include a common area, and the common area is at least one period of the design pattern in the tire width direction.

(Camera movement range)
The above-mentioned cameras 15b and 15c are preferably movable and can capture all the grooves on the tire contact surface. In other words, it is preferable to repeat the movement of the cameras 15b and 15c and the capturing of images by the cameras 15b and 15c to capture images of all the grooves in the total contact area. By repeating the movement of the cameras and the capturing of images for the captured image range divided as described above, the groove depth and groove volume of the entire tire contact surface can be evaluated.

Figure 20 is a diagram showing an example of an image of a tire contact surface. In Figure 20, the camera can move in the tire width direction and tire circumferential direction, and the camera movement range HM is preferably as follows. That is, if the tire contact center 610 is defined as the origin (0,0) and the midpoint position 15P of the two cameras 15b, 15c is defined as (X,Y), the tire circumferential movement range X for the maximum contact length L7 along the tire circumferential direction is preferably -L7/2 or more and L7/2 or less. In addition, the tire width movement range Y for the maximum contact width W7 along the tire width direction is preferably -W7/2 or more and W7/2 or less. By setting the camera movement range HM as described above, the groove depth and groove volume of the entire tire contact surface can be evaluated.

(Total contact area creation process)
Fig. 21 is a diagram showing a total contact area creation process by the total contact area creation unit 42. Fig. 22 is a block diagram showing functions of the total contact area creation unit 42. In these figures, Fig. 21 shows a schematic diagram of the overall configuration of the total contact area creation unit 42, and Fig. 22 shows main functions of the total contact area creation unit 42.

The total contact area creation unit 42 is applied to a system that acquires an image of the contact surface 61 of a pneumatic tire 60 and analyzes the contact surface 61. The total contact area creation unit 42 includes a tire testing machine 2, an imaging device 10, and a tire contact surface analysis device 20.

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

In this 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 of the main surfaces of the road surface plate 221, to impart a load to the tire 60. The road surface plate 221 reproduces a flat road surface. When the tire 60 is pressed against the road surface plate 221, the ground contact surface 61 is deformed in the same manner as when the tire 60 is running on a flat road surface. By driving the road surface plate 221 horizontally, the rolling state of the tire 60 during vehicle running is reproduced with the surface of the road surface plate 221 as the road surface, and dynamic ground contact characteristics can be analyzed. In addition, the support device 300 displaces the rim 400 to adjust the positional relationship between the tire 60 and the road surface plate 221, thereby imparting a slip angle or angle angle to the tire 60. In addition, the drive device 5 can drive the motor 6 by the motor control device 7 to rotate the rim 400 by a predetermined angle. In addition, the support device 300 and drive device 5 can change the test conditions by adjusting the load, rotation speed, slip angle, angle angle, etc.

The road surface plate 221 is a light-transmitting plate that has the property of transmitting light. The road surface plate 221 does not have to transmit 100% of light, as long as it has a light transmittance that allows the surface of the tire 60 to be photographed 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. The contact state between the tire 60 and the flat plate is photographed and image analyzed, so that a more realistic ground contact state of the tire 60 can be analyzed. There are no specifications specified for the road surface plate 221, such as the plate thickness or refraction angle.

The photographing device 10 has a camera 15a, which is a photographing unit that photographs the tire 60, an illumination lamp 16, which is a light source, and a trigger device 17. The camera 15a is, for example, a CCD (Charge Coupled Device) camera. The camera 15a is fixed inside the photographing device 10. The camera 15a photographs the tire 60 through the road plate 221, thereby photographing the ground contact surface 61 of the tire 60 pressed against the road plate 221. In detail, the camera 15a is disposed on the lower surface 221D side, which is the other main surface of the road plate 221, with the optical axis oriented perpendicular to the lower surface 221D side, and photographs the tire 60 from the lower surface 221D side through the road plate 221. 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, for example, a halogen lamp. This illumination lamp 16 is a collective term for the lamps 161 to 168 that are provided in multiple numbers as described below. The illumination lamp 16 irradiates light onto the ground contact surface 61 of the tire 60 that is pressed against the road plate 221. The illumination lamp 16 irradiates light from the lower surface 221D side of the road plate 221 through the road plate 221, or from between the upper surface 221U side of the road plate 221 and the tire 60. The multiple illumination lamps 16 are each disposed at a position other than the position where the road plate 221 moves. Note that as the imaging device 10 moves, the camera 15a and the illumination lamp 16 in the imaging device 10 move together.

The number of these lighting lamps 16 may be varied depending on the test conditions in the tire tester 2. For example, when the load when the tire 60 is pressed against the road plate 221 is small, the contact area is narrow. Therefore, in this case, the number of lighting lamps 16 may be relatively small, and they may be arranged in two places diagonally with respect to the moving direction of the road plate 221. On the other hand, when the load when the tire 60 is pressed against the road plate 221 is large, the contact area is wide, so it is necessary to irradiate light from more directions to the contact surface 61. Therefore, in this case, the lighting lamps 16 are arranged in four or more places surrounding the contact surface 61. Furthermore, these lighting lamps 16 may be of a constant lighting type or a flash lighting type.

The trigger device 17 is a device that outputs a trigger signal that indicates the timing of photographing 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 of the road plate 221, and the semiconductor laser output by the trigger device 17 is reflected by the retroreflective sheet 18. When the detection unit 171 of the trigger device 17 detects the reflected light, 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 contact surface 61 of the tire 60 at the same position can be photographed even if photographing is performed multiple times.

The tire contact patch analysis device 20 is, for example, a PC (Personal Computer) with a predetermined analysis program installed, and processes the image of the tire 60 input from the image capture device 10 to analyze the contact patch 61 of the tire 60. The process of analyzing the contact patch 61 of the tire 60 includes a process of calculating the contact patch 61 based on the image of the captured tire 60. The tire contact patch analysis device 20 has a processing device 30 that performs arithmetic processing such as analysis of the contact patch 61 and data storage, an input unit 21 that an operator performs input operations to the tire contact patch analysis device 20, and a display unit 22 that displays analysis results and various information. The input unit 21 uses a pointing device such as a keyboard or a mouse, and the display unit 22 uses a display device such as a liquid crystal display. The input unit 21 and the display unit 22 are electrically connected to the processing device 30, and thus the tire contact patch analysis device 20 allows the operator to perform input operations on the input unit 21 while visually checking the display unit 22. In addition, 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 images captured by the camera 15a.

The processing device 30 of the tire contact patch analysis device 20 is configured with a processing unit 31 having a CPU (Central Processing Unit) or the like, and a storage unit 50 such as a RAM (Random Access Memory). The processing unit 31 and storage unit 50 thus configured may be provided in the same housing, or in different housings, or multiple storage units 50 may be provided in both forms.

The processing unit 31 of the processing device 30 functionally comprises a ground contact surface image acquisition unit 32, a ground contact characteristic analysis unit 33, and an imprint extraction unit 401. Of these, the ground contact surface image acquisition unit 32 acquires a photographed image of the ground contact surface 61 of the tire 60 to be analyzed. The photographed image is a digital image of the ground contact surface 61 of the tire 60 photographed by the camera 15a. The ground contact characteristic analysis unit 33 creates a contact area image showing the contact area of the tire 60 based on the ground contact surface image acquired by the ground contact surface image acquisition unit 32. In the following description, all photographed images of the ground contact surface 61 are assumed to be composed of 256 gradations, with black defined as luminance "0" and white defined as luminance "255."

The ground characteristic analysis unit 33 includes a groove extraction unit 34 and a ground characteristic calculation unit 35. The groove extraction unit 34 extracts a groove image from the photographed image. The ground characteristic calculation unit 35 subtracts the groove image from the image of the rough ground area obtained by binarization processing with a predetermined brightness as a threshold value for the photographed image. The ground characteristic calculation unit 35 may perform, for example, a smoothing process on the photographed image, and then perform a binarization processing with a brightness threshold value of "220" to obtain an image of the rough ground area. For the smoothing process, for example, a process using a median filter with a region within a radius of 4 pixels from the pixel of interest as the surrounding pixels (hereinafter referred to as median processing) may be used. Note that, as described later, the groove extraction unit 34 may extract the groove image by performing a process of removing a portion corresponding to the marking included in the photographed image. Also, as described later, the ground characteristic calculation unit 35 may extract an image of the rough ground area by performing a process of removing a portion corresponding to the marking included in the photographed image.

The groove extraction unit 34 includes a chamfer 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 a chamfer portion provided at the edge of the groove of the tire 60 from the captured image. The chamfer image extraction unit 34A extracts a portion having a brightness higher than a predetermined brightness from the captured image as a chamfer 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 brightness 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 synthesis unit 34D synthesizes the chamfer image, the groove bottom image, and the main groove bottom image to obtain a groove image.

(Main groove bottom extraction part)
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 superimposition processing unit 344. The smoothing processing unit 341 performs a smoothing process on the captured image in the tire circumferential direction. The first candidate image extraction unit 342 extracts a first candidate image obtained by binarizing the smoothed image smoothed by the smoothing processing unit 341 using a predetermined first brightness threshold. 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 using a second brightness threshold lower than the first brightness threshold. The superimposition processing unit 344 obtains a main groove bottom image by superimposing an image of an isolated object that is included in the first candidate image and does not include a contact block on the second candidate image.

The grooves of the tire 60 are a collective term for the main grooves, sub-grooves, and chamfers at the openings of these grooves on the tread surface of the tire 60. The main grooves are grooves that are required to display a wear indicator as stipulated by JATMA. The sub-grooves are lateral grooves that extend in the tire width direction and function as grooves by opening when the tire is in contact with the ground.

The analysis program used by the tire contact patch analysis device 20 is stored in advance in the memory unit 50, and when analyzing the contact patch 61 of the tire 60, the program stored in the memory unit 50 is called up by the processing unit 31, and each function is executed by having the processing unit 31 execute operations according to the program.

The total contact area creation unit 42 according to this embodiment has the above-mentioned configuration. The operation of the total contact area creation unit 42 will be described below. In the total contact area creation unit 42, first, the tire 60 is attached to the support device 300 of the tire testing machine 2, and the tire 60 is rotated while being pressed against the road plate 221, while the camera 15a photographs the contact surface 61. At that time, the tire 60 is photographed while being irradiated with light from multiple lighting lamps 16 from multiple directions. Therefore, the camera 15a can photograph the tire 60 with a difference in brightness between the contact surface 61 and the parts other than the contact surface 61. The photographed image is acquired by the tire contact surface analysis device 20, which analyzes the contact surface 61 based on the acquired image.

To extract the grooves of the tire 60, a distance sensor that uses triangulation to detect differences in height (depth) can be used. However, to detect the grooves on the entire ground contact surface 61, it is necessary to scan the detection range of the distance sensor. Therefore, it is difficult to analyze the dynamic ground contact characteristics while the tire 60 is rolling by using only a distance sensor.

(Lighting conditions during photography)
When acquiring an image of the contact area of the ground contact surface 61 of the tire 60, it is preferable to arrange the lighting lamps 16 on the upper surface 221U side of the road surface plate 221 so as to surround the ground contact surface 61. When acquiring an image of the contact area of the ground contact surface 61 of the tire 60, it is preferable to acquire the image by irradiating the tire 60 with light from the lighting lamps 16 arranged on the upper surface 221U side so as to surround the contact portion.

(Movement of road plate and operation of trigger device)
23 and 24 are diagrams for explaining the movement of the road plate 221 and the operation of the trigger device 17. Fig. 23 shows the state before the road plate 221 moves and before the trigger device 17 detects the light reflected by the retroreflective sheet 18. Fig. 24 shows the state after the road plate 221 moves and when the trigger device 17 detects the light reflected by the retroreflective sheet 18.

23, the upper surface 221U of the road plate 221 is flat, and the upper surface 221U forms a flat road surface on which the tire 60 rolls. In FIG. 23, the tire 60 is fixed to the rim 400 of the support device 300 in contact with the upper surface 221U of the road plate 221. Therefore, the tire 60 rotates as the road plate 221 moves. The total ground contact area creation unit 42 moves the road plate 221 in the direction of the arrow Y1. As the road 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. As long as the trigger device 17 does not detect the reflected light by the retroreflective sheet 18, the road plate 221 continues to move in the direction of the arrow Y1. Since the imaging device 10 is fixed to the road plate 221, the imaging device 10 moves as the road plate 221 moves. The moving speed of the road plate 221 is, for example, 0.5 km per hour. Note that a rotating drum with a transparent outer surface may be used instead of the road plate 221.

When the road surface plate 221 moves in the direction of 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 ground contact area creation unit 42 outputs a signal to the camera 15a to instruct the camera 15a to take a picture. This allows the ground contact surface 61 of the tire 60 to be photographed. Note that the road surface plate 221 only needs to have a transparent portion 110 that corresponds to the imaging range of the camera 15a, and the portions other than the portion 110 may be opaque. In other words, the road surface plate 221 may be entirely transparent, or only the portion 110 that corresponds to the imaging range may be transparent.

(Operation of total ground contact area creation unit)
25 is a flow diagram showing the operation of the total ground contact area creation unit 42. When analyzing the tire 60, the total ground contact area creation unit 42 irradiates light from the illumination lamp 16 to the tire 60 pressed against the road plate 221 (step S201). Next, the total ground contact area creation unit 42 starts driving the motor 6 by the motor control device 7 (step S202). When the total ground contact area creation unit 42 continues driving the motor 6 (step S203), it determines whether the trigger device 17 has detected the reflected light by the retroreflective sheet 18 (step S204). When the trigger device 17 has not detected the reflected light by the retroreflective sheet 18, the total ground contact area creation unit 42 continues driving the motor 6 (step S204, No → S203).

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

(Examples of specific layouts and photographed images)
Next, a specific example of the arrangement of the camera 15a and the lighting lamps 16 will be described. Figures 26 to 28 are diagrams showing a specific example of the arrangement of the camera 15a and the lighting lamps 16 when the ground contact surface image acquisition unit 32 acquires a ground contact surface image. Figure 26 is a diagram showing the arrangement of the lighting lamps 16 from a direction along the rotation axis of the tire 60. Figure 27 is a diagram showing the arrangement of the lighting lamps 16 from the upper surface 221U side of the road surface plate 221. Figure 28 is a diagram showing 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 called the tire width direction, and the direction perpendicular to the rotation axis is called the tire circumferential direction.

When photographing with this device, the tire 60 to be analyzed had an air pressure of 230 kPa, a load of 6 kN, a rotational 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-number to 4, and the exposure time to 1 ms.

Referring to Figures 26 to 28, a tire 60 is in contact with the upper surface 221U of the road plate 221. A camera 15a is provided on the lower surface 221D side of the road plate 221. The camera 15a is positioned so that its optical axis 151 is located on the normal to the center point of the ground contact surface 61 of the tire 60. By positioning the optical axis 151 of the camera 15a so that it passes through the center point of the ground contact surface 61, the ground contact surface 61 can be photographed from the normal direction of the center point of the ground contact surface 61. This ensures stable analysis accuracy. The closer to the edge of the captured image, the greater the influence of lens aberration, causing spatial resolution to fluctuate and analysis accuracy to become unstable. By positioning the camera 15a in this way, the influence of lens aberration can be minimized.

26 to 28, lamps 161, 162, 163, and 164 are arranged on the upper surface 221U side of the road plate 221 as one main surface side lamps. Lamps 165, 166 and camera 15a are arranged on the 221D side of the road plate 221 as the other main surface side lamps. Lamps 161 and 162 are arranged at positions spaced apart in the tire circumferential direction with respect to the tire 60. Lamps 161 and 162 are provided on different sides of the tire 60. Lamps 163 and 164 are arranged at positions spaced apart in the tire width direction with respect to the tire 60. Lamps 163 and 164 are provided on different sides of the tire 60. In this way, lamps 161 to 164 are arranged to surround the ground contact surface 61 of the tire 60. If the light is not irradiated on all four sides of the ground contact surface 61 of the tire 60, it becomes difficult to obtain the outline of the ground contact shape, and the analysis accuracy may decrease. In response to this, lamps 161-164 are arranged to surround the contact surface 61 of the tire 60, and light is shone on all four sides of the contact surface 61, making it possible to clarify the outline of the contact shape and improving the analysis accuracy.

26 and 28, the heights from the center of the light-emitting surface of each lamp 161-164 to the upper surface 221U of the road plate 221 are designated as H1-H4. In FIG. 26 and FIG. 28, the inclination angles of each lamp 161-164, i.e., the angles of the light irradiation direction with respect to the upper surface 221U of the road plate 221, are designated as θ1-θ4. In FIG. 27, the distances in the tire circumferential direction from the center of the light-emitting surface of each lamp 161, 162 to the center of the tire 60 are designated as distances D1 and D2. In FIG. 27, the distances in the tire width direction from the center of the light-emitting surface of each lamp 163, 164 to the center of the tire 60 are designated as distances D3 and D4. In FIG. 27, the light-emitting surface centers of each lamp 161, 162 at the tire width direction positions coincide with the tire center.

It is preferable that the heights H1 to H4 are 0 mm or more and 201 mm or less. The minimum value of the heights H1 to H4 is 0 mm. This is because the lighting lamps 16 are placed on the road surface plate 221. If the heights H1 to H4 exceed 201 mm, the light from the lighting will not penetrate the ground surface 61 well, the outline of the ground surface will become inaccurate, and the analysis accuracy will decrease, which is not preferable.

The distances D1 and D2 in the tire circumferential direction are preferably greater than half the maximum contact length of the tire 60 and less than 1345 mm. However, it is necessary to ensure that each lighting lamp 16 does not come into contact with the tire 60. It is not preferable to set the minimum value of the distances D1 and D2 smaller than half the maximum contact length of the tire 60. This is to ensure that the lighting lamps 16 do not come into contact with the tire 60. If the distances D1 and D2 exceed 1345 mm, the amount of illumination light hitting the contact surface 61 will be insufficient, making the contour of the contact surface 61 inaccurate and reducing the analysis accuracy, which is not preferable.

The distances D3 and D4 in the tire width direction are preferably greater than half the maximum ground contact width of the tire 60 and less than 300 mm. However, it is necessary to ensure that each lighting lamp 16 does not come into contact with the tire 60. It is not preferable to set the minimum value of the distances D3 and D4 smaller than half the maximum ground contact width of the tire 60. This is to ensure that each lighting lamp 16 does not come into contact with the tire 60. If the distances D3 and D4 exceed 300 mm, the amount of illumination light hitting the ground contact surface 61 will be insufficient, making the contour of the ground contact surface 61 inaccurate and reducing the analysis accuracy, 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 (n=1 to 4). For θ1 to θ4, each lighting lamp 16 preferably irradiates light toward the center of the ground surface 61. Irradiating light in this manner allows the light to penetrate well into the ground surface 61. For this reason, the inclination angles θ1 to θ4 of the lighting lamps 16 are preferably Atan(Hn/Dn)/π*180 (n=1 to 4). However, the allowable range is a measurement error of ±0.6°.

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°.

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

Referring to Figs. 26 to 28, lamps 165 and 166 are arranged on the lower surface 221D side of the road plate 221 as other main surface side lamps. Both lamps 165 and 166 are line lights with the tire circumferential direction as the longitudinal direction. Lamps 165 and 166 are arranged at positions separated in the tire width direction of the tire 60. Lamps 165 and 166 are provided on different sides of the tire 60. In other words, lamps 165 and 166 are width direction lamps that irradiate light onto the ground contact surface 61 from the outside to the inside in the tire width direction. In this way, lamps 165 and 166 are arranged to irradiate light onto the ground contact surface 61 of the tire 60 in the tire width direction. The light from lamps 165 and 166 illuminates the edges of the main grooves, making it easier to determine the main grooves.

Here, in FIG. 28, the heights from the center of the light-emitting surface of the lamps 165, 166 to the lower surface 221D are H5 and H6. In FIG. 28, the inclination angles of the lamps 165, 166, that is, the angles of the light irradiation direction with respect to the lower surface 221D of the road plate 221, are 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, 166 to the center of the tire are D5 and D6. The angles θ5 and θ6 are preferably in the range of 19.4° to 22.4°. If the heights H5 and H6 change, the appropriate angles θ5 and θ6 at that time also change. In that case, the image acquired by the camera 15a is displayed live, and the angles θ5 and θ6 can be adjusted so that the edges of the main grooves are most bright 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 diagrams explaining the inclination angle of lamps 165, 166 with respect to the tire circumferential direction. In FIG. 29, arrows Y5, Y6, which indicate the direction of light from lamps 165, 166, are aligned with the tire width direction. If the light from lamps 165, 166 travels in the tire width direction, the edges of the main grooves extending in the tire circumferential direction can be illuminated with high brightness.

As shown in FIG. 30, the angle θ15 of the longitudinal direction of the lamp 165 relative to the tire circumferential direction and the angle θ16 of the longitudinal direction of the lamp 166 relative to the tire circumferential direction are preferably both 0°. If the angles θ15 and θ16 are both 0°, the longitudinal direction of the lamp 165 and the longitudinal direction of the lamp 166 are parallel, and the brightness of all the chamfers of the main groove present on the ground contact surface 61 can be increased satisfactorily, ensuring stable analysis accuracy. If the angles θ15 and θ16 are 0°±1°, there is no problem in increasing the brightness of the chamfers of the main groove. If the angles θ15 and θ16 exceed the range of 0°±1°, it may not be possible to increase the brightness of all the chamfers of the main groove present on the ground contact surface 61, for example, it may only be possible to increase the brightness of some of the chamfers, which may result in a decrease in analysis accuracy.

Here, when the edge of the sub-groove is chamfered, it is preferable that a lamp that advances light in the tire circumferential direction is provided under the road plate. FIG. 31 is a view of the arrangement of each illumination lamp 16 viewed 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 other main surface side lamps on the lower surface 221D side, which is the other main surface of the road plate 221. Both lamps 167 and 168 are line lights whose longitudinal direction is the tire width direction. The lamps 167 and 168 are arranged at positions separated in the tire circumferential direction of the tire 60. The lamps 167 and 168 are provided on different sides of the tire 60. In other words, the lamps 167 and 168 are circumferential lamps that irradiate light to the ground contact surface 61 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 light to the ground contact surface 61 of the tire 60 in the tire circumferential direction. Lamps 167 and 168 can increase the brightness of the chamfer of the sub-groove. In other words, lamps 167 and 168 irradiate the ground surface 61 with light that increases the brightness of the edge of the sub-groove.

In addition, in FIG. 31, the heights from the center of the light-emitting surface of the lamps 167, 168 to the lower surface 221D are H7 and H8. In FIG. 31, the inclination angles of the lamps 167, 168, that is, the angles of the light irradiation direction with respect to the lower surface 221D of the road plate 221, are θ7 and θ8. FIG. 32 is a diagram showing the arrangement of each lighting lamp 16 from a direction perpendicular to the rotation axis of the tire 60. FIG. 33 is a diagram showing the arrangement of each lighting lamp 16 from the upper surface 221U side of the road plate 221. In order to maximize the illumination of the chamfer of the sub-groove, it is preferable that the angles θ7 and θ8 are 3.5° or more and 6.0° or less. 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, 168 to the center of the tire 60 are designated as D7 and D8. The light from the lamps 167, 168 can increase the brightness of the chamfer of the sub-groove present on the ground contact surface 61. In this embodiment, D7 = D8 = 183 mm.

Figures 34 and 35 are diagrams explaining the inclination angle of lamps 167, 168 with respect to the tire width direction. In Figure 34, arrows Y7, Y8, which indicate the direction of light from lamps 167, 168, are aligned along the tire circumferential direction. If the light from lamps 167, 168 travels in the tire circumferential direction, the edges of the sub-grooves extending in the tire width direction can be illuminated with high brightness.

As shown in FIG. 35, it is preferable that the angle θ17 of the longitudinal direction of the lamp 167 relative to the tire width direction and the angle θ18 of the longitudinal direction of the lamp 168 relative to the tire width direction are both 0°. If the angles θ17 and θ18 are both 0°, the longitudinal direction of the lamp 167 and the longitudinal direction of the lamp 168 are parallel, and the brightness of all the chamfers of the sub-grooves present on the ground contact surface 61 can be increased satisfactorily, ensuring stable analysis accuracy. If the angles θ17 and θ18 are 0°±1°, there is no problem in increasing the brightness. If the angles θ17 and θ18 exceed the range of 0°±1°, it may not be possible to increase the brightness of all the chamfers of the sub-grooves present on the ground contact surface 61, for example, it may be possible to increase the brightness of only some of the chamfers, which may result in a decrease in analysis accuracy.

Figures 36 to 41 are diagrams showing examples of light irradiation from lamps 167 and 168 to increase the brightness of the chamfer of the sub-groove. Figure 36 shows an example of a captured image when the light from lamps 167 and 168 is strong. Figure 36 shows an example of a captured image when light with an illuminance of about 1.3 million lux is irradiated onto the ground contact surface 61. Figure 37 is an enlarged view of a portion 201 of the sub-groove in Figure 36. In Figure 37, the edge E1 of the sub-groove shines white, and it can be seen that the amount of light in the tire circumferential direction is sufficient. Figure 38 is an enlarged view of a portion 202 of the sub-groove in Figure 36. In Figure 38, the edge E2 of the sub-groove shines white, and it can be seen that the amount of light in the tire circumferential direction is sufficient. As shown in Figures 37 and 38, when the light from lamps 167 and 168 is strong and the edges E1 and E2 of the sub-groove are shining white, the difference in brightness between the contact area and the edges of the sub-groove is large, making it easy to separate the edges of the sub-groove from the captured image.

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

As can be seen from Figures 36 to 41, it is preferable to set the light from lamps 167 and 168 to a strong illuminance of about 1.3 million lux to capture an image in which the edges of the sub-grooves are shining.

26 to 35, the illuminance of the lamps 161 to 164 in the tire width direction and the tire circumferential direction may be the same, or one of them may be greater. For the lamps 165 to 168, it is preferable to make the illuminance in the tire circumferential direction greater than the illuminance in the tire width direction. Otherwise, the chamfer of the sub-groove present in the contact surface 61 cannot be illuminated, and the analysis accuracy decreases. Note that the illuminance of each of the lamps 161 to 164 must be equal to or greater than the illuminance of each of the lamps 165 to 168. Otherwise, the outline of the tire contact shape cannot be determined, and the accuracy decreases.

42 and 43 are diagrams showing an example of the arrangement of the camera 15a. FIG. 42 is a diagram showing the camera 15a viewed from a direction along the rotation axis of the tire 60. FIG. 43 is a diagram showing the camera 15a viewed from a direction perpendicular to the rotation axis of the tire 60. As shown in FIG. 42 and FIG. 43, it is preferable that the camera 15a is provided below the ground contact surface 61. As shown in FIG. 42 and FIG. 43, it is preferable that the camera 15a is provided below the range W1 in the tire circumferential direction of the ground contact surface 61 and below the range W2 in the tire width direction of the ground contact surface 61. In other words, the camera 15a is provided in a range surrounded by a line extending from the outline of the ground contact surface 61 in a direction perpendicular to the lower surface 221D side of the road plate 221. By placing the camera 15a in this range, stable analysis accuracy can be ensured. It is not preferable to take an image with the camera 15a away from the ground contact surface 61 because the groove wall gets in the way and the edge of the main groove cannot be observed, resulting in a decrease in analysis accuracy. In Figures 42 and 43, the distance L in the tire radial direction from the lower surface 221D of the road 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 optimal value of the distance L varies depending on the groove width present in the contact surface 61.

(Ground characteristic analysis section processing)
An example of the processing by the ground contact characteristic analysis unit 33 and an image acquired or created by the processing will be described. Fig. 44 is a flow diagram showing an example of the processing by the ground contact characteristic analysis unit 33. Fig. 44 shows an example of the processing by the processing unit 31 centering on the ground contact characteristic analysis unit 33. Figs. 45 to 51 are diagrams showing examples of images acquired or created by the processing by the ground contact characteristic analysis unit 33.

In FIG. 44, first, the ground contact surface image acquisition unit 32 acquires an image of the ground contact surface 61 of the tire (step S31). By the processing 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 processing of step S32, for example, a chamfered image shown in FIG. 46 can be obtained.

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

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

The synthesis unit 34D of the groove extraction unit 34 synthesizes the chamfer image, the groove bottom image, and the main groove bottom image to obtain a groove image (step S35). By the processing of step S35, for example, a groove image shown in FIG. 49 can be obtained.

Next, the ground contact characteristic calculation unit 35 separates the captured image based on a predetermined threshold value, with high brightness areas as white and medium and low brightness areas as black, to obtain a rough ground contact area image (step S36). By the processing of step S36, for example, a rough ground contact area image as shown in FIG. 50 is obtained from the captured image shown in FIG. 45. This makes it possible to obtain a rough ground contact area image in which, for example, the blocks on the non-ground surface, the chamfers of the grooves and the markings are white, and the bottoms of the grooves and the ground contact blocks are black.

Furthermore, the ground contact characteristic calculation unit 35 subtracts the groove image (FIG. 49) from the rough ground contact area image (FIG. 50) to obtain an actual contact area image (hereinafter abbreviated as ACA) (step S37). By the processing of step S37, for example, the ACA shown in FIG. 51 can be obtained.

Here, "subtracting the groove image from the rough contact area image" refers to subtracting the luminance value of the groove from the luminance value of the rough contact area image for each pixel position. In this embodiment, the processing by the contact characteristic analysis unit 33 and the images acquired or created by the processing are all made of 256 gradations, and black is defined as luminance "255" and white is defined as luminance "0" except for the photographed image. However, if the value after subtraction is lower than "0", it is replaced with "0". In this example, after the subtraction processing, the contraction processing is performed in the order of one contraction processing, two expansion processing, one contraction processing, deletion of the occupied area of 100 pixels or less of the black object (=replacement with white pixels. The same applies below), two contraction processing, four expansion processing, and two contraction processing. After that, the occupied area of 200 pixels or less of the white object is deleted (=replacement with black pixels. The same applies below), and the occupied area of 200 pixels or less of the black object is deleted to obtain the ACA shown in FIG. 51.

The ACA shown in FIG. 51 is the total area of the blocks that are in contact with the road surface. Based on the ACA shown in FIG. 51, for example, a total ground contact area image (GCA) shown in FIG. 52 can be obtained.

The GCA is the total area enclosed by the outer ring line of the ACA when the grooves are filled. Figure 52 is a diagram showing an example of a GCA. For the ACA shown in Figure 51, the GCA in Figure 52 can be obtained by processing the ACA in the following order, for example, 5 expansion processes, 10 contraction processes, 12 expansion processes, 14 contraction processes, 17 expansion processes, 20 contraction processes, 109 expansion processes, and 99 contraction processes.

Figure 53 is an explanatory diagram of the expansion process. Figure 54 is an explanatory diagram of the contraction process. As shown in Figure 53, the expansion process is a process in which if there is even one black pixel around the target pixel, the target pixel is replaced with a black pixel. In other words, the expansion process is a process in which a white pixel is set as the center pixel, and if there is even one black pixel among the eight surrounding pixels (one pixel each of the top left, top, top right, right, bottom right, bottom, bottom left, and left closest to the center pixel), the center pixel is replaced with a black pixel. On the other hand, the contraction process is a process in which, for example, when the target pixel is a black pixel, if there is even one white pixel around the target pixel, the target pixel is replaced with a white pixel, as shown in Figure 54. In other words, the contraction process is a process in which a black pixel is set as the center pixel, and if there is even one white pixel among the eight surrounding pixels (one pixel each of the top left, top, top right, right, bottom right, bottom, bottom left, and left closest to the center pixel), the center 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 area, which is the groove-filled area, can be obtained. That is, an image of the groove distribution in the total ground contact area is obtained by subtracting the luminance value of the image showing the ACA in FIG. 51 from the luminance value of the image showing the GCA in FIG. 52 for each identical pixel position. FIG. 55 is a diagram showing an example of the groove distribution in the total ground contact area. Note that after the subtraction process, noise removal may be performed as necessary. For example, FIG. 55 is obtained by subtracting the luminance value of the image showing the ACA in FIG. 51 for each identical pixel position from the luminance value of the image showing the GCA in FIG. 52, then executing the contraction process three times, the expansion process three times, and deleting the area occupied by the black object of 1000 pixels or less in that order.

(groove distribution within total 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. The groove distribution in the total ground contact area shown in FIG. 55 is M(i,j). Here, i indicates the horizontal (tire circumferential) position of the image, and j indicates the vertical (tire width) position of the image. Since i and j in the groove distribution M(i,j) are in pixel units, they need to be converted into length units x and y, as described later. If the groove distribution in the total ground contact area when converted into length units is M(x,y), the groove depth of the tire ground contact surface can be expressed by the following formula (4).
Tire contact surface groove depth=(Z(x,y)−α)×M(x,y) (4)

In formula (4), x is the circumferential position of the tire, y is the widthwise position of the tire, Z(x, y) is the groove height distribution, α is the height of the road plate, and (Z(x, y) - α) is the groove depth. A position where M(x, y) is "1" indicates that a groove exists, and a position where M(x, y) is "0" indicates that something other than a groove exists.

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

Two cameras can also be used to measure the groove height distribution Z(x,y). In this case, the three-dimensional coordinates of the grooves are calculated for the images captured by the two cameras, for example, in the same manner as the above-mentioned sampling moiré method. That is, the three-dimensional shape of the grooves 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. These three-dimensional coordinates consist of the above-mentioned tire circumferential position x, tire width direction position y, and coordinate z in the direction perpendicular to the road plate 221. The directions of x, y, and z are perpendicular to each other. In addition, the directions of x and y are parallel to the upper or lower surface of the road plate. Therefore, the groove height distribution Z(x,y) can be obtained by defining z at the position (x,y) on the road plate as the groove height distribution Z(x,y).

By using equation (4), the groove depth of the tire contact surface can be quantitatively measured. This clarifies the direction of tire development, improving development efficiency.

(Pixel to length unit conversion)
Since i and j in the above-mentioned groove distribution M(i,j) are in pixel units, they need to be converted into length units. To convert to length units, the ratio of the length to the pixel is calculated and the values of i and j are multiplied by this ratio. For example, a square sheet or a grid sheet is provided on the upper surface 221U of the transparent road surface plate 221, and the ratio of the length to the pixel can be calculated by measuring the sheet. Here, a square sheet is defined as one having squares with relatively thin lines like graph paper, and a grid sheet is defined as one having thicker square lines like graph paper.

Figure 56 is a diagram showing the case where one camera is used. As shown in Figure 56, a grid sheet ST1 having grids with known vertical and horizontal lengths is provided on the upper surface 221U of a transparent road plate 221. One camera 15a is provided on the lower surface 221D side of the road plate 221. The camera 15a can determine the spatial resolution for each pixel of the image captured of the grid sheet ST1. Based on the spatial resolution, the above i and j can be converted into length units. Because one camera 15a is used, the camera used to create the total contact area described above can be used as is.

In FIG. 56, a grid sheet having grids with known vertical and horizontal lengths may be used instead of the grid sheet ST1. In that case, the image of the grid sheet photographed by the camera 15a is analyzed by the above-mentioned sampling moire method or the like. That is, the image of the grid sheet photographed is smoothed in the vertical direction (lengthwise direction) and the horizontal direction (horizontal direction), respectively, to obtain the phase distribution of the grid. The grid (grid) advances one period every time the phase value advances by 2π, i.e., 0, 2π, 4π, .... Therefore, the in-screen coordinates of the photographed image corresponding to the phase value of 0, 2π, 4π, ... (hereinafter, 2π addition) are examined, and the difference in the in-screen coordinates at the phase values adjacent by 2π is obtained. For example, the difference in the in-screen coordinates is obtained for 0 and 2π, 2π and 4π, etc. Since the vertical and horizontal lengths are known, that is, the length of one period of the grid along the vertical and horizontal directions is known, the value obtained by dividing the length of one period of the grid by the difference in the in-screen coordinates can be obtained as the ratio of the length to the pixel. Based on the ratio of the length, the above i and the above j are converted into length units. It is preferable to calculate the ratio of the length to the pixel for each pixel of the photographed image. When calculating the ratio of the length to the pixel for each pixel of the photographed image, adjacent phase values that are 2π apart are selected so that the phase value corresponding to the pixel is sandwiched between them, and the difference in the coordinates on the screen is calculated. For example, if the phase value corresponding to a pixel of the photographed image is 7π, the difference in the coordinates on the screen at phase values of 6π and 8π is calculated, and the length of one period of the lattice is divided by this difference to calculate the ratio of the length to the pixel. In addition, the coordinates on the screen of the photographed image that correspond to phase values x, x+2π, x+4π, ... (hereinafter, 2π is added in the same manner; x: any real number) that are adjacent by 2π may be examined to calculate the ratio of the length to the pixel.

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

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

Here, the phase distribution of the images captured by each of the cameras 15a, 15b, and 15c has a unique value for the position on the surface of the lattice sheet ST2, so this is used to perform the following processing. That is, the phase distribution is calculated by applying one of the above-mentioned sampling moiré method, Fourier transform method, and weighted phase analysis method to the images captured by each of the cameras 15a, 15b, and 15c. Next, based on the phase distribution of the images captured by the cameras 15b and 15c and the lines of sight of the cameras 15b and 15c, three-dimensional coordinates are calculated for each phase value. Meanwhile, a phase value corresponding to the pixel position (i, j) to be converted into a length unit is searched for from the phase distribution of the image captured by the camera 15a. When a phase value is found, the three-dimensional coordinates (x, y, z) corresponding to that phase value are quoted from the results of the cameras 15b and 15c described above. The pixel position (i, j) corresponding to that phase value is converted to x, y of the quoted three-dimensional coordinates. This operation is performed similarly for other phase values to convert pixel units into length units. If the phase value is not found, it is excluded from the conversion of length units. Note that the groove distribution M(i,j) is digital data, and has a dotted distribution. In order to make the distribution continuous, the groove distribution within the range of ±1/2 pixel in the horizontal direction of the image and ±1/2 pixel in the vertical direction of the image from the point (i,j) is uniformly set to the value M(i,j). After that, the eight positions (i-1/2, j-1/2), (i, j-1/2), (i+1/2, j-1/2), (i+1/2, j), (i+1/2, j+1/2), (i, j+1/2), (i-1/2, j+1/2), (i-1/2, j+1/2), (i-1/2, j) surrounding the pixel position (i,j) are also converted from pixel units to length units as described above. In other words, the numerical value in pixel units in parentheses is converted to length units.

(Distribution of road plate height)
Fig. 58 is a diagram for explaining 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 of the road surface plate 221 (the surface that comes into contact with the tire 60). The height α can be obtained by the following method.

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

The height α can also be measured 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, and a feature point (for example, a corner of the contact block of the tire 60) that is visible on the upper surface 221U of the road surface plate 221 is searched for, and the in-screen coordinates (X, Y) of each camera at the feature point are calculated. At this time, pattern matching is performed on the images captured by the two cameras. This calculates which in-screen coordinates of each camera a certain 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 camera calibration. Here, camera calibration is a measurement method for determining the line of sight of the two cameras. Therefore, a three-dimensional shape is calculated based on the in-screen coordinates (X, Y) of each camera and the line of sight of each camera, three-dimensional coordinates (x, y, z) are obtained, and the coordinate z of the three-dimensional coordinates in the direction perpendicular to the road surface plate 221 can be extracted as the height α.

Here, the actual height α of the road surface plate 221 varies depending on the location. Therefore, the following method can be used to obtain the distribution R(x, y) of the height α of the road surface plate 221 and correct the above formula (4).

Figure 59 is a diagram showing a configuration for determining the distribution R(x, y) of height α. As shown in Figure 59, a sheet ST is provided on the upper surface 221U side of the road surface plate 221. The sheet ST is, 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 distance meter 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 for each position of the road plate 221. Two cameras may be used as the measuring device SK, and the distance to the sheet ST may be measured for each position of the road plate 221 by image processing. For example, the grid sheet provided on the upper surface 221U side of the road plate 221 is photographed by two cameras, and the phase distribution of the grid is calculated by analyzing it using the sampling moiré 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 three-dimensional coordinates (x, y, z) are obtained. The three-dimensional coordinates consist of the tire circumferential position x, the tire width direction position y, and the coordinate z in the direction perpendicular to the road plate 221. The x, y, and z directions are perpendicular to each other. Therefore, by defining z at position (x, y) on the road plate as the distribution R(x, y) of height α, the distribution R(x, y) of height α can be obtained.

Since the distance to the sheet ST for each position on the road plate 221 is the distribution R(x, y) of height α, by replacing the height α in the above equation (4) with the distribution R(x, y) of height α, the following equation (5) is obtained.
Tire contact surface groove depth=(Z(x,y)−R(x,y))×M(x,y) (5)

By calculating the distribution R(x, y) of the height α of the road plate 221 and using equation (5), which is a corrected version of equation (4) above, the groove depth of the tire contact surface can be measured with high accuracy even if the height of the road plate varies depending on the location. For distribution R(x, y), a height value is stored. For M(x, y), a "1" or "0" is stored.

(Groove depth calculation unit)
Next, a description will be given of the processing performed by the groove depth calculation unit 442. Figures 60 and 61 are diagrams showing the processing performed by 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 tiny rectangular parallelepiped. Each rectangular parallelepiped 8 _ij shown in FIG. 60 has a height that follows the shape of the groove 62. Here, as shown in FIG. 61, the positions of each rectangular parallelepiped 8 _ij , i.e., the measurement points, are defined as x ₁₁ to x _NM (N and M are natural numbers) in terms of coordinates in the tire circumferential direction (x direction) and y ₁₁ to y _NM (N and M are natural numbers) in terms of coordinates in the tire width direction (y direction). Focusing on the position (x _N-1,2 , y _N-1,2 ) shown in FIG. 61, the length (tiny length) of the bottom surface of the rectangular parallelepiped at that position in the tire circumferential direction is dx _N-1,2 , and the length (tiny length) in the tire width direction is dy _N-1,2 .

As shown in Fig. 60, the length of the bottom surface of the rectangular parallelepiped _8ij in the tire circumferential direction is _dxij and the length in the tire width direction is _dyij . Therefore, the bottom area of the rectangular parallelepiped 8ij is _dxij x _dyij . In addition, the height of the rectangular parallelepiped _8ij is Z( _xij , _yij ) - R( _xij , _yij ). Therefore, the volume of the rectangular parallelepiped _8ij is _dxij x _dyij x [Z( _xij , _yij ) - R( _xij , _yij )] obtained by multiplying the bottom 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 calculates the volume of each rectangular parallelepiped _8ij along the shape of the groove 62, and calculates the sum of these volumes. This makes it possible to calculate the volume (capacity) of the groove 62. In other words, the groove volume of the tire contact surface can be calculated by the following formula (6).

Groove volume of tire contact surface = ΣΣ((Z(x _ij ,y _ij )−R(x _ij ,y _ij ))×dx _ij ×dy _ij ×M(x _ij ,y _ij ))
…(6)

It should be noted that when M(x _ij , y _ij ) is "1", it indicates that there is a groove, and when it is "0", it indicates that something other than a groove is present. It is preferable that dx _ij and dy _ij are 1 mm or less. If dx _ij and dy _ij exceed 1 mm, the error with respect to the correct groove volume becomes large (for example, exceeds 1%), which is not preferable. dx _ij and dy _ij may be 0.5 mm or less. This can further reduce the error. However, the processing time will be longer.

The inventors performed processing with dx _ij and dy _ij set to 1 mm, 0.5 mm, 0.1 mm, and 0.05 mm, resulting in errors of 1%, 0.25%, 0.01%, and 0.0025%.

As described above, the groove depth at each position in the groove is approximated by a tiny rectangular parallelepiped, and the sum of the volumes of the approximated rectangular parallelepipeds is calculated as the groove volume within the total contact area, making it possible to quantitatively measure the groove volume of the tire contact surface.

(Tire shape analysis method)
The tire shape analysis system described above realizes the following tire shape analysis method. That is, the tire shape analysis method includes the steps of measuring the three-dimensional shape of the grooves, which are recessed from the surface of the tire to be measured, creating a total contact area, which is an area where the grooves are filled in the contact area of the tire, and measuring the groove depth at the position of the groove within the total contact area based on the three-dimensional shape . This tire shape analysis method makes it possible to quantitatively measure the groove depth of the contact surface of the tire.

1 Tire shape analysis system 2 Tire testing machine 6 Motor 7 Motor control device 8 Rectangular parallelepiped 15AM Fixed rod 15a, 15b, 15c Camera 16 Illumination lamp 17 Trigger device 18 Retroreflective sheet 20 Tire contact patch analysis device 21 Input unit 22 Display unit 30 Processing device 31 Processing unit 32 Contact patch image acquisition unit 33 Contact characteristic analysis unit 34 Groove extraction unit 35 Contact characteristic calculation unit 40 Groove shape measurement unit 41 Analysis unit 42 Total contact area creation unit 44 Groove depth measurement unit 46 Groove volume calculation unit 50 Memory unit 60 Tire 61 Contact surfaces 161 to 168 Lamp 171 Detection unit 221 Road surface plate 221D Lower surface 221U Upper 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 Engraving extraction unit 411, image smoothing unit 412, brightness distribution acquisition unit 413, thinning processing unit 414, moire fringe creation unit 415, phase distribution calculation unit 416, three-dimensional shape calculation unit 419, inverse Fourier transform unit 441, groove distribution data creation unit 442, groove depth calculation unit SK, measuring device

Claims (10)

a groove shape measuring unit for measuring the three-dimensional shape of a groove, which is a recessed portion from the surface of a tire to be measured;
a total ground contact area creation unit that creates a total ground contact area, which is an area where grooves are filled in the ground contact area of the tire;
a groove depth measuring unit for measuring a groove depth at a position of the groove within the total ground contact area based on the three-dimensional shape ;
A tire shape analysis system having the above structure. The groove depth measuring unit is
a groove distribution data creating unit that creates groove distribution data indicating positions of grooves within the total ground contact area;
a groove depth calculation unit that calculates a groove depth at each position indicated by the groove distribution data;
The tire shape analysis system according to claim 1 . The groove depth calculation unit
The tire shape analysis system of claim 2, wherein the shape of a sheet provided on a main surface of a road surface plate simulating a road surface is measured, and the distance from the sheet to the bottom of the groove of the tire that is in contact with the road surface plate is defined as the groove depth. The tire shape analysis system according to claim 2 or 3, further comprising a groove volume calculation unit that approximates the groove depth at each position calculated by the groove depth calculation unit with a tiny rectangular parallelepiped and determines the total volume of the approximated rectangular parallelepiped as the groove volume within the total contact area. The groove shape measuring unit is
5. The tire shape analysis system according to claim 1, wherein a pattern formed in the grooves of the tire is photographed by at least two cameras, and the images photographed by the cameras are analyzed to measure the shape of the grooves. The groove shape measuring unit is
The tire shape analysis system according to claim 5 , wherein the captured image is subjected to a weighted phase analysis method to analyze the pattern, thereby measuring the shape of the grooves. The groove shape measuring unit is
Dividing the imaging range of the groove into two areas including a common area;
The tire shape analysis system according to claim 5 or 6, wherein the common area is one or more periods of the design pattern. The groove shape measuring unit is
8. The tire shape analysis system according to claim 5, wherein the movement of the two cameras and the photographing by the two cameras are repeated to photograph all of the grooves within the total contact area. If the midpoint between the two cameras is defined as (X, Y),
The moving range X of the two cameras in the tire circumferential direction is
- Maximum ground length/2≦X≦Maximum ground length/2
The moving range Y of the two cameras in the tire width direction is
- Maximum ground contact width/2≦Y≦Maximum ground contact width/2
9. The tire shape analysis system according to claim 5, wherein: A tire shape analysis method comprising the steps of: measuring the three-dimensional shape of a groove, which is a portion recessed from the surface of a tire being measured; creating a total contact area, which is an area where the grooves are filled in relative to the tire's contact area ; and measuring the groove depth at the position of the groove within the total contact area based on the three-dimensional shape .

Images