Method for calculating inclination angle of belt wire rod of tire

Abstract

To provide a method for determining a three-dimensional inclination angle to a tire circumferential direction, for a belt wire rod included in a tire.SOLUTION: A method for calculating an inclination angle of a belt wire rod of a tire includes: determining inclination angles of a plurality of belt wire rods 20 to a tire circumferential direction when being viewed from outside in a tire radial direction, on the basis of a belt image which is an image of the belt wire rods 20 when being viewed from the outside in the tire radial direction, as a provisional inclination angle; determining a belt gradient which is an inclination angle of a belt 10 to a tire axial direction, at each tire axial position, on the basis of a cross-sectional image in the tire axial direction; and calculating a three-dimensional inclination angle of the belt wire rods 20 to the tire circumferential direction, at each of the tire axial positions, from the provisional inclination angle and the belt gradient.SELECTED DRAWING: Figure 17

Description

Technical Field

[0001] The present invention relates to a method for calculating the inclination angle of a belt wire of a tire.

Background Art

[0002] A pneumatic tire (hereinafter referred to as "tire") is provided with a plurality of belts. Each belt is formed by covering a large number of belt wires arranged in parallel with rubber. The belt wires are inclined with respect to the tire circumferential direction.

[0003] By the way, since the inclination angle of the belt wire with respect to the tire circumferential direction affects the contact shape of the tire and thus affects the characteristics of the tire, it has been conventionally investigated. The conventional investigation method is a method in which an operator prepares a cut sample obtained by dividing the tire in the circumferential direction, peels off the rubber on the tread side of the cut sample to expose the belt wire, and measures the inclination angle of the belt wire when viewed from the outer side in the tire radial direction with a protractor.

[0004] Also, as disclosed in Patent Document 1, a method for measuring the inclination angle of a belt wire in a belt alone rather than a tire by electrical means has been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, the belt is greatly bent inward in the tire radial direction, particularly on both sides in the tire axial direction. Therefore, the belt wire is also greatly bent inward in the tire radial direction, particularly on both sides in the tire axial direction. However, in the conventional investigation method, only the inclination angle with respect to the tire circumferential direction when viewed from the outside in the tire radial direction has been measured, and the inclination inward in the tire radial direction has not been considered. Therefore, the three-dimensional inclination angle of the belt wire has not been known.

[0007] Also, with the method of Patent Document 1, the inclination angle of the belt wire used in the tire could not be measured.

[0008] Therefore, an object of the present invention is to provide a method for measuring the inclination angle of a belt wire included in a tire, which is a method for obtaining a three-dimensional inclination angle with respect to the tire circumferential direction.

Means for Solving the Problems

[0009] The present invention includes the following embodiments.

[0010] [1] In a method for calculating the inclination angle of a belt wire of a tire with respect to the tire circumferential direction, based on a belt image which is an image of a plurality of the belt wires when viewed from the outside in the tire radial direction, each inclination angle of the belt wires with respect to the tire circumferential direction when viewed from the outside in the tire radial direction is obtained as a provisional inclination angle, and based on a tire axial direction cross-sectional image, at each tire axial direction position, a belt gradient which is the inclination angle of the belt with respect to the tire axial direction is obtained, and from the provisional inclination angle and the belt gradient, at each tire axial direction position, a three-dimensional inclination angle of the belt wire with respect to the tire circumferential direction is calculated. A method for calculating the inclination angle of a belt wire of a tire.

[0011] [2] When the provisional inclination angle is α and the belt gradient is β at the same position in the tire axial direction, the three-dimensional inclination angle θ of the belt wire with respect to the tire circumferential direction is The method for calculating the inclination angle of the belt wire of the tire described in [1], calculated as JPEG2025084598000002.jpg13119.

[0012] [3] By calculating the interpolation of one of the data of the provisional inclination angle data at a plurality of tire axial positions and the belt gradient data at a plurality of tire axial positions, the one angle at the tire axial position of the other data is calculated, and from the calculated one angle and the other angle, the three-dimensional inclination angle of the belt wire with respect to the tire circumferential direction at the same tire axial position is calculated, the method for calculating the inclination angle of the belt wire of the tire according to [1] or [2].

Advantages of the Invention

[0013] According to the present embodiment, a three-dimensional inclination angle with respect to the tire circumferential direction can be obtained as the inclination angle of the belt wire.

Brief Description of the Drawings

[0014]

Figure 1

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Mode for Carrying Out the Invention

[0015] The embodiments will be described with reference to the drawings. Note that the embodiments described below are merely examples, and those appropriately modified without departing from the gist of the present invention are included in the scope of the present invention.

[0016] This embodiment is executed by a CT (Computed Tomography) device that uses X-rays to acquire data on the internal structure of a pneumatic tire (hereinafter referred to as "tire"), and a calculation device that processes the data acquired by the CT device and calculates the inclination angles of the belt and belt wires included in the tire.

[0017] A CT device is a device that uses X-rays to acquire three-dimensional data of the internal structure of a tire and generates a tire internal image, which is an image representing the inside of the tire, based on the three-dimensional data. In the tire internal image, the parts where X-rays are more easily absorbed appear brighter, and the parts where X-rays are more easily transmitted appear darker. Therefore, metal parts such as belt wires (also called cords), bead cores, and rims appear bright, and rubber parts (hereinafter referred to as "rubber parts") appear dark. According to the CT device, information on the internal structure of the tire can be obtained based on the tire internal image with light and dark, without cutting the tire.

[0018] The calculation device is realized by a computer including a processing device, a storage device, an input device, and a display device. As the storage device, RAM (Random Access Memory), ROM (Read Only Memory), HDD (Hard Disk Drive), etc. are provided. In the storage device, programs for executing this embodiment, tire internal images acquired by the CT device, etc. are stored. The processing device is composed of a CPU (Central Processing Unit), etc. The processing device reads and executes the programs stored in the ROM, etc. on the RAM to execute the method of this embodiment. The input device is, for example, a mouse and a keyboard, and receives inputs from the user of the calculation device (hereinafter referred to as "user"). The display device is, for example, a display, and displays an input screen for inputting by the input device, a tire internal image, various data, calculation results, etc.

[0019] Also, the tire in this embodiment is a tire having two belts. The two belts are a first belt that is wide and located inside the tire in the radial direction and a second belt that is narrow and located outside the tire in the radial direction.

[0020] Each belt is formed by arranging a number of belt wires in parallel, covering these belt wires with rubber, and shaping them into a single sheet. The spacing between the belt wires is the same for the first belt and the second belt. Also, each belt wire is inclined with respect to the tire circumferential direction. Further, each belt wire is formed by twisting together a plurality of thinner metal wires to form a single wire. Such a belt wire is also referred to as a cord.

[0021] In this embodiment, first, the user takes a picture of the tire with a CT device to obtain three-dimensional data of the internal structure of the tire. Here, the tire is photographed in an inflated state, that is, in a state where it is mounted on a rim and internal pressure is applied. Next, the user specifies the portion to be imaged in the three-dimensional data of the tire and obtains an internal image of that portion of the tire.

[0022] In this embodiment, as the internal image of the tire, a belt image and a tire axial direction cross-sectional image are obtained. The belt image is an image of one of the plurality of belts included in the tire, projected from the outside in the tire radial direction. The actual belt is in the shape of a curved surface that bends particularly greatly on both sides in the tire axial direction, but the belt image is a planar image. The belt image is a rectangular image that includes both axial ends of the belt in the tire axial direction and is short in the tire circumferential direction. Also, the tire axial direction cross-sectional image is an image when the plane passing through the perpendicular to the tire outer peripheral surface and the tire rotation axis is taken as the cross-section.

[0023] Coordinates are set for the belt image and the tire axial direction cross-sectional image with an arbitrary reference point set to 0 (for example, the axial center position of the tire is set to 0 in the left-right direction coordinates of the image). Since the relationship (calibration value) between one pixel of the image and the length in the actual tire is known in advance, the coordinates can be expressed in mm. When the calibration values are different for the belt image and the tire axial direction cross-sectional image, the coordinates (mm) in each of the belt image and the tire axial direction cross-sectional image are calculated using their respective calibration values.

[0024] FIG. 1 is a belt image showing the first belt, FIG. 2 is a belt image showing the second belt, and FIG. 3 is an image obtained by cutting out the portion of the tire axial direction cross-sectional image where the belt is shown. As shown in FIGS. 1 and 2, in each belt image, a number of belt wires are shown as bright lines extending obliquely with respect to the tire circumferential direction. Further, as shown in FIG. 3, in the tire axial direction cross-sectional image, the cross-sections of the respective belt wires are shown as bright points, the rubber portions such as the tread rubber and the sidewall rubber are shown relatively dark, and the air portion is almost black.

[0025] Next, the user reads the tire internal image into the calculation device. The calculation device performs the processing shown in FIG. 4 on the read tire internal image. Specifically, based on the belt image, the calculation device calculates the inclination angle of the belt wire when viewed from the outside in the tire radial direction (this inclination angle at this time is referred to as the "temporary inclination angle") (S1), calculates the belt gradient with respect to the tire axial direction based on the tire axial direction cross-sectional image (S2), and calculates the three-dimensional inclination angle with respect to the tire circumferential direction based on the temporary inclination angle and the belt gradient (S3).

[0026] First, the calculation of the inclination angle of the belt wire (temporary inclination angle) when viewed from the outside in the tire radial direction (S1 in FIG. 4) will be described. Since the same processing is performed on the two belt images, the first belt will be described here.

[0027] As can be seen from FIG. 5, which is an enlarged view of a part of the belt image, the belt wires shown in the belt image do not have a constant thickness or brightness, but have some thick parts (indicated by reference numeral 1 in FIG. 5) and some thin parts (indicated by reference numeral 2 in FIG. 5), or the brightness is slightly darker in the slightly thin parts. This is because the twist of the belt wire formed by twisting thin wires changes depending on the location, resulting in dense and sparse parts of the thin wires. Due to such changes in thickness and brightness in each belt wire, the belt image appears to have a wavy unevenness. Also, the belt wires shown in the belt image appear to be straight, but are actually curved.

[0028] First, the belt image read into the calculation device is converted into a grayscale image (S1-1 in FIG. 6). By this conversion, the belt image becomes an image with 256 gradations from 0 to 255, where black is 0 and white is 255. In the following description, the numerical value representing the gradation is referred to as luminance. The larger the luminance, the closer it is to white, and the smaller the luminance, the closer it is to black. If the belt image is substantially a 256-gradation grayscale at the time of being read into the calculation device, the conversion to grayscale may be omitted.

[0029] Next, from the belt image, the portion where the belt wire is not shown is cut off, and only the portion where the belt wire is shown is cut out (S1-2 in FIG. 6). In the following description, when simply referring to the belt image, it indicates the image after the portion where the belt wire is shown is cut out. In the belt image, one end to the other end of the 1st belt in the tire axis direction is shown. The left-right direction of the belt image corresponds to the tire axis direction, and the up-down direction of the belt image corresponds to the tire circumferential direction. The belt image is shorter in the up-down direction than in the left-right direction.

[0030] The length of the belt image in the left-right direction corresponds to the length of the 1st belt in the tire axis direction when viewed from the outside in the tire diameter direction. Also, the length of the belt image in the up-down direction is preferably 58 pixels or more. The reason why 58 pixels or more is preferred will be described later.

[0031] As shown in FIG. 7, there is unevenness in luminance in the belt image. Specifically, unevenness occurs such that it is dark at the center in the left-right direction of the image and bright on both sides in the left-right direction of the image.

[0032] Therefore, luminance correction of the belt image is performed so that the average luminance at each location in the left-right direction of the belt image becomes the same (S1-3 in FIG. 6). Specifically, first, the average value (average luminance) of the luminance of all pixels arranged in the up-down direction at each position in the left-right direction of the image is calculated. The average luminance is distributed such that it is small at the center in the left-right direction of the image and large on both sides in the left-right direction of the image, as indicated by reference numeral 3 in FIG. 8.

[0033] Next, the luminance of each pixel is multiplied by a value obtained by dividing the target luminance by the average luminance at the horizontal position of the image to which the pixel belongs. Here, the target luminance is the desired luminance as the average value of the luminances of all pixels in the belt image after luminance correction, and is, for example, about 170.

[0034] Expressed by a mathematical formula, the luminance B'ij after luminance correction of the pixel at the i-th position in the horizontal direction of the image and the j-th position in the vertical direction of the image is obtained by the following formula using the luminance Bij before luminance correction of the pixel, the target luminance BG, and the average luminance BAi at the horizontal position of the image to which the pixel belongs.

[0035]

Number

[0036] By this luminance correction, the unevenness of luminance in the horizontal direction of the image is eliminated. The distribution of the average luminance after luminance correction is shown by reference numeral 4 in FIG. 8.

[0037] Next, binarization processing of the belt image after luminance correction is executed (S1-4 in FIG. 6). By the binarization processing, pixels with luminance greater than the threshold value are converted into white pixels. Also, pixels with luminance less than the threshold value are converted into black pixels. The threshold value for the binarization processing is determined as appropriate and is, for example, about 190. By the binarization processing, a binarized image in which the original belt wire material with high luminance becomes white and the others become black is obtained. The binarized image of the belt image is referred to as a binarized belt image. In the binarized belt image, each belt wire material is a set of a plurality of white pixels.

[0038] As can be seen from FIG. 9, the binarized belt image contains a plurality of noises. As the noises, there are white linear noises extending in the horizontal direction of the image (this noise is pointed by an arrow in the figure) and small white dot-like noises. Therefore, removal of these noises is executed from the binarized belt image (S1-5 in FIG. 6).

[0039] As can be seen from FIG. 10, which is an enlarged view of a part of the binarized belt image, in the part of the belt wire, a large number of white pixels are continuous in the vertical direction. On the other hand, in the part of the white linear noise extending in the left-right direction of the image (the part pointed by the arrow in FIG. 10), the number of consecutive white pixels in the vertical direction is less than that in the part of the belt wire. This can also be confirmed by counting the number of consecutive white pixels on the straight line L-L in FIG. 10. Therefore, a process is executed to convert the part where the number of consecutive white pixels in the vertical direction of the image is less than the number of pixels in the vertical direction of the image of one belt wire from white pixels to black pixels.

[0040] Specifically, a predetermined number is determined such that the part where the number of consecutive white pixels in the vertical direction of the image is more than the predetermined number becomes the part of the belt wire, and the part where the number of consecutive white pixels in the vertical direction of the image is less than or equal to the predetermined number becomes the white linear noise. The predetermined number is set as the "linear noise removal reference number". The linear noise removal reference number is appropriately set according to the thickness of the belt wire and the linear noise, and is, for example, 3 pixels.

[0041] Then, the part where the number of consecutive white pixels in the vertical direction of the image is less than or equal to the linear noise removal reference number is converted from white pixels to black pixels. By repeating this conversion process from one end to the other end in the left-right direction of the image, the white linear noise extending in the left-right direction of the entire binarized belt image is removed.

[0042] However, in the vicinity of the upper and lower sides of the binarized belt image, even for the belt wire, the number of consecutive white pixels is less than or equal to the linear noise removal reference number. Therefore, the upper and lower sides of the binarized belt image within the range of the linear noise removal reference number in the vertical direction of the image are excluded from the range of this noise removal process.

[0043] Also, for small white dot-like noises, the number of aggregated white pixels is less compared to the part of the belt wire material. Therefore, a process is executed to convert the part where the number of aggregated white pixels is less than the number of pixels representing one belt wire material from white pixels to black pixels. Here, aggregation means being in contact with each other.

[0044] Specifically, a predetermined number is determined such that the part where the number of aggregated white pixels is more than the predetermined number becomes the part of the belt wire material, and the part where the number of aggregated white pixels is less than or equal to the predetermined number becomes small white dot-like noises. This predetermined number is set as the "dot-like noise removal reference number". The dot-like noise removal reference number is appropriately set according to the size of the belt wire material and dot-like noises, and is, for example, 10 pixels.

[0045] Then, the part where the number of aggregated white pixels is less than or equal to the dot-like noise removal reference number is converted from white pixels to black pixels. By executing this conversion process on the entire binarized belt image, small white dot-like noises are removed from the entire binarized belt image.

[0046] Furthermore, as one of the noise removal processes, dilation and erosion processing is executed. The execution order of the dilation process and the erosion process depends on the type of noise to be removed. For example, when trying to remove a chip occurring in the belt wire material, one erosion process is executed after one dilation process.

[0047] Here, three types of noise removals are executed, but the execution order is, for example, the removal of white linear noises extending in the left-right direction of the image, the removal of small white dot-like noises, and the dilation and erosion processing, in this order.

[0048] Next, labeling is performed to assign numbers to each belt wire in the binarized belt image after noise removal (S1-6 in FIG. 6). The labeling is performed by assigning different numbers to each continuous part of the white pixels in the binarized belt image. Such labeling can be performed using the bwlabel function, which is a function of MATLAB (registered trademark), a numerical analysis software by MathWorks. By labeling, each belt wire can be managed by a number.

[0049] By the way, since the belt wire has a thickness corresponding to a plurality of pixels, each belt wire has a thickness of a plurality of pixels in the left-right direction of the image at the upper and lower sides of the binarized belt image. Therefore, next, the center coordinates in the left-right direction of the image of each belt wire (that is, the part of the white pixels) at the positions of the upper and lower sides of the binarized belt image are calculated (S1-7 in FIG. 6). This calculation can be performed using the regionprops function of MATLAB. The center points in the left-right direction of the image of the belt wire at the positions of the upper and lower sides of the binarized belt image are used as the end points of the belt wire.

[0050] Next, the inclination angle of each belt wire in the binarized belt image with respect to the tire circumferential direction is calculated (S1-8 in FIG. 6). The inclination angle is calculated as the inclination angle of the straight line connecting the end points on both sides of the extension direction of the belt wire with respect to the up-down direction of the image (the up-down direction of the image coincides with the tire circumferential direction).

[0051] Specifically, first, the upper and lower two endpoints belonging to the same belt wire material are identified. Here, the fact that the upper and lower two endpoints belong to the same belt wire material is recognized by the fact that those endpoints belong to the belt wire material with the same number assigned in the above labeling. Next, from the coordinates of the two endpoints, the interval in the left - right direction of the image and the interval in the up - down direction of the image between the two endpoints are calculated, and the inclination angle is calculated by using the arctangent function with those intervals. In this way, since the inclination angle of the straight line connecting the endpoints on both sides of the extending direction of the belt wire material is calculated, an inclination angle that is not affected by the influence of the bend or the change in thickness of the belt wire material between the upper side and the lower side of the binarized belt image is calculated. By this specific method, the inclination angles of all the belt wire materials in the binarized belt image are calculated.

[0052] The calculated inclination angle of each belt wire material is treated as the inclination angle of each belt wire material at the position of the lower side of the binarized belt image.

[0053] By the way, when the binarized belt image is short in the up - down direction of the image, even if the position of the endpoint of the belt wire material changes by 1 pixel in the left - right direction of the image, the inclination angle of the belt wire material with respect to the up - down direction of the image (tire circumferential direction) changes greatly. Therefore, the number of pixels in the up - down direction of the binarized belt image and the belt image on which it is based is determined so that even if the position of the endpoint changes by 1 pixel in the left - right direction of the image, the influence on the inclination angle of the belt wire material with respect to the up - down direction of the image is less than 1°. Such a number of pixels P is obtained as a value that satisfies the following formula.

[0054]

Equation

[0055] The minimum value of the number of pixels P that satisfies this formula is 58. Therefore, the length of the belt image in the up - down direction is preferably 58 pixels or more.

[0056] In this way, the inclination angles of the belt wire materials at respective positions in the left - right direction of the image (tire axis direction) are obtained. However, in order to improve the accuracy, at each position in the left - right direction of the image, the average of the inclination angles of a plurality of belt wire materials at the same position in the left - right direction of the image is calculated (S1 - 9 in FIG. 6). Then, the average value of the inclination angles of the plurality of belt wire materials at the same position in the left - right direction of the image is taken as the inclination angle of the belt wire material at that position in the left - right direction of the image.

[0057] For example, in FIG. 9, since there are 7 belt wire materials at the position of the vertically long frame F, the average of the inclination angles of these 7 belt wire materials is calculated. And that average value is taken as the inclination angle of the belt wire material at the position of the vertically long frame F.

[0058] Note that in the regions on both sides in the left - right direction of the binarized belt image (the regions indicated by reference numeral 5 in FIG. 9), the belt wire material reaches only one of the upper side and the lower side of the binarized belt image. For such a belt wire material, the inclination angle may not be calculated, or it may be calculated. When it is calculated, the end point on the upper side or the lower side in the binarized belt image and the end point on the left side or the right side in the binarized belt image are specified, and it is calculated as the inclination angle with respect to the up - down direction of the image of the straight line connecting these two end points belonging to the same belt. Note that the end point on the left side or the right side in the binarized belt image is the center point in the up - down direction of the belt wire material at the position of the left side or the right side of the binarized belt image.

[0059] When the inclination angle is not calculated for the belt wire materials that reach only one of the upper side and the lower side of the image on both sides in the left - right direction of the binarized belt image, based on a smaller number of belt wire materials than the center in the left - right direction on both sides in the left - right direction, the average value of the inclination angles of the belt wire materials at the same position in the left - right direction of the image is calculated. Also, when the inclination angle is calculated for the belt wire materials that reach only one of the upper side and the lower side of the image, including those belt wire materials, the average value of the inclination angles of the belt wire materials at the same position in the left - right direction of the image is calculated. And such an average value is taken as the inclination angle of the belt wire material at that position in the left - right direction of the image.

[0060] In this way, the inclination angle of the belt wire with respect to the tire circumferential direction (image up and down direction) at each position in the tire axial direction (image left and right direction) is calculated. The distribution of the calculated inclination angle with respect to the image left and right direction is, for example, as shown in FIG. 11.

[0061] For the second belt as well, the inclination angle of the belt wire when viewed from the outside in the tire radial direction is calculated in the same manner as for the first belt.

[0062] In this way, the inclination angle of the belt wire with respect to the tire circumferential direction, which is calculated based on the belt image when the belt is viewed from the outside in the tire radial direction, is defined as the provisional inclination angle.

[0063] Next, the calculation of the belt gradient with respect to the tire axial direction based on the tire axial direction cross-sectional image (S2 in FIG. 4) will be described.

[0064] First, the tire axial direction cross-sectional image read into the calculation device is converted into a grayscale image (S2-1 in FIG. 12). By the conversion, the tire axial direction cross-sectional image becomes an image with 256 gradations from 0 to 255, where black is 0 and white is 255. Note that when the tire axial direction cross-sectional image is substantially in 256-gradation grayscale at the time of being read into the calculation device, the conversion to grayscale may be omitted.

[0065] Note that in the tire axial direction cross-sectional image, the lower side is the inside in the tire radial direction and the upper side is the outside in the tire radial direction. Therefore, the second belt is shown above the first belt. The first belt extends to both sides in the tire axial direction more than the second belt. Also, the cords of the carcass ply are made of organic fibers and are not shown in the tire axial direction cross-sectional image.

[0066] Next, from the tire axial direction cross-sectional image, the portion on the outer end side rather than the center of the height from the inner end to the outer end in the tire radial direction is cut out. Thereby, unnecessary portions such as the bead core are cut off, and the portion where the entire belt is shown is cut out (S2-2 in FIG. 12). The cut-out image is the image in FIG. 3.

[0067] In the following description, an image in which unnecessary parts such as bead cores are cut off and the part where the entire belt appears is cut out is defined as a tire axial direction cross-sectional image. The tire axial direction cross-sectional image includes the first belt and the second belt from one end to the other end in the tire axial direction. The left-right direction of the tire axial direction cross-sectional image corresponds to the tire axial direction, and the up-down direction of the tire axial direction cross-sectional image corresponds to the tire diameter direction. The tire axial direction cross-sectional image is shorter in the up-down direction than in the left-right direction.

[0068] By the way, the tire axial direction cross-sectional image has unevenness in which the luminance is not constant in the left-right direction of the image, being dark in a part of the left-right direction of the image and bright in other parts. Therefore, luminance correction for eliminating such unevenness is performed (S2-3 in FIG. 12). However, in the case of the tire axial direction cross-sectional image, the average luminance calculated from all the pixels arranged in the up-down direction of the image is small at the location where the main groove is present (therefore, at the location where there are many pixels with low luminance), and the average luminance calculated from all the pixels arranged in the up-down direction of the image is large at the location where there is no main groove. Therefore, the luminance correction performed in S1-3 for the belt image is not optimal as a method of luminance correction for the tire axial direction cross-sectional image.

[0069] Therefore, the following luminance correction is performed on the tire axial direction cross-sectional image. First, for pixels with a luminance of a predetermined value (for example, 50) or less, the luminance is converted to 0. This is a process for setting the luminance of the air part around the tire to 0. By this process, the tire axial direction cross-sectional image becomes an image in which only the tire part made of belt wire and rubber has a luminance greater than 0.

[0070] Next, a calculation range is set that has a length greater than the interval between the two belt wires (the length of the portion without belt wires between the two belt wires) in the left - right direction of the image, and has a range that includes at least from the outer surface to the inner surface of the tire (for example, the range from the upper side to the lower side of the tire axial - direction cross - sectional image) in the up - down direction of the image. Here, the reason why the length of the calculation range in the left - right direction of the image is greater than the interval between the two belt wires is to ensure that pixels of the belt wire with high luminance always fall within the calculation range.

[0071] Next, the calculation range moves in the left - right direction of the image, and the maximum luminance and the minimum luminance in each calculation range are detected. Here, the amount of movement of the calculation range in the left - right direction of the image once is the same as the length of the calculation range in the left - right direction of the image, so that all pixels are included in the calculation range once. Also, the maximum luminance is the luminance of the pixels of the belt wire, and the minimum luminance is the luminance of the pixels of the rubber part. Pixels with luminance of 0 are not treated as pixels of the minimum luminance.

[0072] For each calculation range, a luminance correction value C is obtained from the maximum luminance Bmax and the minimum luminance Bmin in that calculation range according to the following formula.

[0073]

Equation

[0074] Next, the luminance B'ij after luminance correction of the pixel at the i - th position in the left - right direction of the image and the j - th position in the up - down direction of the image is obtained from the luminance Bij before luminance correction of that pixel, the minimum luminance Bmin of the calculation range to which that pixel belongs, and the luminance correction value C of the calculation range to which that pixel belongs according to the following formula.

[0075]

Equation

[0076] As can be seen from this formula, the luminance of each pixel after luminance correction is calculated based on the difference between the maximum luminance and the minimum luminance in the calculation range to which the pixel belongs, and as the ratio of the difference between the luminance of the pixel with respect to this reference and the minimum luminance of the calculation range to which the pixel belongs. Therefore, in the tire axial cross-sectional image after luminance correction based on this formula, not only is the unevenness of luminance in the left-right direction of the image eliminated, but also the contrast increases and the luminance of the belt wire becomes very large. It can also be seen from FIG. 13, which is the tire axial cross-sectional image after luminance correction, that the unevenness of luminance has been eliminated and the contrast has increased compared to before the luminance correction.

[0077] By the way, the difference between the maximum luminance and the minimum luminance becomes smaller in the left-right direction of the image, i.e., in the place where there is no belt wire, that is, in the place where there are no pixels with high luminance. Therefore, as can be seen from the formula [Equation 3], and as shown in FIG. 14, which is the distribution diagram of the luminance correction value in the left-right direction of the image, in the place where there is no belt wire (the place surrounded by the broken-line circle in the figure), the luminance correction value becomes large.

[0078] As a result, as can be seen from FIG. 13, in the place where there is no belt wire in the left-right direction of the image (the place surrounded by the broken-line ellipse in the figure), pixels with high luminance are generated even though it is not a belt wire. Such pixels with high luminance even though they are not belt wires are scattered on both the left and right sides of the tire axial cross-sectional image and are removed as noise later.

[0079] Next, binarization processing of the belt image after luminance correction is executed (S2-4 in FIG. 12). By the binarization processing, pixels with luminance greater than the threshold value are converted into white pixels. Also, pixels with luminance less than the threshold value are converted into black pixels. The threshold value for the binarization processing is determined as appropriate and is, for example, about 120. By the binarization processing, a binarized image is obtained in which the original belt wire with high luminance is white and the rest is black. The binarized image of the tire axial cross-sectional image is referred to as a binarized cross-sectional image. In the binarized cross-sectional image, each belt wire is a set of a plurality of white pixels.

[0080] Next, noise removal from the binarized cross-sectional image is performed (S2-5 in FIG. 12).

[0081] First, on both the left and right sides of the tire axial direction cross-sectional image before binarization, as described above, due to the formula [Equation 3], there are pixels with high luminance even though they are not belt wires. These pixels remain as white pixels in the binarized cross-sectional image. Therefore, from the binarized cross-sectional image, the belt portion and some portions above and below it are cut out. Thereby, the left and right side portions with pixels having high luminance even though they are not belt wires are removed. Such cutting is performed manually by the user or by automatic detection.

[0082] Also, the binarized cross-sectional image contains small white dot-like noises. The small white dot-like noises have fewer aggregated white pixels compared to the belt wire portion. Therefore, a process is executed to convert portions where the number of aggregated white pixels is less than the number of pixels representing one belt wire from white pixels to black pixels. Here, aggregation means being in contact with each other.

[0083] Specifically, a predetermined number is determined such that a portion where the number of aggregated white pixels is more than the predetermined number becomes the belt wire portion, and a portion where the number of aggregated white pixels is less than or equal to the predetermined number becomes small white dot-like noise. This predetermined number is set as the "dot-like noise removal reference number". The dot-like noise removal reference number is appropriately set according to the size of the belt wire and dot-like noise, and is, for example, 3 pixels. Then, portions where the number of aggregated white pixels is less than or equal to the dot-like noise removal reference number are converted from white pixels to black pixels. By performing this conversion process on the entire binarized cross-sectional image, small white dot-like noises are removed from the entire binarized cross-sectional image.

[0084] Next, labeling is performed to assign numbers to each belt wire in the binarized cross-sectional image after noise removal (S2-6 in FIG. 12). The labeling is performed by assigning different numbers to each continuous part of white pixels in the binarized cross-sectional image. Such labeling can be performed using the bwlabel function in MATLAB. By labeling, each belt wire can be managed by a number.

[0085] Next, the separation of the first belt and the second belt is performed (S2-7 in FIG. 12). For this purpose, first, the centroid of all belt wires appearing in the binarized cross-sectional image is calculated. The regionprops function in MATLAB can be used to calculate the centroid.

[0086] Also, a predetermined range in the left-right direction of the image is set as the search range. This search range is approximately the same as the interval in the left-right direction of the image between two adjacent belt wires in one belt. As a specific method for setting this search range, first, the coordinate data of the centroids of all belt wires appearing in the binarized cross-sectional image are arranged in the order from the left to the right of the image. Next, the difference between the coordinates of two adjacent centroids in the left-right direction of the image (the difference in the left-right direction coordinates of the image) is calculated. Then, the largest of the calculated differences is set as the search range. The search range set by this method is usually the interval between two adjacent belt wires in the part of the first belt that does not overlap vertically with the second belt on both sides in the left-right direction of the image.

[0087] Next, belt wires are sequentially selected from one side to the other side in the left-right direction in the binarized cross-sectional image, and an association process is executed each time a selection is made. In the association process, the presence or absence of the centroid of other belt wires within the search range including the centroid of the selected belt wire (itself) is searched. If there are no other belt wires, itself is associated with the first belt. On the other hand, if there are centroids of multiple belt wires including itself within the search range, the belt wire with the centroid at the bottommost side (i.e., the inner side in the tire diameter direction) is associated with the first belt.

[0088] Such a linking process is executed for all the belt wire materials from one belt wire material in the left - right direction of the image to the other belt wire material. Then, all the belt wire materials that were not linked to the first belt are linked to the second belt. The belt wire materials linked to the first belt are treated as constituting the first belt, and the belt wire materials linked to the second belt are treated as constituting the second belt.

[0089] Next, the belt gradient at the position of each belt wire material is calculated as an angle (S2 - 8 in FIG. 12). The method for calculating the belt gradient will be described taking the first belt as an example.

[0090] First, as shown in FIG. 15, from the coordinates of the centroids of two adjacent belt wire materials, the length l in the left - right direction (tire axis direction) of the image and the length h in the up - down direction (tire circumferential direction) of the image between these two centroids are calculated. The lengths l and h are calculated, for example, in terms of the number of pixels.

[0091] Here, the length h in the up - down direction of the image is a value with positive and negative signs. Specifically, taking one of the belt wire materials in the previously determined left - right direction as a reference, if the other belt wire material in the left - right direction is in one of the up - down directions, the length h is positive, and if the other belt wire material in the left - right direction is in the other up - down direction, the length h is negative.

[0092] Next, by the following formula, the belt gradient β (°) at the position of the reference belt wire material (strictly speaking, the centroid position of the belt wire material) is calculated as an angle.

[0093]

Equation

[0094] By this formula, the belt gradients at the positions of all the belt wire materials belonging to the first belt are calculated.

[0095] However, due to the influence of the resolution of the binarized cross-sectional image, the calculated centroid position of the belt wire may not be accurate. For this reason, among others, the change in the image left-right direction position (tire axis direction position) of the calculated belt gradient may not be smooth. In that case, smoothing processing is executed (S2-9 in FIG. 12). The smoothing processing is a process of setting the average value of the belt gradients at a plurality of positions arranged in the left-right direction of the image as the belt gradient at any one of the plurality of positions.

[0096] FIG. 16 shows the distribution of the belt gradient before and after smoothing superimposed. The zigzag line depicts the distribution of the belt gradient before smoothing, and the smooth line depicts the distribution of the belt gradient after smoothing.

[0097] The belt gradient at each position in the left-right direction (tire axis direction) of the image of the second belt is also calculated in the same way as for the first belt.

[0098] Next, the calculation of the three-dimensional inclination angle of the belt wire with respect to the tire circumferential direction based on the provisional inclination angle calculated based on the belt image and the belt gradient calculated based on the tire axis direction cross-sectional image (S3 in FIG. 4) will be described.

[0099] The belt image and the tire axis direction cross-sectional image are obtained in such a form that the tire circumferential direction position at which the provisional inclination angle of the belt wire is calculated (i.e., the position of the lower side of the belt image) and the tire circumferential direction position at which the belt gradient is calculated (i.e., the position of the tire axis direction cross-sectional image) coincide, and the tire axis direction coordinates (tire axis direction position) of each belt wire at the tire circumferential direction position at which the provisional inclination angle is calculated (i.e., the position of the lower side of the belt image) and the tire axis direction coordinates (tire axis direction position) of each belt wire at the tire circumferential direction position at which the belt gradient is calculated (i.e., the position of the tire axis direction cross-sectional image) coincide. However, there may be cases where these do not coincide.

[0100] Therefore, the tire axial coordinates of each belt wire shown in the belt image are aligned with the tire axial coordinates of each belt wire shown in the tire axial cross-sectional image, and a process of calculating the belt gradient at the aligned tire axial coordinates is executed. In this paragraph and the next paragraph, the coordinates are strictly the coordinates of the center of gravity of the belt wire. Also, the same scale of tire axial coordinates with a common reference point (for example, the axial center position of the tire) set to 0 are set for the belt image and the tire axial cross-sectional image.

[0101] For this process, the tire axial coordinates of two adjacent belt wires in the tire axial cross-sectional image and the data of the belt gradients at these two coordinates are used. Based on this data, the belt gradient at any tire axial coordinate between two adjacent belt wires shown in the tire axial cross-sectional image can be calculated by interpolation (for example, linear interpolation). Therefore, the belt gradient can be calculated at the tire axial coordinates of the belt wires shown in the belt image.

[0102] By performing such calculations for at least all belt wires where the tire axial coordinates of the belt wires do not match between the belt image and the tire axial cross-sectional image, the belt gradient is obtained for the tire axial coordinates of all belt wires shown in the belt image. This process can be performed using the resample function in MATLAB. By this process, both the provisional inclination angle and the belt gradient are obtained for the tire axial coordinates of all belt wires shown in the belt image.

[0103] Next, at each tire axial position, the three-dimensional inclination angle of the belt wire with respect to the tire circumferential direction is calculated from the provisional inclination angle and the belt gradient. The calculation method will be described using FIGS. 17 to 20.

[0104] FIG. 17 is a perspective view of the belt 10, FIG. 18 is a view of the same belt 10 seen from the outside in the tire radial direction, FIG. 19 is a view of the same belt 10 in the tire axial cross-section, and FIG. 20 is a view for explaining the length and angle for obtaining the inclination angle. Only a part of the belt 10 is drawn in these figures, but actually the belt 10 extends around the tire in the circumferential direction. As can be seen from these figures, the belt wire 20 included in the belt 10 is inclined not only with respect to the tire circumferential direction when seen from the outside in the tire radial direction, but also along the belt gradient, so it is three-dimensionally inclined with respect to the tire circumferential direction.

[0105] First, looking at FIG. 18, between the inclination angle α of the belt wire 20 with respect to the tire circumferential direction (this inclination angle α is a provisional inclination angle), the length a in the tire circumferential direction of the belt wire 20 (the length between P and Q), and the length b1 in the tire axial direction of the belt wire 20 (the length between Q and R) when seen from the outside in the tire radial direction respectively, the following equation holds. Note that the lengths a and b1 are the lengths within a certain range in the tire circumferential direction and within the range shown in FIGS. 17 to 20.

[0106]

Equation

[0107] Therefore, the following equation holds.

[0108]

Equation

[0109] Next, looking at FIG. 19, between the inclination angle β of the belt wire 20 with respect to the tire axial direction (this inclination angle β is the belt gradient), the length b1 in the tire axial direction of the belt wire 20, and the length b2 in the direction of the inclination angle β of the belt wire 20 (the length between Q and S) when seen in the tire axial cross-section respectively, the following equation holds. Note that the length b2 is the length within a certain range in the tire circumferential direction and within the range shown in FIGS. 17 to 20.

[0110]

Equation

[0111] Next, referring to FIG. 20, it can be seen that the following equation holds for the three-dimensional inclination angle θ of the belt material 20 with respect to the tire axis direction.

[0112]

Equation

[0113] Therefore, the three-dimensional inclination angle θ of the belt material 20 with respect to the tire axis direction is obtained by the following equation.

[0114]

Equation

[0115] For each belt material, the three-dimensional inclination angle with respect to the tire circumferential direction is obtained by this equation. Also, for each of the first belt and the second belt, the three-dimensional inclination angles of the respective belt materials with respect to the tire circumferential direction are obtained.

[0116] The obtained three-dimensional inclination angles are displayed on the display device as a graph as shown in FIG. 21. Although only the inclination angle of the first belt is shown as a representative in FIG. 21, the inclination angle of the second belt is actually also displayed.

[0117] In FIG. 21, the solid lines are the three-dimensional inclination angles of the belt materials with respect to the tire circumferential direction at the respective tire axis direction coordinates. Also, the dashed lines are the provisional inclination angles of the belt materials at the respective tire axis direction coordinates. The center in the left-right direction of FIG. 21 coincides with the center in the tire axis direction, and both sides in the left-right direction of FIG. 21 correspond to both sides in the tire axis direction.

[0118] From the comparison between the solid line and the broken line in FIG. 21, it can be seen that there is a difference between the three-dimensional inclination angle of the belt wire and the provisional inclination angle which is the inclination angle of the belt wire when viewed from the outer side in the tire radial direction on both sides in the tire axial direction. This is the influence of the large belt gradient on both sides in the tire axial direction.

[0119] When the calculation device captures the belt image and the tire axial direction cross-sectional image, it automatically executes up to the display of the graph as shown in FIG. 21 on the display device. However, the user may participate in the form of checking the results up to the intermediate stage of the process and instructing the continuation of the process, or inputting necessary information with the input device between the capture of the belt image and the display of the graph.

[0120] The three-dimensional inclination angle of the belt wire obtained in this way is used for various purposes. For example, in a tire completed through molding, it is possible to check whether the belt wire is arranged as designed, or to check the influence on the belt wire due to the formation of grooves in the tread during molding.

[0121] Next, the effects of the present embodiment will be described. In the present embodiment, based on the belt image, the inclination angle of each belt wire with respect to the tire circumferential direction when viewed from the outer side in the tire radial direction is calculated as the provisional inclination angle. Further, based on the tire axial direction cross-sectional image, the belt gradient which is the inclination angle of the belt with respect to the tire axial direction is calculated at each tire axial direction position. Then, from the provisional inclination angle and the belt gradient, the three-dimensional inclination angle of the belt wire with respect to the tire circumferential direction at each tire axial direction position is calculated. Thereby, it is possible to obtain the three-dimensional inclination angle of the belt wire with respect to the tire circumferential direction, which could not be measured conventionally.

[0122] Here, if the provisional inclination angle is α and the belt gradient is β, the three-dimensional inclination angle θ of the belt wire with respect to the tire circumferential direction is It can be expressed by the formula JPEG2025084598000013.jpg13119, and the inclination angle θ can be easily calculated.

[0123] Further, by interpolation calculation of the data of each belt gradient at a plurality of tire axial positions, the belt gradient at each tire axial position where the provisional inclination angle is calculated is calculated. Then, from the belt gradient calculated in this way and the provisional inclination angle, the three-dimensional inclination angle of the belt wire with respect to the tire circumferential direction at the same tire axial position is calculated.

[0124] Thereby, even if there is a deviation between the tire axial position where the provisional inclination angle is calculated and the tire axial position where the belt gradient is calculated, it can be regarded that the belt gradient has been calculated at each tire axial position where the provisional inclination angle is calculated, and the three-dimensional inclination angle of the belt wire at that tire axial position can be calculated.

[0125] Various changes can be made to the above embodiments. Any one of the modification examples described below may be applied to the above embodiments, or any two or more of them may be combined and applied to the above embodiments. The combination can be freely made.

[0126] <Modification Example 1> The tire may be photographed by a CT device in a deflated state where it is not cut and no internal pressure is applied. Further, a cut sample in which the tire is cut from one end to the other end in the tire axial direction at two locations in its circumferential direction may be photographed by a CT device.

[0127] In any method, three-dimensional data of the entire tire or the cut sample can be acquired by a CT device, and a belt image and a tire axial cross-sectional image can be acquired based on the three-dimensional data.

[0128] <Modification Example 2> One or both of the belt image and the tire axial cross-sectional image may be acquired by an imaging device other than a CT device.

[0129] For example, the belt image may be an image obtained by peeling off the rubber on the tread side of the cut sample to expose the belt wire and then scanning the exposed surface where the belt wire is exposed with a scanner. Also, the tire axial direction cross-sectional image may be an image obtained by scanning the cut surface of the cut sample with a scanner and capturing it.

[0130] <Modified Example 3> As a method for obtaining both the provisional inclination angle and the belt gradient for each tire axial direction coordinate (tire axial direction position), the tire axial direction coordinates of each belt wire appearing in the tire axial direction cross-sectional image are aligned with the tire axial direction coordinates of each belt wire appearing in the belt image, and a process of calculating the provisional inclination angle at the aligned tire axial direction coordinates may be executed.

[0131] For this process, the tire axial direction coordinates of two adjacent belt wires in the belt image and the data of the provisional inclination angles at these two coordinates are used. Based on this data, the provisional inclination angle at any tire axial direction coordinate between two adjacent belt wires appearing in the belt image can be calculated by interpolation (for example, linear interpolation). Therefore, the provisional inclination angle can be calculated at the tire axial direction coordinates of the belt wires appearing in the tire axial direction cross-sectional image.

[0132] By executing such calculations for at least all belt wires where the tire axial direction coordinates of the belt wires do not match between the belt image and the tire axial direction cross-sectional image, the provisional inclination angle can be obtained for the tire axial direction coordinates of all belt wires appearing in the tire axial direction cross-sectional image. By this process, both the provisional inclination angle and the belt gradient can be obtained for the tire axial direction coordinates of all belt wires appearing in the tire axial direction cross-sectional image.

[0133] <Modified Example 4> The method of the above embodiment is applicable to tires with a number of belts other than two.

Explanation of Reference Numerals

[0134] 10… Belt, 20… Belt wire

Claims

1. In a method for calculating the inclination angle of a belt wire of a tire with respect to the circumferential direction of the tire, based on a belt image which is an image of a plurality of the belt wires when viewed from the outside in the tire radial direction, each inclination angle of the belt wires with respect to the circumferential direction of the tire when viewed from the outside in the tire radial direction is obtained as a provisional inclination angle, based on a cross-sectional image in the tire axial direction, at each tire axial position, a belt gradient which is the inclination angle of the belt with respect to the tire axial direction is obtained, from the provisional inclination angle and the belt gradient, at each tire axial position, a three-dimensional inclination angle of the belt wire with respect to the circumferential direction of the tire is calculated, A method for calculating the inclination angle of a belt wire of a tire.

2. When, at the same position in the tire axial direction, the provisional inclination angle is α and the belt gradient is β, the three-dimensional inclination angle θ of the belt wire with respect to the circumferential direction of the tire is calculated as, the method for calculating the inclination angle of a belt wire of a tire according to Claim 1.

3. Of the data of the provisional inclination angles at a plurality of tire axial positions and the data of the belt gradients at a plurality of tire axial positions, by calculating the interpolation of one of the data, the one angle at the tire axial position of the other data is calculated, from the calculated one angle and the other angle, at the same tire axial position, a three-dimensional inclination angle of the belt wire with respect to the circumferential direction of the tire is calculated, The method for calculating the inclination angle of a belt wire of a tire according to Claim 1 or 2.

Images