Method for Measuring Rotational Direction Major Groove Depth of Tire and Measuring Apparatus for Rotational Direction Major Groove Depth Using the Method

Abstract

To provide a device for measuring the depth of a main groove (circumferential main groove) in the tire rotation direction formed on the tread surface of a tire removed from a vehicle.SOLUTION: Disclosed is a method for measuring the depth of a main groove in the rotation direction which includes steps of: irradiating at least two different places on the tread surface of a tire with line laser light; acquiring picked-up images of the line laser light for each place; detecting light-cutting line coordinates which are a coordinate of an image of the line laser light for each picked-up image; calculating the groove depths formed on the tread surface based on triangulation from each light-cutting line coordinate; and determining that the grooves whose coordinates of the calculated groove depths in the rotation direction substantially coincide with each other are rotation direction main grooves, respectively, and determining that the groove depths are the depths of the rotation direction main groove, respectively.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to the measurement of the depth of main grooves in the rotational direction formed on the tread surface of tires for automobiles, motorcycles, etc. The present invention relates to a method for imaging an image of line laser light (image of a light cutting line) irradiated on the surface of a tire and measuring the depth of main grooves in the rotational direction of the tire based on the captured image, and a measuring device using the method.

Background Art

[0002] When the tires of vehicles such as automobiles are worn to a certain extent or more, they may be damaged during the running of the vehicle, which may cause serious accidents. Therefore, it is necessary to replace them with new tires at an appropriate time.

[0003] The lifespan of a tire varies significantly depending not only on the running distance of the vehicle but also on individual factors such as the vehicle type, the condition of the road surface on which it constantly runs, and the driving habits of the driver. Therefore, it is not appropriate to determine the replacement time for new tires based solely on the running distance, and it is important to investigate and judge the wear state of individual tires.

[0004] The main factors that govern the lifespan of a tire include tread wear and the occurrence of damage such as cracks and cuts. The progress of tread wear is often judged from the depth of the grooves in the tire. That is, longitudinal grooves (circumferential grooves) and transverse grooves in the rotational direction of the tire are formed on the tread surface to allow the water sandwiched between the road surface and the tire to escape to the rear or side of the tire.

[0005] When the rubber thickness decreases due to wear, these grooves become shallower. Therefore, the degree of wear can be estimated by measuring the remaining groove depth. Therefore, how to measure the numerical value of the remaining groove depth, especially the measurement of longitudinal grooves (circumferential grooves, hereinafter referred to as main grooves in the rotational direction or simply main grooves in this specification), has become one of the problems in investigating the tire wear state.

[0006] Generally, a laser displacement meter is often used as a means for three-dimensionally measuring the shape of an object surface. There are also reports of cases where a laser displacement meter is used to measure the remaining groove depth of a tire. For example, Patent Document 1 discloses a technique of irradiating incident light from a predetermined direction onto the tread surface of a tire while rotating the tire around its rotation axis, receiving the reflected light at a predetermined angle with respect to this incident light by a light receiving unit, and acquiring data on the depth of the tire groove. However, it is considered that there are the following problems in measuring the remaining groove depth with a laser displacement meter.

[0007] That is, since measurement is performed on the black rubber surface, a strong laser power is required, and there is a risk of damaging the tire. Also, since local interference occurs on a surface that causes diffuse reflection, a rather complicated operation procedure is required to ensure sufficient measurement accuracy. Furthermore, above all, the device becomes expensive and requires a great deal of labor for maintenance.

[0008] On the other hand, Patent Document 2 below discloses a method of measuring the remaining groove depth of a tire by imaging an image of a line laser beam (image of a light cutting line) and measuring the groove depth of the tire by the light cutting method based on the captured image.

[0009] Patent Document 2 below creates a fan-shaped light beam with a laser or a shadowed light emitting diode as a light source that irradiates across the moving direction of the tire. Since the measurement is performed non-orthogonally to the surface of the tire, neither the light source nor the sensor is located directly in the angular direction of reflection. The sensor is a two-dimensional image analysis camera in this case. The evaluation is performed by generating the envelope of the measured tire tread and searching for the deepest part of the tread groove.

[0010] According to the technique described in Patent Document 2 below, the deepest part of the tread groove is determined as the remaining groove depth of the tire by the optical cutting method. However, since longitudinal grooves (circumferential grooves) and transverse grooves in the rotational direction of the tire are formed on the tread surface of the tire, it is impossible to determine whether the determined groove is a longitudinal groove (circumferential groove) or a transverse groove. In addition, there may be various irregularities on the tire during use. For this reason, there is a problem that the groove determined as the circumferential groove may actually not be the circumferential groove.

[0011] Patent Document 3 below discloses a shape measuring apparatus and method for detecting the surface shape of a measured object by imaging an image of a line light (image of an optical cutting line) irradiated on the surface of a measured object that moves relatively (such as the surface of a rotating tire), and performing shape detection by the optical cutting method based on the captured image.

[0012] The technique of Patent Document 3 below includes a line light irradiation means for irradiating a plurality of line lights from a direction different from the detection height direction of the surface of the measured object, so as to form a plurality of separated optical cutting lines that extend in a second direction orthogonal to a first direction which is the moving direction of the surface of the measured object on the surface of the measured object and whose ranges occupied in the second direction are shifted from each other; an imaging means for imaging images of the plurality of separated optical cutting lines formed on the surface of the measured object in a direction in which the principal rays of the plurality of line lights are specularly reflected with respect to the surface of the measured object; for each of the plurality of captured images obtained by the imaging means in response to the movement in a certain unit, from the images of a plurality of independent image processing target regions preset corresponding to each of the plurality of separated optical cutting lines in the coordinate system of the captured image of the imaging means, an optical cutting line coordinate detection means for individually detecting the optical cutting line coordinates which are the coordinates of the image of the optical cutting line; and a surface shape calculation means for calculating the surface height distribution of the measured object in the first direction based on the plurality of optical cutting line coordinates detected by the optical cutting line coordinate detection means. The shape measuring apparatus is characterized by comprising the above.

[0013] The shape measurement device disclosed in Patent Document 3 below measures the shape of an entire tire, for example, by measuring the shape of the side surface of the tire and the shape of the tread surface of the tire while rotating the tire. For this reason, in this technology, a plurality of separated line lights are irradiated onto the tread surface of the tire, and the coordinates of the images of such line lights are detected by light cutting line coordinate detection means corresponding to each of them, so that there is no delay in the process even when the tire is rotating.

[0014] For this reason, in order to measure the main grooves formed on the tread surface of the tire by the technology described in Patent Document 3, the tire must be rotated, and a plurality of line lights separated in a direction transverse to the rotation direction of the tire must be irradiated. For this reason, there is a problem that the measuring device becomes a complicated and costly measuring device. To determine the wear condition of a tire in use, it is not necessary to measure the entire shape of the tire, and it is necessary to accurately measure the depth of the circumferential groove.

[0015]

Prior Art Documents

Patent Documents

[0016]

Patent Document 1

Patent Document 2

Patent Document 3

Disclosure of the Invention

Problems to be Solved by the Invention

[0017] Even for residents in cold regions where snow accumulates or freezes on the road surface in winter, or for residents in areas without snow accumulation, when going to snowy areas by private car for business or leisure, it is necessary to use summer tires and winter tires separately. Therefore, it is necessary to perform tire replacement work at the beginning and end of winter, and it is also necessary to store the unused tires during that period.

[0018] Although it is possible for general private car users to replace tires by themselves, since this is a rather strenuous job that requires a lot of physical strength, in the case of women and the elderly, they have to rely on businesses that perform this job professionally or as a side business, such as tire mass retailers. Also, even if it is possible to replace the tires by oneself, the same is considered to be the case when there is no storage space at home.

[0019] In order to contribute to the safe driving of customers (users) or to advise customers on the appropriate time to replace tires with new ones, businesses that handle such tire replacement and storage need a measuring device that is simple to operate and inexpensive, and can obtain information on the wear state of the tires, especially the depth of the main grooves (remaining grooves) in the rotational direction of the tires.

[0020] Therefore, the present invention aims to provide a device for measuring the depth of the main grooves (circumferential main grooves) in the rotational direction of a tire formed on the tread surface of a tire removed from a vehicle such as an automobile or a motorcycle, which has low manufacturing costs and maintenance costs, and can easily perform the measurement operation.

Means for Solving the Problem

[0021] First, the present invention for solving the above problems is a method for measuring the depth of the main grooves in the rotational direction, which irradiates a line laser beam onto the tread surface of a tire in a direction transverse to the rotational direction of the tire, images the image of the line laser beam on the tread surface with a camera, and detects the depth of the main grooves in the rotational direction formed in plurality on the tread surface by the optical cutting method based on the captured image, Irradiate at least two different locations on the tread surface with line laser light, and image the images of the line laser light respectively. For each of the captured images, detect the optical cutting line coordinates, which are the coordinates of the image of the line laser light. Based on the triangulation method from the optical cutting line coordinates, calculate the groove depths formed on the tread surface respectively. A method for measuring the depth of the main groove in the circumferential direction formed on the tread surface of a tire, characterized in that the groove depths with substantially coincident coordinates in the circumferential direction of the calculated groove depths are respectively determined as the depths of the main grooves in the circumferential direction.

[0022] A second aspect of the present invention is a method for measuring the depth of the main groove in the circumferential direction, which irradiates the tread surface of a tire with line laser light in a direction transverse to the circumferential direction of the tire, images the image of the line laser light on the tread surface with a camera, and detects the depth of the main grooves in the circumferential direction formed on the tread surface by the optical cutting method based on the captured image, Irradiate at least two different locations on the tread surface with line laser light, and acquire the images of the line laser light respectively. For each of the captured images, detect the optical cutting line coordinates, which are the coordinates of the image of the line laser light. Select a point A, which is one coordinate of the optical cutting line coordinates, a point B, which is one coordinate of the optical cutting line coordinates and is w away from the point A in a direction transverse to the circumferential direction of the tire, and a point C, which is one coordinate of the optical cutting line coordinates and is 2w away from the point A in a direction transverse to the circumferential direction of the tire. Repeatedly calculate the area of the triangle formed by the point A, the point B, and the point C until any one of the point A, the point B, and the point C becomes all the coordinates of the optical cutting line coordinates. Calculate the groove depth from the area of the triangle obtained by the integration. Those with the groove depth greater than or equal to a predetermined value are respectively used as main groove candidates. A method for measuring the depth of the main groove in the circumferential direction formed on the tread surface of a tire, characterized in that the groove depths with substantially coincident coordinates in the circumferential direction of the main groove candidates are respectively determined as the depths of the main grooves in the circumferential direction.

[0023] Thirdly, the present invention provides a line laser light irradiation device that irradiates line laser light at at least two different locations on the tread surface of a tire in a direction transverse to the rotational direction of the tire, a camera that images the image of the line laser light on the tread surface, a line laser image detection processing unit that performs detection processing on the image of the line laser light from the captured image captured by the camera, a light cutting line coordinate detection unit that detects the light cutting line coordinates that are the coordinates of the image of the line laser light, a groove depth calculation unit that calculates the depth of the groove formed on the tread surface based on the light cutting method from the light cutting line coordinates, and a main groove determination unit that determines a plurality of grooves whose coordinates in the rotational direction of the calculated groove depth substantially coincide as main grooves in the rotational direction respectively. A measuring device for the depth of the main groove in the rotational direction formed on the tread surface of a tire, characterized by comprising the above.

[0024] In the present invention, line laser light is irradiated at at least two different locations on the tread surface of a tire, and the image of the line laser light on the tread surface of the tire is imaged by a camera. The image of the line laser light is detected from each captured image, and the light cutting line coordinates that are the coordinates of the image of the line laser light are detected.

[0025] Based on the triangulation method using the principle of the light cutting method, the depth of the groove can be calculated from the arrangement of the line laser light irradiation device and the camera and the light cutting line coordinates. There are at least two images of the line laser light, and since the grooves whose coordinates in the rotational direction detected by the light cutting method substantially coincide are vertical grooves, the depth of those grooves is determined as the depth of the main groove. This can prevent, for example, misjudging lateral grooves or irregularities formed on the tread surface as main grooves in the rotational direction.

[0026] In addition to the determination of the rotation direction main groove as described above, for each of the optical cutting line coordinates, a point A which is one coordinate of the optical cutting line coordinate, a point B which is one coordinate of the optical cutting line coordinate and is w away from the point A in a direction transverse to the rotation direction of the tire, and a point C which is one coordinate of the optical cutting line coordinate and is 2w away from the point A in a direction transverse to the rotation direction of the tire are selected. The area of the triangle formed by the point A, the point B, and the point C is repeatedly integrated until any one of the point A, the point B, and the point C becomes all the coordinates of the optical cutting line coordinate. The groove depth is calculated from the integrated area of the triangle. When the groove depth is equal to or greater than a predetermined value and the coordinates in the rotation direction substantially coincide, the depth of the groove is determined as the depth of the rotation direction main groove respectively.

[0027] Here, the tread surface of the tire is a gentle curved surface, and the image of the line laser light captured by the camera is also a gentle curve. Therefore, when calculating the groove depth, it is necessary to calculate the groove depth in a direction orthogonal to the normal line of the optical cutting line that is segmented (separated) at the groove portion. For this purpose, it is preferable to select three points from the optical cutting line coordinates, integrate the area of the triangle formed by the three points for all the optical cutting line coordinates, and determine the maximum value of the groove depth obtained therefrom as the groove depth.

[0028] The above three points are selected as a point A which is one coordinate of the optical cutting line coordinate, a point B which is one coordinate of the optical cutting line coordinate and is w away from the point A in a direction transverse to the rotation direction of the tire, and a point C which is one coordinate of the optical cutting line coordinate and is 2w away from the point A in a direction transverse to the rotation direction of the tire. Then, the area of the triangle formed by the point A, the point B, and the point C is repeatedly integrated until any one of the point A, the point B, and the point C becomes all the coordinates of the optical cutting line coordinate, and the groove depth is calculated from the maximum area. The above w (the base of the triangle) is preferably at least the width of the main groove of the tire to be measured and is a width equal to or greater than that width and twice or less that width.

Advantages of the Invention

[0029] The present invention provides an apparatus for measuring the depth of a main groove (circumferential main groove) in the rotational direction of a tire formed on the tread surface of a tire removed from a vehicle such as an automobile or a motorcycle. It is possible to provide an apparatus for measuring the depth of the main groove in the rotational direction of the tread surface of a tire that is inexpensive in terms of manufacturing cost and maintenance cost of the apparatus and can be easily measured. The apparatus for measuring the depth of the main groove in the rotational direction formed on the tread surface of the tire of the present invention is characterized by low equipment cost, easy maintenance, and simple measurement procedures.

Best Mode for Carrying Out the Invention

[0030] Hereinafter, with reference to the drawings of the embodiments, preferred embodiments of the present invention will be described. FIG. 1 is a perspective view showing the configuration of a measuring apparatus 1 for the depth of the main groove in the rotational direction formed on the tread surface of a tire according to the first embodiment of the present invention. This apparatus includes a table 50 on which the tire 40 is placed, a line laser light irradiation device 10, a camera 20 for imaging the image of the line laser light, and a data processing device 30 for analyzing and processing the captured image of the camera. Although not shown in FIG. 1, it is preferable to provide a light source for clarifying the tread surface of the tire 40 according to environmental conditions.

[0031] The tire 40 is placed on the table 50 such that the side surface of the tire is horizontal. The line laser irradiation device 10 is symmetrically arranged around the camera 20 and irradiates the tread surface of the tire 40 with line laser light in a direction transverse to the rotational direction of the tire, forming images of the line laser light at two different locations on the tread surface. The camera 20 images the images of the line laser light appearing at two different locations on the tread surface, and the captured image is sent to the data processing device 30. The image of the line laser light is for the purpose of obtaining information on the remaining groove depth of the tire 40. In one embodiment shown in FIG. 1, the camera 20 is arranged between the two line laser irradiation devices 20, but the present invention is not limited to this. As long as the arrangement (height, distance, angle, etc.) relationship between the camera 20, the line laser light irradiation device 10, and the tread surface of the tire required by the triangulation method used in the principle of the optical cutting method can be specified.

[0032] The present invention is characterized in that when acquiring an image of the line laser light on the tread surface in a direction transverse to the rotation direction of the tire, the tread surface is irradiated with line laser light at two different locations, and the image is captured by the image camera 20. This is because, in addition to the main grooves in the rotation direction, transverse grooves and diagonal grooves are formed on the tread surface, and unevenness may occur on the tread surface due to use. Irradiating the line laser light at two different locations on the tread surface is for distinguishing the main grooves in the rotation direction from other grooves. Here, it is preferable to irradiate the line laser light simultaneously at two different locations on the tread surface, but it may also be performed by performing a synthesis process on images obtained by irradiating the line laser light at two different locations on the tread surface with a time shift.

[0033] In the present invention, when distinguishing these various grooves from the main grooves in the rotation direction, the feature that the main grooves in the rotation direction always have continuous grooves in the rotation direction is utilized. That is, from the coordinates of the optical cutting line 11 (see FIG. 3), which is an image of the line laser light, a groove having substantially the same coordinates in the rotation direction is determined as the main groove in the rotation direction, and this point is one of the key points of the present invention. However, there may be a case where the main grooves are formed in a meandering shape in the tire rotation direction, and there may also be a case where the main grooves are not necessarily continuous in the rotation direction in relation to the transverse grooves. Even for such main grooves, a groove having substantially the same coordinates in the rotation direction is determined as the main groove in the rotation direction from the coordinates of the optical cutting line 11.

[0034] FIG. 2 is a diagram showing the positional relationship in the height direction between the camera 20 of the measuring device 1, the line laser light irradiating device 10, the tread surface of the tire 40, and the main groove 41 in the rotation direction, which is an embodiment of the present invention shown in FIG. 1. The laser irradiating device 10 is arranged symmetrically with respect to the rotation direction of the tire 40 with the camera 20 interposed therebetween.

[0035] In FIG. 2, the irradiation angle of the line laser irradiation device 10 is set to be the angle for irradiating the center of the tire 40 which is the measurement target. Although the diameters of the tires to be measured vary, for example, it is set as the angle for irradiating the center of the tire with the minimum diameter. The height of the camera 20 from the tread surface is set to be the height at which images of two line laser lights can be obtained (a visual field angle can be ensured), and the camera 20 is installed at the same height. Assuming that the depth of the main groove 41 in the rotational direction of the tire 40 is D, the incident angle of the line laser light 100 on the tread surface of the tire 40 is θ, and the width of the main groove 41 is w, then D = tan θ × w. Here, w is wider than the width of the main groove 41, and it is preferably about 1 to 2 times the width of the main groove 41. This is because the width of the main groove may change due to tire wear, and the main groove may be formed in a meandering shape in the tire rotational direction.

[0036] FIG. 3 is a view showing a tire placed such that its side surface is horizontal, and the tread surface of the tire 40 is irradiated with line laser light by the line laser irradiation device 10. Line laser lights 100 are irradiated from two line laser irradiation devices 10 at two different locations on the tread surface, and two light cutting lines 11 which are images of the line laser light appear on the tread surface. The image of the light cutting line 11 appears as an image due to reflection from the bottom surface of the main groove 41, rather than an image due to reflection from the tread surface, at the location where the main groove 41 in the rotational direction of the tire is formed. That is, as shown in FIG. 2(b), the image of the light cutting line 11 of the main groove 41 of the light cutting line 11 appears on the irradiation direction side of the line laser light 100 according to the depth of the main groove 41, rather than the image appearing on the tread surface.

[0037] As described above, in the present invention, in order to distinguish the main groove in the rotational direction formed on the tread surface from transverse grooves and unevenness, the main groove in the rotational direction is used as a discrimination means based on the feature that the grooves are continuous in the rotational direction. That is, two images of the line laser light are generated on the tread surface, and from the coordinates (light cutting line coordinates) of the light cutting lines 11 (light cutting line 11-1, light cutting line 11-2) which are the images of those line laser lights, the groove whose coordinates in the rotational direction match is discriminated as the main groove in the rotational direction.

[0038] Figure 4 is a diagram showing an embodiment of the present invention for calculating the depth of the main groove in the rotational direction from the image of the line laser light of the cutting line 11. When measuring the groove depth by applying a gauge to an actual tire, a tire groove gauge (tire groove depth gauge) is installed in the normal direction of the tread surface, and the groove depth is measured such that the measuring needle hits the groove bottom at right angles to the normal of the tread surface. This is because the tread surface is a gentle curved surface. The image of the line laser light formed on the tread surface by the measuring device 1 for the main groove in the rotational direction, which is an embodiment of the present invention, also appears as a gentle curve.

[0039] As described above, the depth of the main groove can be calculated by triangulation based on the separation h between the image of the line laser light on the tread surface and the image of the line laser light of the main groove. However, the separation between the optical cutting line coordinates of the tread surface and the optical cutting line coordinates of the main groove varies depending on how the coordinates are taken. Note that the coordinate axes shown in Figure 4 assume that the resolution of the image of the tread surface is 1000×1000 dots, that is, the coordinates of the X-axis are 0 to 1000, and the coordinates of the Y-axis are also 0 to 1000.

[0040] As a method for calculating the depth of the main groove from the cutting line 11 shown in Figure 4, a point A which is a coordinate of the cutting line 11, a point B which is a coordinate of the cutting line 11 at a distance w from point A in a direction transverse to the rotational direction of the tire, and a point C which is a coordinate of the cutting line 11 at a distance 2w from point A in a direction transverse to the rotational direction of the tire are selected.

[0041] Then, the area of the triangle formed by points A, B, and C is obtained. This is repeated until any one of points A, B, or C becomes all the coordinates of the cutting line 11, and when the area of the triangle thus obtained is graphed with the Y coordinate value of the cutting line 11 as the X-axis and the area of the triangle as the Y-axis, a diagram like Figure 4(b) is obtained. From the maximum value of the area of the triangle thus obtained, the respective groove depths are calculated, and among the calculated groove depths, the grooves at locations where the depth is greater than or equal to a predetermined depth, for example, the groove depth indicated by the slip sine (1.6 mm for four-wheel tires and 0.8 mm for two-wheel tires) or more, are determined as the depth of the main groove.

[0042] FIG. 5 is a block diagram showing the configuration of a measuring device 1 for the depth of a main groove in the rotational direction formed on the tread surface of a tire according to an embodiment of the present invention. Two line lasers 10 irradiate line laser light at different locations on the tread surface of the tire. The camera 20 captures an image of the line laser light appearing on the tread surface. The control of the line laser 10 is performed by the line laser control unit 310 of the control unit 31, and the control of the camera 20 is performed by the imaging control unit 311 of the control unit 31.

[0043] The image captured by the camera 20 is sent to the data processing unit 32. The data processing unit 32 includes a line laser image detection unit 320 that detects an image of the line laser light, a light cutting line coordinate detection unit 321 that detects the light cutting line coordinates that are the coordinates of the image of the line laser light detected by the line laser image detection unit 320, a groove depth calculation unit 322 that calculates the groove depth from the coordinates obtained by the light cutting line coordinate detection unit 321, and a main groove determination unit 323 that determines the main groove in the rotational direction from the groove depth calculated by the groove depth calculation unit 322 and the coordinates of the light cutting line 11.

[0044] FIG. 6 is a diagram of the depth of the main groove in the rotational direction obtained by the measuring device 1 for the depth of the main groove in the rotational direction formed on the tread surface of a tire according to an embodiment of the present invention for a tire (size: 215 / 55R17). The line laser has a wavelength of 600 nm, a power consumption of 40 mW, and a power supply voltage of 5 VD, and the resolution of the camera 20 is 2048x1536. As a result of processing the image acquired with such specifications, obtaining the coordinates of the light cutting line 11, and calculating the depth of the main groove in the rotational direction, a depth of 5.4 mm to 5.9 mm was detected as the depth of the three main grooves 42 formed on the tread surface.

[0045] FIG. 7 is a flowchart showing an example of a method for measuring the depth of the main groove in the rotational direction according to an embodiment of the present invention. By irradiating two line laser lights on the tread surface of the tire, the portion of the image of the line laser light appearing on the tread surface is emphasized and filtering processing is performed (S1, S2). Next, after binarizing the image of the line laser light into two colors, for example, red and white, or black and white, processing for removing noise is performed (S3, S4).

[0046] Next, adjust the line widths of the images of the two line laser lights from the average of each coordinate to, for example, 1 dot (1 pixel = 1 dot). Also, linearly interpolate the pixels (missing points) that are originally the images of the line laser lights but have disappeared (S5, S6), and extract the coordinates of the optical cutting line 11 that is the image of the line laser light (S7).

[0047] Next, select points A, B, and C from the coordinates of each optical cutting line 11, and calculate the area of the triangle formed by points A, B, and C (S8, S9). Repeat this until point A becomes the coordinates of all the optical cutting lines 11, calculate the area of the triangle formed by points A, B, and C (S10), and use the area of the triangle as the Y-axis and the Y-axis coordinates of the optical cutting line 11 as the X-axis to find the maximum value of the graph as the candidate for the main groove (S11).

[0048] From among the candidates for the main groove obtained from each optical cutting line coordinate, those in which the Y coordinates of the optical cutting line 11 are approximately the same, for example, among the candidates for the main groove, those in which the Y coordinates do not deviate by more than the width of the rotational direction main groove are determined as the rotational direction main groove. Then, calculate the depth of the main groove from the area of those determined to be the main groove (S12, S13).

Brief Description of the Drawings

[0049]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Explanation of Reference Numerals

[0050] 1: Measuring device for the main groove in the rotational direction of a tire 10: Line laser light irradiation device 20: Camera 30: Data processing device 31: Control unit 32: Data processing unit 40: Tire 41: Main groove in the rotational direction of the tire 50: Table 310: Line laser control unit 311: Imaging control unit 320: Line laser image detection unit 321: Light cut-off line coordinate detection unit 322: Groove depth calculation unit 323: Main groove determination unit

Claims

1. A measuring device for measuring the depth of a rotational-direction main groove, which is a main groove having a bottom surface and formed in a tread surface of the tire in a rotational direction of the tire, comprising: Two line laser light irradiation devices that respectively irradiate line laser light in a direction transverse to the rotational direction of the tire at two different positions on the tread surface; A camera disposed at a predetermined position for imaging images of the line laser light at the two positions on the tread surface; A line laser image detection processing unit that performs detection processing on the images of the line laser light at the two positions from the captured image captured by the camera; A light cutting line coordinate detection unit that detects light cutting line coordinates, which are coordinates of the images of the line laser light at the two positions respectively; A groove depth calculation unit that calculates the depth of a groove having a bottom surface formed in the tread surface based on the light cutting method from the light cutting line coordinates in the line laser light at the two positions respectively; A main groove determination unit that determines the depth of the groove whose coordinates in the direction transverse to the rotational direction of the calculated depth of the groove substantially coincide as the depth of the rotational-direction main groove, and each of the two line laser light irradiation devices is disposed at a predetermined position and irradiates the placed tire with the line laser light at a predetermined incident angle, A measuring device that selects a point A, which is one coordinate of the light cutting line coordinates, a point B, which is the light cutting line coordinates separated by w from the point A in the direction transverse to the rotational direction of the tire, and a point C, which is the light cutting line coordinates separated by 2w from the point A in the direction transverse to the rotational direction of the tire, repeatedly calculates the area of a triangle formed by the point A, the point B, and the point C while shifting the point A, the point B, and the point C, and calculates the depth of the groove from the calculated area of the triangle.

2. The measuring device according to claim 1, wherein the light cutting line coordinate detection unit obtains the light cutting line coordinates after adjusting the line width of the images of the line laser light at the two positions to one pixel and linearly interpolating missing points where the images have disappeared.

3. A measuring method for measuring the depth of a rotational-direction main groove, which is a main groove having a bottom surface, formed in a tread surface of the tire in a rotational direction of the tire, comprising: Irradiating line laser light from two line laser light irradiating devices arranged at predetermined positions to two different locations on the tread surface of the placed tire at a predetermined incident angle and in a direction transverse to the rotational direction of the tire, Imaging images of the line laser light at the two locations by a camera arranged at a predetermined position, Detecting, for the captured imaging image, light cutting line coordinates that are coordinates of the images of the line laser light at the two locations respectively, Calculating, respectively, the depth of a groove having a bottom surface formed in the tread surface based on the light cutting method from the light cutting line coordinates in the line laser light at the two locations respectively, Determining the depth of the groove whose coordinates in the direction transverse to the rotational direction of the calculated depth of the groove substantially coincide as the depth of the rotational-direction main groove, Selecting a point A that is one coordinate of the light cutting line coordinates, a point B that is one coordinate of the light cutting line coordinates separated by w from the point A in the direction transverse to the rotational direction of the tire, and a point C that is one coordinate of the light cutting line coordinates separated by 2w from the point A in the direction transverse to the rotational direction of the tire, repeatedly calculating the area of a triangle formed by the point A, the point B, and the point C while shifting the point A, the point B, and the point C, and calculating the depth of the groove from the calculated area of the triangle. A measuring method.

4. The measuring method according to claim 3, wherein the line width of the images of the line laser light at the two locations respectively is adjusted to one pixel, and after linearly interpolating missing points where the images disappear, the light cutting line coordinates are obtained.

Images