Method for measuring tire rotational direction main groove depth and device for measuring rotational direction main groove depth using said method

Abstract

To provide a device for measuring the depth of a tire rotation direction main groove (circumferential main groove) formed on a tread surface of a tire removed from a vehicle.SOLUTION: Line laser light 100 is irradiated to at least two different places of a tread surface of a tire 40, picked-up images of the line laser light 100 are respectively acquired, light cutting line coordinates being coordinates of the images of the line laser light 100 are detected about each of the picked-up images, groove depths formed on the tread surface are calculated from the respective light cutting line coordinates on the basis of a triangulation method, and the calculated groove depths are respectively determined as the depths of rotation direction grooves 41 with grooves whose rotation direction coordinates of the groove depths approximately coincide respectively regarded as the rotation direction main grooves 41.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the depth of a main groove in the direction of rotation formed on the tread surface of tires for automobiles, motorcycles, etc., and relates to a method for capturing an image of a line laser beam (image of a light-section line) irradiated onto the surface of the tire and measuring the depth of the main groove in the direction of rotation of the tire based on the captured image, and a measuring device that utilizes this method. [Background technology]

[0002] When tires on vehicles such as automobiles become worn to a certain extent, they may break while the vehicle is in motion, which could result in a serious accident. Therefore, it is necessary to replace the tires with new ones at the appropriate time.

[0003] The lifespan of tires varies greatly depending not only on the mileage of a vehicle, but also on individual factors such as the vehicle model, the condition of the road surface on which the vehicle is driven, and the driver's habits. Therefore, it is not appropriate to determine when to replace tires with new ones based solely on the mileage; it is important to investigate the wear and tear of each tire.

[0004] The main factors that determine the lifespan of a tire are wear on the tread surface and the occurrence of scratches such as cracks and cuts. The progress of tread wear is often judged by the depth of the tire's grooves. That is, the tread surface is formed with longitudinal grooves (circumferential grooves) and lateral grooves that run in the direction of tire rotation to allow water trapped between the road surface and the tire to escape to the rear or sides of the tire.

[0005] When the thickness of the rubber decreases due to wear, these grooves become shallower, so the degree of wear can be estimated by measuring the remaining groove depth. Therefore, one of the challenges in investigating the state of tire wear is how to measure the remaining groove depth, particularly for longitudinal grooves (circumferential grooves, hereinafter referred to as rotational direction main grooves or simply main grooves).

[0006] Generally, laser displacement meters are often used as a means for measuring the shape of an object surface in three dimensions. Cases where a laser displacement meter has been used to measure the remaining tread depth of a tire have also been reported. For example, Patent Document 1 discloses a technology in which, while the tire is rotated around its axis of rotation, incident light is irradiated onto the tire tread surface from a predetermined direction, and reflected light at a predetermined angle relative to the incident light is received by a light-receiving unit to obtain data on the tire tread depth. However, measuring the remaining tread depth using a laser displacement meter is thought to have the following problems.

[0007] Specifically, since measurements are performed on black rubber surfaces, a strong laser power is required, which poses the risk of damaging the tire. Furthermore, since localized interference occurs on surfaces that cause diffuse reflection, a fairly complicated operating procedure is required to ensure sufficient measurement accuracy. Furthermore, the most significant drawback is that the equipment is expensive and requires a great deal of maintenance effort.

[0008] Meanwhile, Patent Document 2 below discloses a method for measuring the remaining groove depth of a tire by capturing an image of a line laser beam (image of a light-section line) and measuring the groove depth of the tire by a light-section method based on the captured image.

[0009] In the patent document 2 listed below, a laser or a shadowed light-emitting diode is used as a light source that is irradiated transversely to the direction of tire movement, creating a fan-shaped light beam. Measurements are performed non-orthogonally to the tire surface, so neither the light source nor the sensor is positioned in the angular direction of direct reflection. The sensor in this case is a two-dimensional image analysis camera. Evaluation is performed by generating an envelope of the measured tire tread and by locating the deepest point of the tread grooves.

[0010] According to the technology described in Patent Document 2 below, the deepest point of the tread groove is determined as the remaining groove depth of a tire using a light cutting method. However, because the tire tread surface is formed with longitudinal grooves (circumferential grooves) and lateral grooves that run in the direction of tire rotation, it is not possible to determine whether the determined groove is a longitudinal groove (circumferential groove) or a lateral groove. In addition, a tire in use may have various irregularities. For this reason, there is a problem in that a groove determined to be a circumferential groove may not actually be a circumferential groove.

[0011] The following Patent Document 3 discloses a shape measuring device and method for detecting the surface shape of a measured object by capturing an image of a line of light (an image of a light-section line) irradiated onto the surface of a relatively moving measured object (such as the surface of a rotating tire), and performing shape detection using a light-section method based on the captured image.

[0012] The technology disclosed in Patent Document 3 below relates to a shape measuring device comprising: a line light irradiation means for irradiating a plurality of line lights onto the surface of the object to be measured from a direction different from the detection height direction, thereby forming a plurality of separated light-section lines on the surface of the object to be measured, the separated light-section lines extending in a second direction perpendicular to a first direction, which is the direction of movement of the surface of the object to be measured, and the areas occupied in the second direction being shifted from one another; an imaging means for capturing images of the plurality of separated light-section lines formed on the surface of the object to be measured in a direction in which the chief ray of each of the plurality of line lights is specularly reflected by the surface of the object to be measured; a light-section line coordinate detection means for individually detecting, for each of a plurality of captured images obtained by the imaging means in accordance with the movement by a certain unit, light-section line coordinates, which are the coordinates of the image of the light-section line, from images of a plurality of independent image processing target regions that are preset to correspond to each of the plurality of separated light-section lines in a coordinate system of the captured image of the imaging means; and a surface shape calculation means for calculating the surface height distribution of the object to be measured in the first direction based on the plurality of light-section line coordinates detected by the light-section line coordinate detection means.

[0013] The shape measuring device disclosed in Patent Document 3 listed below measures the overall shape of a tire by measuring the shape of the tire side and the shape of the tire tread surface while the tire is rotating. For this reason, this technology irradiates the tire tread surface with a plurality of separated lines of light, and the coordinates of the images of these lines of light are detected by corresponding light-section line coordinate detecting means, so that there is no delay in processing even when the tire is rotating.

[0014] Therefore, to measure the main grooves formed on the tire tread surface using the technology described in Patent Document 3, the tire must be rotated and multiple line beams separated in directions transverse to the tire rotation direction must be emitted. This poses a problem of making the measuring device complex and expensive. To determine the wear state of a tire in use, it is not necessary to measure the overall shape of the tire, but it is necessary to accurately measure the depth of the circumferential grooves.

[0015] [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Japanese Patent Application Publication No. 2016-161360 [Patent Document 2] Patent No. 5640073 [Patent Document 3] Patent No. 5089286 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0017] Residents of cold regions where snow and ice accumulate on the roads in winter, and even those living in areas without snow, need to use both summer and winter tires when traveling to snowy areas for work or leisure. Therefore, it is necessary to change tires at the beginning and end of winter, and also to store the unused tires during that period.

[0018] Although ordinary car owners can change their tires themselves, it is a rough job that requires considerable physical strength, so women and the elderly have no choice but to rely on businesses that specialize in this task or do it as a side job, such as tire retailers. The same can be said for those who can change their tires themselves but cannot find a place to store them at home.

[0019] Such tire replacement and storage businesses are seeking an easy-to-operate, inexpensive measuring device that can obtain information on tire wear, particularly the depth of the main grooves (remaining grooves) in the direction of tire rotation, to help their customers (users) drive safely or to advise them on the appropriate time to replace their tires with new ones.

[0020] Therefore, the present invention aims to provide an apparatus for measuring the depth of the rotational main grooves (circumferential main grooves) formed on the tread surface of a tire removed from a vehicle such as an automobile or motorcycle, which has low manufacturing and maintenance costs and is easy to operate. [Means for solving the problem]

[0021] A first aspect of the present invention for solving the above problems is a method for measuring rotational direction main groove depth, which includes irradiating a line laser beam onto a tread surface of a tire in a direction transverse to the rotational direction of the tire, capturing an image of the line laser beam on the tread surface with a camera, and detecting depths of a plurality of rotational direction main grooves formed on the tread surface by a light sectioning method based on the captured image, irradiating at least two different locations on the tread surface with a line laser beam and capturing images of the line laser beam; Detecting light section line coordinates, which are coordinates of an image of the line laser light, for each of the captured images; calculating the depth of each groove formed on the tread surface based on the light-section line coordinates using a triangulation method; and determining the depth of a groove whose rotational coordinate approximately matches the calculated groove depth as the depth of the rotational main groove.

[0022] A second aspect of the present invention is a method for measuring a rotational direction main groove depth, comprising: irradiating a line laser beam onto a tread surface of a tire in a direction transverse to the rotational direction of the tire; capturing an image of the line laser beam on the tread surface with a camera; and detecting depths of a plurality of rotational direction main grooves formed on the tread surface by a light sectioning method based on the captured image, A line laser beam is irradiated onto at least two different locations on the tread surface, and images of the line laser beam are obtained, Detecting light section line coordinates, which are coordinates of an image of the line laser light, for each of the captured images; a point A which is one of the coordinates of the light section line coordinates, a point B which is one of the coordinates of the light section line coordinates and which is separated from the point A by w in a direction transverse to the rotation direction of the tire, and a point C which is one of the coordinates of the light section line coordinates and which is separated by 2w in a direction transverse to the rotation direction of the tire from the point A, and the area of ​​a triangle formed by the point A, the point B, and the point C is repeatedly calculated until any of the point A, the point B, and the point C becomes one of the coordinates of the light section line coordinates; Calculating the groove depth from the area of ​​the triangle obtained; The grooves having a depth equal to or greater than a predetermined value are respectively designated as main groove candidates, and determining the depth of the groove whose rotational coordinates of the main groove candidates approximately match as the depth of the rotational main groove.

[0023] A third aspect of the present invention is a line laser light irradiation device that irradiates a line laser light onto a tread surface of a tire at at least two different positions on the tread surface of the tire in a direction transverse to the rotation direction of the tire; a camera that captures an image of the line laser light on the tread surface; a line laser image detection processing unit that detects and processes an image of a line laser beam from the captured image captured by the camera; a light section line coordinate detection unit that detects light section line coordinates, which are coordinates of an image of the line laser light; a groove depth calculation unit that calculates a depth of a groove formed on the tread surface based on the light section line coordinates based on a light section method; a main groove determining section that determines each of a plurality of grooves having substantially the same coordinate in the rotational direction of the calculated groove depth as a rotational direction main groove; and a measuring device for measuring the depth of a rotational direction main groove formed on a tread surface of a tire, the measuring device comprising:

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

[0025] The depth of the groove can be calculated based on the arrangement of the line laser light emitting device and camera and the light section line coordinates, using triangulation that uses the principles of the light section method. There are at least two images of the line laser light, and grooves whose rotational coordinates of the grooves detected by the light section method approximately match are determined to be longitudinal grooves, and the depth of those grooves is determined to be the depth of the main groove. This prevents, for example, lateral grooves or irregularities on the tread surface from being mistakenly determined to be the main groove in the rotational direction.

[0026] In addition to the determination of rotational direction main grooves as described above, for each of the light section line coordinates, point A, which is one of the coordinates of the light section line coordinates, point B, which is one of the coordinates of the light section line coordinates that is w away from point A in a direction transverse to the tire rotation direction, and point C, which is one of the coordinates of the light section line coordinates that is 2w away from point A in a direction transverse to the tire rotation direction, are selected, and the area of ​​the triangle formed by point A, point B, and point C is repeatedly calculated until any of point A, point B, and point C represents all of the coordinates of the light section line coordinates. The groove depth is calculated from the area of ​​the calculated triangle, and groove depths whose groove depth is equal to or greater than a predetermined value and whose rotational direction coordinates approximately match are determined to be the depth of the rotational direction main groove.

[0027] Here, the tire tread surface is a gently curved surface, and the image of the line laser light captured by the camera also has a gently curved shape. Therefore, when calculating the groove depth, it is necessary to calculate the groove depth in a direction perpendicular to the normal of the light section line that is divided (separated) by the groove portion. To do this, it is preferable to select three points from the light section line coordinates, calculate the area of ​​the triangle formed by the three points for all the light section line coordinates, and determine the groove depth as the maximum value obtained from these.

[0028] The three points are point A, which is one coordinate on the light section line coordinate system; point B, which is one coordinate on the light section line coordinate system that is w away from point A in a direction transverse to the tire rotation direction; and point C, which is one coordinate on the light section line coordinate system that is 2w away from point A in a direction transverse to the tire rotation direction. The area of ​​the triangle formed by points A, B, and C is then repeatedly calculated until any of points A, B, and C is found at every coordinate on the light section line coordinate system, and the groove depth is calculated from the maximum area. The above w (the base of the triangle) is at least the width of the main groove of the tire being measured, and it is preferable that it be at least that width but not more than twice that width. [Effects of the Invention]

[0029] The present invention makes it possible to provide an apparatus for measuring the depth of the rotational main grooves (circumferential main grooves) formed on the tread surface of a tire removed from a vehicle such as an automobile or motorcycle, which has low manufacturing and maintenance costs and is easy to operate. The apparatus for measuring the depth of the rotational main grooves formed on the tread surface of a tire of the present invention has the characteristics of low equipment costs, easy maintenance, and simple measurement procedures. BEST MODE FOR CARRYING OUT THE INVENTION

[0030] Preferred embodiments of the present invention will be described below with reference to the drawings of the examples. Fig. 1 is a perspective view showing the configuration of an apparatus 1 for measuring the depth of a rotational direction main groove formed on the tread surface of a tire, which is a first example of the present invention. This apparatus includes a table 50 on which a tire 40 is placed, a line laser light irradiation device 10, a camera 20 that captures an image of the line laser light, and a data processing device 30 that analyzes and processes the image captured by the camera. Although not shown in Fig. 1, it is preferable to include a light source that makes the tread surface of the tire 40 clear depending on environmental conditions.

[0031] The tire 40 is placed on a table 50 with the tire side horizontal. The line laser irradiation devices 10 are arranged symmetrically around the camera 20 and irradiate the tread surface of the tire 40 with a line laser beam in a direction transverse to the tire rotation direction, forming line laser beam images at two different locations on the tread surface. The camera 20 captures the line laser beam images that appear at two different locations on the tread surface, and the captured images are sent to a data processing device 30. The line laser beam images are intended to obtain information on the remaining tread depth of the tire 40. Note that in the embodiment shown in FIG. 1 , the camera 20 is positioned midway between the two line laser irradiation devices 20, but the present invention is not limited to this. It is sufficient if the relative positions (height, separation, angle, etc.) of the camera 20, the line laser beam irradiation device 10, and the tire tread surface, which are required for triangulation used in the principle of light sectioning, can be identified.

[0032] The present invention is characterized in that, when acquiring a line laser light image of the tread surface in a direction transverse to the tire rotation direction, the line laser light is irradiated onto two different locations on the tread surface and the image is captured by the image camera 20. This is because the tread surface has lateral grooves and diagonal grooves in addition to the rotational main grooves, and the tread surface may become uneven with use. The reason for irradiating the line laser light onto two different locations on the tread surface is to distinguish between the rotational main grooves and other grooves. Here, it is preferable to irradiate the line laser light onto two different locations on the tread surface simultaneously, but this may also be done by synthesizing images obtained by irradiating the line laser light onto two different locations on the tread surface with a time lag.

[0033] In the present invention, when distinguishing between these various grooves and rotational direction main grooves, the characteristic that rotational direction main grooves are always continuous in the rotational direction is utilized. That is, grooves whose rotational direction coordinates approximately match based on the coordinates of the light section line 11 (see FIG. 3 ), which is an image of the line laser light, are identified as rotational direction main grooves, and this is one of the key features of the present invention. However, there are also cases where the main grooves are formed in a meandering shape in the tire rotational direction, and there are also cases where the main grooves are formed in a manner that is not necessarily continuous in the rotational direction due to their relationship with the lateral grooves. Even in such cases, grooves whose rotational direction coordinates approximately match based on the coordinates of the light section line 11 are identified as rotational direction main grooves.

[0034] 2 is a diagram showing the positional relationship in the height direction between the camera 20 of the measuring device 1 according to one embodiment of the present invention shown in FIG. 1, the line laser light emitting device 10, the tread surface of the tire 40, and the rotational direction main groove 41. The laser emitting device 10 is disposed symmetrically in the rotational direction of the tire 40 with the camera 20 sandwiched therebetween.

[0035] In FIG. 2, the irradiation angle of the line laser irradiation device 10 is set to an angle at which the center of the tire 40, which is the measurement target, is irradiated. Tires to be measured have various diameters, but for example, this angle is set to irradiate the center of a tire with the smallest diameter. The height of the camera 20 from the tread surface is set to a height at which two line laser beam images can be acquired (ensuring a viewing angle), and the camera 20 is installed at the same height. If the depth of the rotational direction main groove 41 of the tire 40 is D, the angle of incidence of the line laser beam 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 is obtained. Here, w is preferably wider than the width of the main groove 41, for example, approximately one to two 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 serpentine shape in the tire rotational direction.

[0036] FIG. 3 shows a tire 40 placed with its side horizontal and irradiated with a line laser beam by a line laser irradiation device 10 onto the tread surface. Two line laser irradiation devices 10 irradiate two different locations on the tread surface with line laser beams 100, and two light-section lines 11, which are images of the line laser beams, appear on the tread surface. In locations where a tire rotational direction main groove 41 is formed, the image of the light-section line 11 does not appear as an image due to reflection from the tread surface, but as an image due to reflection from the bottom surface of the main groove 41. That is, as shown in FIG. 2(b), the image of the light-section line 11 of the main groove 41 of the light-section line 11 appears closer to the irradiation direction of the line laser beam 100 than the image that appears on the tread surface, depending on the depth of the main groove 41.

[0037] As mentioned above, in the present invention, in order to distinguish the rotational direction main grooves formed on the tread surface from lateral grooves and irregularities, the characteristic that the rotational direction main grooves are continuous in the rotational direction is used as a distinguishing means. That is, two images of line laser light are generated on the tread surface, and the grooves with the same rotational direction coordinates (light section line coordinates) of the light section lines 11 (light section line 11-1, light section line 11-2) that are the images of the line laser light are distinguished as the rotational direction main groove.

[0038] FIG. 4 is a diagram showing an embodiment of the present invention in which the depth of a rotational main groove is calculated from a cutting line 11, which is an image of a line laser beam. When measuring groove depth by placing a gauge on an actual tire, the tire groove gauge (tire groove depth gauge) is placed in the normal direction to the tread surface, and the groove depth is measured so that the measuring needle hits the bottom of the groove at a right angle to the normal to the tread surface. This is because the tread surface is a gently curved surface. The image of the line laser beam formed on the tread surface by the rotational main groove measuring device 1, which is an embodiment of the present invention, also appears as a gently curved line.

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

[0040] One method for calculating the depth of the main groove from the optical cutting line 11 shown in Figure 4 is to select point A, which is one coordinate of the optical cutting line 11, point B, which is one coordinate of the optical cutting line 11 that is w away from point A in a direction transverse to the direction of tire rotation, and point C, which is one coordinate of the optical cutting line 11 that is 2w away from point A in a direction transverse to the direction of tire rotation.

[0041] The area of ​​the triangle formed by points A, B, and C is then calculated. This process is repeated until point A, B, or C is found at all coordinates on light-section line 11, and the areas of the triangles calculated in this way are graphed with the Y-coordinate value of light-section line 11 as the X-axis and the area of ​​the triangle as the Y-axis, resulting in a diagram like that shown in Figure 4(b). The groove depth of each triangle is calculated from the maximum value of the area of ​​the triangles thus obtained, and the groove depth at a location that is equal to or greater than a predetermined depth, for example, the groove depth indicated by the slip sign (1.6 mm for four-wheeled vehicles, 0.8 mm for two-wheeled vehicles), is determined to be the main groove depth.

[0042] 5 is a block diagram showing the configuration of an apparatus 1 for measuring the depth of a rotational direction main groove formed on a tire tread surface, which is one embodiment of the present invention. Two line lasers 10 irradiate different locations on the tire tread surface with line laser light. A camera 20 captures an image of the line laser light that appears on the tread surface. The line lasers 10 are controlled by a line laser control unit 310 of the control unit 31, and the camera 20 is controlled by an imaging control unit 311 of the control unit 31.

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

[0044] FIG. 6 is a diagram of the depth of the rotational main grooves formed on the tread surface of a tire (size: 215 / 55R17) obtained using a tire rotational main groove depth measuring device 1 that is one embodiment of the present invention. The line laser used had a wavelength of 600 nm, power consumption of 40 mW, and a power supply voltage of 5 VD, and the resolution of the camera 20 was 2048 x 1536. The image acquired using these specifications was processed to determine the coordinates of the light cutting line 11 and calculate the rotational main groove depth. As a result, the depth of the three main grooves 42 formed on the tread surface was detected to be between 5.4 mm and 5.9 mm.

[0045] 7 is a flowchart showing an example of a method for measuring the rotational direction main groove depth according to one embodiment of the present invention. Two line laser beams are irradiated onto the tire tread surface, and the image of the line laser beams that appears on the tread surface is emphasized and filtered (S1, S2). Next, the image of the line laser beams is binarized into two colors, for example, red and white or black and white, and then noise is removed (S3, S4).

[0046] Next, the line width of the two line laser light images is adjusted to, for example, 1 dot (1 pixel = 1 dot) from the average of each coordinate. Also, pixels (missing points) that are originally present in the line laser light images but have disappeared are linearly interpolated (S5, S6), and the coordinates of the light-section line 11, which is the image of the line laser light, are extracted (S7).

[0047] Next, points A, B, and C are selected from the coordinates of each light-section line 11, and the area of ​​the triangle formed by points A, B, and C is calculated (S8, S9). This process is repeated until point A is found to be the coordinate of all light-section lines 11, and the area of ​​the triangle formed by points A, B, and C is calculated (S10), and the maximum value of a graph with the area of ​​the triangle as the Y-axis and the Y-axis coordinate of the light-section line 11 as the X-axis is determined to be a candidate for the main groove (S11).

[0048] Among the candidates for the main groove determined from the coordinates of each light-section line, those whose Y coordinates approximately match those of the light-section line 11, for example, those whose Y coordinates do not deviate by more than the width of the rotational direction main groove, are determined to be the rotational direction main groove.The depth of the main groove is then calculated from the area of ​​the candidate determined to be the main groove (S12, S13). [Brief explanation of the drawings]

[0049] [Figure 1] 1 is a perspective view showing the configuration of a device for measuring the depth of a rotational direction main groove formed on the tread surface of a tire according to one embodiment of the present invention. [Figure 2] 1 is a diagram showing the positional relationship in the height direction between the camera and line laser light irradiation device of a tire rotational direction main groove measuring device according to one embodiment of the present invention and the tire tread surface. FIG. [Figure 3] 1 is a diagram showing a line laser beam projected onto a tire tread surface by a line laser projection device according to an embodiment of the present invention; FIG. [Figure 4] 10 is a diagram showing an embodiment of the present invention in which the depth of a rotational direction main groove is calculated from cutting line coordinates 11, which are an image of a line laser beam. FIG. [Figure 5]1 is a block diagram showing the configuration of an apparatus 1 for measuring the depth of a rotational direction main groove formed on the tread surface of a tire, which is an embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing the depth of a rotational direction main groove obtained by a line laser irradiation device according to an embodiment of the present invention. [Figure 7] 1 is a flowchart showing an example of a method for measuring the depth of a rotational direction main groove formed on the tread surface of a tire according to an embodiment of the present invention. [Explanation of symbols]

[0050] 1: Measurement device for tire rotational direction main grooves 10: Line laser light irradiation device 20: Camera 30: Data processing device 31: Control unit 32: Data processing section 40: Tires 41: Main groove in the direction of tire rotation 50: Table 310: Line laser control unit 311: Imaging control unit 320: Line laser image detection unit 321: Optical cutting line coordinate detection unit 322: Groove depth calculation unit 323:Main groove determination section

Claims

1. A measuring device for measuring the depth of a groove having a bottom surface formed on a tread surface of a tire in a rotational direction of the tire, a line laser light irradiation device that irradiates line laser light onto two different locations on the tread surface in a transverse direction that is transverse to the rotation direction; a camera that captures images of the line laser light at the two locations on the tread surface; a line laser image detection processing unit that detects images of the line laser light at the two locations from an image captured by the camera; a light section line coordinate detection unit that detects light section line coordinates, which are coordinates of the image of the line laser light at each of the two locations; a groove depth calculation unit that calculates the depth of the groove from the light section line coordinates of the line laser beam at each of the two locations; a main groove determination unit that determines the depth of the grooves that are equal to or greater than a predetermined value and whose coordinates in the transverse direction substantially coincide with each other as the depth of the main groove in the rotational direction, The groove depth calculation unit selects a first point which is one coordinate of the light section line coordinates, a second point which is the light section line coordinates a first distance away from the first point in the transverse direction, and a third point which is the light section line coordinates a second distance away from the first point in the transverse direction, and calculates the area of ​​a triangle formed by the first point, the second point, and the third point by repeatedly shifting the first point, the second point, and the third point until any of the first point, the second point, and the third point reaches all of the coordinates of the light section line coordinates, and calculates the depth of the groove from the area of ​​the triangle thus calculated.

2. The measuring device according to claim 1 , wherein the groove depth calculation unit calculates the depth of the groove from a maximum value of the area of ​​the triangles obtained by the calculation.

3. 3. The measuring device according to claim 1, wherein the second distance is twice the first distance.

4. The measuring device according to claim 1 , wherein the first distance is equal to or greater than one time and equal to or less than two times the width of the groove.

5. The candidate for the main groove is determined based on the maximum value of the area of ​​the triangles obtained by the calculation; 2. The measuring device according to claim 1, wherein the main groove determining unit determines, from among the candidates, a candidate whose transverse coordinate does not deviate by more than a width of the main groove as the main groove.

6. A method for measuring the depth of a groove having a bottom surface formed on a tread surface of a tire in a rotational direction of the tire, comprising: A line laser beam is irradiated onto two different locations on the tread surface in a transverse direction transverse to the rotation direction, capturing images of the line laser light at the two locations; Detecting light section line coordinates, which are coordinates of the images of the line laser light at each of the two locations, from the captured images; calculating a depth of the groove from the coordinates of the light section line of the line laser beam at each of the two locations; determining the depth of the grooves that are equal to or greater than a predetermined value and whose coordinates in the transverse direction substantially coincide with each other as the depth of the main groove in the rotational direction; In calculating the depth of the groove, selecting a first point which is one coordinate of the light section line coordinates, a second point which is the light section line coordinates and is a first distance away from the first point in the transverse direction, and a third point which is the light section line coordinates and is a second distance away from the first point in the transverse direction; The area of ​​the triangle formed by the first point, the second point, and the third point is repeatedly calculated while shifting the first point, the second point, and the third point until any of the first point, the second point, and the third point becomes a coordinate of the light-section line coordinate system; A measurement method in which the depth of the groove is calculated from the area of ​​the triangle.

Images