Tire inspection method

The electromagnetic radiation source arranged at the first position apart from the tire irradiates the electromagnetic radiation rays to the first and second points on the tire, respectively, and the first and second coordinates on the camera are acquired, the first and second coordinates corresponding to the first and second points, respectively. The electromagnetic radiation source moved from the first position to the second position along with an axial direction irradiates the electromagnetic radiation rays to the first and second points, respectively, and the third and fourth coordinates on the camera are acquired, the third and fourth coordinates corresponding to the first and second points, respectively. The coordinate of the first point is found by finding the intersection of the straight line connected between the first point and the first coordinate and the straight line connected between the second point and the third coordinate. At the same time, and the coordinate of the second point is found by finding the intersection of a straight line connected between the first position and the second coordinate and the straight line connected between the second position and the fourth coordinate. The real distance between the first point and the second point is calculated based on the coordinates of the first and second points. The length between the first point and the second point on the image is transformed into the real distance between the first point and the second point.

TECHNICAL FIELD

The present invention relates to a tire inspection method for acquiring an image inside of a tire arranged between an electromagnetic radiation source and a camera at an opposed position of the electromagnetic radiation source and inspecting an arrangement of a belt cord (a steel cord) inside of the tire based on the acquired image.

RELATED ART

In a conventional tire inspection, as described in Japanese Patent Application Laid Open No. 341,930/1994, an inside of a tire is observed by observing an image of the tire acquired from a camera using an electromagnetic radiation ray such as an X-ray and a gamma ray.

However, in the conventional tire inspection, since the image acquired from the camera shows a width or a size of the tire larger than a real size of the tire in accordance with a principle of imaging, it is impossible to know a real distance between belt cords or a belt cord width inside of the tire. Therefore, since the tire width or the tire size on the image is different from a real tire width or a real tire size, it is difficult to improve a detection accuracy in a check with eyes or an automatic judgment of the tire.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a tire inspection method which is capable of improving the detection accuracy in the check with eyes or the automatic judgment of the tire.

In an aspect of the present invention, there is provided a tire inspection method for acquiring an image inside of a tire arranged between an electromagnetic radiation source and a camera at an opposed position of the electromagnetic radiation source and inspecting an arrangement of a belt cord inside of the tire based on the acquired image; the method comprising steps of:arranging the electromagnetic radiation source at a first position apart from the tire, irradiating electromagnetic radiation rays from the electromagnetic radiation source to first and second points on the tire, respectively, and acquiring first and second coordinates on the camera, the first and second coordinates corresponding to the first and second points, respectively;moving the electromagnetic radiation source from the first position to a second position along with an axial direction, irradiating the electromagnetic radiation rays from the electromagnetic radiation source to the first and second points, respectively, and acquiring third and fourth coordinates on the camera, the third and fourth coordinates corresponding to the first and second points, respectively;finding a coordinate of the first point by finding an intersection of a straight line connected between the first point and the first coordinate and a straight line connected between the second point and the third coordinate, and finding a coordinate of the second point by finding an intersection of a straight line connected between the first position and the second coordinate and a straight line connected between the second position and the fourth coordinate;calculating a real distance between the first point and the second point based on the coordinates of the first and second points; andtransforming a length between the first point and the second point on the image into a real distance between the first point and the second point.

When acquiring the image inside of the tire arranged between the electromagnetic radiation source and the camera at an opposed position of the electromagnetic radiation source and inspecting the arrangement of the belt cord inside of the tire based on the acquired image, it is necessary to correct the belt cord width or the size between the belt cords on the acquired image in order to acquire the real belt cord width of the belt cord and the real distance between the belt cords inside of the tire.

However, since a belt of the tire does not bend at a constant curvature but the belt at a central area of a tread extends in a horizontal direction and the curvature at an end of the tread is larger than that at the central area of the tread, the belt cord inside of the tire is not always arranged in the horizontal direction and the belt cord inside of the tire sometimes bends because of the tire size and the curvature of inner surface of the tire. Therefore, when correcting the belt cord width or the size between the belt cords, a correction using a similarity of a triangle is not effective if the belt cord inside of the tire is not arranged in the horizontal direction.

According to the present invention, there are (1) to (5) steps in the following.(1) The electromagnetic radiation source arranged at the first position apart from the tire irradiates the electromagnetic radiation rays to the first and second points on the tire, respectively, and the first and second coordinates on the camera are acquired, the first and second coordinates corresponding to the first and second points, respectively.(2) The electromagnetic radiation source moved from the first position to the second position along with an axial direction irradiates the electromagnetic radiation rays to the first and second points, respectively, and the third and fourth coordinates on the camera are acquired, the third and fourth coordinates corresponding to the first and second points, respectively.(3) The coordinate of the first point is found by finding the intersection of the straight line connected between the first point and the first coordinate and the straight line connected between the second point and the third coordinate, and the coordinate of the second point is found by finding the intersection of a straight line connected between the first position and the second coordinate and the straight line connected between the second position and the fourth coordinate.(4) The real distance between the first point and the second point is calculated based on the coordinates of the first and second points.(5) The length between the first point and the second point on the image is transformed into the real distance between the first point and the second point.

In this way, by radiating the electromagnetic radiation rays from the first and second positions and finding the first and second points from the intersections between the electromagnetic radiation rays from the first position and that from the second position, it is possible to calculate the real distance between the first point and the second point in consideration of a degree of inclination of the belt even in the end of the tread with the high curvature. As a result, it is possible to improve the detection accuracy in the check with eyes or the automatic judgment of the tire.

When the first point is one end of the belt cord and the second point is the other end of the belt cord, it is possible to calculate the real belt cord width. When the first point is one end of the belt cord and the second point is one end of another belt cord neighboring to one end of the belt cord, it is possible to calculate a step of two belt ends that is a distance between the two belt cord ends with different width from each other.

BEST MODE FOR CARRING OUT THE INVENTION

A preferred embodiment of the tire inspection method according to the invention is described with reference to accompanying drawings.

FIG. 1is a diagram showing a tire inspection apparatus carrying out the tire inspection method according to the present invention. The tire inspection apparatus comprises an X-ray source1, X-ray camera2, an image processing section3and a monitor4.

The X-ray source1is movable along a y-axis direction of a three-dimensional coordinate system (The y-axis direction corresponds to a horizontal direction.) and irradiates an X-ray to a tire5to be inspected. The X-ray through the tire5is incident on the X-ray camera2and the X-ray camera2acquires an image of a tire5to be inspected. The image processing section3processes the acquired image as described later and the processed image is output to the monitor4.

FIG. 2is a diagram explaining the tire inspection method according to the present invention andFIG. 3is a flow chart of steps of the tire inspection method according to the present invention. These steps are to acquire an image inside of a tire13arranged between an X-ray radiation source11and a X-ray camera12at an opposed position of the X-ray radiation source11and to inspect an arrangement of a belt cord inside of the tire13based on the acquired image. At first, in Step S1, the X ray source11is arranged on a position of an x-y coordinate (0, y1).

Next, the x-ray source11irradiates radiation rays α1, α2to points A, B of the tire13, respectively (Step S2), and an x-y coordinates (x1,0), (x2,0) on the camera12is acquired (Step S3), the x-y coordinates (x1,0), (x2,0) corresponding to the points A, B, respectively. Next, the X-ray source11is arranged on a position of an x-y coordinate (0, y2) (Step S4), the x-ray source11irradiates radiation rays α3, α4to the points A, B of the tire13, respectively (Step S5), and an x-y coordinates (x3,0), (x4,0) on the camera12is acquired (Step S6), the x-y coordinates (x3,0), (x4,0) corresponding to the points A, B, respectively.

When acquiring the x coordinates x1to x4, points of reference (marks) of an object to be measured (in the embodiment, the points A, B) are determined and the coordinates are calculated from the X-ray12camera acquiring the marks. Therefore, when the point A is one end of the belt cord and the point B is the other end of the belt cord, it is possible to calculate the real belt cord width. On the other hand, the point A is one end of the belt cord and the point B is one end of another belt cord neighboring to one end of the belt cord, it is possible to calculate a step of two belt ends that is a distance between the two belt cord ends with different width from each other. For an object having no points of reference (mark) of metal, it is possible to find the x coordinates x1to x4by preliminarily fixing a metal piece to an inclined portion of an object to be inspected. Further, a point C which is an intersection of a y-axis and the tire13is known and the x-y coordinate on the X-ray camera12corresponding to the point C is (0,0).

Next, an x-y coordinate (ax, ay) of the point A is found by finding an intersection of the radiation ray α1(which is a straight line connected between the x-y coordinate (0, y1) and the x-y coordinate (x1,0)) and the radiation ray α3(which is a straight line connected between the x-y coordinate (0, y2) and the x-y coordinate (x3,0)), and an x-y coordinate (bx, by) of the point B is found by finding an intersect of the radiation ray a2(which is a straight line connected between the x-y coordinate (0, y1) and the x-y coordinate (x2,0)) and the radiation ray α4(which is a straight line connected between the x-y coordinate (0, y2) and the x-y coordinate (x4,0)). (Step S7).

Next, a real length t between the point A and the point B is calculated (Step S8). The distance t becomes {(ax−by)2+(ay−by)2}1/2. At the end, the distance between the point A and the point B on the image is transformed into the length t.

Hereinafter, an experimental result of the tire inspection method according to the present invention will be explained. An experiment was carried out where four belt cords21a,21b,21cand21dwith 12.4 mm width were arranged inside of a tire22. (Refer toFIG. 4) In this case, a belt cord width to be imaged was a multiplication of the number of pixels and the pixel width occupied by the belt cord to be imaged. (The multiplication of the number of pixels and the pixel width corresponded to 4 mm.)

FIG. 5is a diagram showing an experimental result of the tire inspection method according to the present invention. The four belt cord widths to be imaged were 19.6 mm, 17.2 mm, 16.8 mm and 16.4 mm, respectively, as shown in a line a ofFIG. 5. By correcting four belt cord widths to be imaged with the tire inspection method according to the present invention, the four belt cord widths to be imaged were transformed into 12.0 mm, 12.00 , 12.4 m and 12.8 mm, respectively as shown in a line b ofFIG. 5. Therefore, the four belt cord widths as shown in the line b substantially corresponded to real belt cord widths, respectively.

While the preferred embodiment of the present invention is explained with reference to the accompanying drawings, many changes and many modifications may be made without departing from the scope of the invention.

For example, other kinds of the electromagnetic radiation ray such as gamma ray may be used instead of the X-ray.