METHOD FOR DETERMINING THE TRAFILM DEPTH OF A VEHICLE TIRE

Description

[0001] The invention relates to a method for determining a tread depth of a vehicle tire.

[0002] The invention is based on a method for determining a tread depth of a vehicle tire, comprising the following steps: Providing a vehicle tire; providing an image recording device, wherein the image recording device is configured to record an image of the vehicle tire; recording an image of the vehicle tire using the image recording device; providing a model of a cylinder, wherein the cylinder encloses the vehicle tire and wherein a straight line running along a height and symmetry axis of the cylinder is, in particular, equal to a straight line running along a rotation axis of the vehicle tire; determining the rotation axis of the vehicle tire, wherein the vehicle tire is configured to rotate about the rotation axis in a circumferential direction of the vehicle tire; providing an image processing device, wherein the image processing device is configured to generate a 3D model of the vehicle tire based on the image of the vehicle tire and the model of the cylinder and the rotation axis.Generating a 3D model of the vehicle tire based on the image of the vehicle tire and the model of the cylinder and the rotation axis by means of the image processing device within a spatial coordinate system provided by the image recording device; Providing an evaluation device, wherein the evaluation device is designed to determine a tread depth of the vehicle tire depending on the 3D model of the vehicle tire.

[0003] It is a recording of an image of the surface of a vehicle tire. A surface of a vehicle tire is an area of ​​the vehicle tire oriented away from the vehicle tire. This surface can also be referred to as the outer surface.

[0004] In the method step of recording an image of the vehicle tire, an image of at least one area of ​​the vehicle tire, i.e. an area of ​​the surface of the vehicle tire, or an image of the entire vehicle tire, i.e. the entire surface of the vehicle tire, is recorded by means of the image recording device.

[0005] The image capture device could be a camera, for example. The image processing device could be a computer, for example.

[0006] In the process step of creating a 3D model, i.e., a three-dimensional model, of the vehicle tire, a 3D model of a region of the vehicle tire or a 3D model of the entire vehicle tire is created. The 3D model is thus a 3D model of a region of the surface of the vehicle tire or a 3D model of the entire surface of the vehicle tire.

[0007] The cylinder is a model of a cylinder with a circular cross-section. The model is, for example, a mathematical and / or computer-generated model of a cylinder. A tire zenith of the vehicle tire runs along the lateral surface of the cylinder and parallel to the circular cross-section of the cylinder. The cylinder's axis of symmetry is perpendicular to the circular cross-section of the cylinder. The use of the cylinder enables a geometric analysis and observation of the surface of the vehicle tire.

[0008] The evaluation device is, for example, an electronic evaluation device or a computer.

[0009] The vehicle tire can, for example, be a passenger car tire, a truck tire or a two-wheeler tire.

[0010] Methods for determining the tread depth of a vehicle tire are known from the prior art. It is also known from the prior art that a model of a cylinder is provided, wherein the cylinder encloses the vehicle tire, and wherein a straight line running along a height and symmetry axis of the cylinder is, in particular, equal to a straight line running along the rotation axis of the vehicle tire. According to the methods known from the prior art, for example, errors could occur when adapting the cylinder to the surface of the vehicle tire. Although the cylinder would partially enclose the vehicle tire, the spatial coordinate system provided by the image recording device, in which the cylinder is also viewed and used, could be shifted or rotated relative to a coordinate system that can be defined by the vehicle tire itself.A 3D model of the vehicle tire, which has been generated depending on the image of the vehicle tire and the model of the cylinder and the rotation axis within a spatial coordinate system provided by the image recording device, but shifted from the coordinate system defined by the vehicle tire itself, could lead to an incorrect determination of the tread depth of the vehicle tire.

[0011] For example, the vehicle tire itself can be used to define a coordinate system based on the tire's rotational axis and the gravitational vector at the tire's location, as well as a third vector. The third vector, for example, is perpendicular to the tire's rotational axis and the gravitational vector.

[0012] The invention is therefore based on the object of providing a method for determining a tread depth of a vehicle tire, wherein by means of the method a 3D model of the vehicle tire can be viewed in a coordinate system defined by the vehicle tire itself, whereby a tread depth of the vehicle tire can be correctly determined with greater certainty.

[0013] The object of the invention is achieved in that the method comprises the following further steps: Determining a normal vector of a lateral surface of the cylinder, wherein the normal vector of the lateral surface of the cylinder is parallel to an image recording direction of the image of the vehicle tire; Determining a gravitational vector of the earth at the location of the vehicle tire; Generating a spatial reference coordinate system depending on the rotation axis of the vehicle tire, the gravitational vector of the earth at the location of the vehicle tire, and the normal vector of the lateral surface of the cylinder; Transferring the 3D model of the vehicle tire from the spatial coordinate system provided by the image recording device into the spatial reference coordinate system; Determining the tread depth of the vehicle tire depending on the 3D model of the vehicle tire transferred into the spatial reference coordinate system.

[0014] The gravitational vector of the Earth at the location of the vehicle tire is essentially the same as the gravitational vector of the Earth at the location of the imaging device.

[0015] The 3D model of the vehicle tire is transferred from the spatial coordinate system provided by the image acquisition device to the spatial reference coordinate system by converting the provided spatial coordinate system into the spatial reference coordinate system. The conversion is performed, for example, by transforming the coordinates, which can be in Cartesian or polar form. The transfer or conversion can be performed, for example, electronically or by means of the evaluation device.

[0016] The spatial reference coordinate system corresponds to the coordinate system defined by the vehicle tire itself. The 3D model is thus viewed in the coordinate system defined by the vehicle tire itself. Using this model, the tread depth of the vehicle tire can be accurately determined with greater certainty.

[0017] Thus, an improved method for determining a tread depth of a vehicle tire is provided.

[0018] Further advantageous embodiments of the present invention are the subject of the subclaims.

[0019] According to a preferred embodiment of the present invention, a cross product of the normal vector of the cylinder's lateral surface is formed with the Earth's gravitational vector at the location of the vehicle tire. The rotation axis of the vehicle tire is determined as a function of a result vector of the cross product. In particular, the 3D model of the vehicle tire is determined as a function of this rotation axis, and the 3D model of the vehicle tire is transferred from the spatial coordinate system provided by the image recording device to the spatial reference coordinate system.

[0020] According to a further preferred embodiment of the present invention, the image recording direction is compared with a normal vector of the cylinder's outer surface. If the image recording direction is not parallel to any normal vector of the cylinder's outer surface, the spatial coordinate system provided by the image recording device is spatially aligned with the vehicle tire until the image recording direction is parallel to a normal vector of the cylinder's outer surface. This alignment of the spatial coordinate system provided by the image recording device can be achieved, for example, using a cross product.For example, a third vector can be generated using a cross product of the Earth's gravitational vector at the location of the vehicle tire with a vector parallel to the rotation axis of the vehicle tire, whereby the gravitational vector at the location of the vehicle tire, the vector parallel to the rotation axis, and the third vector define the reference coordinate system. The vehicle tire under consideration is initially represented by the image recording device in the spatial coordinate system provided by the image recording device. The cross product can be used to rotate the spatial coordinate system provided by the image recording device into the spatial reference coordinate system. This conversion can be carried out, for example, using a transformation matrix.The transformation matrix mathematically describes the transition from the spatial coordinate system provided by the image recording device to the spatial reference coordinate system.

[0021] Thus, the spatial coordinate system provided by the image acquisition device is aligned to coincide with the spatial reference coordinate system.

[0022] Further advantages, features and details, to which the invention is not limited in its scope, will now be described in more detail with reference to the drawing.

[0023] It shows: Fig. 1 : A schematic representation of a vehicle tire.

[0024] In the Figure 1A vehicle tire 1 is shown schematically in a radial sectional view. The vehicle tire 1 is rotatable about a rotation axis 2 in a direction of rotation 3. An image recording device 8 can capture an image of a surface 11 of the vehicle tire 1.

[0025] According to the invention, a model of a cylinder 4 is provided, wherein the cylinder 4 envelops the vehicle tire 1 and wherein a straight line 12 running along a height and symmetry axis of the cylinder 4 is in particular equal to a straight line 13 running along the rotation axis 2 of the vehicle tire 1.

[0026] According to the invention, an image processing device 14 is provided, wherein the image processing device 14 is configured to generate a 3D model of the vehicle tire 1 based on the image of the vehicle tire 1 and the model of the cylinder 4 and the rotation axis 2.

[0027] A 3D model of the vehicle tire 1 is generated based on the image of the vehicle tire 1 and the model of the cylinder 4 and the rotation axis 2 by means of the image processing device 14 within a spatial coordinate system 9 provided by the image recording device 8.

[0028] According to the invention, an evaluation device 15 is provided, wherein the evaluation device 15 is provided for determining a tread depth of the vehicle tire 1 as a function of the 3D model of the vehicle tire 1,

[0029] Furthermore, a normal vector 6 of a lateral surface 16 of the cylinder 4 is determined, wherein the normal vector 6 of the lateral surface 16 of the cylinder 4 is parallel to an image recording direction 7 of the image of the vehicle tire 1. The image recording direction 7 corresponds to the direction in which the image recording device 8 is oriented to record an image of a surface 11 of the vehicle tire 1.

[0030] Furthermore, a gravitational vector 5 of the Earth is determined at the location 17 of the vehicle tire 1.

[0031] According to the invention, a spatial reference coordinate system 10 is generated as a function of the rotation axis 2 of the vehicle tire 1, the gravitational vector 5 of the earth at the location 17 of the vehicle tire 1 and the normal vector 6 of the lateral surface 16 of the cylinder 4.

[0032] Finally, the 3D model of the vehicle tire 1 is transferred from the spatial coordinate system 9 provided by the image recording device 8 into the spatial reference coordinate system 10. This transfer is carried out in particular by converting coordinate data from the 3D model of the vehicle tire 1.

[0033] The tread depth of the vehicle tire 1 is determined depending on the 3D model of the vehicle tire 1 transferred into the spatial reference coordinate system 10. List of reference symbols

[0034] 1Vehicle tire 2Axis of rotation 3Direction of rotation 4Cylinder 5Gravity vector 6Normal vector 7Image acquisition direction 8Image acquisition device 9Spatial coordinate system of the image acquisition device 10Spatial reference coordinate system 11Surface of the vehicle tire 12Straight line parallel to the axis of symmetry of the cylinder 13Straight line parallel to the axis of rotation 14Image processing device 15Evaluation device 16Surface of the cylinder 17Location of the vehicle tire

Claims

1. Method for determining a tread depth of a vehicle tyre (1), comprising the following steps: - providing a vehicle tyre (1); - providing an image recording device (8), wherein the image recording device (8) is intended to record an image of the vehicle tyre (1); - recording an image of the vehicle tyre (1) by means of the image recording device (8); - providing a model of a cylinder (4), wherein the cylinder (4) envelops the vehicle tyre (1) and wherein a straight line (12) running along a vertical axis and axis of symmetry of the cylinder (4) is in particular identical to a straight line (13) running along a rotation axis (2) of the vehicle tyre (1); - determining the rotation axis (2) of the vehicle tyre, wherein the vehicle tyre (1) is intended for rotation about the rotation axis (2) in a direction (3) of rotation of the vehicle tyre (1); - providing an image processing device (14), wherein the image processing device (14) is designed to generate a 3D model of the vehicle tyre (1) on the basis of the image of the vehicle tyre (1) and the model of the cylinder (4) and the rotation axis (2); - generating a 3D model of the vehicle tyre (1) on the basis of the image of the vehicle tyre (1) and the model of the cylinder (4) and the rotation axis (2) by means of the image processing device (14) within a spatial coordinate system (9) provided by the image recording device (8); - providing an evaluation device (15), wherein the evaluation device (15) is intended for determining a tread depth of the vehicle tyre (1) depending on the 3D model of the vehicle tyre (1); - characterized by the further steps of: - determining a normal vector (6) of a lateral surface (16) of the cylinder (4), wherein the normal vector (6) of the lateral surface (16) of the cylinder (4) is parallel to an image recording direction (7) of the image of the vehicle tyre (1); - determining a gravitational vector (5) of the Earth at the location (18) of the vehicle tyre (1); - generating a spatial reference coordinate system (10) depending on the rotation axis (2) of the vehicle tyre (1), the gravitational vector (5) of the Earth at the location (17) of the vehicle tyre (1) and the normal vector (6) of the lateral surface (16) of the cylinder (4); - converting the 3D model of the vehicle tyre (1) from the spatial coordinate system (9) provided by the image recording device (8) into the spatial reference coordinate system (10); - determining the tread depth of the vehicle tyre (1) depending on the 3D model of the vehicle tyre (1) converted into the spatial reference coordinate system (10).

2. Method according to Claim 1, characterized in that a cross product of the normal vector (6) of the lateral surface (16) of the cylinder (4) with the gravitational vector (4) of the Earth at the location (17) of the vehicle tyre (1) is formed and wherein the rotation axis (2) of the vehicle tyre (1) is determined depending on a result vector of the cross product.

3. Method according to either of the preceding Claims 1 and 2, characterized in that the image recording direction (7) is compared with a normal vector (6) of the lateral surface (16) of the cylinder (4), wherein in the event that the image recording direction (7) is not parallel to any normal vector (6) of the lateral surface (16) of the cylinder (4), the spatial coordinate system (9) provided by the image recording device (8) is oriented spatially with respect to the vehicle tyre 1 until the image recording direction (7) is parallel to a normal vector (6) of the lateral surface (16) of the cylinder (4).