Tire tread depth measurement method, full-circumference tread depth measurement method and system

Abstract

The present invention relates to tire tread depth measurement, and in particular to a tire tread depth measurement method, a full-circumference tread depth measurement method and a system. A tire tread depth measurement method comprises the following steps: using a fixed transmitting unit and a receiving unit, using triangulation to measure the distance L1 from the outer surface of the tread to the transmitting unit and the distance L2 from the bottom surface of the tread to the transmitting unit; using a fixed camera to obtain an image of the tire, and using a machine vision unit to identify the center coordinate O of the sidewall. The beneficial effects of the present invention are: the measurement method has high measurement accuracy and can measure tires of different sizes.

Description

Technical Field

[0001] The invention relates to tire tread depth measurement, and in particular to a tire tread depth measurement method, a full-circumference tread depth measurement method and a system. Background Art

[0002] The main function of automobile tire tread is to increase the friction between the tread and the road surface, remove water and prevent the wheels from slipping. Excessive wear of the tire tread will increase the braking distance and reduce the grip, thus affecting driving safety. Therefore, it is one of the important guarantee conditions for the safe driving of automobiles that the tread depth of the tires of vehicles in use is not less than the limit requirement.

[0003] According to the national standard GB 38900-2020 "Motor Vehicle Safety Technical Inspection Items and Methods", the tread depth on the crown of passenger car and trailer tires should be greater than or equal to 1.6mm, and the tread depth on the crown of motorcycle tires should be greater than or equal to 0.8mm; the crown pattern depth of the steering wheels of other motor vehicles should be greater than or equal to 3.2mm, and the tire tread wear signs should be visible.

[0004] At present, the more common tire tread depth measurement methods are mainly divided into manual measurement and pass-through measurement. Among them, manual measurement means that the inspector uses a handheld depth gauge (mechanical or digital) or a handheld tread depth meter to measure. Pass-through measurement means that the measuring equipment is placed on the surface or buried underground, and the vehicle to be tested slowly passes over the measuring equipment, and the tread depth of the contact position between the tire surface and the measuring equipment can be measured.

[0005] Of the two current measurement methods, manual measurement is not only labor-intensive, but also results in differences in measurement results due to the different measurement habits of different measurement personnel (depth gauge reading estimation, measurement strength, etc.); while through-type measurement can only measure the tread depth value at the contact point between the tire and the equipment. The data is incomplete and cannot represent the tread depth of the entire tire circumference. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a tire tread depth measurement method and a full-circumference tread depth measurement method and system.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for measuring the tread depth of a tire comprises the following steps:

[0009] Using a fixed transmitting unit and a receiving unit, the distance L1 from the outer surface of the tread to the transmitting unit and the distance L2 from the bottom surface of the pattern to the transmitting unit are measured by triangulation;

[0010] A fixed camera is used to obtain an image of the tire, and a machine vision unit is used to identify the center coordinate O of the sidewall;

[0011] Since the transmitting unit and the camera are both fixedly arranged, the coordinates of the transmitting unit and the angle of the emitted light are known, and the straight line equation of the emitted light can be obtained. According to L1 and L2, the coordinates A of the intersection of the emitted light and the outer surface of the tread and the coordinates B of the intersection of the emitted light and the bottom surface of the pattern can be obtained from the straight line equation;

[0012] Afterwards, the true value of the pattern depth L3 can be obtained by two methods:

[0013] The first method is: use coordinates to calculate the OA distance and OB distance, and the difference between OA and OB is the true value of the pattern depth L3;

[0014] The second method is: use the coordinates of O, A, and B to calculate the cosine value cosα of the angle OAB. The product of the difference between L1 and L2 and cosα is the true value of the pattern depth L3.

[0015] According to the above technical solution, preferably, the transmitting unit is a line laser transmitter.

[0016] A method for measuring the full-circumference tread depth of a tire adopts the above-mentioned measuring method to measure the full-circumference data of the tread depth by rotating the tire.

[0017] A tire tread depth measurement system, comprising:

[0018] Braking platform, used to support and limit the tire;

[0019] The first module includes a transmitting unit and a receiving unit, the transmitting unit is used to transmit laser light to the tire tread, and the receiving unit is used to receive the laser light reflected back by the tread;

[0020] The second module includes a camera unit and a lighting unit, wherein the camera unit is used to capture an image of the tire sidewall, and the lighting unit is used to fill in light for the image;

[0021] The control unit is used to collect the data output by the first module and the second module, and obtain the true value of the pattern depth according to the above-mentioned measurement method.

[0022] According to the above technical solution, preferably, the brake platform is provided with a pair of parallel rollers.

[0023] According to the above technical solution, preferably, a shell is provided outside the first module, the shell is provided with a window, and an air knife is provided on the side of the window.

[0024] The beneficial effects of the present invention are: the measuring method has high measuring accuracy and can measure tires of different sizes;

[0025] By using this system in conjunction with a brake stand, the tire tread depth can be tested at the same time as the brake test, combining the two steps into one, simplifying the measurement process, and completing the installation structure away from the brake stand. On-site construction and subsequent maintenance do not need to involve the brake stand itself, thus improving operability and maintainability.

[0026] The design used in conjunction with the brake platform can measure the full circumference of the tire's tread depth, which is superior to manual measurement and the pass-through method that can only measure the depth of a single cross-section position;

[0027] The design of the self-cleaning function reduces the test error caused by dirt during the measurement process and reduces overly frequent manual maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram showing the triangulation measurement principle of an embodiment of the present invention is shown.

[0029] Figure 2 A schematic diagram of the error of the tread depth measurement value according to an embodiment of the present invention is shown.

[0030] Figure 3 A schematic diagram of a first calculation method according to an embodiment of the present invention is shown.

[0031] Figure 4 A schematic diagram of a second calculation method according to an embodiment of the present invention is shown.

[0032] Figure 5 A schematic diagram of the structure of a measurement system according to an embodiment of the present invention is shown.

[0033] Figure 6 A schematic diagram of the first module structure of an embodiment of the present invention is shown.

[0034] In the figure: 1. First module, 2. Brake platform, 3. Tire, 4. Air knife, 5. Fill light, 6. Industrial camera, 7. Control box, 8. Line laser, 9. Industrial camera. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiments.

[0036] As shown in the figure, the present invention

[0037] Embodiment 1:

[0038] The transmitting unit adopts a line laser, the receiving unit adopts an industrial camera, and the triangulation method is used to measure the distance L1 from the outer surface of the tread to the transmitting unit and the distance L2 from the bottom surface of the pattern to the transmitting unit.

[0039] The trigonometric method is as follows:

[0040] Since the transmitting unit and the receiving unit are fixedly arranged, the length s of the reference line between the transmitting unit and the receiving unit, the focal length f of the industrial camera, and the angle β between the laser head and the reference line are all known constants.

[0041] like Figure 1 As shown, the line laser irradiates the object to be measured and then reflects to the imaging plane of the industrial camera as point P. The triangle formed by the line laser, the industrial camera, and the object to be measured is similar to the triangle formed by the industrial camera, point P and the auxiliary point P'. From similar triangles, it can be obtained that: f / x=q / s, that is, q=fs / x, where x is the distance between P and P'. X can be obtained by summing x1 and x2, where x1=f / tanβ, and x2 can be read from the distance between the imaging point P and the vertical projection point of the industrial camera on the imaging platform. The distance between the line laser and the object to be measured is d=q / sinβ=fs / (f / tanβ+x2)sinβ. The above trigonometric method can be used to measure the distance L1 from the outer surface of the tread to the transmitting unit and the distance L2 from the bottom surface of the pattern to the transmitting unit.

[0042] like Figure 2 As shown, since the transmitting unit is fixed and the tire size (radius or diameter) is different, or the relative position between the tire and the transmitting unit is different each time the measurement is performed, the difference between L1 and L2 is not the actual tread depth and the tread depth needs to be corrected.

[0043] First, the image of the tire sidewall is captured by a camera. Then, the center coordinate O of the sidewall image is identified by a machine vision unit. The specific method is as follows:

[0044] 1. Binarize the image: The materials of wheels and tires are often quite different, which is reflected in the image as the grayscale value of the wheels is larger and the grayscale value of the tire is smaller. Due to the change in the material of the wheels, the adaptive threshold binarization method is used to separate the wheels.

[0045] 2. Perform contour search on the binarized image: The so-called contour is the edge of each connected domain in each image. Since the styles of the hubs are quite diverse, the contour found in this step contains many small contours inside in addition to the contour of the largest hub circle.

[0046] 3. Based on the two conditions that the wheel hub's contour area is the largest and it is like a circle, the wheel hub's contour is selected from the contour obtained in step 2. The least squares fitting is performed based on the points on this contour to preliminarily obtain the wheel hub fitting circle and the coordinates of the center of the circle.

[0047] 4. Perform sub-pixel extraction on each previously obtained point on the circumference to obtain the point on the circumference more accurately, and perform least squares fitting based on these sub-pixel points to obtain the hub fitting circle and the coordinates of the center of the circle.

[0048] 5. Repeat step 4. The iteration termination condition is that the change in the center coordinate is less than 0.1 pixel.

[0049] Since the transmitting unit and the camera are both fixedly arranged, the coordinates of the transmitting unit and the angle of the emitted light are known, and the straight line equation of the emitted light can be obtained. According to L1 and L2, the coordinates A of the intersection of the emitted light and the outer surface of the tread and the coordinates B of the intersection of the emitted light and the bottom surface of the pattern can be obtained from the straight line equation;

[0050] Based on the above known quantities, the true value of the tread depth L3 can be calculated in the following two ways:

[0051] like Figure 3 As shown, the first method is: use the coordinates to calculate the OA distance and the OB distance, and the difference between OA and OB is the true value of the pattern depth L3;

[0052] like Figure 4 As shown, the second method is: use the coordinates of O, A, and B to calculate the cosine value cosα of the angle OAB, and the product of the difference between L1 and L2 and cosα is the true value of the pattern depth L3.

[0053] According to the above embodiment, preferably, the full circumference data of the tread depth is measured by rotating the tire.

[0054] Embodiment 2:

[0055] A tire tread depth measurement system, comprising:

[0056] The brake stand is used to support and limit the tire. The brake stand is an existing vehicle detection device. The brake stand is equipped with a pair of parallel rollers that can drive the tire to rotate and realize the measurement of the full-circle pattern depth.

[0057] The first module is used to complete the triangulation measurement steps of the above-mentioned embodiment 1. The first module is installed on the front side of the brake platform to facilitate the measurement of L1 and L2. The first module includes a transmitting unit and a receiving unit. The transmitting unit is used to transmit laser to the tire tread, and the transmitting unit can use a line laser transmitter. The receiving unit is used to receive the laser reflected back from the tread, and the receiving unit is composed of an industrial camera, a lens and a filter. The first module is provided with a shell outside, and the shell is provided with a window. The window is located at the transmitting unit and the receiving unit, and the window is provided with hardened glass. An air knife is provided on the side of the window to clean the glass of the window. In addition, two first modules can be set on a brake platform to measure the left and right tires of the same vehicle.

[0058] The second module is used to complete the machine vision unit to identify the center coordinate O of the sidewall image. The second module is installed on the outside of the brake platform to facilitate the identification of the center coordinate of the sidewall. The second module includes a camera unit and a lighting unit. The camera unit is used to capture the image of the sidewall. The lighting unit is used to fill in the image with light, and an LED fill light can be used.

[0059] The control unit is used to collect the data output by the first module and the second module, and obtain the true value of the pattern depth according to the measurement method of the first embodiment.

[0060] The working principle of this embodiment is:

[0061] 1. Install the first module on the brake platform with the industrial camera side close to the brake platform, and install the second module on the side of the vehicle's driving direction. The specific installation distance is determined by the field of view of the industrial camera in the second module, and the field of view is required to capture the entire tire diameter;

[0062] 2. Perform overall measurement and calibration on the first and second modules;

[0063] 3. The vehicle to be tested drives onto the brake platform roller, and the airbag is controlled to make the lifting beam fall down (no measurement is performed during the lifting process);

[0064] 4. The drum starts to rotate;

[0065] 4. The tire tread depth measurement system receives an external signal to start measuring, and controls the first and second modules to start working simultaneously through the industrial computer;

[0066] 5. The line laser in the first module irradiates the surface of the tire to be tested and the bottom of the groove, forming stripes with surface profile height differences. The stripes are imaged on the target surface of the industrial camera by the filter and the lens. The use of the filter can reduce the interference of external stray light on the photographic effect of the industrial camera. The air knife works synchronously to clean the surface of the module window to prevent the glass surface from being affected by dirt and affecting the measurement. By calculation, the distance from the tire surface to the bottom of the groove measured along the propagation direction of the line laser at the incident angle can be obtained;

[0067] 6. The industrial camera in the second module takes a full picture of the tire from the side, and determines the coordinates of the center of the circle by extracting the diameter information. The angle between the incident light and the radial direction at the incident point can be obtained by calculation;

[0068] 7. Through angle correction processing, the actual depth of the tire tread at the measurement position at the time of taking the photo can be obtained;

[0069] 8. As the roller rotates continuously, the depth value of each position around the tire can be measured.

[0070] The beneficial effects of the present invention are: the measuring method has high measuring accuracy and can measure tires of different sizes;

[0071] By using this system in conjunction with a brake stand, the tire tread depth can be tested at the same time as the brake test, combining the two steps into one, simplifying the measurement process, and completing the installation structure away from the brake stand. On-site construction and subsequent maintenance do not need to involve the brake stand itself, thus improving operability and maintainability.

[0072] The design used in conjunction with the brake platform can measure the full circumference of the tire's tread depth, which is superior to manual measurement and the pass-through method that can only measure the depth of a single cross-section position;

[0073] The design of the self-cleaning function reduces the test error caused by dirt during the measurement process and reduces overly frequent manual maintenance.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for measuring tire tread depth, characterized in that: The following steps are involved: Using a fixed transmitting unit and a receiving unit, the distance L1 from the outer surface of the tread to the transmitting unit and the distance L2 from the bottom surface of the pattern to the transmitting unit are measured by triangulation; A fixed camera unit is used to obtain an image of the tire, and a machine vision unit is used to identify a center coordinate O of the sidewall; The linear equation of the emitted light is obtained by the relative positions of the cameras of the emitting unit and the receiving unit. The intersection coordinates A of the emitted light and the outer surface of the tread and the intersection coordinates B of the emitted light and the bottom surface of the pattern can be obtained from the linear equation according to L1 and L2; There are two ways to get the true value of the pattern depth L3: The first method is: use coordinates to calculate the OA distance and OB distance, and calculate the difference between OA and OB as the true value of the pattern depth L3; The second method is: use the coordinates of O, A, and B to calculate the cosine value cosα of the angle OAB, and the product of the difference between L1 and L2 and cosα is the true value of the pattern depth L3.

2. A tire tread depth measurement method according to claim 1, characterized in that: The transmitting unit is a line laser transmitter.

3. A method for measuring the tread depth of a tire all around, using the measurement method described in any one of claims 1 to 2, characterized in that: The tread depth is measured around the circumference of the tire by rotating it.

4. A tire tread depth measurement system, characterized in that: include: Braking platform, used to support and limit the tire; The first module includes a transmitting unit and a receiving unit, the transmitting unit is used to transmit laser light to the tire tread, the receiving unit is used to receive the laser light reflected back by the tread, and the receiving unit transmits data to the control unit; The second module includes a camera unit and a lighting unit, wherein the camera unit is used to capture an image of the tire sidewall, the lighting unit is used to fill in light for the image, and the camera unit transmits the image to the control unit; The control unit is used to collect data output by the first module and the second module, and obtain the true value of the pattern depth according to the measurement method described in any one of claims 1 to 3.

5. A tire tread depth measurement system according to claim 4, characterized in that: The brake platform is provided with a pair of parallel rollers.

6. A tire tread depth measurement system according to claim 4, characterized in that: A shell is arranged outside the first module, a window is arranged on the shell, and an air knife is arranged on the side of the window.

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