A tire bulge detection and analysis method and system

Abstract

The present invention discloses a tire bulge detection and analysis method and system, the method comprises the following steps: step 1, obtaining a swing displacement curve of any measuring point of a tire without bulge; step 2, obtaining a swing displacement curve of any measuring point of the tire to be tested by image acquisition; step 3, comparing the swing displacement curve of any measuring point of the tire to be tested obtained in step 2 with the swing displacement curve of the corresponding measuring point of the tire without bulge obtained in step 1, and judging that the measuring point corresponding to the position where the bulge of the tire to be tested appears is the target measuring point; step 4, establishing a local coordinate system, converting the coordinates of the target measuring point in the world coordinate system to the local coordinate system, and calculating the strain tensor of the target measuring point. The system disclosed in the present invention comprises a binocular image acquisition system for collecting tire images and a data processing system for implementing the method. The present invention can obtain the strain data of the tire surface at the position where the bulge appears, and there is no false alarm problem caused by tire swing.

Description

Technical Field

[0001] The present invention relates to the field of tire detection methods, and in particular to a tire bulge detection and analysis method and system. Background Art

[0002] Tires are important parts of cars. They look simple but are actually very complicated. In the actual use of tires, various bulges will appear. The reasons for the bulges are also varied. Most of them are caused by unexpected strong impacts during use. Therefore, a series of tests will be conducted on tires before they leave the factory.

[0003] Tire bulges not only affect driving, but also pose a risk of tire blowout, which is a major hidden danger to vehicle driving. Most of the existing detection methods rely on naked eye observation. However, in actual high-speed testing, there may only be a short moment from the beginning of tire bulge to explosion, and it is difficult for the human eye to observe the entire process. It is also difficult to effectively analyze the material.

[0004] In order to solve the problem that it is difficult to detect tire bulges with human eyes, a Chinese patent application numbered 201110334203.0 describes a wheel tire bulge detection device that detects bulges through hardware, by placing fixed fixtures on both sides of the tire to determine the bulge. The technical solution disclosed in the patent has a low degree of automation, and there are two disadvantages of using hardware to detect bulges: 1) the alarm will only be triggered when the bulge reaches a certain threshold; 2) it cannot resist the vibration caused by the high-speed movement of the tire, which may lead to misjudgment due to vibration.

[0005] The Chinese patent application number 202010808325.8 describes a method of detecting bulges by using a high-speed camera and a line laser, and judging whether there is a fault on the tire surface by changing the curvature of the laser line in the captured image. The newly-opened technical solution of this patent can only obtain results but cannot analyze the entire process. In fact, more useful information is the strain analysis of the entire process from the beginning to the final explosion of the bulge. By analyzing the data of the entire bulge process, the tire material can be better analyzed, thereby improving the modification of the tire. This patent cannot obtain the strain analysis results before and after the bulge is formed. Summary of the invention

[0006] The purpose of the present invention is to provide a tire bulge detection and analysis method and system to solve the problem that vibration causes misjudgment and it is difficult to obtain strain analysis results during tire bulge detection in the prior art.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A tire bulge detection and analysis method comprises the following steps:

[0009] Step 1, establishing a swing displacement curve model of any measuring point of the tire tread without bulge during high-speed rotation, thereby obtaining a swing displacement curve of any measuring point of the tire without bulge;

[0010] Step 2, acquiring an image of the tread of the tire to be tested during high-speed rotation, and obtaining a swing displacement curve of any measuring point of the tread of the tire to be tested during high-speed rotation according to the acquired image;

[0011] Step 3, comparing the swing displacement curve of any measuring point of the tire to be tested obtained in step 2 with the swing displacement curve of the corresponding measuring point of the tire without bulge obtained in step 1, if the swing displacement curve of a measuring point of the tire to be tested in step 2 changes compared with the swing displacement curve of the corresponding measuring point of the tire without bulge in step 1, then the measuring point is determined to be the location where the bulge of the tire to be tested occurs;

[0012] Step 4: Taking the measurement point where the bulge appears on the tire to be tested determined in step 3 as the target measurement point, a local coordinate system is established with the target measurement point as the origin according to the image of the tread of the tire to be tested obtained in step 2, and the coordinates of the target measurement point in the world coordinate system are converted to the local coordinate system, and then the strain tensor of the target measurement point is calculated according to the coordinates of the target measurement point in the local coordinate system.

[0013] Furthermore, in step 1, the tread of the tire without bulge is divided into several sub-areas, and each sub-area is used as a measurement point of the tire without bulge. Correspondingly, in step 2, the tread of the tire to be tested is divided into the same several sub-areas, and each sub-area is used as a measurement point of the tire to be tested.

[0014] Furthermore, in step 2, an image of the tread of the tire to be measured during high-speed rotation is acquired based on the binocular measurement principle.

[0015] Furthermore, in step 2, the position of each measuring point in the tread image of the tire to be tested is first determined, and then a curve formed by the displacement of each measuring point changing with time is determined, that is, a swing displacement curve of each measuring point.

[0016] Furthermore, in step 3, an amplitude difference threshold is preset in step 3. When the amplitude of the swing displacement curve position of a certain measuring point of the tire to be tested changes to be lower than the amplitude of the swing displacement curve of the corresponding measuring point of the tire without a bulge, and the amplitude difference is greater than the preset amplitude difference threshold, the measuring point is judged to be the position where the bulge of the tire to be tested occurs.

[0017] Furthermore, in step 4, the rotation matrix and translation vector of the local coordinate system and the world coordinate system are calculated, and then the coordinates of the target measurement point in the world coordinate system are converted to the local coordinate system through the rotation matrix and the translation vector.

[0018] Furthermore, in step 4, based on the coordinates of the target measurement point converted into the local coordinate system, a displacement field function is obtained by quadratic surface fitting, and then the strain tensor of the target measurement point is calculated by the displacement field function.

[0019] A tire detection system for a tire bulge detection and analysis method comprises a binocular image acquisition system and a data processing system. The binocular image acquisition system is a binocular camera for respectively acquiring images of the tread of a tire without bulges and the tread of a tire to be detected. The binocular camera is connected to the data processing system for data transmission, and the binocular camera transmits the acquired image data to the data processing system. The data processing system is provided with program instructions, and the above-mentioned tire bulge detection and analysis method is executed when the data processing system runs the program instructions.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] The existing technology basically stops at detecting the final bulge result, and temporarily cannot analyze the tire surface strain process before and after the bulge occurs, and obtain the strain field of the bulge in the whole process. However, the present invention can complete the analysis of the complete process before and after the bulge occurs, and analyze and obtain the strain data of the tire surface at the location where the bulge occurs.

[0022] At the same time, when the prior art is conducting a tire detection experiment, the high-speed rotation of the tire will cause the two sides of the tire to swing, which will cause false alarms during bulge detection. However, the present invention uses binocular image acquisition and a tire swing displacement curve based on the time domain tire swing to detect tire bulges using the tire swing displacement curve, converting the factors that cause false alarms in the prior art into detection factors, so there is no false alarm problem caused by tire swinging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flowchart of the method of the present invention.

[0024] Figure 2 It is a working principle diagram of the binocular image acquisition system in the present invention.

[0025] Figure 3 It is the local coordinate system of the present invention With the world coordinate system Schematic diagram.

[0026] Figure 4 It is a schematic diagram of the detection system of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, a tire bulge detection and analysis method of the present invention comprises the following steps:

[0029] Step 1: Establish a swing displacement curve model for any measuring point on the tread of a tire without bulges during high-speed rotation.

[0030] When an actual tire rotates at high speed, it will introduce a certain amplitude of swing, which has a great impact on the tire detection experiment. In order to solve this problem, the present invention models the swing of a tire without bulges at a fixed speed and obtains a swing displacement curve of the tire tread, which is used to eliminate the impact of the swing during the actual tire bulge detection process.

[0031] In actual modeling, the tread of a tire without bulges can be divided into several 32x32 sub-areas, each of which contains multiple points. Each sub-area is used as a measurement point, and each sub-area is numbered to facilitate the distinction between different sub-areas.

[0032] The present invention assumes that the single-order vibration curve of a tire without a bulge is ,in, .

[0033] Under high-speed motion, it can be assumed that the tire without bulge moves in a periodic manner and its vibration is a high-order vibration. The swing model of the tire tread without bulge is obtained as shown in formula (1):

[0034] (1),

[0035] In formula (1): The swing displacement curve of any measuring point of the tire without bulge, indicating the swing displacement over time The displacement of the measurement point relative to the equilibrium position; represents the initial amplitude value; Indicates the amplitude corresponding to each frequency order; Indicates the amplitude corresponding to each frequency order; represents angular velocity; For time; is a constant coefficient.

[0036] Among them, k=1 is the fundamental frequency vibration, and the kth harmonic frequency vibration is collectively referred to as the kth resonance. In the present invention, setting k=3 can well describe the motion curve of the tire without bulges over time, that is, to obtain an accurate swing model of any measuring point on the tread of the tire without bulges. According to the swing model of any measuring point on the tread of the tire without bulges, the

[0037] The swing displacement curve of any measuring point on the tread of a bulging tire.

[0038] Step 2: Acquire an image of the tread of the tire to be tested during high-speed rotation, and obtain a swing displacement curve of any measuring point of the tread of the tire to be tested during high-speed rotation according to the acquired image.

[0039] When the present invention specifically collects images, several sub-areas similar to step 1 can be set on each side of the tire to be tested as measuring points, and each sub-area is numbered the same way.

[0040] In the present invention, the binocular image acquisition system formed by binocular cameras can acquire images of the tread of the tire to be tested during high-speed rotation, and then obtain the swing displacement curve of the tread of the tire to be tested based on the images acquired by the binocular image acquisition system. Figure 2 As shown, two high-speed cameras 2.1 and 2.2 are arranged on the left and right sides of the tire 1 to be tested to form a binocular camera. The two high-speed cameras 2.1 and 2.2 on the tread collect images of the corresponding sides of the tire to be tested when it rotates at high speed based on the binocular measurement principle.

[0041] During measurement, two types of markers can be sprayed on the tread of the tire to be tested: 1) Mark points, which are used for distance measurement by the binocular camera; 2) Random speckles, which are mainly used to form several sub-area measurement points for subsequent surface stress and strain analysis. The calibration algorithm of the binocular camera is already very mature, and the present invention uses Zhang's calibration method for calibration. After the dual camera calibration is completed, the data after three-dimensional reconstruction can be obtained based on the intrinsic and extrinsic parameters of the camera, and then the initial vibration curve of each sub-area, i.e., the measurement point, is established.

[0042] The displacement of each measurement point can be obtained through binocular measurement of the image and 3D reconstruction data. Specifically, based on the measured image and 3D reconstruction data, a displacement point cloud map of the tire to be tested can be established. The xy coordinates of the displacement point cloud map are the uv coordinates of the single shot image, and the z coordinate is the calculated displacement.

[0043] For a certain sub-area In, after the tire rotates one circle, the sub-area In can be found at the same position. After rotating N circles, the position of the sub-area In can also be found. Therefore, a displacement time sequence diagram of each sub-area (measurement point) displacement changing with time can be obtained. The present invention adopts an image matching algorithm, and the matching algorithm is as follows:

[0044]

[0045] Where M is the radius of the sub-area, x and y represent the horizontal and vertical positions of the sub-area, Indicates the sub-area at the next position, and are the grayscale values ​​of each point in the reference sub-region and the target sub-region respectively. This function describes the difference between the reference sub-region and the target sub-region. When the function takes the minimum value of 0, it can be considered that there is no difference between the reference sub-region and the target sub-region, that is, the best match. is the parameter of the shape function, which is a first-order or multi-order function that describes the deformation of the reference area and the target area.

[0046] Theoretically, the time-displacement curve of each sub-area should be a horizontal straight line. However, due to the high-speed rotation of the tire, it will cause the tire to vibrate in both horizontal and vertical directions. Therefore, the curve of each sub-area actually obtained is a periodic curve, that is, the swing displacement curve of the sub-area (measurement point).

[0047] Step 3: Compare the swing displacement curve of any measuring point of the tire to be tested obtained in step 2 with the swing displacement curve of the corresponding measuring point of the tire without bulge obtained in step 1. If the swing displacement curve of a measuring point of the tire to be tested in step 2 changes compared with the swing displacement curve of the corresponding measuring point of the tire without bulge in step 1, it is determined that the measuring point is the position where the bulge of the tire to be tested occurs.

[0048] According to formula (2) in step 2, theoretically, the displacement value of the sub-area at the next moment can be predicted based on the displacement of the current sub-area. However, if the tire to be tested has a bulge, the displacement value of the sub-area where the bulge is located will become abnormal, causing the displacement value of the sub-area to increase over time. Based on this, it can be determined that a bulge has occurred in the sub-area, i.e., the measurement point.

[0049] If a bulge appears at a certain measuring point of the tire to be tested, then the measuring point of the tire to be tested will also change accordingly (the amplitude becomes lower). Therefore, when the amplitude of a certain measuring point of the tire to be tested changes to be lower than the amplitude of the corresponding position of the swing displacement curve of the corresponding side of the tire without bulge, the measuring point is judged to be the position where the bulge appears. Specifically, an amplitude difference threshold can be preset, and when the amplitude difference is greater than the preset amplitude difference threshold, the measuring point is judged to be the position where the bulge appears.

[0050] Step 4: Taking the measurement point where the bulge appears on the tire to be tested determined in step 3 as the target measurement point, a local coordinate system is established with the target measurement point as the origin according to the image of the tread of the tire to be tested obtained in step 2, and the coordinates of the target measurement point in the world coordinate system are converted to the local coordinate system, and then the strain tensor of the target measurement point is calculated according to the coordinates of the target measurement point in the local coordinate system.

[0051] In the present invention, the strain tensor calculation is mainly based on the coordinates of the acquired image after three-dimensional reconstruction, and the process is as follows:

[0052] 1. Establishment of local coordinate system:

[0053] Since the surface of the tire to be tested is curved, its surface motion includes in-plane motion and out-of-plane motion. Therefore, in order to calculate the target measurement point of the tire to be tested, The strain tensor at the position needs to establish a local coordinate system first. .

[0054] The establishment process is as follows: First, assume that the target measurement point The sub-areas in the domain S are all in the same plane Q. The plane equation is fitted using the least square method, and then the plane is translated so that it passes through the point , and finally get the form The equation of , which is the initial surface equation. Then, Establish a local coordinate system with point as the origin , select the direction perpendicular to the surface of the object to be measured as The positive direction of the axis can be directly obtained from the above plane equation The direction of the axis is or Finally, determine the and Axis direction. Since the choice of coordinate axis in the plane is not unique, one of the more typical selection methods is to use the original world coordinate system. The intersection of the plane and plane Q is Axis, i.e. vector , ensuring that The positive angle is an acute angle; Axis through Axis and The vector outer product is obtained in the axis direction to ensure Axis and Axis vertical, Axis vertical. Determine the local coordinate system Then, calculate the local coordinate system Rotation matrix with respect to the world coordinate system with translation vector .

[0055] 2. Translation calculation

[0056] The three-dimensional coordinates and displacements of the grid points in the neighborhood of the target measurement point in the world coordinate system are transformed into plane Q.

[0057] First, calculate The three-dimensional displacement of all grid points in the neighborhood S is shown in formula (3):

[0058] (3),

[0059] In formula (3), and are the three-dimensional spatial coordinates of the target measurement point before and after the deformation of the swing displacement curve, is the displacement vector.

[0060] Then, the three-dimensional coordinates and displacement vector of the grid point in the world coordinate system before deformation are obtained by and Transform to local coordinate system In, get and ,in

[0061] To transform to the local coordinate system The corresponding coordinates in is the displacement vector.

[0062] 3. Strain tensor calculation

[0063] The displacement field function is obtained by quadratic surface fitting, and the strain tensor is calculated by the field function. First, three field functions are obtained by fitting as shown in formula (4):

[0064] (4),

[0065] In formula (4), , and are the function coefficients of each field respectively.

[0066] Then, the strain tensor of the target surface is calculated by formula (5):

[0067] (5),

[0068] In formula (5) It is the strain tensor of the target measurement point.

[0069] The logic of the method of the present invention is actually to establish the displacement vibration curve of each sub-area before deformation, and then compare the displacement vibration curve of each sub-area with the one established initially during actual measurement. If the vibration curve during actual measurement deviates from the initial curve beyond a preset threshold, it indicates that a bulge has occurred. When a bulge occurs, strain calculation needs to be added to calculate the strain tensor of the sub-area.

[0070] So far, the present invention has completed the entire process of tire bulging and detection. For the strain at the bulge, the present invention can be used for further analysis of the material. It is used to analyze the defect problems of the material in order to further improve the material. For different application fields, there may be different analysis requirements. For example, some scenarios require stress-strain curves, and some scenarios require elastic modulus, etc., which will not be repeated in this patent.

[0071] like Figure 4 As shown, the present invention also discloses a tire detection system for realizing the tire bulge detection and analysis method, which includes the above-mentioned binocular image acquisition system and a data processing system. The data processing system uses a computer 3. The high-speed cameras 2.1 and 2.2 constituting the binocular camera in the binocular image acquisition system are respectively connected to the computer 3 for data transmission, and the high-speed cameras 2.1 and 2.2 transmit the image data collected by each to the computer 3. The memory of the computer 3 stores program instructions. When the processor of the computer 3 calls and runs the program instructions from the memory, the tire bulge detection method of the present invention is executed according to steps 1 to 4.

[0072] The embodiments described in the present invention are merely descriptions of the preferred implementation modes of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should fall within the protection scope of the present invention. The technical contents for which protection is sought in the present invention have all been recorded in the claims.

Claims

1. A tire bulge detection and analysis method, characterized in that: The following steps are involved: Step 1, establishing a swing displacement curve model of any measuring point of the tire tread without bulge during high-speed rotation, thereby obtaining a swing displacement curve of any measuring point of the tire without bulge; Step 2, acquiring an image of the tread of the tire to be tested during high-speed rotation, and obtaining a swing displacement curve of any measuring point on the tire to be tested during high-speed rotation according to the acquired image; Step 3, comparing the swing displacement curve of any measuring point of the tire to be tested obtained in step 2 with the swing displacement curve of the corresponding measuring point of the tire without bulge obtained in step 1, if the swing displacement curve of a measuring point of the tire to be tested in step 2 changes compared with the swing displacement curve of the corresponding measuring point of the tire without bulge in step 1, then the measuring point is determined to be the location where the bulge of the tire to be tested occurs; Step 4: Taking the measurement point where the bulge appears on the tire to be tested determined in step 3 as the target measurement point, a local coordinate system is established with the target measurement point as the origin according to the image of the tread of the tire to be tested obtained in step 2, and the rotation matrix and translation vector of the local coordinate system and the world coordinate system are calculated, and then the coordinates of the target measurement point in the world coordinate system are converted to the local coordinate system through the rotation matrix and the translation vector, and based on the coordinates of the target measurement point converted to the local coordinate system, a displacement field function is obtained by quadratic surface fitting, and the strain tensor of the target measurement point is calculated by the displacement field function.

2. A tire bulge detection and analysis method according to claim 1, characterized in that: In step 1, the tread of the tire without bulge is divided into several sub-areas, and each sub-area is used as a measurement point of the tire without bulge. In step 2, the tread of the tire to be tested is divided into several sub-areas, and each sub-area is used as a measurement point of the tire to be tested.

3. A tire bulge detection and analysis method according to claim 1, characterized in that: In step 2, an image of the tread of the tire to be measured during high-speed rotation is acquired based on the binocular measurement principle.

4. A tire bulge detection and analysis method according to claim 1, characterized in that: In step 2, the position of each measuring point in the tread image of the tire to be tested is first determined, and then a curve formed by the displacement of each measuring point changing with time is determined, that is, a swing displacement curve of each measuring point.

5. A tire bulge detection and analysis method according to claim 1, characterized in that: In step 3, an amplitude difference threshold is preset in step 3. When the amplitude of the swing displacement curve position of a certain measuring point of the tire to be tested changes to be lower than the amplitude of the swing displacement curve of the corresponding measuring point of the tire without bulge, and the amplitude difference is greater than the preset amplitude difference threshold, the measuring point is judged to be the position where the bulge of the tire to be tested occurs.

6. A tire detection system for use in the tire bulge detection and analysis method according to any one of claims 1 to 5, characterized in that: The invention comprises a binocular image acquisition system and a data processing system. The binocular image acquisition system is a binocular camera for respectively acquiring images of the tread of a tire without bulge and the tread of a tire to be tested. The binocular camera is connected to the data processing system for data transmission, and the binocular camera transmits the acquired image data to the data processing system. The data processing system is provided with program instructions, and the tire bulge detection and analysis method described in any one of claims 1 to 5 is executed when the data processing system runs the program instructions.

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