Three-dimensional laser etching method based on cylindrical coordinates of tire

Abstract

The invention provides a tire cylindrical coordinate-based three-dimensional laser etching method, which comprises the following steps of: establishing a plane design polar coordinate during design based on the appearance characteristics of a tire, giving a polar radius and a polar angle of a reference point coordinate and an etching coordinate, and obtaining a polar radius deviation value and a polar angle deviation value through operation; the relative plane position from the etching point to the reference point is determined; establishing polar coordinates on the tire conveying surface, wherein the pole is the circle center of the tire; establishing a polar axis in a reverse direction by connecting the pole and a projection point of the origin of the base coordinate of the robot in the polar coordinate; the Z axis passes through the pole, the vertical polar coordinate plane faces upwards, and three-dimensional cylindrical coordinates are established; based on the three-dimensional coordinates, the robot carries out 3D camera scanning and modeling; and after the center of the sixth axis of the robot moves to the second center, the sixth axis rotates by an angle to carry out laser etching by calculating the operation coordinate of the sixth axis and coordinate transformation of the base coordinate of the robot.

Description

Technical Field

[0001] The invention belongs to the field of tire production and manufacturing, and in particular relates to a three-dimensional laser etching method based on tire cylindrical coordinates. Background Art

[0002] Tire vulcanization molding technology is a traditional tire production technology. However, since the year and week number active blocks on the mold need to be replaced regularly every week, it is easy to damage the mold and affect the appearance quality of the tire. Second, the replacement of the active blocks will affect the startup efficiency and energy consumption loss. Third, it generates large labor maintenance costs and mold replacement costs every year. Fourth, the timeliness of the year and week number replacement cannot be guaranteed. Secondly, the production number of all-steel radial tires is formed by placing "small steel sheets" on the lower mold of the sidewall. Each tire requires manual intervention, which is not ideal in terms of accuracy, product aesthetics and consumables. It is also easy to cause damage to the appearance of the tire and mismatch tire information. In addition, the commercial demand for some personalized customized logos is increasing, which also increases the frequency of mold replacement and the increase in production costs.

[0003] In recent years, with the rapid development of domestic laser technology and intelligent technology, tire surface laser etching technology has begun to develop in the industry and is rapidly being promoted. At present, domestic leading tire companies have adopted laser etching technology to etch production numbers, year and week numbers, customized logos and other information on the tire surface. Because this technology is extremely flexible and advanced, it has replaced some functions of tire molding technology, bringing fresh vitality and innovative value to the traditional tire production process.

[0004] However, due to the lack of a deep technical understanding of the tire shape and the layout of the tire surface pattern logo, the traditional rectangular coordinate system is used in the description of the tire scanning imaging and etching positioning. As a result, the tire logo cannot be accurately positioned on site during the large-scale mixed automated production of tires of different specifications and varieties, which also affects the aesthetics of the logo etching; or the logo positioning is determined entirely by manual adjustment on site, which is inefficient, increases the etching cycle and labor costs, and cannot achieve rapid response production. Summary of the invention

[0005] The present invention provides a tire laser etching method based on a six-axis robot and a laser of tire cylindrical coordinates. The invention is characterized in that the etching position of the workpiece-tire and the center coordinates and rotation angle of the sixth axis of the robot are expressed by cylindrical coordinates, and finally the running trajectory of the robot is realized. The process flow includes the following steps: after the tire arrives at the etching station, it is clamped and positioned by a centering mechanism, and the height of the tire is detected by a laser ranging sensor; the robot moves to a preset position, performs barcode recognition and 3D modeling; a 3D camera scans the sidewall, generates a three-dimensional model, and determines the mark position by image intelligent recognition; according to the three-dimensional coordinates of the tire, the laser performs etching. Through the three-dimensional cylindrical coordinate system, the system converts the six-axis center of the etching robot into rectangular coordinates for operation, and then runs the angle in joint coordinates to accurately control the laser etching positioning process. In this process, the six-axis robot not only carries a laser, but also is equipped with a 3D camera for identifying the mark position to achieve accurate laser etching. This process can be adaptively adjusted according to the different shapes and sizes of tires to achieve higher etching accuracy and flexibility.

[0006] The present invention provides a three-dimensional laser etching method based on tire cylindrical coordinates. The method establishes plane design polar coordinates based on the shape characteristics of the tire during design, gives the polar diameter and polar angle of the reference point coordinates and the etching coordinates, obtains the polar diameter deviation value and the polar angle deviation value by calculation, and determines the relative plane position of the etching point to the reference point; establishes polar coordinates on the tire conveying surface, and the pole is the center of the tire; connects the pole and the projection point of the robot's base coordinate origin on the polar coordinate, and establishes the polar axis in the opposite direction; the Z axis passes through the pole, and the vertical polar coordinate plane faces upward to establish a three-dimensional cylindrical coordinate; through installation adjustment and correction, the initial center (motion origin) of the robot's sixth axis is on the Z axis of the three-dimensional cylindrical coordinate, the 6-axis joint coordinate is parallel to the tire conveying polar coordinate, and the posture of the 5th axis is kept parallel to the Z axis or on the Z axis. Based on this three-dimensional coordinate, the robot performs 3D camera scanning and modeling; by calculating the running coordinates of the sixth axis and the coordinate conversion with the robot's base coordinates, after the robot's sixth axis center runs to the second center, the sixth axis rotates an angle to perform laser etching. It is understandable that although the method uses robot laser etching, the method based on tire cylindrical coordinates and the basic principle of etching are also applicable to tire laser etching of other equipment types.

[0007] Specifically, the three-dimensional laser method provided by the present invention includes the following steps: 1. A method for establishing polar coordinates of a tire: 1.1 The polar coordinate system of the tire design plane is established as follows: According to the top view of the tire mold design, the center of the tire is taken as the pole O, and the connecting ray from the pole O to the tire mark position is taken as the polar axis, and the polar coordinate system is established in the counterclockwise direction; 1.2 The three-dimensional cylindrical coordinate system of the tire is established as follows: Based on the tire conveying bottom surface used to convey the tire, the center of the tire is taken as the pole O, and the ray perpendicular to the tire conveying direction is taken as the polar axis, and the polar coordinate system is established in the counterclockwise direction. The ray perpendicular to the plane of the polar coordinate system is taken as the Z axis to establish the three-dimensional cylindrical coordinate system of the tire; when the tire enters the equipment during actual automated large-scale production, the polar angle direction of the polar coordinate is disordered, so the polar axis of the polar coordinate at the production site is based on the position of the combined equipment, which is different from the design. The three-dimensional etching method includes the following steps when the equipment is running:

[0008] Step 1) The tire reaches the conveyor belt of the engraving station, the centering mechanism clamps the tire, and the laser ranging sensor detects the height of the tire;

[0009] Step 2) The six-axis robot drives the 3D camera to descend to a preset shooting focal depth height from the tire surface;

[0010] Step 3) The robot maintains its position with axes 1-5, and the sixth axis drives the barcode reader and 3D camera to rotate 365° to read images and barcodes;

[0011] Step 4) The barcode reader reads and identifies the tire barcode, and the system interacts with the MES management system, and the system provides the etching content and etching location information;

[0012] Step 5) The 3D camera scans the tire sidewall for three-dimensional modeling, and OCR recognition or template comparison retrieves the reference mark in the model; the absolute position of the polar coordinates of the etching mark is obtained based on the reference point coordinates and the relative polar coordinate position of the etching mark.

[0013] Step 6) The etching position is focused and etched by a laser galvanometer. Based on the three-dimensional cylindrical coordinates of the tire, the 3D camera scans the tire to confirm the three-dimensional cylindrical coordinates that need to be etched. The system converts the three-dimensional cylindrical coordinates of the etching center into three-dimensional rectangular coordinates so that the laser moves to the etching center based on the rectangular coordinates and the joint coordinate angle.

[0014] In some embodiments, the robot is provided with a 3D camera and a laser emission lens, O' is the initial position of the sixth axis of the robot, O2 is the coordinate of the sixth axis when the robot 3D camera scans, O3 is the laser etching target position of the sixth axis of the robot, when the sixth axis of the robot reaches the scanning target position O2, the robot rotates through the sixth axis, driving the 3D lens and the code reader to reach the depth of field range of the tire reading for scanning, and after completion, the sixth axis of the robot runs to the focal depth height above the center point of the laser etching, and laser etching is performed through the galvanometer. After completion, the axis and the rotation angle return to the original position. The rotation angle and positioning are performed according to the cylindrical coordinates.

[0015] In some embodiments, in step 2), the laser operation trajectory is calculated as follows:

[0016] Step i) The sixth axis of the robot moves from the initial coordinates O'(X0, Y0, Z0) to O2(X22, Y22, Z22).

[0017] X0=D1 (Formula 1)

[0018] Y0=0 (Formula 2)

[0019] Z0=Zdmax+F1+H1+D2+C (Formula 3)

[0020] D1: The distance between the robot base coordinates and the tire cylindrical coordinates on the X-axis, which is a constant;

[0021] D2: The distance between the robot base coordinates and the tire cylindrical coordinates on the Z axis, which is a constant;

[0022] Zdmax: Maximum tire section height;

[0023] F1: scanning focal length of 3D camera;

[0024] H1: The height distance from the center of the 3D camera lens to the axis of motion in the Z-axis direction;

[0025] C: set constant.

[0026] X22=X0=D1 (Formula 4)

[0027] Y22=Y0=0 (Formula 5)

[0028] Z22=Zd+F1+H1+D2 (Formula 6)

[0029] Zd: Laser distance sensor detects tire height;

[0030] After the sixth axis is in place, the sixth axis rotates 365 degrees for scanning and barcode scanning.

[0031] The tire laser etching method according to claim 2, characterized in that in step 5) to step 6), the laser running trajectory is calculated as follows:

[0032] Step ii) calculating the three-dimensional rectangular coordinates O3 (X3, Y3, Z3) of the axis center of the robot's sixth axis running to the etching task;

[0033] Step 2a) Let M0(ρ0, θ0, Z0) be the reference position point identified in the 3D camera scanning image, and projected to the tire conveyor bottom surface polar coordinates M0'(ρ0, θ0);

[0034] Step 2b) Calculate the three-dimensional coordinates of the etching: M2 (ρ2, θ2, Z2) is the center point of the laser etching on the tire, P2 (ρ2, θ2, Z12) is the center coordinate of the laser etching lens, and the projection to the polar coordinate point is M2' (ρ2, θ2);

[0035]

[0036] In the formula The polar diameter deviation value between the etching position and the reference point position;

[0037] In the formula Polar angle deviation value between etching position and reference point position;

[0038] According to ρ2, θ2, and the 3D cylindrical coordinates of the 3D tire, the Z2 value is retrieved;

[0039] Step 2c) Calculate the lens coordinates of the scanning point: When scanning to the etching center point M2, the lens center point of the 3D camera is at P1 (ρ1, θ1, Z11), the vertical scanning point on the tire is M1 (ρ1, θ1, Z1), and the projection coordinates on the bottom surface of the tire are M1' (ρ1, θ1)

[0040] θ1=θ2 (Equation 9)

[0041] ρ1=R1 (Equation 10)

[0042] R1: 3D camera arm length, the distance from the scanning lens center to the rotation axis, is a constant;

[0043] Z11=Z2-H2+H1 (Formula 11)

[0044] H1: The height distance from the center of the 3D camera lens to the center of the sixth axis movement.

[0045] H2: The height distance from the laser etching center to the sixth axis movement axis;

[0046] Step 2d) Calculating etching polar coordinates: Calculating the polar coordinates O3 (ρ3, θ3) of the sixth axis of the tire during etching according to the results of steps 2b and 2c;

[0047]

[0048] R2: The length of the laser etching robot arm, the polar diameter distance from the center of the etching lens to the pole O;

[0049] R1: 3D camera scanning arm length, the polar diameter distance from the center of the scanning lens to the pole O;

[0050] Y12: The distance from the etching center to the center of the 3D camera scanning lens in steps 2b and 2c;

[0051] Step 2e) Coordinate conversion: The rectangular coordinates of O3 in the robot's three-dimensional rectangular coordinate system are (X33, Y33, Z33). According to equations (13) and (14) and the coordinate conversion formula, we get:

[0052]

[0053] Z33=Z2+F2+H2+D2 (Formula 17)

[0054] F2: Laser etched focal length

[0055] H2: The height distance from the laser etching center to the motion axis in the Z-axis direction;

[0056] D1: The distance between the robot base coordinates and the tire cylindrical coordinates on the X-axis, which is a constant;

[0057] D2: The distance between the robot base coordinates and the tire cylindrical coordinates on the Z axis, which is a constant;

[0058] Step iii) The sixth axis arm rotates in joint coordinates, and the operating angle is equal to θ3:

[0059] θ3=θ2+180=θ0+▽θ+180 (Equation 18)

[0060] Step IV) Calculate the sixth axis center coordinates and the sixth axis rotation angle of the subsequent multiple tasks according to the above principle.

[0061] Step v) After the etching task is completed, the axis of the sixth axis returns to the O' coordinate, and the rotation angle of the axis arm returns to 0 degrees.

[0062] Through the present invention, the precise control of the etching position is carried out through the three-dimensional cylindrical coordinate system of the tire, which takes the tire center as the pole and calculates the etching position in combination with the tire height and the scanning distance. In addition, the invention describes in detail the coordinate changes of the robot axis, and calculates the motion trajectory from the scanning position O2 to the laser etching target position O3 from the center of the robot's sixth axis through a series of formulas, as well as the rotation angle of the sixth axis joint arm, to ensure the accuracy of laser etching.

[0063] The laser etching technology provided by the present invention is based on the polar coordinates and cylindrical coordinates of the tire, and through the robot technology combined with 3D camera scanning, it realizes the efficient, accurate and beautiful etching of the tire surface logo. This not only greatly improves the automation level of tire production, but also reduces production costs and mold loss, so that production efficiency and logo accuracy are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 Schematic diagram of tire polar coordinate system;

[0065] Figure 2 It is a schematic diagram of the three-dimensional cylindrical coordinate system of the tire;

[0066] Figure 3 This is the relationship diagram of the three-dimensional coordinate system of the tire and the robot;

[0067] Figure 4 It is a top view of the tire laser etching coordinate system;

[0068] Figure 5 This is a plane side view of the tire laser etching coordinate system;

[0069] Figure 6 Reference photos for laser etching of passenger car tires;

[0070] Figure 7 Reference photo for truck tire laser etching. DETAILED DESCRIPTION

[0071] 1. The equipment uses a laser light source with laser parameters of carbon dioxide and a wavelength of 10.6μm;

[0072] 2. The equipment uses a six-axis robot to move the tool. The sixth axis has a double rotating arm, and one arm carries a core tool; the 3D camera scan and code reader are on one rotating arm, and the laser etching lens is on the other rotating arm. The two arms differ by 180 degrees.

[0073] 3. Use the conveyor line to transport the tire and use the arm to center the tire. The line connecting the center of centering and the robot origin is perpendicular to the conveying direction of the tire, and the tire is within the working range of the robot.

[0074] 4. For positioning accuracy requirements and instructions, see the table below.

[0075] Table 1 Positioning accuracy reference requirements

[0076] Project (Unit) parameter 1 Circumferential error of marking position (mm) ±2.00 2 Radial error of marking position (mm) ±2.00 3 Marking position rotation error (mm) ±3.00 4 Repeatability deviation(mm) ±2.0

[0077] Note:

[0078] 1. Radial error laser etching positioning center, coordinates marked as M2 (ρ, θ, z), refers to the difference between the actual value ρ' and the set value ρ of the polar diameter, the coordinates refer to the attached Figure 2 .

[0079] 2. Circumferential error

[0080] The laser etching positioning center, coordinates are denoted by M2 (ρ, θ, z), which refers to the difference between the actual polar angle θ' and the set value θ. The corresponding arc length with ρ as the radius is denoted by L. The coordinates refer to the attached Figure 2 .

[0081] 3. Rotation error

[0082] The laser etching positioning center, with coordinates denoted by M(ρ,θ,z), refers to the difference in vertical distance from the two ends of the etching mark in the length direction to the circle with a radius of ρ. The distance inside the circle is recorded as negative, and the distance outside the circle is recorded as positive. The coordinates refer to the attached Figure 2 .

[0083] 5. Establish the tire coordinate system

[0084] 5.1.1 Establishing the tire plane design coordinate system

[0085] Please see attached Figure 1 According to the top view of the tire mold design, a polar coordinate system is established with the mold center as the pole, the connecting ray from the pole to the tire mark position as the polar axis, and the counterclockwise direction as the positive direction; the reference point coordinates and the etching point coordinates are determined, and their relative positions are calculated.

[0086] 5.1.2 Establishing the tire three-dimensional coordinate system

[0087] Please see attached Figure 2 Based on the bottom surface of the tire conveyor, with the tire center as the pole, the tire conveyor centerline as the polar axis, and the counterclockwise direction as the positive direction, a polar coordinate system is established; with the ray perpendicular to the polar coordinate system plane as the Z axis, a three-dimensional cylindrical coordinate system is established.

[0088] 5.1.3 According to the positional relationship between the tire three-dimensional cylindrical coordinate system and the robot three-dimensional base coordinate system, the robot's operating parameters and posture are set and corrected, and the original position of the sixth axis of the six-axis robot is set to the robot's rectangular base coordinate (X0, Y0, Z0), which is calculated as follows:

[0089] X0=D1 (Formula 1)

[0090] Y0=0 (Formula 2)

[0091] Z0=Zdmax+F1+H1+D2+C (Formula 3)

[0092] D1: The distance between the robot base coordinates and the tire cylindrical coordinates on the X-axis, which is a constant;

[0093] D2: The distance between the robot base coordinates and the tire cylindrical coordinates on the Z axis, which is a constant;

[0094] Zdmax: Maximum tire section height;

[0095] F1: scanning focal length of 3D camera;

[0096] H1: The height distance from the center of the 3D camera lens to the axis of motion in the Z-axis direction;

[0097] C: set constant.

[0098] 6 Tire laser etching process, which includes the following steps

[0099] Step 1) The sixth axis of the six-axis robot is at the original position O'(X0, Y0, Z0), the tire is transported to the conveyor belt of the lettering station, the centering mechanism clamps the tire, and the laser ranging sensor detects the tire section height Zd;

[0100] Step 2) The sixth axis of the six-axis robot descends from the original position O' to the shooting height of the preset focal depth and reaches O2 (X22, Y22, Z22); the coordinates are calculated as follows:

[0101] X22=X0=D1 (Formula 4)

[0102] Y22=Y0=0 (Formula 5)

[0103] Z22=Zd+F1+H1+D2 (Formula 6)

[0104] Zd: Laser distance sensor detects tire height;

[0105] Step 3) The robot's sixth axis drives the code reader, 3D camera and laser to rotate 365° to ensure panoramic scanning;

[0106] Step 4) The barcode reader reads and identifies the tire barcode, and the system interacts with the process management system; the factory management system gives the etching information to the laser control system;

[0107] The 3D camera scans the tire sidewall to perform three-dimensional modeling, and retrieves reference point markers in the model through intelligent image recognition;

[0108] Step 5) Laser galvanometer focused etching: Based on the three-dimensional cylindrical coordinates and reference point marker coordinates processed by the tire 3D camera scanning, as well as the coordinate deviation values ​​of the reference marker and the etching marker, the actual three-dimensional coordinates of the etching marker are calculated. Based on the coordinates of the etching marker, the center running cylindrical coordinates O3 (ρ3, θ3, z3) of the robot's sixth axis are calculated, and through coordinate conversion, the robot base coordinates O3 (X33, Y33, Z33) of the robot's operation are calculated.

[0109] The axis of the robot's sixth axis moves to the etching center O3 according to the rectangular coordinate; according to the polar angle deviation between the reference mark and the etching mark, the robot's sixth axis mechanical arm rotates by an angle of θ3 to drive the laser lens to move above the etching center; the laser etches according to the etching content and parameters.

[0110] Step 6) The system continues to drive the laser lens to the second, third, ... positions for etching in sequence according to the multiple etching tasks.

[0111] Step 7) After completing the laser etching task, the robot returns to the origin O'.

[0112] In this example, see Figure 2-Figure 5 In step 5) to step 6), the robot drives the tool, and the trajectory is calculated as follows:

[0113] Step ii) calculating the axis of the robot's sixth axis from the three-dimensional rectangular base coordinate O2 (X22, Y22, Z22) to the three-dimensional rectangular base coordinate O3 (X3, Y3, Z3) of the etching task;

[0114] Step 2a) M0 (ρ0, θ0, Z0) is the reference position point identified in the 3D camera scanning image, and its polar coordinates projected onto the tire conveyor bottom surface are M0' (ρ0, θ0);

[0115] Step 2b) Refer to the attached Figure 2 , calculate the etching three-dimensional coordinates: M2 (ρ2, θ2, Z2) is the etching center point of the laser etching on the tire, P2 (ρ2, θ2, Z12) is the center coordinate of the laser etching lens, and the projection to the polar coordinate point is M2' (ρ2, θ2);

[0116]

[0117] In the formula The polar diameter deviation value between the etching position and the reference point position is given by the MES system;

[0118] In the formula The polar angle deviation value between the etching position and the reference point position is given by the MES system;

[0119] According to ρ2, θ2, and the 3D cylindrical coordinates of the 3D tire, the Z2 value is retrieved;

[0120] Step 2c) Calculate the lens coordinates of the scanning point: When scanning to the etching center point M2, the lens center point of the 3D camera is at P1 (ρ1, θ1, Z11), the vertical scanning point on the tire is M1 (ρ1, θ1, Z1), and the projection coordinates on the bottom surface of the tire are M1' (ρ1, θ1)

[0121] θ1=θ2 (Equation 9)

[0122] ρ1=R1 (Equation 10)

[0123] R1: 3D camera scanning arm length, the distance from the scanning lens center to the rotation axis, is a constant;

[0124] Z11=Z2-H2+H1 (Formula 11)

[0125] H1: The height distance from the center of the 3D camera scanning lens to the center of the sixth axis movement.

[0126] H2: The height distance from the laser etching center to the sixth axis movement axis;

[0127] Step 2d) Refer to the attached Figure 4 , Calculate etching polar coordinates: Calculate the polar coordinates O3 (ρ3, θ3) of the sixth axis of the tire during etching according to the results of steps 2b and 2c;

[0128]

[0129] R2: The length of the laser etching robot arm, the polar distance from the center of the etching lens to the center of the sixth axis;

[0130] R1: 3D camera scanning robot arm length, the polar distance from the center of the scanning lens to the center of the sixth axis;

[0131] Y12: The distance from the etching center to the center of the 3D camera scanning lens in steps 2b and 2c;

[0132] Step 2e) Refer to the attached Figure 3 and attached Figure 5 , coordinate conversion and calculation: The coordinates of O3 in the robot's three-dimensional rectangular base coordinate system are (X33, Y33, Z33). According to equations (13) and (14) and the coordinate conversion formula, we get:

[0133]

[0134] Z33=Z2+F2+H2+D2 (Formula 17)

[0135] F2: Laser etched focal length

[0136] H2: The height distance from the laser etching center to the motion axis in the Z-axis direction;

[0137] D1: The distance between the robot base coordinates and the tire cylindrical coordinates on the X-axis, which is a constant;

[0138] D2: The distance between the robot base coordinates and the tire cylindrical coordinates on the Z axis, which is a constant;

[0139] Step iii) The sixth axis arm moves in joint coordinates, and the running angle is equal to θ3, referring to formula 14:

[0140] Step IV) Calculate the sixth axis center coordinates and the rotation angle of the sixth axis arm for the following multiple tasks based on the above principle.

[0141] 6. Quality testing methods

[0142] a) Use a vernier caliper or laser equipment to perform 5*5 repeatability measurements, select 5 tires of the same specifications and 5 tires of different specifications for measurement, test each etching parameter of each tire 5 times, and calculate the deviation, error and standard deviation of the plane size and positioning of the etching mark.

[0143] The standard deviation (σi) of each parameter {i = 1, 2, ..., M} of each tire is calculated using formula (1), and the average standard deviation of the M tires is calculated using formula (2). The calculated etching accuracy should meet the requirements of 4.2.3 to 4.2.5. The standard deviation It should not exceed 1 / 2 of the repeatability deviation requirement.

[0144]

[0145] Where:

[0146] N - number of measurements = 5

[0147] Xj—Measurement value

[0148] σi—Standard deviation of a single tire

[0149] Reproducibility Mean Standard Deviation Defined as:

[0150]

[0151] Where:

[0152] M—Number of tires = 5

[0153] σ—average standard deviation of 5 tires

[0154] b) Visually inspect the clarity and integrity of the etched marking content.

[0155] Test Example 1 Passenger Car Tire Marking

[0156] The contents etched on the passenger car tires are the year and week number and the QR code, which are arranged circumferentially with the production code. The circumferential distance is measured by measuring the character margins, and the radial distance is measured by measuring the character height center distance. Figure 6 and Table 2.

[0157] Table 2 Repeatability accuracy inspection of 5*5 laser etching of passenger car tires

[0158]

[0159] Test Example 2 Truck Tire

[0160] The contents etched on the load-carrying tire are the tire production code, year and week number, and QR code. The year and week number and the production code are arranged circumferentially, while the QR code and the year and week number are arranged radially. The circumferential distance between the year and week number and the tire code is measured by measuring the character margins, and the radial distance is measured by the character height center distance. The radial distance from the production code to the tire code and from the QR code to the year and week number is measured by the character radial margins; the circumferential distance of the production code is measured by the circumferential margins of the starting characters, and the circumferential distance of the QR code is measured by the circumferential center distance of the mark. For details, see Figure 7 and Table 3.

[0161] Table 3 Repeatability accuracy inspection of 5*5 laser etching of truck tires

[0162]

[0163] Through the 5*5 repeatability accuracy check of the equipment tire laser etching, the etching accuracy was confirmed, which indirectly proved the accuracy of the etching method.

Claims

1. A three-dimensional laser etching method based on tire cylindrical coordinates, characterized in that:

1. Establish tire polar coordinates 1.1 The polar coordinate system of tire design plane is established as follows: According to the top view of the tire mold design, the center of the tire is taken as the pole O, the connecting ray from the pole O to the tire mark position is taken as the polar axis, and the polar coordinate system is established with the counterclockwise direction as the positive direction; 1.2 The tire three-dimensional cylindrical coordinate system is established as follows: Based on the tire conveying bottom surface used to convey the tire, the tire center is taken as the pole O, the ray perpendicular to the tire conveying direction is taken as the polar axis, the polar coordinate system is established in the counterclockwise direction, and the ray perpendicular to the polar coordinate system plane is taken as the Z axis to establish the tire three-dimensional cylindrical coordinate system; 2. The three-dimensional laser etching method comprises the following steps: Step 1) The tire reaches the conveyor belt of the engraving station, the centering mechanism clamps the tire, and the laser ranging sensor detects the height of the tire; Step 2) The six-axis robot drives the 3D camera to descend to a preset shooting focal depth height from the tire surface; Step 3) The six-axis robot maintains its posture with axes 1 to 5, and the sixth axis drives the barcode reader and 3D camera to rotate 365° to read images and barcodes; Step 4) The barcode reader reads and identifies the tire barcode, and the system interacts with the MES management system, and the system provides the etching content and etching location information; Step 5) The 3D camera scans the tire sidewall to generate a three-dimensional model, and retrieves the reference mark in the model through OCR recognition or template comparison; the absolute position of the polar coordinates of the etching mark is obtained according to the reference point coordinates and the relative polar coordinate position of the etching mark; Step 6) The etching position is focused and etched by a laser galvanometer. According to the three-dimensional cylindrical coordinates of the tire, the 3D camera scans the tire and confirms the three-dimensional cylindrical coordinates that need to be etched. The system converts the three-dimensional cylindrical coordinates of the etching center into three-dimensional rectangular coordinates, so that the robot drives the laser lens to move to the etching center according to the rectangular coordinates and the joint coordinate angle, and then the logo is engraved on the tire surface through the laser galvanometer.

2. The tire laser etching method according to claim 1, characterized in that: The robot is provided with a 3D camera and a laser emission lens, O' is the initial point of the axis of the robot's sixth axis, O2 is the coordinate position of the axis of the sixth axis when the robot's 3D camera scans, and O3 is the laser etching coordinate position of the axis of the sixth axis of the robot. When the axis of the sixth axis of the robot reaches the scanning target position O2, the robot rotates through the sixth axis to drive the 3D lens and the code reader to reach the depth of field range of tire reading and 3D camera scanning for scanning. After completion, the axis of the sixth axis of the robot runs to the focal depth height above the center point of laser etching, and laser etching is performed through the galvanometer. After completion, the sixth axis drives the axis arm to rotate back to the original angle; the axis of the sixth axis rises back to the initial point O'.

3. The tire laser etching method according to claim 2, characterized in that: The equipment runs based on the cylindrical three-dimensional coordinate system of the tire, and combines the three-dimensional base coordinate system and joint coordinate system of the robot to perform coordinate conversion. The robot running trajectory is calculated as follows: Step i) The sixth axis of the robot moves from the initial coordinates O'(X0, Y0, Z0) to O2(X22, Y22, Z22). X0=D1 (Formula 1) Y0=0 (Formula 2) Z0=Zdmax+F1+H1+D2+C (Formula 3) D1: The distance between the robot base coordinates and the tire cylindrical coordinates on the X-axis, which is a constant; D2: The distance between the robot base coordinates and the tire cylindrical coordinates on the Z axis, which is a constant; Zdmax: Maximum tire section height; F1: scanning focal length of 3D camera; H1: The height distance from the center of the 3D camera lens to the axis of motion in the Z-axis direction; C: set constant; X22=X0=D1 (Formula 4) Y22=Y0=0 (Formula 5) Z22=Zd+F1+H1+D2 (Formula 6) Zd: Laser distance sensor detects tire height; After the sixth axis is in place, the sixth axis rotates 365 degrees for scanning and barcode scanning.

4. The tire laser etching method according to claim 2, characterized in that: In step 2) to step 6), the laser trajectory is calculated as follows: Step ii) calculating the three-dimensional rectangular coordinates O3 (X33, Y33, Z33) of the robot's sixth axis running from O2 (X22, Y22, Z22) to the etching task; Step 2a) Let M0 (ρ0, θ0, Z0) be the reference position point identified in the 3D camera scanning image, and projected to the tire conveyor bottom surface polar coordinates M0' (ρ0, θ0); Step 2b) Calculate the three-dimensional coordinates of the etching: M2 (ρ2, θ2, Z2) is the center point of the laser etching on the tire, P2 (ρ2, θ2, Z12) is the center coordinate of the laser etching lens, and the projection to the polar coordinate point is M2' (ρ2, θ2); ρ2=ρ0+▽ρ; (Formula 7) θ2=θ0+▽θ; (Equation 8) Where ▽ρ: the polar diameter deviation value between the etching position and the reference point position; Where ▽θ: the polar angle deviation between the etching position and the reference point position; According to ρ2, θ2, and the 3D cylindrical coordinates of the 3D tire, the Z2 value is retrieved; Step 2c) Calculate the lens coordinates of the scanning point: When scanning to the etching center point M2, the lens center point of the 3D camera is at P1 (ρ1, θ1, Z11), the vertical scanning point on the tire is M1 (ρ1, θ1, Z1), and the projection coordinates on the bottom surface of the tire are M1' (ρ1, θ1) θ1=θ2 (Equation 9) ρ1=R1 (Equation 10) R1: 3D camera arm length, the distance from the scanning lens center to the rotation axis, is a constant; Z11=Z2-H2+H1 (Formula 11) H1: The height distance from the center of the 3D camera lens to the center of the sixth axis movement. H2: The height distance from the laser etching center to the sixth axis movement axis; Step 2d) Calculating etching polar coordinates: Calculating the polar coordinates O3 (ρ3, θ3) of the sixth axis of the tire during etching according to the results of steps 2b and 2c; Y12=ρ2-ρ1=ρ0+▽ρ-R1 (Equation 12) ρ3=R2-R1+Y12=R2+ρ0+▽ρ-2R1 (Formula 13) θ3=θ2+180=θ0+▽θ+180 (Equation 14) R2: The length of the laser etching robot arm, the polar distance from the center of the etching lens to the center of the sixth axis; R1: 3D camera arm length, the polar distance from the center of the scanning lens to the center of the sixth axis; Y12: The distance from the etching center to the center of the 3D camera scanning lens in steps 2b and 2c; Step 2e) Coordinate conversion: The rectangular coordinates of O3 in the robot's three-dimensional rectangular coordinate system are (X33, Y33, Z33). According to equations (13) and (14) and the coordinate conversion formula, we get: X33=ρ3COSθ3+D1=(R2+ρ0+▽ρ-2R1)COS(θ0+▽θ+180)+D1 (Equation 15) Y33=ρ3SINθ3=(R2+ρ0+▽ρ-2R1)SIN(θ0+▽θ+180) (Equation 16) Z33=Z2+F2+H2+D2 (Formula 17) F2: Laser etched focal length H2: The height distance from the laser etching center to the motion axis in the Z-axis direction; D1: The distance between the robot base coordinates and the tire cylindrical coordinates on the X-axis, which is a constant; D2: The distance between the robot base coordinates and the tire cylindrical coordinates on the Z axis, which is a constant; Step iii) The sixth axis arm moves in joint coordinates, and the running angle is equal to θ3: θ3=θ2+180=θ0+▽θ+180 (Equation 18) Step IV) Calculate the sixth axis center coordinates and the sixth axis rotation angle of the subsequent multiple tasks according to the above principle. Step v) After the etching task is completed, the axis of the sixth axis returns to the O' coordinate, and the rotation angle of the axis arm returns to 0 degrees.

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