A detection method for an inner ball cage mold of an automobile universal joint

Abstract

The application discloses a detection method for an inner ball cage die of an automobile universal joint. The outer contour protruding point of the inner ball cage die of the automobile universal joint is measured and determined through a rotating platform and a vertical laser displacement sensor, and point cloud data of the edge where the most convex point of the outer cylindrical surface is located is collected. Then, the point cloud data of the edge where the most concave point of the inner cylindrical surface is located is collected. The data is converted into coordinate values in a spatial rectangular coordinate system. An auxiliary function is introduced, and the least square method is used to solve the circle centers of the fitting circles of the outer cylindrical surface and the inner cylindrical surface at different heights. The circle centers of the fitting circles of the inner and outer cylindrical surfaces are fitted into corresponding straight lines respectively, and the coaxiality is determined according to the fitting straight lines and the positioning hole axis of the inner ball cage die of the automobile universal joint. After the data points corresponding to the chamfer in the point cloud data set of the edge where the most convex point of the outer cylindrical surface is located and the data points not on the point of the convex surface at both ends are deleted, the straightness of the outer cylindrical surface is calculated.

Description

Technical Field

[0001] This invention relates to mechanical measurement technology, and more particularly to a method for detecting the inner ball cage mold of an automotive universal joint. Background Technology

[0002] With the continuous development of industrial automation, the requirements for safety monitoring of the production environment and quality monitoring of products are increasing. As a key component of the vehicle transmission system, the automotive universal joint's main function is to transmit engine power from the transmission to the drive wheels, ensuring smooth and efficient torque transmission under various driving conditions. Automotive universal joints are generally manufactured into near-final shapes through die forging. The quality of the die has a crucial impact on the production process and the final product quality. After prolonged use, the die inevitably experiences wear and aging due to the continuous exposure to high temperatures, high pressures, and friction. These changes will affect product quality. Over time, the working surface of the die will gradually wear, causing changes in its shape and dimensions. As wear intensifies, the die's precision decreases, leading to inaccurate product dimensions and affecting the product pass rate. Uneven die wear or localized damage can result in inconsistent product dimensions, or even deformation and misalignment, affecting product consistency.

[0003] The mold shape of automotive universal joints has three main technical indicators that significantly impact the production quality of the parts: the coaxiality of the outer cylindrical surface of the mold side profile and the central locating hole, the coaxiality of the inner cylindrical surface of the side profile and the central locating hole, and the straightness of the side cylindrical surface. Coaxiality refers to the alignment between the axis of the outer cylindrical surface of the mold and the central locating hole. In mold quality inspection, coaxiality measurement is crucial because it directly affects the product quality and consistency, and indirectly impacts the assembly accuracy and performance of the part. Straightness refers to the straightness of the outer cylindrical surface relative to its upper end face. It is an important indicator in mold quality inspection and directly affects the inner contour shape of the stamped part.

[0004] The coaxiality and straightness of automotive universal joint molds directly affect subsequent assembly performance and use. Patent 202321422290X discloses a post insulator inspection device that uses multiple measuring tools to inspect the straightness, parallelism, and coaxiality of post insulators. Although it can simultaneously measure multiple shape and position tolerances, it requires reading data from each measuring tool separately, which is cumbersome and prone to significant errors due to manual reading. Furthermore, because automotive universal joint molds have multiple outer contour features and some areas have chamfered features, existing 3D scanning technology cannot fully identify some subtle features such as chamfers, resulting in significant errors in straightness calculations during the measurement process. Summary of the Invention

[0005] Purpose of the invention: The present invention aims to provide a detection method for the inner ball cage mold of automotive universal joints that can improve straightness calculation for chamfer recognition.

[0006] Technical Solution: The present invention describes a method for detecting an inner ball cage mold for an automotive universal joint. The inner ball cage mold consists of t outer cylindrical surfaces and t inner cylindrical surfaces, where t is not less than 3. The detection device for implementing the detection method includes a rotating platform, a horizontal moving slide, a vertical moving slide, and a PLC. The inner ball cage mold is mounted on the rotating platform, the vertical moving slide is slidably mounted on the horizontal moving slide, and a laser displacement sensor is slidably mounted on the vertical moving slide. The detection method includes the following steps:

[0007] (1) The laser displacement sensor starts measuring from the first initial position, and acquires the outer contour point cloud set of the ball cage mold of the automobile universal joint after the rotating platform has rotated one revolution, and determines the protruding points of the outer contour and their corresponding angles θ. min The rotating platform rotates θ min ;

[0008] (2) Measurements were taken using a laser displacement sensor and a magnetic grating sensor to obtain different heights Z. p Point cloud data of the edges containing the protruding points of the outer contour, p = 1, 2…m; determine the rotation of the rotating platform. Then, the point cloud data of the edge containing the corresponding outer cylindrical surface is obtained by acquiring the outer sampling point; the rotation and sampling are repeated t-2 times to obtain the first data set S1, S2…S t ,in

[0009]

[0010] in, q = 1, 2…t, p = 1, 2…m, Z represents the distance Z that the laser displacement sensor detects at the p-th point on the q-th outer cylindrical surface from bottom to top. p The magnetic grating sensor detects the height, and proceeds to step (3).

[0011] (3) The laser displacement sensor moves to the second initial position to determine the rotation of the rotating platform. Then, the inner sampling points on the corresponding inner cylindrical surface are used to obtain the point cloud data of the edges where the inner sampling points are located. This process is repeated t-1 times to obtain the second data set G1, G2...G t ;in

[0012]

[0013] in, q = 1, 2…t, p = 1, 2…m, Z represents the distance Z that the laser displacement sensor detects from the p-th point on the q-th outer cylindrical surface upwards on the inner cylindrical surface. p The magnetic grating sensor detects the height.

[0014] (4) Convert the data in the first and second data sets into coordinate values ​​in a spatial rectangular coordinate system;

[0015] (5) Introduce auxiliary functions and use the least squares method to solve for the center of the fitted circles of the outer and inner cylindrical surfaces at different heights;

[0016] (6) Fit the centers of the fitted circles of the inner / outer cylindrical surfaces into corresponding straight lines respectively, and determine the coaxiality based on the fitted straight lines and the positioning hole axis of the ball cage mold of the automotive universal joint.

[0017] (7) Delete the first data set S1, S2…S t After calculating the data points corresponding to the chamfered center and the points not on the two end protrusions, the straightness of the outer cylindrical surface is calculated.

[0018] Furthermore, in step (1), a spatial rectangular coordinate system is first established, with the center of the mounting plate of the ball cage mold in the automotive universal joint as the origin, the upward direction perpendicular to the mounting plate as the positive z-axis, the direction from the laser displacement sensor to the origin as the positive x-axis, and the direction perpendicular to the xoz plane forward as the positive y-axis according to the right-hand rule of the Cartesian coordinate system.

[0019] The initial position of the laser displacement sensor is L1 at the x-axis distance from the origin and Z0 at the z-axis distance from the origin, Z0 > 0 and Z0 - 0 ≤ ε, where ε is the height threshold. The laser displacement sensor detects distances of l1 to l2, where d1 is the diameter of the outer cylindrical surface. At each interval of o, the PLC sends a pulse signal to trigger the laser displacement sensor to perform detection. The detection is based on the number of measurement data obtained by the laser displacement sensor on the outer surface of the mold with a length of h.

[0020] Furthermore, in step (3), the second initial position is L2 from the origin on the x-axis and Z0 from the origin on the z-axis. The rotary table rotates to angle Q, where...

[0021]

[0022] Where d2 is the diameter of the inner cylindrical surface.

[0023] Furthermore, in step (4), the data in the first data set is converted into coordinate values ​​in a spatial rectangular coordinate system, as follows:

[0024]

[0025] in, To detect the x-coordinate of the p-th point on the q-th outer cylindrical surface from bottom to top, To detect the ordinate of the p-th point on the q-th outer cylindrical surface from bottom to top. Let p be the vertical coordinate of the p-th point on the q-th outer cylindrical surface from bottom to top. For a laser displacement sensor to detect the measurement value of the p-th point on the q-th outer cylindrical surface from bottom to top, θ q R1 is an intermediate variable.

[0026] Furthermore, in step (4), the data in the second data set is converted into coordinate values ​​in a spatial rectangular coordinate system, as follows:

[0027]

[0028] in, Let p be the x-coordinate of the point detected on the q-th inner cylindrical surface from bottom to top. Let p be the ordinate of the point detected on the q-th inner cylindrical surface from bottom to top. Detect the vertical coordinate of the p-th point on the q-th outer cylindrical surface from bottom to top. R2 is the measurement value of the p-th point on the q-th inner cylindrical surface detected by the laser displacement sensor from bottom to top, and R2 is an intermediate variable.

[0029] Furthermore, in step (5), the auxiliary function T(x,y) is

[0030] T(x,y)=(x i -X) 2 +(y i -Y) 2 -R 2

[0031] Where x i Let y be the x-coordinate of the point detected from bottom to top. i X is the ordinate of the detected point from bottom to top, Y is the abscissa of the center of the fitted circle, and R is the radius of the fitted circle.

[0032] Furthermore, in step (5), Z at different heights p The center of the fitted circle on the outer cylindrical surface of p = 1, 2…m for

[0033]

[0034] in, Let x be the x-coordinate of the center of the p-th outer cylindrical surface fitted from bottom to top. The ordinate of the center of the p-th outer cylindrical surface fitted from bottom to top.

[0035] Furthermore, in step (5), Z at different heights p The center of the fitted circle on the inner cylindrical surface of p = 1, 2…m for

[0036]

[0037] in, Let x be the x-coordinate of the center of the p-th inner cylindrical surface fitted from bottom to top. The ordinate of the center of the p-th inner cylindrical surface fitted from bottom to top.

[0038] Furthermore, in step (6), the coaxiality is determined based on the fitted straight line and the positioning hole axis of the ball cage mold inside the automotive universal joint, as follows:

[0039] When the fitted line is parallel to the axis of the positioning hole (a1,b1,c1)=(0,0,1), if the fitted line passes through the axis of the positioning hole, the coaxiality is 0; otherwise, the coaxiality is the perpendicular distance from the fitted line to the axis of the positioning hole.

[0040] When the direction vector (a2, b2, c2) of the fitted straight line is not parallel to the axis of the positioning hole, the coaxiality ⊙ is...

[0041]

[0042] Where, x 21 To fit the x-coordinate of the first point on the straight line, y 21 The ordinate of the first point on the fitted line is determined.

[0043] Furthermore, step (7) is as follows:

[0044] The length of the lower protrusion of the mold is h1, the length of the upper protrusion is h2, and the length of the middle recess is h3. U points are determined on the lower protrusion, v points on the upper protrusion, and w points are detected for the maximum chamfer length Δ. These are all defined in the first data set S1, S2…S… t In the process, at each chamfer location, delete w points, take u1 = u-2w points on the lower segment protrusion, and v1 = v-2w points on the upper segment protrusion, to obtain the remaining required point set ξ1, ξ2…ξ t ,in,

[0045] According to ξ t Calculate the centroid of all points, subtract the coordinates of the centroid from each point to obtain the decentralized points, and construct the covariance matrix;

[0046] Eigenvalue decomposition is performed on the covariance matrix, and the eigenvector corresponding to the largest eigenvalue is transformed into a unit vector, which is the direction of the best-fit line.

[0047] Calculate ξ t Distance of all points in the set to the best-fitting line calculate The root mean square error is used to obtain the corresponding straightness.

[0048] Beneficial Effects: Compared with the prior art, the significant advantages of this invention are: 1. This invention uses a laser displacement sensor and a magnetic grating sensor to convert measurement data into three-dimensional coordinate values, and introduces an auxiliary function based on the least squares method for fitting calculation, thereby accurately locating the spatial coordinates of each acquisition point and fitting the center coordinates of the circle and the spatial straight line; 2. This invention further improves the accuracy and reliability of straightness measurement by eliminating some data points, such as chamfer areas; 3. This invention effectively expands the measurement range of the measuring device by adjusting the position of the laser displacement sensor, while ensuring the measurement range of the hot forging die of the ball cage in the automotive universal joint by selecting a higher precision small-range sensor, reducing the number of detection units in the measuring device, thus reducing costs and improving measurement accuracy. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the device used in this invention;

[0050] Figure 2 Diagram of the horizontal sliding table;

[0051] Figure 3 Diagram of the vertically moving slide;

[0052] Figure 4 Diagram of the rotating platform;

[0053] Figure 5 This is a schematic diagram of the structure of the workpiece being measured;

[0054] Figure 6 A schematic diagram of the established coordinate system;

[0055] Figure 7 This is a flowchart of the present invention;

[0056] Figure 8 Z is the height along the z-axis. p A schematic diagram of a two-dimensional coordinate system. Detailed Implementation

[0057] The invention will now be further described with reference to the accompanying drawings.

[0058] The present invention describes a method for detecting an inner ball joint mold for automotive universal joints. The inner ball joint mold comprises t outer cylindrical surfaces and t inner cylindrical surfaces, where t is not less than 3. The detection device for implementing the method includes...

[0059] It includes a work platform 1, a horizontal moving slide 2, a support 3, a vertical moving slide 4, a rotating platform 5, a control cabinet 7, and a touch screen 8.

[0060] The work platform 1 is a rectangular workbench welded from 8 angle steels and 5 rectangular plates. The workbench surface has mounting holes corresponding to the horizontal moving part 2 and the rotating platform part 5.

[0061] like Figure 2 The horizontal moving component 2 shown includes a motor 21, a reducer 22, a linear guide rail 23, and a slide table 24.

[0062] Preferably, the motor 21 is a servo motor, which has more precise position, speed and torque control capabilities.

[0063] The reducer 22 is connected to the selected servo motor 21 by screws, and the output shaft of the reducer is connected to the linear guide 23 by a coupling, mainly to increase the torque output of the servo motor 21.

[0064] The bracket 3 is an L-shaped bracket, consisting of a vertical main plate and a horizontal base plate. The vertical main plate has threaded holes corresponding to the mounting holes of the vertical moving part 4. The horizontal base plate has countersunk through holes, which are connected to the threaded holes of the slide 24 on the horizontal moving part by screws.

[0065] like Figure 3 The vertical moving component 4 shown includes a displacement sensor 41, a linear guide rail 42, a motor 43, a reducer 44, a displacement sensor 45, a sensor bracket 46, and a slide table 47.

[0066] Preferably, the motor 43 is a servo motor, which has more precise position, speed and torque control capabilities.

[0067] The reducer 44 is connected to the selected servo motor 43 by screws, and the output shaft of the reducer is connected to the linear guide 42 by a coupling, mainly to increase the torque output of the servo motor 43.

[0068] Preferably, one of the displacement sensors is a magnetic grating sensor 41, used to detect the moving distance of the vertical moving component slide 47.

[0069] The magnetic grating sensor 41 is connected to the threaded hole on the side of the slide table 47 by screws.

[0070] Preferably, the other displacement sensor is a laser sensor 45, which receives pulse signals and is used for distance detection.

[0071] The sensor bracket 46 is an L-shaped bracket, consisting of a vertical main plate and a horizontal base plate. The horizontal main plate has through holes corresponding to the mounting holes of the slider 47 on the vertical moving component, and is secured with screws. The vertical base plate has through holes corresponding to the mounting holes of the laser displacement sensor 45, and is connected to the laser displacement sensor 45 with screws.

[0072] like Figure 4 The rotating platform component 6 shown includes a rotary table 61, a workpiece mounting plate 62, an angle sensor 63, a motor 64, and a reducer 65.

[0073] The rotary table 61 is a selected rotating platform used to rotate the ball cage mold 5 inside the automotive universal joint. The rotary table 61 is fixed to the working platform 1 by screws.

[0074] The workpiece mounting plate 62 is a disc with a central boss. The boss at its center corresponds to the countersunk hole at the bottom of the CV joint inner ferrule mold 5, and the boss has threads corresponding to the threaded holes at the bottom of the CV joint inner ferrule mold 5. The workpiece mounting plate 62 has a ring of mounting holes corresponding to the mounting positions of the rotary table 61, and is fixed to the rotary table 61 by screws.

[0075] The angle sensor 63 is mainly used to detect the rotation angle of the rotary table 61 and is fixed to the side of the rotary table 61 by screws.

[0076] Preferably, the motor 64 is a servo motor, which has more precise position, speed and torque control capabilities.

[0077] The reducer 65 is connected to the selected servo motor 64 by screws, and the output shaft of the reducer is connected to the rotary table 61 by a coupling.

[0078] The control cabinet 7 mainly consists of a touch screen 8, a servo driver, and a PLC.

[0079] The touchscreen 8 is an operating interface used to read data.

[0080] The PLC is a control center that mainly controls the movement of the horizontal moving slide 24, the vertical moving slide 47, and the rotary table 61.

[0081] The servo driver mainly receives instructions sent by the PLC, controls the servo motor, and receives feedback signals from the servo motor.

[0082] This invention uses a PLC as the control core, receiving signals from sensors and performing calculations, judgments, and control according to preset logic. The detection method for the ball cage mold inside the universal joint when t=3 specifically includes the following steps:

[0083] Step 1: Establish a spatial rectangular coordinate system. Define the center of the workpiece mounting plate 62 as the origin, the upward direction perpendicular to the workpiece mounting plate 62 as the positive z-axis, the direction from the laser displacement sensor 45 to the origin as the positive x-axis, and the direction perpendicular to the xoz plane and forward as the positive y-axis according to the right-hand rule of the Cartesian coordinate system.

[0084] Theoretically (under no wear conditions), the outer cylindrical surface diameter of the mold 5 side profile is d1 = 69.3 mm, the inner cylindrical surface diameter is d2 = 43.6 mm, and the length is h = 145 mm. Figure 5 The mold 5 shown has three bosses and three grooves. The three bosses form the outer cylindrical surface of the side profile, and the three grooves form the inner cylindrical surface of the side profile. The laser displacement sensor 45 has a detection distance of 10mm to 150mm, i.e., a range l = 140mm. The PLC is set to send a pulse signal to trigger the laser displacement sensor 45 to perform detection at intervals of o = 36mm. Calculate the number of measurement data m = 4 obtained by the laser displacement sensor on the outer surface of the mold with a length of h = 145 mm.

[0085] Step 2: Fix the mold to be tested 5 at the center of the workpiece mounting plate 62, select the specifications and type of the mold to be tested on the touch screen 8 of the control cabinet and start the test. The touch screen sends the corresponding instructions to the PLC.

[0086] Step 3: The PLC controls the initial position of the laser displacement sensor's x-axis, L1 = 114.65 mm, and the initial height position, Z0 (Z0 > 0 and Z0 - 0 ≤ ε = 0.05 mm, where ε is the height threshold).

[0087] Step 4: The PLC controls the rotary table 61 to rotate 360°, and the laser displacement sensor 45 begins to detect the distance between the outer cylindrical surface of the mold 5 and the laser displacement sensor 45 in real time, obtaining a set of data. And obtain the data The corresponding angle θ min =45.45° and marked as the outer contour protrusion point, the PLC obtains the position data and rotates it to θ. min Location.

[0088] Step 5: The PLC controls the laser displacement sensor 45 to move linearly from bottom to top. Every interval o = 36mm, the laser displacement sensor 45 detects the distance between the outer cylindrical surface of the mold 5 and the laser displacement sensor 45, until the laser displacement sensor 45 has moved h = 145mm. At this point, a set of data is obtained.

[0089] Step 6: The PLC controls the rotary table 61 to rotate by an angle P = 120°; the laser displacement sensor 45 returns to the initial height position Z0 (Z0 > 0 and Z0 - 0 ≤ ε = 0.05 mm, where ε is the height threshold). The process of step 5 is repeated until the motor 64 rotates twice. At this point, a total of data sets S1, S2, and S3 are obtained.

[0090]

[0091] Step 7: The PLC moves the laser displacement sensor 45 to the position L2 = 101.8mm on the x-axis and the initial height position Z0 (Z0 > 0 and Z0 - 0 ≤ ε = 0.05mm, where ε is the height threshold), and rotates the rotary table 61 to an angle Q = 60°.

[0092] Step 8: The PLC controls the laser displacement sensor 45 to move linearly from bottom to top. Every interval o = 36mm, the laser displacement sensor detects the distance between the inner cylindrical surface of the mold 5 and the laser displacement sensor 45, until the laser displacement sensor 45 has moved h = 145mm. At this point, a set of data is obtained.

[0093] Step 9: The PLC controls the rotary table 61 to rotate by an angle P = 120°; the laser displacement sensor 45 returns to the initial height position Z0 (Z0 > 0 and Z0 - 0 ≤ ε = 0.05 mm, where ε is the height threshold). Step 8 is repeated until the motor rotates twice. At this point, a total data set G1, G2, G3 is obtained, where...

[0094]

[0095] Step 10: Convert the measurements obtained by the sensor into coordinate values ​​in three-dimensional space; according to the formula The coordinates of the outer cylindrical surface of the mold can be obtained. According to the formula

[0096]

[0097] The coordinates of the inner cylindrical surface of the outer surface of the mold can be obtained.

[0098]

[0099] Step 11: Determine the z-axis of the inner cylindrical surface of the mold's outer surface.p The center of the fitted circle is determined by the height. From the preceding steps, the coordinates of the outer cylindrical surface of the mold are obtained. q = 1, 2, 3, p = 1, 2, 3, 4, where point q = 1, 2, 3, p = 1, 2, 3, 4 represent different heights Z. p The three points on the three grooves.

[0100] Take three points with z-axis height Z1 = 144.95 mm: (34.55, 0), (-17.33, 30.15), and (-17.38, -30.23). Determine the coordinates of the circle's center using these three points. Similarly, for different heights Z p The three detected points were fitted with m = 4 circles. p = 1, 2, 3, 4, and the coordinates of the center of the circle are: p = 1, 2, 3, 4, where

[0101]

[0102] in

[0103]

[0104] The formula for the center of a circle can be derived by the following steps, given a series of data points (x... i ,y i (i = 1, 2, ..., n), these data points approximately lie on a circle. We fit a circle O using the least squares method, let the equation of the circle be...

[0105] (xX) 2 +(yY) 2 =R 2

[0106] The center of the circle is at coordinates (X, Y), and the radius is R.

[0107] The usual least squares fitting requires minimizing the sum of squared distances, i.e.

[0108]

[0109] The smallest possible solution is found, but the equation is quite complex and cannot be solved analytically. Therefore, we solve the following equation.

[0110] f=∑((x i -X) 2 +(y i -Y) 2 -R 2 ) 2

[0111] Constructing auxiliary functions

[0112] T(x,y)=(x i -X) 2 +(y i -Y) 2 -R 2

[0113] The above formula can then be expressed as

[0114] f=∑T(x i ,y i ) 2

[0115] According to the least squares method, the condition for f to attain an extreme value is...

[0116]

[0117] in

[0118]

[0119] We know that the radius of a circle cannot be 0, therefore we have

[0120] ΣT(x i ,y i ) = 0, the remaining two equations can be obtained

[0121]

[0122] Right now

[0123]

[0124] set up

[0125]

[0126] in

[0127]

[0128] achievable

[0129]

[0130] Substituting the above equation into... achievable

[0131]

[0132] We know ΣU i =0、∑V i =0, then the expansion is:

[0133]

[0134] but

[0135]

[0136] The coordinates of the center of the circle are

[0137]

[0138] Step 12: Determine the z-axis of the inner cylindrical surface of the mold's outer surface. p The center of the fitted circle is determined by the height. From the preceding steps, the coordinates of the outer cylindrical surface of the mold are obtained. q = 1, 2, 3, p = 1, 2, 3, 4, where point q = 1, 2, 3, p = 1, 2, 3, 4 represents the height Z along the z-axis. p The three points on the three grooves.

[0139] Take three points (17.26, 30.06), (-34.65, 0), and (17.36, -30.23) with a z-axis height of Z1 = 144.95 mm. Determine the coordinates of the circle's center using these three points. Similarly, for the three points detected at different heights Zp, fit m=4 circles. p = 1, 2, 3, 4, and the coordinates of the center of the circle are: p = 1, 2, 3, 4, where

[0140]

[0141] in

[0142]

[0143] Step 13: Measurement of the coaxiality ⊙1 between the outer cylindrical surface of the mold and the locating hole. Given that the direction vector of the locating hole axis F1 (z-axis) is (a1,b1,c1)=(0,0,1), [the following steps are taken]... The coordinates p = 1, 2, 3, 4 are transmitted to the PLC, and a straight line is fitted to form the two-point equation of F2 in three-dimensional space as follows:

[0144]

[0145] The direction vector of the line is calculated as (a2, b2, c2), where...

[0146] a2=x 22 -x 21 =0

[0147] b2 = y 22 -y 21 =0.01

[0148] c2 = z 22 -z 21 =-36

[0149] according to

[0150] Step 14: Measurement of the coaxiality ⊙2 between the inner cylindrical surface of the mold outer surface and the positioning hole. Given that the direction vector of the positioning hole axis F1 (z-axis) is (a1, b1, c1) = (0, 0, 1), the four centers... The coordinates p = 1, 2, 3, 4 are transmitted to the PLC, and a straight line F3 is fitted in two-point form as follows:

[0151]

[0152] The direction vector of the line is calculated as (a3, b3, c3), where...

[0153] a3=x 32 -x 31 =0

[0154] b3 = y 32 -y 31 =0

[0155] c3 = z 32 -z 31 =-36

[0156] according to

[0157] Step 15: Measurement of the straightness of the outer cylindrical surface of the mold side profile.

[0158] (151) Remove points located at the chamfer and not on the two protrusions in the measurement data. Based on step 6, S1, S2, and S3 are obtained. Since the outer cylindrical surface of the mold side profile has a shape with protrusions at both ends and a concave middle, we only need to measure the straightness of all points on the protruding parts, such as... Figure 5 As shown, given h = 145mm and o = 36mm, based on the preset parameters of different molds to be tested, the length of the lower protruding part of the mold is h1 = 45mm, the length of the upper protruding part is h2 = 45mm, and the length of the middle concave section is h3 = 55mm. This yields one point on the lower protruding part and one point on the upper protruding part. Given that the maximum chamfer length at the mold edge is Δ = 1mm, zero points can be detected. Zero points are discarded at each chamfer location, and one point on the lower protruding part and one point on the upper protruding part are taken. Therefore, the remaining required points are set as ξ1, ξ2, and ξ3.

[0159]

[0160] u1 = u - 2w

[0161] v1 = v - 2w

[0162]

[0163] (152) Calculation of the straightness of points on the outer cylindrical surface 51. Taking the set of points ξ1 on the outer cylindrical surface 51 as an example, calculate the straightness of the outer cylindrical surface 51 of the mold side profile. The calculation of the straightness of the outer cylindrical surfaces 52 and 53 is similar.

[0164] (1521) Calculate the centroid. First, determine the centroid of all points in set ξ1. in

[0165]

[0166] (1522) Construct the covariance matrix. Subtract the centroid coordinates from each point to obtain the decentralized points. And construct a 3×3 covariance matrix M

[0167]

[0168] (1523) Determine the direction of the best-fit line. Perform eigenvalue decomposition on the covariance matrix M to find the eigenvector τ = (a... s ,b s ,c s This is then normalized to a unit vector. This direction is the direction of the best-fitting line.

[0169] (1524) Calculate the distance from a point to a line. For each point in set ξ1... Calculate its distance to the line. The equation of the straight line passes through the centroid. And the direction vector is τ, and the distance formula is...

[0170]

[0171] (1525) Calculate the straightness I1 of the point on the outer cylindrical surface 51. Straightness is usually expressed by the root mean square error (RMSE), and the calculation formula is as follows:

[0172]

[0173] (153) The calculation of the straightness Ι2,Ι3 from the outer cylindrical surface 52 to the points on the outer cylindrical surface 53 is the same as above.

Claims

1. A method for inspecting an inner ball cage mold for an automotive universal joint, wherein the inner ball cage mold for the automotive universal joint consists of t outer cylindrical surfaces and t inner cylindrical surfaces, where t is not less than 3, characterized in that... The detection device for implementing the detection method includes a rotary platform, a horizontal sliding table, a vertical sliding table, and a PLC. The automotive universal joint inner ball cage mold is mounted on the rotary platform, the vertical sliding table is slidably mounted on the horizontal sliding table, and a laser displacement sensor is slidably mounted on the vertical sliding table. The detection method includes the following steps: (1) The laser displacement sensor starts measuring from the first initial position, and acquires the outer contour point cloud set of the automobile universal joint inner ball cage mold after the rotating platform has rotated one revolution, and determines the protruding points of the outer contour and their corresponding angles. The rotating platform rotates ; (2) Measurements were taken using laser displacement sensors and magnetic grating sensors to obtain different heights. Point cloud data of the edges containing the protruding points of the outer contour; determine the rotation of the rotating platform. Then, the point cloud data of the edge containing the corresponding outer cylindrical surface is obtained by acquiring the outer sampling point; the rotation and sampling are repeated t-1 times to obtain the first data set. ,in ， in, , The distance detected by the laser displacement sensor from the p-th point on the q-th outer cylindrical surface from bottom to top is the distance on the outer cylindrical surface. The magnetic grating sensor detects the height, and proceeds to step (3). (3) The laser displacement sensor moves to the second initial position to determine the rotation of the rotating platform. Then, the inner sampling points on the corresponding inner cylindrical surface are used to obtain the point cloud data of the edge where the inner sampling points are located. This process is repeated t-1 times to obtain the second data set. ,in ， in, , The distance detected by the laser displacement sensor from the p-th point on the q-th outer cylindrical surface (from bottom to top) to the inner cylindrical surface is the distance to the inner cylindrical surface. The magnetic grating sensor detects the height; (4) Convert the data in the first and second data sets into coordinate values ​​in a spatial rectangular coordinate system; (5) Introduce auxiliary functions and use the least squares method to find the center of the fitted circle of the outer cylindrical surface and the inner cylindrical surface at different heights; (6) Fit the centers of the fitted circles of the inner / outer cylindrical surfaces into corresponding straight lines respectively, and determine the coaxiality based on the fitted straight lines and the positioning hole axis of the ball cage mold of the automotive universal joint. (7) Delete the first data set After calculating the data points corresponding to the chamfer and points not on the two end protrusions, the straightness of the outer cylindrical surface is calculated; In step (1), a spatial rectangular coordinate system is first established, with the center of the mounting plate of the ball cage mold in the automotive universal joint as the origin, the upward direction perpendicular to the mounting plate as the positive z-axis, the direction from the laser displacement sensor to the origin as the positive x-axis, and the direction perpendicular to the xoz plane forward as the positive y-axis according to the right-hand rule of the Cartesian coordinate system. The initial position of the laser displacement sensor is at a distance of 0.5 x from the origin. Distance from the origin on the Z-axis , and ,in, The height threshold; Among them, the detection distance of the laser displacement sensor is , The diameter of the outer cylindrical surface; each interval The PLC sends a pulse signal to trigger the laser displacement sensor to perform detection. The number of measurement data obtained by the laser displacement sensor on the outer surface of the mold with a length of h is then used to determine the detection method. ; In step (5), the center of the fitted circle on the outer cylindrical surface at different heights is determined. for in, Let x be the x-coordinate of the center of the p-th outer cylindrical surface fitted from bottom to top. The ordinate of the center of the p-th outer cylindrical surface fitted from bottom to top; To detect the x-coordinate of the p-th point on the q-th outer cylindrical surface from bottom to top, To detect the ordinate of the p-th point on the q-th outer cylindrical surface from bottom to top; The center of the fitted circle on the inner cylindrical surface at different heights for in, Let x be the x-coordinate of the center of the p-th inner cylindrical surface fitted from bottom to top. The ordinate of the center of the p-th inner cylindrical surface fitted from bottom to top; Let p be the x-coordinate of the point detected on the t-th inner cylindrical surface from bottom to top. Let p be the ordinate of the point detected on the t-th inner cylindrical surface from bottom to top.

2. The method for detecting the inner ball cage mold of an automotive universal joint according to claim 1, characterized in that, In step (3), the second initial position is located at a distance of 0.5 times from the origin along the x-axis. Distance from the origin on the Z-axis The rotary table rotates to the angle Among them in, It is the diameter of the inner cylindrical surface.

3. The method for detecting the inner ball cage mold of an automotive universal joint according to claim 2, characterized in that, In step (4), the data in the first data set is converted into coordinate values ​​in a spatial rectangular coordinate system, as follows: in, Let p be the vertical coordinate of the p-th point on the q-th outer cylindrical surface from bottom to top. The laser displacement sensor measures the value at the p-th point on the q-th outer cylindrical surface from bottom to top. , It is an intermediate variable.

4. The method for detecting the inner ball cage mold of the automotive universal joint as described in claim 3, characterized in that, In step (4), the data in the second dataset is converted into coordinate values ​​in a spatial rectangular coordinate system, as follows: in, Let p be the x-coordinate of the point detected on the q-th inner cylindrical surface from bottom to top. Let p be the ordinate of the point detected on the q-th inner cylindrical surface from bottom to top. Detect the vertical coordinate of the p-th point on the q-th outer cylindrical surface from bottom to top. The laser displacement sensor measures the value at the p-th point on the q-th inner cylindrical surface from bottom to top. It is an intermediate variable.

5. The method for detecting the inner ball cage mold of an automotive universal joint according to claim 4, characterized in that, In step (5), the auxiliary function for in The x-coordinate of the point detected from bottom to top. The vertical coordinate of the points detected from bottom to top. To fit the x-coordinate of the center of the circle, To fit the ordinate of the center of the circle, The radius of the fitted circle is denoted as .

6. The method for detecting the inner ball cage mold of an automotive universal joint according to claim 1, characterized in that, In step (6), the coaxiality is determined based on the fitted straight line and the positioning hole axis of the ball cage mold inside the automotive universal joint, as follows: When the fitted straight line and the axis of the positioning hole If the fitted straight line passes through the axis of the positioning hole, the coaxiality is 0; otherwise, the coaxiality is the perpendicular distance from the fitted straight line to the axis of the positioning hole. When the direction vector of the fitted line If it is not parallel to the axis of the positioning hole, then the coaxiality is... for in, To fit the x-coordinate of the first point on the straight line, The ordinate of the first point on the fitted line is determined.

7. The method for detecting the inner ball cage mold of an automotive universal joint according to claim 6, characterized in that, Step (7) is as follows: Length of the lower section of the mold The length of the upper protrusion Length of the concave section in the middle Determine the upper point of the lower section protrusion. One, the upper part protrudes at the top point One, chamfer length is the largest Detected Points in the first data set In the middle, delete at each chamfer. Take the point on the protrusion of the lower segment. One, the upper part protrudes at the top point , thus obtaining the remaining required set of points. ;in, , , ; according to Calculate the centroid of all points, subtract the coordinates of the centroid from each point to obtain the decentralized points, and construct the covariance matrix; Eigenvalue decomposition is performed on the covariance matrix, and the eigenvector corresponding to the largest eigenvalue is transformed into a unit vector, which is the direction of the best-fit line. calculate Distance of all points in the set to the best-fitting line ,calculate The root mean square error is used to obtain the corresponding straightness.

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