Internal thread geometric parameter measuring method and system

Abstract

The invention discloses an internal thread geometric parameter measuring method and system, and the method comprises the steps: transmitting laser through a laser, guiding the laser to the internal thread surface of a to-be-measured piece through a reflector, capturing the laser spot information reflected by the internal thread surface through an optical imaging module, and transmitting the laser spot information to an image sensor; and the data processing module combines a laser triangulation measurement principle and a matrix compensation algorithm to calculate a geometrical relationship of the point cloud data of the internal thread surface so as to obtain geometrical parameters of the internal thread. The method effectively solves the problems of light beam jitter and eccentricity caused by rotation of the reflector, and ensures the accuracy of a measurement result.

Description

Technical Field

[0001] The present invention relates to the field of precision measurement technology, and in particular to a method and system for measuring internal thread geometric parameters. Background Art

[0002] Internal thread geometry, including pitch, thread angle and thread pitch diameter, is critical to ensure the fit accuracy and strength of threaded connections. The accuracy of these parameters is directly related to the performance and safety of mechanical equipment. In critical areas, such as nuclear power plant reactor pressure vessels (RPVs), the accuracy and integrity of threads are particularly critical to the reliable operation of equipment. These devices work under high pressure and high temperature environments, and any slight error in threaded connections may lead to serious consequences, so accurate measurement of thread parameters is particularly important.

[0003] However, traditional methods for measuring internal thread geometry, such as contact techniques such as thread gauges, probes or mechanical measuring instruments, have a series of limitations. These methods may cause accumulation of measurement errors due to physical contact during the measurement process, especially in complex internal thread structures, where this error is more obvious. In addition, contact tools may also cause wear or scratches on the workpiece surface, which may affect the performance of high-precision equipment. At the same time, these traditional methods are also low in measurement efficiency and cannot meet the needs of modern manufacturing for rapid detection. In addition, traditional methods are not adaptable enough to internal threads with high aspect ratios, large diameters or irregular shapes.

[0004] In contrast, laser triangulation, as an advanced non-contact measurement technology, shows obvious advantages. It is based on the triangular geometric relationship between the laser and the surface of the object. It calculates geometric parameters by capturing the changes in the position of the reflected laser, thereby avoiding physical damage to the surface of the workpiece and achieving sub-micron measurement resolution. It is particularly suitable for the measurement of complex geometric shapes. The high efficiency of this method enables it to quickly collect data and meet the inspection needs of mass production. However, in practical applications, laser triangulation also faces challenges when measuring internal threads. For example, the size of the traditional laser unit may make it difficult to enter the narrow bolt hole to complete the measurement, the beam jitter and eccentricity that may be caused by the rotation of the reflector, and the irregularity of the thread surface and the dynamic changes of the laser reflection put forward higher requirements for the data processing algorithm. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for measuring the geometric parameters of an internal thread in view of at least one defect of the related technology mentioned in the above background technology: the problem of beam jitter and eccentricity that may be caused when the reflector rotates.

[0006] The technical solution adopted by the present invention to solve the technical problem is: constructing a method for measuring the geometric parameters of an internal thread, the method comprising the following steps:

[0007] The laser emits laser light, and the laser light is guided to the internal thread surface of the workpiece to be tested through a reflector;

[0008] The laser spot information reflected by the internal thread surface is captured by the optical imaging module, and the laser spot information is transmitted to the image sensor to obtain the point cloud data of the internal thread surface;

[0009] The data processing module combines the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data on the internal thread surface and obtain the geometric parameters of the internal thread.

[0010] In some embodiments, the matrix compensation algorithm includes:

[0011] Introduce translation matrix calculation to compensate for eccentricity error;

[0012] The rotation matrix calculation is introduced to compensate the laser beam jitter error.

[0013] In some embodiments, the translation matrix is ​​obtained by measuring a circumferential calibration block; and the rotation matrix is ​​obtained by measuring an axial calibration block.

[0014] In some embodiments, a plurality of steps are provided on the circumference of the inner wall of the tubular calibration test block, and each step forms a sector with the same angle with the central axis to obtain a circumferential calibration test block;

[0015] A plurality of equally spaced and coaxial steps are arranged axially on the inner wall of the tubular calibration test block to obtain an axial calibration test block.

[0016] In some embodiments, the translation matrix is ​​obtained by measuring a circumferential calibration block, including: calculating the translation matrix by comparing point cloud data of circumferential steps of the circumferential calibration block.

[0017] In some embodiments, the rotation matrix is ​​obtained by measuring an axial calibration block, including: calculating the rotation matrix by comparing point cloud data of an axial step of the axial calibration block.

[0018] In some embodiments, a laser emits a laser, which is guided to the internal thread surface of the test piece through a reflector, including: fixing the test piece at the center of the rotating axis of the rotation drive module, the laser emits a laser, which is guided to the internal thread surface of the test piece through a reflector entering the internal thread hole of the test piece, and adjusting the laser to cover the internal thread position of the test piece.

[0019] In some embodiments, the internal thread geometric parameters include: a pitch diameter of the internal thread, a pitch of the internal thread, and a thread angle of the internal thread.

[0020] The present invention also constructs an internal thread geometric parameter measurement system, comprising:

[0021] Laser, used for emitting laser light;

[0022] A reflector, used to guide the laser to the internal thread surface of the workpiece to be tested;

[0023] An optical imaging module is used to capture the laser spot information reflected from the internal thread surface;

[0024] An image sensor, used to receive laser spot information and obtain point cloud data of the internal thread surface; and

[0025] The data processing module is used to combine the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data on the internal thread surface and obtain the geometric parameters of the internal thread.

[0026] In some embodiments, it also includes: a rotation drive module, which is used to drive the reflector to rotate around the rotation axis to control the laser beam to cover the internal thread of the test piece.

[0027] By implementing the present invention, the following beneficial effects are achieved:

[0028] The present invention emits laser through a laser, guides the laser to the internal thread surface of the test piece through a reflector, captures the laser spot information reflected by the internal thread surface through an optical imaging module, and transmits the laser spot information to an image sensor to obtain point cloud data of the internal thread surface. The data processing module combines the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data of the internal thread surface to obtain the geometric parameters of the internal thread. This method effectively solves the problems of light beam jitter and eccentricity caused by the rotation of the reflector, thereby ensuring the accuracy of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0030] Figure 1 A flow chart of an embodiment of a method for measuring internal thread geometric parameters of the present invention is shown;

[0031] Figure 2 A schematic diagram of a laser reflection optical path in an embodiment of a method for measuring internal thread geometric parameters of the present invention is shown;

[0032] Figure 3 A schematic diagram showing the rotation of a reflector in an embodiment of a method for measuring internal thread geometric parameters of the present invention is shown;

[0033] Figure 4 A horizontal cross-sectional view of a circumferential calibration test block in an embodiment of a method for measuring geometric parameters of an internal thread of the present invention is shown;

[0034] Figure 5 A vertical cross-sectional view of an axial calibration test block of an embodiment of a method for measuring internal thread geometric parameters of the present invention is shown;

[0035] Figure 6 A schematic diagram of an internal thread profile in an embodiment of a method for measuring internal thread geometric parameters of the present invention is shown;

[0036] Figure 7 A thread point cloud diagram of an embodiment of a method for measuring internal thread geometric parameters of the present invention is shown. DETAILED DESCRIPTION

[0037] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0038] It should be noted that the flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor do they have to be executed in the order described. For example, some operations / steps can be decomposed, while some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0039] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities may be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0040] Some embodiments of the present invention disclose a method for measuring internal thread geometric parameters, such as Figure 1 As shown, the method comprises the following steps:

[0041] The laser emits laser light, which is guided to the inner thread surface of the test piece by the reflector. Figure 2 As shown;

[0042] The laser spot information reflected by the internal thread surface is captured by the optical imaging module, and the laser spot information is transmitted to the image sensor to obtain the point cloud data of the internal thread surface;

[0043] The data processing module combines the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data on the internal thread surface and obtain the geometric parameters of the internal thread.

[0044] In some embodiments, the laser spot refers to the distribution of the laser beam in space. After the laser is output, the laser beam will focus to form a small and bright spot. The shape of the laser spot can be circular, elliptical or other shapes. The circular, elliptical or other shapes here are only examples and are not intended to limit the present application.

[0045] In some embodiments, point cloud data is a data set consisting of a large number of points, each of which contains coordinates in three-dimensional space, usually X, Y, and Z coordinates, and may contain additional information, such as laser color, laser intensity, normal vector, etc. The laser color, laser intensity, and normal vector here are only examples and are not intended to limit the present application.

[0046] In some embodiments, laser triangulation is a non-contact measurement technology that uses optical reflection laws and the principle of similar triangles to measure the surface of an object. In this method, the laser beam emitted by the laser irradiates the surface of the object to be measured and undergoes diffuse reflection. The reflected light is then focused at another angle by the imaging system to image the light spot on the image sensor. When the surface of the object is displaced along the laser axis, the angle of the reflected light changes, causing the imaging position of the light spot on the image sensor to move accordingly. By measuring the center position of the light spot, the optical geometric relationship between the light spot and its image point position can be used to calculate the depth coordinates of the light spot. This is only an example and is not intended to limit the present application.

[0047] In some embodiments, Figure 3 As shown, the rotation drive module drives the reflector to rotate around the rotation axis, and controls the laser beam to cover the internal thread of the test piece.

[0048] In some embodiments, the matrix compensation algorithm includes: introducing a translation matrix calculation to compensate for the eccentricity error, and introducing a rotation matrix calculation to compensate for the laser beam jitter error. Specifically, the translation matrix calculation is introduced to compensate for the eccentricity error caused by the rotation of the reflector; the rotation matrix calculation is introduced to compensate for the laser beam jitter error caused by the rotation of the reflector. For example, the matrix compensation algorithm calculation formula is:

[0049] x′=R(θ)·x+T p

[0050] Among them, R(θ) is the rotation matrix, which represents the change of the beam caused by the rotation angle of the reflector, T p is the translation matrix, which represents the static offset in the system layout, x is the original coordinate of the light spot, and x' is the coordinate after the light spot compensation.

[0051] In some embodiments, the data processing module uses fitting algorithms and filtering techniques to remove noise and external interference during the spot acquisition process.

[0052] In some embodiments, the translation matrix is ​​obtained by measuring a circumferential calibration block, and the rotation matrix is ​​obtained by measuring an axial calibration block.

[0053] In some embodiments, a plurality of steps are provided on the circumference of the inner wall of the tubular calibration block, and each step forms a sector with the same angle with the central axis of the tubular calibration block, so as to obtain a circumferential calibration block, for example: Figure 4 As shown, a plurality of steps are provided on the circumference of the inner wall of the tubular calibration block, each step forms a sector with the same angle with the central axis of the tubular calibration block, and the radii of the plurality of sectors gradually increase in sequence. This is only an example and is not intended to limit the present application.

[0054] A plurality of equally spaced and coaxial steps are provided on the inner wall of the tubular calibration block axially to obtain an axial calibration block, for example: Figure 5 As shown, a plurality of equally spaced and coaxial steps are provided in the axial direction of the inner wall of the tubular calibration block, and the radius of the plurality of steps gradually increases along the central axis of the tubular calibration block. This is only an example and is not intended to limit the present application.

[0055] In some embodiments, the translation matrix is ​​obtained by measuring the circumferential calibration block, including: calculating the translation matrix by comparing the point cloud data of the circumferential step of the circumferential calibration block. Specifically, the eccentricity of the rotation axis of the reflector is calculated by comparing the theoretical center of the circumferential step of the circumferential calibration block with the actual point cloud center of the circumferential step, and the translation matrix is ​​calculated according to the eccentricity of the rotation axis of the reflector. The theoretical center is the center of the center corresponding to the central axis when designing the circumferential calibration block.

[0056] In some embodiments, the rotation matrix is ​​obtained by measuring the axial calibration block, including: calculating the rotation matrix by comparing the point cloud data of the axial steps of the axial calibration block. Specifically, the angular offset of the rotation axis of the reflector is obtained by comparing the theoretical height difference of the axial steps of the axial calibration block with the actual point cloud height difference of the adjacent axial steps of the calibration piece, and the rotation matrix is ​​calculated by the angular offset of the rotation axis of the reflector. Among them, the theoretical height difference is the height difference of the adjacent axial steps when designing the axial calibration block.

[0057] In some embodiments, the laser emits laser light, and guides the laser light to the internal thread surface of the test piece through a reflector, including: fixing the test piece at the center of the rotating shaft of the rotation drive module, the laser emits laser light, and guides the laser light to the internal thread surface of the test piece through a reflector that enters the internal thread hole of the test piece, and adjusting the position of the internal thread of the test piece covered by the laser light. Figure 6 As shown, the laser emitted by the laser is guided to the narrow bolt hole through a compact reflector, and the double lenses of the compact reflector are arranged back to back, projecting the two laser beams of the laser to two points 180° apart from each other in the circumference of the internal thread. This is only an example and is not intended to be a limitation of the present application.

[0058] In some embodiments, the internal thread geometric parameters include: the mean diameter of the internal thread, the pitch of the internal thread and the thread angle of the internal thread. This is only an example. The internal thread geometric parameters also include the major diameter of the internal thread, the minor diameter of the internal thread and the lead of the internal thread. This is not a limitation of the present application.

[0059] The following is a specific implementation method of measuring internal threads of the present invention:

[0060] The present invention has wide application value in the field of industrial detection with high precision and high reliability requirements, and is particularly suitable for the detection of geometric parameters of the main bolt holes of nuclear reactor pressure vessels (RPVs). By identifying the damage and deformation of the threads in advance, the method can significantly reduce the risk of leakage or failure of the equipment during operation, thereby improving the reliability and safety of the equipment.

[0061] In the measurement principle of the present invention, two beams of laser light are guided by a dual-lens reflector to form a circumferential spot of 180° to each other on the thread surface, and the point cloud signal is collected by an image sensor. Due to processing errors and insufficient mechanical assembly precision, there may be a certain eccentricity between the rotation axis and the thread center axis, and the rotation axis is not completely parallel to the depth direction of the screw hole, resulting in the rotation of the dual-lens reflector. The beam may be offset and measurement errors may occur. The present invention calculates the geometric relationship of the point cloud data of the internal thread surface through a data processing module combined with the laser triangulation principle and the matrix compensation algorithm to obtain the geometric parameters of the internal thread. The specific steps include:

[0062] Step 1: Through the double-lens reflector, the two laser beams emitted by the laser form two points at 180° on the circumference of the internal thread surface, thereby obtaining point cloud data of the two points.

[0063] Step 2: Calculate the difference in point cloud data between the two points to obtain the spatial offset caused by the dual-lens reflector.

[0064] Step 3: Compensate for the spatial offset and finally obtain the true internal thread geometric parameters.

[0065] The spatial coordinate offset calculation in step 2 includes point cloud acquisition and offset analysis and offset model calculation, as follows:

[0066] In point cloud acquisition and offset analysis, it is assumed that the two beams of light projected by the laser are located at P1 (x1, y1, z1) and P2 (x2, y2, z2) on the threaded surface at 180° to each other in the circumferential direction. Due to the offset caused by the rotation of the lens, the actual acquisition points are P1' (x1', y1', z1') and P2' (x2', y2', z2'). The spatial offset ΔP is obtained by point cloud difference calculation:

[0067]

[0068] In the offset model calculation, the spatial offset ΔP of the lens rotation error can be decomposed into two parts: translation error and rotation error:

[0069] Translation error affects the overall offset of the point cloud:

[0070] P'=P+T px ,T px =(t x ,t y ,t z )

[0071] Rotation error causes angular deviation of the point cloud:

[0072] P″=R·P′,

[0073] Considering the translation error and rotation error comprehensively, the actual point cloud position P after compensation c for:

[0074] P c =P”―(T px +(R―I)·P)

[0075] Among them, P is the point cloud coordinates that are not affected by translation error and rotation error. P', as an intermediate step, is the point cloud coordinates after the translation error. P" is the point cloud coordinates after the translation and rotation errors. px is the translation error obtained by calibration. R is the rotation error obtained by calibration. I is the unit matrix, which represents the coordinates without rotation.

[0076] The process of obtaining the actual thread size data in step 3 is as follows:

[0077] By calculating the compensated point cloud data, the real thread geometry parameters are obtained:

[0078] Calculation of thread diameter, based on compensation data of thread point cloud, thread diameter d m The calculation formula is:

[0079]

[0080] Where n is the number of sampling points along the thread circumference; x i ,y i : The coordinates of the i-th sampling point.

[0081] Pitch calculation, through the thread axial point cloud data, calculate the distance p between adjacent thread peaks:

[0082]

[0083] Among them, z iand z i+1 : Axial coordinates of adjacent thread peaks.

[0084] Thread angle calculation: The calculation of thread angle α is based on the geometric fitting of the circumferential point cloud:

[0085]

[0086] Among them, Δz: axial change of thread point cloud, Δr: radial change of thread point cloud, the axial change of thread point cloud and the radial change of thread point cloud are as follows: Figure 7 shown.

[0087] The following is a specific implementation of the present invention based on step calibration of the rotation axis eccentricity and angle offset, which is used to calculate the translation matrix and rotation matrix in the matrix compensation algorithm:

[0088] Calibration target: The eccentricity of the rotating shaft is calibrated by the circumferential step signal of the laser calibration part, and the rotation angle offset is calibrated by the axial step signal to improve the calibration accuracy of the rotating system.

[0089] Calibration part design: Circumferential step processing: A set of equally spaced steps are processed on the circumference of the calibration part. The step height is h, and the circumferential position of each step forms a known theoretical angle θ with the rotation axis. i . Axial step processing: Process a set of equally spaced step surfaces in the axial direction of the calibration part, with a step surface spacing of d z , used to record the axial height change during rotation. For example: the number of circumferential steps n = 12, the interval angle is 30°; the axial step spacing d z =1.0mm, height accuracy 0.01mm.

[0090] Calibration equipment: laser system, dual-lens configuration, projecting two laser beams 180° to each other; optical imaging system: high-resolution CMOS sensor, used to collect step point cloud signals; rotation drive device: accuracy 0.01°.

[0091] Specific calibration process:

[0092] Fixing the calibration part and initializing the system: Fix the calibration part at the center of the rotating axis and adjust the laser system to cover the step position; collect the initial point cloud of the circumferential and axial steps.

[0093] Circumferential eccentricity calibration: Rotate the reflector for one circle and collect the step boundary points (x i ,y i ); Compare the theoretical center (x c ,y c ) and the actual point cloud center (x′ c ,y′ c ), calculate the eccentricity Δr of the rotating axis:

[0094]

[0095] Eccentricity compensation:

[0096] Perform eccentricity calibration on the measuring point (x,y):

[0097] (x′,y′)=(x―Δx,y―Δy)

[0098] Where (x′, y′) is the coordinates of the measured point after calibration, Δx=x′ c ―x c , Δy=y′ c ―y c , calculate the translation error T according to the eccentricity Δr of the rotation axis px and the translation matrix.

[0099] Axial angle offset calibration: collect axial step height point cloud z i ; Calculate the theoretical height difference between adjacent steps Δz = d z The difference Δz′ from the actual height gives the rotation angle offset Δθ:

[0100]

[0101] Where r is the radius of the calibration object, and the rotation error R and the rotation matrix are calculated according to the rotation angle offset Δθ.

[0102] Comprehensive calibration compensation:

[0103] Apply eccentricity compensation and angle offset compensation to the rotation system and substitute into the formula of the above embodiment to obtain the actual point cloud position P after compensation. c :

[0104] P c =P″―(T px +(R―I)·P)

[0105] Among them, P is the point cloud coordinates that are not affected by translation error and rotation error. P′, as an intermediate step, is the point cloud coordinates after the translation error correction. P″ is the point cloud coordinates after the translation and rotation errors. px is the translation error obtained by calibration. R is the rotation error obtained by calibration. I is the unit matrix, which represents the coordinates without rotation.

[0106] Calibration results: After circumferential eccentricity calibration, the point cloud error is less than 0.01mm; after axial angle offset calibration, the system rotation accuracy is improved to 0.01°.

[0107] The following is a specific implementation of the circumferential error rapid calibration of the present invention, which is another way to calculate the translation matrix in the matrix compensation algorithm:

[0108] In order to ensure the detection accuracy of the system, a rapid calibration test block is designed to calibrate the circumferential coordinate system and laser measurement system errors.

[0109] Calibration test block design: standard cylindrical threaded hole, with equally spaced threads and circumferential calibration steps on the surface.

[0110] Calibration steps: fix the test block, adjust the laser beam to cover the test block measurement range, collect the point cloud data of the marked points, calculate the difference between the actual and theoretical coordinates, and calibrate the circumferential coordinate offset Δθ1 of the laser system:

[0111]

[0112] Among them, x1, y1, x2, y2: are the collected coordinates of the marking points; θ0: is the theoretical circumferential angle of the marking point, and the translation matrix is ​​calculated based on Δθ1.

[0113] The following is a specific implementation of the present invention based on the calibration system to measure the thread geometric parameters:

[0114] Measurement target: High-precision measurement of the geometric parameters (mid-diameter, pitch, and thread angle) of an internal thread with a diameter of 25.0 mm.

[0115] Measuring equipment: Laser: Two sets of line lasers with a wavelength of 405nm, projected onto the thread surface. Optical imaging system: High-resolution CMOS sensor, collecting point cloud signals. Calibration system: Calibration test blocks including circumferential step and axial step processing.

[0116] Measurement process: Calibration of the calibration parts. Use the method in the above embodiment to compensate for the eccentricity and angle offset of the rotation system to ensure the accuracy of the system's rotation axis and the stability of the point cloud data.

[0117] Thread point cloud collection: The laser and the rotation system are started to collect point cloud data of the thread surface at 180° around each other.

[0118] Calculation of geometric parameters: Analyze the collected compensation point cloud and calculate the thread geometric parameters using the method in the above embodiment:

[0119] Test result output: Display the measured thread diameter, pitch, thread angle, and store the test report.

[0120] The present invention is an advanced internal thread geometric parameter measurement technology, which is particularly based on the laser triangulation method and realizes non-contact high-precision measurement of the internal thread geometric characteristics, belonging to the field of optical measurement and precision manufacturing detection technology. Through the technical solution of the present invention, the geometric parameters of complex threads, such as pitch, thread angle and thread mid-diameter, can be efficiently measured, and it is particularly suitable for the detection of internal threads of the main bolt holes of nuclear reactor pressure vessels (RPV). The present invention not only overcomes the surface damage of the workpiece that may be caused by traditional contact measurement methods, solves the problem that the laser unit is too large to directly enter the bolt hole, but also uses a matrix algorithm to avoid jitter and eccentricity during the rotation of the lens. By comprehensively using optical measurement technology, precision mechanical design and efficient data processing algorithms, the present invention not only improves the accuracy and efficiency of thread geometric parameter measurement, but also provides a new design idea for the field of non-contact measurement, and has important application value in the fields of industrial manufacturing and equipment quality control with high precision and high reliability requirements.

[0121] Some embodiments of the present invention further disclose an internal thread geometric parameter measurement system, comprising:

[0122] Laser, used for emitting laser light;

[0123] A reflector, used to guide the laser to the internal thread surface of the test piece;

[0124] An optical imaging module, used to capture the laser spot information reflected from the internal thread surface;

[0125] An image sensor, used to receive laser spot information and obtain point cloud data of the internal thread surface; and

[0126] The data processing module is used to combine the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data on the internal thread surface and obtain the geometric parameters of the internal thread.

[0127] In some embodiments, the reflector is a triangular structure, which reflects the laser to the internal threads on both sides. The fact that the reflector is a triangular structure is only an example and is not intended to limit the present application.

[0128] In some embodiments, the optical imaging module is a high-resolution lens, and the image sensor is a CMOS image sensor. For example, the CMOS sensor is arranged behind the laser sensor to capture the laser reflected back by the reflector. The CMOS sensor here is only an example and is not intended to limit the present application.

[0129] In some embodiments, the data processing module is used to combine the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data of the internal thread surface, and perform dynamic compensation through difference analysis to calculate the spatial offset of the dual lens position to obtain the geometric parameters of the internal thread.

[0130] In some embodiments, the internal thread geometric parameter measurement system also includes: a rotation drive module, which is used to drive the reflector to rotate around the rotation axis and control the laser beam to cover the internal thread of the workpiece to be measured. The rotation drive module is composed of a rotation unit and a lifting unit. The control of the reflector is achieved through the rotation and lifting actions of the unit.

[0131] In some embodiments, the laser spot refers to the distribution of the laser beam in space. After the laser is output, the laser beam will focus to form a small and bright spot. The shape of the laser spot can be circular, elliptical or other shapes. The circular, elliptical or other shapes here are only examples and are not intended to limit the present application.

[0132] In some embodiments, point cloud data is a data set consisting of a large number of points, each of which contains coordinates in three-dimensional space, usually X, Y, and Z coordinates, and may contain additional information, such as laser color, laser intensity, normal vector, etc. The laser color, laser intensity, and normal vector here are only examples and are not intended to limit the present application.

[0133] In some embodiments, laser triangulation is a non-contact measurement technology that uses optical reflection laws and the principle of similar triangles to measure the surface of an object. In this method, the laser beam emitted by the laser irradiates the surface of the object to be measured and undergoes diffuse reflection. The reflected light is then focused at another angle by the imaging system to image the light spot on the image sensor. When the surface of the object is displaced along the laser axis, the angle of the reflected light changes, causing the imaging position of the light spot on the image sensor to move accordingly. By measuring the center position of the light spot, the optical geometric relationship between the light spot and its image point position can be used to calculate the depth coordinates of the light spot. This is only an example and is not intended to limit the present application.

[0134] In some embodiments, the matrix compensation algorithm includes: introducing a translation matrix calculation to compensate for the eccentricity error, and introducing a rotation matrix calculation to compensate for the laser beam jitter error. Specifically, the translation matrix calculation is introduced to compensate for the eccentricity error caused by the rotation of the reflector; the rotation matrix calculation is introduced to compensate for the laser beam jitter error caused by the rotation of the reflector. For example, the matrix compensation algorithm calculation formula is:

[0135] x′=R(θ)·x+T p

[0136] Among them, R(θ) is the rotation matrix, which represents the change of the beam caused by the rotation angle of the reflector, T p is the translation matrix, which represents the static offset in the system layout, x is the original coordinate of the spot, and x' is the coordinate after the spot compensation.

[0137] In some embodiments, the data processing module uses fitting algorithms and filtering techniques to remove noise and external interference during the spot acquisition process.

[0138] In some embodiments, the translation matrix is ​​obtained by measuring a circumferential calibration block, and the rotation matrix is ​​obtained by measuring an axial calibration block.

[0139] In some embodiments, a plurality of steps are provided on the circumference of the inner wall of the tubular calibration block, and each step forms a sector with the same angle with the central axis of the tubular calibration block, so as to obtain a circumferential calibration block, for example: Figure 4 As shown, a plurality of steps are provided on the circumference of the inner wall of the tubular calibration block, each step forms a sector with the same angle with the central axis of the tubular calibration block, and the radii of the plurality of sectors gradually increase in sequence. This is only an example and is not intended to limit the present application.

[0140] A plurality of equally spaced and coaxial steps are provided on the inner wall of the tubular calibration block axially to obtain an axial calibration block, for example: Figure 5 As shown, a plurality of equally spaced and coaxial steps are provided in the axial direction of the inner wall of the tubular calibration block, and the radius of the plurality of steps gradually increases along the central axis of the tubular calibration block. This is only an example and is not intended to limit the present application.

[0141] In some embodiments, the translation matrix is ​​obtained by measuring the circumferential calibration block, including: calculating the translation matrix by comparing the point cloud data of the circumferential step of the circumferential calibration block. Specifically, the eccentricity of the rotation axis of the reflector is calculated by comparing the theoretical center of the circumferential step of the circumferential calibration block with the actual point cloud center of the circumferential step, and the translation matrix is ​​calculated according to the eccentricity of the rotation axis of the reflector. The theoretical center is the center of the center corresponding to the central axis when designing the circumferential calibration block.

[0142] In some embodiments, the rotation matrix is ​​obtained by measuring the axial calibration block, including: calculating the rotation matrix by comparing the point cloud data of the axial steps of the axial calibration block. Specifically, the angular offset of the rotation axis of the reflector is obtained by comparing the theoretical height difference of the axial steps of the axial calibration block with the actual point cloud height difference of the adjacent axial steps of the calibration piece, and the rotation matrix is ​​calculated by the angular offset of the rotation axis of the reflector. Among them, the theoretical height difference is the height difference of the adjacent axial steps when designing the axial calibration block.

[0143] In some embodiments, the laser emits laser light, and guides the laser light to the internal thread surface of the test piece through a reflector, including: fixing the test piece at the center of the rotating shaft of the rotation drive module, the laser emits laser light, and guides the laser light to the internal thread surface of the test piece through a reflector that enters the internal thread hole of the test piece, and adjusting the position of the internal thread of the test piece covered by the laser light. Figure 6As shown, the laser emitted by the laser is guided to the narrow bolt hole through a compact reflector, and the double lenses of the compact reflector are arranged back to back, projecting the two laser beams of the laser to two points 180° apart from each other in the circumference of the internal thread. This is only an example and is not intended to be a limitation of the present application.

[0144] In some embodiments, the internal thread geometric parameters include: the mean diameter of the internal thread, the pitch of the internal thread and the thread angle of the internal thread. This is only an example. The internal thread geometric parameters also include the major diameter of the internal thread, the minor diameter of the internal thread and the lead of the internal thread. This is not a limitation of the present application.

[0145] The following is a specific implementation method of measuring internal threads of the present invention:

[0146] The present invention has wide application value in the field of industrial detection with high precision and high reliability requirements, and is particularly suitable for the detection of geometric parameters of the main bolt holes of nuclear reactor pressure vessels (RPVs). By identifying the damage and deformation of the threads in advance, the method can significantly reduce the risk of leakage or failure of the equipment during operation, thereby improving the reliability and safety of the equipment.

[0147] In the measurement principle of the present invention, two beams of laser light are guided by a dual-lens reflector to form a circumferential spot of 180° on the thread surface, and the point cloud signal is collected by an image sensor. Due to processing errors and insufficient mechanical assembly precision, there may be a certain eccentricity between the rotation axis and the thread center axis, and the rotation axis is not completely parallel to the depth direction of the screw hole, resulting in the rotation of the dual-lens reflector. The beam may be offset and measurement errors may occur. The present invention uses a data processing module, combined with the laser triangulation principle and the matrix compensation algorithm, to calculate the geometric relationship of the point cloud data on the internal thread surface, and obtain the geometric parameters of the internal thread, specifically:

[0148] Step 1: Through the double-lens reflector, the two laser beams emitted by the laser form two points at 180° on the circumference of the internal thread surface, thereby obtaining point cloud data of the two points.

[0149] Step 2: Calculate the difference in point cloud data between the two points to obtain the spatial offset caused by the dual-lens reflector.

[0150] Step 3: Compensate for the spatial offset and finally obtain the true internal thread geometric parameters.

[0151] The spatial coordinate offset calculation in step 2 includes point cloud acquisition and offset analysis and offset model calculation, as follows:

[0152] In point cloud acquisition and offset analysis, it is assumed that the two beams of light projected by the laser are located at P1 (x1, y1, z1) and P2 (x2, y2, z2) on the threaded surface at 180° to each other in the circumferential direction. Due to the offset caused by the rotation of the lens, the actual acquisition points are P1' (x1', y1', z1') and P2' (x2', y2', z2'). The spatial offset ΔP is obtained by point cloud difference calculation:

[0153]

[0154] In the offset model calculation, the spatial offset ΔP of the lens rotation error can be decomposed into two parts: translation error and rotation error:

[0155] Translation error affects the overall offset of the point cloud:

[0156] P'=P+T px ,T px =(t x ,t y ,t z )

[0157] Rotation error causes angular deviation of the point cloud:

[0158] P″=R·P′,

[0159] Considering the translation error and rotation error comprehensively, the actual point cloud position P after compensation c for:

[0160] P c =P”―(T px +(R―I)·P)

[0161] Among them, P is the point cloud coordinates that are not affected by translation error and rotation error. P', as an intermediate step, is the point cloud coordinates after the translation error. P" is the point cloud coordinates after the translation and rotation errors. px is the translation error obtained by calibration. R is the rotation error obtained by calibration. I is the unit matrix, which represents the coordinates without rotation.

[0162] The process of obtaining the actual thread size data in step 3 is as follows:

[0163] By calculating the compensated point cloud data, the real thread geometry parameters are obtained:

[0164] Calculation of thread diameter, based on compensation data of thread point cloud, thread diameter d m The calculation formula is:

[0165]

[0166] Where n is the number of sampling points along the thread circumference; x i ,y i : The coordinates of the i-th sampling point.

[0167] Pitch calculation, through the thread axial point cloud data, calculate the distance p between adjacent thread peaks:

[0168]

[0169] Among them, z i and z i+1 : Axial coordinates of adjacent thread peaks.

[0170] Thread angle calculation: The calculation of thread angle α is based on the geometric fitting of the circumferential point cloud:

[0171]

[0172] Among them, Δz: axial change of thread point cloud, Δr: radial change of thread point cloud, the axial change of thread point cloud and the radial change of thread point cloud are as follows: Figure 7 shown.

[0173] The following is a specific implementation of the present invention based on step calibration of the rotation axis eccentricity and angle offset, which is used to calculate the translation matrix and rotation matrix in the matrix compensation algorithm:

[0174] Calibration target: The eccentricity of the rotating shaft is calibrated by the circumferential step signal of the laser calibration part, and the rotation angle offset is calibrated by the axial step signal to improve the calibration accuracy of the rotating system.

[0175] Calibration part design: Circumferential step processing: A set of equally spaced steps are processed on the circumference of the calibration part. The step height is h, and the circumferential position of each step forms a known theoretical angle θ with the rotation axis. i . Axial step processing: Process a set of equally spaced step surfaces in the axial direction of the calibration part, with a step surface spacing of d z , used to record the axial height change during rotation. For example: the number of circumferential steps n = 12, the interval angle is 30°; the axial step spacing d z =1.0mm, height accuracy 0.01mm.

[0176] Calibration equipment: laser system, dual-lens configuration, projecting two laser beams 180° to each other; optical imaging system: high-resolution CMOS sensor, used to collect step point cloud signals; rotation drive device: accuracy 0.01°.

[0177] Specific calibration process:

[0178] Fixing the calibration part and initializing the system: Fix the calibration part at the center of the rotating axis and adjust the laser system to cover the step position; collect the initial point cloud of the circumferential and axial steps.

[0179] Circumferential eccentricity calibration: Rotate the reflector for one circle and collect the step boundary points (x i ,y i ); Compare the theoretical center (x c ,y c ) and the actual point cloud center (x′ c ,y′ c ), calculate the eccentricity Δr of the rotating axis:

[0180]

[0181] Eccentricity compensation:

[0182] Perform eccentricity calibration on the measuring point (x,y):

[0183] (x′,y′)=(x―Δx,y―Δy)

[0184] Where (x′, y′) is the coordinates of the measured point after calibration, Δx=x′ c ―x c , Δy=y′ c ―y c , calculate the translation error T according to the eccentricity Δr of the rotation axis px and the translation matrix.

[0185] Axial angle offset calibration: collect axial step height point cloud z i ; Calculate the theoretical height difference between adjacent steps Δz = d z The difference Δz′ from the actual height gives the rotation angle offset Δθ:

[0186]

[0187] Where r is the radius of the calibration object, and the rotation error R and the rotation matrix are calculated according to the rotation angle offset Δθ.

[0188] Comprehensive calibration compensation:

[0189] Apply eccentricity compensation and angle offset compensation to the rotation system and substitute into the formula of the above embodiment to obtain the actual point cloud position P after compensation. c :

[0190] P c =P″―(T px +(R―I)·P)

[0191] Among them, P is the point cloud coordinates that are not affected by translation error and rotation error. P′, as an intermediate step, is the point cloud coordinates after the translation error correction. P″ is the point cloud coordinates after the translation and rotation errors. px is the translation error obtained by calibration. R is the rotation error obtained by calibration. I is the unit matrix, which represents the coordinates without rotation.

[0192] Calibration results: After circumferential eccentricity calibration, the point cloud error is less than 0.01mm; after axial angle offset calibration, the system rotation accuracy is improved to 0.01°.

[0193] The following is a specific implementation of the circumferential error rapid calibration of the present invention, which is another way to calculate the translation matrix in the matrix compensation algorithm:

[0194] In order to ensure the detection accuracy of the system, a rapid calibration test block is designed to calibrate the circumferential coordinate system and laser measurement system errors.

[0195] Calibration test block design: standard cylindrical threaded hole, with equally spaced threads and circumferential calibration steps on the surface.

[0196] Calibration steps: fix the test block, adjust the laser beam to cover the test block measurement range, collect the point cloud data of the marked points, calculate the difference between the actual and theoretical coordinates, and calibrate the circumferential coordinate offset Δθ1 of the laser system:

[0197]

[0198] Among them, x1, y1, x2, y2: are the collected coordinates of the marking points; θ0: is the theoretical circumferential angle of the marking point, and the translation matrix is ​​calculated based on Δθ1.

[0199] The following is a specific implementation of the present invention based on the calibration system to measure the thread geometric parameters:

[0200] Measurement target: High-precision measurement of the geometric parameters (mid-diameter, pitch, and thread angle) of an internal thread with a diameter of 25.0 mm.

[0201] Measuring equipment: Laser: Two sets of line lasers with a wavelength of 405nm, projected onto the thread surface. Optical imaging system: High-resolution CMOS sensor, collecting point cloud signals. Calibration system: Calibration test blocks including circumferential step and axial step processing.

[0202] Measurement process: Calibration of the calibration parts. Use the method in the above embodiment to compensate for the eccentricity and angle offset of the rotation system to ensure the accuracy of the system's rotation axis and the stability of the point cloud data.

[0203] Thread point cloud collection: The laser and the rotation system are started to collect point cloud data of the thread surface at 180° around each other.

[0204] Calculation of geometric parameters: Analyze the collected compensation point cloud and calculate the thread geometric parameters using the method in the above embodiment:

[0205] Test result output: Display the measured thread diameter, pitch, thread angle, and store the test report.

[0206] The implementation of the present invention has the following beneficial effects: the present invention emits laser light through a laser, guides the laser light to the internal thread surface of the test piece through a reflector, captures the laser spot information reflected by the internal thread surface through an optical imaging module, and transmits the laser spot information to an image sensor to obtain point cloud data of the internal thread surface. The data processing module combines the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data of the internal thread surface and obtain the geometric parameters of the internal thread. This method effectively solves the problems of beam jitter and eccentricity caused by the rotation of the reflector, thereby ensuring the accuracy of the measurement results.

[0207] The present invention proposes a method for measuring the geometric parameters of internal threads based on the laser triangulation method. Through an innovative reflector system and a matrix data processing algorithm, the method overcomes the limitations of traditional contact measurement and existing laser measurement technology and realizes high-precision non-contact measurement. This method can identify thread damage and deformation in advance and is suitable for industries with extremely high requirements for equipment reliability, such as nuclear power and aerospace. The non-contact measurement method is adopted to protect the surface of the workpiece, which is suitable for thread detection with high precision and complex geometric structures, and avoids the measurement errors and surface scratches caused by traditional probe contact. The laser is guided into the bolt hole through the reflector system, which solves the problem that the laser cannot directly enter the bolt hole due to its large size, and the matrix error compensation algorithm eliminates the lens rotation error, ensuring high precision and high consistency of the measurement. Combined with matrix operation and dynamic filtering technology, the method can achieve sub-micron measurement accuracy, significantly improve the measurement speed, and meet the requirements of rapid detection in online measurement and mass production environments. In addition, combined with an automated positioning system and multi-angle laser projection, the present invention has high reliability and adaptability, can adapt to thread structures of different sizes and shapes, and is particularly suitable for quality detection of high aspect ratio threads and large diameter threads.

[0208] In summary, the present invention provides a new solution for the precise measurement of internal thread geometric parameters, meets the demand of modern industry for high-quality measurement technology, and provides technical guarantee for equipment safety and manufacturing quality control in the fields of nuclear energy, aviation, automobiles, etc.

[0209] It is understandable that the above embodiments only express some implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, the above embodiments or technical features can be freely combined, and several deformations and improvements can be made, which all belong to the protection scope of the present invention, that is, the embodiments described in "some embodiments" can be freely combined with any of the above and below embodiments. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the scope of the claims of the present invention.

Claims

1. A method for measuring internal thread geometric parameters, characterized in that: The method comprises the following steps: The laser emits laser light, and the laser light is guided to the internal thread surface of the workpiece to be tested through a reflector; The laser spot information reflected by the internal thread surface is captured by the optical imaging module, and the laser spot information is transmitted to the image sensor to obtain the point cloud data of the internal thread surface; The data processing module combines the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data on the internal thread surface and obtain the geometric parameters of the internal thread.

2. The method for measuring internal thread geometric parameters according to claim 1, characterized in that: The matrix compensation algorithm includes: Introduce translation matrix calculation to compensate for eccentricity error; The rotation matrix calculation is introduced to compensate the laser beam jitter error.

3. The method for measuring internal thread geometric parameters according to claim 2, characterized in that: The translation matrix is ​​obtained by measuring the circumferential calibration block; the rotation matrix is ​​obtained by measuring the axial calibration block.

4. The method for measuring internal thread geometric parameters according to claim 3, characterized in that: A plurality of steps are arranged on the circumference of the inner wall of the tubular calibration test block, each step forms a sector with the same angle with the central axis, and a circumferential calibration test block is obtained; A plurality of equally spaced and coaxial steps are arranged axially on the inner wall of the tubular calibration test block to obtain an axial calibration test block.

5. The method for measuring internal thread geometric parameters according to claim 4, characterized in that: The translation matrix is ​​obtained by measuring the circumferential calibration test block, including: calculating the translation matrix by comparing the point cloud data of the circumferential steps of the circumferential calibration test block.

6. The method for measuring internal thread geometric parameters according to claim 4, characterized in that: The rotation matrix is ​​obtained by measuring the axial calibration test block, including: calculating the rotation matrix by comparing the point cloud data of the axial step of the axial calibration test block.

7. The method for measuring internal thread geometric parameters according to claim 1, characterized in that: The laser emits laser, and guides the laser to the internal thread surface of the test piece through the reflector, including: fixing the test piece at the center of the rotating shaft of the rotating drive module, the laser emits laser, and guides the laser to the internal thread surface of the test piece through the reflector entering the internal thread hole of the test piece, and adjusting the laser to cover the internal thread position of the test piece.

8. The method for measuring internal thread geometric parameters according to claim 1, characterized in that: The internal thread geometric parameters include: the internal thread pitch, the internal thread pitch and the internal thread angle.

9. An internal thread geometric parameter measurement system, characterized in that: include: Laser, used for emitting laser light; A reflector, used to guide the laser to the internal thread surface of the workpiece to be tested; An optical imaging module is used to capture the laser spot information reflected from the internal thread surface; An image sensor, used to receive laser spot information and obtain point cloud data of the internal thread surface; and The data processing module is used to combine the laser triangulation principle and the matrix compensation algorithm to calculate the geometric relationship of the point cloud data on the internal thread surface and obtain the geometric parameters of the internal thread.

10. The internal thread geometric parameter measurement system according to claim 9, characterized in that: Also includes: The rotation drive module is used to drive the reflector to rotate around the rotation axis and control the laser beam to cover the internal thread of the test piece.

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