Thread detection device and method suitable for long shaft parts of an aero-engine

Abstract

The application discloses a thread detection device and method suitable for long shaft parts of an aero-engine, which combines radial size measurement and projection measurement, makes up for the shortcomings that radial size measurement cannot measure axial details and projection measurement has insufficient radial resolution, improves the measurement accuracy and measurement range of the projection measurement method, can realize thread parameter measurement with an accuracy of about 0.01 millimeter under the condition that the shaft diameter is more than 100 millimeters, can meet the detection requirements of large axial size span and high detail accuracy of the long shaft parts of the aero-engine, and is non-contact optical detection, cannot be additionally assisted, can greatly improve the thread measurement efficiency, and meets the large batch thread detection requirements.

Description

Technical Field

[0001] The present invention relates to the field of precision measurement technology, and in particular to a thread detection device and method suitable for long-axis parts of aircraft engines. Background Art

[0002] The flexible long shaft of a turboshaft aircraft engine is a key component responsible for transmitting the engine's thrust to the aircraft. The threaded connections on the long shaft are critical structures that withstand high-speed rotation, high temperatures, high pressures, and complex stress environments. Their quality directly impacts the engine's reliability, safety, and performance. Threaded connections on long shafts typically require high precision, high strength, and high wear resistance. These requirements make the machining and measurement of threads on aircraft engine long shafts technically challenging. Thread measurement is a key step in ensuring that thread quality meets design requirements. By measuring the thread pitch diameter and its runout, deviations in the machining process can be detected and corrected before assembly, ensuring assembly stability and fit strength. Furthermore, high-quality threaded connections can improve engine efficiency, reduce fuel consumption, and increase aircraft range.

[0003] However, due to the long length of the flexible long shaft of an aircraft engine, generally exceeding 600mm, and some even exceeding 1000mm, the commonly used thread detector has a maximum stroke of only 400mm, which cannot be used to install long shaft parts, making it impossible to measure the threads of the flexible long shaft. Optical shaft detectors can only detect external conventional geometric dimensions such as outer diameter and length, and cannot measure thread parameters. In addition, the existing combined measurement methods using thread gauges, three-needle methods, etc., have the problem of low measurement efficiency due to the use of offline measurement methods. Moreover, due to the lack of a unified benchmark, it is difficult to analyze and measure key parameters such as runout. Therefore, the existing thread measurement methods cannot meet the high-precision, large-scale thread detection needs of aircraft engine long shaft parts. Summary of the Invention

[0004] The present invention provides a thread detection device and method suitable for long shaft parts of aircraft engines, so as to solve the technical problem that existing thread measurement methods cannot meet the high-precision and large-scale thread detection requirements of long shaft parts of aircraft engines.

[0005] According to one aspect of the present invention, there is provided a thread detection device suitable for long shaft parts of aircraft engines, comprising:

[0006] Radial dimension measurement module, used to measure any radial dimension of long axis parts;

[0007] Machine vision measurement module, used to capture the projection image of the long-axis part in the radial direction;

[0008] A motion shaft module is configured to drive the radial dimension measurement module and the machine vision measurement module to move along the axial direction of the long shaft part, and to axially position and clamp the long shaft part;

[0009] A control module is electrically connected with the radial dimension measurement module, the machine vision measurement module and the motion shaft module, and is configured to control the motion shaft module to drive the radial dimension measurement module to move to an arbitrary optical axis position on the long shaft part, to measure the radial dimension at the reference position based on the optical axis position, to control the motion shaft module to drive the machine vision measurement module to align with the reference position, to capture the projection image at the reference position, to control the motion shaft module to drive the machine vision measurement module to align with the thread and capture the projection image of the thread, and to take the radial dimension at the reference position measured by the radial dimension measurement module as the radial reference dimension, and to calculate the major diameter value, the middle diameter value and the pitch of the thread based on the projection image at the reference position and the projection image of the thread captured by the machine vision measurement module.

[0010] Further, the motion shaft module is further configured to drive the long shaft part to rotate, and the control module is further configured to control the motion shaft module to rotate for one revolution, and to control the machine vision measurement module to capture images at fixed intervals at preset angles during the rotation to obtain a plurality of thread projection images, and to calculate the middle diameter value of the thread in each thread projection image to calculate the middle diameter runout of the thread.

[0011] Further, the radial dimension measurement module is a light curtain type shaft diameter measurement sensor, which is oppositely arranged on two sides of the long shaft part along the radial direction, the machine vision measurement module includes an imaging unit and a light source unit, the imaging unit and the light source unit are oppositely arranged on two sides of the long shaft part along the radial direction, the imaging unit is an industrial camera matched with a telecentric lens, the light source unit is a parallel backlight source, the center of the light curtain type shaft diameter measurement sensor is aligned with the rotation center of the long shaft part, and the edge of the field of view of the imaging unit is aligned with the rotation center of the long shaft part.

[0012] Further, the control module is further configured to perform occlusion distortion compensation on the thread projection image after obtaining the thread projection image.

[0013] Further, the control module performs occlusion distortion compensation on the thread projection image in the following process:

[0014] A three-dimensional coordinate system is established with the rotation axis of the long shaft part as the z-axis;

[0015] A cutting plane parallel to the xoz plane is obtained by intersecting the cutting plane with the single-spiral surface, and a spiral curve is obtained;

[0016] Derivation of the z-axis coordinate equation of the spiral curve is performed to obtain the actual measured thread cross-section profile;

[0017] The compensation value is calculated based on the actual measured thread cross-section profile and the theoretical thread cross-section profile, and the occlusion distortion compensation is performed on the thread projection image based on the compensation value to obtain the real image.

[0018] Further, the calibration module is further included for image calibration of the machine vision measurement module.

[0019] Further, the motion shaft module includes a measurement shaft movement unit, a clamping shaft movement unit and a rotary table unit, the measurement shaft movement unit is arranged on both sides of the long shaft part in a radial direction and can move in an axial direction, the radial size measurement module and the machine vision measurement module are fixedly installed on the measurement shaft movement unit, the clamping shaft movement unit is fixedly installed on the rotary table unit and can move in an axial direction, and is used for axial clamping and positioning of the long shaft part, and the rotary table unit is used for driving the clamping shaft movement unit and the long shaft part to rotate synchronously.

[0020] In addition, the present application also provides a thread detection method suitable for long shaft parts of an aero-engine, which adopts the thread detection device as described above, and includes the following contents:

[0021] The motion shaft module is controlled to drive the radial size measurement module to move to an arbitrary optical axis position on the long shaft part, and the radial size at the reference position is measured based on the optical axis position as a reference;

[0022] The motion shaft module is controlled to drive the machine vision measurement module to align with the reference position to shoot the projection image at the reference position;

[0023] The motion shaft module is controlled to drive the machine vision measurement module to align with the thread to shoot the projection image of the thread;

[0024] The radial size at the reference position measured by the radial size measurement module is taken as the radial reference size, and the major diameter value, the middle diameter value and the pitch of the thread are calculated based on the projection image at the reference position and the projection image of the thread shot by the machine vision measurement module.

[0025] Further, the following contents are further included:

[0026] The motion shaft module is controlled to drive the long shaft part to rotate for one revolution, and the machine vision measurement module is controlled to shoot at fixed intervals at a preset angle during the rotation to obtain a plurality of thread projection images, and the middle diameter value of the thread in each thread projection image is calculated to calculate the middle diameter runout of the thread.

[0027] Further, after the projection image of the thread is obtained, the following contents are further included:

[0028] Compensate for occlusion distortion on the thread projection image.

[0029] The present application has the following effects:

[0030] The thread detection device for long shaft parts of an aero-engine of the present application takes any optical axis position on the long shaft part as a reference position, first measures the radial dimension data of the reference position by using the radial dimension measurement module, takes the radial dimension data as the actual radial reference dimension for measuring the major diameter and the middle diameter of the thread. After taking the radial projection image at the reference position by using the machine vision measurement module, the corresponding relationship between the projection radial dimension at the reference position and the actual radial reference dimension can be obtained. Then, the projection image at the thread is taken by using the machine vision measurement module, the major diameter profile of the thread can be obtained by high point straight line fitting based on the projection image at the thread, and the profile at the reference position is extracted based on the projection image at the reference position, so that the pixel distance between the major diameter profile of the thread and the profile at the reference position can be calculated, the pixel distance is converted into an actual distance, and the radial dimension data of the reference position measured by the radial dimension measurement module is combined, so that the major diameter value of the thread can be calculated. Similarly, the thread edge is determined based on the projection image at the thread, the pixel distance between the middle diameter position and the major diameter position is calculated and converted into an actual distance after the middle diameter position is found, and the major diameter value of the thread is combined, so that the middle diameter value of the thread can be calculated. The present application combines radial dimension measurement and projection measurement, makes up for the shortcomings that the radial dimension measurement cannot measure axial details and the projection measurement has insufficient radial resolution, improves the measurement accuracy and measurement range of the projection measurement method, can realize thread parameter measurement with an accuracy of about 0.01 millimeter under the condition that the shaft diameter is more than one hundred millimeters, can meet the detection requirements of large span and high detail accuracy of the shaft size of the long shaft part of the aero-engine, and is a non-contact optical detection method, which cannot be additionally assisted, can greatly improve the thread measurement efficiency, and can meet the large batch thread detection requirements.

[0031] In addition, the thread detection method for long shaft parts of an aero-engine of the present application also has the above advantages.

[0032] In addition to the objects, features and advantages described above, the present application has other objects, features and advantages. The present application will be further described below with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0033] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application, illustrate the preferred embodiment of the application and assist in the explanation of the application. In the drawings:

[0034] Figure 1is a structure schematic view of a thread detection device for aero-engine long shaft parts according to a preferred embodiment of the present application.

[0035] Figure 2 is a position schematic view of a machine vision measurement module and a rotation center of a long shaft part according to a preferred embodiment of the present application.

[0036] Figure 3 is a projection image schematic view of a half of a long shaft part taken by a machine vision measurement module according to a preferred embodiment of the present application.

[0037] Figure 4 is a schematic view of a calibration module according to a preferred embodiment of the present application.

[0038] Figure 5 is a schematic view of an intersection of a cutting plane and a single-surface helical surface according to a preferred embodiment of the present application.

[0039] Figure 6 is a schematic view of a compensation for occlusion distortion of a thread projection image according to a preferred embodiment of the present application.

[0040] Figure 7 is a flow schematic view of a thread detection method for aero-engine long shaft parts according to another embodiment of the present application.

[0041] Figure 8 is another flow schematic view of a thread detection method for aero-engine long shaft parts according to another embodiment of the present application.

[0042] Figure 9 is a flow schematic view of a compensation for occlusion distortion of a thread projection image according to another embodiment of the present application.

[0043] Legend of reference signs

[0044] 100, radial dimension measurement module; 200, machine vision measurement module; 300, motion axis module; 400, calibration module; 201, imaging unit; 202, light source unit; 301, measurement axis motion unit; 302, clamped axis motion unit; 303, rotary table unit. DETAILED DESCRIPTION

[0045] The embodiments of the present application will be described in detail below with reference to the accompanying drawings, but the present application can be implemented in various different ways as defined and covered by the following description.

[0046] It can be understood that, as Figure 1As shown, the preferred embodiment of the present application provides a thread detection device suitable for long shaft parts of an aero-engine, which comprises a radial dimension measurement module 100 for measuring any radial dimension of the long shaft part, a machine vision measurement module 200 for taking a projection image of the long shaft part in the radial direction, a motion shaft module 300 for driving the radial dimension measurement module 100 and the machine vision measurement module 200 to move along the axial direction of the long shaft part and for axially positioning and clamping the long shaft part, and a control module (not shown in the figure) electrically connected with the radial dimension measurement module 100, the machine vision measurement module 200 and the motion shaft module 300. The control module is generally a host computer, which is used to first control the motion shaft module 300 to drive the radial dimension measurement module 100 to move to any optical axis position on the long shaft part, and then to measure the radial dimension at the reference position based on the optical axis position, and then to control the motion shaft module 300 to drive the machine vision measurement module 200 to align with the reference position, so as to take a projection image of the reference position, and then to control the motion shaft module 300 to drive the machine vision measurement module 200 to align with the thread and take a projection image of the thread, and finally to take the radial dimension at the reference position measured by the radial dimension measurement module 100 as the radial reference dimension, and to calculate the major diameter, the middle diameter and the pitch of the thread based on the projection image of the reference position and the projection image of the thread taken by the machine vision measurement module 200. Wherein, after obtaining the projection image of the thread, the control module performs linear fitting on the high points in the image, so as to obtain the major diameter of the thread, and then calculates the pixel distance between the fitted straight line and the contour of the projection image at the reference position, and converts the actual distance, so as to calculate the major diameter of the thread.

[0047] It can be understood that the thread detection device suitable for the long shaft part of the aero-engine of the embodiment takes any optical axis position on the long shaft part as a reference position, first measures the radial dimension data of the reference position by using the radial dimension measuring module 100, and takes the radial dimension data as the actual radial reference dimension of the major diameter and the pitch diameter measurement. After the radial projection image at the reference position is shot by the machine vision measuring module 200, the corresponding relationship between the projection radial dimension at the reference position and the actual radial reference dimension can be obtained. Then, the projection image at the thread is shot by using the machine vision measuring module 200, the high point straight line fitting based on the projection image at the thread can obtain the major diameter profile of the thread, and the profile extraction based on the projection image at the reference position can be performed, so that the pixel distance between the major diameter profile of the thread and the profile at the reference position can be calculated, and the pixel distance is converted into an actual distance, and combined with the radial dimension data of the reference position measured by the radial dimension measuring module 100, the major diameter value of the thread can be calculated. Similarly, the thread edge is determined based on the projection image at the thread, after the pitch diameter position is found, the pixel distance between the pitch diameter position and the major diameter position is calculated and converted into an actual distance, and then the major diameter value of the thread is collected to calculate the pitch diameter value of the thread, and the pitch is the axial distance between two pitch diameter measurement points, which can be calibrated and converted into an actual distance based on the pixel distance between the two pitch diameter measurement points. The present application combines radial dimension measurement and projection measurement, which makes up for the shortcomings of radial dimension measurement that cannot measure axial details and the radial resolution of projection measurement is insufficient, and at the same time improves the measurement accuracy and measurement range of the projection measurement method, can realize the thread parameter measurement with an accuracy of about 0.01 millimeter under the condition that the shaft diameter is more than one hundred millimeters, can meet the detection requirements of the large span of the shaft size and the high precision of the details of the long shaft part of the aero-engine, and adopts a non-contact optical detection, which cannot be additionally assisted to set, can greatly improve the thread measurement efficiency, and meets the large batch thread detection requirements.

[0048] It can be understood that the radial dimension measurement module 100 is a light curtain shaft diameter measurement sensor, which is oppositely arranged on both sides of the long shaft part in the radial direction, can measure the radial dimension of the long shaft part at any position, and provides a reference for thread major diameter and pitch diameter measurement. The machine vision measurement module 200 comprises an imaging unit 201 and a light source unit 202, which are oppositely arranged on both sides of the long shaft part in the radial direction. The imaging unit 201 is an industrial camera matched with a telecentric lens, the optical axis of the industrial camera is perpendicular to the axis of the long shaft part, and is used for capturing a projection image. The telecentric lens is used for receiving light generated by the light source unit 202, and ensures that the received light is parallel incident. The light source unit 202 is a parallel backlight source, which is used for generating stable and uniform light to ensure the definition and accuracy of the projection image. As preferred, when installed, the center of the light curtain shaft diameter measurement sensor is aligned with the rotation center of the long shaft part to be measured, and the machine vision measurement module 200 is placed in a biased manner, that is, the edge of the field of view of the imaging unit 201 is aligned with the rotation center of the long shaft part, as shown in Figure 2 The advantage of this structure layout is that the measurement range shortage caused by the aperture limitation of the telecentric lens can be improved by the light curtain shaft diameter measurement sensor, and the blind area caused by the light curtain thickness of the light curtain shaft diameter measurement sensor cannot detect the subtle features of the shaft shoulder can be compensated by the longitudinal resolution of the telecentric lens. Therefore, in the present application, the machine vision measurement module 200 only needs to capture the projection image of one half of the long shaft part, as shown in Figure 3 The pixel position of the major diameter / pitch diameter is extracted, and the pixel position is compared with the pixel position at the reference position, and then the actual radial dimension at the reference position measured by the light curtain shaft diameter measurement sensor is combined to calculate the major diameter value / pitch diameter value, so that the high-speed, high-precision and multi-feature measurement of the long shaft part is realized through the complementation of the two sets of measurement systems.

[0049] Alternatively, the motion shaft module 300 is further used to drive the long shaft part to rotate, and the control module is further used to control the motion shaft module 300 to rotate for one revolution, and control the machine vision measurement module 200 to capture images at fixed intervals at a preset angle during rotation to obtain a plurality of thread projection images, and calculate the pitch diameter value of the thread in each thread projection image to calculate the pitch diameter runout of the thread. The present application realizes the thread pitch diameter runout detection by adopting the rotating shooting mode, and greatly improves the measurement speed.

[0050] It can be understood that the motion shaft module 300 comprises a measurement shaft movement unit 301, a clamping shaft movement unit 302 and a rotary table unit 303, the measurement shaft movement unit 301 is oppositely arranged on both sides of the long shaft part along the radial direction and can move along the axial direction, the radial size measurement module 100 and the machine vision measurement module 200 are fixedly installed on the measurement shaft movement unit 301, and specifically, are installed on the same slide plate of the measurement shaft movement unit 301, wherein the radial size measurement module 100 is installed below the machine vision measurement module 200, and of course, in other embodiments of the present application, the radial size measurement module 100 can also be installed above the machine vision measurement module 200. Wherein the measurement shaft movement unit 301 can adopt a linear driving mechanism such as an electric telescopic rod or a linear motor. The clamping shaft movement unit 302 is fixedly installed on the rotary table unit 303 and can move relatively along the axial direction, and is used for axially clamping and positioning the long shaft part, and the rotary table unit 303 is used for driving the clamping shaft movement unit 302 and the long shaft part to rotate synchronously. Wherein the clamping shaft movement unit 302 comprises two clamping heads, the lower clamping head is fixedly installed on the rotary table unit 303, and the upper clamping head is adjustably installed on the rotary table unit 303, and the upper clamping head is controlled to move relatively towards the lower clamping head, so as to position and clamp the axial two ends of the long shaft part. It can be understood that the rotary table unit 303 can be omitted when the detection of the pitch diameter runout of the screw is not required.

[0051] In addition, the screw detection device further comprises a calibration module 400 for image calibration of the machine vision measurement module 200. Optionally, as shown in Figure 4 The calibration module 400 is a checkerboard calibration plate for calibration of the size of the CCD pixel, the size of the pixel in the image is calculated and converted into the actual size, so that the conversion relationship between the pixel size and the actual size can be obtained.

[0052] It can be understood that for the photographed screw projection image, because the optical axis of the CCD camera is perpendicular to the screw axis, when the screw projection enters the camera, occlusion distortion will be generated, the obtained screw edge is not the real contour on the axial section, and the selected pitch diameter position is not accurate, thereby leading to poor accuracy of the detected pitch diameter value. Therefore, it is necessary to inverse the real image on the basis of the distorted image, so as to obtain the real screw section, thereby ensuring the accuracy of the selected pitch diameter position and further improving the measurement precision of the pitch diameter value. Optionally, the control module is further used for compensating the occlusion distortion of the screw projection image after obtaining the projection image of the screw. Wherein the process of the control module for compensating the occlusion distortion of the screw projection image is as follows:

[0053] A three-dimensional coordinate system is established with the rotation axis of the long shaft part as the z axis;

[0054] A cutting plane parallel to the xoz plane intersects the single helical surface to obtain a helical curve;

[0055] The z-axis coordinate equation of the helical curve is differentiated to obtain an extreme value, and an actual measured thread cross-sectional profile is obtained;

[0056] A compensation value is calculated based on the actual measured thread cross-sectional profile and the theoretical thread cross-sectional profile, and the thread projection image is compensated for occlusion distortion based on the compensation value to obtain a real image.

[0057] Specifically, as shown in Figure 5 A three-dimensional coordinate system oxyz is established with the axis of revolution of the long-axis part as the z-axis, and the single helical surface can be represented as: Wherein, φ represents the angle between a point on the single helical surface and the x-axis in the xoy plane, P represents the pitch, d represents the major diameter of the thread, α represents the thread angle, and t represents a variable parameter, d1 represents the minor diameter of the thread.

[0058] Then, in the present application, the backlight source is projected along the x direction, so a cutting plane (y=D) parallel to the xoz plane intersects the single helical surface to obtain a helical curve, and the helical curve can be represented as: Wherein, And

[0059] It can be seen that z is a function of φ, and then the derivative of z with respect to φ is obtained: Then, the extreme value is obtained, and z′=0 is obtained:

[0060]

[0061]

[0062] Then, the above formula is substituted into the equation of the helical curve, so that the actual boundary point of the projection image can be obtained, that is, the thread profile actually measured by the machine vision measurement module 200 can be obtained, which can be represented as:

[0063]

[0064] And the theoretical thread cross-sectional profile is: Therefore, the compensation value is: Δz=z max -z real Based on the compensation value, the thread projection image is compensated for occlusion distortion, that is, a real image is obtained, as shown in Figure 6 The real pitch position point is selected in the real image calculated back to calculate the pitch value of the thread.

[0065] It can be understood that the working process of the thread detection device of the present application is specifically as follows:

[0066] First, turn on the light source unit 202 to generate stable and uniform light, then turn on the imaging unit 201, and clamp the calibration module 400. Rotate it manually to make its direction as perpendicular to the optical axis of the industrial camera as possible. Then, take a picture of the calibration board, and calculate the relationship between the image pixel size and the real size through the distance between the corner points of the checkerboard. After that, remove the calibration module 400. Then control the upper clamping block in the clamping shaft movement unit 302 to move for clamping positioning, and fix the aero-engine long shaft part on the rotating table unit 303.

[0067] Then, select any optical axis position on the long shaft part as the reference position, control the axial movement of the measurement shaft movement unit 301 to align the reference position for measurement by the light curtain type shaft diameter measurement sensor, and obtain the radial size data at the reference position.

[0068] Then, control the axial movement of the measurement shaft movement unit 301 to align the reference position for shooting by the machine vision measurement module 200, obtain the projection image at the reference position, and perform contour extraction.

[0069] Next, control the axial movement of the measurement shaft movement unit 301 to align the thread for shooting by the machine vision measurement module 200, obtain the projection image of the thread, and perform contour extraction. Linear fitting is performed on the high points in the thread projection image to obtain the major diameter of the thread. Then, calculate the pixel distance between the contour at the major diameter position and the contour at the reference position, and convert it into the actual distance through the calibration result, so as to calculate the major diameter value of the thread.

[0070] Then, perform occlusion distortion compensation on the photographed thread image to obtain the real image, select the real pitch diameter position, convert the pixel distance between the pitch diameter position and the major diameter position into the actual distance, and combine the major diameter value of the thread to calculate the pitch diameter value of the thread. The axial distance between the two pitch diameter position points is the pitch.

[0071] Next, control the rotating table unit 303 to start, control the rotating table to rotate 360°, take a picture every n° (usually n < 1), and take a total of 360 / n pictures. Calculate the pitch diameter value of the measured thread in each picture to calculate the pitch diameter runout value.

[0072] Finally, compare the measured major diameter value, pitch diameter value, pitch, and pitch diameter runout value with the preset threshold value to determine whether the thread processing quality meets the requirements, and output the measurement result to the display device or export the data to the data storage device.

[0073] In addition, as Figure 7As shown, another embodiment of the present application also provides a thread detection method suitable for long shaft parts of an aero-engine, preferably using the thread detection device as described above, which method comprises the following steps:

[0074] Step S1: controlling the motion shaft module to drive the radial size measurement module to move to an arbitrary optical axis position on the long shaft part, and measuring the radial size at the reference position based on the optical axis position;

[0075] Step S2: controlling the motion shaft module to drive the machine vision measurement module to align with the reference position to take a projection image at the reference position;

[0076] Step S3: controlling the motion shaft module to drive the machine vision measurement module to align with the thread and take a projection image of the thread;

[0077] Step S4: taking the radial size at the reference position measured by the radial size measurement module as the radial reference size, and combining the projection image at the reference position and the projection image of the thread taken by the machine vision measurement module to calculate the major diameter value, the middle diameter value and the pitch of the thread.

[0078] It can be understood that the thread detection method suitable for the long shaft part of the aero-engine of the embodiment takes any optical axis position on the long shaft part as a reference position, first measures the radial dimension data of the reference position by using the radial dimension measurement module, takes the radial dimension data as the actual radial reference dimension of the major diameter and the pitch diameter measurement, and obtains the corresponding relationship between the projected radial dimension at the reference position and the actual radial reference dimension after shooting the radial projection image at the reference position by using the machine vision measurement module. Then, the projected image at the thread position is shot by using the machine vision measurement module, the high point straight line fitting based on the projected image at the thread position can obtain the major diameter profile of the thread, and the profile extraction based on the projected image at the reference position can be performed, so that the pixel distance between the major diameter profile of the thread and the profile at the reference position can be calculated, the pixel distance is converted into an actual distance, and the major diameter value of the thread can be calculated by combining the radial dimension data of the reference position measured by the radial dimension measurement module. Similarly, the thread edge is determined based on the projected image at the thread position, the pixel distance between the pitch diameter position and the major diameter position is calculated after the pitch diameter position is found, and the pixel distance is converted into an actual distance, and the pitch diameter value of the thread can be calculated by combining the major diameter value of the thread. The pitch is the axial distance between the two pitch diameter measurement points, which can be calibrated and converted into an actual distance based on the pixel distance between the two pitch diameter measurement points. The present application combines radial dimension measurement and projection measurement, makes up for the shortcomings that radial dimension measurement cannot measure axial details and projection measurement has insufficient radial resolution, improves the measurement accuracy and measurement range of the projection measurement method, realizes thread parameter measurement with an accuracy of about 0.01 mm under the condition that the shaft diameter is more than 100 mm, meets the detection requirements of the aero-engine long shaft part with large axial size span and high detail accuracy, and adopts non-contact optical detection, which cannot be additionally assisted and set, can greatly improve the thread measurement efficiency, and meets the large batch thread detection requirements.

[0079] Optionally, as shown in Figure 8 the thread detection method further comprises the following contents:

[0080] Step S5: controlling the motion shaft module to drive the long shaft part to rotate one revolution, and controlling the machine vision measurement module to shoot at fixed intervals during the rotation, obtaining a plurality of thread projection images, and calculating the pitch diameter value of the thread in each thread projection image, so as to calculate the pitch diameter runout of the thread.

[0081] Optionally, in the step S3, after obtaining the projection image of the thread, the following contents are further included:

[0082] The thread projection image is subjected to occlusion distortion compensation.

[0083] Optionally, as shown in Figure 9As shown, the process of occlusion distortion compensation on the thread projection image is specifically:

[0084] Step S31: Establish a three-dimensional coordinate system with the axis of revolution of the long-axis part as the z-axis;

[0085] Step S32: Intersect the cutting plane parallel to the xoz plane with the single-surface helical surface to obtain a helical curve;

[0086] Step S33: Derive the z-axis coordinate equation of the helical curve to obtain the actual measured thread cross-sectional profile;

[0087] Step S34: Calculate the compensation value based on the actual measured thread cross-sectional profile and the theoretical thread cross-sectional profile, and compensate the occlusion distortion on the thread projection image based on the compensation value to obtain the real image.

[0088] It can be understood that the method embodiment corresponds to the above-mentioned device embodiment, and the specific execution process of each step of the method can refer to the description of the above-mentioned device embodiment, and will not be repeated here.

[0089] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A thread inspection device suitable for use with long shaft parts of an aeroengine, characterised in that, The application relates to a long-axis part radial size measurement device, which comprises the following parts: a radial size measurement module (100) for measuring any radial size of a long-axis part; a machine vision measurement module (200) for shooting a projection image of the long-axis part in a radial direction; a motion axis module (300) for driving the radial size measurement module (100) and the machine vision measurement module (200) to move along the axial direction of the long-axis part, and for axially positioning and clamping the long-axis part; a control module electrically connected with the radial size measurement module (100), the machine vision measurement module (200) and the motion axis module (300), which is used for controlling the motion axis module (300) to drive the radial size measurement module (100) to move to any optical axis position on the long-axis part, and then controlling the motion axis module (300) to drive the machine vision measurement module (200) to align with the reference position to shoot a projection image at the reference position, and then controlling the motion axis module (300) to drive the machine vision measurement module (200) to align with the thread and shoot a projection image of the thread, and finally taking the radial size at the reference position measured by the radial size measurement module (100) as a radial reference size, and combining the projection image at the reference position and the projection image of the thread to calculate the major diameter value, the middle diameter value and the pitch of the thread; the motion axis module (300) is further used for driving the long-axis part to rotate, and the control module is further used for controlling the motion axis module (300) to rotate for one circle, and controlling the machine vision measurement module (200) to shoot at fixed intervals at a preset angle during the rotation to obtain a plurality of thread projection images, and calculating the middle diameter value of the thread in each thread projection image to obtain the middle diameter runout of the thread; the control module is further used for carrying out occlusion distortion compensation on the thread projection image after the thread projection image is obtained; the process of carrying out occlusion distortion compensation on the thread projection image by the control module is as follows: a three-dimensional coordinate system is established with the rotation axis of the long-axis part as the z axis; a cutting plane parallel to the xoz plane is made to intersect the single-surface helical surface to obtain a helical curve; the z-axis coordinate equation of the helical curve is differentiated to obtain an actually measured thread cross-section profile; a compensation value is calculated based on the actually measured thread cross-section profile and a theoretical thread cross-section profile, and the thread projection image is compensated based on the compensation value to obtain a real image.

2. The thread inspection device for long shaft parts of an aeroengine according to claim 1, characterized in that, The radial dimension measuring module (100) is a light curtain shaft diameter measuring sensor, which is oppositely arranged along the radial direction on both sides of the long shaft part, the machine vision measuring module (200) comprises an imaging unit (201) and a light source unit (202), the imaging unit (201) and the light source unit (202) are oppositely arranged along the radial direction on both sides of the long shaft part, the imaging unit (201) is an industrial camera matched with a telecentric lens, the light source unit (202) is a parallel backlight source, the center of the light curtain shaft diameter measuring sensor is aligned with the rotation center of the long shaft part, and the field of view edge of the imaging unit (201) is aligned with the rotation center of the long shaft part.

3. The thread inspection device for long shaft parts of an aeroengine according to claim 1, characterized in that, Further comprising a calibration module (400) for image calibration of the machine vision measuring module (200).

4. The thread inspection device for long shaft parts of an aeroengine according to claim 1, characterized in that, The motion shaft module (300) comprises a measuring shaft movement unit (301), a clamping shaft movement unit (302) and a rotary table unit (303), the measuring shaft movement unit (301) is oppositely arranged along the radial direction on both sides of the long shaft part and can move along the axial direction, the radial dimension measuring module (100) and the machine vision measuring module (200) are fixedly installed on the measuring shaft movement unit (301), the clamping shaft movement unit (302) is fixedly installed on the rotary table unit (303) and can oppositely move along the axial direction, for axially clamping and positioning the long shaft part, and the rotary table unit (303) is used for driving the clamping shaft movement unit (302) and the long shaft part to synchronously rotate.

5. A method for thread inspection of long shaft parts of an aeroengine, using a thread inspection device according to any one of claims 1 to 4, characterized in that, The following is included: The motion shaft module (300) is controlled to drive the radial dimension measuring module (100) to move to any optical axis position on the long shaft part, and the radial dimension at the reference position is measured based on the optical axis position as the reference; The motion shaft module (300) is controlled to drive the machine vision measuring module (200) to align with the reference position, so as to shoot the projection image at the reference position; The motion shaft module (300) is controlled to drive the machine vision measuring module (200) to align with the thread and shoot the projection image of the thread; The radial dimension at the reference position measured by the radial dimension measuring module (100) is taken as the radial reference dimension, and the major diameter value, the middle diameter value and the pitch of the thread are calculated in combination with the projection image at the reference position and the projection image of the thread shot by the machine vision measuring module (200); The motion shaft module (300) is controlled to drive the long shaft part to rotate for one revolution, and the machine vision measuring module (200) is controlled to shoot at fixed intervals at a preset angle during the rotation, so as to obtain multiple projection images of the thread, and the middle diameter value of the thread in each projection image of the thread is calculated, so as to calculate the middle diameter runout of the thread; After obtaining the projection image of the thread, the following is included: The occlusion distortion of the projection image of the thread is compensated.

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