Compressor blade axial displacement flexible endoscopic test system and test method

Abstract

The invention relates to the technical field of compressor component performance testing, in particular to a compressor blade axial displacement flexible endoscopic testing system and method.The compressor blade axial displacement flexible endoscopic testing system comprises an endoscope lens arranged on a compressor casing, the endoscope lens comprises a lens cone and a sleeve, and the sleeve is of a stainless steel metal shell structure; comprising a sleeve front section, a sleeve middle section and a sleeve rear section, a lens cone is connected with the sleeve front section, a light input end of a flexible optical fiber bundle is arranged in the sleeve rear section, and a high-speed camera is arranged on an imaging surface corresponding to a light output end of the flexible optical fiber bundle; the endoscopic imaging lens is matched with the flexible optical fiber bundle and the high-speed camera to collect blade images in a high-temperature and strong-vibration environment in the gas compressor, blade tip position changes are recognized according to the images, the axial displacement of the blades is calculated, and a basis is provided for recognizing potential failures such as pneumatic excitation and detecting structure looseness or cracks. And the method can be used as an important reference for verifying modal characteristics of the blade and developing health monitoring and life evaluation.

Description

Technical Field

[0001] This invention relates to the field of performance testing technology for aero-engine compressor components, and in particular to a flexible endoscopic testing system and method for axial displacement testing of compressor blades. Background Technology

[0002] In modern aero-engines, the compressor, as one of the core components, directly impacts the overall engine efficiency and flight safety through its performance stability and reliability. Compressor blades, operating at high speeds, endure immense centrifugal force, aerodynamic forces, and thermal loads; their operating condition directly determines the compressor's aerodynamic performance and structural integrity. In recent years, as aero-engines have evolved towards higher thrust-to-weight ratios and wider stable operating ranges, the problem of abnormal compressor blade motion has received increasing attention. Axial displacement of blades under high-speed rotation alters tip clearance, affecting compressor aerodynamic performance and, in severe cases, potentially leading to blade-casing rubbing or even surge and other instability phenomena. Accurate measurement of axial displacement not only provides a basis for assessing blade health but also offers data support for key technologies such as active clearance control and vibration suppression, playing a crucial role in improving engine reliability and efficiency.

[0003] Currently, the main technologies for monitoring the axial displacement of compressor blades include tip timing technology and fiber optic sensing technology. Tip timing technology detects changes in the arrival time of the blades using optical or eddy current sensors mounted on the casing, indirectly calculating the vibration displacement. However, tip timing technology struggles to decouple axial and circumferential displacements, and its measurement accuracy is severely affected by rotational speed and installation position. Fiber optic sensing technology measures changes in tip clearance using reflective or transmissive fiber optic probes, enabling direct monitoring of axial displacement. However, its measurement range is limited, and it is extremely sensitive to environmental factors such as temperature and humidity. Under harsh operating conditions inside the compressor, including high temperatures, oil contamination, and strong airflow, signal attenuation is severe, making long-term reliability difficult to guarantee. In contrast, directly capturing images of the blades using imaging equipment and calculating the displacement through coordinate changes during their movement is more intuitive and offers higher accuracy and precision, which is beneficial for the study of blade motion.

[0004] Therefore, this invention provides a flexible endoscopic testing system and method for compressor blade axial displacement. The compressor casing is characterized by high temperatures (>1000K), intense vibrations (>2g), and high blade rotation speeds (20000rpm), requiring the blade axial displacement testing system to be heat-resistant, vibration-resistant, and have high temporal resolution. Simultaneously, to ensure the structural stability of the casing, the observation window on the side wall should be as small as possible; therefore, the imaging lens needs to have a small aperture and a large field of view. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a flexible endoscopic testing system and method for the axial displacement of compressor blades. By setting an endoscopic imaging lens in the compressor casing, and combining it with a flexible fiber optic bundle and a high-speed camera, the system can acquire images of compressor blades under high temperature and strong vibration environments. It can acquire images of blades inside the compressor casing, identify blade contours, measure axial displacement parameters of blades during operation, determine instability, and monitor the aerodynamic performance of the compressor.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a flexible endoscopic testing system for axial displacement of compressor blades, characterized in that it includes an endoscope lens installed on the compressor casing for acquiring images of the blades on the compressor impeller. The endoscope lens includes a sleeve and a lens barrel. One end of the lens barrel is installed on the sleeve, and the other end of the lens barrel extends into the compressor casing. A flexible optical fiber bundle is installed in the rear cavity of the sleeve. The flexible optical fiber bundle extends into the rear cavity of the sleeve as a light input end. The light input end is set corresponding to the lens barrel of the endoscope lens. A high-speed camera is installed correspondingly on the imaging surface of the light output end of the flexible optical fiber bundle. The microscope tube is a cylindrical tube structure composed of an upper semi-cylindrical microscope tube shell and a lower semi-cylindrical microscope tube shell. The interior of the upper and lower semi-cylindrical microscope tube shells are provided with objective lens mounting slots, image transmission lens mounting slots, aperture stop mounting slots, and eyepiece mounting slots in sequence along the axial direction. The end of the microscope tube near the eyepiece mounting slot is provided with an external thread that connects to the sleeve. The objective lens, image transmission lens, aperture stop, and eyepiece are respectively installed in the objective lens mounting slot, image transmission lens, aperture stop, and eyepiece mounting slot.

[0007] The sleeve is a stainless steel cylindrical shell structure with a three-section through-hole structure inside, including a front section, a middle section, and a rear section. The sleeve is provided with a flange and corresponding screw holes for connecting with the compressor casing. The rear section of the sleeve is provided with an optical fiber bundle fixing hole for fixing the inserted flexible optical fiber bundle. The front section of the sleeve is connected to the end of the lens barrel by an external thread to achieve a fixed connection between the sleeve and the lens barrel.

[0008] The interior of the flexible fiber bundle is an optical fiber array formed by orderly arranged optical fiber filaments of the same diameter and length. The fiber bundle fixing holes are evenly arranged in four circumferentially along the rear section of the sleeve. The flexible fiber bundle extending into the sleeve is fixed by bolts in the four fiber bundle fixing holes to form a complete imaging end.

[0009] The objective lens is a plano-concave lens, the image transmission lens is a plano-convex lens for focusing light, and the eyepiece is a plano-convex lens; the eyepiece and the image transmission lens form a symmetrical structure, which corrects aberrations while further focusing light so that the light is projected onto the imaging surface.

[0010] The width of the front section of the sleeve is 5mm~8mm; the diameter of the through hole in the middle section of the sleeve is 30mm~40mm, and the width of the through hole is 20mm~25mm; the diameter of the through hole in the rear section of the sleeve is 43mm~48mm, and the width of the through hole is 60mm~75mm.

[0011] The origin of the described endoscope is the intersection of the optical axis and the surface of the endoscope barrel. O Using the direction of light transmission into the endoscope as... x In the positive direction of the axis, we have: The objective lens mounting slot is close to the origin. O The groove on one side is connected to the front end face of the lens barrel by a through hole structure. The diameter of the through hole is 9mm~10mm and the width of the through hole is 0.3mm~1mm. The diameter of the objective lens mounting groove is 10.4mm~13mm and the width is 2.1mm~4.6mm. The diameter of the image transmission lens mounting groove is 10.4mm~13mm, and the groove width is 1.6mm~2.1mm; the image transmission lens mounting groove and the objective lens mounting groove are connected by a cylindrical through hole with a diameter of 9mm~10mm and a width of 2.4mm~2.6mm. The aperture stop mounting groove has a diameter of 10.4mm to 13mm and a groove width of 0.2mm to 0.5mm; the aperture stop mounting groove and the image transmission lens mounting groove are connected by a cylindrical through hole with a diameter of 9mm to 10mm and a width of 2.8mm to 3.1mm. The eyepiece mounting slot has a diameter of 10.4mm to 13mm and a width of 1.6mm to 2.1mm; the eyepiece mounting slot and the aperture stop mounting slot are connected by a cylindrical through hole with a diameter of 9mm to 10mm and a width of 1.3mm to 1.6mm. The eyepiece mounting groove and the rear end face of the lens tube are connected by a cylindrical through-hole structure with a diameter of 9mm~10mm and a width of 5mm~8mm.

[0012] The present invention also provides a testing method implemented by the flexible endoscopic testing system for axial displacement of compressor blades, comprising the following steps: Step 1: Assemble the endoscope lens of the flexible endoscopic testing system for compressor blade axial displacement, fix the endoscope lens to the side wall of the compressor casing to acquire images of the blades inside the casing, and connect the endoscope lens to the high-speed camera via a flexible fiber optic bundle. Step two: When the compressor starts working, activate the high-speed camera and use the endoscopic lens to acquire continuous images. Leaf images under a time series , ... ; Step 3, image parameterization, using a single leaf image For example, the image's pixel grayscale value matrix is ​​read to achieve image parameterization; the Sobel edge operator is used to convolve with the image's grayscale value matrix to calculate the image's edge position. x , y The gradient in the direction is calculated, and the gradient magnitude map of the synthesized image is obtained. Step 4: Perform histogram statistics on the gradient magnitude map and use Otsu's method to calculate the optimal threshold for gray value segmentation; use the optimal threshold to binarize the gradient magnitude map to obtain the edge binary map depicting the leaf outline. Step 5: Identify the pixel coordinates of the blade outline and extract the two coordinate positions where the horizontal coordinate is at its minimum and maximum. , , serving as the coordinates for the positions of the left and right leaf tips; Step 6: For all leaf images ... Perform the above operations to extract the same leaf tip position. x The coordinate sequence is obtained by subtracting adjacent values ​​to get the displacement of the blade tip position in pixel coordinates; the correspondence between pixels and spatial dimensions is obtained through calibration, and multiplied with the displacement to get the axial displacement of the blade tip position in space; the average value of the sequences of two blade tip positions is calculated to get the axial displacement change sequence of the blade tip, and the blade instability phenomenon is identified.

[0013] Furthermore, the specific process of step three includes: A single image captured by a high-speed camera For example, extract the grayscale matrix of image pixels. Using Sobel convolution kernels in the horizontal and vertical directions respectively Convolution is performed to obtain the gradient map: , In the formula, Indicates the horizontal direction (i.e.) x gradient plot (direction), Indicates the vertical direction (i.e.) y gradient plot (direction), This represents a horizontal Sobel convolution kernel used for detecting vertical edges. This represents a Sobel convolution kernel in the vertical direction, used for detecting horizontal edges, specifically: , Next, the results from the two directions are combined to obtain the gradient magnitude map: .

[0014] Furthermore, the specific process of step four includes: First, statistical gradient magnitude plot The grayscale distribution is used to obtain the histogram. ,in It is the number of gray levels (usually 256).

[0015] Next, the histogram is normalized to obtain the probability distribution for each gray level: , In the formula, This represents the probability of each gray level. N This represents the total number of pixels.

[0016] Set a candidate threshold T Pixel grayscale values ​​are divided into two categories: foreground (edge) category with grayscale values ​​≥ T The grayscale of the background class (non-edge) < T Calculate the between-class variance of the two classes: , In the formula, Represents the variance between classes. Represents the probability of the foreground and background classes. The average gray level of the two classes is represented by the following calculation method: , Calculate all candidate thresholds T Inter-class variance , find The largest threshold is used as the Otsu threshold. The gradient magnitude map is binarized using this threshold, setting the gray values ​​of pixels greater than the threshold to 0 and the gray values ​​of pixels less than the threshold to 1, resulting in a binary edge image. Black pixels (gray value of 0) represent leaf edges, and white pixels (gray value of 1) represent the background.

[0017] Furthermore, the specific process of step six includes: Repeat steps three to five above for all leaf images to obtain the left and right leaf tip coordinates at all shooting times, forming the left leaf tip coordinate sequence and the right leaf tip coordinate sequence; Extract all x-coordinate values ​​from the left leaf tip coordinate sequence x The coordinate displacement sequence of the left leaf tip position on the pixel is obtained by successively subtracting adjacent values. X 1. Positive numbers represent forward displacement, and negative numbers represent backward displacement. The same operation is performed on the right leaf tip coordinate sequence to obtain the left leaf tip coordinate displacement sequence. X 2; The correspondence between pixels and spatial dimensions is obtained through calibration. The specific calibration method is as follows: First, measure the distance between the endoscope and the blade. After removing the endoscope from the housing, install it on the flat mounting plate, keeping the rest of the parts unchanged. Secondly, place a checkerboard calibration board at the same distance and use a camera to capture images of the calibration board; Finally, the physical size of a single calibration grid in the standard calibration board is 5mm, and the width of ten calibration grids is 50mm. The starting and ending points of ten consecutive calibration grids are marked in the calibration board image. The difference between the horizontal coordinates of the two points is calculated, and the spatial size δmm / pixel corresponding to a single pixel is obtained by dividing 50mm by the difference between the coordinates. will sequence X 1. X Multiplying 2 by δmm / pixel yields the left blade tip axial displacement sequence. X S1 Right leaf tip axial displacement sequence X S2 Finally, for the sequence X S1 , X S2 The time series of blade tip axial displacement is obtained by averaging the corresponding elements in the data. X In the sequence, positive numbers represent forward displacement, and negative numbers represent backward displacement; The time series of blade tip axial displacement can not only reflect the instantaneous displacement of the blade during operation, but also extract the main frequency, harmonics and resonance characteristics through spectrum analysis to reveal the dynamic response law of the blade. At the same time, the changes in displacement amplitude, velocity and acceleration can characterize the vibration intensity and load characteristics, thus providing a basis for identifying aerodynamic excitation and detecting potential failures such as structural loosening or cracks.

[0018] The beneficial effects of this invention are as follows: The flexible endoscopic testing system and method for axial displacement of compressor blades, by setting an endoscopic imaging lens in the compressor casing, and combining it with a flexible fiber optic bundle and a high-speed camera, enables the acquisition of compressor blade images under high temperature and strong vibration environments. Based on the image, the system identifies changes in the blade tip position and calculates the axial displacement of the blade. This provides a basis for identifying aerodynamic excitation, detecting potential failures such as structural loosening or cracks, and can also serve as an important reference for verifying blade modal characteristics, conducting health monitoring, and life assessment. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is the present invention. Figure 1 A schematic diagram of the structure of a mid-endoscopic imaging lens; Figure 3 This is the present invention. Figure 1 A schematic diagram of the lens barrel structure of a mid-endoscopic imaging lens; Figure 4 This is the present invention. Figure 1 A schematic diagram of the sleeve structure of a central endoscopic imaging lens; Figure 5 This is a schematic diagram illustrating the binarization of the leaf image and the identification of the leaf tip position during the implementation of this invention.

[0020] In the diagram, 1. Lens tube; 1-1. Upper semi-cylindrical lens tube housing; 1-2. Lower semi-cylindrical lens tube housing; 1-3. Objective lens mounting slot; 1-4. Image transmission lens mounting slot; 1-5. Aperture stop mounting slot; 1-6. Eyepiece mounting slot; 1-7. External thread; 2. Sleeve; 2-1. Front section of sleeve; 2-2. Middle section of sleeve; 2-3. Rear section of sleeve; 2-4. Fiber optic bundle fixing hole; 2-5. Flange; 2-6. Screw hole; 3. Objective lens; 4. Image transmission lens; 5. Aperture stop; 6. Eyepiece; 7. Flexible fiber optic bundle; 8. High-speed camera; 9. Compressor casing; 10. Impeller; 10-1. Blade. Detailed Implementation

[0021] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0022] To achieve the above objectives, the present invention provides the following specific embodiments: Example 1: As Figure 1 As shown, a flexible endoscopic testing system for axial displacement of compressor blades includes an endoscope lens installed in the compressor casing 9. The endoscope lens includes a sleeve 2 and a lens barrel 1. The sleeve 2 is a stainless steel cylindrical shell structure, divided into a front section 2-1, a middle section 2-2, and a rear section 2-3. The lens barrel 1 is installed inside the front section 2-1. The light input end of a flexible fiber optic bundle 7 is installed inside the rear section 2-3. The other end of the flexible fiber optic bundle 7 is the light output end. A high-speed camera 8 is installed on the imaging surface corresponding to the output end of the flexible fiber optic bundle 7. like Figure 2As shown, the microscope tube 1 is a cylindrical tube structure composed of two identical upper semi-cylindrical lens shells 1-1 and 1-2. The interiors of the upper and lower semi-cylindrical lens shells 1-1 and 1-2 are sequentially arranged along the axial direction with objective lens mounting slot 1-3, image transmission lens mounting slot 1-4, aperture stop mounting slot 1-5, and eyepiece mounting slot 1-6. An external thread structure 1-7 is provided at the end of the microscope tube 1 near the eyepiece mounting slot 1-6. The objective lens 3, image transmission lens 4, aperture stop 5, and eyepiece 6 are respectively installed in the objective lens mounting slot 1-3, image transmission lens mounting slot 1-4, aperture stop mounting slot 1-5, and eyepiece mounting slot 1-6. The objective lens 3 is a plano-concave lens to meet the requirement of a large field of view; the image transmission lens 4 is a plano-convex lens for focusing light; and the eyepiece 6 is a plano-convex lens, forming a symmetrical structure with the image transmission lens, correcting aberrations and further focusing light so that it is projected onto the imaging plane.

[0023] In an endoscope, the point where the optical axis intersects with the surface of the endoscope barrel 1 is taken as the origin. O Using the direction of light transmission into the endoscope as... x Positive axis direction Objective lens mounting slots 1-3 are close to the origin. O One side of the groove surface and the front end face of the lens barrel 1 are connected by a through hole structure. The diameter of the through hole is 9mm~10mm and the width of the through hole is 0.3mm~1mm. The diameter of the objective lens mounting groove 1-3 is 10.4mm~13mm and the width is 2.1mm~4.6mm. The image transmission lens mounting slot 1-4 has a diameter of 10.4mm~13mm and a slot width of 1.6mm~2.1mm; the image transmission lens mounting slot 1-4 and the objective lens mounting slot 1-3 are connected by a cylindrical through hole with a diameter of 9mm~10mm and a through hole width of 2.4mm~2.6mm. The aperture stop mounting slot 1-5 has a diameter of 10.4mm~13mm and a slot width of 0.2mm~0.5mm; the aperture stop mounting slot 1-5 and the image transmission lens mounting slot 1-4 are connected by a cylindrical through hole with a diameter of 9mm~10mm and a width of 2.8mm~3.1mm. The eyepiece mounting slot 1-6 has a diameter of 10.4mm~13mm and a slot width of 1.6mm~2.1mm; the eyepiece mounting slot 1-6 and the aperture stop mounting slot 1-5 are connected by a cylindrical through hole with a diameter of 9mm~10mm and a width of 1.3mm~1.6mm; the eyepiece mounting slot 1-6 and the rear end face of the lens tube 1 are connected by a cylindrical through hole with a diameter of 9mm~10mm and a width of 5mm~8mm. The inner side of the front section 2-1 of the sleeve has a threaded structure with a width of 5mm~8mm; the through hole diameter of the middle section 2-2 of the sleeve is 30mm~40mm and the through hole width is 20mm~25mm; the through hole diameter of the rear section 2-3 of the sleeve is 43mm~48mm and the through hole width is 60mm~75mm. A flange 2-5 is provided on the outer wall of the front section 2-1 of the sleeve, and a fiber optic bundle fixing hole 2-4 is also provided on the rear section 2-3 of the sleeve. After the endoscope tube 1 is connected and fixed to the front end 2-1 of the sleeve through the external thread structure 1-7, one end of the endoscope tube 1 extends into the compressor casing 9 and is fixedly connected to the side wall of the compressor casing 9 through the screw hole 2-6 on the flange 2-5. The light input end of the flexible fiber bundle 7 corresponds to the endoscope tube 1. The interior of the flexible fiber bundle 7 is an optical fiber array formed by orderly arrangement of optical fiber filaments of the same diameter and length. After the light input end extends into the interior of the sleeve 2, bolts are installed in the four optical fiber bundle fixing holes 2-4 in the rear section 2-3 of the sleeve, and simultaneously tightened in the axial direction to form a complete imaging end.

[0024] Example 2: Same as Example 1, except that, as Figure 3 As shown, one embodiment of the microscope tube 1 of the present invention is as follows: The microscope tube 1 is composed of identical upper semi-cylindrical tube shells 1-1 and 1-2, joined together. The outer diameter of the semi-cylindrical tube is 12.6 mm, the total length is 21.8 mm, and the interior has groove-shaped structures with different diameters. Specifically, the objective lens mounting groove 1-3 has a diameter of 10.6 mm and a width of 4.6 mm; the image transmission lens mounting groove 1-4 has a diameter of 10.6 mm and a width of 1.7 mm; the aperture stop mounting groove 1-5 has a diameter of 10.6 mm and a width of 0.2 mm; and the eyepiece mounting groove 1-6 has a diameter of 10.6 mm and a width of 1.7 mm. The objective lens mounting groove 1-3 is located near the origin. OOne side of the groove surface is connected to the front end face of the lens barrel 1 by a through hole structure with a diameter of 9.6 mm and a width of 0.5 mm; the image transmission lens mounting groove 1-4 is connected to the objective lens mounting groove 1-3 by a cylindrical through hole with a diameter of 9.6 mm and a width of 2.6 mm; the aperture stop mounting groove 1-5 is connected to the image transmission lens mounting groove 1-4 by a cylindrical through hole with a diameter of 9.6 mm and a width of 3 mm; the eyepiece mounting groove 1-6 is connected to the aperture stop mounting groove 1-5 by a cylindrical through hole with a diameter of 9.6 mm and a width of 1.5 mm; the eyepiece mounting groove 1-6 is connected to the rear end face of the lens barrel 1 by a cylindrical through hole structure with a diameter of 9.6 mm and a width of 6 mm.

[0025] Example 3 is the same as Example 1, except that, as Figure 3 As shown, one embodiment of the lens group of the present invention is as follows: Objective lens 3 is a plano-concave lens to meet the requirements of a large field of view, with a diameter of 10mm, a concave surface curvature radius of 5.73mm, and a center thickness of 1.5mm; Image transmission lens 4 is a plano-convex lens for focusing light, with a diameter of 10mm, a convex surface curvature radius of 7.34mm, a center thickness of 3.3mm, and a distance of 3.5mm between the center of the convex surface and the center of the concave surface of objective lens 3; Aperture stop 5 is a hollow circular structure with an outer diameter of 10mm and a central thickness of 1.5mm. The hollow circle of the center has a diameter of 1.5 mm and a thickness of 0.2 mm. The distance between the plane of the aperture stop 5 near the origin and the plane of the image transmission lens 4 is 3 mm. The eyepiece 6 is a plano-convex lens, which forms a symmetrical structure with the image transmission lens. While correcting aberrations, it further focuses the light so that it can be projected onto the imaging plane. It has a diameter of 10 mm, a convex surface curvature radius of 7.34 mm, and a center thickness of 3.3 mm. The distance between the plane of the eyepiece 6 and the plane of the aperture stop 5 away from the origin is 1.5 mm.

[0026] Example 4 is the same as Example 1, except that, as Figure 4 As shown, one embodiment of the sleeve 2 of the present invention is as follows: the inner side of the front section 2-1 of the sleeve has a threaded structure with a width of 6mm; the through hole diameter of the middle section 2-2 of the sleeve is 36mm and the through hole width is 20mm; the through hole diameter of the rear section 2-3 of the sleeve is 44mm and the through hole width is 75mm; a flange 2-5 is provided on the outer wall surface of the front section 2-1 of the sleeve, and the flange 2-5 has a thickness of 20mm; the rear section 2-3 of the sleeve is also provided with an optical fiber bundle fixing hole 2-4; Example 5: The present invention also provides a testing method implemented by the flexible endoscopic testing system for compressor blade axial displacement as described in Examples 1-4, comprising the following steps: Step 1: Assemble the endoscope lens of the flexible endoscopic testing system for compressor blade axial displacement, fix the endoscope lens to the side wall of the compressor casing to acquire images of the blades inside the casing, and connect the endoscope lens to the high-speed camera via a flexible fiber optic bundle. Specifically, such as Figure 3 As shown, place the lower semi-cylindrical lens shell 1-2 of the lens tube 1 horizontally with the groove structure facing upwards. Place the objective lens 3 in the objective lens mounting slot 1-3, the image transmission lens 4 in the image transmission lens mounting slot 1-4, the aperture stop 5 in the aperture stop mounting slot 1-5, and the eyepiece 6 in the eyepiece mounting slot 1-6. Assemble the upper semi-cylindrical lens shell 1-1 with the groove structure facing downwards. Then, assemble the assembled lens tube 1 along... x Screw the axially threaded structure 1-7 into the front section 2-1 of the sleeve to complete the assembly of the endoscope. like Figure 1 As shown, one end of the endoscope lens barrel 1 is inserted into the opening of the compressor casing 9, and the lens is fixed by screws passing through the screw holes 2-6 of the flange 2-5; then the light input end of the flexible fiber bundle 7 is inserted into the rear section 2-3 of the sleeve, and the insertion depth is adjusted so that the endoscope lens can clearly image onto the light input end. The light input end is fixed by bolts passing through the fiber bundle fixing holes 2-4 on the side wall. The endoscope lens and the light input end of the flexible fiber bundle 7 are coaxial; the lens of the high-speed camera 8 is coaxial with the light output end of the flexible fiber bundle 7 and receives the image from the light output end.

[0027] Step two: When the compressor starts working, activate the high-speed camera and use the endoscopic lens to acquire continuous images. Leaf images under a time series , ... ; Specifically, after the compressor starts working, the impeller 10 inside the compressor casing 9 begins to rotate. Light from the blades 10-1 enters the objective lens 3, passes through the image transmission lens 4, aperture stop 5, and eyepiece 6, and is focused and imaged at the light input end of the flexible fiber bundle 7. Simultaneously, the light is transmitted to the light output end, where the image formed is received by the high-speed camera 8, thus obtaining an image of the blades. Continuous image acquisition is performed at a fixed frame rate over a continuous period of time. Leaf images under a time series , ... .

[0028] Step 3, image parameterization, using a single leaf image For example, the pixel grayscale value matrix of the image is read to achieve image parameterization; the Sobel edge operator is used to convolve with the image grayscale value matrix to calculate the gradient of the image in the x and y directions, and the gradient magnitude map of the image is synthesized. Specifically, a single image captured by a high-speed camera For example, assuming the number of pixels in an image is a×b, the gray value of each pixel is extracted to obtain an a×b gray value matrix that reflects the brightness, thus achieving image parameterization.

[0029] Using Sobel convolution kernels in the horizontal and vertical directions respectively and Convolution is performed to obtain the gradient map: , In the formula, Indicates the horizontal direction (i.e.) x gradient plot (direction), Indicates the vertical direction (i.e.) y gradient plot (direction), This represents a horizontal Sobel convolution kernel used for detecting vertical edges. This represents a Sobel convolution kernel in the vertical direction, used for detecting horizontal edges, specifically: , Next, the results from the two directions are combined to obtain the gradient magnitude map: , Step 4: Perform histogram statistics on the gradient magnitude map and use Otsu's method to calculate the optimal threshold for gray value segmentation; use the optimal threshold to binarize the gradient magnitude map to obtain the edge binary map depicting the leaf outline. Specifically, statistical gradient magnitude plot The grayscale distribution is used to obtain the histogram. ,in It is the number of gray levels (usually 256). Next, the histogram is normalized to obtain the probability distribution for each gray level:

[0030] In the formula, This represents the probability of each gray level. N Total number of pixels Set a candidate threshold T Pixel grayscale values ​​are divided into two categories: foreground (edge) category with grayscale values ​​≥ T The grayscale of the background class (non-edge) < T Calculate the between-class variance of the two classes: , In the formula, Represents the variance between classes. Represents the probability of the foreground and background classes. The average gray level of the two classes is represented by the following calculation method: , Calculate all candidate thresholds T Inter-class variance , find The largest threshold is used as the Otsu threshold. .

[0031] like Figure 5 As shown, using the Otsu threshold Binarize the gradient magnitude map by setting the gray values ​​of pixels with values ​​greater than the threshold to 0 and the gray values ​​of pixels with values ​​less than the threshold to 1, to obtain a binary edge image, where black pixels (gray value of 0) represent leaf edges and white pixels (gray value of 1) represent the background.

[0032] Step 5: Identify the pixel coordinates of the blade outline and extract the two coordinate positions where the horizontal coordinate is at its minimum and maximum. , , serving as the coordinates for the positions of the left and right leaf tips; Specifically, extract the set of pixel coordinate distributions at the edge of the leaf. Compare all coordinate positions x Value, selection x The coordinates of the position with the smallest value are taken as the coordinates of the left leaf tip. x The coordinates of the position with the largest value are used as the coordinates of the right leaf tip.

[0033] Step 6: For all leaf images ... Perform the above operations to extract the same leaf tip position. x The coordinate sequence is obtained by subtracting adjacent values ​​to get the displacement of the blade tip position in pixel coordinates; the correspondence between pixels and spatial dimensions is obtained through calibration, and multiplied with the displacement to get the axial displacement of the blade tip position in space; the average value of the sequences of two blade tip positions is calculated to get the axial displacement change sequence of the blade tip, and the blade instability phenomenon is identified.

[0034] Repeat steps three through five for all leaf images to obtain the left and right leaf tip coordinates at all shooting times, forming left and right leaf tip coordinate sequences. Extract all x-coordinate values ​​from the left leaf tip coordinate sequence. x The coordinate displacement sequence of the left leaf tip position on the pixel is obtained by successively subtracting adjacent values. X 1. Positive numbers represent forward displacement, and negative numbers represent backward displacement. The same operation is performed on the right leaf tip coordinate sequence to obtain the left leaf tip coordinate displacement sequence. X 2.

[0035] Measure the distance between the endoscope and the blade. After removing the endoscope from the housing, install it on the flat mounting plate, keeping the rest unchanged. Next, place a checkerboard calibration plate at the same distance and use a camera to capture images of the calibration plate. Finally, the physical size of a single calibration grid in the standard calibration plate is 5mm, and the width of ten calibration grids is 50mm. Mark the start and end points of the ten consecutive calibration grids in the calibration plate image. Calculate the difference between the x-coordinates of the two points and use 50mm as the quotient to obtain the spatial size δmm / pixel corresponding to a single pixel.

[0036] will sequence X 1. X Multiplying 2 by δmm / pixel yields the left blade tip axial displacement sequence. X S1 Right leaf tip axial displacement sequence X S2 .

[0037] For sequence X S1 , X S2 The time series of blade tip axial displacement is obtained by averaging the corresponding elements in the data. X In the sequence, positive numbers represent forward displacement and negative numbers represent backward displacement.

[0038] The time series of blade tip axial displacement can not only reflect the instantaneous displacement of the blade during operation, but also extract the main frequency, harmonics and resonance characteristics through spectrum analysis to reveal the dynamic response law of the blade. At the same time, the changes in displacement amplitude, velocity and acceleration can characterize the vibration intensity and load characteristics, thus providing a basis for identifying aerodynamic excitation and detecting potential failures such as structural loosening or cracks.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flexible endoscopic testing system for axial displacement of compressor blades, characterized in that, This includes an endoscope mounted on the compressor casing for acquiring images of the blades on the compressor impeller; The endoscope includes a sleeve and a tube. One end of the tube is mounted on the sleeve, and the other end of the tube extends into the compressor casing. A flexible fiber bundle is installed in the rear cavity of the sleeve. The flexible fiber bundle extends into the rear cavity of the sleeve as the light input end. The light input end is set in the tube of the endoscope. A high-speed camera is set in the imaging surface of the light output end of the flexible fiber bundle. The lens barrel is a cylindrical tube structure composed of an upper semi-cylindrical lens tube shell and a lower semi-cylindrical lens tube shell. The upper and lower semi-cylindrical lens tube shells are provided with the following in sequence along the axial direction: objective lens mounting slot, image transmission lens mounting slot, aperture stop mounting slot and eyepiece mounting slot. The end of the lens barrel near the eyepiece mounting slot is provided with an external thread that connects to the sleeve. The objective lens, image transmission lens, aperture stop, and eyepiece are respectively installed in the objective lens mounting slot, image transmission lens mounting slot, aperture stop, and eyepiece mounting slot.

2. The flexible endoscopic testing system for axial displacement of compressor blades as described in claim 1, characterized in that, The sleeve is a stainless steel cylindrical shell structure with a three-section through-hole structure inside, including a front section, a middle section, and a rear section. The sleeve is provided with a flange and corresponding screw holes for connecting with the compressor casing. The rear section of the sleeve is provided with an optical fiber bundle fixing hole for fixing the inserted flexible optical fiber bundle. The front section of the sleeve is connected to the end of the lens barrel by an external thread to achieve a fixed connection between the sleeve and the lens barrel.

3. A flexible endoscopic testing system for axial displacement of compressor blades as described in claim 1 or 2, characterized in that, The interior of the flexible fiber bundle is an optical fiber array formed by orderly arranged optical fiber filaments of the same diameter and length. The fiber bundle fixing holes are evenly arranged in four circumferentially along the rear section of the sleeve. The flexible fiber bundle extending into the sleeve is fixed by bolts in the four fiber bundle fixing holes to form a complete imaging end.

4. The flexible endoscopic testing system for axial displacement of compressor blades as described in claim 1, characterized in that, The objective lens is a plano-concave lens, the image transmission lens is a plano-convex lens for focusing light, and the eyepiece is a plano-convex lens; the eyepiece and the image transmission lens form a symmetrical structure, which corrects aberrations while further focusing light so that the light is projected onto the imaging surface.

5. The flexible endoscopic testing system for axial displacement of compressor blades as described in claim 2, characterized in that, The width of the front section of the sleeve is 5mm~8mm; the diameter of the through hole in the middle section of the sleeve is 30mm~40mm, and the width of the through hole is 20mm~25mm; the diameter of the through hole in the rear section of the sleeve is 43mm~48mm, and the width of the through hole is 60mm~75mm.

6. The flexible endoscopic testing system for axial displacement of compressor blades as described in claim 1, characterized in that, The origin of the described endoscope is the intersection of the optical axis and the surface of the endoscope barrel. O Using the direction of light transmission into the endoscope as... x In the positive direction of the axis, we have: The objective lens mounting slot is close to the origin. O The groove on one side is connected to the front end face of the lens barrel by a through hole structure. The diameter of the through hole is 9mm~10mm and the width of the through hole is 0.3mm~1mm. The diameter of the objective lens mounting groove is 10.4mm~13mm and the width is 2.1mm~4.6mm. The image transmission lens mounting groove has a diameter of 10.4mm to 13mm and a groove width of 1.6mm to 2.1mm; the image transmission lens mounting groove and the objective lens mounting groove are connected by a cylindrical through hole with a diameter of 9mm to 10mm and a through hole width of 2.4mm to 2.6mm. The aperture stop mounting groove has a diameter of 10.4mm to 13mm and a groove width of 0.2mm to 0.5mm; the aperture stop mounting groove and the image transmission lens mounting groove are connected by a cylindrical through hole with a diameter of 9mm to 10mm and a width of 2.8mm to 3.1mm. The eyepiece mounting slot has a diameter of 10.4mm to 13mm and a width of 1.6mm to 2.1mm; the eyepiece mounting slot and the aperture stop mounting slot are connected by a cylindrical through hole with a diameter of 9mm to 10mm and a width of 1.3mm to 1.6mm. The eyepiece mounting slot and the rear end face of the lens tube are connected by a cylindrical through-hole structure with a diameter of 9mm~10mm and a width of 5mm~8mm.

7. A testing method implemented by the flexible endoscopic testing system for axial displacement of compressor blades as described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Assemble the endoscope lens of the flexible endoscopic testing system for compressor blade axial displacement, fix the endoscope lens to the side wall of the compressor casing to acquire images of the blades inside the casing, and connect the endoscope lens to the high-speed camera via a flexible fiber optic bundle. Step two: When the compressor starts working, activate the high-speed camera and use the endoscopic lens to acquire continuous images. Leaf images under a time series , ... ; Step 3, image parameterization, using a single leaf image For example, the image's pixel grayscale value matrix is ​​read to achieve image parameterization; the Sobel edge operator is used to convolve with the image's grayscale value matrix to calculate the image's edge position. x , y The gradient in the direction is calculated, and the gradient magnitude map of the synthesized image is obtained. Step 4: Perform histogram statistics on the gradient magnitude map and use Otsu's method to calculate the optimal threshold for gray value segmentation; use the optimal threshold to binarize the gradient magnitude map to obtain the edge binary map depicting the leaf outline. Step 5: Identify the pixel coordinates of the blade outline and extract the two coordinate positions where the horizontal coordinate is at its minimum and maximum. , , serving as the coordinates for the positions of the left and right leaf tips; Step 6: For all leaf images ... Perform the above operations to extract the same leaf tip position. x The coordinate sequence is obtained by subtracting adjacent values ​​to get the displacement of the blade tip position in pixel coordinates; the correspondence between pixels and spatial dimensions is obtained through calibration, and multiplied with the displacement to get the axial displacement of the blade tip position in space; the average value of the sequences of two blade tip positions is calculated to get the axial displacement change sequence of the blade tip, and the blade instability phenomenon is identified.

8. The flexible endoscopic testing method for axial displacement of compressor blades as described in claim 7, characterized in that, The specific process of step three includes: A single image captured by a high-speed camera For example, extract the grayscale matrix of image pixels. Using Sobel convolution kernels in the horizontal and vertical directions respectively Convolution is performed to obtain the gradient map: ， In the formula, Indicates the horizontal direction (i.e.) x gradient plot (direction), Indicates the vertical direction (i.e.) y gradient plot (direction), This represents a horizontal Sobel convolution kernel used for detecting vertical edges. This represents a Sobel convolution kernel in the vertical direction, used for detecting horizontal edges, specifically: ， Next, the results from the two directions are combined to obtain the gradient magnitude map: 。 9. The flexible endoscopic testing method for axial displacement of compressor blades as described in claim 7, characterized in that, The specific process of step four includes: First, statistical gradient magnitude plot The grayscale distribution is used to obtain the histogram. ,in It represents the number of gray levels, typically 256. Next, the histogram is normalized to obtain the probability distribution for each gray level: ， In the formula, This represents the probability of each gray level. N Total number of pixels; Set a candidate threshold T Pixel grayscale values ​​are divided into two categories: foreground category with grayscale values ​​≥ T The grayscale of the background class < T Calculate the between-class variance of the two classes: ， In the formula, Represents the variance between classes. Represents the probability of the foreground and background classes. The average gray level of the two classes is represented by the following calculation method: ， Calculate all candidate thresholds T Inter-class variance , find The largest threshold is used as the Otsu threshold. The gradient magnitude map is binarized using this threshold, setting the gray values ​​of pixels greater than the threshold to 0 and the gray values ​​of pixels less than the threshold to 1, resulting in a binary edge image. Black pixels (gray values ​​of 0) represent leaf edges, while white pixels (gray values ​​of 1) represent the background.

10. The flexible endoscopic testing method for axial displacement of compressor blades as described in claim 7, characterized in that, The specific process of step six includes: Repeat steps three to five above for all leaf images to obtain the left and right leaf tip coordinates at all shooting times, forming the left leaf tip coordinate sequence and the right leaf tip coordinate sequence; Extract all x-coordinate values ​​from the left leaf tip coordinate sequence x The coordinate displacement sequence of the left leaf tip position on the pixel is obtained by successively subtracting adjacent values. X 1. Positive numbers represent forward displacement, and negative numbers represent backward displacement. The same operation is performed on the right leaf tip coordinate sequence to obtain the left leaf tip coordinate displacement sequence. X 2; The correspondence between pixels and spatial dimensions is obtained through calibration. The specific calibration method is as follows: First, measure the distance between the endoscope and the blade. After removing the endoscope from the housing, install it on the flat mounting plate, keeping the rest of the parts unchanged. Secondly, place a checkerboard calibration board at the same distance and use a camera to capture images of the calibration board; Finally, the physical size of a single calibration grid in the standard calibration board is 5mm, and the width of ten calibration grids is 50mm. The starting and ending points of ten consecutive calibration grids are marked in the calibration board image. The difference between the horizontal coordinates of the two points is calculated, and the spatial size δmm / pixel corresponding to a single pixel is obtained by dividing 50mm by the difference between the coordinates. will sequence X 1. X Multiplying 2 by δmm / pixel yields the left blade tip axial displacement sequence. X S1 Right leaf tip axial displacement sequence X S2 Finally, for the sequence X S1 , X S2 The time series of blade tip axial displacement is obtained by averaging the corresponding elements in the data. X In the sequence, positive numbers represent forward displacement, and negative numbers represent backward displacement; The time series of blade tip axial displacement can not only reflect the instantaneous displacement of the blade during operation, but also extract the main frequency, harmonics and resonance characteristics through spectrum analysis to reveal the dynamic response law of the blade. At the same time, the changes in displacement amplitude, velocity and acceleration can characterize the vibration intensity and load characteristics, thus providing a basis for identifying aerodynamic excitation and detecting potential failures such as structural loosening or cracks.

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