Modular coaxial schlieren imaging system

Abstract

The utility model relates to the field of optical imaging, in particular to a modularized coaxial schlieren imaging system. A modularized coaxial schlieren imaging system comprises a light source module, a spectroscope module, a knife edge module, a camera module, a test area module and a reflector module. According to the system, high flexibility and expandability are realized through modular design, and free adjustment and configuration can be carried out according to different experiment requirements. Due to the design of the coaxial optical path, the optical path error is greatly reduced, the imaging precision is improved, and a high-resolution schlieren image is ensured. Meanwhile, the system is compact and portable in overall design, and can be conveniently used in a scene with limited space or needing frequent movement. Besides, through the application of a high-precision optical element and the knife edge module with adjustable sensitivity, tiny fluid density change can be accurately captured, the device is suitable for scientific research, engineering application and high-precision industrial detection, and the experiment and detection efficiency is greatly improved.

Description

Technical Field

[0001] The utility model relates to the field of optical imaging, in particular to a modular coaxial schlieren imaging system. Background Technique

[0002] Schlieren imaging technology is an optical technology used to visualize fluid density changes, especially to display minute refractive index differences in air or other gas media. The core principle of schlieren imaging technology is based on the deflection of light when it propagates through different media due to minute changes in refractive index, thereby generating brightness differences in the imaging system. This difference can reflect the density gradient in the fluid, making the invisible gas flow phenomenon visible.

[0003] Traditional schlieren imaging systems typically include components such as a point light source, a collimating lens, a test area, a knife edge, an imaging lens, and a camera. With the progress of technology and the diversification of application requirements, however, traditional schlieren imaging systems have certain limitations in terms of modularity, flexibility, and coaxial design.

[0004] 1. Bulky volume: Due to its complex optical path and relatively large-scale optical components, it is difficult to be used in environments with limited space or high portability requirements.

[0005] 2. Lack of flexibility: Traditional systems cannot adjust components such as the light source and imaging device according to specific experimental needs, lack modular design, and have limited application scope.

[0006] 3. Complex optical coaxial design: Since the optical axes of each optical component are not collinear, the optical path is prone to deviation, resulting in reduced imaging accuracy and difficulty in maintaining consistency.

[0007] It is difficult for the existing technology to achieve coaxialization and modularization of the system while maintaining high-precision imaging. This has given rise to an urgent need for a more advanced, modular, and coaxial-designed schlieren imaging system. Summary of the Invention

[0008] In order to solve the above problems, the utility model proposes a modular coaxial schlieren imaging system to achieve high-precision and flexible-configured schlieren imaging.

[0009] A modular coaxial schlieren imaging system includes a light source module, a beam splitter module, a knife edge module, a camera module, a test area module, and a mirror module; the light source module, the beam splitter module, the knife edge module, and the camera module are assembled through a detachable cage bracket, the knife edge module is located between the camera module and the beam splitter module, the light source module is fixed on one side of the beam splitter module, the test area module and the mirror module are placed on the other side of the beam splitter module and in the vertical direction of the connection line between the beam splitter module and the camera module;

[0010] The light source module includes an energy fiber and an LED light source. The light source module outputs a point light source by coupling the energy fiber to the LED light source. The core diameter of the energy fiber is adapted to the brightness of the light source. The numerical aperture of the energy fiber is adapted to the diameter and focal length of the concave reflector in the reflector module. The point light source of the light source module is located at the center of curvature of the concave reflector of the reflector module, so that the light is reflected along the incident path and accurately returns to the position of the point light source.

[0011] Furthermore, the intensity, color temperature and spot size of the light source of the light source module are adjustable; the spectrometer module, knife-edge module, test area module and reflector module are all provided with adjustment devices, which are adjusted according to the different objects to be tested or the environment to be tested, so that the optical axes of the light source, concave reflector, knife-edge and camera module are strictly aligned.

[0012] Furthermore, the cage bracket includes an upper bottom, a lower bottom, an upper partition, a lower partition and several pillars. The pillars are installed on the upper and lower bottoms by screws. The upper and lower partitions installed on the pillars have through holes. The spectrometer module is installed below the upper bottom, and the camera module is installed on the pillars through the lower partition; the knife edge module is installed on the upper partition between the camera module and the spectrometer module, and the light source module is installed on one side of the upper partition so that the emission point of the point light source is located directly behind the spectrometer; the cage bracket is surrounded by partitions of uniform thickness, and the partitions are provided with an opening in front of the spectrometer for the light beam to pass through.

[0013] Furthermore, the spectrometer of the spectrometer module is mounted on the upper end of the cage bracket, the spectrometer is fixed on the mounting bracket, and the mounting bracket is mounted on the upper bottom of the cage bracket through precision fine-thread adjustment screws, and the precision fine-thread adjustment screws fine-tune the reflection direction of the spectrometer.

[0014] Furthermore, the blade module includes a blade, a fixing plate with a groove, and a circular ring-shaped lever with a protrusion. The blade is adhered to the fixing plate, one end of the fixing plate is fixed to the circular ring of the lever by a pin, and the protrusion at the other end corresponds to the limiting hole in the groove of the fixing plate. Driven by the lever, the blade swings slightly in the groove of the fixing plate with the protrusion of the fixing plate as a fulcrum; the blade position is precisely adjusted by the lever according to the sensitivity requirements of the refractive index change in the experiment, thereby increasing or decreasing the system's sensitivity to tiny light deflections.

[0015] Furthermore, the test area module includes a box with optical windows at both ends and a clamping device installed on the bottom surface of the box. The clamping device can adjust the height and rotation angle to fix experimental objects of different sizes and shapes, flexibly adjust the position and angle of the object to be tested, and ensure that the light beam can fully pass through the area to be tested; the reserved optical window ensures that the light beam can pass through the test area without interference.

[0016] Furthermore, the camera module includes a high-resolution imaging sensor, which adjusts exposure time, frame rate or resolution parameters according to different experimental environments to ensure that the clarity and dynamic range of the schlieren images reach the best effect.

[0017] Furthermore, the mirror module includes a bracket and a concave mirror mounted on the bracket by a buckle. Three adjusting screws are provided around the concave mirror.

[0018] For the modular coaxial schlieren imaging system of the present application, the optical path is designed as follows:

[0019] ① The light source module generates light, and outputs a point light source through fiber optic coupling;

[0020] ② The light beam passes through the beam splitter and is divided into two perpendicular paths; one path serves as the illumination beam of the illumination structure light source of the system, and the other path is shielded;

[0021] ③ After the illumination beam passes through the test area and is incident on the concave mirror, the light is reflected along the incident path. The reflected light beam is divided into two perpendicular paths again by the beam splitter; one path returns to the position where the light source is located, and the other path converges to the knife-edge position;

[0022] ④ In the test area, due to the small change in refractive index, the light beam is deflected. After passing through the knife-edge module, the knife-edge intercepts part of the deflected light to form a bright-dark contrast;

[0023] ⑤ The remaining light enters the camera module, and the lens focuses the light on the sensor of the camera module; the image captured by the camera shows the brightness difference after passing through the refractive index change, forming a visual schlieren image.

[0024] In addition, the present application also provides a method for using the modular coaxial schlieren imaging system.

[0025] The method for using the modular coaxial schlieren imaging system includes the following steps:

[0026] (1) First, according to different objects to be measured or measurement environments, select concave mirrors with different diameters and focal lengths, and then select light sources and energy fibers with different core diameters and numerical apertures;

[0027] (2) According to the structural design, assemble each module, and then test and adjust different modules in sequence to make the light emitted from the light source propagate along the coaxial path in the whole system;

[0028] (3) Select a camera based on the reference light source and parameters such as the frame rate and resolution of the shot;

[0029] (4) Place the object to be measured or the measurement environment into the test area to conduct an experiment.

[0030] Among them, the method for adjusting different modules in step (2) includes the following steps:

[0031] a. Observe the light output hole of the optical fiber and the image of the knife edge reflected by the beam splitter through the window in front of the point light source. Then adjust the lever of the knife edge to ensure that the light output hole and the knife edge can be clearly seen simultaneously. Then adjust the three precision fine-thread adjusting screws of the beam splitter module so that the depth of field of the light output hole and the knife edge is on the same imaging plane. Finally, finely adjust the lever of the knife edge to make the knife edge cut half of the light output hole;

[0032] b. Place the assembled module in the correct position according to the optical path design. Then turn on the light source, place a piece of white paper above the beam splitter module close to the two rear adjusting screws. Finally, counterclockwise adjust the bottom adjusting screw of the concave mirror until a reflected light spot of the point light source appears on the white paper;

[0033] c. Adjust the two adjusting screws on the concave mirror to horizontally move the reflected light spot so that the reflected light spot, the point light source, and the center of the concave mirror are in the same vertical plane. Then slightly move the assembly where the beam splitter is located back and forth to make the reflected light spot focused. Finally, clockwise adjust the bottom adjusting screw of the concave mirror to move the reflected light spot to a position near the point light source;

[0034] d. Open the control software of the industrial camera on the computer side, play the image captured by the camera, and adjust the lever of the knife edge. When the reflected light spot is completely unobstructed, a circular bright field can be seen in the center of the image. When the reflected light spot is completely blocked, the field of view is completely black. When the reflected light spot is blocked by half, three situations will appear in the field of view observed in the center of the image. One is that the upper half of the circular field of view is bright and the lower half is dark, one is that the upper half of the circular field of view is dark and the lower half is bright, and the third is that the overall circular field of view becomes darker and the upper and lower parts are equally bright;

[0035] e. If the first two situations occur in the previous step, it is necessary to finely adjust the position of the assembly where the beam splitter is located back and forth until the third situation appears.

[0036] The following details the technical implementation of the present invention.

[0037] (1) System composition:

[0038] The modular coaxial schlieren imaging system of the present invention mainly consists of the following parts:

[0039] Light source module: Used to provide the illumination light source for the system. The light source can be an LED light source, a laser, etc. Specifically, the selection of parameters such as color temperature and spot size depends on the experimental requirements. The light source module is equipped with an adjustment device to control the intensity of the light source. In the light source module, the coupling design of the optical fiber and the LED lamp is very crucial. The optical fiber can effectively limit the spot diameter transmitted from the LED light source, making the output of the optical fiber an approximately ideal point light source.

[0040] Beam splitter module: Located behind the light source module, it is responsible for splitting the light beam into two perpendicular beams. The reflection direction of the beam splitter can be finely adjusted.

[0041] Test area module: The core area of the system, used to place the object or environment to be tested (such as air flow, heat flow, etc.). This module is equipped with an adjustable clamping device for fixing experimental objects of different sizes and shapes. Optical windows are reserved on both sides of the test area to ensure that the light beam can pass through the test area without interference.

[0042] Mirror module: A concave mirror, located behind the experimental area. The point light source is located at the center of curvature of the concave mirror, and the light is reflected along the incident path and accurately returns to the position where the light source is located.

[0043] Edge slit module: Installed after the test area, it is used to cut the deflected light after passing through the test area. The edge slit module can precisely adjust the position of the edge slit up and down to adjust the sensitivity of imaging. The precise adjustment of the edge slit is the key to the imaging effect of the system.

[0044] Camera module: Used to collect the optical image after passing through the imaging lens. The camera module contains a high-resolution imaging sensor, and parameters such as exposure time and sampling frequency can be adjusted according to different experimental requirements to ensure the best imaging quality.

[0045] (2) Modular adjustment function:

[0046] The modular design of the present utility model allows each component to be adjusted according to experimental requirements:

[0047] Light source adjustment: The brightness, spot size, and color temperature of the light source module can be adjusted according to experimental requirements.

[0048] Edge slit sensitivity adjustment: The fine adjustment device of the edge slit allows the user to precisely adjust its position according to the sensitivity requirements of the refractive index change in the experiment. By adjusting the position of the edge slit, the sensitivity of the system to small light deflections can be increased or decreased. Test area adjustment: The devices in this area can flexibly adjust the position and angle of the object to be tested to ensure that the light beam can fully pass through the area to be tested.

[0049] Camera parameter setting: The camera module allows the user to adjust parameters such as exposure time, frame rate, and resolution according to different experimental environments to ensure that the schlieren image clarity and dynamic range reach the best effect.

[0050] The utility model provides a modular coaxial schlieren imaging system. Through modular design, the system achieves high flexibility and scalability, and can be freely adjusted and configured according to different experimental requirements. The design of the coaxial optical path significantly reduces the optical path error, improves the imaging accuracy, and ensures high-resolution schlieren images. At the same time, the overall design of the system is compact and portable, making it convenient to use in scenarios with limited space or frequent movement. In addition, through the application of high-precision optical elements and a knife-edge module with adjustable sensitivity, the utility model can accurately capture minute fluid density changes, and is applicable to scientific research, engineering applications, and high-precision industrial inspections, greatly improving the experimental and inspection efficiency.

[0051] It has the following beneficial effects:

[0052] (1) All components of the system (such as light source, beam splitter, knife-edge, camera, test area, mirror) adopt modular design and can be flexibly adjusted and combined according to different experimental requirements. The characteristics of the modular design include:

[0053] · Components are detachable and replaceable: The light source, camera, mirror, etc. can be replaced or adjusted according to experimental requirements, improving the versatility of the system.

[0054] · Flexible configuration: Different modules can be customized as needed to adapt to different scenarios and conditions of the experiment.

[0055] · Scalability: The modular design allows new functions to be added or existing components to be upgraded in the future to adapt to changing research needs.

[0056] (2) Coaxial optical design

[0057] The system adopts a precise cage-type coaxial optical design to ensure that the propagation path of light in the system always remains coaxial. The design key points include:

[0058] · Coaxial arrangement of the optical system: The optical axes of the light source, knife-edge, camera, and mirror are kept consistent, reducing the optical path error and ensuring the clarity of the image.

[0059] · Reducing errors and light losses: Through coaxial design, the complexity of optical path adjustment in traditional schlieren systems is reduced, the error and optical loss are decreased, and the imaging accuracy is improved.

[0060] · System simplification: The coaxial design reduces the overall complexity of the system, making the equipment more compact and convenient for deployment.

[0061] (3) High-precision imaging

[0062] This system ensures the accuracy and clarity of imaging through high-precision optical elements and design schemes:

[0063] · High-resolution imaging: The system is equipped with a high-resolution camera, which can clearly capture minute changes in fluid density gradients, enhancing the accuracy of experimental data.

[0064] · Sensitivity adjustment: The position of the knife edge in the system can be flexibly adjusted to enhance the sensitivity to refractive index changes and adapt to different experimental environments.

[0065] · Minimization of optical distortion: High-quality optical mirrors and precise alignment techniques are used to ensure that light does not become distorted after passing through the test area, guaranteeing the accuracy of the images.

[0066] (4) Portability and compact design

[0067] The system pays particular attention to a compact design, enabling it to be used in space-constrained environments and featuring good portability:

[0068] · Small size: The components are 3D printed, making the overall system small and compact, facilitating transportation and rapid deployment in different experimental scenarios.

[0069] · Quick assembly: The modular design allows for the rapid assembly and disassembly of the system, suitable for experimental scenarios that require frequent movement and setup.

[0070] · High integration: While maintaining high performance, the system has a simple design, reducing unnecessary components and making the installation and debugging of the system more convenient.

[0071] (5) Adaptation to different experimental conditions

[0072] · Adjustable light source: According to experimental requirements, parameters such as the brightness and color temperature of the light source can be adjusted to ensure optimal imaging effects under different conditions.

[0073] · Multi-scenario application: The system is designed to adapt to a variety of experimental scenarios, including laboratory fixed test environments and outdoor portable applications, with strong versatility.

[0074] The modular coaxial schlieren imaging system of this application is mainly used for visualizing refractive index changes in gases and is widely applied in the following fields:

[0075] (1) Fluid mechanics: Used to study density gradients and vortex phenomena in airflows, such as pressure waves in airflows.

[0076] (2) Aerodynamics: Used for the aerodynamic performance testing of aircraft, rockets and other aircraft, observing the airflow distribution and aerodynamic effects in the air.

[0077] (3) Combustion research: Used to monitor the hot airflows generated during the combustion process and their changes, helping to optimize the combustion process.

[0078] (4)Thermophysical research: Used to study the density gradient of fluids during heat conduction to understand the changes in heat transfer.

[0079] (5)Industrial applications: Can be used to detect phenomena such as air leakage, gas mixing, and spray cooling, suitable for non-contact measurements in engineering and industrial scenarios.

[0080] This application provides a flexible, precise, and efficient schlieren imaging solution that can capture minute refractive index changes in transparent gases in real-time and non-contact, suitable for scientific research experiments, engineering tests, and high-precision industrial inspection occasions. (4)Specific embodiments

[0082] In aerodynamic experiments, the system is used to observe the flow field changes when high-speed airflows pass over the surface of an object. By placing the object in the test area, the system successfully captured the density gradient changes in the air flow, generating clear schlieren images that demonstrated the flow field structure and turbulent phenomena when the air flow bypassed the object. Description of the drawings

[0083] Figure 1 This is the overall system diagram after the system of this application is assembled.

[0084] Figure 2 This is the assembly drawing of the beam splitter module and the upper base of the cage mount.

[0085] Figure 3 This is the assembly drawing of the knife-edge module structure and the upper partition of the cage mount. a is the schematic diagram after assembly, and b is the exploded view.

[0086] Figure 4 This is the assembly drawing of the camera module and the lower partition of the cage mount.

[0087] Figure 5 This is the assembly schematic diagram of the test area module and the mirror module. a is the assembly drawing, and b is the perspective view.

[0088] Figure 6 This is the optical path schematic diagram when the system of this application is in use.

[0089] Figure 7 This is the schlieren imaging - heat convection of the embodiment.

[0090] Light source module 1, LED light source 1-1, energy optical fiber 1-2, and point light source (emission port) 1-3; beam splitter module 2, beam splitter 2-1, fine-thread adjusting screw 2-2, knife-edge module 3, blade 3-1, paddle 3-2, fixing part 3-3, fixing plate 3-4, positioning hole 3-5, camera module 4, test area module 5, optical window 5-1, box body 5-2, clamping device 5-3, mirror module 6, reflecting mirror 6-1, bracket 6-2, adjusting screw 6-3, buckle 6-4, cage mount 7, upper bottom 7-1, upper partition 7-2, support column 7-3, lower partition 7-4. Detailed implementation

[0091] A modular coaxial schlieren imaging system, assembling the light source module 1, beam splitter module 2, knife-edge module 3, and camera module 4 onto the cage mount 7. The cage mount 7 includes an upper bottom 7-1, a lower bottom, an upper partition 7-2, a lower partition 7-3, and several support columns 7-4. The support columns 7-4 are installed on the upper and lower bottoms through screws. The upper and lower partitions 7-3 installed on the support columns 7-4 have through holes. The beam splitter module 2 is installed below the upper bottom 7-1, and the camera module 4 is installed on the support columns 7-4 through the lower partition 7-3; the knife-edge module 3 is installed on the upper partition 7-2 between the camera module 4 and the beam splitter module 2, and the light source module 1 is installed on one side of the upper partition 7-2, so that the emission point of the point light source is located directly behind the beam splitter; there are evenly thick partitions around the cage mount 7, and the partitions are provided with openings for the beam to pass through in front of the beam splitter. The knife-edge module 3 is located between the camera module 4 and the beam splitter module 2, the light source module 11 is fixed on one side of the beam splitter module 2, and the test area module 5 and the mirror module 6 are placed on the other side of the beam splitter module 2 and in the vertical direction of the connection line between the beam splitter module 2 and the camera module 4.

[0092] The beam splitter 2-1 of the beam splitter module 2 is installed at the upper end of the cage mount 7. The beam splitter 2-1 is fixed on the mounting bracket 2-3. The mounting bracket 2-3 is installed on the upper bottom 7-1 of the cage mount 7 through the precision fine-thread adjusting screw 2-2. The precision fine-thread adjusting screw 2-2 finely adjusts the reflection direction of the beam splitter 2-1. The knife-edge module 3 includes a knife-edge 3-1, a fixing plate 3-4 with a groove, and a ring-shaped lever 3-2 with a protrusion. The knife-edge 3-1 is pasted on the fixing piece 3-3. One end of the fixing piece 3-3 is fixed to the ring of the lever 3-2 through a pin, and the other end protrusion corresponds to the limit hole 3-5 in the groove of the fixing plate 3-4. The knife-edge 3-1 makes a small swing in the groove of the fixing plate 3-4 with the protrusion of the fixing piece 3-3 as the fulcrum under the drive of the lever 3-2; according to the sensitivity requirement of the refractive index change in the experiment, the position of the knife-edge is precisely adjusted through the lever 3-2 to increase or decrease the sensitivity of the system to the small light deflection. The test area module 5 includes a box body 5-2 with optical windows 5-1 at both ends and a clamping device 5-3 fixed on the bottom surface of the box body. The clamping device 5-3 can adjust the height and rotation angle, and is used to fix experimental objects of different sizes and shapes, flexibly adjust the position and angle of the object to be measured, and ensure that the light beam can fully pass through the area to be measured; the reserved optical window 5-1 ensures that the light beam can pass through the test area without interference. The mirror module 6 includes a bracket 6-2 and a concave mirror 6-1 installed on the bracket 6-2 through a buckle 6-4. Three adjusting screws 6-3 are provided around the concave mirror 6-1.

[0093] According to the objects to be measured: the hot ascending air flow formed by the candle flame and the cold descending air flow formed by the ice lolly, adjust the beam splitter module 2, the knife-edge module 3, the test area module 5, the mirror module 6, etc., so that the optical axes of the light source, the concave mirror, the knife-edge and the camera module 4 are strictly aligned. The specific operation is as follows:

[0094] (1) First, according to different objects to be measured or measurement environments, select concave mirrors with different diameters and focal lengths, and then select light sources and energy optical fibers with different core diameters and numerical apertures; the light source brightness is 1000 LX (1000 lumens per square meter).

[0095] (2) According to the structural design, assemble each module, and then test and adjust different modules in sequence according to the following steps to make the light rays emitted from the light source propagate along the coaxial path in the whole system;

[0096] a. Observe the light output hole of the optical fiber and the image of the knife-edge reflected by the beam splitter through the window directly in front of the point light source, and then adjust the lever of the knife-edge to ensure that the light output hole and the knife-edge can be clearly seen at the same time. Then adjust the three precision fine-thread adjusting screws of the beam splitter module to make the depth of field of the light output hole and the knife-edge on the same imaging plane. Finally, finely adjust the lever of the knife-edge to make the knife-edge cut half of the light output hole;

[0097] b. Place the assembled module in the correct position according to the optical path design. Then turn on the light source. Place a piece of white paper above the beam splitter module, close to the two adjusting screws at the rear. Finally, adjust the bottom adjusting screw of the concave mirror counterclockwise until a reflected light spot of the point light source appears on the white paper.

[0098] c. Adjust the two adjusting screws on the concave mirror to horizontally move the reflected light spot so that the reflected light spot, the point light source, and the center of the concave mirror are in the same vertical plane. Then slightly move the assembly where the beam splitter is located back and forth to focus the reflected light spot. Finally, adjust the bottom adjusting screw of the concave mirror clockwise to move the reflected light spot to a position near the point light source.

[0099] d. Open the control software of the industrial camera on the computer side, play the captured image of the camera, and adjust the lever of the knife edge. When the reflected light spot is completely unobstructed, a circular bright field of view can be seen in the center of the image. When the reflected light spot is completely blocked, the field of view is completely black. When the reflected light spot is blocked by half, three situations will appear in the field of view observed in the center of the image. One is that the upper half of the circular field of view is bright and the lower half is dark. One is that the upper half of the circular field of view is dark and the lower half is bright. The third is that the overall circular field of view becomes darker and the upper and lower parts are equally bright.

[0100] e. If the first two situations occur in the previous step, it is necessary to slightly adjust the position of the assembly where the beam splitter is located back and forth until the third situation appears.

[0101] (3) Acquisition parameters of the camera: 3072 * 2048 (pixels), 30 FPS (frame rate), exposure time 1000 us (microseconds); (4) Place the object to be measured or the environment to be measured in the test area to conduct the experiment.

[0102] The experimental schlieren imaging of the thermal updraft formed by the candle flame and the cold downdraft formed by the ice lolly is shown as follows.

[0103] f. If the first two situations occur in the previous step, it is necessary to slightly adjust the position of the assembly where the beam splitter is located back and forth until the third situation appears.

[0104] (3) Acquisition parameters of the camera: 3072 * 2048 (pixels), 30 FPS (frame rate), exposure time 1000 us (microseconds); (4) Place the object to be measured or the environment to be measured in the test area to conduct the experiment.

[0105] The experimental schlieren imaging of the thermal updraft formed by the candle flame and the cold downdraft formed by the ice lolly is shown as follows. Figure 7 as shown.

Claims

1. A modular coaxial schlieren imaging system comprising a light source module, a beam splitter module, a knife-edge module, a camera module, a test area module, and a reflector module; the light source module, the beam splitter module, the knife-edge module, and the camera module are assembled via a detachable cage bracket, the knife-edge module is positioned between the camera module and the beam splitter module, the light source module is fixed to one side of the beam splitter module, and the test area module and the reflector module are positioned on the other side of the beam splitter module, perpendicular to the line connecting the beam splitter module and the camera module; The light source module includes an energy fiber and an LED light source. The light source module outputs a point light source by coupling the energy fiber to the LED light source. The core diameter of the energy fiber is adapted to the brightness of the light source. The numerical aperture of the energy fiber is adapted to the diameter and focal length of the concave reflector in the reflector module. The point light source of the light source module is located at the center of curvature of the concave reflector of the reflector module, so that the light is reflected along the incident path and accurately returns to the position of the point light source.

2. The modular coaxial schlieren imaging system according to claim 1, wherein: The light source of the light source module is an LED light source or a laser, and the intensity, color temperature and spot size of the light source are adjustable; the spectrometer module, knife-edge module, test area module and reflector module are all provided with adjustment devices, which are adjusted according to the different objects to be tested or the environment to be tested, so that the optical axes of the light source, concave reflector, knife-edge and camera module are strictly aligned.

3. The modular coaxial schlieren imaging system according to claim 1, characterized in that: The cage bracket includes an upper bottom, a lower bottom, an upper partition, a lower partition and several pillars. The pillars are installed with the upper and lower bottoms by screws. The upper and lower partitions installed on the pillars have through holes. The spectrometer module is installed below the upper bottom, and the camera module is fixed to the pillars through the partition; the knife edge module is installed on the partition between the camera module and the spectrometer module, the light source module is installed on the side of the partition where the knife edge is located, and the emission point of the point light source is located directly behind the spectrometer; the cage bracket is surrounded by partitions with uniform thickness, and the partitions are provided with an opening in front of the spectrometer for the light beam to pass through.

4. The modular coaxial schlieren imaging system according to claim 1, wherein: The spectrometer of the spectrometer module is mounted on the upper end of the cage bracket, which is fixed to the mounting bracket. The mounting bracket is mounted on the upper bottom of the cage bracket through precision fine-thread adjustment screws. The precision fine-thread adjustment screws fine-tune the reflection direction of the spectrometer.

5. The modular coaxial schlieren imaging system according to claim 1, characterized in that: The knife-edge module includes a knife edge, a fixing plate with a groove, and a circular ring-shaped lever with a protrusion. The knife edge is adhered to the fixing plate. One end of the fixing plate is fixed to the circular ring of the lever by a pin, and the protrusion at the other end corresponds to the limiting hole in the groove of the fixing plate. Driven by the lever, the knife edge swings slightly in the groove of the fixing plate with the protrusion of the fixing plate as a fulcrum. The lever is used to accurately adjust the position of the knife edge according to the sensitivity requirements of the refractive index change in the experiment, thereby increasing or decreasing the system's sensitivity to tiny light deflections.

6. The modular coaxial schlieren imaging system according to claim 1, wherein: The test area module includes a box with optical windows at both ends and a clamping device fixed to the bottom of the box. The clamping device can adjust the height and rotation angle to fix experimental objects of different sizes and shapes, flexibly adjust the position and angle of the object to be tested, and ensure that the light beam can fully pass through the test area; the reserved optical window ensures that the light beam can pass through the test area without interference.

7. The modular coaxial schlieren imaging system according to claim 1, wherein: The camera module includes a high-resolution imaging sensor, which adjusts the exposure time, frame rate or resolution parameters according to different experimental environments to ensure the best clarity and dynamic range of the schlieren images.

8. The modular coaxial schlieren imaging system according to claim 1, characterized in that: The mirror module includes a bracket and a concave mirror mounted on the bracket by a snap. Three adjusting screws are provided around the concave mirror.

9. The modular coaxial schlieren imaging system according to claim 1, wherein: The optical path design is as follows: ① The light source module generates light, and outputs a point light source through fiber optic coupling; ② The light beam passes through the beam splitter and is divided into two perpendicular paths; one path serves as the illumination beam of the illumination structure light source of the system, and the other path is shielded; ③ After passing through the test area, the illumination beam is incident on the concave mirror, and the light is reflected along the incident path. The reflected beam passes through the beam splitter again and is divided into two perpendicular paths; one path returns to the position where the light source is located, and the other path converges to the knife-edge position; ④ In the test area, deflection occurs due to a slight change in the refractive index. The deflected beam passes through the knife-edge module, and the knife-edge intercepts part of the deflected light to form a light-dark contrast; ⑤ The remaining light enters the camera module, and the lens focuses the light on the sensor of the camera module; the image captured by the camera shows the brightness difference after the refractive index change, forming a visual schlieren image.

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