CN108280824A - Laser speckle-shearing interferometry defect detecting system based on image registration and fusion - Google Patents

Abstract

The invention discloses a laser shearing speckle interference defect detection system based on image registration and fusion, comprising: a laser light source, a beam expander, a beam splitter, a cutter, a phase shifter, an image collector and an integrated image PC with processing algorithm and phase shifter control algorithm; first use the dual-camera image collector to simultaneously record the laser shearing interference fringe pattern and the original image of the measured object before and after thermal loading, and then through the image processing algorithm and phase shifter The shifter control algorithm processes the laser shearing scattered interference fringe pattern before and after thermal loading to obtain a phase difference image, and finally fuses and registers the phase difference image with the original image to realize fast and accurate positioning of defect position detection.

Description

Laser Shear Speckle Interference Defect Detection System Based on Image Registration and Fusion

technical field

The invention belongs to the technical field of defect detection, and more specifically relates to a laser shearing speckle interference defect detection system based on image registration and fusion.

Background technique

Laser shear speckle interferometry technology has full-field, non-contact, strong anti-interference ability to the environment, and high precision. It can directly measure the displacement derivative of the surface of the measured object due to defects such as internal debonding under thermal loading conditions. The environmental requirements are relatively low. These characteristics enable the laser shearing bulk interferometry technology to go out of the laboratory and be widely used in the debonding of aerospace composite materials and other tiny internal defects. Although this technology has been widely used in non-destructive testing in terms of principle or in practical experiments and applications, and has achieved many innovative and breakthrough progress, the current research, especially in the precise positioning of defect locations, has little clarity. The progress is mainly in the qualitative and quantitative detection of defects and application fields.

Laser shear interferometry technology can directly measure the differential of object displacement, which is very beneficial to strain. The basic principle is to combine general speckle interferometry and shearing mechanism, and add a dislocation element before the lens of the general speckle interferometry optical path. The sheared speckle is formed by different shearing elements. Taking the classic Michelson interferometer as an example, the object is irradiated with coherent laser light, and an object point is divided into two image points on the imaging surface by means of a birefringent crystal, thereby generating a pair of lateral dislocation images on the image sensor of the camera. The two speckle images before and after loading deformation are collected and digitized by CCD, and stored in the computer through frame storage. The two speckle images are subtracted to form new interference fringes. From the change of the interference fringe images, it can be judged whether there is defect. Combined with the new phase shift technology to extract the phase information of the image, further processing can realize automatic and fast defect visual detection. However, the current research is only limited to the detection of defects, and has not achieved precise positioning on the measured object, and precise positioning is one of the important measures for the prediction and estimation of material structure health management.

In the article "A new optical method forstrain measurement and nondestructive testing" in Volume 21, No. 3 of "Optical Engineering" in 1982, it was proposed for the first time to apply the laser shearing bulk interferometry technology to the field of stress detection and nondestructive testing. The device used A prism with a small wedge angle is placed in front of the CCD camera. The size of the prism is just half of the area of the CCD camera. The reflected light on the surface of the measured object passes through the prism to form a dislocation and directly passes through the original image of the CCD camera for shear interference. Although the device is simple, its shortcomings are also very obvious. The fixed prism wedge angle is directly related to the size of the shear angle, which is inflexible, introduces a lot of noise, and has extremely low sensitivity.

In the article "Dual-beam phaseShift Shearography for Measurement of In-plane Strains" in Volume 24 of "Optics and Laser in Engineering" in 1996, a single-observation laser shearing of a dual-beam symmetric light source based on a Michelson interferometer was introduced. Scattered interferometric devices can measure the gradient of surface displacement derivatives, but the requirements for precise positioning of defects cannot be realized.

In the article "Applications of digital shearography for testing of composite structures" in the 30th volume of "Composites: Part B Engineering" in 1999, the single-irradiation-source single-observation shear bulk interferometer based on the classic Michelson interferometer was used. The device is simple and easy to implement, but it is only for result detection, and if phase information needs to be extracted and phase shifting technology is required, the simple device cannot realize online automatic real-time defect detection.

In the article "A compact dual-purpose camera forshearography and electronic speckle-pattern interferometry" in Volume 8 of "Meas.Sci.Techno" in 1997, a detection of a combined electronic speckle-pattern interferometry and shear speckle-pattern interferometry device was published. system, the device can simultaneously obtain the information of scattered interferometry and shear interferometric interference of the measured object, and obtain the information of the two technologies at the same time, but one of the biggest disadvantages is that the optical path is relatively complicated, and the external error is relatively large; at the same time, the light energy The utilization rate is low, and the energy of the laser is required to be high; in addition, the accurate comparison and positioning of the defect position cannot be realized.

"Multiwavelength shearography for quantitative measurements of two-dimensional strain distributions" in Volume 38, No. 1 of "Applied Optics" in 1999, "Time-division-multiplexed 3Dshearography in Volumes 3744 and 3745 of "Proceeding of SPIE" in 1999 " and "Compact shearography system for the measurement of 3Ddeformation" used three square light sources at three vertex positions and a single-observation laser shearing bulk interferometer based on Michelson interferometers to detect object planes The internal displacement gradient makes it possible to measure the in-plane displacement gradient in all directions, but the device is extremely complicated, so it is difficult to separate the interference fringe information of the three light sources illuminating the object in the later stage, and the noise signal introduced will also increase accordingly. .

"Quantitative evaluation of digital shearing interferogram using the spatial carrier method" in Volume 5, No. 313 of "Applied Optics" in 1996, "A new set-up for pulsed" in Volume 42 of "Optics and Lasers in Engineering" in 2004 digitalshearography applied to defect detection in composite structures” introduced the laser shear bulk interferometric detection system based on the Mach-Zehnder interferometer device, combined with the space carrier technology to improve the accuracy of defect detection, but in the accurate positioning of defects in composite materials No technical progress.

In the article "Surface strain measurement of rotating objects using pulsed laser shearography with coherent fiber-optic imaging bundles" in Volume 19 of "Measurement Science and Technology" in 2008, four camera lenses based on Mach-Zehnder interferometer were used for coherent fiber imaging detection system, the system uses four small lenses to collect images of the measured object from four angles, and transmits them to the Mach-Zehnder interferometer through four optical cables at the same time to form a shear interference image, which is finally fused to the four corners of the CCD camera, and then fringe Image analysis and processing to extract useful information. This device improves the detection accuracy, but the disadvantages are very obvious. First, the system is very complicated to set up and the cost is relatively expensive. Secondly, the interference fringe pattern collected by the CCD contains very complex and various information, which makes it difficult to separate the signals, and may also introduce additional noise information.

Doctoral thesis "Research on Vector Light Field Control Based on Liquid Crystal Spatial Light Modulator" in 2014, "Synchronous Phase-shifting Common Optical Path Interference Based on Liquid Crystal Spatial Light Modulator" in "Journal of Optoelectronics Laser" Volume 24 Issue 6 in 2013 Technology", "Digitalsckle shearing interferometer using a liquid-crystal spatial lightmodulator" in Volume 45, No. 10 of "Optical Engineering" in 2006. The device does reduce the phase information acquisition time, improve the energy utilization of light and reduce the interference of other light to the system, but the spatial light modulator is very expensive, and it is not involved in the accurate positioning of defect detection.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, to provide a laser shearing speckle interference defect detection system based on image registration and fusion, and to realize the visual detection of precise positioning of defect position information through image fusion and registration , has the characteristics of simple optical path, low cost, high sensitivity and high detection accuracy.

In order to achieve the purpose of the above invention, the present invention provides a laser shearing speckle interference defect detection system based on image registration and fusion, which is characterized in that it includes: a laser light source, a beam expander, a beam splitter, a shear, a phase shifter device, image collector and PC with integrated image processing algorithm and phase shifter control algorithm;

The shearer includes a 55-5 beam splitter, a phase-shifting mirror and a shearing mirror;

Described image acquisition device adopts double CCD camera, and wherein CCD1 camera is used for collecting original image, and CCD2 camera is used for collecting laser shear scattered class interference fringe image;

When the measured object is at normal temperature, the laser light source is expanded by the beam expander, and the laser light is irradiated to the surface of the measured object, and then the reflected light on the surface of the measured object is passed through the beam splitter, so that the light is divided into the same light energy. Two beams of light, one beam of light is directly recorded by the CCD1 camera to obtain the original image; the other beam of light enters the 55-5 beam splitter of the cutter, and the 55-5 beam splitter divides this beam of light into two beams of equal light energy. The light beam enters the phase-shifting mirror and the shearing mirror connected to the phase shifter respectively, the phase shifting of the phase-shifting mirror is controlled by the phase shifter, and the shearing amount is adjusted by the shearing mirror, thereby forming an object surface image and Interferes with the sheared image dislocated in a certain direction, and records it with the CCD2 camera to obtain four laser sheared discrete interference fringe images with known phase shift information on the surface of the measured object at room temperature;

When the object under test is under thermal loading, the laser light source is also expanded by the beam expander, and the laser light is irradiated to the surface of the object under test, and then the reflected light on the surface of the object under test passes through the beam splitter, so that the light is divided into equal beams. Two beams of light with high energy, one of which is directly recorded by the CCD1 camera to obtain the original image; The two beams of light enter the phase shift mirror and the shear mirror connected to the phase shifter respectively, and the phase shift mirror is controlled by the phase shifter to produce a small displacement to achieve the purpose of phase shift, and the phase shift is adjusted by the shear mirror The amount of shearing, so as to form the surface image of the object and the shearing image dislocated in a certain direction for interference, and record it with the CCD2 camera to obtain four laser shearing images with known phase shift information on the surface of the measured object under thermal loading. Class interference fringe image;

The CCD1 camera transmits the two images obtained in the two states and the eight images obtained by the CCD2 camera in the two states respectively, a total of ten images are sent to the PC, and the PC controls the algorithm accurately through the built-in phase shifter. Control the phase shifter to generate four known phase shifts, extract the phase diagrams of the laser shear scattering interference fringe images in the two states through the four-step phase shift algorithm, and then make a numerical difference to obtain the phase difference image, and then pass the phase difference The images are sequentially processed by the adaptive threshold filtering and the unwrapping algorithm of the least squares method to obtain the phase difference image of the laser shear discrete interference fringe image that directly reflects the surface deformation and displacement gradient of the measured object. Finally, a random image collected by the CCD1 is selected. The original image and the above-mentioned phase difference image are registered and fused according to the CCD resolution optical system and the proportional calculation of the shear amount, so as to realize the accurate visual positioning of defect detection.

The purpose of the invention of the present invention is achieved like this:

The laser shearing speckle interference defect detection system based on image registration and fusion of the present invention includes: a laser light source, a beam expander, a beam splitter, a cutter, a phase shifter, an image collector, and an integrated image processing algorithm and phase PC with shifter control algorithm; first use the dual-camera image collector to simultaneously record the laser shear scattering interference fringe pattern and the original image of the measured object before and after thermal loading, and then use the image processing algorithm and phase shifter control algorithm Process the laser-sheared scattered interference fringe images before and after thermal loading to obtain a phase difference image, and finally fuse and register the phase difference image with the original image to realize fast and accurate positioning of defect position detection.

At the same time, the laser shearing speckle interference defect detection system based on image registration and fusion of the present invention also has the following beneficial effects:

(1), the present invention is based on the classic Michelson interferometer combined with the phase shift technology of automatic fringe phase information acquisition, and adopts dual camera fusion technology to collect images, wherein one channel is integrated with a four-step phase shift algorithm based on adaptive threshold After the smoothing algorithm of filtering and the improved least square method unwrapping algorithm are processed on the PC side, the image is converted into a transparent image, and the contour of the defect is clearly visible. Accurately map fusion and registration according to the resolution of the CCD camera and the distance ratio of the optical path to achieve fast defect visual detection with precise positioning.

(2), the present invention overcomes the shortcomings of complex optical path, high cost and low precision. The key is to realize intuitive and precise positioning of defects, and directly realize fast visual detection of defect preparation online, which provides structural detection, health management and life expectancy of composite materials. It is estimated to make a breakthrough contribution, especially when detecting large-area objects in practical applications, the system's advantages are particularly prominent.

Description of drawings

Fig. 1 is a schematic diagram of the laser shearing speckle interference defect detection system based on image registration and fusion of the present invention;

Fig. 2 is a plan view of the laser shearing speckle interference defect detection system based on image registration and fusion of the present invention;

Figure 3 is the original image of the surface of the object;

Fig. 4 is the image after the phase difference image is processed through adaptive threshold filtering;

Fig. 5 is the image processed by the unwrapping algorithm of the least squares method of the phase difference map;

Fig. 6 is the image after fusion and registration of Fig. 3 and Fig. 5 .

Detailed ways

Specific embodiments of the present invention will be described below in conjunction with the accompanying drawings, so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

Example

Fig. 1 is a schematic diagram of the laser shearing speckle interference defect detection system based on image registration and fusion of the present invention.

In this embodiment, as shown in Figure 1, the laser shearing speckle interference defect detection system based on image registration and fusion of the present invention includes: laser light source, beam expander, beam splitter, shearer, phase shifter device, image collector and PC with integrated image processing algorithm and phase shifter control algorithm;

In this embodiment, the laser light source is a helium-neon laser; the cutter includes a five-fifth beam splitter, a phase shift mirror and a shear mirror; the phase shifter is a piezoelectric ceramic phase shifter; the image collector uses a double CCD Camera, wherein, the CCD1 camera is used to collect the original image, and the CCD2 camera is used to collect the laser shearing scattered interference fringe image;

Fig. 2 is a plan view of the laser shearing speckle interference defect detection system based on image registration and fusion according to the present invention.

In this embodiment, the object to be measured is a circular waxed layer with a diameter of 10mm, 20mm, 30mm, 50mm and a rectangular waxed layer of 10x10mm, 10x20mm, 10x30mm. The waxed layer is used to simulate the peeling off of multilayer composite materials. Adhesive defects, the size of the measured object is 500mmx500mm multi-layer heterogeneous film composite material.

When the measured object 2 is at normal temperature, the laser light source 3 irradiates the laser beam to the surface of the measured object 2 after being expanded by the beam expander 4, and then the reflected light from the surface of the measured object 2 passes through the beam splitter 6 to make the light Divided into two beams of light with the same light energy, one of which is directly recorded by the CCD1 camera to obtain the original image, as shown in Figure 3; The mirror 5 divides this beam of light into two beams of equal light energy, and then respectively enters the phase shift mirror 1 and the shear mirror 7 connected to the phase shifter, and the phase shift mirror 1 is controlled by the phase shifter. The shearing amount is adjusted by the shearing mirror 7, so that the surface image of the object is formed to interfere with the shearing image dislocated in a certain direction, and is recorded by the CCD2 camera to obtain four images of the surface of the measured object at normal temperature with known Phase-shift information laser shear scattered class interference fringe image;

When the measured object 2 is under thermal loading, after the laser light source 3 is expanded by the beam expander 4, the laser light is irradiated to the surface of the measured object 2, and then the reflected light on the surface of the measured object 2 passes through the beam splitter 6, so that The light is divided into two beams of light with the same light energy, one of which is directly recorded by the CCD1 camera to obtain the original image; The light is divided into two beams of light with the same light energy, and then respectively enter the phase shift mirror 1 and the shear mirror 7 connected to the phase shifter, and the phase shift of the phase shift mirror 1 is controlled by the phase shifter, and the phase shift mirror 1 is controlled by the phase shifter. The reflector 7 adjusts the shearing amount to form an image of the surface of the object to interfere with the shearing image dislocated in a certain direction, and is recorded by the CCD2 camera to obtain four images with known phase shift information on the surface of the measured object under thermal loading. Laser shear scattered interference fringe image;

The dual CCD cameras transmit all the ten images obtained in the two states to the PC, and the PC sends instructions to the piezoelectric ceramic phase shifter, so that the control driving voltage starts from 40v, and the phase changes by π/2 every 4v, Therefore, under the precise control of the phase shifter control algorithm, the piezoelectric ceramic phase shifter produces four known phase shifts of 0, 90°, 180°, and 270°. It is known that the sheared speckle image can be expressed by Equation (1.1), where I is the light intensity distribution of the speckle pattern on the CCD; where I ₀ is the background light intensity. μ is the modulation amplitude of the speckle pattern. is the random phase angle.

By performing a four-step phase shift on the sheared speckle pattern represented by Equation 1.1, the following four speckle patterns can be generated:

The four-step phase shift algorithm increases by π/2 in each step, and the above four sheared speckle patterns can be generated. , phase It can be determined by Equation 1.3, and the image after thermal loading can be obtained by repeating the above four-step phase shift algorithm to obtain Equation 1.4,

By doing numerical difference, that is, subtracting Equation 1.3 from Equation 1.4, you can get the phase difference Δ caused by the deformation of the measured object, and then pass the phase difference image through the image processing algorithm that comes with the PC: adaptive threshold filtering and least squares method The unwrapping algorithm is processed sequentially to obtain the phase difference image of the laser shear discrete interference fringe image that directly reflects the surface deformation and displacement gradient of the measured object. Among them, the image after adaptive threshold filtering is shown in Figure 4. The image processed by the unwrapping algorithm of the least squares method is shown in Figure 5;

Finally, randomly select an original image collected by CCD1, that is, Figure 3, and the phase difference image after the above processing, that is, Figure 5, and perform registration and fusion according to the ratio calculation of the CCD resolution optical system and the shear amount to obtain the image 6, so as to realize the precise visual positioning of defect detection.

Although the illustrative specific embodiments of the present invention have been described above, so that those skilled in the art can understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, As long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are included in the protection list.

Claims (3)

1. a kind of laser speckle-shearing interferometry defect detecting system based on image registration and fusion, which is characterized in that including：Swash Radiant, beam expanding lens, beam splitter, clipper, phase-shifter, image acquisition device and integrated image processing algorithm and phase-shifter control are calculated The PC machine of method；

The clipper includes five or five beam splitters, phase shift reflection mirror and shearing speculum；

The image acquisition device is used using double CCD cameras, wherein CCD1 cameras for acquiring original image, CCD2 cameras Class's interference fringe image is dissipated in acquisition laser shearing；

Testee is under normal temperature state, and laser light source is after beam expanding lens expands, by the surface of laser irradiation to testee, Light is set to be divided into the two-beam of mutually same light energy, wherein light beam by beam splitter the reflected light on testee surface again It is directly recorded by CCD1 cameras, obtains original image image；Another light beam enters five or five beam splitters of clipper, five or five beam splitting This Shu Guang is divided into the two-beam of same light energy by mirror, then has respectively entered phase shift reflection mirror and the shearing reflection of connection phase-shifter Mirror, by phase-shifter control phase shift reflection mirror phase shift, by shear mirror adjust shearing displacement, to formed body surface image and Interfered from the clip image to misplace in certain direction, and recorded by CCD2 cameras, obtains measured object table under normal temperature state There is four width in face the laser shearing of known phase shift information to dissipate class's interference fringe image；

Testee is under hot stress state, and laser light source also passes through after beam expanding lens expands, by laser irradiation to testee Surface, then by the reflected light on testee surface by beam splitter, light is made to be divided into the two-beam of mutually same light energy, wherein Light beam is directly recorded by CCD1 cameras, obtains original image；Another light beam enters five or five beam splitters of clipper, five or five points This Shu Guang is divided into the two-beam of same light energy by Shu Jing, then is had respectively entered the phase shift reflection mirror of connection phase-shifter and sheared anti- Mirror is penetrated, controlling phase shift reflection mirror by phase-shifter generates micro-displacement to reach phase shift, adjusts and shears by shear mirror Amount to form body surface image and be interfered from the clip image to misplace in certain direction, and is remembered by CCD2 cameras There is the laser shearing of known phase shift information to dissipate class's interference fringe picture for record, four width for obtaining measured object surface under hot stress state Picture；

Double CCD cameras all send the eight width images obtained under two states to PC machine respectively, and PC machine passes through included phase It moves device control algolithm and accurately controls phase-shifter four known phase shifts of generation, normal temperature state is extracted by four-step phase-shifting algorithm and heat adds The phase diagram that the laser shearing under latter two state dissipates class's interference fringe image is carried, numerical difference is then done and obtains phase difference image, It is handled by carrying out the unwrapping algorithm of adaptive threshold filter and least square method to phase difference image, is directly reacted again The laser shearing of measured object surface deformation displacement gradient dissipates the phase difference image of class's interference fringe image, finally selects a width at random By the original image and above-mentioned phase difference image of CCD1 acquisitions according to CCD resolution ratio light path system and the scale operation of shearing displacement It is registrated, merged, realize the precise visualizationization positioning of defects detection.

2. the laser speckle-shearing interferometry defect detecting system according to claim 1 based on image registration and fusion, It is characterized in that, the image processing algorithm carried in the PC machine includes that the unpacking of adaptive threshold filter and least square method is calculated Method.

3. the laser speckle-shearing interferometry defect detecting system according to claim 1 based on image registration and fusion, Be characterized in that, phase-shifter control algolithm control phase-shifter generate four known phase shift values be 0,90 °, 180 °, 270.