Insulating material defect detection method based on high-frequency laser reflected light signal analysis

Abstract

The invention is suitable for the technical field of insulation material detection, and provides an insulation material defect detection method based on laser reflected light signal analysis, the method adopts a high-frequency pulse laser as a light source, the high-frequency pulse laser is projected to the surface of a detected insulation material after collimation, beam splitting and focusing, and rapid scanning is realized through a two-dimensional galvanometer scanning system; a parabolic mirror is used for collecting reflected light signals and converting the reflected light signals into electric signals, and then detection of internal defects of the insulating material is achieved through signal processing, defect positioning and classification model analysis. According to the scheme, the detection sensitivity, speed and positioning precision can be improved, the defect type can be accurately recognized, non-contact detection is adopted, and the method is suitable for various scenes.

Description

Technical Field

[0001] This invention belongs to the field of insulation material testing technology, and particularly relates to a method for detecting defects in insulation materials based on high-frequency laser reflected light signal analysis. Background Technology

[0002] In fields such as power equipment and electronic devices, the integrity of insulation materials is crucial to the safe operation and service life of equipment. Therefore, insulation material testing technology has always been a key focus of the industry. With the development of related industries, the requirements for the accuracy, efficiency, and safety of insulation material testing are constantly increasing, and various testing technologies are continuously developing and improving.

[0003] Currently, traditional methods for testing insulation materials include ultrasonic testing and X-ray testing. In recent years, laser testing technology has gained attention due to its advantages such as non-contact, high precision, and fast response, and has been applied in the field of insulation material testing.

[0004] However, ultrasonic testing is not sensitive to surface defects and requires a coupling agent, making it unsuitable for online testing; X-ray testing equipment is expensive and poses radiation safety hazards; existing laser testing methods suffer from weak signals, poor anti-interference capabilities, and difficulty in accurately distinguishing defect types when detecting minute defects inside insulating materials. In particular, for multi-layered insulating structures or insulating materials with uneven surfaces, improper optical path design can easily lead to distortion of reflected light signals, affecting testing accuracy. Summary of the Invention

[0005] The purpose of this invention is to provide a method for detecting defects in insulating materials based on high-frequency laser reflected light signal analysis, aiming to solve the technical problems existing in the prior art as identified in the background art.

[0006] This invention is implemented as follows: a method for detecting defects in insulating materials based on high-frequency laser reflected light signal analysis, the method comprising:

[0007] A high-frequency pulsed laser is used as the light source to output pulsed laser light. The laser beam is collimated by a collimating lens group to form a parallel beam with a diameter of D.

[0008] The resulting parallel beam is used as the main beam. Diffractive optical elements are used to divide the main beam into N sub-beams, forming a specific light and shadow pattern. The angular distribution of the sub-beams satisfies:

[0009] ;

[0010] In the formula, For DOE grating period, For the first The exit angle of the diffracted light;

[0011] The generated N sub-beams are focused onto different positions on the surface of the insulating material under test by a focusing lens array, forming a spot diameter of... The light spot array, through a two-dimensional galvanometer scanning system, enables rapid scanning of the measured area, with a scanning range of L×W;

[0012] After the focused sub-beam is irradiated onto the surface of the insulating material being tested, a reflected light signal is generated. A parabolic reflector is used to collect the reflected light signal and convert it into an electrical signal.

[0013] A digital lock-in amplifier is used to demodulate the converted electrical signal, extract the frequency components related to the defects, and determine the defect location using triangulation based on the position information of the light spot array and the changes in the reflected light signal. A defect classification model is then established to classify the identified defects.

[0014] The beneficial effects of this invention are:

[0015] This invention improves the detection sensitivity of minute defects inside insulating materials through high-frequency lasers and optimized optical path design; based on multi-beam parallel scanning and high-speed signal processing, it has rapid detection capabilities to meet the needs of industrial online inspection; employing triangulation algorithms and multi-beam cross measurement improves defect location accuracy and accurately determines the spatial position of defects; the classification model based on support vector machine (SVM) can effectively distinguish different types of defects and improve the defect type recognition rate; at the same time, the use of non-contact laser detection avoids damage to the tested material and is suitable for the inspection of insulating materials of various shapes and sizes. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the optical path system structure provided in an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] A method for detecting defects in insulating materials based on high-frequency laser reflected light signal analysis, the method comprising:

[0019] A high-frequency pulsed laser is used as the light source, outputting a pulsed laser with a wavelength of λ, a pulse width of τ, and a repetition frequency of f∈[10kHz,100MHz]. The laser beam is collimated by a collimating lens group to form a parallel beam with a diameter of D.

[0020] ;

[0021] In the formula, The focal length of the collimating lens. This is the divergence angle of the laser beam.

[0022] The resulting parallel beam is used as the main beam. Diffractive optical elements are used to divide the main beam into N sub-beams, forming a specific light and shadow pattern. The angular distribution of the sub-beams satisfies:

[0023] ;

[0024] In the formula, For DOE grating period, For the first The exit angle of the diffracted light;

[0025] The generated N sub-beams are focused onto different positions on the surface of the insulating material under test by a focusing lens array, forming a spot diameter of... The light spot array, through a two-dimensional galvanometer scanning system, enables rapid scanning of the measured area, with a scanning range of L×W;

[0026] ;

[0027] In the formula, The focal length of the focusing lens is used. A two-dimensional galvanometer scanning system is employed to achieve rapid scanning of the measured area, with a scanning speed of [missing information]. ;

[0028] After the focused sub-beam illuminates the surface of the insulating material under test, a reflected light signal is generated. This reflected light signal is collected by a parabolic mirror and converted into an electrical signal. The collection efficiency is [not specified]. satisfy:

[0029]

[0030] In the formula, Let be the radius of the central hole of the parabolic mirror. Let be the radius of the parabolic mirror. Angle of incidence;

[0031] The parabolic reflector converges the reflected light signal and reflects it to the photodetector. The photodetector converts the reflected light signal into an electrical signal, which is then transmitted to the signal processing module for processing.

[0032] Light and shadow design and defect identification methods:

[0033] Light and shadow pattern design: Specific light and shadow patterns, such as grid, radial, or checkerboard patterns, are designed using DOE (Design of Objects) to create an array of light spots with a spacing of Δx between adjacent sub-beams on the measured surface. The expression is:

[0034]

[0035] Reflected light signal analysis: The reflected light signal is converted into an electrical signal by a photodetector, and specific frequency components are extracted using lock-in amplification technology. For internal defects in insulating materials, the amplitude of the reflected light signal... and phase Changes occur, satisfying:

[0036] ;

[0037] In the formula, and This is the proportionality coefficient. For defect density, This represents the defect volume.

[0038] Defect location algorithm: Based on the position information of the light spot array and the changes in the reflected light signal, the triangulation method is used to determine the defect location. For a defect point P(x,y,z) in three-dimensional space, the following conditions are met:

[0039] ;

[0040] In the formula, Let i be the position of the i-th light spot. For the optical path length when there are no defects, This is the change in optical path length. At the speed of light, This is a time delay.

[0041] A digital lock-in amplifier is used to demodulate the converted electrical signal, extract the frequency components related to the defects, and determine the defect location using triangulation based on the position information of the light spot array and the changes in the reflected light signal. A defect classification model is then established to classify the identified defects.

[0042] The converted electrical signal is demodulated using a digital lock-in amplifier, and the demodulated output is... satisfy:

[0043] ;

[0044] In the formula, For input signal, For reference frequency, As a reference phase, The time for integration.

[0045] The defect classification model is based on a support vector machine (SVM), with input feature vectors. :

[0046] ;

[0047] Output defect type y:

[0048] y∈{no defects, surface cracks, internal pores, delamination defects};

[0049] The classification decision function is:

[0050] ;

[0051] In the formula, For Lagrange multipliers, For training sample labels, For kernel function, This is a bias term.

[0052] like Figure 1 As shown, a high-frequency pulsed laser is located on the far left of the optical path system, and its emitted laser beam propagates into the adjacent collimating lens group. The collimating lens group processes the diverging laser beam into a parallel beam before it enters the diffractive optical element (DOE). In the DOE, the main laser beam is split into N sub-beams, which are dispersed at a certain angle and then enter the focusing lens array together. Each lens in the focusing lens array corresponds to one sub-beam, focusing it and projecting it perpendicularly onto the surface of the insulating material under test. A two-dimensional galvanometer scanning system is installed beside the optical path between the focusing lens array and the insulating material under test, rapidly oscillating to change the scanning position and path of the sub-beams on the insulating material surface. When the sub-beams illuminate the insulating material surface, the resulting reflected light signal is collected by a parabolic mirror. The parabolic mirror converges the reflected light signal and reflects it to a photodetector. The photodetector converts the optical signal into an electrical signal, which is transmitted through a circuit to the signal processing module for subsequent analysis and processing.

[0053] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0054] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

[0055] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting defects in insulating materials based on high-frequency laser reflected light signal analysis, characterized in that, The method includes: A high-frequency pulsed laser is used as the light source to output pulsed laser light. The laser beam is collimated by a collimating lens group to form a parallel beam with a diameter of D. The resulting parallel beam is used as the main beam. Diffractive optical elements are used to divide the main beam into N sub-beams, forming a specific light and shadow pattern. The angular distribution of the sub-beams satisfies: ； In the formula, For DOE grating period, For the first The exit angle of the diffracted light; The generated N sub-beams are focused onto different positions on the surface of the insulating material under test by a focusing lens array, forming a spot diameter of... The light spot array, through a two-dimensional galvanometer scanning system, enables rapid scanning of the measured area, with a scanning range of L×W; After the focused sub-beam is irradiated onto the surface of the insulating material being tested, a reflected light signal is generated. A parabolic reflector is used to collect the reflected light signal and convert it into an electrical signal. A digital lock-in amplifier is used to demodulate the converted electrical signal, extract the frequency components related to the defects, and determine the defect location using triangulation based on the position information of the light spot array and the changes in the reflected light signal. A defect classification model is then established to classify the identified defects.

2. The method according to claim 1, characterized in that, The N sub-beams formed are spaced apart on the surface being measured. The light spot array is expressed as: ； in, For the focal length of the focusing lens, λ is the wavelength of the pulsed laser.

3. The method according to claim 2, characterized in that, For internal defects in insulating materials, the amplitude of the reflected light signal and phase Changes occur, satisfying: ； In the formula, and This is the proportionality coefficient. For defect density, This represents the defect volume.

4. The method according to claim 1, characterized in that, The laser beam output by the high-frequency pulsed laser is a pulsed laser with a pulse width of τ and a repetition frequency of f∈[10kHz,100MHz].

5. The method according to claim 1, characterized in that, The parabolic reflector converges the reflected light signal and reflects it to the photodetector. The photodetector converts the reflected light signal into an electrical signal, which is then transmitted to the signal processing module for processing.

6. The method according to claim 1, characterized in that, The triangulation method determines the defect location. For a defect point P(x,y,z) in three-dimensional space, the following conditions are met: ； In the formula, Let i be the position of the i-th light spot. The optical path length when there are no defects. This is the change in optical path length. At the speed of light, This is a time delay.

7. The method according to claim 1, characterized in that, The converted electrical signal is demodulated using a digital lock-in amplifier, and the demodulated output is... satisfy: ； In the formula, For input signal, For reference frequency, As a reference phase, The time for integration.

8. The method according to claim 1, characterized in that, The defect classification model is input with feature vectors. : ； Output defect type y: y∈{no defects, surface cracks, internal pores, delamination defects}; The classification decision function is: ； In the formula, For Lagrange multipliers, For training sample labels, For kernel function, This is a bias term.

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