Defect detection method based on laser measurement, and use

Abstract

A defect detection method based on laser measurement, which has a simple structure, achieves low cost and is convenient to use, and comprises: obtaining a detection device, wherein the device comprises a laser (1), a first cylindrical lens unit (2), a second cylindrical lens unit (3), a marking unit (4), an operation unit (5), a photoelectric probe (6), and a product conveyor belt (7), and using the first cylindrical lens unit (2) to convert point light emitted by the laser (1) into linear light, wherein the linear light is parallel light; obtaining a product (8) under test, using the product conveyor belt (7) to convey the product (8) under test for detection, using the product conveyor belt (7) to limit the product under test, and enabling the linear light to cover an area under test on the product under test for detection; and performing detection from the time when the linear light illuminates the area under test to the time when the linear light moves beyond the area under test.

Description

A defect detection method based on laser measurement and its application Technical Field

[0001] The present invention belongs to the field of laser measuring instruments, and specifically relates to a defect detection method based on laser measurement and its application. Background Art

[0002] Non-destructive defect detection is an indispensable part of industrial production. Optical-based defect detection methods are becoming increasingly popular. However, conventional optical detection methods, which are performed through machine learning or neural network algorithms, require training data. A large number of small and medium-sized enterprises in the industry, such as mobile phone screen protector companies, do not have training data and find it difficult to apply them directly.

[0003] Based on laser testing of the quality of mobile phone screen protector products, existing technologies include the following:

[0004] CN116465332A discloses a method for detecting the flatness of a mobile phone display screen protective film, comprising the following steps: S1: transporting the mobile phone display screen protective film, wherein the mobile phone display screen protective film is transported to the bottom of a CCD camera fixing plate via a conveyor belt on a detection table, and a CCD camera disposed below the CCD camera fixing plate photographs and identifies the mobile phone display screen protective film, and simultaneously controls the conveyor belt via the signal from the CCD camera photographing, so that the conveyor belt conveys a fixed distance. The above technical solution is used for detecting mobile phone display screen protective films on an assembly line, wherein the mobile phone display screen protective film can be clamped by a clamping assembly to prevent the mobile phone display screen protective film from shaking during the detection process, thereby improving the detection accuracy, wherein the upper and lower clamping seats in the clamping assembly can be opened, and the mobile phone display screen protective film is detected via a light emitter and a photosensitive plate inside the detection frame. The problem with this technical solution is that it requires taking photos and then processing the photos, which is slow and requires high hardware performance of the image processing equipment, and requires taking photos one by one by first clamping the products and then releasing them, which affects the assembly line speed.

[0005] CN114659454B discloses a device for detecting the thickness of a mobile phone protective film, comprising a base, a rotating clamping mechanism, and a detecting mechanism. The rotating clamping mechanism comprises a main shaft rotatably connected to the base, the end of the main shaft being fixedly connected to a rotating disk, the side of the rotating disk close to the base being provided with rotating heads evenly distributed around the axis of the main shaft, the rotating heads being rotatably connected to an end of a first rotating plate close to the main shaft, and the end of the first rotating plate being provided with a suction head away from the main shaft. The detecting mechanism is disposed on the side of the rotating disk away from the base, comprising a rotating seat fixedly connected to the rotating disk, the end of the rotating seat being rotatably connected to a second rotating plate coplanar with the first rotating plate. During operation, the entire device of the above invention requires an operator to constantly insert or remove the protective film, resulting in a low degree of automation. Furthermore, the device can only measure the thickness of the mobile phone protective film and is unable to reflect other problems with the mobile phone protective film.

[0006] CN112902882A discloses a device for detecting the flatness of mobile phone protective films. The device comprises a laser, a beam splitter, a first plane mirror, a second plane mirror, and a CCD imaging system. Based on the principle of a Michelson interferometer, the device detects the flatness of mobile phone protective films. Specifically, if the interference fringes obtained by the CCD imaging system are standard circular, the mobile phone film to be tested is flat; if the interference fringes are non-standard circular, the mobile phone film to be tested is uneven. While the device has a detection accuracy exceeding 40nm, manual determination of whether the interference fringes are non-standard circular is required, resulting in a low degree of automation. Furthermore, the device can only detect thickness and does not simultaneously detect defects other than thickness.

[0007] Therefore, a defect detection method with wide adaptability and easy application is needed to solve the problem of product defect detection.

[0008] Summary of the Invention

[0009] In order to solve the above technical problems existing in the prior art, the present invention provides a defect detection method based on laser measurement with simple structure, low cost and easy use, comprising the following steps:

[0010] S1 obtains a detection device, wherein the device includes a laser, a first cylindrical lens unit, a second cylindrical lens unit, a marking unit, a computing unit, a photoelectric probe, and a product conveyor belt;

[0011] Using the laser to emit a laser beam to illuminate the first cylindrical lens unit;

[0012] Using the first cylindrical lens unit, the point light emitted by the laser is converted into a line light; the line light is parallel light;

[0013] S2: Obtain a product to be tested, wherein the product to be tested has a test area on it, the test area is in the form of a sheet, and the design thickness of any point on the sheet-shaped test area is the same, and the surface roughness of the test area is much smaller than the wavelength of the laser emitted by the laser;

[0014] The product conveyor belt is used to convey the product to be tested for testing, and the product conveyor belt is used to limit the product to be tested, and the relative positions of the laser and the first cylindrical lens unit and the area to be tested are adjusted so that the area covered by the line light does not exceed the area to be tested;

[0015] Using the line light to illuminate the area to be measured, and obtaining reflected light of the line light;

[0016] The linear direction of the line light is not parallel to the running direction of the product conveyor belt; the product to be tested is moved by the product conveyor belt so that the line light covers the area to be tested on the product to be tested;

[0017] S3: the detection starts from when the line light can irradiate the area to be tested and ends when the line light irradiates outside the area to be tested;

[0018] When the detection starts, the laser emits a laser beam with variable light intensity according to a preset rule, and the variable light intensity means that the light intensity changes with time according to the preset rule;

[0019] When there is no defect in the area to be measured, the reflected light is also a line light, and the second cylindrical lens unit is used to convert the reflected light into a point light to obtain a reflected point light;

[0020] Using a photoelectric probe to obtain the reflected point light, and output an electrical signal to a computing unit;

[0021] The computing unit is used to process the intensity of the electrical signal, set a threshold, and determine whether the electrical signal is consistent with a preset rule. If the difference between the electrical signal and the preset rule is greater than the threshold, there is a defect in the area to be tested corresponding to the electrical signal, and the marking unit is used to mark the defective product to be tested.

[0022] Preferably, in step S3, the variable intensity laser beam is a laser beam whose intensity does not change with time;

[0023] In step S3, determining whether the electrical signal is consistent with a preset rule includes:

[0024] After the detection starts, the light intensity reflected by the electrical signal collected for the first time is recorded as the initial light intensity I1. The light intensity It transmitted by the photoelectric probe is collected every 1 ms using the computing unit and compared with the initial light intensity I1. When the difference between the light intensity It and the light intensity I1 is greater than the set threshold, it is considered that a defect exists.

[0025] Preferably, in step S3, the variable intensity laser beam is a laser beam whose intensity changes continuously with time;

[0026] In step S3, determining whether the electrical signal is consistent with a preset rule includes:

[0027] After the detection is completed, the computing unit is used to collect the light intensity It transmitted by the photoelectric probe every 1ms until the detection is completed. The computing unit is used to compare whether the change pattern of It is the same as the pattern of continuous change of the light intensity of the laser beam over time. If the degree of difference is greater than the set threshold, it is considered that there is a defect.

[0028] Preferably, in step S3, the laser includes n lasers capable of emitting lasers of different wavelengths.

[0029] Preferably, the product conveyor belt is configured to be height-adjustable.

[0030] The present invention also provides an application of a defect detection method based on laser measurement in the detection of mobile phone films, characterized in that the product to be tested is a mobile phone film, so for mobile phones of the same model, the width of the product to be tested is consistent, and the detection of products to be tested of different thicknesses can be achieved by adjusting the height of the product conveyor belt without adjusting the position of any of the laser, the first cylindrical lens unit, the second cylindrical lens unit, and the photoelectric probe.

[0031] Beneficial effects of the present invention:

[0032] The device of the present invention is simple, and the operation unit can be made of low-cost components such as a single-chip microcomputer, which is convenient for integration with an existing production line and has low modification and upgrading costs.

[0033] The present invention requires little computation and does not require a large amount of existing data for model training.

[0034] The present invention has wide adaptability and is applicable to all kinds of flat surfaces. When the present invention is applied to mobile phone films, the adjustment of the device can be simplified by taking advantage of the relatively fixed width of the mobile phone films.

[0035] The present invention can be adapted to automated detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the specific embodiments or the description of the prior art. Hereinafter, some specific embodiments of the present invention will be described in detail in an illustrative and non-limiting manner with reference to the drawings. The same reference numerals in the drawings indicate the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0037] FIG1 is a schematic structural diagram of the device used in the present invention.

[0038] Figure 2 is a schematic diagram of an embodiment of equipment construction.

[0039] FIG3 is a schematic diagram showing the relationship between the product to be tested and the area to be tested when the product to be tested is a mobile phone film. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0041] As shown in Figure 1, the detection device used in the present invention is described as follows. The device includes: a laser 1, a first cylindrical lens unit 2, a second cylindrical lens unit 3, a marking unit 4, an operation unit 5, a photoelectric probe 6, a product conveyor belt 7, and a product to be tested 8. 21 is a line light generated by the first cylindrical lens unit; the line light can be controlled into parallel light through existing technology.

[0042] To save costs, the present invention uses only one laser. The light emitted by the laser passes through the first cylindrical lens unit 2 to form a line light 21. After being reflected by the product to be tested, the line light 21 can be converged into a point light by the second cylindrical lens unit and enter the photoelectric probe, which converts the optical information into electrical information for calculation and processing by the calculation unit 5.

[0043] The first cylindrical lens unit and the second cylindrical lens unit can select different cylindrical lenses or cylindrical lens arrays according to actual conditions. By adjusting the angles of the first cylindrical lens unit and the second cylindrical lens unit, the point light can be converted into line light and then into point light. Therefore, the reflected light can be collected through a photoelectric probe, saving costs.

[0044] The intensity of the light irradiated onto the product to be tested changes continuously according to a certain rule. After the light is reflected by the product to be tested, the light intensity received by the photoelectric probe will also change continuously according to the same normal rule. When the mobile phone film of the product to be tested has defects such as thickness changes, bubbles, dents, cracks or stains, the refraction, reflection or scattering of the line light 21 caused by the defect will cause the intensity of the light that should have entered the photoelectric probe through the second cylindrical lens unit to suddenly decrease or increase, thereby causing the change in light intensity received by the photoelectric probe to be different from the normal continuous change. The calculation unit calculates this difference. When the difference exceeds the set threshold, it can be considered that a defective product has been identified. At this time, the calculation unit sends a signal to the marking unit, and the marking unit marks the defective area to be tested.

[0045] When there is no obvious defect in the area to be measured, the reflected light is also a line light, and the second cylindrical lens unit is used to convert the reflected light into a point light to obtain a reflected point light;

[0046] Using a photoelectric probe to obtain the reflected point light, and output an electrical signal to a computing unit;

[0047] The computing unit is used to process the intensity of the electrical signal, set a threshold, and determine whether the electrical signal changes according to a preset rule. If the difference between the change of the electrical signal and the change of the preset rule is greater than the threshold, then there is a defect in the area to be tested corresponding to the above electrical signal, and the marking unit is used to mark the defective area to be tested.

[0048] Example 1:

[0049] The product to be tested in this embodiment is a mobile phone film, and the light intensity of the light irradiated onto the product to be tested is a fixed value.

[0050] As shown in FIG3 , the mobile phone film is a rectangle with vertices ABCD, and its length and width are L and W respectively. The width w of the rounded corners of the mobile phone film is obtained, and the area abcd outside the edge of the rectangular mobile phone film is the area to be tested on the mobile phone film.

[0051] By adjusting the relative positions of the laser and the first cylindrical lens unit and the area to be measured, the width of the area covered by the line light is made to be bd. By adjusting the positions of the second cylindrical lens unit and the photoelectric probe, the line light reflected by the product to be measured is converted into point light, and the photoelectric probe is used to collect the light intensity of the point light.

[0052] The mobile phone film is controlled by a conveyor belt to move rightward perpendicular to the direction of the line light. When the line light irradiates the bd line, the detection starts; the light intensity fed back to the calculation unit by the photoelectric probe is I1.

[0053] As the mobile phone film moves to the right, the computing unit collects light intensity It every 1 ms and compares it with the initial light intensity I1. When the difference between the light intensity It and the light intensity I1 is greater than the set threshold, it is considered that there is a defect. The defective mobile phone film is marked by the marking unit, and the detection ends.

[0054] When the line light moves along with the mobile phone film, if the difference between the light intensity It and the light intensity I1 does not exceed the set threshold value during the process of the line light scanning the rectangle abcd, the detection ends when the line light scans the ac line, and no defects are detected in the mobile phone film;

[0055] The threshold value is set manually before detection, and the threshold value can be determined by the following method: using defective products that have been detected in the same batch of products for testing, the defective products preferably include common defects such as cracks, bubbles, dents, stains, etc., detecting the defective products using the above method, recording the absolute difference between the light intensity at the defective part of the defective product and the initial light intensity, and setting the threshold value based on the absolute difference.

[0056] Example 2

[0057] Based on the fact that the relative positions of the laser, the first cylindrical lens unit, the second cylindrical lens unit, and the photoelectric probe have been determined in Example 1, and the position of any one of the laser, the first cylindrical lens unit, the second cylindrical lens unit, and the photoelectric probe relative to the surface of the product to be tested in Example 1.

[0058] The product conveyor belt is set to be height-adjustable so that when different batches of products have different thicknesses, the height of the product conveyor belt can be adjusted so that the position of the surface of the next batch of products relative to any one of the laser, the first column lens unit, the second column lens unit, and the photoelectric probe in Example 1 is the same as in Example 1, thereby eliminating the need to adjust the relative positions of the laser, the first column lens unit, the second column lens unit, and the photoelectric probe, thereby increasing convenience.

[0059] Example 3

[0060] On the basis of Example 1, the product to be tested is replaced with a flat plastic sheet with uniform color and isotropy. In order to improve the detection accuracy, the above detection process is repeated several times using a laser emitting lasers of different wavelengths to overcome the problem that the pigment on the plastic sheet interferes with some specific wavelengths of laser light.

[0061] Example 4

[0062] The difference from Example 1 is that the light intensity of the light irradiated onto the product to be tested is set to change according to a certain rule, such as being set to a value that changes periodically in a sinusoidal wave.

[0063] The advantage of setting the light intensity to change regularly is that if the light intensity is the same, the value at the beginning of the test needs to be obtained as If defects in the edge of the area to be tested have no impact on the product, it is easy to report an error during testing;

[0064] Accordingly, this embodiment does not need to use the value at the beginning of the detection as Instead, the computing unit is used to process the strength of the electrical signal to determine whether the electrical signal changes according to a preset rule. If the difference between the change of the electrical signal and the change of the preset rule is greater than the threshold, then the area with a large difference in the electrical signal is defective, and the marking unit is used to mark the defective area to be tested.

[0065] The above description is only part of the specific implementation methods of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the art within the technical scope disclosed in the present invention should be covered by the protection scope of the present invention.

Claims

1. A defect detection method based on laser measurement, characterized in that: The following steps are involved: S1 obtains a detection device, wherein the device includes a laser, a first cylindrical lens unit, a second cylindrical lens unit, a marking unit, a computing unit, a photoelectric probe, and a product conveyor belt; Using the laser to emit a laser beam to illuminate the first cylindrical lens unit; Using the first cylindrical lens unit, the point light emitted by the laser is converted into line light; the line light is parallel light; S2: obtaining a product to be tested, wherein there is a test area on the product to be tested, the test area is in the form of a sheet, and the design thickness of any point on the sheet-shaped test area is the same, and the surface roughness of the test area is much smaller than the wavelength of the laser emitted by the laser; The product conveyor belt is used to convey the product to be tested for testing, and the product conveyor belt is used to limit the product to be tested, and the relative positions of the laser and the first cylindrical lens unit and the area to be tested are adjusted so that the area covered by the line light does not exceed the area to be tested; Using the line light to illuminate the area to be measured, and obtaining reflected light of the line light; The linear direction of the line light is not parallel to the running direction of the product conveyor belt; the product to be tested is moved by the product conveyor belt so that the line light covers the area to be tested on the product to be tested; S3, the detection starts from when the line light can irradiate the area to be tested and ends when the line light irradiates outside the area to be tested; When the detection starts, the laser emits a laser beam with variable light intensity according to a preset rule, and the variable light intensity means that the light intensity changes with time according to the preset rule; When there is no defect in the area to be tested, the reflected light is also line light, and the second cylindrical lens unit is used to convert the reflected light into point light to obtain reflected point light; Using a photoelectric probe to obtain the reflected point light, and output an electrical signal to a computing unit; The computing unit is used to process the strength of the electrical signal, a threshold is set, and it is determined whether the electrical signal is consistent with a preset rule. If the difference between the electrical signal and the preset rule is greater than the threshold, there is a defect in the test area corresponding to the electrical signal, and the marking unit is used to mark the defective product to be tested.

2. A defect detection method based on laser measurement as claimed in claim 1, characterized in that: In step S3, the variable intensity laser beam is: a laser beam whose intensity does not change with time; In step S3, determining whether the electrical signal is consistent with a preset rule includes: After the detection starts, the light intensity reflected by the electrical signal collected for the first time is recorded as the initial light intensity I1. The light intensity It transmitted by the photoelectric probe is collected every 1 ms using the computing unit and compared with the initial light intensity I1. When the difference between the light intensity It and the light intensity I1 is greater than the set threshold, it is considered that a defect exists.

3. A defect detection method based on laser measurement as claimed in claim 1, characterized in that: In step S3, the variable intensity laser beam is: a laser beam whose intensity changes continuously with time; In step S3, determining whether the electrical signal is consistent with a preset rule includes: After the detection is completed, the computing unit is used to collect the light intensity It transmitted by the photoelectric probe every 1ms until the detection is completed. The computing unit is used to compare whether the change pattern of It is the same as the pattern of continuous change of the light intensity of the laser beam over time. If the difference is greater than the set threshold, it is considered that there is a defect.

4. A defect detection method based on laser measurement as claimed in claim 1, characterized in that: In the step S3, the laser includes n lasers capable of emitting lasers of different wavelengths.

5. A defect detection method based on laser measurement as claimed in any one of claims 2 to 4, characterized in that: The product conveyor belt is arranged to be height-adjustable.

6. The application of a defect detection method based on laser measurement in mobile phone film detection as claimed in claim 5, characterized in that: The product to be tested is a mobile phone film, so for mobile phones of the same model, the width of the product to be tested is consistent, and the detection of products of different thicknesses can be achieved by adjusting the height of the product conveyor belt.

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