Optical detection device and detection method for element surface liquid

Abstract

The invention discloses an optical detection device and detection method for element surface liquid, and the optical detection device comprises a stripe projection light source, a first telecentric lens, a middle imaging surface, a detection station, a second telecentric lens and a black and white camera, the first telecentric lens is used for focusing the stripe light, and the middle imaging surface is used for projecting a stripe image after focusing the stripe light; the second telecentric lens is used for focusing the stripe light after the stripe light is reflected by the element to be measured; and the black-and-white camera is used for focusing the stripe light to generate a stripe image. According to the invention, the high-contrast fringes are projected on the middle imaging surface, the high-contrast fringes are reflected by the element to be measured and then are imaged by the imaging system, and then the global optical transfer function is introduced to represent the mapping relation between the MTF and the surface liquid in real time, so that the non-contact real-time monitoring of the presence or absence of the liquid on the surface of the workpiece and the distribution area can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and in particular relates to an optical detection device and a detection method for liquid on the surface of a component. Background Art

[0002] Detection of transparent liquids (such as glue, water stains, films, etc.) on the surface of components is a major challenge. When using an optical system perpendicular to the surface of the component to be tested, the light will directly pass through the transparent liquid, making it extremely difficult to detect whether there is transparent liquid on the surface of the component to be tested and the distribution of the transparent liquid. Light, as a non-contact sensing medium, can feedback its illumination information, and its optical path characteristics have excellent accuracy. Therefore, sensing systems using light as a sensing medium are widely used in the field of ultra-precision machining.

[0003] The Chinese patent with publication number CN 116379974 B discloses a device and method for detecting the surface characteristics of optical components using a multi-wavelength light source. The device uses a scattering detection module to collect scattering signals from each sampling point to achieve high-sensitivity detection of scattering signals. A light source with a specific wavelength is used to illuminate the optical component. The scattering signal reflects the characteristics of the optical component surface with respect to the incident wavelength, including two types of information: surface roughness and damage threshold. Multi-wavelength light source detection is based on scattering technology, has a complex optical structure, requires high-precision motion platform scanning, has low speed and high cost.

[0004] The Chinese patent with publication number CN111707221A discloses a surface roughness measurement method using multi-exposure scattered signal fusion. The system uses CCD to receive reflected light and scattered light from the surface of the laser incident optical element, collects images of different exposure times at the same position, and processes these images through a fusion algorithm to obtain the roughness value of the sample. The surface roughness measurement method using multi-exposure scattered signal fusion has a slow detection speed and cannot detect the impact of tiny defects.

[0005] At the same time, the current detection is mostly for roughness detection, and there is no accurate detection of transparent liquid on the surface of the component. Therefore, an optical detection device and detection method for liquid on the surface of the component are urgently needed. Summary of the invention

[0006] In order to solve the defects in the prior art, the present invention provides an optical detection device and a detection method for liquid on the surface of a component.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The first purpose of the present invention is to provide an optical detection device for liquid on the surface of a component, comprising an optical acquisition device, a calculation and processing module, and a comparison module. The output end of the optical acquisition device is electrically connected to the input end of the calculation and processing module, and the output end of the calculation and processing module is electrically connected to the input end of the comparison module. The optical acquisition device is used to collect a stripe image after the projected high-contrast stripe light is reflected by the component to be tested. The calculation and processing module calculates the system overall optical transfer function of the component to be tested based on the stripe image. The comparison module compares the system overall optical transfer function of the component to be tested with a preset system overall optical transfer function threshold to determine whether there is liquid on the surface of the original component to be tested.

[0009] Preferably, the optical collection device includes a stripe projection light source, a first telecentric lens, an intermediate imaging plane, a detection station, a second telecentric lens, and a black and white camera. The stripe projection light source, the first telecentric lens, and the intermediate imaging plane are arranged in sequence at 45° from top to bottom on the left side of the detection station, and the second telecentric lens and the black and white camera are arranged in sequence at 45° from bottom to top on the right side of the detection station. The stripe projection light source is used to project high-contrast stripe light, the first telecentric lens is used to focus the stripe light, and the intermediate imaging plane is used to project a stripe image after focusing the stripe light; the second telecentric lens is used to focus the stripe light after being reflected by the component to be measured; and the black and white camera is used to generate a stripe image after focusing the stripe light.

[0010] Preferably, the stripe projection light source includes a rear focal length adjustment seat, a grid angle adjustment seat, a stripe grid, a lens module, a light board and LED lamp beads, the light board is arranged on the rear focal length adjustment seat, the LED lamp beads are arranged on the light board and the imaging point of the LED lamp beads is at the aperture diaphragm of the first telecentric lens, the lens module is located on the light-emitting side of the LED lamp beads, and the stripe grid is arranged on the grid angle adjustment seat and is located on the light-emitting side of the lens module.

[0011] Preferably, the line width of the striped grid sheet is 0.05 mm, and the line spacing is 0.45 mm.

[0012] Preferably, the first telecentric lens has a magnification of 0.2-1.5 times, a nominal working distance of L1, an actual working distance of S1, a magnification of β1, an angle with the vertical direction of θ1, and a front end diameter of The interface at the image plane end matches the interface of the fringe projection light source 1, and the working distances match, so as to form a Kohler illumination optical path;

[0013] The second telecentric lens has a magnification of 0.2-1.5 times, a nominal working distance of L2, an actual working distance of S2, a magnification of β2, an angle with the vertical direction of θ2, and a front end diameter of The interface of the image plane matches the black and white camera, and the target surface and resolution match each other;

[0014] For clear imaging, S1+S2=L1+L2 is satisfied.

[0015] To form a virtual image, satisfy S1 <L1,S2<L2,

[0016] According to the law of reflection θ1=θ2, to avoid mechanical conflict, satisfy

[0017] The second object of the present invention is to provide an optical detection method for liquid on the surface of a component, comprising the following steps:

[0018] S1. Place a reflector on the detection station of the optical detection device as described in any one of claims 1 to 5. After the fringe projection light is projected through the reflector, a first system fringe image is obtained. The optical transfer function of the reflector surface is defined as 1. The MTF can be measured according to the calculation formula of the overall optical transfer function of the system. a and MTF b The product of is used to complete the calibration;

[0019] S2, placing the component to be tested on the detection station of the optical detection device as described in any one of claims 1-5, obtaining a second system fringe image after the fringe projection light is projected through the component to be tested, firstly dividing the fringe image into a plurality of preset small areas, each small area including two stripes, one black and one white, and using an MTF calculation algorithm to calculate the MTF value within each small area of ​​the second system fringe image according to the gray value of the fringe image, and then calculating the surface optical transfer function within each small area according to the overall optical transfer function formula of the system, and finally obtaining the surface optical transfer function value within the entire area of ​​the image;

[0020] S3, comparing the surface optical transfer function within each small area with a preset surface optical transfer function threshold, if the surface optical transfer function within the small area is smaller than the preset surface optical transfer function threshold, then mark these small areas on the surface of the component to be tested as having no liquid; if the surface optical transfer function within the small area is larger than the preset surface optical transfer function threshold, then mark these small areas on the surface of the component to be tested as having liquid; then use a mapping marking algorithm to mark each small area with or without liquid, so as to obtain whether there is liquid on the surface of the component to be tested and the distribution area of ​​the liquid;

[0021] MTF refers to the function of modulation as the spatial frequency changes. MTF is calculated by finding the contrast between the maximum brightness point and the minimum brightness point in the line pair. The MTF calculation algorithm is as follows:

[0022] MTF = (maximum brightness - minimum brightness) / (maximum brightness + minimum brightness)

[0023] The overall optical transfer function of the system is calculated as follows:

[0024] MTF 总 =MTF a .×STF×MTF b

[0025] Among them, MTF 总 is the overall optical transfer function of the system, MTF a MTF is the optical transfer function of the system composed of the fringe projection light source and the first telecentric lens. b is the optical transfer function of the system composed of the second telecentric lens and the black and white camera, and STF is the optical transfer function of the surface of the original under test.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention projects high-contrast stripes onto an intermediate imaging surface, which are then imaged by an imaging system after being reflected by the component to be tested. The global optical transfer function is then introduced to characterize the mapping relationship between MTF and surface liquid in real time, thereby realizing non-contact real-time monitoring of the presence and distribution area of ​​liquid on the workpiece surface.

[0028] The illumination structure used in the present invention is a Kohler illumination structure. The light source is high-brightness white light, and the illumination is uniform. No reflection of the light source beads will be produced at the image plane of the imaging system, so the contrast of the projection stripes is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of one of the present invention;

[0030] Figure 2 It is a schematic diagram of the structure of the stripe projection light source of the present invention;

[0031] Figure 3 The present invention is a schematic diagram of a Kohler illumination light path formed by combining a stripe projection light source and a first telecentric lens. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0033] In the description of the present invention, it should be understood that the terms "left" and "right" indicate directions or positional relationships based on the accompanying drawings. Figure 1The orientation or positional relationship shown is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] The present embodiment provides an optical detection device for liquid on the surface of a component, comprising an optical acquisition device, a calculation processing module, and a comparison module. The output end of the optical acquisition device is electrically connected to the input end of the calculation processing module, and the output end of the calculation processing module is electrically connected to the input end of the comparison module. The optical acquisition device is used to collect a stripe image after projecting high-contrast stripe light and reflecting from the component to be tested. The calculation processing module calculates the system overall optical transfer function of the component to be tested based on the stripe image. The comparison module compares the system overall optical transfer function of the component to be tested with a preset system overall optical transfer function threshold to determine whether there is liquid on the surface of the original component to be tested.

[0036] like Figure 1 As shown, the optical acquisition device includes a stripe projection light source 1, a first telecentric lens 2, an intermediate imaging surface 3, a detection station, a second telecentric lens 5, and a black-and-white camera 6. The stripe projection light source 1, the first telecentric lens 2, and the intermediate imaging surface 3 are sequentially arranged on the left side of the detection station at an angle of 45° from top to bottom, and the second telecentric lens 5 and the black-and-white camera 6 are sequentially arranged on the right side of the detection station at an angle of 45° from bottom to top. The stripe projection light source 1 is used to project high-contrast stripe light, the first telecentric lens 2 is used to focus the stripe light, and the intermediate imaging surface 3 is used to project the stripe light into a stripe image after focusing; the second telecentric lens 5 is used to focus the stripe light after being reflected by the component to be measured 4; the black-and-white camera 6 is used to generate a stripe image after focusing the stripe light.

[0037] like Figure 2As shown, the stripe projection light source 1 includes a rear focal length adjustment seat, a grid sheet angle adjustment seat, a stripe grid sheet 13, a lens module 12, a lamp board and an LED lamp bead 11, wherein the lamp board is arranged on the rear focal length adjustment seat, the LED lamp bead 11 is arranged on the lamp board and the imaging point of the LED lamp bead is at the aperture stop of the first telecentric lens 2, the lens module 12 is located on the light emitting side of the LED lamp bead 11, and the stripe grid sheet 13 is arranged on the grid sheet angle adjustment seat and on the light emitting side of the lens module 12. The line width of the stripe grid sheet 13 is 0.05 mm, and the line spacing is 0.45 mm.

[0038] like Figure 3 As shown, the stripe projection light source 1 and the first telecentric lens 2 are combined into a Kohler illumination optical path, the imaging point of the LED lamp bead 11 is at the aperture stop of the first telecentric lens 2, and the imaging point is then imaged by the rear lens of the first telecentric lens, and the light is evenly distributed on the middle imaging plane 3. Therefore, no matter the central point light source of the LED lamp bead or the edge point light source, the output after the Kohler illumination system is a uniform light beam, that is, the entire Kohler illumination system images the light source to infinity, and will not produce the reflection of the light bead of the light source at the imaging system image plane; and the stripe grid sheet 13 is imaged by the first telecentric lens 2. The imaging point is directly at the middle imaging plane 3. By adjusting the angle of the stripe grid sheet 13, the entire stripe grid sheet feature can be accurately focused, and the adjustment range of the stripe grid sheet is within 45 degrees.

[0039] In this embodiment, the magnification of the first telecentric lens is 0.2-1.5 times, the nominal working distance is L1, the actual working distance is S1, the magnification is β1, the angle with the vertical direction is θ1, and the front end diameter is The interface at the image plane end matches the interface of the fringe projection light source 1, and the working distances match, so as to form a Kohler illumination light path.

[0040] In this embodiment, the magnification of the second telecentric lens is 0.2-1.5 times, the nominal working distance is L2, the actual working distance is S2, the magnification is β2, the angle with the vertical direction is θ2, and the front end diameter is The interface on the image plane matches the black and white camera, and the target surface and resolution match each other.

[0041] For clear imaging, S1+S2=L1+L2 is satisfied.

[0042] To form a virtual image, satisfy S1 <L1,S2<L2,

[0043] According to the law of reflection θ1=θ2, to avoid mechanical conflict, satisfy

[0044] This embodiment also provides an optical detection method for liquid on the surface of a component, comprising the following steps:

[0045] S1. Place a reflector on the detection station of the optical detection device as described in any one of claims 1 to 5. After the fringe projection light is projected through the reflector, a first system fringe image is obtained. The optical transfer function of the reflector surface is defined as 1. The MTF can be measured according to the calculation formula of the overall optical transfer function of the system. a and MTF b The product of is used to complete the calibration;

[0046] S2, placing the component to be tested on the detection station of the optical detection device as described in any one of claims 1-5, obtaining a second system fringe image after the fringe projection light is projected through the component to be tested, firstly dividing the fringe image into a plurality of preset small areas, each small area including two stripes, one black and one white, and using an MTF calculation algorithm to calculate the MTF value within each small area of ​​the second system fringe image according to the gray value of the fringe image, and then calculating the surface optical transfer function within each small area according to the overall optical transfer function formula of the system, and finally obtaining the surface optical transfer function value within the entire area of ​​the image;

[0047] S3. Compare the surface optical transfer function within each small area with a preset surface optical transfer function threshold. If the surface optical transfer function within the small area is smaller than the preset surface optical transfer function threshold, mark these small areas on the surface of the component to be tested as having no liquid; if the surface optical transfer function within the small area is greater than the preset surface optical transfer function threshold, mark these small areas on the surface of the component to be tested as having liquid; then use a mapping marking algorithm to mark each small area with or without liquid, so as to obtain whether there is liquid on the surface of the component to be tested and the distribution area of ​​the liquid.

[0048] In this embodiment, when there is no liquid on the surface of the component to be tested, the optical transfer function value of the surface is approximately 0-0.4, and when there is liquid on the surface of the component to be tested, the optical transfer function value of the surface is approximately 0.6-1.

[0049] MTF is the abbreviation of Modulation Transfer Function in English, which means the function of modulation degree changing with spatial frequency. Spatial frequency is expressed in "line pairs per millimeter", (LP / mm), that is, how many line pairs there are in one millimeter of width. MTF is calculated by finding the contrast between the maximum brightness point and the minimum brightness point in the line pair. The MTF calculation algorithm is as follows:

[0050] MTF = (maximum brightness - minimum brightness) / (maximum brightness + minimum brightness).

[0051] The modulation degree is between 0 and 1. The larger the modulation degree, the greater the black-white contrast and the better the imaging effect.

[0052] The overall optical transfer function of the system is calculated as follows:

[0053] MTF 总 =MTF a .×STF×MTF b

[0054] Among them, MTF 总 is the overall optical transfer function of the system, MTF a MTF is the optical transfer function of the system composed of the fringe projection light source and the first telecentric lens. b is the optical transfer function of the system composed of the second telecentric lens and the black and white camera, and STF is the optical transfer function of the surface of the original under test.

[0055] In this embodiment, for any reflector, its surface transfer function STF can be expressed as:

[0056]

[0057] Among them, ^ represents the normalization of the physical quantity to the working wavelength λ, θ is the incident angle of the light on the surface, σ S is the surface irregularity, is the surface autocorrelation function, A is the specular reflection coefficient, and B is the surface scattering coefficient, which are expressed as

[0058]

[0059] A=1-B

[0060] Among them, σ M , σ H are the RMS values ​​of the surface medium and high frequency errors, respectively, M , l H are the correlation lengths of medium and high frequency errors on the surface, respectively. For a single-point diamond turning surface, l M =1mm, l H =0.01mm.

[0061] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An optical detection device for liquid on the surface of a component, characterized in that: The optical acquisition device comprises an optical collection device, a calculation processing module, and a comparison module. The output end of the optical collection device is electrically connected to the input end of the calculation processing module, and the output end of the calculation processing module is electrically connected to the input end of the comparison module. The optical collection device is used to collect a stripe image after the projected high-contrast stripe light is reflected by the component to be tested. The calculation processing module calculates the system overall optical transfer function of the component to be tested according to the stripe image. The comparison module compares the system overall optical transfer function of the component to be tested with a preset system overall optical transfer function threshold to determine whether there is liquid on the surface of the original component to be tested.

2. The optical detection device for liquid on the surface of a component according to claim 1, characterized in that: The optical acquisition device comprises a stripe projection light source (1), a first telecentric lens (2), an intermediate imaging surface (3), a detection station, a second telecentric lens (5), and a black-and-white camera (6). The stripe projection light source (1), the first telecentric lens (2), and the intermediate imaging surface (3) are arranged on the left side of the detection station at an angle of 45 degrees from top to bottom, and the second telecentric lens (5) and the black-and-white camera (6) are arranged on the right side of the detection station at an angle of 45 degrees from bottom to top. The stripe projection light source (1) is used to project high-contrast stripe light, the first telecentric lens (2) is used to focus the stripe light, and the intermediate imaging surface (3) is used to project a stripe image after focusing the stripe light; the second telecentric lens (5) is used to focus the stripe light after being reflected by the component to be measured (4); and the black-and-white camera (6) is used to generate a stripe image after focusing the stripe light.

3. The optical detection device for liquid on the surface of a component according to claim 2, characterized in that: The stripe projection light source (1) comprises a rear focal length adjustment seat, a grid sheet angle adjustment seat, a stripe grid sheet (13), a lens module (12), a lamp board and an LED lamp bead (11); the lamp board is arranged on the rear focal length adjustment seat, the LED lamp bead (11) is arranged on the lamp board and the imaging point of the LED lamp bead (11) is at the aperture stop of the first telecentric lens (2); the lens module (12) is located on the light emitting side of the LED lamp bead (11); and the stripe grid sheet (13) is arranged on the grid sheet angle adjustment seat and on the light emitting side of the lens module (12).

4. The optical detection device for liquid on the surface of a component according to claim 3, characterized in that: The line width of the striped grid sheet is 0.05 mm, and the line spacing is 0.45 mm.

5. The optical detection device for liquid on the surface of a component according to claim 2, characterized in that: The first telecentric lens has a magnification of 0.2-1.5 times, a nominal working distance of L1, an actual working distance of S1, a magnification of β1, an angle with the vertical direction of θ1, and a front end diameter of The interface at the image plane end matches the interface of the fringe projection light source 1, and the working distances match, so as to form a Kohler illumination optical path; The second telecentric lens has a magnification of 0.2-1.5 times, a nominal working distance of L2, an actual working distance of S2, a magnification of β2, an angle with the vertical direction of θ2, and a front end diameter of The interface of the image plane matches the black and white camera, and the target surface and resolution match each other; For clear imaging, S1+S2=L1+L2 is satisfied. To form a virtual image, satisfy S1 <L1,S2<L2, According to the law of reflection θ1=θ2, to avoid mechanical conflict, satisfy 6. An optical detection method for liquid on the surface of a component, characterized in that: The following steps are involved: S1. Place a reflector on the detection station of the optical detection device as described in any one of claims 1 to 5. After the fringe projection light is projected through the reflector, a first system fringe image is obtained. The optical transfer function of the reflector surface is defined as 1. The MTF can be measured according to the calculation formula of the overall optical transfer function of the system. a and MTF b The product of is used to complete the calibration; S2, placing the component to be tested on the detection station of the optical detection device as described in any one of claims 1-5, obtaining a second system fringe image after the fringe projection light is projected through the component to be tested, firstly dividing the fringe image into a plurality of preset small areas, each small area including two stripes, one black and one white, and using an MTF calculation algorithm to calculate the MTF value within each small area of ​​the second system fringe image according to the gray value of the fringe image, and then calculating the surface optical transfer function within each small area according to the overall optical transfer function formula of the system, and finally obtaining the surface optical transfer function value within the entire area of ​​the image; S3, comparing the surface optical transfer function within each small area with a preset surface optical transfer function threshold, if the surface optical transfer function within the small area is smaller than the preset surface optical transfer function threshold, then marking these small areas on the surface of the component to be tested as having no liquid; if the surface optical transfer function within the small area is greater than the preset surface optical transfer function threshold, then marking these small areas on the surface of the component to be tested as having liquid; Then, the mapping marking algorithm is used to mark each small area with or without liquid, so as to obtain the presence or absence of liquid and the distribution area of ​​the liquid on the surface of the component to be tested; MTF refers to the function of modulation as the spatial frequency changes. MTF is calculated by finding the contrast between the maximum brightness point and the minimum brightness point in the line pair. The MTF calculation algorithm is as follows: MTF = (maximum brightness - minimum brightness) / (maximum brightness + minimum brightness) The overall optical transfer function of the system is calculated as follows: MTF 总 =MTF a .×STF×MTF b Among them, MTF 总 is the overall optical transfer function of the system, MTF a MTF is the optical transfer function of the system composed of the fringe projection light source and the first telecentric lens. b is the optical transfer function of the system composed of the second telecentric lens and the black and white camera, and STF is the optical transfer function of the surface of the original under test.

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