A lens defect detection system, detection method, structured light generation method and image processing method using structured light

Abstract

The application discloses a lens defect detection system and method using structured light, a structured light generation method and an image processing method thereof. The structured light projection scheme is adopted, the projected grating pattern is realized by programming, the fineness of the grating stripe can be adjusted according to the actual lens condition, and the defects of the lens surface in different conditions can be more clearly reflected. The designed structured light projection lens can effectively correct various aberrations and has good imaging quality. The projection lens is a zoom system, the focal length range of the system is 11mm-22mm, has a two-fold zoom effect, and can adapt to most lens sizes. The structured light projection system and the collection system adopt a symmetrical structure, can effectively eliminate system distortion and reduce errors. The image processing algorithm of the application can accurately obtain the lens surface defect information.

Description

TECHNICAL FIELD

[0001] The present application relates to the fields of projection technology, structured light and lens defect detection, in particular to a lens defect detection system using structured light, a detection method, a structured light generation method and an image processing method thereof. BACKGROUND

[0002] The optical lens surface defect detection has always adopted the manual detection method, and the detection process is slow and inefficient, and the accuracy is low. In the current era of advocating automatic production detection and fast and efficient work, the traditional manual detection method has no development space. At the same time, other detection methods such as microscopic detection and visual detection are constantly developing, and related detection equipment has appeared, but it has not been widely promoted. On the one hand, the lens needs to be kept relatively clean before detection to prevent dust on the surface from interfering with detection, and how to clean the lens and keep it clean is a difficulty; in addition, due to the transparent nature of the lens, special lighting methods need to be used for visual detection to clearly show the defects, and it is a difficulty to ignore background interference; in addition, large curvature lenses have very small focal lengths, and the light source is easy to image near the surface, forming a halo that interferes with detection, and how to detect large curvature lenses is a difficulty, and so on. It is these difficulties that make the development of optical lens defect automatic detection very difficult.

[0003] Structured light is a system structure composed of a projector and a camera. After projecting specific light information onto the surface of an object and the background by the projector, it is collected by the camera. According to the changes in the light signal caused by the object, the position and depth of the object are calculated. The phase deflection method in structured light three-dimensional measurement technology is mainly used for measuring planar mirror objects, and can quickly, fully, accurately and non-destructively measure the surface information of mirror objects. Its application to the field of lens defect detection can provide a new method for clearly displaying lens defects, and the design of the projection system is very critical. SUMMARY

[0004] To solve the above problems, the present application aims to provide a lens defect detection system and method, a structured light generation method and an image processing method thereof. The present application designs a zoom projection lens and introduces structured light for lens defect detection.

[0005] The lens defect detection system designed by the application comprises a structured light generation system, a structured light projection system, a structured light collection system and an image processing system; the structured light generation system is used for generating a grating fringe reflecting lens defects; the structured light projection system is used for projecting the grating fringe to a surface of a lens to be detected; the structured light collection system is used for collecting a grating fringe image after deformation, which will contain defect information of the lens surface, and then converting an image signal into a digital signal for computer processing; the image processing system is used for analyzing and detecting the collected image information, and finally outputting a detection result.

[0006] The structured light generation system is realized based on DLP (Digital Light Processing) projection technology. The whole system comprises an LED light source, an illumination system, a DMD (Digital Micromirror Devices) chip and a DLP circuit board. Specifically, the LED light source emits light, the light is converged to the DMD chip through the illumination system, and after the DMD chip receives the light signal and the electric signal from the DLP circuit board, each micro-mirror on the DMD chip reflects the incident light at different angles according to the corresponding electric signal, and finally presents a required structured light pattern. The structured light pattern is a sinusoidal grating fringe with accurately designed fringe width, and the pattern is realized by MATLAB programming and the picture format is BMP format.

[0007] The structured light projection system is a zoom projection lens module composed of ten lenses.

[0008] Specifically, the lens module of the structured light projection system comprises, in order from the object side to the image side: a first lens G1 with negative focal power, which is a double-concave lens and is fixed during zooming; a second lens G2 with negative focal power, which is a meniscus lens with the convex surface facing the object side and can move along the optical axis; a third lens G3 with negative focal power, which is a double-concave lens and is fixed during zooming; a fourth lens G4 with positive focal power, which is a double-convex lens and is fixed during zooming; a fifth lens G5 with positive focal power, which is a double-convex lens and is fixed during zooming; a sixth lens G6 with positive focal power, which is a double-convex lens and is fixed during zooming; a seventh lens G7 with negative focal power, which is a double-concave lens and can move along the optical axis; an eighth lens G8 with positive focal power, which is a meniscus lens with the convex surface facing the object side and can move along the optical axis; a ninth lens G9 with positive focal power, which is a double-convex lens and can move along the optical axis; a tenth lens G10 with positive focal power, which is a meniscus lens with the convex surface facing the image side and is fixed during zooming; and the diaphragm assembly is arranged between the sixth and seventh lenses and can move along the optical axis.

[0009] The lens material used in the application is glass, which has better thermal stability.

[0010] The structural light projection lens module is suitable for monochromatic green light projection, the object height is 12mm, the projection ratio is 0.67, wherein the projection ratio refers to the ratio of the projection distance to the projection picture width, the F number of the projection lens is 2, which can meet the requirement of the projection lens on brightness, wherein the F number refers to the ratio of the focal length to the aperture diameter, and the field angle of the projection lens is 30°, wherein the field angle is also referred to as the field of view, and the size of the field angle determines the field of view range of the optical instrument.

[0011] The structural light collection system adopts the same lens combination as the projection system, and the overall imaging system constitutes a symmetrical structure, so that the system distortion can be effectively eliminated.

[0012] The image processing system selects the defect characterization mode of the image information, prepares the mask, denoises the defect image, enhances the defect image, binarizes the defect image and the like by using the structural light information collected by the CCD through the computer, and finally obtains the required image information and detection result through the above processing.

[0013] The beneficial effects of the present application are as follows:

[0014] (1) In terms of how to display the defects on the lens surface, the structural light projection scheme is adopted, the grating pattern is realized by programming, the fineness of the grating stripe can be adjusted according to the actual lens situation, and the defects on the lens surface in different situations can be more clearly reflected;

[0015] (2) The projection lens can effectively correct various aberrations and has good imaging quality; the projection lens is a zoom system, the focal length range of the system is 11mm-22mm, has a two-fold zoom effect, and can adapt to most lens sizes;

[0016] (3) The structural light projection system and the collection system adopt a symmetrical structure, which can effectively eliminate system distortion and reduce errors;

[0017] (4) The image processing algorithm of the present application can accurately obtain the defect information on the lens surface. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a whole optical path system plane structure diagram of the embodiment of the present application;

[0019] Figure 2 It is an LED driving circuit diagram in the embodiment of the present application;

[0020] Figure 3 It is a grating stripe legend in the embodiment of the present application;

[0021] Figure 4 It is a projection lens barrel mechanical structure diagram in the embodiment of the present application;

[0022] Figure 5The schematic diagram of the optical system of the telephoto end of the zoom lens of the embodiment of the present application is shown in the figure.

[0023] Figure 6 The astigmatism, distortion and longitudinal spherical aberration of the telephoto end of the present application are shown in the figure.

[0024] Figure 7 The astigmatism, distortion and longitudinal spherical aberration of the telephoto end of the present application are shown in the figure.

[0025] Figure 8 The MTF of the telephoto end of the present application is shown in the figure.

[0026] Figure 9 The schematic diagram of the optical system of the middle-long focus end of the zoom lens of the embodiment of the present application is shown in the figure.

[0027] Figure 10 The astigmatism, distortion and longitudinal spherical aberration of the middle-long focus end of the present application are shown in the figure.

[0028] Figure 11 The astigmatism, distortion and longitudinal spherical aberration of the middle-long focus end of the present application are shown in the figure.

[0029] Figure 12 The MTF of the middle-long focus end of the present application is shown in the figure.

[0030] Figure 13 The schematic diagram of the optical system of the wide-angle end of the zoom lens of the embodiment of the present application is shown in the figure.

[0031] Figure 14 The astigmatism, distortion and longitudinal spherical aberration of the wide-angle end of the present application are shown in the figure.

[0032] Figure 15 The astigmatism, distortion and longitudinal spherical aberration of the wide-angle end of the present application are shown in the figure.

[0033] Figure 16 The MTF of the wide-angle end of the present application is shown in the figure.

[0034] Figure 17 The structural light projection effect diagram of the present application is shown in the figure.

[0035] The meanings of the numerical reference signs in the figure are as follows:

[0036] 1-DMD chip, 2-LED light source, 3-CCD, 4-lens to be tested, 5-mirror, 6-structural light projection system, 7-structural light collection system, 8-image processing system, 9-TIR prism, 10-illumination system. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present application clearer, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0038] ATTACHMENT Figure 1 The schematic diagram of the overall optical system plane structure of the embodiment of the present application is shown in the figure, and the subsequent embodiment introduction is in accordance with theFigure 1 The whole structure is shown.

[0039] The LED light source 2 of the structured light generation system is selected as CLM2D-GEC / BEC:PLCC4 Green & Blue SMD LEDs of Cree LED Company, which provides high-intensity monochromatic green light output and wide viewing angle, has a size of 3.2mm*2.8mm, small volume and compact structure. The LED driving part adopts a high-brightness LED constant-current driving IC LM3404 of National Semiconductor, USA, which can adapt to an input voltage range of 6V-42V. The application circuit is shown in the figure. Figure 2 SNS R is a sampling resistor, which can be determined according to a constant-current value of design; R ON Generally, a resistor of about 100k is selected, which can determine a switching frequency; L1 is an output inductor, which can be determined according to parameters such as ripple and switching frequency.

[0040] The illumination system 10 is composed of a homogenizer, an eye lens and a converging lens. The DMD chip 1 adopts a 0.47-inch chip with a display resolution of 1920*1080 (1080p) and a micromirror spacing of 5.4um, and the model is DLP4710. The DLP4710 digital micromirror device is a numerical control micro-optical-electromechanical system (MOEMS) spatial illumination modulator (SLM). When used with a suitable optical system, the DLP4710 LC DMD can display very clear high-quality images or videos. The overall DLP circuit board is a chip set component composed of a DLP4710 DMD, a DLPC3479 controller and a DLPA3000 / DLPA3005 PMIC / LED driver. The advantage of adopting the DLP4710 LC is that it is small in size, and together with the controller and the LED driver, it forms a complete system solution, so that the application realizes the performance of small size, low power consumption and high-resolution high-definition display.

[0041] The projection pattern designed by the application is a surface grating fringe. When the surface grating fringe is projected onto a lens, corresponding deformation occurs. Since the fringe width can be set to a size of several microns, when there is a tiny flaw on the surface of the lens, the grating fringe projected onto the flaw surface will be obviously bent. The deformed fringe is captured by a CCD camera and sent to a computer for processing, so that the flaw information of the measured lens surface can be separated from the fringe.

[0042] The structured light projection pattern is generated by a fringe grating algorithm, and the fringe grating algorithm includes phase demodulation and phase unwrapping, specifically:

[0043] It is assumed that the light intensity distribution of the reference surface can be represented by the following formula:

[0044] ​I0(x, y) = r0(x, y) {A(x, y) + B(x, y)cos[2πf0x + φ0(x, y)]} (1)

[0045] In the above formula, x and y are the horizontal and vertical coordinates of the reference surface pixel point, f0 is the base frequency, I0(x, y) is the light intensity of the reference surface, r0(x, y) represents the reflectivity on the reference surface which changes slowly relative to the base frequency f0, A(x, y) is the light intensity of the slowly changing background, and B(x, y) is the initial phase of the system.

[0046] The above formula (1) adds an equal interval phase shift 2π / N to the initial phase φ0(x, y), and the obtained fringe pattern is:

[0047] I0(x, y) = r0(x, y) {A(x, y) + B(x, y)cos[2πf0x + φ0(x, y) + 2iπ / N]} (2)

[0048] Where i = 1,..., N, and the tangent of the corresponding folded phase φ0(x, y) is:

[0049]

[0050] In formula (3), N needs to be at least 3 to obtain the tangent value of the folded phase, and in actual calculation, N is preferably 4 for the convenience of algorithm implementation. In this way, four fringe patterns with a phase interval of 2π / 4 are represented as:

[0051] I 01 (x, y) = r0(x, y) {A(x, y) + B(x, y)cos[2πf0x + φ0(x, y)]}

[0052]

[0053] I 03 (x, y) = r0(x, y) {A(x, y) + B(x, y)cos[2πf0x + φ0(x, y) + π]}

[0054]

[0055] The above light intensity is generated into four sinusoidal fringe patterns by MATLAB programming, and the format is BMP. In this embodiment, four sinusoidal fringe patterns with a frequency of 100 Hz are generated, as shown in the following figures: Figure 3 Figure 3 Only one is shown, because the frequencies of the other generated fringe patterns are the same as this one, and the formed fringe patterns are also the same.

[0056] The detection method based on the lens defect detection system proposed by the application has the following specific process:​

[0057] First, the power is turned on, the LED constant current drive circuit based on LM3404 starts to work, driving the LED light source 2 to emit light, the monochromatic green light emitted by the LED is converged and collimated through the illumination system 10, and then reflected into the TIR prism 9 through the reflector 5, and then uniformly converged on the DMD chip 1 after being reflected by the TIR prism 9. At the same time, the data image signal processing circuit on the DLP circuit board inputs the electric signal containing the generated grating fringe information designed in advance to the DMD chip 1, then the microlens on the DMD chip 1 starts to work and displays the grating fringe to be projected; when the image data stream is too large, the image data is pre-stored in the image buffer storage system SDRAM system, and the SDRAM memory provides the image signal for the data image processing circuit to process at a fast access speed, and the next frame of image signal of the SDRAM is also received after a frame of image is processed.

[0058] Further, the grating fringe displayed by the DMD chip 1 is projected onto the lens to be measured 4 through the structured light projection system 6, and the fringe will be deformed accordingly, and the deformed fringe is collected by the structured light collection system 7, and then the image signal containing the lens surface defect information is converted into a digital signal, which is processed, analyzed and detected by the picture processing system 8 according to the corresponding algorithm, and finally the detection result is output.

[0059] Specifically, the structured light projection system 6 comprises a zoom projection lens group composed of ten lenses. From the object side to the image side, they are: a first lens G1 with negative focal power, which is a double-concave lens and fixed during zooming; a second lens G2 with negative focal power, which is a meniscus lens with the convex surface facing the object side and can move along the optical axis; a third lens G3 with negative focal power, which is a double-concave lens and fixed during zooming; a fourth lens G4 with positive focal power, which is a double-convex lens and fixed during zooming; a fifth lens G5 with positive focal power, which is a double-convex lens and fixed during zooming; a sixth lens G6 with positive focal power, which is a double-convex lens and fixed during zooming; a seventh lens G7 with negative focal power, which is a double-concave lens and can move along the optical axis; an eighth lens G8 with positive focal power, which is a meniscus lens with the convex surface facing the object side and can move along the optical axis; a ninth lens G9 with positive focal power, which is a double-convex lens and can move along the optical axis; and a tenth lens G10 with positive focal power, which is a meniscus lens with the convex surface facing the image side and fixed during zooming. The diaphragm assembly is arranged between the sixth and seventh lenses and is fixed during zooming. The zoom projection system has a constant Fno, and for the effective focal length of the projection system:

[0060] The focal length of the projection lens is f, and 11.0mm<f<22.0mm;

[0061] The focal length of the first lens G1 is f1, -40mm. <f1<-30mm;

[0062] The focal length of the second lens G2 is f2, -310mm. <f2<-290mm;

[0063] The third lens G3 has a focal length of f3, -45mm. <f3<-30mm;

[0064] The fourth lens, G4, has a focal length of f / 4, 50mm. <f4<60mm;

[0065] The fifth lens, G5, has a focal length of f / 5, 45mm. <f5<55mm;

[0066] The sixth lens, G6, has a focal length of f / 6, 45mm. <f6<55mm;

[0067] The seventh lens, G7, has a focal length of f / 7, -30mm. <f7<-20mm;

[0068] The eighth lens, G8, has a focal length of f / 8, 95mm. <f8<85mm;

[0069] The focal length of the ninth lens, G9, is f / 9.65mm. <f9<75mm;

[0070] The focal length of the tenth lens G10 is f 10 70mm <f 10 <80mm;

[0071] In this embodiment, the optical power distribution is uniform, resulting in lower tolerance sensitivity for each lens, which improves the lens yield and facilitates mass production.

[0072] Regarding the thickness of the projection lens:

[0073] The total optical length of the projection system is 130mm. <T<140mm;

[0074] The lens thicknesses in the projection lens are as follows:

[0075] The thickness of the first lens G1 is T1, 0 mm. <T1<1mm;

[0076] The thickness of the first lens G2 is T2, 5mm. <T2<10mm;

[0077] The thickness of the first lens G3 is T3, 4mm. <T3<6mm;

[0078] The thickness of the first lens G4 is T4, 5mm. <T4<9mm;

[0079] The thickness of the first lens G5 is T5, 2mm. <T5<8mm;

[0080] The lens thickness of the first lens G6 is T6, 4mm < T6 < 10mm;

[0081] The lens thickness of the first lens G7 is T7, 1mm < T7 < 4mm;

[0082] The lens thickness of the first lens G8 is T8, 1mm < T8 < 5mm;

[0083] The lens thickness of the first lens G9 is T9, 6mm < T9 < 10mm;

[0084] The lens thickness of the first lens G10 is T10, 6mm < T10 < 10mm.

[0085] The specific parameters are shown in Table 1 below:

[0086] Table 1

[0087]

[0088]

[0089] In the present example, the intervals between the first lens G1 and the second lens G2, the second lens G2 and the lens group G0, the seventh lens G7 and the eighth lens G8, and the ninth lens G9 and the tenth lens G10 gradually decrease during the zooming process from the wide-angle end to the telephoto end; the intervals between the stop and the seventh lens G7 and the eighth lens G8 and the ninth lens G9 gradually increase.

[0090] In the present example, the total length of the lens remains unchanged during the zooming process, and the zooming data of the present example is shown in Table 2 below:

[0091] Table 2

[0092]

[0093] The mechanical structure of the projection lens barrel is shown in the attached drawings Figure 4As shown, 6063 aluminum alloy is used as the packaging shell 1, and the internal main body 2 is provided with 6063 aluminum alloy spacers to determine the relative positions between each lens (the spacers are not shown in the figure for the sake of drawing beauty), so as to ensure that the distance between the first lens and the second lens is D2, the distance between the second lens and the third lens is D4, the distance between the third lens and the fourth lens is 3.978 mm, the distance between the fourth lens and the fifth lens is 2.552 mm, the distance between the fifth lens and the sixth lens is 8.187 mm, the distance between the sixth lens and the diaphragm is 2.859 mm, the distance between the diaphragm and the seventh lens is D13, the distance between the seventh lens and the eighth lens is D15, the distance between the eighth lens and the ninth lens is D17, the distance between the ninth lens and the tenth lens is D19, the fixed main body is provided with a guide rail structure 3 for axial movement of the optical lens group as a whole, and the lens barrel is fixed at both ends by glue, so that the entire lens group is fixed inside the lens barrel.

[0094] Figure 5 A schematic view of the optical system at the telephoto end of the zoom lens according to the embodiment of the present application is shown in FIG. 6.

[0095] Figure 6 A curve diagram of the optical aberration at the telephoto end of the zoom lens according to the embodiment of the present application is shown in FIG. 7. For the same field of view, the curve with the ordinate "TANGENTIAL" represents the tangential aberration curve, and the curve with the ordinate "SAGITTAL" represents the sagittal aberration curve. Each curve represents the focusing condition of the meridional / sagittal beam on the image plane for a field of view. As can be seen from the figure, the two kinds of aberration curves for the three fields of view are close to 0, which indicates that the light rays at each field of view at the telephoto end of the zoom lens are well focused on a point.

[0096] Figure 7 From left to right, the curve diagrams of the longitudinal spherical aberration, the field curvature and the distortion at the telephoto end of the zoom lens according to the embodiment of the present application are shown in FIG. 8. The longitudinal spherical aberration represents the relationship between the spherical aberration and the height of the light ray, and reflects the difference between the actual image point and the ideal image point. The abscissa represents the offset (unit: mm), and the ordinate represents the normalized pupil radius. As can be seen from the figure, the offset is controlled within ±0.01 mm, which indicates that the longitudinal spherical aberration at the telephoto end of the zoom lens can be well corrected. The field curvature represents the bending degree of the light rays of different wavelengths on the meridional image plane and the sagittal image plane. The abscissa represents the offset (unit: mm), and the ordinate represents the half field angle (unit: °). As can be seen from the figure, the field curvature of the meridional image plane and the sagittal image plane is controlled within ±0.05 mm, which indicates that the field curvature at the telephoto end of the zoom lens can be well corrected. Distortion refers to the difference in magnification of different parts of an object when the object is imaged through an optical assembly. The abscissa represents the distortion (unit: %), and the ordinate represents the half field angle (unit: °). As can be seen from the figure, the distortion of the zoom lens is controlled within ±15%, which indicates that the distortion at the telephoto end of the zoom lens can be extremely well corrected.

[0097] Figure 8 is a MTF (Modulation Transfer Function) curve diagram of the tele end of the embodiment of the present application, which represents the imaging modulation degree of the lens at different spatial frequencies under each field of view, the horizontal axis represents spatial frequency (unit: lp / mm), and the vertical axis represents MTF value. As can be seen from the diagram, the MTF value of the embodiment is above 0.6 in the full field of view, and in the range of 0-150 lp / mm, the MTF curve uniformly and smoothly decreases from the center to the edge of the field of view, and has good imaging quality and good detail resolution capability in the case of low frequency and high frequency.

[0098] Figure 9 is a schematic diagram of the optical system of the tele end of the zoom lens of the embodiment of the present application;

[0099] Figure 10 is a ray aberration curve diagram of the tele end of the embodiment of the present application, as can be seen from the diagram, the two kinds of aberration curves under three fields of view are close to 0, which indicates that the rays under each field of view of the tele end of the zoom lens are well focused on a point.

[0100] Figure 11 From left to right are the longitudinal spherical aberration, field curvature and distortion curve diagrams of the tele end of the embodiment of the present application. As can be seen from the diagram, the spherical aberration offset is controlled within ±0.01 mm, which indicates that the longitudinal spherical aberration can be well corrected in the tele state of the zoom lens; as can be seen from the diagram, the field curvature of the meridional image surface and the sagittal image surface is controlled within ±0.05 mm, which indicates that the field curvature can be well corrected in the tele state of the zoom lens; as can be seen from the diagram, the distortion of the zoom lens is controlled within ±15%, which indicates that the distortion can be very well corrected in the tele state of the zoom lens.

[0101] Figure 12 is a MTF (Modulation Transfer Function) curve diagram of the tele end of the embodiment of the present application, which represents the imaging modulation degree of the lens at different spatial frequencies under each field of view, the horizontal axis represents spatial frequency (unit: lp / mm), and the vertical axis represents MTF value. As can be seen from the diagram, the MTF value of the embodiment is above 0.6 in the full field of view, and in the range of 0-150 lp / mm, the MTF curve uniformly and smoothly decreases from the center to the edge of the field of view, and has good imaging quality and good detail resolution capability in the case of low frequency and high frequency.

[0102] Figure 13 is a schematic diagram of the optical system of the wide-angle end of the zoom lens of the embodiment of the present application;

[0103] Figure 14 is a ray aberration curve diagram of the wide-angle end of the embodiment of the present application, as can be seen from the diagram, the two kinds of aberration curves under three fields of view are close to 0, which indicates that the rays under each field of view of the wide-angle end of the zoom lens are well focused on a point.

[0104] Figure 15From left to right are the wide-angle end longitudinal spherical aberration, field curvature and distortion curves of the embodiment of the application. As can be seen from the figure, the spherical aberration offset is controlled within ±0.05mm, which shows that the wide-angle state of the zoom lens can correct the longitudinal spherical aberration well; as can be seen from the figure, the field curvature of the meridional image surface and the sagittal image surface is controlled within ±0.05mm, which shows that the wide-angle state of the zoom lens can correct the field curvature well; as can be seen from the figure, the distortion of the zoom lens is controlled within ±15%, which shows that the wide-angle state of the zoom lens can correct the distortion very well.

[0105] Figure 16 is the MTF (modulation transfer function) curve of the wide-angle end in the embodiment of the application, from which it can be seen that the MTF value of the embodiment is above 0.6 in the full field of view, and in the range of 0-150lp / mm, the MTF curve uniformly and smoothly decreases from the center to the edge of the field of view, and has good imaging quality and good detail resolution ability in the case of low frequency and high frequency.

[0106] Further, the grating fringe image projected by the structured light projection system 6 is projected onto the surface of the lens to be measured 4, and the surface of the lens to be measured modulates the structured light, and the gradient change of the lens to be measured causes the phase of the structured light to change, resulting in deformation of the fringe. In order to more clearly introduce the projection effect of the structured light, simulation experiment effect diagrams are provided in this embodiment, as shown in Figure 17 , in order to more obviously reflect the working effect of the structured light, Figure 17 , the grating fringe interval is relatively large, and in actual application, the thickness of the grating fringe can be adjusted to the required size at will.

[0107] Further, the structured light collection system 7 collects the pictures to be processed containing the deformed structured light, specifically, the structured light collection system 7 is a lens combination symmetrical to the structured light projection system 6, and the image surface of the structured light projection system 6 is the object surface of the imaging system, wherein G11-G20 correspond to G1-G10 respectively. This symmetrical system can effectively eliminate system distortion. The CCD 3 adopts the model: GT 1660C, the resolution: 1600*1200, and the target pixel size: 5.5μm×5.5μm.

[0108] Further, the image processing system 8 acquires the picture information collected by the CCD 3 and analyzes and processes the picture.

[0109] Specifically, the process of the image processing system 8 processing the picture is as follows:

[0110] Firstly, the phase information is obtained from N frames of light intensity by least square method, and then the modulation distribution map is obtained by N-step phase shift method. Modulation is an important parameter of modulated wave, which reflects the degree of carrier amplitude, frequency or phase controlled by low frequency modulation signal. It is not affected by ambient light and performs well at the edge of the lens. The small defects on the lens surface can be effectively reflected by using modulation table.

[0111] Further, the specific implementation method of the picture processing unit 8 is that the mask in digital image processing is used to do "and" operation with the selected image to control the process of the region of interest (ROI). The mask is generally a binary image. After the "and" operation between the mask and the image to be processed, the pixel value of the non-ROI region is 0, and the pixel value of the target region does not change. A mask of the size of the lens region is made to act as a filter effect, and the background part is filtered out, and only the measured part is displayed.

[0112] Further, the curve wave denoising method is used for denoising the image. The curve wave transform denoising method is: first, the noisy image is decomposed into subbands of different scales, and the curve wave transform coefficients corresponding to each subband are obtained through Plancherel operation; then the obtained curve wave transform coefficients are processed by hard threshold method (discard small transform coefficients and retain large transform coefficients), so as to filter out the noise in the image and retain the edge characteristics of the image.

[0113] Finally, the image is binarized through global threshold binarization processing, and finally the binarized picture of the lens defect is obtained.

[0114] Finally, the picture information is analyzed and detected according to the detection index, and the detection result is output. Subsequently, the lens can be discarded or corresponding defect removal processing.

[0115] The above series of detailed descriptions are only specific descriptions of the feasible implementation modes of the present application, and are not used to limit the protection scope of the present application. Any equivalent mode or change without departing from the technology of the present application should be included in the protection scope of the present application.

Claims

1. A lens defect detection system using structured light, characterized by, The application relates to a lens defect detection system. The system comprises a structured light generation system, a structured light projection system, a structured light collection system and an image processing system. The structured light generation system is used for generating grating fringes reflecting lens defects, the structured light projection system is used for projecting the grating fringes to a lens surface to be detected, the structured light collection system is used for collecting grating fringe images of the lens surface, the images will contain defect information of the lens surface, then the image signals are converted into digital signals for subsequent processing, and the image processing system is used for processing the collected image information and outputting defect detection results. The structured light generation system comprises an LED light source, an illumination system, a DMD chip and a DLP circuit board; the LED light source emits light, the light is converged to the DMD chip through the illumination system, the DMD chip receives the light signals and the electric signals from the DLP circuit board at the same time, each micro-reflector on the DMD chip reflects the incident light at different angles according to the corresponding electric signals, and finally the required structured light pattern is presented. The structured light projection system adopts a zoom projection lens module. The zoom projection lens module comprises, from the object side to the image side, a first lens G1 with negative focal length, a double-concave lens, fixed during zooming, a second lens G2 with negative focal length, a meniscus lens with the convex surface facing the object side and movable along the optical axis, a third lens G3 with negative focal length, a double-concave lens, fixed during zooming, a fourth lens G4 with positive focal length, a double-convex lens, fixed during zooming, a fifth lens G5 with positive focal length, a double-convex lens, fixed during zooming, a sixth lens G6 with positive focal length, a double-convex lens, fixed during zooming, a seventh lens G7 with negative focal length, a double-concave lens, movable along the optical axis, an eighth lens G8 with positive focal length, a meniscus lens with the convex surface facing the object side, movable along the optical axis, a ninth lens G9 with positive focal length, a double-convex lens, movable along the optical axis, and a tenth lens G10 with positive focal length, a meniscus lens with the convex surface facing the image side, fixed during zooming. The intervals between the first lens G1 and the second lens G2, the second lens G2 and the lens group G0, the seventh lens G7 and the eighth lens G8 and the ninth lens G9 and the tenth lens G10 gradually decrease, the intervals between the diaphragm and the seventh lens G7 and the eighth lens G8 and the ninth lens G9 gradually increase, and the lens group G0 is composed of the third lens G3, the fourth lens G4, the fifth lens G5 and the sixth lens G6.

2. The system for lens defect detection using structured light according to claim 1, wherein, The structured light pattern is a sinusoidal grating fringe with accurately designed fringe width, and the pattern is realized by MATLAB programming and has a BMP format.

3. The system for lens defect detection using structured light according to claim 1, wherein, The structured light projection system has a constant Fno, the focal length of the zoom projection lens module is f, and 11.0mm The focal length of the first lens G1 is f1, and -40mm The focal length of the second lens G2 is f2, and -310mm The focal length of the third lens G3 is f3, and -45mm < f3 < -30mm; The focal length of the fourth lens G4 is f4, and 50mm < f4 < 60mm; The focal length of the fifth lens G5 is f5, and 45mm < f5 < 55mm; The focal length of the sixth lens G6 is f6, and 45mm < f6 < 55mm; The focal length of the seventh lens G7 is f7, and -30mm < f7 < -20mm; The focal length of the eighth lens G8 is f8, and 95mm < f8 < 85mm; The focal length of the ninth lens G9 is f9, and 65mm < f9 < 75mm; The focal length of the tenth lens G10 is f 10 , 70mm < f 10 < 80mm.

4. The system for lens defect detection using structured light according to claim 1, wherein, The total optical length of the zoom projection lens module is 130mm < T < 140mm; The thickness of each lens is respectively: The lens thickness of the first lens G1 is T1, and 0mm < T1 < 1mm; The lens thickness of the second lens G2 is T2, and 5mm < T2 < 10mm; The lens thickness of the third lens G3 is T3, and 4mm < T3 < 6mm; The lens thickness of the fourth lens G4 is T4, and 5mm < T4 < 9mm; The lens thickness of the fifth lens G5 is T5, and 2mm < T5 < 8mm; The lens thickness of the sixth lens G6 is T6, and 4mm < T6 < 10mm; The lens thickness of the seventh lens G7 is T7, and 1mm < T7 < 4mm; The lens thickness of the eighth lens G8 is T8, and 1mm < T8 < 5mm; The lens thickness of the ninth lens G9 is T9, and 6mm < T9 < 10mm; The lens thickness of the tenth lens G10 is T10, and 6mm < T10 < 10mm.

5. The system for lens defect detection using structured light according to claim 1, wherein, The structured light collection system and the structured light projection system adopt the same lens combination, and the overall imaging system constitutes a symmetrical structure.

6. A method of detecting a lens defect using a structured light-based lens defect detection system according to claim 1, characterized in that, It comprises the following: The LED light source emits monochromatic green light, which is converged and collimated by the illumination system, then reflected by the reflector into the TIR prism, and uniformly converges on the DMD chip after reflection. At the same time, the data image signal processing circuit on the DLP circuit board inputs the electrical signal containing the generated grating fringe information to the DMD chip in advance. Then, the microlens on the DMD chip starts to work and displays the grating fringe that needs to be projected. The grating fringe displayed by the DMD chip is projected onto the lens to be tested by the structured light projection system. The lens surface modulates the structured light, and the gradient change of the lens surface causes the phase of the structured light to change, resulting in deformation of the fringe. The deformed fringe is collected by the structured light collection system, and the image signal containing the lens surface defect information is converted into a digital signal. The digital signal is processed, analyzed and detected by the image processing system according to the corresponding algorithm, and finally the detection result is output.

7. A structured light generation method for the structured light lens defect detection system of any one of claims 1-5, characterized in that, Assuming that the light intensity distribution of the reference surface is represented by the following formula: (1) In the above formula, are the horizontal and vertical coordinates of the reference surface pixel, is the light intensity of the reference surface, denotes the relative phase of the fundamental frequency is the reflectivity on the slowly varying reference surface, is the light intensity of the slowly varying background, is the initial phase of the system; The above equation (1) is based on the initial phase adding equal interval phase shift The resulting fringe pattern is: (2) wherein = 1,..., N, the corresponding folding phase the tangent of which is: (3) (3) N=4, corresponding to four phase intervals The fringe pattern is represented as: The above light intensity is programmed by MATLAB to generate four sinusoidal fringe patterns, and the format is BMP.

8. A structured light image processing method for the structured light lens defect detection system of any one of claims 1-5, wherein, It comprises the following processes: S1 obtains phase information from N frames of light intensity by least square method, and then obtains modulation distribution map by N-step phase shift method; S2, the image processing system obtains the structured light information collected by the CCD, selects a defect characterization method for the image information, prepares a mask, denoises the defect image, enhances the defect image, binarizes the defect image, and finally obtains the required image information and detection result through the above processing. The specific method is as follows: the mask is obtained by performing an AND operation on the selected image and the image to be processed to control the process of the region of interest. After performing the AND operation on the mask and the image to be processed, the pixel values of the non-ROI region are 0, and the pixel values of the target region are not changed. A mask with the size of the lens region is prepared to act as a filter effect, filter out the background part, and only display the measured part; S3, a curvelet denoising method is used to denoise the image. First, the noisy image is decomposed into subbands of different scales, and the curvelet transform coefficients corresponding to each subband are obtained through Plancherel operation. Then, the obtained curvelet transform coefficients are processed by a hard threshold method to filter out the noise in the image and retain the edge characteristics of the image; S4, the image is binarized through global threshold binarization processing, and finally a binarized picture of the lens defect is obtained.

Images