A coaxial spectral confocal imaging system and apparatus for three-dimensional measurement

Abstract

The application discloses a coaxial spectrum confocal imaging system, comprising a light source module, a dispersion lens module, a spectrum imaging side slit device and a spectrometer; the light source module provides a wide-spectrum light beam and makes the light beam enter the dispersion lens module through a light source side slit device; the dispersion lens module makes the incident light sequentially pass through a first dispersion lens module, a light splitting device and a second dispersion lens module, and then is shot to a surface of a measured object, and also makes the light reflected by the surface of the measured object sequentially pass through the second dispersion lens module, is reflected by the light splitting device and passes through a third lens module, and then is converged to the spectrum imaging side slit device; the spectrometer images the light of different wavelengths converged to the spectrum imaging side slit device. The application overcomes the shielding problem of the prior art when measuring a relatively steep pit or hole by the mode that the incident light path and the reflected light path share a second dispersion lens module coaxially, and realizes the measurement of a deeper pit on the surface.

Description

Technical Field

[0001] This application relates to the field of optical precision measurement technology, and more specifically, to a coaxial spectral confocal imaging system and a device for three-dimensional measurement. Background Technology

[0002] With the full-scale rollout of Industry 4.0 and intelligent manufacturing globally, and the upgrading of industries, the demands for precision measurement technology are increasing. 3D measurement technology, as the foundation of geometric precision measurement, is becoming an indispensable and preferred technology in intelligent manufacturing process control, product quality inspection and assurance, and equipment service testing. Especially in the field of precision components and microstructures, such as the inspection of 3D mobile phone cover glass, transparent materials, lens surface shapes (spherical and aspherical), surface roughness, and texture, traditional 2D inspection can no longer meet the requirements. High-speed, high-precision 3D inspection has become one of the rapidly developing directions in visual inspection.

[0003] Linear scanning confocal spectroscopy offers significant advantages in rapid and high-precision 3D inspection of multilayer media, bright metallic surfaces, and vividly colored surfaces. Its basic principle is to establish a correlation between the height of the measured surface and its spectrum based on optical dispersion principles. A spectrometer decodes the spectral information to obtain the positional information. The basic technical solution involves emitting a broad-spectrum polychromatic light from a white light source. This light passes through a dispersive lens to generate color bands of different wavelengths along the depth direction on the surface of the object being measured. Only a specific wavelength of monochromatic light is focused onto the surface of the object and simultaneously reflected back to the optical system. The reflected wavelengths are separated by a diffraction element to obtain the wavelength value at the measured location. The distance to the measured object can then be calculated using wavelength-distance calibration. Due to the use of confocal technology, this method exhibits excellent tomographic characteristics, improved resolution, and is insensitive to the characteristics of the measured object and stray light. It can reliably measure even strongly absorbing materials (such as black rubber) or transparent materials (such as glass or liquids).

[0004] Regarding dispersive confocal microscopy, the commonly used technology on the market, such as Haibosen's patent CN110849271A, performs dispersion only after spectral dispersion, resulting in a relatively small dispersion strength and a relatively low instrument range. Moreover, because it does not compensate for the optical path of the image, the contour of the measured object will produce a slight distortion. Summary of the Invention

[0005] To address at least one deficiency or improvement requirement of the prior art, the present invention provides a coaxial spectral confocal imaging system to overcome the occlusion problem caused by the prior art when measuring the surface of deep pits, and to achieve precise measurement of surfaces with deeper holes or pits.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a coaxial spectral confocal imaging system, comprising,

[0007] Light source module, dispersive lens module, spectral imaging side slit device and spectrometer;

[0008] The light source module is used to provide a wide-spectrum light beam and incident it onto the dispersive lens module through a light source-side slit device;

[0009] The dispersive lens module includes a beam splitter and a first dispersive lens module for dispersive purposes located above the beam splitter, a second dispersive lens module for dispersive purposes located below the beam splitter, and a third lens module for focusing located on the side of the beam splitter.

[0010] The dispersive lens module is used to pass the incident light beam through the first dispersive lens module, the beam splitter and the second dispersive lens module in sequence, so that the light of different wavelengths in the light beam is focused at different heights on the surface of the object to be tested. It is also used to converge the light reflected from the surface of the object to be tested to the spectral imaging side slit device after passing through the second dispersive lens module, being reflected by the beam splitter and passing through the third lens module in sequence.

[0011] The spectrometer is used to image light of different wavelengths that converge to the spectral imaging side slit device, with the light of different wavelengths being imaged at different positions on the spectrometer.

[0012] Furthermore, there is an offset between the optical axes of the first dispersive lens module and the second dispersive lens module.

[0013] Furthermore, the light source-side slit device includes a first slit in a "straight line" shape; the spectral imaging-side slit device includes a second slit in a "straight line" shape, a slide block, and a rotating platform;

[0014] The second slit is fixedly mounted on the slide block, which can translate radially on the rotating platform. The rotating platform can rotate in the direction of rotation of the optical axis with the optical axis as the axis.

[0015] By adjusting the orientation of the second slit in the translation and / or rotation directions, the second slit can be made parallel to the first slit in the direction of slit length extension and / or the direction of slit length extension of the second slit can be aligned with the spectral focusing lines of different heights of the light reflected from the surface of the object under test.

[0016] Furthermore, the light source module also includes a light mixing device for mixing the provided broadband light beam.

[0017] Furthermore, the beam splitter is a beam splitter, the first surface of which is coated with an antireflective film; the second surface of which is coated with a semi-reflective and semi-transparent film.

[0018] Furthermore, the spectrometer is arranged sequentially along the propagation path of the reflected light, including a collimating lens group, a grating assembly, an optical path compensation assembly, a condenser lens group, and an area array camera;

[0019] The collimating lens group is used to maintain the collimation of the reflected light beam;

[0020] The grating assembly includes a grating for diffracting the reflected light beam;

[0021] The optical path compensation component is used to compensate the light passing through the grating component, so that the light of the preset center wavelength diffracted by the grating component is emitted horizontally after passing through the optical path compensation component.

[0022] The optical axis of the condenser lens group coincides with the optical axis of the collimating lens group and the third lens module;

[0023] The area array camera is used to image the light transmitted through the condenser lens group.

[0024] Furthermore, the optical path compensation component is a sawtooth lens, and light of a preset center wavelength diffracted by the grating component is refracted by the sawtooth lens and emitted horizontally.

[0025] Furthermore, the optical path compensation component is a deflecting prism, and the light of the preset center wavelength diffracted by the grating component is refracted by the deflecting prism and then emitted horizontally.

[0026] Furthermore, the preset center wavelength is 550nm.

[0027] Furthermore, the deflecting prism has at least a first surface and a second surface, the first surface being parallel to the grating, and the angle between the second surface and the first surface being an acute angle.

[0028] Furthermore, the collimating lens group and the condensing lens group are lenses with the same focal length.

[0029] Furthermore, the light mixing device is a solid light mixing rod or a hollow light mixing cavity.

[0030] Furthermore, the third lens module is the same as the first dispersive lens module.

[0031] Furthermore, the back of the system also includes a base for supporting the entire coaxial spectral confocal imaging system. The base has a cutout portion for holding or adjusting the coaxial spectral confocal imaging system.

[0032] In a second aspect, the present invention provides a device for three-dimensional measurement, the device comprising the coaxial spectral confocal imaging system described in any of the preceding claims.

[0033] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0034] (1) By using a second dispersive lens module that is coaxial with the incident light path and the reflected light path, the present invention enables the incident light to be almost parallel to the optical axis of the incident dispersive light path and almost perpendicular to the surface of the object to be measured, thereby overcoming the occlusion problem of the prior art when measuring surfaces with steeper pits or holes, and realizing the precise measurement of surfaces with deeper pits.

[0035] (2) The two adjustable "I-shaped" slits set in this invention are easier to align in orientation than the pinhole array / DMD pixel array in the prior art, and provide cleaner blocking of stray light from above and below, with less noise crosstalk.

[0036] (3) The light mixing device provided in this invention can mix the colors of a wide spectrum of light sources to form a very uniform spectral distribution near the first slit position. The spectral uniformity can exceed 99%, thereby ensuring the accuracy of the focusing position of different wavelengths on the surface of the object being measured and reducing the error in the height direction of the surface of the object being measured caused by spectral inhomogeneity.

[0037] (4) The present invention provides a sawtooth lens or deflector with a high refractive index and a low scattering coefficient that is placed close to the grating along the propagation path of the reflected light source. This avoids the technical solution of relying on software to calibrate for different wavelengths when correcting field curvature in the existing technology, and realizes compensation for field curvature in a physical way. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the measurement architecture of the prior art patent number US9476707B2 concerning line scan dispersive confocal technology; Figure 1In the middle: 124 - Signal processing unit; 108 - Detector; 104 - Source; 602 - Reference detector; 106 or 110 - Optical radiation processing unit;

[0040] Figure 2 This is an isometric side view of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0041] Figure 3 This is an isometric exploded view of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0042] Figure 4 This is a cross-sectional view of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0043] Figure 5 This is a side view of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0044] Figure 6 This is a rear view of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0045] Figure 7 An exploded view of the spectral imaging side slit device of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0046] Figure 8 This is a cross-sectional view of the dispersive lens module of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0047] Figure 9 This is an optical path diagram of the spectral incident dispersion optical path of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0048] Figure 10 This is a schematic diagram showing the optical axis offset of the spectral incident dispersion optical path of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application, located above and below the beam splitter.

[0049] Figure 11 The optical path diagram of the spectral output and reflection optical path (from the surface under test to the position of the second slit) of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application;

[0050] Figure 12 The image shows the spectral dispersion simulation results of the spectral incident dispersion optical path of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application at the position of the measured surface.

[0051] Figure 13 This is a computer simulation diagram of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application measuring a surface model with periodic grooves.

[0052] Figure 14 This is a diagram showing the distribution of light spots reflected from a groove-shaped surface under test by the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application.

[0053] Figure 15 This is a simulation result of the spectral imaging of the groove-shaped contour line on the area array camera of the coaxial scanning 3D spectral imaging system provided in Embodiment 1 of this application.

[0054] Figure 16 This is an overall structural diagram of the coaxial scanning 3D spectral imaging system provided in Embodiment 2 of this application;

[0055] Figure 17 This is a schematic diagram of the optical path for correcting the diffraction angle of the grating and sawtooth lens of the coaxial scanning 3D spectral imaging system provided in Embodiment 2 of this application.

[0056] Figure 18 This is a schematic diagram of the sawtooth bevel angle of the sawtooth lens in the coaxial scanning 3D spectral imaging system provided in Embodiment 2 of this application.

[0057] Figure 19 This is an overall structural diagram of the coaxial scanning 3D spectral imaging system provided in Embodiment 3 of this application;

[0058] Figure 20 This is a schematic diagram of the optical path for correcting the diffraction angle of the grating and deflecting prism of the coaxial scanning 3D spectral imaging system provided in Embodiment 3 of this application.

[0059] Figure 21 This is a schematic diagram of the reflection spectrum simulation of the stepped test surface provided in an embodiment of this application;

[0060] Figure 22 This is a spectral imaging simulation result of the measured surface of the step provided in Embodiment 1 of this application;

[0061] Figure 23 This is a spectral imaging simulation result of the measured surface of the step provided in Embodiment 2 of this application;

[0062] Figure 24 This is a spectral imaging simulation result of the measured surface of the step provided in Embodiment 3 of this application. Detailed Implementation

[0063] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0064] The terms "first," "second," or "third," etc., used in the specification, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a particular order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or apparatus.

[0065] refer to Figures 2-6 In one embodiment 1, a coaxial scanning 3D spectral imaging system includes a light source module 100, a light source-side slit device 200, a dispersive lens module 300, a spectral imaging-side slit device 400, and a spectrometer (also referred to as a spectral imaging module, hereinafter the same).

[0066] The light source module 100 provides a broadband light source and directs it through the light source-side slit device 200 onto the dispersive lens module 300. Specifically, the light source module 100 includes a heat sink 110, a broadband high-power COB module LED 120, and a light mixing device 130. The broadband high-power COB module LED 120 is a broadband white LED with a wavelength range of 400nm to 700nm. The light mixing device 130, which is either a solid mixing rod or a hollow mixing cavity, mixes the light emitted by the broadband white LED to form a highly uniform spectral distribution near the light source-side slit device 200, with a spectral uniformity exceeding 99%. This ensures the accuracy of the focusing positions of different wavelengths on the measured surface and reduces errors in the height direction of the measured surface caused by spectral inhomogeneity.

[0067] The light source side slit device 200 is provided with a first slit 201 in a "straight line" shape (reference). Figure 3 , Figure 8 and Figure 9 The length direction of the groove in the first slit 201 is parallel to the length direction of the groove in the "I-shaped" second slit 402 located on the side of the spectral imaging.

[0068] refer to Figure 8The dispersive lens module 300 includes a first dispersive lens module 310, a beam splitter 320, a second dispersive lens module 330, and a third lens module 340. The dispersive lens module 300 is used to direct the incident light source through the first dispersive lens module 310, the beam splitter 320, and the second dispersive lens module 330 to the surface of the object under test. It is also used to converge the light source reflected from the surface of the object under test to the spectral imaging side slit device 400 after passing through the second dispersive lens module 330, being reflected by the beam splitter 320, and passing through the third lens module 340.

[0069] Spectral imaging module (in Embodiment 1, the spectral imaging module may actually include) Figure 2 The collimating lens group 500, grating assembly 600, condenser lens group 700, and area array camera 800 are used to image light sources of different wavelengths that converge to the spectral imaging side slit device 400.

[0070] This invention achieves precise measurement of surfaces with deeper pits or holes by using a second dispersion lens module 330 coaxially for the incident and reflected light paths. This is achieved by using a second dispersion lens module 330 coaxially for the incident light path and the reflected light path, so that the incident light can be almost parallel to the optical axis of the incident dispersion light path and almost perpendicular to the surface of the object to be measured.

[0071] More specifically, the spectral imaging side slit device 400 is disposed on the side, and a second slit 402 is disposed inside it, with its plane set perpendicular to the surface being measured.

[0072] The collimating lens group 500 and the condenser lens group 700 may have identical focal lengths or different focal lengths. When the X-direction of the sensing surface of the area array camera 800 is aligned with the slit length, the magnification ratio of the spectral imaging lens is 1:1, and the focal lengths of the collimating lens group 500 and the condenser lens group 700 are identical. However, when the X-direction of the sensing surface of the area array camera 800 is not aligned with the slit length, the magnification ratio of the spectral imaging lens is not 1:1, and the focal lengths of the collimating lens group 500 and the condenser lens group 700 have a magnification ratio relationship. In this embodiment 1, the collimating lens group 500 and the condenser lens group 700 are preferably identical lenses with identical focal lengths.

[0073] The optical axis of the condenser lens group 700 is along the direction of the diffraction light at a wavelength of 550 nm from the grating 610, i.e., the spectral imaging at the center of the imaging sensor of the area array camera 800 is a spectral focusing line at 550 nm. The tilt angle between the optical axis of the condenser lens group 700 and the horizontal line is between 19° and 22°.

[0074] The grating assembly 600 contains a grating 610, which can be a transmission diffraction grating or a holographic grating. In this embodiment 1, it is preferably a transmission diffraction grating.

[0075] The collimating lens group 500, the grating assembly 600, the condenser lens group 700, and the area array camera 800 together constitute the aforementioned spectral imaging module, which images light of different wavelengths reflected from the surface under test and converged to the second lateral slit 402. Light of different wavelengths is imaged at different positions, thereby forming a contour image of the surface of the object under test with high information.

[0076] In Example 1, reference Figure 2 and Figure 3 A base 900 is also provided on the back of a coaxial scanning 3D spectral imaging system. The base 900 has a square first fixing device 920 for fixing the dispersive lens module 300, which is used to fix the housing of the beam splitter 320 in the dispersive lens module 300. The base 900 also has a second fixing device 910 for fixing the spectral imaging module. A fine-tuning knob is located above the second fixing device 910, which can be used for horizontal fine-tuning of the straight lens group 500, grating assembly 600, condenser lens group 700, and area array camera 800, focusing the spectral image converged to the second slit 402 on the side, so that the contour lines of the object being measured are obtained in a clear image. A square cutout is located near the center of the base 900, allowing a hand to reach in from behind to grasp and adjust the spectral imaging.

[0077] The spectral imaging side slit device 400 is disposed on one side of the spectral output and reflection optical path of the dispersive lens module 300, and its exploded view is shown below. Figure 7As shown, it includes a slide block 406, an upper fixing block 404, a lower fixing block 405, a slit fixing block 403, a second slit 402, and a rotating platform 401. The second slit 402 is mounted on the upper fixing block 404 and then fixed above the slide block 406. Slide rails 4061 are provided on both sides of the slide block 406, which can drive the second slit 402 to make fine adjustments along the Y direction. Spectra reflected from the surface being measured at different heights are converged by the beam splitter 320 and the lens located in the horizontal part of the spectral output reflection path, and then converge to the position of the second slit 402. The upper and lower fixing blocks 404 and 405 are mounted to the upper and lower ends of the rotating platform 401 through four screw holes. The screws are used for positioning and tightening, limiting the vertical sliding distance of the slide block 406, and locking it in the Y direction after the second slit 402 is finely adjusted and aligned. The left and right sides of the rotating stage 401 end face are also provided with slide rails 4011 / 4012, which cooperate with the slide rails 4061 on the left and right sides of the slide rail block 406 for fine-tuning the up and down of the second slit 402. Simultaneously, the rotating stage 401 can be rotated and fine-tuned along the θ direction. By fine-tuning the translation of the second slit 402 in the Y direction and the rotation in the θ direction, the second slit 402 can be precisely aligned with the spectral focusing lines at different heights reflected from the measured surface. The two adjustable-orientation "I-shaped" slits provided in this invention are easier to align in orientation compared to the pinhole array / DMD pixel array in the prior art, provide cleaner blocking of stray light from above and below, and have less noise crosstalk.

[0078] The dispersive lens module 300 includes an incident spectral dispersive light path and an outgoing spectral reflective light path, and internally houses a beam splitter 320. A cross-sectional view of the lens element of the dispersive lens module 300 is shown below. Figure 8 As shown.

[0079] refer to Figure 9The spectral incident dispersive optical path includes a first dispersive lens module (upper lens module) 310, a beam splitter 320, and a second dispersive lens module (lower lens module) 330. It is placed vertically with its optical axis perpendicular to the surface being measured. The upper lens module 310 of the spectral incident dispersive optical path includes cemented doublets 3101 / 3102, 3103 / 3104, 3105 / 3106, a single lens 3107, and 3108 / 3109. The cemented doublet in this embodiment 1 functions exactly the opposite of a conventional cemented doublet used for chromatic aberration correction; it is used to generate chromatic aberration. The concave lens inside the cemented doublet has a higher Abbe number than the convex lens cemented with it. The beam splitter 320 in the spectral incident dispersive light path is tilted at 45°. Its upper surface 3201 is coated with an anti-reflective film with a transmittance >99%, and its lower surface 3202 is coated with a semi-reflective film with both reflectance and transmittance of 50%. The lower lens group 330 in the spectral incident dispersive light path includes cemented doublets 3301 / 3302, 3303 / 3304, 3305 / 3306, and 3307 / 3308. The function of the cemented doublets here is also to generate chromatic aberration. As mentioned above, the concave lens inside the cemented doublet has a higher Abbe number than the convex lens cemented with it.

[0080] In the spectral incident dispersive optical path, the object plane of the spectral dispersive lens module 300 is the first slit 201 on the light source side, and the image plane is the spectral focusing lines λ1, λ2, and λ3 located on the surface under test and separated by height. The wavelengths λ1 to λ3 cover the visible light range of 400 nm to 700 nm. The first slit 201 and the spectral focusing lines λ1, λ2, and λ3 separated by height are mutually conjugate in object-image relationship. The broadband white light output from the first slit 201 on the light source side, after uniform color mixing, passes sequentially through the upper lens module 310, the beam splitter 320, and the lower lens module 330. Light of different wavelengths gradually separates after passing through the dispersive cemented doublet lens and converges at different heights near the surface under test.

[0081] refer to Figure 11The spectral outgoing and reflected light path collects the spectra reflected from different height positions on the measured surface and converges them at the second slit 402 on the side. A portion of the spectral outgoing and reflected light path is located below the beam splitter 320 and shares a lens 330 with the spectral incident and dispersive light path. The light reflected from the measured surface returns to the second dispersive lens module 330 almost in the opposite direction of incidence. Another portion of the spectral outgoing and reflected light path is located to the right of the beam splitter 320, and is horizontally oriented; this is the third lens module 340. The light reflected from the measured surface is reflected and deflected by the beam splitter 320, then splits horizontally and converges at the second slit 402 on the side. The third lens module 340 includes cemented doublet lenses 3401 / 3402, a single lens 3402, cemented doublet lenses 3404 / 3405, cemented doublet lenses 3406 / 3407, and cemented doublet lenses 3408 / 3409. The portions of the spectral outgoing reflected light path and the spectral incoming dispersive light path below the beam splitter 320 completely overlap, i.e., they share the second dispersive lens module 330, whose optical axis is set perpendicular to the surface of the object being measured. The portion 340 of the spectral outgoing reflected light path in the horizontal direction has the same lens assembly and materials as the portion of the spectral incoming dispersive light path above the beam splitter 320 (i.e., the first dispersive lens module 310).

[0082] In the spectral emission and reflection optical path, the object plane of the spectral dispersive lens module 300 is the height-separated spectral focusing lines λ1, λ2, and λ3 located on the surface under test, and the image plane is the second slit 402 located on the side of the lens. The height-separated spectral focusing lines λ1, λ2, and λ3 on the surface under test are simultaneously imaged onto the same position of the second slit 402 on the side of the lens. The height-separated spectral focusing lines λ1, λ2, and λ3, and the second slit 402 on the side, are mutually conjugate in object-image relationship. The spectra reflected from the surface under test at different heights are collected by the second dispersive lens module 330, reflected by the beam splitter 320, and transmitted through the third lens module 340 before being imaged onto the same position of the second slit 402 on the side.

[0083] The optical path diagram of the incident dispersion light path is as follows: Figure 9As shown, its optical path includes an upper lens group 310, a beam splitter 320, and a lower lens group 330. The optical axis of the upper lens group 310 is S1B1, which intersects at point B1 of the beam splitter 320. The optical axis of the lower lens group 330 is B2Z, which intersects at point B2 of the beam splitter 320. In the spectral incident dispersion optical path, the working wavelength and the working distance (the distance from the vertex of the lower surface of 3308 to the spectral focusing line) have a certain correspondence. This embodiment 1 uses a high-power COB (Chip on Board) module LED (Light Emitting Diode) with an output power exceeding 20W and a wavelength covering 400nm to 700nm. However, the light intensity at the two ends of the spectral curve, 400nm and 700nm, is relatively weak. In this embodiment, when designing the spectral incident dispersion optical path, the spectrum at both ends is cut off, and the position of the spectral focusing line is designed only for the 450nm to 650nm range. This ensures that the height difference between the working distance of the focusing line at 650nm and the working distance of the focusing line at 450nm is 2mm. That is, the depth of the emitted color band from blue to red light is greater than 2mm, thereby ensuring that the measurement depth of the system can reach at least 2mm. The peripheral principal rays Ray L and Ray R of the spectral incident dispersion optical path are located at approximately 320° of the beam splitter. They are almost parallel to the optical axis S1B1 of the incident dispersion optical path. The angle between the incident direction of the peripheral principal rays Ray L and Ray R and the optical axis S1B1 is set to be less than 1°, thereby further ensuring that the incident light can be incident on the surface of the object being measured as perpendicularly as possible.

[0084] Points B1 and B2 are misaligned by a vertical distance D, such as... Figure 10 As shown. The misalignment D is determined by the glass thickness and material of the beam splitter. The misalignment D ranges from 0.5mm to 1mm. In this embodiment 1, the thickness of the beam splitter 320 is preferably 2mm, the material is H-K9L, and the axial offset D of the upper and lower optical paths is 0.6725195mm. The angle between the edge rays RayL and RayR of the spectral incident dispersive optical path and the optical axis S1B1 is set to be less than 1°, and the optical axis offset D of the upper and lower lens groups 310 and 330 is set to 0.6725195mm, thereby ensuring that the additional astigmatism and coma generated by the beam splitter 320 when tilted are minimized, and thus ensuring that the optical system has a high MTF (modulation transfer function) value in both the meridional and sagittal directions. The dispersive lens module of this embodiment 1 has a beam splitter 320 inside, which is lighter than the traditional method of using a beam splitter prism and has less stray light, thus maximizing the measurement accuracy. Traditional beam splitters, with their four corners being square pyramids, cause stray light in the optical path to undergo total internal reflection within these pyramids, which can affect spectral imaging at the side slits.

[0085] Figure 12The results show the spectral dispersion simulation of the coaxial scanning 3D spectral imaging system of Example 1 at the measured surface location. Figure 12 The computer model above shows a receiving screen placed below the dispersive lens module on the surface being measured. A broadband slit line light source is set at the first slit 201 on the light source side for ray tracing and simulation to obtain the spectral dispersion distribution at the measured surface. In this embodiment 1, the length of the slit line light source is set to 11.5 mm, and the simulated spectral band length is 11.5 mm. From blue light at the top to red light at the bottom, the spectral depth of the band is 2 mm, meaning the system can measure objects with a height of 2 mm.

[0086] Figure 13 This is a schematic diagram of the overall computer simulation of the line-scan 3D spectral imaging system of Example 1. Assuming the model of the measured surface is a groove-shaped object, including a boss with a height or depth of 1.5 mm, the measured surface model is placed at the position of the spectral band. Simultaneously, a collimating lens group, a grating assembly, a condenser lens group, and an area array sensor are set up for overall computer simulation. The distribution of the light spot reflected from the groove-shaped measured surface is as follows... Figure 14 As shown. The intensity distribution of the contour image on the sensing surface of the area array camera is as follows. Figure 15 As shown, the XY dimensions of the sensing surface are 12mm x 12mm, which can clearly obtain the contour map of the measured surface. The point cloud of the contour image is output. When the moving stage moves the measured object, a 3D precision measurement image of the entire surface of the measured object can be obtained by fusing multiple frames of point cloud images.

[0087] The focusing lens group 700 of the line scan 3D spectral imaging system in Embodiment 1 described above has its optical axis positioned along the diffraction direction of the grating 610 for a wavelength of 550 nm. The tilt angle between the optical axis of the focusing lens group 700 and the horizontal line is between 19° and 22°, and the center position of the area array imaging sensor of the area array camera 800 corresponds to the spectral focusing line for a wavelength of 550 nm.

[0088] Because the central axis of the condenser lens group 700 is aligned with the diffraction direction of the 550nm wavelength of green light, it has an angle of inclination with the horizontal line. Furthermore, because the ratio of the diffraction angles of the grating 610 for 450nm blue light, 550nm green light, and 650nm red light to the wavelength is non-linear, when the central axis of the condenser lens group 700 is placed along the diffraction direction of the 550nm wavelength of green light, the distances between the spectral focusing lines formed by the contour lines of the 450nm blue light and 650nm red light on the top and bottom of the imaging sensor of the area array camera 800 and the center line of the sensor are not proportional. The spectral focusing contour lines are deformed in one direction, bending towards the red light direction, as shown below. Figure 15As shown, the spectral focusing line distortion is smaller at the blue light position and larger at the red light position. This distortion of the spectral focusing profile is called "smile distortion" or "field curvature" in spectral imaging systems, and it is a relatively common type of distortion. Currently, existing technologies generally rely on software calibration for different wavelengths and then correct the field curvature at each wavelength; there is no physically sound method for this.

[0089] This embodiment 2 proposes a physical compensation method to address the "smile distortion" (i.e., field curvature) in spectral imaging systems, which can largely compensate for the "smile distortion" caused by spectral focusing. The optical path compensation structure for spectral imaging is as follows: Figure 16 As shown in the diagram. Specifically, a sawtooth lens 620 with a high refractive index and low scattering coefficient is placed behind the diffraction grating 610. Through refraction by the sawtooth bevel, the 550nm green diffracted light is redirected back to a horizontal position. In this way, the diffraction angles of the upper and lower spectral focusing lines, after refraction by the sawtooth bevel, result in a more uniform image on the sensing surface relative to the center line of the sensing surface, approximating a proportional linearity. Furthermore, the use of a horizontally placed "I-shaped" slit makes the spectral imaging optical path easier to assemble and adjust.

[0090] The sawtooth lens 620 in this embodiment 2 is crown glass (the glass originally used to manufacture lenses was ordinary window glass or the bumps on wine bottles, shaped like a "crown," hence the name crown glass or crown glass. Optical glass with an Abbe number > 50 is usually called crown glass), with a refractive index greater than 1.7 and an Abbe number greater than 55.

[0091] The sawtooth lens 620, through refraction by its sawtooth bevel, redirects the diffracted green light with a center wavelength of 550nm back to a horizontal position. The optical path of the sawtooth bevel lens 620 is as follows: Figure 17 As shown, a light ray OP, collimated by collimating lens 500, is incident on point P of diffraction grating 610, and diffracts at point Q on the grating surface. The diffracted rays QR1, QR2, and QR3 have wavelengths of 450nm, 550nm, and 650nm, respectively, and are incident on sawtooth lens 620. After refraction by sawtooth lens 620, the refracted rays R1S1, R2S2, and R3S3 are incident on positions S1, S2, and S3 of sawtooth inclined surface 622. By setting the tilt angle of the sawtooth inclined surface and rotating the angle of the output ray S2T2, the output ray S2T2 is directed to exit horizontally. The tilt angle of the sawtooth inclined surface is set as follows... Figure 18As shown. The 550nm wavelength diffracted ray QR2 emitted from grating 610 has an angle δi with the horizontal direction, which is the diffraction angle of grating 610 for the 550nm wavelength. After the ray QR2 is refracted by the first surface 621 of the sawtooth lens, the angle of the refracted ray at point R2 is δo. After the green 550nm diffracted ray is rotated back to the horizontal position, the diffraction angles of the upper and lower spectral focusing lines of wavelengths 450nm and 650nm, after being refracted by the sawtooth inclined surface, will be relatively uniform in the image on the sensing surface relative to the center line of the sensing surface, as close as possible to a proportional linearity. At the same time, the use of a horizontally placed "I-shaped" slit makes the spectral imaging optical path easier to assemble and adjust.

[0092] To address the "smile distortion" in slit spectral imaging produced in Example 1, this invention proposes another physical compensation method, as described in Example 3. Example 3 employs a method of adding a deflecting prism 630 behind the grating 610, which can significantly compensate for the curvature of the spectral focusing lines. The optical path compensation structure for spectral imaging is as follows: Figure 19 As shown in the diagram. Specifically, a high-refractive-index, low-scattering-coefficient deflecting prism 630 is placed behind the diffraction grating 610. Through refraction by the prism's inclined surface, the diffracted green light at 550nm is redirected back to a horizontal position. In this way, the diffraction angles of the blue light at 450nm and the red light at 650nm at the vertical positions, after refraction by the sawtooth inclined surface, result in a more uniform distribution of the image on the sensing surface relative to the center line of the sensing surface, approximating a proportional linearity. The deflecting prism 630 in this embodiment 3 also uses crown glass, with a refractive index greater than 1.7 and an Abbe number greater than 55.

[0093] The function of the sawtooth lens 630 is to reverse the 550nm diffracted green light back to a horizontal position through refraction by the inclined surface of the deflecting prism SiSiii. The optical path of the sawtooth lens 630 is as follows: Figure 20 As shown, a light ray OP, collimated by collimating lens 500, is incident on point P of diffraction grating 610, and diffracts at point Q on the grating surface. The diffracted rays QR1, QR2, and QR3 have wavelengths of 450nm, 550nm, and 650nm, respectively, and are incident on deflecting prism 630. After refraction by deflecting prism 630, the refracted rays R1S1, R2S2, and R3S3 are incident on positions S1, S2, and S3 of inclined plane SiSii. S1T1, S2T2, and S3T3 are the refracted rays of blue light (450nm), green light (550nm), and red light (650nm) output from the inclined plane. When the green light (550nm) is rotated back to the horizontal position, according to... Figure 20 The geometric relationship is such that the tilt angle τ of the inclined plane SiSii of the deflecting prism is consistent with the tilt angle τ of Example 2 above.

[0094] Figure 21This is a schematic diagram simulating the spectral reflectance of a stepped surface placed at the measurement location. The steps consist of 10 levels with a total height of 2 mm. From top to bottom, the total width of the steps is 10 mm, falling within the range of the spectral measurement band.

[0095] Figures 22-24 The images show a comparison of the simulation results of the imaging systems in Examples 1 to 3 on the stepped test surface. It can be seen that the overall contour imaging of the stepped test surface in Example 1 is relatively curved, while the contour imaging of the stepped surface in Examples 2 and 3 is relatively linear, basically correcting the curvature of the imaging. From blue light 450nm to red light 650nm, its nonlinearity can be corrected to within 0.5%.

[0096] In one embodiment, a device for precision three-dimensional measurement is also provided. The device includes the coaxial scanning 3D spectral imaging system described in any of the above claims. It establishes the correspondence between the height of the measured surface and the spectrum through the principle of optical dispersion, and decodes the spectral information with a spectrometer to obtain position information, thereby realizing precise three-dimensional measurement of the surface unevenness of an object.

[0097] The above description is merely an exemplary embodiment of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Other embodiments of this disclosure will be readily apparent to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.

[0098] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described in detail. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coaxial spectral confocal imaging system, characterized in that, include, Light source module, dispersive lens module, spectral imaging side slit device and spectrometer; The light source module is used to provide a wide-spectrum light beam and incident it onto the dispersive lens module through a light source-side slit device; The dispersive lens module includes a beam splitter and a first dispersive lens module for dispersive purposes located above the beam splitter, a second dispersive lens module for dispersive purposes located below the beam splitter, and a third lens module for focusing located on the side of the beam splitter. The dispersive lens module is used to pass the incident light beam through the first dispersive lens module, the beam splitter and the second dispersive lens module in sequence, so that the light of different wavelengths in the light beam is focused at different heights on the surface of the object to be tested. It is also used to converge the light reflected from the surface of the object to be tested to the spectral imaging side slit device after passing through the second dispersive lens module, being reflected by the beam splitter and passing through the third lens module in sequence. The spectrometer is used to image light of different wavelengths that converge to the spectral imaging side slit device, and the light of different wavelengths is imaged at different positions of the spectrometer; The spectrometer is arranged along the propagation path of the reflected light, including a collimating lens group, a grating assembly, an optical path compensation assembly, a condenser lens group, and an area array camera. The collimating lens group is used to maintain the collimation of the reflected light beam; The grating assembly includes a grating for diffracting the reflected light beam; The optical path compensation component is used to compensate the light passing through the grating component, so that the light of the preset center wavelength diffracted by the grating component is emitted horizontally after passing through the optical path compensation component. The optical axis of the condenser lens group coincides with the optical axis of the collimating lens group and the third lens module; The area array camera is used to image the light transmitted through the condenser lens group.

2. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, There is an offset between the optical axes of the first dispersive lens module and the second dispersive lens module.

3. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, The light source side slit device includes a first slit in a "one-line" shape; the spectral imaging side slit device includes a second slit in a "one-line" shape, a slide block, and a rotating platform; The second slit is fixedly mounted on the slide block, which can translate radially on the rotating platform. The rotating platform can rotate in the direction of rotation of the optical axis with the optical axis as the axis. By adjusting the orientation of the second slit in the translation and / or rotation directions, the second slit can be made parallel to the first slit in the direction of slit length extension and / or the direction of slit length extension of the second slit can be aligned with the spectral focusing lines of different heights of the light reflected from the surface of the object under test.

4. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, The light source module also includes a light mixing device, which is used to mix the provided broadband light beam.

5. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, The beam splitter is a beam splitter, and the first surface of the beam splitter is coated with an anti-reflection film; the second surface of the beam splitter is coated with a semi-reflective and semi-transparent film.

6. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, The optical path compensation component is a sawtooth lens. Light of a preset center wavelength, diffracted by the grating component, is refracted by the sawtooth lens and emitted horizontally.

7. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, The optical path compensation component is a deflecting prism. Light of a preset center wavelength, diffracted by the grating component, is refracted by the deflecting prism and emitted horizontally.

8. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, The preset center wavelength is 550nm.

9. The coaxial spectral confocal imaging system as described in claim 7, characterized in that, The deflecting prism has at least a first surface and a second surface, the first surface being parallel to the grating, and the angle between the second surface and the first surface being an acute angle.

10. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, The collimating lens group and the condensing lens group use lenses with the same focal length.

11. The coaxial spectral confocal imaging system as described in claim 4, characterized in that, The light mixing device is a solid light mixing rod or a hollow light mixing cavity.

12. The coaxial spectral confocal imaging system as described in claim 1, characterized in that, The third lens module is the same as the first dispersive lens module.

13. The coaxial spectral confocal imaging system according to any one of claims 1 to 12, characterized in that, The system also includes a base on the back for supporting the entire coaxial spectral confocal imaging system. The base has a cutout for holding or adjusting the coaxial spectral confocal imaging system.

14. A device for three-dimensional measurement, characterized in that, The device includes the coaxial spectral confocal imaging system according to any one of claims 1 to 13.

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