Dark field lighting device based on rotary off-axis even-order aspheric curved mirror

Abstract

The dark field illumination device is used for illuminating a workpiece to be detected and comprises the annular off-axis even-order aspheric curved mirror and an annular light source set, the annular off-axis even-order aspheric curved mirror is provided with a reflecting surface, the annular light source set is located near the focal point of the reflecting surface, and the annular light source set is located near the focal point of the reflecting surface. Light emitted by the annular light source group is reflected by the reflecting surface and then forms an illuminating surface at the axis of the annular off-axis even-order aspheric curved mirror, and a workpiece to be detected is located on the illuminating surface. Collimated or converged high-quality light beams can be generated by utilizing the excellent optical characteristics of even aspheric surfaces, the imaging contrast ratio and the defect detection capability are remarkably improved, and light spot hot spots and dark areas in a traditional scheme are fundamentally eliminated by combining the annular light source with the optical design of rotational symmetry.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of machine vision, industrial detection and optical imaging technology, in particular to a dark field illumination device based on a rotary off-axis even aspherical curved mirror. BACKGROUND

[0002] In the field of industrial detection, dark field illumination is a crucial technology for highlighting small scratches, depressions, particles, fingerprints and other uneven features on the surface of an object. The basic principle is to make the light obliquely incident on the surface of the object to be detected at a large angle, so that the smooth surface cannot reflect the light into the imaging lens, thereby appearing as a dark field in the image; while the defects on the surface will scatter the light, and part of the scattered light will enter the lens, thereby forming a bright defect image in the dark background.

[0003] The existing dark field illumination schemes mainly include the following: 1. Ring LED direct illumination: arrange LEDs in a ring shape to directly illuminate the object. This method is simple in structure, but the light is not collimated, the angle is chaotic, the illumination is uneven, and it is difficult to achieve consistent illumination, which is prone to stray light and low contrast.

[0004] 2. Lens collimation scheme: add collimating lenses (such as convex lenses or conical lenses) outside or inside the ring-shaped LED to converge the light. This method improves collimation, but usually has the following problems: Large size: in order to achieve good collimation effect, a long light path distance is required, resulting in a large device size; Aberration problem: ordinary lenses have spherical aberration, chromatic aberration, etc., affecting the quality and uniformity of the collimated light beam; Complex assembly: the calibration and fixation of multiple lenses increase the manufacturing difficulty and cost.

[0005] 3. Optical fiber light guiding scheme: use optical fiber bundles to guide light from a remote light source to a ring-shaped light outlet. This scheme can achieve flexible light distribution, but has low light energy utilization, high system cost, and the uniformity control of the light outlet is still a challenge.

[0006] Therefore, there is an urgent need in the art for a dark field illumination device that can simultaneously achieve high collimation, high uniformity, compact structure and easy assembly.

[0007] To this end, we propose a dark field illumination device based on a rotary off-axis even aspherical curved mirror. SUMMARY

[0008] The present application aims to provide a dark field illumination device based on a rotary off-axis even aspherical curved mirror to solve the problems raised in the background art.

[0009] In order to achieve the above object, the application provides the following technical scheme: a dark field illumination device based on a rotary off-axis even aspherical curved mirror, which is used for illuminating a workpiece to be detected, comprising a ring-shaped off-axis even aspherical curved mirror and a ring-shaped light source group, the ring-shaped off-axis even aspherical curved mirror has a reflecting surface, the ring-shaped light source group is located near the focal point of the reflecting surface, and the light emitted by the ring-shaped light source group forms an illumination surface at the axis of the ring-shaped off-axis even aspherical curved mirror after being reflected by the reflecting surface, and the workpiece to be detected is located on the illumination surface. The reflecting surface includes but is not limited to even aspherical surfaces and special and approximate forms thereof, such as spherical surfaces, parabolic surfaces, ellipsoidal surfaces, hyperbolic surfaces or approximate fitting arc segments thereof.

[0010] Optionally, the oblique light rays forming the illumination surface are all reflected light rays of the ring-shaped light source group.

[0011] Optionally, the side of the ring-shaped off-axis even aspherical curved mirror away from the reflecting surface is a plane, and the outer side of the ring-shaped off-axis even aspherical curved mirror is fixedly installed with a connecting mechanism, the connecting mechanism is movably connected with the ring-shaped light source group, and the ring-shaped light source group can be moved along the axis of the ring-shaped off-axis even aspherical curved mirror through the connecting mechanism.

[0012] Optionally, a linear groove adjusting mechanism is arranged between the connecting mechanism and the ring-shaped light source group, and the linear groove adjusting mechanism is used for moving the ring-shaped light source group along the axis of the ring-shaped off-axis even aspherical curved mirror and adjusting the distance between the ring-shaped light source group and the ring-shaped off-axis even aspherical curved mirror.

[0013] Optionally, the ring-shaped light source group comprises a plane substrate fixedly installed with the linear groove adjusting mechanism, the plane substrate is located in the interior of the connecting mechanism, a through groove is formed in the middle part of the plane substrate, and a plurality of LED chips are arranged on the top of the plane substrate.

[0014] Optionally, the ring-shaped light source group is located near one focal plane or focal point of the ring-shaped off-axis even aspherical curved mirror.

[0015] Optionally, the plurality of LED chips are arranged in a ring shape on the top of the plane substrate with a certain radius.

[0016] Optionally, the light emitting surface of the LED chip faces the reflecting surface of the ring-shaped off-axis even aspherical curved mirror.

[0017] Optionally, the plane substrate is fixedly installed with the movable end of the linear groove adjusting mechanism, and the plane substrate is located in the interior of the connecting mechanism.

[0018] Compared with the prior art, the application has the following beneficial effects: 1. Excellent beam quality and imaging contrast: using the excellent optical properties of conic surfaces, a high-quality collimated or convergent beam can be generated, significantly improving the imaging contrast and defect detection capability.

[0019] 2. Extremely high illumination uniformity: the combination of ring light source and rotationally symmetric optical design fundamentally eliminates the spot hot spots and dark areas in traditional solutions, achieving 360-degree uniform illumination.

[0020] 3. High compactness: using a reflective optical path folding design, the long optical path effect required by traditional solutions is achieved in a very short axial space, greatly reducing the device volume and facilitating integration into space-limited equipment.

[0021] 4. Unparalleled design flexibility and versatility: the core of the invention is to construct a versatile optical transformation paradigm. By selecting different types of conic surfaces (parabolic, ellipsoidal, etc.) and adjusting their geometric parameters and the position relationship with the LED ring, it can be very flexible to design illumination solutions that meet different angles, different working distances, and different spot characteristics, with extremely wide application range.

[0022] Simplified manufacturing and assembly process: the core optical component is a single rotationally symmetric element, reducing the number of components and simplifying the assembly and calibration process, thereby reducing manufacturing cost and difficulty. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The optical path diagram of the dark field illumination device based on the rotationally off-axis aspheric surface mirror of the present invention; Figure 2 The relationship between the components of the dark field illumination device of the present invention; Figure 3 The overall structure schematic diagram of the dark field illumination device based on the annular off-axis even aspheric surface mirror of the present invention; Figure 4 The side view of the dark field illumination device based on the rotationally off-axis even aspheric surface mirror of the present invention; Figure 5 Dark field light source front light schematic diagram; Figure 6 Dark field light source back light schematic diagram; Figure 7 Bright field light source, dark field light source front light, bright field light source back light effect diagram; Figure 8 The side view of the annular off-axis even aspheric surface mirror in the dark field illumination device based on the rotationally off-axis even aspheric surface mirror of the present invention; Figure 9 Conic curve principle schematic diagram; Figure 10 Fig. 1 is a schematic diagram of a conic curve light reflection principle; Figure 11 Fig. 2 is a schematic diagram of a rotation ellipse eccentricity; Figure 12 Fig. 3 is a schematic diagram of a prior art dark field light path structure.

[0024] In the figure: 1, connecting mechanism; 2, annular off-axis even-order aspheric curved mirror; 201, connecting surface; 202, observation hole; 203, reflecting surface; 3, ring light source group; 301, plane substrate; 302, through slot; 303, LED chip; 4, straight slot adjusting mechanism. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0026] As is known, a quadratic aspheric surface or a higher-order aspheric surface can better eliminate imaging aberration than a spherical lens, and can also realize specific light convergence capability.

[0027] Typical quadratic aspheric surfaces (conic aspheric surfaces) include parabolic surfaces, ellipsoidal surfaces and hyperbolic surfaces. The generatrixes of the three aspheric surfaces can be obtained by cutting different positions of a conic, and the cut edge is a conic curve. The conic aspheric surface can be obtained by rotating around the symmetry axis of the conic generatrix.

[0028] The conic aspheric surface has some good characteristics. For example, a parabolic surface (having only one focus) emits light from the focus, and the reflected light is parallel to the outgoing light after being reflected by a parabolic mirror. A flashlight adopts a reflective parabolic surface. An ellipsoidal surface (having two conjugate foci) can emit light from one focus, and the reflected light converges to the other focus after being reflected by an ellipsoidal aspheric surface. A hyperbolic surface (having two foci) can emit light from one focus, and the reflected light converges to the other focus after being reflected by a hyperbolic surface.

[0029] Dark field illumination has many applications in the field of microscopy, mainly because the targets observed by microscopy are mostly transparent objects, and the contrast of the image observed by microscopy is very low. The dark field illumination separates the imaging light path and the illumination light path, and the light passing through the transparent object will directly pass through without being received by the imaging light path, while the low transparency target will scatter the light, and the scattered light will cover the imaging light path and thus be seen, so it will have good contrast with the transparent background. The basic idea of the existing dark field illumination of the microscope objective is to block the central area of the illumination light source and only let the edge light pass. The light source can be transmitted and collimated by a lens, or reflected and collimated by a parabolic mirror. However, such reflective aspheric surfaces are mostly obtained by rotating along the symmetric axis passing through the focal point, which has two disadvantages difficult to overcome in the industrial field: 1. The focal point of the aspheric reflective surface is on the symmetric axis, and the light emitting surface must also be on the focal point, so the light emitting surface is mostly a small light emitting surface light source, and the energy cannot be improved, the brightness is limited, and it is difficult to meet the requirements of high-speed monitoring for industrial applications; 2. Generally, the light emitting light source is placed on the back of the target or around the imaging objective. For industrial applications, if it is placed on the back of the target, it will limit many application scenarios, because many detected targets can only be placed on the opaque bottom plate, and cannot be placed on the standard transparent glass slide, which has become a tradition and habit in the microscopy industry. For the industrial field, the object platform is diverse and cannot be unified, and it is also difficult to cooperate with the corresponding rectification of the monitoring equipment; and the transmission method needs to arrange the light emitting light source around the lens, and a half-reflective and half-transmissive lens is needed to achieve it, which does not have enough flexibility and usability in many scenarios.

[0030] If the parabolic mirror is rotated by an angle α and translated upward by d, and then only a part of the parabolic mirror is selected to reflect the light to the target surface, we get a dark field illumination with an inclination angle of α. However, the brightness of this illumination is not high, and we can rotate this generatrix around the horizontal axis by 360 degrees to get a revolved conical aspheric surface, and the axis of rotational symmetry is no longer the axis of symmetry of the generatrix itself passing through the focal point. In this way, the light emitting surface becomes a ring-shaped area at the height of the focal point of the parabolic mirror, which can be rotated by 360 degrees around the horizontal axis. This configuration can greatly improve the area and energy of the illumination light source, thereby improving the brightness at the target. The design of the light emitting source and the reflector can form a module, thereby having high flexibility and can be placed separately without being integrated with the imaging light path. In addition, this setting can be placed on the same side as the imaging light path, thereby improving its adaptability and range of use.

[0031] Please refer to Figures 1 to 12The application provides a dark field illumination device based on a rotary off-axis even aspherical curved mirror, which is used for illuminating a workpiece to be detected and comprises a ring-shaped off-axis even aspherical curved mirror 2 and a ring-shaped light source group 3. The rotary shaft of the reflecting surface 203 and the axis of the ring-shaped off-axis even aspherical curved mirror 2 form a certain angle, and the angle is the angle at which the light emitted by the ring-shaped light source group 3 is obliquely irradiated on the illumination surface. The reflecting surface 203 includes but is not limited to even aspherical surface and its special and approximate forms, such as spherical surface, parabolic surface, ellipsoidal surface, hyperboloidal surface or its approximate fitting arc segment, etc.

[0032] The oblique light rays forming the illumination surface are formed by reflecting the light emitted by the ring-shaped light source group 3 by the reflecting surface 203.

[0033] The side of the ring-shaped off-axis even aspherical curved mirror 2 away from the reflecting surface 203 is a plane, and the outer side of the ring-shaped off-axis even aspherical curved mirror 2 is fixedly provided with a connecting mechanism 1, the connecting mechanism 1 is movably connected with the ring-shaped light source group 3, and the ring-shaped light source group 3 can be moved along the axis of the ring-shaped off-axis even aspherical curved mirror 2 through the connecting mechanism 1.

[0034] A linear groove adjusting mechanism 4 is arranged between the connecting mechanism 1 and the ring-shaped light source group 3, and is used for moving the ring-shaped light source group 3 along the axis of the ring-shaped off-axis even aspherical curved mirror 2 and adjusting the distance between the ring-shaped light source group 3 and the ring-shaped off-axis even aspherical curved mirror 2.

[0035] The ring-shaped light source group 3 comprises a plane base plate 301 fixedly provided with the linear groove adjusting mechanism 4, the plane base plate 301 is located in the interior of the connecting mechanism 1, a through groove 302 is formed in the middle of the plane base plate 301, and a plurality of LED chips 303 are arranged on the top of the plane base plate 301.

[0036] The ring-shaped light source group 3 is located near a focal plane or a focal point of the ring-shaped off-axis even aspherical curved mirror 2.

[0037] The plurality of LED chips 303 are arranged in a ring shape on the top of the plane base plate 301 with a certain radius.

[0038] The light emitting surface of the LED chip 303 faces the reflecting surface 203 of the ring-shaped off-axis even aspherical curved mirror 2.

[0039] The plane base plate 301 is fixedly provided with the movable end of the linear groove adjusting mechanism 4 and is located in the interior of the connecting mechanism 1.

[0040] The divergent light emitted by the LED chip 303 illuminates the reflecting surface 203 of the annular off-axis even-order aspherical curved mirror 2. According to the optical characteristics of the conic section, the light will be efficiently focused or collimated, and finally a high-quality beam at a specific angle to the optical axis will be formed, which will then illuminate the object through the through slot 302.

[0041] like Figures 5-6 As shown, a camera is provided on one side of the annular off-axis even-order aspherical surface mirror 2. The camera is located on the axis of the annular off-axis even-order aspherical surface mirror 2. When the workpiece is illuminated from the front, the annular off-axis even-order aspherical surface mirror 2 is located between the workpiece to be inspected and the camera. When the workpiece is illuminated from the back, the workpiece to be inspected is located between the annular off-axis even-order aspherical surface mirror 2 and the camera. The annular off-axis even-order aspherical surface mirror 2 is provided with a connecting surface 201 connected to the camera body and an observation hole 202 for the camera lens to observe the workpiece to be inspected.

[0042] The rotation axis of the reflecting surface 203 forms a certain angle with the axis of the annular off-axis even-order aspherical curved surface mirror 2. This angle is the angle at which the light emitted by the annular light source group 3 obliquely illuminates the illumination surface.

[0043] Furthermore, since the light emitted by the ring light source group 3 is obliquely illuminating the workpiece on the surface to be inspected, the light emitted by the ring light source group 3 will not be interfered with by the camera, ensuring that when the camera performs visual inspection on the workpiece, there will be no areas on the workpiece that are not illuminated by the optical fiber.

[0044] Example 1 When the reflecting surface 203 is a parabola, the ring light source group 3 needs to be set at the focal plane of the parabola. The reflected light is parallel light at a fixed angle to the optical axis. The illumination angle θ is determined by the diameter of the ring-shaped off-axis even-order aspherical curved mirror 2 and the LED chip 303 in the ring light source group 3. By adjusting these parameters, a continuous design from a very small angle (e.g., <10°) to a very large angle (e.g., >60°) can be achieved to meet different lighting needs such as bright field, low-angle dark field, and high-angle dark field.

[0045] 2 is a 25-degree off-axis parabolic mirror with an annular even-order aspherical surface. Includes: ring light source group 3, and ring-shaped off-axis even-order aspherical surface mirror 2; Eight high-brightness LED chips 303 are soldered on the planar substrate 301, arranged in a circle with a diameter D1=40.3mm and a radius of curvature of 88.2mm. The reflecting surface 203 of the annular off-axis even-order aspherical curved mirror 2 is a parabolic mirror with a conic coefficient of -1, an off-axis amount of 58.88mm, and a tilt angle of 25°. The focal length of the off-axis parabolic mirror is 44.1mm. During assembly, ensure that the center of the LED light emission is precisely located at the focal plane of the off-axis parabolic mirror.

[0046] The rotation off-axis parabolic mirror can make the included angle between the reflected parallel light and the central optical axis be ±25°, realize standard dark field illumination, the light emitting diameter of the LED chip 303 is 4.3 mm, the light emitting angle of the LED itself is less than 30 degrees, and about 22.5°-27.5° illumination angle can be realized on the same mirror.

[0047] Embodiment two When the reflecting surface 203 is an ellipsoidal surface, the LED chip 303 of the ring light source group 3 can be arranged near a focal point, the light is reflected and converged to the other focal point (i.e. the working surface) to form convergent light illumination, and the distance between the ring light source group 3 and the ring-shaped off-axis even aspherical mirror 2 can be adjusted by the straight slot adjusting mechanism 4, so that the working surface can obtain higher brightness at certain specific working distance.

[0048] The embodiment only takes the rotation parabolic mirror as an example, but in actual application, it is not necessary to be a strict parabolic surface, for the extended ring light source, the curve slightly deviates from the parabolic surface and is a rotation ellipsoidal surface or a rotation hyperbolic surface, then the light emitting source of different diameter ring bands can be considered. At the same time, the target area does not necessarily have the best effect of the collimated light source, and can be slightly convergent or divergent, so as to adjust the size or brightness of the illumination area at the target, to meet the more important needs of the customers. But the light path can also reduce the cost, use the rotation spherical surface instead of the rotation aspherical surface, the uniformity will be slightly reduced, but the processing difficulty can be reduced.

[0049] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A dark field illumination device based on a rotary off-axis even-order aspherical surface mirror, used for illuminating a workpiece to be inspected, comprising an annular off-axis even-order aspherical surface mirror (2) and an annular light source group (3), characterized in that, The annular off-axis even-order aspherical surface mirror (2) has a reflecting surface (203). The annular light source group (3) is located near the focal point of the reflecting surface (203). The light emitted by the annular light source group (3) is reflected by the reflecting surface (203) and forms an illumination surface at the axis of the annular off-axis even-order aspherical surface mirror (2). The workpiece to be inspected is located on the illumination surface. The reflecting surface (203) includes even-order aspherical surfaces and their special and approximate forms, such as spheres, parabolic surfaces, ellipsoids, hyperboloids or their approximate fitted arc segments.

2. The dark field illumination device based on a rotary off-axis even-order aspherical surface mirror according to claim 1, characterized in that, The oblique rays that form the illumination surface are all formed by the light emitted from the ring light source group (3) reflected by the reflective surface (203).

3. The dark field illumination device based on a rotary off-axis even-order aspherical surface mirror according to claim 1, characterized in that, The side of the annular off-axis even-order aspherical mirror (2) away from the reflecting surface (203) is a plane. A connecting mechanism (1) is fixedly installed on the outer side of the annular off-axis even-order aspherical mirror (2). The connecting mechanism (1) is movably connected to the ring light source group (3). The ring light source group (3) can be moved along the axis of the annular off-axis even-order aspherical mirror (2) through the connecting mechanism (1).

4. A dark field illumination device based on a rotary off-axis even-order aspherical surface mirror according to claim 3, characterized in that, A straight groove adjustment mechanism (4) is provided between the connecting mechanism (1) and the annular light source group (3). The straight groove adjustment mechanism (4) is used to move the annular light source group (3) along the axis of the annular off-axis even-order aspherical surface mirror (2) and adjust the distance between the annular light source group (3) and the annular off-axis even-order aspherical surface mirror (2).

5. A dark field illumination device based on a rotary off-axis even-order aspherical surface mirror according to claim 4, characterized in that, The ring light source group (3) includes a planar substrate (301) fixedly installed with the straight groove adjustment mechanism (4). The planar substrate (301) is located inside the connecting mechanism (1). A through groove (302) is opened in the middle of the planar substrate (301). Multiple LED chips (303) are arranged on the top of the planar substrate (301).

6. A dark field illumination device based on a rotary off-axis even-order aspherical surface mirror according to claim 5, characterized in that, Multiple LED chips (303) are arranged in a ring with a certain radius on the top of the planar substrate (301).

7. A dark field illumination device based on a rotary off-axis even-order aspherical surface mirror according to claim 5, characterized in that, The light-emitting surface of the LED chip (303) faces the reflective surface (203) of the annular off-axis even-order aspherical curved mirror (2).

8. A dark field illumination device based on a rotary off-axis even-order aspherical surface mirror according to claim 5, characterized in that, The planar substrate (301) is fixedly installed at the movable end of the linear groove adjustment mechanism (4), and the planar substrate (301) is located inside the connecting mechanism (1).

9. A dark field illumination device based on a rotary off-axis even-order aspherical surface mirror according to claim 1, characterized in that, The ring light source group (3) is located near a focal plane or focal point of the annular off-axis even-order aspherical surface mirror (2).

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