Sammer lens and industrial camera

Abstract

The invention relates to a Samm lens, which comprises a light-splitting lens group, a compensating lens group and an imaging lens group which are sequentially arranged from an object side to an image side along an optical axis of the lens, the light-emitting lens group is a negative-focal-power lens group, the compensation lens group is a positive-focal-power lens group, and the imaging lens group is a positive-focal-power lens group; and the ratio of the clear aperture of the imaging lens group to the clear aperture of the light splitting lens group is 0.1-1.2. According to the invention, the distortion of the lens can be greatly reduced, the aberration of large-angle target plane inclination can be eliminated, and the image resolution can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical systems, in particular to a Sham lens. Background Art

[0002] With the development of optics, image processing, and computer technology, 3D line laser measurement technology has become widely used. This technology obtains corresponding image information through shooting and then performs a series of image processing to extract key information for measurement. However, 3D line laser measurement technology requires capturing targets at a certain angle to the lens. Due to the limited depth of field, the lens used in related technologies cannot simultaneously and clearly image the entire field of view of the tilted target.

[0003] Therefore, the currently commonly used 3D line laser measurement technology usually adopts Sham lens to obtain a wide range of clarity. Figure 1 , referring to patent document with application number "202310116019.1", wherein the Sham lens includes a first lens group 1, a second lens group 2, and a third lens group 3, arranged in sequence along the lens optical axis from the object side to the image side, wherein the first lens group 1, the second lens group 2, and the third lens group 3 are all positive optical power lens groups; wherein the clear aperture of the second lens group 2 serves as the aperture stop of the Sham lens, the ratio of the clear aperture of the third lens group 3 to the clear aperture of the first lens group 1 is 0.6-1.1, and the number of lenses in the first lens group 1 and the number of lenses in the third lens group 3 are equal. The object side is the side of the Sham lens close to the object, and the image side is the side of the Sham lens far from the object.

[0004] Specifically, see Figure 2 Unlike the traditional imaging optical path where the principal plane of the lens is parallel to the CMOS chip surface, in the imaging optical path of the Sham lens, the principal plane O of the Sham lens intersects the target plane D to be clearly imaged and the extension line of the CMOS chip surface F on the same straight line. At this time, the entire target plane can be clearly imaged on the CMOS chip surface, satisfying the Sham relationship:

[0005]

[0006] Among them, α is the angle between the target plane and the lens optical axis, β is the angle between the imaging plane and the lens optical axis, and a ′ is the object distance at point D on the lens optical axis, b ′ is the image distance of point D on the optical axis of the lens, However, the existing Sham lens still cannot adequately compensate for the distortion caused by the large inclination angle between the target plane and the lens principal plane, resulting in low image accuracy. Summary of the Invention

[0007] Based on this, the purpose of the present invention is to provide a Sham lens that can significantly reduce lens distortion, eliminate aberrations for large-angle target plane tilt, and improve resolution.

[0008] A Sham lens comprises a light-dividing lens group, a compensating lens group, and an imaging lens group, which are arranged in sequence from the object side to the image side along the lens optical axis; the light-dividing lens group is a negative optical power lens group, the compensating lens group is a positive optical power lens group, and the imaging lens group is a positive optical power lens group; and the ratio of the clear aperture of the imaging lens group to that of the light-dividing lens group is 0.1-1.2.

[0009] Furthermore, the total focal length of the Sham lens is 25mm-35mm, the working spectrum range is 400-700nm, the ratio of the total optical length to the image half height TTL / IH is 10.7:1, and the angle between the target plane and the optical axis of the lens is 60°-85°; wherein, the total optical length TTL is the distance from the front surface of the first spherical surface to the image plane, and the image half height IH is the half image height of the diagonal of the curved arrangement.

[0010] Furthermore, the focal length of the light-extracting lens group is -35mm to -45mm, the focal length of the compensating lens group is 10mm to 20mm, the focal length of the imaging lens group is 15mm to 25mm, the air gap between the light-extracting lens group and the compensating lens group on the optical axis of the lens is 3mm to 5mm, and the air gap between the compensating lens group and the imaging lens group on the optical axis of the lens is 5mm to 6mm.

[0011] Furthermore, the light analyzing lens group includes four spherical lenses, the compensation lens group includes three spherical lenses, and the imaging lens group includes one spherical lens.

[0012] Furthermore, the light-extracting lens group includes a first light-extracting lens, a second light-extracting lens, a third light-extracting lens, and a fourth light-extracting lens, which are arranged in sequence from the object side to the image side along the optical axis of the lens; the first light-extracting lens has positive focal power and both surfaces of the two sides are convex; the second light-extracting lens has positive focal power and the object-side surface is convex and the image-side surface is concave; the third light-extracting lens has negative focal power and the object-side surface is convex and the image-side surface is concave; the fourth light-extracting lens has negative focal power and both surfaces of the two sides are concave.

[0013] Furthermore, the compensation lens group includes a first compensation lens, a second compensation lens and a third compensation lens arranged in sequence from the object side to the image side along the optical axis of the lens; the first compensation lens has positive optical focal length and both side surfaces are convex; the second compensation lens has positive optical focal length and both side surfaces are convex; the third compensation lens has negative optical focal length and both side surfaces are concave.

[0014] Furthermore, the imaging lens group includes a first imaging lens; the first imaging lens has positive optical power and both side surfaces are convex, and the curvature radii of the two side surfaces are equal.

[0015] The present invention also provides an industrial camera, comprising the above-mentioned Sham lens, a detector and a cover plate; the detector is arranged on the imaging plane of the Sham lens, and the cover plate is a transparent flat plate arranged on the surface of the detector.

[0016] Furthermore, the cover plate is perpendicular to the optical axis of the Sham lens.

[0017] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of an existing Sham lens.

[0019] Figure 2 Schematic diagram of the principle of Sham lens.

[0020] Figure 3 This is a schematic diagram of the Sham lens structure of this application.

[0021] Figure 4 This is the optical diffusion pattern of the Sham lens of this application.

[0022] Figure 5 Schematic diagram of the modulation transfer function (MTF) of the Sham lens of this application.

[0023] Figure 6 Schematic diagram of the field curvature of the Sham lens of this application.

[0024] Figure 7 Schematic diagram of astigmatism of the Sham lens of this application.

[0025] Figure 8 This is a schematic diagram of the industrial camera structure of this application.

[0026] Figure 9 This is a schematic diagram of the optical path of the industrial camera of this application when it is working. DETAILED DESCRIPTION

[0027] This applicant carefully analyzed existing Sham lenses and discovered that they are unable to handle large tilts of the target plane. This is because the lens assembly, designed to offset its own distortion, is symmetrical, but this is unable to offset the distortion caused by large tilts of the target plane. Therefore, this applicant attempts to modify the nearly symmetrical structure of the lens assembly, rearranging the position, number, and curvature of each lens to eliminate the distortion caused by large tilts of the target plane.

[0028] Based on this, see Figure 3 The present application designs a Sham lens, comprising a light analyzing lens group 1, an aperture 2, a compensation lens group 3, and an imaging lens group 4, arranged in sequence from the object side to the image side along the lens optical axis. A light beam from a target plane forms a corresponding real image after passing through the Sham lens.

[0029] In one embodiment, the light-extracting lens group 1 includes four spherical lenses, the compensating lens group 2 includes three spherical lenses, and the imaging lens group 4 includes one spherical lens. It should be understood that the number of lenses in each lens group is not fixed; this embodiment illustrates only one combination. The number of lenses in the light-extracting lens group 1 can be increased or decreased, the number of lenses in the compensating lens group 2 can be increased or decreased, and the number of lenses in the imaging lens group 4 can be increased.

[0030] Specifically, the light-extracting lens assembly 1 is a negative-power lens assembly, comprising a first light-extracting lens 11, a second light-extracting lens 12, a third light-extracting lens 13, and a fourth light-extracting lens 14, arranged sequentially along the lens optical axis from the object side to the image side. The first light-extracting lens 11 has positive power and has convex surfaces on both sides; the second light-extracting lens 12 has positive power, has a convex object-side surface, and a concave image-side surface; the third light-extracting lens 13 has negative power, has a convex object-side surface, and a concave image-side surface; and the fourth light-extracting lens 14 has negative power and has concave surfaces on both sides. This combination of positive, negative, and negative power lenses allows for rapid optical path integration and effective lens distortion correction, thereby alleviating the burden of aberration correction on the rear lens group.

[0031] The diaphragm 2 is disposed between the light-dividing lens group 1 and the compensating lens group 2. Adjusting the diaphragm 2 adjusts the clear aperture between the light-dividing lens group 1 and the compensating lens group 2, thereby controlling the ratio of the clear apertures of the imaging lens group 4 to the light-dividing lens group 1. This ratio is preferably set to 0.679:1.

[0032] The compensating lens group 2 is a positive-power lens group, comprising a first compensating lens 31, a second compensating lens 32, and a third compensating lens 33, arranged in sequence from the object side to the image side along the lens optical axis. The first compensating lens 31 has positive power and both sides have convex surfaces; the second compensating lens 32 has positive power and both sides have convex surfaces; and the third compensating lens 33 has negative power and both sides have concave surfaces.

[0033] The imaging lens group 4 is a positive power lens group, comprising a first imaging lens 41. The first imaging lens has positive power and both side surfaces are convex, and the curvature radii of the two side surfaces are equal.

[0034] Under the above settings, the focal length L1 of the light-extracting lens group 1 is -35mm to -45mm, the focal length L2 of the compensating lens group 2 is 10mm to 20mm, the focal length L3 of the imaging lens group 4 is 15mm to 25mm, the air gap h1 between the light-extracting lens group 1 and the compensating lens group 2 on the lens optical axis is 3mm to 5mm, and the air gap h2 between the compensating lens group 2 and the imaging lens group 4 on the lens optical axis is 5mm to 6mm.

[0035] The total focal length of the Sham lens is 25 mm to 35 mm, the operating spectrum range is 400 nm to 700 nm, the ratio of the total optical length to the image half height (TTL / IH) is 10.7:1, and the angle between the target plane and the lens optical axis is 60° to 85°. The total optical length (TTL) is the distance from the front surface of the first spherical surface to the image plane, and the image half height (IH) is the half image height of the diagonal line of the curved arrangement.

[0036] The following uses a Sham lens with a total focal length of f=30 mm as an example. The specific design parameters are shown in Table 1 below.

[0037] Table 1

[0038]

[0039] At this time, the relative aperture of the Sham lens is F / # = 2.8, the image half height is IH = 4.66, the ratio of the total optical length to the image half height is TTL / IH = 10.7:1, the angle between the target plane and the lens optical axis is α = 78.7°, the angle between the imaging plane and the lens optical axis is β = 22.86°, and the magnification of the lens is 0.0852. Figure 4 , Figure 4 shows the optical fringes of a Sham lens; see Figure 5 , Figure 5 shows the MTF curve of the Sham lens; see Figure 6 , Figure 6 shows the field curvature of the Sham lens; see Figure 7 , Figure 7 The astigmatism of the Sham lens is demonstrated. The diffuse spot size of the Sham lens remains within 1.5 times the radius of the Airy disk, with minimal astigmatism and field curvature. The MTF curve shows a contrast ratio of 50% at 150 lp / mm and 20% at 300 lp / mm. The field curvature is within 20 μm, and the astigmatism is near ideal, with distortion less than 0.2% across the full field of view. Therefore, the Sham lens of this application offers the advantages of high resolution, compact size, and low distortion.

[0040] In addition to the Sham lens, there is also a detector inside the industrial camera. Since the detector is a light-sensitive element, it is relatively fragile, so a cover plate is required on the surface of the detector to play a protective role. The conventional cover plate is set parallel to the surface of the detector, which causes spherical aberration to the converging light beam. Moreover, since the cover plate is not perpendicular to the optical axis of the lens, it also causes coma and astigmatism, resulting in a large difference in the imaging quality in the meridian and sagittal directions of the optical path. Specifically, in the image, the contrast between the horizontal and vertical directions is very different, which is not conducive to the focusing of the optical path and the actual imaging effect. The thicker the cover plate or the larger the size of the detector target surface, the greater the difference in imaging quality, which is not conducive to the image to truly and accurately present the object information.

[0041] Based on this, see Figure 8 and Figure 9 This application combines the above-mentioned Sham lens and sets the cover plate to be perpendicular to the optical axis of the Sham lens to design an industrial camera, including the above-mentioned Sham lens, a detector 5 and a cover plate 6.

[0042] The Sham lens images the target plane D to form an image plane F; the detector 5 is arranged at the image plane F of the Sham lens to receive the imaging image of the target; specifically, the detector 5 can be a COMS chip, and the minimum pixel size it can adapt to can be as small as 3.4um, so as to perform high-precision measurement of the target.

[0043] The cover plate 6 is a flat plate, which is arranged on the surface of the detector 5 perpendicular to the optical axis of the lens to protect the detector 5 from damage. The cover plate 6 is made of a transparent material, preferably colorless transparent glass. Compared with the cover plate 6 arranged parallel to the detector 5 in the prior art, the imaging quality of the cover plate 6 arranged perpendicular to the optical axis of the lens in the industrial camera of the present application is greatly improved. This is because when the inclination angle of the target plane increases, the degradation of the imaging quality caused by the cover plate 6 arranged parallel to the detector 5 increases exponentially. Although setting the cover plate 6 perpendicular to the optical axis requires additional cost so that the cover plate 6 can be installed on the surface of the detector 5 in a sealing and fitting manner, for target planes inclined at large angles, sacrificing part of the manufacturing cost in exchange for a significant improvement in imaging quality is of significant value.

[0044] This application eliminates lens aberrations by resetting the parameters, number and position of each lens in the Sham lens, and can be used for target planes with large angle inclinations. At the same time, in order to adapt to the new parameters of the Sham lens and the target planes with large angle inclinations, the cover plate on the detector surface is set to be perpendicular to the lens optical axis, thereby meeting the imaging quality requirements.

[0045] The above-described embodiments merely represent the best modes of carrying out the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that variations and modifications are possible, as would be apparent to those skilled in the art, without departing from the spirit of the present invention, and the present invention is intended to encompass such variations and modifications.

Claims

1. A Sham lens, characterized in that: The lens comprises a light analyzing lens group, a compensation lens group and an imaging lens group, which are arranged in sequence from the object side to the image side along the optical axis of the lens; the light analyzing lens group is a negative optical power lens group, the compensation lens group is a positive optical power lens group, and the imaging lens group is a positive optical power lens group; The ratio of the clear aperture of the imaging lens group to the light-analyzing lens group is 0.1-1.

2.

2. The Sham lens according to claim 1, wherein: The total focal length of the Sham lens is 25 mm to 35 mm, the operating spectrum range is 400 nm to 700 nm, the ratio of the total optical length to the image half height (TTL / IH) is 10.7:1, and the angle between the target plane and the lens optical axis is 60° to 85°. The total optical length (TTL) is the distance from the front surface of the first spherical surface to the image plane, and the image half height (IH) is the half image height of the diagonal line of the curved arrangement.

3. The Sham lens according to claim 2, wherein: The focal length of the light-extracting lens group is -35mm to -45mm, the focal length of the compensating lens group is 10mm to 20mm, the focal length of the imaging lens group is 15mm to 25mm, the air distance between the light-extracting lens group and the compensating lens group on the optical axis of the lens is 3mm to 5mm, and the air distance between the compensating lens group and the imaging lens group on the optical axis of the lens is 5mm to 6mm.

4. The Sham lens according to claim 3, wherein: The light-analyzing lens group includes four spherical lenses, the compensating lens group includes three spherical lenses, and the imaging lens group includes one spherical lens.

5. The Sham lens according to claim 4, characterized in that: The light-extracting lens group includes a first light-extracting lens, a second light-extracting lens, a third light-extracting lens, and a fourth light-extracting lens, which are arranged in sequence from the object side to the image side along the optical axis of the lens; the first light-extracting lens has positive focal power and both surfaces of the two sides are convex; the second light-extracting lens has positive focal power and the object side surface is convex and the image side surface is concave; the third light-extracting lens has negative focal power and the object side surface is convex and the image side surface is concave; the fourth light-extracting lens has negative focal power and both surfaces of the two sides are concave.

6. The Sham lens according to claim 5, characterized in that: The compensation lens group includes a first compensation lens, a second compensation lens, and a third compensation lens arranged in sequence from the object side to the image side along the optical axis of the lens; the first compensation lens has positive optical focal length and both side surfaces are convex; the second compensation lens has positive optical focal length and both side surfaces are convex; the third compensation lens has negative optical focal length and both side surfaces are concave.

7. The Sham lens according to claim 6, characterized in that: The imaging lens group includes a first imaging lens; the first imaging lens has positive optical power and both side surfaces are convex, and the curvature radii of the two side surfaces are equal.

8. An industrial camera, characterized in that: It comprises the Sham lens, detector and cover plate as described in claims 1-7; the detector is arranged on the imaging plane of the Sham lens, and the cover plate is a transparent flat plate arranged on the surface of the detector.

9. The industrial camera according to claim 8, characterized in that: The cover plate is perpendicular to the optical axis of the Sham lens.

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