A dispersion lens of a spectral confocal displacement sensor

Abstract

The present invention relates to a chromatic dispersion lens of a spectral confocal displacement sensor, which has a retrofocus structure, and the aperture stop is arranged on the first surface of the front group of lenses facing the image side; the front group of lenses includes a first lens, which is a biconcave lens with a negative focal length; the rear group of lenses includes a meniscus convex lens second lens, a biconvex lens third lens, a meniscus convex lens fourth lens and a fifth lens arranged in sequence from the image side to the object side, and the rear group of lenses has a positive focal length; the first lens and the fourth lens are made of the same kind of glass material, and the second lens, the third lens and the fifth lens are made of the same kind of glass material. The chromatic dispersion lens structure provided by the present invention can effectively correct spherical aberration and generate nearly linear axial chromatic dispersion, and at the same time can obtain a larger numerical aperture on the image side; by adding a negative lens on the image side to form a retrofocus structure, the overall length of the chromatic dispersion lens caused by the smaller numerical aperture on the image side is reduced; the chromatic dispersion lens only uses two kinds of glass materials, which reduces the processing complexity and production cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, and particularly relates to a chromatic dispersion lens of a spectral confocal displacement sensor. Background Art

[0002] Spectral confocal displacement sensors have received increasing attention in the field of precision detection. Compared with other detection methods, spectral confocal displacement sensors have the following characteristics: First, it belongs to non-contact measurement and will not cause damage to the measured object during detection; second, it establishes a correspondence between wavelength and height or distance, and obtains height information by detecting the wavelength, so it can be used to detect the three-dimensional shape information of an object; third, it can obtain height and distance without axial scanning, and the detection speed is fast.

[0003] The chromatic dispersion lens is an important part of the spectral confocal displacement sensor. Its axial chromatic dispersion range determines the measurement range of the sensor, and the numerical aperture determines the maximum measurement inclination angle and transverse resolution of the sensor. According to the Schott formula of glass refractive index, a single lens cannot produce linear axial chromatic dispersion. In order to obtain a large chromatic dispersion range and numerical aperture, existing spectral confocal chromatic dispersion lenses use a large number of lens elements and types of glass (see the literature: Design of a Linear Chromatic Dispersion Objective for a Spectral Confocal Displacement Sensor. [J]. Chinese Journal of Lasers, 2019, 46(07): 219 - 225.). Chinese invention patent CN114136215A discloses a large-angle spectral confocal measurement lens, which uses 7 lens elements to design the chromatic dispersion lens and adopts a variety of glass materials. The excessive number of lens elements and types of glass make the assembly of the chromatic dispersion lens difficult. At the same time, the production cost of the product is high, which is not conducive to the popularization and application of spectral confocal displacement sensors. Summary of the Invention

[0004] The present invention aims at the deficiencies of the existing technology and provides a high-performance chromatic dispersion lens for a spectral confocal displacement sensor with a small image-side numerical aperture, a large object-side numerical aperture, a compact volume, and a long axial chromatic dispersion.

[0005] The technical solution for achieving the object of the present invention is a chromatic dispersion lens of a spectral confocal displacement sensor, which has a retrofocus structure and includes a diaphragm, a front group of lenses, and a rear group of lenses. They are arranged in sequence from the image side to the object side as the diaphragm, the front group of lenses, and the rear group of lenses;

[0006] The diaphragm is disposed on the first surface of the front group of lenses facing the image side;

[0007] The front group of lenses includes a first lens, which is a biconcave lens, and the focal length of the front group of lenses is negative;

[0008] The rear lens group includes a second lens, a third lens, a fourth lens, and a fifth lens arranged in sequence from the image side to the object side, and the focal length of the rear lens group is positive; the focal lengths of the second lens, the third lens, the fourth lens, and the fifth lens are all positive; the second lens is a meniscus convex lens convex towards the object side, the third lens is a biconvex lens, and the fourth lens and the fifth lens are meniscus convex lenses convex towards the image side;

[0009] The focal length of the dispersion lens is f, the focal length of the first lens is f1, and f1 satisfies -2f < f1 < -1.9f; the focal length of the second lens is f2, and f2 satisfies 5f < f2 < 6f; the focal length of the third lens is f3, and f3 satisfies 4f < f3 < 5f; the focal length of the fourth lens is f4, and f4 satisfies 6f < f4 < 7f; the focal length of the fifth lens is f5, and f5 satisfies 5f < f5 < 6f;

[0010] For the first lens described above, the refractive index ND1 satisfies ND1 > 1.5, and the Abbe number VD1 satisfies VD1 > 60; for the second lens, the refractive index ND2 satisfies ND2 > 1.8, and the Abbe number VD2 satisfies VD2 > 20; for the third lens, the refractive index ND3 satisfies ND3 > 1.8, and the Abbe number VD3 satisfies VD3 > 20; for the fourth lens, the refractive index ND4 satisfies ND4 > 1.5, and the Abbe number VD4 satisfies VD4 > 60; for the fifth lens, the refractive index ND5 satisfies ND5 > 1.8, and the Abbe number VD5 satisfies VD5 > 60.

[0011] In a preferred technical solution, 1.5 < ND1 < 1.6, 60 < VD1 < 70, 1.8 < ND2 < 1.9, 20 < VD2 < 30, 1.8 < ND3 < 1.9, 20 < VD3 < 30, 1.5 < ND4 < 1.6, 60 < VD4 < 70, 1.8 < ND5 < 1.9, 20 < VD5 < 30.

[0012] In a preferred technical solution, the first lens and the fourth lens of the present invention are made of the same kind of glass material, and the second lens, the third lens, and the fifth lens are made of the same kind of glass material. By using only two kinds of glass, a dispersion lens with better performance is obtained, effectively reducing the cost, and the dispersion range can reach 4 mm or more, and the numerical aperture is greater than or equal to 0.5. The present invention uses two kinds of glass materials to generate nearly linear axial dispersion. In order to reduce spherical aberration, the two pieces of glass are divided into four pieces by the method of splitting the optical power equally, and a negative lens is added on the image side to form a retrofocus structure, reducing the overall length of the dispersion lens caused by the small numerical aperture on the image side.

[0013] The dispersive lens provided by the present invention adopts a retrofocus structure. The front group of lenses is a single lens, which only uses one lens element with a negative focal length. Its main function is to increase the divergence angle to reduce the overall system length, and at the same time reduce the field angle of the rear group of lenses, thereby reducing the incident height and angle-of-incidence burden of light at the rear group. The rear group of lenses consists of four lens elements with a positive focal length; the first two lenses are composed of two meniscus lenses or one meniscus lens and one biconvex lens, and the curvature of the meniscus lens bends towards the image side; the last two lenses are two meniscus lenses with the curvature bending towards the object side; this structure can correct spherical aberration and generate nearly linear axial dispersion, and at the same time can obtain a relatively large numerical aperture on the image side.

[0014] The aperture stop is set on the front surface of the first lens and does not change with different wavelengths.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. The dispersive lens adopts a retrofocus structure. The main function of the front group of lenses is to increase the divergence angle and at the same time reduce the field angle of the rear group of lenses, so as to reduce the incident height and angle-of-incidence burden of light at the rear group. The main function of the front group of lenses is to correct spherical aberration and generate nearly linear axial dispersion, and at the same time can obtain a relatively large numerical aperture on the object side. The aperture stop is set on the surface of the first lens facing the image side, and its size does not change with different wavelengths.

[0017] 2. The dispersive lens provided by the present invention can use only two types of glass materials. The first lens and the fourth lens are made of the same type of glass material, and the second lens, the third lens and the fifth lens are made of the same type of glass material, which reduces the processing complexity and production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 FIG. is a schematic structural diagram of a dispersive lens of a spectral confocal displacement sensor provided by an embodiment of the present invention;

[0019] In the figure, 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Aperture stop.

[0020] Figure 2 FIG. is a spot diagram of a dispersive lens of a spectral confocal displacement sensor provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments.

[0022] Embodiment 1

[0023] See the appendix Figure 1, is a schematic structural diagram of the dispersion lens provided in this embodiment; from the image side to the object side, it successively includes: a diaphragm 6, a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, and a fifth lens 5.

[0024] Among them, the first lens 1 is a biconcave lens, the second lens 2 is a meniscus convex lens with the convex side facing the object side, the third lens 3 is a biconvex lens, and the fourth lens 4 and the fifth lens 5 are meniscus convex lenses with the convex side facing the image side.

[0025] The focal length of the dispersion lens is f, the focal length of the first lens 1 is f1, and f1 satisfies -2f < f1 < -1.9f; the focal length of the second lens 2 is f2, and f2 satisfies 5f < f2 < 6f; the focal length of the third lens 3 is f3, and f3 satisfies 4f < f3 < 5f; the focal length of the fourth lens 4 is f4, and f4 satisfies 6f < f4 < 7f; the focal length of the fifth lens 5 is f5, and f5 satisfies 5f < f5 < 6f.

[0026] The refractive index ND1 of the first lens 1 satisfies ND1 > 1.5; the refractive index ND2 of the second lens 2 satisfies ND2 > 1.8; the refractive index ND3 of the third lens 3 satisfies ND3 > 1.8; the refractive index ND4 of the fourth lens 4 satisfies ND4 > 1.5; the refractive index ND5 of the fifth lens 5 satisfies ND5 > 1.8.

[0027] The Abbe number VD1 of the first lens 1 satisfies VD1 > 60; the Abbe number VD2 of the second lens 2 satisfies VD2 > 20; the Abbe number VD3 of the third lens 3 satisfies VD3 > 20; the Abbe number VD4 of the fourth lens 4 satisfies VD4 > 60; the Abbe number VD5 of the fifth lens 5 satisfies VD5 > 60.

[0028] In this embodiment, the parameters of each lens are as follows:

[0029] The focal length f1 of the first lens 1 is -34.27 mm, ND1 is 1.5168, and VD1 is 64.1987;

[0030] The focal length f2 of the second lens 2 is 97.14 mm, ND2 is 1.8466, and VD2 is 23.7873;

[0031] The focal length f3 of the third lens 3 is 83.40 mm, ND3 is 1.8466, and VD3 is 23.7873;

[0032] The focal length f4 of the fourth lens 4 is 121.15 mm, ND4 is 1.5168, and VD4 is 64.1987;

[0033] The focal length f5 of the fifth lens 5 is 97.46 mm, ND5 is 1.8466, and VD5 is 23.7873.

[0034] For the dispersion lens provided in this embodiment, the axial dispersion between the working wavelengths of 450 to 800 nm is 4.17 mm, the object space numerical aperture is 0.5, the overall length of the lens is 162 mm, and the maximum aperture is 46 mm.

[0035] See Attachment Figure 2 , which is the spot diagram of the dispersion lens provided in this embodiment. The results show that: at wavelengths of 450 nm, 500 nm, 600 nm, 700 nm, and 800 nm, the spot radius is basically near the Airy disk, the spherical aberration is corrected, and the imaging quality is good.

Claims

1. A chromatic dispersion lens of a spectral confocal displacement sensor, characterized in that: It has a retrofocus structure, including a diaphragm, a front lens group and a rear lens group, which are arranged in sequence from the image side to the object side as the diaphragm, the front lens group, and the rear lens group; The diaphragm is arranged on the first surface of the front lens group facing the image side; The front lens group includes a first lens (1), which is a biconcave lens, and the focal length of the front lens group is negative; The rear lens group includes a second lens (2), a third lens (3), a fourth lens (4), and a fifth lens (5) arranged in sequence from the image side to the object side. The focal length of the rear lens group is positive; the focal lengths of the second lens, the third lens, the fourth lens, and the fifth lens are all positive; the second lens is a meniscus convex lens convex toward the object side, the third lens is a biconvex lens, and the fourth lens and the fifth lens are meniscus convex lenses convex toward the image side; The focal length of the dispersion lens is f, the focal length of the first lens is f1, and f1 satisfies -2f < f1 < -1.9f; the focal length of the second lens is f2, and f2 satisfies 5f < f2 < 6f; the focal length of the third lens is f3, and f3 satisfies 4f < f3 < 5f; the focal length of the fourth lens is f4, and f4 satisfies 6f < f4 < 7f; the focal length of the fifth lens is f5, and f5 satisfies 5f < f5 < 6f; For the first lens, the refractive index ND1 satisfies ND1 > 1.5, and the Abbe number VD1 satisfies VD1 > 60; for the second lens, the refractive index ND2 satisfies ND2 > 1.8, and the Abbe number VD2 satisfies VD2 > 20; for the third lens, the refractive index ND3 satisfies ND3 > 1.8, and the Abbe number VD3 satisfies VD3 > 20; for the fourth lens, the refractive index ND4 satisfies ND4 > 1.5, and the Abbe number VD4 satisfies VD4 > 60; for the fifth lens, the refractive index ND5 satisfies ND5 > 1.8, and the Abbe number VD5 satisfies VD5 > 60.

2. The dispersion lens of the spectral confocal displacement sensor according to claim 1, wherein: The first lens and the fourth lens are made of the same kind of glass material, and the second lens, the third lens, and the fifth lens are made of the same kind of glass material.

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