CN106291890A - A kind of-0.1 × doubly telecentric machine vision object lens - Google Patents

Abstract

The invention discloses a -0.1× bi-telecentric machine vision objective lens, which comprises a front objective lens group and a rear objective lens group, and the aperture stop is placed on the image focal plane of the front lens group and the object focal plane of the rear lens lens The bi-telecentric imaging optical path formed is different from the prior art in that it adopts a symmetrical structure and is composed of 10 lenses. The arrangement of the 10 lenses on the diaphragm from the object surface to the mirror surface is as follows: 1 concave lens, 2 convex lenses, 3, convex lenses 4, concave lenses, 5 concave lenses, 6 concave lenses, 7 concave lenses, 8 convex lenses, 9 concave lenses, 10 convex lenses, the object space working distance is 215mm, the object field of view is 80mm; the back intercept is 34.217mm, The image square field of view is 8mm, the magnification is -0.1 times, the image square imaging resolution of the whole field of view reaches 2001p/mm, and the distortion is less than 0.015%. It has small distortion, low telecentricity, large depth of field, high resolution, and structure Simple and easy to adjust.

Description

A -0.1×bi-telecentric machine vision objective lens

technical field

The patent of the invention relates to optical imaging technology, especially suitable for machine vision detection equipment with large depth of field, long working distance, high resolution and low distortion, specifically a -0.1× bi-telecentric machine vision objective lens.

Background technique

In the past ten years, the rapid development and continuous improvement of machine vision has made it an indispensable part of the field of industrial online inspection, and imaging lenses are particularly important as the eyes of machine vision. The cost of using traditional fixed-focus or zoom lenses is low, but it has the following defects: large image distortion, especially for large field of view imaging, which will seriously affect the measurement accuracy; small depth of field, imaging objects with a certain depth will make the object The side projection imaging is easy to be confused with the image that needs to be detected, which reduces the measurement accuracy; the defocus is large, and the defocus imaging of ordinary fixed focus or zoom lenses will cause large measurement errors.

The telecentric light path is divided into the object-space telecentric light path and the image-space telecentric light path. The principle is to place the aperture stop on the focal plane of the image space and the focal plane of the object space respectively, so that the chief rays of the object space and the image space are parallel to the optical path. axis. Combining these two telecentric optical paths constitutes a double-telecentric imaging optical path, that is, the position of the aperture stop in the middle is not only the image focal plane of the front objective lens group, but also the object focal plane of the rear objective lens group. In this way, the principal rays of the object and image are parallel to the optical axis, combining the advantages of the object and image telecentric optical paths, eliminating object and image distortions, and further improving the detection accuracy.

Chinese patent 201420137000.1 proposes a bi-telecentric lens with a symmetrical structure. The advantage of this lens is that the distortion of the lens is controlled within 0.005% when the magnification is -1×. The disadvantage is that the magnification of the object is -1×, a CCD with a large target surface is required, and 4 pieces of lanthanide glass are used, which is expensive.

Contents of the invention

The purpose of the present invention is to overcome the defects of the prior art of ordinary lens, and provide a kind of -0.1× bi-telecentric machine vision objective lens with simple structure, low distortion, low magnification, high resolution and large depth of field for machine vision detection.

The technical scheme that realizes the object of the present invention

A -0.1× bi-telecentric machine vision objective lens, including a bi-telecentric imaging optical path formed by placing the aperture stop on the image focal plane of the front lens group and the object focal plane of the rear lens group, which is different from the prior art The difference is that it adopts a symmetrical structure and consists of 10 lenses. The arrangement of the 10 lenses on the stop from the object plane to the mirror surface is: concave lens, convex lens, convex lens, concave lens, concave lens, concave lens, concave lens, convex lens, concave lens, Convex lens.

The 10 lenses are divided into a front objective lens group and a rear objective lens group, the front objective lens group includes a first lens unit and a second lens unit, and the rear lens group is called a third lens unit and a fourth lens unit.

The first lens unit is a doublet lens with positive refractive power composed of a convex lens and a concave lens,

The second lens unit is composed of a doublet lens with positive refractive power and a concave lens,

The third lens unit is composed of a doublet lens with positive refractive power and a concave lens

The fourth lens unit is composed of a doublet lens with positive refraction power consisting of a convex lens and a concave lens.

The axial distance between the first lens unit and the second lens unit is far,

The distance between the doublet lens and the concave lens of the second lens unit is relatively close,

In the rear objective lens group, the distance between the third lens unit and the fourth lens unit is relatively far,

In the third lens unit, the distance between the concave lens and the doublet lens is relatively short,

The concave lens of the second lens unit and the concave lens of the third lens unit are both bent towards the diaphragm,

The performance of this objective lens, its object space working distance is 215mm, the object space field of view is 80mm; the back intercept is 34.217mm, the image square field of view is 8mm, the magnification is -0.1 times, and the image square imaging resolution of the whole field of view reaches 2001p/mm, the distortion is less than 0.015%.

Beneficial effects of the present invention

The main characteristics of the double telecentric optical system are that the field of view of the object is large, the distortion is small, and the telecentricity is low; the depth of field is large, the resolution is high, the structure is simple, and it is easy to install and adjust. Wide range of applications.

Description of drawings

The optical path figure of Fig. 1 double telecentric objective lens of the present invention;

The MTF figure of Fig. 2 double telecentric objective lens of the present invention;

The spot diagram of the double telecentric objective lens of the present invention of Fig. 3;

Fig. 4 field curvature distortion diagram of the bi-telecentric objective lens of the present invention;

Fig. 5 is an energy distribution diagram around the diffraction of the bi-telecentric objective lens of the present invention;

The point spread function figure of Fig. 6 bi-telecentric objective lens of the present invention;

The RanFan figure of Fig. 7 bi-telecentric objective lens of the present invention;

Fig. 8 is the RMS vs field diagram of the bi-telecentric objective lens of the present invention.

In the figure: L1, concave lens L2, convex lens L3, convex lens L4, concave lens L5, concave lens L6, concave lens L7, concave lens L8, convex lens L9, concave lens L10, convex lens

The specific implementation is as follows:

The present invention will be further described below in conjunction with accompanying drawing, but not limitation of the present invention

With reference to Fig. 1, a kind of bi-telecentric objective lens of the present invention, the front group lens GF of bi-telecentric objective lens and rear group lens GR all have positive refractive power, and front group comprises first unit U1 and second unit U2, and described first unit One unit is a cemented lens composed of a convex lens and a concave lens, the second unit includes a doublet lens composed of a convex lens and a concave lens and a concave lens, and the rear group includes a third unit U3 and a fourth unit U4, the said The third unit includes a concave lens and a cemented lens composed of a convex lens and a concave lens. The fourth unit is made up of a doublet lens made of a convex lens and a concave surface.

The arrangement from the object plane to the image plane in the patent of the present invention is as follows: the first lens L1, the second lens L2, the third lens L3, the fourth lens L4 and the fifth lens L5 of the front lens group; On the surface; the rear group of lenses sequentially includes the sixth lens L6, the seventh lens L7, the eighth lens L8, the ninth lens L9 and the tenth lens L10. The axial distance between them is shown in Table 1—the structural data table of the objective lens.

According to the magnification requirement, β=-0.1, the resolution requirement is 0.05mm, and the full field of view of the object side is 80mm, it can be determined that the image plane receiving device uses a 1/2" CCD industrial camera, and the image plane field of view is 8mm , the pixel size is 5.4μm×5.4μm.

Since the image plane is connected to a CCD camera, a certain back focus needs to be left, so the size of the back focus must be taken into account when assigning the optical power to the rear group. Generally, the installation distance of a C-mount CCD camera is not less than 17mm. In order to facilitate installation and adjustment, and not to cause the front group to bear too much optical power, in this example, the focal length of the rear group is f' _R = 30.056mm. The ratio requirement β=-0.1, the focal length of the front group f' _F =300mm can be obtained.

In the structural design of the bi-telecentric objective lens of the present invention, a nearly symmetrical structure is adopted, which can well correct lateral aberrations such as vertical axis chromatic aberration, distortion and coma. In order to form a bi-telecentric optical path, the aperture stop is placed in the front The focal plane of the image side of the group objective lens, and the position of the diaphragm is also the object side focal plane of the rear group of objective lens, so that the chief ray is incident in parallel, and the chief ray is emitted in parallel.

The first unit of the front group lens is double cemented, which can better correct the spherical aberration, and use the refractive index difference and the Abbe number difference between the cemented surface and the cemented lens to better correct the chromatic aberration. The second unit can better offset the aberration produced by the first unit. In the symmetrical structure, the lens close to the diaphragm is bent towards the diaphragm, so that the deflection angle of the chief ray is as small as possible, which can facilitate the correction of off-axis aberrations. In the same way, the design of the rear group refers to the front group, and the front and rear approximately symmetrical two groups of lenses can offset the lateral aberration generated by each other. After optimizing the lens, the aberration can be corrected within the required range.

The aberration curves are shown in attached drawings 2 to 8. It can be seen from accompanying drawing 2 that the RMS spot radius at the maximum field of view is 2.532 μm, which is smaller than the CCD pixel size of 5.4 μm; the full field of view MTF value of accompanying drawing 3 reaches 200 lp/mm, and the image quality is excellent; The distortion of the objective lens <-0.015%. According to accompanying drawings 5 to 7, it can be seen that the comprehensive aberration, image quality and illuminance of this embodiment all meet the requirements.

The specific structural data of the embodiment adopting the above-mentioned structure is shown in Table 1, and the telecentricity data of different fields of view of the patent of the present invention are shown in Table 2.

Table 1

Surf type Radius Thickness glass Diameter OBJ STANDARD Infinity 215 80 1 STANDARD 190.5256 6.00005 1.806100,33.3 86.63449 2 STANDARD 103.0009 24.0002 1.620410,60.8 86.63449

3 STANDARD -1680.014 240.002 83.00384 4 STANDARD 175.9715 12.0001 1.743300,49.2 30.21895 5 STANDARD -69.80058 4.000033 1.595510,39.2 30.21895 6 STANDARD -274.0023 10.00008 27.08507 7 STANDARD -104.9669 6.00005 1.607380,56.8 22.6992 8 STANDARD 176.0015 51.94043 21.3668 STO STANDARD Infinity 7.287 3.695286 10 STANDARD -27.856 1.2 1.517420,52.2 9.58776 11 STANDARD 14.66 4.1 9.997626 12 STANDARD 35.285 1.5 1.595510,39.2 12.56882 13 STANDARD 15.64 6.3 1.743300,49.2 13.1174 14 STANDARD -32.822 13 13.1174 15 STANDARD 41.019 2.5 1.672700,32.2 15.94137 16 STANDARD 12.67 8.6 1.516800,64.2 15.78914 17 STANDARD -30.5 34.2167 15.94137 IMA STANDARD 8.033797

Table 2

Object height(mm) 10 20 28 40 Telecentricity (rad) 3.831×10 ^-5 1.680×10 ^-4 2.97×10 ^-4 1.568×10 ^-5

The bi-telecentric imaging optical system includes a bi-telecentric imaging optical path formed by placing the aperture stop on the image focal plane of the front lens group and the object focal plane of the rear lens group. The bi-telecentric objective lens of the present invention adopts a nearly symmetrical structure and adopts 10 lenses, including four doublet lenses and two concave lenses.

The bi-telecentric objective lens of the present invention is characterized in that: .

The front objective lens group GF includes a first lens unit _{U 1} and a second lens unit U ₂ , wherein the first lens unit is a doublet lens with positive refractive power, and the doublet lens is composed of a convex lens and a concave lens. The second lens unit is composed of a doublet with positive refractive power and a concave lens.

The rear objective lens group G _R includes a third lens unit U ₃ and a fourth lens unit U ₄ , wherein the third lens unit is composed of a doublet lens with positive refractive power and a concave lens, and the fourth lens unit is composed of a positive A doublet lens of refractive power consists of a convex lens and a concave lens.

As a further improvement of the present invention, the axial distance between the first unit and the second unit is relatively long, in order to reduce the burden of the front group of optical power and improve the degree of curvature of the lens; the double cemented and concave lens of the second unit Closer to each other, it is good for aberration correction. The aperture is located on the image-side focal plane of the front group of lenses, and simultaneously on the object-side focal plane of the rear group of objective lenses, thereby forming a bi-telecentric optical path. Similarly, the distance between the front and rear units of the rear lens group is relatively long, and in the third unit, the distance between the concave lens and the double cement is relatively short. The nearly symmetrical optical structure can offset the lateral aberration and improve the image quality.

As a further improvement of the present invention, both the fifth lens and the sixth lens are bent toward the diaphragm. The first lens unit satisfies n _1n -n _1p >0.1, v _1p -v _1n >25. Wherein n _1n is the refractive index of said first lens, n _1p is the refractive index of said second lens; v _1p is the Abbe number of said second lens, v _1n is the Abbe number of said first lens .

The bi-telecentric imaging system uses an area-array CCD industrial camera with a target surface of 1/2" inch and a pixel size of 5.4 μm×5.4 μm.

The bi-telecentric imaging optical system of the present invention has an object-space working distance of 215 mm, an object-space field of view of 80 mm; a back intercept of 34.217 mm, an image-space field of view of 8 mm, a magnification of -0.1 times, and a full-field image field The imaging resolution reaches 2001p/mm, and the distortion is less than 0.015%.

Claims (4)

1.-0.1 × doubly telecentric machine vision object lens, including aperture diaphragm being positioned over the image space focal plane of front group of lens, and the rear focal plane, thing side organizing lens, and the doubly telecentric imaging optical path formed, it is characterised in that take symmetrical structure form, being made up of 10 eyeglasses, 10 eyeglasses layout from object plane to minute surface on diaphragm is followed successively by: concavees lens, convex lens, convex lens, concavees lens, concavees lens, concavees lens, concavees lens, convex lens, concavees lens, convex lens.

One the most according to claim 1-0.1 × doubly telecentric machine vision object lens, it is characterized in that: described 10 eyeglasses are divided into, pre-objective group and rearmounted objective lens, pre-objective group contains the first lens unit, with the second lens unit, rearmounted battery of lens cries out the 3rd lens unit and the 4th lens unit, wherein:

First lens unit is a convex lens and the cemented doublet with positive refractive power of a concavees lens composition,

Second lens unit is made up of the cemented doublet with positive refractive power and concavees lens,

3rd lens unit is made up of the cemented doublet and concavees lens with positive refractive power

The cemented doublet with positive refractive power that 4th lens unit is made up of a convex lens and concave lens is constituted.

One the most according to claim 2-0.1 × doubly telecentric machine vision object lens, it is characterised in that

The first described lens unit and the second lens unit axial distance farther out,

The cemented doublet of the second described lens unit is close together with concavees lens,

In described rearmounted objective lens, the 3rd lens unit and the 4th lens unit are distant,

In the 3rd described lens unit, concavees lens are close together with cemented doublet.

One the most according to claim 2-0.1 × doubly telecentric machine vision object lens, it is characterised in that the concavees lens of the second described lens unit and the concavees lens of the 3rd lens unit all bend towards diaphragm.