CN106199913A - Large format apochromatic F-theta lens - Google Patents

Abstract

The invention discloses a large-format apochromatic F-theta lens, comprising first, second, third, fourth and fifth lenses arranged in sequence along the direction of incident light, wherein the first lens is concave facing the incident light The meniscus lens with a negative focal length on the side, the second lens is a positive lens, the third lens is a curved lens with a negative focal length with a concave surface facing the light incident side, and the fourth lens is a meniscus lens, so The fifth lens is a meniscus lens with a positive focal length with a concave surface facing the incident light side; the present invention proposes a scanning mirror group that uses multiple materials to combine achromatism, and an f-theta mirror group composed of 5 lenses. Achromatic treatment is performed between the RGB three-color light, the imaging quality is high, and the distortion is small; the lens can only use two kinds of materials, and the common SF and K materials that are more suitable for optical processing are selected, which are cheap and have good processing performance, and are suitable for industrial applications. .

Description

Large Format Apochromatic F-theta Lenses

technical field

The invention relates to an optical lens, in particular to an F-theta optical lens, which is mainly used in a large format RGB three-color light printing system.

Background technique

With the continuous development of science and technology, laser application technology has penetrated into the current modern life. For example, laser marking machines are constantly expanding their application range due to their high speed and other advantages. Currently, lasers are expanding their applications in various industries.

In the printing industry, large-format printing needs are often encountered, and its working format can usually reach more than 830mm (A0, A1 drawings). In order to achieve the purpose of large-format printing, the current practice in the industry is: choose an achromatic focusing lens, fix the lens on a one-dimensional moving part with high speed and precise positioning, and when the lens is moving, the roller carries the paper to make Rotate, so that a two-dimensional motion platform is formed, which can perform two-dimensional scanning motion on the drawing. Among them, the lens movement range is at least equal to the length of the narrowest part of the drawing. In this method, it is necessary to use different reflectors and beam combiners to combine the required RGB (three-color) light and import it into the focusing lens, and the focusing lens will focus the RGB three-color light on the working surface. When the focusing mirror moves at a high speed, the inertia of the focusing mirror causes the parts of the focusing mirror to vibrate. This vibration will blur the image printed on the paper. Therefore, the efficiency and printing quality of this one-dimensional movement method for printing large formats are not high enough.

F-Theta lens is also called scanning focusing lens, which is mainly used to realize scanning and printing functions. It is mostly used in laser marking machines, stage lighting, and can also be used in scientific experiments and laser measuring instruments. In the optical system, the F-theta mirror has a special distribution of distortion, and it is this distortion that makes the scanning algorithm a linear algorithm, making the scanning easier to control. Its specific algorithm is:

Y=f×theta

Among them, Y is the working distance, f is the focal length of the lens, and theta is the incident angle. Undoubtedly, it is much easier to control the rotation angle than to control the precise position of a point on a long guide rail. Therefore, in order to achieve high-efficiency printing, it is only necessary to find a large-format F-theta lens with achromatic function, and use it to realize multi-color light scanning printing. However, the design and processing of this system is very difficult. How to realize a low-cost and high-efficiency F-theta lens is an urgent problem in the industry.

Contents of the invention

The purpose of the present invention is to provide a large-format apochromatic F-theta lens, which can realize the achromatic treatment of RGB three-color light while maintaining the distortion performance of the F-theta lens, so as to meet the use requirements of three-color light scanning and printing.

In order to achieve the purpose of the above invention, the technical solution adopted by the present invention is: a large-format apochromatic F-theta lens, comprising first, second, third, fourth and fifth lenses arranged in sequence along the incident light direction, The lenses are arranged coaxially on the optical axis, wherein the first lens is a meniscus lens with a negative focal length with a concave surface facing the incident light, the second lens is a positive lens, and the third lens is a concave surface facing the incident light a meniscus lens with a negative focal length, the fourth lens is a positive lens, and the fifth lens is a meniscus lens with a positive focal length whose concave surface faces the incident light.

In the above technical solution, the first, second, and third lenses form a negative lens group, which has a negative focal power and plays a role of beam expansion; the fourth and fifth lenses form a positive lens group, which plays a role in compressing the opening angle. role.

In the above technical solution, along the direction of the optical axis, the negative lens group composed of the first, second and third lenses is located at the front end of the positive lens group composed of the fourth and fifth lenses, and the incident light is first diffused by the negative lens group and then imaged by the positive lens group. onto the drawing.

In the above technical solution, in order to eliminate the chromatic aberration of the large-format apochromatic F-theta lens, it is necessary to use glass whose refractive index and Abbe number are staggered to achieve the purpose of achromatic. In the system, the first and third lenses use the same material with a refractive index n1 and the Abbe number is V1; the second, fourth and fifth lenses use the same material with a refractive index n2 and the Abbe number is V2; Wherein the refractive index n1>n2 and the Abbe number V1<V2. In this solution, the refractive index of the first material is much higher than that of the second material, and the Abbe number of the first material is smaller than that of the second material. Generally speaking, ZF, SF, and K materials are the most used in optical workshops and have relatively stable performance and relatively stable processing technology. Through comparison, SF type materials and K type materials are selected to be used in this technical solution. Obviously, the refractive index of SF material is relatively high and the Abbe number is very low. The refractive index of k-type material is much lower than that of SF-type material, but the Abbe number is much higher.

Preferred technical solution: the second lens can be a plano-convex positive lens, a meniscus positive lens, or a double-convex positive lens; the lens group composed of the first, second, and third lenses has negative focal power and has a beam expansion effect; The focal length and direction of the fourth lens are not limited, as long as the lens group formed by the fourth and fifth lenses is a positive lens group, it can compress the opening angle.

In the above technical solution, in order to reduce the difficulty of processing and manufacturing, all surfaces are spherical, which greatly reduces the processing and manufacturing cost of a single part.

Due to the use of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art:

1. The present invention proposes a scanning lens group that uses multiple materials to combine achromatism. Five lenses constitute the f-theta lens group. Achromatic processing is performed between the RGB three-color light, and the imaging quality is high and the distortion is small.

2. The lens of the present invention only uses two kinds of materials, and selects ordinary SF and K materials that are more suitable for optical processing, which is cheap and has good processing performance, and is suitable for industrial applications.

Description of drawings

Fig. 1 is a kind of optical system structure schematic diagram that adopts F-theta lens;

Fig. 2 is a schematic structural diagram of a negative lens group in Embodiment 1 of the present invention;

3 is a schematic structural diagram of a positive lens group in Embodiment 1 of the present invention;

Fig. 4 is a ray tracing diagram of an F-theta lens in Embodiment 1 of the present invention;

Fig. 5 is a schematic diagram of distortion in Embodiment 1 of the present invention;

Fig. 6 is a schematic diagram of energy concentration in Embodiment 1 of the present invention;

Fig. 7 is a point diagram in Embodiment 1 of the present invention;

in:

1 is the first lens;

2 is the second lens;

3 is the third lens;

4 is the fourth lens;

5 is the fifth lens.

detailed description

The present invention will be further described below in conjunction with accompanying drawing and embodiment: a kind of large-format apochromatic F-theta lens requires: the wavelength of light used is RGB three-color light (0.486 μm/0.587 μm/0.656 μm) and requires scanning diameter to reach 830mm ( It is used with drawings A0 and A1), the relative distortion is controlled within 0.3%, and the spot size is within 100um.

The F-theta lens needs to correct astigmatism in a large field of view. The system uses the form shown in Figure 1. The positive and negative lens groups are separated. In order to flatten the image field, the positive lens group is behind and the negative lens group is in front. As shown in Figure 2 and Figure 3, the F-theta lens includes first, second, third, fourth and fifth lenses arranged in sequence along the direction of incident light, wherein the first lens is concave facing the incident light A meniscus lens with a negative focal length, the second lens is a positive lens, the third lens is a meniscus lens with a negative focal length whose concave surface faces the incident light, the fourth lens is a meniscus lens, and the first The five lenses are meniscus lenses with a positive focal length whose concave surface faces the incident light; the first, second and third lenses form a negative lens group; the fourth and fifth lenses form a positive lens group.

The lens is used in a multi-color light environment, so it is necessary to carry out achromatic design for these three kinds of color light, so different materials need to be selected. Among the lenses produced in industrialization, the BK material with better stability (called K material in China) ), SF, ZK materials. In this embodiment, the most commonly used materials BK7 and SF6 are selected. The refractive index of the BK7 material is 1.517, and the Abbe number is 64.167. The refractive index of the SF6 material is 1.805, and the Abbe number is 25.432.

In conjunction with the above designs, the present invention provides two preferred design examples, and their specific data are as follows:

Embodiment one:

The first lens 1 is composed of two curved surfaces S1 and S2 with curvature radii of -62.32mm and -68.78mm respectively, the central thickness of which is 13.2mm, the material is SF6, and the focal length is -9398mm;

The second lens 2 is composed of two curved surfaces S3 and S4 with curvature radii of -716.91mm and -229.26mm respectively, the central thickness of which is 20mm, the material is BK7, and the focal length is 643.2mm;

The third lens 3 is composed of two curved surfaces S5 and S6 with curvature radii of -152.69mm and -249.13 respectively, the central thickness of which is 14.74mm, the material is SF6, and the focal length is -525.75mm;

The fourth lens 4 is composed of two curved surfaces S7 and S8 with curvature radii of -2456.1mm and -555.56mm respectively, the central thickness of which is 9.13mm, the material is BK7, and the focal length is 1387mm;

The fifth lens 5 is composed of two curved surfaces S9 and S10 with curvature radii of -604.07mm and -336.65mm respectively, the central thickness of which is 19.9mm, the material is BK7, and the focal length is 1435.1mm;

The list is as follows:

According to the above design scheme, the simulation results shown in Fig. 4 to Fig. 7 can be obtained through computer simulation. 4 is a schematic diagram of the optical path layout of the above embodiment; FIG. 5 is a distortion distribution diagram; FIG. 6 is a schematic diagram of energy concentration; and FIG. 7 is a spot diagram. It can be seen from the above figures that the distortion of the system is less than 0.25%, and the energy concentration is greater than 80% within a pixel size of 100um. This system meets the needs of large-format printing.

Embodiment two:

The first lens is composed of two curved surfaces S1 and S2 with curvature radii of -72.7mm and -80.24mm respectively, the central thickness of which is 15.4mm, the material is SF6, and the focal length is -10964mm;

The second lens is composed of two curved surfaces S3 and S4 with curvature radii of -836.39mm and -267.46mm respectively, the central thickness of which is 23.3mm, the material is BK7, and the focal length is 750.4mm;

The third lens is composed of two curved surfaces S5 and S6 with curvature radii of -178.14mm and -290.66 respectively, the central thickness of which is 17.2mm, the material is SF6, and the focal length is -613.4mm;

The fourth lens is composed of two curved surfaces S7 and S8 with curvature radii of -2865.5mm and -648.16mm respectively, the central thickness of which is 10.7mm, the material is BK7, and the focal length is 1618mm;

The fifth lens is composed of two curved surfaces S9 and S10 with curvature radii of -704.74mm and -392.76mm respectively, the central thickness of which is 23.2mm, the material is BK7, and the focal length is 1674.3mm;

The list is as follows:

The f-theta mirror group composed of 5 lenses proposed by the present invention performs achromatic treatment between the RGB three-color light, the lens distortion is small, and the imaging quality is high; the lens can only use two kinds of materials, and select the one that is more suitable for optical processing Ordinary SF and K materials are cheap, good processing performance, and suitable for industrial applications. If the cost factor is not considered, on the basis of the technical solution, an appropriate increase in the number of lenses or the use of aspheric surfaces on the front and rear surfaces of five lenses can be optimized to obtain better imaging effects.

Claims (8)

1. A large-format apochromatic F-theta lens is characterized in that: it is made up of the first, second, third, fourth and fifth lenses arranged successively along the incident light direction, and each lens is on the optical axis at the same time axis setting, wherein the first lens (1) is a meniscus lens with a negative focal length with a concave surface facing the incident light, the second lens (2) is a positive lens, and the third lens (3) is a concave surface facing the incident light A meniscus lens with a negative focal length for light, the fourth lens (4) is a positive lens, and the fifth lens (5) is a meniscus lens with a positive focal length whose concave surface faces incident light. 2. The large-format apochromatic F-theta lens according to claim 1, wherein: the first, second, and third lenses form a negative lens group; the fourth and fifth lenses form a positive lens group; lens group. 3. The large-format apochromat F-theta lens according to claim 2, characterized in that: the optical materials used in the first to fifth lenses are two kinds of glass materials; wherein the first lens and the third lens The refractive index of the material used is n1, and the Abbe number is V1; the refractive index of the materials used in the second, fourth and fifth lenses is n2, and the Abbe number is V2; wherein the refractive index n1>n2 and the Abbe number V1<V2. 4. The large-format apochromat F-theta lens according to claim 3, wherein the glass material is SF type material and k type material. 5. The large-format apochromatic F-theta lens according to claim 4, characterized in that: the achromatic materials are SF6 and BK7. 6. The large-format apochromatic F-theta lens according to any one of claims 2-5, wherein the second lens can be a plano-convex positive lens, a meniscus positive lens, or a double-convex positive lens. 7. The large-format apochromat F-theta lens according to any one of claims 2-5, characterized in that: the negative lens group composed of the first, second and third lenses along the optical axis direction is located at the fourth and fifth The front end of the positive lens group composed of lenses. 8. The large-format apochromatic F-theta lens according to any one of claims 2-5, wherein each surface of the first to fifth lenses is a spherical surface.