Short-focus projection lens and application thereof

Abstract

This invention proposes a short-throw projection lens and its application, relating to the technical field of optical lenses. The short-throw projection lens employs a front and rear lens group to form a reverse telephoto structure. The effective combination of lenses with positive and negative optical power results in a distance from the front surface of the projection lens to the focal plane that is less than the focal length. This short focal length reduces the structural size, facilitating miniaturization and integration. Furthermore, it features a large field of view, high edge illumination of the image plane, and a long back-working distance. This invention also proposes the application of the short-throw projection lens in DLP projection for DLP rapid 3D printing. It is suitable for large-size DMD chips, which is beneficial for the miniaturization of DLP rapid 3D printers and better meets market demands.

Description

Technical Field

[0001] This invention relates to the technical field of optical lenses, and more specifically, to a short-throw projection lens and its application. Background Technology

[0002] With the development of 3D printing technology and the increasing demands of people, DLP (Digital Light Processing) rapid 3D printing technology has emerged. DLP rapid 3D printing projects an entire layer of image onto photosensitive resin through a projection lens, and then stacks the layers one by one to form the final product. It can complete the printing of an entire layer in one pass, featuring high printing speed and high precision. It can achieve the precision of injection molding in terms of material properties, detail, and surface roughness. In application, the required image information is projected using digital processing technology, and visualized digital information can be displayed based on a DMD (digital micro-mirror device) chip.

[0003] A 3D printing system based on DLP technology consists of the following parts: a DLP projection system, a mechanical motion system, and a main control system with control and computing capabilities. The DLP projection system uses a DMD chip to provide image illumination for this type of 3D printing. When selecting a chip model, factors such as printing size, printing accuracy, printing speed, and light source wavelength must be considered comprehensively. Furthermore, the inherent aberrations in the optical systems suitable for DMD chips place extremely high demands on the projection lens in DLP rapid 3D printing.

[0004] Currently, there are few 3D printing projection lenses on the market suitable for large-size DMD chips, and their focal lengths are relatively long. For example, a projection lens for a 3D printer is disclosed in the prior art. The projection lens is arranged in sequence from the object plane to the image plane along the light direction: a first meniscus lens, a second meniscus lens, a biconcave negative lens, a first biconvex lens, a second biconvex lens, a third meniscus lens, a fourth meniscus lens, a fifth meniscus lens, a third biconvex lens, and a fourth biconvex lens. Through the organic combination of the lenses, it can be used for 0.47-inch DMD chips, but the effective focal length is as long as 23.65mm, which is not conducive to the miniaturization of 3D printers. Summary of the Invention

[0005] To address the issue of long focal lengths in existing projection lenses, this invention proposes a short-focal-length projection lens and its application. The proposed lens features a short focal length, high resolution, and high image quality, making it suitable for large-size DMD chips. This facilitates the miniaturization of DLP rapid 3D printers and better meets market demands.

[0006] To solve the above problems, the technical solution adopted in this application is as follows:

[0007] On the one hand, this application proposes a short-throw projection lens, comprising: a front lens and a rear lens arranged sequentially from the object plane to the image plane along the light direction;

[0008] The front lens group includes a first lens with positive optical power, a second lens with negative optical power, a third lens with negative optical power, a fourth lens with negative optical power, a fifth lens with negative optical power, a sixth lens with positive optical power, and a seventh lens with positive optical power, arranged sequentially from the object plane to the image plane along the light direction.

[0009] The rear lens group includes an eighth lens with negative optical power, a ninth lens with positive optical power, a tenth lens with positive optical power, an eleventh lens with positive optical power, and a twelfth lens with positive optical power, arranged sequentially from the object plane to the image plane along the light direction.

[0010] This technical solution uses a front lens and a rear lens to form an anti-long-distance structure. The effective combination of a lens with positive optical power and a lens with negative optical power makes the distance from the front surface of the projection lens to the focal plane smaller than the focal length. The short focal length reduces the structural size, facilitates miniaturization and integration, and has the characteristics of a large field of view, large edge illumination of the image plane, and a long working distance.

[0011] Preferably, the first lens is an aspherical lens, and the aspherical surface shape expression satisfied by the first lens is:

[0012]

[0013] Where Z represents the distance from a point on the aspherical surface of the first lens to the vertex of the aspherical surface in the direction of the ray; Let represent the distance from a point on the aspherical surface of the first lens to the direction of the light ray, and let c represent the central curvature of the aspherical surface of the first lens. k Represents the conicity. This indicates the higher order of an aspherical surface.

[0014] Based on the above technical means, using aspherical lenses can more effectively eliminate aberrations, thereby ensuring better image quality.

[0015] Preferably, the second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh and twelfth lenses are all spherical lenses, wherein the fifth and eighth lenses are cemented lenses composed of two lenses cemented together.

[0016] Based on the above technical means, two cemented lenses are used to enable the short-throw projection lens to have a low sensitivity tolerance.

[0017] Preferably, an aperture stop is provided between the front lens group and the rear lens group.

[0018] Preferably, the short-throw projection lens has a working wavelength of 405nm, a total optical length of 120mm, an effective focal length of 13mm, and a working F-number of 3.2.

[0019] Preferably, the projection lens has the following resolution under the projected image: when the resolution is 93lp / mm, the lens MTF>68%, which means high resolution, good image quality, high image quality, large projection size, and strong stability.

[0020] Preferably, the projection lens is suitable for a 0.66-inch DMD chip with a projection ratio of 0.767, which is suitable for larger DMD chips compared to traditional projection lenses.

[0021] Preferably, all lenses in the front and rear lens groups are made of glass, and the optical constants of the glass material satisfy the following:

[0022] 1.43 < <1.88

[0023] 35 < <95

[0024] in, , These represent the refractive index and Abbe number of the glass material used for d-rays, respectively.

[0025] Based on the above technical means, using glass material can effectively reduce the impact of lens performance degradation caused by heat deformation of plastic lenses, ensuring that the projection lens has the characteristics of uniform illumination and high image quality.

[0026] Preferably, along the light direction from the object plane to the image plane, a prism and a DMD chip are sequentially arranged after the twelfth lens.

[0027] On the other hand, this application also proposes an application of a short-throw projection lens, which is used in DLP projection for DLP rapid 3D printing.

[0028] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0029] This invention proposes a short-throw projection lens and its application. The short-throw projection lens employs a front and rear lens group to form a reverse telephoto structure. The effective combination of lenses with positive and negative optical power results in a distance from the front surface of the projection lens to the focal plane that is less than the focal length. This short focal length reduces the structural size, facilitating miniaturization and integration. Furthermore, it features a large field of view, high edge illumination, and a long back-working distance. This invention also proposes the application of the short-throw projection lens in DLP projection for DLP rapid 3D printing. This application is suitable for large-size DMD chips, promoting the miniaturization of DLP rapid 3D printers and better meeting market demands. Attached Figure Description

[0030] Figure 1 This is a schematic diagram showing the optical arrangement of the short-throw projection lens proposed in an embodiment of the present invention;

[0031] Figure 2 The MTF plots of each field of view transfer function are shown for specific lens examples proposed in the embodiments of the present invention.

[0032] Figure 3 A field-of-view diagram illustrating specific lens examples presented in the embodiments of the present invention;

[0033] Figure 4 A view showing the field curvature of a specific lens example presented in the embodiments of the present invention as a function of the field of view;

[0034] Figure 5 This is a view showing how distortion varies with the field of view in a specific lens example presented in the embodiments of the present invention.

[0035] Among them, 1-front lens; 2-rear lens; 11-first lens; 12-second lens; 13-third lens; 14-fourth lens; 15-fifth lens; 16-sixth lens; 17-seventh lens; 21-eighth lens; 22-ninth lens; 23-tenth lens; 24-eleventh lens; 25-twelfth lens; 3-aperture; 4-prism; 5-DMD chip. Detailed Implementation

[0036] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this application.

[0037] To better illustrate this embodiment, some parts of the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions;

[0038] It is understandable to those skilled in the art that some well-known details may be omitted from the accompanying drawings.

[0039] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments;

[0040] Example 1

[0041] like Figure 1 As shown, this embodiment proposes a short-throw projection lens, including: a front lens 1 and a rear lens 2 arranged sequentially from the object plane to the image plane along the light direction;

[0042] See Figure 1 The front lens group 1 includes a first lens 11 with positive optical power, a second lens 12 with negative optical power, a third lens 13 with negative optical power, a fourth lens 14 with negative optical power, a fifth lens 15 with negative optical power, a sixth lens 16 with positive optical power, and a seventh lens 17 with positive optical power, arranged sequentially from the object plane to the image plane along the light direction.

[0043] The rear lens group 2 includes an eighth lens 21 with negative optical power, a ninth lens 22 with positive optical power, a tenth lens 23 with positive optical power, an eleventh lens 24 with positive optical power, and a twelfth lens 25 with positive optical power, arranged sequentially from the object plane to the image plane along the ray direction.

[0044] The front lens 1 and rear lens 2 used in this embodiment form an anti-long-distance structure. The effective combination of the lens with positive optical power and the lens with negative optical power makes the distance from the front surface of the projection lens to the focal plane smaller than the focal length. The short focal length reduces the structural size, which is convenient for miniaturization and integration. It also has the characteristics of a large field of view, large edge illumination of the image plane, and a long working distance.

[0045] See Figure 1 In this embodiment, an aperture stop 3 is provided between the front lens group 1 and the rear lens group 2, extending from the object plane to the image plane along the light direction. After the twelfth lens 25, a prism 4 and a DMD chip 5 are also provided in sequence.

[0046] Example 2

[0047] This embodiment provides a detailed description of the specific lenses used in short-throw projection. In this embodiment, the first lens 11 is an aspherical lens. Using an aspherical lens can more effectively eliminate aberrations, thereby ensuring better image quality. The aspherical surface shape expression satisfied by the first lens 11 is:

[0048]

[0049] Where Z represents the distance from a point on the aspherical surface of the first lens 1 to the vertex of the aspherical surface in the direction of the light ray; Let represent the distance from a point on the aspherical surface of the first lens 1 to the direction of the light ray, c represent the central curvature of the aspherical surface of the first lens 1, and k represent the conicity. This indicates the higher order of the aspherical surface. Table 1 shows the details of the aspherical coefficients of the aspherical lens proposed in this embodiment.

[0050] Table 1

[0051]

[0052] In Table 1, surfaces [1] and [2] represent the first and second surfaces of the first lens 11 along the light direction, respectively.

[0053] In this embodiment, the second lens 12, the third lens 13, the fourth lens 14, the fifth lens 15, the sixth lens 16, the seventh lens 17, the eighth lens 21, the ninth lens 22, the tenth lens 23, the eleventh lens 24, and the twelfth lens 25 are all spherical lenses. Among them, the fifth lens 15 and the eighth lens 21 are cemented lenses composed of two lenses cemented together. In this case, the use of two cemented lenses allows the short-throw projection lens to have a low sensitivity tolerance.

[0054] Table 2 shows the specific parameters of the lenses involved in this embodiment. For each lens, its first surface and second surface represent the surfaces on which light rays are incident and emitted in sequence. The parameters include: radius of curvature, thickness, refractive index, Abbe number, and semi-diameter.

[0055] Table 2

[0056]

[0057] Among them, surface numbers [1] and [2] respectively represent the first surface and the second surface of the first lens 11;

[0058] Surface numbers [3] and [4] represent the first and second surfaces of the second lens 12, respectively;

[0059] Surface numbers [5] and [6] represent the first and second surfaces of the third lens 13, respectively;

[0060] Surface numbers [7] and [8] represent the first and second surfaces of the fourth lens 14, respectively;

[0061] Surface numbers [9],

[10] , and

[11] respectively represent the front surface, cemented surface, and rear surface of the fifth lens 15 (cemented lens);

[0062] Surface numbers

[12] and

[13] represent the first and second surfaces of the sixth lens 16, respectively;

[0063] Surface numbers

[14] and

[15] represent the first and second surfaces of the seventh lens 17, respectively;

[0064] Surface number

[16] indicates aperture 3;

[0065] Surface numbers

[17] ,

[18] , and

[19] respectively represent the front surface, cemented surface, and rear surface of the eighth lens 21 (cemented lens);

[0066] Surface numbers

[20] and

[21] represent the first and second surfaces of the ninth lens 22, respectively;

[0067] Surface numbers

[22] and

[23] represent the first and second surfaces of the tenth lens 23, respectively;

[0068] Surface numbers

[24] and

[25] represent the first and second surfaces of the eleventh lens 24, respectively;

[0069] Surface numbers

[26] and

[27] represent the first and second surfaces of the twelfth lens 25, respectively;

[0070] Surface numbers

[28] and

[29] indicate prism 4;

[0071] Surface numbers

[30] and

[31] represent DMD window 5;

[0072] In this embodiment, the short-throw projection lens has a working wavelength of 405nm, a total optical length of 120mm, an effective focal length of 13mm, and a working F-number of 3.2.

[0073] The projection lens exhibits the following resolution characteristics: at a projection resolution of 93 lp / mm, the lens MTF > 68%, indicating high resolution, good image quality, large projection size, and strong stability. It is suitable for 0.66-inch DMD chips with a throw ratio of 0.767, making it suitable for larger DMD chips compared to traditional projection lenses.

[0074] In this embodiment, all lenses in the front lens group 1 and the rear lens group 2 are made of glass. Using glass effectively reduces the performance degradation caused by heat deformation of plastic lenses, ensuring that the projection lens has uniform illumination and high image quality. The optical constants of the glass material used in this embodiment satisfy the following:

[0075] 1.43 < <1.88

[0076] 35 < <95

[0077] in, , These represent the refractive index and Abbe number of the glass material used for d-rays, respectively.

[0078] The MTF (Modulus of the OTF) curve can reflect the image quality performance of the projection lens from the center to the edge. It reflects the projection lens's ability to transmit frequency domain information. Therefore, it can objectively and comprehensively evaluate the imaging quality of the projection lens. MTF represents the degree of contrast (amplitude) attenuation after various sinusoidal intensity distribution functions of different frequencies are imaged by the optical system.

[0079] Figure 2 The image shows the MTF (Mean Transfer Function) of the entire field of view as a function of spatial frequency. The closer the MTF is to the diffraction limit, the better the imaging quality. At a spatial frequency of 93 lp / mm, the MTF of each field of view is >0.68, indicating good imaging quality.

[0080] Figure 3 The point plots for each field of view show that the RMS radius of the lens across the entire field of view is no greater than 2.269. Much smaller than the pixel size 5.4 It can produce clear images.

[0081] Figure 4 This image shows the field curvature of the short-throw projection lens proposed in this embodiment as a function of the field of view, with the field curvature at -20°. By 20 Within the range.

[0082] Figure 5 This embodiment shows that the distortion of the image varies with the field of view, and the distortion is controlled within 0.91%.

[0083] As shown in the above figures, the short-throw projection lens proposed in this embodiment exhibits a resolution of 93 lp / mm and a lens MTF > 68%. This lens boasts high resolution, excellent image quality, high image quality, large projection size, and strong stability. Furthermore, the absolute value of the lens's distortion across the entire field of view is less than 0.91%, and the field curvature across the entire field of view is below -20°. By 20 Within this range, it can better meet market demand.

[0084] Example 3

[0085] This embodiment proposes an application of a short-throw projection lens, specifically, applying a short-throw projection lens to DLP projection in DLP rapid 3D printing.

[0086] The core component of DLP projection is the DMD chip, a digital image chip exclusively developed and mastered by Texas Instruments (TI). It integrates microelectromechanical systems (MEMS) circuit units and is made using CMOS and SRAM memory units. When the DMD chip is working normally, the light source illuminates the chip, which is then illuminated by optical lenses. The tiny circuits covering the DMD surface control the rotation of the lenses to reflect the light, separating and processing the pixels. The image is then projected onto a resin layer through a projection lens. The resin is cured using a light source. As the resin cures, its monomers cross-link to create a polymer chain, which forms a solid material. This chain then creates a series of cross-sections that can assemble into a 3D object, thus enabling DLP rapid 3D printing.

[0087] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A short-throw projection lens, wherein the short-throw projection lens is composed of 12 lenses, characterized in that, include: A front lens (1) and a rear lens (2) are arranged sequentially from the object plane to the image plane along the direction of light rays; The front lens group (1) includes a first lens (11) with positive optical power, a second lens (12) with negative optical power, a third lens (13) with negative optical power, a fourth lens (14) with negative optical power, a fifth lens (15) with negative optical power, a sixth lens (16) with positive optical power, and a seventh lens (17) with positive optical power, arranged sequentially from the object plane to the image plane along the light direction. The rear lens group (2) includes an eighth lens (21) with negative optical power, a ninth lens (22) with positive optical power, a tenth lens (23) with positive optical power, an eleventh lens (24) with positive optical power, and a twelfth lens (25) with positive optical power, arranged sequentially from the object plane to the image plane along the light direction. The short-throw projection lens has a working wavelength of 405nm, a total optical length of 120mm, an effective focal length of 13.00mm, and a working F-number of 3.

2. The short-throw projection lens is suitable for a 0.66-inch DMD chip and has a throw ratio of 0.

767. The short-throw projection lens is used in DLP projection for DLP rapid 3D printing.

2. The short-throw projection lens according to claim 1, characterized in that, The first lens (11) is an aspherical lens, and the aspherical surface shape expression satisfied by the first lens (11) is: Where Z represents the distance from a point on the aspherical surface of the first lens (11) to the vertex of the aspherical surface in the direction of the ray; ρ represents the distance from a point on the aspherical surface of the first lens (11) to the direction of the ray; c represents the central curvature of the aspherical surface of the first lens (11); k represents the conicity; and A n This indicates the higher order of an aspherical surface.

3. The short-throw projection lens according to claim 1, characterized in that, The second lens (12), the third lens (13), the fourth lens (14), the fifth lens (15), the sixth lens (16), the seventh lens (17), the eighth lens (21), the ninth lens (22), the tenth lens (23), the eleventh lens (24) and the twelfth lens (25) are all spherical lenses. Among them, the fifth lens (15) and the eighth lens (21) are cemented lenses composed of two lenses cemented together.

4. The short-throw projection lens according to claim 1, characterized in that, An aperture stop (3) is provided between the front lens group (1) and the rear lens group (2).

5. The short-throw projection lens according to claim 1, characterized in that, The resolution of the short-throw projection lens is as follows: when the resolution is 93 lp / mm, the lens MTF > 68%.

6. The short-throw projection lens according to claim 1, characterized in that, All lenses in the front lens group (1) and the rear lens group (2) are made of glass, and the optical constants of the glass material satisfy the following: 1.43＜N d ＜1.88 35＜V d ＜95 Where, N d V d These represent the refractive index and Abbe number of the glass material used for d-rays, respectively.

7. The short-throw projection lens according to any one of claims 1 to 6, characterized in that, Along the light path from the object plane to the image plane, after the twelfth lens (25), there are also: a prism (4) and a DMD chip (5).

Images