Microlens array for an image projector

Abstract

A microlens array (100-A, 100-B) for an image projector (200) comprises a carrier (105-A, 105-B) and an arrangement (101-A, 101-B) in the form of a matrix and having a multiplicity of lenses (103-A, 103-B) that are arranged on the carrier (105-A, 105-B).

Description

[0001] Microlens array for an image projector

[0002] The invention relates to a microlens array for an image projector, an image projector with a microlens array, a microlens array arrangement and a method for producing a microlens array.

[0003] For small projectors built as a stack along the optical axis, image projectors with a microlens array (MLA) have been used in recent years, especially in the automotive sector. This projector typically includes collimating optics that generate collimated light with a certain small residual divergence, an optical stack with an illumination lens array, a slide plane (made of a chromium layer) in which the image information is provided by apertures, a substrate (made of glass) with the thickness of the focal length, and a projection lens array, which is often identical to the illumination lens array.

[0004] The image projector also includes electronics, a housing, and a lens. This creates a multi-channel, low-profile optic in which each channel can project the entire image with a high depth of field.

[0005] The publication DE 10 2009 024 894 A1 relates to a projection display with a light source and regularly arranged optical channels. The optical channels contain a field lens, each of which is assigned an object structure to be imaged and a projection lens. The distance between the projection lenses and the assigned object structures corresponds to the focal length of the projection lenses, while the distance between the object structures to be imaged and the assigned field lens is selected such that Köhler illumination of the assigned projection lens is enabled. The individual projections are then superimposed to form the overall image.

[0006] The inventive microlens array for an image projector, comprising a carrier and a matrix-like arrangement of a plurality of lenses arranged on the carrier, offers the technical advantage that the microlens array can be manufactured using a more cost-effective manufacturing process than the expensive polymer-on-glass technology. Furthermore, a wider selection of materials is possible, especially for the carrier. Instead of polished glass wafers, any optical injection-molding materials can be used.

[0007] In a further advantageous embodiment of the microlens array, the carrier and the lenses are made of the same material. This further simplifies the manufacture of the microlens array.

[0008] In an advantageous embodiment of the microlens array, the carrier has a thickness between 400 pm and 1200 pm, preferably between 500 pm and 700 pm. This enables the microlens array to be manufactured using injection molding or compression molding processes.

[0009] In a further advantageous embodiment of the microlens array, the matrix-like arrangement of the plurality of lenses and the carrier are formed integrally. This allows the microlens array to be manufactured using an injection molding process.

[0010] In a further advantageous embodiment of the microlens array, the microlens array is a thermoplastic polymer. This also allows the microlens array to be manufactured using an injection molding process.

[0011] In a further advantageous embodiment of the microlens array, the thermoplastic polymer comprises a polymethyl methacrylate (PMMA), cycloolefin polymer (COP), polycarbonate (PC), or optical silicone. This makes it possible to use particularly suitable materials for the production of the microlens array.

[0012] The microlens array arrangement according to the invention, comprising a first microlens array on an illumination side and a second microlens array on a projection side, can be used as a component in an image projector. A slide plane comprising specially designed openings for the passage of light can be arranged between the first and second microlens arrays. This results in a further simplified structure. In an advantageous embodiment of the microlens array arrangement, the first carrier has a thickness in the range of 400 μm to 1200 μm, and the second carrier has a thickness in the range of 2 mm to 5 mm.

[0013] In an advantageous embodiment of the microlens array arrangement, the lenses of the first microlens array on the illumination side have a greater focal length than the lenses of the second microlens array on the projection side. This achieves a sharp projection and a high depth of field.

[0014] In an advantageous embodiment of the microlens array arrangement, the lenses on the illumination side have a focal length in the material that is equal to the sum of the thicknesses of the carrier of the first microlens array and the carrier of the second microlens array. This increases the performance of the microlens array arrangement.

[0015] In an advantageous embodiment of the microlens array arrangement, a slide plane is arranged between the first microlens array and the second microlens array.

[0016] The image projector according to the invention with the microlens array arrangement enables the same technical advantages as the microlens array.

[0017] The method according to the invention is used to manufacture a microlens array, comprising the step of injection molding or hot stamping the microlens array. The method achieves the same technical advantages as the microlens array.

[0018] Embodiments of the invention are explained in more detail with reference to the following figures.

[0019] Fig. 1 is a schematic representation of an image projector with a microlens array;

[0020] Fig. 2 is a schematic cross-sectional view of the microlens array;

[0021] Fig. 3 is a schematic cross-sectional view of a microlens array arrangement; and

[0022] Fig. 4 shows a block diagram of a method for manufacturing a microlens array arrangement. Fig. 1 shows a schematic representation of an image projector 200 with a microlens array arrangement 300 (MLA projector). The microlens array arrangement 300 comprises a first microlens array 100-A on an illumination side 107-A and a second microlens array 100-B on a projection side 107-B.

[0023] The image projector 200 projects a static, non-changing image 109 onto a screen, such as a street or a wall. The goal is to generate the greatest possible luminous flux (lumens) using the smallest possible image projector 200.

[0024] The image projector 200 comprises a light source 113 and a collimating lens 115 for generating parallel light beams. Nevertheless, the spatial dimensions of the image projector 200, particularly along the axis of the light propagation direction, and the number of components should be kept as small as possible. This is particularly advantageous given the space constraints for automotive lighting. For this purpose, the image projector 200 is designed as a multi-aperture approach in which miniaturized projectors (channels), each with separate lenses 103-A and 103-B, are arranged in parallel, thus achieving a miniaturized structure in terms of thickness.

[0025] In addition, a high depth of field can be achieved with a small spatial extension of lenses 103-A and 103-B. This enables a sharp image of image 109 on an inclined screen with different projection distances without tilting the object and lens planes (Scheimpflug condition).

[0026] In this embodiment, the same microlens arrays 100-A and 100-B with the same focal length are used for the lenses 103-A on the illumination side 107-A and the lenses 103-B on the projection side 107-B. The focal length is selected such that the respective focus lies on the opposite lens 103-A and 103-B (BL <-> PL). This means that for good illumination with appropriate collimation, as little distance as possible is desired between the lenses 103-A on the illumination side 107-A and the slide plane 111.

[0027] The lenses 103-A, 103-B are manufactured using an injection molding process. The slide plane 111 is made of a chromium layer in which the image information is provided by openings. The carrier 105-A is manufactured together with the lenses 103-A and arranged on the illumination side 101-A. This typically has a thickness between 400 pm and 800 pm, in this embodiment 550 pm. The carrier 105-A or 105-B can be made of polymethyl methacrylate (PMMA) or cycloolefin polymer (COP). This has the technical advantage that these materials have low dispersion. This prevents color errors and color fringes in a polychromatic white projection. However, the carrier 105-A and 105-B can also be made of polycarbonate or optical silicone. The carrier 105-A and 105-B may have a length between 5 mm and 50 mm and a width between 5 mm and 50 mm, preferably 10 mm by 10 mm.For example, the carrier 105-A has a thickness between 400 pm and 1200 pm and the carrier 105-B has a thickness between 2 mm and 5 mm.

[0028] The lenses 103-A and 103-B on the carrier 105-A and 105-B have, for example, a mutual distance from lens center to lens center of 500 pm to 1,000 pm, in this embodiment 800 pm. The lenses 103-A, 103-B are arranged hexagonally on the carrier 105-A and 105-B and have a focal length between 1.5 mm and 4 mm, in this embodiment 2 mm. The lenses 103-A, 103-B can, for example, be formed from the same or a different material as the carrier 105-A or 105-B. For example, 12 by 12 lenses 103-A, 103-B are arranged on the carrier 105-A and 105-B in a dimension of 10 mm by 10 mm. For example, the focal length of the lenses 103-A, 103-B is greater than the thickness of the carrier 105.

[0029] The sufficient thickness of these supports 105-A and 105-B allows the microlens arrays 100-A and 100-B to be manufactured using an injection molding or compression molding process. The focal length of the lenses 103-A on the illumination side 107-1 can be slightly increased to achieve the best possible illumination of the slide structures (image information) in the slide plane 111 and the associated lenses 103-B on the projection side 107-B. The supports 105-A and 105-B and the respective lenses 103-A and 105-B of each microlens array 100A and 100-B can be manufactured in one piece from the same material.

[0030] In this embodiment, different focal lengths of the lenses 103-A and 103-B on the illumination and projection sides 107-A and 107-B are used, so that the focal plane of the lenses 103-A on the illumination side 107-A lies exactly in the lenses 103-B on the projection side 107-B. This results in a maximum acceptance angle of the residual divergence of the collimation. The focal length of the lenses 103-B on the projection side 107-B is selected such that the focal plane lies in the slide plane 111. This enables a sharp projection with the same advantages, such as a high depth of field for projection on an inclined plane.

[0031] Fig. 2 shows a schematic cross-sectional view of the microlens array 100-A. The layer of the carrier 105-A has a thickness of 520 pm. Due to the thickness of the carrier 105-A, the microlens array 100-A can be manufactured using an injection molding process.

[0032] Opposite is an adhesive layer 119 (bonding design) with a thickness of 40 pm. The slide plane 111 is attached using the adhesive layer 119. This results in a total distance from the vertex of the lens 103-A to the slide plane 111 of 670 pm. The microlens array 100-B on the projection side 107-B is constructed similarly to the microlens array 100-A on the illumination side 107-A, except that the latter can have a carrier 107-B with a greater thickness.

[0033] The alternative integrated design of the microlens array 100-A allows it to be manufactured using a more cost-effective and less complex manufacturing process, such as injection molding. During injection molding of the microlens array 100-A, the matrix-like arrangement 101-A of the plurality of lenses 103-A and the carrier 105-A are molded from a thermoplastic polymer.

[0034] Fig. 3 shows a schematic cross-sectional view of a microlens array arrangement 300. On the slide plane 111, each subpattern is defined in the area Dia2. The area Dia2 is smaller than the area Dial. The area Dia2 of the pattern is defined by the focal length of the lens 103-A and the distance d1. The area outside the circle containing the area Dia2 can be covered with an absorbing or reflective material 121 to prevent light from passing through. The distance d1 can be smaller than the focal length of the matrix-like arrangement 101-A.

[0035] The carriers 105-A and 105-B can comprise multiple layers of different materials. Special material combinations can be technically advantageous for manufacturing due to specific material properties and requirements, such as a carrier for a chromium layer.

[0036] Fig. 4 shows a block diagram of a method for manufacturing a microlens array arrangement 300. In step S101, a first microlens array 100-A comprising a matrix-like arrangement 101-A with a plurality of lenses 103-A is injection-molded from a thermoplastic polymer, which lenses are arranged on the carrier 105-A. The microlens array 100-A can also be manufactured from the carrier 105-A by hot stamping (embossing). The lenses 103-A are created on the surface of the carrier 105-A using an embossing die.

[0037] In step S102, a second microlens array 100-B comprising a matrix-like arrangement 101-B with a plurality of lenses 103-B is injection-molded from a thermoplastic polymer, arranged on a carrier 105-B. The second microlens array 100-B can also be manufactured by hot stamping.

[0038] In step S103, the slide plane 111, in which the image information is present through specially designed openings, is arranged between the first microlens array 100-A and the second microlens array 100-B. In step S104, the first microlens array 100-A and the second microlens array 100-B are connected to one another, while the slide plane 111 is arranged therebetween. This makes it easy to produce a microlens array arrangement 300 that can be inserted into the image projector 200. These manufacturing processes also allow for a wider selection of materials for the lenses 103-A and 103-B and the carriers 105-A and 105-B. This has optical advantages, but also reduces manufacturing costs.

[0039] The technical advantage of the invention lies in the more cost-effective manufacturing process compared to the expensive polymer-on-glass technology. This also allows for a wider range of materials, especially for the carriers 105-A and 105-B. Instead of expensive polished glass wafers, any optical injection-molding material can be used.

[0040] Due to its dimensions, the described microlens array arrangement 300 is particularly suitable for the automotive sector, for example as a luminaire for a light carpet, as a symbol projection in hotels, as a safety projection in aircraft displays, as effect lighting, as a guidance projection or as a danger zone projection in buildings.

[0041] All features explained and shown in connection with individual embodiments of the invention can be provided in different combinations in the subject matter according to the invention in order to simultaneously realize their advantageous effects.

[0042] All method steps can be implemented by devices suitable for performing the respective method step. All functions performed by physical features can be a method step of a method.

Claims

PATENT CLAIMS 1. Microlens array (100-A, 100-B) for an image projector (200), comprising: - a carrier (105-A, 105-B), and - a matrix-shaped arrangement (101-A, 101-B) with a plurality of lenses (103-A, 103-B) arranged on the carrier (105-A, 105-B).

2. Microlens array (100-A, 100-B) according to claim 1, wherein the carrier (105-A, 105-B) and the lenses (103-A, 103-B) are made of the same material.

3. Microlens array (100-A, 100-B) according to claim 2, wherein the carrier (105-A) has a thickness between 400 pm and 1200 pm, preferably between 500 pm and 700 pm.

4. Microlens array (100-A, 100-B) according to one of the preceding claims, wherein the matrix-shaped arrangement (101-A, 101-B) of the plurality of lenses (103-A, 103-B) and the carrier (105-A, 105-B) are formed in one piece.

5. Microlens array (100-A, 100-B) according to one of the preceding claims, wherein the microlens array (100-A, 100-B) is a thermoplastic polymer.

6. The microlens array (100-A, 100-B) of claim 5, wherein the thermoplastic polymer comprises a polymethyl methacrylate (PMMA), cycloolefin polymer (COP), polycarbonate (PC) or optical silicone.

7. A microlens array arrangement (300), comprising: a first microlens array (100-A) according to any one of claims 1-6 on an illumination side (107-A); and a second microlens array (100-B) according to any one of claims 1-6 on a projection side (107-B).

8. Microlens array arrangement (300) according to claim 7, wherein the lenses (103-A) of the first microlens array (100-A) on the illumination side (107-A) have a have a greater focal length than the lenses (103-B) of the second microlens array (100-B) on the projection side (107-B). Microlens array arrangement (300) according to claim 7 or 8, wherein the first carrier (105-A) has a thickness in the range of 400 µm to 1200 µm and the second carrier (105-B) has a thickness in the range of 2 mm to 5 mm. Microlens array arrangement (300) according to one of claims 7 to 9, wherein the lenses (103-A) on the illumination side have a focal length in the material that is equal to the sum of the thicknesses of the carrier (105-A) of the first microlens array (100-A) and the carrier (105-B) of the second microlens array (100-B). Microlens array arrangement according to one of claims 8 to 10, wherein a slide plane (111) is arranged between the first microlens array (100-A) and the second microlens array (100-B). Image projector (200) with a microlens array arrangement (300) according to one of claims 7 to 11.A method for producing a microlens array (100-A, 100-B) according to any one of the claims, comprising the step:. Injection molding or hot stamping the microlens array (100-A, 100-B) according to one of claims 1 to 6.

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