Microlens array for image projector

Abstract

A microlens array (100-A, 100-B) for an image projector (200), the microlens array having a carrier (105-A, 105-B) and a matrix device (101-A, 101-B), the matrix device having a plurality of lenses (103-A, 103-B) arranged on the carrier (105-A, 105-B).

Description

Technical Field

[0001] The present invention relates to a microlens array for an image projector, an image projector having a microlens array, a microlens array device, and a method for manufacturing a microlens array. Background Art

[0002] In recent years, for small projectors configured as a stack along the optical axis - especially in the automotive field - image projectors with a microlens array (Micro Lens Array - MLA) have been used. The projector typically includes collimating optics, an optical stack having an illumination lens array, a mask surface (made of a chromium layer), a substrate with a thickness of the focal length (made of glass), and a projection lens array that is usually the same as the illumination lens array, wherein the collimating optics generate collimated light with a specific small remaining divergence, and image information is obtained through openings in the mask surface.

[0003] In addition, the image projector includes an electronic device, a housing, and a cover plate. This results in a multi - channel optical device with a small extension, in which each channel can project the entire image with a high depth of field.

[0004] Document DE 10 2009 024 894 A1 relates to a projection display having a light source and regularly arranged optical channels. The optical channels contain field lenses, and each field lens is associated with an object structure to be imaged and a projection lens. The distance between the projection lens and the associated object structure corresponds to the focal length of the projection lens, and the distance between the object structure to be imaged and the associated field lens is selected such that Köhler illumination of the associated projection lens is achieved. Then, the individual projections are superimposed to form a total image. Summary of the Invention

[0005] The microlens array of the matrix - type device for an image projector according to the present invention, having a carrier and a plurality of lenses arranged on the carrier, achieves the following technical advantages. Compared with expensive polymer - on - glass technology, the microlens array can be manufactured by a more cost - favorable manufacturing method. In addition, a greater range of material selection is achieved, especially for the carrier. In principle, all optical injection - molding materials can be used to replace polished glass wafers.

[0006] In another 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.

[0007] In an advantageous embodiment of the microlens array, the carrier has a thickness between 400 μm and 1200 μm, preferably between 500 μm and 700 μm. This enables the production of the microlens array by means of an injection molding or extrusion method.

[0008] In another advantageous embodiment of the microlens array, the matrix arrangement of the plurality of lenses and the carrier are formed in one piece. Thereby, the microlens array can be produced by means of an injection molding method.

[0009] In another advantageous embodiment of the microlens array, the microlens array is a thermoplastic polymer. The microlens array can likewise be produced by means of an injection molding method.

[0010] In another advantageous embodiment of the microlens array, the thermoplastic polymer comprises polymethyl methacrylate (PMMA), cycloolefin polymer (COP), polycarbonate (PC) or optical silicone resin. Thereby, particularly suitable materials are used for the production of the microlens array.

[0011] A microlens array device according to the invention having a first microlens array on the illumination side and a second microlens array on the projection side can be used as a component in an image projector. A mask surface (Diaebene) can be provided between the first microlens array and the second microlens array, the mask surface comprising specifically designed openings for the passage of light. This results in a further simplified construction.

[0012] In an advantageous embodiment of the microlens array device, the first carrier has a thickness in the range from 400 μm to 1200 μm, while the second carrier has a thickness in the range from 2 mm to 5 mm.

[0013] In an advantageous embodiment of the microlens array device, 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 enables sharp projection and a high depth of field.

[0014] In an advantageous embodiment of the microlens array device, the material of the lenses on the illumination side has the following focal length: the focal length is equal to the sum of the thicknesses of the carriers of the first microlens array and the second microlens array. This improves the performance of the microlens array device.

[0015] In an advantageous embodiment of the microlens array device, a mask surface is provided between the first microlens array and the second microlens array.

[0016] An image projector according to the invention having a microlens array device achieves the same technical advantages as the microlens array.

[0017] The method according to the invention is used for manufacturing a microlens array, and the method has the steps of injection molding or hot embossing the microlens array. The same technical advantages as those achieved by the microlens array are realized by the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Embodiments of the present invention will be elaborated in detail according to the following drawings. It is shown here:

[0019] Figure 1 A schematic diagram showing an image projector having a microlens array;

[0020] Figure 2 A schematic cross-sectional view showing the microlens array;

[0021] Figure 3 A schematic cross-sectional view showing a microlens array device; and

[0022] Figure 4 A block diagram showing a method for manufacturing a microlens array device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Figure 1 A schematic diagram showing an image projector 200 (MLA projector) having a microlens array device 300. The microlens array device 300 includes a first microlens array 100-A on the illumination side 107-A and a second microlens array 100-B on the projection side 107-B.

[0024] The image projector 200 projects a static and immutable image 109 onto a screen, such as a road or a wall. Here, it should be possible to generate as large a luminous flux (lumens) as possible with the smallest possible image projector 200.

[0025] The image projector 200 includes a light source 113 and a collimating lens 115 for generating a parallel light beam. Nevertheless, the spatial dimensions of the image projector 200, especially the spatial dimensions along the axis of the light propagation direction and the number of components, should be kept as small as possible. This is especially advantageous in the automotive field when the structural space of the lamp is limited. For this purpose, the image projector 200 is configured in a multi-aperture manner, in which micro-projectors (channels) having respectively separate lenses 103-A and 103-B are arranged in parallel, so that a miniaturized structure is achieved in terms of thickness.

[0026] In addition, a high depth of field can be generated by means of the small spatial extension of the lenses 103-A and 103-B. This enables clear imaging of the image 109 on an inclined screen having different projection distances without tilting the object- and lens planes (Scheimpflug condition).

[0027] In the embodiment, the same microlens arrays 100-A and 100-B with the same focal length are used for the lens 103-A on the illumination side 107-A and the lens 103-B on the projection side 107-B. The focal length is selected such that the corresponding foci are on the opposing lenses 103-A and 103-B (BL <-> PL). From this, it follows that in order to illuminate well in a suitable collimation, it is desirable that there is as little spacing as possible between the lens 103-A on the illumination side 107-A and the mask surface 111.

[0028] The lenses 103-A, 103-B are manufactured by means of an injection molding process. The mask surface 111 is made of a chromium layer, in which the image information is obtained through openings.

[0029] The carrier 105-A is manufactured together with the lens 103-A and is arranged on the illumination side 101-A. The carrier typically has a thickness between 400 μm and 800 μm, which is 550 μm in the embodiment. The carrier 105-A or 105-B can be formed of polymethyl methacrylate (PMMA) or cycloolefin polymer (COP). This has the technical advantage that the material has low dispersion. Thereby, color errors and color fringes in multicolor white projection can be prevented. However, the carriers 105-A and 105-B can also be made of polycarbonate or optical silicone resin. The carriers 105-A and 105-B can 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 μm and 1200 μm, and the carrier 105-B has a thickness between 2 mm and 5 mm.

[0030] For example, the lenses 103-A and 103-B on the carriers 105-A and 105-B have an interspacing of 500 μm to 1000 μm from lens center to lens center, which is 800 μm in the embodiment. The lenses 103-A, 103-B are arranged on the carriers 105-A and 105-B in a hexagonal pattern and have a focal length between 1.5 mm and 4 mm, which is 2 mm in the embodiment. The lenses 103-A, 103-B can be formed of the same or different materials as the carrier 105-A or 105-B, for example. For example, 12 by 12 lenses 103-A, 103-B are arranged on carriers 105-A and 105-B of a size of 10 mm by 10 mm. The focal length of the lenses 103-A, 103-B is, for example, greater than the thickness of the carrier 105.

[0031] Achieved through the sufficient thickness of the carriers 105-A and 105-B, the microlens arrays 100-A and 100-B can be manufactured by means of an injection molding method or an extrusion method. The focal length of the lens 103-A on the illumination side 107-1 can be easily increased in order to obtain the best possible illumination of the aperture structure (image information) in the mask plane 111 and the associated lens 103-B on the projection side 107-B. The carriers 105-A and 105-B of each one microlens array 100A and 100-B and the corresponding lenses 103-A and 105-B can be manufactured in one piece from the same material.

[0032] In the said embodiment, different focal lengths of the lenses 103-A and 103-B are used on the illumination side and the projection sides 107-A and 107-B, such that the focal plane of the lens 103-A on the illumination side 107-A is exactly in the lens 103-B on the projection side 107-B. This results in the maximum acceptance angle of the collimated residual divergence. The focal length of the lens 103-B on the projection side 107-B is selected such that the focal plane is in the mask plane 111. This enables a sharp projection with the same advantages, for example a high depth of field for projection on an inclined plane.

[0033] Figure 2 A schematic cross-sectional view of the microlens array 100-A is shown. The layer of the carrier 105-A has a thickness of 520 μm. Through the thickness of the carrier 105-A, the microlens array 100-A can be manufactured by means of an injection molding method.

[0034] There is a bonding layer 119 (bonding design) with a thickness of 40 μm present oppositely. The mask plane 111 is fastened by means of the bonding layer 119. This results in a total spacing of 670 μm from the vertex of the lens 103-A to the mask plane 111. The microlens array 100-B on the projection side 107-B is constructed correspondingly to the microlens array 100-A on the illumination side 107-A, except that the thickness of the carrier 107-B of the microlens array on the projection side can be greater.

[0035] Through an alternative integrated construction of the microlens array 100-A, the microlens array can be manufactured by means of a more cost-effective and less time-consuming manufacturing method, such as an injection molding method. In the injection molding of the microlens array 100-A, a matrix arrangement 101-A of a plurality of lenses 103-A and the carrier 105-A is injection-molded from a thermoplastic polymer.

[0036] Figure 3A schematic cross-sectional view of the microlens array device 300 is shown. On the mask surface 111, each sub-pattern is defined in the region Dia2. The region Dia2 is smaller than the region Dia1. The region Dia2 of the pattern is defined by the focal length of the lens 103-A and the distance d1. The region with the region Dia2 outside the circle can be covered with an absorption or reflection material 121 to prevent light from passing through. The distance d1 can be smaller than the focal length of the matrix device 101-A.

[0037] The carriers 105-A and 105-B can include multiple layers made of different materials. Special material combinations can be technically advantageous for manufacturing due to special material properties and requirements, such as carriers for chromium layers.

[0038] Figure 4 A block diagram of a method for manufacturing the microlens array device 300 is shown. In step S101, a first microlens array 100-A having a matrix device 101-A is injection-molded from a thermoplastic polymer, and the matrix device has a plurality of lenses 103-A disposed on a carrier 105-A. The microlens array 100-A can also be manufactured from the carrier 105-A by hot embossing. Here, the lenses 103-A are produced on the surface of the carrier 105-A by means of an embossing punch.

[0039] In step S102, a second microlens array 100-B having a matrix device 101-B is injection-molded from a thermoplastic polymer, and the matrix device has a plurality of lenses 103-B disposed on a carrier 105-B. The second microlens array 100-B can also be manufactured by hot embossing.

[0040] In step S103, a mask surface 111 is disposed between the first microlens array 100-A and the second microlens array 100-B, and image information exists in the mask surface through specially designed openings. In step S104, the first microlens array 100-A and the second microlens array 100-B are connected to each other, and the mask surface 111 is disposed therebetween. Thus, the microlens array device 300 can be produced in a simple manner, and the microlens array device can be used in the image projector 200. The manufacturing method also enables a wider range of material selection for the lenses 103-A and 103-B and the carriers 105-A and 105-B. This has optical advantages, but also advantages in terms of manufacturing cost.

[0041] The technical advantage of the present invention lies in a manufacturing method that is more cost-effective compared to the expensive polymer-on-glass technology. This also enables a wider range of material selection, especially for the carriers 105-A and 105-B. Instead of expensive polished glass wafers, in principle, all optical injection-molded materials can be used.

[0042] The described microlens array device 300 is particularly suitable for the automotive field due to its size, for example as a lamp for a light carpet, as a symbol projection in a hotel, as a safety projection in an aircraft, as effect lighting, as a guiding projection or as a projection of a danger zone in a building.

[0043] All features described and illustrated in connection with the various embodiments of the invention can be presented in different combinations in the subject matter according to the invention in order to achieve their advantageous effects simultaneously.

[0044] All method steps can be implemented by a device suitable for performing the corresponding method steps. All functions implemented by the subject matter features can be method steps of a method.

Claims

1. A microlens array (100-A, 100-B) for an image projector (200), the microlens array having: - a carrier (105-A, 105-B), and - a matrix device (101-A, 101-B) having a plurality of lenses (103-A, 103-B) disposed on the carrier (105-A, 105-B).

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

4. The microlens array (100-A, 100-B) according to any one of the above claims, wherein the matrix device (101-A, 101-B) of the plurality of lenses (103-A, 103-B) and the carrier (105-A, 105-B) are integrally formed.

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

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

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

8. The microlens array device (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 longer focal length than the lenses (103-B) of the second microlens array (100-B) on the projection side (107-B).

9. The microlens array device (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.

10. The microlens array device (300) according to any one of claims 7 to 9, wherein the material of the lens (103-A) on the illumination side has a focal length 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).

11. The microlens array device according to any one of claims 8 to 10, wherein a mask surface (111) is provided between the first microlens array (100-A) and the second microlens array (100-B).

12. An image projector (200) having the microlens array device (300) according to any one of claims 7 to 11.

13. A method for manufacturing the microlens array (100-A, 100-B) according to any one of the claims, the method having the following steps: - Injection molding or hot embossing the microlens array (100-A, 100-B) according to any one of claims 1 to 6.

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