Projection device for a head-up display, head-up display and vehicle with a projection device

Abstract

Projection device (1) for a head-up display with an imaging device (6) configured to generate an image, wherein the projection device (1) is configured to project the image generated by the imaging device (6) onto a projection surface (11), wherein the projection device (1) has one or more polarization-rotating elements (12, 14) configured to rotate the polarization direction of linearly polarized light by approximately 90° as it passes through the respective polarization-rotating element (12, 14), characterized in that - the image produced by the imaging device (6) exhibits s-polarized light, the polarization direction of which is rotated by 90° by a first of the polarization-rotating elements (12), thereby obtaining p-polarized light, the polarization of which is rotated by 90° by a second of the polarization-rotating elements (14), thereby obtaining s-polarized light, or - the image produced by the imaging device (6) has p-polarized light, the polarization direction of which is substantially preserved in the beam path within the projection device (1), wherein the polarization direction of the p-polarized light is rotated by 90° by a polarization-rotating element arranged between the imaging device (6) and the projection surface (11) in the region of the output opening of the housing (13) of the projection device (1), thereby obtaining s-polarized light.

Description

[0001] The invention relates to a projection device for a head-up display according to the preamble of claim 1, as well as a head-up display and a vehicle with such a projection device.

[0002] With a head-up display, relevant driving information is projected as an image onto the windshield of a vehicle and thus directly into the driver's field of vision, allowing them to quickly absorb the information without having to take their eyes off the traffic.

[0003] From DE 10 2009 057 033 A1 a projection unit for a head-up display is known in which a circular polarizer in the form of a quarter-wave plate is arranged in the beam path between a condenser lens and an imaging unit in the form of a TFT display, by which disturbing reflections of the sunlight penetrating the projection unit from the outside are eliminated at the condenser lens.

[0004] With projection units of this type, it cannot be ruled out that double images may occur when the light generated within the projection unit itself passes through, in particular, plane-parallel optical components. These double images can even overlap with double images that may arise from the reflection of the projected images off the windshield. In any case, it is possible that the images reflected off the windshield may be perceived as blurry by the driver.

[0005] DE 10 2004 003 282 A1 discloses a head-up display with an LCD display that can be illuminated by a light source, wherein the light rays of the image generated in the LCD display are directed via optics onto a front window and a polarization converter is arranged between the light source and the LCD display, which has a polarizing beam splitter, a deflecting mirror and a retarder.

[0006] EP 0 710 866 A1 discloses a projection unit for a head-up display comprising a housing, a display source mounted in the housing, a semi-reflective plate, and a curved mirror. The semi-reflective plate directs light from the display source to the curved mirror, which reflects the light back to the semi-reflective plate and then to a desired location. In one embodiment, the polarization plane of the reflected light is rotated by 90° by a double pass through a quarter-wave plate or half-wave plate positioned between a semi-reflective hologram and the curved mirror.

[0007] US 5,212,471 A discloses a head-up display for a vehicle with a windshield having a first and a second opposing air-cutting surface for the partial reflection of an imaging illumination to create a primary virtual image visible to the driver of the vehicle. A half-wave retarder is positioned between the first and second air-cutting surfaces, rotating the linear polarization of the illumination passing through it. An image source delivers linearly polarized imaging illumination to the first air-cutting surface at an angle chosen to enhance the reflection of s-polarized light and the transmission of p-polarized light, with the polarization being chosen to provide s-polarized imaging illumination at the air-cutting surface.

[0008] The object of the present invention is to provide a projection device for a head-up display, a head-up display and a vehicle with such a projection device, in which the sharpest possible images, in particular images free from double images, are obtained.

[0009] This problem is solved by the projection device, the head-up display and the vehicle according to claim 1, 8 and 9 respectively.

[0010] The projection device according to the invention for a head-up display comprises an imaging device designed to generate an image and is designed to project the image generated by the imaging device onto a projection surface, such as a vehicle windshield. The projection device further comprises one or more polarization-rotating elements, which are designed to rotate the polarization direction of linearly polarized light by approximately 90° as it passes through the respective polarization-rotating element.

[0011] The head-up display according to the invention comprises a projection surface, for example a windshield of a vehicle, and the projection device according to the invention.

[0012] The vehicle according to the invention has a projection surface, in particular in the form of a windscreen, and the projection device according to the invention.

[0013] A vehicle within the meaning of the present invention is preferably a motor vehicle, in particular a passenger car, truck or bus, or a motorcycle, which in particular has an internal combustion engine or an electric drive. In principle, however, the vehicle can also be an aircraft or a watercraft.

[0014] The invention is based on the approach of designing and / or arranging one or more polarization-rotating elements such that multiple reflections of the light generated in the projection device, in particular the light emanating from the imaging device, are suppressed or at least reduced at one or more optically transparent components of the projection device. Such multiple reflections can occur, in particular, at optically thick and / or plane-parallel components of the projection device. The at least one polarization-rotating element is designed such that the polarization direction of linearly polarized light is rotated by 90° when it passes through the polarization-rotating element.If the light exiting the imaging device is, for example, s-polarized and strikes a plane-parallel optical component equipped with a polarization-rotating element on its side facing the imaging device, the polarization direction of the originally s-polarized light is rotated as it passes through the polarization-rotating element, resulting in p-polarized light. Since the reflectivity of p-polarized light within the component, especially at angles of incidence up to 60° or 70°, is significantly lower than that of s-polarized light, multiple reflections within the component and the resulting double images are reduced by a factor of up to 100 compared to the actual main image. Any double images are therefore practically imperceptible to the driver.

[0015] Overall, the invention efficiently suppresses double images, resulting in significantly sharper images.

[0016] In a preferred embodiment of the invention, the projection device comprises at least one optical element arranged between the imaging device and the projection surface, which has two substantially plane-parallel surfaces, on each of which one of the polarization-rotating elements is provided. This prevents the image generated by the imaging device from being impaired by multiple reflections at the downstream optical element.

[0017] The optical element, preferably a transparent plate or layer of glass or plastic, can be positioned, in particular, in the area of ​​an output opening of a housing of the projection device in which the imaging device is located. In this case, the optical element serves as a cover for the output opening without simultaneously impairing the sharpness of the image produced by the imaging device through multiple reflections or double images. The polarization-rotating elements provided on both plane-parallel surfaces of the cover, which rotate the polarization by 90° each, ensure that the polarization direction of the light exiting the projection device is essentially identical to the polarization direction of the light emitted by the imaging device.

[0018] The image generated by the imaging device essentially consists of only s-polarized light, the polarization of which is rotated by 90° by a first polarization-rotating element, resulting in p-polarized light. The polarization of this p-polarized light is then rotated by 90° by a second polarization-rotating element, again yielding s-polarized light. If both polarization-rotating elements are located on the cover element of the projection device, s-polarized light exits the projection device and is reflected with high efficiency at the vehicle's windshield, allowing the driver to perceive images without double images, with high intensity and high contrast.

[0019] It is further preferred to provide one or more components arranged at different locations in the projection device, in particular optically thick and / or plane-parallel components, with the polarization-rotating element(s), so that originally s-polarized light only briefly exhibits p-polarization when passing through the respective component, thereby greatly reducing multiple reflections at the plane-parallel surfaces of the components and thus double images.

[0020] Alternatively, the image generated by the imaging device consists essentially of p-polarized light, the polarization direction of which is essentially preserved in the subsequent beam path within the projection device. As explained above, this allows multiple reflections, particularly at plane-parallel surfaces of optical components, to be suppressed very simply and efficiently in the beam path. Here, the polarization direction of the p-polarized light emitted by the imaging device is rotated by 90° by a polarization-rotating element located between the imaging device and the projection surface in the region of the projection device's output aperture, thus producing s-polarized light. This alternative also offers the advantages mentioned above regarding the reflection of s-polarized light at the front lens.

[0021] It is further preferred that the polarization-rotating element(s) is / are designed as a λ / 2 retarder plate. A λ / 2 retarder plate is also called a half-wave retarder and has the property of retarding light polarized parallel to a specific axis by half a wavelength, or by a phase π, relative to light polarized perpendicular to that axis. This allows the polarization direction of polarized light to be rotated by a selectable angle, in this case by approximately 90°. The change in polarization occurs because light components along two mutually perpendicular polarization directions pass through the medium of the polarization-rotating element at different speeds, thus shifting their phases relative to each other.

[0022] A λ / 2 retardation plate preferably comprises a layer of a birefringent crystal or a birefringent polymer. Preferably, the thickness of the layer and / or the orientation of the crystal or polymer structures within the layer is selected such that it causes a rotation of the polarization of the light by approximately 90°.

[0023] Preferably, the at least one layer of a birefringent polymer is applied to at least one surface of an optical element of the projection device by lamination or coating.

[0024] In principle, it is possible to provide optical elements located at any point in the beam path within the projection device, especially if they are optically thick and / or have plane-parallel surfaces, with at least one polarization-rotating element on one or both outer surfaces in order to efficiently prevent the occurrence of multiple reflections or double images.

[0025] Preferably, it is also possible to design and / or arrange the polarization-rotating element(s) in such a way that the polarization direction of the light is p-polarized over the entire beam path of the light within the projection device or at least in certain sections of the beam path. It may be preferred to convert the p-polarized light into s-polarized light by means of a polarization-rotating element provided in the region of the output of the projection device, which is then reflected at the windshield with particularly high efficiency, so that the double-image-free image projected onto the windshield can be perceived particularly well by the driver.

[0026] Further features, advantages, and applications of the invention will become apparent from the following description in conjunction with the figures. The figures show: Fig. 1. An example of a head-up display with a projection device in a schematic representation; and Fig. 2 an example of an optical element of the projection device with two polarization-rotating elements.

[0027] Fig. Figure 1 shows an example of a head-up display with a projection device 1 and a projection surface 11, for example a windshield of a vehicle, which is also referred to as a combining element or combiner.

[0028] The projection device 1 comprises radiation sources 2, for example in the form of light-emitting diodes, which emit light in preferably different spectral ranges. Furthermore, a so-called light shaft 3 is provided in which the light emitted by the radiation sources 3 is mixed by reflections at the inner walls of the light shaft 3. The light exiting at the end of the light shaft 3 strikes a diffuser 4, where the light is further mixed to ultimately obtain a light distribution that is as spectrally and spatially homogeneous as possible.

[0029] A condenser lens arrangement 5 is connected to the diffuser 4, shaping the largely homogenized light to illuminate an imaging device 6. In the example shown, the condenser lens arrangement 5 consists of two plano-convex lenses with the diffuser 4 at their focal point. This results in substantially parallel beams on the opposite side of the condenser lens arrangement 5, which strike the imaging device 6 perpendicularly. The latter can preferably be a transparent liquid crystal display (LCD), for example, in the form of a so-called TFT display.

[0030] After passing through an optional optical element 7 and being reflected by a plane mirror 8, and subsequently by a concave mirror 9, the light passes through a further optical element 10 in the form of a cover element that covers the exit opening of the housing 13 of the projection device 1, and finally strikes the windshield 11, where the light is reflected and can be perceived by the driver, as indicated in this illustration by a schematically depicted eye 18. The driver perceives the image generated by the imaging device 6 and projected onto the windshield 11 as a virtual image superimposed on the real image of the vehicle's surroundings in front of the windshield 11.

[0031] In addition, the representation chosen here includes a so-called eyebox 19, which essentially indicates the spatial area within which the driver can move without significantly impairing the virtual image perceived on the windscreen 11.

[0032] Preferably, at least one of the optical elements with substantially plane-parallel outer surfaces, namely the diffuser 4 and / or the imaging unit 6 and / or the optional optical element 7 and / or the translucent cover element 10, is provided with at least one polarization-rotating element by which the polarization direction of linearly polarized light is rotated by about 90° as it passes through the polarization-rotating element.

[0033] If, for example, the image generated by the imaging device 6 exhibits essentially s-polarized light, multiple reflections would occur, particularly on the subsequent optical components 7 and 10 with essentially plane-parallel outer surfaces, which would appear as double or multiple images in the projection onto the windscreen 11 and could make the virtual image perceived by the driver appear blurred.

[0034] To avoid this disadvantage, the optical element 7 can, for example, be equipped with a polarization-rotating element or be itself designed as a polarization-rotating element, which can convert the s-polarized light emitted by the imaging device 6 into p-polarized light by rotating the polarization direction by 90°. Multiple reflections at thick and / or plane-parallel optical components of the projection device 1, such as at the optical component 7 itself and / or at the cover element 10, are thereby significantly reduced compared to s-polarized light.In order to achieve the highest possible reflectivity of the light emerging from the projection device 1 at the front window 11, the outer side of the cover element 10 is preferably also provided with a polarization-rotating element which converts the incident p-polarized light into s-polarized light by rotating the polarization direction by 90°, which is then reflected at the front window 11 with high reflectivity.

[0035] Alternatively, it is also possible to provide the translucent cover element 10 in the area of ​​the output opening of the housing 13 of the projection device 1 with a polarization-rotating element on both the inner surface facing the interior of the projection device 1 and on the opposite outer surface, by which the s-polarized light incident on the cover element 10 from the inside is rotated in its polarization direction by 90°, so that essentially only p-polarized light is present inside the cover element 10, for which the respective interfaces have a considerably lower reflectivity than for s-polarized light.As the p-polarized light exits the cover element 10, it is converted back into s-polarized light by a polarization rotation of 90° by the polarization rotating element located on the outside of the cover element 10 and is therefore reflected with high efficiency at the front window 11.

[0036] This will be demonstrated using Fig.Figure 2 explains in more detail, showing an example of an optical element of the projection device 1 in the form of the cover element 10, which is provided on both its inner and outer surfaces with a polarization-rotating element 12 and 14, respectively, in the form of a so-called λ / 2 retarder plate and a so-called half-wave retarder. When s-polarized light strikes the first polarization-rotating layer 12 on the inner surface of the cover element 10, it is converted into p-polarized light, which is only slightly reflected inside the cover element 10, as indicated by thinly drawn beam paths. The p-polarized light exiting the outer surface of the cover element 10 is converted back into s-polarized light by polarization rotation through a second polarization-rotating layer 14.Multiple reflections, which are indicated in the illustration by thinly drawn ray paths, are reduced so much in this way that any double images are so weak in relation to the actual virtual image that they are no longer perceptible.

[0037] The double-sided coating of the optical element 10 with polarization-rotating elements, which was explained in more detail above in connection with the cover element, can in principle be provided on all plane-parallel components of the projection device 1 located in the beam path, i.e. e.g. also on the diffuser 4 and / or on the imaging device 6 and / or on the optical element 7, in order to efficiently suppress multiple reflections on these components and thus the formation of double images.

[0038] In addition to the advantages already mentioned, the invention further increases the flexibility in the design of the installation space of head-up displays and also allows for universal suppression of double images in a wide variety of head-up display concepts with different imaging devices, such as TFTs, Digital Micromirror Devices (DMD), laser-based units and colored or monochrome imaging devices. Reference symbol list 1 Projection device 2 light sources 3 light shafts 4 Diffuser 5 Condenser lens arrangement 6 Imaging equipment 7 optical element 8 Plan mirror 9 Concave mirrors 10 optical element (cover element) 11 Windscreen 12 first polarization-rotating element 13 cases 14 second polarization-rotating element 18 Eye 19 Eyebox

Claims

[1] Projection device (1) for a head-up display with an imaging device (6) configured to generate an image, wherein the projection device (1) is configured to project the image generated by the imaging device (6) onto a projection surface (11), wherein the projection device (1) has one or more polarization-rotating elements (12, 14) configured to rotate the polarization direction of linearly polarized light by about 90° as it passes through the respective polarization-rotating element (12, 14), characterized by , that - the image produced by the imaging device (6) exhibits s-polarized light, the polarization direction of which is rotated by 90° by a first of the polarization-rotating elements (12), thereby obtaining p-polarized light, the polarization of which is rotated by 90° by a second of the polarization-rotating elements (14), thereby obtaining s-polarized light, or - the image produced by the imaging device (6) has p-polarized light, the polarization direction of which is substantially preserved in the beam path within the projection device (1), wherein the polarization direction of the p-polarized light is rotated by 90° by a polarization-rotating element arranged between the imaging device (6) and the projection surface (11) in the region of the output opening of the housing (13) of the projection device (1), thereby obtaining s-polarized light. [2] Projection device (1) according to claim 1 with at least one optical element (7, 10) arranged between the imaging device (6) and the projection surface (11), which has two substantially plane-parallel surfaces on which one of the polarization-rotating elements (12 or 14) is provided. [3] Projection device (1) according to claim 2 with a housing (13) in which the imaging device (6) is housed, wherein an output opening is provided in the housing (13) on which the optical element (10) is arranged. [4] Projection device (1) according to claim 2 or 3, wherein the optical element (10) comprises a plate or layer of glass or plastic. [5] Projection device (1) according to one of the preceding claims, wherein the polarization rotating element(s) (12, 14) is / are designed as a λ / 2 delay plate. [6] Projection device (1) according to one of the preceding claims, wherein the polarization rotating element(s) (12, 14) each comprises at least one layer of a birefringent crystal or a birefringent polymer. [7] Projection device (1) according to claim 6, wherein the at least one layer of a birefringent polymer is applied by lamination or by coating to at least one surface of an optical element (7, 10) of the projection device (1). [8] Head-up display comprising a projection surface (11) and a projection device (1) according to one of the preceding claims. [9] Vehicle, in particular motor vehicle, with a projection surface (11), in particular in the form of a windscreen, and a projection device (1) according to any one of claims 1 to 7.

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