Display device with an image-forming unit with a folding mirror

Abstract

The invention relates to a display device and to transport means comprising a display device of this type. The display device has an image-forming unit (1) for generating an image and an optical unit (2) for projecting the image using a mirror unit. The image-forming unit (1) has a folding mirror (15), which is arranged between a light source (12) and a display element (11) transilluminated by the light (L1) from the light source (12). The folding mirror (15) has microstructures (16) having first mirror surfaces, which are arranged at a first angle relative to a direction of propagation (ABR1) of the light (L1) and are spaced apart from one another to form gaps. Second surfaces are arranged in the gaps, at a second angle relative to the direction of propagation (ABR1) of the light (L1). The width of the gaps varies over a surface of the folding mirror (15).

Description

[0001] Description

[0002] Display device with an imaging unit with a folding mirror

[0003] The present invention relates to a display device having an imaging unit with a folding mirror. The invention also relates to a means of transportation having such a display device.

[0004] A head-up display, also known as a HUD, is a display system that allows the viewer to maintain their line of sight by projecting the content into their field of vision. While such systems were originally used primarily in aviation due to their complexity and cost, they are now also being installed in large-scale production in the automotive sector.

[0005] Head-up displays generally consist of an imaging unit or PGU (Picture Generating Unit), an optical unit, and a mirror unit. The imaging unit generates the image using at least one display element. Most current head-up displays use LCD-based displays (LCD: Liquid Crystal Display;

[0006] Liquid crystal display). The optical unit directs the image onto the mirror unit. The mirror unit is a partially reflective, translucent pane. The viewer thus sees the content displayed by the imaging unit as a virtual image and, at the same time, the real world behind the pane. In the automotive sector, the windshield often serves as the mirror unit, whose curved shape must be taken into account in the display. Due to the interaction of the optical unit and the mirror unit, the virtual image is an enlarged representation of the image generated by the imaging unit.

[0007] DE 102021 214 549 B3 describes a head-up display for a means of transportation, comprising an imaging unit for generating an image and an optical unit for projecting the image through a mirror unit. The imaging unit comprises a folding mirror arranged between a light source and a display element illuminated by the light source at an angle of incidence relative to the propagation direction of the light incident on it from the light source. The folding mirror comprises microstructures, wherein the microstructures comprise first mirror surfaces arranged at a first angle different from the angle of incidence of the folding mirror and spaced apart from one another to form gaps, wherein second surfaces are arranged at a second angle in the gaps.

[0008] US 2019 / 0212 560 A1 describes a head-up display for a means of transportation, comprising an imaging unit for generating an image and an optical system that performs a predetermined correction of the image generated by the imaging unit. The imaging unit comprises a light guide with an inclined reflective surface. The reflective surface has a structure with a plurality of reflective partial surfaces.

[0009] Depending on the size of the virtual image, head-up displays suffer from a greater or lesser loss of homogeneity due to different angles of incidence of the light, particularly on a transparent cover of the optical unit and the windshield. This can lead to conflicts with customer requirements, particularly in the case of augmented reality head-up displays (i.e., head-up displays for displaying content in the form of augmented reality), with correspondingly large angular spectra on the cover and windshield. Even with an ideally illuminated imager, customer requirements regarding homogeneity may no longer be met due to the inhomogeneity caused by the projection system alone.

[0010] The inhomogeneities caused by the projection system are primarily vertical due to the corresponding geometries. While an anti-reflective coating on both sides of the cover can mitigate this effect, it cannot sufficiently reduce it. Furthermore, such a coating is expensive and therefore not common.

[0011] This makes it necessary to compensate for the inhomogeneity by contrasting, inhomogeneous illumination of the imager in order to achieve acceptable homogeneity of the virtual image. For example, the light-emitting diodes (LEDs) responsible for the respective display areas in a planar LED matrix lighting system can be supplied with different currents. However, high-resolution LED matrix lighting severely limits design freedom because it requires more installation space. Furthermore, more expensive LED drivers and higher-performance LEDs are required.

[0012] Similar problems also occur with other projection systems that use additional optical elements that have a negative impact on the homogeneity of the projected image.

[0013] It is an object of the present invention to provide alternative solutions for the design of a display device which achieve a good homogeneity of the projected image.

[0014] This object is achieved by a display device having the features of claim 1. Preferred embodiments of the invention are the subject of the dependent claims.

[0015] According to a first aspect of the invention, a display device comprises an imaging unit for generating an image and an optical unit for projecting the image by means of a mirror unit. The imaging unit comprises a folding mirror arranged between a light source and a display element illuminated by the light from the light source, wherein the light incident on the folding mirror is collimated. The folding mirror has microstructures which have first mirror surfaces with always the same orientation and extent, which are arranged at a first angle relative to a propagation direction of the light and are spaced from one another to form gaps. Second surfaces are arranged in the gaps at a second angle relative to the propagation direction of the light. A width of the gaps varies over a surface of the folding mirror.

[0016] In the inventive solution, a local intensity change on the display element is achieved by varying the width of the gaps across the surface of the folding mirror, i.e., by varying the distance between adjacent first mirror surfaces. The first mirror surfaces represent slats of the folding mirror. According to the invention, the reflective slats responsible for an area of ​​the display element that appears too dark are positioned locally at a smaller distance from one another, thereby brightening these areas in the projected image. In this way, all areas of the projected image can be brought to a uniform luminance.

[0017] According to the invention, the light incident on the folding mirror is collimated. In the described solution, the angle of the first mirror surfaces relative to the direction of propagation of the light is constant. This is particularly advantageous for collimated input light, as the collimation of the incident light beam is maintained.

[0018] According to one aspect of the invention, the variation in the width of the gaps across the surface of the folding mirror is designed to compensate for inhomogeneity in the projected image caused by components in a projection path of the display device. By varying the distance between the first mirror surfaces, those parts of the display element that exhibit poorer efficiency in the projection path can be more strongly illuminated along the corresponding axis than those parts of the display element that experience better efficiency in the projection path. For this purpose, the efficiency of the projection path can be simulated for different pixels, resulting in a limiting homogeneity. Based on this inhomogeneity data, a polynomial function can be fitted, from which the local width of the gaps in the microstructures can ultimately be calculated, which is required to optimize system homogeneity.

[0019] According to one aspect of the invention, the folding mirror is part of a transparent body with a substantially wedge-shaped cross-section, in which the wedge base is the light entry surface facing the light source, the microstructures are arranged on one of the large side surfaces, and the other large side surface is the light exit surface facing the display element. In this way, the folding mirror can be realized as part of a large-volume component, which is less vulnerable than very thin components. This simplifies handling during production.

[0020] According to one aspect of the invention, a polarizer directs light of a first polarization to the display element and light of a second polarization into the gaps, and a retarder converts the polarization of the light directed into the gaps into the first polarization. The light directed into the gaps is guided towards the display element after passing through the gaps. This embodiment has the advantage that polarization recycling is achieved and light also reaches the display element from the gaps. Typically, only one of the polarization directions generated by the light source is used when using a display element that modulates linearly polarized light. This is the case, for example, with liquid crystal displays (LCDs).The normally unused polarization is then converted into the polarization required by the display element using a polarizer and retarder and then directed to the display element, utilizing the gaps in the folding mirror. The light directed into and passing through the gaps has the same polarization as the light polarized by the first mirror surfaces. The display element is thus seamlessly illuminated with light of a single polarization. However, since the recycled light generally has a lower intensity than the light reflected by the first mirror surfaces, additional scatterers are preferably included in the system to ensure sufficient homogenization. This way, intensity differences can be avoided.

[0021] According to one aspect of the invention, the polarizer is designed as a reflective polarizer and is formed by the first mirror surfaces. The retarder is designed as a retarder that rotates the polarization direction by 90° and is formed by the gaps. Such a retarder is also referred to as an X / 2 plate or half-wave plate. This embodiment has the advantage that the functions of reflecting light at the mirror surfaces and filling the gaps between the mirror surfaces with light are combined in a single component. Such a component can be prefabricated and tested separately. Furthermore, assembly is simplified.

[0022] According to one aspect of the invention, the polarizer is designed as a reflective polarizer and is arranged between the folding mirror and the display element. The retarder is designed as a retarder that converts linear polarization into circular polarization and is arranged between the folding mirror and the polarizer. In this embodiment, the retarder converts linear polarization into circular polarization and is passed through by the light twice. Such a retarder is also referred to as a quarter-wave plate or quarter-wave plate. Here, the effect of a half-wave plate is split, and the delay is distributed over two passes. The retarder in this embodiment is arranged between the folding mirror and the polarizer. This has the advantage that the components can be designed as a flat surface, allowing the use of cost-effective, mass-produced components.

[0023] According to one aspect of the invention, the reflective polarizer is inclined at an angle other than 90° to the propagation direction of the light incident on it from the folding mirror. The second surfaces are designed as mirror surfaces and arranged parallel to the reflective polarizer. This has the advantage that light reflected by the reflective polarizer, which is not or hardly divergent, is not reflected back onto the first mirror surfaces, but rather, with a suitable choice of angle and distance, onto one of the second mirror surfaces in the gaps. From there, it is reflected parallel to the light reflected by the first mirror surfaces towards the polarizer, from which it is transmitted after the polarization direction has been adjusted by means of the retarder. Thus, a very large proportion of the light of both polarizations is utilized, and almost no dark areas are caused by the gaps.

[0024] A display device according to the invention is preferably used in a means of transportation. The means of transportation can be, for example, a motor vehicle, but alternatively also an aircraft, a rail vehicle, or a watercraft. In particular, the display device can be designed as a head-up display. Of course, a display device according to the invention can also be used in other applications and configured as a different type of projection system.

[0025] Further features of the present invention will become apparent from the following description and the appended claims taken in conjunction with the figures.

[0026] Figure overview

[0027] Fig. 1 shows schematically a head-up display according to the prior art for a motor vehicle;

[0028] Fig. 2 schematically shows the imaging unit of a head-up display; Fig. 3 schematically shows the imaging unit of a display device according to the invention;

[0029] Fig. 4 shows schematically a folding mirror of the imaging unit from Fig. 3;

[0030] Fig. 5 shows schematically a first embodiment of the invention with polarization recycling;

[0031] Fig. 6 shows schematically a second embodiment of the invention with polarization recycling;

[0032] Fig. 7 shows schematically a third embodiment of the invention with polarization recycling; and

[0033] Fig. 8 shows schematically a means of transport in which a solution according to the invention is implemented.

[0034] Character description

[0035] For a better understanding of the principles of the present invention, embodiments of the invention are explained in more detail below with reference to the figures. The same reference numerals are used in the figures for the same or similarly acting elements and are not necessarily described again for each figure. It is understood that the invention is not limited to the embodiments shown and that the described features can also be combined or modified without departing from the scope of the invention as defined in the appended claims. Fig. 1 shows a schematic diagram of a head-up display for a motor vehicle according to the prior art as an example of a display device 10. The head-up display has an imaging unit 1, an optical unit 2 and a mirror unit 3.A beam SB1 emanates from a display element 11, which is reflected by a first mirror 21 onto a curved mirror 22, which reflects it toward the mirror unit 3. The mirror unit 3 is depicted here as the windshield 31 of the motor vehicle. From there, the beam SB2 travels toward an eye 61 of an observer.

[0036] The viewer sees a virtual image VB, which is located outside the motor vehicle above the hood or even in front of the motor vehicle. Due to the interaction of optical unit 2 and mirror unit 3, the virtual image VB is an enlarged representation of the image displayed by display element 11. A speed limit, the current vehicle speed, and navigation instructions are symbolically displayed here. As long as the eye 61 is within the eyebox 62 indicated by a rectangle, all elements of the virtual image are visible to the eye 61. If the eye 61 is outside the eyebox 62, the virtual image VB is only partially visible to the viewer or not visible at all. The larger the eyebox 62, the less restricted the viewer is in choosing their seating position.The curvature of the curved mirror 22 is adapted to the curvature of the windshield 31 and ensures that the image distortion is stable across the entire eyebox 62. The curved mirror 22 is rotatably mounted by means of a bearing 221. The resulting rotation of the curved mirror 22 enables the eyebox 62 to be moved and thus the position of the eyebox 62 to be adjusted to the position of the eye 61. The first mirror 21 serves to ensure that the path traveled by the beam SB1 between the display element 11 and the curved mirror 22 is long, while at the same time the optical unit 2 remains compact. The optical unit 2 is separated from the environment by a transparent cover 23. The optical elements of the optical unit 2 are thus protected, for example, against dust present in the interior of the motor vehicle.A glare shield 24 serves to reliably absorb the light reflected across the boundary surface of the cover 23, preventing glare to the viewer. In addition to sunlight SL, light from another interfering light source 63 can also reach the display element 11.

[0037] Fig. 2 schematically shows the imaging unit 1 of a head-up display. It shows the light source 12, whose light is collimated by a collimator 13. The collimated light beam is reflected by a mirror 14, which in the example shown is arranged at an angle of y=45° to the propagation direction ABR1 of the light L1, and, in its propagation direction ABR2, which is oriented at an angle of 90° to the propagation direction ABR1, illuminates the display element 11, from where it enters the optical unit 2, which is only indicated here, as a beam SB1. The display element 11 is not necessarily arranged at a right angle to the propagation direction ABR2, but can also be arranged at an angle other than 90°.

[0038] Fig. 3 schematically shows the imaging unit 1 of a display device 10 according to the invention. The folding mirror 15 according to the invention can be seen, which is arranged in the optical path between the light source 12 and the display element 11 illuminated by the light L1 from the light source 12. Fig. 4 schematically shows an enlarged view of the folding mirror 15. The upper boundary surface 150 of the folding mirror 15 has microstructures 16. The lower boundary surface 151, on the other hand, has no particular essential optical or geometric properties. The microstructures 16 have first mirror surfaces 160, which are arranged at a first angle α relative to a propagation direction ABR1 of the light L1 and are spaced from one another to form gaps 162. Second surfaces 161 are arranged in the gaps 162 at a second angle β relative to the propagation direction ABR1 of the light L1.In the example shown, the first angle a=45°, whereas the second angle is 0°. A width bi of the gaps 162 varies over an area of ​​the folding mirror 15. The reflective flanks, i.e. the first mirror surfaces 160, always have the same orientation and extent. This means that the area of ​​the folding mirror 15 is not defined by a flat base surface. For those image areas Bh of the display element 11 for which a higher luminance is desired, the folding mirror 15 has gaps 162 with a small width bi. For those image areas B nof the display element 11, for which a lower luminance is desired, the folding mirror 15, however, has gaps 162 with a larger width bi. The size of the microstructures 16 shown is exaggerated for better recognizability of the principle of the inventive solution. In Fig. 4, the width bi of the gaps 162 increases from left to right, for example. However, it is not specified that the areas B n always lie on the right and the areas Bh always lie on the left of the image sensor. This depends in particular on the number of mirrors in the projection optics. In the opposite case, the gaps 162 between the first mirror surfaces 160 would become smaller from left to right, not larger. Thus, the folding mirror 15 would be curved in the opposite direction.

[0039] Fig. 5 schematically shows a first embodiment of the invention with polarization recycling. The folding mirror 15 with its microstructures 16 can again be seen. In this example, the first mirror surfaces 160 of the microstructures 16 have an angle of 45° to the propagation direction ABR1 of the incident light. Depending on the installation space requirements, angles other than 45° can also be realized. The second surfaces 161 arranged in the gaps 162 between the first mirror surfaces 160 are also designed as reflective surfaces. In this example, the second surfaces 161 are aligned parallel to the propagation direction ABR1 of the incident light, although this is not necessarily the case. A retarder 18 and a polarizer 17 are arranged above the folding mirror 15. In the example shown, these are separated by air, but can alternatively be installed in a laminated manner.In the present embodiment, the retarder 18 has the properties of a quarter-wave plate, so that it converts linearly polarized input light into circularly polarized output light, and vice versa. The polarizer 17 is a reflective polarizer that allows linearly polarized light of a first polarization direction to pass through and reflects light polarized perpendicularly to it. The display element is located at a distance above the polarizer 17 and is not shown here.

[0040] From the left, collimated unpolarized light L1 falls onto the folding mirror 15 in the propagation direction ABR1. As already explained above, variants can also be realized in which no collimated light is incident. For the sake of clarity, only one light beam is shown here as an example. This unpolarized light L1 is reflected by the first mirror surfaces 160. It reaches the retarder 18 in the propagation direction ABR2 as unpolarized light L2, passes through it, and leaves it as unpolarized light L3. It strikes the reflective polarizer 17, which in the example shown lets s-polarized light L4s pass through (transmits) and reflects p-polarized light L4p. For the sake of clarity, this is shown schematically in the figure offset to the right. The p-polarized light L4p passes through the retarder 18 and leaves it as circularly polarized light L5z.This light strikes the reflective second surface 161 and is reflected by it as circularly polarized light L6z back to the retarder 18. It passes through the retarder and exits it as s-polarized light L7s. This light passes through the reflective polarizer 17, since it now has a polarization direction that it transmits rather than reflects. Thus, further s-polarized light L8s reaches the display element. It is understood that the polarization directions are interchangeable, i.e., the reflective polarizer 17 can alternatively transmit p-polarized light and reflect s-polarized light. In this case, p-polarized light reaches the display element.

[0041] In the figure, the light described in each case is drawn parallel to the respective propagation direction ABR1, ABR2 and, after reflection by the polarizer 17 or by a reflective second surface 161, is imaged laterally offset. The latter indicates that, despite the collimation, the light does not normally consist of ideally parallel rays, but of at least slightly divergent rays. As soon as an extended real light source is used, the collimated beam always has a certain angular spectrum. In practice, a slight diffuser can be provided between the collimator and the folding mirror 15 for sufficient homogenization, thereby further increasing the angular spectrum. The slightly divergent rays are largely reflected obliquely by the polarizer 17, so that they reach one of the reflective second surfaces 161 and are reflected there again.Additionally or alternatively, the first mirror surfaces 160 can be provided with a slight curvature, which makes the light L2 reflected by them more divergent than the light L1 incident on them. Further possibilities consist of undulating or inclining the polarizer 17. When inclined, the inclination of the reflective second surfaces 161 is advantageously adjusted in order to minimize the angular deviation. With one or more of these measures, a portion of the light L4s transmitted by the polarizer 17 already fills some of the dark areas caused by the gaps 162 in the light that approaches the display element. On the other hand, light L8s also reaches these dark areas. Thus, more of the originally incident light L1 reaches the display element.

[0042] Fig. 6 schematically shows a second embodiment of the invention with polarization recycling. In this embodiment, the folding mirror 15 is designed as a transparent body 19. The transparent body 19 has a substantially wedge-shaped cross-section. The tip of the wedge, which is located on the right in the figure, is capped and therefore not shown. The wedge base surface 190 is the light entry surface facing the light source. The microstructures 16 are arranged on one of the large side surfaces 191 of the wedge. The other large side surface 192 of the wedge forms the light exit surface facing the display element. In the embodiment shown here, the first mirror surfaces 160, as previously described, are arranged at an angle of 45° to the propagation directions ABR1, ABR2. However, the reflective second surfaces 161 are not arranged parallel to the propagation direction ABR1, but are tilted at an acute angle thereto.They are inclined such that they do not obstruct the light L1 incident from the left on its path to one of the first mirror surfaces 160, but are inclined away from one first mirror surface 160 to the next, as seen in the direction of propagation. The other large side surface 192 of the wedge-shaped transparent body 19 has the same inclination as the reflective second surfaces 161. This can be seen from the acute angle between the normal 192N of the side surface 192 and the direction of propagation ABR2. The polarizer, designed here as a reflective circular polarizer 170, which also combines the function of the retarder, is arranged on the side surface 192 and thus has the same inclination. The first large side surface 191 is provided with a mirror coating.

[0043] From the left, collimated unpolarized light L1 falls onto the folding mirror 15 in the propagation direction ABR1. For the sake of clarity, only a few light rays are shown here as examples. This unpolarized light L1 is reflected by the first mirror surfaces 160. It reaches the reflective circular polarizer 170 in the propagation direction ABR2 as unpolarized light L2. This polarizer transmits s-polarized light L4s and reflects circularly polarized light L5z. Due to the slight tilt of the perpendicular on the side surface 192 to the propagation direction ABR2, this circularly polarized light L5z propagates at an angle deviating from 0° to the propagation direction ABR2. This light strikes the reflective second surfaces 161 and is reflected back to the retarder as circularly polarized light L6z.Due to the inclined arrangement of the reflective second surfaces 161, it now propagates again parallel to the propagation direction ABR2. It strikes the reflective circular polarizer 170 and is transmitted by it. Thus, further s-polarized light L8s reaches the display element. The embodiment shown in Fig. 6 is an example of the variant of the invention in which the reflective polarizer 170 is inclined at an angle other than 90° to the propagation direction ABR2 of the light L2 incident on it from the folding mirror 15, and in which the reflective second surfaces 161 are arranged parallel to the reflective polarizer 170. The design of the folding mirror 15 as a transparent body 19 can of course also be used independently of polarization recycling.

[0044] Fig. 7 schematically shows a third embodiment of the invention with polarization recycling. Here, the folding mirror 15 has an upper interface 150 and a lower interface 151, both of which are arranged parallel to one another and have microstructures 16, 16' arranged offset from one another. In the illustrated embodiment, the offset is selected such that, in the propagation direction ABR1 of the light L1 coming from the light source, first mirror surfaces 160 of the upper interface 150 and first mirror surfaces 160' of the lower interface 151 follow one another. In the propagation direction ABR2 perpendicular thereto, first mirror surfaces 160 of the upper interface 150 and second surfaces 161' of the lower interface 151 follow one another, as do second surfaces 161 of the upper interface 150 and first mirror surfaces 160' of the lower interface 151. The first mirror surfaces 160 of the upper boundary surface 150 are designed as a reflective polarizer 17.The second surfaces 161 of the upper boundary surface 150 are designed as a retarder 18 that rotates the polarization direction by 90°. The first mirror surfaces 160' of the lower boundary surface 151 are designed as mirrors that do not influence the polarization. The first mirror surfaces 160, 160' are arranged at an angle of 45° to both the propagation direction ABR1 of the light L1 coming from the light source and the propagation direction ABR2 of the light traveling to the display element. The second surfaces 161, 161' are arranged parallel to the propagation direction ABR1 of the light L1 coming from the light source. From the left, collimated unpolarized light L1 is incident on the folding mirror 15 in the propagation direction ABR1. For the sake of clarity, only one light beam is shown here as an example. This unpolarized light L1 is reflected by the first mirror surfaces 160 in this example as s-polarized light L2s and transmitted as p-polarized light L2p.The s-polarized light L2s travels in the propagation direction ABR2 toward the display element. The p-polarized light L2p is reflected by the first mirror surfaces 160' of the lower interface 151 and travels as p-polarized light L3p from the inside to the second surfaces 161 of the upper interface 150. Since these are designed as retarders 18 that rotate the polarization by 90°, they transmit the light incident on them, which leaves them as s-polarized light L4s in the propagation direction ABR2 in the region of the gaps 162. Thus, further s-polarized light L4s travels toward the display element. Of course, the polarization directions are also interchangeable in this embodiment.

[0045] Fig. 8 schematically shows a means of transportation 100 in which a solution according to the invention is implemented. In this example, the means of transportation 100 is a motor vehicle. Data on the vehicle's surroundings can be acquired using a sensor system 101. The sensor system 101 can, in particular, comprise sensors for environmental detection, e.g.

[0046] Ultrasonic sensors, laser scanners, radar sensors, lidar sensors, or cameras. The information acquired by the sensor system 101 can be used to generate content to be displayed on the display device 10. Further components of the motor vehicle in this example are a navigation system 102, which can provide position information, and a data transmission unit 103. Using the data transmission unit 103, a connection to a backend can be established, for example, to obtain updated software for components of the motor vehicle. A memory 104 is provided for storing data. Data exchange between the various components of the motor vehicle takes place via a network 105.

[0047] List of reference symbols

[0048] 1 imaging unit

[0049] 10 Display device

[0050] 11 Display element

[0051] 12 Light source

[0052] 13 Collimator

[0053] 14 mirrors

[0054] 15 folding mirrors

[0055] 150 Upper boundary surface

[0056] 151 Lower interface

[0057] 16, 16' Microstructure

[0058] 160, 160' First mirror surface

[0059] 161 , 161 ' Second area

[0060] 162 gap

[0061] 17 Polarizer

[0062] 170 Reflective Circular Polarizer

[0063] 18 retarders

[0064] 19 Transparent body

[0065] 190 wedge base area

[0066] 191 side surface

[0067] 192 side area

[0068] 192N Normal

[0069] 2 optical unit

[0070] 21 First Mirror

[0071] 22 Curved Mirror

[0072] 221 Storage

[0073] 23 Cover

[0074] 24 Anti-glare protection

[0075] 3 Mirror unit

[0076] 61 Eye 62 Eyebox

[0077] 63 stray light source

[0078] 100 means of transport

[0079] 101 Sensor Technology

[0080] 102 Navigation system

[0081] 103 Data transmission unit

[0082] 104 memory

[0083] 105 Network

[0084] ABR1 propagation direction

[0085] ABR2 propagation direction bi width

[0086] Bh, Bn image area

[0087] L1 -L8 light

[0088] SB1 beam

[0089] SB2 beam

[0090] SL Sunlight

[0091] VB Virtual Image a, ß, Y Angle

Claims

Patent claims 1. Display device (10), with: - an imaging unit (1) for generating an image; and - an optical unit (2) for projecting the image by means of a mirror unit (3); wherein: - the imaging unit (1) has a folding mirror (15); - the folding mirror (15) is arranged between a light source (12) and a display element (11) illuminated by the light (L1) of the light source (12), wherein the light (L1) incident on the folding mirror (15) is collimated; - the folding mirror (15) has microstructures (16); - the microstructures (16) have first mirror surfaces (160) with always the same orientation and extent, which are arranged at a first angle (α) relative to a propagation direction (ABR1) of the light (L1) and are spaced apart from one another to form the gaps (162); - second surfaces (161) are arranged in the gaps (162) at a second angle (ß) relative to the propagation direction (ABR1) of the light (L1); and - a width (bi) of the gaps (162) varies over a surface of the folding mirror (15).

2. Display device (10) according to claim 1, wherein the variation of the width (bi) of the gaps (162) over the surface of the folding mirror (15) is designed to compensate for an inhomogeneity of the projected image caused by components (3, 23, 31) in a projection path of the display device (10).

3. Display device (10) according to claim 1 or 2, wherein the folding mirror (15) is part of a transparent body (19) with a substantially wedge-shaped cross-section, in which the wedge base surface (190) is the light entry surface facing the light source (12), the microstructures (16) are arranged on one of the large side surfaces (191) and the other large side surface (192) is the light exit surface facing the display element (11).

4. Display device (10) according to one of the preceding claims, wherein: - a polarizer (17) directs light of a first polarization to the display element (11) and directs light of a second polarization into the gaps (162); - a retarder (18) converts the polarization of the light (L2p, L4p) guided into the gaps (162) into the first polarization; and - the light guided into the gaps (162) is guided towards the display element (11) after passing through the gaps (162).

5. Display device (10) according to claim 4, wherein: - the polarizer (17) is designed as a reflective polarizer (17) and is formed by the first mirror surfaces (160); and - the retarder (18) is designed as a retarder (18) rotating the polarization direction by 90° and is formed by the gaps (162).

6. Display device (10) according to claim 4, wherein: - the polarizer (17) is designed as a reflective polarizer (17) and is arranged between the folding mirror (15) and the display element (11), and - the retarder (18) is designed as a retarder (18) converting linear into circular polarization and is arranged between the folding mirror (15) and the polarizer (17).

7. Display device (10) according to claim 6, wherein the reflective polarizer (17) is inclined at an angle different from 90° to the propagation direction (ABR2) of the light (L2) coming from the folding mirror (15) and incident on it, and the second surfaces (161) are designed as mirror surfaces and are arranged parallel to the reflective polarizer (17).

8. Means of transport (100) with a display device (10) according to one of the preceding claims.

9. Means of transport (100) according to claim 8, wherein the display device (10) is designed as a head-up display.

Images