Head-up display image generation unit with folding mirror

Abstract

This invention relates to a head-up display for a vehicle, comprising an imaging unit for generating an image and an optical unit for projecting the image through a mirror unit. The imaging unit (1) has a folding mirror arranged at an angle of attack between the light source and a display element transmitted through the light source, relative to the propagation direction of light incident from the light source onto the folding mirror. The folding mirror has microstructures having first mirror surfaces arranged at a first angle different from the angle of attack of the folding mirror, the microstructures being spaced apart from each other in a manner forming gaps, and second surfaces arranged at a second angle within these gaps. A polarizer guides first-polarized light to the display element and second-polarized light into these gaps. A phase delayer converts the polarization of the light guided into these gaps into the first polarization. The light guided into the gaps is directed toward the display element after passing through these gaps.

Description

Technical Field

[0001] The present invention relates to a head-up display having an image generation unit with a folding mirror. Background Technology

[0002] A head-up display (also known as a HUD) is understood as a display system in which an observer can maintain their gaze direction because the content to be displayed is within their field of vision. Such systems were initially used primarily in the aviation industry due to their complexity and cost, but they are now also widely used in the automotive industry.

[0003] Head-up displays (HUDs) typically consist of an imaging unit or image generating unit (PGU), an optical unit, and a mirror unit. The imaging unit generates an image and uses at least one display element for this purpose. Most modern HUDs use LCD (Liquid Crystal Display)-based displays to generate images. The optical unit directs the image onto the mirror unit. The mirror unit is a partially reflective, transparent sheet. Therefore, the observer sees the content displayed by the imaging unit as a virtual image and simultaneously sees the real world behind the sheet. In the automotive industry, windshields are often used as mirror units, and their curved shape must be taken into account when displaying images. Through the combined action of the optical and mirror units, the virtual image is a magnified version of the image generated by the imaging unit.

[0004] DE 41 02 678 A1 discloses a head-up display for a transportation vehicle, which includes: an imaging unit for generating an image, an optical unit for projecting the image onto a virtual image plane via a mirror unit, and a folding mirror whose incident and exit angles are not equal. This feature is achieved, for example, by means of a holographic component (using a diffraction grating or a Fresnel mirror).

[0005] US 5,313,326A, WO 2014 / 041689 A, US 2015 / 0362221 A1 and US2018 / 252917A1 also show a head-up display that uses a folding mirror whose angle of incidence and angle of exit are not equal.

[0006] In these known head-up displays, folding mirrors with unequal incident and exit angles are positioned along the imaging path. At this point, folding mirrors with this characteristic can adversely affect image quality and / or stray light sensitivity.

[0007] US 2010 / 0195022 A1 discloses a backlight system for a liquid crystal display, wherein the edges of a light guide are provided with multiple reflective surfaces that broaden a tightly focused laser beam into a wide beam. The use of laser sources is known in head-up displays, but primarily in the use of micromirror units (so-called DMDs, digital micromirror devices), which require beams with very small cross-sections and small opening angles.

[0008] US 2019 / 0212560 A1 discloses a head-up display in which the optical elements have mirrors with microstructures that project light onto the display elements. A disadvantage is that the illumination of the display elements is not uniform, exhibiting dark bands.

[0009] US 2020 / 0033600 A1 discloses a head-up display in which the liquid crystal display element should use as much unpolarized light generated by the light source as possible by means of a polarization converter.

[0010] Therefore, an improved head-up display is desired compared to known head-up displays. Summary of the Invention

[0011] The head-up display according to the invention is given in claim 1. The head-up display has an imaging unit for generating an image and an optical unit for projecting the image through a mirror unit. The imaging unit has a folding mirror. The folding mirror is arranged at an angle of attack between the light source and the display element transmitted through the light source, relative to the propagation direction of light incident upon it from the light source. The angle of attack is preferably less than 45°, which enables a flatter structural space. The folding mirror has microstructures. These microstructures have first mirror surfaces arranged at a first angle different from the angle of attack of the folding mirror, and these microstructures are spaced apart from each other in a manner forming gaps. Second surfaces are arranged at a second angle in these gaps. A polarizer guides first-polarized light to the display element and guides second-polarized light into these gaps. A phase delayer converts the polarization of the light guided into these gaps into the first polarization. The light guided into the gaps is directed toward the display element after passing through these gaps. This has the advantage of achieving polarization cycling, and the light exposed from the gaps is also transmitted to the display element. Under normal circumstances, when the display element is a display element that modulates linearly polarized light, only one polarization direction generated by the light source is used. This is the case, for example, in a liquid crystal display (LCD). According to the invention, by means of a polarizer and a phase delayer, the normally unused polarization is converted to the polarization required by the display element in a manner that makes full use of the gaps in the folding mirrors, and then guided to the display element. The light guided into and through these gaps has the same polarization as the light polarized by the mirrors. Therefore, the display element is illuminated with a single polarized light in a gapless manner. Ideally, this also saves on additional homogenization measures. Such an ideal situation exists, for example, for a specific duty cycle. In a real system, the strip structure is also dispersed, for example, by means of a scatterer. Such scattering is then also used to illuminate the eyebox.

[0012] According to an improved scheme, the first mirrors have different first angles relative to each other / have other first angles. In this case, a group of first mirrors having the same first angle can also have different first angles between groups. However, each first mirror in particular has a first angle different from the corresponding other first mirrors. This has the effect of when the folding mirror is a curved folding mirror (also called a cylindrical mirror). Here, from a macroscopic perspective, the folding mirror is not curved, but rather the first mirrors and second surfaces with microstructures are arranged such that the folding mirror functions like a cylindrical mirror. In this way, diffused radiation or astigmatism is achieved, which is desired in certain cases of head-up displays.

[0013] Advantageously, the first mirror is designed as a reflective polarizer, and the gap is designed as a phase delayer that rotates the polarization direction by 90°. Such a phase delayer is also called a λ / 2 plate or a half-wave plate. The advantage of this variant according to the invention is that it integrates the functions of reflecting light on the mirror surface and filling the gap between the mirror surfaces with light into a single component that can be prefabricated and tested individually. This also simplifies assembly.

[0014] According to the invention, the folding mirror has two parallel interfaces with identical microstructures arranged offset from each other. This design is particularly advantageous when the gap and the mirror surface have the same extension dimension in the projection onto the direction of light propagation. Thus, the offset is advantageously as large as or an integer multiple of this extension dimension. It is also advantageous that the folding mirror can be manufactured in one process, thus eliminating the need for adjustments to the macrostructures.

[0015] According to an improved embodiment, the folding mirror has two parallel interfaces, wherein the upper interface has a first mirror surface and the lower interface has a first mirror surface. Advantageously, the first mirror surfaces of the lower interface have different second angles relative to each other. For example, this can be achieved by having multiple sets of first mirror surfaces, one set of mirror surfaces correspondingly having the same second angle, however the second angles differ between sets. In a preferred variant, each first mirror surface of the lower interface has a second angle different from the corresponding other first mirror surface. This has the advantage that diffused radiation or astigmatism is also achieved by means of the first mirror surfaces of the lower interface. Each first mirror surface of the lower interface has a certain angle (referred to as the second angle), and the value of this angle lies between the values ​​of the angles of two adjacent first mirror surfaces of the upper interface. The angle of the first mirror surface of the upper interface is referred to as the first angle. It is also advantageous here that the folding mirror can be manufactured in one process, thus eliminating the need for adjustments between macroscopic structures.

[0016] According to a variant of the invention, the polarizer is designed as a reflective polarizer and arranged between the folding mirror and the display element. According to this variant, the phase delayer is a phase delayer that converts linear polarization into circular polarization and allows light to pass through twice. Such a phase delayer is also called a λ / 4 plate or a quarter-wave plate. Therefore, the effect of the λ / 2 phase delayer is divided here, and the delay is distributed between the two passes. The phase delayer of this variant is arranged between the folding mirror and the polarizer. The advantage of this is that the component can be designed as a planar structure, thereby allowing the use of cost-effective components for mass production.

[0017] Advantageously, a polarizer on the coupling side of a display element (e.g., a liquid crystal display element) is used as the polarizer, requiring polarized coupled light. This saves on components and also results in lower light output loss and less interference due to a smaller number of interfaces through which light needs to pass.

[0018] Advantageously, the polarizer and phase de-delay unit of this variant are also designed as a one-piece reflective circular polarizer.

[0019] Advantageously, the reflective polarizer is tilted at an angle different from 90° relative to the propagation direction of light triggered from the folding mirror and incident on it, and these reflective second surfaces are arranged parallel to the reflective polarizer. This has the advantage that the light reflected by the reflective polarizer (light that is not divergent or has almost no divergence) is not reflected back to the first mirror surface, but is reflected back to one of the second reflective surfaces in the gap, depending on the appropriately chosen angle and distance. The light is reflected by the second reflective surface in a direction parallel to the light reflected from the first mirror surface toward the polarizer, and after the polarization direction is adjusted by means of a phase delayer, the light is transmitted from the polarizer. Therefore, a very large portion of the light with both polarizations is utilized, and these gaps hardly cause any dark areas. The display element is illuminated very uniformly.

[0020] According to a variant of the invention, the folding mirror is part of a transparent body having a wedge-shaped cross-section, wherein the wedge-shaped base is the light incident surface facing the light source, the microstructures are arranged on one of the larger sides of the wedge, and the other larger side of the wedge is the light emitting surface facing the display element. This has the advantage that the transparent body is a large-volume component, which is less susceptible to damage compared to very thin components, simplifying the manufacturing process. The transparent body is, for example, cast in a large mold and subsequently provided with polarizer and phase de-delay functions (e.g., by providing corresponding coatings) on the light emitting surface. This is a proven manufacturing method that provides reliable results.

[0021] Advantageously, reflective second surfaces are provided, which accordingly form retroreflectors in pairs. Such an arrangement is robust for angular tilt. Even if the folding mirror is not precisely aligned with the incident light, the reflection of the folding mirror is such that the outgoing light extends parallel to the incident light.

[0022] Advantageously, the first mirrors have different angles relative to each other. As mentioned above, this can be achieved in a grouped manner. According to a preferred variant, each first mirror has a different first angle, and the reflective polarizer has a first polarizer surface and a second polarizer surface, which are correspondingly paired to form retroreflectors. Thus, in the case of reflection occurring at the reflective polarizer, the light scattered by the first mirror is reflected 180°, regardless of the angle at which the light hits the reflective polarizer. When the second surface is also designed as a retroreflector, reflection on the second surface also occurs at 180°. Thus, after the two reflections, the angular dispersion caused by the first mirror is maintained, and the light, whose polarization has been rotated, passes through the reflective polarizer at the same angle as the light that was polarized to allow it to pass through the reflective polarizer when it first hit it. This also achieves scattered radiation or astigmatism, which is desirable in certain cases of head-up displays.

[0023] Advantageously, the folding mirror and the display element are oriented parallel to each other. Therefore, the light beam originating from the folding mirror and reaching the display element travels a path of equal length. This achieves uniform illumination of the display element, as there is no deviation caused by differences in path distance.

[0024] This advantage also occurs when a folding mirror, which typically has unequal incident and exit angles (from a macroscopic perspective) in a head-up display, is oriented parallel to the display element of the head-up display. Attached Figure Description

[0025] Other features of the invention will become apparent from the following description and appended claims in conjunction with the accompanying drawings.

[0026] Figure 1 A head-up display for a motor vehicle according to the prior art is schematically shown;

[0027] Figure 2 The imaging unit of the head-up display is shown schematically;

[0028] Figure 3 An imaging unit of a head-up display according to the present invention is schematically shown;

[0029] Figure 4 The folding mirror of the head-up display is shown schematically;

[0030] Figure 5 A portion of the first embodiment is shown schematically;

[0031] Figure 6 A portion of the second embodiment is shown schematically;

[0032] Figure 7A portion of the third embodiment is shown schematically;

[0033] Figure 8 A variant of the first embodiment is shown;

[0034] Figure 9 Another implementation method is shown;

[0035] Figure 10 A first embodiment with a curved folding mirror is shown;

[0036] Figure 11 A second embodiment with a curved folding mirror is shown. Detailed Implementation

[0037] To better understand the principles of the present invention, embodiments thereof are described in more detail below with the aid of the accompanying drawings. The same reference numerals are used in the drawings for the same or equivalent elements, and it is not necessary to re-describe each drawing. It should be understood that the present invention is not limited to the illustrated embodiments, and the described features may be combined or modified without departing from the scope of protection defined in the appended claims.

[0038] Figure 1 A schematic diagram of a head-up display (HUD) for a motor vehicle according to the prior art is shown. The HUD has an imaging unit 1, an optical unit 2, and a mirror unit 3. A beam SB1 is emitted from a display element 11 and reflected by a first reflector 21 onto a curved reflector 22, which causes the beam to be reflected toward the mirror unit 3. The mirror unit 3 is shown here as the windshield 31 of the motor vehicle. A beam SB2 is transmitted from there toward the observer's eye 61.

[0039] An observer sees a virtual image VB, which is positioned above the hood of the vehicle or even in front of it. Through the combined action of optical unit 2 and mirror unit 3, the virtual image VB is a magnified view of the image displayed by display element 11. It symbolically displays the speed limit, current vehicle speed, and navigation instructions. All elements of the virtual image can be seen by eye 61 as long as eye 61 is within the eyebox 62 indicated by the rectangle. If eye 61 is outside the eyebox 62, the virtual image VB can only be partially seen or even not seen at all by the observer. The larger the eyebox 62, the fewer restrictions the observer faces when choosing their seating position.

[0040] The curvature of the curved reflector 22 matches the curvature of the windshield 31, ensuring stable image distortion across the entire eye box 62. The curved reflector 22 is rotatably supported by a support member 221. This achievable rotation of the curved reflector 22 allows the eye box 62 to be displaced, thus aligning its position with that of the eye 61. The first reflector 21 ensures a longer path for the beam SB1 between the display element 11 and the curved reflector 22 while maintaining a compact optical unit 2. The optical unit 2 is isolated from the surrounding environment by a transparent cover plate 23. This protects the optical elements of the optical unit 2 from dust, for example, within the vehicle's interior space. A light shield 24 reliably absorbs light reflected onto the interface of the cover plate 23, preventing glare for the observer. In addition to sunlight SL, light from other stray light sources 64 may also reach the display element 11.

[0041] Figure 2 The imaging unit 1 of the head-up display is schematically shown. A light source 12 is shown, whose light is collimated by a collimator 13. The collimated beam has a height h on the image plane perpendicular to its propagation direction ABR1. The beam is reflected by a mirror 14 arranged at an angle α = 45° relative to the propagation direction ABR1 and transmitted through a display element 11 along a propagation direction ABR2 oriented at an angle 90° relative to the propagation direction ABR1. From this display element, the beam, as a beam SB1, is incident on an optical unit 2 (not shown here). The display element 11 is not arranged perpendicular to the propagation direction ABR2, but at an angle different from 90° (this angle is shown here as being particularly distinct from 90°).

[0042] Figure 3 The imaging unit of a head-up display according to the invention is schematically shown. A folding mirror 15 according to the invention is shown, which is arranged at an angle β < 45°. Due to the characteristic that the incident angle and the exit angle of the folding mirror are not equal, the principle propagation direction ABR1 of the light emanating from the light source 12, incident on the folding mirror, and the light reflected by the folding mirror in the direction of propagation ABR2 toward the display element 11 remains unchanged compared to the previous illustration. However, compared to the previous illustration, the extended dimensions of the light source 12 and the collimator 13, as well as the height h' of the collimated beam, are smaller. This results in a saving of structural space. The height h' in this illustration is smaller than the height h in the previous illustration. This not only means a smaller space requirement for the components, but also means that the illumination unit (here, the light source 12) only needs to produce a flatter beam, thereby making the light source 12 more compact. An equally important structural space advantage is based on the fact that the light source can be positioned more freely while maintaining the desired angle within the display area. Furthermore, in this implementation, a smaller light source saves space, for example, the light source being a light-emitting diode.

[0043] For clarity, the distance between the display element 11 and the folding mirror 15 is shown as greater than the actual distance in the illustration. In this illustration, the structural space saving achieved according to the invention can be primarily seen in terms of height h', which is smaller than the height h in the aforementioned illustration. The illuminated area of ​​the display element 11 also appears smaller than in the aforementioned illustration, but this is not due to actual size but rather to schematic illustration.

[0044] Figure 4 A folding mirror 15 of a head-up display is schematically shown. The folding mirror 15 has a first interface 151 (on which light incident is reflected) and a second interface 152. It can be seen that the folding mirror 15 has a plurality of microstructures 16 on its first interface 151 (reflective surface), each microstructure itself satisfying a known rule that the incident angle is equal to the exit angle. Macroscopically, the first interface 151 and the second interface 152 are parallel to each other by averaging over the microstructures 16. Each microstructure 16 has a first mirror surface 161, which, in the illustrated embodiment, forms a 45° angle with respect to the propagation directions ABR1 and ABR2. In the propagation direction ABR1, a gap 163 exists between corresponding pairs of mirror surfaces 161. The mirror surfaces 161 are interconnected at the gaps 163 by suitable second surfaces 162.

[0045] From a macroscopic perspective, the incident angle θ1 of the folding mirror 15 is greater than its exit angle θ2, which are indicated by perpendicular lines relative to interfaces 151 and 152, respectively. In the illustrated embodiment, θ1 = 90° - β and θ2 = β. An incident beam ESB along the propagation direction ABR1 is shown, which, after reflection at the folding mirror 15, exits as an exit beam ASB along the propagation direction ASR2.

[0046] A pre-collimated light source (which may consist of multiple single light sources arranged side-by-side, a so-called array) either shines directly onto a diffuser behind the display element (hereinafter referred to as the display) or is pre-directed by a folding mirror. In the case of these light sources, macroscopically, the angle of incidence equals the angle of incidence. This leads to structural spatial conflicts. Particularly severe color and brightness deviations may occur at corners or edges between array units. Light-emitting diodes (LEDs) are typically used as the light source. The polarization direction of the LED light, which is incompatible with the display's polarizer, is blocked and lost by the display. This requires additional components or occurs within the display and heats it up. Tilting the folding mirror at a certain angle changes the angle of the illumination light by a factor of two.

[0047] Such solutions have the following drawbacks: increased structural space requirements (which limit image size), a relatively high number of cells in the array, color and brightness non-uniformity, and efficiency loss due to polarization component loss. An improved solution for image generation cells that can be consistent with given structural space requirements is desired and illustrated according to the present invention.

[0048] The core concept of this invention lies in the finely graded folding mirror 15, which, from a macroscopic perspective, differs from the conventional reflecting mirror 14 where the incident angle equals the exit angle (see...). Figure 4 Furthermore, polarization cycling can be achieved using the improved scheme described below. The properties and degrees of freedom obtained in this way provide a complete set of feasible design options, with advantages beyond just saving structural space.

[0049] Thus, a particularly space-saving feasible solution is obtained to fold the optical path of the image generation unit 1 into the structural space. The light distribution is expanded by dividing it into strips that are stretched apart from each other. This allows for a reduction in the original illumination unit. This helps avoid array boundaries within the image area and improves uniformity. Embodiments of the invention allow for tolerance-insensitive designs and allow for improved efficiency through polarization cycling.

[0050] Figure 5 A portion of a first embodiment according to the invention is schematically illustrated. A folding mirror 15 is shown, its upper interface 151 having a microstructure 16, while its lower interface 152 does not possess any particular, fundamental optical or geometric properties for the purposes of this invention. The microstructure 16 has first mirror surfaces 161, which are angled at 45° relative to the propagation direction ABR1 of the incident light. Gap 163 exists between the first mirror surfaces 161, and a second surface 162, also designed as a reflective surface, is arranged in these gaps. The second surface 162 is oriented parallel to the propagation direction ABR1 of the incident light. A phase de-polarizer 18 and a polarizer 17 are arranged above the folding mirror 15. In this embodiment, the phase de-polarizer 18 has the characteristics of a quarter-wave plate, that is, the phase de-polarizer converts linearly polarized incident light into circularly polarized outgoing light, and vice versa. The polarizer 17 is a reflective polarizer that allows linearly polarized light with a first polarization direction to pass through and reflects polarized light perpendicular to it.

[0051] Unpolarized light L1, generated by light source 12 and collimated by collimator 13, is incident on folding mirror 15 from the left along the propagation direction ABR1. For clarity, only one beam is shown here as an example. Unpolarized light L1 is reflected by mirror 161. Unpolarized light L2 is transmitted along the propagation direction ABR2 to phase de-polarizer 18, passes through it, and exits as unpolarized light L3. Unpolarized light is incident on reflecting polarizer 17, which allows s-polarized light L4s to pass through (transmit) and causes p-polarized light L4p to be projected back (reflected). For clarity, this is schematically shown offset to the right in this illustration. p-polarized light L4p passes through phase de-polarizer 18 and exits as circularly polarized light L5z. This circularly polarized light is incident on reflective second surfaces 162 and is reflected again by these reflective second surfaces as circularly polarized light L6z back to phase de-polarizer 18. Circularly polarized light passes through the phase de-depressor and exits as s-polarized light L7s. This s-polarized light passes through the reflecting polarizer 17 because the reflecting polarizer, instead of reflecting, transmits the polarization direction of the s-polarized light, which now has a polarization direction. Therefore, the additional s-polarized light L8s propagates towards the display element 11.

[0052] In this illustration, the corresponding described light Lxn (x = 1, 2, ...; n = p / z / s / _) is indicated parallel to the corresponding propagation directions ABR1, ABR2, and the reflection occurring at polarizer 17 or at the reflective second surface 162 is drawn in a lateral offset manner. The latter indicates that the light, under normal conditions, is not formed by ideally parallel rays, but rather by rays that are at least slightly divergent. A large portion of these rays are obliquely reflected by polarizer 17, thus reaching the reflective second surface 162 and being reflected again there. Additionally or alternatively, the first mirror 161 can be provided with an arc such that the light L2 reflected by the first mirror is more divergent than the light L1 incident upon it. Other feasible options include making the polarizer wavy or tilted. In the case of tilting, the tilt of mirror 162 can be advantageously adjusted to minimize angular deviation. Using one or more of these measures, a portion of the light L4s transmitted by polarizer 17 has filled a portion of the dark area caused by gap 163 in the light transmitted toward display element 11. On the other hand, light L8s also transmits into said dark area. This light transmits more to display element 11 than the originally incident light L1 and has a more uniform brightness characteristic curve. Display element 11 is positioned above polarizer 17 at a certain distance and is not shown here. The marked area F8 can be advantageously designed according to the variant described further below.

[0053] Figure 6A portion of the second embodiment is schematically shown. Here, the folding mirror 15 is part of the transparent body 19. The transparent body 19 has a wedge-shaped cross-section, which is shown in cross-section here. The apex of the wedge (located on the right side of the illustration) is truncated and therefore not shown. The wedge base surface 191 is the wedge-shaped base surface facing the light incident surface of the light source. The microstructure 16 is arranged on one of the larger side surfaces 192 of the wedge. The other larger side surfaces 193 of the wedge form the light emitting surface facing the display element 11.

[0054] In embodiments not shown here, the microstructure 16, polarizer 17, and phase delayer 18 are arranged as shown in the foregoing figures. In the embodiment shown here, the first reflecting mirror 161 (as previously described) is arranged at a 45° angle relative to the propagation directions ABR1, ABR2. However, the reflective second surface 162 is not arranged parallel to the propagation direction ABR1, but is tilted at an acute angle relative to that direction. The reflective second surfaces are tilted in such a way that they do not block the path of light L1 incident from the left to one of these first mirrors 161, but rather (viewed in the direction of light propagation) tilt from one first mirror 161 to the next. The other larger side surfaces 193 of the wedge-shaped transparent body 19 have the same slope as the reflective second surface 162. This can be seen from the acute angle between the normal 193N of the side surface 193 and the propagation direction ABR2. The polarizer (designed here as a reflective circular polarizer 172 and incorporating the function of the phase delayer 18) is arranged on the side 193 and therefore has the same slope. The larger first side 192 is provided with a mirror coating.

[0055] Unpolarized light L1, generated by light source 12 and collimated by collimator 13, is incident on folding mirror 15 from the left along the propagation direction ABR1. For clarity, only a few beams are shown here as an example. Unpolarized light L1 is reflected by mirror 161. This unpolarized light, as unpolarized light L2, is transmitted along the propagation direction ABR2 to reflective circular polarizer 172. This reflective circular polarizer transmits s-polarized light L4s and reflects circularly polarized light L5z. Because the vertical line on side 193 is slightly inclined relative to the propagation direction ABR2, circularly polarized light L5z propagates at an angle different from 0° relative to the propagation direction ABR2. This circularly polarized light is incident on reflective second surface 162 and, as circularly polarized light L6z, is reflected again by these reflective second surfaces to phase delayer 18. Due to the inclined arrangement of the reflective second surface 162, the circularly polarized light now propagates parallel to the propagation direction ABR2 again. The circularly polarized light is incident on reflective circular polarizer 172 and transmitted by it. Therefore, the additional s-polarized light L8s propagates in the direction of the display element 11.

[0056] Therefore, this illustration is also an example of a variant of the invention, in which the reflective polarizer 172 is tilted at an angle different from 90° relative to the propagation direction ABR2 of the light L2 originating from the folding mirror 15 and incident on the reflective polarizer, and the reflective second surface 162 is arranged parallel to the reflective polarizer 172.

[0057] Figure 7 A portion of the third embodiment is schematically shown. Here, the folding mirror 15 has a first interface 151 and a second interface 152, which are arranged parallel to each other and have microstructures 16, 16' arranged offset from each other. In the illustrated embodiment, the offset is selected such that the first mirror surface 161 of the first interface 151 and the first mirror surface 161' of the second interface 152 are successive to each other in the propagation direction ABR1 of the light L1 emitted from the light source 12. The first mirror surface 161 of the first interface 151 and the second surface 162' of the second interface 152, as well as the second surface 162 of the first interface 151 and the first mirror surface 161' of the second interface 152, are successive to each other in the propagation direction ABR2 perpendicular to the propagation direction. The mirror surface 161 of the first interface 151 is designed as a reflective polarizer 17. The second surface 162 of the first interface 151 is designed as a phase delayer 18 that rotates the polarization direction by 90°. The first mirror surface 161' of the second interface 152 is designed as a reflector that does not affect polarization. The first mirror surfaces 161 and 161' are arranged at an angle of 45° relative to both the propagation direction ABR1 of the light L1 emitted from the light source 12 and the propagation direction ABR2 of the light extending toward the display element 11. The second surfaces 162 and 162' are arranged parallel to the propagation direction ABR1 of the light L1 emitted from the light source 12.

[0058] Unpolarized light L1, generated by light source 12 and collimated by collimator 13, is incident on folding mirror 15 from the left along the propagation direction ABR1. For clarity, only one beam is shown here as an example. Unpolarized light L1 is reflected by mirror 161 as s-polarized light L2s and transmitted as p-polarized light L2p. S-polarized light L2s propagates along the propagation direction ABR2 toward display element 11. P-polarized light L2p is reflected by the first mirror 161' of the second interface 152 and transmitted from the inside to the second surface 162 of the first interface 151 as p-polarized light L3p. Since these second surfaces are designed as phase de-polarizers 18 that rotate polarization by 90°, they transmit light incident upon them, which exits these second surfaces as s-polarized light L4s along the propagation direction ABR2 in the region of gap 163. Therefore, additional s-polarized light L4s propagates toward display element 11.

[0059] Figure 8 The advantageous variant is shown in Figure 5The region F8 is marked in the middle. Here, two reflective second surfaces 1621 and 1622 are provided instead of a single surface, and these two reflective second surfaces are arranged at right angles to each other. Therefore, it is used as a retroreflector. Here, the incident light L5z is always reflected such that the outgoing light L6z is oriented parallel to it. Figure 5 In the variant shown, the incident and outgoing light are parallel to each other only when the incident light strikes the reflective surface 162 at exactly right angles, while in the case of the retroreflector, this is also the case even if there is an angular deviation.

[0060] Figure 9 Imaging unit 1 is shown, such as... Figure 3 As described. However, here, the display element 11 is arranged at the same angle β as the folding mirror 15. The folding mirror 15 and the display element 11 are therefore oriented parallel to each other. Therefore, the light beams originating from the folding mirror 15 and incident on the display element 11 have equal path distances. Thus, uniform illumination of the display element 11 is achieved, because in this case, there is no deviation caused by path differences. This is particularly advantageous when using a planar display element 11, which is, for example, composed of a single planar light-emitting element or an LED array in which multiple LEDs are arranged to be distributed on a surface. This advantage also occurs when a folding mirror, which typically has unequal incident and exit angles (macroscopically) in a head-up display, is oriented parallel to the display element of the head-up display.

[0061] Figure 10 A portion of a first embodiment with a curved folding mirror 15 is schematically shown. Macroscopically, the folding mirror 15 is not actually curved; rather, the microstructure 16 is arranged such that the folding mirror 15 functions like a cylindrical mirror. The folding mirror 15 has two interfaces 151 and 152 parallel to each other. The upper interface 151 is the interface to which the incident light L1 first arrives. The upper interface 151 has first mirror surfaces 161-i, where i = 1, 2, 3, ..., and in the embodiment shown here, mirror surfaces 161-1, 161-2, and 161-3 are shown. The upper interface 151 has second surfaces 162-i, where i = 1, 2, 3, ..., and in the embodiment shown here, second surfaces 162-1, 162-2, and 162-3 are shown. These second surfaces are located at the gap 163 between the mirror surfaces 161-i. The lower interface 152 is where the light L2p (transmitted through the upper interface 151) strikes. The lower interface 152 has mirror surfaces 161'-1, 161'-2 and 161'-3.

[0062] In the illustrated first mirror 161-i, first mirror 161-1 forms a first angle δ1 relative to the propagation direction ABR1, first mirror 161-2 forms a first angle δ2 relative to the propagation direction ABR1, and first mirror 161-3 forms a first angle δ3 relative to the propagation direction ABR1. Here, the first angles δ1, δ2, and δ3 are slightly different from each other. Therefore, each first mirror 161-i has a different first angle δi. The first mirror 161'-1 of the lower interface 152 has a second angle φ1 relative to the propagation direction ABR1. The first mirror 161'-2 has a second angle φ2 relative to the propagation direction ABR1. The first mirror 161'-3 has a second angle φ3 relative to the propagation direction ABR1. Therefore, each first mirror in the first mirror 161'-i of the lower interface 152 has a second angle φi different from the corresponding other first mirror 161'-i. The first angle δi and the second angle φi decrease from left to right in the illustrated embodiment. The following holds true: δ1 < φ1 < δ2 < φ2 < δ3 < φ3. Therefore, the value of each second angle φi lies between the values ​​of the first angle δi of the two adjacent first mirror surfaces 161-i. The beam Lxs exiting the folding mirror 15 upwards is thus uniformly dispersed. The second surfaces 162-i and 162-i' are arranged parallel to the propagation direction ABR1 of the light L1 emitted from the light source 12.

[0063] The mirror 161-i of the upper interface 151 is designed as a reflective polarizer 17. The second surface 162-i of the first interface 151 is designed as a phase delayer 18 that rotates the polarization direction by 90°. The first mirror 161'-i of the lower interface 152 is designed as a reflector that does not affect polarization.

[0064] Unpolarized light L1, generated by light source 12 and collimated by collimator 13, is incident on folding mirror 15 from the left along the propagation direction ABR1. For clarity, only a few beams are illustrated here by way of example. Unpolarized light L1 and L5 are reflected by mirror 161-i as s-polarized light L2s and L6s and transmitted as p-polarized light L2p and L6p. S-polarized light L2s and L6s propagate upwards toward display element 11. P-polarized light L2p and L6p are reflected by first mirrors 161'-1 and 161'-2 of second interface 152 and transmitted from the inside as p-polarized light L3p and L7p to second surface 162-i of first interface 151. Since these second surfaces are designed as phase de-polarizers 18 that rotate polarization by 90°, they transmit light incident upon them, which, as s-polarized light L4s and L8s, exits these second surfaces upwards in the region of gap 163 in this illustration. Therefore, the additional s-polarized light L4s and L8s propagate toward the display element 11. Clearly, the light Lxs extending toward the display element 11 consists of a diffused beam.

[0065] Figure 11 A portion of a second embodiment with a curved folding mirror 15 is schematically shown. Macroscopically, the folding mirror 15 is not actually curved, but rather the microstructure 16 is arranged such that the folding mirror 15 functions like a cylindrical mirror. The upper interface 151 of the folding mirror 15 has the microstructure 16, and its lower interface 152 does not possess any particular, fundamental optical or geometric properties for the purposes of this invention. The microstructure 16 has first mirror surfaces 161-i, of which mirror surfaces 161-1 to 161-5 are shown. Each of these first mirror surfaces 161-i has a first angle δi relative to the propagation direction ABR1 of the incident light, which is different from the other first angles δi. Gap 163 exists between the first mirror surfaces 161-i, and second surfaces 162 are arranged in these gaps, the second surfaces also being designed as reflective surfaces. Instead of a single surface, two reflective second surfaces 1621 and 1622 are provided as second surfaces 162, arranged at right angles to each other. Therefore, it is used as a retroreflector. A phase delayer 18 and a polarizer 17 are arranged above the folding mirror 15. In this embodiment, the phase delayer 18 has the characteristics of a quarter-wave plate, that is, the phase delayer converts linearly polarized incident light into circularly polarized outgoing light, and vice versa. The polarizer 17 is a reflective polarizer that allows linearly polarized light with a first polarization direction to pass through and reflects polarized light perpendicular to it. Instead of a single surface, the polarizer has multiple polarizer surfaces 1701, 1702 arranged in pairs, these polarizer surfaces being arranged perpendicular to each other. Therefore, it is used as a retroreflector.

[0066] Unpolarized light L1, generated by light source 12 and collimated by collimator 13, is incident on folding mirror 15 from the left along the propagation direction ABR1. For clarity, only a few beams are illustrated here. Unpolarized light L1 is reflected by mirrors 161-3. The unpolarized light travels upward as unpolarized light L2 to phase de-diverter 18, passes through it, and exits as unpolarized light L3. The unpolarized light strikes a reflective polarizer 17, designed as an antireflector, which allows s-polarized light L4s to pass through (transmit) and causes p-polarized light L4p to be projected back (reflected). P-polarized light L4p passes through phase de-diverter 18 and exits as circularly polarized light L5z. Circularly polarized light strikes one of the reflective second surfaces 162, also designed as an antireflector, and is reflected again by these reflective second surfaces as circularly polarized light L6z back to phase de-diverter 18. Circularly polarized light passes through the phase de-depressor and exits as s-polarized light L7s. This s-polarized light passes through the reflecting polarizer 17 because the reflecting polarizer, instead of reflecting, transmits the polarization direction of the s-polarized light, which now has a polarization direction. Therefore, the additional s-polarized light L8s propagates towards the display element 11.

[0067] According to other variations not detailed here, such as those for Figure 6 A transparent body 19 is provided as described, which has a corresponding microstructure. There, the functions of the reflective polarizer 17 and the phase delayer 18 are realized in a circular polarizer 172, which is designed as a retroreflector by means of a first polarizer surface and second polarizer surfaces 1701 and 1702.

[0068] In other words, the present invention relates to a head-up display having an imaging unit 1 that improves efficiency, saves cost and structural space, and having a folding mirror 15 in which the incident angle and the exit angle are not equal from a macroscopic perspective. Such a unit is also referred to as a "blazed-mirror-PGU" (PGU: Picture Generating Unit). The present invention relates to the field of head-up displays (HUDs) and other display systems that use oriented light with a specific polarization, such as those based on liquid crystal display elements. Most current LED-based TFT-HUDs (TFT: Thin Film Transistor, a variant of liquid crystal displays) have almost complete light output loss for the polarization component of the illumination light. This light output loss is typically mitigated in an external polarization filter to reduce the heat generated by the display element 11. First systems that reuse partially "incorrectly polarized" light exist in the market and in the literature. These efficiency-enhancing systems require additional components and therefore additional structural space and cost. Conventional systems require more energy, a fact that is increasingly being considered (e.g., the driving range of electric vehicles). In particular, the increasing size of images makes thermal loads increasingly critical for systems / components. It is desirable to achieve, or a combination thereof, improved efficiency, reduced structural space or increased virtual image size while maintaining structural space, reduced cost, and uniform illumination. At least one of these is achieved according to the present invention.

[0069] When using a folding mirror (blazed mirror) with unequal incident and exit angles, stripes that do not emit any light are produced when viewed from the display element 11. According to the invention, these regions, i.e., gaps 163, are used to reuse light with undesired polarization components by changing the polarization state of the light and redirecting it back to the display element 11, thereby making the light usable for backlighting the display element 11. As a result, the HUD is cheaper and has lower energy, structural space, and / or cooling requirements, and more uniform illumination. The invention can also be more generally used for other backlit display elements with narrower viewing angles and efficiency sensitivity. The invention can also be used in projection systems, such as those based on DMD (Digital Micromirror Device, where light deflection is based on one or more digitally controlled micromirrors) or LCoS (Liquid Crystal on Silicon, where light modulation is based on liquid crystals mounted on a silicon substrate). This then relates to a display unit having an imaging unit 1 for generating an image, wherein the imaging unit has a folding mirror arranged at an angle of attack between the light source and a display element transmitted from the light source relative to the propagation direction of light incident upon it from the light source. The folding mirror has microstructures having first mirror surfaces arranged at a first angle different from the angle of attack of the folding mirror, and these microstructures are spaced apart from each other in a manner forming gaps, wherein second surfaces are arranged at a second angle in these gaps. A polarizer guides first-polarized light to the display element and guides second-polarized light into these gaps; a phase delayer converts the polarization of the light guided into these gaps to the first polarization, and the light guided into the gaps is directed toward the display element after passing through these gaps. According to a variation of the invention, light with undesired polarization is projected back to the folding mirror 15 by a reflective circular polarizer 172 below the display, where the light is reflected into a previous dead zone (i.e., gap 163), then converted to an effective direction by the circular polarizer 172 and thus reused.

[0070] According to one variant, the angle of the folding mirror (also known as a blazed mirror) is optimized for the tilt of the display element. An advantageous implementation involves orienting the blazed mirror as parallel to the display element as possible. Its structure is then dispersed in a manner that maximizes uniformity. In currently used imaging units with LED arrays, there is a significant relative difference in the distance between the LEDs and the scattering elements arranged below the display element, partly due to the tilt of the display element. This results in varying visibility of the LED array. A scheme using a folding mirror and a parallel orientation of the display element significantly reduces this undesirable effect. A constant distance between the display element and the folding mirror implies a smaller relative path difference.

[0071] The scattering function (i.e., the scattering of light transmitted to the display element 11) is implemented according to a variant of the invention as follows. The angle δi of the surface 161-i reflecting the light incident from the left gradually changes its angle value. Therefore, in a narrow sense, there is no longer a folding mirror 15, but rather a folding mirror 15 designed to be curved in a certain direction. That is, there is a so-called blazed lenticular lens. This blazed lenticular lens should be gently beveled, i.e., have a flat mirror surface 161-i, for example in... Figure 11 As shown in the diagram. Here, after reflection occurs on folding mirror 15, the light that is no longer perpendicular to the reflecting polarizer 17 must be processed. The reflected beams may therefore separate from each other. Therefore, in Figure 11 In one embodiment, it is proposed that the two reflective structures be designed as retroreflectors so that the recycled light also has the desired radiation direction toward the corresponding position.

Claims

1. A head-up display for a transportation vehicle, the head-up display having: - Imaging unit (1) for generating images; - Optical unit (2) for projecting the image by means of mirror unit (3); in - The imaging unit (1) has a folding mirror (15). - The folding mirror (15) is arranged at an angle of attack (β) between the light source (12) and the display element (11) transmitted by the light source, relative to the propagation direction (ABR1) of the light (L1) incident on the folding mirror from the light source (12). - The folding mirror (15) has a microstructure (16). -- in, These microstructures (16) have first mirror surfaces (161, 161-i, 161', 161'-i), which are arranged at a first angle different from the angle of attack (β) of the folding mirror (15); and these microstructures are spaced apart from each other in a manner that forms gaps (163). -- wherein the second surface (162, 162-i, 162', 162'-i) is arranged in these gaps (163) at a second angle; - Polarizers (17, 172) guide light of the first polarization to the display element (11) and guide light of the second polarization into the gaps (163). - The phase de-polarizer (18) converts the polarization of the light (L2p, L4p) guided into these gaps (163) to that first polarization, and - The light guided into these gaps (163) is directed toward the display element (11) after passing through these gaps (163), wherein these first mirrors (161, 161-i) are designed as reflective polarizers (17), the gaps (163) are designed as phase de-polarizers (18) that rotate the polarization direction by 90°, and the folding mirror (15) has two interfaces (151, 152) that are parallel to each other and have the same microstructure (16, 16') that are arranged offset from each other.

2. The head-up display according to claim 1, wherein, These first mirrors (161-i) have different first angles (δi) relative to each other.

3. The head-up display according to claim 1 or 2, wherein - The folding mirror (15) has two parallel interfaces (151, 152), with the upper interface (151) having a first mirror surface (161-i) and the lower interface (152) having a first mirror surface (161'-i). - The first mirror surfaces (161'-i) of the lower interface (152) have different second angles relative to each other. i), and - Each second angle ( The value of i) lies between the values ​​of the first angle (δi) of the two adjacent first mirrors (161-i).

4. The head-up display according to claim 1, wherein - The polarizer (17) is designed as a reflective polarizer (17) and is arranged between the folding mirror (15) and the display element (11). - The phase de-polarizer (18) is designed to convert linear polarization into circular polarization and is arranged between the folding mirror (15) and the polarizer (17).

5. The head-up display according to claim 4, wherein, These reflective second surfaces (1621, 1622) are correspondingly paired to form retroreflectors.

6. The head-up display according to claim 5, wherein - These first mirrors (161-i) have different first angles (δi) relative to each other, and - The reflective polarizer (17) has a first polarizer surface (1701) and a second polarizer surface (1702), which are respectively paired to form retroreflectors.

7. The head-up display according to claim 3, wherein, The reflective polarizer (17) is tilted at an angle different from 90° relative to the propagation direction (ABR2) of the light (L2) originating from the folding mirror (15) and incident on the reflective polarizer, and these reflective second surfaces (162) are arranged parallel to the reflective polarizer (17).

8. The head-up display according to claim 4, wherein, The folding mirror (15) is part of a transparent body (19) with a wedge-shaped cross-section. The wedge-shaped base surface (191) is the light incident surface facing the light source (12). These microstructures (16) are arranged on one of the larger side surfaces (192), and the other larger side surface (193) is the light emitting surface facing the display element (11).

9. The head-up display according to claim 1 or 2, wherein, The folding mirror (15) and the display element (11) are oriented parallel to each other.

Images