Projection device

Abstract

The invention relates to a projection device comprising: a beam generator (140) for generating a modulated collimated light beam (LBM), a projection surface (21), and a mirror unit (73) for reflecting the modulated collimated light beam (LBM) and for moving the reflected light beam (LBR) over the projection surface (21), wherein a lens arrangement (157) is positioned between the mirror unit (73) and the projection surface (21), said lens arrangement having a plurality of light-guiding elements (1570) arranged parallel to one another, and wherein a light-guiding element (1570) has a light entry surface (1575), a light-guiding region (1576) and a light exit surface (1577), and wherein the surface area of the light entry surface (1575) is larger than or equal to the area of the of the beam diameter (DLBR) of the reflected light beam (LBR).

Description

[0001] 202405054

[0002] 1

[0003] Projection device

[0004] The present invention relates to a projection device. Such projection devices are used, for example, in a head-up display to generate a virtual image on the windshield or to project it onto other windows or surfaces of a motor vehicle. A head-up display, also known as a HUD, is a display system in which the viewer can maintain their line of sight because the displayed content is projected 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 mass-produced in the automotive industry.

[0005] Head-up displays generally consist of an image-generating unit (PGU), an optical unit, and a mirror unit. The image-generating unit creates the image, using at least one display element. Modern head-up displays typically use displays or scanning systems for image generation. Displays can be, for example, LCDs (LC: Liquid Crystal), p-LED displays (LED: Light Emitting Diode), LCoS displays (LCoS: Liquid Crystal on Silicon), or DMD systems (DMD: Digital Micromirror Device). A laser scanning system is an example of a scanning system. The optical unit directs the image onto the mirror unit. The mirror unit is a partially reflective, translucent disc.The viewer thus sees the content displayed by the imaging unit as a virtual image and simultaneously the real world behind the glass. In automotive applications, the windshield often serves as the mirror unit, its curved shape being taken into account in the display, for example, by pre-distorting the image displayed by the imaging unit. Through the interaction of the optical unit and the mirror unit, the virtual image is a magnified and distorted representation of the image generated by the imaging unit. 202405054.

[0006] 2

[0007] Projection devices generally consist of an image-generating unit (PGU) and a projection surface on which a real image is visible. The projection surface can be a transparent window pane of a vehicle or an opaque projection surface, such as one mounted on a vehicle's dashboard. The image-generating unit creates the image, using at least one display element. Modern projection devices typically use displays or scanning systems for image generation. Displays can include, for example, LCDs (Liquid Crystal), p-LED displays (Light Emitting Diode), LCoS displays (Liquid Crystal on Silicon), or DMD systems (Digital Micromirror Devices).An example of a scanning system is a laser beam scanner (often abbreviated as LBS). In this system, a laser beam modulated with image information is guided across the projection surface. This can be done, for example, in a line grid. If the projection surface has a diffuser, the image drawn by the laser beam can be seen by a viewer. Since the laser beam has a small angular spread (small aperture angle), the light coming from the diffuser is also generally limited to a specific angular range. This depends on the diffuser's scattering properties. If the diffuser scatters over a large angular range, then less light reaches the viewer's eye than with a diffuser that has a small angular range. For energy-saving reasons, a diffuser that scatters over a relatively small angular range is therefore usually used.

[0008] The diffuser can, for example, be a partially reflective, translucent pane. The viewer then sees the content displayed by the imaging unit as a virtual image and simultaneously the real world behind this pane. In the automotive sector, a side window or the rear window, another transparent or reflective surface, or even an opaque surface, such as a dashboard surface or the headliner, whose curved shape is used in the projection, often serves as the projection surface.

[0009] 3 is taken into account, for example by pre-distortion of the image displayed by the imaging unit.

[0010] The viewer can only perceive the virtual image of a head-up display or the real image emanating from a diffuser from the position of the so-called eyebox. The eyebox is defined as an area whose height and width correspond to a theoretical viewing window. The size of the eyebox depends on the angle of incidence of the light coming from the display element or the diffuser. As long as the viewer's eye is within the eyebox, all elements of the virtual or real image are visible. If, however, the eye is outside the eyebox, the virtual or real image is only partially visible or not visible at all. Therefore, the larger the eyebox, the less restricted the viewer is in their choice of seating position.

[0011] The optical unit of a head-up display typically comprises several mirrors to minimize the required installation space. Light emitted from the imaging unit is reflected by a folding mirror onto a curved mirror, which then reflects it towards the windshield. Currently used curved mirrors are essentially flat plates with a high degree of curvature, tailored to the desired optical function. These curved mirrors are manufactured using methods such as injection molding or compression molding.

[0012] In laser beam scanner systems, the light from RGB color laser diodes is scanned across the display area by a scanner that, for example, incorporates oscillating MEMS mirrors (MEMS: micro-electro-mechanical system). The image is then generated on the display area by modulating the power of the color laser diodes synchronously with the movement of the mirrors.

[0013] Laser scanning systems, compared to LCD-based display solutions, are characterized by less complex optics, higher energy efficiency, and lower cooling requirements. As an alternative to RGB color laser diodes, a short-wavelength laser can also be used, with which a 202405054

[0014] 4

[0015] RGB wavelength converter scanned in a suitable intermediate image plane.

[0016] With coherent light, such as that emitted by a laser light source, unwanted speckle patterns often appear, which should be reduced or eliminated to achieve a good image. Speckle patterns, light granulation, laser granulation, or simply speckle, refer to the granular interference phenomena that can be observed, for example, when optically rough object surfaces (unevenness on the order of the wavelength) are illuminated with sufficient coherence. In more ordered structures, such as lens arrays, the interfering interference effects can also exhibit a higher degree of order. Here, we use the term speckle or speckle pattern more broadly to include such effects as well.

[0017] The term "speck," which refers to both a single spot of light and the entire interference pattern, is derived from the English word "speckle." Depending on the imaging system used, the predominantly English-language literature also distinguishes between "subjective speckle" and "objective speckle": If the speckle is projected directly onto a screen without the aid of a lens or other optical devices, it is called objective speckle. In contrast, subjective speckle refers to the imaging of the interference pattern using a lens or more complex optical systems. This includes the human eye.

[0018] To ensure that a real image is created in the right place, a diffuser or a multi-lens array (MLA) is typically used, which also ensures that the angles are widened to guarantee visibility from different angles or to illuminate the entire eyebox.

[0019] In the case of a diffuser, unwanted effects can occur, such as speckle, visible granularity (structure of the diffuser) or chromatic aberration for the respective scattering center (different colors at different angles 202405054

[0020] 5 deflected). Furthermore, diffusers typically scatter light back when illuminated, which brightens the image and thus reduces contrast and visual appeal. Additionally, image blurring can be observed the thicker the diffuser is. (The image is formed at both interfaces).

[0021] In the case of MLA (multifocal laser imaging), the lens diameter should always correspond to the size of the incident spot diameter to prevent unwanted effects such as moiré. This is generally difficult to achieve.

[0022] A way is sought to replace a diffuser (surface or volume diffuser) or an MLA, as these do not provide sufficiently good image quality.

[0023] A projection device according to the invention comprises:

[0024] - a beam generator for producing a modulated collimated light beam;

[0025] - a projection surface; and

[0026] - A mirror unit for reflecting the modulated collimated light beam and for moving the reflected light beam across the projection surface, wherein an optical system is arranged between the mirror unit and the projection surface, comprising a multitude of parallel light-guiding elements. These are essentially microscopic light mixing rods, which can be designed in various ways.

[0027] According to the invention, a light-guiding element has a light-intake surface, a light-guiding area, and a light-emission surface, wherein the area of ​​the light-intake surface is greater than or equal to the area of ​​the beam diameter of the reflected light beam. The light-intake surface therefore does not need to be adapted as precisely as possible to the size of the beam diameter.

[0028] According to one embodiment, the optics are arranged on a spherical surface. Advantageously, the light beam then strikes the surface of the optics perpendicularly in every direction determined by the mirror element. 202405054

[0029] 6

[0030] According to one design, a light guide element has a round or polygonal cross-section. Depending on the cross-sectional design, the resulting angles of incidence can be varied. The resulting change in polarization leads to a de-speckle effect, which is more pronounced with a round cross-section.

[0031] In one embodiment, the cross-section is constant along the length of the light guide. In an alternative embodiment, the cross-section has a shape that varies along the length of the light guide. The resulting light cone can be influenced by the size of the two cross-sections. If the cross-section at the beginning is larger than the one at the end, the angular range increases; conversely, if it is smaller, it decreases.

[0032] In one embodiment, a light-guiding element has a light-guiding area comprising an interior space and a surrounding wall. In an alternative embodiment, the light-guiding area is a monolithic block. In the hollow version, no refraction into the medium occurs, and therefore no change in angle. For the same length of light-guiding element, multiple interactions with the walls thus take place, resulting in better mixing.

[0033] According to one embodiment, a light-guiding element has a light-guiding area with a faceted wall. Facets provide more degrees of freedom and can, for example, widen or adapt the projected angular range more effectively. This ensures better mixing of light within the light-guiding element.

[0034] According to one embodiment, a light-guiding element has a light-guiding area containing scattering elements. Scattering centers within the light-guiding element can further widen or adjust the emitted angular range. This ensures greater mixing within the light-guiding element. 202405054

[0035] 7

[0036] According to one embodiment, vignetting is provided between individual light-guiding elements of the optics. This reduces the probability that the light beam falls on two adjacent light-guiding elements simultaneously.

[0037] In other words, the invention is an (e.g., equidistant) array of either:

[0038] - round or rectangular tubes (microscopic French fry cutter) that

[0039] - may be hollow or filled,

[0040] - can be designed to be straight or tapered,

[0041] - may be faceted or may contain one or more sprinklers.

[0042] These light-guiding elements represent the individual pixels and are sequentially illuminated by the laser-based scanner. It is advantageous if the spot, or rather the cross-section of the light beam, falls entirely within the light-guiding element and not onto the surrounding area. If the beam falls within the described element, it is either reflected multiple times, scattered, or influenced by facets so that the exiting beam leaves the element at a wider angle. The goal of the head-up display is for each element to illuminate the entire eyebox.

[0043] The thickness of the optics is not critical, as the image is formed at the optics' exit point. To achieve better mixing, the thickness of the optics can be varied. The resulting image is sharper and exhibits less speckle compared to conventional approaches. Backscatter is easier to control and lower in comparison. Good control of the generated angles is possible, making it efficient.

[0044] A device according to the invention can be used wherever laser beam scanners generate images in transmitted light.

[0045] Further embodiments of the invention and its advantages can also be found in the following description of the figures. Figures 202405054 show...

[0046] 8

[0047] Fig. 1 schematically shows a head-up display;

[0048] Fig. 2 schematically shows an embodiment of an imaging unit;

[0049] Fig. 3 shows an imaging unit according to the invention;

[0050] Fig. 4 schematically shows a projection system;

[0051] Fig. 5 shows a section of an optic;

[0052] Fig. 6 shows exemplary designs of light guiding elements;

[0053] Fig. 7 a light guiding element;

[0054] Fig. 8 a light guiding element; and

[0055] Fig. 9 shows a light guiding element.

[0056] Character description

[0057] To better understand 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 identical or equivalently 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 protection of the invention as defined in the appended claims.

[0058] Fig. 1 schematically shows a head-up display for a vehicle as an example of an image generation system 1. The head-up display comprises an imaging unit 2, an optical unit 3, and a mirror unit 4. A beam of light SB1 originates from a projection surface 21 and is reflected by a first mirror 31 onto a curved mirror 32, which reflects it towards the mirror unit 4. The mirror unit 4 is represented here as the windshield 41 of the vehicle. From there, the beam of light SB2 travels towards the eye 61 of a viewer.

[0059] The viewer sees a virtual image VB, which is located outside the vehicle above the hood or even in front of the vehicle 202405054

[0060] 9. Through the interaction of optical unit 3 and mirror unit 4, the virtual image VB is a magnified representation of the image coming from the projection surface 21. Here, a speed limit, the current vehicle speed, and navigation instructions are symbolically represented. 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 or not visible at all to the viewer. The larger the eyebox 62, the less restricted the viewer is in choosing their seating position. The curvature of the curved mirror 32 is adapted to the curvature of the windshield 41 and ensures that the image distortion is as stable as possible across the entire eyebox 62. The curved mirror 32 is rotatably mounted by means of a bearing 321.The resulting rotation of the curved mirror 32 allows the eyebox 62 to be moved, thus adjusting its position to that of the eye 61. The first mirror 31 ensures that the path traveled by the beam SB1 between the projection surface 21 and the curved mirror 32 is long, while simultaneously maintaining the compact size of the optical unit 3. The optical unit 3 is separated from its surroundings by a transparent cover 33. This protects the optical elements of the optical unit 3, for example, from dust present in the vehicle's interior. A glare shield 34 reliably absorbs light reflected across the interface of the cover 33, preventing glare for the viewer. In addition to sunlight SL, light from another ambient light source 64 can also reach the projection surface 21.

[0061] Fig. 2 schematically shows an embodiment of an imaging unit 2 with light sources 14R, 14G, 14B that emit coherent light. The figure shows a controllable mirror unit 73 in the imaging unit 2, which acts as a display element 11. The mirror unit 73 consists, for example, of a two-dimensional arrangement of micromirrors, which, when controlled, are each in one of two positions. A light beam LB striking the mirrors is thus modulated in a pixel grid to display the virtual image VB.

[0062] 10 generate. This is a DMD. According to another variant, the controllable mirror unit 73 consists of a mirror adjustable on several axes, which is controlled in such a way that an incident laser beam is reflected according to a two-dimensional grid and in this way generates the virtual image VB.

[0063] The light beam LB, which strikes the micromirrors of mirror unit 73, or the laser beam that falls on the mirror adjustable about several axes, originates from the light sources 14R, 14G, 14B. The light sources 14R, 14G, 14B are indicated here as schematic boxes. They can be designed as conventional light sources, for example as light-emitting diodes (LEDs), or as laser light sources.

[0064] Fig. 3 shows an imaging unit 2 according to the invention. The light sources 14R, 14G, 14B are designed as laser diodes. The light emitted by them is collimated, indicated here by lenses 151. By means of a mirror 161 or by means of two dichroics 162, 163, the light emitted by the three light sources is combined in a common direction of propagation. It passes through a lens, which here schematically represents an illumination optic 155. It is then deflected by means of the mirror unit 73 as an image transmitter 11 according to an image to be displayed. It then reaches a lens, which here schematically represents a projection optic 156. It then reaches an optic 157 arranged in the projection surface 21 of the projection optic 156, which is arranged at the position where a diffuser 172 is conventionally often located. According to optics 157, the light continues as a beam SB1.

[0065] Fig. 4 schematically shows a projection system comprising a projection device as the imaging unit 2, here a laser beam scanner 22 (LBS), which is installed inside a vehicle 100. The LBS 22 is shown, by way of example, mounted on a rearview mirror of the vehicle 100. The LBS 22 projects an image onto the instrument panel, which here serves as the projection surface 21. The projected image is indicated here as a direction and speed indication. A computer unit 52 carries out a 202405054

[0066] 11

[0067] An algorithm controls the output of the LBS 22 to generate a desired image at the desired location. Since the dashboard is not a flat surface but a three-dimensionally curved one, the projection surface 21 is also curved accordingly. The processing unit takes this curvature into account when controlling the LBS 22. As an example, another LBS 22' is positioned on the vehicle's rearview mirror. This LBS 22' is aimed at a side window, which forms its projection surface 21'. A circular diffuser 172 is mounted on the side window. The laser light coming from the LBS 22' is scattered by the diffuser 172 into a limited angular range. Depending on the scattering properties of the diffuser 172, a real image is visible both from inside the vehicle and from outside, as long as the viewer's eye is within the corresponding angular range, i.e., within the eyebox.

[0068] Fig. 5 shows a section of an optical system 157. A multitude of parallel light-guiding elements 1570 can be seen. Each light-guiding element 1570 has a light-intake surface 1575, a light-guiding area 1576, and a light-emission surface 1577. The area of ​​the light-intake surface 1575 is greater than or equal to the area of ​​the beam diameter DLBR of the reflected light beam LBR. The light beam LBR is shown here, by way of example, as striking an eccentric light-intake surface 1575 of a light-guiding element 1570. It can also be seen that the diameter D of a light-guiding element 1570 is smaller than its length L, which is equal to the length L of the light-guiding area 1576. Not shown in the figure is an optic 157 arranged on a spherical surface. In the left area of ​​the figure it is indicated that a vignetting 1574 is provided between individual light guiding elements 1570 of the optic 157.

[0069] Fig. 6 shows exemplary configurations of light guide elements 1570. The right and left parts of the figure show light guide elements 1570R, 1570R', 1570K, 1570K, which have a round cross-section. The middle part of the figure shows light guide elements 1570V, 1570V, which have a polygonal, here rectangular, cross-section. The middle and right parts of the figure show light guide elements 1570V, 1570V, 1570R, 1570R', in which the 202405054

[0070] 12

[0071] The cross-sectional area Q is constant over the length L of the light-guiding area 1576. The left part of the figure shows light-guiding elements 1570K, 1570K', in which the cross-sectional area Q varies in shape over the length L of the light-guiding area 1576. The figure shows that the size of the shape changes. In the figures shown, the size of the cross-section decreases from the light-entry surface 1575 to the light-emission surface 1577. The light-guiding elements 1570 shown in the figure each have a light-guiding area 1576 that is a monolithic block. The lower part of the figure shows light-guiding elements 1570 in whose light-guiding area 1576 there are scattering elements 15761.

[0072] Fig. 8 shows a light-guiding element 1570, whose light-guiding area 1576 has an interior space 15762 and a surrounding wall 15763. The interior space 15762 can be hollow, i.e., filled with air or another fluid, or filled with another solid material. In the left area of ​​the light-guiding area 1576, facets 15764 on the surface of the inner side of the wall 15763 are shown as an example. These ensure good light mixing. It can be seen that here, too, the area of ​​the light-entry surface 1575 is greater than or equal to the area of ​​the beam diameter DLBR of the reflected light beam LBR.

[0073] Fig. 7 shows a light guide element 1570 with a light guide area 1576 that narrows conically from the light entry surface 1575 to the light exit surface 1577. A light beam LBRS with a narrow angular distribution strikes the light entry surface 1575. This light beam would not be able to fill the entire eyebox. Inside the interior 15762, the light beam is reflected multiple times off the inner surface of the wall 15763, which is indicated here by a zigzag line Z. This increases the angular distribution of the light beam. A light beam LBRW with a wider angular distribution thus exits the light guide element 1570 at its light exit surface 1577. The angular distribution increases as the cross-section of the light guide element decreases. Conversely, the angular distribution decreases as the cross-section of the light guide element increases. 202405054

[0074] 13

[0075] Fig. 9 shows a light-guiding element 1570Q in which the shape of the cross-section Q varies over the length L of the light-guiding area 1576. The variable shape of the cross-section Q is square at the light-entry surface 1575, while it is rectangular at the light-emission surface 1577. For comparison, the dotted line indicates what the outer shape of the light-guiding element would look like if the cross-section Q retained its square shape unchanged over the length L.

[0076] The cross-section QE of the light beam LBR at the light-entry surface 1575 is shown in the figure below left. It can be seen that it has a round shape. Further to the upper right, the narrow horizontal angular distribution WVSH and the narrow vertical angular distribution WVSV of the light beam LBR as it enters the light-guiding element 1570Q are schematically indicated. Due to the shape of the cross-section Q varying from the light-entry surface 1575 to the light-emission surface 1577, maintaining its horizontal extent while decreasing its vertical extent, the horizontal angular distribution remains unchanged, while the vertical angular distribution changes. This is shown in the upper right: The cross-section QA of the light beam LBR after passing through the light-guiding element 1570Q has an elliptical shape. The wide horizontal angular distribution WVWH indicated to the upper right is almost unchanged compared to the narrow horizontal angular distribution WVSH.In contrast, the wide vertical angle distribution WVWV is much more spread out than the narrow vertical angle distribution WVSV.

[0077] In other words, the invention discloses a projection device with a micro-array diffuser. Essentially, this is an (equidistant) array of either:

[0078] - round or rectangular tubes (microscopic French fry cutter) that

[0079] - may be hollow or filled,

[0080] - can be designed to be straight or tapered,

[0081] - can be faceted or contain one or more diffusers. These are essentially microscopic light mixing rods that can be designed in various ways. These elements represent the individual pixels and are sequentially illuminated by the laser-based scanner. The system ensures that the spot is integrated into element 202405054.

[0082] 14 and does not fall on the neighboring region. If the beam falls into the described element, it is either reflected multiple times, scattered, or influenced by facets in such a way that the exiting beam leaves the element at a wider angle. The goal of a head-up display is for each element to illuminate the entire eyebox.

[0083] The light-guiding elements 1570 of the optics 157 according to the invention are not limited to optical fibers such as those suitable for optical data transmission. Such optical fibers are generally filled optical guides. Rather, the light-guiding elements 1570 preferably used in an optics 157 according to the invention are short tubes that can be filled or hollow. They can be straight or conical (tapering). Due to their short length, they are not usually referred to as optical fibers suitable for optical data transmission. A real image is formed at the light-exit surface of the optics 157, which is formed by the entirety of the light-exit surfaces 1577 of all the light-guiding elements 1570 of the optics 157. The entirety of the light-exit surfaces 1577 thus forms an intermediate image plane. It therefore assumes the function of a diffuser 157 that would otherwise be provided at this location.

[0084] The invention requires a scanning system, preferably a laser beam scanner 22, in which the individual pixels are switched on precisely when they fall upon a light-intake surface 1575 of the optics 157. The light-intake surfaces 1575 are preferably round or polygonal structures, but can also have a differently shaped cross-section. The control of the laser beam scanner 22 is precisely adapted and synchronized for this purpose. Each light-guiding element 1575 then corresponds to a pixel. This further mixes and / or shapes the light forming the light point of a pixel.

[0085] The light point formed by the reflected light beam LBR is, so to speak, captured in the light guiding element 1570 and, after multiple reflections, coupled back out at its light emission surface 1577. 202405054

[0086] 15

[0087] A conical (tapered) variant allows the outgoing angular range, i.e., its wide vertical angular distribution WVWV and / or its wide horizontal angular distribution WVWH, to be advantageously varied for a pixel compared to the incoming angular range, i.e., its narrow vertical angular distribution WVWV and / or its narrow horizontal angular distribution WVWH. This enables a simple adjustment of the desired angular distribution.

Claims

202405054 16 Patent claims 1. Projection device, comprising - a beam generator (140) for generating a modulated collimated light beam (LBM); - a projection surface (21); and - a mirror unit (73) for reflecting the modulated collimated light beam (LBM) and for moving the reflected light beam (LBR) over the projection surface (21), wherein an optic (157) is arranged between the mirror unit (73) and the projection surface (21), the optic having a plurality of parallel light guiding elements (1570), and wherein a light guiding element (1570) has a light entry surface (1575), a light guiding area (1576) and a light exit surface (1577), and wherein the area of ​​the light entry surface (1575) is greater than or equal to the area of ​​the beam diameter (DLBR) of the reflected light beam (LBR).

2. Projection device according to claim 1, wherein the optics (157) are arranged on a spherical surface.

3. Projection device according to one of the preceding claims, wherein a light guide element (1570) has a round or polygonal cross-section (Q).

4. Projection device according to claim 3, wherein the cross-section (Q) is constant over the length (L) of the light guide area (1576).

5. Projection device according to claim 3, wherein the cross-section (Q) has a shape that varies over the length (L) of the light guide area (1576).

6. Projection device according to one of the preceding claims, wherein a light guide element (1570) has a light guide area (1576) which has an interior 202405054 17 (15762) and has a surrounding wall (15763), or the light guiding area (1576) is a monolithic block.

7. Projection device according to one of the preceding claims, wherein a light guiding element (1570) has a light guiding area (1576) with a faceted wall (15763).

8. Projection device according to one of the preceding claims, wherein a light guiding element (1570) has a light guiding area (1576) in which scattering elements (15761) are located.

9. Projection device according to one of the preceding claims, wherein a vignetting (1574) is provided between individual light guiding elements (1570) of the optics (157).

Images