Projection system

Abstract

The invention relates to a projection system comprising - a beam generator (140) for generating a collimated modulated light beam (LBM); - a projection surface (21); - and a mirror unit (73) for reflecting the modulated light beam (LBM) and moving the reflected light beam (LBR) over the projection surface (21), wherein a gray gradient (210) is disposed on the projection surface (21).

Description

[0001] 202405095

[0002] 1

[0003] Projection system

[0004] The present invention relates to a projection system. Projection systems typically comprise a projection device and a projection surface. 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 imaging unit, also called a PGU (Picture Generating Unit), and an optical unit or mirror unit. The imaging unit generates the image and uses at least one display element for this purpose. 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 DLP (Digital Light Processing).

[0006] These are DMD systems (DMD: Digital Micromirror Device). An example of a scanning system is a laser 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 disc. In the automotive sector, 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. 202405095

[0007] 2

[0008] A laser beam scanner (often abbreviated as LBS) uses a laser beam modulated with image information, which 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 with a small angular range. For energy-saving reasons, a diffuser that scatters over a relatively small angular range is therefore usually used.

[0009] 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 the dashboard or headliner, often serves as the projection surface. The curved shape of these surfaces is taken into account during the display, for example, by pre-distorting 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. However, if the eye is outside the eyebox, the virtual or real image is not visible to the viewer.

[0011] 3. Only partially visible or not visible at all. The larger the eyebox, the less restricted the viewer is in choosing their seating position.

[0012] 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.

[0013] 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.

[0014] Laser scanning systems offer advantages over LCD-based display solutions, characterized by less complex optics and higher energy efficiency. As an alternative to RGB color laser diodes, a short-wavelength laser can also be used to scan an RGB wavelength converter in a suitable intermediate image plane.

[0015] 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 disturbing 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. 202405095

[0016] 4

[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] In known designs, the MEMS mirror of the laser beam scanner is a flat element which is connected to the surrounding structure via thin elements and is excited to vibrate via further elements, such as piezoelectric elements.

[0019] The oscillating MEMS mirror reflects the incoming collimated, modulated laser beam and subsequently directs it through a projection optic to focus the beam in order to create the desired pixel at the desired distance.

[0020] Typical laser beam scanners operate in TV scan mode or Lissajous scan mode. In TV scan mode, the laser beam is scanned line by line across the image area to be illuminated, following a pattern familiar from television signals. An interlaced mode may also be available, in which all even-numbered lines and then all odd-numbered lines are scanned alternately. At the end of a line, the scanner usually jumps to the beginning of the next line. This requires either significant acceleration and deceleration of the movement of a mirror guiding the laser beam, which can lead to mechanical problems, or switching off the laser beam during the line return, resulting in a less bright image. In Lissajous mode, the laser beam is scanned across the image area according to a Lissajous pattern. This generally focuses on the edges of the image.

[0021] 5

[0022] The light passes through the image area more slowly than its central area, resulting in higher resolution and brightness at the edges than in the center. Generally, uniform brightness and resolution across the entire illuminated image area are desirable.

[0023] A disadvantage of known Lissajous scans is that Lissajous figures cause a stronger concentration of light at the edges of the scanned image. This results in an inhomogeneous image with respect to luminance. While known applications attempt to compensate for this through pulse width modulation using software or hardware, these methods introduce other adverse optical side effects, such as losses in color dynamics or brightness dynamics.

[0024] An improved version is desired.

[0025] A projection system according to the invention has:

[0026] - a beam generator for producing a modulated collimated light beam;

[0027] - a projection surface; and

[0028] - A mirror unit for reflecting the modulated light beam and moving the reflected light beam across the projection surface, wherein a gray gradient is arranged on the projection surface. The gray gradient is, for example, a coating on the projection surface or a component arranged on the projection surface. The gray gradient reduces the brightness where it is too high due to the prevailing conditions.

[0029] According to one embodiment, the mirror unit guides the reflected light beam across the projection surface according to a scanning pattern, and the gray gradient represents the inverse brightness profile of the white image produced by the scanning pattern. According to the invention, the projection surface / screen / image surface / projection display is provided with a gray gradient that represents the inverse brightness profile of the white image. A white image produced by a Lissajous figure typically has a slightly darker center and slightly lighter edges. The gray gradient with inverse 202405095

[0030] 6

[0031] The brightness gradient therefore has a highly transparent center and gradually less transparent outer areas. The transmission, or transmissive image plane, thus decreases towards the outside. Such an embodiment can also be advantageously used for a raster scan, e.g., a row-wise or column-wise raster scan.

[0032] According to one interpretation, the projection surface is a reflective surface, and the gray gradient is designed as a reflection gradient. In the case of a reflective image plane, its reflectance decreases towards the outside due to the reflection gradient.

[0033] The gray gradient resulting from a coating gradient, black printing, and a laser-treated surface is advantageous. A coating gradient, black printing, or even targeted laser treatment of the projection surface can be implemented technically without significant effort. This acts as an absorption or transmission gradient.

[0034] According to one embodiment, the gray gradient features areas of switchable gray levels. This can be achieved, for example, with a monochrome display element such as an LCD, a switchable hologram layer, or a layer with switchable absorbers, such as one based on so-called e-paper technology. These switchable gray levels allow the gray gradient to be adapted to different scanning patterns. The mirror unit can thus be operated with different scanning patterns, even if these result in significantly different white images, without producing any noticeable effects for the viewer. In the case of different scanning patterns that only result in white images with slightly different brightness distributions, a constant gray gradient is sufficient.

[0035] The proposed solution is subtractive and therefore not the most energy-efficient. However, it allows for a more homogeneous representation, which is not easily achievable otherwise. The potential applications of laser beam scanner systems are discussed in 202405095.

[0036] 7. The invention extends the laser beam scanner systems with regard to appearance and optical properties. The solution according to the invention can reduce algorithms implemented in software or hardware, thereby reducing computational effort and energy consumption on the ASIC / chip side, while simultaneously positively influencing the color dynamic range and the luminance dynamic range. The solution according to the invention with a projection screen / optics with a gray filter or black print gradient for homogeneity compensation of a laser beam scanner system can, in principle, be applied wherever Lissajous figures are used.

[0037] Further aspects and details of the invention are also given in the following figure description. This shows:

[0038] Fig. 1 shows a head-up display.

[0039] Fig. 2 shows an embodiment of an imaging unit.

[0040] Fig. 3 shows an imaging unit according to the invention.

[0041] Fig. 4 a projection system

[0042] Fig. 5 a projection system

[0043] Fig. 6 shows a radiation generator.

[0044] Fig. 7 shows a grey gradient according to the invention.

[0045] 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.

[0046] Fig. 1 schematically shows a head-up display for a means of transportation as an example of an image generation system 1. The head-up display has a 202405095

[0047] The system consists of 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 motor vehicle. From there, the beam of light SB2 travels towards the eye 61 of an observer.

[0048] The viewer sees a virtual image VB, which is located outside the vehicle, above the hood or even in front of the vehicle. 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 displayed. 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. 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. This rotation of the curved mirror 32 allows the eyebox 62 to be moved, thus adjusting its position to the position 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 environment by a transparent cover 33. The optical elements of the optical unit 3 are thus protected, for example, from dust present in the interior of the vehicle.A glare shield 34 serves to reliably absorb light reflected across the interface of the cover 33, thus preventing glare for the viewer. Except for sunlight SL 202405095.

[0049] 9 The light from another interfering light source 64 can also reach the projection surface 21.

[0050] 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, each of which is positioned in one of two positions when controlled. A light beam LB incident on it is thus modulated in a pixel grid to generate the virtual image VB. This is a DMD. According to another embodiment, the controllable mirror unit 73 consists of a mirror adjustable about several axes, which is controlled such that an incident laser beam is reflected according to a two-dimensional grid, thereby generating the virtual image VB.

[0051] 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.

[0052] 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 means of 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 a

[0053] 10

[0054] Projection surface 21 of the projection optics 156 arranged diffuser 172. After the diffuser 172, the light continues as a beam SB1.

[0055] 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 serves here as the projection surface 21. The projection image is indicated here as a direction and speed indication. A computing unit 52 executes an algorithm that controls the output of the LBS 22 to generate the desired image at the desired location. Since the instrument panel is not a flat surface but a three-dimensionally curved surface, the projection surface 21 is also curved accordingly; the computing unit takes this curvature into account when controlling the LBS 22. An additional LBS 22' is shown, by way of example, mounted on the rearview mirror of the vehicle.This LBS 22' is aligned with a side window, which forms its projection surface 21'. A circular diffuser 172 is arranged 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 the vehicle, as long as the viewer's eye is within the corresponding angular range, i.e., within the eyebox.

[0056] Fig. 5 schematically shows a projection system. The light source 140 generates a modulated collimated light beam LBM. The light source 140 contains, for example, light sources 14R, 14G, 14B, lenses 151, mirrors 161, dichroics 162, 163, illumination optics 155, and electronic control elements, which are not shown in this figure. The modulated light beam LBM is reflected by the mirror unit 73. The reflected light beam LBR passes through a projection optic 156 and reaches the projection surface 21. Due to the modulation, the light beam LBM carries image information that is synchronized with a movement of the mirror unit 73, so that the image to be displayed changes with movement.

[0057] 11 of the reflected light beam LBR is formed on the projection surface 21. A gray gradient 210 is arranged on the projection surface 21.

[0058] Fig. 6 shows a light source 140 that generates a modulated collimated light beam LBM. This light beam LBM strikes a mirror element 730 of a mirror unit 73 and is reflected by it. The reflected light beam LBR strikes a projection surface 21. The mirror element 730 is arranged to be oscillatable about a first axis ARot1 and about a second axis ARot2. The oscillation of the mirror element 730 is indicated by double arrows Rot1, Rot2. The oscillation about the first axis ARot1 occurs at a first frequency F1. The oscillation about the second axis ARot2 occurs at a second frequency F2. The first frequency F1 is five times the value of the second frequency F2. The amplitudes A1, A2 of the light beam LBR moving across the projection surface 21 are selected according to the desired image area. For an image area in 16:9 format, the amplitude ratio A1 :A2=16:9.Accordingly, the Lissajous figure LJF indicated on the projection surface 21 is formed. It can be seen that the light beam LBR moving across the projection surface 21 is less frequently located in its central area than in its outer area. Consequently, with a continuously illuminating light beam LBR, a higher brightness occurs in the outer area than in the center of the projection surface 21. If the light beam LBR is pulsed, the corresponding pulses produce more finely resolved luminous traces in the outer area than in the center. The resolution of an image generated by means of a pulse-modulated light beam is therefore lower in the center than in the outer area. The mirror unit 73 guides the light beam LBR across the projection surface 21 according to a scanning pattern LJF, which corresponds to the Lissajous figure LJF. The gray gradient 210, which represents the inverse brightness profile of the white image generated by the scanning pattern LJF, is arranged on this surface.

[0059] Fig. 7 shows an example of a gray gradient 210 according to the invention. The transmission profile of a projection surface provided with a corresponding gray gradient 210 can be seen. The transmission is high in the center 21001 and decreases sharply towards the outside in the edge region 21002.

Claims

202405095 12 Patent claims 1. Projection system, featuring - a beam generator (140) for generating a collimated modulated light beam (LBM); - a projection surface (21); and - a mirror unit (73) for reflecting the modulated light beam (LBM) and moving the reflected light beam (LBR) over the projection surface (21) , wherein a gray gradient (210) is arranged on the projection surface (21 ).

2. Projection system according to claim 1, wherein the mirror unit (73) guides the reflected light beam (LBR) according to a scanning pattern (LJF) over the projection surface (21) and the gray gradient (210) represents the inverse brightness profile of the white image produced by the scanning pattern (LJF).

3. Projection system according to one of the preceding claims, wherein the projection surface (21 ) is a reflective surface, and the gray gradient (210) is designed as a reflection gradient (211 ).

4. Projection system according to one of the preceding claims, wherein the gray gradient (210) is one of a coating gradient, black print and laser-treated surface.

5. Projection system according to one of the preceding claims, wherein the gray gradient (210) has areas of switchable gray levels.

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