Projection device

Abstract

The invention relates to a projection device comprising a beam generator (140) for generating a modulated collimated or convergent light beam (LBM) and a mirror unit (73) for reflecting the modulated light beam (LBM) and for moving the reflected light beam (LBR) over a predetermined solid angle range. The mirror unit (73) comprises at least one mirror element (730, 7301, 7302), which is or is suspended, individually or together, to oscillate about two non-parallel axes (ARot1, ARot2), being driven to oscillate about the first axis (ARot1) at a first frequency (F1) and about the second axis (ARot2) at a second frequency (F2). The first frequency (F1) and the second frequency (F2) are the same, and the first amplitude (A1) and / or the second amplitude (A2) vary over time. The frequencies (F1,F2) can also vary over time.

Description

[0001] 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.

[0002] Head-up displays generally consist of an imaging unit (PGU), an optical unit, and a mirror unit. The imaging unit generates 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), micro-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.

[0003] 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 (LC: Liquid Crystal), micro-LED displays (LED: Light Emitting Diode), LCoS displays (LCoS: Liquid Crystal on Silicon), or DMD systems (DMD: Digital Micromirror Device).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.This also benefits the brightness of the image, which can be achieved with the given, usually quite limited, projector output. The smaller the angle of dispersion of the diffuser, the greater the perceived brightness of the image.

[0004] The diffuser can be, for example, a scattering, possibly backscattering, and transparent disc. Partial scattering or backscattering is desirable for the projection to be visible. The viewer then sees the content displayed by the imaging unit as a virtual image and simultaneously the real world behind this disc. 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 projection, for example, by pre-distorting the image displayed by the imaging unit.

[0005] 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.When using a diffuser, the eyebox is not sharply cut off at the edge, as is the case with a head-up display without a diffuser. Instead, the image brightness decreases towards the edge of the eyebox, but it may still be visible further outside. In this case, the eyebox boundary can be defined, for example, by a relative decrease in the image brightness.

[0006] 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.

[0007] In laser beam scanner systems, 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. Compared to LCD-based display solutions, laser scanning systems are characterized by less complex optics, higher energy efficiency, and different cooling requirements. LCD-based display solutions can often be passively cooled, while laser-based systems in the automotive sector tend to require active cooling, such as cooling with Peltier elements. Particularly with red laser diodes, efficiency drops quite rapidly with temperature and is already too low within the temperature range typical for automotive applications.However, Peltier elements are also not very efficient, so system power losses worsen, especially at high ambient temperatures. 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] The oscillating MEMS mirror reflects the incoming collimated, modulated laser beam and guides it through a subsequent projection optic to focus the beam and create the desired pixel at the desired distance. However, there are also variants with a convergent modulated laser beam.

[0012] 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. Such switching off, also called blanking, is always necessary, even in a conventional television set without moving parts. The question is what proportion of the scan time is required for this blanking.The oscillation can be made more bandwidth-friendly by using a triangular pattern instead of a sawtooth pattern for deflection and by using both the forward and reverse directions for image scanning. In Lissajous mode, the laser beam is guided across the image area to be illuminated according to a so-called Lissajous figure. Generally, the edges of the image area are traversed more slowly than the central area, resulting in higher resolution and brightness at the edges than in the center. Uniform brightness and resolution across the entire illuminated image area are generally desirable.

[0013] A disadvantage of known designs is that TV scanning is particularly susceptible to vibrations, especially in the automotive sector. Lissajous scanning has the highest scan density at the edges of the image, resulting in the greatest resolution and brightness there. Typically, the laser beam is even switched off at the edges because the brightness levels are difficult to manage there. Typical automotive applications prefer the highest brightness and resolution in the center of the image.

[0014] An improved version is desired.

[0015] A projection device according to the invention comprises a beam generator for producing a modulated collimated or modulated convergent light beam and a mirror unit for reflecting the modulated light beam and for moving the reflected light beam over a predetermined solid angle range. The mirror unit comprises one or more mirror elements. If it is a single mirror element, it is suspended so as to be oscillatable about two axes that are not parallel to each other. If it is a multi-element mirror, these are collectively suspended so as to be oscillatable about two axes that are not parallel to each other. For example, each of these mirror elements is suspended so as to be oscillatable about one axis, and the axes are arranged non-parallel, i.e., at an acute angle to each other other than zero degrees.In the simplest case, the axes are arranged at right angles to each other, but they can also be arranged at any angle other than zero degrees. The latter results in an elliptical scan pattern, which is desirable in certain configurations. An elliptical scan pattern can also be achieved using different vibration amplitudes. By cleverly combining axes arranged at acute angles with different vibration amplitudes, a circular scan pattern can also be obtained. More than two axes are also within the scope of the invention. In this case, each corresponding mirror element only needs to contribute a smaller deflection. Furthermore, more complex scan patterns or differently shaped scan surfaces can be easily generated by the interaction of several axes.The mirror unit is driven to oscillate around the first axis at a first frequency and to oscillate around the second axis at a second frequency. Advantageously, the first and second frequencies are the same, and the first amplitude and / or the second amplitude varies over time. According to the invention, instead of a Lissajous scan, both mirror axes are driven at the same frequency but with a variable amplitude. This allows elliptical scan fields to be generated that do not exhibit edge enhancement and tend towards higher resolution in the center of the image.

[0016] Advantageously, the two axes oscillate out of phase with each other, and at least one of the amplitudes follows a triangular modulation. The two axes oscillate out of phase, which can be achieved through a phase-shifted drive. Depending on the design, a phase-shifted oscillation can also be achieved with an in-phase drive. Thus, with a clever arrangement, a phase-shifted oscillation of both axes can still be achieved with a single excitation.

[0017] Advantageously, the frequencies and amplitudes are chosen such that the area swept over by the reflected light beam on a projection surface deviates from a rectangular shape.

[0018] Advantageously, the frequencies and amplitudes are chosen such that the reflected light ray is less frequently located in the outer area of ​​the swept solid angle than in its central area.

[0019] According to the invention, spiral laser scanning is enabled. Other scan modes with harmonic excitation are also possible according to the invention.

[0020] It is advantageous to modulate the first frequency and / or the second frequency. By modulating one or both frequencies, and with a suitable choice of modulation signal, the tangential density or resolution in the tangential direction can be adapted to a desired profile.

[0021] Advantageously, the mirror element exhibits a resonance characteristic and is mechanically designed such that modulation of the first frequency and / or the second frequency results in modulation of the first amplitude and / or the second amplitude. In this way, the desired amplitude modulation is achieved without requiring a separately adapted amplitude control signal.

[0022] Further advantages and embodiments of the invention can also be seen in the following description of exemplary embodiments with reference to figures. These show: Fig. 1 Head-Up Display; Fig. 2. Design of an imaging unit; Fig. 3 imaging unit according to the invention; Fig. 4 Projection system; Fig. 5 Projection system; Fig. 6. Schematic view of a mirror unit; Fig. 7 additional projection systems; Fig. 8 additional projection systems; Fig. 9 additional projection systems; Fig. 10 radiation sources; and Fig. 11 radiation sources. Character description

[0023] 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.

[0024] Fig. Figure 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.

[0025] 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. In addition to sunlight SL, light from another ambient light source 64 can also reach the projection surface 21.

[0026] Fig. Figure 2 schematically shows an embodiment of an imaging unit 2 with light sources 14R, 14G, 14B that emit focused light. These are, for example, lasers whose light is also coherent. Coherence can be undesirable in certain applications because, for example, it promotes speckles. 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, upon control, are each in one of two positions. A light beam LB striking the unit is thus modulated in a pixel grid to generate the virtual image VB. This is a DMD.According to another variant, the controllable mirror unit 73 consists of a mirror adjustable about several axes, which is controlled in such a way that an incident laser beam is reflected and scans a two-dimensional surface and, in conjunction with the modulation of the light sources, generates the virtual image VB.

[0027] 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.

[0028] Fig. Figure 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 a diffuser 172 arranged in the projection surface 21 of the projection optic 156. After the diffuser 172, the light continues as a beam SB1.

[0029] Fig. Figure 4 schematically shows a projection system comprising a projection device as the imaging unit 2, in this case a laser beam scanner 22 (LBS), which is installed inside a vehicle 100. The LBS 22 is shown, for example, mounted on a rearview mirror of the vehicle 100. The LBS 22 projects an image onto the instrument panel, which serves as the projection surface 21. The projection is indicated here as a direction and speed indication. A computing unit 52 executes an algorithm that controls the LBS 22 to generate the desired image at the desired location. Since the instrument panel is not a flat surface, but rather a regularly or irregularly curved surface in three-dimensional space, the projection surface 21 is also curved accordingly. The computing unit takes this curvature into account to control the LBS 22.As an example, another LBS 22' is arranged on the rearview mirror of the vehicle. This LBS 22' is aimed at 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 (backward scattering by the diffuser) and from outside the vehicle (forward scattering by the diffuser), as long as the viewer's eye is within the corresponding angular range, i.e., within the eyebox. For a laterally correct display, it is important to note whether the image is viewed from inside the vehicle or from outside.If the image to be displayed is critical in this respect, for example because it contains written text, it is intended to reinforce the desired direction of dispersion (inwards or outwards) compared to the undesired direction of dispersion.

[0030] Fig. Figure 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 is formed on the projection surface 21 when the reflected light beam LBR is moved.

[0031] Fig. Figure 6 shows a schematic view of a mirror unit 73. A round mirror element 730 is visible, which is connected to an annular support element 733 via first suspension elements 731. This support element 733 is connected to a base plate 734 by means of second suspension elements 732. The first suspension elements 731 and the second suspension elements 732 are preferably aligned at an angle of 90° to each other. They can also be arranged at an angle to each other, as long as they are not parallel, i.e., as long as they can be used to span a surface. Actuators, here indicated as piezoelectric elements 735, 736, cause the base plate 734 to vibrate. This vibration is transmitted via the suspension elements 731, 732 to the mirror element 730, which vibrates at resonance and thereby moves the light beam LBR reflected by it across the projection surface 21.The oscillating movement of the mirror element 730 about the axes ARot1, ARot2 of the suspension elements 731, 732 is indicated by two double arrows Rot1, Rot2. The suspension and drive are shown schematically here. Other configurations can also be used.

[0032] Fig. Figure 7 schematically shows another 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, which here consists of two mirror elements 7301, 7302. The first mirror element 7301 is rotatably mounted about a first axis ARot1. The second mirror element 7302 is rotatably mounted about a second axis ARot2. The two axes ARot1, ARot2 are perpendicular to each other. Double arrows Rot1, Rot2 indicate a back-and-forth oscillation about the two axes ARot1, ARot2. The reflected light beam LBR reaches the projection surface 21 - possibly after passing through a projection optic 156 (not shown here).Through modulation, the light beam LBM carries image information that is coordinated with a movement of the mirror unit 73, so that the image to be displayed is formed on the projection surface 21 when the reflected light beam LBR is moved.

[0033] Fig. Figure 8 schematically shows another 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 first reflected by a stationary mirror 141 and then by the mirror unit 73. Here, too, the mirror unit 73 consists of two mirror elements 7301, 7302. The first mirror element 7301 is rotatably mounted about a first axis ARot1. It oscillates at a high frequency, preferably at its resonant frequency, and is thus suitable for rapidly scanning the lines of a line-by-line scanned image area. The second mirror element 7302 is rotatably mounted about a second axis ARot2.It is designed to be wider so that the light beam coming from the first mirror element can travel a line across it. The second mirror element 7302 oscillates at a lower frequency and is therefore suitable for the slower scanning of the image lines from top to bottom and vice versa. The two axes ARot1, ARot2 are arranged perpendicular to each other. Double arrows Rot1,Rot2 indicate a back-and-forth oscillation around the two axes ARot1, ARot2. The reflected light beam LBR reaches the projection surface 21 – possibly after passing through a projection optic 156 (not shown here). Through 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 is formed on the projection surface 21 when the reflected light beam LBR moves.

[0034] Fig. Figure 9 schematically shows another projection system. The light source 140 generates a light beam LB. This is reflected by the mirror unit 73. Here, too, the mirror unit 73 consists of two mirror elements 7301 and 7302. The first mirror element 7301 is rotatably mounted about a first axis ARot1. The second mirror element 7302 is rotatably mounted about a second axis ARot2. The two axes ARot1 and ARot2 are arranged perpendicular to each other. Double arrows Rot1 and Rot2 indicate a back-and-forth oscillation about the two axes ARot1 and ARot2. The reflected light beam LBR passes through a projection optic 156 and reaches the projection surface 21. Through modulation, the light beam LB carries image information that is synchronized with a movement of the mirror unit 73, so that the image to be displayed is formed on the projection surface 21 when the reflected light beam LBR is moved.

[0035] Fig. Figure 10 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 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 illuminated light beam LBR, the brightness is higher at the edges 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 at the edges than in the center. The resolution of an image generated by an intensity-modulated light beam is therefore lower at the center than at the edges. The frequency ratio shown here is chosen for illustrative purposes and is not necessarily representative of practical applications. The vertical resolution is very low at this frequency ratio.A frequency ratio of 4.99 would result in a continuous figure, causing the lines to wander after each iteration.

[0036] Fig.Figure 11 shows the light source 140, mirror element 730, and projection surface 21 as shown in the previous figure. In contrast, the mirror element 730 is driven about both axes ARot1, ARot2 with the same frequency F1=F2, but with a phase shift. In this embodiment, the amplitudes of the light beam LBR moving across the projection surface 21 increase and decrease slowly. The changes in the amplitudes A1, A2 preferably follow a triangular shape. This forms the spiral figure SFF indicated on the projection surface 21. The spiral is traversed alternately from the inside out and then from the outside in. The direction of rotation (clockwise or counterclockwise) remains constant; only the spiral is traversed with alternating increasing and decreasing radii. Therefore, the figure shows only a portion of the entire traversed shape.It can be seen that the light beam LBR moving across the projection surface 21 is located more frequently in its central area than in its outer area. Accordingly, with a continuously illuminating light beam LBR, a higher brightness occurs in the center of the projection surface 21 than in its outer area. If the light beam LBR is operated with intensity / power modulation, the corresponding pulses produce more finely resolved luminous traces in the center than in the outer area. The resolution of an image generated by a light beam with time-modulated power at the same frequency is therefore higher in the center than in the outer area. The scanner axes ARot1, ARot2 are thus driven with a phase shift at the same frequency F1=F2. The amplitude A1,A2 is modulated in a triangular pattern. According to a preferred embodiment, equal amplitudes A1=A2 are also provided.In this case, the light beam LBR is moved not over a rectangular, but over a circular or elliptical area of ​​the projection surface 21. Particularly in automotive applications, a rectangular image area is often unnecessary. On the contrary, a circular or elliptical image area is even desirable for automotive applications. According to a preferred embodiment, the amplitude modulation is optimized so that the density increase in the center is not excessive.

[0037] The invention thus relates to a projection device comprising a beam generator 140 for generating a modulated collimated or convergent light beam LBM and a mirror unit 73 for reflecting the modulated light beam LBM and for moving the reflected light beam LBR over a predetermined solid angle range. The mirror unit 73 comprises at least one mirror element 730, 7301, 7302, which is or is suspended, individually or together, so as to be oscillatable about two non-parallel axes (ARot1, ARot2), being driven to oscillate about the first axis (ARot1) at a first frequency (F1) and about the second axis (ARot2) at a second frequency (F2). The first frequency (F1) and the second frequency (F2) are preferably the same, and the first amplitude (A1) and / or the second amplitude (A2) vary over time. The frequencies (F1,F2) can also vary over time.For more complex scan patterns that make a bigger difference, you need oscillations not only in the fundamental frequency, but also in harmonic frequencies.

Claims

[1] Projection device, comprising - a beam generator (140) for generating a modulated collimated or convergent light beam (LBM); - a mirror unit (73) for reflecting the modulated light beam (LBM) and for moving the reflected light beam (LBR) over a predetermined solid angle range, wherein the mirror unit (73) has a mirror element (730) which is suspended oscillatibly about at least two mutually angled axes (ARot1,ARot2), or has several mirror elements (7301,7302) which are suspended oscillatibly about an axis (ARot1,ARot2), which axes (ARot1,ARot2) are angularly aligned to each other, wherein a first frequency (F1) is driven to oscillate about the first axis (ARot1), and a second frequency (F2) is driven to oscillate about the second axis (ARot2), wherein the first frequency (F1) and the second frequency (F2) are the same, and the first amplitude (A1) and / or the second amplitude (A2) vary over time. [2] Projection device according to claim 1, wherein the two axes (ARot1,ARot2) oscillate with phase shift relative to each other, and at least one of the amplitudes (A1,A2) follows a triangular modulation. [3] Projection device according to one of the preceding claims, wherein the frequencies (F1,F2) and the amplitudes (A1,A2) are selected such that the area swept over on a projection surface (21) by the reflected light beam (LBR) is not rectangular. [4] Projection device according to one of the preceding claims, wherein the frequencies (F1,F2) and the amplitudes (A1,A2) are selected such that the reflected light ray (LBR) is not more frequently located in the outer region of the swept solid angle area than in its central region. [5] Projection device according to one of the preceding claims, wherein the first frequency (F1) and / or the second frequency (F2) is modulated. [6] Projection device according to claim 5, wherein one or more mirror elements (730, 7301, 7302) have a resonance characteristic and are mechanically designed such that the modulation of the first frequency (F1) and / or the second frequency (F2) causes a modulation of the first amplitude (A1) and / or the second amplitude (A2).

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