DE102019127580A1 - Projection unit for a field of view display device in a motor vehicle - Google Patents

Abstract

The invention relates to a projection unit for a field of view display device, which is designed to generate and project a projection light beam with a display content onto a projection screen that is reflective on the user side and transparent on the rear side, in particular a front screen of a motor vehicle, in order to generate a virtual display image behind it, comprising: a flat one , in particular planar, optical waveguide, in whose flat surface a decoupling element for decoupling the projection light beam towards the projection screen is formed, as well as an image generation unit for generating the projection light beam to be coupled into the waveguide; - an electrically controllable spatial phase modulator arranged in the beam path of the projection light beam; and a control unit which is set up to control the spatial phase modulator for such a phase front change of the projection light beam that compensates for an undesired influence of a projection screen curvature during its subsequent reflection on the projection screen.

Description

Technical area

The invention relates to visual field display devices, in particular head-up displays for motor vehicles, the projection units of which comprise an optical waveguide. In particular, the present invention relates to measures to compensate for undesirable effects of a projection screen curvature, such. B. a distortion of the virtual display image or undesired focus effects that are caused by the reflection of a projection light beam on a curved projection screen, in particular a windshield of the vehicle.

Technical background

Field of view display devices in a motor vehicle are known in particular under the designation head-up display (HUD). In this way, for example, information about a speed limit is superimposed as a virtual display image on the real environment in front of the vehicle observed by the driver. For this purpose, a field of view display device comprises a projection unit that generates a projection light beam with the desired display content and typically projects it onto the windshield of the vehicle, from which it is reflected towards the driver, whereby the virtual display image is faded into his field of view in front of the vehicle.

In a classic HUD design in the automotive sector, the projection unit is immersed in the interior of the instrument panel and contains, among other things, a concave mirror in the beam path for image enlargement and / or image correction. The size of this concave mirror typically scales linearly with the size of the eyebox (i.e. an area of space from which the virtual display image can be seen for the user) and with the size of the virtual display image that can be displayed with the HUD. If you want to enlarge the HUD display image or the field-of-view that can be covered with it, for example to enable a contact-analog AR display (Augmented Reality) with virtual objects oriented towards real environmental objects, such a large concave mirror can be used with the classic design and thus result in such a large volume of the projection unit that it would be difficult to integrate it in a motor vehicle. In addition to this installation space problem, with the classic projection unit, the virtual display image is usually generated at a constant distance in front of the windshield outside the vehicle, which is determined by the optical structure of the projection unit.

The use of an optical waveguide in the form of a glass plate is known as a potential solution to the installation space problem described. In this context, the waveguide serves as a so-called pupil expander and thereby in principle enables a very flat projection unit with a very large virtual display image or field-of-view of the HUD.

• - Einsatz einer Fresnel-Linse über dem Auskoppelelement des Wellenleiters: Dieser Ansatz kann zu einer Reduktion der Auflösung des optischen Systems und damit zu Qualitätseinbußen beim HUD-Anzeigebild führen. Zusätzlich kann ein Risiko von Sonnenreflexen an den Kanten der Fresnel-Struktur und eine Reduktion des Kontrasts im HUD-Anzeigebild aufgrund von Streulichteffekten entstehen.
• - Einsatz einer klassischen Linse über dem Auskoppelelement: Diese würde sich zwar nicht negativ auf die Bildqualität auswirken, wäre jedoch bei den relevanten HUD-Abmessungen einige cm hoch, entsprechend schwer und sehr teuer in der Fertigung. Darüber hinaus würde sich auch das Risiko für Sonnenreflexe an der gekrümmten Linsen-Oberfläche deutlich erhöhen.
• - Frontscheibenkompensation, die bereits im Auskoppelelement des Waveguides erfolgt: Dieser Ansatz funktioniert nur bei holographischen Auskoppelelementen. Die Fertigung der Master solcher Auskoppelelemente ist allerdings extrem zeitaufwändig und damit kostenintensiv.

One problem with this approach is that with waveguide technology, in contrast to concave mirror technology, it is difficult to compensate for undesired influences of the curvature of the windshield. This windshield compensation can be essential for a good image quality of the HUD display image, since the vehicle-related windshield curvature, in addition to an often useful display image enlargement, also has an undesirable influence on the projection light beam, e.g. B. a distortion of the virtual display image or undesirable focus effects that have a negative effect on the image quality. In the best case, these focus effects can be noticeable as a field curvature, in the worst case, however, as blurring in the virtual display image. There are certainly approaches to achieve such a windshield compensation with a waveguide HUD. However, each of these approaches has significant disadvantages, such as:

• - Use of a Fresnel lens above the coupling-out element of the waveguide: This approach can lead to a reduction in the resolution of the optical system and thus to a loss of quality in the HUD display image. In addition, there may be a risk of sun reflections on the edges of the Fresnel structure and a reduction in the contrast in the HUD display image due to the effects of stray light.
• - Use of a classic lens above the decoupling element: This would not have a negative effect on the image quality, but with the relevant HUD dimensions it would be a few cm high, correspondingly heavy and very expensive to manufacture. In addition, the risk of solar reflections on the curved lens surface would also increase significantly.
• - Windshield compensation, which already takes place in the waveguide's decoupling element: This approach only works with holographic decoupling elements. However, the manufacture of the master of such decoupling elements is extremely time-consuming and therefore cost-intensive.

All previously known approaches of this type also have in common that they only allow static windshield compensation. On the one hand, this means that specially manufactured tools are used for each windshield geometry associated manufacturing costs would require, while existing projection units are not readily usable for retrofitting when the vehicle geometry changes. Furthermore, the image distance at which the virtual display image is generated is usually fixed here as well. This can mean a major disadvantage, especially for use in an AR-HUD: In the city, a shorter image distance to the user would be more suitable, while significantly wider image distances would be more suitable for cross-country trips.

For head-mounted displays (HMD), in particular for AR glasses, with a waveguide display arranged directly in front of the user's eyes, it is, for example, off WO 2018/231784 A1 known to use a Pancharatnam-Berry-Optical-Element (PBOE) as a switchable wave plate between the waveguide and the user's eye or between the waveguide and the environment in order to switch between different image planes and thus between different display image distances to the user for the displayed virtual display image, switch.

Also disclosed EP 2 972 595 B1 a display device comprising a pixel-based display system, a reconfigurable spatial light modulator (SLM), a waveguide, and a controller, wherein the reconfigurable SLM is configured to be illuminated by a pixel-based image provided by the display system, and the controller is configured to use the dynamically reconfiguring the reconfigurable SLM to modulate, based on a parameter for a shape of the waveguide, a phase of the pixel-based image through which the phase modulated image is displayed, thereby mitigating distortion by the waveguide. The parameter for the shape of the waveguide can in particular include an angle of an incident beam and a waveguide entry position. The reconfigurable
SLM can also be designed to scatter, split, or transmit light rays incident thereon, and be implemented as a hologram.

It is the object of the present invention to provide a waveguide-based projection unit, which is improved in particular with regard to the quality and display options of the virtual display image and / or with regard to production costs, for a field of view display device of the type mentioned, in particular for a motor vehicle, and a suitable method indicate their operation, a corresponding field of view display device and a corresponding motor vehicle.

Disclosure of the invention

This object is achieved by a projection unit according to claim 1 and a method for its operation, a corresponding field of view display device and a corresponding motor vehicle according to the independent claims. Further refinements are given in the dependent claims. All of the additional features and effects mentioned in the claims and the description for the projection unit also apply with regard to its operating method, the field of view display device or the motor vehicle, and vice versa.

According to a first aspect, a projection unit is provided for a field of view display device, for example for a head-up display (HUD), which can be used in a motor vehicle in particular as outlined at the beginning. The projection unit is designed to generate and project a projection light beam with a display content onto a projection screen that is reflective on the user side and is at least partially transparent on the rear side, in order to generate a virtual display image behind it. The projection screen can in particular be designed as a section of a front screen of the motor vehicle, which is usually curved. However, the invention is not limited to this application, but it can also be a different type of curved projection screen with similar properties, such as. B. another already existing protective disk or a specially provided Com binerscheibe.

The projection unit comprises a flat, in particular planar, optical waveguide for the projection light beam, for example in the form of a glass plate. The waveguide can in particular be designed in a manner known per se as a pupil expander for two-dimensional eyebox expansion. In its flat surface, which faces the projection screen during operation of the field of view display device, a decoupling element for decoupling the projection light beam towards the projection screen, in particular over a large area, is formed. Furthermore, the projection unit comprises an image generation unit which is designed to generate and couple the projection light beam with the display content into the waveguide.

The projection unit also has a spatial light modulator (spatial light modulator, SLM) in the form of an electrically controllable spatial phase modulator arranged in the beam path of the projection light beam generated by the image generation unit before or after the passage of the waveguide. To control the spatial phase modulator, a control unit is provided which is set up to effect such a phase front change in the projection light beam that counteracts or compensates for the undesired influences of a projection screen curvature during the subsequent reflection of the projection light beam on the projection screen.

The projection screen curvature means the curvature of a projection screen surface which is provided for reflecting the projection light beam to be projected onto it by the projection unit. The control unit can be set up in particular for the aforementioned compensation of the windshield curvature for a predetermined type and geometry of the projection screen and / or enable flexible adaptation to different types and geometries of projection screens, each of which has different negative effects on the projection light beam. For this purpose, the projection screen curvature can be characterized, for example, by one or more suitable projection screen parameters, which can be fed into the control unit to provide a corresponding set of control commands for controlling the spatial phase modulator. In particular, with the projection unit of the type set forth herein, a dynamic, i. H. Time-variable, phase front change of the projection light beam can be implemented by dynamic control of the spatial phase modulator.

One idea of the present invention consists in adapting the phase front of the projection light coupled out of the waveguide HUD in the direction of the projection screen by suitable control of the spatial phase modulator so that its curvature is compensated and therefore has no negative effect on the generated virtual display image. In addition, the phase front can be dynamically controlled simply by a suitable change in the set of control commands for controlling the spatial phase modulator and can therefore be flexibly adapted, for example, to different projection screen geometries without the need for a hardware change on the projection unit. All the disadvantages of windscreen compensation based on previous technologies described at the beginning can be eliminated by using such a spatial phase modulator.

In contrast to a usable display image enlargement, an undesired influence of a vehicle-specific predetermined projection screen curvature on the projection light beam can include, for example, a distortion of the virtual display image and / or undesired focus effects that have a negative effect on the image quality.

In particular, the spatial phase modulator can be designed as a flat phase modulation pixel matrix composed of phase modulation elements that can be electrically controlled independently of one another, in particular as a liquid crystal matrix (LC matrix) or PBOE matrix (Pancharatnam-Berry-Optical-Element that can be controlled pixel by pixel by applying electrical voltage) ). The planar phase modulation pixel matrix is arranged transversely to a direction of propagation of the projection light beam, for example perpendicular to a main beam direction corresponding to the optical axis of the projection unit, and can therefore in particular cover the entire cross section of the projection light beam that is relevant for the display image generation.

An LC or PBOE matrix is an arrangement of liquid crystals that are located between two transparent electrodes. In the PBOE in particular, the liquid crystals have a helical structure which affects the phase of the projection light transmitted through the PBOE. This effect on the phase of the projection light can be controlled by the electrical voltage applied between the two electrodes. If the electrodes are subdivided into a pixel structure, for example analogous to that of a TFT display, the phase of the transmitted projection light can be checked pixel by pixel, and thus locally at different positions in the beam cross-section. With such an arrangement it is therefore possible to adapt the phase front of the light coupled out from the waveguide HUD in such a way that the curvature of the front pane is compensated. In addition, the phase front can be dynamically controlled via the voltage applied to each pixel.

In particular, the spatial phase modulator can be arranged in the beam path of the coupled-out projection light beam between the coupling-out element and the projection screen and, for example, cover the coupling-out element over a large area. The spatial phase modulator can in particular be placed directly on the decoupling element or with one or more further functional layers, such as, for. B. a polarization element in the form of a λ / 4 retarder film, be formed in between.

In particular, the spatial phase modulator and the control unit can be designed and set up for a dynamic and / or continuous, in particular in an interval from 0 to π or from 0 to 2π, phase front change of the projection light beam, each locally within its cross section.

In particular, the projection unit can also have a polarization element for converting linearly polarized projection light into circularly polarized projection light, in particular a λ / 4 retarder film or λ / 4 retarder plate, in the beam path of the projection light beam in front of the spatial phase modulator. This can be particularly useful with the PBOE-based spatial phase modulator, since the effect of the PBOE is limited to circularly polarized light. For example, a λ / 4 retarder film can be integrated in the beam path of the projection light between the waveguide surface and the PBOE matrix in order to set the required polarization in the projection light that is coupled out. This measure is superfluous if the waveguide already decouples circularly polarized projection light. In the above-mentioned alternative approach with classic liquid crystals, the projection light can also be linearly polarized.

• - Bereitstellen mindestens eines Projektionsscheibenparameters, der die Krümmung einer Projektionsscheibenfläche charakterisiert, die zum Reflektieren des darauf von der Projektionseinheit projizierten Projektionslichtstrahlenbündels vorbestimmt ist;
• - Bereitstellen eines Steuerbefehlssatzes für den räumlichen Phasenmodulator abhängig von dem bereitgestellten mindestens einen Projektionsscheibenparameter, welcher Steuerbefehlssatz eine entsprechende Phasenfrontänderung des Projektionslichtstrahlenbündels bewirkt, um einem unerwünschten Einfluss der Projektionsscheibenkrümmung bei der Reflexion des Projektionslichtstrahlenbündels an der gekrümmten Projektionsscheibe entgegenzuwirken oder diesen zu kompensieren; und
• - Betreiben der Steuereinheit gemäß dem bereitgestellten Steuerbefehlssatz.

According to a further aspect, a method for operating a projection unit of the type set out herein is provided, comprising the steps:

• - providing at least one projection screen parameter which characterizes the curvature of a projection screen surface which is predetermined for reflecting the projection light beam projected thereon by the projection unit;
• - Provision of a control command set for the spatial phase modulator as a function of the provided at least one projection screen parameter, which control command set causes a corresponding phase front change of the projection light beam in order to counteract or compensate for an undesired influence of the projection screen curvature when the projection light beam is reflected on the curved projection screen; and
• - Operating the control unit in accordance with the set of control commands provided.

The projection screen parameter mentioned can be a mere type designation if control command sets for a set of different predetermined projection screen types are already provided in the control unit or at another storage location and only need to be selected appropriately. However, it can also be, for example, one or more geometry parameters under which a suitable algorithm is used which z. B. is implemented in the control unit, can generate a suitable control command set.

The control unit can in particular be set up for at least partially automated implementation of this method, in its specific variants mentioned hereinabove or below.

• - Bereitstellen mindestens eines Bildabstandsparameters, der für mindestens ein Bildelement des zu erzeugenden virtuellen Anzeigebilds einen geeigneten Bildabstand zum Benutzer charakterisiert;
• - Änderung des obigen bereitgestellten Steuerbefehlssatzes für den räumlichen Phasenmodulator abhängig von dem bereitgestellten mindestens einen Bildabstandsparameter so, dass das mindestens eine Bildelement des virtuellen Anzeigebilds in dem geeigneten Bildabstand zum Benutzer erzeugt wird; und
• - Betreiben der Steuereinheit gemäß dem so geänderten Steuerbefehlssatz.

In particular, the method can further comprise the following steps:

• Providing at least one image distance parameter which characterizes a suitable image distance to the user for at least one image element of the virtual display image to be generated;
• Changing the above provided control command set for the spatial phase modulator as a function of the provided at least one image distance parameter such that the at least one picture element of the virtual display image is generated at the appropriate image distance from the user; and
• - Operation of the control unit in accordance with the thus modified set of control commands.

In this variant, the freedom is also used to dynamically set an image distance of the HUD display image to the user by suitable control of the spatial phase modulator and to adapt it to the respective driving situation, for example. No negative effects on the image quality or the risk of reflections from the sun are to be expected.

If any dispersion effects in the spatial phase modulator, for example due to the PBOE / LC elements, have a negative effect on the image quality of the virtual display image, this can be counteracted by sequentially importing the basic colors into the waveguide and the optical function of the spatial phase modulator, z. B. the PBOE / LC matrix, via whose control adapts to the respective fed color.

• - das Projektionslicht von der Bilderzeugungseinheit in mehreren unterschiedlichen Farbvarianten, insbesondere in drei Grundfarben wie z. B. Rot/Grün/Blau, erzeugt und zeitlich sequentiell in den Wellenleiter eingespeist wird;
• - für jede dieser Farbvarianten ein jeweils unterschiedlicher Steuerbefehlssatz für den räumlichen Phasenmodulator bereitgestellt wird; und
• - die Steuereinheit synchron mit dem Einkoppeln der jeweiligen Farbvariante des Projektionslichts in den Wellenleiter gemäß dem für diese Farbvariante bereitgestellten Steuerbefehlssatz betrieben wird.

In particular, it can therefore be implemented in the operating method mentioned that

• - The projection light from the image generation unit in several different color variants, in particular in three basic colors such. B. red / green / blue, generated and sequentially fed into the waveguide in time;
• a different set of control commands for the spatial phase modulator is provided for each of these color variants; and
• the control unit is operated synchronously with the coupling of the respective color variant of the projection light into the waveguide according to the set of control commands provided for this color variant.

• - Bereitstellen eines Eye-Tracking-Signals, das eine Augenposition des Benutzers charakterisiert, beispielsweise durch das Empfangen eines Signals von einem im Kraftfahrzeug vorgesehenen Eye-Tracking-System;
• - Änderung des obigen bereitgestellten Steuerbefehlssatzes für den räumlichen Phasenmodulator abhängig von dem bereitgestellten Eye-Tracking-Signal, um damit eine von der tatsächlichen Position der Augen des Benutzers abhängige Phasenfront zu erzeugen; und
• - Betreiben der Steuereinheit gemäß dem so geänderten Steuerbefehlssatz.

As an alternative or in addition to the above variants, the method can further comprise the following steps:

• Provision of an eye tracking signal that characterizes an eye position of the user, for example by receiving a signal from an eye tracking system provided in the motor vehicle;
• Modification of the above provided control command set for the spatial phase modulator as a function of the provided eye tracking signal in order to generate a phase front that is dependent on the actual position of the eyes of the user; and
• - Operation of the control unit in accordance with the thus modified set of control commands.

With this variant of the method, a vehicle-specific calibration of each individual motor vehicle can be carried out depending on the user and the geometric tolerances of the windshield can be compensated.

• - eine Projektionseinheit der hierin dargelegten Art und
• - eine im Blickfeld eines Benutzers angeordnete Projektionsscheibe, die insbesondere als Teil einer Frontscheibe des Kraftfahrzeugs ausgebildet sein kann,
• - wobei die Projektionsscheibe benutzerseitig für das Projektionslichtstrahlenbündel reflektierend und rückseitig für das in Richtung des Benutzers einfallende Umgebungslicht zumindest teilweise transparent ist, und die Ausbildung und die gegenseitige Anordnung der Projektionseinheit und der Projektionsscheibe derart sind, dass das von der Projektionseinheit erzeugte Projektionslichtstrahlenbündel auf die Projektionsscheibe fällt und von dieser zum Benutzer reflektiert wird, wodurch das virtuelle Anzeigebild in seinem Blickfeld hinter der Projektionsscheibe erzeugt wird.

According to a further aspect, a field of view display device is provided, in particular for a motor vehicle, which comprises the following:

• - a projection unit of the type set out herein and
• - A projection screen arranged in the field of vision of a user, which can in particular be designed as part of a front screen of the motor vehicle
• - the projection screen being reflective on the user side for the projection light beam and at the rear at least partially transparent for the ambient light incident in the direction of the user, and the design and mutual arrangement of the projection unit and the projection screen are such that the projection light beam generated by the projection unit falls on the projection screen and is reflected by this to the user, whereby the virtual display image is generated in his field of view behind the projection screen.

• - eine zumindest abschnittsweise eine Krümmung aufweisende Frontscheibe, die einen Insassenraum des Kraftfahrzeugs in Fahrtrichtung nach vorn begrenzt und schützt, und
• - eine Blickfeldanzeigevorrichtung der hierin dargelegten Art, deren Projektionsscheibe als ein Abschnitt der Frontscheibe mit Krümmung ausgebildet ist.

According to a further aspect, a motor vehicle is provided, comprising:

• a windshield which has a curvature at least in sections and which delimits and protects a passenger compartment of the motor vehicle in the direction of travel, and
• a field of view display device of the type set out herein, the projection screen of which is designed as a section of the front screen with a curvature.

The motor vehicle can in particular have an instrument panel arranged in the front area of the passenger compartment below the windshield, and the projection unit, which can be made flat overall thanks to the flat waveguide, can extend in or on an upper side of the instrument panel, for example integrated therein or subsequently attached to it. In the first case, the waveguide surface with the spatial phase modulator extending over the surface of the decoupling element can be designed, for example, essentially flush with the top of the instrument panel.

Because the windshield compensation can be dynamically adjusted by the electrically controllable spatial phase modulator, the same projection unit or the same spatial phase modulator can be used for many or all of the different vehicle derivatives by only controlling the spatial phase modulator, i. H. adjusts the applied voltage pattern to the respective vehicle derivative. No hardware adaptation of the waveguide, the decoupling element or the element provided for the windscreen compensation, in this case the spatial phase modulator with the control unit, is necessary. This leads to a considerable cost reduction for such a system.

Figure list

• Figur eine schematische seitliche Querschnittsansicht einer Blickfeldanzeigevorrichtung der hierin dargelegten Art für ein Kraftfahrzeug.

The above aspects of the invention and its embodiments and specific configurations are explained in more detail below with reference to the example shown in the accompanying drawing. The drawing is purely schematic; in particular, it should not be read as being true to scale. It shows the only one

• FIG. 1 shows a schematic side cross-sectional view of a field of view display device of the type set forth herein for a motor vehicle.

Description of embodiments

All of the various embodiments, variants and specific design features of the projection unit according to the first aspect of the invention, its operating method, the field of view display device and the motor vehicle according to the further aspect mentioned above in the description and the following claims can be implemented in the example shown in the figure . They are therefore not all repeated again below. The same applies accordingly to the definitions of terms and effects already given above in relation to individual features that are shown in the figure.

The single FIGURE shows a field of view display device in a highly simplified schematic vertical cross-sectional view 1 of the type set forth herein in a motor vehicle 2 , in particular a head-up display (HUD). The field of view display device 1 comprises a projection unit 3 of the type set forth herein, for example in a top of an instrument panel (not shown) of the motor vehicle 2 can be formed or subsequently mounted on it.

Above and opposite the projection unit 3 extends in the field of view of a user 4th , for example the driver of the motor vehicle 2 , a projection screen 5 in this example as a section of a windshield 6th of the motor vehicle 2 is trained. The field of view display device 1 is designed to bring a virtual display image (not shown) into the user's field of vision 6th to be displayed.

The projection unit provides this 3 a projection light beam in a suitable manner during operation L. with a display content in the direction of a user-side reflective surface 7th the projection screen 5 from which it is to the user 4th is reflected. The projection screen 5 is up to the user 4th facing away from the rear 8th for that towards the user 4th incident ambient light is at least partially transparent, so that the virtual display image of the user 4th observed the real environment in front of the motor vehicle 2 is superimposed.

The invention is in no way intended for this application in a motor vehicle 2 limited. Rather, the field of view display device 1 also a different type of curved projection screen 5 with the above properties, such as: B. another already existing protective disc or a specially provided combiner disc.

The projection unit 3 includes a planar optical waveguide 9 for the projection light beam L. , for example in the form of a glass plate. The waveguide 9 can in particular be used in a manner known per se as a pupil expander for the two-dimensional expansion of an eyebox 10 in a cross-sectional plane of the projection light beam L. be trained. There is the eyebox 10 defined as the area of space from which the user 4th that from the field of view display device 1 generated virtual display image can see.

In a flat surface 11 of the waveguide 9 that the projection screen 5 is facing, a decoupling element (not shown separately) for decoupling the projection light beam is over a large area L. to the projection screen 5 trained towards. The projection unit also includes 3 an image generation unit indicated purely schematically and enlarged in the figure 12th that are used to generate and couple the projection light beam L. with the display content in the waveguide 9 is formed via the coupling element (not shown separately). The imaging unit 12th can for example be designed as a projector with a projection light source and an imaging display. The coupling-in element and / or the coupling-out element of the optical waveguide 9 can be designed in any manner suitable for the functionality described, in particular known per se, for example as an optical grating or as a holographic optical element.

The projection unit 3 also has a spatial light modulator (SLM) in the form of an electrically controllable spatial phase modulator 14th on. For controlling the spatial phase modulator 14th includes the projection unit 3 also a control unit 15th which are used to bring about a phase front change of the projection light beam L. is set up that has an undesirable influence of a projection screen curvature in the subsequent reflection of the projection light beam L. on the projection screen 5 compensated.

The curvature of the projection screen means the curvature of the reflection surface 7th the projection screen 5 for reflecting the on it from the projection unit 3 projected projection light beam L. is provided.

In this example the spatial phase modulator is 14th designed as an LC matrix (liquid crystal, liquid crystal) or PBOE matrix (Pancharatnam-Berry-Optical-Element) that can be controlled pixel by pixel by applying electrical voltage. As shown in the figure, such a planar phase modulation pixel matrix is transverse to a direction of propagation of the projection light beam L. arranged and can therefore in particular cover its entire cross-section relevant for the display image generation.

An LC or PBOE matrix is an arrangement of liquid crystals that are located between two transparent electrodes. In the PBOE in particular, the liquid crystals have a helical structure that affects the phase of the projection light transmitted through the PBOE. This effect on the phase of the projection light can be controlled by the electrical voltage applied between the two electrodes. If the electrodes are subdivided into a pixel structure, for example analogous to that of a TFT display, the phase of the transmitted projection light can be checked pixel by pixel, and thus locally at different positions in the beam cross-section. With such an arrangement, it is therefore possible that the Phase front of the from the waveguide 9 Adjust the coupled projection light so that the curvature of the windshield 6th is compensated.

In this example the spatial phase modulator is 14th in the beam path of the extracted projection light beam L. between the decoupling element and the projection screen 5 arranged, covering the decoupling element over a large area. The spatial phase modulator 14th can in particular directly on the decoupling element or with an optional polarization element 16 in the form of a λ / 4 retarder film in between.

The polarization element 16 can be provided for converting linearly polarized projection light into circularly polarized projection light, in particular when using PBOE, since the effect of the PBOE is limited to circularly polarized light. This measure is superfluous if the waveguide 9 already circularly polarized projection light decouples. In the above-mentioned alternative approach with classic liquid crystals (LC), the projection light can also be linearly polarized.

The control unit 15th can in particular for at least partially automated implementation of a method of the type set out herein for operating the projection unit 3 be set up.

In this method, in particular at least one projection screen parameter, which is the curvature of the reflection surface 7th characterized, provided and dependent thereon a control command set for the spatial phase modulator 14th are provided that a corresponding phase front change of the projection light beam L. causes undesirable effects of the projection screen curvature when it is reflected on the curved projection screen 5 to compensate. With the set of control commands provided in this way, the control unit can 15th when operating the field of view display device 1 operate.

The projection screen parameter mentioned can be a mere type designation if control command sets for a set of different predetermined projection screen types are in the control unit 15th or are already provided in another storage location and only need to be selected appropriately. However, it can also be, for example, one or more geometry parameters under which a suitable algorithm is used which z. B. in the control unit 15th is implemented, can generate a suitable set of control commands.

In this way the windshield compensation is done by the spatial phase modulator 14th dynamically adjustable. Therefore, the same projection unit 3 or the same spatial phase modulator 14th can be used for all vehicle derivatives: you only need to control the spatial phase modulator 14th , ie adapt the applied voltage pattern to the respective vehicle derivative. There is no hardware adaptation to any components of the projection unit 3 necessary, which leads to a considerable reduction in costs.

In addition, the freedom can also be used through suitable control of the spatial phase modulator 14th an image distance of the virtual display image to the user 6th to be set dynamically and, for example, to adapt to the respective driving situation.

Should there be any dispersion effects in the spatial phase modulator 14th , for example due to the PBOE / LC elements, have a negative effect on the image quality of the virtual display image, this can be counteracted by sequentially adding the primary colors to the waveguide 9 and adapts the optical function of the PBOE / LC matrix to the color fed in by controlling it.

List of reference symbols

1

Field of view display device

2

Motor vehicle

3

Projection unit

4th

user

5

Projection screen

6th

Windshield

7th

Reflection surface of the projection screen

8th

Back of the projection screen

9

optical waveguide

10

Eyebox

11

flat surface of the waveguide

12th

Imaging unit

14th

electrically controllable spatial phase modulator

15th

Control unit

16

Polarizing element

L.

Projection light beam

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2018/231784 A1 [0007]
• EP 2972595 B1 [0008]

Claims (10)

Projection unit (3) for a field of view display device (1), in particular for a motor vehicle (2), which is used to generate and project a projection light beam (L) with a display content onto a projection screen (5) that is reflective on the user side and is transparent on the rear side, in particular a front screen (6) of the motor vehicle (2), is designed to generate a virtual display image behind it, comprising: - A flat, in particular planar, optical waveguide (9), in whose flat surface (11) a decoupling element for decoupling the projection light beam (L) guided in the waveguide (9) towards the projection screen (5) is formed, as well as an image generation unit (12) which is designed to generate the projection light beam (L) to be coupled into the waveguide (9) with the display content; - An electrically controllable spatial phase modulator (14) arranged in the beam path of the projection light beam (L) to be coupled in or coupled out; and - A control unit (15) which is set up to control the spatial phase modulator (14) to bring about such a phase front change in the projection light beam (L) that compensates for an undesired influence of a projection screen curvature during its subsequent reflection on the projection screen (5). Projection unit (3) Claim 1 , wherein the spatial phase modulator (14) is a planar phase modulation pixel matrix arranged transversely to a direction of propagation of the projection light beam (L) and composed of phase modulation elements that can be electrically controlled independently of one another, in particular as a liquid crystal matrix or PBOE matrix that can be controlled pixel by pixel by applying electrical voltage, is trained. Projection unit (3) Claim 1 or 2 , wherein the spatial phase modulator (14) is arranged in the beam path of the coupled-out projection light beam (L) between the coupling-out element and the projection screen (5), in particular covering the coupling-out element over a large area. Projection unit (3) according to one of the preceding claims, wherein the spatial phase modulator (14) and the control unit (15) to a dynamic and / or continuous, in particular in an interval of 0 to 2π, phase front change of the projection light beam (L), each locally within its cross-section, designed and set up Projection unit (3) according to one of the preceding claims, further comprising a polarization element (16) for generating a circular polarization of the projection light, in particular a λ / 4 retarder film or λ / 4 retarder plate, in the beam path of the projection light beam (L) in front of the spatial phase modulator (14). Method for operating a projection unit (3) according to one of the preceding claims, comprising the steps: - providing at least one projection screen parameter which characterizes the curvature of a projection screen surface (7) which is provided for reflecting the projection light beam (L) projected thereon by the projection unit (3); - Providing a set of control commands for the spatial phase modulator (14) as a function of the provided at least one projection screen parameter, which causes a corresponding phase front change of the projection light beam (L) in order to compensate for an undesired influence of the projection screen curvature when it is reflected on the projection screen (5); and - Operation of the control unit (15) in accordance with the set of control commands provided. Procedure according to Claim 6 , further comprising the steps of: - providing at least one image distance parameter which characterizes a suitable image distance to the user (4) for at least one image element of the virtual display image to be generated; - changing the control command set for the spatial phase modulator (14) depending on the provided at least one image distance parameter so that the at least one picture element of the virtual display image is generated at the appropriate image distance from the user (4); and - operating the control unit (14) in accordance with the changed control command set. Procedure according to Claim 6 or 7th wherein - the projection light is generated by the image generation unit (12) in several different color variants, in particular in three basic colors such as red / green / blue, and is coupled into the waveguide (9) sequentially over time; - a respectively different set of control commands for the spatial phase modulator (14) is provided for each of these color variants; and - the control unit (15) is operated synchronously with the coupling of the respective color variant of the projection light into the waveguide (9) according to the set of control commands provided for this color variant. Field of view display device (1), in particular for a motor vehicle (2), comprising: a projection unit (3) according to one of the Claims 1 to 5 and - a projection screen (5) arranged in the field of vision of a user (4), which is designed in particular as part of a front screen (6) of the motor vehicle (2), - the projection screen (5) being reflective on the user side for the projection light beam (L) and on the rear side is at least partially transparent to the ambient light incident in the direction of the user (4), and the design and mutual arrangement of the projection unit (3) and the projection screen (5) are such that the projection light beam (L) generated by the projection unit (3) falls on the projection screen (5) and is reflected by this to the user (4), whereby the virtual display image is generated in his field of view behind the projection screen (5). Motor vehicle (2), comprising: - a windshield (6) having a curvature at least in sections and - a field of view display device (1) after Claim 9 whose projection screen (5) is designed as a section of the front screen (6) with a curvature.

Images