Head-up display of an aircraft

Abstract

A head-up display (10) of an aircraft is disclosed, wherein the head-up display (10) comprises an eyebox (1), a projection unit (8) which includes an imager (5), and a combiner (2) arranged in the beam path (11) between the imager (5) and the eyebox (1). The combiner (2) has a front side (16) and a rear side (17), and the beam path (11) runs from the imager (5) to the eyebox (1) through the rear side (17) and the front side (16) of the combiner (2).

Description

The present invention relates to a head-up display, in particular a head-up display of an aircraft, for example an aircraft.Head-up displays (HUD) have meanwhile been used in a wide variety of applications, including in connection with viewing windows of aircraft. Head-up displays are used in aviation for projecting image data into the field of vision of the pilot* interior. In this case, the light waves for generating a virtual image are guided from an imager or projector via a projection surface to an eyebox.A head-up display usually comprises an imaging unit (PGU) or a projector, also called an imager, a projection surface, an eyebox and a virtual image plane. An image is generated by means of the image generator or the projector. The image is projected onto the projection surface and projected from the projection surface into the eyebox. The eyebox is a spatial region in which the projected image can be perceived as a virtual image by a user or observer. The virtual image plane, i.e. the plane on which the virtual image is generated, is arranged on or behind the projection surface.If a user looks through the projection surface of a head-up display, he sees superimposed on his image of the real world ("real image") an "virtual image" which is coupled in or reflected in. This allows the flight information displayed in the virtual image and the real world to be viewed simultaneously without the pilot / pilot* having to lower the gaze in order to look at a display device in the instrument panel. Projected information on the attitude and flight direction is displayed in a manner conforming (i.e. correctly scaled and aligned) to the real world.This superposition is achieved by a beam combiner, also called combiner, which is transparent to the ambient light on the one hand and also directs a beam generated by an external imager into an eyebox in which the eye of a user can be located. This beam of rays is perceived by the eye as a virtual image.In connection with aircraft, there is a particular challenge in integrating the components of the HUD into the available installation space of the cockpit without restricting or obstructing the pilot*in / s. One possibility for this is the integration of HUD components into a predefined display and instrument panel of the aircraft. It is to be ensured that the unimpeded view of the pilot / pilot*in on the display and instrument panel is ensured.Against this background, it is an object of the present invention to provide a head-up display, in particular of a vehicle, e.g. of an aircraft. This object is achieved by a head-up display of an aircraft according to claim 1. The dependent claims contain further advantageous embodiments of the invention.The head-up display according to the invention, in particular of an aircraft, for example an aircraft or helicopter, comprises an eyebox, a projection unit which comprises an imager, and a combiner arranged in the beam path between the imager and the eyebox. An imager is understood to mean a projector or an image-forming device. A combiner is understood to mean a beam combiner described at the beginning. The head-up display according to the invention is designed for aviation applications, in particular for arrangement in the cockpit of an aircraft, e.g. an aircraft or helicopter. The head-up display according to the invention can also be designed for other applications.The combiner has a front side, e.g. a front side arranged on the eyebox side, and a rear side, e.g. a rear side arranged on the imager side. The beam path extends from the imager to the eyebox through the back and front of the combiner. In other words, the combiner is configured to be transmissive overall for light radiated from the imager to the eyebox. In addition, the combiner is preferably also transmissive or at least predominantly transmissive for ambient light.The HUD according to the invention has the advantage that it can be integrated into a display and / or instrument panel by the transmissive projection through the combiner into the eyebox. This allows the required installation space to be reduced and a spatially favorable arrangement in otherwise hardly used regions of the fitting, for example in lateral or front regions, is possible.The distance between the center of the eyebox and the combiner is preferably between 150 mm and 450 mm. This is the preferred and most favorable area for aeronautical applications.Furthermore, the head-up display can be designed for projecting a virtual image starting from the center of the eyebox into a distance of at least 10 m. It is thus projected into a virtual image plane at a distance from the center of the eyebox of 10 m or more. Preferably, projection is to infinity with nearly parallel beams. This enables the projected image to be perceived in a relaxed state for the eyes.The head-up display can have a field of view (FOV) of at least 20 degrees in the horizontal direction, i.e. an azimuthal solid angle range of 20 degrees with respect to the eyebox, and / or at least 15 degrees in the vertical direction, i.e. a meridional solid angle range of 15 degrees with respect to the eyebox.As already mentioned above, the combiner is preferably designed to be transmissive in the viewing direction or see-through direction or a central see-through axis starting from the eyebox. It is therefore arranged in the viewing direction with respect to the eyebox and enables unimpeded view of the environment.The head-up display can be designed for projecting, for example the exclusive projection, single-color or monochrome light into the eyebox. For aviation applications, it is advantageous if the head-up display is designed for projecting only monochrome, preferably green light into the eyebox.For example, the combiner can have an optical effect, in particular a diffractive effect and / or a refractive power, in a spectral range with a full width at half maximum of 50 nm, in particular at most 30 nm, preferably at most 15 nm, e.g. at most 2 nm. The combiner is preferably designed to be diffractive. The spectral range is preferably in the green spectral range, i.e. in the range between 500 and 565 nm. In order to ensure optimum unimpeded see-through by the combiner, the combiner can have optical effect exclusively in a green spectral range, in particular a diffractive effect and / or a refractive power. Outside this spectral range, the combiner allows an undisturbed view of the outside world or environment.The projection unit can be designed to be integratable into a display or instrument panel of an aircraft, for example an aircraft. Additionally or alternatively, the projection unit can have an optical axis or an emission direction from the imager to a projector cover, that is to say an optical axis within the projection unit, which is arranged at an angle between 0 degrees and 30 degrees with respect to a viewing direction, in particular a central viewing axis or a straight-line orientation, for example with respect to the aircraft, from the eyebox or with respect to a direction running perpendicular to a central plane of the eyebox. In other words, the projection unit in this variant is configured to project horizontally with respect to an instrument panel. This enables a favorable arrangement of the projection unit in a display or instrument panel from the standpoint of installation space.In a further variant, the projection unit comprises a projector cover which is arranged in the beam path between the imager and the combiner and which has an optical effect. The projector cover is preferably designed as a transmissive cover element. It has, for example, a front side and a rear side, wherein the beam path runs through both. The optical effect can be refractive power or another imaging or beam-shaping or image-shaping or wavefront-shaping effect. The projector cover may be designed to be diffractive in order to achieve the optical effect. A refractive configuration is likewise possible.In addition, the projection unit can comprise an optical arrangement, such as an optics or an optical system, which is arranged in the beam path between the imager and the combiner, in particular between the imager and the projector cover. The optical arrangement can have an optical effect. The optical effect can be, for example, refractive power or another imaging or beam-forming or image-forming or wavefront-forming effect. This enables the light beam to be directed in the desired direction and aberrations to be corrected. The optical arrangement can comprise reflective, refractive and / or diffractive optical elements.The combiner and / or the projector cover can be designed for beam deflection in the horizontal and / or vertical direction, e.g. with respect to the eyebox or the viewing direction. As a result, the position of the individual components of the HUD can be very easily adapted to the available installation space.Furthermore, the eyebox can have a longitudinal central plane. The longitudinal middle plane is understood to mean the middle plane extending perpendicular to the viewing direction or a central viewing axis, i.e. a plane bisecting the eyebox in the longitudinal direction. An image of the longitudinal center plane may be projected onto the projector cover. This projection can have an imaging scale of between 2:1 and 1:3.Preferably, the combiner and / or the projector cover comprise a holographic optical arrangement. The holographic optical arrangement can comprise at least two holographic elements arranged directly one behind the other in the beam path, wherein a first holographic element is assigned to a second holographic element for reflection. In other words, no further optical element or component is arranged between the at least two holographic elements. For example, the first holographic element and the second holographic element can have a distance of a maximum of 15 mm from one another.The holographic elements of the holographic optical arrangement may be enclosed between two transparent supports or may be applied to the opposite outer surfaces of a transparent support. The supports may preferably consist of glass or comprise glass.The combiner and / or the projector cover can be provided on the outer surfaces with an optically effective coating, for example a reflection-suppression layer.The at least two holographic elements are designed reflective, for example, for at least one defined wavelength and a defined angle of incidence range. Light waves of the at least one defined wavelength and of the defined angle of incidence range are thus efficiently diffracted. Preferably, the holographic elements are in the form of holographic elements.The rest of the transmission is designed, in other words transmissive for wavelengths which do not correspond to the at least one defined wavelength and have an angle of incidence outside the defined angle of incidence range.Preferably, a first holographic element comprises at least one hologram which is assigned to a hologram of a second holographic element for reflection. In other words, the at least two holographic elements are designed such that light reflected by a first holographic element of at least one wavelength and at least one angle of incidence is reflected by the second holographic element.The use of reflection holograms has the advantage that the intrinsic properties of reflection holograms can be made useful. These have efficiency curves which fundamentally deviate from transmission holograms, wherein the efficiency curves of reflection holograms offer a wavelength selectivity, as a result of which, inter alia, the formation of double images can be prevented. Due to the otherwise transmissive configuration and the use of reflection holograms, filter effects between the holograms are reduced or avoided. The at least two holographic elements are preferably arranged directly one behind the other in the beam path in such a way that light entering the wavefront manipulator is reflected by a first of the holographic elements and the light reflected by the first of the holographic elements is reflected by a second of the holographic elements.The at least one holographic arrangement is preferably designed in the present case for the diffraction of light of only one wavelength or of a narrow wavelength range.The use of two holographic elements arranged directly one behind the other and configured to be at least partially reflective has the advantage that, in particular in conjunction with a head-up display, the imaging quality can be improved considerably by the individual configuration of the holographic elements. For this purpose, the holographic elements require almost no installation space, so that a high imaging quality can be achieved with only a small available installation space. The holographic arrangement achieves in particular a high refractive power, comparable to the refractive power as is achieved, for example, by a transmissive optical component. Due to the high refractive power, the light can be deflected at a large angle, e.g. horizontally and / or vertically, which in turn opens up a variety of arrangement options.Compared to transmission holograms, reflective holograms offer a broader angular spectrum for a defined wavelength with a high efficiency and a higher wavelength selectivity. The holographic arrangement thus enables a large field of view (FOV) with simultaneously high efficiency and is therefore suitable for applications with a large field of view and large numerical aperture.A further advantage achieved by the holographic arrangement is that, owing to the high diffraction angle of the holographic arrangement, the proportion of the light from unused diffraction orders which is reflected into the eyebox is reduced.The holographic elements can be designed as volume holograms or relief holograms.In a preferred variant, the first holographic element and / or the second holographic element are embodied as volume holograms and have a refractive index modulation of at least 0.02, in particular at least 0.03 or 0.04, for example more than 0.05. In this way, a short distance, e.g. a distance between 150 mm and 450 mm, from the combiner to the eyebox and / or a large sickle (FOV) can be realized.In a preferred variant, the first holographic element and / or the second holographic element are designed as a free-form hologram. The respective holographic element can thus contribute to an improvement in the resolution by a corresponding configuration of the free-form phase surface and allows a targeted correction of imaging errors. In this way, therefore, it is also significantly contributed to an improvement in the imaging quality of a head-up display of compact design.In a hologram, the local beam deflection is given by the spatial line density distribution. The line density distribution of the hologram results from the gradient of the local phase of the phase surface.A free-form phase surface is to be understood in the broader sense as a non-trivial continuously differentiable function which can be represented in particular by means of a set of orthogonal basic functions or regionally defined functions, in particular twice continuously differentiable regionally defined functions. Examples of suitable orthogonal basis functions are polynomials, Zernike polynomials or Czebyschow polynomials. Examples of suitable regionally defined functions are piecewise polynomial functions (in particular polynomial splines, such as bicube splines, higher-degree splines of fourth degree or higher, or polynomial non-uniform rational B splines (NURBS)). A free-form phase surface need in particular not have any axial symmetry and no point symmetry.A free form hologram has been exposed to free form wavefronts. It produces a defined free-form wavefront upon irradiation with a wavefront. This allows a manipulation of the wavefront with a high number of degrees of freedom to be realized. This is advantageous for correcting aberrations and for guiding and shaping beams. The holographic arrangement, in particular at least one of the holographic elements, can be designed, for example, such that a free-form wave front is transformed into another free-form wave front.At least one hologram can be recorded or exposed with waves which have at least one free-form hologram. This enables various aberrations to be corrected and the image quality to be improved. Because, in such a configuration, light having any desired wavefront, as can also be generated, for example, by means of free-form surfaces, it is possible to reduce the number of components having free-form surfaces, such as lenses and / or mirrors. Plane waves and / or spherical waves can also be used for the exposure of the holograms. By using wavefronts of the simplest possible design for the exposure of the holograms, the production costs can be reduced.In a further variant, the imager can comprise a diffuser with a location-dependent scattering function. The diffuser can be arranged close to the image plane of the image generator, e.g. at a distance of a maximum of 10 mm. The diffuser provides a location-dependent illumination cone. The extent of the illumination cone is preferably designed such that the area illuminated by the HUD outside the volume of the eyebox is minimized.In a further variant, the combiner and the projection unit can be arranged offset with respect to one another radially, that is to say upwards or downwards and / or to the left or to the right, with respect to a viewing direction, for example a straight alignment with respect to the aircraft, or a central viewing axis, starting from the eyebox or with respect to a direction running perpendicular to a central plane of the eyebox. In other words, they can be arranged horizontally and / or vertically offset with respect to one another. These variants also make it possible to position the projection unit flexibly in the cockpit of an aircraft.In summary, the HUD according to the invention offers a system that is powerful and optimally integratable for aviation applications.The invention is explained in more detail below on the basis of exemplary embodiments with reference to the appended figures. Although the invention is illustrated and described in more detail by the preferred exemplary embodiments, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.The figures are not necessarily drawn to detail and scale, and may be exaggerated or minimized to provide a better overview. Therefore, functional details disclosed herein are not to be interpreted as limiting, but merely as an illustrative basis that will provide guidance to those skilled in the art to variously employ the present invention.As used herein, the term "and / or," when used in a series of two or more elements, means that each of the listed elements may be used alone, or any combination of two or more of the listed elements may be used. For example, when describing a composition containing components A, B, and / or C, the composition may contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination. FIG. 1 schematically shows the beam path of a head-up display according to the invention of an aircraft in a side view. FIG. 2 schematically shows the beam path of the head-up display shown in FIG. 1 in a plan view. FIG. 3 schematically shows the beam path through a holographic arrangement of a combiner or a projector cover.FIGS. 1 and 2 schematically show the beam path 11 of a head-up display 10 according to the invention of an aircraft. The beam path is shown in a side view in FIG. 1 and in a top view in FIG. 2.The head-up display 10 comprises a projection unit 8, a combiner 2 and an eyebox 1. the projection unit 8 comprises an imager 5, a projector cover 3 and an optical arrangement 4, for example an optical system, arranged in the beam path 11 between the imager 5 and the projector cover 3. The optical arrangement 4 can consist of conventional refractive or reflective optical elements or comprise such elements. However, the optical arrangement 4 can also contain diffractive optical elements. Furthermore, the imager 5 can comprise a diffuser, not explicitly shown, which is preferably arranged in the vicinity of the image plane of the imager 5 and has a location-dependent scattering function. The diffuser can thus provide a location-dependent illumination cone which limits the illuminated region to the eyebox 1.Combiner 2 has a front side 16 and a back side 17. The projector cover 3 has a front side 18 and a rear side 19. Both the projector cover 3 and the combiner 2 are configured to be transmissive overall. This means that light enters the respective component 2 or 3 through the rear side 17 or 19 and leaves the latter through the respective front side 16 or 18.Light emitted by the projection unit 8 via the projector cover 3 is guided to the combiner 2 and deflected by the combiner 2 in the direction of the eyebox 1. If a user, preferably a / e pilot*in, looks through combiner 2 starting from eyebox 1 in viewing direction 9, an image projected by projection unit 8 is perceptible to the user as a virtual image, for example at infinity. The field of view (FOV) provided by the head-up display 10 is identified by arrows with the reference numerals 6 and 7. In the present case, a field of view 7 of at least 20° is achieved in the horizontal direction and a field of view 6 of at least 15° is achieved in the vertical direction. The distance between the center eyebox 1 and combiner 2 is between 150 and 450 mm.The combiner 2 is configured transmissive overall and has an optical effect, in particular refractive power, in a defined spectral range, preferably in the green spectral range, with a half-value width of at most 50 nm, in particular at most 30 nm, preferably at most 15 nm, e.g. at most 2 nm.The projection unit 8 shown can be arranged integrated into an instrument panel of an aircraft, for example an aircraft. The combiner 2 can be arranged suspended from a ceiling of a cockpit of the aircraft. The combiner 2 can have a rectangular base surface, for example with beveled or rounded corners.In the variant shown, the projection unit 8 is designed to project predominantly horizontally. This means that an optical axis 12 of the projector unit 8, i.e. an optical axis 12 of the region of the beam path 11 between the imager 5 and the projector cover 3, extends substantially in the horizontal direction. The optical axis 12 thus encloses an angle 14 of a maximum of 30°, preferably less than 20°, with a direction 13 running perpendicular to a central plane or central plane of the eyebox 1.As shown in FIGS. 1 and 2, the combiner 2 and the projector cover 3 are used to effect beam deflection in both the horizontal and vertical directions. For this purpose, the combiner 2 and / or the projector cover 3 can comprise a holographic optical arrangement 15, which are preferably designed as a pair of reflecting holograms 21, 22 in a Z arrangement or as a stack or arranged directly one on top of the other. The beam path through such a holographic optical arrangement is shown schematically in FIG. 3.The holographic arrangement 15 shown by way of example in FIG. 3 comprises a first holographic element 21 and a second holographic element 22, which are arranged directly one behind the other, preferably lying against one another, in the beam path. For the purpose of illustration, a distance 23 between the two holographic elements 21 and 22 is shown in FIG. 3, but this should actually be less than 15 mm, preferably less than 1 mm.Light beams 11 irradiated through the rear side 17, 19 pass first through the first holographic element 21, are subsequently reflected by the second holographic element 22 and irradiated back to the first holographic element 21. The light reflected back from the second holographic element 22 in the direction of the first holographic element 21 is reflected by the first holographic element 21 and then passes the second holographic element 22 through the front side 16, 18.The holographic elements 21 and 22 can be designed as volume holograms or relief holograms. In an embodiment as a volume hologram, they can have a refractive index modulation of at least 0.02, preferably 0.04 or greater. The holographic elements 21 and 22 can have free-form holograms and can be designed in particular for correcting imaging errors and / or for beam guidance or beam deflection.List of reference numbers:1 Eyebox 2 combiner 3 projector cover 4 optical arrangement 5 imager 6 vertical field of view 7 horizontal field of view 8 projection unit 9 viewing direction 10 head-up display 11 beam path 12 optical axis 13 direction perpendicular to the central plane of eyebox 14 angle 15 holographic arrangement 16 front side 17 rear side 18 front side 19 rear side 21 first holographic element 22 second holographic element 23 distance

Claims

A head-up display (10) of an aircraft, wherein the head-up display (10) comprises an eyebox (1), a projection unit (8) which comprises an imager (5), and a combiner (2) arranged in the beam path (11) between the imager (5) and the eyebox (1), characterized in that the combiner (2) has a front side (16) and a rear side (17), and the beam path (11) from the imager (5) to the eyebox (1) extends through the rear side (17) and the front side (16) of the combiner (2).Head-up display (10) according to Claim 1, characterized in that the distance between the centre of the eyebox (1) and the combiner (2) is between 150 mm and 450 mm.Head-up display (10) according to Claim 1 or 2, characterized in that the head-up display (10) is designed to project a virtual image starting from the eyebox (1) at a distance of more than 10 m.Head-up display (10) according to one of Claims 1 to 3, characterized in that the head-up display (10) has a field of view of at least 20 degrees in the horizontal direction (7) and / or at least 15 degrees in the vertical direction (6).Head-up display (10) according to one of Claims 1 to 4, characterized in that the combiner (2) is designed to be transmissive in the viewing direction (9) proceeding from the eyebox (1).Head-up display (10) according to one of Claims 1 to 5, characterized in that the head-up display (10) is designed for projecting monochrome light into the eyebox (1).Head-up display (10) according to one of Claims 1 to 6, characterized in that the combiner (2) has an optical effect in a spectral range having a full width at half maximum of 50 nm.Head-up display (10) according to one of Claims 1 to 7, characterized in that the projection unit (8) can be integrated into an instrument panel of an aircraft and / or the projection unit (8) has an optical axis (12) within the projection unit (8), which is arranged at an angle (14) between 0 degrees and 30 degrees with respect to a viewing direction (9) from the eyebox (1) or with respect to a direction (13) running perpendicular to a central plane of the eyebox (1).Head-up display (10) according to one of Claims 1 to 8, characterized in that the projection unit (8) comprises a projector cover (3) which is arranged in the beam path (11) between the imager (5) and the combiner (2) and which has an optical effect.Head-up display (10) according to one of Claims 1 to 9, characterized in that the projection unit (8) comprises an optical arrangement (4) which is arranged in the beam path (11) between the imager (5) and the combiner (2).Head-up display (10) according to one of Claims 1 to 10, characterized in that the combiner (2) and / or the projector cover (3) comprises a holographic optical arrangement (15) which comprises at least two holographic elements (21, 22) arranged directly one behind the other in the beam path (11), wherein a first holographic element (21) is assigned to a second holographic element (22) for reflection.Head-up display (10) according to Claim 11, characterized in that the first holographic element (21) and / or the second holographic element (22) are embodied as a volume hologram and have a refractive index modulation of at least 0.02.Head-up display (10) according to Claim 11 or 12, characterized in that the first holographic element (21) and / or the second holographic element (22) are designed as a free-form hologram.Head-up display (10) according to one of Claims 1 to 13, characterized in that the combiner (2) and / or the projector cover (3) are designed for beam deflection in the horizontal (7) and / or vertical (6) direction, and / or the eyebox (1) has a central plane and an image of the central plane is projected onto the projector cover (3).Head-up display (10) according to one of Claims 1 to 14, characterized in that the imager (5) comprises a diffuser having a location-dependent scattering function.

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