WO2004090607A1

WO2004090607A1 - Head-up display with superposition of images

Info

Publication number: WO2004090607A1
Application number: PCT/EP2004/002715
Authority: WO
Inventors: Alexander Pesch; Reinhard Steiner; Robert Brunner
Original assignee: Carl Zeiss Jena Gmbh
Priority date: 2003-04-10
Filing date: 2004-03-16
Publication date: 2004-10-21
Also published as: DE10316518A1

Abstract

The invention relates to an image generating device for a user, comprising an image generating unit (1) for generating an image, and projection optics (2) which project the image so that it can be observed by the user. The projection optics (2) contain a diffractive optics unit (5) with a transmission grating that transmits the light, which emanates from the image generating unit and which serves to generate images, and, due to diffraction, redirects this light to the eye (A) of the user. The diffractive optics unit (5) transmits ambient light whereby enabling an augmented representation.

Description

HEAD UP DISPLAY WITH IMAGE OVERLAY

The present invention relates to an image generation device for an augmented representation (that is, a superimposition of a generated image with the perceptible environment for a user).

In the case of image generation devices for an augmented representation, the generated image has to be brought into overlay for a user with the perceptible environment. Such image generation devices are, for example, HMD devices (Head Mounted Display Device). For the necessary overlay, the image generated by the H D device is often reflected into the user's field of vision by reflection on glass plates or beam splitter cubes. Partial mirroring is necessary for this, but this disadvantageously weakens the light to be transmitted from the surroundings.

Proceeding from this, it is an object of the invention to provide an image generation device for an augmented display in which the light from the surroundings is attenuated only as little as possible.

According to the invention, the object is achieved by an image generation device which comprises an image generation unit for generating an image and an imaging optics which images the image in such a way that it can be perceived by a user, the imaging optics containing a diffractive optics unit with a transmission grating upstream of the user's eye , which transmits the light for image generation that comes from the image generation unit and is deflected due to diffraction towards the eye, the diffractive optical unit additionally transmitting ambient light, so that an augmented display is possible.

By using the transmission grating for beam deflection, a very large deflection angle with very small component dimensions in the direction of the deflected light is possible. This can provide a very compact imaging device become. If the image-forming device is designed, for example, as a pair of glasses or a helmet, as an HMD device, the image-forming unit can be arranged to the side or above the head of the viewer, since even at an angle of incidence of up to 80 ° onto the transmission grille (i.e. almost perpendicular to the viewer's viewing direction) desired redirection towards the eye of the beholder can be realized. Another advantage of this large angle of incidence or the flat radiation is that an extraordinarily high image magnification can be realized without distortion.

The use of a transmission grating as a deflection unit leads to an image-forming device with improved optical properties, since transmission grids as a rule have higher diffraction efficiencies than with reflection gratings under the condition of the augmented display (since, for example, reflection mirrors can dispense with necessary partial reflections) and the absorption of the overall system is lower.

The transmission grating can in particular be designed such that a non-zero diffraction order (in particular the first or second diffraction order) is used for beam deflection of the light for image generation and the zero diffraction order for the transmission of the ambient light. This leads to the advantage that the non-zero order diffraction efficiency can be optimized for the imaging light, while the zero order diffraction can be optimized for the transmission of the ambient light that is incident substantially perpendicular to the transmission grating. Such optimized grids can be calculated by means of computer-implementable optimization processes and then can be produced, for example, holographically or by means of other microstructuring processes known from semiconductor production.

In particular, the angle of incidence of the light directed onto the transmission grating (or the diffractive optical element) for image generation can be greater than 45 °, preferably greater than 70 °. A device with an angle of incidence of 80 ° was realized. However, it is entirely possible to achieve even larger angles of incidence with optimized grids. Due to this large angle of incidence, the light for image generation can strike the diffractive optical element almost perpendicular to the viewing direction of the viewer, as a result of which the image generation device can be made very compact overall. At the same time, gratings (here in particular the transmission grating) with high diffraction angles (correspondingly high spatial frequencies) hardly allow the occurrence of interference spectra that can arise from other light sources in the field of view of the observation. The transmission grating can in particular be designed as a line grating. Such a line grating can now be easily manufactured with the required accuracy, so that the image forming device according to the invention can be easily implemented.

In particular, the line grating can only be used for beam deflection. In this case, the focusing (imaging) effect of the imaging optics is realized by further refractive or diffractive elements. By separating the deflection effect on the one hand and the focusing effect on the other hand, the diffractive optical unit can be optimized particularly easily for the specific application.

Of course, it is also possible for the line grating to serve for beam deflection and at the same time as an imaging (focusing) element. This makes it possible to implement extremely compact imaging optics, as a result of which the imaging device as a whole can be made small and light.

It is particularly advantageous if its lattice constant (or the furrow width) is varied for the imaging effect of the transmission grating. This allows the desired imaging effect to be set extremely precisely.

The line grid can be formed on or in a flat material interface. This simplifies production, since flat surfaces are extremely well mastered in production and a grid can be formed with high accuracy on flat surfaces. In order to provide the effect of curved material interfaces in this embodiment, if desired, the line grid can be designed accordingly. In particular, the lattice constant (or furrow width) is varied accordingly, so that the optical element formed in this way acts as if it had a curved material interface.

It is also possible to form the line grid on or in a curved, in particular a spherically curved material interface. This material interface can be, for example, an interface of a refractive element of the imaging optics. This makes it possible to implement a compact imaging optic with few elements, which can result in weight savings. When forming in or on a spherically curved interface, there is the advantage that spherically curved interfaces can be manufactured with extremely high accuracy. The desired or required aspherical effect can then be achieved by means of the grating formed (in this case the grating thus serves for beam deflection and for imaging). This provides an easy-to-manufacture optical element with excellent imaging properties. Furthermore, the part of the imaging optics which transmits the ambient light can have a refractive effect for the correction of visual errors for the user. Then glasses for correcting ametropia are immediately integrated in the image forming device according to the invention.

The imaging unit can be a self-illuminating display, such as an LED display, or a non-self-illuminating display (e.g. a transmissive or reflective LCD display). In particular, the image generation unit can have a spatial light modulator, such as e.g. a tilting mirror matrix or an LCD module or an LCoS module which is controlled accordingly, a separate light source also being provided, if necessary.

In the imaging device according to the invention, the imaging optics can have partial optics that are designed such that the light for imaging generates a parallel beam that strikes the transmission grating. This significantly simplifies the design of the transmission grating.

The partial optics, which are arranged between the imaging unit and the diffractive optics unit and deflect light for imaging from the imaging unit to the diffractive optics unit, can in particular have a mirror, a prism or a diffractive optical element.

If the imaging optics have a second diffractive optical unit, it is particularly preferred to design the two diffractive optical units in such a way that their dispersion errors are compensated for. In this case, even a polychromatic image that is generated by means of the image generation unit can be presented to the user without noticeably perceptible color errors. In this case, the two diffractive optical units can also be used to achieve two beam deflections of almost 90 ° each.

Compensation for the dispersion errors of the two diffractive optical units is understood here to mean that after the deflection, imaging-related imaging errors are eliminated as completely as possible, but are at least less than when only one diffractive optical unit is used.

The imaging optics preferably produce a virtual (in particular also enlarged) image for the viewer, which he then perceives. The image generation device can generate images for one or both eyes, the images being displayed for both eyes in particular for a three-dimensional image impression. Of course, the image generation device can also have further elements, in particular if these are necessary for operation. For example, a computer can be provided which contains the image data of the images to be displayed and transmits them to the image generation unit (for example wirelessly) or which controls the image generation unit accordingly.

The imaging unit can e.g. have an intensity control with which the display brightness (preferably continuously) is adapted to the ambient brightness. For this purpose, the intensity control can have a sensor for detecting the ambient brightness, which (preferably continuously) emits a signal that is evaluated, the display brightness being set or changed as a function of the evaluation result.

It is particularly preferred to design the image forming device as an HMD device (which the user must wear on the head). This provides an HMD device for an augmented display, in which the generated image can be transmitted transmissively into the field of view of the user wearing the HMD device by means of the diffractive optical unit.

Of course, it is also possible to design the image forming device in such a way that the diffractive optical unit is formed on the outside or inside of a vehicle window, so that an augmented representation of the surroundings takes place for the vehicle driver. The image generation unit can be provided in the vehicle interior or outside the vehicle. The same applies to at least parts of the imaging optics. In this embodiment, the vehicle driver can see important information or data in his field of vision.

The invention is explained in more detail below in principle on the basis of the drawings. Show it:

Figure 1 is a schematic representation of the image forming device according to the invention.

Fig. 2 is an enlarged cross-sectional view of a section of the grid of Fig. 1 to explain the grid profile, and

FIG. 3 shows an alternative grid profile in the same representation as in FIG. 2. 1 schematically shows the optical structure of an embodiment of the image-forming device according to the invention, in which case the image-forming device is designed as an HMD device.

The HMD device comprises an image generation unit 1 for generating monochromatic images, which is followed by imaging optics 2 which serve to image the image generated by the image generation unit 1 to the desired virtual image width (here, for example, infinite) into the eye A of the HMD device the viewer.

The imaging optics 2 comprise a lens 3 (which is shown here as representative of one or more refractive optical elements), a deflecting mirror 4 and a diffractive optical unit 5 connected upstream of the eye A, which is essentially designed as a plane-parallel plate made of a transmissive material, on the one of which A line grid 6 is formed on the side facing away from the eye A. The individual grid furrows of the line grid 6 run perpendicular to the plane of the drawing and each have a constant furrow width. The grating 6 is designed such that it has its greatest diffraction efficiency for the light of the image forming unit 1 for the first order in transmission. The beam path of this first order of diffraction is drawn in by the solid lines in the schematic illustration in FIG. 1. The diffracted light of other diffraction orders is diffracted in such a way that it does not get into the user's eye A. In Fig. 1, the light of the zeroth diffraction order is represented by the arrow P1 and the light of the second diffraction order by the arrow P2. In particular, one or more diaphragms can be arranged between the diffractive optical unit 5 and the eye A, if this is desired, which ensure that light of undesired diffraction orders does not get into the eye A.

Furthermore, the diffractive optics unit 6 is optimized so that the diffraction efficiency for the zeroth diffraction order of the essentially perpendicular ambient light (arrow P3) is as high as possible, so that the user can perceive an overlay of the image generated by the image generation unit 1 with the surroundings. To optimize the diffraction efficiencies, the profile shape of the line grating is selected accordingly, in particular, for example, blazed profile shapes can be used. An example of such a blazed profile shape is shown in FIG. 2. However, other profile shapes are also possible, an example is shown in FIG. 3.

In the exemplary embodiment described here, the groove width of the line grid 6 is constant. However, the furrow width can also be varied (in particular perpendicular to the longitudinal direction of the furrows), as a result of which a focussing effect (imaging effect) of the Grating is achieved, which can be used to make the deflecting optics 3 even more compact and lighter.

Instead of the deflecting mirror 4, a deflecting prism, another deflecting element (e.g. a reflective deflecting element) or a further line grating can be provided. If a further line grating is provided, the two line grids 4 and 6 are preferably designed so that their dispersion errors are compensated for. An image generation unit 1 can then be used to generate polychromatic images. Due to the compensation of the dispersion errors, the polychromatic images can be displayed without color errors perceptible to the viewer.

Claims

claims

1. Image generation device for a user, with an image generation unit (1) for generating an image and an imaging optics (2), which images the image so that it from

The image optics (2) contains a diffractive optics unit (5) with a transmission grating (6) that transmits the light for image generation that comes from the image generation unit (1) and thereby due to diffraction to the eye ( A) deflected towards the user, the diffractive optical unit (5) transmitting ambient light, so that an augmented display is possible.

2. Apparatus according to claim 1, wherein the transmission grating (6) is designed such that a non-zeroth diffraction order for beam deflection of the light of the image generation and the zeroth diffraction order is used for the transmission of the ambient light.

3. Device according to one of the above claims, wherein the angle of incidence of the light directed onto the transmission grating (6) for image generation is greater than 45 °, preferably greater than 70 °.

4. Device according to one of the above claims, wherein the transmission grating is designed as a line grating (6).

5. The device according to claim 4, wherein the line grating (6) is used only for beam deflection.

6. The device according to claim 4, wherein the line grating (6) for beam deflection and also serves as an imaging optical element for the light for image generation.

7. The device according to claim 6, wherein the lattice constant of the line grating (6) is varied for the imaging effect.

8. Device according to one of claims 4 to 7, wherein the line grating (6) is formed on or in a curved, in particular a spherically curved material interface.

9. Device according to one of claims 4 to 7, wherein the line grid (6) is formed on or in a flat material interface.

10. Device according to one of the above claims, wherein the imaging optics (2) includes a partial optics (3, 6) which is designed such that the light for image generation strikes the transmission grating (6) as a parallel beam.

11. Device according to one of the above claims, wherein the imaging optics (2) contains a second diffractive optics unit for beam deflection, wherein both diffractive optics units (5) are designed so that their dispersion errors are compensated.

12. Device according to one of the above claims, wherein the image forming device is designed as an HMD device for an augmented display.

13. The device according to claim 12, wherein the part (5) of the imaging optics (2) which transmits ambient light has a refractive effect for correcting vision defects for the user wearing the HMD device.