Spectacle lens for a display device which can be placed on the head of a user and which generates an image, and display device comprising such a spectacle lens

Abstract

The invention relates to a spectacle lens for a display device (1) which can be placed on the head of a user and which generates an image, wherein the spectacle lens (3) has a front face (23) and a rear face (11), an entry portion (28) and a deflection portion (18) spaced apart from the entry portion (28), and a light-guiding channel (21), wherein the spectacle lens (3) has a channel shell (13) in which the light-guiding channel (21) runs, and has a first lens (24; 25), wherein the light-guiding channel (21) guides light beams (L1) of the generated image, which are coupled into the spectacle lens (3) via the entry portion (28), up to the deflection portion (18), from which they are deflected in order to exit the spectacle lens (3) via the rear face (11), wherein a first supplemental layer (26; 27) made of a nanoporous material having a refractive index of less than 1.3 is located between the first lens face and the first channel face at least along the light-guiding channel such that the first supplemental layer (26; 27) is in direct contact with the first channel face, in order to enable total internal reflection of the light beams guided in the light-guiding channel (21) off the first channel face (36; 39), wherein the first lens comprises a first stack composed of a first plastic shell (30; 32) and a first reinforcement shell (31; 33), wherein the first reinforcement shell (31; 33) has a higher bending rigidity than the first plastic shell (30; 32).

Description

[0001] patent attorneys

[0002] GEYER, FEH NERS & PARTNER

[0003] Munich - Jena tooz technologies GmbH

[0004] Attorney's file: PAT 4377 / 071 -PCT

[0005] Spectacle lens for a display device that can be placed on a user's head and produces an image, and display device with such a spectacle lens

[0006] The present invention relates to a spectacle lens for a display device that can be placed on the head of a user and produces an image, and to a display device comprising such a spectacle lens.

[0007] Such a spectacle lens can have two lenses (a push lens and a pull lens) and a waveguide located between them. When the lens is used as intended, the pull lens is closer to the user's eye than the push lens. Since collimated light with a focal plane at infinity is generally used to transport the generated image in the waveguide, the pull lens typically has a negative refractive power to shift the focus of the virtual image towards near vision. If farsightedness correction is required, the pull lens may have a positive refractive power. For viewing the surroundings, the influence of the pull lens is at least partially compensated by the positive refractive power of the push lens. The push-lens-waveguide-pull-lens arrangement is also referred to as the ARx stack.

[0008] Push and pull lenses serve two purposes: firstly, to "pull" the augmented image (or the virtually displayed image) from infinity to a finite distance from the user, and secondly, to implement visual correction for the user. An immersive experience requires a large field of view (FoV > 50°) for the augmented image. The field of view for a high-refractive-index waveguide is maximized when the adjacent medium is air (the medium with the lowest refractive index in the visible spectral range, where n=1). Therefore, an air gap is often used between the waveguide and the adjacent optical components (push and pull lenses).

[0009] Alternatively, media with a low refractive index (or low refractive number) can be used, with fluorine-containing organic and inorganic compounds often forming the basis for such materials. However, the possible refractive indices of bulk media are limited to approximately 1.3. Compared to air, the use of such materials restricts the field angle (FoV) of the transported, augmented light.

[0010] GEYER, FEH NERS & PARTNER

[0011] Munich - Jena

[0012] The field of view (FoV) is reduced by 30 to 50% in two images. This is particularly problematic with diffractive waveguides (waveguides where the coupling of light out and / or into the waveguide occurs via diffractive structures) due to their limited FoV budget. For example, the theoretical FoV of a high-refractive-index waveguide is reduced from 60° (n=1) to approximately 40° (n=1,3), which significantly reduces the immersive experience for the user.

[0013] To minimize reduction by an adjacent medium, nanostructured, porous materials can be used. Due to the trapped air, such materials have an effective refractive index that can be below 1.3. For materials with an extremely low refractive index (approximately 1.1), this generally requires a porosity of at least 60%. Furthermore, the pore size and the wall thickness of the remaining matrix are in the range of a few tens of nanometers. This means that such materials often withstand only low mechanical stresses and must therefore be protected against abrasion and other external influences.

[0014] For example, pressure forces occur when cleaning the lens surfaces and are tested in the ophthalmology environment according to ISO 14889 (static pressure test) or FDA - 21 CFR 801 .410 (ball drop test) for medical approval.

[0015] Lightweight spectacle lenses made of polymer materials (thiourethanes, episulfides, Mitsui Resin (MR-8, MR-7, MR-10, MR-174), polycarbonate (PC), polyallyldiglycol carbonate (CR-39), and polyamide) represent the state of the art in ophthalmology. The elastic modulus of the polymers used is approximately 20 times lower than that of mineral glass (~80 GPa), so their flexural stiffness is reduced by the same factor. Flexural stiffness determines, for example, the thickness of a spectacle lens, which is why plastic lenses are significantly thicker.

[0016] For such spectacle lenses, form factor and weight are critical factors, as they are used in a display device worn on a user's head when used as intended.

[0017] Based on this, the object of the invention is to provide a spectacle lens of the type mentioned above in which the form factor and / or weight can be reduced. Furthermore, a display device with such a spectacle lens and a method for manufacturing such a spectacle lens are to be provided.

[0018] The invention is defined in independent claims 1, 18, and 19. Advantageous embodiments are specified in dependent claims. Patent attorneys

[0019] GEYER, FEH NERS & PARTNER

[0020] Munich - Jena

[0021] 3. A spectacle lens is provided for a display device that can be placed on a user's head and generates an image. The spectacle lens has a front and a back, an entry section and a deflection section spaced apart from the entry section, as well as a light-guiding channel. The spectacle lens further has a channel shell in which the light-guiding channel runs and a first lens. The light-guiding channel guides light beams of the generated image, which are coupled into the spectacle lens via the entry section, to the deflection section, from which they are deflected to exit the spectacle lens via the back. The first lens has a first lens side facing the channel shell and a second lens side facing away from the channel shell, and the channel shell has a first channel side facing the first lens. The first lens has an imaging effect (e.g.,for refractive error correction) and wherein a first additional layer made of a nanoporous material with a refractive index of less than 1.3 is arranged between the first lens side and the first channel side at least along the light-guiding channel such that the first additional layer is in direct contact with the first channel side to enable total internal reflection of the light beams guided in the light-guiding channel at the first channel side. The first lens has a first stack consisting of a first plastic shell and a first reinforcing shell, wherein the first reinforcing shell has a higher flexural stiffness than the first plastic shell.

[0022] According to the invention, a small form factor (low overall thickness and low weight) of the spectacle lens can be achieved while simultaneously correcting vision using the spectacle lens.

[0023] The first additional layer rests against the channel shell. If a second lens is provided, a further additional layer is preferably in direct contact with a second channel side to enable total internal reflection of the light beams guided in the light channel at the second channel side.

[0024] Due to the reinforcing shell with its higher flexural stiffness compared to the plastic shell, a reduction in the thickness of the first lens can be achieved. The invention enables the use of a very thin first lens (and / or a very thin second lens) in combination with the additional layer. Furthermore, the first additional layer is protected from mechanical stress, so that it does not suffer irreversible deformation (and thus destruction).

[0025] The first plastic shell can be connected to the first reinforcing shell. This can be done, for example, by means of a first adhesive and / or a clamping unit (e.g., at the edge of the patent holders).

[0026] GEYER, FEH NERS & PARTNER

[0027] Munich - Jena

[0028] 4 shells). Alternatively, the first plastic shell can be formed or shaped on the first reinforcing shell, e.g. by casting.

[0029] The first lens surface is preferably planar and / or the first channel surface is preferably planar. The first lens surface can be planar. The first additional layer can (but need not) have a constant thickness along the light-guiding channel. In particular, the planar first lens surface and the planar first channel surface can be parallel to each other.

[0030] However, it is also possible that the first lens side and / or the first canal side are curved.

[0031] The first plastic shell can be made of a polymer material (e.g., thiourethane, episulfide, Mitsui Resin (MR-8, MR-7, MR-10, MR-174), polycarbonate (PC), polyallyldiglycol carbonate (CR-39), and polyamide). The first reinforcing shell can be made of glass (e.g., mineral glass), a transparent ceramic, or a nanoparticle-reinforced composite and / or may contain one or more diamond layers. In particular, the material forming the reinforcing shell has a higher modulus of elasticity than the polymer material of the plastic shell.

[0032] This allows the effective elastic modulus of the first lens, and thus the bending stiffness of the first lens, to be increased, while at the same time maintaining the optical properties such as transparency.

[0033] The flexural stiffness is preferably chosen to be so large that the first additional layer is not subjected to irreversible deformation under compressive load.

[0034] The following scenarios can preferably be taken into account when designing the first lens so that the first additional layer is not subjected to irreversible deformation under pressure:

[0035] Gripping / pressing of the outer surfaces during cleaning etc. (forces <10 N, see Lee et al., Science 370, 2020, 966-970 and DIN ISO 9211-4), static loads of up to 100 N according to DIN EN ISO 14889 and / or impact loads according to FDA ball drop test, 21 CFR 801.410.

[0036] Preferably, the refractive index of the reinforcing shell can be matched to the refractive index of the plastic shell. Patent attorneys

[0037] GEYER, FEH NERS & PARTNER

[0038] Munich - Jena

[0039] 5

[0040] The bending stiffness can be characterized by the product of the modulus of elasticity and the area moment of inertia, where the modulus of elasticity of the first reinforcing layer is at least ten times the modulus of elasticity of the first plastic layer. Furthermore, the modulus of elasticity of the first reinforcing layer can be x times the modulus of elasticity of the first plastic layer, where x can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 50, 100, or higher (e.g., up to 1000). For diamond, with the theoretically highest modulus of elasticity of approximately 1000 GPa, the difference compared to the plastic materials (modulus of elasticity 1–5 GPa) can be approximately three orders of magnitude (a factor x of 1000).

[0041] The first plastic shell and / or the first reinforcing shell can / may produce the imaging effect of the first lens.

[0042] Both the first plastic shell and the first reinforcing shell in the first stack can extend to a peripheral edge of the first lens. Alternatively, the first plastic shell and the first reinforcing shell can be flush with the peripheral edge of the first lens. Additionally or alternatively, neither the first plastic shell nor the first reinforcing shell can extend laterally beyond the first plastic shell. Additionally or alternatively, the first additional layer can extend to the peripheral edge of the first lens and / or be flush with the peripheral edge of the first lens.

[0043] The spectacle lens may have a first frame (e.g. a first clamping unit) that clamps the first stack (or the first lens) all the way around.

[0044] The first version or the first clamping unit can additionally enclose the first additional layer gas- and moisture-tight together with the channel shell.

[0045] The first reinforcing shell can extend beyond the first plastic shell in the first stack, as viewed from above. Alternatively, the first plastic shell in the first stack can extend beyond the first reinforcing shell, as viewed from above. In particular, the shell in the first stack that extends beyond the others, as viewed from above, can serve to enclose the first additional layer in a gas- and moisture-tight manner.

[0046] Additionally or alternatively, the shell in the first stack, which projects beyond the others when viewed from above, can serve to enclose or encapsulate the first channel side. In particular, this can create a gas- and moisture-tight seal for the first channel side. For example, the first reinforcing shell can serve as a cover glass (preferably without patent attorneys).

[0047] GEYER, FEH NERS & PARTNER

[0048] Munich - Jena

[0049] 6 optical imaging effect) may be formed, which includes the first channel side of the channel shell, and the first plastic shell may be formed over part of the side of the first reinforcement shell pointing away from the channel shell and may have an optical imaging effect.

[0050] The first lens can be refractive and / or diffractive. Additionally or alternatively, the first lens can be a Fresnel lens.

[0051] The first plastic shell and the first reinforcing shell can be arranged in the first stack such that the first reinforcing shell is closer to the first additional layer than the first plastic shell.

[0052] The first reinforcing shell can be in direct contact with the first additional layer and / or connected to the first additional layer.

[0053] Furthermore, the reinforcing shell and the plastic shell can be bonded with an adhesive having the same refractive index. Therefore, the interfaces have no optical effect.

[0054] The difference between the refractive index of the first plastic shell for a first wavelength of 550 nm and the refractive index of the first reinforcing shell for the first wavelength can be less than or equal to 0.2.

[0055] The difference between the refractive index of the first plastic shell for the first wavelength and the refractive index of the adhesive for the first wavelength can be less than or equal to 0.1 (preferably less than 0.01 and most preferably less than 0.001).

[0056] Alternatively or additionally, surfaces forming the interfaces can have an anti-reflective coating to reduce reflections.

[0057] Preferably, the connection between the reinforcing shell and the plastic shell is reversible and / or detachable, allowing the plastic shell to be replaced and / or renewed. If the refractive error correction is achieved by means of the plastic shell (or if it contributes to the refractive error correction), adjustments can easily be made to accommodate changes in the user's refractive error.

[0058] The surfaces of the first lens that are exposed to air can be coated with an anti-reflective coating. Patent attorneys

[0059] GEYER, FEH NERS & PARTNER

[0060] Munich - Jena

[0061] 7

[0062] The first reinforcing shell can completely enclose the first additional layer together with the channel shell. This protects the first additional layer against, for example, moisture, dirt and / or other environmental influences.

[0063] The first reinforcing shell can also have an optical function and contribute, for example, to the imaging of the virtual image and / or to viewing the surroundings through the spectacle lens.

[0064] The first reinforcement shell can enable bonding (e.g., including chemical bonding) of further optical components (e.g., lenses) without affecting the condition of total internal reflection for light guidance in the channel shell. The bonding can be reversible, allowing the lenses to be replaced.

[0065] The first reinforcing layer can be designed as an antireflective coating or have one. Additionally or alternatively, the first reinforcing layer can have at least one other optical functionality, such as active optics and electrochromism.

[0066] The first reinforcement layer can be applied directly to the first additional layer. However, it is also possible for the first additional layer to be bonded to the first additional layer using a suitable adhesive (or similar). Support structures (e.g., spacers) can also be used in this process.

[0067] A full-surface application of the first reinforcing layer is preferred. However, it is also possible for the first reinforcing layer to only cover a portion of the first additional layer.

[0068] The side of the first lens facing away from the channel shell may be provided with a hard layer, a hard coating or a hardcoat.

[0069] The plastic shell alone or the first lens as a whole can be designed as a refractive spectacle lens or as a refractive and diffractive Fresnel lens.

[0070] The reinforcing shell can be integrated into the design of the first lens, giving it not only a purely mechanical but also an optical function. This approach can further reduce the thickness of the first lens. Patent attorneys

[0071] GEYER, FEH NERS & PARTNER

[0072] Munich - Jena

[0073] 8 The reinforcement shell can have a laminate made of several layers of different materials.

[0074] The first lens preferably has a first mount that connects the reinforcing shell to the plastic shell and / or the first lens to the canal shell. The first mount can be designed to prevent rotation of the reinforcing shell relative to the plastic shell and / or rotation of the first lens relative to the canal shell. Preferably, the first mount clamps the reinforcing shell to the plastic shell circumferentially. This increases the bending stiffness compared to a resting position of the first lens on the canal shell without clamping (loose bearing).

[0075] The first lens holder or clamp can also be designed to athermize the first lens. Athermizing the first lens in this context means, in particular, that the optical properties of the first lens are (as far as possible) insensitive to changes in ambient temperature, or that the optical properties of the first lens do not change, or only change slightly, when the ambient temperature changes.

[0076] The first version or the surrounding clamp can be used for the hermetic encapsulation of the first additional layer to prevent contamination, condensation and the like.

[0077] The spectacle lens can have a second lens comprising a third lens face facing the channel shell, a fourth lens face facing away from the channel shell, and the channel shell having a second channel face facing the second lens, wherein the second lens can have an imaging function. Between the third lens face and the second channel face, at least along the light-guiding channel, a second additional layer made of a nanoporous material with a refractive index of less than 1.3 can be arranged such that the second additional layer is in direct contact with the second channel face to enable total internal reflection of the light beams guided in the light-guiding channel at the second channel face. The second lens can have a second stack consisting of a second plastic shell and a second reinforcing shell, wherein the second reinforcing shell has a higher flexural stiffness than the second plastic shell.

[0078] The second lens can be formed in the same way as the first lens and may be further developed.

[0079] For example, both the second plastic shell and the second reinforcing shell in the second stack can extend to a circumferential edge of the second lens. You can also consult patent attorneys.

[0080] GEYER, FEH NERS & PARTNER

[0081] Munich - Jena

[0082] 9 states that the second plastic shell and the second reinforcing shell form a flush periphery of the second lens. Additionally or alternatively, neither the second plastic shell extends laterally beyond the second reinforcing shell, nor does the second reinforcing shell extend laterally beyond the second plastic shell. Additionally or alternatively, the second additional layer may extend to the periphery of the second lens and / or be flush with the periphery of the second lens.

[0083] The second plastic shell can be connected to the second reinforcing shell. This can be achieved, for example, using a second adhesive and / or a clamping unit (e.g., at the edge of the shells). Alternatively, the second plastic shell can be formed or molded onto the second reinforcing shell, e.g., by casting.

[0084] The spectacle lens according to the invention makes it possible to provide display devices (e.g. HMDs) that can be placed on a user's head and generate an image, with smaller form factors and large viewing angles due to the first additional layer.

[0085] The spectacle lens can have an exit point on its back surface through which the deflected light beams exit the lens. Furthermore, the deflecting section can redirect the light beams, which have been guided up to it, towards the exit point in such a way that they exit the lens through the exit point and are thus coupled out of the lens.

[0086] The deflection section and the exit section can be spatially separated sections. However, it is also possible for the deflection section and the exit section to coincide spatially, e.g., if the deflection section is designed as a surface lattice.

[0087] In the first spectacle lens, the deflection section can have a single reflective or semi-reflective deflection element or several reflective and / or semi-reflective deflection elements arranged side by side. With several reflective or semi-reflective deflection elements arranged side by side, a desired deflection function and, if necessary, a certain imaging function of the deflection section can be achieved, for example, in a Fresnel-like manner (this can, of course, also be achieved with a single reflective or semi-reflective deflection element). The reflective or semi-reflective deflection elements can be reflective or semi-reflective surface sections, which can also be referred to as reflective or semi-reflective facets. The reflective or semi-reflective surface sections can each be planar. However, it is also possible that the reflective or semi-reflective surfaces are not flat or spherical.The partially reflective surface sections themselves are curved (for example, spherically or aspherically curved, or freeform). Similarly, the only reflective patent attorneys can...

[0088] GEYER, FEH NERS & PARTNER

[0089] Munich - Jena

[0090] 10 or partially reflective deflection element may be planar or curved (for example, spherically or aspherically curved or freeform shaped).

[0091] Additionally or alternatively, the deflection section can have at least one holographic element, at least one volume holographic element and / or at least one diffractive element.

[0092] The reflectivity of the respective reflective deflection elements (or the single reflective deflection element) can, for example, range from 2% to 100% (including the limits of this range). Thus, the reflective deflection elements can be partially reflective or fully reflective.

[0093] The spectacle lens according to the invention can in particular have a curved back surface and / or a curved front surface. The entry section can be formed in the back surface and / or in the channel shell.

[0094] The back and / or the front can have a spherical curvature, an aspherical curvature, a toric curvature and / or a freeform curvature.

[0095] If only the back surface is curved, the front surface is flat. Conversely, if only the front surface is curved, the back surface is flat.

[0096] The light beams of the image generation module are preferably guided through one or more internal total internal reflections to the deflection section.

[0097] A display device is provided comprising a holding device that can be placed on the user's head, an image generation module attached to the holding device which generates an image, and a spectacle lens according to the invention (including all further developments) attached to the holding device, wherein the generated image is coupled into the first shell via the entry section, guided in the first shell by at least reflection to the deflection section and deflected at the first deflection section in order to exit the spectacle lens via the inner shell, so that the user can perceive it as a virtual image in the state of the holding device being placed on the head.

[0098] The display device can include a control unit that controls the image generation module. In particular, the control unit can control the image generation module based on supplied image data. Patent attorneys

[0099] GEYER, FEH NERS & PARTNER

[0100] Munich - Jena

[0101] 11

[0102] The image generation module and / or an image sensor unit of the image generation module may, in particular, comprise a planar image sensor, such as an LCD module, an LCoS module, an OLED module, a pLED, or a tilting mirror matrix. Each image sensor may have a plurality of pixels, which may be arranged, for example, in rows and columns. Each image sensor may, for example, be self-illuminating or non-self-illuminating.

[0103] Each image sensor can preferentially produce a monochromatic image, while different image sensors can produce monochromatic images with different wavelengths.

[0104] The image generation module can, for example, comprise a polychromatic image source, a combination of two or more monochromatic image sources, or a combination of a duochromatic and a monochromatic image source. Typical configurations of such image generation modules with multiple image sources include a superposition unit that combines the light beams of the multiple image sources into a single, common light beam. Such a superposition unit can be implemented, for example, as a beam splitter cube (also called an X-cube) or as a so-called rod combiner, both of which are known to those skilled in the art.

[0105] The image generation module can produce the image with a first lateral chromatic aberration that (partially or completely) compensates for a second lateral chromatic aberration caused by the spectacle lens in the virtual image.

[0106] Since the diverting section should be as invisible as possible and should also have as little impact as possible on the light reaching the viewer's eye from the surroundings, diverting sections with high transmission and, consequently, low reflectivity for the light beam(s) of the at least two-color image are generally preferred. Typical reflectivity values ​​are, for example, 50%, 30%, 10%, or 2%, uniformly across the visible wavelength range.

[0107] Furthermore, a method for manufacturing a spectacle lens for a display device that can be placed on the head of a user and produces an image is provided, wherein the spectacle lens has a front, a back, an entry section, a deflecting section spaced apart from the entry section and a light guiding channel extending from the entry section to the deflecting section, wherein the method comprises:

[0108] - Providing a channel shell in which the light guiding channel extends, wherein the light guiding channel is used to guide light rays of the generated image, which are directed via the patent attorneys

[0109] GEYER, FEH NERS & PARTNER

[0110] Munich - Jena

[0111] 12. The entry section is coupled into the spectacle lens until the deflection section is formed, from which they are deflected to exit the spectacle lens via the back side.

[0112] - Arranging a first additional layer made of a nanoporous material with a refractive index of less than 1.3 on a first channel side of the channel shell at least along the light guiding channel such that the first additional layer is in direct contact with the first channel side in order to enable total internal reflection of the light rays guided in the light guiding channel at the first channel side, and

[0113] - Providing a first lens with a first lens side facing the first channel side of the channel shell and a second lens side facing away from the channel shell, such that the first additional layer is arranged between the first lens side and the first channel side, wherein the first lens has an imaging effect and comprises a first stack of a first plastic shell and a first reinforcing shell, wherein the reinforcing shell has a higher bending stiffness than the first plastic shell.

[0114] The step of providing the first lens may include providing the first plastic shell and the first reinforcing shell such that both the first plastic shell and the first reinforcing shell extend to a circumferential edge of the first lens in the first stack. Furthermore, the method may include providing a first clamping unit that clamps the first lens circumferentially.

[0115] The step of providing the first lens may include: providing the first reinforcing shell in direct contact and / or connected to the first additional layer in such a way that the first reinforcing shell encloses the first additional layer in a gas- and moisture-tight manner, and

[0116] - Placing the first plastic shell on the first reinforcement shell in the first stack, with the first reinforcement shell extending beyond the first plastic shell in plan view.

[0117] The step of providing the first plastic shell may include forming (e.g., casting) the first plastic shell over the first reinforcing shell and / or joining the first plastic shell to the first reinforcing shell.

[0118] The process for manufacturing the spectacle lens may further include:

[0119] - Arranging a second additional layer made of a nanoporous material with a refractive index of less than 1.3 on a second channel side of the channel shell opposite the first channel side, at least along the light-guiding channel, such that the second additional layer is in direct contact with the second channel side in order to enable total internal reflection of the light rays guided in the light-guiding channel at the second channel side, and patent attorneys

[0120] GEYER, FEH NERS & PARTNER

[0121] Munich - Jena

[0122] 13

[0123] - Providing a second lens with a third lens side facing the second channel side of the channel shell and a fourth lens side facing away from the channel shell, wherein the second lens has an imaging effect and comprises a second stack of a second plastic shell and a second reinforcing shell, wherein the second reinforcing shell has a higher bending stiffness than the second plastic shell.

[0124] The step of providing the second lens can be carried out by placing the second additional layer between the third lens side and the second channel side.

[0125] The method for manufacturing the spectacle lens may include further steps that have already been described and / or that will be described below. In particular, the method for manufacturing the spectacle lens may include steps that are described and / or necessary for manufacturing the spectacle lens according to the invention (including its further developments).

[0126] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations given, but also in other combinations or on their own, without leaving the scope of the present invention.

[0127] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings, which also disclose essential features of the invention. These exemplary embodiments serve only for illustration and are not to be interpreted as limiting. For example, a description of an exemplary embodiment with a plurality of elements or components is not to be interpreted as meaning that all of these elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components of different exemplary embodiments may be combined with one another unless otherwise specified. Modifications and variations described for one of the exemplary embodiments may also be applicable to other exemplary embodiments.To avoid repetition, identical or corresponding elements in different figures are designated with the same reference symbols and are not explained multiple times. The figures show:

[0128] Fig. 1 is a schematic perspective view of an embodiment of the display device according to the invention; Patent Attorneys

[0129] GEYER, FEH NERS & PARTNER

[0130] Munich - Jena

[0131] 14 Fig. 2 an enlarged partial sectional view of the first spectacle lens including a schematic representation of the first image generation module according to Fig. 1 ;

[0132] Fig. 3 shows a diagram showing the relative reduction of the opening angle for a duct shell in which the deflection section has a diffractive deflection element, with the refractive index of the material in direct contact with the duct sides (e.g. the additional layer (26, 27)) along the abscissa and the relative reduction of the opening angle (field of view) (relative to the case where air is in direct contact with the duct sides) along the ordinate;

[0133] Fig. 4 shows an enlarged partial sectional view of a conventional spectacle lens;

[0134] Fig. 5 shows an enlarged partial sectional view of a spectacle lens according to a further embodiment of the invention, and

[0135] Fig. 6 shows an enlarged partial sectional view of a spectacle lens according to the invention in a further embodiment.

[0136] In the embodiment shown in Fig. 1, the display device 1 according to the invention comprises a holding device 2 that can be placed on the user's head, which can, for example, be designed in the manner of a conventional eyeglass frame, as well as a first and a second lens 3, 4, which are attached to the holding device 2. The first lens 3 and / or the second lens 4 can each be designed as a lens according to the invention. The holding device 2 with the lenses 3, 4 can, for example, be designed as sports glasses, sunglasses, and / or glasses for correcting a visual impairment, wherein a virtual image can be projected into the user's field of vision via the first lens 3, which can also be referred to as a multifunctional lens, as described below.

[0137] The display device 1 includes an image generation module 5, which can be arranged in the area of ​​the right temple of the holding device 2, as shown schematically in Fig. 1.

[0138] The image generation module 5 can include an image sensor unit 7 for generating a first image, as schematically illustrated in Fig. 2. For this purpose, the image sensor unit 7 comprises a planar image generation element 8, to which an image sensor optic 9 is arranged. However, it is also possible that the image sensor optic 9 is not provided and can therefore be omitted. The planar image generation element 8 can, for example, comprise an OLED element, an LCD element, an LCoS element, a pLED, or a tilting mirror matrix, each comprising a plurality of pixels arranged, for example, in rows and columns. A single light beam L1 is shown schematically as a representative of the light beams emitted by the planar image generation element 8. Patent Attorneys

[0139] GEYER, FEH NERS & PARTNER

[0140] Munich - Jena

[0141] 15

[0142] As can be further seen in Fig. 2, a control unit 10 with, for example, a processor P and a memory M is provided for controlling the image generation module 5. The control unit 10, which can, for example, be arranged on the holding device 2, controls the image generation module 5 and, in particular, the image generation element 8, depending on the supplied image data, so that the first image is generated according to the image data. The light beams L1 emitted by the image generation element 8 pass through the image sensor optics 9 and then enter the first spectacle lens 3. The area of ​​entry can also be referred to as the entry surface 12.

[0143] The first spectacle lens 3 is multi-layered and has a channel shell 13, an outer shell 24 (hereinafter also referred to as outer lens 24), and an inner shell 25 (hereinafter also referred to as inner lens 25). The channel shell 13 is the middle shell located between the outer shell 24 and the inner shell 25.

[0144] In order to minimize the thickness of the outer and inner lenses 24, 25 and / or to provide the outer and inner lenses 24, 25 with the lowest possible weight, both the outer lens 24 and the inner lens 25 each have a sandwich-like composite or stack of a plastic shell 30, 32 and a reinforcing shell 31, 33, wherein the respective reinforcing shell 31, 33 has a higher bending stiffness than the respective plastic shell 30, 32.

[0145] The outer lens 24 has a lens side 34 facing the channel shell 13 and a lens side 35 facing away from the channel shell 13, and the channel shell 13 has a channel side 36 facing the outer lens 24, wherein an additional layer 26 made of a nanoporous material with a refractive index of less than 1.3 is arranged between the lens side 34 and the channel side 36 such that the additional layer 26 is in direct contact with the channel side 36 in order to enable total internal reflection of the light beams L1 guided in the light guidance channel 21 at the channel side 36.Similarly, the inner lens 25 has a lens side 37 facing the channel shell 13 and a lens side 38 facing away from the channel shell 13, and the channel shell 13 has a channel side 39 facing the inner lens 25, wherein an additional layer 27 made of a nanoporous material with a refractive index of less than 1.3 is arranged between the lens side 37 and the channel side 39 such that the additional layer 27 is in direct contact with the channel side 39 in order to enable total internal reflection of the light beams L1 guided in the light-guiding channel 21 at the channel side 39. Patent attorneys.

[0146] GEYER, FEH NERS & PARTNER

[0147] Munich - Jena

[0148] 16 For example, a socket 40 can be provided which connects the outer lens 24 and the additional layer 26 to the channel shell 13 in such a way that the additional layer 26 is sealed gas- and moisture-tight from the environment. Furthermore, a socket 41 can be provided which connects the inner lens 25 and the additional layer 27 to the channel shell 13 in such a way that the additional layer 27 is sealed gas- and moisture-tight from the environment.

[0149] In the embodiment described here, the channel shell 13 is designed as a plane-parallel plate, except for the area of ​​the entrance surface 12. The inner shell 25 is designed as a lens 25 with negative refractive power, and the outer shell 24 is designed as a lens with positive refractive power. The side of the outer shell 24 facing away from the channel shell 13 forms the front 23 of the first spectacle lens 3, and the side of the inner shell 25 facing away from the channel shell 13 forms the back 11 of the first spectacle lens 3.

[0150] Due to the additional layers 26, 27, the light beams L1 are only reflected if their angle of incidence is 9°. E With respect to the surface perpendicular F (shown as a dashed line in Fig. 2) of a surface element where total internal reflection is to take place, the corresponding critical angle 0 is larger. C For angles of incidence in the range from 0° to the critical angle 0 C The canal shell 13 is transmissive, so that the user can perceive the surroundings with his eye A through the first lens 3, as indicated by the arrow U in Fig. 2.

[0151] These transmission and reflection properties are predominantly present for radiation from the visible wavelength range.

[0152] Furthermore, the channel shell 13 has a buried deflection section 18, which includes one (or more, not shown in Fig. 2) partially reflective deflection element 19, which can also be referred to as a partially reflective facet 19. Alternatively or additionally, the deflection section 18 can have a diffractive deflection element 19.

[0153] As already described, the light beams L1 enter the first lens 3 via the entrance surface 12. The entrance surface 12 is formed on a lateral entrance section 28 of the channel shell 13, which, in the embodiment described here, projects laterally beyond the outer and inner shells 24, 25. In addition to the entrance surface 12, the lateral entrance section 28 has a (here planar) deflecting surface 29 that deflects the light beams L1 in a first direction (here the y-direction) towards the deflecting section 18, such that the light beams L1 are guided by total internal reflection at the interfaces of the channel shell 13 to the corresponding additional layer 26, 27 and up to the deflecting section 18. The deflecting surface 29 can be, for example, reflective or partially reflective. It is also possible to design the deflecting surface 29 to be diffractive. In this case, the deflecting surface can (but does not have to) be parallel to the

[0154] GEYER, FEH NERS & PARTNER

[0155] Munich - Jena

[0156] 17 Channel side 36 or 39, or a part of channel side 36 (e.g., as a reflective grating or as a reflective hologram) or of channel side 39 (e.g., as a transmissive grating or transmissive hologram), can be such that the inclined side for the deflection surface 29 does not need to be provided. The channel shell 13 can, for example, be designed as a plane-parallel plate.

[0157] The deflecting section 18 then deflects the light beams L1 such that the deflected light beams L1 exit the first lens 3 via the inner lens 25 and thus via the back surface 11, creating a virtual image that the user can perceive with their eye A. The area through which the light beams L1 exit can also be referred to as the exit section 22 or exit surface 22.

[0158] Thus, in the channel shell 13 there is a light guidance channel 21 which extends along the first direction from the entry section 12 to the deflection section 18.

[0159] Since collimated light L1 with a focal plane at infinity is generally used to transport the generated image in the channel shell 13 (which can also be called a waveguide), the inner lens 25 typically has a negative refractive power to pull the focus of the virtual image towards the near range for the user (e.g., 0.5 m - 2 m). Therefore, the inner lens 25 can also be called a pull lens 25. For correcting the refractive error of highly hyperopic spectacle wearers, it may be necessary for the inner lens 25 to have a positive refractive power.

[0160] For viewing the surroundings, the influence of the pull lens 25 is compensated by the outer lens 24 with positive refractive power. Therefore, the outer lens 24 can also be referred to as a push lens 24. Optionally, the outer lens 24 can be omitted. The outer shell 24 can be omitted, for example, if the focus position of the virtual image is not adjusted. In this case, the pull lens 25 is preferably only required for refractive error correction.

[0161] In addition to adjusting the focus plane of the virtual image, the Pull lens 25 can be used for individual refractive correction for users with visual impairments.

[0162] Since the outer and inner lenses basically have the same structure, the outer lens 24 will be described mainly below.

[0163] The outer lens 24 is designed so that, although it deforms under pressure loads occurring during normal use (e.g., when cleaning the spectacle lens 3), the additional layer 26 is not damaged in the process. Since the additional layer 26 is made of a patented material,

[0164] GEYER, FEH NERS & PARTNER

[0165] Munich - Jena

[0166] Because the outer lens 24 is formed from nanostructured porous material, the additional layer 26 can only withstand minor mechanical stresses. However, since the outer lens 24 has the reinforcing shell 31, the additional layer is effectively protected against mechanical stresses.

[0167] Since the additional layer 26 has a refractive index of less than 1.3, the virtual image is presented to the user with a large field of view (FoV). Figure 3 shows, by way of example, the relative reduction of the field of view for a channel shell 13 in which the deflection section 18 has a diffractive deflection element 19. The abscissa represents the refractive index of the material in direct contact with the channel sides 36 and 39, and the ordinate represents the relative reduction of the field of view (relative to the case where air is in direct contact with the channel sides 36 and 39). Line K1 shows this for a channel shell with a refractive index of 2.0, line K2 for a channel shell with a refractive index of 1.8, and line K3 for a channel shell with a refractive index of 1.6.

[0168] It follows that nanoporous materials with the lowest possible refractive index would be advantageous as an additional layer. Available nanoporous materials can have a refractive index of less than 1.2 and, in particular, a refractive index of 1.1. Although porosity increases with decreasing refractive index, thus reducing the ability to withstand mechanical stress, the reinforcing shell 31 provides the necessary protection for the additional layer, ensuring the desired optical properties of the channel shell 13.

[0169] The bending stiffness D, characterized by the product of the modulus of elasticity E and the area moment of inertia I (D = E • I), is therefore selected accordingly for the outer lens 24. Thus, the effective modulus of elasticity of the outer lens 24 can be adjusted by combining the thin plastic shell 30 with the reinforcing glass shell 31 to achieve the desired bending stiffness for the outer lens 24. Compared to a conventional outer lens made entirely of plastic, the desired bending stiffness can be achieved with a smaller form factor (e.g., thickness and / or weight of the outer lens 24).

[0170] Provided that the outer lens 24 is clamped around its edge (e.g. by means of the mount 40, as shown in Figure 5), the maximum deflection w can be determined. maxThe composite of plastic shell 30 and reinforcing shell 31 is calculated as follows, assuming a circular disk of constant thickness for both the plastic shell 30 and the reinforcing shell 31: patent attorneys

[0171] GEYER, FEH NERS & PARTNER

[0172] Munich - Jena

[0173] 19 where P is the compressive force, r is the radius of the respective shell 30, 31 and D is the bending stiffness of the

[0174] Outer lens 24 with D = ^D t is. Each shell has a thickness of t t , the

[0175] modulus of elasticity and the transverse contraction number . Thus, shell thickness (design) and modulus of elasticity (material selection) are important parameters to influence the deflection or to determine it in such a way that the additional layer 26 is not damaged.

[0176] If the outer and inner lenses 24, 25 are each designed in the conventional manner as pure polymer lenses 24', 25', a deflection would occur under a pure point load P1' and P2', as shown schematically in Figure 4. This would cause the polymer lens 24', 25' to undesirably contact the channel shell 13', thereby damaging an additional layer.

[0177] Additionally, the outer lens 24 can be designed such that the side 34 facing the canal shell 13 is concavely curved (Figure 6), so that the area inertial element of the outer lens 24 is larger compared to the design of the outer lens 24 in which the side 34 facing the canal shell 13 is planar.

[0178] As shown in Figure 6, the reinforcement shell 31 can laterally touch the channel shell 13, so that the additional layer 26 can be sealed against the environment by means of the reinforcement shell 31.

[0179] In the embodiment shown in Figure 6, the side of the plastic shell 30 facing the channel shell 13 is flat. However, it is also possible to make this side concave. This is shown in Figure 6 for the plastic shell 32 of the inner shell 25.

[0180] In the display device 1 according to the invention, the virtual image is projected into the user's field of vision via the first lens 3. Projection via the second lens 4 is also possible. Furthermore, the display device 1 can be designed such that information or virtual images are projected via both lenses 3 and 4. The projection can be arranged to create a three-dimensional image impression. However, this is not mandatory.

[0181] The lenses 3, 4 can have a refractive power of zero or a non-zero refractive power (especially for correcting refractive errors). In particular, both the front surface 23 and the back surface 11 can be curved. The front surface 23 is, in particular, spherically curved. However, the front surface 23 can be in the patent attorneys

[0182] GEYER, FEH NERS & PARTNER

[0183] Munich - Jena

[0184] 20 Generally, the back surface can be spherically, aspherically, toricly, and / or freeform shaped. If the spectacle lens 3, 4 has a non-zero refractive power to correct a refractive error, the curvature of the back surface 11 is usually chosen accordingly to achieve the appropriate correction. The back surface 11 can have a curvature other than spherical (including a shape that provides a progression or multifocal lens effect). Generally, the back surface can be spherically, aspherically, toricly, and / or freeform shaped. Of course, it is also possible that the curvature of the back surface, together with the curvature of the front surface 23, produces the desired refractive error correction.

[0185] The holding device 2 need not be designed as a spectacle-like holding device. Any other type of holding device is also possible, which allows the display device 1 to be placed on and worn on the head.

Claims

patent attorneys GEYER, FEH NERS & PARTNER Munich - Jena 21 tooz technologies GmbH Attorney's file: PAT 4377 / 071 -PCT Patent claims 1. Spectacle lens for a display device (1) that can be placed on a user's head and generates an image, wherein the spectacle lens (3) has a front (23) and a back (11), an entry section (28) and a deflection section (18) spaced apart from the entry section (28), and a light guiding channel (21), wherein the spectacle lens (3) has a channel shell (13) in which the light guiding channel (21) runs and a first lens (24; 25), wherein the light guiding channel (21) guides light beams (L1) of the generated image, which are coupled into the spectacle lens (3) via the entry section (28), to the deflection section (18), from which they are deflected to exit the spectacle lens (3) via the back (11), wherein the first lens (24; 25) has a first lens side (34; 37) facing the channel shell (13). as well as a second lens side (35; 38) facing away from the canal shell (13) and the canal shell (13) one of the first lenses (24;25) having a first channel side (36; 39) facing the first channel side, wherein the first lens (24; 25) has an imaging effect, wherein a first additional layer (26; 27) made of a nanoporous material with a refractive index of less than 1.3 is arranged between the first lens side and the first channel side at least along the light-guiding channel such that the first additional layer (26; 27) is in direct contact with the first channel side to enable total internal reflection of the light beams guided in the light-guiding channel (21) at the first channel side (36; 39), wherein the first lens has a first stack of a first plastic shell (30; 32) and a first reinforcing shell (31; 33), wherein the first reinforcing shell (31; 33) has a higher flexural stiffness than the first plastic shell (30; 32).

2. Spectacle lens according to claim 1, wherein the bending stiffness is the product of the modulus of elasticity and the area moment of inertia, and wherein the modulus of elasticity of the first reinforcing shell (31; 33) is at least ten times the modulus of elasticity of the first plastic shell (30; 32). patent attorneys GEYER, FEH NERS & PARTNER Munich - Jena 22 3. Spectacle lens according to one of the above claims, wherein the first reinforcing shell (31 ; 33) comprises glass material, transparent ceramic material and / or at least one diamond layer.

4. Spectacle lens according to one of the above claims, wherein the first reinforcing shell (31 ; 33) comprises a laminate of several different materials.

5. Spectacle lens according to one of the above claims, wherein the first plastic shell (30; 32) comprises a polymer material.

6. Spectacle lens according to one of the above claims, wherein the first plastic shell (30; 32) and / or the first reinforcing shell (31; 33) enhances the imaging effect of the first lens (24; 25) effect.

7. Spectacle lens according to one of the above claims, wherein a first clamping unit (40; 41 ) is provided which clamps the first lens (24; 25) circumferentially and / or wherein both the first plastic shell (30; 32) and the first reinforcing shell (31 ; 33) extend in the first stack to a circumferential edge of the first lens (24; 25).

8. Spectacle lens according to claim 7, wherein the first clamping unit (40; 41 ) together with the channel shell (13) and the first lens (24; 25) encloses the first additional layer (26; 27) in a gas- and moisture-tight manner.

9. Spectacle lens according to one of claims 1 to 6, wherein the first reinforcing shell (31 ; 33) extends beyond the first plastic shell (30; 32) in the first stack in a top view, so that the first additional layer (26; 27) is enclosed in a gas- and moisture-tight manner.

10. Spectacle lens according to one of the above claims, wherein the first plastic shell and the first reinforcing shell (31 ; 33) are arranged in the first stack such that the first reinforcing shell (31 ; 33) is in direct contact with the first additional layer (26; 27) and / or is connected to the first additional layer (26; 27).

11. Spectacle lens according to one of the above claims, wherein the first reinforcing shell (31 ; 33) is designed as an anti-reflective layer or has an anti-reflective layer.

12. Spectacle lens according to one of the above claims, wherein the difference between the refractive index of the first plastic shell (30; 32) for a first wavelength of 550 nm and the refractive index of the first reinforcing shell (31; 33) for the first wavelength is less than or equal to 0.

2. patent attorneys GEYER, FEH NERS & PARTNER Munich - Jena 23 13. Spectacle lens according to one of the above claims, wherein the side of the first plastic shell (30; 32) facing the first reinforcing shell (31; 33) has an anti-reflective coating and / or wherein the side of the first reinforcing shell (31; 33) facing the first plastic shell (30; 32) has an anti-reflective coating.

14. Spectacle lens according to one of the above claims, wherein the first plastic shell (30; 32) is connected to the first reinforcing shell (31; 33) with a releasable adhesive, wherein preferably the difference between the refractive index of the first plastic shell (30; 32) for the first wavelength and the refractive index of the adhesive for the first wavelength is less than or equal to 0.

1.

15. Spectacle lens according to one of the above claims, wherein the side of the first plastic shell (30; 32) facing away from the first reinforcing shell (31; 33) has an anti-reflective coating and / or wherein the side of the first plastic shell (30; 32) the guiding side of the first reinforcement shell (31 ; 33) has an anti-reflective coating.

16. Spectacle lens according to one of the above claims, wherein the side of the first plastic shell facing away from the first reinforcing shell (31 ; 33) has a hard coating.

17. Spectacle lens according to one of the above claims, wherein a second lens (24; 25) is provided, the lens having a third lens side (34; 37) facing the channel shell (13) and a fourth lens side (35; 38) facing away from the channel shell (13), and the channel shell (13) having a second channel side (36; 39) facing the second lens (24; 25), wherein the second lens (24; 25) has an imaging effect, wherein a second additional layer (26; 27) made of a nanoporous material with a refractive index of less than 1.3 is arranged between the third lens side (34; 37) and the second channel side (36; 39) at least along the light-guiding channel (21) such that the second additional layer (26; 27) is in direct contact with the second channel side (36; 39) to prevent total internal reflection of the light in the light guide channel (21) to allow light beams guided to the second channel side (36; 39), wherein the second lens (24; 25) has a second stack of a second plastic shell (30; 32) and a second reinforcing shell (31 ; 33), wherein the second reinforcing shell (31 ; 33) has a higher bending stiffness than the second plastic shell (30; 32).

18. Display device with a holding device (2) that can be placed on the head of a user, patent attorneys GEYER, FEH NERS & PARTNER Munich - Jena 24 an image generation module (5) attached to the holding device (2), which generates an image, a spectacle lens (3) attached to the holding device (2) according to one of the above claims, wherein the generated image is coupled into the spectacle lens via the entry section (28), guided in the channel shell (13) by at least one internal total reflection to the deflection section (18) and deflected at the deflection section (18) to exit the spectacle lens (3) via the back, so that the user can perceive the generated image as a virtual image when the holding device (2) is placed on the head.

19. Method for manufacturing a spectacle lens (3) for a display device (1) that can be placed on the head of a user and produces an image, wherein the spectacle lens (3) has a front (23), a back (11), an entry section (28), a deflection section (18) spaced apart from the entry section (28) and a light guiding channel (21) extending from the entry section (28) to the deflection section (18), wherein the method comprises: - Providing a channel shell (13) in which the light guiding channel (21) extends, wherein the light guiding channel (21) is designed to guide light rays (L1) of the generated image, which are coupled into the spectacle lens (3) via the entry section (28), to the deflection section (18), from which they are deflected to exit the spectacle lens (3) via the back (11), - Arranging a first additional layer (26; 27) made of a nanoporous material with a refractive index of less than 1.3 on a first channel side (36; 39) of the channel shell (13) at least along the light guiding channel (21) such that the first additional layer (26; 27) is in direct contact with the first channel side (36; 39) in order to enable total internal reflection of the light rays guided in the light guiding channel (21) at the first channel side (36; 39), and - Providing a first lens (24; 25) with a first lens side (34; 37) facing the first channel side (36; 39) of the channel shell (13) and a second lens side (35; 38) facing away from the channel shell (13), such that the first additional layer (26; 27) is arranged between the first lens side (34; 37) and the first channel side (36; 39), wherein the first lens (24; 25) has an imaging effect and comprises a first stack of a first plastic shell (30; 32) and a first reinforcing shell (31; 33), wherein the reinforcing shell (31; 33) has a higher bending stiffness than the first plastic shell (30; 32).

20. Method according to claim 19, wherein the step of providing the first lens (24; 25) is a provision of the first plastic shell (30; 32) and the first reinforcing shell (31; 33) such that both the first plastic shell (30; 32) and the first patent attorneys GEYER, FEH NERS & PARTNER Munich - Jena 25 Reinforcing shell (31 ; 33) in the first stack extending to a circumferential edge of the first lens (24; 25), and wherein the method further comprises providing a first clamping unit (40; 41) which clamps the first lens (24; 25) circumferentially.

21. Method according to claim 19, wherein the step of providing the first lens (24; 25) comprises: Providing the first reinforcement shell (31; 33) in direct contact and / or connected with the first additional layer (26; 27) such that the first reinforcement shell (31; 33) encloses the first additional layer (26; 27) in a gas- and moisture-tight manner, and - Providing the first plastic shell (30; 32) on the first reinforcing shell (31; 33) in the first stack, wherein the first reinforcing shell (31; 33) extends beyond the first plastic shell (30; 32) in plan view.

22. Method according to claim 21, wherein the step of providing the first plastic shell (30; 32) comprises forming the first plastic shell (30; 32) over the first reinforcing shell (31; 33) and / or joining the first plastic shell (30; 32) to the first reinforcing shell (31; 33).

23. A method according to any one of claims 19 to 22, further comprising: - Arranging a second additional layer (26; 27) made of a nanoporous material with a refractive index of less than 1.3 on a second channel side (36; 39) of the channel shell (13) opposite the first channel side (36; 39) at least along the light guiding channel (21) such that the second additional layer (26; 27) is in direct contact with the second channel side (36; 39) in order to enable total internal reflection of the light rays guided in the light guiding channel (21) at the second channel side (36; 39), and - Providing a second lens (24; 25) with a third lens side (34; 37) facing the second channel side (36; 39) of the channel shell (13) and a fourth lens side (35; 38) facing away from the channel shell (13), wherein the second lens (24; 25) has an imaging effect and comprises a second stack of a second plastic shell (30; 32) and a second reinforcing shell (31; 33), wherein the second reinforcing shell (31; 33) has a higher bending stiffness than the second plastic shell (30; 32).

Images