Image projection assembly and associated head-up display
The image projection system within the helmet's inner shell uses a prism-based optical projection block to compensate for visor aberrations, addressing bulkiness and regulatory issues, providing a clear virtual image.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- EYELIGHTS
- Filing Date
- 2025-12-23
- Publication Date
- 2026-07-02
AI Technical Summary
Existing helmet-mounted displays are bulky and expensive due to numerous optical elements, requiring external mounting and modification of the visor, and face regulatory challenges in the consumer market.
An image projection system integrated within the helmet's inner shell uses the existing visor to project a virtual image, employing a prism-based optical projection block with non-planar faces to compensate for optical aberrations, minimizing bulk and complexity.
The system projects a clear virtual image at a desired distance, minimizing bulk and mechanical complexity, while adhering to regulatory standards and integrating seamlessly with standard helmets.
Smart Images
Figure EP2025088857_02072026_PF_FP_ABST
Abstract
Description
[0001] DESCRIPTION
[0002] TITLE: Image projection system and associated head-up display
[0003] The present invention relates to an image projection system. The present invention also relates to an associated head-up display.
[0004] In the military, helmet-mounted displays (HMDs) use complex optical systems, often very bulky and expensive due to the large number of optical elements involved. Because of their size, these systems are often mounted on the outside of the helmet and frequently require the design of a specific visor.
[0005] In the consumer market, there are various head-up display helmet systems (products often sold as accessories) which place an optical system in front of the wearer's eye, but do not use the standard visor to project the virtual image.
[0006] Unlike in the military sector, manufacturers of consumer helmets are reluctant to modify the design of their visors, let alone adapt them for head-up display purposes. Furthermore, accessories such as communication systems and helmet-mounted head-up displays are now subject to new regulations (like ECE R22-06) and must pass various tests.
[0007] There is therefore a need for a head-up display solution that uses the existing visor of a helmet and is compact enough to be integrated as original equipment into the inner shell of helmets.
[0008] To this end, the invention relates to an image projection system for a head-up display using an existing helmet visor to form a virtual image in a viewing window for a helmet wearer. The image projection system is intended to be positioned within the helmet such that the light beam from the image projection system forms a virtual image visible in a viewing window for a helmet wearer after reflection from a specific area, referred to as the useful area, of the helmet visor. The image projection system comprises:
[0009] an image generation unit capable of generating an image in the form of a light beam, and
[0010] an optical projection block comprising at least one prism), the prism or prisms having three faces useful for projecting the light beam from the image generation unit to the visor of the helmet, the useful faces comprising: an input face receiving the light beam, an intermediate reflective face suitable for reflecting the light beam received by the input face, and an output face for the reflected light beam, the output face and at least one of the input face and the intermediate face being non-planar faces chosen so as to compensate for the optical aberrations of the virtual image induced by the shape of the useful area of the visor.
[0011] According to other advantageous aspects of the invention, the image projection assembly comprises one or more of the following features, taken individually or in any technically possible combination:
[0012] - the entrance face is not planar in order to compensate for the aberrations induced by the local shape of the useful area of the visor, and to optimize the flatness of the generated virtual image;
[0013] - the entrance face is aspherical;
[0014] - the intermediate face is not flat in order to compensate for the aberrations induced by the shape of the useful area of the visor, and to optimize the flatness of the generated virtual image;
[0015] - the intermediate face satisfies a polynomial equation, advantageously of order greater than two;
[0016] - the output face is the useful face with the highest power.
[0017] - when the useful area of the visor has a toroidal shape, at least the exit face is aspherical biconical,
[0018] - when the useful area of the visor has a spherical shape, at least the exit face is aspherical, and
[0019] -when the useful area of the visor has a shape other than a toric or spherical shape, at least the exit face is freeform;
[0020] - when the entrance face is convergent, the intermediate face is divergent, and when the entrance face is divergent, the intermediate face is convergent.
[0021] - the optical projection block includes at least one lens between the image generation unit and the prism or between the prism and the visor, so as to optimize the correction of optical aberrations of the virtual image, the lens being advantageously decentered so as to optimize the correction of optical aberrations of the virtual image in the whole of the observation window of the helmet wearer.
[0022] The present invention also relates to a head-up display using an existing helmet visor to form a virtual image in a viewing window for a helmet wearer, the head-up display comprising:
[0023] the helmet visor, and an image projection system as described above. The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:
[0024] [Fig. 1] Figure 1 is a schematic side-sectional representation of an example of a helmet shell with an existing visor, and into which an image projection system is integrated, and
[0025] [Fig. 2] Figure 2 is a schematic representation of an example of an image generation unit and an optical projection block of an image projection set, as well as an area of the visor of a helmet, useful for projection.
[0026] An example of a helmet 10 in which a head-up display 12 is integrated is illustrated by figure 1.
[0027] Helmet 10 is typically designed to be worn by the driver of a vehicle. The vehicle could be, for example, a motorcycle, scooter, quad bike, sidecar, Segway, moped, motorbike, bicycle, tricycle, or cargo bike. More generally, the vehicle could be any type of land, air, or sea vehicle.
[0028] Alternatively, helmet 10 is a personal protective helmet with an integrated visor.
[0029] The helmet 10 has a visor 14 integrated into the helmet 10. The visor 14 is an existing visor, that is, a visor that was not specifically designed for the head-up display 12. The visor 14 is typically a standard, off-the-shelf visor. The visor 14 has a semi-reflective property.
[0030] The head-up display 12 uses the visor 14 of the helmet 10 to form a virtual image in an observation window of a helmet wearer 10. It is understood that the visor 14 of the helmet 10 is deployed so that the reflection can take place.
[0031] The viewing window, also called the eyebox, is the volume in which the eye of the helmet wearer sees the virtual image in its entirety and the field of vision along and around the line of sight in which the entire image can be seen completely.
[0032] The virtual image to be generated is, for example, an image containing vehicle control information for the driver while the vehicle is being driven. Such control information includes, for example, navigation, safety, or communication information from an on-board vehicle system or an electronic device in the driver's possession, such as a smartphone. Alternatively, particularly in the case of a personal protective helmet, the virtual image may include safety information, alerts, or assembly instructions.
[0033] The head-up display 12 is, therefore, formed of the visor 14 and an image projection assembly 16.
[0034] The image projection assembly 16 is suitable for being positioned in the helmet 10 so that the light beam from the image projection assembly 16 forms a virtual image visible in an observation window of a wearer of the helmet 10 after reflection on the visor 14 of the helmet 10.
[0035] Preferably, the image projection assembly 16 is designed to be positioned in the helmet 10 so as to minimize the bulk of the image projection assembly 16 in the helmet 10.
[0036] In particular, an image projection system 16 generating such a light beam which is reflected on the visor 14 of a helmet 10, is visible in the examples in Figures 1 and 2.
[0037] The image projection assembly 16 includes an image generation unit 20 and an optical projection block 22.
[0038] The image generation unit 20 (in English PGU for "Projection Generation Unit") is designed to generate an image in the form of a beam of light.
[0039] The image generation unit 20 is, for example, a screen.
[0040] In one example, the image generation unit 20 is chosen so that the resolution of the generated image is sufficient for the resolution of the virtual image projected at the desired distance to be compatible with the resolving power of the eye. The image generation unit 20 is also chosen to satisfy luminance constraints and so that its pixel matrix is compatible with the amount of information to be displayed.
[0041] The optical projection block 22 is designed to send the light beam generated by the image generation unit 20 onto the visor 14 of the helmet 10.
[0042] The optical projection block 22 includes at least one prism 30.
[0043] Each prism 30, for example, is made of plastic or glass. In particular, a plastic prism is easily injection-molded on an industrial scale.
[0044] Each prism 30 has three useful faces for projecting the light beam from the image generation unit 20 to the visor 14 of the helmet 10. The useful faces are the faces of the prism 30 on the optical path of the light beam from the image generation unit 20. The useful faces include an input face F1 receiving the light beam, an intermediate reflective face F2 to reflect the light beam received by the input face F1, and an output face F3 for the reflected light beam.
[0045] The exit face F3 and at least one of the entrance face F1 and the intermediate face F2 are non-planar faces chosen to compensate for the optical aberrations of the virtual image induced by the shape of the area, called the useful area, of the visor 14 receiving the light beam. Advantageously, all three useful faces are non-planar to improve the compensation of aberrations induced by the shape of the useful area of the visor 14.
[0046] Preferably, the entrance face F1 is non-planar so as to compensate for the aberrations induced by the shape of the useful area of the visor 14, and to optimize the flatness of the generated virtual image.
[0047] The entrance face F1 is, for example, aspherical.
[0048] The reflective intermediate face F2 allows the light beam from the image generation unit 20 to be folded back. This minimizes the volume to be integrated into the helmet shell 10, and therefore reduces the bulk.
[0049] Preferably, the intermediate face F2 is not planar so as to compensate for the aberrations induced by the shape of the useful area of the visor 14, and to optimize the flatness of the generated virtual image.
[0050] The intermediate face F2 satisfies, for example, a polynomial equation, advantageously of order greater than two.
[0051] Preferably, when the input face F1 is convergent, the intermediate face F2 is divergent, and when the input face F1 is divergent, the intermediate face F2 is convergent. This optimizes aberration correction.
[0052] Preferably, the curvature of the output face F3 is chosen to adjust the magnification of the image projection assembly 16. The output face F3 is thus the useful face with the highest power. The significant curvature of the output face F3 allows the rays to be bent and also minimizes the volume of the prism 30.
[0053] An example of implementation:
[0054] when the useful area of the visor 14 has a toroidal shape, at least the exit face F3 is aspherical biconical,
[0055] when the useful area of the visor 14 has a spherical shape, at least the exit face F3 is aspherical, and
[0056] when the useful area of the visor 14 has a shape other than toric and spherical, at least the exit face F3 is freeform. In particular, in the example illustrated by figure 2, the inlet face F1 is an aspheric face, the intermediate face F2 is a polynomial reflective face, and the exit face F3 is an aspheric biconical face because the useful area is toric.
[0057] In one implementation example, the optical projection unit 22 comprises two prisms 30, and therefore six working faces. In this case, the prisms are arranged, for example, to bend the beam and reduce the bulk within the inner shell of the helmet 10. For example, the first prism 30 is arranged to receive the light beam from the image projection unit 16 and reflect it towards the second prism 30, which in turn reflects it towards the working area of the visor 14. The use of two prisms allows for even better correction of optical aberrations and chromatic aberration. Furthermore, it provides greater flexibility for integrating the image projection unit 16 into the helmet 10.
[0058] Optionally, one or more lenses are positioned between the 30 prisms.
[0059] Alternatively, the optical projection block 22 comprises a number of prisms 30 strictly greater than two, with possibly one or more lenses between at least two prisms 30.
[0060] Alternatively, the optical projection block 22 includes a single prism 30.
[0061] As an optional feature, the projection optical unit 22 includes at least one lens assembly between the image generation unit 20 and the prism 30, or between the prism 30 and the visor 14, in order to optimize the correction of optical aberrations in the virtual image. The lens assembly consists of one or more lenses. In particular, a lens assembly between the image generation unit 20 and the prism 30 reduces optical aberrations and partially corrects chromatic aberration. A lens assembly between the prism 30 and the visor 14 effectively reduces chromatic aberration, minimizes optical aberrations, and allows for adjustment of the projection distance if necessary.
[0062] Advantageously, the lens is decentered so as to optimize the correction of optical aberrations of the virtual image throughout the observation window of the helmet wearer 10.
[0063] The operation of the head-up display 12 integrated into the helmet 10 will now be described.
[0064] First, the image generation unit 20 generates an image in the form of a light beam. The light beam is received by the input face F1 of the prism 30, then reflected by the intermediate face F2 and exits through the output face F3 to be sent to the useful area of the visor 14.
[0065] The reflection of the light beam on the useful area of the visor 14 of the helmet 10 makes it possible to generate a virtual image visible to the wearer of the helmet 10.
[0066] Thus, the head-up display 12 described allows a virtual image to be projected from the existing visor 14 of a helmet 10. In particular, the image projection assembly based on a prism 30 comprising several useful optical faces makes it possible to achieve the compactness necessary for the integration of the system into the inner shell of most helmets, while minimizing the bulk and the complexity of mechanical integration.
[0067] The prism 30, having at least two non-planar working faces, corrects aberrations induced by the working area of the visor 14 and the asymmetry of the head-up display 12 (for example, an eyebox not perpendicular to the optical axis). This minimum of two non-planar working faces allows the virtual image to be generated at a distance of several meters, ideally at a desired distance, known as distance VI D, of 3 to 5 m, which is considered infinity for the eye, thus avoiding accommodation efforts.
[0068] Conversely, a prism 30 with only one non-planar optical face cannot provide visual aberration (VI) and optical correction, or the horizontal projection angle (LOA) becomes very unsuitable because the optical design will attempt to place the principal ray incident and reflected by the visor 14 in the same vertical plane to minimize optical aberrations induced by the visor 14 in the case of a visor with a vertical plane of symmetry. Note that if the visor 14 does not have a vertical plane of symmetry, it is impossible to obtain a virtual image with a prism 30 that only has one non-planar optical face.
[0069] In the case of a projection optical block 22 integrating only the prism 30, the design does not require opto-mechanical adjustment (retraction, centering, ...) between the different optical functions.
[0070] A person skilled in the art will understand that the embodiments described above are likely to be combined with each other when such combinations are compatible.
Claims
1. CLAIMS 1. Image projection assembly (16) for a head-up display (12) using an existing visor (14) of a helmet (10) to form a virtual image in a viewing window of a helmet wearer (10), the image projection assembly (16) being intended to be positioned in the helmet (10) such that the light beam from the image projection assembly (16) forms a virtual image visible in a viewing window of a helmet wearer (10) after reflection on an area, referred to as the useful area, of the visor (14) of the helmet (10), the image projection assembly (16) comprising: - an image generation unit (20) capable of generating an image in the form of a light beam, and - an optical projection block (22) comprising at least one prism (30), the prism or each prism (30) having three faces useful for projecting the light beam from the image generation unit (20) to the visor (14) of the helmet (10), the useful faces comprising: an input face (F1) receiving the light beam, an intermediate reflective face (F2) suitable for reflecting the light beam received by the input face (F1), and an output face (F3) for the reflected light beam, the output face (F3) and at least one of the input face (F1) and the intermediate face (F2) being non-planar faces chosen so as to compensate for the optical aberrations of the virtual image induced by the shape of the useful area of the visor (14).
2. Image projection assembly (16) according to claim 1, wherein the input face (F1) is non-planar so as to compensate for the aberrations induced by the local shape of the useful area of the visor (14), and to optimize the flatness of the generated virtual image.
3. Image projection assembly (16) according to claim 2, wherein the input face (F1) is aspherical.
4. Image projection assembly (16) according to any one of claims 1 to 3, wherein the intermediate face (F2) is non-planar so as to compensate for the aberrations induced by the shape of the useful area of the visor (14), and to optimize the flatness of the generated virtual image.
5. Image projection assembly (16) according to claim 4, wherein the intermediate face (F2) satisfies a polynomial equation, advantageously of order higher than two.
6. Image projection assembly (16) according to any one of claims 1 to 5, wherein the output face (F3) is the useful face having the highest power.
7. Image projection assembly (16) according to any one of claims 1 to 6, wherein: - when the useful area of the visor (14) has a toroidal shape, at least the exit face (F3) is aspherical biconical, - when the useful area of the visor (14) has a spherical shape, at least the exit face (F3) is aspherical, and - when the useful area of the visor (14) has a shape other than a toric or spherical shape, at least the exit face (F3) is freeform.
8. Image projection assembly (16) according to any one of claims 1 to 7, wherein when the input face (F1) is convergent, the intermediate face (F2) is divergent, and when the input face (F1) is divergent, the intermediate face (F2) is convergent.
9. Image projection assembly (16) according to any one of claims 1 to 8, wherein the optical projection block (22) comprises at least one lens between the image generation unit (20) and the prism (30) or between the prism (30) and the visor (14), so as to optimize the correction of optical aberrations of the virtual image, the lens being advantageously decentered so as to optimize the correction of optical aberrations of the virtual image in the whole of the observation window of the helmet wearer (10).
10. Head-up display (12) using an existing visor (14) of a helmet (10) to form a virtual image in a viewing window of a helmet wearer (10), the head-up display (12) comprising: - the visor (14) of the helmet (10), and - an image projection assembly (16) according to any one of claims 1 to 9.