Head-up display without ghosting

Abstract

An image generation system for providing a ghost-free head-up display, the system comprising a display screen having a front surface and a rear surface, an image generation unit for projecting an image onto the display screen to reflect toward a predetermined eye-friendly zone, and a field lens, wherein the image generation unit is configured to project light through the field lens so that the light is incident on the front surface of the display screen to form a first virtual image, wherein a portion of the light is transmitted through the display screen and is incident on the rear surface of the display screen to form a second virtual image, wherein the first virtual image and the second virtual image have an offset, wherein the field lens is configured so that the offset is less than a threshold amplitude, and the first virtual image and the second virtual image substantially overlap when viewed from the eye-friendly zone.

Description

Technical Field

[0001] The present invention relates to display systems. In particular, but not exclusively, the present invention relates to apparatus for displaying images on a screen in a ghost-free manner. Background Art

[0002] A head-up display (HUD) is a known display in which an image is projected onto a transparent surface, such as a windshield or sun visor. Such displays are well known in many different environments, including vehicles.

[0003] In the automotive industry, most commercial HUDs use a separate optical screen (combined HUD) or are displayed directly on the windshield (windshield HUD). Combination HUDs can be installed in most types of cars without extensive modifications. They combine the real driving environment with the projected virtual image using a transparent plastic projection screen. While relatively inexpensive to install, plastic screens partially block the driver's field of view and perform poorly when the device is subjected to vibration.

[0004] Windshield-type HUDs utilize the vehicle's windshield to combine virtual images with the real environment. Because the windshield has a finite thickness (typically much thicker than the screen used in a combination HUD), the projected image will be reflected both on the front surface of the windshield and on the rear surface of the windshield, resulting in the original image and a secondary offset "ghost image." The term ghosting is used in the art and is used throughout this specification to describe the secondary offset image. To eliminate this effect, a special film can be coated on the windshield to enhance reflections from the front surface (thereby reducing subsequent reflections from the rear surface and reducing ghosting). While relatively low cost, such films may be visually unappealing, adversely affect image quality, and become less effective after long-term exposure to sunlight. Another solution is to provide a special multi-layer wedge-shaped windshield that effectively overlaps the two reflected images to present a single, clear image to the driver. Figure 1 A schematic diagram of a wedge-shaped windshield is shown. These purpose-built windshields must be designed specifically for each application and are expensive to manufacture.

[0005] Another approach is to design a windshield with one or more layers of emitting / scattering nanoparticles. When excited by a scanning laser projector, each layer produces visible emission in one of the R / G / B bands. By superimposing images from multiple bands, a color image is displayed on the windshield. This so-called full windshield HUD has infinite viewing angles, infinite display positions, and no laser speckle, but is equally expensive and complex to produce. In addition, because the driver must focus on the windshield to view the displayed information, multi-depth images (i.e., images with elements of different apparent depths) cannot be experienced.

[0006] Further difficulties arise when designing a HUD for applications where the windshield has a large tilt angle, such as those found in trains and trucks. For small cars, the tilt angle of the windshield is typically between 30° and 45°, and the HUD system is mounted just below the dashboard, making the design of the HUD system easier. However, for larger vehicles, the tilt angle of the windshield may vary over a range of time. For example, most train windshields have a tilt angle of 60° to 80°. For trucks and buses, the tilt angle can be even higher—up to 90°. Not only does the larger tilt angle, but the thicker windshields used in large vehicles make the ghosting problem more prominent by increasing the offset of the image reflected by the front and rear surfaces of the windshield, which also increases the cost of the traditional mitigation techniques discussed earlier.

[0007] Therefore, existing approaches do not allow for ghosting reduction across multiple different systems.

[0008] It is an object of the present invention to alleviate some of the above-mentioned disadvantages of the prior art. Summary of the invention

[0009] Aspects and embodiments of the invention provide apparatus as claimed in the accompanying claims.

[0010] According to a first aspect of the present invention, there is provided an image generating system for providing a ghost-free head-up display, the system comprising a display screen having a front surface and a rear surface, an image generating unit for projecting an image onto the display screen so as to reflect it toward a predetermined eye-adaptive zone, and a field lens, wherein the image generating unit is configured to project light through the field lens so that the light is incident on the front surface of the display screen to form a first virtual image, wherein a portion of the light is transmitted through the display screen and is incident on the rear surface of the display screen to form a second virtual image, wherein the first virtual image and the second virtual image have an offset, wherein the field lens is configured so that the offset is less than a threshold amplitude, and the first virtual image and the second virtual image substantially overlap when viewed from the eye-adaptive zone.

[0011] This approach allows for ghost-free projection without requiring any modifications to the display surface or internal structure. In addition, the technology is applicable to displays with a wide range of tilt angles up to 90°.

[0012] Optionally, the image generation unit and the field lens are configured such that light incident on the front surface of the display screen is collimated.

[0013] Optionally, the first virtual image is projected onto a first virtual image plane at a first projection distance from the eye zone, and the second virtual image is projected onto a second virtual image plane at a second projection distance from the eye zone.

[0014] Optionally, the field lens is configured to project the first virtual image and the second virtual image to a first projection distance and a second projection distance, so that an offset between the first virtual image and the second virtual image is lower than a threshold angular resolution.

[0015] Optionally, the threshold angular resolution is equal to the size of a pixel.

[0016] Optionally, the threshold angular resolution is equal to the angular resolution of the human eye.By reducing the offset to a value below the limit of the display and / or the resolution capability of the human eye, ghosting is effectively eliminated.

[0017] Optionally, the first virtual image and the second virtual image are offset in a plane perpendicular to the optical axis.

[0018] Optionally, the field mirror is provided by one of a concave mirror, a freeform surface, a Fresnel lens, a waveguide, a diffractive optical element, a holographic optical element or one or more tapered optical fibers. In particular, tapered optical fibers allow lensless enlargement of the projected image fiber space, thereby shortening the optical path of the light and allowing the overall space footprint of the system to be reduced.

[0019] Optionally, the image generating unit comprises a light source and a spatial light modulator.

[0020] Optionally, the image generating unit comprises a projector and a diffuser for realizing a projected image.

[0021] Optionally, the image generating unit comprises a laser and a 2D scanning mirror.

[0022] Optionally, the image generating unit comprises a holographic unit for producing a computer generated hologram and a diffuser for realizing the hologram.

[0023] Optionally, the image generation unit includes one or more of an LCD device, an LED device, a micro-LED device, an OLED device, or a digital light processing digital micromirror device. These devices can be activated by applying an electric current, which can be positioned and modulated as desired. They can also provide flexible multi-color displays.

[0024] Optionally, the system further comprises intermediate optics between the image generating unit and the field lens and / or between the field lens and the display screen.

[0025] Optionally, the intermediate optics comprises one of a folding mirror, a cylindrical mirror, a cylindrical lens, a waveguide, a diffractive optical element or a holographic optical element.Such intermediate optics allow the path of the light to be arranged around the physical confines of the installation environment and compensate for any optical effects of the windshield itself.

[0026] Optionally, the system further comprises an image processor in communication with the light field display, wherein the image processor is configured to resolve distortion caused by the optical setup so that the image perceived by the observer appears undistorted. This eliminates the need for any post-image generation correction and bulky correction optics. In addition, it provides greater flexibility to accommodate different display surfaces and optical setups.

[0027] Optionally, the screen of the head-up display is the windshield of the vehicle.

[0028] Optionally, the first virtual image and the second virtual image relate to a first image of a stereoscopic image pair. This enables a user to view an object or scene from multiple angles depending on which overlapping images they focus on.

[0029] Optionally, one or more of the field lens, the projection unit and / or the intermediate optical components (if present) are movable relative to each other.

[0030] Optionally, the first virtual image and the second virtual image are multi-dimensional images. Projecting three-dimensional images through the HUD system enables these images to be displayed with appropriately varying depths, thereby producing a convincing representation of real objects.

[0031] Optionally, the first virtual image and the second virtual image include image subsets, wherein each image of the subset is realized at a different distance from the focal length of the field lens, so that when it is projected onto the display screen, each image of the subset has a different apparent depth when viewed from the eyepiece zone.

[0032] Optionally, the system further comprises a photosensor arranged to capture light reflected by the display screen via the field lens. This allows the system to act as a camera that can be used to monitor the environment and / or users within said environment.

[0033] According to a second aspect of the present invention, a method for providing a ghost-free head-up display is provided, the method comprising generating an image at an image generating unit, the image to be presented on a display screen to be reflected toward a predetermined eye-adaptive zone, the display screen having a front surface and a rear surface, a field lens being provided between the image generating unit and the display screen, wherein a portion of light incident on the front surface of the display screen is reflected to form a first virtual image, and a portion of the light is transmitted through the display screen and incident on the rear surface to form a second virtual image offset from the first virtual image, and configuring the field lens so that the offset is less than a threshold amplitude and the first virtual image and the second virtual image are substantially overlapping as viewed from the eye-adaptive zone.

[0034] Further aspects of the invention will appear from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0036] Figure 1 is a schematic diagram of a known HUD system using a wedge-shaped windshield.

[0037] Figure 2 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0038] FIG. 3 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0039] Figure 4 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0040] FIG. 5 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0041] Figure 6 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0042] Figure 7 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0043] Figure 8 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0044] 9 is a pair of graphs showing the relationship between the angle of incidence and (a) longitudinal displacement and (b) lateral displacement for display screens of varying thicknesses, given that the refractive index of the windshield is 1.5.

[0045] Fig.10 is a graph showing the longitudinal and lateral displacement of the ghost image over the range of refractive indices of the display screen, given that the thickness of the windshield is 8 mm.

[0046] Fig.11The operation of an amplification system according to an embodiment of the present invention is described.

[0047] Fig.12 It is a graph showing the relationship between the focal length of the field lens and the distance from the image plane to the focal plane at different projection distances.

[0048] Fig.13 The operation of a diffuser according to an embodiment of the present invention is depicted.

[0049] Fig.14 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0050] FIG. 15 shows a schematic 3D model and prototype of a HUD system according to an embodiment of the present invention.

[0051] Fig.16 is a flow chart showing steps for designing and implementing components of a HUD system according to an embodiment of the present invention.

[0052] FIG. 17 shows a simulation of a HUD system according to an embodiment of the present invention.

[0053] Fig.18 is a model of a HUD installation environment according to an embodiment of the present invention.

[0054] Fig.19 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0055] FIG. 20 shows a simulation of a HUD system according to an embodiment of the present invention.

[0056] FIG. 21 shows a simulation of a HUD system according to an embodiment of the present invention.

[0057] Fig. 22 is a schematic diagram of a HUD system according to an embodiment of the present invention.

[0058] FIG. 23 shows a simulation of a HUD system according to an embodiment of the present invention.

[0059] FIG. 24 shows a simulation of a HUD system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0060] In one aspect of the invention, the device and display are mounted in a vehicle, such as a motor vehicle. Although the following description is described with reference to a HUD for a motor vehicle using a windshield as a display screen, the inventions and concepts described herein are applicable to other forms of HUDs (e.g., those mounted on other forms of vehicles, wearable platforms such as helmets or goggles, or other known types of HUDs), as well as displays in general.

[0061] In particular, it is envisioned that the present invention is installed and used in a restricted environment, such as a vehicle that can be operated on land (road / off-road, or track), under or at sea, in the air or in space. Examples may be, but are not limited to, cars, buses, trucks, excavators, exoskeleton suits for heavy tasks, motorcycles, trains, theme park rides; submarines, ships, small boats, yachts, motorboats and other types of marine vehicles; airplanes, gliders and other types of aircraft, spacecraft and space shuttles. In addition, the technology can be installed / integrated in a mobile platform, such as a driver / operator's head / eye protection device, such as a helmet or goggles. Therefore, any activity involving wearing a protective helmet / goggles can utilize the present invention described herein. These protective helmets / goggles can be, but are not limited to, worn by motorcyclists / bicyclists, skiers, astronauts, exoskeleton operators, military personnel, miners, scuba divers and construction workers. In addition, it can be used in a stand-alone environment of a game console, arcade, and used with a combination of external 2D / 3D displays, which can be used as a simulation platform. In addition, it can also be used in institutions and museums for educational and entertainment purposes.

[0062] Figure 1 A conventional HUD system using a wedge-shaped windshield is described.

[0063] A picture generating unit (PGU) 100a is shown projecting an image onto a windshield 1a, the image being reflected by both the front surface 2a and the rear surface 3a of the windshield 1a. The windshield 1a is formed of three layers: a first glass layer 4a, a second glass layer 5a, and an intermediate wedge layer 6a that offsets the first and second glass layers apart at an angle α. Due to the wedge layer 6a, the front surface 2a and the rear surface 3a of the windshield 1a are at different angles to the incident light, so that the images reflected by each surface overlap each other - and are perceived as a single image by the observer 200a, effectively removing any ghosting. However, this type of wedge-shaped windshield is expensive, difficult to manufacture and install, and is generally less flexible and strong than conventional windshields.

[0064] Figure 2 A HUD system 10 is shown according to an embodiment of the present invention.

[0065] The HUD system 10 consists of a PGU 100, a diffuser 110, a field lens 120, and a conventional windshield 1. The PGU 100 is provided by a projector, but the skilled person will appreciate that any suitable light source and imaging device may be used as long as they can be operated in the manner described below. Therefore, in one embodiment, the PGU 100 is formed by a laser and a 2D scanning mirror or a holographic unit that produces a computer-generated hologram to be formed on the diffuser 110. In an alternative embodiment, the PGU 100 is a light field unit to produce a three-dimensional stereoscopic light field image and to be formed on the diffuser 110. Digital micromirror devices (DMDs), liquid crystal display (LCD) devices, liquid crystal on silicon (LCoS) displays, laser projectors, light emitting diode (LED) displays, organic light emitting diode (OLED) displays, quantum dot light emitting diode (QLED) displays, and micro light emitting diode (μLED) displays may also be used in or as the PGU 100. The skilled person will appreciate that in DMD, LCoS and LCD embodiments, the PGU 100 will further include an initial light source. In contrast, a PGU 100 including LEDs will not require any other light emitting components. Furthermore, in DMD, LCoS, LCD or LED, OLED, QLED, μLED embodiments, no external image realization surface is required, so that the diffuser 110 is not present.

[0066] In one embodiment, the PGU 100 is capable of resolving any distortion caused by light transmission through components used to manipulate the optical path so that the final image visible to the user is displayed correctly. In one embodiment, this is achieved by a software-based distortion correction module in the PGU 100 (or otherwise communicating with it), which applies pre-compensating anti-distortion to the image in the digital domain before projection. In one embodiment, the distortion correction module calculates the expected distortion based on the optical components of the projection optical device and the display, and determines the anti-distortion that must be applied so that the final image visible to the user is not distorted. This allows the PGU to take into account asymmetries in the optical path of each image. This pre-compensating distortion can be determined by software in a known manner. This eliminates the need for any post-image generation correction and bulky correction optics. In addition, it provides greater flexibility to accommodate different display surfaces and optical settings.

[0067] In use, the PGU 100 projects light onto the diffuser 110 to form an image. The image is then projected through the field lens 120, which converges the projected image onto the windshield 1 and reflects the image on the windshield 1 towards the observer 200. The skilled person will understand that any suitable focusing and magnification optics may be used, provided they meet the requirements set forth below. In one embodiment, the field lens 120 is provided by a Fresnel lens. In one embodiment, the field lens 120 is configured so that a divergent light beam from the PGU 100 is changed into a nearly parallel light beam.

[0068] The path that light from the PGU 100 takes through the field lens 120 and is transmitted to the windshield 1 is referred to as the optical path. The skilled person will understand that any number of intermediate reflectors / lenses or other optical components may be placed along the optical path between the PGU 100 and the field lens 120 or between the field lens 120 and the windshield 1 to manipulate the optical path as necessary (e.g., to minimize the overall size of the HUD system 10).

[0069] One aspect of the present invention is that it allows for a flexible, configurable system that will result in ghosting being reduced in a non-installation specific manner. As described in detail below, by requiring the angular separation between the original image and the ghost to be less than the angular resolution of the human eye, and implementing the HUD system accordingly, variations in user height, display angle, size, etc. can be accounted for.

[0070] 3 , 4 and 5 depict embodiments including such intermediate optics, but for the sake of convenience neither the field lens 120 nor the windshield 1 are shown.

[0071] FIG3( a) shows a HUD system 10 composed of a PGU 100, a diffuser 110, first, second and third mirrors 111, 112, 113 and a field lens 114. Figure 2 1, the PGU 100 may be provided by any suitable image generating device, including those that do not require the diffuser 110. The field lens 120 and the windshield 1 are not shown, but are similar to Figure 2 As in the embodiment of the present invention, they will be arranged further along the optical path.

[0072] In use, the PGU 100 and diffuser 110 (if present) are arranged to project an image onto a mirror 111, which reflects the image onto a mirror 112. Mirror 112 is rotatable about the z-axis, as indicated by the curved arrow. The image is in turn reflected onto a mirror 113, which redirects the image and transmits it through a field lens 114.

[0073] Advantageously, this arrangement is flexible, thus allowing a ghost-free image to be projected onto the display under a variety of different conditions, such as different windshield thicknesses or driver's tilt angle heights, etc. In this embodiment, the PGU 100 and mirror 112 can be adjusted to ensure a ghost-free projection.

[0074] FIG3( b ) shows an alternative embodiment of a HUD system 10 consisting of a PGU 100, a diffuser 110, first and second mirrors 111, 112, and a field lens 113 a. As with the embodiment of FIG3( a ), any suitable image generation and implementation means may be employed. Again, the windshield 1 is not depicted, but is similar to the Figure 2 As is the case with , they will be arranged along the light path.

[0075] In use, as described above in relation to Figure 3(a), the PGU 100 and diffuser 110 are arranged to project an image onto mirrors 111 and 112. In this embodiment, mirror 112 is fixed and serves to redirect the image towards field lens 113a.

[0076] In this embodiment, the adjustability of the system comes from a folding mirror that can be rotated to compensate for differences in system variables.

[0077] All of these folding mirrors can be replaced by concave mirrors or free-form surfaces to compensate for imaging distortion or act as magnifying elements, thereby reducing the magnification of the field lens.

[0078] Figure 4 Still another alternative embodiment of a HUD system 10 is shown, consisting of a PGU 100, a diffuser 110, and first, second, and third mirrors 111b, 112b, 113b. As with the embodiments of FIGS. 3(a) and 3(b), any suitable image generation and implementation means may be employed. Although the field lens 120 and windshield are not depicted, they will be further described along the same lines. Figure 2 Consistent optical path arrangement.

[0079] In use, the PGU 100 and mirror 111b are arranged to reflect light from the PGU 100 to the diffuser 110, which in turn reflects the image onto the mirror 112b and finally onto the mirror 113b. The skilled person will appreciate that the diffuser 110 may be located at any point along the optical path before the field lens 120. Both mirrors 112b and 113b may be rotated about the x-axis to precisely control the direction of the projected image and adjust for any variations in the system, thereby providing a more adjustable system.

[0080] FIG5(a) depicts one embodiment in which waveguide 115a is located behind field lens 120 and is used to redirect light emitted by PGU 100 toward windshield 1 (not shown). FIG5(b) depicts an alternative embodiment in which waveguide 115b is used to redirect and diffuse light from PGU 100 to magnify the image. Although not shown, it is contemplated that waveguides 115a and 115b will be implemented as Figure 2-4 . In another embodiment, the waveguides 115a and 115b are replaced by diffractive optical elements (DOE) or holographic optical elements (HOE). The skilled person will understand that any suitable reflective or refractive optical components may be used as long as they operate in the manner described.

[0081] The arrangement of the optical devices of the present invention depicted in Figures 3, 4 and 5 enables the HUD system 10 to adapt to windshields with different thicknesses or tilt angles, or to observers with different heights. This can also be achieved by changing the tilt of the image generation unit 100 relative to the field lens 120. The area in which the user's eyes must be located in order to see the image reflected by the windshield 1 is called the eye-adaptive zone. In each of Figures 3-5, it is envisaged that the rotatable mirrors are provided with one or more actuators that communicate with the control device - thereby allowing their rotation angle to be changed. In another embodiment, additional actuators are provided on each mirror, diffuser 110 and PGU 10 to change their relative position and angular component in each of the x, y and z planes.

[0082] In one embodiment, the HUD system 10 is also configured to provide a 3D effect via autostereoscopy, where binocular parallax is used to create depth perception.

[0083] Figure 6 An embodiment of a HUD system 10 is depicted that includes two PGUs 100a, 100b and a pair of field lenses 120a, 120b. Figure 2 Each of the PGUs 100a, 100b may be provided by any suitable image generating device. For simplicity, the diffuser 110, the field lens 120 and the windshield 1 are not shown, but are similar to Figure 2 As with the embodiments described above, they will be arranged further along the optical path.

[0084] In use, each of the PGUs 100a, 100b projects one image of a stereoscopic image pair into one of the eyes 200a, 200b of an observer through a dedicated field lens 120a, 120b. Thus, the observer sees two substantially identical images with different binocular parallaxes. For each eye of the observer, a ghost-free image is generated according to the principles discussed below.

[0085] Figure 7 An alternative embodiment of the HUD system 10 is depicted consisting of the PGU 100, the field lens 120, the beam splitter 116, the first and second mirrors 112a, 112b, and another pair of field lenses 120a, 120b.

[0086] In use, the PGU 100 generates two images of a stereoscopic image pair by projecting a single image through the field lens 120 and onto the beam splitter 111. The image is then projected toward each of the mirrors 112a and 112b and through the field lenses 120a and 120b to the respective eyes 200a, 200b of the observer.

[0087] The optical system of HUD can be divided into three parts based on their different functions and logical order: combiner system, magnification system and intermediate optics. The combiner system defines the overall relationship between HUD and the installation environment. For example, Figure 8 As shown, the mounting position of the HUD system 10, the angle of incidence of the light beam emitted from the HUD to the windshield 1, and the angle of the light beam reflected from the windshield 1 to the observer / driver 200. Once the geometry of the combiner system is defined, the magnification system can be designed to magnify the projected image to an appropriate size so that the driver can comfortably observe the information. The magnification system can be designed so that the angular offset between the images reflected from the front surface 2 and the rear surface 3 of the windshield 1 is close to the minimum resolution capability of the human eye, thereby solving the ghosting problem. As described above, one advantage of the present invention is that the magnification system and / or the combiner system can be adjusted to ensure that a ghost-free image is produced in the event of a change in the geometry of the system.

[0088] When designing the magnification system, several important parameters of the HUD need to be considered, such as resolution, field of view (FoV), and eye zone. After the combiner system and magnification system are defined, the requirements of the intermediate optical device system are known, such as the size and position of the mirror and the diffusion angle of the diffuser 110 (if used).

[0089] Combiner System

[0090] In order to design a combiner system, it is necessary to understand the system requirements and the limitations of the installation environment. Figure 8 An exemplary environment is depicted.

[0091] Figure 8 A HUD system 10 is depicted that utilizes a vehicle's windshield 1 as a combiner device. The PGU 100, diffuser 110, and field lens 120 (not shown) are positioned so as to project an image from position (x1, y1) or position (x2, y2). The image P0 is reflected from the front and rear surfaces 2, 3 of the windshield 1 toward a location at L x ,L yThe windshield 1 is characterized by several parameters: the refractive index n of the windshield, the thickness d of the windshield c and the inclination angle α of the windshield. These factors define the lateral displacement δ between the original image reflected by the front surface 2 of the windshield 1 and the ghost image reflected by the rear surface 3 of the windshield 1 y and longitudinal displacement δ x . The relationship is given by the following equation:

[0092]

[0093]

[0094] where γ is the incident angle of the light beam emitted from the HUD system 10. In practice, the lateral displacement δ y is the main concern, since the driver will only observe the lateral displacement between the original image and the ghost image. As we can see in Eq. (1), δ y Subject to n, d c The typical refractive index n is usually in a small range of 1.5 to 1.52. If n is taken as n = 1.5, the relationship between the incident angle and the displacement between the double images can be plotted for a range of windshield thicknesses, for example, from 0 mm to 10 mm. The results are shown in Figures 9(a) and 9(b).

[0095] As can be seen from Figure 9(b), for the same incident angle, as the thickness of the windshield increases, the lateral displacement increases. As can be seen from Figure 9(a), for windshields of different thicknesses, as the incident angle increases, δ y It first increases and reaches its maximum value at about 50°, then decreases until it reaches 0°. In practical cases, γ is less than 50°, in which case a smaller incident angle is required to reduce or eliminate the longitudinal displacement δ y .

[0096] Fig.10 The lateral displacement and longitudinal displacement are plotted as a function of the incident angle for a refractive index range between 1.49 and 1.54. This shows that the refractive index does not have much effect and is therefore a less important factor when designing the HUD system 10.

[0097] For a given vehicle model, the refractive index, thickness and tilt angle α of the windshield 1 are set. At the same time, the position of the observer is usually fixed, which means that L x and L y The value of is known. Therefore, for a given n, d c ,α,L x and Ly , we can adjust the position of the HUD (x, y) to obtain the following relationship for different incident angles:

[0098]

[0099] It can be seen from equation (3) that the incident angle to the windshield 1 is determined by the inclination angle of the windshield 1 and the position of the observer 200. In order to reduce the lateral displacement of the double image, the degree of the incident angle must be reduced by increasing the value of y and reducing the value of x. Figure 8 , position (x2, y2) provides a smaller γ value than position (x1, y1).

[0100] Amplification system

[0101] Once the installation environment parameters and the location of the HUD system 10 are determined, δ y You can then define the projection distance required to achieve a ghost-free projection.

[0102] The minimum angular resolution that the human eye can discern is 0.02 degrees or 0.0003 radians, which means that if the δ y If the distance between the image and the observer 200 is less than 0.0003 radians, the observer 200 will see the two images as one image. The distance between the image and the observer 200 is d ei , which allows the condition for removing ghost images to be written as:

[0103]

[0104] Therefore, d ei =δ y A value of / 0.0003 or greater is sufficient, which can be achieved by modifying the amplification system.

[0105] Fig.11 Describes the key features of an abstract amplification system. For ease of understanding, Fig.11 A system with a single field lens 120 of focal length f is depicted. An image of size h is formed at a distance d from the field lens 120. o The light is transmitted to the image plane 300 and transmitted through the lens 120 to form an image of size H on the image plane 400. ei is the distance between the projected image and the left eye L and right eye R of the observer 200, given by equation (4). The environmental installation parameter defines the distance d between the exit aperture and the observer v , so that the distance d between the virtual image plane 400 and the lens i =d ei -d vAnd the magnification M = H / h is known. The imaging equation can be written as:

[0106]

[0107] Since the magnification system produces a virtual image, d i The sign in front is negative to keep d i Is a positive number.

[0108] Rearranging equation (5) gives:

[0109]

[0110] Due to d i Known, so d o As f changes, d o The value of will also increase.

[0111] When choosing the focal length of a lens, distortion effects must also be considered. When the image plane is close to the focal plane, barrel distortion of the target image may be observed, which increases as the square of the distance from the center point. One way to address this problem is to choose a lens with a larger aperture or a longer focal length. For a fixed projection distance, the relationship between the focal length and the distance between the image plane and the focal plane is as follows: Fig.12 As shown. It can be seen that for a given projection distance, a longer focal length provides a larger fd o value, which can reduce distortion. However, a longer focal length may increase the overall optical path of the system, making it bulky. Therefore, the focal length of the lens needs to be selected to balance image quality and overall HUD size.

[0112] Another important factor to consider is the aperture of the lens. The HUD has a specific field of view (FoV) and projects the image into the eyebox. The FoV is the angular size of the virtual image visible to the observer 200, while the eyebox is generally defined as a rectangular box within which the observer 200 can move their head and still see the virtual image. A larger FoV allows the observer 200 to see a larger image, and a larger eyebox defines the effective area where the driver can see the HUD content. The theoretical FoV of the HUD system 10 is determined by the size of the target image and the magnification of the lens, while the eyebox of the HUD system 10 is determined by the aperture of the lens. The FOV value can be expressed as:

[0113]

[0114] refer to Fig.11The model in , considers three different aperture sizes W1-W3. The minimum aperture size to achieve the theoretical FoV, W1, the aperture size that allows both eyes to see the virtual image, W2, and the aperture size that allows the driver to move his head within the eye zone, W3. Then the following equation is given:

[0115]

[0116]

[0117]

[0118] Where ipd represents the interpupillary distance, S e Represents the size of the eye zone. In practical applications, S e Usually greater than ipd, so W3>W2>W1, therefore, the minimum aperture size of the lens is determined by W3. ei and d v The required aperture size of the lens is given by equation (10).

[0119] Therefore, theoretical considerations drive and determine system requirements to ensure that the generated image is always ghost-free.

[0120] Intermediate optics

[0121] The previous sections detailed the determination of the HUD mounting location, the corresponding projection distance, and the selection of appropriate lenses. Intermediate optics are used to further customize the optical path and can be used to achieve high efficiency with a small overall system volume. Intermediate optics can include additional lenses, diffusers, mirror waveguides, diffractive optical elements, holographic optical elements, or clear glass.

[0122] The field lens 120 is the main optical element in the system and directly affects the quality of the projected image. Considering the eye-adaptive zone of the HUD system 10, the aperture size usually required is very large. Therefore, a Fresnel lens is selected as the field lens 120. However, the imaging quality of the Fresnel lens is not as good as that of an ordinary optical lens, which will cause distortion and aberration to the projected image. Therefore, in one embodiment, in order to optimize the imaging quality, a lens group can be used instead of a single Fresnel lens to improve the imaging quality.

[0123] In one embodiment, another important optical component is the diffuser 110. In a conventional HUD, a PGU 100, such as an LED panel or an LCD screen, is used as an image source, where the diffuser 110 is not required. However, a key disadvantage of LED panels and LCD screens is that the brightness and contrast of the images produced by such PGUs are quite low, making it difficult to see the projected image during the day. In order to improve the brightness and contrast of the HUD system 10, a digital micromirror device (DMD) projector can be used as the PGU 100. This requires placing a diffuser 110 after the projector to diffuse the light from the DMD so that the observer 200 can see the complete image.

[0124] There are three important factors when choosing diffuser 110: transmittance, diffusion angle and size. For transmittance, the higher the better. As for the diffusion angle and size, they are determined by the magnification system discussed above.

[0125] Fig.13 A portion of a HUD system 10 consisting of a PGU 100, a diffuser 110, and a field lens 120 is depicted. For simplicity, the diffuser 110 and the field lens 120 are represented by single lines indicating their positions and orientations - referred to as the diffuser plane and the lens plane, respectively. The diffuser 110 is located at a distance d from the PGU 100. d The diffuser 110 and the field lens are separated by a distance d1. a is the aperture size of the field lens 120.

[0126] In use, the PGU 100 projects light onto the diffuser 110 to form an image, which in turn is directed through the field lens 120. Thus, the diffuser plane is equivalent to Fig.11 The image plane depicted in the enlarged system is shown.

[0127] exist Fig.13 Where η is the divergence angle of PGU 100 and ε is the diffusion angle of diffuser 110. Fig.11 , the size of the image is defined as h, which is determined by the magnification system to meet the requirements of FoV and eye zone. To obtain the correct h value, the distance between PGU 100 and diffuser 110 must meet the following conditions:

[0128]

[0129] Then the size of the diffuser 110 should be larger than h. As for the choice of diffusion angle, it can be selected from Fig.11 Derived from this:

[0130]

[0131] Selecting a small diffusion angle limits the effective viewing angle, while selecting a large diffusion angle reduces the light intensity of the display. Additionally, the aperture size should be as large as possible to at least reach the required eyebox area. Therefore, the diffusion angle should satisfy W a the requirement of W3 in order to achieve the maximum light efficiency.

[0132] The mirror is another important optical device in the system, which is used to change the optical path to reduce the volume of the entire system or facilitate system design. Once the main structure of the magnifying system is defined, the size and position of the mirror added to the system can be calculated through the established optical path calculation to ensure that the mirror does not act as the aperture stop and have a negative impact on the performance of the HUD system 10.

[0133] System Settings

[0134] Fig.14 An exemplary installation environment is shown, where the HUD system 10 is arranged in the same way as Figure 2 and Figure 8 depicted in Fig. 15(a), where each component is depicted. The windshield tilt angle is 72°, the refractive index of the windshield is 1.5, and the thickness of the windshield is 8 mm. L x is 1.22 m, and Ly is 70 mm. The distance d between the observer 200 and the Fresnel lens v is approximately 1.5 m. According to the method described in the above section, 29° is selected as the minimum incident angle, allowing the longitudinal displacement of the double image to be calculated as 4.78 mm. Therefore, the ideal projection distance is approximately 14 m. To achieve a projection distance of 14 m, a Fresnel lens with a focal length of 400 mm and an aperture size of 300 mm × 300 mm is used. According to Equation (6), the image plane should be located 20 mm from the focal plane of the Fresnel length. The target FoV is 8° × 4°, and the eyebox area is set to 130 mm × 50 mm. Therefore, the theoretically required aperture size of the Fresnel lens is 344 mm × 172 mm. Therefore, using a Fresnel lens with an aperture size of 300 mm × 300 mm, the actual eyebox area is approximately 100 mm × 50 mm. For the diffuser 110, a holographic diffuser with a transmittance of 90% and a diffusion angle of 30° is selected.

[0135] To achieve a high projection angle and reduce the installation size, as shown in Fig. 15, two mirrors 111, 112 are located between the diffuser 110 and the field lens 120. Fig. 15 shows the HUD system 10 composed of the PGU 100, the diffuser 110, two mirrors 111, 112, and the field lens 120. The system 10 operates in the same way as at least Figure 2-4 described previously.

[0136] Fig.16 Summarizes the process for designing the HUD system 10 described previously.

[0137] In step S100, environmental conditions are input. These include the tilt angle, thickness and refractive index of the windshield 1, the position of the observer 200 and the available installation volume. These are then used to calculate the longitudinal displacement of the double image and the virtual image distance.

[0138] In step S110 , the required focal length of the field lens 120 is defined using the calculated virtual image distance and the desired FoV and eye zone size.

[0139] At step S120, the output characteristics of field lens 120 and PGU 100 are used to calculate the necessary position and parameters of diffuser 110 (if used) and the aperture of any mirrors employed in system 10. Thus, the output parameters are adjusted according to environmental conditions.

[0140] Figures 17(a) and (b) depict simulations of an embodiment of the present invention using a PGU 100, a diffuser 110, two reflectors 111, 112, and a field lens 120. The simulations are based on a windshield with an inclination angle of 78°, a thickness of 8 mm, and a refractive index of 1.5. In this case, the image is projected at a distance of 15 m to achieve a ghost-free image.

[0141] FIG. 17( c ) shows the footprint of the projected light on the field lens 120 to demonstrate that if the dimensions of each component are set correctly, there is no vignetting effect.

[0142] Applications involving asymmetrical or highly curved windshields

[0143] Compared to conventional automotive windshields, the thickness of windshields used in high-speed trains is much greater, as is the curvature. In addition, these windshields are generally much more expensive than windshields for conventional road vehicles. Therefore, it is economically impractical to manufacture wedge-shaped windshields for high-speed trains. However, based on the principles of the present invention, a ghost-free HUD is provided that does not require modification of the windshield.

[0144] A representative model of a high-speed train cockpit is shown in Figure 1. Fig.18 As shown, in the area of ​​interest (i.e., the area on the inner windshield surface where the image is projected), it has a windshield tilt angle of 20°, a windshield glass refractive index of 1.5, a windshield thickness of 28 mm, and a focal length of 714 mm for the cylindrical profile. The typical mounting position of the HUD provides an incident angle of 59° from the HUD to the windshield. According to equations (1) and (2), to achieve ghost-free projection, the projection distance needs to be higher than 66.67 meters. However, to achieve such a long-distance projection, the accuracy of the optical components must be very high and the image size must also be very large. As a compromise, a target projection distance of 20 meters was used.

[0145] Therefore, the design goal of the high-speed train HUD is to project the image to 20 meters away, with a field of view of H7°xV4° and an eye area of ​​130mm×50mm. Due to its curvature and thickness, the windshield will act as an anisotropic optical component with different magnifications along the horizontal direction (secondary direction) and vertical direction (primary direction, along which ghosting is mainly visible). The rest of the HUD system needs to be designed to accommodate this situation.

[0146] Likewise, if a single lens is used to project an image 20 meters away, the windshield will act as a cylindrical mirror, re-imaging it according to the off-axis imaging rules, so that the final image appears at a very short projection distance in front of the driver (e.g., less than one meter). Therefore, the curvature of the windshield must be compensated by using an additional optical component - such as a second anisotropic optical component, such as a cylindrical lens or a cylindrical mirror. In one embodiment, the additional optical component can be a free-form lens or a free-form mirror for more complex windshield contours.

[0147] Fig.19 An embodiment of a HUD system 10 formed by a fold mirror 211, an isotropic field mirror 220, and a concave cylindrical lens 221 is depicted, the HUD system 10 being configured to project an image onto a windshield 201 for viewing by an observer 200. For simplicity, an image generation unit or diffuser is not shown, but any suitable image generation and implementation means may be employed.

[0148] In use, the generated optical object is projected by the PGU and first imaged by the field lens 220 so that the image is within one focal length of the windshield 2011 so that the windshield 201 images it 20 meters away. Since the windshield 201 acts like a cylindrical mirror, it only has magnification along its power direction, which is a secondary direction that has no significant effect on the generation of ghost images (i.e., δ x ). Along the primary direction, the image is only at an apparent projection distance of 1.5 meters from the observer, so ghost-free projection is not achieved. To achieve ghost-free projection, a cylindrical lens 221 is used, which has optical power only in the primary direction. The cylindrical lens 221 is placed 10 mm after the ordinary lens and is configured so that the final projection distance along the primary direction is 20 meters, thereby matching the projection distance in the secondary direction. In short, the image is projected to 20 meters in both directions.

[0149] Figures 20 and 21 depict Fig.19 2D and 3D simulation results for the optical setup shown. Figure 21(a) is an imaging spot diagram of the full eye area showing nine fields of view of the generated optical object. Figure 21(b) shows the resulting image distortion due to the optical components, including the windshield 201.

[0150] To further optimize the imaging quality, more optical devices can be introduced into the system along the optical path as needed. In addition, as shown in FIG21( b ), due to the difference in magnification along the horizontal viewing direction and the vertical viewing direction provided by the illustrated arrangement, the image viewed by the observer 201 in the above embodiment will appear squeezed in the horizontal direction. In one embodiment, this is corrected in a known manner using a pre-compensated image generation device.

[0151] Fig. 22 Shown with Fig.19 The same alternative embodiment, except that a cylindrical mirror 212 is used instead of the mirror 211 and the cylindrical lens 221. Fig.19 The same principle is used to image the generated optical object using lens 220, and then further image it to 20 meters away in the secondary direction by windshield 201. Then, using cylindrical mirror 212, the optical power is increased in the primary direction to affect the ghost image to match the projection distance of 20 meters in the primary direction, thereby achieving ghost-free projection.

[0152] Figures 23 and 24 depict Fig. 22 2D and 3D simulation results of the optical setup shown in . It can be seen that although the use of cylindrical mirror 212 has a negative impact on the absolute distortion and overall image quality, it can reduce the achromatic dispersion in the full color image.

[0153] Thus, a HUD system 10 according to one aspect of the present invention is provided.

Claims

1. An image generation system for providing a ghost-free head-up display, the system comprising: a display screen having a front surface and a rear surface, the display screen having a first configuration, an image generating unit, configured to project an image onto a display screen so as to reflect the image to a first predetermined eye-friendly area, and a field lens having a predetermined aperture size, wherein the field lens (120) is configured to change a divergent light beam from the image generating unit (100) into a nearly parallel light beam, wherein the image generating unit is configured to project light through the field lens so that the light incident on the front surface of the display screen is collimated and forms a first virtual image, wherein a portion of the light passes through the display screen and is incident on the rear surface of the display screen to form a second virtual image, wherein the first virtual image and the second virtual image have an offset, wherein the field lens is configured such that the offset is below a threshold magnitude and the first virtual image and the second virtual image substantially overlap as viewed from the eye area, The offset between the first virtual image and the second virtual image is below a threshold angular resolution, and The aperture size allows the eye area to be larger than the pupil distance. The image generation unit and / or the field lens is further configured to adjust the offset between the first virtual image and the second virtual image when one of the configurations of the display screen or the predetermined eye-friendly zone changes.

2. The image generation system according to claim 1, characterized in that The first virtual image is projected onto a first virtual image plane at a first projection distance from the eye zone, and the second virtual image is projected onto a second virtual image plane at a second projection distance from the eye zone.

3. The image generation system according to claim 1, characterized in that: The field lens is configured to project the first virtual image and the second virtual image to a first projection distance and a second projection distance such that an offset between the first virtual image and the second virtual image is below a threshold angular resolution.

4. The image generation system according to claim 3, characterized in that: The threshold angular resolution is equal to the size of a pixel.

5. The image generation system according to claim 3, characterized in that: The threshold angular resolution is equal to the angular resolution of the human eye.

6. The image generation system according to claim 1, characterized in that: The first virtual image and the second virtual image are offset in a plane perpendicular to the optical axis.

7. The image generation system according to claim 1, characterized in that: The field mirror is provided by one of a concave mirror, a free-form surface, a Fresnel lens, a waveguide, a diffractive optical element, a holographic optical element or one or more tapered optical fibers.

8. The image generation system according to claim 1, characterized in that: The image generating unit includes a light source and a spatial light modulator.

9. The image generation system according to any one of claims 1 to 8, characterized in that: The image generating unit includes a projector and a diffuser for realizing a projected image.

10. The image generation system according to any one of claims 1 to 8, characterized in that: The image generation unit includes a laser and a 2D scanning mirror.

11. The image generation system according to any one of claims 1 to 8, characterized in that: The image generation unit comprises a holographic unit for producing a computer-generated hologram and a diffuser for realizing the hologram.

12. The image generation system according to any one of claims 1 to 8, characterized in that: The image generating unit includes one or more of an LCD device, an LED device, a micro LED device, an OLED device, or a digital light processing digital micro mirror device.

13. The image generation system according to claim 1, characterized in that: Also included are intermediate optics between the image generating unit and the field lens and / or between the field lens and the display screen.

14. The image generation system according to claim 13, characterized in that: The intermediate optical device includes one of a folding mirror, a cylindrical mirror, a cylindrical lens, a waveguide, a diffractive optical element or a holographic optical element.

15. The image generation system according to claim 1, characterized in that: Also included is an image processor in communication with the image generation unit, wherein the image processor is configured to resolve distortion caused by the optical setup so that the image appears undistorted on the display screen.

16. The image generation system according to claim 1, characterized in that: The display screen of the head-up display is the windshield of the vehicle.

17. The image generation system according to claim 1, characterized in that: The first virtual image and the second virtual image relate to first images of a stereoscopic image pair.

18. The image generation system according to claim 1, characterized in that: The field lens and the projection unit are movable relative to each other.

19. The image generation system according to claim 13 or 14, characterized in that: One or more of the field lens, the projection unit and / or the intermediate optics can be moved relative to each other.

20. The image generation system according to claim 1, characterized in that: The first virtual image and the second virtual image are multi-dimensional images.

21. The image generation system according to claim 1, characterized in that: The first virtual image and the second virtual image include image subsets, wherein each image of the subset is realized at a different distance from the focal length of the field lens, so that when it is projected onto the display screen, each image of the subset has a different apparent depth when viewed from the eye zone.

22. The image generation system of claim 1, further comprising a photosensitive device arranged to capture light reflected by the display screen through the field lens.

23. A method for providing a ghost-free head-up display, the method comprising: generating an image at an image generating unit, the image to be presented on a display screen to be reflected toward a predetermined eye zone, the display screen having a front surface and a rear surface, A field lens is provided between the image generating unit and the display screen, wherein the field lens has a predetermined aperture size and is configured to change a divergent light beam from the image generating unit into a nearly parallel light beam, A portion of the light incident on the front surface of the display screen is collimated and reflected to form a first virtual image, and a portion of the light is incident on the rear surface through the display screen to form a second virtual image offset from the first virtual image, and configuring the field lens so that the offset is below a threshold magnitude and the first virtual image and the second virtual image substantially overlap as viewed from the eyepiece, The offset between the first virtual image and the second virtual image is below a threshold angular resolution, and The aperture size allows the eye area to be larger than the pupil distance. A change in the eye zone or display screen is identified and an image generated at the image generating unit and / or field is adjusted so that the first virtual image and the second virtual image substantially overlap when viewed from the eye zone.

24. The method according to claim 23, further comprising projecting the first virtual image onto a first virtual image plane at a first projection distance from the eye zone, and projecting the second virtual image onto a second virtual image plane at a second projection distance from the eye zone.

25. The method according to claim 23, characterized in that The threshold angular resolution is equal to the size of a pixel.

26. The method according to claim 23, characterized in that The threshold angular resolution is equal to the angular resolution of the human eye.

27. The method according to claim 23, characterized in that The first virtual image and the second virtual image are offset in a plane perpendicular to the optical axis.

Images