Patent Application
20200124847
The teachings herein relate generally to head's up displays, and particularly to head's up displays for off-highway vehicles.
Typical problem with head's up displays (HUDs) is small field-of-view (FOV) and small eye-box (EB) size. This problem becomes particularly severe in off-highway vehicles (OHV) where FOV and EB requirements are particularly large, such as tractors, combine harvesters and forestry harvesters, for example.
Conventional solutions for increasing FOV and EB are to use curved combiner (U.S. Pat. No. 7,095,562B) or holographic combiner (JP2011201352A) or use of very large optics. However, these solutions are not desirable, as typical OHV cabins are limited in space, and curved or holographic combiners are precision components which are not easily integrated with the windshield.
Another typical problem with HUDs is that the combiner needs to be mounted in a specific position or angle to obtain optical functionality, which takes large amount of space from the cabin, or is disturbing the movements of the operator.
Optimal HUD has large FOV and ER, is small in size, has good image quality, and has a combiner integrated with the cabin windshield, or has combiner which takes only small amount of space from the cabin and is not disturbing the operator.
The present invention seeks to overcome at least some of the above difficulties and undesirable tradeoffs.
According to an exemplary embodiment of the invention there is a device for a head's up display, the device comprising:
In this embodiment the picture generating unit is arranged to deliver a beam of light, containing an image, to the projector optics. The projector optics and the combiner are arranged to form a virtual image of the image by reflecting a portion of the said beam from the micro-optical structures. In said reflection, for at least a part of the beam reflected from the micro-optical structure, the resulting reflection deviating from the hypothetical reflection from the extrapolated substrate surface.
The foregoing and other aspects of these teachings are made more evident in the following Detailed Description of the Preferred Embodiments, when read in conjunction with the attached Drawing Figures, wherein:
The advantages of the present invention include, without limitation, the following:
Referring now to the invention in more detail, in
Micro-optical structures are micro-sized structures, such as micro-scale prisms, grooves, notches, pyramids, wedges, etc. which has at least one facet whose surface direction deviates from the surface direction of the substrate, and so is able to provide reflection by that facet to a different angle than from the substrate. The facet of facets used for reflecting the light can also be curved. There may be one or two, or even more, reflections per micro-structure, depending on what is the most effective way to bend light into the desired direction. The reflection may be based for example on partial reflection from micro-prism surface optical interface, or on total-internal-reflection from air interface, or reflection from mirror-coated or thin-film coated micro-prism surface, depending on most effective method in each position on the combiner surface.
Advantages of these micro-optical structures are suitability for mass-production, good efficiency and contrast, for example, when compared to diffractive or holographic structures. The width of the facets of the micro-optical structures along the substrate surface may vary for example between 2 and 2000 micrometers, or more particularly between 20 and 400 micrometers. The height of the micro-optical structure facets may vary for example between 1 and 2000 micrometers, or more particularly between 10 and 400 micrometers, in direction perpendicular to substrate surface.
The purpose of the combiner is to reflect predetermined part of the light arriving from the HUD visualization means to the observer, while being substantially transparent so that observer can see through the combiner substantially unobscured way. Another purpose of the combiner is to form the virtual image of the image source as a part of the HUD visualization means to a predetermined location, by combining and merging the HUD virtual image to the see-through scenery. In addition, the combiner of the invention is capable to perform optical function to the reflected light, similar to for example curved mirror or lens, by the described micro-optical structures. The described structures allow specifying the optical function very freely, so that the combiner can work for example as convex or concave mirror, which can have spherical, aspherical, biconic, cylindrical or freeform optical function.
Existing curved combiners have severe disadvantage coming from the geometrical domain: their base shape (i.e. substrate form) defines the optical function. Even Fresnel lenses have the same limitation because of the continuity requirement along the fringes. This causes severe limitations how the combiner and the whole HUD system can be integrated to the cabin.
The combiner of the invention is advantageous in that the optical function is defined by the micro-structures and not by the substrate shape. This makes the cabin integration much easier, and for example allows larger FOV and larger EB in smaller space.
Some embodiments of the invention contain micro-optical prisms structures on a substrate. The following figures show exemplary cross-sections of some micro-optical prisms used in some HUD combiners of the invention.
Projector-up configuration means that the HUD visualization means reflects the image towards the observer from substantially above the eye-box, whereas projector-down configuration means that the image is reflected from substantially below the eye-box. In some embodiments of the invention the image may be reflected towards the observer from substantially the same vertical position than the eye-box, which may be interpreted as either projector-up or projector-down configuration.
As shown in
The reflecting micro-prism surfaces (702) can be coated by a thin-film coating or dichroic coating so that they are reflecting on only one or few bands of visible spectrum, or so that the reflection is enhanced or suppressed at one or few bands.
By adjusting the exact shape and directions of the prism surfaces (702), the direction of the reflected tight can be precisely adjusted.
The micro-prisms (202) can be arranged in an array to the same transparent substrate (204, 708). The array may be a discrete array, where large portion of transparent substrate is prism-free. By discrete array we mean an array of separate micro-structures. When micro-structures are separate, they share only the same substrate, or the same substrates, and they have no other common facets.
In this kind of discrete array arrangement by adjusting the distance between the prisms and the size of the prisms, the portion of the light transmitted unobscured through the transparent substrate can be adjusted and correspondingly the portion of the light which is reflected to the eye-box can be adjusted.
The advantage of the described discrete array arrangement is that its operation does not necessarily require thin-film or dichroic coatings which reflect different portions of the visible spectrum with different reflectance, but the discrete array arrangement may work substantially equal efficiency through the substantially whole visible range ranging from approximately 400 nanometers to approximately 700 nanometers.
Another advantage of the discrete array arrangement is that the most of the combiner area may be free of micro-structures, which ensures good see-through image quality.
The spacing of the micro-structures may be selected to be substantially smaller than size of the light beam which is arriving through the eye pupil of the observer. The spacing may be for example between 10 and 3000 micrometers, or between 50 and 1000 micrometers more particularly. This may make the micro-structures substantially invisible to eye in normal operation when the eye is focused to the virtual image.
The above described micro-prisms can be used to guide light to the desired direction. When micro-prisms are arranged in array form, their ray-guiding properties can be arranged so that it resembles function of a curved mirror. This kind of arrangement is free of many restrictions of continuous surfaces, or even restrictions of grooved Fresnel lens forms. As the micro-structures are separate, their shape can vary freely over the substrate.
This discrete micro-prism array works as a beam-splitter, which passes large portion of the beam through the array unchanged and reflects the other portion of the beam With desired manner. For the reflected portion of the beam, the film is a reflective mirror with optical function such as optical power for example. The reflective mirror can resemble operation of an aspherical mirror, cylindrical mirror, elliptical mirror, biconic mirror or any form or combination of them just by varying the aforementioned prism surface orientations in different portions of the discrete array.
The optimal arrangement of micro-structures may be circular instead of rectangular, too, depending on the desired optical function.
The described discrete array of micro-prism structures can be manufactured on a rigid substrate, or on a flexible film which can be attached to a rigid substrate such as planar combiner substrate or windshield for example.
This new kind of component, discrete micro-prism array film, can be used as a combiner in a HUD in the following ways.
Due to the optical power, a real image of the image source may be formed between the projector unit and the combiner.
Although described in the context of particular embodiments, it will be apparent to those skilled in the art that a number of modifications and various changes to these teachings may occur. Thus, while the invention has been particularly shown and described with respect to one or more preferred embodiments thereof, it will be understood by those skilled in the art that certain modifications or changes may be made therein without departing from the scope and spirit of the invention as set forth above, or from the scope of the ensuing claims.
This application claims priority to U.S. Provisional Application Ser. No. 62/846,954, filed on Oct. 17, 2018 and entitled “Head's up display combiner”, the contents of which are incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62746954 | Oct 2018 | US |
