HEAD UP DISPLAY SYSTEM

Abstract

The present invention relates to a head up display system, in particular for a motor vehicle, comprising: a picture generating unit having a picture projection optics, a tilted mirror and an intermediate image plane, wherein light from the picture projection optics is deflected by the mirror toward the backside of the intermediate image plane, and an optical lens and/or mirror arrangement for magnifying and/or conveying a picture generated on the intermediate image plane to an optical combiner, wherein a pair of prisms is inserted in the optical path between the tilted mirror and the intermediate image plane to eliminate or mitigate specific light beams emanating from the intermediate image plane and traveling toward the tilted mirror and/or specific light beams emanating from the intermediate image plane already being reflected from the tilted mirror and traveling back toward the intermediate image plane.

Claims

1. A head up display system, in particular for a motor vehicle, comprising: a picture generating unit having picture projection optics, a tilted mirror and an intermediate image plane, wherein light from the picture projection optics is deflected by the mirror toward the backside of the intermediate image plane, and an optical lens and/or mirror arrangement for magnifying and/or conveying a picture generated on the intermediate image plane to an optical combiner, and a pair of prisms arranged in the optical path between the tilted mirror and the intermediate image plane to eliminate or mitigate undesired light beams emanating from the intermediate image plane and traveling toward the tilted mirror or undesired light beams emanating from the intermediate image plane being reflected from the tilted mirror and traveling back toward the intermediate image plane.

2. The head up display system of claim 1, wherein each one of the pair of prisms is a total internal reflection prism.

3. The head up display system of claim 1, wherein each one of the prisms is a triangular prism, a wedge-formed prism or a right angle prism.

4. The head up display system of claim 3, wherein the slanted surfaces of the pair of prisms are facing each other or wherein the thin end of a first one of the pair of prisms is located in proximity to the thick end of the second one of the pair of prims.

5. The head up display system of claim 3, wherein the surfaces of the two prisms facing each other are separated from another by an air gap smaller than 1 mm, preferably smaller than 0.2 mm or wherein the surfaces of the two prisms facing away from each other are arranged to be parallel.

6. The head up display system of claim 1, wherein the prisms of the pair of prisms are formed identical to each other.

7. The head up display system of claim 1, wherein the pair of prisms comprises a wedge-formed prism and a surface side of the wedge-formed prism is blackened to absorb total internal reflection light, wherein preferably the surface side is a side opposite to the angle defining the slope of the wedge-formed prism or a side parallel to the side opposite to the angle defining the slope of the wedge-formed prism.

8. The head up display system of claim 1, wherein the pair of prisms is adapted to eliminate rays having an angle of incidence significantly different, in particular larger than 5°, preferably larger than 10°, from an expected angle of incidence of rays originating from the picture projection optics and being deflected by the mirror onto the pair of prisms, wherein, in particular, a ray having an angle of incidence of more than 50° is totally internally reflected within a prism of the pair of prisms whereby the ray is guided to a blackened side surface of the prism for absorption.

9. The head up display system of claim 1, wherein the intermediate image plane is a diffusor screen.

10. The head up display system of claim 1, wherein the optical combiner comprises transparent glass, in particular a windshield of a motor vehicle or any other diffuse screen able to display the picture conveyed by the optical lens arrangement.

11. The head up display system of claim 10, wherein the optical combiner is arranged in the field of view of a user of the head up display, in particular a driver of a motor vehicle.

12. A head up display system, in particular for a motor vehicle, comprising: a picture generating unit for generating a picture on an image plane, and an optical lens arrangement for conveying a picture generated on the image plane to an optical combiner, and a pair of prisms arranged in the optical path between the image plane and the optical combiner to eliminate or mitigate undesired light beams traveling from the optical combiner toward the image plane or undesired light beams reflected from the image plane and traveling back toward the optical combiner.

13. The head up display system of claim 12, wherein each one of the pair of prisms is a total internal reflection prism or wherein each one of the prisms is a triangular prism, a wedge-formed prism or a right angle prism.

14. The head up display system of claim 13, wherein the slanted surfaces of the pair of prisms are facing each other or wherein the thin end of a first prism of the pair of prisms is located in proximity to the thick end of a second prism of the pair of prims.

15. The head up display system of claim 13, wherein the surfaces of the two prisms facing each other are separated from another by an air gap smaller than 1 mm, preferably smaller than 0.2 mm or wherein the surfaces of the two prisms facing away from each other are arranged to be parallel.

16. The head up display system of claim 12, wherein the prisms of the pair of prisms are formed identical to each other.

17. The head up display system of claim 12, wherein the pair of prisms comprises a wedge-formed prism and a surface side of the wedge-formed prism is blackened to absorb total internal reflection light, wherein preferably the surface side is a side opposite to the angle defining the slope of the wedge-formed prism or a side parallel to the side opposite to the angle defining the slope of the wedge-formed prism.

18. The head up display system of claim 12, wherein the pair of prisms is adapted to eliminate rays having an angle of incidence significantly different, in particular larger than 5°, preferably larger than 10°, from an expected angle of incidence of rays originating from the picture projection optics and being deflected by the mirror onto the pair of prisms, wherein, in particular, a ray having an angle of incidence of more than 50° is totally internally reflected within a prism of the pair of prisms whereby the ray is guided to a blackened side surface of the prism for absorption.

19. The head up display system of claim 12, wherein the image plane is a diffusor screen.

20. The head up display system of claim 12, wherein the optical combiner comprises transparent glass, in particular a windshield of a motor vehicle or any other diffuse screen able to display the picture conveyed by the optical lens arrangement or wherein the optical combiner is arranged in the field of view of a user of the head up display, in particular a driver of a motor vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] FIG. 1 depicts a side view of a situation in that glare arises due to the sun being at a specific orientation and sunlight entering the HUD system and getting reflected at the tilted mirror in the PGU,

[0053] FIG. 2 depicts a front view of the situation from FIG. 1 in that glare arises due to the sun being at a specific orientation and sunlight entering the HUD system and getting reflected at the tilted mirror in the PGU,

[0054] FIG. 3 depicts the details of the picture generation unit PGU with the desired light forming an intermediate image on the diffuser screen,

[0055] FIG. 4a depicts a top view of the picture projection unit PGU during the sunlight glare situation depicted in FIG. 1 and FIG. 2,

[0056] FIG. 4b depicts a top view of the picture projection unit PGU during the sunlight glare situation depicted in FIG. 1 and FIG. 2,

[0057] FIG. 5 depicts an embodiment of the invention with a TIR prism pair arranged between the diffuser screen and the tilted mirror and also illustrates the concept of total internal reflection,

[0058] FIG. 6 depicts a maximum evaluation area in which the eyes of a driver are located during normal head motion which needs to be monitored for sun glare, and

[0059] FIG. 7 depicts an embodiment of the invention comprising a TIR prism pair illustrating how sunlight causing glare in the HUD system is captured by the TIR prism pair and directed toward the absorption surface of the TIR prism pair.

DETAILED DESCRIPTION

[0060] FIG. 1 shows a side view of a situation in that glare arises due to the sun being at a specific orientation to generate glare in the driver's field of view.

[0061] Sunlight crosses the windshield 7 and enters the HUD system. Via the optical lens and/or mirror arrangement 6, the sunlight hits the diffuser screen 5, diffuses within the diffuser screen 5, hits the tilted mirror 4 in the PGU 2, is reflected back through the diffuser screen 5, and travels toward the driver's eye through the HUD Optics 6, and reflection by the windshield 7.

[0062] FIG. 2 depicts a front view of the situation of FIG. 1. In addition to FIG. 1, in FIG. 2 the SLM 15, Spatial Light Modulator, and the picture projection optics 2 guiding the light to the backside of the intermediate image plane 5 via the tilted mirror 4, are shown.

[0063] FIG. 3 shows the details of the picture generation unit 2, PGU, with the desired light forming an intermediate image on the diffuser screen 5.

[0064] The light beams 17 are modulated by the SLM 15, projected through the picture projection optics 3 and reflected by the tilted mirror 4 to form an intermediate image on the diffuser screen 5. When undesired sunlight reaches the diffuser screen 5, it diffuses therein and travels towards the mirror 4. The situation may arise that the mirror reflects parts of the sunlight back onto the diffuser screen 5 leading to glare in the view of the driver.

[0065] FIG. 4a shows a top view of the picture projection unit PGU 2 during the sunlight glare situation depicted in FIG. 1 and FIG. 2. The rays 18 of sunlight reach the tilted mirror 4 via the optical lens and/or the mirror arrangement 6 and the diffuser plane 5.

[0066] FIG. 4b shows the same top view of the picture projection unit PGU 2 during the sunlight glare situation as FIG. 4a, and indicates how the rays of sunlight 18 having reached the tilted mirror 4 are reflected back to the diffuser plane 5.

[0067] From there, the optical lens and/or mirror arrangement 6 guides these rays 18 to the windshield 7 and, finally, to the driver's eye.

[0068] FIG. 5 depicts one embodiment of the present invention with a TIR (Total Internal Reflection) prism pair 8 arranged between the diffuser screen 5 and the tilted mirror 4. FIG. 5 also illustrates the total internal reflection performed by the TIR prism pair 8.

[0069] The pair of prisms 8 is arranged in the optical beam path between the tilted mirror 4 of the PGU 2 and the intermediate image plane 5 (also: diffuser screen).

[0070] In this embodiment, each one of the prisms 9 forming pair of prisms 8 has the shape of a wedge, wherein the surfaces defining the thick end 12 and the thin end 11 are each blackened and are thus are adapted to absorb light.

[0071] The two wedge-shaped prisms 9 are aligned with each other in such a way that their sloping side surfaces face each other and their sides facing away from each other are aligned to be parallel to each other.

[0072] Further, there is an air gap 13 between the side surfaces facing each other which is preferably smaller than 0.2 mm. The air gap is preferably 0.1 mm wide.

[0073] Since the refractive index of the prisms is larger than the refractive index of the surrounding air, the effect of total internal reflection, TIR, may occur for any rays trying to travel out of a respective one of the prisms 9.

[0074] That means, once a ray has entered one of the prisms 9 it can leave the prism 9 only if the angle of incidence at the outgoing border of the prism 9 is below the so-called critical angle of the prism 9.

[0075] The critical angle depends on the refractive indexes of the prism 9 and the medium surrounding the prism, in the present case air. The refractive index of the prism 9 of the present embodiment is n.sub.d=1.8052 and the refractive index of air is assumed to be 1.0. Thus, when applying the formula for determining the critical angle θc,

θc=arcsin(n.sub.2/n.sub.1), if n.sub.1>n.sub.2

[0076] total internal reflection occurs for rays having an angle of incidence greater than the critical angle of 33.64°. Rays with an angle of incidence larger that the critical angle do not leave the prism 9 but are guided to one of its side surfaces 11, 12 which are colored black for absorption.

[0077] Thus, light from an external light source, e.g. sunlight, having an angle of incidence greater than the critical angle and reaching the diffuser plane 5 is absorbed and removed by the prism pair 8 on its way to the tilted mirror 4.

[0078] Rays emanating from the diffuser plane 5 which do not leave the prism 9 due to an angle of incidence at the prism border larger than the critical angle are deflected towards one of the blackened side surfaces 11, 12. The same applies to rays having passed the pair of prisms 8 already once travelling from the diffuser plane 5 to the tilted mirror 4 and being reflected back to the diffuser plane 5 through the prism pair 8.

[0079] As a result, the vast majority of sunlight rays are absorbed when trying to pass the pair of prisms, whereby glare situations are avoided and the comfort of the driver is increased.

[0080] FIG. 6 depicts a maximum evaluation area in which the eyes of a driver are located during normal head motion which needs to be monitored for sun glare.

[0081] Installing a HUD system 1 into the dashboard of a vehicle normally requires a lot of simulation to safeguard against glare situations. In particular, glare situations should under no circumstances occur in the eye box area 19, where the driver's eyes are located during normal head motion and positioning.

[0082] However, in order to reliably avoid any glare situations, glare situations are preferably suppressed within the larger evaluation area 20.

[0083] The present invention facilitates the implementation of HUD systems 1 into a vehicle, since occurrence of glare situations is suppressed by the pair of prisms 9 in the optical beam path. The pair of prisms 9 can be configured in such a way to avoid glare from occurring even in the larger evaluation area 20.

[0084] FIG. 7 depicts an embodiment of the invention comprising the TIR prism pair and illustrates how sunlight causing glare in the HUD system 1 is being captured and directed towards the absorption surfaces 11, 12 of the TIR prism pair 9.

[0085] If the prism pair 8 is not provided, the sunlight enters the HUD system through the optical lens and/or mirror arrangement 6 to hit the diffuser screen 5, diffuses within the diffuser screen 5, hits the mirror 4, is reflected back to the diffuser screen 5 and finally reaches the driver's eye through the optical lens and/or mirror arrangement 6 and reflection by the windshield 7.

[0086] As shown in FIG. 7, the prism pair 8 is interposed in the beam path to absorb undesired light entering the HUD system from external sources by total internal reflection. The undesired light can enter the prism pair 8 from the side of the diffuser screen 5 or from side of the tilted mirror 4 to be absorbed by the prism pair 8.

[0087] While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.