VISUAL DISPLAY APPARATUS

Abstract: Display apparatus comprising a generally transparent injection moldable plastic substrate, a dichroic coating associated with the substrate, a solid state image generator operatively associated with the substrate and the dichroic coating, such that the image generated by the solid state image generator in a given wavelength range is reflected from the substrate to an observer while light of wavelengths outside of the given wavelength range passes through the substrate to the observer.

Description: VISUAL DISPLAY APPARATUS FIELD OF THE INVENTION The present invention relates to visual display apparatus and more particularly to displays which are superimposed on a transparent surface. BACKGROUND OF THE INVENTION Various types of displays exist wherein information is superimposed on the user's view of the outside world. Generally, such displays are known as Head-Up Displays or HUDs and are commonly employed in aircraft to enable a pilot to obtain necessary information without removing his eyes from the outside and needing to refocus his eyes in doing so. Conventional head up displays are relatively complex and expensive. These typically include high brightness CRTs and may employ a holographic combiner for providing relatively high optical quality and contrast with respect to background. The cost and complexity of conventional head up displays renders them unsuitable for most civilian applications and impracticable for mass market consumer applications. SUMMARY OF THE INVENTION The present invention seeks to provide a relatively inexpensive and simple superimposed display which, due to its simplicity and cost effectiveness is suitable for a wide range of applications . There is thus provided in accordance with a preferred embodiment of the present invention display apparatus comprising a generally transparent injection moldable plastic substrate, a dichroic coating associated with the substrate, a solid state image generator operatively associated with the substrate and the dichroic coating, such that the image generated by the solid state image generator in a given wavelength range is reflected from the substrate to an observer while light of wavelengths outside of the given wavelength range passes through the substrate to the observer. In accordance with a preferred embodiment of the invention, the substrate has optical power for reflection and the image generator is disposed in the focal plane of the substrate. Further in accordance with a preferred embodiment of the invention, the dichroic coating is formed directly on the substrate. According to an alternative embodiment of the invention, the dichroic coating is formed on a coating substrate which is in turn associated with the substrate. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: Fig. 1 is a schematic illustration of display apparatus constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 2A is a graph illustrating transparency/reflection of a dichroic coating formed on a polycarbonate visor for red illumination at an angle of incidence of 15 degrees; Fig. 2B is a graph illustrating transparency/reflection of a dichroic coating formed on a polycarbonate visor for green illumination at an angle of incidence of 15 degrees; Fig. 3 is a schematic illustration of display apparatus for an automobile windshield constructed and operative in accordance with a preferred embodiment of the invention; and Fig. 4 is a schematic illustration of display apparatus for an automobile windshield constructed and operative in accordance with a preferred embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Fig. 1 which illustrates schematically imaging apparatus constructed and operative in accordance with a preferred embodiment. A substrate 10, typically formed of a plastic material such as polycarbonate, defines goggles or a visor, which is shown in section in Fig. 1. A dichroic coating 12 is formed on the substrate 10, preferably on an inner surface thereof, either by direct vacuum deposition using a technique available from Denton Vacuum of Cherry Hill, New Jersey, U.S.A. or alternatively by means of a dichroic coated substrate, such as a film of polycarbonate which is adhered as by transparent adhesive to substrate 10. According to a preferred embodiment of the invention the substrate 10 is configured to have optical power for reflection but no optical power for transmission and may be formed with spheric or aspheric curvature as appropriate. An image generator 14 is arranged out of the line of sight between the user's eye or eyes and the substrate and so as to display an image which is reflected by the dichroic coating 12 back to the user's eye or eyes . A preferred image generator 14 may be a solid state high brightness green or red x 7 dot matrix such as model numbers HDSP2002 or HDSP2003 manufactured by Hewlett Packard. The image generator preferably provides a peak luminous intensity per LED of approximately 1000 microcandle, with a duty cycle of 20 % for a LED area of 5-8 x 10 " ? square feet, providing an average brightness of lOΘOFt Lm. The transmission/reflection curves of two suitable dichroic coatings are set forth in Figs. 2A and 2B. This average brightness is low compared with an average brightness of 5Θ00FtLm which can be realized from a cathode ray tube. It is a particular feature of the present invention that by use of the dichroic coating on the substrate 10 and by avoiding any attenuation through elimination of optics between the coating 12 and the image generator 1 , acceptable contrast is provided even against clear sky. It is a particular feature of the present invention that due to the fact that no optics are required or provided between coating 12 and the image generator l4, an extremely wide exit pupil 15 is provided, whose size is limited only by the size of the substrate area covered by coating 12. As a result, the user is free to move his head within a relatively large volume, while still obtaining a good image of the displayed information. The configuration and arrangement of the substrate 10 with respect to the eye or eyes of the user are such that the image reflected from the image generator 14 by the dichroic coating 12 to the eye or eyes of the user arrives at the user's eyes in generally parallel rays, as if coming from infinity and thus does not require constant refocusing of the user's eyes to see the reflected images. Reference is now made to Fig. 3. which illustrates display apparatus for an automobile windshield constructed and operative in accordance with a preferred embodiment of the invention and comprising a windshield 30 typically formed of polycarbonate optical plastic having a spherical or aspheric curvature, such as an off-axis parabolic curvature. A dichroic coating 32 is formed on the windshield 30. An image generator 34, which may be identical to the image generator 14 described hereinabove, is located preferably in the focal plane of the windshield, such that the images generated thereby are reflected by dichroic coating 3 to the eyes of a driver in parallel rays so as to appear to come from infinity. Reference is now made to Fig. 4 which illustrates an alternative arrangement of display apparatus wherein the dichroic coating is not formed directly on the window or windshield but rather on a second substrate 40 which is adhered by any suitable means onto the windshield. The arrangement of Fig. 4 is particularly useful for retrofit applications and for applications where coating of a large substrate is impractical or unacceptably costly. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow:

Claims: C L A I M S 1. Display apparatus comprising: a generally transparent injection moldable plastic substrate; a dichroic coating associated with said substrate; and a solid state image generator operatively associated with the substrate and the dichroic coating, such that the image generated by the solid state image generator in a given wavelength range is reflected from the substrate to an observer while light of wavelengths outside of the given wavelength range passes through the substrate to the observer. 2. Apparatus according to claim 1 and wherein said substrate has optical power in reflection and the image generator is disposed in the focal plane of the substrate. 3- Apparatus according to claim 1 and wherein said dichroic coating is formed directly on the substrate. 4. Apparatus according to claim 2 and wherein said dichroic coating is formed directly on the substrate. 5- Apparatus according to claim 1 and wherein said dichroic coating is formed on a coating substrate which is in turn associated with the substrate. 6. Apparatus according to claim 2 and wherein said dichroic coating is formed on a coating substrate which is in turn associated with the substrate. 7• An automobile comprising: a windshield; a dichroic coating associated with said windshield; and a solid state image generator operatively associated with the windshield and the dichroic coating, such that the image generated by the solid state image generator in a given wavelength range is reflected from the windshield to an observer while light of wavelengths outside of the given wavelength range passes through the windshield to the observer. 8. Apparatus according to claim 1 and wherein no optical elements are interposed between said image generator and said coating, thereby providing a wide exit pupil. 9 . Apparatus according to claim 2 and wherein no optical elements are interposed between said image generator and said coating, thereby providing a wide exit pupil. 10. Apparatus according to claim ~ and wherein no optical elements are interposed between said image generator and said coating, thereby providing a wide exit pupil. 11. Apparatus according to claim 1 and wherein the arrangement of the image generator and the coating is such that the resulting exit pupil is effectively limited only by the area of the substrate that is coated by said coating. 12. Apparatus according to claim 2 and wherein the arrangement of the image generator and the coating is such that the resulting exit pupil is effectively limited only by the area of the substrate that is coated by said coating. 13 • Apparatus according to claim 7 and wherein the arrangement of the image generator and the coating is such that the resulting exit pupil is effectively limited only by the area of the substrate that is coated by said coating. 14. Apparatus according to claim 1 and wherein the displayed image appears to an observer as being located at infinity. 15- Apparatus according to claim 2 and wherein the displayed image appears to an observer as being located at infinity. 16. Apparatus according to claim ~ and wherein the displayed image appears to an observer as being located at infinity.

Inventors: GERLITZ YONATAN, MORAN DAN, GERLITZ, YONATAN, MORAN, DAN
Applicants: GERLITZ YONATAN, MORAN DAN, GERLITZ, YONATAN, MORAN, DAN
Application year: 1992
Main classification: G02B27
IPC codes: B60K35, G02B5, G02B27