Method for modifying a CRT display arrangement

Abstract: A display arrangement particularly suitable for replacing a conventional CRT in a pilot's helmet mounted display includes a light source 8 having an output which is modulated at 10 and scanned by a scanner 4 across a screen 6 to produce an image. The image is transferred into the pilot's field of view by relay optics 7. The scanner 4 and screen 6 are mounted on the pilot's helmet 2 and the light source 8 is remote therefrom.

Description: This invention relates to display arrangements and more particularly, but not exclusively, to helmet-mounted displays used by aircraft pilots. In a conventional helmet-mounted display, a small cathode ray tube (CRT) is mounted on the helmet of the pilot or other member of the air crew. The electron beam of the CRT is scanned over its faceplate to generate an image. Specially designed relay optics interface with the CRT faceplate to convey the image into the field of view of the pilot, typically being presented on a combiner attached to the helmet. The relay optics are generally quite complex, involving several elements for focussing and directing the image, and require a significant degree of design effort to integrate them with the CRT and with the part of the system which the pilot actually views. For example, if the image is to be projected onto a visor, the curvature of the visor, which may present a complex optical surface, must be taken into account. Electrical cabling connects, the CRT to the power supply and also includes an electrical path for applying control signals to the CRT for scanning the electron beam and modulating it with the required information. The present invention seeks to provide a display arrangement modification which is particularly suitable for use in helmet-mounted displays but which could also have application in other fields and in non-military environments. EP-A-0435523 discloses a helmet mountable display system for presenting a stereoscopic image to a viewer by displaying a raster scanned image to each eye of the viewer when wearing the helmet. This is done via optical fibres on the helmet conveying a modulated light beam through the helmet mounted lens systems to oscillatable deflecting surfaces on the helmet for generating the raster. EP-A-0367534 discloses a helmet mounted display system for presenting a stereoscopic image to a viewer by displaying a mechanically scanned image to each eye of the viewer when wearing the helmet. This is done via point light sources on the helmet conveying modulated light beams through helmet mounted input lens, horizontal and vertical mechanically movable deflecting surfaces on the helmet, and output lens for focusing the scanned rays onto respective screens. GB-B-1505873 discloses a visored helmet, a hologram formed on or carried by the visor and a reconstructing light source on the helmet for illuminating, and thereby reconstructing, the hologram. EP-A-0661574 discloses a helmet mountable display using a solid combiner block to move the exit-pupil of a user further away from the display than would be the case with direct transmission of the display image through air. This allows the user to see the display if wearing glasses. No one of the systems of these four earlier published documents makes any mention of replacing an existing cathode ray tube on a helmet by a much lighter scanner and an existing faceplate on the helmet by a much lighter screen, thereby reducing the weight carried by the user on his head and by his neck muscles. According to the invention, there is provided a method of modifying a display arrangement which includes a helmet to be worn on a user's head and having a display surface positioned forwardly of the user's eyes, a cathode ray tube supported by the helmet and having a faceplate on which an image to be displayed is scanned, and an optical relay supported by the helmet and interfaced with the faceplate, for relaying the image on the faceplate to the display surface for viewing by the user, The method including the steps of: a) replacing the cathode ray tube with a scanner, and positioning a generally planer, light transmissive screen in a position on the helmet formerly occupied by the faceplate; and b) connecting an optical fibre to the scanner, and conveying, from a light source located remotely from the helmet, a light beam modulated with information relating to the image to the scanner, for scanning the modulated light beam over the screen to produce the image on the screen, and for relaying the image on the screen to the display surface for viewing by the user. By employing the invention, it is possible to provide to a user an image of the same or superior quality as would be achieved with a CRT-based display arrangement and also provide a number of advantages. A CRT display is located close to the user's head and requires a high voltage supply. It also requires a relatively large and unwieldy umbilical cable to provide the electrical supply to the CRT. This leads to difficulties in adequately shielding the long run of cable to prevent electromagnetic interference effects. The size and weight of the umbilical may also inhibit the pilot's head movements and can be particularly problematical where the aircraft is expected to undergo manoeuvres involving high gravitational forces. Also, the designer must ensure that if a pilot is forced to eject from the aircraft, the umbilical will readily detach. In contrast, a scanning display arrangement does not require a high voltage supply to produce an image on the screen. The light source is remotely located from the user's head and is connected to the scanner via fibre optic means. It may be sufficient to have only a single, mono-filament optical fibre connecting the light source and scanner. Thus, the potential danger of having a high voltage supply is avoided and the umbilical to supply the display arrangement is of considerably less weight than the HV supply of a conventional CRT arrangement, is less restrictive of head movement and easier to detach in the event of pilot ejection. Also, electromagnetic interference problems are greatly reduced. Any electrical supply to the light source can be much more easily shielded as it is compact and may be included in already existing shielding arrangements for other electrical systems in a cockpit. Also, the head-mounted parts of a modified display arrangement in accordance with the method of the invention can be made much lighter in weight than the CRT components and also occupy the same or a reduced volume as compared to a CRT. The modified display apparatus includes an optical relay designed for use with a CRT and a display arrangement wherein the screen is located substantially in a position which would be occupied by a CRT faceplate if a CRT were included instead of the display arrangement. A modified display arrangement made in accordance with the invention may be used as a straight replacement for the CRT of a previously designed and installed display arrangement. It is not therefore necessary to completely redesign the relay optics or other means for conveying the image to the user. Replacement may be carried out with very little disruption to the part of the system already installed and the advantages which arise from using the invention may thus be incorporated into a previously existing, conventional arrangement with what is effectively a minor modification. The modification is also relatively inexpensive to implement as there is no significant redesign involved in installing it. A further advantage arising from the invention is that the display may be a colour display although, of course, monochrome may be provided. In normal helmet-mounted displays using CRTs, monochrome only is available because the shadow mask required for colour cannot be accommodated in the small space available and also vibration can be a problem. Furthermore, a very bright display is required and this is difficult to achieve in small colour CRT displays. In a display arrangement made in accordance with the invention, the light source may be a single laser or a single LED (light emitting diode). Modulation of the light may be implemented by using a modulated light source, for example, a modulated LED or miniature laser diode or by modulating light subsequent to its generation. In other embodiments, a plurality of lasers or a plurality of LEDs may be included or it may be desirable, in some arrangements, to have a combination of the two types of light source. The plurality of lasers and/or LEDs may emit light of different wavelengths to give a colour display. The image produced for viewing by the user may include alphanumeric information, for example, data concerning an aircraft's altitude, heading and velocity or other information concerning aircraft systems or weapon status, in the case of military aircraft. Alternatively, or in addition, the image may be a pictorial display, for example, giving representation of the view outside the cockpit as sensed, for example, by infrared imagers or image intensifiers. Alternatively, such pictorial information may comprise map data, for example. The scanner may be arranged to direct the light beam using, for example, electromagnetic, electro-mechanical or acousto-optic means, for example. In the latter case, the scanner may be operable without requiring a direct electrical supply to be provided from the aircraft, control being by way of modulated light signals transmitted along an optical fibre link. The screen of the display arrangements mounted on the helmet may, for example, be a plain glass plate or, for example, could be a dispersive hologram. In some embodiments the screen may comprise a phosphor faceplate. A laser beam, for example, an ultraviolet laser beam, by be scanned over the phosphor to produce a display. One way in which the invention may be performed is now described, by way of example, with reference to the accompanying drawing in which the sole figure schematically illustrates a display arrangement. With reference to the figure, an aircraft pilot 1 wears a helmet 2 on which is mounted a display arrangement shown generally at 3 which is arranged to present an image to him on a visor or combiner. The display arrangement 3 includes an acousto-optical scanner 4 for scanning a light beam transmitted to it via an optical fibre bundle 5 across a screen 6 which interfaces with relay optics 7 to transmit the image produced at the screen 6 into the pilot's field of view. The optical fibre bundle 5 is connected at its other end, remote from the helmet 2, to a light source 8 comprising a plurality of lasers 9 having outputs at respective different wavelengths and a plurality of modulators 10 associated with respective ones of the lasers 9. An image processor 11 is connected to the modulators 10 to control the outputs of the light source 8, the light beams being combined following modulation and transmitted along the optical fibre 5 to the scanner 4. The scanner 4 causes the modulated light beam to be scanned across the diffusive screen 6 in a raster pattern to produce an image for viewing by the pilot 1. The image may comprise alphanumerical information concerning the aircraft's flight, for example, or may consist of a pictorial display, for example, as may be obtained by an infra-red camera mounted to view the scene ahead of the aircraft. A combination of the two types of image information may also be produced at the screen 6 and then conveyed via relay optics 7 for viewing by the pilot 1. In this arrangement, the relay optics 7 were originally designed for use with a CRT display in which the faceplate of the CRT would have been located in the position now occupied by the screen 6. The pilot's cockpit includes an additional display 12 to be viewed as a head-down display, the head-down display 12 is also produced by scanning a modulated photon beam using a scanner 13 across a screen 14 to produce the desired image. An optical fibre 15 conveys modulated light from the light source 16 and modulator 17 which is also controlled by image processor 11 to produce the required image.

Claims: A method of modifying a previously existing display arrangement which includes a helmet (2) to be worn on a user's head (1) and having a display surface (3) positioned forwardly of the user's eyes, a cathode ray tube supported by the helmet (2) and having a faceplate on which an image to be displayed is scanned, and an optical relay (7) supported by the helmet (2) and interfaced with the faceplate, for relaying the image on the faceplate to the display surface (3) for viewing by the user (1), The method including the steps of: a) replacing the cathode ray tube with a scanner (4), and positioning a light transmissive screen (6) in a position on the helmet (2) formerly occupied by the faceplate; and b) connecting an optical fibre (5) to the scanner (4), and conveying, from a light source (8) located remotely from the helmet (2), a light beam modulated with information relating to the image to the scanner (4), for scanning the modulated light beam over the screen (6) to produce the image on the screen (6), and for relaying the image on the screen (6) to the display surface (3) for viewing by the user (1) by passing through relay optics (7) which were originally designed for use with the cathode ray tube display. A method according to claim 1, in which the display surface (3) utilised is a front curved part of the helmet (2) extending in use, over. the user's eyes. A method according to claim 2, in which the front curved part utilised is a visor or a combiner. A method according to any one of claims 1 to 3, in which the light beam is generated from a light source (8) which comprises at least one laser (9). A method according to any one of claims 1 to 3, in which the light beam is generated from a light source (8) which comprises at least one light emitting diode. A method according to claim 4 or claim 5, in which different light beams of different wavelengths are generated from a plurality of light sources (8) to produce a colour image. A method according to claim 6, in which different light beams are modulated with a plurality of modulating components (10). A method according to any one of claims 1 to 7, in which the connecting step is performed by an optical fibre (5) comprises a bundle of light carriers. A method according to claim 1, in which the scanning step is performed by sweeping the modulated light beam over a glass plate which constitutes the screen (6) to produce the image in the form of at least one of alphabetical, numerical and pictorial information. A method according to claim 1, in which the scanning step is performed by sweeping the modulated light beam over a holographic plate which constitutes the screen to produce the image in the form of at least one of alphabetical, numerical, and pictorial information.

Inventors: BARTLETT CHRISTOPHER TRAVERS, BARTLETT, CHRISTOPHER TRAVERS
Applicants: BAE SYS ELECTRONICS LTD, BAE SYSTEMS ELECTRONICS LTD.
Application year: 1999
Main classification: G09G3
IPC codes: G02B27, G09G3, G09G5, H04N5