WO2005034522A1

WO2005034522A1 - Projection system having a secured optical engine comprising a supplementary image source

Info

Publication number: WO2005034522A1
Application number: PCT/EP2004/052431
Authority: WO
Inventors: Lilian Lacoste
Original assignee: Thales
Priority date: 2003-10-07
Filing date: 2004-10-04
Publication date: 2005-04-14
Also published as: FR2860602B1; FR2860602A1

Abstract

The invention concerns image projection systems having an optical engine and, in particular, secured systems that are highly resistant to malfunctions. Traditionally, projection systems have a color optical engine (1) having 3 sources of monochrome primary images. The aim of the invention is to realize a projector having a secured color optical engine comprising a supplementary image source (34, 44) or standby source capable of compensating for the malfunction of one of three monochrome primary image sources. The supplementary image source simply comprises an imager (34) of the same type as the imagers of the primary image sources and a light source (44) capable of emitting in a selectable spectral band. An optical mixing unit (2) provided in the shape of a cube having three semireflecting edges (21, 22, 23) makes it possible to mix the four images originating from the four image sources. The advantages of this arrangement are numerous. A high reliability of the optical engine is obtained without loss in quality of the image while involving only a marginal increase in costs, bulkiness and complexity.

Description

PROJECTION SYSTEM WITH SECURE OPTICAL MOTOR COMPRISING AN ADDITIONAL SOURCE OF IMAGES

The field of the invention is that of projection systems, in particular with optical valves, and more particularly secure systems having a high resistance to breakdowns. 5 To make presentations of information, direct vision displays of the flat screen type are generally used, for example with liquid crystal matrices. For certain applications, in particular for the presentation of information on aircraft dashboards 10, the presentation of information by means of several large displays has certain drawbacks. These are essentially: • Resistance to breakdowns. When a screen is down, the total area for presenting information decreases. This problem is all the more important as the number of initial screens is low. However, for some aeronautical applications, the presentation is made on only 4 main screens. We can, of course, reconfigure the screens that are still functional to limit the loss of information, but always at the cost of degraded presentation ergonomics, especially if the broken screen is placed in front of the pilot. In this case, the availability of information may be affected. • Adaptability. Depending on the carrier, the dimensions and ergonomics of the dashboard vary. The size, shape and resolution of the screens must then be adapted, but it is not possible to adapt the screen sizes without studying and developing new arrays and new light boxes, which require costs. and considerable development times. • Ergonomics. Each screen has a mechanical frame necessary for housing the control circuits of the matrix type displays, which necessarily limits the area available for displaying information. Also, in recent years, other display devices have been developed. These are image projection devices. Figure 1 shows a device of this type. It includes: • A source of color images 1 also called an optical engine providing a color image of small size (typically a few centimeters on the side) and at high resolution (typically a few million pixels). • A projection screen 11 placed before the eyes 12 of the user. • A projection optic 10 which focuses the image supplied by the optical engine on the projection screen 11 and thus presents the user with an enlarged final image. The propagation of the beams is represented by dotted lines in FIG. 1. Generally, the optical engine consists of three sources of monochrome primary images each generating one of the three components of the initial color image. These image sources include a primary imager and an associated light source. Imagers are also called micro-displays in Anglo-Saxon terminology. Primary imagers operate by modulating the light from the associated colored light source. The superimposition of the three images from the primary image sources by a mixing device forms the initial color image. Imagers can operate either by reflection or by transmission. The imagers operating by reflection are in particular imagers of the LCOS type (acronym for Liquid Crystal On Silicon) or DMD (acronym for Digital Mirror Device) or DLP (acronym for Digital Light Projector). Imagers operating by transmission are also called optical valves. The optical valves are, for example, liquid crystal arrays. Each optical valve is then lit by a monochrome light source. The diagram in FIG. 2 shows a color imager operating from optical valves. It includes three optical valves 31, 32 and 33 illuminated by light sources 41, 42 and 43 emitting in different spectral bands, typically in blue, green and the red. A mixing cube 2 comprising two semi-reflecting plates 21 and 22 perpendicular to one another makes it possible to mix the three optical beams 61, 62 and 63 coming from the optical valves 31, 32 and 33 to reconstitute the color image. This system has several advantages. From a single color optical engine, it is of course possible, by modifying the optical parameters of the projection system, to change the magnification of the system and consequently the size of the final image. The size of the system can easily be adapted to different configurations of dashboards. In addition, by placing several display devices side by side, it is possible to perform a panoramic display without image cuts. It is also possible to build a secure visualization system architecture from primary projection devices. To secure the display system, the display area is then separated into independent areas (screen tiling) associated with one or more redundant primary projection devices. US Patent 6,497,486 describes a system of this type comprising at least two projection devices. As shown in FIG. 1 of this patent, a specific magnification lens placed in front of one of the color imagers makes it possible to double the size of the image coming from said projector in the event of failure of the second projector. The user thus keeps an image of constant size in the event of a breakdown. Of course, the resolution of the image is halved and this system requires at least two projectors to be operational. The object of the invention is to improve the security of a system with several redundant projectors from a single projector with a single color optical engine comprising an additional image source or backup source capable of compensating for the failure. from one of the three sources of monochrome primary images. The additional image source includes an imager of the same type as that of the primary imagers and a light source capable of emitting in a selectable spectrum. This source can thus substantially emit any one of the three spectra of the 3 light sources of the primary displays. A specific mixer optical unit allows the four images from the four image sources to be mixed. More specifically, the subject of the invention is an optical engine for a device for projecting color images comprising a first imager lit by a first light source emitting in a first spectrum, a second imager lit by a second light source emitting in a second spectrum, a third imager illuminated by a third light source emitting in a third spectrum and an optical mixer, the images of the three imagers through the optical mixer being perfectly combined so as to form a single color image, characterized in that said optical motor also comprises at least a fourth imager illuminated by a fourth light source emitting in a spectrum adjustable by control means, the image of said fourth imager through the optical mixer also being perfectly merged with the images of the first, of the second and third imager so that in case of pan of one of the three imagers or their associated light source, the fourth imager can replace it without altering the quality of the final color image.

The invention will be better understood and other advantages will appear on reading the description which follows given without limitation and thanks to the appended figures among which: • Figure 1 represents a general view of a motorized projection device optics; • Figure 2 shows an optical engine with 3 optical valves according to the prior art; • Figure 3 shows a first embodiment of the optical engine according to the invention; • Figure 4 shows a second embodiment of the optical engine according to the invention; • Figure 5 shows an exploded view of the optical mixer according to this second embodiment; • Figure 6 shows a first embodiment of the lighting in the case where the imagers are optical valves; • Figure 7 shows a second embodiment of the lighting of the optical valves; • Figure 8 shows the electronic control architecture of an optical engine according to the invention.

FIG. 3 represents a sectional view of a first embodiment of the optical engine according to the invention. Image source imagers are light valves. The optical engine then includes: • 4 identical optical valves 31, 32, 33 and 34 operating by transmission; • 4 light sources 41, 42, 43 and 44. Each source is associated with an optical valve. The optical valve-light source association constitutes a primary image source. Thus, the first optical valve 31 is lit by the first light source 41 emitting in a first spectrum, the second optical valve 32 is lit by the second light source 42 emitting in a second spectrum, the third optical valve 33 is lit by the third light source 43 emitting in a third spectrum. The fourth optical valve serving as an emergency valve 34 is illuminated by the fourth light source 44 emitting in an adjustable spectrum by control means; • 1 mixing optical unit 2 monobloc composed of 5 elementary prisms with flat faces as shown in figure 3. 3 prisms are identical roof prisms, the other two are prisms whose section is a rectangular trapezoid as shown in figure 3 Certain faces of the prisms are treated so that once assembled, the mixer unit comprises 3 semi-reflecting plates 21, 22 and 23 arranged as shown in FIG. 3. The first plate 21 transmits the first and the second spectrum and reflects the third spectrum, the second plate 22 reflects the first spectrum and transmits the second and the third spectrum. The third semi-reflecting plate 23 does not have to have special photometric properties. Indeed, it is always possible to adjust the emission level of each of the light sources so that after crossing this third plate, the colorimetry of the image is respected. This arrangement makes it possible to optimize the transmissions of the colored light beams 61, 62 and 63 coming from the light sources and circulating through the mixer block. Thus, for example, the beam 61 coming from the light source 41 is first of all perfectly transmitted by the semi-reflecting plate 21 then reflected by the semi-reflecting plates 22 and 23. Of course, this arrangement of the mixer unit can also be adapted to other types of displays operating either by reflection or by transmission. The geometry of the mixer block and the arrangement of the semi-reflecting plates and the optical valves is such that the four images of the optical valves through the mixer block are perfectly combined. In normal operation, the primary image sources consisting of the optical valves 31, 32 and 33 associated with the light sources 41, 42 and 43 provide the modulated light beams 61, 62 and 63 which after reflection and transmission through the mixer block form the initial colored image. Under these conditions, the optical valve 34 as well as its light source 44 are switched off. In the event of a simple failure, either of an optical valve 31, 32 or 33, or of a light source 41, 42 or 43, the optical valve and the corresponding light source are switched off. In this case, the optical valve 34 and the light source 44 are activated. The video information dedicated to the disconnected optical valve is sent to said optical valve 34 and the light source 44 is controlled to emit the spectrum of the disconnected light source. Thus, the optical valve 34 completely replaces the failed optical valve. Optical quality and resolution of the final image are perfectly maintained. Failure of the backup optical valve 34 or its illuminating light source is highly improbable since these are only activated in the event of failure of the primary image sources. Therefore, these components are intended to operate only for limited periods of time. Furthermore, the failure of the backup image source has no immediate consequences in normal operating mode and can be detected on initialization of the projection device by a simple integrated test. The operation of the optical engine as just described can be applied to all types of imagers operating both by reflection and by transmission. FIG. 4 represents a perspective view of a second embodiment of the device according to the invention. The optical engine also includes: • 4 identical optical valves 31, 32, 33 and 34 operating by transmission; • 4 light sources 41, 42, 43 and 44. Each source is associated with an optical valve. The combination of optical valve and light source constitutes a primary image source; • 1 optical mixer 2 monobloc cube-shaped composed of 8 elementary prisms with flat faces. The structure of the prisms and their arrangement is indicated in the exploded view of FIG. 4. Certain faces of the prisms are treated so that once assembled, the mixing unit comprises 3 semi-reflecting blades 21, 22 and 23. The first blade 21 transmits the first and the second spectrum and reflects the third spectrum, the second plate 22 reflects the first spectrum and transmits the second and the third spectrum. The first semi-reflecting strip 21 is arranged perpendicular to a first face of said cube and along one of the diagonals of said face, the second semi-reflecting strip 22 is also arranged perpendicular to said first face and along the second diagonal of said face, the third semi-reflecting plate 23 being arranged perpendicular to a second face perpendicular to the first face and along one of the diagonals of said second face. This arrangement makes it possible to optimize the transmissions of the colored light beams 61, 62 and 63 coming from the light sources and circulating through the mixing cube. The geometry of the mixer block and the arrangement of the semi-reflecting plates and the optical valves is such that the four images of the optical valves through the mixer block are perfectly combined. This solution has the advantage of great compactness and great robustness. Of course, this arrangement of the mixer unit can also be adapted to other types of imagers operating either by reflection or by transmission. Other arrangements of the mixer block are possible. For example, the first semi-reflecting plate can reflect the first spectrum and transmit at least the second spectrum, the second plate can transmit the third spectrum and reflect the first and the second spectrum. When the optical valves are liquid crystal, the transmitted light is naturally polarized. It is then possible to improve the photometric yields of the semi-reflecting plates by using suitable polarizing treatments making it possible to optimize the reflection and the transmission of the polarized beams. It is also possible to mix the beams using discrete optical components such as semi-reflecting plates with flat and parallel faces. There are different embodiments of the lighting of the optical imagers forming the initial colored image. FIG. 6 illustrates a first embodiment. A single white light source 40 is positioned in front of a set of optical separators 51 and 52 and of mirrors 53 making it possible to create the colored light sources 41, 42 and 43. The spectral width of the light source 40 is wide enough to cover the three spectra needed to light the imagers. For example, the separator 51 of the figure transmits a first spectrum and reflects the other two, the separator 52 transmits one of the two spectra reflected by the separator 51 and reflects the other. In the event of one of the imagers failing, shutters 71, 72 and 73 placed in front of each of the three light beams constituting the light sources make it possible to suppress the beam corresponding to the imager inoperative so as to remove any stray light in the colorful picture. These shutters can be mechanical shutters (diaphragms, movable shutters, etc.) or electro-optical shutters (optical valves). The white source must be particularly robust to avoid total loss of lighting. Its robustness can be increased by choosing long-life sources (fluorescent tubes also called CCFL: Cold Cathode Fluorescent Lamp) or by multiplying the primary sources constituting the white source, for example in the case of arc lamps whose duration of life is lower. FIG. 7 illustrates a second embodiment of the light sources. Three independent light sources emitting in three different spectral bands are then used. Light emitting diodes emitting in the visible can be used as primary sources. This produces compact and highly reliable light sources. In Indeed, not only do the light-emitting diodes have a long lifespan, but, moreover, it is possible to produce each source from a plurality of diodes, the loss of a diode having only limited consequences. The additional light source 44 must be capable of emitting in the 3 spectral bands. It is possible to perform this function simply by using three types of light-emitting diodes or three fluorescent tubes emitting in three visible spectral bands.

In a non-secure viewing device, the 3 primary imagers consisting of optical valves 31, 32 and 33 and of light sources 41, 42 and 43 constituting the imager are controlled by a data bus 82 via cards. interface 83. 15 In a secure display device according to the invention, the management of the optical engine can be carried out according to the control architecture described in FIG. 8. This includes: • The 4 imagers 31, 32, 33 and 34 illuminated by light sources 41, 42, 43 and 44. The first three sources

20 lighting are monochrome and the fourth lighting source 44 is capable of emitting in an adjustable spectral band. Each imager associated with a light source constitutes a primary image source; • The 4 four identical 83 interface cards used to drive the 4 primary image sources; • A control module 84; • A data bus 82 serving the 4 interface cards 83; • A control bus 81 connected to the control module 84 and to the interface cards 83.

The control module periodically checks, via the control bus 81, the proper functioning of the imagers 31, 32 and 33 and of the light sources 41, 42 and 43. If their operation is correct, then the imager 34 and the light source 44 are not activated. If one of the 3 optical imagers 31, 32 or 33 or one of the 3 light sources 41, 42 or

35 43 is detected defective by the control module, then all of the corresponding image source is disconnected, the backup image source consisting of the imager 34 and the lighting source 44 is activated, the image dedicated to the disconnected imager is then sent by the data bus on the imager 34 and the light source 44 is controlled to emit light in the spectral band corresponding to the disconnected light source so that the backup image source completely replaces the primary image source broken down without alteration of the final image.

Claims

1. Optical motor (1) for color image projection device comprising a first imager (31) illuminated by a first light source (41) emitting in a first spectrum, a second imager (32) illuminated by a second source of light (42) emitting in a second spectrum, a third imager (33) illuminated by a third light source (43) emitting in a third spectrum and an optical mixer (2), the images of the three imagers through the optical mixer being perfectly combined so as to form a single color image, characterized in that said optical motor also comprises at least a fourth imager (34) illuminated by a fourth light source (44) emitting in a spectrum adjustable by control means, the image of said fourth imager through the optical mixer (2) also being perfectly merged with the images of the first, second and third imagers so that, in the event failure of one of the three imagers or their associated light source, the fourth imager can replace it without altering the quality of the final color image, the mixer having substantially the shape of a cube comprising three semi-reflecting plates ( 21, 22, 23), the first semi-reflecting strip (21) being arranged perpendicular to a first face of said cube and along one of the diagonals of said face, the second semi-reflecting strip (22) being also arranged perpendicular to said first face and along the second diagonal of said face, the third semi-reflecting strip (23) being arranged perpendicular to a second face perpendicular to the first face and along one of the diagonals of said second face.

2. Optical motor (1) according to claim 1, characterized in that at least one of the semi-reflecting plates (21, 22, 23) has coefficients of reflection and transmission depending on the polarization of the light.

3 optical motor (1) according to one of the preceding claims, characterized in that the first, the second and the third light source (41, 42, 43) come from a single source (40) emitting on a spectrum wide said white and comprising spectral separation means (51, 52) making it possible to generate the three sources and shutters (71, 72, 73) making it possible to extinguish each of the three sources (41, 42, 43) independently.

4. Optical engine (1) according to one of claims 1 to 3, characterized in that the fourth light source (44) consists of three types of visible light sources, the first type emitting in a first spectrum, the second type emitting in a second visible spectrum different from the first spectrum and the third type emitting in a third visible spectrum different from the first and second spectrum.

5. Optical motor (1) according to one of claims 1 to 4, characterized in that at least one of the four light sources (41, 42, 43, 44) consists of visible light-emitting diodes.

6. Optical engine (1) according to one of claims 1 to 4, characterized in that at least one of the four light sources (41, 42, 43, 44) consists of fluorescent tubes emitting in the visible.

7. Optical motor (1) according to one of the preceding claims, characterized in that the imagers are optical valves with liquid crystal matrices.

8. Optical motor (1) according to one of claims 1 to 6, characterized in that the imagers are of the LCOS (English acronym for Liquid Crystal On Silicon) or DMD (English acronym for Digital Mirror Device) type. or DLP (acronym for Digital Light Projector).

9. Display device comprising at least one optical motor (1) according to one of the preceding claims, characterized in that that said device comprises an electronic control bus (81) and an electronic control module (84), said module comprising means making it possible to determine the failure of one of the first three optical imagers (31, 32, 33) or of one of the first three associated light sources (41, 42, 43) and means for activating the fourth light source (44) and the fourth imager (34) so that they replace the faulty colored image source .