FR2776881A1 - Three dimensional display mechanism - Google Patents

Abstract

The two output responses are fast switched using a left and right hand circular polarization obtained with a voltage operated liquid crystal display.

Description

The present invention relates to a display device

in three dimensions.

  Visualization devices are used in particular in recreational simulators, such as simulators for piloting airplanes or land vehicles. When one wants to produce a realistic simulation of visual effects, it is necessary that these effects produce an impression of three-dimensional space to the user. Such display devices

  are referred to below as 3D devices.

  To produce such effects, a known solution consists in providing

  the user of special glasses to which glasses are attached

  thin ches with liquid crystals which are alternately, and at high speed, made opaque then transparent for each eye, in synchronism with the projection of images alternately intended for the left eye and for the right eye. Such a solution provides the desired effect, but requires

  the use of glasses constituting a nuisance for the user.

  Another solution, described in US Patent 5,132,839, has

  course in a spatial modulator arranged between an imaging system and the user. This modulator, of the liquid crystal type, comprises several adjacent zones, each of which is cyclically made, in turn, transparent for a few milliseconds, in synchronism with the projection of a corresponding synthetic image, the different successive images of each cycle corresponding to different points of view. Such a solution also provides the desired visual effect, but requires, on the one hand, great computing power on the part of the image computing processor, due to the large number of images to be displayed at each cycle, and , on the other hand, an expensive refractive optics system

  to obtain a wide field image with a cathode ray tube.

  The subject of the present invention is a device for viewing three-dimensional images, in particular synthetic images, which does not

  does not require the wearing of specific glasses by the user, which does not

  site not a large computing power on the part of the generator of synthetic images, and which can produce images with large field

  observation without requiring an expensive optical system.

  The display device according to the invention comprises a

  image source alternately producing near images and ima-

  distant from an observation point, and a selective collimating device

  Close and distant images.

  The present invention will be better understood on reading the detailed description of two embodiments, taken by way of nonlimiting examples and illustrated by the appended drawing, in which:

  - Figure 1 is a schematic view of a display device -

  tion in accordance with the invention with spherical mirror and half-45 blade

  polarized reflective, - Figure 2 is a schematic view of a variant of the device of Figure 1, and

  - Figure 3 is a schematic view of a display device -

  tion according to the invention with semi-reflecting spherical mirror, polarizer

  circular and semi-reflective polarized plate.

  The invention is described below with reference to a display device for a driving driving leisure simulator, but it is understood that it is not limited to this single application, and that it can be implemented. in simulators of other types as well as in various equipment requiring a visualization in 3 dimensions of synthetic and / or real images, and this, using a single image source (in this case, a cathode ray tube monitor but others

sources can be used).

  The display device 1 represented in FIG. I comprises, as image source, a cathode ray tube 2, in front of the screen of which there is an optic 3. This optic 3 is constituted by a stack comprising, in a manner not shown in detail on the drawing, a linear polarizer, a liquid crystal plate and a quarter wave plate. This optic 3 allows, depending on the voltage applied to the control electrodes

  of the liquid crystal slide, get circular polarized light-

  lie left or right. Advantageously, in the case where the source

  2 is a scanning cathode ray tube, the change in polarization

  left-right and vice versa is controlled during the frame return of the scan. Also, advantageously, the liquid crystal blade is a ferroelectric liquid crystal blade, the switching time of which

is less than 500 pS.

  In front of the optic 3 there is a polarized reflective optic

  health 4, oriented at 45 relative to the optical axis of the source 2. This opti-

  that 4 comprises, in the present example, a film such as the film "DBEF" from the company "3M" sandwiched between two quarter wave plates. This film has the property of reflecting linearly polarized light in one direction

  and let the linearly polarized one go in the other direction. The the-

  my quarter wave transform circular polarized light-

  lo in linearly polarized light (P or S, depending on the orientation

  port to the film "DBEF") and vice versa. Thus, this optic 4 has the property of reflecting the light circularly polarized in one direction (on the right in the present example) and of letting that of the circularly polarized light in

  the other direction (left in this example).

  On the other side of the optics 4 with respect to the source 2, there is

  poses, perpendicular to the optical axis of the source, a plane mirror 5. A

  spherical mirror 6 is arranged in front of the optic 4, symmetrically with respect to

  port at the source, that is to say that the optical axis of the mirror 6 is perpendicular to

  the source 2 and cut the latter on the entry plane of

  optics 4. In addition, the source 2 and the mirror 6 are such and are arranged at.

  such distances from the optics 4 that the source screen is in the plane of the focal surface of the mirror 6 (taking into account the orthogonality of their respective optical axes), and that the source 2 with its optics 3 n '' do not obscure the rays reflected by the spherical mirror. The observer is located near the

center of curvature of the mirror 6.

  In a first elementary phase, by a command command

  property of the voltage applied to the electrodes of the liquid crystal slide

  from optics 3, the light rays coming from source 2 are circularly polarized to the right by optics 3. They are reflected by optics 4 (which only lets through those circularly polarized to the left) towards the mirror

  spherical 6. The reflection on this mirror reverses the direction of circular polarization

  beam of rays, which therefore become circularly polarized to the left.

  These rays polarized on the left can therefore pass through optics 4 practical-

  without attenuation. The corresponding source image, formed on the screen of the source 2, being located on the focal sphere of the spherical mirror 6, it

  results that the light rays reflected by the spherical mirror 6 are coll-

  and that this image is seen by the observer as if it were so-

endlessly killed.

  At the following elementary phase, a voltage is applied to the liquid crystal plate of optics 3 which makes the optics 3 pass to the left circular polarizer state. The rays from the source 2 therefore pass through the optics 4 practically without attenuation and arrive at the plane mirror 5 which reflects them, reversing their direction of polarization. Consequently, the rays reflected by the plane mirror 5 are circularly polarized to the right, and are therefore i0 reflected by optics 4 towards the observer, located at 7. The observer therefore has the impression of seeing, opposite itself, an image at a finite distance, equal to the length of the ray path between source 2 and its

  eyes, through the plane mirror 5.

  It follows that, according to the direction of polarization of the optics 3 (therefore according to the voltage applied to its liquid crystal plate),

  the observer sees either an infinitely collimated image or a close image.

  When one reverses alternately and very quickly (for example at the frequency of at least 100 Hz) this direction of polarization, the observer has the impression of seeing simultaneously, thanks to the retinal persistence, a near image and an image distant superimposed, so to see a picture

in three dimensions.

  According to an advantageous variant of this embodiment

  (referenced 8 in FIG. 2), it is possible to form images close to distances

  these different finishes. For this purpose, we have on axis 2A extending the axis

  source optics 2, beyond optics 4, in order, a semi-lamina

  reflecting 9, oriented at 45 relative to this axis, a shutter 10A and a plane mirror 11A, these last two elements being perpendicular to the axis. Let 2B be an axis perpendicular to the axis 2A and cutting the latter on the entry face of the blade 9. On the axis 2B, there is, on one side of the blade 9 for example on the left in the drawing, a shutter 1 OB followed by a plane mirror 11B. The shutter 10OB and the mirror 11B are perpendicular to the axis 2B. The

  two optical paths between source 2 and the observer and passing through the mid

  blacks 11A and 11B are respectively equal to the two different finite distances

  rents to which one wishes to present to the observer images of objects

  relatives. The positions of the shutters 10A and 10B are not critical.

  These shutters are for example of the ferroelectric liquid crystal type.

  which, depending on the voltage applied to them, are either opaque or practically transparent. In operation, these shutters are normally opaque, and are only made transparent when the source 2 forms the image to be seen at a finite distance respectively equal to that

  of the optical path between the source and the observer via the cor- rect mirror

  respondent. The source 2 alternately and cyclically produces images to be seen at infinity and images to be seen at each of the finite distances corresponding to the positions of the mirrors 1 1 A to 1 1 B. We will now explain the operation of the device 8 for the display at two different finite distances, the display at infinity being

  in the same way as for device 1 in FIG. 1.

  When the optics 3 polarizes the light coming from the source 2 circulating

  left, this crosses optics 4 practically without attenuation

  tion. When this polarized light arrives on the blade 9, 50% is reflected

  shit to the mirror 11B, and 50% is transmitted to the mirror 11A. If the shutter 10B is "closed" (opaque) and if 10A is "open", the light reflected by the blade 9 towards 10 OB is lost, but the light passing through the

  blade 9 reaches the mirror 11A and, reflecting on it, changes its direction of pola-

  circular risation. Thus, the light circularly polarized to the right leaves towards the plate 9, which it crosses, and is reflected on the optics 4 in the direction of the observer. Similarly, when the shutter 1 OB is open and 1 OA closed, the light from the source, circularly polarized to the left, passes through the optics 4, and the part which is reflected on the plate 9 arrives at the mirror 11 B , reflects on it by changing the direction of circular polarization, reflects on

  again on slide 9, then is reflected on optics 4 towards the observer.

  The switching of the liquid crystal cell of the optics 3 and of the shutters 10A, 10B taking place at high frequency (for example Hz), in synchronism with the display on the screen of the source 2

  corresponding images, the observer has the impression of seeing simultaneous

  infinity images superimposed on images seen at two distances

  different finishes, close to the observer.

  Due to the fact that an ordinary semi-reflecting plate (9) is introduced into the path of light corresponding to close objects, the partial reflection and transmission which it simultaneously causes halves the intensity of each of the beams ( reflected and transmitted) from the incident beam, and this, each time the blade passes. This means that the intensity of the beams returning to optics 4 after reflection on one of the

  mirrors 11 A or 1 1 B is reduced by 75%.

  Of course, we could further increase the number of images

  at different finite distances by cascading other assemblies [semi-blade

  reflective + shutter + plane mirror], but the intensity of the beams

  sultants would be greatly reduced, which could nevertheless pre-

  feel an interest in the formation of "ghost" images at different

o tances finished.

  According to another advantageous variant (not shown), in the device 8 of FIG. 2, the polarized reflective optics 4 consists of a quarter-wave plate attached to a DBEF film. Indeed, in transmission,

  the output light is linearly polarized and is directly compared

  target with 10A and 10 OB ferroelectric liquid crystal shutters which

  work in linear polarization. To keep the polarity reversal effect

  risation of the mirror it is necessary to work in circular polarization, and for that rajou-

  ter between the shutters 10A and 10OB and the mirrors 11A and 11B, a blade

  quarter wave to transform circular polarization into polarization

neary and vice versa.

  FIG. 3 shows a second embodiment 12

  of the display device of the invention.

  In this embodiment, all the optical elements have the same rectilinear optical axis, and the image source 2 (which can be the same

  that that of the device of FIGS. 1 and 2) is arranged facing the observer.

  In front of the source screen 2, we have the same optics 3 as

  that of FIGS. 1 and 2, then, in order, a semi-spherical mirror

  reflective 13 whose focus is oriented opposite the source 2, and a polarized reflecting optic 14. The optic 14 is located on the optical axis

  from mirror 12 at the same distance as its focal sphere. The racing center

  bure of the mirror 9 is referenced 15, and the observer places himself as close as pos-

  sible of this center. The optic 14 comprises a quarter-wave plate attached to a “DBEF” type film such as that mentioned above with reference to the optic 4. This optic 14 reflects the circularly polarized light

  in one direction (right in this example) and transmits polar light

  laughed circularly in the other direction (on the left in this example).

  The operation of the device 12 is as follows. When the liquid crystal plate of optics 3 receives a voltage such that this optics 3 polarizes the light circularly to the right, this light is reflected by

  optics 14 towards the spherical mirror 13. The reflection of light on the mid

  black 13 reverses its direction of polarization, and it therefore becomes polarized circu-

  left to the left. This light can therefore pass through optics 14 practical-

  without attenuation. Thanks to the fact that the image reflected by the optics 14 is located on the focal sphere (at least at the level of the optical axis) of the

  spherical mirror 13, the light rays reflected by this mirror are collimated

  tees, this image is seen endlessly by the observer.

  When the optic 3 circularly polarizes the light to the left, by an appropriate control of its liquid crystal plate, this light passes through the mirror 13 and the optic 14 practically without attenuation, and the observer sees the image directly opposite it formed on the screen of the

source 2.

  Thus, when the polarization of the optics 14 is very quickly switched (for example at Hz), in synchronism with the formation on the screen of the source 2 of corresponding images (at infinity and at a distance

  finished), the observer also has the illusion of seeing a three-dimensional image

sions.

Claims (8)

  1. Three-dimensional image display device, character-   terized in that it comprises a single source of images (2) producing alter-   natively near images and images distant from an observation point (7), and a device (4, 6 or 13, 14) selectively collimating distant and close images.   2. Device according to claim 1, characterized in that the selective collimation device comprises an optic (3) of circular polarization with switchable direction, disposed in front of the source (2), a polarized reflecting optic (4) letting polarized light pass circularly in one direction, and reflecting that circularly polarized in the other direction, this optic being arranged at 45 with respect to the optical axis of the   source, a spherical mirror (6) whose optical axis is arranged at 45 relative to   port with polarized reflecting optics, the observer being located near the focal point of the mirror, and a plane mirror (5) disposed on the optical axis of the source,   beyond the polarized reflective optics.   3. Device according to claim 1, characterized in that the selective collimation device comprises a polarization lens (3)   switchable circular, arranged in front of the source, a spherical mirror   that semi-reflecting (13) and a polarized reflecting optic (14) leaving   being able to pass the light circularly polarized in one direction and reflecting that circularly polarized in the other direction, all these elements having the same rectilinear optical axis, the observer being located near the focus (15) of the spherical mirror.   4. Device according to claim 2 or 3, characterized in that the circular polarization optic comprises a linear polarizer attached to   a liquid crystal slide and a quarter wave slide.   5. Device according to claim 2, characterized in that the polarized semi-reflecting optics (4) comprises a quarter wave plate   attached to a "DBEF" type film and another quarter-wave plate.   6. Device according to claim 3, characterized in that the polarized semi-reflecting plate (14) comprises a quarter wave plate   attached to a "DBEF" type film.   7. Device according to claim 2, characterized in that it comprises, on the optical path downstream of the polarized reflecting plate (4), at   minus a semi-reflecting plate (9) on the reflected (2B) and trans-   put (2A) from which there is each time a shutter (10A, 10OB) followed by a plane mirror (l11A, 11B), the plane mirrors being at distances   O different from the semi-reflecting plate, and the shutters being controlled   opening dice when displayed by the source of images to be seen   at corresponding different finite distances.   8. Device according to one of the preceding claims, character-   laughed at that the source produces images at a frequency of at least 1 00 Hz.