Virtual Image Projection Device

A. Field of the Invention

The present invention relates to a device for the virtual display of an image. More specifically the present invention relates to a device for the virtual display of moving images such as video, motion pictures and the like.

B. Discussion of the Prior Art

Devices are known for the production of a virtual image outside of such devices using an illuminated real object which is included fixedly or rotatably within the devices. In one such device, the virtual image is produced outside the housing by means of a fresnel lens which is arranged in the housing opening. The object can either be arranged lying directly opposite the fresnel lens inside th housing or staggered with respect to the fresnel lens, with the object then being depicted onto the fresnel lens by a suitable mirror arrangement. Such a three-dimensional image device is disclosed in European Patent No. EP-B1-0 410 968 by Raul Orlandi.

While suited for their intended purpose, a disadvantage of devices of this type is that only illuminated real objects can be depicted, which is complicated in practice and greatly restricts the use of this image device to objects which can be maintained in the housing. Whereas flat objects can be depicted with such a device with relatively no difficulty, three-dimensional distortions occur in the depicting of objects with greater three-dimensional depth. In addition, the observation of the image is substantially limited to a particular viewing axis which is determined by the foci of the fresnel lens. In other words, this known device suffers from a very tight viewing angle. To increase the viewing angle, a 3 to 1 size ratio is desired between the object and the lens. Thus, the object is generally 3 times smaller than the lens to increase the viewing angle.

The disadvantages set out above also apply to an alternative embodiment known in which the depiction of the real object takes place by means of a concave mirror arranged in the path of light rays and a partially translucent mirror, instead of with a fresnel lens. Finally, it is disadvantageous that an observer always has to look into the fresnel lens or into the concave mirror in order to observe the object, which is very disturbing due to the enlargement of the mirror image of the observer.

An object of the present invention consists of largely eliminating the above-mentioned disadvantages and providing a virtual image device in accordance with the present invention in which the range of applications for the device is expanded and which ensures an undistorted image reproduction of the subject which is to be depicted, with a greater viewing angle than hitherto.

These disadvantages are solved by the features of the virtual image device of the present invention comprising a housing with an observation opening in a wall of the housing, an image source for the virtual image to be depicted, and imaging optics arranged in the housing for projecting the image onto a fresnel lens, located in the observation opening. The imaging optics have a part-spherical mirror arranged in the path of light rays between the image source and the fresnel lens. The image source, which may be a real object, is preferably generated by a two-dimensional (2-D) projection device.

The invention overcomes the problems disclosed above by featuring an improved imaging system based on the combination of a fresnel lens and a part-spherical mirror. The part spherical mirror is preferably a concave mirror, but a convex mirror is acceptable. In addition, as a substitute for the real object disclosed in the prior art, the virtual image is generated by an image projection device that creates a 2-D image at the image source.

According to the invention, through the combination of a concave mirror and fresnel lens, the viewing angle can be increased without a costly (oversized) fresnel lens being used as in the prior art, which is desireably 3 times greater than the image which is to be depicted, for the enlargement of the viewing angle.

Through the use of a 2-D projection device to produce an image at the image source, rather than using a real object, distortions are virtually eliminated. A further advantage of the use of a 2-D projection device to produce an image rather than using a real object is that complex animation can also be depicted without difficulty, for example, several objects can be displayed moving simultaneously. Another feature of the 2-D projection device according to the invention is that a re-adjustment of the device is not required when real objects are exchanged as in the prior art. Furthermore, an opening in the housing of the device necessary for exchanging real objects is not required. Hence, completely new fields of applications become possible for the device according to the present invention, in particular for advertising, because images which are to be projected can be played back in a simple manner by video for example, preferably controlled by computer.

A variety of imaging means come into consideration for the two-dimensional projection device, such as for example slide or film projector or a video or laser image production device. The video image production device preferably comprises a video projector, a video monitor, a television set, an LCD screen or the like.

Other objects, advantages, and features of the invention will become apparent from the foregoing detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of a first embodiment of a virtual image device according to the present invention;

FIG. 2 is a diagrammatic view of a second embodiment of a virtual image device according to the present invention;

FIG. 3 is a perspective view of the present invention as shown in FIG. 1; and

FIG. 4 is a perspective view of the present invention as shown in FIG. 2.

The virtual image production device as shown in FIGS. 1-4 for purposes of illustration, generally includes a chamber or a housing 20, which is closed on all sides and has an observation opening 22 in one wall, which opening is closed by a fresnel lens 24 which runs co-planer to this wall. The fresnel lens 24 is part of an imaging arrangement which in both embodiments of the device shown in FIGS. 1-- has a concave mirror 26 which is arranged opposite the fresnel lens 24 in the housing 20. A ray divider 30 in the form of a partially translucent mirror is arranged between the concave mirror 26 and the fresnel lens 24.

The imaging arrangement with the elements 24, 26 and 30 produces a virtual image 28 (FIGS. 3 and 4) on the exterior of the housing 20 that appears to an observer (not shown) to be in front of the fresnel lens 24. The field of view of the observer is shown by reference numeral 29 (FIGS. 1 and 2).

In the embodiment of the device illustrated by FIGS. 1 and 3, the image is produced by means of a 2-D projection device or video display 32 such as a video-monitor, television or computer monitor, with a screen 34 of the display 32 pointing towards the ray divider 30. The screen 34 is positioned relative to the ray divider 30 to function as the image source. As indicated by reference numeral 36, light rays originate from the screen 34, extend to the ray divider 30, reflect onto the concave mirror 26 and from this, are directed through the ray divider 30, onto the fresnel lens 24 to define a light ray path.

The use of the ray divider 30 which is arranged between the concave mirror and the fresnel lens 24 lying opposite thereto and directs the light rays 36 from the display device 32 onto the concave mirror 26 is advantageous for the compact structure of the device. Advantageously, the ray divider 30 is coated so as to be anti-reflective on its face directed towards the fresnel lens 24 and so as to be reflecting on its other face, facing the concave mirror 26.

According to a particularly advantageous further development of the invention, a partially translucent mirror 37, a so-called "spy mirror", is arranged on the viewing side of the fresnel lens 24, i.e., outside the housing 20, which mirror 37 prevents visibility into the housing. Owing to this partially translucent mirror 37, which has preferably a transmission capacity of 5%, the illusion of a virtual image 28 appearing in front of the device is perfected for the observer, because in this mirror 37 the observer sees exclusively his/her own mirror image undistorted and in the original size together with the virtual image 28. Preferably, the partially translucent mirror 37 is illuminated by an external light source 40 from the observer's side. Through the use of the partially translucent mirror 37 in cooperation with the external light source 40, the illusion effect of a virtual image 28 standing in the space in front of the housing 20 is increased.

In order to avoid undesired reflections inside the housing 20, its inner walls are produced from non-reflective material. Likewise, partition walls 42 and 44, which close the space between the concave mirror 26, the ray divider 30 and the screen 34 are produced from non-reflective material.

In an alternative embodiment of the device according to the invention, shown in FIGS. 2 and 4 where like reference numerals with FIGS. 1 and 3 refer to like structure, a back projection medium 50 is positioned relative to the ray divider 30 to function as the image source. The back projection medium 50 (FIGS. 2 and 4) is positioned at the site of the screen 34 (FIGS. 1 and 3), onto which a 2-D image is projected by means of deflector mirrors 52 and 54 (FIGS. 2 and 4) from an image projector 56, for example a video, laser, slide or film projector. Using the arrangement of the concave mirror 26, ray divider 30 and fresnel lens 24, the virtual image is produced from the image formed on the back projection medium 50 in the same manner as in the device of FIGS. 1 and 3 using the display screen 32. The back projection medium 50 is preferably made from conventional flat material capable of back projection which generally requires a partially transparent material having a light intercepting medium on which two-dimensional images may be viewed, for example a cloth movie screen, a fog screen, water screen, or other medium which allows the projected 2-dimensional images to be viewed.

In summary, the invention relates to a device for the production of a virtual image, with a housing 20, a screen 34 or back projection medium 50, which produces an image to be displayed. The housing has an observation opening in a wall of the housing 20 with imaging optics arranged in the housing 20 for projecting the object onto a fresnel lens 24 which is arranged in the observation opening. In order to ensure a large number of applications for this device, the imaging optics have a concave mirror 26 arranged in the path of light rays 36 between the image source 34 or 50, which provides the virtual image to be displayed, and the fresnel lens 24. The image to be depicted is generated by a two-dimensional projection device 32 and 56. Advantageously the concave mirror 26 lies opposite the fresnel lens 24 and a ray divider 30 is provided therebetween. To increase the illusion effect, a partially translucent mirror 37 (spy mirror) is additionally arranged on the observation side of the fresnel lens 24.

With reference to FIGS. 1-4, an example of the virtual image device of the present invention is constructed from the following:

a ray divider 30, 400.times.550 mm in size, having a 2 sided coating, 1 coating reflective at 45 degrees, 1 coating non-reflective, and providing 50% light transmission;

a concave mirror 26, 350 mm in diameter, having a focal length=600 mm;

a fresnel lens 24, 406 mm in diameter, having a focal length=558 mm; and

a semitransparent mirror 37, having a 5% light transmission.

It will be appreciated by those skilled in the art that a convex mirror (not shown) having generally the same optical properties may be substituted for the concave mirror 26; however, the arrangement of the convex mirror, ray divider 30 and fresnel lens 24 would need to be adjusted accordingly.

When these components are arranged as shown in FIGS. 1-4, a virtual image 28 is produced generally 55.8 cm in front of the housing 20 with a field of view in the range of 20 to 25 degrees about a line perpendicular to a plane formed by the observation opening as indicated by reference numeral 29. Alternatively, when used with a fresnel lens 24 having focal length of 400 mm, the image 28 is formed 30 cm in front of the housing 20.

While the present invention has been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but to the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit of the invention, which are set forth in the appended claims, and which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures.