Television – Video display – Projection device
Reexamination Certificate
2001-06-04
2004-08-31
Kostak, Victor R. (Department: 2614)
Television
Video display
Projection device
C348S781000, C353S098000
Reexamination Certificate
active
06784946
ABSTRACT:
The invention relates to an arrangement in which the light emitted by a source of light is directed by means of an illumination optics onto a surface on which an image can be focussed that can be detected by means of a projection optics.
Examples of such arrangements are slide or film projectors in which, for purposes of attaining uniform illumination, a light bundle stemming from a light source is projected by means of a condenser onto a slide or film image that is then subsequently displayed on a screen with an objective as the projection optics.
In particular, however, the subject matter being addressed here is a recent technology in which deformable mirror matrices serve to generate video images. These deformable mirror matrices consist of an array of individual deformable mirrors that can assume two states, namely, zero and one, depending on the selected direction of reflection. The number of rows and columns of the array corresponds to the video standard for lines and pixels per line of the video image to be depicted. In order to also allow gray scale or colors on the part of individual pixels, the deformable mirrors associated thereto are pulse code modulated, depending on the pixel information, so as to rapidly switch these deformable mirrors back and forth between reflection in one of the two directions and reflection in the other direction, so that, on the average over time, the duty cycle between the states zero and one gives rise to a corresponding intermediate value between light and dark. Such deformable mirror matrices can be obtained, for instance, from Texas Instruments Incorporated.
As in the case of the known projectors mentioned above, the optics employed for such deformable mirror matrices consist of an illumination optics of the deformable mirror matrix and of a projection optics that is normally referred to as an objective, in order to project the image content onto a screen, a process in which both front and rear projection is possible.
The term screen as used here should be understood in its broadest sense. Especially for show applications, screen here also refers, for example, to the vapor of a smoke-making machine or to a wall of water.
Owing to space problems with the illumination, up until now, optics having a long focal length have been used as the illumination optics and as the projection optics, so that a certain size has always been necessary for these projectors with deformable mirrors. Moreover, due to the long light distances, loss of light is possible, which is why a greater input power is required and thus more heat also needs to be dissipated which, in turn, calls for a larger size. Consequently, with smaller projectors, and thus also with the demand for reduced heat generation, an image with large screen diagonals is not possible at all.
However, there is an avid interest in small and bright projectors. They should be easy to transport and capable of generating a sufficiently bright image of a suitable size under normal indoor lighting conditions. Efforts are already under way to replace the portable projectors that are just now coming onto the market by the next generation of considerably smaller projectors, the so-called palm-top projectors. Such projectors call for substantially smaller optics systems, both for the illumination optics and for the projection optics. It would be conceivable to try to achieve this through the miniaturization of the known optics, although the size of the light bulb, the heat problem and the resultant additional cooling means would always define a lower limit. Moreover, the deformable mirror matrices always have to be of a certain size in order to be able to reflect a sufficient amount of light.
A similar set of problems is also found when it comes to reflective LCD's.
The objective of the invention is to provide a new arrangement for illumination and projection purposes which allows the construction of such miniaturized projectors.
This objective, which at first appeared to be unattainable in view of the above-mentioned requirements, is achieved on the basis of the above-referenced state of the art in that the illumination optics (first optics) has an optical means located beyond the source of light and a prism positioned between the surface and the optical means, whereby the light coming from the optical means is deflected without reflection by means of the prism. In this manner, the first optics, namely, the illumination optics, can be situated very close to the other optical elements of the projection optics (second optics) and, in the extreme case, parallel to the optical axis of the second optics. As a result, the compactness of the projector can be drastically increased, as will be elaborated upon in greater detail below with reference to embodiments. The essential aspect here is that the light incident upon the prism is only deflected by refraction.
Even greater compactness can be achieved according to another refinement in which the second optics is divided into a first and a second partial optics, whereby the first and second partial optics have a shared optical axis. The first optics contains the optical means and the second partial optics, so that the second partial optics is a component of the first partial optics as well as of the second partial optics. The incident light needed for the illumination stems from the optical means (third partial optics). In order to allow a projection, the light that comes from the third partial optics and that is incident upon the second partial optics includes an angle relative to the shared optical axis, whereby the third partial optics lies outside of an area that is traversed from the second to the first partial optics by the light that is reflected off the surface.
The fact that such a breakdown into a first, second and third partial optics is possible is, at first, unexpected since, in view of the prescribed long focal lengths, the current state of the art requires small apertures for the illumination of the deformable mirror matrix cited as an example as well as for depicting their image content; as experience has shown, this leads to the situation wherein the beam paths of the illumination light and of the reflected light then have to overlap. Due to the small aperture angles that are normally employed, it would fundamentally not be possible to use partial optics to uncouple the light path lengths of the light bundle that is incident upon the deformable mirror matrix from that of the light reflected by the deformable mirror matrix. Only now, with the arrangement according to the invention, has it become possible to realize partial optics having appropriately short focal lengths, as a result of which the useable apertures can be selected so as to be sufficently large, and a sufficiently large path can be kept free for the third partial optics, so that the light emerging from the deformable mirror matrix can pass through unhindered. The special configuration of such optics is known to the person skilled in the art.
This further development differs markedly from the familiar approaches for the miniaturization of known devices. In particular, it could have been expected that the person skilled in the art, after recognizing the heat problem associated with miniaturization, would have dedicated a great deal of her/his thoughts to designing a particularly space-saving cooling system.
A suitable cooling system, however, generally does not pose any problem with this arrangement, since the main heat-generating elements, namely, the deformable mirror matrix as well as the source of light, are located outside of the three partial optics. The back of these elements remains completely free, so that, in contrast to the known arrangements, no special attention needs to be paid to the space for the cooling means, a space that might have to be left free for optical elements. Consequently, a compact, efficient cooling system can be used for the deformable mirror matrix.
Unexpectedly, it has turned out that this arrangement also accounts for increased light intensity
Schröter Gudrun
Symanowski Christfried
Carl Zeiss Jena GmbH
Kostak Victor R.
Renz, Jr. Eugene E.
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