Optics: image projectors – Reflector
Reexamination Certificate
2000-03-17
2002-08-27
Dowling, William (Department: 2851)
Optics: image projectors
Reflector
C353S084000, C348S743000
Reexamination Certificate
active
06439726
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of The Invention
The invention is directed to an arrangement in which light is directed onto a surface proceeding from a light source by means of first optics, so that an image is formed which can be detected by means of second optics.
2. Description of The Invention
Arrangement in which light is directed onto an object from a light source for illumination, for example, in order to be able to observe an image through second optics, are known from microscopy, for example. Further, transparency or film projectors are known in which a light bundle originating from a light source is projected by means of a condenser for uniform illumination on a transparency or film image which is then shown on a screen by an objective serving as second optics.
However, under present consideration is a more recent technology in which video images are-generated by means of tilting mirror arrays. These tilting mirror arrays comprise a field of individual tilting mirrors which can assume two states, zero and one, depending on the adjusted reflection direction. The quantity of rows and columns of the field correspond to the video standard for lines and image points/lines of the video image to be displayed. To enable gray values or colors of individual image points as well, the image mirrors allocated to the latter are acted upon by a pulse train depending on the image point information, wherein this pulse train switches the tilting mirrors rapidly between reflection in one of two directions and reflection in the other direction, so that a corresponding intermediate value between light and dark is adjusted in the timing means by the pulse repetition rate between the zero and one states. Such tilting mirror arrays are available, for example, from Texas Instruments.
As in the above-mentioned projectors, the optics used in tilting mirror arrays of the type mentioned above are formed of optics for illumination of the tilting mirror array and second optics which are normally referred to as an objective for the projection of the image content onto a screen, wherein both front projection and rear projection are possible.
The term “screen” is meant herein in a very broad sense. In particular for laser shows, for example, screen also refers to the mist from a fog machine or a water wall.
Because of space problems in illumination, optics with long intersection lengths were previously used as first optics and second optics, so that a determined size was always required for these projectors with tilting mirrors. Moreover, because of the long light distances, light losses are possible so that input power requirement and therefore also the heat output to be carried off increase, which likewise causes a larger structural shape. Therefore, in smaller projectors which accordingly also have desirable reductions in heat output, an image with large screen diagonals is no longer possible at all.
However, small and light-intensive projectors are in demand. They should be portable and under normal room illumination should generate a sufficiently bright image of suitable dimensions. Efforts are already being made to replace the portable projectors just now appearing on the market with the newest generation of significantly smaller projectors, so-called palm top projectors. These projectors need substantially smaller optical systems for the illumination optics as well as for the projection objective. An effort could be made to achieve this through miniaturization of the known optics, but the heat problem and the resulting additional expenditure on cooling would still represent a barrier. Further, the tilting mirror arrays must still have a certain size in order to reflect a sufficient amount of light.
A similar set of problems also results in reflective LCDs, especially those with tilted LCD elements.
It is the object of the invention to find a novel arrangement for illumination and projection which will allow miniaturized projectors of the kind mentioned above to be realized.
This object which at first appears unattainable in view of the requirements mentioned above is met proceeding from the prior art indicated above by means of dividing the first and second optics into first, second and third partial optics, wherein the first and second partial optics have, in each instance, a common optical axis and form the second optics. The incident light for illumination proceeds from the third partial optics and the third partial optics and second partial optics form the first partial optics. To enable projection, the light coming from the third partial optics and falling on the second partial optics encloses an angle to the common optical axis at which the third partial optics lie outside of an area traversed by the light reflected by the surface from the second partial optics to the first partial optics.
First of all, it is unexpected that a such a division into first, second and third partial optics is possible, since the preceding prior art, due to the long intersection distances for the illumination of the tilting mirror arrays mentioned by way of example as well as for imaging the image contents of the latter, required small apertures, as a result of which, as experience shows, the beam paths of the illumination light and of the reflected light must then overlap. Because of the small aperture angles normally used, it would not be possible to uncouple the light paths of the light bundle falling on the tilting mirror array through partial optics from that of the light reflected by the tilting mirror array. Only the arrangement according to the invention makes it possible to realize the partial optics with appropriately short intersection lengths, so that the usable apertures can be selected so as to be suitably large enough and a sufficiently large path for the third partial optics is kept open so that the light proceeding from the tilting mirror array is passed without hindrance. The special design of optics of this type is known to the person skilled in the art.
This solution differs sharply from the usual solutions for miniaturization of known devices. In particular, it would have been expected that the person skilled in the art would have devoted a substantial amount of thought to the realization of a particularly space-saving cooling means based on recognition of the heat-related problems occurring in miniaturization.
However, suitable cooling means generally do not pose a problem in the arrangement according to the invention because the substantial heat-generating elements, the tilting mirror array and the light source, lie outside of the three partial optics. The backs of these elements thus remain entirely free, so that, in contrast to known arrangements, with respect to cooling no particular attention need be paid to the space that must be reserved for optical elements. Accordingly, compact, efficient cooling means can also be used for the tilting mirror array.
It has turned out unexpectedly that an increased light intensity is also achieved with the arrangement according to the invention. This stems from the fact that due to the smaller intersection lengths for illumination and for collecting the light which originates from the tilting mirror array and is to be projected, the distance of the tilting mirror array from the optics is substantially less than can be maintained in the prior art, so that fewer light losses occur.
The third partial optics can be introduced in principle between the first and,second partial optics with respect to the optical axis. However, still greater compactness can be achieved according to an advantageous further development of the invention in which an optical axis of the third optics encloses an angle of less than or equal to 90° with the optical axis of the second partial optics and in which there is provided a device for deflecting the light bundle, especially a mirror or a prism, by which the light proceeding from the third partial optics is directed into the second partial optics. Compactness can be further improved by means of the mirror or prism wh
Carl Zeiss Jena GmbH
Dowling William
Reed Smith LLP
LandOfFree
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