Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1997-03-28
2001-07-17
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000
Reexamination Certificate
active
06262786
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of optical devices for dynamic display of images.
PRIOR ART
Devices of this type are known which make use of matrix of cells, each of which is able to change its state. Liquid crystal display devices (LCD) having polarizing filters and display devices with micro-mirrors are known. There are two types of liquid crystal projection systems, namely the systems with three LCDs and those with a single LCD. The systems with three LCDs include a source of white light and lenses for dividing the light beam in order to generate three colored beams of the three primary colors red, green and blue; three monochromatic LCDs change the three colored beams into three images. These images are superimposed on each other by three dichroic elements and are finally projected on a screen by a lens. This type of projection system has the advantages of using the whole spectrum of the light source, but is expensive and bulky, since it requires three LCDs and dichroic lenses; furthermore it is difficult to align.
The systems with a single LCD are more compact and less expensive since typically the image of a single color LCD is projected on the screen as it is done with a diapositive projecting device. The type of LCD which is used has a mosaic of colored filters which correspond to each sub-pixel. Less then one third of light passes through the LCD while the remaining portion is absorbed by the mosaic filter. As a result of this, the projectors with a single LCD has a lower brightness then those with three LCDs.
In order to avoid the use of mosaic colored filters, the use is known of a rotating filter described for example by M. Doubler et al in “An improved frame sequential color projector with modified CdSe-TFTs”, SID' 91 Digest pages 427-429 (1991).
Another projector with a single LCD and no mosaic filter has been proposed with a square rotating prism described in P. Jansen: “A novel single light valve high brightness HD color projector”, EURO Display' 93, pages 249-252 (1993). This system does not have the losses of the mosaic color filters, but requires a memory synchroniser, a high speed LCD and a mechanism for rotating the prism.
The application of a matrix of microlenses coupled to a TFT-LCD panel and a mosaic of colored filters is disclosed for example in H. Hamada et al: “Bright enhancements of a liquid crystal projector by a microlens array”, SID' 92 Digest pages 269-272 (1992).
Similarly, the technology has also been applied to the case of the single LCD projection panel and described in T. Takamaatsu et al: “Single panel LCD projector with a planar microlens array”, Japan display 92 Digest, page 875 (1992).
A solution of an LCD projector using a matrix of microlenses, but having no mosaic of microfilters is instead disclosed by Sharp Corporation in H. Hamada et al: “A new bright single panel LC-projection system without a mosaic color filter”.
FIG. 1A
of the annex drawings shows the solution, in which three dichroic mirrors
101
arranged downstream of each other divide the white light beam into three beams of the three primary colors red (R), green (G) and blue (B) which are projected on a single TFT-LCD
120
at different angles by a matrix
103
of microlenses
103
a
(FIG.
1
B). To each microlens
103
a
there are associated three pixels
120
a
of the TFT-LCD
120
. The beams going out of the TFT-LCD
120
are caused to converge by a field lens
106
into a lens
107
for projection on a screen
108
. In this solution there are still more problems, since it requires a relatively collimated light beam, since otherwise the dichroic filters would operate in a non efficient way and the use of the dichroic mirrors, which are expensive and can operate only in reflection, would cause a bending of the beam. The liquid crystal panel is still necessary. At each subclass of pixel R or G or B there are applied one of the respective R G B signals. In a solution from DISPLAYTECH, Inc., a liquid crystal of a multi-layer ferroelectric type called “RGB fast filter” can be controlled electronically to pass the red, green or blue colors to pass in a sequential way.
Alternatively, filters which can change the transmitted color are known also with series of twist nematic liquid crystals and polarizing filters. A further alternative is possible also without polarizers with series of layers of high twisted liquid crystals, composed by mixtures of colisteric nematic liquid crystals which are dye-colored, arranged between glasses and coated with an electrically conductive ITO coating.
In all cases making use of liquid crystals, there is the problem of the cost both of the base materials and the required technologies. Another problem is associated to the limited field of temperatures of use; as a matter of fact, liquid crystals cease to operate outside a range between −20° C. and +80° C.
In the field of displays for the projection of static images, a diapositive is illuminated uniformly by a polychromatic beam, and a lens projects the image on a screen. Each time that one wishes to change the image it is necessary to replace the diapositive.
OBJECT OF THE INVENTION
The object of the present invention is that of providing a device for dynamic selection of colors and images which is free from the drawbacks of the prior art.
MAIN FEATURES OF THE INVENTION
In order to achieve this object, the invention provides a device having the features indicated in the annexed claim
1
. Further preferred features of the device according to the invention are described in the sub-claims.
In the present invention, the problems of the prior art are overcome by using a matrix of micro-filters and a matrix of electrostatic micro-choppers. The materials are conventional and the technologies required for carrying out the invention are of low cost.
REFERENCES:
patent: 4985816 (1991-01-01), Seko et al.
patent: 5323002 (1994-06-01), Sampsell et al.
patent: 5506701 (1996-04-01), Ichikawa
patent: 5764389 (1998-06-01), Grinberg et al.
patent: 5781257 (1998-07-01), Gal et al.
patent: 4431749 (1995-03-01), None
patent: 0644450 (1995-03-01), None
patent: WO 9512286 (1995-05-01), None
Hamada et al. “Brightness Enhancement of an LCD Projector by a Planar Microlens Array”, SID Int'l Symposium Digest of Papers, US, Playa Del Rey, SID, vol. 23, pp. 269-272.
Conference on Binary Optics, Huntsville, AL, Feb. 23-25, 1993, NASA Publication 3227, M.F. Farn et al. Color Separation Gratings, pp. 409-421.
H. Dammann “Color separation gratings”, Applied Optics, vol. 17, No. 15, Aug. 1, 1978, pp. 2273-2279.
Sweeney D>W. et al. “Harmonic Diffractive Lenses”, Applied Optics, U.S. Optical Socity of America, Washington, vol. 34, No. 14, pp. 2469-2475.
SID Int'l. Symposium, Digest of Technical Papers, Society for Information Display, 1991, vol. 22, pp. 427-429, M. Doebler et al. “An Improved Frame-Sequential Color Projector with Modified CdSe-TFTs”.
Euro Display 93, LCP-1, pp. 249-252, P. Janse “A novel signle light valve hight brightness HD color projector”.
Japan Display 92 Digest, p. 875, T. Takamatsu et al. “PD-1 Single-Panel LC Projector with a Planar Microlens Array”.
Perlo Piero
Repetto Piermario
Sinesi Sabino
C.R.F. Societa Consortile per Azioni
Duong Tai V.
Sikes William L.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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