Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Reexamination Certificate
1997-03-26
2001-01-30
Font, Frank G. (Department: 2877)
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
C353S098000
Reexamination Certificate
active
06181388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projector of a reflection type. More particularly, the present invention relates to a projector of a reflection type having a body, where an image of a transparency can be projected, has a small height.
2. Description Related to the Prior Art
An overhead projector is an apparatus for presentation to a great number of onlookers or audience with an image of a transparency in an enlarged size on a screen. It is known to use a liquid crystal display (LCD) panel of a transmittance type in combination with the overhead projector. The LCD panel projects a video image, such as a motion picture image, to a screen, and also smooths an operation of setting one image after another. An example of the LCD panel consists of a twisted nematic (TN) type of liquid crystal device, and is placed on a stage of the overhead projector. The LCD panel is connected to a video player, a microcomputer, or the like to receive an input of an image, and displays the image in the form of a motion picture or computer-graphic (CG) image.
There are suggestions of an LCD-fitted overhead projector in which the LCD panel is built in the overhead projector. In the LCD-fitted overhead projector, the LCD panel of the twisted nematic type is contained in the stage of the overhead projector. There is also a proposal of using a nematic-cholesteric phase-transition (NCPT) type of the LCD panel in the LCD-fitted overhead projector. The LCD panel of the nematic-cholesteric phase-transition type is characteristically capable of having a maximized optical transmittance as high as 80-90%. This is advantageous as high contrast and sharpness are obtained in projecting an image of the LCD panel or the transparency.
The overhead projector herein is a reflection type more recent than a transmittance type of overhead projector. The transmittance-type projector contains a light source in its base. The transparency is illuminated by the light source directly in an upward direction. The disposition of the light source in the transmittance-type projector is a short-coming as it enlarges the height of the projector. The reflection type of the overhead projector has the light source contained in the rear of a projector head as a top of the projector. The illuminating light is initially passed down to the transparency, and is reflected upward to the projector head upon illuminating the transparency. The reflection type is more advantageous over the transmittance-type projector, as the height of projector is the smaller because of the disposition of the light source.
In
FIG. 4
, a reflection type of LCD-fitted overhead projector
2
is illustrated. The overhead projector
2
includes a stage
7
and a stay
8
disposed erectly from the stage
7
. The stage
7
includes a Fresnel lens
3
, a liquid crystal display (LCD) panel
4
, an illuminating mirror
5
and a driver circuit board
6
, which are overlaid on one another. The LCD panel
4
is a nematic-cholesteric phase-transition type. The stay
8
supports a light source
9
, a condenser lens
10
, path converter mirrors
11
and
12
and a projector head
14
. The projector head
14
includes a projection lens
13
.
In the overhead projector
2
, the light from the light source
9
of the projector head
14
is reflected not only by the illuminating mirror
5
but by a surface of the Fresnel lens
3
. This additional partial reflection of the surface of the Fresnel lens
3
does not affect a projecting operation of an image of the LCD panel
4
, but affect a projecting operation of an image of a transparency
16
, as depicted in the enlarged drawing. The reflected light from the surface of the Fresnel lens
3
illuminates the transparency
16
. Due to a considerable thickness of the LCD panel
4
between the Fresnel lens
3
and the illuminating mirror
5
, the light reflected by the illuminating mirror
5
is remarkably deviated from the light reflected by the surface of the Fresnel lens
3
. A double-projection phenomenon occurs, as an image is projected in a double manner on a screen
17
.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present invention is to provide a projector of a reflection type in which an image of a transparency can be projected even by the projector of which a body has a small height.
In order to achieve the above and other objects and advantages of this invention, a projector of a reflection type includes a Fresnel lens disposed on a first side with respect to a stage surface on which a transparency is set. A light source is disposed on the first side with respect to the Fresnel lens, for illuminating the stage surface through the Fresnel lens. An illuminating mirror is disposed on a second side with respect to the stage surface opposite to the first side, for reflecting light passed through the transparency after emanation from the light source to illuminate the transparency from the second side toward the first side. A projection lens projects an image of the transparency via the Fresnel lens to a screen. There is a liquid crystal display panel disposed so that the stage surface lies thereon, the liquid crystal display panel being transparent when the transparency is set on the stage surface, for enabling projection of the image, the liquid crystal display panel displaying an image to be projected to the screen when the stage surface lacks a transparency set thereon.
In a preferred embodiment, the liquid crystal display panel is a nematic-cholesteric phase-transition type.
Furthermore, there is a projector body in which the light source, the Fresnel lens and the projection lens are incorporated. A sheet cover is disposed on the projector body in a rotatable manner, and has the illuminating mirror incorporated therein.
The liquid crystal display panel is secured to the projector body, and has a top face on which the stage surface lies.
In another preferred embodiment, the liquid crystal display panel is secured to the sheet cover and covers the illuminating mirror.
REFERENCES:
patent: 5206673 (1993-04-01), Kawahara et al.
patent: 5617226 (1997-04-01), Ohmae et al.
Font Frank G.
Fuji Photo Film Co. , Ltd.
Nguyen Tu T.
Young & Thompson
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