Optical: systems and elements – Projection screen – With reflector or additional screen
Reexamination Certificate
2000-03-07
2002-01-01
Mahoney, Christopher E. (Department: 2851)
Optical: systems and elements
Projection screen
With reflector or additional screen
Reexamination Certificate
active
06335829
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a projection screen for image reproduction devices which comprise projectors and screens, an image being projected onto the rear side of a screen with the aid of a projector. The field of application is that of multi-screen displays.
In the case of a multi-screen display of this nature, the viewer is situated in front of the screens, which are positioned next to and/or above one another, optionally at an angle, so that they form an image surface onto which an image, optionally composed of a plurality of subimages, can be projected. A subimage may cover one or more screens of the image surface and may occur at any desired location on the image surface. These subimages may be projected dependently or independently. The images may be moving or still.
In the case of multi-screen displays, there are the same number of (at least two) projectors as screens for projecting images onto the screens. As a result of their layout, the screens form a surface in the space which lies between the projectors and the viewer. There is a joint or seam where the screens which are positioned next to and/or above one another contact one another. With existing multi-screen displays, it is constantly being sought to limit the visibility of the seams between the assembled screens to a minimum for the viewer and to keep them at a minimum level over the course of time.
BACKGROUND ART
In practice, multi-screen displays are known in which a larger screen is assembled from a plurality of smaller screens or screen panels.
FIG. 1
shows a front view of a multi-screen display
1
according to the prior art, which is a combination of M screens
2
in the width direction and N screens
2
in the height direction, optionally with a stand
3
at the bottom.
FIG. 2
shows a side view of the same multi-screen display
1
, showing screens
2
, supporting structures
5
(one per screen or one for a plurality of, or for all the screens together) and projectors
6
. In
FIGS. 1 and 2
, some of the seams
4
between the separate screens
2
are indicated.
A multi-screen display may be composed of a number of identical basic units which are stacked on top of and/or next to one another as modules and are optionally attached to one another in addition. A basic unit of this nature is composed of a partially or completely light-screening, supporting structure, a screen which is mounted either fixedly or removably on the supporting structure or is mounted in front of or behind the arrangement of the multi-screen display, and a projector which is prefitted, optionally extendibly, entirely or partially in the supporting structure or is mounted in front of or behind the arrangement of the multi-screen display. Assembly by means of basic units requires a stable, perfectly flat supporting surface if, during installation, it is desired to obtain and retain an optimum connection between the basic units. Changing climatological conditions, such as temperature and relative atmospheric humidity, may alter the distance between the basic units and have an adverse effect on the connection between them.
FIGS. 3
a,
3
b,
3
c
and
3
d
together illustrate how, in the case of three combinations, one above the other, of a screen
7
and a supporting structure
5
, differences in expansion cause the dimensions of the screens
7
to change with respect to the dimensions of the supporting structures
5
under the influence of climatological conditions. The screens
7
and the supporting structures
5
are illustrated separately from one another and are joined by means of auxiliary lines
8
in order to make the differences between their dimensions clear.
FIG. 3
a
shows three correctly installed, adjacent screens
7
and supporting structures
5
under the nominal climatological conditions. In comparison to
FIG. 3
a,
FIG. 3
b
and
FIG. 3
c
show the screens
7
once they have become smaller with respect to the supporting structures
5
as a result of climatological conditions. In
FIG. 3
b,
the three screens
7
are not attached any more to one another. Consequently, therefore, the seam
4
between two screens
7
becomes larger. In
FIG. 3
c,
the three screens
7
are still attached to one another; the total screen surface area has become smaller while the seams
4
have in principle not changed. In
FIG. 3
d,
by comparison with
FIG. 3
a
the screens
7
have become larger with respect to the supporting structures
5
as a result of climatological conditions. The total screen surface area has become larger and the seams
4
have in principle not changed. Similar changes to those illustrated in
FIG. 3
for screens which are situated above one another may also arise in the case of screens which are situated next to one another.
The effect of climatological conditions is important not only for multi-screen displays assembled from basic units but also for the multi-screen displays from the prior art which are described below and in which larger screens are obtained by joining together smaller screens, for example by adhesive bonding.
The basic units of the prior art which have been described above often have a frame around the screen, which frame holds this screen flat, often also serves to attach the screen to the housing of the basic unit and protects the edges of the screen from damage. This frame prevents an image from being projected all the way as far as the outer edge of the front side of the basic unit and makes the visual joint or seam between the basic units larger. EP-0 650 295 and EP-0 523 427 describe basic units of this nature and the assembly of a plurality of basic units of this nature to form a multi-screen display. A solution for allowing images to be projected right up to the edge of the front side of the basic unit is described in WO 95/28664 and consists in a special treatment of the outer edges of the screen and a special attachment of the said screen to a supporting structure, so that the light from the projector is able to reach the front edges of the screen—which are also the front edges of the basic unit—without being impeded. In principle, it is possible to achieve a perfect connection between screens of basic units at a specific temperature. However, the edges of a basic unit of this nature are fragile during transportation and the other drawbacks which are inherent to the assembly of basic units continue to exist.
Another solution is to adhesively bond together relatively small optical screens to form larger screens. Adhesively-bonded larger screens of this nature cannot be produced at the location where the projection screen is to be installed, but rather can be produced only at the premises of the constructor, following which they have to be transported in very robust and large packaging. In order to prevent damage and contamination to the screens during attachment to a supporting structure, installation has to take place with the greatest possible care.
U.S. Pat. Nos. 5,011,277 and 5,085,495 disclose projection screens comprising one or more horizontally arranged basic units comprising multiple screen panels which are arranged one above the other. The screen panels, a single front sheet, a single re-inforcing sheet and a support body are pulled together by means of wire and coil spring combinations. The horizontal seams between contacting screen panels arranged above each other are minimised. The vertical seams between screen panels of horizontally neighboring basic units are however not sufficiently minimised. Attaching basic units of this nature to one another not only has the abovementioned drawbacks which are inherent to the use of relatively large single screens or adhesively-bonded larger screens, but also drawbacks which are inherent to modular multi-screen displays assembled from identical basic units, such as the need for a flat and stable base and the fact that the connection between the basic units is dependent on temperature and humidity.
The abovementioned multi-screen displays which are known from the prior art are difficult to transport owing to
Barco N.V.
Mahoney Christopher E.
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