Optics: image projectors – Housing
Reexamination Certificate
2000-12-07
2003-05-20
Dowling, William (Department: 2851)
Optics: image projectors
Housing
C353S061000
Reexamination Certificate
active
06565215
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image projector, more particularly to an image projector with optical valves such as liquid-crystal valves, which is used to display a computer or video image on an external screen.
One example of an image projector using liquid-crystal optical valves is shown in FIG.
1
. This projector comprises an illumination system
1
having a lamp
10
, such as a metal halide, xenon or similar lamp, and a reflector
11
surrounding the lamp
10
. The illumination system
10
is combined with an optical integrator
2
, the role of which is to uniformly distribute the light emitted by the lamp
10
of the illumination system, over the components of the optical unit
3
which will be described hereinafter. The optical unit
3
has, schematically, colour separation means so as to supply each optical valve
30
,
31
,
32
with the corresponding colour component and a means
20
of recombining the images supplied by the three optical valves. As shown in
FIG. 1
, the image recombination means is formed by a cube
20
constituting a set of mirrors
22
and
24
occupying the diagonal planes of the cube
20
. The three liquid-crystal valves
30
,
31
,
32
are placed parallel to three faces of the cube. More accurately, the optical valve
30
is parallel to the face
26
of the cube. The optical valve
32
is parallel to the opposite face
28
of the cube, the two valves
30
and
32
being parallel to each other and the optical valve
31
is parallel to the face
27
of the cube and perpendicular to the other two valves
30
and
32
.
As the illumination system
1
emits white light, colour separation means are therefore provided in the optical system
3
. These means are formed by dichroic mirrors combined with plane mirrors in order to direct, respectively, the blue colour component onto the optical valve
30
, the green colour component onto the optical valve
31
and the red colour component onto the optical valve
32
. More specifically, the light emitted by the illumination system
1
passes through a first dichroic mirror
33
placed immediately downstream of the integrator
2
. The normal N to the plane of the mirror
33
forms an angle of 45° with the optical axis O. Because of this, the dichroic mirror
33
transmits the blue colour component to a plane mirror
34
positioned so as to illuminate the optical valve
30
via a field lens
40
and reflects the remainder of the spectrum towards a second dichroic mirror
35
parallel to the first dichroic mirror
33
. This second dichroic mirror
35
reflects the green colour component of the spectrum towards the optical valve
31
through a field lens
41
similar to the lens
40
. The dichroic mirror
35
transmits the remainder of the spectrum, i.e. the red colour component. This red component passes through a first lens
42
then is reflected by a plane mirror
36
parallel to the dichroic mirrors
38
and
40
. The component reflected by the plane mirror
36
passes through a lens
44
then is reflected again by a plane mirror
37
in such as way as to be sent back to the optical valve
32
through a field lens
43
identical to the lenses
40
and
41
. The images formed on the optical valves
30
,
31
and
32
are then recombined by reflection and transmission inside the cube
20
so as to obtain a synthetic image on the face
29
of the cube, this image being sent to a projection lens
5
.
The apparatus described with reference to
FIG. 1
comprises numerous components, especially optical and electronic components, which have to operate in a clean environment and at acceptable temperature levels. Now, in order to obtain good quality images having a high luminosity, it is generally necessary to use powerful projection lamps. The use of bright lamps which are more and more powerful makes the thermal aspects more critical within the projector. This leads to the use of more and more elaborate cooling systems which must also take into account parameters such as the increase in the resolution of the optical valves, the desire to have the minimum overall size, the noise level of ventilation systems and the increase in the functions offered.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide an image projector with an improved cooling system which especially enables the following advantages to be obtained, viz.:
to ensure that all the critical parts are kept below their limit temperature;
to allow the proper operation of the projector up to ambient temperatures which may reach 50° C.;
to ensure the system is placed away from dust and to minimize as far as possible the noise level.
As a consequence, the subject of the present invention is an image projector comprising a casing containing at least:
an illumination system;
an optical unit comprising at least one optical valve modulating the light emitted by the illumination system;
a projection lens projecting the modulated light outside the casing;
a power supply, control electronics and cooling means;
the casing being provided with at least one aperture forming an air inlet,
characterized in that it further comprises a specific air filtration means positioned under the optical unit and in such a way as to surround the latter.
According to a preferred embodiment, the air filtration means is a component in the shape of a cage, the side walls of which are covered with wire mesh.
Preferably, the present invention is applicable to a colour image projector the optical unit of which comprises three optical valves each provided for one colour, colour separation means to supply each optical valve with the corresponding colour component from the light emitted by the illumination system and a means of recombining images supplied by the three optical valves.
According to another characteristic of the present invention, the projector further comprises at least one cooling means for the optical valve or valves. Preferably, it comprises three turbines positioned inside the specific air filtration means, under each optical valve respectively.
To obtain better cooling of the projector, it further comprises a cooling means for the illumination system formed by a turbine positioned horizontally close to the illumination system, this turbine being extended by two air guides, a first air guide sending part of the air to the illumination system and a second air guide sending the other part of the air to the optical unit.
BRIEF DESCRIPTION OF THE DRAWINGS
Moreover, the projector may comprise additional cooling means and air extraction means generally formed by fans.
According to an additional characteristic of the present invention, the speed of the turbines and of the fans is variable according to the temperature, the temperature being detected by at least one thermistor combined with an electrical control circuit for each fan.
Moreover, according to yet another characteristic of the present invention, the casing has an aperture forming an air inlet on each side face and at least one air extraction aperture on the rear face.
REFERENCES:
patent: 5666171 (1997-09-01), Nakamura et al.
patent: 5683160 (1997-11-01), Fukaya et al.
patent: 6007205 (1999-12-01), Fujimori
patent: 6033077 (2000-03-01), Iwase
patent: 6132049 (2000-10-01), Yamaguchi et al.
patent: 6254238 (2001-07-01), Takamatsu
patent: 6280038 (2001-08-01), Fuse et al.
patent: 6290360 (2001-09-01), Konuma et al.
patent: 19631945 (1998-02-01), None
patent: 0829750 (1998-03-01), None
Barrau Jérôme
Carle Jean-Michel
Sacre Jean-Jacques
Dowling William
Fried Harvey D.
Kolodka Joseph J.
Tripoli Joseph S.
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