Projector

Details Projector Projector

1999-02-24

2001-05-01

Sikes, William L. (Department: 2871)

Liquid crystal cells, elements and systems

Liquid crystal system

Projector including liquid crystal cell

C359S819000, C353S101000

Reexamination Certificate

active

06226055

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to projectors by which images displayed on a liquid-crystal panel, or the like, are projected on a screen.
BACKGROUND OF THE INVENTION
FIG. 7
shows a projector already proposed which comprises three liquid-crystal panels
7
,
7
a
,
7
b
corresponding to R, G, B, such that the panels are irradiated with beams from a light source
35
to project color images by combining the beams passing through the liquid-crystal panels. In the following description, a beam, opposite ends of which are parallel to the optical axis, will be referred to as parallel rays.
Inside a chassis
3
, the liquid-crystal panels
7
a
,
7
b
corresponding respectively to B and R are arranged as opposed to each other on opposite sides of the optical axis of a projection lens
67
, and a prism body
30
is disposed between the two liquid-crystal panels
7
a
,
7
b
. The prism body
30
has, in its interior, reflecting planes
31
,
32
orthogonal to each other. The liquid-crystal panel
7
corresponding to G is disposed at one side of the prism body
30
opposite to the projection lens
67
.
The light source
35
is provided at an optical path inlet for the chassis
3
, and a condenser lens
79
for concentrating light is disposed inwardly of the light source
35
. Arranged on the optical path, inclined with respect thereto, are total reflection mirrors
75
,
76
,
77
,
78
and dichroic mirrors
45
,
46
. The dichroic mirror
45
passes B while reflecting G and R. The dichroic mirror
46
reflects G while passing R.
B passing through the dichroic mirror
45
is reflected at the total reflection mirror
76
, irradiates the liquid-crystal panel
7
a
corresponding to B, and is caused to impinge on the projection lens
67
by the reflecting plane
32
within the prism body
30
. R is reflected from the total reflection mirrors
77
,
78
and thereafter incident on the projection lens
67
upon reflecting at the plane
31
within the prism body
30
. Thus, R, G, B to be incident on the projection lens
67
are combined by the prism body
30
.
With the projector of
FIG. 7
, the optical path length of R is greater than those of G and B. It is therefore likely that R, emanating from the light source
35
and separated off, will diffuse before reaching the liquid-crystal panel
7
b
, failing to fully irradiate the liquid-crystal panel
7
b.
To obviate this problem, convex lenses called relay lenses
80
,
8
,
81
are fixedly mounted on the chassis
3
between the dichroic mirror
46
and the liquid-crystal panel
7
b
to sufficiently irradiate the panel
7
b
corresponding to R. Of the three relay lenses
80
,
8
,
81
, the middle relay lens
8
serves to make the emanating light into approximately parallel rays.
However, the above projector has the following problems.
The optical path is likely to deflect from the normal position owing to variations in the dimensions of optical components, such as lenses and mirrors, mounted on the chassis
3
and to errors involved in mounting. R, with an elongated optical path, is especially susceptible to this influence.
A minimum required range of irradiation is predetermined for liquid-crystal panels of the type mentioned. Suppose the minimum required range is a range A indicated in a solid line in FIG.
2
. If the optical path is deflected from the normal position, the light incident on the liquid-crystal panel
7
b
will irradiate a range A
1
of broken line, as displaced from the range A.
Consequently, R will not be accurately combined with the other rays G, B, producing color irregularities in the composed image, whereas the relay lenses
8
,
80
,
81
, which are fixed to the chassis
3
, are not adjustable for correcting the deflection of the optical path. For this reason, it has been conventional practice to set a wide range A
2
including A and A
1
and shown in
FIG. 2
for irradiating the liquid-crystal panel
7
b
, and to set irradiation ranges A
2
also for the other liquid-crystal panels
7
,
7
a.
Thus, color irregularities in the projected composite images are precluded by superposing R, G, B, with the ranges of irradiation made wider than should be set.
When the light source
35
has constant brightness, the brightness per unit area, i.e., illuminance, on the screen is inversely proportional to the square of the area of the irradiation range, as is well known, so that the illuminance is lower than is intended if a wider irradiation range is set.
Nevertheless, a higher illuminance is required of projectors of the type mentioned. The conventional projector, wherein the irradiation range is wider than is needed, fails to fulfill this requirement. In view of this point, the present applicant has conceived the idea of achieving a higher illuminance by adjusting the position of the relay lens to set a minimum required range of irradiation for the liquid-crystal panel
7
b.
SUMMARY OF THE INVENTION
An object of the present invention is to realize a higher illuminance in a projector.
The present invention provides a projector which comprises an adjusting mechanism
5
mounted on a chassis
3
. A relay lens
8
, provided on the longest optical path, is moved upward, downward, leftward or rightward in a plane orthogonal to the optical path by manipulating the adjusting mechanism
5
. When thus moved, the relay lens
8
permits light to be incident on a liquid-crystal panel
7
b
within a minimum required range of irradiation.
As shown in
FIG. 3A
, light is likely to be incident, as deflected on the relay lens
8
, for example, owing to an error involved in mounting optical components inside the chassis
3
. As a result, the liquid-crystal panel
7
b
will be irradiated at a portion deflected from the minimum required range of irradiation. In this case, the relay lens
8
is adjusted leftward, rightward, upward or downward in a plane orthogonal to the optical path. Since the relay lens
8
is a convex lens, the angle of refraction of light differs with the position at which the light is incident on the relay lens
8
. Thus, the range of irradiation of the liquid-crystal panel
7
b
can be altered by moving the relay lens
8
as shown in FIG.
3
B.
Since the liquid-crystal panel
7
b
can be irradiated accurately over the minimum required range of irradiation, there is no need to widen the irradiation range of the liquid-crystal panel
7
b
more than is necessary as conventionally practiced. This serves to diminish the conventional irradiation range of the liquid-crystal panel
7
b
to prevent a reduction in the illuminance of irradiation images.


REFERENCES:
patent: 3359849 (1967-12-01), Friedman
patent: 5398132 (1995-03-01), Otani
patent: 5751396 (1998-05-01), Masuda et al.
patent: 5777340 (1998-07-01), Ueno
patent: 5865521 (1999-02-01), Hashizume et al.
patent: 5889576 (1999-03-01), Fujieda
patent: 5917460 (1999-06-01), Kodama
patent: 5917653 (1999-06-01), Taniguchi
patent: 4-65594 (1992-10-01), None

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