Projector device

Details Projector device Projector device

2002-05-29

2003-07-08

Dowling, William (Department: 2851)

Optics: image projectors

Prism in light path

C348S771000

Reexamination Certificate

active

06588908

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projector device, and more particularly to a projector device for projecting images on a screen by using a digital micromirror device (DMD).
2. Description of the Related Art
A DMD is configured of a large number of micromirrors arranged in a matrix, in which each micromirror constitutes one pixel of a displayed image. Each micromirror takes one of two inclined states, an ON state and an OFF state. In the ON state, illuminating light is reflected into a projecting optical system, while in the OFF state it is projected away from the projecting optical system. Therefore, in a projector device using a DMD, the projecting optical system projects only the light reflected by micromirrors in the ON state, resulting in the formation of a displayed image composed of a pattern of different levels of brightness on the screen.
FIG. 5
shows a plan of a micromirror drive structure in a DMD, and
FIG. 6
shows the
6
—
6
section in FIG.
5
. The drawings show expanded views of one extracted out of many micromirrors constituting the DMD, which actually is configured of a large number of micromirrors arranged in a matrix.
As illustrated in
FIG. 5
, a micromirror
2
of a DMD
1
can take either an ON state inclined by +12° or an OFF state inclined by −12° to the DMD surface by turning around a rotation axis ab. This rotation axis ab of the micromirror
2
is set in a direction inclined by 45° to the long (or short) side of the DMD, and illuminating light L
o
irradiates the surface of the DMD at an incidence angle of 24° in a direction orthogonal to this rotation axis ab. The illuminating light L
o
irradiating the DMD, if reflected by the micromirror
2
in the ON state, turns into projecting light L
1
whose angle of reflection by the DMD surface is 0° or, if reflected by the micromirror
2
in the OFF state, turns into projecting light L
2
whose angle of reflection by the DMD surface is −48°. Only the projecting light L
1
, which is a luminous flux reflected by the micromirror
2
in the ON state at 0° in the angle of reflection, comes incident on the projecting optical system, and a displayed image composed of a pattern of different levels of brightness is formed on the screen. Known projector devices using such a DMD include ones disclosed in Japanese Patent Application Publication Nos. 9-98442 and 12-206452.
Incidentally, for a projector device using a DMD as stated above, on account of the above-described structure of the DMD
1
, the illuminating optical system has to be configured to meet two constraints that the illuminating light L
o
should be brought to incidence in a direction orthogonal to the rotation axis of the micromirror
2
(a direction inclined by 45° to the long or short side of the DMD
1
) and the illuminating light L
o
should further be brought to incidence at an angle of 24° to the surface of the DMD
1
.
For this reason, in a projector device according to the prior art, as shown in FIG.
7
and
FIG. 8
, a total internal reflection prism (TIR prism) is used to guide the illuminating light onto the DMD
1
. Thus, light emitted from a light source
3
is condensed into a rod integrator
5
via a color wheel
4
, guided by a first mirror
6
and a second mirror
7
to a TIR prism
8
and totally reflected by that TIR prism
8
thereby to irradiate the DMD
1
in a predetermined direction (a direction inclined by 45° to the long or short side of the DMD
1
) and at a predetermined incidence angle (24°). By causing the illuminating light irradiating the DMD
1
in this way to be reflected by the DMD
1
, optical modulation is performed, and the light transmitted by the TIR prism
8
after that optical modulation is projected by a projecting optical system
9
onto a screen.
This TIR prism
8
, as shown in
FIG. 9
, is configured of a first prism
8
A and a second prism
8
B. By causing illuminating light guided in from an illuminating optical system to be totally reflected by the total reflection plane P of the first prism
8
A, the DMD
1
is irradiated in the predetermined direction and the predetermined incidence angle, and the reflected light from the DMD
1
is guided to the projecting optical system
9
by causing it to be wholly transmitted by the total reflection plane P of the first prism
8
A.
Now, in the conventional TIR prism
8
, as illustrated in
FIG. 9
, the inclination angle &agr; of the total reflection plane P is so set as to totally reflect the incident illuminating light and to totally transmit the reflected light from the DMD
1
and the direction of the total reflection plane P is such that the projection line representing its normal vector as viewed in the direction vertical to the surface of the DMD
1
forms an angle of 45° to the long side of the DMD
1
(in
FIG. 9
, the normal vector of the total reflection plane shown in the front view and the rear view corresponds to the projection line representing the normal vector of the total reflection plane as viewed in the direction vertical to the surface of the DMD
1
). The illuminating light, as is the total reflection plane normal vector, is brought to incidence on this TIR prism
8
at a predetermined incidence angle (50.2° here) in a direction at 45° to the long side of the DMD
1
, and caused to be reflected by the total reflection plane
4
P to be guided to the DMD
1
.
However, this projector device according to the prior art, since the illuminating light should be brought to incidence on the TIR prism
8
in a direction at 45° to the long side of the DMD
1
as shown in FIG.
8
and
FIG. 9
, involves the disadvantage of being increased in thickness.
SUMMARY OF THE INVENTION
An object of the present invention, attempted in view of this circumstance, is to provide a projector device that permits a reduction in thickness.
In order to achieve the object stated above, the present invention is directed to a projector device in which light from a light source is guided by an illuminating optical system to a total internal reflection prism, the light totally reflected by the total internal reflection prism is optically modulated by having the light reflected by a digital micromirror device, and the light transmitted by the total internal reflection prism after the optical modulation is projected by a projecting optical system on a screen, wherein: the total internal reflection prism has a total reflection plane which totally reflects illuminating light to guide the illuminating light to the digital micromirror device and totally transmits the light having undergone optical modulation by the digital micromirror device, and is so arranged relative to the digital micromirror device that a projection line representing a normal vector of the total reflection plane as viewed in a direction vertical to a surface of the digital micromirror device forms an angle smaller than 45° to one of a long side and a short side of the digital micromirror device; and the illuminating optical system so brings the illuminating light into incidence on the total reflection plane that a projection line representing the optical axis of the illuminating light emitted from the total internal reflection prism to the digital micromirror device, as viewed in the direction vertical to the surface of the digital micromirror device, forms an angle of 45° to the one of the long side and the short side of the digital micromirror device.
According to the invention, the TIR prism is so arranged relative to the DMD that a projection line representing the normal vector of the total reflection plane as viewed in a direction vertical to the surface of the DMD forms an angle smaller than 45° to the long or short side of the DMD. Relative to the total reflection plane so arranged, the illuminating optical system so brings the illuminating light into incidence that a projection line representing the optical axis of the illuminating light emitted from the TIR prism to the DMD, as viewed in a direction vertical to the surface of the

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