JP2001092006A - Projection display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the depth of a back projection display device by realizing oblique projection without requiring expansion of an image circle of a projection lens. SOLUTION: In the projection display device which magnifies a display picture on a LCD 1 by a projection lens 2 to project it on a screen 4, a back glass 5 of which the thickness is changed like a wedge is inserted between the projection lens 2 and the LCD 1 to continuously change the optical path length between the projection lens 2 and the LCD 1, and a picture is projected on the screen 4 from a direction inclined to the optical axis of the projection lens 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a projection type display device, and more particularly to a rear projection type display device capable of reducing the thickness of the device.

[0002]

2. Description of the Related Art A rear projection display device using a liquid crystal display panel (hereinafter referred to as an LCD) as a display device and enlarging and displaying a display image displayed on the LCD with a projection lens has attracted attention as a device capable of increasing the screen size. ing.

In this type of rear projection display device, as shown in FIG. 7, an image light emitted from an optical engine 101 having an LCD, a light source and a projection lens is provided on the entire surface of a housing 100 inside the housing 100. The image is projected onto the projection screen 103 from the rear side. In these devices, a total reflection mirror 1
02, the optical path is bent to reduce the thickness of the housing 100.

In order to further reduce the thickness of the housing of the above-described apparatus, the angle of the projection lens must be increased, or
As disclosed in Japanese Patent Application No. 151994 (G02B 27/18), an image circle larger than the display device size is secured, and the display device is offset from the lens optical axis to form an oblique projection configuration. There is a method. However, both of these are disadvantageous in terms of cost because the projection lens becomes large.

[0005]

In a conventional projection optical system, a display surface such as a screen and a display device such as an LCD are usually arranged in parallel. It is necessary to perform a so-called lens shift in which a large image circle is secured and the display device is offset from the lens optical axis.
However, a projection lens having a large image circle has a problem that the projection lens becomes large and the cost increases.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described conventional problems, and realizes oblique projection without requiring an enlargement of an image circle of a projection lens, thereby reducing the depth of a rear projection display device. With the goal.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a projection type display apparatus for enlarging a display image of a display device by a projection lens and projecting the image on a screen surface. The optical path length between the projection lens and the display device is continuously changed by inserting an optical transparent body that changes, and the image is projected onto the screen from an oblique direction with respect to the optical axis of the projection lens. .

Further, the present invention is configured such that a display image of a display device is projected on a half side of a center axis of the projection lens.

When a light beam passes through an optically transparent member such as glass having two parallel surfaces, the light path length of the light beam is uniformly extended by an equal length, and an optimum image is formed on a plane parallel to the display device. On the other hand, according to the present invention, when the thickness of one surface of the optically transparent member is changed in a wedge shape or a step shape inclined with respect to the other surface, the optical path length varies depending on the optical thickness that has passed. The optimal image plane will be inclined with respect to the display device.

Further, it is preferable that the display screen itself has a trapezoidal shape corresponding to the trapezoidal distortion generated in the oblique projection optical system. In this manner, by making the display screen a trapezoid, it is possible to cancel the trapezoidal distortion.

[0011]

Embodiments of the present invention will be described below.

First, as an example, as a display device, the diagonal is 1.3 inches, and the effective display area is 26 m in the horizontal direction (H).
Consider a projection lens 2 of f20 mm, which enlarges a transmission LCD 1 of m, vertical direction (V) 20 mm to a screen 4 having a projection screen size of 40 inches at a projection distance of 600 mm. The light from the light source 3 is modulated by the LCD 1, enlarged by the projection lens 2, and projected on the screen 4.

The depth of the housing is such that the projection lens 2 reflects once using a total reflection mirror in a state where the center of the LCD 1 coincides with the center of the optical axis of the lens and the lens shift amount is 0. As shown in FIG. 1, the length is about 300 mm only with the optical system.

Next, as shown in FIG. 2, consider a state in which the projection surface of the screen 4 is inclined by 60 ° from this projection state.

When the 4: 3 display surface is projected onto the projection surface of the screen 4 inclined at 60 °, a trapezoid whose vertical direction is doubled is displayed. Since the projection screen size is the same 40 inches, the lower end of the screen is made coincident with the center of the projection lens 2 (O in the figure) on the optical axis, and the vertical (V) size 610 mm of the 40 inch screen is located at the upper end of the screen. become. The required projection light flux in this case is indicated by the hatched portion in the figure.

Next, a specific method for focusing on the screen 4 inclined at 60 ° will be described with reference to FIGS. Here, an outline based on the lens imaging system will be shown.

Since the projection distance of the lower end of the screen of the screen 4 is 600 mm in this example, the air-equivalent distance from the object side main surface of the projection lens 2 to the LCD 1 is 20.7 m.
m. Next, the projection distance of the upper end of the screen is 1120 mm, and the air-equivalent distance from the object side main surface of the projection lens 2 to the LCD 1 is 20.37 mm.

Therefore, an optically transparent body whose thickness changes in a wedge-like or step-like manner, for example, a back glass 5 may be inserted between the projection lens 2 and the LCD 1. That is, when a light beam passes through an optically transparent member such as glass whose surfaces are parallel to each other, the light path length is extended by the same length as the total light beam, and L
An optimal image is formed on a plane parallel to the display screen of CD1. However, when the thickness of one surface of the optically transparent member changes in a wedge shape or a stepped shape inclined with respect to the other surface, the optical path length varies depending on the optical thickness that has passed, and the optimal image formation surface is LC
It will be inclined with respect to the display screen of D1.

FIGS. 2 and 3 show an example in which a wedge-shaped glass is arranged as the back glass 5. In order to generate an optical path difference of 0.37 mm using the wedge-shaped back glass 5, the air-equivalent distance (nd) of the back glass 5 is set to 1.
If it is set to 51, a thickness difference of 0.56 mm may be given. As shown in the figure, the center portion (O) of the projection lens 2 is made thinner and gradually thicker toward the lower side in the figure, and the difference in thickness between the center portion and the lowermost position is reduced by 0.5.
What is necessary is just to make it 6 mm.

In the example shown in FIG. 4, the thickness of the back glass 5 is changed stepwise. Center (O)
The thickness of the step portion is gradually increased from the step portion located at the bottom to the lower side in the figure, and the difference in thickness between the center portion and the step portion at the lowest position is 0.56 mm.

Next, a method of displaying a 4: 3 raster without trapezoidal distortion on a screen inclined at 60 ° will be described. Since the vertical direction is doubled, the vertical direction is 10 mm. The top side of the screen with a projection distance of 1120 mm,
In order to enlarge the screen to a 40-inch horizontal size of 813 mm at the lower side of the screen with a projection distance of 600 mm, the display screen of the LCD 1 needs to have a trapezoidal shape with an upper base of 14 mm and a lower base of 26 mm.

In the trapezoid, similarly to the correction, the pixel arrangement density is changed, and the display screen of the LCD 1
If a display device having a square arrangement is used while being projected on the screen 4 inclined at an angle, a dot-compatible display such as a personal computer (PC) is also possible.

As shown in FIG. 5, 1.3 inch LCD
1 requires at least the image circle of the projection lens 2 for φ33 mm, but in this embodiment, the required projection light flux is half, and as shown in FIG.
For the trapezoidal display screen of D1, the image circle is φ
26 mm is sufficient. In this way, the margin due to the image circle being reduced by about 20% can be used for correcting the aberration generated by inserting the wedge-shaped or step-shaped back glass 5.

FIG. 6 shows a case where the shaded effective light beam shown in FIG. According to this configuration, when the size of the optical system is set to 40 inches, the depth of the optical system is about 140 mm, which is equal to or less than 1/2 of FIG.

[0025]

As described above, according to the present invention,
This makes it possible to perform steep oblique projection without requiring an enlargement of the image circle of the projection lens, thereby realizing a significant reduction in the thickness of the housing of the rear projection display device.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state where an image is enlarged and projected on a screen surface parallel to an LCD at a lens center and a state where the image is bent by reflection.

FIG. 2 shows an example of a display screen of an LCD according to the present invention;
FIG. 6 is a schematic diagram showing an effective projection light beam when tilted by an angle of °.

FIG. 3 is a schematic diagram showing a relationship between an LCD according to the present invention and a back glass inserted between a projection lens.

FIG. 4 is a schematic diagram showing a relationship between an LCD according to the present invention and a back glass inserted between a projection lens.

FIG. 5 is a schematic diagram showing a conventional image circle required for a 1.3-inch LCD, a display screen shape for projecting a rectangle on a screen in a projection state in the present invention, and an image circle required.

FIG. 6 is a schematic diagram showing a state in which a projection light beam according to the present invention is bent by reflection.

FIG. 7 is a schematic side view showing a conventional rear projection display device.

[Explanation of symbols]

 1 LCD 2 Projection lens 3 Screen 5 Back glass

Claims (3)

[Claims] 1. A projection display device for enlarging a display image of a display device by a projection lens and projecting the enlarged image on a screen surface, wherein an optical transparent body having a wedge-shaped or step-like thickness change is provided between the projection lens and the display device. A projection display device wherein the optical path length between the projection lens and the display device is continuously changed by being inserted, and the projection is performed on the screen surface in an oblique direction with respect to the optical axis of the projection lens. 2. The projection display apparatus according to claim 1, wherein a display image of a display device is projected on a half side of a center axis of the projection lens. 3. The projection display device according to claim 1, wherein the display screen itself is canceled out as a trapezoidal shape in response to trapezoidal distortion generated in the oblique projection optical system.