JPH0623105Y2 - Rear projection display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a rear projection display device.

[Prior art]

As an image display device such as a television receiver, a display body (liquid crystal display panel or cathode ray tube) and a projection lens are provided in a case having a display window on the front surface and a transmissive screen provided in the display window. There is a rear projection display device in which an image to be displayed is magnified by the projection lens and projected and displayed on a transmissive screen.

This rear projection display device is generally a direct projection system in which a projection lens for enlarging and projecting a display image of a display body is arranged facing a transmissive screen, and the image light passing through the projection lens is directly projected on the screen. However, the rear projection type display device of the direct projection system has a problem that the device is large compared to the size of the screen projection image. This is because the projection optical path from the projection lens to the screen is a straight optical path. That is, in the projection type display device, the longer the projection optical path from the projection lens to the screen is, the larger the luminous flux of the image light passing through the projection lens reaches the screen, so that the projection optical path length from the projection lens to the screen is increased. If it is enlarged, a large screen image can be projected on the screen, but in the above rear projection display device of the direct projection system,
Since the projection optical path from the projection lens to the screen is a straight optical path, the projection lens must be placed far away from the screen in order to increase the projection optical path length. Since the size must be increased according to the position, the display device becomes larger than the size of the screen projection image.

For this reason, conventionally, there has been proposed an indirect projection type rear projection display device as shown in FIG. 4 in which image light having passed through a projection lens is sequentially reflected by a plurality of mirrors and projected on a screen.

The structure of this rear projection type display device will be described. In FIG. 4, reference numeral 1 denotes a case of the rear projection type display device, and a display provided with a large-area transmissive screen 3 on substantially the upper half of the front surface of the case 1. A window 2 is provided. Reference numeral 4 denotes a display body, for example, a transmissive liquid crystal display panel, which is arranged in the lower part of the case 1.
Is provided, and the light source 5 is provided in front of the liquid crystal display panel 4.
It is incident on the liquid crystal display panel 4 from this liquid crystal display panel 4
A projection lens 6 is arranged for enlarging and projecting the light transmitted through, that is, the display image of the liquid crystal display panel 4. Further, in the case 1, a plurality of, for example, three projection mirrors 7, 8 and 9 for guiding the image light having passed through the projection lens 6 toward the screen 3 are provided in an arrangement as shown. The area of each of the projection mirrors 7, 8 and 9 is increased in order from the one closest to the projection lens 6, and of these mirrors, the large-area final projection mirror 9 that reflects the image light toward the screen 3 is , Is diagonally opposed to the screen 3. The second projection mirror 8 in front of the final projection mirror 9 is arranged outside the optical path of the image light so as not to block the image light reflected by the final projection mirror 9 and traveling toward the screen 3. The first projection mirror 7 before that is arranged outside the optical path of this image light so as not to block the image light reflected by the second projection mirror 8 and traveling toward the final projection mirror 9. The liquid crystal display panel 4 and the projection lens 6 face the first projection mirror 7, and the image light passing through the projection lens 6 is sequentially spread by the projection mirrors 7, 8 and 9 while spreading the light flux. It is reflected and projected on the transmissive screen 3.

That is, in this rear projection display device, the projection optical path from the projection lens 6 to the screen 3 is a bent optical path provided with a plurality of projection mirrors, and thus the image light is bent in a zigzag manner on the screen 3. If the projection is performed, the straight line distance between the screen 3 and the projection lens 6 can be shortened while the projection optical path length from the projection lens 6 to the screen 3 is sufficiently taken. Therefore, the case 1 can be made smaller accordingly. Can be miniaturized.

By the way, in this indirect projection type rear projection display device, the final projection mirror 9 that finally projects an image on the screen 3 reflects the image light reflected by the projection mirror 8 before that toward the screen 3. The final projection mirror 9 needs to be provided at an angle with respect to the screen 3, but since the area of the final projection mirror 9 is quite large, if the tilt angle (angle with respect to the screen surface) θ is large, the final projection mirror 9 The bottom edge of the is backward (opposite screen 3)
Therefore, it is desirable to reduce the tilt angle θ of the final projection mirror 9 in order to make the display device thin and have a small depth.

[Problems to be solved by the invention]

However, in the conventional rear projection display device described above, the projection mirror 8 that reflects the image light toward the final projection mirror 9 is outside the optical path of the image light that is reflected by the final projection mirror 9 and travels toward the screen 3. In order to reflect the image light reflected by the projection mirror 8 toward the screen 3 by the final projection mirror 9, it is necessary to set the inclination angle θ of the final projection mirror 9 to a certain degree. Since the lower end side of the mirror 9 greatly extends backward, there is a problem that the depth length of the device becomes large.

The present invention has been made in view of the above-mentioned circumstances, and the purpose thereof is to reduce the inclination angle of the final projection mirror with respect to the screen surface to reduce the depth length of the device. It is to provide a rear projection display device.

[Means for solving problems]

In order to achieve the above object, the invention projects a display body and a display image of the display body toward the screen in a case having a display window on the front surface and a transmissive screen provided in the display window. A projection means and a final projection mirror diagonally opposed to the screen are arranged, and the final projection of the image light projected toward the screen by the projection means on the light incident surface side of the screen. A prism plate is provided in which a large number of stripe-shaped prism portions that are reflected toward a mirror and transmit the image light reflected toward the screen by the final projection mirror are formed continuously in the width direction.

[Action]

That is, in this invention, the image light projected onto the screen by the projection means is reflected toward the final projection mirror by the prism plate provided on the light incident surface side of the screen, and the image light is reflected onto the final projection mirror. By reflecting the light toward the screen again by, the image light reflected by the final projection mirror is transmitted through the prism plate and projected onto the screen. According to this rear projection display device, Since the final projection mirror may be provided at an angle for reflecting the image light reflected by the prism plate provided on the light incident surface side of the screen toward the screen, the inclination angle of the final projection mirror with respect to the screen surface can be reduced, The depth length of the device can be reduced.

〔Example〕

1 to 3 show an embodiment of the present invention,
FIG. 1 shows a cross section of a rear projection display device.

In FIG. 1, reference numeral 11 denotes a case of a rear projection type display device, a large-area display window 2 is opened on the front surface of the case 11, and a transmissive screen 13 is provided in the display window 12. Reference numeral 14 is a transmissive liquid crystal display panel disposed in the lower part of the case 1, 15 is a light source for irradiating the liquid crystal display panel 14, and 16 is light reflected from the light source 15 toward the liquid crystal display panel 14. In front of the liquid crystal display panel 14, which is a light source side mirror, a projection lens 17 for enlarging and projecting the light transmitted through the liquid crystal display panel 14, that is, the display image of the liquid crystal display panel 14 is arranged. Further, a plurality of, for example, three projection mirrors 18, 19, 20 for guiding the image light passing through the projection lens 17 toward the transmissive screen 13 are provided in the case 1 in an arrangement as shown in the drawing. Has been. This each projection mirror 1
The areas of the projection mirrors 8, 19 and 20 are made larger in order from those closer to the projection lens 17, and the final projection mirror 20 having a large area among these mirrors is provided with its reflecting surface facing obliquely downward. It is diagonally opposed to 13. In addition, the second projection in front of the final projection mirror 20
The projection mirror 19 is located below the final projection mirror 20 and is provided with its reflecting surface facing obliquely upward, and diagonally faces the screen 13 with an inclination opposite to that of the final projection mirror 20. Further, the first projection mirror 18 in front of the second projection mirror 19 is provided on the front side of the case 11 below the display window 2, and the liquid crystal display panel 4 and the projection lens 6 are It is arranged so as to face the first projection mirror 18. The projection lens 17, the first projection mirror 18, and the second projection mirror 19 display the image displayed on the liquid crystal display panel 4 on the screen 1.
A projection means for projecting toward 3 is configured.

On the other hand, 21 is a prism plate provided on the light incident surface (back surface) side of the transmissive screen 13. This prism plate 21 has its rear surface, that is, the final projection mirror 20 and the second projection mirror 20.
Horizontal stripe-shaped narrow-width prism portions 21a, 21a orthogonal to the inclination directions of the final projection mirror 20 and the second projection mirror 19 are formed continuously on the surface facing the projection mirror 19 in the width direction. , This prism plate 2
The surface of No. 1, that is, the surface facing the screen 13 is a plane parallel to the surface of the screen 13. This prism plate 2
Each of the prism portions 21a, 21a of No. 1 reflects the image light reflected by the second projection mirror 19 toward the screen 13 toward the final projection mirror 20 and reflected by the final projection mirror 20 toward the screen 13. The prisms 21a, 21a of the prism plate 21 have an inclination angle α (see FIGS. 2 and 3) which is reflected by the second projection mirror 19 and is reflected by the prism. The light incident on the plate 21 is refracted to an angle at which it is totally reflected on the prism plate surface, and the light reflected by the final projection mirror 20 and incident on the prism plate 21 is refracted to an angle at which it is not totally reflected on the prism plate surface. ing. Further, the lower end side of the prism plate 21 is extended downward from the lower edge of the screen 13 in accordance with the spread of the image light reflected by the second projection mirror 19, and the extended portion of the prism plate surface has the light. The reflective film 22 is formed. This light reflection film 2
2 is not always necessary, but this light reflection film 22
By providing, even if the light incident on the lower end side of the prism plate 21 out of the image light reflected by the second projection mirror 19 deviates from the total reflection angle, this light is reflected toward the final projection mirror 20. Can be made. The light reflection film 22
May be shared by the first projection mirror 18 by extending the first projection mirror 18 upward.

In this rear projection display device, the image light that has passed through the projection lens 17 is converted into a first projection mirror 18 and a second projection mirror 19.
The image light reflected by the second projection mirror 19 toward the screen 13 is sequentially reflected by the screen 1.
The prism plate 21 provided on the light incident surface side of 3 reflects the light toward the final projection mirror 20, and the image light reflected by the final projection mirror 20 is transmitted through the prism plate 21 and projected on the screen 13. The second one
The image light reflected by the projection mirror 19 toward the screen 13 is reflected by the prism plate 21 provided on the light incident surface side of the screen 13 toward the final projection mirror 20 as shown in FIG. The image light reflected by the mirror 20 toward the screen 13 again becomes the third light.
As shown in the figure, the screen 1 is transmitted through the prism plate 21.
3 is projected.

In the rear projection display device, the image light that has passed through the projection lens 17 is reflected by the projection mirrors 18 and 19 toward the screen 13, and the image light is provided on the light incident surface side of the screen 13. The image light reflected by the final projection mirror 20 is reflected by the prism plate 21 toward the final projection mirror 20, and the image light is reflected again by the final projection mirror 20 toward the screen 13. Since the image is reflected by the prism plate 21 provided on the light incident surface side of the screen 13 through the final projection mirror 20, the image light reflected by the prism 21 is directed toward the screen 13. Therefore, according to this rear projection type display device, the screen 13 of the final projection mirror 20 can be provided. Inclination angle θ is made smaller, it is possible to reduce the depth length of the device for.

The projection means for projecting the display image of the liquid crystal display panel 4 toward the screen 13 is composed of the projection lens 17, the first projection mirror 18 and the second projection mirror 19, and the first projection mirror 18 is used. Without projection lens 1
7 may be opposed to the second projection mirror 19, and the image light passing through the projection lens 17 may be directly reflected by the second projection mirror 19 toward the screen 13. Also,
Although the rear projection type display device using the liquid crystal display panel 14 as the display body has been described in the above embodiment, the display body may be, for example, a cathode ray tube. In that case, the light source 15 is used.
Is unnecessary.

[Effect of device]

According to the rear projection display device of the present invention, the depth angle of the device can be reduced by reducing the inclination angle of the final projection mirror with respect to the screen surface.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention,
FIG. 1 is a vertical sectional side view of a rear projection display device, FIG. 2 is a view showing a reflection state of image light reflected by a projection mirror on a prism plate, and FIG. 3 is a final projection mirror on a prism plate. It is a figure which shows the transmission state of image light. FIG. 4 is a vertical cross-sectional side view of a conventional rear projection display device. 11 ... Case, 12 ... Display window, 13 ... Transmissive screen, 14 ... Liquid crystal display panel, 15 ... Light source, 18
...... First projection mirror, 19 ...... Second projection mirror, 20 ...
... Final projection mirror, 21 ... Prism plate, 21a ... Prism section.

Claims (1)

[Scope of utility model registration request] 1. A display body, a projection means for projecting a display image of the display body toward the screen, and a screen in a case having a display window on the front surface and a transmissive screen provided in the display window. And a final projection mirror that is diagonally opposed to the screen, and reflects the image light projected toward the screen by the projection means toward the final projection mirror on the light incident surface side of the screen. A rear projection display device comprising a prism plate having a large number of stripe-shaped prism portions which are continuous with each other in the width direction and which transmit image light reflected by the final projection mirror toward the screen.