Patent Application
20070222951
The present invention contains subject matter related to Japanese Patent Application JP 2006-083546 filed with the Japanese Patent. Office on Mar. 24, 2006, the entire contents of which being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rear projection display device for displaying a video image by projecting the video image to a transmission screen from the rear side thereof, and relates also to such a transmission screen used in the rear projection display device.
2. Description of the Related Art
In general, a rear projection display device has a housing, a transmission screen provided on the front surface of the housing, and a video projector installed in the housing for projecting a video image to the transmission screen from the rear side thereof. The transmission screen used in the rear projection display device employs a lens sheet such as a lenticular lens sheet and a Fresnel lens sheet to obtain a desired image displaying performance.
Such a lens sheet has a low rigidity in itself and it is therefore demanded to use any means for maintaining a given flat shape. In general, the flat shape of the lens sheet is maintained by attaching the lens sheet to a molded resin plate or a glass plate as a rigid body.
However, in the case of using the molded resin plate, warpage occurs because of a difference in coefficient of linear expansion between the molded resin plate and the lens sheet. In the case of using the glass plate, the total weight of the screen is increased, so that a frame for supporting the screen is demanded to have a large rigidity. Accordingly, the material cost tends to become high. Further, the thickness of the frame is increased, causing limitations to design of the transmission screen.
Japanese Patent No. 3341229 discloses a transmission screen such that the flat shape of a lens sheet can be maintained without using a molded resin plate or a glass plate. This transmission screen has a quadrilateral lens sheet and a pressure member (projection) provided near at least one of the two opposite sides of the lens sheet, wherein the pressure member is strongly pressed on the sheet surface of the lens sheet to thereby apply a tension to the lens sheet, thus maintaining the flat shape of the lens sheet.
In this transmission screen, however, the lens sheet has a thickness of about 300 μm, so that the pressure member is pressed on the lens sheet by a considerably large pressure to obtain a demanded tension, and a complicated configuration is demanded to provide a mechanism for producing such a large pressure.
There is accordingly a need for the present invention to provide a transmission screen which can obtain a sufficient tension of a lens sheet with a simple configuration. There is another need for the present invention to provide a rear projection display device using such a transmission screen.
In accordance with an embodiment of the present invention, there is provided a rear projection display device, including a housing; a transmission screen provided on the front surface of the housing; and a video projector installed in the housing configured to project a video image to the transmission screen from the rear side. The transmission screen including a frame, a quadrilateral lens sheet mounted to the frame, a rod-shaped pressure member arranged along at least one of the two opposite sides of the lens sheet, and an elastic section configured to apply a pressure to the pressure member to press the pressure member on the sheet surface of the lens sheet, providing a tension to the lens sheet. The lens sheet including a main sheet to which the video image is projected, and a subsheet continuously joined to an end portion of the main sheet, the subsheet having a flexural rigidity smaller than that of the main sheet, the pressure member being pressed on the sheet surface of the subsheet.
Preferably, the frame is formed with a groove extending along the pressure member so as to be opposed, the pressure member is pressed on the sheet surface of the subsheet in the condition where the subsheet is interposed between the groove and the pressure member, the subsheet comes into contact with an opening edge of the groove of the frame to form a contact surface at the opening edge, and a low-friction tape is attached to the contact surface to reduce the friction between the subsheet and the frame.
Preferably, the pressure member has a pressure applying portion pressed on the sheet surface of the lens sheet, the pressure applying portion having a substantially semicircular cross section, and the contact surface formed at the opening edge of the groove is roundedly chamfered.
Preferably, the elastic section includes a plurality of elastic sections uniformly spaced along the pressure member.
Preferably, the subsheet is formed of the same material as that of the main sheet and has a thickness smaller than the main sheet.
Preferably, the pressure member is arranged along at least one of the upper and lower sides of the lens sheet to provide a vertical tension to the lens sheet.
According to an embodiment of the present invention, the rod-shaped pressure member is arranged along at least one of the two opposite sides of the lens sheet and is pressed on the sheet surface of the lens sheet by the elastic section to apply a tension to the lens sheet. Accordingly, even when expansion and contraction due to changes in environment occur in the lens sheet, the expansion and contraction can be effectively absorbed, so that the occurrence of wrinkles and slack of the lens sheet can be reliably suppressed.
In particular, the pressed portion of the lens sheet pressed by the pressure member is provided by the subsheet having a small flexural rigidity. Accordingly, the applied pressure by the pressure member for providing a demanded tension to the lens sheet can be minimized, so that any complicated mechanism is not demanded and the cost can be suppressed with a simple configuration.
Preferred embodiments of the present invention will now be described in detail with reference to the drawings.
As shown in
The transmission screen 5 is composed of a Fresnel lens plate 6 for converging light and a lenticular lens sheet 7 juxtaposed to the Fresnel lens plate 6 for uniformly distributing the light over the screen to provide a contrast. The Fresnel lens plate 6 is composed of a base plate such as a molded resin plate or a glass plate and a Fresnel lens sheet attached to the base plate. The lenticular lens sheet 7 does not include a base plate as used in the Fresnel lens plate 6, but is arranged in the form of a sheet, thereby realizing a reduction in thickness and weight of the transmission screen 5.
The lenticular lens sheet 7 is demanded to maintain a stable flat shape, so as to ensure a good video displaying performance of the transmission screen 5. To meet this demand, the transmission screen 5 according to this preferred embodiment has the following configuration.
As shown in
On the other hand, each subsheet 9 is a sheet having a flexural rigidity smaller than that of the main sheet 8. The upper and lower subsheets 9 are respectively connected to the upper and lower end portions of the main sheet 8 by means of a pair of adhesive tapes 10 in an overlapping manner. In this preferred embodiment, each subsheet 9 is formed of the same material as that of the main sheet 8 and has a thickness smaller than that of the main sheet 8. More specifically, each subsheet 9 is formed from a PET film having a thickness of about 38 to 75 μm. As shown in
As shown in
Each pressure member 15 is a round rod having a circular cross section, which is formed of a rigid material such as aluminum. The upper and lower pressure members 15 are respectively pressed on the sheet surfaces of the upper and lower subsheets 9 in a direction perpendicular thereto by the elastic forces of a plurality of compression coil springs 16 as elastic section. These compression coil springs 16 are respectively held by a plurality of brackets 17 screwed to the frame 11. In this preferred embodiment, these brackets 17 are arranged along the upper and lower sides of the frame 11 at five equally spaced positions for each side in such a manner that these five positions are set in symmetrical relationship with respect to the horizontally central position. With this configuration, each pressure member 15 is pressed on the sheet surface of the corresponding subsheet 9 uniformly over the length of each pressure member 15 by the plural compression coil springs 16 arranged at uniform internals along each pressure member 15.
The frame 11 is formed with a pair of upper and lower grooves 18 respectively opposed to the upper and lower pressure members 15. As best shown in
According to the transmission screen as mentioned above, the upper and lower rod-shaped pressure members 15 are arranged along the upper and lower sides of the lenticular lens sheet 7 and are pressed on the sheet surface of the lenticular lens sheet 7 by the compression coil springs 16 as elastic section, thereby providing a vertical tension to the lenticular lens sheet 7. Accordingly, even when expansion and contraction due to changes in environment such as temperature and humidity occur in the lenticular lens sheet 7, the expansion and contraction can be effectively absorbed by the compression coil springs 16, so that the occurrence of wrinkles and slack of the lenticular lens sheet 7 can be reliably suppressed.
Further, the direction of applying a tension to the lenticular lens sheet 7 by the pressure members 15 is the same as the direction of gravity, so that a tension can be efficiently applied to the lenticular lens sheet 7, thereby more reliably suppressing the occurrence of wrinkles and slack of the lenticular lens sheet 7.
As a result, the flat shape of the lenticular lens sheet 7 can be reliably maintained, so that a degradation in image quality such as image distortion and focusing degradation can be reliably prevented.
In particular, the pressed portion of the lenticular lens sheet 7 pressed by the pressure members 15 is provided by the upper and lower thin subsheets 9 each having a small flexural rigidity. Accordingly, a sufficient tension can be applied to the lenticular lens sheet 7 with a small pressure (load) applied by the pressure members 15.
To the contrary, in the case that the sheet thickness is 38 μm and 75 μm, a larger tension can be obtained by a smaller applied pressure as compared with the sheet having a thickness of 300 μm. Accordingly, no excess applied pressure is necessary to obtain a demanded tension. Further, the smaller the sheet thickness, the smaller the bending stress in the sheet, so that the creep is less prone to occur in the sheet.
According to this preferred embodiment, the applied pressure by the pressure members 15 for providing a sufficient tension to the lenticular lens sheet 7 can be minimized, so that any complicated mechanism is not demanded, but a lightweight frame not demanding a high rigidity is used to suppress the cost with a simple configuration.
Further, the subsheets 9 and main sheet 8 constituting the lenticular lens sheet 7 are formed of the same material, i.e., PET film. Accordingly, a difference in rate of expansion and contraction between the each subsheet 9 and main sheet 8 due to changes in environment such as temperature and humidity can be suppressed to thereby more reliably prevent the occurrence of wrinkles and slack of the lenticular lens sheet 7.
According to the transmission screen as mentioned above, a sufficient tension can be applied to the lenticular lens sheet 7 with a simple configuration, thereby reliably maintaining the flat shape of the lenticular lens sheet 7. As a result, a degradation in image quality such as image distortion and focusing degradation can be reliably prevented.
While the pressure members 15 are arranged along both the upper and lower sides of the lenticular lens sheet 7 to apply a vertical tension to the lenticular lens sheet 7 at its upper and lower end portions in this preferred embodiment, a single pressure member similar to each pressure member 15 may be arranged along any one of the upper and lower sides of the lenticular lens sheet 7 to apply a vertical tension to the lenticular lens sheet 7 at its only one vertical end portion.
As another modification, the pressure member or members 15 may be arranged along at least one of the right and left sides of the lenticular lens sheet 7 to apply a horizontal tension to the lenticular lens sheet 7.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-083546 | Mar 2006 | JP | national |
