JPH07192661A - Rear projector - Google Patents

Abstract

PURPOSE:To shorten a focal distance of a projection lens, so that a set can formed in small size, by distorting a scanning region of a cathode-ray tube into a pin type and further the projection lens into a barrel type. CONSTITUTION:In a scanning region 21 of a CRT, an ordinary rectangular scanning region 20 is distorted in a pin type, to spread a scanning region area in the periphery. An almost squared region S1 is formed into a diamond shape S2 distorting the periphery. When an area of the CRT scanning region is thus enlarged, an electron beam amount per unit area in a fluorescent screen, that is, current density is decreased. Also current density of a phosphor in the limit by this characteristic is decreased, to further enable the electron be am amount to increase. That is, in proportion to enlarging an area of the peripheral scanning region, also the beam amount is increased, and brightness in the periphery of the scanning region can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear projector, and more particularly to a rear projector which makes it easy to see an image of a cathode ray tube (CRT).

[0002]

2. Description of the Related Art A rear projector is a large-sized picture tube for projecting a received image on a large screen from the back so that many people can simultaneously see a television (TV).

FIG. 8 is a schematic view showing an example of a rear projector. The rear projector 10 shown in FIG. 8 is a CRT.
It is composed of a (cathode ray tube) 1, a projection lens 2, a mirror 3 and a screen (transmissive type) 4 (the mirror 3 may not be arranged in some cases). The rear projector 10 configured in this way magnifies the image of the fluorescent screen of the CRT 1 through the large-diameter projection lens 2 arranged in front of the fluorescent screen, reflects the image on the mirror 3, and reflects it on the screen 4. Project and image on.

Conventionally, in the above-mentioned rear projector, the focal length of the projection lens 2 has been shortened along with the miniaturization of the set. In the case of a single-tube color rear projector, as shown in a perspective view in FIG. 9, it is composed of a CRT 1, a mirror 3 and a lenticular lens 5 as a screen. As the lenticular lens 5, conventionally, a vertical stripe structure is mainly used in order to improve the viewing angle in the left-right direction. Usually, a phosphor stripe on the phosphor screen,
It is arranged so that the stripes of the lenticular lens 5 are parallel to each other.

Conventionally, the rear projector is fixed so that the center of the Fresnel lens is located at the center of the screen. That is, as shown in FIG. 10, the light emitted from the center of the projector CRT passes through the center of the Fresnel lens-equipped screen 6 as a transmissive screen.

[0006]

As described above, when the focal length of the projection lens of the rear projector is shortened to reduce the size of the set, the amount of light is reduced in the peripheral portion, resulting in a blurred image. At this time, the projection lens is also distorted as a pin (pincushion) shape or a barrel shape.

In order to increase the amount of peripheral light, it is sufficient to increase the amount of the beam hitting the fluorescent screen of the CRT toward the peripheral portion, but at present, the fluorescent screen current density has reached its limit. Therefore, the brightness does not increase simply by increasing the beam amount.

In view of the above problems, it is an object of the present invention to provide a rear projector capable of reducing the focal length of a projection lens and downsizing the set. Further, as shown in FIG. 9, since the phosphor stripes 1a on the phosphor screen of the CRT 1 and the stripes 5a of the lenticular lens 5 are arranged in parallel, if the pitches of the phosphor screen stripes and the lenticular stripes are not aligned, the interference pattern There is a drawback that moire occurs.

Further, in order to match the pitch of the fluorescent screen stripe and the lenticular stripe in order to prevent the occurrence of the moire, the stripe pitch accuracy of each stripe, C
High-precision technology is required for the RT and lenticular mounting accuracy.

In view of the above problems, it is another object of the present invention to provide a rear projector capable of preventing the moire of the phosphor stripe and the lenticular stripe.
Further, in the rear projector, as described above, the Fresnel lens is fixed so that the center of the screen is located at the center of the screen. Therefore, when viewed from the center of the screen as shown in FIG. When viewed not obliquely from above but from diagonally above and below (FIG. 10 (b)), the peripheral image is dark (low in brightness), which is difficult to see.

In view of the above problems, it is an object of the present invention to provide a rear projector using a Fresnel lens which eliminates the difference in brightness between the central portion and the peripheral portion and makes the image bright and easy to see.

[0012]

In order to solve the above problems, a rear projector according to claim 1 of the present invention enlarges and projects an image of a cathode ray tube on a transmissive screen through a projection lens system to form a large screen. In the rear projector configured to obtain, the scanning area of the cathode ray tube is distorted into a pin shape and the projection lens is formed into a barrel shape.

A rear projector according to a second aspect of the present invention is a rear projector in which an image of a cathode ray tube is enlarged and projected on a transmissive screen through a projection lens system to obtain a large screen. It is characterized in that the stripes of the lenticular lens forming the screen are arranged so as to be substantially orthogonal to the phosphor stripes on the phosphor screen of the cathode ray tube.

Furthermore, a rear projector according to a third aspect of the present invention is a rear projector in which an image of a cathode ray tube is enlarged and projected on a transmissive screen through a projection lens system to obtain a large screen. It is characterized in that a Fresnel lens forming a transmissive screen is movably arranged.

A rear projector according to a fourth aspect of the present invention is characterized in that the Fresnel lens is of a winding type and is movable.

Furthermore, a rear projector according to a fifth aspect of the present invention is characterized in that the Fresnel lens is slidable and movable.

[0017]

According to the rear projector of the first aspect of the present invention, since the scanning area of the cathode ray tube 11 is distorted into a pin shape and the projection lens is barrel-shaped, the amount of light in the peripheral CRT scanning area is increased. In addition, the projection lens 22 can be made to have a short focal point and graphic distortion can be eliminated.

Further, according to the rear projector of the second aspect of the present invention, the stripe 5a of the lenticular lens 5 forming the transmissive screen is substantially orthogonal to the phosphor stripe 11a of the phosphor screen of the cathode ray tube 11. Stripe pitch 4 that causes moire because it is placed in
The parallel state can be eliminated, and the stripe pitch of the phosphor can be changed.

Furthermore, in the rear projector according to the third aspect of the present invention, since the Fresnel lens 6 constituting the transmissive screen is movably arranged, the bright portion of the screen can be vertically moved, for example. As a result, the difference in brightness from the surrounding area is reduced, making it easier to see. In addition, claims 4 and 5
In the present invention, the Fresnel lens screen can be easily moved by a winding type and a sliding type, as shown in FIG.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view of a first embodiment for explaining a rear projector according to the present invention, and particularly a schematic view showing a scanning area 20 of a CRT. FIG. 2 is an enlarged schematic view of the corner portion of FIG.

The scanning area 20 of the CRT shown in FIG. 1 is a normal rectangular scanning area. In this embodiment, as shown in FIG. 1, the rectangular scanning area 20 is improved to a pin (thread winding) type. Is a scanning area 21 indicated by a broken line. That is, in the scanning area 21 of the CRT of the present embodiment, the normal rectangular scanning area 20 is distorted into a pin shape and the peripheral scanning area area is enlarged. In particular, as shown in FIG. 2 in which the corners of the normal scanning area are enlarged, the substantially rectangular area S1 becomes a rhombic S2 with curved sides. Thus, when the area of the CRT scanning region is increased, the amount of electron beams per unit area on the phosphor screen, that is, the current density is reduced.

Due to this characteristic, the current density of the phosphor, which has reached the limit, is also lowered, and the electron beam amount can be increased. That is, the beam amount increases in proportion to the area expansion of the peripheral scanning region, and the luminance around the scanning region can be improved. As shown in FIG. 3, the barrel-shaped projection lens 2 is used for the above-described graphic distortion in the CRT.
By disposing 2, the distortion can be offset and a normal human image can be projected and imaged on the screen.

Next, FIG. 4 is a schematic perspective view of a second embodiment for explaining the projector according to the present invention. As shown in FIG. 4, in this embodiment, a rear projector is constructed by a single tube (color CRT), which comprises a CRT 11, a mirror 3 and a lenticular lens 5. In the figure, the projection lens is omitted. In this configuration, the fluorescent screen stripe 11a of the CRT 11 and the stripe 5a of the lenticular lens 5 are arranged so that their directions are orthogonal to each other. Thus, by arranging the stripes at right angles to each other, it was possible to eliminate moire caused by overlapping of stripe patterns. Moreover, in this embodiment, each stripe 5
It is not necessary to match the pitches of a and 11a, the CRT size and the stripe pitch can be changed, and the CRT design can be freely performed.

FIG. 5 is a schematic diagram of a third embodiment for explaining the projector according to the present invention. The rear projector shown in FIG. 5 is mainly configured by a CRT 11 and a screen 6 (6a or 6b) with a Fresnel lens, and the screen with the Fresnel lens is movable according to the position of the viewer. That is, in FIG. 5, the position of the screen with the Fresnel lens is at 6a, and there is no problem when viewed from directly in front of P1, but the position of the screen with the Fresnel lens is at 6a, and when viewed from P2, as described above, The image becomes dark.

In the present embodiment, as shown below, since the screen with the Fresnel lens can be moved downward as shown in FIG. 5, it becomes possible to bring the center of the screen closer to the eye level P2, and before the screen is moved. The image above can be transmitted brightly. As described above, in this embodiment, the Fresnel lens screen is vertically movable according to the position of the viewer.

A method of moving the Fresnel lens screen up and down will be described below. 6 shows a take-up type rear projector in which a Fresnel lens screen is wound up and down by a motor or the like, and FIG. 7 shows a slide rear projector in which the Fresnel lens screen can be moved up and down by a motor or the like. That is, in FIG. 6, 11 is a projector C
RT, 3 are mirrors, 16 is a winding type Fresnel lens screen, and 17 is a screen winding roller. CRT11
The image emitted from is reflected by the mirror 3 and is formed on the winding type Fresnel lens screen 16. In this case, when the position of the winding type Fresnel lens screen 16 is high, the winding type Fresnel lens screen is lowered by rotating the screen winding roller 17 in a predetermined direction by a motor (not shown).

In FIG. 7, 11 and 3 are the same CRTs and mirrors as described above, 18 is a slide type Fresnel lens screen, and 19 is a screen slide roller driven by a motor (not shown). CR
The image emitted from T11 is reflected by the mirror 3 and is formed on the slide type Fresnel lens screen 18. In this case, when the position of the slide type Fresnel lens screen 18 is high, the screen type slide roller 19 is rotated in a predetermined direction by the motor to lower the slide type Fresnel lens screen 18. In this way, it is possible to eliminate the brightness difference from the peripheral portion and make the image bright and easy to see.

[0029]

As described above, according to the present invention, C
It is possible to distort the RT scanning region into a pin shape and increase the peripheral scanning area. Therefore, the amount of peripheral light can be increased, the focal length of the projection lens can be shortened, and the size of the set can be reduced.

Further, according to the present invention, since the fluorescent screen stripes and the lenticular stripes are orthogonal to each other in the single-tube color rear projector, fringe interference does not occur, and moire is eliminated. Therefore, the design of the CRT size, the stripe pitch number, etc. can be freely changed. Furthermore, in the present invention, since the Fresnel lens screen is movable, it is possible to move the bright part of the image up and down to make the image bright and easy to see.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a first embodiment according to the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a schematic diagram of a projection lens according to Example 1 of the present invention.

FIG. 4 is a schematic perspective view for explaining a second embodiment according to the present invention.

FIG. 5 is a schematic perspective view for explaining a third embodiment according to the present invention.

FIG. 6 is a schematic view showing a winding method of the third embodiment shown in FIG.

FIG. 7 is a schematic diagram showing a slide system of the third embodiment shown in FIG.

FIG. 8 is a schematic diagram for explaining a conventional technique.

FIG. 9 is a perspective view for explaining a conventional single-tube rear projector.

FIG. 10 is a schematic diagram for explaining a conventional screen with a Fresnel lens.

[Explanation of symbols]

 1 CRT (Cathode Ray Tube) 1a Phosphor Stripe on Fluorescent Surface 2 Projection Lens 3 Mirror 4 Screen 5 Lenticular Lens 5a Lenticular Lens Stripe 6 Fresnel Lens Screen 6a Fresnel Lens Screen (Before Moving) 6b Fresnel Lens Screen (After Moving) 10 Rear Projector 11 CRT 11a Fluorescent Surface Stripe 16 Winding Fresnel Lens Screen 17 Screen Winding Roller 18 Slide Fresnel Lens Screen 19 Screen Sliding Roller 20 CRT Scan Area 21 Improved Scan Area 22 Projection Lens (barrel type)

Claims (5)

[Claims] 1. A rear projector in which an image of a cathode ray tube is enlarged and projected onto a transmissive screen through a projection lens system to obtain a large screen, and a scanning region of the cathode ray tube is distorted into a pin shape. A rear projector, characterized in that the projection lens is barrel-shaped. 2. A rear projector in which an image of a cathode ray tube is enlarged and projected on a transmissive screen through a projection lens system to obtain a large screen, and stripes of lenticular lenses forming the transmissive screen are formed. A rear projector, wherein the rear projector is arranged so as to be substantially orthogonal to a phosphor stripe on a phosphor screen of the cathode ray tube. 3. A rear projector in which an image of a cathode ray tube is enlarged and projected on a transmission screen through a projection lens system to obtain a large screen, and a Fresnel lens constituting the transmission screen is movably arranged. A rear projector characterized by the following. 4. The rear projector according to claim 3, wherein the Fresnel lens is of a retractable type and is movable. 5. The rear projector according to claim 3, wherein the Fresnel lens is slidable and movable.