JPS6233425Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a rear projection device (rear projector).

FIG. 1 is a schematic diagram showing the basic configuration of a rear projection device. In the figure, 1 is a cathode ray tube (CRT), 2
is a lens, and 3 is a screen. The light beam emitted from the fluorescent surface of the CRT 1 is projected onto the back surface of the screen 3 via the lens 2, and the projected image is observed from the front surface of the screen 3. d indicates the distance from the rear end of the CRT 1 to the screen 3, and as shown in the figure, this distance d is generally large. Therefore,
If it were to be stored in a case as it is, it would require a case with an extremely large depth, resulting in a large size.

FIGS. 2 and 3 are schematic side views showing an example of a conventional rear projection device that uses a reflector to reduce the distance d mentioned above. In these figures, parts corresponding to those in FIG. 1 are designated by the same or similar symbols. In Figure 2, 4 is 45 to the optical axis.
゜It is a tilted reflector. The position of this reflecting mirror 4 corresponds to the position of the diagonal line 4' shown in FIG. 5
indicates a case. In this example, the height of the device is high, but the required depth is _d1 , which is very small compared to d above. The angle of inclination of the reflector 4 is normally 45 degrees, and although theoretically it is not possible to change the angle of inclination to a value other than 45 degrees by changing the position of the CRT 1, the actual design is troublesome. In Figure 3,
4 ₁ and 4 ₂ are reflecting mirrors each tilted at 45° with respect to the optical axis. These two reflectors 4 ₁ and 4
₂ is located along the diagonal dotted lines 4' ₁ and 4' ₂ shown in Figure 1.
corresponds to the position of Comparing this example with the one in FIG. 2, although the height of the device is low, the distance d ₂ from the rear end of the CRT 1 to the screen 3 is large. However, in this example as well, the angle of inclination of the reflecting mirrors ₄₁ and ₄₂ was set to 45 degrees, but as in the example of FIG. 2, the angle of inclination can be set to other than 45 degrees by changing the position of the CRT 1. In this case, the height of the device becomes somewhat higher, but it is possible to make the depth smaller than _d2 . However, it is difficult to make the depth smaller than d ₁ in FIG. 2.

In this way, in the conventional method, the values of d ₁ and d ₂ mentioned above are regulated by the positions of the reflecting mirrors 4, 4 ₁ and 4 ₂ and the structure of the CRT 1, and the depth is reduced (thickness is reduced). There are limits to things. The present invention attempts to provide a rear projection device whose thickness can be further reduced by using a unique reflecting mirror. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 4 is an enlarged sectional view showing an example of a reflecting mirror used in the present invention. In the figure, 6 indicates the reflecting mirror as a whole, 6 ₁ is its base, 6 ₂ is its base,
6 ₃ is a minute reflective surface formed on a surface opposite to the base surface 6 ₂ . A large number of minute reflective surfaces ₆₃ are provided at a certain angle with respect to the base surface ₆₂ . In the illustrated example, the inclination angle is θ-φ. OP indicates a line perpendicular to one minute reflective surface, and O'P' indicates a line perpendicular to the base surface ₆₂ passing through point O. When AO is the incident light to point O and OB is the reflected light, the angles of the incident light and the reflected light with respect to the perpendicular OP are equal to each other.
However, if the perpendicular O′P′ is used as a reference, the angle i of the incident light AO with respect to the perpendicular O′P′ is the perpendicular of the reflected light OB.
It is greater than the angle i′ with respect to O′P′ (i>i′). now,
When CD is a vertical plane and θ=45°, the incident light AO parallel to the vertical plane CD is reflected at the minute reflective surface ₆₃ and becomes horizontal reflected light OB. Here, φ<θ, that is, the angle φ of the base surface ₆₂ with respect to the vertical plane CD
is the angle θ of the minute reflective surface ₆₃ with respect to the vertical plane CD
smaller. This means that in order to obtain the horizontally reflected light OB from the vertically incident light AO, a conventional reflector in which the base surface and the reflecting surface are parallel must be tilted by θ=45° from the vertical plane CD; According to the reflecting mirror 6, the φ is smaller than 45° with respect to the vertical plane CD.
This means that it is only necessary to incline by (<θ).

FIG. 5 is a schematic side view showing an embodiment of the present invention constructed using the reflecting mirror 6 as described above. In the figures, parts corresponding to those described above are designated by the same or similar symbols. Fourth
The reflecting mirror 6 shown in the figure is arranged at an angle of φ with respect to the vertical plane. In the figure, 4 indicated by a dotted line is the second
This is the same reflecting mirror as shown in the figure, and is drawn for comparison with reflecting mirror 6. As can be seen from the figure, when the reflector 6 is used, it is not necessary to tilt it at 45 degrees with respect to the vertical plane unlike the conventional reflector 4, and the angle of inclination is small, so the required depth is reduced by Δd and d ₁ − It becomes Δd. Therefore, the thickness of the case 5 can also be reduced accordingly.

However, in this case, the conventional CCRT shown in Figure 6a
1, the optical path length from the fluorescent surface of the CRT 1 to the screen 3 via the lens 2 and the reflecting mirror 6 will be different from that shown in FIG. In the case of Figure 2,
The above-mentioned optical path length is the same as the basic configuration shown in FIG. 1 and there is no problem, but in the case of FIG. 5, there is a considerable difference in the above-mentioned optical path length between the upper end and the lower end of the screen 3. A conceivable way to correct this is to use a CRT 1' with an inclined fluorescent surface as shown in FIG. 6b. However, such a CRT with an inclined fluorescent surface
1' causes trapezoidal distortion in the image, so it is necessary to add a trapezoidal distortion correction circuit.

As explained above, according to the present invention, the thickness of the rear projection device can be made even thinner than that of the conventional device. For example, in a rear projector set with a diagonal of 40 inches, we were able to make it approximately 5 cm thinner.

Note that the present invention is not limited to the above-described embodiments, and can be modified and changed in various ways without departing from the gist of the invention as set forth in the claims for utility model registration.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the basic configuration of a rear projection device;
2 and 3 are schematic side views showing a conventional example, and FIG. 4 is an enlarged sectional view showing an example of a reflecting mirror used in the present invention.
FIG. 5 is a schematic side view showing an embodiment of the present invention, and FIG. 6 is an external view showing an example of a cathode ray tube that can be used in the present invention. 1, 1'...Cathode ray tube, 2...Lens, 3...
Screen, 6... Reflector, 6 ₂ ... Its base,
6 ₃ ...Minute reflective surface.

Claims (1)

[Claims for Utility Model Registration] In a rear projection device having a cathode ray tube, a lens, a reflecting mirror, and a screen, the reflecting mirror has a large number of minute reflecting surfaces inclined with respect to its base surface, and the reflecting mirror has a vertical surface of the base surface. A rear projection device characterized in that the angle with respect to the vertical plane is smaller than the angle of the minute reflective surface with respect to the vertical plane.