JPS626219B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a rear projection screen equipped with a Fresnel lens and a unique vertical lenticular lens, and provides a rear projection screen that widens the viewing angle and significantly reduces the moiré phenomenon, making it almost unnoticeable. This is what I am trying to do. Rear projection screens used in video projection televisions and the like must have high brightness and be able to view images over a wide range. For this reason, various measures have been taken in the past, such as forming lenticules on the screen substrate.
The limit is that the viewing angle can be expanded to around 30 degrees horizontally from the center, and improvements to this have been desired. Therefore, the applicant investigated ways to expand the viewing angle in the horizontal direction, and as a result, a portion of the light incident on the screen from the light source is totally reflected by a portion of the vertical lenticular lens and emitted to the viewing side. proposed to widen the viewing angle by
No. 56-91896 (Japanese Unexamined Patent Publication No. 57-207235) and Japanese Patent Application No. 57-29178 (Unexamined Japanese Patent Application No. 58-145933). While widening the viewing angle in this way, a circular Fresnel lens is formed on the projection side to maintain the brightness of the periphery of the screen and provide uniform brightness. The above proposal also includes such a combination. However, when a Fresnel lens and a lenticular lens are used in close proximity in this way, a moiré phenomenon occurs, which adversely affects the image being observed. This moiré phenomenon appears on the left and right sides of the center when the Fresnel lens and lenticular lens intersect at a small angle, but this phenomenon is because the Fresnel lens and lenticular lens produce brightness and darkness according to the pitch. Even if they cannot be identified with each lens alone, by combining the two, it becomes possible to identify them with the naked eye. One way to reduce the moire phenomenon is to interpose an air layer between the Fresnel lens and the lenticular lens, or to form fine irregularities on the lenticular lens surface. This is not an effective method when the situation is severe. The strength of moiré is determined by the ratio of the widths of both lenses, and setting this ratio is important. For this reason, the applicant has already proposed a rear projection screen in which the ratio of the width of the lenticular lens to the Fresnel lens is in the range of 1:1.35 to 1.43 (or 1/1.43 to 1/1.35) (Japanese patent application No. 56 −77736 (Unexamined Japanese Patent Publication No. 57)
However, in the present invention, this proposal is applied to a lenticular lens with a wide viewing angle. That is, the gist of the present invention is a rear projection screen in which a vertical lenticular lens is formed on the observation side surface and a Fresnel lens is formed on the projection side surface, and the lenticular lens is formed on the top side. The first lens unit includes a first lens unit having a side surface and a second lens unit adjacent to the second lens unit, and the top of the first lens unit is directly connected to this part. The lens unit is formed to emit incident light rays, and at least a part of each side surface of the lens unit is formed with a total reflection surface that totally reflects the incident light rays, and the total reflection surface totally reflects the incident light rays. Most of the reflected light rays exit from the top, and the second lens unit is formed with a lens surface that emits the light rays directly incident on this part, and the width of the Fresnel lens is set to 1. Then, the width ratio of the unit is N+0.35~0.43 or 1/N+0.35~0.43 or 1/N+0.35~
0.43 (where N is a natural number from 1 to 12). Hereinafter, the present invention will be explained in detail with reference to drawings of embodiments. FIG. 1 is a schematic explanatory diagram showing a projection system of a rear projection screen according to the present invention, where P is a projector, S is a rear projection screen, and M is an observer. Generally speaking, with a rear projection screen, the image projected from the back of the screen is viewed from the opposite side of the screen, as shown in the figure. It is hoped that it will be something that can be viewed. In Figures 1 and 2, the observation side surface A
A vertical lenticular lens 1 is formed on the surface B, and a circular Fresnel lens 2 is formed on the projection side surface B. Providing such a Fresnel lens 2 is effective because it can uniformly brighten the screen S even to the corners. In the present invention, the first lens unit is provided with a total reflection surface T such that the light incident on the observation side surface A as the lenticular lens 1 is once totally reflected and then transmitted through the top surface and emitted. 11 and a second lens unit 12 adjacent between the lens units 11 and having a circular or non-circular cross section form a unit U. The second lens unit 12 used in the present invention is
Those with a circular or non-circular cross section are used,
A circular lens refers to a lens that is made up of a part of a circle.
Furthermore, the term "non-circular" refers to a combination of parabolas and other non-circular lens shapes. First, the characteristics of the first lens unit 11 having such a total reflection surface T will be explained based on FIG. That is, a total reflection surface T is provided on at least a portion of both side surfaces 11b of the first lens unit 11, and the parallel light beams _X1 - _Y1 and _X2-
Y2 is totally reflected by the total reflection surface T and exits from the convex lens-shaped top surface 11a as each range. The light in this range will be emitted as strong light at a location where the bending angle is large, as shown in FIG. On the other hand, X ₁ −X ₂ directly incident on the top surface 11a
The light is emitted in the range of ω, such as X ₁ ′−X ₂ ′. The sum of the ω and φ lights is emitted as the light in FIG. In the figure, the brightness ratio is the ratio of the gain at each bending angle when the maximum gain (P gain) is 1 when the bending angle is 0°. Inclination angle θ of lens 11 having total reflection surface T
is determined by the refractive index n of the material and Snell's equation as follows: θ≧90°−1/2 sin ⁻¹ 1/n. For example, when an acrylic resin with n of 1.492 is used, θ will be 69° or more according to the above equation, but in consideration of practicality, it is selected in the range of 70 to 80°. Note that, if the first lens unit 11 and the second lens unit 12 having the total reflection surface T are combined as in the present invention, the gap between the light beams in FIG. 4 can be reduced. The present invention provides a first reflector having a total reflection surface T as described above.
Although the field of view is greatly expanded by the lens unit 11, as shown in Fig. 2, the lenticular lens 1
Since the Fresnel lenses 2 and 2 are formed on both sides of the base material, moiré is generally likely to occur. For example, if the width of the Fresnel lens 2 is set to 1 and the width of the lenticular lens 1 is set to 1, the parabolic moire will be severe, and even if the width is set to 1.5, fine moire will not disappear. When this ratio is set to 1:1.5, the moiré does not disappear because a 1:1 ratio is formed every other time. ), a similar phenomenon occurs, and it has been found that moiré cannot be eliminated with this combination. The present invention investigated such moire phenomenon and found that there is a region where moire is less likely to occur at a ratio of 1: about 1.4.The present invention has recently applied for a patent, but this ratio was changed to a total reflection surface. It was found that it is effective when applied to a lenticular unit composed of a unit U consisting of a first lens unit and a second lens, and further study revealed that 1: about 2.4, 1: about 3.4, 1: about It was found that there is also a preferable region where the ratio is 1:2.4 or more, such as 4.4. Therefore, in the present invention, when the width P ₁ of the Fresnel lens 2 is 1, the unit U
The width P ₂ of N+0.35 to 0.43 or 1/N+0.35 to 0.
43 (where N is a natural number from 1 to 12). The reason why the ratio in the vertical lenticular lens 1 is set in unit U is that the repetition of the intensity of light that causes moiré occurs in each unit U. Such a range is effective when the width of the Fresnel lens 2 or the lenticular lens 1 is reduced in order to improve the resolution. This is because as the width of either one of them is made smaller, the ratio of the widths tends to increase, and it is preferable to increase the ratio of both widths. It should be noted that a range in which N exceeds 12 in terms of width ratio is impractical and also has restrictions in terms of mold production. 5 and 6 are cross-sectional views showing other examples of the present invention, and FIG. 5 is a total reflection surface T explained in the above example.
Fig. 6 shows the top part 11a of the first lens unit 11 having a total reflection surface, with the top part 11a of the first lens unit 11 having a total reflection surface changed from a convex lens shape to a concave lens shape.
1a is shown in which a convex lens divided into two is formed. It should be noted that the present invention is not limited to these examples, and may be a lenticular unit in which a plurality of lens units each having total reflection surfaces of different shapes are combined to form a unit. In the above example, acrylic resin was used as the medium used in the rear projection screen of the present invention, and this is because acrylic resin is particularly excellent in terms of optical properties and moldability.
However, vinyl chloride resin, polycarbonate resin, olefin resin, styrene resin, etc. can also be used instead, and when these synthetic resins are used, the present invention can be made by extrusion molding, hot pressing, or injection molding. A rear projection screen according to the invention can be manufactured. Furthermore, although the rear projection screen of the present invention may be constructed of a transparent material, the use of a diffusing agent is effective in suppressing moiré. In other words, it is effective to uniformly mix a diffusing agent into the screen, but examples of the diffusing agent in this case include SiO ₂ , CaCO ₃ , Al ₂ O ₃ , TiO ₂ ,
Inorganic diffusing agents such as BaSO ₄ , ZnO, and fine glass powder or organic diffusing agents can be used. Furthermore, in order to reduce specular reflection on the surface and improve contrast, it is also effective to form fine irregularities on the observation side surface B, the projection side surface A, or both surfaces A and B. Specific examples will be described below. When manufacturing a methacrylic resin plate, silicon oxide was uniformly mixed in as a light diffusing agent to produce a resin plate as a base material. Then, a mold with a Fresnel lens surface on one side of this resin plate and a mold with a lenticular lens on the other side are applied and heated (approximately 150 to 170
℃), then pressurize (40-60Kg/cm ³ ) to about the second level.
We created three types of single-screen rear projection screens as shown in the figure. The appearance of moiré on the sample was observed and the results were as shown in Table 1.

[Table] In the above embodiments and explanations of drawings, etc., the width of the lenticular lens 1 is smaller than the width of the Fresnel lens 2.
Although the combination in which the width of the unit U is larger has been described, the ratio may be reversed within the range of 1/N+0.35 to 0.43. The present invention has the configuration as described in detail above, and the vertical lenticular lens has a first lens having a total reflection surface such that the incident light is once totally reflected and then transmitted through the top surface and exits. lens unit and the second
It consists of units arranged alternately, and the ratio of the width of the Fresnel lens to the unit width of the lenticular lens is set within a specific range, so the viewing angle is widened as much as possible. It has the advantage that it can significantly reduce the occurrence of moiré phenomena, and can be obtained using the same equipment and methods as conventional methods.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention; FIG. 1 is an explanatory diagram of the projection system of the rear projection screen, FIG. 2 is a perspective view of the rear projection screen, and FIG. 3 is a cross section showing the transmission state of the lenticular unit. Figure, 4th
The figure is a graph thereof, and FIGS. 5 and 6 are cross-sectional views showing other embodiments of rear projection screens. A... Observation side surface, B... Projection side surface, 1...
Vertical lenticular lens, 11...first lens unit, 12...second lens unit, T...
Total reflection surface, θ...Tilt angle, 2...Fresnel lens.

Claims (1)

[Scope of Claims] 1. A rear projection screen in which a vertical lenticular lens is formed on the observation side surface and a Fresnel lens is formed on the projection side surface, the lenticular lens having a top portion and both side surfaces. and a second lens unit adjacent between the lens units;
The top part of the first lens unit is formed so as to emit the light rays directly incident on this part,
Furthermore, at least a part of each side surface of the lens unit is formed with a total reflection surface that totally reflects the light rays incident on this part, and most of the light rays totally reflected by the total reflection surface exits from the top. In addition, the second lens unit is formed with a lens surface that emits the light rays directly incident on this part, and when the width of the Fresnel lens is 1, the ratio of the width of the unit is as follows. N+0.35～
0.43 or 1/N+0.35 to 0.43 (where N is a natural number from 1 to 12). 2. The rear projection screen according to claim 1, wherein a diffusing agent is added. 3. The rear projection screen according to claim 1 or 2, wherein fine irregularities are formed on the viewing side surface. 4. The rear projection screen according to claim 1, 2, or 3, characterized in that fine irregularities are formed on the projection side surface.