JP4128599B2 - Fresnel optical element - Google Patents

Description

  The present invention relates to a Fresnel optical element that reflects light emitted from a projector toward an observer, a display screen incorporating the Fresnel optical element, and a projection display device including the projector and the display screen. .

  In a conventional projection display device, a projector installed on the front side of a display screen projects image light onto a flat display screen and emits the reflected light in the direction of an observer.

When the oblique incidence of the light beam irradiated from the projector to the display screen is extreme, the incident angle of the light beam with respect to the screen normal increases. Since the incident angle and the reflection angle are equal to the screen normal according to Snell's law, the light incident at the extreme oblique incidence is in a direction symmetric to the screen normal, that is, a direction greatly deviated from the observer's direction. Emitted.
For this reason, the amount of light emitted in the direction of the observer is reduced and the image is observed dark.

  Therefore, in order to increase the number of light rays emitted in the direction of the observer, the Fresnel prism reflection surface is inclined by an angle ξ so that the emission angle φ of the incident light at the incident angle θ is substantially horizontal. A display screen using an optical element is disclosed in Patent Document 1 below.

The incident angle θ, the outgoing angle φ, and the reflection surface angle ξ are expressed by the following relational expression.
φ = 2ξ−θ
Here, the solution for ξ is as follows.
ξ = (θ + φ) / 2
Therefore, when the emission angle is horizontal (φ = 0), it is necessary to incline the reflecting surface at ξ = θ / 2.

In the above-mentioned Fresnel optical element, the non-incident surface of the Fresnel prism where the light beam from the projector is not incident is formed to be perpendicular to the surface of the substrate on which the Fresnel prism is disposed.
Therefore, when processing the root part of the Fresnel optical element having such a shape, processing is performed using a cutting tool having a tip angle β that is narrower than at least the apex angle τ (angle of the non-incident surface with respect to the reflecting surface) of the Fresnel prism. There is a need to.

JP 53-11728 (page 8, FIG. 3)

  Since the conventional Fresnel optical element is configured as described above, if a tool with a tip angle β smaller than the apex angle τ (angle of the non-incident surface with respect to the reflecting surface) of the Fresnel prism is used, The non-incident surface of the Fresnel prism can be formed so as to be vertical. However, since the cutting tool having a thin tip angle β is vulnerable to wear, there is a problem that the manufacturing accuracy of the Fresnel prism may be deteriorated. In addition, it is necessary to form a non-incident surface with high roughness by moving the tip of the cutting tool by dragging it after forming a reflective surface with high specularity. .

The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a Fresnel optical element that can be processed using a bite having a large tip angle.
Another object of the present invention is to obtain a display screen incorporating a Fresnel optical element with high manufacturing accuracy.
Furthermore, an object of the present invention is to obtain a projection display device on which a display screen with high manufacturing accuracy is mounted.

In the Fresnel optical element according to the present invention, the angle of the non-incident surface with respect to the surface of the substrate on which the Fresnel prism is disposed is smaller than 90 degrees and larger than the incident angle of the light beam, and a part of the non-incident surface is the surface of the substrate And formed in parallel .

As a result, since the tip angle can be processed using a tool that is thicker than the apex angle τ (angle of the non-incident surface with respect to the reflecting surface) of the Fresnel prism and is resistant to wear, the manufacturing accuracy of the Fresnel prism can be increased. effective.
In addition, since the root portion of the Fresnel optical element can be processed only by changing the angle at which the tool is laid down, the degree of freedom in processing is increased, and the manufacturing can be easily performed.

It is a block diagram which shows the projection type display apparatus by Embodiment 1 of this invention. 1 is a perspective view showing a projection display apparatus according to Embodiment 1 of the present invention. It is a block diagram which shows the display screen by Embodiment 1 of this invention. It is a schematic diagram which shows the Fresnel optical element by Embodiment 1 of this invention. It is a block diagram which shows the Fresnel optical element with which the reflective surface of the Fresnel prism was inclined only the angle (xi). It is a schematic diagram which shows the metal mold | die used as the mother die of a Fresnel prism, and the cutting tool for metal mold | die cutting. It is explanatory drawing which shows the processing method of a Fresnel optical element. It is a schematic diagram which shows the metal mold | die used as the mother die of a Fresnel prism, and the cutting tool for metal mold | die cutting. It is a block diagram which shows the display screen by Embodiment 2 of this invention. It is a block diagram which shows the display screen by Embodiment 3 of this invention. It is explanatory drawing which shows the processing method of a Fresnel optical element. It is explanatory drawing which shows the processing method of a Fresnel optical element. It is explanatory drawing which shows the processing method of a Fresnel optical element. It is explanatory drawing which shows the processing method of a Fresnel optical element. It is explanatory drawing which shows the processing method of a Fresnel optical element. It is a block diagram which shows the display screen by Embodiment 4 of this invention. It is explanatory drawing which shows the addition method of a light absorption function. It is explanatory drawing which shows the addition method of a light absorption function. It is explanatory drawing which shows the addition method of a light absorption function. It is explanatory drawing which shows the addition method of a light absorption function. It is explanatory drawing which shows the addition method of a light absorption function. It is a block diagram which shows the display screen by Embodiment 5 of this invention. It is a perspective view which shows the projection type display apparatus by Embodiment 6 of this invention. It is explanatory drawing which shows the relationship between an incident angle and a similar reduction ratio.

Hereinafter, in order to describe the present invention in more detail, the best mode for carrying out the present invention will be described with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a projection display apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a perspective view showing the projection display apparatus according to Embodiment 1 of the present invention.

In the figure, a projector 1 which is a light emitter irradiates a Fresnel optical element 2 with light rays for image projection.
The Fresnel optical element 2 is formed with a plurality of Fresnel prisms in a sawtooth shape having a reflecting surface that reflects the light beam emitted from the projector 1 and a non-incident surface that is not irradiated with the light beam.
A Fresnel prism of the Fresnel optical element 2 is two-dimensionally arranged on the base 3.

  3 is a block diagram showing a display screen according to Embodiment 1 of the present invention. In the figure, a reflecting surface 11 which is an incident surface of a Fresnel prism forming the Fresnel optical element 2 reflects light rays emitted from the projector 1.

The non-incident surface 12 of the Fresnel prism is a surface on which no light is directly incident from the projector 1, the angle α of the non-incident surface 12 with respect to the surface 13 of the substrate 3 on which the Fresnel prism is disposed is smaller than 90 degrees, and the incident light is incident. It is larger than the angle θ (π / 2−θ ≦ α).
FIG. 4 is a schematic diagram showing a Fresnel optical element according to Embodiment 1 of the present invention.

Next, the operation will be described.
Even in the case where the projector irradiates the light beam obliquely on the display screen, the reflection surface 21 of the Fresnel prism is arranged as shown in FIG. Is tilted by an angle ξ (see Patent Document 1 above).

  In the Fresnel optical element disclosed in Patent Document 1, the non-incident surface 22 of the Fresnel prism to which no light from the projector is incident is formed so as to be perpendicular to the surface 23 of the substrate on which the Fresnel prism is disposed. ing.

Here, the processing method of the Fresnel optical element, particularly the mirror surface processing and the rough surface processing will be described.
FIG. 6 is a schematic diagram showing a die 31 that is a mother die of a Fresnel prism and a cutting tool 32 for die cutting.

First, the tool 31 is pressed obliquely against the mold 31 and the mold 31 is cut to form a highly specular surface 31a (surface for forming the reflecting surface 21). 7, the surface 31b (surface for forming the non-incident surface 22) with high roughness is formed by moving the tip of the cutting tool 32 so as to be dragged.
However, since the non-incident surface 22 is perpendicular to the surface 23 of the base, when processing the mold 31 and processing the root portion of the Fresnel optical element, at least from the apex angle τ of the Fresnel prism, It is necessary to use a cutting tool with a thin tip angle β.

Since the cutting tool 32 having a narrow tip angle β is vulnerable to wear, the processing accuracy of the Fresnel prism may be deteriorated when the die 31 of the Fresnel prism is processed using such a cutting tool 32.
Therefore, in the first embodiment, the shape of the Fresnel prism is devised so that it can be processed using the cutting tool 33 (β> τ) having a large tip angle β.

That is, the angle α of the non-incident surface 12 of the Fresnel prism with respect to the surface 13 of the base 3 is set to be smaller than 90 degrees.
That is, when the incident angle θ of the light beam emitted from the projector 1 is extremely large (in the case of extreme oblique incidence), the light beam is blocked by the reflecting surface (for example, paying attention to the line segment FG in FIG. 4), and the Fresnel prism. Since a light beam is not incident on the root portion (for example, a triangular portion having two sides of the line segments CK and CH), the non-incident surface 12 (for example, the line segment CG in FIG. It does not necessarily have to be formed vertically. However, if the angle α of the non-incident surface 12 is smaller than the incident angle θ of the light beam, the light beam is directly incident on the non-incident surface 12. Therefore, the angle α of the non-incident surface 12 needs to be larger than the incident angle θ of the light beam. There is. That is, it is necessary to satisfy π / 2−θ ≦ α.

When the angle α of the non-incident surface 12 with respect to the surface 13 of the substrate 3 is smaller than 90 degrees, it can be processed using a cutting tool 33 (β> τ) having a large tip angle β.
FIG. 8 is a schematic diagram showing a mold 31 that is a mother mold of a Fresnel prism and a cutting tool 33 for cutting the mold.

When the cutting tool 33 having a large tip angle β (β> τ) is used, as shown in FIG. 8, it can be processed only by changing the angle at which the cutting tool 33 is laid down while keeping the tip angle β constant.
However, when the Fresnel prism is warped in the opposite direction (when the angle of the non-incident surface 12 is α> 90 °), for example, a photo-curing resin is poured into the mold 31 and the photo-curing resin is hardened by ultraviolet irradiation or the like. After that, by extracting the resin, it becomes difficult to use the method of obtaining the Fresnel prism.

That is, when the following formula is established, the Fresnel prism is warped in the reverse direction, and it becomes difficult to release the resin from the mold 31.
α = π−τ−ξ> π / 2
Therefore, it is necessary to determine the shape of the Fresnel prism so that the Fresnel prism does not warp in the reverse direction.

As apparent from the above, according to the first embodiment, the angle α of the non-incident surface 12 with respect to the surface 13 of the substrate 3 on which the Fresnel prism is disposed is smaller than 90 degrees and larger than the incident angle θ of the light beam. As a result, the tip angle β can be machined using the cutting tool 33 that is thicker than the apex angle τ of the Fresnel prism and is resistant to wear. As a result, the manufacturing accuracy of the Fresnel prism can be improved. There is an effect.
In addition, the root portion of the Fresnel optical element can be processed only by changing the angle at which the cutting tool 33 is laid down, and the degree of freedom of processing is increased and the wear is reduced. There is an effect.

Embodiment 2. FIG.
In the first embodiment, the reflection surface 11 having a high specularity is shown. However, as shown in FIG. 9, the reflection surface 11 may have a light diffusing function for diffusing light rays.

Specifically, when the tip of the cutting tool 33 is pressed against the mold 31 and deleted, for example, the reflecting surface 11 has a light diffusing function by roughing the reflecting surface 11 by deleting little by little. To do.
Alternatively, in the same manner as in the first embodiment, the reflecting surface 11 has a light diffusing function by rubbing a portion of the mold 31 forming the reflecting surface 11 with a rough surface typified by sandpaper or the like. To do.
Alternatively, the reflective surface 11 is provided with a light diffusing function by applying a coating material having light diffusibility to the surface.

  As apparent from the above, according to the second embodiment, since the reflecting surface 11 is configured to have a light diffusing function for diffusing light, it is possible to expand the field of view through which an observer can observe an image. Play.

Embodiment 3 FIG.
In Embodiment 1 described above, the one using the Fresnel optical element 2 in which a plurality of Fresnel prisms each having the reflecting surface 11 and the non-incident surface 12 are formed in a sawtooth shape is shown, but the reflecting surface 11 and the non-incident surface 12 are used. The Fresnel prisms do not need to be connected, and as shown in FIG. 10, a Fresnel optical element 2 in which a plurality of Fresnel prisms are formed may be used at a predetermined interval.
That is, the Fresnel optical element 2 in which a part 14 of the non-incident surface 12 is formed in parallel with the surface 13 of the substrate 3 may be used.

  In the first embodiment, when processing the mold 31 of the Fresnel prism, the cutting tool 33 having a large tip angle β (β> τ) is used, and the angle at which the cutting tool 33 is laid down is changed while the tip angle β remains constant. In this way, when processing the Fresnel prism, as shown in FIG. 11, the tip portion (the portion surrounded by the dotted line in FIG. 11) bends during processing, etc. May occur.

In the third embodiment, the part 14 of the non-incident surface 12 is formed to be parallel to the surface 13 of the base 3 in order to prevent the occurrence of problems such as bending of the tip portion.
Specifically, it is as follows.

First, as shown in FIG. 12, the tool 31 is pressed obliquely against the mold 31 to cut the mold 31. However, the cutting depth is shallower than in the case of FIG.
That is, as shown in FIG. 13, the cutting tool 33 is once removed without cutting the dotted line portion.

Next, as shown in FIG. 14, the cutting tool 33 is moved to the right by the length of the plane portion (part 14 of the non-incident surface 12) formed in parallel with the surface 13 of the base 3.
Next, as shown in FIG. 15, the cutting tool 33 is obliquely pressed against the mold 31 to cut the mold 31.
By repeatedly executing the above processing (the processing of FIGS. 12 to 15), the mold 31 in which a part 14 of the non-incident surface 12 is parallel to the surface 13 of the substrate 3 is processed, and the Fresnel optical element 2 is formed. Form.

In this way, forming the Fresnel optical element 2 so that the part 14 of the non-incident surface 12 is parallel to the surface 13 of the substrate 3 is obtained by reducing the prism portion ΔCGF in FIG. 4 to be similar to ΔKGM. It is equivalent to forming.
As shown in FIG. 4, when the similarity reduction ratio is 1, for example, the similarity reduction ratio 1 may be as follows.
l = 1 − {(tan ξ) / (tan α)}
[{Tan α-tan (π / 2−θ)}
/ {Tanξ + tan (π / 2−θ)}]

FIG. 24 shows a specific calculation example. FIG. 24 shows a calculation example in which the emission angle φ = 0 and the prism apex angle is 90 °.
In the figure, the horizontal axis represents the incident angle θ, and the vertical axis represents the similarity reduction ratio l.
When the incident angle θ is large, that is, when the incident angle is extremely oblique, the similar reduction ratio l decreases. That is, the ratio of the prism is small, and the ratio of the portion 14 of the non-incident surface 12 is large.

When the Fresnel optical element is formed so that the part 14 of the non-incident surface 12 is parallel to the surface 13 of the base 3 in this way, there is no tip part as shown in FIG. It is possible to prevent the occurrence of the problem.
In this case, since the volume to be cut is reduced, the processing time is shortened. As a result, the temperature change and the influence of the outside world at the time of die machining are reduced, and the die machining accuracy is improved.

  Furthermore, since the volume of the prism portion is reduced, it is easy to release the poured resin from the mold, and the shape transfer accuracy is improved.

Embodiment 4 FIG.
In the third embodiment, the case where the Fresnel optical element 2 is formed so that the part 14 of the non-incident surface 12 is parallel to the surface 13 of the substrate 3 is shown. A part 14 of 12 may have a light absorbing function for absorbing light. Alternatively, the entire non-incident surface 12 may have a light absorption function for absorbing light (the entire non-incident surface 12 in FIG. 3 or the entire non-incident surface 12 in FIG. Including a light absorption function).
The reflective surface 11 may have a light diffusing function like the reflective surface 11 of FIG.

Specifically, a part 14 of the non-incident surface 12 is provided with a light absorption function for absorbing light as follows.
When the mold 31 is processed in the same manner as in the third embodiment (see FIG. 15), as shown in FIG. 17, a medium 34 having a light absorption function is applied to the planar portion of the mold 31 in the manner of printing. By doing so, the light absorption medium 35 is formed in the plane portion. For example, the light absorbing medium may be a black dye or pigment, or an opaque photocuring resin or thermosetting resin.
Then, as shown in FIG. 18, the light absorbing medium 35 is cured.

Next, the photocurable resin 36 is poured into the mold 31 as shown in FIG. 19, the base 3 is pressed from above the photocurable resin 36 as shown in FIG. 20, and the photocurable resin 36 is cured by applying light. Let
Finally, as shown in FIG. 21, by separating the Fresnel optical element 2 from the mold 31, the Fresnel optical element 2 in which the light absorbing medium 35 is attached to a part 14 of the non-incident surface 12 is formed. Is done.

  As apparent from the above, according to the fourth embodiment, since the portion 14 of the non-incident surface 12 is configured to have a light absorption function for absorbing light, the portion 14 of the non-incident surface 12 is externally attached. Even if light is incident, the external light is absorbed. As a result, there is an effect that an image with high contrast can be displayed even when the outside light is strong.

Embodiment 5. FIG.
In the fourth embodiment, the part 14 of the non-incident surface 12 has a light absorbing function for absorbing light. However, as shown in FIG. 22, the part 14 of the non-incident surface 12 diffuses light. A light diffusing function may be provided. Alternatively, the entire non-incident surface 12 may have a light diffusing function for diffusing light (the entire non-incident surface 12 in FIG. 3 or the entire non-incident surface 12 in FIG. Including a light diffusing function).
The reflective surface 11 may have a light diffusing function like the reflective surface 11 of FIG.

For example, after forming the Fresnel optical element 2 so that a part 14 of the non-incident surface 12 is parallel to the surface 13 of the substrate 3 in the same manner as in the third embodiment, a rough surface represented by sandpaper or the like is used. By rubbing, the part 14 of the non-incident surface 12 is roughened so that the part 14 of the non-incident surface 12 has a light diffusing function.
Alternatively, the surface of the mold 31 is rubbed in advance with a rough surface typified by sandpaper or the like and then processed so that the part 14 of the non-incident surface 12 has a light diffusing function.
Alternatively, the part 14 of the non-incident surface 12 can be roughened by moving the part 14 of the non-incident surface 12 so as to drag the tip of the cutting tool 33. Can have a light diffusing function.

  As apparent from the above, according to the fifth embodiment, since the part 14 of the non-incident surface 12 is configured to have the light diffusing function of diffusing light, the part 14 of the non-incident surface 12 is externally attached. Even if light is incident, the external light is diffused. As a result, there is an effect that an image with high contrast can be displayed even when the outside light is strong.

In the fifth embodiment, the portion 14 of the non-incident surface 12 is provided with a light diffusing function for diffusing light. However, an optical function other than the light absorbing function and the light diffusing function may be provided. Good.
For example, an anti-reflection function may be provided.
Further, a part 14 of the non-incident surface 12 may be translucent or transparent.

Embodiment 6 FIG.
FIG. 23 is a perspective view showing a projection display apparatus according to Embodiment 6 of the present invention.
In the figure, the same reference numerals as those in FIG.

A Fresnel optical element 2 is concentrically arranged on the base 3, and an edge 4 is formed on the outer periphery of the Fresnel optical element 2. When the projector 1 and the display screen are installed, the display area 5 of the image projected by the projector 1 is installed so as to coincide with the inside of the edge 4.
The vertical adjustment mechanism 6 that is a position adjustment means moves the display screen up and down to adjust the irradiation position of the light beam on the Fresnel optical element 2.

Next, the operation will be described.
When displaying the image projected by the projector 1 on the display screen, it is necessary to adjust the relative positional relationship between the projector 1 and the display screen.

Optically, for example, it is necessary to align the reference point X of the projector 1 that is the optical axis and the reference point Y of the display screen, and set the projection distance to a predetermined interval.
However, the reference points X and Y are often not clearly described in the actual projector 1.

Therefore, in the sixth embodiment, the edge 4 is formed on the outer periphery of the Fresnel optical element 2, and only the display area 5 of the image projected by the projector 1 is installed so as to coincide with the inside of the edge 4. Thus, adjustment of the relative positional relationship between the projector 1 and the display screen can be completed.
Since the edge 4 is formed on the outer periphery of the Fresnel optical element 2, even when the image by the projector 1 is distorted, the distortion in the display area 5 is hidden by the edge 4 and the appearance is improved.

When the light incident by the projector 1 is extremely oblique incidence, the projection distance from the projector 1 to the display screen becomes sensitive. Therefore, by moving the display screen up and down using the vertical adjustment mechanism 6, the Fresnel optical element 2. The irradiation position of the light beam with respect to is adjusted to absorb the error of the projection distance.
y = f × tan θ
Where f: projection distance
θ: Incident angle
y: Height of display screen

Further, in the case of extreme oblique incidence, if the projection distance is slightly changed, the incident position of the light beam is greatly changed. Therefore, when the display screen is bent, the projected image is greatly distorted.
Therefore, it is highly necessary to dispose the Fresnel optical element 2 on the flat substrate 3 having high flatness.

In the sixth embodiment, the Fresnel optical element 2 is arranged concentrically. However, according to the incident angle θ, the angle of the reflecting surface 11 is farther from the side closer to the center of the concentric circle. The Fresnel optical element 2 may be changed so as to be larger.
In the sixth embodiment, the Fresnel optical element 2 is arranged concentrically. However, the similar reduction ratio l of the prism according to the incident angle θ is on the side farther from the side closer to the center of the concentric circle. The Fresnel optical element 2 may be changed so that the direction becomes smaller.
Further, in the sixth embodiment, the Fresnel optical element 2 is arranged concentrically. However, the Fresnel optical element 2 is not necessarily arranged concentrically, and the Fresnel optical element 2 is arranged linearly. May be.

  Although not particularly mentioned in the first to sixth embodiments, an image with high resolution can be displayed if the pitch of the Fresnel optical element 2 is made finer than the pixels of the screen.

  As described above, the Fresnel optical element according to the present invention is suitable for use in a projection display device in which the projector is arranged not on the back side of the display screen but on the front side (observer side) of the display screen.

Claims (2)

In a Fresnel optical element in which a plurality of Fresnel prisms having a reflective surface that reflects light rays emitted from a light emitter and a non-incident surface that is not irradiated with the light rays are formed in a sawtooth shape, a base on which the Fresnel prisms are arranged less than 90 degrees angle of the non-incident surface to the surface, and, Fresnel optical, characterized in that rather larger than the angle of incidence of the light beam, a portion of the non-incident surface are formed in parallel with the surface of the substrate element. Light absorption function portion of the non-incident surface absorbs light, or Fresnel optical element according to claim 1, characterized in that it comprises a light diffusion function that diffuses the light.

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