JP6056604B2 - Rear projection display device and Fresnel lens used therefor - Google Patents

Description

  The present invention relates to a rear projection display device and a Fresnel lens used therefor.

  In recent years, rear projection display devices (rear projection displays) have been developed. FIG. 5 is a side view showing an example of a schematic configuration of the rear projection display device. The rear projection display apparatus 101 includes a light source unit 20 having a light source, an illumination optical system, and a display element, a projection lens 30, a Fresnel lens 140, and a screen 50 in this order from the right in the drawing.

  In such a rear projection display device 101, the light emitted from the light source is irradiated onto the display element by the illumination optical system, and the image generated on the display element is enlarged by the projection lens 30 and projected onto the screen 50. The observer looks at the screen 50 from the front side of the screen 50.

  By the way, the screen 50 is a rectangular plate made of acrylic resin, for example, and a diffusion surface is formed on the front surface by blasting or the like, so that the image light is diffused by the screen 50 and recognized by the observer. Since the diffusion characteristics of the screen 50 are dependent on the incident angle, if the image light is incident at a uniform angle from the center of the screen 50 to the peripheral portion (over the entire back surface), the luminance of the entire screen of the screen 50 is increased. Becomes uniform and a display image with good visibility is obtained. Therefore, in order for the diffused light from the projection lens 30 to enter the entire back surface of the screen 50 as parallel light parallel to the optical axis, the Fresnel lens 140 is located between the projection lens 30 and the screen 50 and in the vicinity of the screen 50. Is arranged.

Such a Fresnel lens 140 is a disk-shaped plate made of, for example, acrylic resin (refractive index n ₁ = 1.49). The projection lens 30 side is a flat surface 41, and the screen 50 side is a plurality of concentric circular arrays. It is a prism. The prism has a Fresnel surface 42 for allowing image light to enter at an incident angle substantially perpendicular to the back surface of the screen 50, and a rise surface 143 that connects the Fresnel surfaces 42 to each other. The inclination (Fresnel angle) φ _fn of each Fresnel surface 42 changes according to the distance from the center of the Fresnel lens 40 (n increases), and the diffused light from the projection lens 30 is largely refracted at the peripheral part. The light at the center is refracted small. That is, φ _f1 <φ _f2 <φ _f3 <... <Φ _{f (n−1)} <φ _fn . Note that the inclination (rise angle) φ _rn of each rise surface 143 is all vertical. That is, φ _r1 = φ _r2 = φ _r3 =... = Φ _{r (n−1)} = φ _rn = 90 °.

Here, an example of an optical path by the Fresnel lens 140 will be described. FIG. 6 is an optical path diagram by the Fresnel lens 140. Incident light (a-1) is refracted by the plane 41 and enters the inside. When the incident light (a-2) refracted by the plane 41 reaches the nth Fresnel surface 42, normal light (a-3) refracted by the nth Fresnel surface 42 and emitted to the screen 50; It is divided into ghost light (a-4) reflected by the nth Fresnel surface 42. The ghost light (a-4) passes through the n-th rise surface 143 and the (n-1) -th Fresnel surface 42 while being refracted one after another, and the ghost light (a-5) is incident on the plane 41. Incident at an angle θ _out ′ (more than total reflection angle). As a result, the ghost light (a-5) is totally reflected by the plane 41, and becomes ghost light (a-6) again toward the prism. That is, the ghost light (a-6) is refracted by the (ni) rise surface 143, the (ni) Fresnel surface 42, etc., and is emitted to the screen 50. Then, an arc-shaped ghost is formed on the screen 50. In particular, at a position away from the center of the Fresnel lens 140 (n increases), the incident angle θ _in of the incident light (a-1) to the plane 41 of the Fresnel lens 140 is large and the Fresnel angle φ _fn is large. As a result of increasing the incident angle of the incident light (a-2) to the Fresnel surface 42, the reflectance of the incident light (a-2) at the Fresnel surface 42 is increased, and the intensity of the ghost light (a-4) is increased. Become. FIG. 7 is a calculation result of an optical path diagram simulating a part of the Fresnel lens 140.

  For this reason, various measures have been proposed to prevent the formation of ghosts on the screen 50. For example, (1) a light absorber is provided on the rise surface to absorb ghost light (a-6), or a light scatterer is provided to diffuse ghost light (a-6) (for example, a patent Reference 1), (2) one provided with two Fresnel lenses, (3) a light absorber mixed in the Fresnel lens to attenuate ghost light (a-4) to (a-6) ( For example, see Patent Document 2), (4) The rise angle of the Fresnel lens is incident from the plane side of the Fresnel lens, partially reflected by the Fresnel surface of the Fresnel lens, and then totally reflected by the plane. The projection light reaching the surface is set to totally reflect (see, for example, Patent Document 3).

JP-A-4-163539 JP-A-5-346620 JP-A-9-218465

  However, with the technique (1) described above, it is difficult to manufacture as described first, and even if it can be manufactured, the cost is very high. In addition, the technique (2) has a demerit that it can be manufactured but the cost and size are increased. The technique (3) has various problems such that the amount of normal light (a-3) is reduced.

Furthermore, the technique (4) has a problem in that the degree of freedom (structure and position) of the screen is lowered because ghost light is emitted to the screen side.
Accordingly, an object of the present invention is to provide a rear projection display device capable of preventing the occurrence of a ghost on a screen and a Fresnel lens used therefor.

A rear projection display device of the present invention made to solve the above-described problem includes a screen, a light source, and a Fresnel lens disposed between the screen and the light source, and the light source side of the Fresnel lens is The screen side of the Fresnel lens becomes a plurality of prisms having a rise surface and a Fresnel surface, and the light incident inside from the plane of the Fresnel lens is refracted by the Fresnel surface and emitted to the screen. In the projection display device, after the light reflected without being emitted from the nth Fresnel surface is refracted through the rise surface and the Fresnel surface and reflected by the (n−i) rise surface. The rise surface is inclined so that the light is emitted from the light source side plane of the Fresnel lens to the outside (not totally reflected).

According to the rear projection display device of the present invention, the ghost light that causes the ghost to be formed on the screen is prevented by being emitted to the plane side (the side opposite to the screen) of the Fresnel lens. For example, as shown in FIG. 2, the incident light (b-1) is refracted in a plane and enters the inside. When the incident light (b-2) refracted by the plane reaches the nth Fresnel surface, the normal light (b-3) refracted by the nth Fresnel surface and emitted to the screen, and the nth Fresnel surface It is divided into ghost light (b-4) reflected by the surface. The ghost light (b-4) is transmitted (b-5) while being refracted one after another on the nth rise surface, the (n-1) th Fresnel surface, etc., and the ghost light (b-6) is It is reflected when it reaches the (n−i) th rise surface. Furthermore, the ghost light (b-7) is incident on the plane at an incident angle θ _out ′ (less than the total reflection angle). As a result, the ghost light (b-8) is refracted on a plane and emitted to the outside. That is, ghost light (b-8) is emitted to the opposite side of the screen.

As described above, according to the rear projection display device of the present invention, the ghost light is emitted to the opposite side of the screen, so that the generation of the ghost on the screen can be prevented .

In addition, in order to prevent the occurrence of ghost, only the setting of the rise angle needs to be changed, which facilitates the production.

Here, “n” is a numerical value indicating the magnitude of the distance from the center of the Fresnel lens, and “i” is an arbitrary numerical value preset by the producer or the like. As will be described later, the smaller i is, the more ghost can be reduced, for example, “1”, “2”, and the like.

(Means and effects for solving other problems)
In the above invention, the light reflected without being emitted from the Fresnel surface is incident on the rise surface at a total reflection angle or more, and the light totally reflected on the rise surface is incident on the plane at a angle less than the total reflection angle. You may be made to do.

Furthermore, the Fresnel lens used in the rear projection display device of the present invention includes a screen, a light source, and a Fresnel lens disposed between the screen and the light source, and the light source side of the Fresnel lens is a flat surface. The screen side of the Fresnel lens is a plurality of prisms having a rise surface and a Fresnel surface, and the rear projection type in which light incident inside from the plane of the Fresnel lens is refracted by the Fresnel surface and emitted to the screen. In the Fresnel lens used in the display device, the light reflected without being emitted from the nth Fresnel surface is transmitted while being refracted through the rise surface and the Fresnel surface, and the (ni) rise surface . After the reflection, the rise surface is inclined so as to be emitted from the plane to the outside.

The side view which shows an example of schematic structure of the rear projection type display apparatus which concerns on this invention. The optical path diagram by the Fresnel lens of FIG. The calculation result of the optical path diagram which simulated a part of Fresnel lens of FIG. The optical path figure by the Fresnel lens which concerns on another Example of this invention. The side view which shows an example of schematic structure of the conventional rear projection type display apparatus. FIG. 6 is an optical path diagram by the Fresnel lens of FIG. 5. The calculation result of the optical path diagram which simulated a part of Fresnel lens of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and it goes without saying that various aspects are included without departing from the spirit of the present invention.

<First embodiment>
FIG. 1 is a side view showing an example of a schematic configuration of a rear projection display device according to the present invention. The same reference numerals are assigned to the same components as those in the rear projection display device 101.
The rear projection display device 1 includes a light source unit 20 including a light source, an illumination optical system, and a display element, a projection lens 30, a Fresnel lens 40, and a screen 50 in this order from the right in the drawing.

The Fresnel lens 40 is a disk-shaped plate made of, for example, acrylic resin (refractive index n1 = 1.49). The projection lens 30 side is a flat surface 41, and the screen 50 side is a plurality of prisms arranged concentrically. ing. The prism includes a Fresnel surface 42 for allowing image light to enter the screen 50 at an incident angle substantially perpendicular to the screen 50, and a rise surface 43 that connects the Fresnel surfaces 42.
The inclination φ _fn of each Fresnel surface 42 changes according to the distance from the center of the Fresnel lens 40 (n becomes larger), and the diffused light from the projection lens 30 is refracted greatly at the peripheral part, The light is refracted small. That is, φ _f1 <φ _f2 <φ _f3 <... <Φ _{f (n−1)} <φ _fn .

The inclination φ _rn of each rise surface 43 changes according to the distance from the center of the Fresnel lens 40 (n increases), refracts the light reflected without being emitted from the nth Fresnel surface 42, and (n + 1) th The light reflected from the Fresnel surface 42 without being emitted is totally reflected so as to be emitted from the plane 41 to the outside. At this time, the light reflected by the (n + 1) th Fresnel surface 42 enters the nth rise surface 43 at a total reflection angle or more, and the light reflected by the nth rise surface 43 is totally reflected by the plane 41. It is designed to be incident at less than an angle.
Such a Fresnel lens 40 is manufactured by changing the angle of the cutting tool for cutting the Fresnel surface 42. Further, it is preferable that φ _r1 > φ _r2 > φ _r3 >...> Φ _{r (n−1)} > φ _rn .

Next, an example of an optical path by the Fresnel lens 40 will be described. FIG. 2 is an optical path diagram of the Fresnel lens 40. Incident light (b-1) is refracted by the plane 41 and enters the inside. When the incident light (b-2) refracted by the plane 41 reaches the nth Fresnel surface 42, normal light (b-3) refracted by the nth Fresnel surface 42 and emitted to the screen 50; It is divided into ghost light (b-4) reflected by the nth Fresnel surface 42. The ghost light (b-4) passes through (b-5) while being refracted through the nth rise surface 43 and the (n-1) th Fresnel surface 42, and the ghost light (b-6) It is totally reflected when it reaches the rise surface 43 of (n-1). Furthermore, the ghost light (b-7) is incident on the plane 41 at an incident angle θ _out ′ (less than the total reflection angle). The ghost light (b-8) is refracted by the plane 41 and is emitted to the outside. That is, the ghost light (b-8) is emitted to the opposite side of the screen 50. FIG. 3 is a calculation result of an optical path diagram simulating a part of the Fresnel lens 40.

Here, the light φ reflected without being emitted from the nth Fresnel surface 42 is reflected, and the inclination φ _{r (} ni) of the (ni) rise surface 43 emitted from the plane 41 to the outside is set. An example of the calculation method for this will be described. Here, φ _rn = φ _{r (n−1)} = φ _{r (n−2)} =... = Φ _{r (n−i)} .
First, assuming that the refractive index of the Fresnel lens is n ₁ , the refractive index of air is n ₀ , the incident angle to the plane 41 is θ _in, and the exit angle from the plane 41 is θ _in ′, the following formula (1) Is established.
θ _in ′ = sin ⁻¹ {(n ₀ / n ₁ ) · sin θ _in } (1)

When the n-th Fresnel angle is φ _fn , the n-th rise angle is φ _rn, and the incident angle to the n-th rise surface 43 is θ _n , the following equation (2) is established.
θ _n = 180−2φ _fn −φ _rn + θ _in ′ (2)
Further, assuming that the incident angle to the (n−i) th rise surface 43 is θ _n−i , the following equation (3) is obtained.
θ _{n− (i + 1)} = 180−φ _fn −φ _rn −sin ⁻¹ {(n ₀ / n ₁ ) · sin (180−φ _fn −φ _rn −sin ⁻¹ {{(n ₁ / n ₀ ) · sin θ _ni })} (3)
However, i = 1, 2,.

On the other hand, when the following formula (4) is established, total reflection occurs at the (n−i) th rise surface 43.
θ _n−i > sin ⁻¹ (n ₀ / n ₁ ) (4)
However, i = 0, 1, 2,...

Further, when the following formula (5) is established, the light totally reflected by the (n−i) th rise surface 43 is transmitted without being totally reflected by the plane 41.
θ _out ′ = | φ _rn −θ _n−i | <sin ⁻¹ (n ₀ / n ₁ ) (5)

In addition, since incident light (b-2) may be scraped by the rise surface 43, it is preferable that the following formula (6) is satisfied.
90 ≧ φ _rn > 90−θ _in ′ (6)

If the equations (1) to (5) are satisfied, the (n−i) -th rise surface 43 totally reflects the light reflected without being emitted from the n-th Fresnel surface 42 to obtain a plane. 41 can be emitted to the outside. In addition, a ghost can be reduced, so that i is small.
Therefore, for example, in the Fresnel lens 40 made of acrylic resin, the incident angle θ _n−i of the ghost light incident on the (n−i) th rise surface 43 causing total reflection from the equation (4) is air (refracted). The total reflection angle between the refractive index n ₀ = 1.00 and the acrylic (refractive index n ₁ = 1.49) may be designed to be 42.2 °, and the incident angle θ _in = 40 ° of incident light. Is θ _in '= 25.5 ° according to the equation (1), and when the Fresnel angle φ _fn = 60 °, if the rise angle φ _{r (n−i)} <63.1 °, then i = 1 satisfies Equation (4).

  As described above, according to the rear projection display device 1 of the first embodiment, since the ghost light is emitted to the opposite side of the screen 50, the occurrence of the ghost on the screen 50 can be prevented. Further, the normal light (b-3) from the nth Fresnel surface 42 is actually a light beam having an error or a width, so that the (n + 1) th rise surface 43 is inclined and the (n + 1) th rise surface 43 is tilted. It is possible to prevent a non-perpendicular light beam from hitting, and as a result, it is possible to prevent luminance unevenness caused by light hitting the (n + 1) th rise surface 43.

<Second Embodiment>
The rear projection display device includes a light source unit including a light source, an illumination optical system, and a display element, a projection lens, a Fresnel lens 240, and a screen in this order from the right. Since the second embodiment differs from the first embodiment only in the configuration of the Fresnel lens, only the Fresnel lens will be described.

The Fresnel lens 240 is a disk-shaped plate made of, for example, acrylic resin (refractive index n ₁ = 1.49), the projection lens 30 side is a flat surface 41, and the screen 50 side is a plurality of prisms arranged concentrically. It has become. The prism has a Fresnel surface 242 for allowing image light to enter the screen 50 at an incident angle substantially perpendicular to the screen 50, and a rise surface 243 that connects the Fresnel surfaces 242 to each other.
The inclination φ _fn of each Fresnel surface 242 changes according to the distance from the center of the Fresnel lens 240 (n becomes larger), and the diffused light from the projection lens 30 is largely refracted and refracted at the central part. The light is refracted small. That is, φ _f1 <φ _f2 <φ _f3 <... <Φ _{f (n−1)} <φ _fn .

The inclination φ _rn of each rise surface 243 changes according to the distance from the center of the Fresnel lens 240 (n becomes larger), and the light reflected by the nth Fresnel surface 242 without being emitted is totally reflected, so that the plane 41 It is formed so as to be emitted from the outside. In other words, the n-th rise surface 243 of the same prism totally reflects the light reflected without being emitted from the n-th Fresnel surface 242. At this time, the light reflected by the nth Fresnel surface 242 enters the nth rise surface 243 at a total reflection angle or more, and the light reflected by the nth rise surface 243 is less than the total reflection angle to the plane 41. It comes to be incident.
For example, in the Fresnel lens 240 made of acrylic resin, the incident angle θ _n of the ghost light incident on the nth rise surface 243 causing total reflection is air (refractive index n ₀ = 1. 00) and acrylic (refractive index n ₁ = 1.49) may be designed to be 42.2 °, and when the incident angle θ _in = 40 ° of incident light, From 1), when θ _in ′ = 25.5 ° and the Fresnel angle φ _fn = 60 °, if the rise angle φ _rn <43.4 °, then i = 0 and the expression (4) is satisfied.

Next, an example of an optical path by the Fresnel lens 240 will be described. FIG. 4 is an optical path diagram by the Fresnel lens 240. Incident light (c-1) is refracted by the plane 41 and enters the inside. When the incident light (c-2) refracted by the plane 41 reaches the nth Fresnel surface 242, the normal light (c-3) refracted by the nth Fresnel surface 242 and emitted to the screen 50; It is divided into ghost light (c-4) reflected by the nth Fresnel surface 242. The ghost light (c-4) reaches the nth rise surface 243 and is totally reflected. Furthermore, the ghost light (c-5) is incident on the plane 41 at an incident angle θ _out ′ (less than the total reflection angle). Thereby, the ghost light (c-5) is refracted by the plane 41 and is emitted to the outside. That is, ghost light (c-6) is emitted to the opposite side of the screen 50.

  As described above, according to the Fresnel lens 240 of the second embodiment, the ghost light is emitted to the opposite side of the screen 50, so that the generation of the ghost on the screen 50 can be prevented. Further, the normal light (c-3) from the n-th Fresnel surface 242 is actually a light flux having an error or a width. It is possible to prevent a non-perpendicular light beam from hitting, and as a result, it is possible to prevent luminance unevenness caused by light hitting the (n + 1) th rise surface 243.

<Other embodiments>
(1) In the rear projection display device 1 described above, the nth rise surface 43 refracts the reflected light without being emitted from the nth Fresnel surface 42 and emits it from the (n + 1) th Fresnel surface 42. Although the configuration is shown in which the reflected light is reflected to be emitted to the outside from the plane 41, the reflected light is not refracted by the nth Fresnel surface and the (n + 1) th Fresnel surface. In addition, the light reflected from the (n + 2) -th Fresnel surface may be reflected so that the light is emitted from the plane to the outside. That is, “i” may be an arbitrary numerical value.

(2) In the rear projection display device 1 described above, the inclination φ _rn of each rise surface 43 has been shown to change according to the distance from the center of the Fresnel lens 40 (n increases), but in a certain n range A configuration may be adopted in which light is reflected from the (n + 1) th Fresnel surface without being reflected by (for example, n> 10) so as to be emitted from the plane to the outside.

  The present invention can be used for a rear projection display device including a Fresnel lens.

1: rear projection display device 20: light source 40, 240: Fresnel lens 41: plane 42, 242: Fresnel surface 43, 243: rise surface 50: screen

Claims (3)

A screen, a light source, and a Fresnel lens disposed between the screen and the light source,
The light source side of the Fresnel lens is a plane, and the screen side of the Fresnel lens is a plurality of prisms having a rise surface and a Fresnel surface,
The rear projection display device in which light incident inside from the plane of the Fresnel lens is refracted by the Fresnel surface and emitted to the screen,
The light reflected without being emitted from the nth Fresnel surface passes through the refracting surface and the Fresnel surface while being refracted, reflected by the (n−i) th rising surface, and then on the light source side of the Fresnel lens. A rear projection display device, wherein the rise surface is inclined so as to be emitted from a flat surface to the outside. The light reflected without being emitted from the Fresnel surface is incident on the rise surface at a total reflection angle or more, and the light totally reflected on the rise surface is incident on the plane with a total reflection angle less than the total reflection angle. The rear projection display device according to claim 1 . A screen, a light source, and a Fresnel lens disposed between the screen and the light source,
The light source side of the Fresnel lens is a plane, and the screen side of the Fresnel lens is a plurality of prisms having a rise surface and a Fresnel surface,
A Fresnel lens used in a rear projection display device in which light incident inside from the plane of the Fresnel lens is refracted by the Fresnel surface and emitted to the screen,
The light reflected without being emitted from the n-th Fresnel surface is transmitted while being refracted by the rise surface and the Fresnel surface, and after being reflected by the (ni) rise surface , exits from the plane to the outside. As described above, an inclination of the rise surface is formed.

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