Transparent screen, projection display device, and method of receiving control signal light

A transparent screen is constructed in such a way that a plurality of Fresnel prisms 12d each of which is smaller than a plurality of Fresnel prisms 12a and has a shape approximately similar to that of each of the plurality of Fresnel prisms 12a are arranged in a sawtooth shape on a non-light incidence surface portion of a Fresnel lens 12 on a light incidence side to which any image light PB applied from a projector 1 is not applied directly because blocked by a Fresnel prism 12a placed frontwardly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transparent screen which receives image light projected onto a rear side thereof as viewed from a side thereof which faces a viewer so as to display an image, a projection display device which projects image light onto the rear side of the screen so as to display an image, and a method of condensing control signal light applied to the transparent screen from a remote controller onto a photo detector to receive the control signal light.

2. Description of Related Art

A projection display device is an image display device which consists of a Fresnel lens screen, a diffusion sheet (a diffusion layer), and so on. Unlike a CRT (Cathode Ray Tube) and a PDP (Plasma Display Panel), this projection display device is of non-light-emitting type. The projection display device is provided with, as a projector, an illuminating optical system for guiding light applied from a light source in a predetermined direction, a light valve for applying the light guided by the illuminating optical system, and for adjusting the amount of the light according to an image signal so as to form an image, and a projection optical system for expanding and projecting the image formed by the light valve onto a screen.

Projection display devices include a display device of rear projection type which projects image light onto a rear side of the screen thereof as viewed from a viewer and a display device of front projection type which projects image light onto a front side of the screen thereof as viewed from a viewer. A transparent screen for use in a display device of back projection type, among these projection display devices, includes a Fresnel lens screen for bending image light expanded and projected by a projector toward the viewer, and an image display element for forming an image of the image light from the Fresnel lens screen and for providing an angle of divergence for the image light so as to expand the image light.

There is a remote controller as a means for operating a projection display device by remote control. The remote controller uses a light signal having a wavelength which falls within a wavelength band of infrared rays including visible light rays. Because the Fresnel lens screen of a projection display device has a function of bending image light expanded and projected from a light source toward the direction of the viewer, the Fresnel lens screen also has a function of condensing control signal light from a remote controller applied thereto from the direction of the viewer onto a projector inversely. In other words, by using the Fresnel lens as a condensing lens, the control signal light applied from the remote controller can be condensed onto a photo detector efficiently.

A method of receiving such control signal light applied from a remote controller is disclosed by, for example, the following patent reference 1.[Patent reference 1] JP,63-2477,A (FIG. 2)

Because conventional projection display devices are constructed as mentioned above, if a Fresnel lens screen functions as a condenser lens which condenses incident light onto the optical axis of an optical system, the Fresnel lens screen can condense control signal light applied from a remote controller onto a photo detector efficiently. However, a problem with a case in which a Fresnel lens screen, which is an eccentric optical system, for use in thin-type projection display devices which have seen in recent years is used is that most of the Fresnel lens cannot guide control signal light applied from a remote controller to a photo detector, and therefore the control signal light applied from the remote controller cannot be condensed onto the photo detector efficiently.

SUMMARY OF THE INVENTION

The present invention is made in order to solve the above-mentioned problem, and it is therefore an object of the present invention to provide a transparent screen, a projection display device, and a control signal light receiving method which can guide control signal light applied from a remote controller to a photo detector efficiently even when using a Fresnel lens screen which is an eccentric optical system.

In accordance with the present invention, there is provided a transparent screen in which, on a non-light incidence surface portion of a Fresnel optical element to which any light ray applied from a light emitting body is not applied directly because blocked by a Fresnel prism placed frontwardly, a plurality of Fresnel prisms each of which is smaller than the above-mentioned Fresnel prism and has a shape approximately similar to that of the above-mentioned Fresnel prism are arranged in a sawtooth shape.

In accordance with the present invention, the transparent screen is constructed in such a way that, on the non-light incidence surface portion of the Fresnel optical element to which any light ray applied from a light emitting body is not applied directly because blocked by a Fresnel prism placed frontwardly, the plurality of Fresnel prisms each of which is smaller than the above-mentioned Fresnel prism and has a shape approximately similar to that of the above-mentioned Fresnel prism are arranged in a sawtooth shape. Therefore, the present embodiment offers an advantage of being able to guide control signal light applied from a remote controller toward a photo detector efficiently even when using the Fresnel lens screen which is an eccentric optical system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a configuration diagram showing a projection display device in accordance with Embodiment 1 of the present invention.FIG. 2is a perspective view showing the projection display device in accordance with Embodiment 1 of the present invention, andFIG. 3is a perspective view showing the interior of the projection display device in accordance with Embodiment 1 of the present invention. As shown inFIG. 1, a projector1is a light emitting body which is installed in a housing7of the projection display device, and which emits a light ray which is image light PB. The projector1is comprised of an illuminating optical system2, a light valve3, and a projection optical system4. The illuminating optical system2guides light applied thereto from a light source (not shown) in a predetermined direction. The light valve3applies the light guided by the illuminating optical system2to the projection optical system4, and carries out a process of adjusting the amount of the light according to an image signal to form an image. The projection optical system4expands and projects the image formed by the light valve3onto a transparent screen10.

A remote controller5is remote operation equipment with which a user performs an operation of, for example, switching among images, and emits control signal light CB showing the operation. A photo detector6is equipment installed in the vicinity of the projector1for receiving the control signal light CB applied thereto from the remote controller5.

The transparent screen10is comprised of a Fresnel lens screen11and an image display element14, and receives the image light PB applied thereto from the projector1and then emits the image light PB toward the viewer while receiving the control signal light CB applied thereto from the remote controller5and then emitting the control signal light CB toward the photo detector6. The Fresnel lens screen11is comprised of a light entering surface side Fresnel lens12and a base13, and has a function of bending the image light PB applied thereto from the projector1toward the direction of the viewer.

The light entering surface side Fresnel lens12is a Fresnel optical element formed in the Fresnel lens screen11on a side of the light source (a light entering surface side) which is opposite to the viewer's side, in which a plurality of Fresnel prisms12aeach of which has a refractive surface12bfor refracting the image light PB applied thereto from the projector1and a reflecting surface12cfor reflecting the image light PB refracted by the refractive surface12bare arranged in a sawtooth shape. A plurality of Fresnel prisms12dwhich are smaller than the Fresnel prisms12aand have a shape approximately similar to that of the Fresnel prisms12aare arranged in a sawtooth shape on each non-light incidence surface portion upon which the image light PB emitted from the projector1is not incident directly because the image light is blocked by a Fresnel prism placed frontwardly.

The image display element14is comprised of a lens element15, a light diffusing member16, a base17, and a surface processing member18, and has a function of forming an image of the image light PB whose optical path has been bent by the Fresnel lens screen11, and also providing the image light PB with an angle of divergence so as to expand the image light PB. The lens element15has a function of providing the image light PB with an angle of divergence. The light diffusing member16has a function of forming an image of the image light PB. The base17holds the lens element15, the light diffusing member16, etc., and is formed of a resin such as PMMA (Poly Methyl Meth Acrylate), MS (Methyl methacylate Styrene), MBS (Methyl metacylate Butadiene Styrene), or PC (Polycarbonate).

The surface processing member18can be comprised of various types of layers which are formed on a surface side of the image display element14which is the nearest to the viewer. For example, the various types of layers can be an antireflection layer for reducing reflection of light in order to reduce the influence of ambient light, an anti glare layer for reducing visual glare, an antistatic layer for preventing adhesion of dust due to static electricity, and a hard coating layer for protecting the surface of the image display element14. In this Embodiment 1, it is assumed that when the base17is formed, the light diffusing member16is incorporated into the base in the form of layers so that a pair of light diffusing layers are formed, though, in a case in which the base17is made of glass, the light diffusing member16in the form of a film can be bonded to the base with a bonding layer. In this Embodiment 1, although the light diffusing member16and the base17are arranged from the side of the light source to the side of the viewer in the order of the light diffusing member16and the base17, they can be inversely arranged in the order of the base17and the light diffusing member16. Furthermore, the base17can be integral with the light diffusing member16.

In the example ofFIG. 1, O shows the optical axis of the optical system, and the optical system is arranged in an eccentric form in such a way that the optical axis O is aligned outside the transparent screen10which serves as the screen. As shown inFIGS. 2 and 3, the concentric circular Fresnel lens whose center is on the optical axis O is placed eccentrically in such a way that the optical axis O is shifted from the center O′ of the screen.

Next, the operation of the projection display device will be explained. The Fresnel lens screen11of the transparent screen10is a field lens which deflects the image light PB applied thereto from the projector1toward the direction of the viewer, and is designed so as to have the functions of a collimate lens for collimating the image light PB in such a way that the image light becomes substantially-collimated light. Considering that light is inputted to and outputted from the Fresnel lens screen11after traveling along a path inverse to the above-mentioned path, the light entering surface side Fresnel lens12of the Fresnel lens screen11has the functions of a condenser lens for condensing light applied thereto from the direction of the viewer toward the direction of the projection optical system4.

Considering the outward appearance of a television set in which this projection display device is mounted, the most of the television set is occupied by the transparent screen10which constructs the screen, an operation which is performed on the television by using the remote controller5, which is remote operation equipment, is equivalent to an operation which is performed on the transparent screen10. In a case in which the photo detector6which receives the control signal light CB applied thereto from the remote controller5is installed in the vicinity of the projector1, the control signal light CB applied from the remote controller5is efficiently condensed by the Fresnel lens screen11and is guided toward the direction of the projection optical system4. However, taking into consideration that the control signal light CB applied from the remote controller5is incident upon the screen at an angle with the normal to the screen, and passes through the light diffusing member16, the lens element15, etc., it can be assumed that the light does not necessarily reach the projection optical system4and is received by the photo detector6located before the projection optical system4.

It can be seen by examining the optical path in detail that only a control signal light ray, among the control signal light rays CB applied from the remote controller5, which travels along an optical path inverse to the optical path of the image light PB applied from the projector1is condensed toward the projection optical system4, and the other control signal light rays which travel along the other optical paths are not condensed correctly. Hereafter, this point will be explained in detail.FIG. 4is an explanatory drawing showing a deflection of the optical path of the image light PB and deflections of the optical path of the control signal light CB in the transparent screen10in accordance with Embodiment 1 of the present invention.FIG. 5is an explanatory drawing showing a deflection of the optical path of the image light PB and deflections of the optical path of the control signal light CB in a case in which no Fresnel prisms12dare arranged on each non-light incidence surface portion of the light entering surface side Fresnel lens12in the transparent screen10ofFIG. 4.

The light entering surface side Fresnel lens12is constructed in such a way that the plurality of Fresnel prisms12aeach of which has a refractive surface12bfor refracting the image light PB applied thereto from the projector1and a reflecting surface12cfor reflecting the image light PB refracted by the refractive surface12btoward the viewer are arranged in a sawtooth shape. The image light PB which is incident upon each Fresnel prism12aat an angle θinis emitted at an angle θref1by the refractive surface12band the reflecting surface12cof each Fresnel prism12a.On the basis of geometry and the Snell's law, this relationship is shown by the following equation (1).

[Equation⁢⁢1]θrefl⁡(θi⁢⁢n;α,τ)=sin-1⁡(n1n0⁢sin⁡[τ-α+sin-1(n0n1⁢sin⁡(π-τ-α-θi⁢⁢n)])(1)
where τ is the vertical angle of each Fresnel prism12a,ξ is the angle of the refractive surface12b, and α is the angle (total reflection surface angle) of the reflecting surface12c.Furthermore, n0is the refractive index of the atmosphere, and n1is the refractive index of each Fresnel prism12aand the refractive index of the base13. The angle ζ is shown by the following equation (2).

By transforming the equation (1), the total reflection surface angle α can be shown by the following equation (3).

This equation (3) means that the total reflection surface angle α is a function of the incident angle θin, the function type being determined by two degrees of freedom: the total reflection surface angle α and the vertical angle τ of each Fresnel prism12a.That is, because the viewer is placed in substantially front of the transparent screen10and the angle at which the image light is emitted from the screen is determined as θref1≈0, the total reflection surface angle α at the incident angle θincan be determined automatically when the vertical angle τ of each Fresnel prism12ais determined. Because the angle ξ of the refractive surface12bcan be determined, as shown in the following equation (4), from the sum of the triangular interior angles, the shapes (angles) of the surfaces which construct the light entering surface side Fresnel lens12are determined uniquely.
[Equation 4]
ξ=π−τ−α  (4)

Each diagonally shaded portion ofFIG. 5shows the optical path of the image light PB applied from the projector1. Because the shape of the light entering surface side Fresnel lens12is determined in such a way as mentioned above, the image light PB applied from the projector1is bent toward the direction of the viewer. In contrast, the control signal light traveling along the optical path (each diagonally shaded portion) of the image light PB in the reverse direction (i.e., the control signal light shown by a dotted line), among the rays of control signal light CB applied from the remote controller5, is bent toward the projector1, while because the control signal light which does not travel along the optical path (each diagonally shaded portion) of the image light PB in the reverse direction (i.e., the control signal light shown by a dashed dotted line) propagates through a plurality of Fresnel prisms12aand then becomes stray light, the control signal light is not condensed correctly.

The condensing efficiency of the control signal light CB at that time approximately becomes equal to the percentage of each diagonally shaded portion, as shown inFIG. 5, to the pitch m of the plurality of Fresnel prisms12a.In the example ofFIG. 5, because the size of each diagonally shaded portion is about one-third of the pitch m of the plurality of Fresnel prisms12a,about one-third of the control signal light CB can be condensed efficiently, but about two-thirds of the control signal light CB is lost. The percentage h of each diagonally shaded portion to the pitch m of the plurality of Fresnel prisms12ais shown by the following equation (5).

In this Embodiment 1, in order to condense the control signal light CB applied from the remote controller5efficiently, a plurality of Fresnel prisms12dare arranged on each non-light incidence surface portion of the light entering surface side Fresnel lens12in the transparent screen10. More specifically, in the light entering surface side Fresnel lens12, the refractive surface12band the reflecting surface12cof each Fresnel prism12awhich serve as the optical path (each diagonally shaded portion) of the image light PB are remained, and a plurality of Fresnel prisms12dwhich are a supplementary lens are arranged in each portion which does not serve as the optical path (each diagonally shaded portion) of the image light PB. The percentage l of the lens portion remained in the light entering surface side Fresnel lens12is calculated according to the following equation (6). It cannot be overemphasized that in actual, the percentage l can be set to a somewhat larger value by making the percentage have some margin (from 10% to 20%).

Because the role of each set of plural Fresnel prisms12dwhich is a supplementary lens is to guide the control signal light CB applied from the remote controller5toward a neighborhood of the projection optical system4, each of the plural Fresnel prisms12dhas only to have a shape substantially similar to that of each Fresnel prism12awhich consists of the refractive surface12band the reflecting surface12cin the easiest example. However, in the case in which each set of Fresnel prisms12dwhich is a supplementary lens is formed in such a way as to have such a similar shape, the control signal light CB may propagate through a plurality of Fresnel prisms12aand may become stray light (refer to a dashed dotted line ofFIG. 4), like in the case of the light entering surface side Fresnel lens12.

To solve this problem, each set of Fresnel prisms Fresnel prism12dwhich is a supplementary lens is configured in such a way that the control signal light CB applied from the remote controller5is emitted out while being shifted slightly (in the example ofFIG. 4, being shifted slightly upwardly) so that the control signal light CB is not blocked by each Fresnel prism12aplaced frontwardly (refer to the dashed line ofFIG. 4). For example, in a case in which the lens shape of each of the plurality of Fresnel prisms12dwhich are a supplementary lens is similar to that of each Fresnel prism12a,what is necessary is just to slant each of the Fresnel prisms12dwhich are a supplementary lens. Each Fresnel prism12darranged in a portion A2shown inFIG. 4has a shape similar to that of each Fresnel prism12a,but its slanting surface is slightly slanted against a corresponding slanting surface of each Fresnel prism12a.InFIG. 4, in order to explain the effect of the plurality of Fresnel prisms12d,a portion A1and the portion A2are aligned in the light entering surface side Fresnel lens12, as illustrated, but it cannot be overemphasized that it is not necessary to form the portions A1and A2in this way. Furthermore, each Fresnel prism12aand each Fresnel prism12dwhich is a supplementary lens are not necessarily similar to each other. The reason why each Fresnel prism12aand each Fresnel prism12dwhich is a supplementary lens are not necessarily similar to each other will be explained with reference toFIG. 6.

FIG. 6is an explanatory drawing showing an example in which the light entering surface side Fresnel lens12is produced through cutting using different cutting bites52and53. Generally, the light entering surface side Fresnel lens12is produced by transferring the surface shape of a master mold51in which the shape of the Fresnel lens is carved onto a lens material. In the example ofFIG. 6, each supplementary lens portion is cut by using the cutting bite52and each Fresnel lens portion is cut by using the cutting bite53, and, as a result, each Fresnel prism12dwhich is a supplementary lens and each Fresnel prism12acan be formed in such a way that they do not necessarily have shapes similar to each other. Because by thus eliminating the constraints to make the shape of each Fresnel prism12dwhich is a supplementary lens be similar to that of each Fresnel prism12a,each set of a plurality of Fresnel prisms12dwhich are a supplementary lens can be designed in such a way as to specialize in guiding the control signal light CB applied from the remote controller5toward a neighborhood of the projection optical system4, the control signal light CB can be condensed efficiently.

Each set of a plurality of Fresnel prisms12dwhich are a supplementary lens is formed so as to guide the control signal light CB applied from the remote controller5to the photo detector6, and needs to be small compared with the pitch m of the plurality of Fresnel prisms12ain such a way as not to block the image light PB. However, when the supplementary lens has a size which is of order of about several times to several ten times (a size of 5 microns) the wavelength of the control signal light, the image light is influenced not only by geometrical optics but by wave optics (for example, diffraction phenomena of light). Therefore, the pitch of the supplementary lens needs to be smaller than the pitch m of the plurality of the Fresnel prism12a,and needs to be larger than the wavelength lambda of the control signal light.

By thus forming a plurality of Fresnel prisms12dwhich are a supplementary lens in each non-light incidence surface portion to which the image light PB applied from the projector1is not applied directly because blocked by a Fresnel prism12aplaced frontwardly, the sensitivity of the reception of the control signal light CB applied from the remote controller5can be improved without having a bad influence on the image light PB. Because the Fresnel lens screen11condenses light traveling in a direction normal to the screen efficiently, the Fresnel lens screen11can selectively condense only the control signal light CB applied from the remote controller5which is operated by the viewer who can be expected to stay in a direction substantially normal to the screen without condensing noise, such as light emitted from a fluorescent lamp.

As can be seen from the above description, the projection display device in accordance with this Embodiment 1 is constructed in such a way that a plurality of Fresnel prisms12deach of which is smaller than each Fresnel prism12aand has a shape approximately similar to that of each Fresnel prism12aare arranged in a sawtooth shape on each non-light incidence surface portion, to which the image light PB applied from the projector1is not applied directly, of the light entering surface side Fresnel lens12because the image light PB is blocked by a Fresnel prism12aplaced frontwardly. Therefore, the present embodiment offers an advantage of being able to guide the control signal light applied from the remote controller5toward the photo detector6efficiently even when using the Fresnel lens screen11which is an eccentric optical system.

In this Embodiment 1, the Fresnel lens screen11receives the image light PB which is applied directly thereto from the projector1, as previously shown. As an alternative, as shown inFIG. 7, at least one or more reflecting mirrors19are placed between the projector1and the Fresnel lens screen11in such a way that the Fresnel lens screen11receives the image light PB reflected by the one or more reflecting mirrors19. In addition, the projection display device can have, as its component, a holding mechanism, an air conditioner, a speaker, a television stand, an electrical circuit, a geometrical correction circuit, or a color correction circuit. Furthermore, the light emitting body which serves as the light source can be a lamp having a continuous spectrum, or a laser or LED (Light Emitting diode) having a discrete spectrum.