JP2015055856A - Rear projection type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reduction in take-in efficiency of video light at peripheral parts of a screen surface leading to fall-off of illumination conspicuous at the peripheral parts thereof upon proceeding with a short focus and wide-angle in rear projection type display devices.SOLUTION: A rear projection type display device 100 comprises: a transmission type screen 10 that has a Fresnel lens member 11 on an incidence plane Sin; and a video source 20 that projects video light L on the rear of the screen. The Fresnel lens member is arranged so as to have a direction causing a Fresnel lens surface Sf to be an emerging surface So of the video light, and causing a non-lens surface on an opposite side of the Fresnel lens surface to be an incidence plane into which the video light enters. Let an angle of incidence at which the video light is incident to the incidence plane of the Fresnel lens member be denoted as θi, and a maximum angle point of incidence at which the angle of incidence θi is maximum in a plane of the incidence plane be denoted as Pθmax, at the maximum angle point of incidence Pθmax, the video light is such that, as a polarization component to be defined by the incidence plane Sir, a P-wave component is greater than a S-wave component.

Description

  The present invention relates to a rear projection display device that projects image light from a rear surface onto a screen.

In recent years, in a rear projection display device that projects image light from the back to a transmissive screen, in order to be able to project image light from a close range due to the need for a larger screen, a smaller device, a thinner device, etc. Video sources have become shorter and wider in angle. Such rear projection type display devices are attracting attention in the field of vehicles such as amusement machines and automobiles.
However, when the focal length is shortened and the angle is increased, the difference in brightness between the central portion and the peripheral portion of the screen increases. For such in-plane uniformity of brightness of the display screen, that is, luminance uniformity, various devices have been conventionally made in order to obtain a good video quality. For example, this is a technique in which a Fresnel lens and a light diffusion layer are provided on a transmission screen (Patent Document 1).
The configuration using the Fresnel lens includes a configuration in which the Fresnel lens surface is directed toward the observer side and a configuration in which the Fresnel lens surface is directed toward the image source side. Correspondingly, it is easy to ensure brightness uniformity.
However, the configuration in which the Fresnel lens surface is directed to the image source side has drawbacks that it is difficult to remove dust adhering to the irregularities of the Fresnel lens surface, the irregularities are easily damaged and deformed, and the video quality is deteriorated.

  On the other hand, there is also a technology that uses polarized light to improve image quality. For example, Patent Literature 2 discloses a technique for improving a decrease in bright room contrast due to external light reflection. The technology disclosed in Patent Document 2 allows screen light to pass outside light incident on the screen surface through a quarter-wave plate and a polarizing plate disposed on the viewer side of the screen surface to form circularly polarized light. When the light is reflected and returned, the external light that has become circularly polarized light in the opposite direction is blocked by the quarter-wave plate and the polarizing plate, so that the external light reflection is reduced and the bright room contrast is improved. It is a technology.

JP 2005-338681 A JP-A-3-256020

  However, in a configuration where the Fresnel lens surface is directed toward the viewer, particularly as a transmissive screen, when the focal length and the wide angle are increased, the image light from the image source is not exposed to the Fresnel lens that forms the back of the transmissive screen. The incident angle incident on the light incident surface which is a lens surface is further increased. For this reason, the reflectance at the light incident surface increases, and the image light that can be captured inside the Fresnel lens decreases accordingly, and the capture efficiency decreases. It will decline.

  That is, an object of the present invention is to improve the reduction in the efficiency of capturing image light in the peripheral portion that leads to a decrease in brightness in the peripheral portion of the screen surface, which becomes noticeable when shortening the focus and widening the angle. It is to provide a rear projection type display device capable of performing the above.

Therefore, the rear projection type display device according to the present invention has the following configuration.
(1) A rear projection display device comprising a transmissive screen and an image source for projecting image light on the rear surface of the transmissive screen,
The transmission screen has a Fresnel lens member on the light incident surface side thereof,
The Fresnel lens member is disposed in an orientation in which the Fresnel lens surface is the light exit surface of the image light, and the non-lens surface opposite to the Fresnel lens surface is the light incident surface on which the image light is incident,
An incident angle θi is an angle at which the image light is incident on the light incident surface of the Fresnel lens member, and an angle of a portion where the incident angle θi is the largest in the surface of the light incident surface is a maximum incident angle θmax. When the portion that gives the maximum incident angle θmax is the maximum incident angle point Pθmax,
At the maximum incident angle point Pθmax,
The image light is a polarized light having a P wave component larger than an S wave component as a polarized light component defined by the incident surface Sir.
Rear projection display device.
(2) The transmission screen has a circumscribed rectangle circumscribing the screen surface,
The image light has a polarization direction parallel to a plane that includes a long side of the circumscribed rectangle and is perpendicular to the light incident surface.
(1) The rear projection type display device.

  According to the rear projection type display device of the present invention, when the focus is shortened and the angle is increased, the image light capturing efficiency is reduced at the peripheral portion which leads to a decrease in brightness at the peripheral portion of the screen surface. Can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the rear projection type display apparatus by this invention by the one Embodiment, (a) is a top view, (b) is the front view seen from the observer side, (c) is a side view. It is a figure explaining the behavior of the P wave and S wave with respect to reflection and refraction of light at the boundary surface of a substance, (a) is a sectional view, (b) is a perspective view. The graph which shows an example of the difference of the P wave and the S wave of the reflectance of the light in the boundary surface of a substance. 6 is a graph showing a part of a simulation result showing a difference in transmission efficiency depending on a polarization state of image light in a Fresnel lens member, and showing a case of P-wave light as Example 1. FIG. This is based on the same simulation as in FIG. 4-A, and the light as Comparative Example 1 is non-polarized light. FIG. 4A is a simulation similar to that in FIG. The figure explaining the optical system at the time of simulation of the graph of FIG. The front view explaining the behavior as a P wave and an S wave in the horizontal direction of the screen and the vertical direction of the screen when the screen is horizontally long. The front view which shows the example of a shape of a screen surface, its circumscribed rectangle, and the setting example of the polarization direction of the image light according to the position of an image source. In the case of a horizontally long screen surface, it is a figure which shows the example of a setting of the polarization direction of the image light according to the position of an image source, (a) is a side view, (b) is a front view. The top view which illustrates the case where the transmission type screen is a curved surface as an example in which the maximum incident angle is different even though the distance from the image source to the maximum incident angle point is the same. The figure which shows typically an example of the whole structure of a rear projection type display apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are conceptual diagrams, and the scale relationships, aspect ratios, and the like of components may be exaggerated.
First, in the present invention, the short distance, the short focus, and the wide angle are the projection conditions of the image light L at the maximum incident angle θmax of 35 ° or more, preferably 45 ° or more, more preferably 55. It means a condition that is at least °, more preferably at least 65 °.
In the present invention, the polarization direction Dp means the vibration direction of the electric field of the light.
The capturing efficiency means the efficiency of capturing image light on the light incident surface, and has the same meaning as the transmittance of image light on the light incident surface.

FIG. 1 is a diagram for explaining a rear projection display device according to an embodiment of the present invention, in which FIG. 1 (a) is a plan view, FIG. 1 (b) is a front view seen from an observer V side, FIG. (C) is a side view.
In this figure, the vertical direction with respect to the ground is the Z-axis direction, the left-right direction with respect to the observer V standing on the ground is the X-axis direction, and the front-rear direction is the Y-axis direction. The screen surface of the transmissive screen 10 is a plane that is parallel to the XZ plane.
In the drawings other than FIG. 1, for the drawings in which the coordinate axes are clearly shown, the way of taking the coordinate axes is the same as in FIG. 1.

A rear projection display device 100 shown in FIG. 1 is a display device that includes a transmissive screen 10 and a video source 20 that projects video light L on the rear surface of the transmissive screen 10.
The transmissive screen 10 has a Fresnel lens member 11 on the light incident surface Sin side of the back surface thereof. The Fresnel lens member 11 uses the Fresnel lens surface Sf as the light exit surface So of the image light L and is opposite to the Fresnel lens surface Sf. The non-lens surface is arranged in a direction to be a light incident surface Sin on which the image light L is incident.
The transmissive screen 10 is generally composed of a Fresnel lens member 11 and a screen main body 12 disposed via the Fresnel lens member 11 and an air layer 13 as in the embodiment shown in FIG. The screen main body 12 usually has at least a light diffusion layer, and can further include a lenticular lens.

  Such a transmissive screen 10 has a Fresnel lens member 11 on the light incident surface Sin side. The Fresnel lens member 11 uses the Fresnel lens surface Sf as the light exit surface So of the image light L, and the Fresnel lens surface Sf There is no particular limitation as long as the configuration is such that the opposite non-lens surface is arranged to be the light incident surface Sin on which the image light L is incident, and any conventionally known one can be appropriately employed.

In the present embodiment, the transmissive screen 10 has a plane in which the screen surface Ss, which is an area in which an image can be displayed, is a horizontally long rectangular shape having a large size in the horizontal direction of the screen relative to the vertical size of the screen. The screen surface Ss and the light incident surface Sin are parallel to each other. Therefore, the circumscribed rectangle Rc with respect to the screen surface Ss is the same as the outer shape of the screen surface Ss.
The arrangement position of the image source 20 with respect to the transmissive screen 10 is an extension of the normal line standing from the geometric center CtS of the screen surface Ss of the transmissive screen 10 toward the back side thereof. That is, the optical axis As of the image light L from the image source 20 is arranged so as to coincide with the normal line set at the center CtS of the screen surface Ss.

  However, in FIG. 1 of the present embodiment, the screen surface Ss has a considerably horizontal direction compared to the aspect ratio 9:16 for displaying a high-definition image from the viewpoint that the improvement effect on the brightness reduction according to the present invention appears more remarkably. It has a long rectangular shape. In the drawing, the aspect ratio is drawn at about 1: 4.5. Of course, each drawing is a conceptual diagram, and the aspect ratio may be exaggerated, and the same applies to this embodiment.

If the image source 20 is a conventional rear projection type display device, a general projector, particularly an ultra-short focus type projector capable of projecting from a close range, etc. can be adopted. In particular, as the image light L, one that can project polarized light whose polarization direction Dp is a specific direction corresponding to the positional relationship between the screen surface Ss of the transmission screen 10 and the image source 20 is used.
The image source 20 is not particularly limited as long as the image light L can be projected with polarized light whose polarization direction Dp is a specific direction. Therefore, the video generation method of the video source 20 is not particularly limited, for example, a DLP (registered trademark) method, an LCD method, an LCOS method, or the like. The video source 20 will be described in detail later.

Therefore, in the present invention, as the specific direction of the polarization direction Dp, the angle at which the image light L of the image source 20 is incident on the light incident surface Sin that is a non-lens surface of the Fresnel lens member 11 is defined as an incident angle θi. When the angle at which the incident angle θi is the largest in the plane of Sin is the maximum incident angle θmax, and the portion that gives this maximum incident angle θmax is the maximum incident angle point Pθmax,
At the maximum incident angle point Pθmax, the image light L is in a direction in which the P wave component is polarized light having more P wave components than the S wave component as a polarized light component defined by the incident surface Sir.

  In the present embodiment, the incident angle θi of the image light L with respect to the light incident surface Sin that is the back surface of the transmissive screen 10 is the maximum incident angle point Pθmax at the four corners that are both ends in the vertical direction of the screen. The angle becomes the largest and becomes the maximum incident angle θmax. Therefore, at this maximum incident angle point Pθmax, conventionally, the image light L from the image source 20 is an incident surface Sin of the transmission screen 10, more specifically, an incident lens surface of the Fresnel lens member 11. The ratio of the light that is refracted by the light surface Sin and is reflected and wasted without entering the inside of the Fresnel lens member 11 becomes the largest. That is, at the maximum incident angle point Pθmax that is the maximum incident angle θmax, the light reflectance is the highest and the capturing efficiency is the lowest.

  Therefore, in the present invention, in order to improve the reduction in capture efficiency in the peripheral portion of the screen surface Ss, a P wave component is used as a polarization component defined by the incident surface Sir of the image light L at the maximum incident angle point Pθmax. The polarized light is more than the S wave component. Specifically, in this embodiment, the setting of the polarization direction Dp in a specific direction is performed as follows.

<Setting of polarization direction Dp>
Hereinafter, how to set the polarization direction Dp of the image light L so that the P-wave component of the image light L is larger than the S-wave component at the maximum incident angle point Pθmax will be described.
The method of setting the polarization direction Dp described below discloses a preferred method as a method applicable in the approximate case. In the present invention, the setting of the polarization direction Dp is limited to the method described below. It is not something. In the present invention, it is essential that the P-wave component of the image light L is a polarized light having more than the S-wave component at the maximum incident angle point Pθmax.

In the present embodiment, the maximum incident angle point Pθmax is not one, but four. For this reason, if the most effective polarization direction Dp is adopted in any one of the four places, the same level of effect cannot be expected in all the remaining three places. However, in the present embodiment, the position of the video source 20 is directly behind the center CtS of the screen surface Ss in the front view of FIG.
For this reason, as shown in the front view of FIG. 1B, in the plane parallel to the screen surface Ss, the line segment x1 connecting the upper left maximum incidence angle point Pθmax from the image source 20 and the lower right from the image source 20 Are parallel to each other and line segments x2 connecting the maximum incident angle points Pθmax are overlapped with each other. Further, the same relationship applies to the line segment x3 and the line segment x4 connecting the remaining two maximum incident angle points Pθmax and the video source 20. Accordingly, the line segment x12 connecting the line segment x1 and the line segment x2 and the line segment x34 connecting the line segment x3 and the line segment x4 are two line segments x12 and x34 that intersect each other. Thus, there are two directions, a direction d12 and a direction d34, which intersect each other as the extending direction of the line segment x12 and the line segment x34.

Therefore, as shown in the front view of FIG. 1 (b), in the present embodiment, the angle α, which is the smaller one of the angles formed by the direction d12 and the direction d34 (referred to as a subordinate angle), is 2 A direction that is equally divided to α / 2 is adopted as a reference for the polarization direction Dp of the image light L. The direction of α / 2 is a direction parallel to the long side of the circumscribed rectangle Rc of the screen surface Ss. The polarization direction Dp is drawn parallel to the X-axis direction in FIG. In the process of adopting the reference, although it was considered in a plane parallel to the screen surface Ss, in other words, in a plane parallel to the XZ plane, the path of the image light L also has a component in the Y-axis direction perpendicular to the screen surface Ss. This also needs to be considered in setting the polarization direction Dp.
Therefore, in the present embodiment, the image light L from the image source 20 is set to the polarization direction Dp in the direction parallel to the XY plane parallel to the X-axis direction that is the horizontal direction of the screen and also parallel to the Y-axis direction. As polarized light. In other words, the polarization direction Dp is set so as to be parallel to a plane that includes the long side of the circumscribed rectangle Rc and is perpendicular to the light incident surface Sin.
By doing so, the image light L at the maximum incident angle point Pθmax cannot be completely made up of only the P wave component as the polarization component defined by the incident surface Sir, but the polarized light having the P wave component larger than the S wave component. It becomes possible to use light.
In FIG. 1, the polarization direction Dp of the image light L is representative of the image light L in the plane parallel to the XZ plane including the center CtS of the screen surface Ss in the plan view of FIG. It is drawn. Further, in the side view of FIG. 1C, the image light L in the plane including the center CtS of the screen surface Ss and parallel to the XY plane is representatively drawn.

  Thus, in the rear projection display device 100 of the present embodiment, the image light L at the peripheral portion that leads to a decrease in brightness at the peripheral portion of the screen surface Ss that becomes prominent when shortening and widening of the angle are advanced. It is possible to improve the reduction in the capture efficiency.

<Reflectance and polarization state of light at the interface between materials>
Next, the reason why the reflectance at the light incident surface Sin can be reduced and the transmittance can be increased will be described in detail.

FIGS. 2A and 2B are diagrams for explaining the behavior of the P wave and the S wave due to reflection and refraction of light at the boundary surface Sb of the substance, FIG. 2A is a cross-sectional view, and FIG. 2B is a perspective view. . In this figure, the boundary surface Sb of the substance is an XY plane including the origin, and when the incident light Li hits the boundary surface Sb, part of it is reflected and part of it is transmitted and refracted. Here, the incident light Li is non-polarized light. Non-polarized light can be handled as a combined wave of two polarized lights whose polarization directions are orthogonal to each other. The two polarized lights will be described as a P wave and an S wave, which are polarized lights defined by the incident surface Sir when the incident light Li strikes the boundary surface Sb at the incident angle θi. The P wave is polarized light whose polarization direction is parallel to the incident plane Sir, and the S wave is polarized light whose polarization direction is perpendicular to the incident plane Sir.
Since the incident surface Sir for the incident light Li is a surface perpendicular to the boundary surface Sb and includes the incident light Li in the surface, in FIG.

The reflected light Lr reflected by the incident light Li hitting the boundary surface Sb is light that contains more S waves whose polarization direction is perpendicular to the incident surface Sir than the P waves whose polarization direction is parallel to the incident surface Sir. It becomes. On the other hand, the light that is refracted and transmitted becomes the transmitted light Lt containing the P wave more than the S wave.
In the drawing, for the sake of simplicity, the reflected light Lr is drawn to include only the S wave, and the transmitted light Lt is illustrated to include only the P wave. When the minimum value of the reflectance Rp of the P wave becomes zero at a certain incident angle θi, the reflected light Lr becomes only the S wave and the transmitted light Lt becomes only the P wave at the incident angle θi ( (See FIG. 3 below). However, the incident angle θi of the image light L with respect to the light incident surface Sin on the back surface of the transmissive screen 10 differs depending on the location of the light incident surface Sin on which the image light L is incident (this location is referred to as an incident point). Since there is a certain range, the action of the P wave and the S wave is considered assuming the range of the incident angle θi according to the projection optical system.
From the above, in order to reduce the reflected light Lr and increase the transmitted light Lt, it is only necessary to reduce the S wave and increase the P wave as the polarization component of the incident light Li.

In FIG. 2, when the incident light Li is reflected and refracted by the boundary surface Sb of the substance, the polarization state of the reflected light Lr and the transmitted light Lt changes with respect to the incident light Li.
Next, with reference to FIG. 3, the ratio of the P wave and the S wave in the reflected light Lr changes depending on the incident angle θi when the incident light Li is reflected and refracted by the boundary surface Sb of the substance. To do.
FIG. 3 is a graph schematically showing an example of the difference between the P wave and the S wave in the reflectance of the incident light Li at the boundary surface Sb of the substance. The light reflectance varies depending on the incident angle θi of the light incident on the boundary surface Sb, and also varies depending on the polarization state of the light incident on the boundary surface Sb. In the graph of the figure, the P wave is indicated by Wp, and the S wave is indicated by Ws.
As shown in the figure, when the incident angle θi is not 0 ° but finite, the S-wave reflectance Rs is always larger than the P-wave reflectance Rp and is not the entire region of the incident angle θi. As the incident angle θi increases from 0 °, the difference increases up to a certain incident angle θi. The certain incident angle θi is an angle at which the reflectance Rp of the P wave becomes a minimum value. However, when the incident angle θi is vertical incidence of 0 °, the P-wave reflectivity Rp and the S reflectivity Rs are the same.

  When the incident light Li is non-polarized light, the incident light Li can be treated as a combined light in which the P wave and the S wave are halved. Therefore, the reflectance of the unpolarized light with respect to the incident light Li is the reflection of the P wave. It is an average value of the rate Rp and the reflectance Rs of the S wave.

  The difference between the P wave and the S wave of reflectivity is known as the Fresnel equation of [Equation 1] shown below. As in [Formula 1], the reflectance Rp of the P wave and the reflectance Ps of the S wave can be calculated from the incident angle θi and the refraction angle θr.

  The relationship between the incident angle θi and the refraction angle θr is known according to Snell's law of the following [Equation 2].

n1 × sin θi = n2 × sin θr [Formula 2]
(Where n1 is the refractive index of the substance on the incident light Li side, and n2 is the refractive index of the substance on the transmitted light Lt side.)

  Thus, utilizing the fact that the reflectance of the light incident obliquely on the light incident surface Sin on the back surface of the transmissive screen 10 is different between the P wave and the S wave, the reflected light particularly in a portion where the incident angle θi is larger. Can be more effectively reduced, and the capture efficiency of the image light L captured by the Fresnel lens member 11 can be increased. As a result, it is possible to improve the decrease in the brightness of the image light L particularly on the periphery of the screen surface Ss.

<Improvement result of capture efficiency and transmission efficiency Ref when the image light L is polarized light in a specific direction>
Next, since the capturing efficiency of the image light L on the light incident surface Sin of the Fresnel lens member 11 is improved, the image light L further captured by the Fresnel lens member 11 is transmitted through the Fresnel lens member 11 and the Fresnel lens surface. It will be described that the transmission efficiency Ref until light exits from the light exit surface So, which is Sf, can be improved.

In the present invention, “uptake efficiency” means the vibration direction of the electric field of the light. The capturing efficiency means the efficiency of capturing image light on the light incident surface, and has the same meaning as the transmittance of image light on the light incident surface.
In the present invention, “transmission efficiency Ref” refers to the transmittance Ri of the image light L on the light incident surface Sin of the Fresnel lens member 11 and the light output surface So of the Fresnel lens member 11 as shown in [Equation 3] below. This is multiplied by the transmittance Ro. Each transmittance can be calculated from the reflectance.
Ref = Ri × Ro [Formula 3]
The transmission efficiency Ref is also related to the transmittance Ro of the light exit surface So, and therefore the incident angle θi of the image light L with respect to the light exit surface So when passing through the light exit surface So is also related. The incident angle θi is related to the inclination angle (relative to the light incident surface Sin) of the portion of the Fresnel lens surface Sf that becomes the light exit surface So, and this is usually the light beam emitted from the Fresnel lens member 11 as a substantially parallel light beam. The setting of the direction of travel is also relevant. The traveling direction of the image light L is in accordance with the use direction in consideration of the traveling direction of the image light L finally emitted from the light exit surface So as the transmission screen 10. Here, a case where the traveling direction is a direction perpendicular to the screen surface Ss will be described.

  The graphs shown in FIGS. 4A, 4B, and 4C as FIG. 4 show that the transmission efficiency Ref of the image light L that passes through the Fresnel lens member 11 is not present when the incident light Li is only a P wave. In the case of polarized light, the result is a simulation of only the S wave. As for the incident light Li, FIG. 4-A shows the case of P-wave light as Example 1, FIG. 4-B shows the case of non-polarized wave as Comparative Example 1, and FIG. 4-C shows the S wave as Comparative Example 2. This is the case of light.

FIG. 5 is a diagram for explaining an optical system at the time of simulation of the graph of the transmission efficiency Ref of FIG. The Fresnel lens member 11 receives the image light L, which is divergent light from the image source 20, at the light incident surface Sin, and the parallel light flux in the direction perpendicular to the screen surface Ss from the light exit surface So that is the Fresnel lens surface Sf. It is assumed that the light path is deflected. The refractive index n of the Fresnel lens member 11 was 1.55.
The Fresnel lens member 11 that is a constituent element of the transmissive screen 10 is a circular Fresnel lens in which a plurality of unit Fresnel lenses are formed concentrically, and the Fresnel center CtF that is the optical center of the Fresnel lens is on the screen surface Ss. Located at the center CtS. The Fresnel lens member 11 and the image source, in which the optical axis As of the image light L from the image source 20 passes through the Fresnel center CtF, and the image source 20 is located on the center CtS of the screen surface Ss and the perpendicular from the Fresnel center CtF. 20 and the positional relationship.
The focal length F of the projection optical system of the image source 20 is the distance on the optical axis As from the image source 20 to the light incident surface Sin of the Fresnel lens member 11, and the image light L emitted from the image source 20 is the Fresnel lens. The distance from the Fresnel center CtF of the incident point incident on the light incident surface Sin which is the non-lens surface of the member 11 is the distance Df.

  Under the above conditions, the simulation of the incident light Li shown in FIG. 4 shows that in the case of the P-wave light in FIG. 4-A, the transmission distance increases as the distance from the Fresnel center CtF increases. The efficiency Ref decreases approximately, but is not so remarkable. The decrease in the transmission efficiency Ref is almost the same when the focal length F is 800 mm and 400 mm. However, when the focal length F is 200 mm, the distance Df from the Fresnel center CtF to the incident point is 600 mm. .82 can be stopped.

  On the other hand, in the case of the non-polarized light in FIG. 4-B, as the focal length F is shortened to 800 mm, 400 mm, and 200 mm, the reduction in the transmission efficiency Ref is larger than the P-wave light in FIG. 4-A. I understand that. For example, when the focal length F is 200 mm and the distance Df from the Fresnel center CtF to the incident point is 600 mm, the transmission efficiency Ref decreases to 0.58. On the other hand, in the case of the P-wave light in FIG. 4-A, the decrease in the transmission efficiency Ref is 0.82, which can be suppressed considerably compared to the case of non-polarized light.

  Incidentally, it is impossible to improve the transmission efficiency Ref uniformly in all regions of the screen surface Ss. By making the image light L a polarized light whose specific direction is the polarization direction Dp, the polarized light is a linearly polarized light, and therefore the direction in which the maximum effect is obtained in a plane parallel to the screen surface Ss. For orthogonal directions, it may be necessary to allow some improvement to be sacrificed. Hereinafter, a description will be given with reference to FIG. 6 and FIG.

FIG. 6 is a front view for explaining the behavior as the P wave Wp and the S wave Ws in the horizontal direction of the screen and the vertical direction of the screen with respect to the image light L having a specific polarization direction Dp when the screen surface Ss is horizontally long. . The positional relationship between the screen surface Ss of the transmissive screen 10 and the video source 20 is the same as in FIG.
The polarization direction Dp of the image light L is a direction parallel to the XY plane. Accordingly, since the incident points Px at the upper and lower centers at the left and right ends of the screen surface Ss are in a positional relationship parallel to the X-axis direction with respect to the video source 20, the incident surface Sir at the incident point Px is parallel to the XY plane. A plane parallel to the polarization direction Dp. Accordingly, the image light L that is polarized light having the polarization direction Dp is only the P wave Wp having the polarization direction in the direction parallel to the incident surface Sir at the incident point Px. For this reason, the transmission efficiency Ref is improved.

  On the other hand, since the positional relationship between the left and right incident points Pz at the upper and lower ends of the screen surface Ss and the image source 20 is parallel to the YZ plane, the incident surface Sir at the incident point Pz is on the YZ plane. The planes are parallel and do not include the polarization direction Dp of the image light L. Speaking of the image light L from the image source 20 toward the incident point Pz, the direction of the polarization direction Dp parallel to the XY plane is the X-axis direction in the XY plane and is a direction orthogonal to the incident surface Sir. Therefore, the image light L which is the polarized light having the polarization direction Dp becomes an S wave Ws having the direction perpendicular to the incident surface Sir as the polarization direction at the incident point Pz. For this reason, at the incident point Pz, the improvement of the transmission efficiency Ref cannot be expected.

  Note that, at the maximum incident angle point Pθmax that gives the maximum incident angle θmax, the image light L that has been polarized in the polarization direction Dp is not shown in the positional relationship between the horizontally long screen surface Ss and the image source 20 as shown in FIG. In the front view of FIG. 6, the incident surface Sir and the polarization direction Dp (the minor angle) form an angle smaller than 45 °, so that the polarization component of the P wave whose polarization direction is parallel to the incident surface Sir is It can be regarded as a synthesized wave to which a polarization component of S wave having a polarization direction in a direction perpendicular to the incident surface Sir is added. Accordingly, the transmission efficiency Ref can be expected to have a corresponding improvement effect that is close to that of the incident point Px but slightly decreases.

Then, it can be confirmed from the case of S-wave light in FIG.
That is, in the front view of FIG. 1B, the improvement effect for the brightness reduction near both ends in the horizontal direction of the screen is the case of the P wave light of FIG. 4-A with respect to the non-polarized light of FIG. 4-B. As can be seen from FIG. 4C, the degree of sacrifice for the improvement effect with respect to the decrease in brightness in the vicinity of both ends in the vertical direction of the screen can be understood in the case of S wave light in FIG. When the incident surface Sir is 45 ° with respect to the XY plane, this is also the case where the incident surface Sir is 45 ° with respect to the YZ plane. For the incident point, the P wave is a combined wave of 1/2 and the S wave is 1/2.

When compared with the focal length F of 200 mm and the distance Df600 from the Fresnel center CtF to the incident point, the transmission efficiency Ref decreases to 0.35 in the case of the S-wave light in FIG. . However, as shown in FIG. 1B, the shape of the screen surface Ss is horizontally long, and the aspect ratio is not 1: 1. Therefore, the position of the incident point for evaluating the transmission efficiency Ref by the S wave is not a point where the distance Df is 600 mm. If the aspect ratio of the screen surface Ss is 1: 4.5 drawn in FIG. 1B, the distance Df is 600 mm. The transmission efficiency Ref should be evaluated at a point of a distance Df that is 1 / 4.5th of the distance and 600 / 4.5 = 133 mm. Then, the transmission efficiency Ref at the distance Df 133 mm stops at about 0.80. This value can be said to be almost equivalent to 0.81 of the transmission efficiency Ref at a distance Df of 600 mm in the P wave.
That is, it is shown that the brightness reduction at both ends of the screen surface Ss in the left-right direction of the screen and the brightness reduction in the screen upper limit direction can be made the same level.
Of course, this result depends on the shape of the screen surface Ss, such as the aspect ratio of the screen surface Ss, and different results are obtained if the shape of the screen surface Ss is different. For example, as shown in FIG. 1B, if the aspect ratio is not 1: 4.5 but 9:16, the reduction in transmission efficiency Ref at the left and right central portions at both ends in the vertical direction of the screen is larger. Become.

As can be seen from the above description, in the present invention, at the maximum incident angle point Pθmax, the image light L may be composed only of P waves, and is not limited to being composed only of P waves. In short, it is sufficient that the P-wave component is more polarized light than the S-wave component. Rather, this is more realistic, and the present invention can be applied more widely.
Even if it can be established only at a certain maximum incident angle point Pθmax, if there are two or more maximum incident angle points Pθmax, the remaining maximum incident angles can be established. This is because the point Pθmax may not be established.

  In this way, it is possible to improve the reduction in the capture efficiency of the image light L in the peripheral portion that leads to a decrease in brightness in the peripheral portion of the screen surface Ss, which becomes noticeable when shortening the focus and widening the angle.

<Shape of screen surface Ss and circumscribed rectangle Rc>
In the present embodiment, the shape formed by the outer shape of the screen surface Ss is a rectangle, and the circumscribed rectangle Rc is the same as the screen surface Ss.
However, in the present invention, the outer shape of the screen surface Ss of the transmissive screen 10 is arbitrary. FIG. 7 is a front view showing a part of the shape example. In the figure, shapes other than a quadrangle are particularly illustrated. The screen surface Ss is assumed to be a plane parallel to the XZ plane.
In the same figure, an example of the position of the image source 20 with respect to the screen surface Ss having such a shape is also shown.

FIG. 7A and FIG. 7B show a case where a circumscribed rectangle Rc circumscribing the screen surface Ss of the transmissive screen 10 is provided. For such a screen surface Ss having a circumscribed rectangle Rc, the image light L has a polarization direction Dp whose direction of polarization Dp includes a long side of the circumscribed rectangle and is parallel to a plane perpendicular to the light incident surface Sin. It is preferable to use polarized light. Therefore, in FIG. 7A, since the long side of the circumscribed rectangle Rc is parallel to the X-axis direction, the polarization direction Dp in this case is parallel to the XY plane and is the left-right direction in the drawing.
On the other hand, in FIG. 7B, since the long side of the circumscribed rectangle Rc is parallel to the Z-axis direction, the polarization direction Dp in this case is parallel to the YZ plane and is vertical in the drawing.

  In FIG. 7C, since the screen surface Ss is circular, there is no circumscribed rectangle Rc circumscribing it, but there is a circumscribed rectangle. In such a case, the polarization direction Dp cannot be set generally. Rather, the positional relationship between the screen surface Ss and the video source 20 is important. In FIG. 7C, since the video source 20 is on the lower side of the screen with respect to the center CtS of the screen surface Ss, in the polarization direction Dp, the line segment connecting the center CtS and the video source 20 is parallel to the YZ plane. For this reason, the vertical direction is preferable in the drawing parallel to the YZ plane.

  The same thing as FIG.7 (c) may arise depending on the position with respect to the screen surface Ss of the video source 20 also in FIG.7 (a) and FIG.7 (b). For example, in FIG. 7A, the video source 20 is installed at a position deviating from the screen surface Ss in the horizontal direction of the drawing with respect to the screen surface Ss. However, such a positional relationship is not usually taken. Therefore, in the present invention, when a normal case is assumed, the image light L is polarized light whose polarization direction Dp includes a long side of the circumscribed rectangle Rc and is parallel to a plane perpendicular to the light incident surface Sin. Is preferred.

In the present invention, the position of the video source 20 with respect to the screen surface Ss is not limited to the positional relationship illustrated in FIG. However, when the screen surface Ss in FIG. 7C is circular, in the rear projection display device 100 of the present invention, the center CtS of the screen surface Ss is obtained in that the improvement effect according to the present invention can be enjoyed. The video source 20 is not installed. If the image source 20 is arranged in the direction on the extension line directly behind the center CtS, the incident angle θi is the same at the entire outer periphery of the circular screen surface Ss. As a result, the brightness is increased at the entire outer periphery. This is because the decrease is the same and polarized light having more P wave components than S wave components cannot be projected onto the incident surface Sir whose direction rotates 360 ° around the entire circumference.
However, depending on the application, the screen surface Ss has a circular shape. However, if the setting is made such that, for example, the left and right edges are bright and the vertical edges are dark without making the brightness decrease the same around the entire periphery. The improvement effect by this invention can be utilized effectively.

(Curved surface shape)
The circumscribed rectangle Rc when the transmissive screen 10 has a curved surface shape is that when the transmissive screen 10 is observed from the direction in which the screen surface Ss can be seen most greatly, the screen surface Ss seen from this direction is regarded as a plane. A rectangle circumscribing this virtual plane screen surface Ss can be defined as a circumscribed rectangle Rc.

<Setting of the polarization direction Dp according to the shape of the screen surface Ss and the positional relationship with the image source 20>
7A and 7B, there are a plurality of maximum incident angle points Pθmax, specifically two places. In the case of FIG. 1B, there are four maximum incident angle points Pθmax.
Thus, in the case where there are a plurality of maximum incident angle points Pθmax, the polarization direction Dp can be set by the method described in FIG.
7A and 7B where the maximum incident angle point Pθmax is two, and FIG. 1B where the maximum incident angle point Pθmax is four, along the outer periphery of the screen surface Ss. With respect to the adjacent maximum incident angle point Pθmax, a line segment connecting each of these two maximum incident angle points Pθmax and the image source 20 (more precisely, these maximum incident angle point Pθmax and line segment are screens forming a plane). A point parallel to the surface Ss and a line segment) is taken as an angle α, and a half angle α / 2 is generated, and is perpendicular to the light incident surface Sin. The polarization direction Dp can be set as a direction parallel to a flat surface.

(Curved surface shape)
When the transmissive screen 10 has a curved surface shape, the “plane parallel to the screen surface Ss” in which the maximum incident angle point Pθmax and the line segment connecting the maximum incident angle point Pθmax and the image source 20 are projected in parallel is originally the screen surface Ss. Does not exist because is a curved surface rather than a flat surface. Therefore, in such a case, the same way as described in the circumscribed rectangle Rc can be taken. That is, when the transmissive screen 10 is observed as a “plane parallel to the screen surface Ss” from the direction in which the screen surface Ss can be seen largest, the screen surface Ss seen from this direction is regarded as a plane, and this virtual plane Are treated as planes parallel to the screen surface Ss. The light incident surface Sin is treated as a surface parallel to the virtual plane screen surface Ss.

<Polarization direction Dp depending on the positional relationship between the screen surface Ss and the image source 20>
FIG. 8 shows a setting example of the polarization direction Dp of the image light L in accordance with the position of the image source 20 in the case of the horizontally long screen surface Ss, FIG. 8A is a side view, and FIG. FIG.
In the embodiment shown in FIG. 1, the image source 20 is on an extension line directly behind the center CtS of the screen surface Ss in order to simplify the description.
However, the position of the video source 20 with respect to the screen surface Ss may be a position deviated from the screen surface Ss as illustrated in FIG.
The setting of the polarization direction Dp varies depending on the positional relationship between the screen surface Ss and the video source 20 even when the maximum incident angle point Pθmax is the same. Therefore, generally, in the case of a horizontally long screen surface Ss, the polarization direction Dp is not limited to a direction parallel to a surface that includes the long side of the circumscribed rectangle Rc of the screen surface Ss and is perpendicular to the light incident surface Sin. .

  FIG. 8 shows a comparison when the video source 20 is at the position P1 and the position P2. The maximum incident angle point Pθmax is the same regardless of whether the video source 20 is at the position P1 or the position P2. However, as shown in the front view of FIG. 8B, the polarization direction Dp of the image light L is set in a direction parallel to the YX plane at the position P1, as described in FIG.

  On the other hand, at the position P2, the polarization direction Dp is set in a direction parallel to the YZ plane. This is because the image light L can be regarded as parallel light parallel to the YZ plane when the image source 20 is moved to an infinitely far position below the position P2 in the drawing, and the incident surface Sir is the YZ plane. It can be easily understood from being parallel to

When the angle formed by the two line segments at the intersection is captured as the minor angle, the minor angle distinguished by the superiority of the angle at the intersection (large or small relationship) can be defined when it is less than 90 °. Is expanded to 90 °), the maximum angle formed by the line segments connecting the two maximum incident angle points Pθmax and the image source 20 is 90 °, and the position P3 corresponds to this.
The position P3 is a turning point where the setting of the polarization direction Dp changes. Therefore, as described above, the polarization direction Dp with respect to the position P1 where the image source 20 is closer to the screen surface Ss than the position P3 and the polarization direction Dp with respect to the position P2 where the image source 20 is further from the screen surface Ss than the position P3. , (In a plane parallel to the screen surface Ss).
At the turning point P3, the polarization direction Dp can be either a direction parallel to the YX plane or a direction parallel to the YZ plane orthogonal to the YX plane as long as it is parallel to the plane perpendicular to the light incident surface Sin. is there. It may be determined in consideration of other factors, such as which part of the screen surface Ss is to be emphasized.

<Maximum incident angle point Pθmax and curved transmission screen 10>
FIG. 9 shows an example in which the maximum incident angle θmax giving the maximum incident angle θmax and the maximum optical path length DLmax from the image source 20 to the maximum incident angle point Pθmax up to the maximum incident angle point Pθmax are the same, but the maximum incident angle θmax is different. It is a top view which illustrates the case where the transmissive screen 10 has a curved surface shape. FIG. 9A shows the transmissive screen 10 having the curved surface shape, and FIG. 9B shows the transmissive screen 10 having the flat shape as a comparison.
Similarly, in the embodiment shown in FIG. 1, all of the plurality of maximum incident angle points Pθmax are incident points that are also the maximum optical path length DLmax.
However, when the screen surface Ss is curved and the light incident surface Sin of the Fresnel lens member 11 is curved, the maximum incident angle point Pθmax is not always the maximum optical path length DLmax.
For this reason, a method of setting the polarization direction Dp according to the positional relationship between the image source 20 and the incident point having the maximum optical path length DLmax related to the darkened outer peripheral portion of the screen surface Ss is also conceivable. However, in the present invention, paying attention to the maximum incident angle point Pθmax that gives the maximum incident angle θmax that is directly related to the capture efficiency, the polarization direction depends on the positional relationship between the maximum incident angle point Pθmax and the image source 20. By setting Dp, it is possible to improve the capture efficiency.

  Hereinafter, each component will be described in detail.

<< Transmissive screen 10 >>
The transmissive screen 10 has a Fresnel lens member 11 on the light incident surface Sin side. The Fresnel lens member 11 uses the Fresnel lens surface Sf as the light exit surface So of the image light L and is opposite to the Fresnel lens surface Sf. There are no particular limitations as long as the non-lens surface on the side is arranged in a direction that makes the incident light surface Sin on which the image light L is incident, and conventionally known ones can be appropriately employed.

<Fresnel lens member 11>
As the Fresnel lens member 11, a conventionally known one can be appropriately employed. However, the orientation of the arrangement is the direction in which the Fresnel lens surface Sf is the light exit surface So of the image light L on the viewer V side, as described above.
The Fresnel lens member 11 receives the image light L projected from the image source 20 as a divergent light beam,
The transmission screen 10 has a function of deflecting the traveling direction of light so as to be a substantially parallel light beam toward the viewer V side. The image light L is converted into, for example, a light beam substantially perpendicular to the screen surface Ss by the Fresnel lens member 11, so that the luminance uniformity of the image on the screen surface Ss is improved. In particular, in the rear projection display device 100 that is suitable for shortening the focus and widening the angle as in the present invention, an optical element having such a function is essential.

In the present invention, the direction in which the image light L is deflected by the Fresnel lens member 11 depends on the position assumed by the observer V with respect to the screen surface Ss corresponding to the use of a vehicle such as an automobile or an amusement device. It may not be the front direction of Ss.
The Fresnel lens member 11 can be manufactured by known materials and forming methods such as resin molding such as acrylic resin and polycarbonate resin.

In the present invention, the Fresnel lens member 11 has columnar unit lens elements according to the positional relationship between the transmissive screen 10 and the image source 20 and the positional relationship between the screen surface Ss and the assumed viewer V. Circular Fresnel lenses arranged concentrically or arcuately or linear Fresnel lenses in which unit lens elements extending in a straight line are arranged in parallel may be used.
In the present invention, in the case of a circular Fresnel lens, the Fresnel center CtF depends on the positional relationship between the transmission screen 10 and the image source 20 and the positional relationship between the screen surface Ss and the assumed viewer V. It may be outside the area of the surface Ss.

In the present invention, the Fresnel lens member 11 may have a curved shape corresponding to the curved screen surface Ss in addition to the planar shape corresponding to the flat screen surface Ss.
The “curved surface” may be a combined curved surface of “three-dimensional curved surface” and “two-dimensional curved surface”. The “curved surface” may be on either the observer V side or the image source 20 side on the convex side. With the curved surface shape, the “curved surface” may be in the whole area or part of the screen surface Ss. That is, the curved surface shape is a shape having “curved surface” at least in part.

<Screen body 12>
The screen main body 12 usually has at least a light diffusing layer and can be a laminate including a lenticular lens, a light control layer, and the like. These may be appropriately selected from known materials and forming methods.

For example, the light diffusion layer is a layer having a function of normally diffusing the image light L incident from the light incident surface side and emitting the image light L from the light output surface side. As a result, the viewing angle of the image displayed on the screen surface Ss can be widened. The light diffusion layer is composed of, for example, a base material made of a transparent resin and a diffusion component dispersed in the base material.
The lenticular lens has a function of controlling the viewing angle by spreading the image light L in the horizontal direction and the vertical direction.
The light beam control layer can control the optical path of the image light L and absorb external light. As a result, the light control layer can improve a decrease in bright room contrast due to external light. The light control layer may have a structure in which light transmitting portions and light absorbing portions are alternately arranged in a certain direction, and may have a fine louver structure.
The relative positional relationship between the screen main body 12 and the Fresnel lens member 11 can be maintained by a clip, a frame, or the like.

<< Image Source 20 >>
If the image source 20 is a conventional rear projection type display device, a general projector, particularly an ultra-short focus type projector capable of projecting from a close range can be adopted. However, in the present invention, In particular, as the image light L, one that can project polarized light having a polarization direction Dp in a specific direction corresponding to the shape of the transmissive screen 10 and the positional relationship with the transmissive screen 10 is used.
The video source 20 is not particularly limited as long as the video light L can be projected with polarized light whose polarization direction Dp is a specific direction.

Therefore, for example, as a video generation method of the video source 20,
DLP (Digital Light Processing; registered trademark) method (also called DMD (Digital Micromirror Device; registered trademark) method) using a plurality of mirrors by MEMS (Micro Electro Mechanical Systems),
LCD (Liquid Crystal Display) method using a transmissive liquid crystal panel,
There is no particular limitation such as an LCOS (Liquid Crystal on Silicon) method using a reflective liquid crystal panel.
In addition, in the case of color display, in addition to a single plate method using one video generation element, a three-plate method using a total of three video generation elements independent for each of the three primary colors red, green, and blue, etc. There is no particular limitation.

  In order to project the image light L as polarized light having the polarization direction Dp as a specific direction, for example, when the image generation method is the image source 20 that does not use polarization in principle as in the DLP method, the image light L is As it is, it becomes non-polarized light. For this reason, a polarizer is disposed between the image generation element and the transmission screen 10 until the image light L from the image generation element is emitted by the projection lens and reaches the transmission screen 10. By adjusting the direction of the transmission axis of this polarizer, the polarization direction Dp in a specific direction can be obtained.

On the other hand, when the image generation method is the image source 20 that uses polarization in principle as in the LCD method or the LCOS method, the image light L is originally polarized light. In other words, the light from the liquid crystal panel of the image generating element becomes the image light L containing the target image information in a state where it can be seen for the first time by passing through the polarizer. However, the image light L is only polarized light as a result of using the liquid crystal panel, and the polarization direction thereof depends on the maximum incident angle point Pθmax that gives the maximum incident angle θmax on the transmission screen 10. The polarization direction Dp in a specific direction is not intentionally set.
Therefore, in the image source 20 using the image generation element using such polarized light, a polarizer installed in a light path from the image generation element and a polarizer for polarizing light incident on the image generation element. For both, a specific polarization direction Dp can be obtained by adjusting the direction of their transmission axes.

  In the present invention, as illustrated in FIGS. 7 and 8, the position of the image source 20 with respect to the screen surface Ss is in a plane parallel to the screen surface Ss in addition to the embodiment shown in FIG. 1. May be outside the area of the screen surface Ss. By adjusting the position of the video source 20, it is possible to respond to the shape, installation space, and the like of the rear projection type display device 100.

<Other components>
In the present invention, the rear projection display device 100 can employ other components in the conventionally known rear projection display device as appropriate in addition to the above-described components. For example, the housing described below.

<Case 30>
In the present invention, as shown in FIG. 10, the rear projection display device 100 has a casing 30 that fixes them in a predetermined positional relationship in addition to the transmissive screen 10 and the video source 20. Also good. By fixing the transmissive screen 10 and the video source 20 to a predetermined positional relationship, it is possible to suppress a decrease in video quality due to a shift in the positional relationship. In addition, by providing the housing 30, it is possible to suppress the image quality from being deteriorated due to dust or the like adhering to the light incident surface Sin of the transmissive screen 10.

DESCRIPTION OF SYMBOLS 10 Transmission type screen 11 Fresnel lens member 12 Screen main body part 13 Air layer 20 Image source 30 Case 100 Rear projection type display device As (image light) optical axis CtF Fresnel center CtS Screen surface center d12 Direction of extension of line segment x12 d34 The direction in which the line segment x34 extends Df (from the center of the Fresnel to the incident point) DLmax Maximum optical path length Dp (image light) polarization direction F Focal length (distance on the optical axis from the image source to the light incident surface)
L image light Li incident light Lr reflected light Lt transmitted light (refracted light)
P1, P2, P3 Image source position Px, Pz Incident point Pθmax Maximum incident angle point Rc circumscribed rectangle Sb Boundary surface Sf Fresnel lens surface Sin (image light) incident surface Sir incident surface So (image light) exit surface Ss screen surface V observer Wp P wave Ws S wave x1, x2, x3, x4 line segment α minor angle θi incident angle θr refraction angle θmax maximum incident angle

Claims (2)

A rear projection display device comprising a transmissive screen and a video source for projecting video light on the back of the transmissive screen,
The transmission screen has a Fresnel lens member on the light incident surface side thereof,
The Fresnel lens member is disposed in an orientation in which the Fresnel lens surface is the light exit surface of the image light, and the non-lens surface opposite to the Fresnel lens surface is the light incident surface on which the image light is incident,
An incident angle θi is an angle at which the image light is incident on the light incident surface of the Fresnel lens member, and an angle of a portion where the incident angle θi is the largest in the surface of the light incident surface is a maximum incident angle θmax. When the portion that gives the maximum incident angle θmax is the maximum incident angle point Pθmax,
At the maximum incident angle point Pθmax,
The image light is a polarized light having a P wave component larger than an S wave component as a polarized light component defined by the incident surface Sir.
Rear projection display device. The transmission screen has a circumscribed rectangle circumscribing the screen surface,
The image light has a polarization direction parallel to a plane that includes a long side of the circumscribed rectangle and is perpendicular to the light incident surface.
The rear projection type display device according to claim 1.