Patent Publication Number: US-2011069242-A1

Title: Projection desplay apparatus

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuing application according to 37 C.F.R. 1.53(b) and (j) of the international application number PCT/JP2009/056077 filed on Mar. 26, 2009, which in turn claims the benefit of Japanese patent application number 2008-088347, filed on Mar. 28, 2008 and Japanese application number 2009-068944, filed on Mar. 19, 2009, the disclosures of which applications are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a projection display apparatus having a projection optical unit for projecting image light on a projection plane. 
     BACKGROUND ART 
     Conventionally, there has been known a projection display apparatus having: a light valve for modulating light emitted from a light source; and a projection lens for projecting the light emitted from the light valve on a projection plane (screen). 
     Hence, a long distance between the projection lens and the screen needs to be assured for displaying a large-size image on the screen. In contrast to this, a projection display system has been proposed which aims to shorten a distance between the projection display apparatus and the screen by using a reflection mirror for reflecting the light emitted from the projection lens, toward the screen side (for example, Japanese Patent Application Publication No. 2006-235516). 
     With the aim of shortening a distance between the projection display apparatus and the screen, the projection display apparatus becomes in proximity to the screen, and the projection display apparatus becomes within a user&#39;s field of view. Thus, there is a need to perform vertically or laterally oblique projection of the screen. For example, in the above-described projection display system, a projection distance is shortened and oblique projection is performed by shifting a positional relationship between a light valve and a projection optical unit in a vertical direction and employing a concave mirror as a reflection mirror. 
     Incidentally, as a method of setting up a projection display apparatus which aims to shorten a projection distance, there is considered a new setup method, such as a method of setting up a projection display apparatus on a wall surface or the like, since the device is capable of projecting an image even in a small space, or alternatively, a method of setting up a projection display apparatus on a ceiling or a floor surface. On the other hand, a screen provided on a projection plane is not considered so much. 
     DISCLOSURE OF THE INVENTION 
     A first aspect of a projection display apparatus, includes: an image light generating unit (image light generating unit  200 ) configured to generate image light; and a projection optical unit (projection optical unit  300 ) configured to project the image light on a projection plane (projection plane  210 ). The projection optical unit has a reflection mirror (reflection mirror  320 ) configured to reflect the image light emitted from the image light generating unit. The projection display apparatus further includes a screen (screen  220 ) provided on the projection plane. The screen is switchably configured as to whether to diffuse the image light reflected by the reflection mirror or to transmit the image light reflected by the reflection mirror. 
     According to the above aspect, the screen is switchably configured as to whether or not the image light reflected by the reflection mirror forms an image. Therefore, the display/non-display of an image can be readily switched. 
     In the first aspect, the screen comprised of a dispersive liquid crystal. The dispersive liquid crystal adjusts a diffusion ratio of the image light reflected by the reflection mirror, in accordance with a voltage applied to the dispersive liquid crystal. 
     In the first aspect, the screen has an image forming region (image forming region  220   a ) in which an image is comprised of the image light, and a non-image forming region (non-image forming region  220   b ) in which an image is not comprised of the image light. The screen is configured to be slidable on the projection plane. The non-image forming region is comprised of a light-transmissive member and is adjacent to the image forming region in a sliding direction of the screen. 
     In the first aspect, the projection display apparatus further includes a protection cover (protection cover  400  provided on an optical path of the image light reflected by the reflection mirror. The protection cover has a transmissive region (transmissive region  410 ) for transmitting the image light. The reflection mirror focuses the image light emitted from the image light generating unit, between the reflection mirror and the projection plane. The transmissive region is disposed in proximity to a position at which the image light is focused by the reflection mirror. 
     In the first aspect, the protection cover has an opening communicating from a side of the reflection mirror to a side of the projection plane. The transmissive region is the opening. 
     In the first aspect, at least part of the protection cover is comprised of a light-transmissive member. The transmissive region is comprised of the light-transmissive member. 
     In the first aspect, the screen includes a first screen and a second screen. A respective one of the first screen and the second screen is switchably configured as to whether to diffuse the image light reflected by the reflection mirror or to transmit the image light reflected by the reflection mirror. 
     In the first aspect, the screen is comprised of a plurality of regions. The screen is switchably configured, in a respective one of the plurality of regions as to whether to diffuse the image light reflected by the reflection mirror or to transmit the image light reflected by the reflection mirror. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a projection display apparatus  100  according to a first embodiment. 
         FIG. 2  is a view showing a configuration of an image light generating unit  200  according to the first embodiment. 
         FIG. 3  is a view showing a configuration of a screen  220  according to the first embodiment. 
         FIG. 4  is a view showing the configuration of the screen  220  according to the first embodiment. 
         FIG. 5  is a view showing a display example according to the first embodiment. 
         FIG. 6  is a view showing the display example according to the first embodiment. 
         FIG. 7  is a view showing the display example according to the first embodiment. 
         FIG. 8  is a view showing the display example according to the first embodiment. 
         FIG. 9  is a view showing a configuration of a screen  220  according to a second embodiment. 
         FIG. 10  is a view showing sliding of the screen  220  according to the second embodiment. 
         FIG. 11  is a view showing sliding of the screen  220  according to the second embodiment. 
         FIG. 12(A)  and  FIG. 12(B)  are views showing examples of application of a projection display apparatus  100  according to a third embodiment. 
         FIG. 13(A)  to  FIG. 13(C)  are views showing examples of application of the projection display apparatus  100  according to the third embodiment. 
         FIG. 14  is a view showing a screen  500  according to a fourth embodiment. 
         FIG. 15  is a view showing the screen  500  according to the fourth embodiment. 
         FIG. 16  is a view showing the screen  500  according to the fourth embodiment. 
         FIG. 17  is a view showing the screen  500  according to the fourth embodiment. 
         FIG. 18  is a further view showing the screen  500  according to the fourth embodiment. 
         FIG. 19  is a view showing a display example according to the fourth embodiment. 
         FIG. 20  is a view showing the display example according to the fourth embodiment. 
         FIG. 21  is a view showing the display example according to the fourth embodiment. 
         FIG. 22  is a view showing the display example according to the fourth embodiment. 
         FIG. 23  is a view showing the display example according to the fourth embodiment. 
         FIG. 24  is a view showing the display example according to the fourth embodiment. 
         FIG. 25  is a view showing a screen  600  according to a fifth embodiment. 
         FIG. 26  is a view showing the screen  600  according to a sixth embodiment. 
         FIG. 27  is a view showing a display example according to the sixth embodiment. 
         FIG. 28  is a view showing the display example according to the sixth embodiment. 
         FIG. 29  is a view showing the display example according to the sixth embodiment. 
         FIG. 30  is a view showing the display example according to the sixth embodiment. 
         FIG. 31  is a view showing the display example according to the sixth embodiment. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, a projection display apparatus according to embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar reference signs are attached to the same or similar units and portions. 
     It should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. Therefore, specific dimensions and the like should be determined in consideration of the following description. Moreover, as a matter of course, the drawings also include portions having different dimensional relationships and ratios from each other. 
     First Embodiment 
     Configuration of Projection Display Apparatus 
     Hereinafter, a configuration of a projection display apparatus according to a first embodiment will be described with reference to the drawings.  FIG. 1  is a view showing a configuration of a projection display apparatus  100  according to the first embodiment. 
     As shown in  FIG. 1 , the projection display apparatus  100  has an image light generating unit  200 , a projection optical unit  300 , a protection cover  400 , and a screen  220 . 
     The image light generating unit  200  generates image light. Specifically, the image light generating unit  200  has at least a display element  40  for emitting image light. The display element  40  is provided at a position which is shifted relative to an optical axis L of the projection optical unit  300 . The display element  40  is a reflective liquid crystal panel, a transmissive liquid crystal panel, a DMD (Digital Micromirror Device) or the like, for example. A detailed description of the image light generating unit  200  will be given later (see  FIG. 2 ). 
     The projection optical unit  300  projects the image light emitted from the image light generating unit  200 . Here, the projection optical unit  300  projects the image light on a projection plane  210  (screen  220 ). Specifically, the projection optical unit  300  has a projection lens  310  and a reflection mirror  320 . 
     The projection lens  310  emits the image light emitted from the image light generating unit  200 , to the side of the reflection mirror  320 . 
     The reflection mirror  320  reflects the image light emitted from the projection lens  310 . The reflection mirror  320  widely angles the image light after focusing the image light. The reflection mirror  320  is a non-spherical mirror having a concave face on the side of the image light generating unit  200 , for example. 
     The protection cover  400  is a cover for protecting the reflection mirror  320 . The protection cover  400  is provided on an optical path of the image light reflected by the reflection mirror  320 . The protection cover  400  has a transmissive region  410  for transmitting image light. That is, the transmissive region  410  transmits the image light reflected by the reflection mirror  320  to the side of the screen  220 . 
     In this manner, the projection optical unit  200  projects the image light transmitting the transmissive region  410  on the screen  220  provided on the projection plane  210 . 
     The screen  220  is provided on the projection plane  210  on which image light is to be projected. The screen  220  is switchably configured as to whether to diffuse the image light reflected by the reflection mirror  320  or transmit the image light reflected by the reflection mirror  320 . In other words, the screen  220  is switchably configured as to whether or not an image is formed by the image light reflected by the reflection mirror  320 . The screen  220  is a screen comprised of a dispersive liquid crystal, for example. The dispersive liquid crystal, as described later, adjusts a diffusion ratio of the image light reflected by the reflection mirror  320 , in accordance with a voltage to be applied to the dispersive liquid crystal (see  FIG. 3  and  FIG. 4 ). 
     It is preferable that the screen  220  is transparent. In addition, the screen  220  may be a reflective screen or may be a transmissive screen. 
     (Configuration of Image Light Generating Unit) 
     Hereinafter, a configuration of an image light generating unit according to the first embodiment will be described with reference to the drawings.  FIG. 2  is a view mainly showing an image light generating unit  200  according to the first embodiment. The image light generating unit  200  has a power circuit (not shown) and an image signal processing circuit (not shown) or the like in addition to the constituent elements shown in  FIG. 2 . Here is illustrated a case in which a display element  40  is a transmissive liquid crystal panel. 
     The image light generating unit  200  has a light source  10 , a fly-eye lens unit  20 , a Polarizing Beam Splitter (PBS) array  30 , a plurality of liquid crystal panels  40  (liquid crystal panel  40 R, liquid crystal panel  40 G, liquid crystal panel  40 B), and a crass-dichroic prism  50 . 
     The light source  10  is a UHP lamp or the like comprised of a burner and a reflector. The light emitted from the light source  10  includes red component light, green component light, and blue component light. 
     The fly-eye lens unit  20  uniformizes the light emitted from the light source  10 . Specifically, the fly-eye lens unit  20  is comprised of a fly-eye lens  20   a  and a fly-eye lens  20   b.    
     The fly-eye lens  20   a  and the fly-eye lens  20   b  are comprised of a plurality of micro-lenses, respectively. Each micro-lens focuses the light emitted from the light source  10  so that the light emitted from the light source is irradiated to all over the liquid crystal panel  40 . 
     The PBS array  30  coordinates a polarization state of the light emitted from the fly-eye lens unit  20 . In the first embodiment, the PBS array  30  coordinates the light emitted from the fly-eye lens  20  with P-polarization. 
     The liquid crystal panel  40 R modulates red component light by rotating the polarization direction of the red component light. An incidence-side polarization plate  41 R, for transmitting the light having one polarization direction (for example, P-polarization) and interrupting the light having the other polarization direction (for example, S-polarization), is provided on the light-incidence plane side of the liquid crystal panel  40 R. An emission-side polarization plate  42 R, for interrupting the light having one polarization direction (for example, P-polarization) and transmitting the light having the other polarization direction (for example, S-polarization), is provided on the light-emission plane side of the liquid crystal panel  40 R. 
     Similarly, the liquid crystal panel  40 G and the liquid crystal panel  40 B modulate green component light and blue component light by rotating the polarization direction of the green component light and the blue component light, respectively. The incidence-side polarization plate  41 G is provided on the light-incidence plate side of the liquid crystal panel  400  and an emission-side polarization plate  42 G is provided on the light-emission plane side of the liquid crystal panel  40 G. An incidence-side polarization plate  41 B is provided on the light-incidence plane side of the liquid crystal panel  40 B and an emission-side polarization plate  42 B is provided on the light-emission plane side of the liquid crystal panel  40 B. 
     The cross-dichroic prism  50  combines the light emitted from the liquid crystal panel  40 R, the liquid crystal panel  40 G, and the liquid crystal panel  40 B with each other. The cross-dichroic prism  50  emits the combined light to the side of the projection lens  310 . 
     In addition, the image light generating unit  200  has: a mirror group (dichroic mirror  111 , dichroic mirror  112 , reflection mirror  121  to reflection mirror  123 ); and a lens group (condenser lens  131 , condenser lens  140 R, condenser lens  1400 , condenser lens  140 B, relay lens  151  and relay lens  152 ). 
     The dichroic mirror  111  transmits red component light and green component light of the light emitted from the PBS array  30 . The dichroic mirror  111  reflects blue component light of the light emitted from the PBS array  30 . 
     The dichroic mirror  112  transmits red component light of the light transmitting the dichroic mirror  111 . The dichroic mirror  112  reflects green component light of the light transmitting the dichroic mirror  111 . 
     The reflection mirror  112  reflects blue component light and guides the reflected light to the side of the liquid crystal panel  4013 . The reflection mirror  122  and the reflection mirror  123  reflect red component light and guide the reflected light to the side of the liquid crystal panel  40 R. 
     The condenser lens  131  is a lens for focusing incandescent light emitted from the light source  10 . 
     The condenser lens  140 R substantially collimates red component light so that the liquid crystal panel  40 R is irradiated with the red component light. The condenser lens  140 G substantially collimates green component light so that the liquid crystal panel  40 G is irradiated with the green component light. The condenser lens  140 B substantially collimates blue component light so that the liquid crystal panel  40 B is irradiated with the blue component light. 
     The relay lens  151  and the relay lens  152  substantially form an image with the red component light on the liquid crystal panel  40 R while restraining expansion of the red component light. 
     (Configuration of Dispersive Liquid Crystal) 
     Hereinafter, a dispersive liquid crystal configuring the screen  220 , according to the first embodiment, will be described with reference to the drawings.  FIG. 3  and  FIG. 4  are views showing the dispersive liquid crystal configuring the screen  220 , according to the first embodiment. Here is illustrated a case in which the screen  220  is a transmissive screen. 
     As shown in  FIG. 3  and  FIG. 4 , the dispersive liquid crystal configuring the screen  220  has a transparent conductive film  221  (transparent conductive film  221   a  and transparent conductive film  221   b ); a liquid crystal capsule  222  having a plurality of liquid crystal elements  222   a ; and a polymer  223 . 
     The transparent conductive film  221  is a transparent film having conductivity. Indium Tin Oxide (ITO) can be employed as the transparent conductive film  221 , for example. 
     The liquid crystal capsule  222  is comprised of the plurality of liquid crystal elements  222   a . As the liquid crystal element  222   a , for example, a nematic liquid crystal or a cholesteric liquid crystal can be employed. The liquid crystal capsule  222  disperses in the polymer  223 . 
     The polymer  223  is comprised of a high polymer. As the high polymer, polymethyl methacrylate (PMMA) can be employed, for example. The polymer  223  is filled between the transparent conductive film  221   a  and the transparent conductive film  221   b.    
     Here, as shown in  FIG. 3 , in a case where a voltage is applied to the transparent conductive film  221 , the liquid crystal element  222   a  included in the liquid crystal capsule  222  is uniform in its orientation direction. Therefore, the light with which the screen  220  is irradiated transmits a dispersive liquid crystal. That is, the screen  220  disallows an image to be comprised of the image light reflected by the reflection mirror  320 . 
     On the other hand, as shown in  FIG. 4 , in a case where a voltage is not applied to the transparent conductive film  221 , the liquid crystal element  222   a  included in the liquid crystal capsule  222  is not uniform in its orientation direction. Therefore, the light with which the screen  220  is irradiated diffuses. That is, the screen  220  allows an image to be comprised of the image light reflected by the reflection mirror  320 . 
     It is preferable that a ratio (transmission/diffusion ratio) of a dispersive liquid crystal diffusing image light is adjustable in accordance with a voltage applied to the transparent conductive film  221 . In addition, in a case in which the screen  220  is a reflective screen as well, it is also preferable that a ratio (reflection/diffusion ratio) of the dispersive liquid crystal diffusing image light is adjustable in accordance with the voltage applied to the transparent conductive film  221 . 
     Here, from the viewpoint of energy saving or the like, it is preferable that the screen  220  is configured in a state in which image light is diffused in a case where no voltage is applied. In this manner, in a case where the projection display apparatus  100  is not powered on, a voltage does not need to be applied to the screen  220 , disabling an object or the like provided on the rear side of the screen  220  to be seen by default. 
     In addition, from the viewpoint of energy saving or the like, in a case where the screen  220  is controlled in a state in which image light is transmitted, it is preferable that the projection display apparatus  100  is powered off. In a case where the screen  220  is controlled in a state in which image light is transmitted, there is no need for the image light from the projection display apparatus  100 , thus enabling energy saving to be achieved by turning off the power of the projection display apparatus  100 . 
     (Image Display Example(s)) 
     Hereinafter, image display examples according to the first embodiment will be described with reference to the drawings.  FIG. 5  to  FIG. 8  are views showing image display examples according to the first embodiment. Hereinafter is illustrated a case in which the screen  220  is a transparent. 
     First, a case in which the screen  220  is provided on a wall surface will be described with reference to  FIG. 5  and  FIG. 6 .  FIG. 5  and  FIG. 6  each illustrate a case in which the screen  220  is a reflective screen. 
     As shown in  FIG. 5 , the projection display apparatus  100  is embedded in a floor and the screen  220  is provided on a transparent wall surface (projection plane  210 ). On the other hand, as shown in  FIG. 6 , the projection display apparatus  100  is embedded in ceiling and the screen  220  is provided on a transparent wall surface (projection plane  210 ). In these cases, the projection display apparatus  100  projects image light on the screen  220  provided on the transparent wall surface (projection plane  210 ). 
     As described above, in a case where no voltage is applied to the screen  220 , the image light emitted from the projection display apparatus  100  forms an image on the screen  220 . Therefore, a user can see the image formed on the screen  220 . 
     On the other hand, in a case where a voltage is applied to the screen  220 , the image light emitted from the projection display apparatus  100  does not form an image on the screen  220 . Here, in a case where the voltage is applied to the screen  220 , it is preferable that the projection display apparatus  100  provides black display. That is, no image light is emitted from the projection display apparatus  100 . As described above, since the screen  220  is transparent, a user can see an opposite scene of the screen  220  from the user&#39;s field of view. 
     In “black display”, for example, a polarization plate provided at the light incidence-side or light emission-side of the display element  40  interrupts the light emitted from a light source  10 . That is, it should be kept in mind that the light source  10  does not need to migrate to a non-illuminative state. In the “black display”, the light source  10  may migrate to the non-illuminative state”. 
     As the cases shown in  FIG. 5  and  FIG. 6 , it is considered that the screen  200  is provided at a display window. In this manner, the contents of the display window and an image can be switched from each other as an object to be shown to a user. In addition, it is considered that the screen  220  is provided at a window. In this manner, the scene outside of the window and an image can be switched from each other as an object to be shown to a user. 
     Next, a case in which the screen  220  is provided on a floor surface will be described with reference to  FIG. 7  and  FIG. 8 .  FIG. 7  illustrates a case in which the screen  220  is a reflective screen.  FIG. 8  illustrates a case in which the screen  220  is a transparent screen. 
     As shown in  FIG. 7 , the projection display apparatus  100  is embedded in a wall, and the screen  220  is provided on a floor surface (projection plane  210 ). On the other hand, as shown in  FIG. 8 , the projection display apparatus  100  is embedded beneath a floor, and the screen  220  is provided on a floor surface (projection plane  210 ). In these cases, the projection display apparatus  100  projects image light on the screen  220  provided on the floor surface (projection plane  210 ). 
     As described above, in a case where no voltage is applied to the screen  220 , the image light emitted from the projection display apparatus  100  forms an image on the screen  220 . Therefore, a user can see the image formed on the screen  220 . 
     On the other hand, in a case where a voltage is applied to the screen  220 , the image light emitted from the projection display apparatus  100  does not form an image on the screen  220 . Here, in a case where a voltage is applied to the screen  220 , it is preferable that the projection display apparatus  100  provides black display. That is, no image light is emitted from the projection display apparatus  100 . As described above, since the screen  220  is transparent, a user can see an opposite scene of the screen  220  from the user&#39;s field of view. 
     As the cases shown in  FIG. 7  and  FIG. 8 , it is considered that an ornamental object, an appreciative object or the like is provided beneath a floor. In this manner, the ornamental object, the appreciative object or the like and its related image can be switched from each other as an object to be shown to a user. Here, since the screen  220  is provided on a floor surface, it is preferable that a reinforce glass is provided on the screen  220 . That is, it is preferable to protect the screen  220  by means of the reinforce glass. 
     In the case shown in  FIG. 8 , it should be kept in mind that even where a voltage is applied to the screen  220 , the projection display apparatus  100  is hardly within the user&#39;s field of view, since the projection display apparatus  100  performs oblique projection. 
     (Function(s) and Advantageous Effect(s)) 
     In the first embodiment, the protection cover  400  is provided on an optical path of the image light that is reflected by the reflection mirror  320 . Therefore, an angle or the like of the reflection mirror  320  can be restrained from being varied by a user touching the reflection mirror  320 . In addition, the protection cover  400  has a transmissive region  410  for transmitting the image light reflected by the reflection mirror  320 . Therefore, the image light emitted on the screen  220  provided on the projection plane  210  is never interrupted by the protection cover  400 . In this manner, the disposition precision of the reflection mirror  320  provided to shorten a distance between the projection display apparatus  100  and the screen  220  can be appropriately maintained. 
     In the first embodiment, the screen  220  is switchably configured as to whether or not the image light reflected by the reflection mirror  320  forms an image. Therefore, the display/non-display of an image can be readily switched. 
     In addition, in a case where the screen  220  is not illuminated with the image light reflected by the reflection mirror  320 , where the screen  220  is transparent, the opposite scene of the screen  220  from the user&#39;s field of view and an image can be switched as an object to be shown to a user. 
     Second Embodiment 
     Hereinafter, a second embodiment will be described with reference to the drawings. Hereinafter, differences between the first embodiment and the second embodiment will be mainly described. 
     In the first embodiment, the screen  220  is comprised of a dispersive liquid crystal. On the other hand, in the second embodiment, the screen  220  has an image forming region and a non-image forming region, and is configured to be slidable on the projection plane  210 . 
     (Screen Configuration) 
     Hereinafter, a configuration of a screen according to the second embodiment will be described with reference to the drawings.  FIG. 9  is a view showing the screen  220  according to the second embodiment. As shown in  FIG. 9 , the screen  220  has an image forming region  220   a  and a non-image forming region  220   b.    
     The image forming region  220   a  is a region in which the image light reflected by the reflection mirror  320  forms an image. The image forming region  220   a  has a configuration which is similar to that of a reflective screen or a transmissive screen. 
     The non-image forming region  220   b  is a region in which the image light reflected by the reflection mirror  320  does not form an image. The non-image forming region  220   b  is adjacent to the image forming region  220   a  in a sliding direction of the screen  220 . The non-image forming region  220   b  is comprised of a light-transmissive member. 
     It is preferable that the non-image forming region  220   b  has its shape and size which are substantially similar to those of the image forming region  220   a.    
     (Screen Sliding) 
     Hereinafter, sliding of the screen according to the second embodiment will be described with reference to the drawings.  FIG. 10  and  FIG. 11  are views showing sliding of the screen  220  according to the second embodiment. 
     As shown in  FIG. 10  and  FIG. 11 , the screen  220  is mounted to a winding mechanism  230  (winding mechanism  230   a  and winding mechanism  230   b ). 
     The winding mechanism  230   a  and the winding mechanism  230   b  have a mechanism of winding the screen  220 . Similarly, the winding mechanism  230   a  and the winding mechanism  230   b  have a mechanism of feeding out the screen  220 . For example, the winding mechanism  230   a  and the winding mechanism  230   b  are turnably configured around a rotary shaft  231   a  and a rotary shaft  231   b , respectively. 
     As shown in  FIG. 10 , in a case where the image forming region  220   a  is employed as the projection plane  210 , the non-image forming region  220   b  is wound on the side of the winding mechanism  230   b . On the other hand, as shown in  FIG. 11 , in a case where the non image forming region  220   b  is employed as the projection plane  210 , the image forming region  220   a  is wound on the side of the winding mechanism  230   a.    
     In this manner, the screen  220  is configured to be slidable on the projection plane  210  by means of the winding mechanism  230 . 
     As a matter of course, a method of sliding the screen  220  is not limitative to winding of the screen  220 . 
     (Function(s) and Advantageous Effect(s)) 
     In the second embodiment, the screen  220  is configured to be slidable on the projection plane  210 . Therefore, a configuration, which is capable of switching whether or not the image light emitted from the projection display apparatus  100  forms an image even without a need to employ a screen comprised of a dispersive liquid crystal, can be achieved with ease and at a low cost. 
     Third Embodiment 
     Hereinafter, a third embodiment will be described with reference to the drawings. The third embodiment describes examples of application of the above-described projection display apparatus  100 . 
     First, a case in which the screen  220  is provided at a display window&#39;s glass at a shop will be described with reference to  FIG. 12(A)  and  FIG. 12(B) .  FIG. 12(A)  is a view showing a shop at noon and  FIG. 12(B)  is a view showing a shop at night. 
     As shown in  FIG. 12(A) , at noon, an inside view of a shop is caused to be seen from the outside without forming an image on the screen  220 . Alternatively, in a case where a demonstrative action such as cooking demonstration is taken, such demonstration is caused to be seen from the outside of the shop without forming an image on the screen  220 . 
     On the other hand, as shown in  FIG. 12(B) , at night, an image displayed on the screen  220  is caused to be seen from the outside of the shop while the image (for example, advertisement image) is formed on the screen  220 . Alternatively, after the shop has been closed, the image displayed on the screen  220  is caused to be seen from the outside of the shop while the image (for example, advertisement image) is formed on the screen  220 . 
     Subsequently, a case in which the screen  220  is provided at a shop&#39;s display window will be described with reference to  FIG. 13(A)  to  FIG. 13(C) .  FIG. 13(A)  and  FIG. 13(C)  are views showing a state in which commodity products are displayed in a display window and  FIG. 13(B)  is a view showing a state in which a layout change of commodity products is made in the display window. 
     As shown in  FIG. 13(A)  and  FIG. 13(C) , in a state in which commodity products are displayed in the display window, namely in a state in which a layout change of commodity products is not made, the commodity products displayed in the display window is caused to be seen from the outside of the shop without forming an image on the screen  220 . 
     On the other hand, as shown in  FIG. 13(B) , in a state in which a layout change of commodity products is made in the display window, the image displayed on the screen  220  is caused to be seen from the outside of the shop while the image (for example, advertisement image) is formed on the screen  220 . 
     Fourth Embodiment 
     Hereinafter, a fourth embodiment will be described with reference to the drawings. Hereinafter, differences from the first embodiment will be mainly described. 
     Specifically, in the fourth embodiment, a screen includes a first screen and a second screen, and a respective one of the first and second screens is switchably configured as to whether to diffuse image light or transmit image light. 
     (Screen Configuration) 
     Hereinafter, a configuration of a screen according to the fourth embodiment will be described with reference to the drawings.  FIG. 14  to  FIG. 16  are views showing a screen  500  according to the fourth embodiment. 
     As shown in  FIG. 14  to  FIG. 16 , the screen  500  includes a first screen  510  and a second screen  520 . The first screen  510  and the second screen  520  are disposed in a superimposed manner. 
     A respective one of the first screen  510  and the second screen  520  has a configuration which is similar to that of the screen  220 . For example, the respective one of the first screen  510  and the second screen  520  is comprised of a dispersive liquid crystal or the like. 
     Specifically, the respective one of the first screen  510  and the second screen  520  is switchably configured as to whether to diffuse the image light reflected by the reflection mirror  320  or transmit the image light reflected by the reflection mirror  320 . 
     As shown in  FIG. 14 , in a case where a voltage is applied to both of the first screen  510  and the second screen  520 , the first screen  510  and the second screen  520  transmit the image light reflected by the reflection mirror  320 . Therefore, the first screen  510  and the second screen  520  are transparent, and no image is formed on the screen  500 . 
     As shown in  FIG. 15 , in a case where a voltage is applied to neither of the first screen  510  and the second screen  520 , the first screen  510  and the second screen  520  diffuse the image light reflected by the reflection mirror  320 . That is, the image light reflected by the reflection mirror  320  is diffused twice. In this case, an image is formed on the screen  500 . 
     As shown in  FIG. 16 , in a case where a voltage is applied to only one of the first screen  510  and the second screen  520  (herein, the first screen  510 ), one of the first screen  510  and the second screen  520  (herein, the first screen  510 ) transmits the image light reflected by the reflection mirror  320  and the other one of the first screen  510  and the second screen  520  (herein, the second screen  520 ) diffuses the image light reflected by the reflection mirror  320 . That is, the image light reflected by the reflection mirror  320  is diffused once. In this case, an image is formed on the screen  500 . 
     Here, as shown in  FIG. 17 , in a case where a voltage is applied to neither of the first screen  510  and the second screen  520 , the directivity of image light is low, since the image light emitted from the projection display apparatus  100  diffuses twice. Therefore, the luminance of an image projected on the screen  500  is low, whereas a viewing angle of the image projected on the screen  500  is wide. 
     On the other hand, as shown in  FIG. 18 , in a case where a voltage is applied to only one of the first screen  510  and the second screen  520 , the directivity of image light is high, since the image light emitted from the projection display apparatus  100  diffuses once. Therefore, the viewing angle of the image projected on the screen  500  is narrow, whereas the luminance of the image projected on the screen  500  is high. 
     In this manner, a viewing angle priority (see  FIG. 17 ) and a luminance priority (see  FIG. 18 ) can be switched from each other by controlling the voltage applied to the first screen  510  and the second screen  520 . 
     (Image Display Example(s)) 
     Hereinafter, image display examples according to the fourth embodiment will be described with reference to the drawings.  FIG. 19  to  FIG. 24  are views showing the image display examples according to the fourth embodiment 
     First, a case in which the projection display apparatus  100  is embedded beneath a floor and the screen  500  is provided on a floor surface will be described with reference to  FIG. 19  to  FIG. 21 . 
     As shown in  FIG. 19 , in a case where a user takes a position remotely of the screen  500 , a voltage is applied to only one of the first screen  510  and the second screen  520 . Therefore, the directivity of image light is high, allowing an image to be shown to the user taking the position remotely of the screen  500 . In other words, while the user takes a position remotely of the screen  500 , since the luminance of the image projected on the screen  500  is high, the image can be shown to the user. 
     As shown in  FIG. 20 , in a case where a user takes a position proximal to the screen  500 , a voltage is applied to neither of the first screen  510  and the second screen  520 . Therefore, since the directivity of image light is low, an image can be shown to the user that takes the position proximal to the screen  500 . In other words, while the luminance of the image projected on the screen  500  is low, since the user takes a position proximal to the screen  500 , the image can be shown to the user. 
     As shown in  FIG. 21 , in a case where a user takes a position on the screen  500 , a voltage is applied to both of the first screen  510  and the second screen  520 . Therefore, the screen  500  becomes rapidly transparent, enabling provision of a user-startling effect. In addition, an object disposed under the screen  500  can be shown to a user. 
     Second, a case in which the projection display apparatus  100  is embedded in a wall and the screen  500  is provided on a wall surface will be described with reference to  FIG. 22  to  FIG. 24 . 
     As shown in  FIG. 22 , two projection display apparatuses  100  (projection display apparatus  100 A and projection display apparatus  100 B) are embedded in a wall while the screen  500  provided on a wall surface is sandwiched therebetween. Here, the projection display apparatus  100 A and the projection display apparatus  100 B display images which are similar to each other on the screen  500 . 
     As shown in  FIG. 23 , in a case where a user does not take a position proximal to the screen  500 , a voltage is applied to only one of the first screen  510  and the second screen  520 .  FIG. 23  is a top view of the projection display apparatus  100  and the screen  500 . Here, since the directivity of the image light emitted from the projection display apparatus  100 A is high, an image can be shown to a user taking an A-side position. Similarly, since the directivity of the image light emitted from the projection display apparatus  100 B is high, an image can be shown to a user taking a B-side position. 
     As shown in  FIG. 24 , in a case where a user takes a position proximal to the screen  500 , a voltage is applied to neither of the first screen  510  and the second screen  520 .  FIG. 24  is a top view of the projection display apparatus  100  and the screen  500 . Here, since the directivity of the image light emitted from the projection display apparatus  100 A and the projection display apparatus  100 B is low, an image can be shown to the user taking the position proximal to the screen  500 . 
     Although not set forth in the fourth embodiment, the user&#39;s position may be detected by means of a sensor or a camera provided on a wall surface or a floor surface. 
     (Function(s) and Advantageous Effect(s)) 
     In the fourth embodiment, the screen  500  includes the first screen  510  and the second screen  520 . The respective one of the first screen  510  and the second screen  520  transmits the image light reflected by the reflection mirror  320  or diffuses the image light reflected by the reflection mirror  320 . 
     Therefore, the directivity of the image light emitted from the projection display apparatus  100  can be controlled. In addition, an image displayed on the screen  500  can be appropriately shown to a user in accordance with the user&#39;s position. 
     Fifth Embodiment 
     Hereinafter, a fifth embodiment will be described with reference to the drawings. Hereinafter, differences from the fourth embodiment will be mainly described. 
     Specifically, in the fifth embodiment, a screen has a plurality of dispersive liquid crystal films sandwiched between glass plates. The glass plates and the dispersive liquid crystal films are bonded with each other by means of adhesive. 
     (Screen Configuration) 
     Hereinafter, a configuration of a screen according to the fifth embodiment will be described with reference to the drawings.  FIG. 25  is a view showing a screen  600  according to the fifth embodiment. 
     As shown in  FIG. 25 , the screen  600  has a dispersive liquid crystal film  610 , a dispersive liquid crystal film  620 , a glass plate  630 , and a glass plate  640 . The dispersive liquid crystal film  610  and the glass plate  630  are bonded with each other by means of adhesive  651 . The dispersive liquid crystal film  610  and the glass plate  620  are bonded with each other by means of adhesive  652 . The dispersive liquid crystal film  620  and the glass plate  640  are bonded with each other by means of adhesive  653 . 
     The respective one of the dispersive liquid crystal Mm  610  and the dispersive liquid crystal film  620  transmits the image light reflected by the reflection mirror  320  or diffuses the image light reflected by the reflection mirror  320 . It is preferable that an interval between the dispersive liquid crystal Mm  610  and the dispersive liquid crystal Mm  620 , namely, the thickness of the adhesive  652  is smaller than a pixel interval on the screen  600 . For example, in a case where the size of the screen  600  is 100 inches and the pixel interval on the screen  600  is on the order of 500 microns, the interval between the dispersive liquid crystal film  610  and the dispersive liquid crystal film  620  is 20 microns. 
     Since the dispersive liquid crystal film  610  and the dispersive liquid crystal film  620  have a configuration which is similar to those of the first screen  510  and the second screen  520 , a detailed description of the dispersive liquid crystal film  610  and the dispersive liquid crystal film  620  is omitted. 
     Sixth Embodiment 
     Hereinafter, a sixth embodiment will be described with reference to the drawings. Hereinafter, differences from the first embodiment will be mainly described. 
     Specifically, in the sixth embodiment, a screen is comprised of a plurality of regions. In addition, the screen is switchably configured as to whether or not to diffuse image light or transmit image light in a respective one of a plurality of regions. 
     (Screen Configuration) 
     Hereinafter, a configuration of a screen according to the sixth embodiment will be described with reference to the drawings.  FIG. 26  is a view showing a screen  700  according to the sixth embodiment. 
     As shown in  FIG. 26 , the screen  700  is comprised of a plurality of regions  710 . An electrode  720  is connected to a respective one of the regions  710 . The screen  700  is comprised of a dispersive liquid crystal, for example. The screen  700  is configured to switch whether to diffuse image light or to transmit image light in accordance with the voltage applied via a respective one of the electrodes  720  in a respective one of the regions  710 . 
     (Image Display Example(s)) 
     Hereinafter, image display examples according to the sixth embodiment will be described with reference to the drawings.  FIG. 27  to  FIG. 31  are views showing the image display examples according to the sixth embodiment. 
     First, utilization of the screen  700  will be described with reference to  FIG. 27 . In  FIG. 27 , a voltage is applied to a region  710 A via an electrode  720 A, whereas no voltage is applied to a region  710 B via an electrode  720 B. That is, the region  710 A is transparent, whereas an image is displayed in the region  710 B. 
     As shown in  FIG. 27 , an object provided on the rear side of the region  710 A can be seen via the region  710 A from a user taking a position on the front side of the screen  700 . On the other hand, an image displayed on the region  710 B can be seen from the user taking a position on the front side of the screen  700 . 
     Second, a case in which the projection display apparatus  100  is provided on a ceiling and the screen  700  is disposed in substantially parallel to a wall surface  810  will be described with reference to  FIG. 28  to  FIG. 30 . Racks for placing objects (rack  821  and rack  282 ) are provided between the wall surface  810  and the screen  700 . The screen  700  has a front plane  701  provided on the user&#39;s side and a rear plane  702  provided on the side of the wall surface  810 . 
     As shown in  FIG. 28 , in a case where the projection display apparatus  100  is provided on the user&#39;s side rather than on the side of the screen  700 , the image light emitted from the projection display apparatus  100  is projected on the front plane  701  of the screen  700 . In such a case, the image light emitted from the projection display apparatus  100  is never interrupted by the rack  821  or the object placed on the rack  821 . Therefore, the depth of the rack  821  can be reduced. 
     As shown in  FIG. 29  and  FIG. 30 , in a case where the projection display apparatus  100  is provided on the side of the wall surface  810  rather than on the side of the screen  700 , the image light emitted from the projection display apparatus  100  is projected on the rear plane  702  of the screen  700 . In such a case, there is a possibility that the image light emitted from the projection display apparatus  100  is interrupted by the rack  821  or the object placed on the rack  821 . 
     Therefore, as shown in  FIG. 29 , it is preferable that the rack  821  is disposed remotely from the screen  700  to the side of the wall surface  810 . Alternatively, as shown in  FIG. 30 , it is preferable that the rack  821  is comprised of a transparent member. As shown in  FIG. 29  and  FIG. 30 , it is preferable that the object placed on the rack  821  is disposed remotely from the screen  700  to the side of the wall surface  810  so as to disallow the image light to be interrupted by the object placed on the rack  821 . 
     Third, a case in which the projection display apparatus  100  is embedded beneath a floor and the screen  700  is provided on a floor surface will be described with reference to  FIG. 31 . 
     As shown in  FIG. 31 , the projection display apparatus  100  can be used in an application (for example, amusement) to an extent such that a user feels as if he or she were floating in the air, by displaying an image in a region  710  in which a user takes a position and making the region  710  transparent, which is provided around the region  710  in which a user takes a position. 
     (Alignment Processing) 
     Hereinafter, alignment processing according to the sixth embodiment will be described. Specifically, alignment between an image, which is displayed by the projection display apparatus  100 , and the region  710 , which is provided on the screen  700 , will be described. 
     (1) The projection display apparatus  100  displays a white image, for example. 
     (2) An edge of the white image displayed by the projection display apparatus  100  is manually aligned with an edge of the screen  700 . 
     (3) Among a plurality of regions  710  provided on the screen  700 , any one region  710  is controlled in a dispersive state, and the remaining regions  710  are controlled in a transparent state. 
     (4) The region  710  in the dispersive state is picked up by means of an image pickup device provided in the projection display apparatus  100 . 
     (5) The position (coordinate) of the region  710  in the diffusive state is specified by way of image picked up by means of the image pickup device. 
     (6) The positions (coordinates) of all, of the regions  710  are specified by performing the processes (3) to (5) as to all of the regions  710  provided on the screen  700 . 
     In this manner, the positions (coordinates) of all of the regions  710  are specified by means of the projection display apparatus  100 , so that the projection display apparatus  100  can project the image light to be projected on the region  710  (region  710 B), on the region  710  (region  710 B) on which an image is to be displayed. That is, the projection display apparatus  100  can display an appropriate image on the region  710  (region  710 B). 
     (Function(s) and Advantageous Effect(s)) 
     In the sixth embodiment, the screen  700  is comprised of the plurality of regions  710 . The screen  700  is configured to switch whether to diffuse image light or transmit image light in a respective one of the regions  710 . Therefore, it is possible to selectively use the region  710 A (transparent state) for showing an object provided on the rear-plane side of the region  710  and the region  7108  (diffusive state) for showing an image displayed on the region  710 . In this manner, application and usage of the projection display apparatus  100  expand. 
     Other Embodiments 
     As described above, the details of the present invention have been described by using the embodiments of the present invention. However, it should not be understood that the description and drawings which constitute part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples, and operation techniques will be easily found by those skilled in the art. 
     Although not set forth in the foregoing embodiments in particular, the protection cover  400  may have an opening communicating from the reflection mirror  320  to the side of the projection plane  210 . The transmissive region  410  may be such an opening. 
     Although not set forth in the foregoing embodiments in particular, at least part of the protection cover  400  may be comprised of a light-transmissive member such as a transparent resin or a glass. The transmissive region  410  may be comprised of such a light-transmissive member. 
     Although not set forth in the foregoing embodiments in particular, the reflection mirror  320  focuses the image light emitted from the image light generating unit  200 , between the reflection mirror  320  and the projection plane  210 . It is preferable that the transmissive region  410  is provided in proximity to a position at which image light is focused by means of the reflection mirror  320 . 
     Although the foregoing embodiments illustrated a case in which a non-spherical mirror is employed as the reflection mirror  320 , the reflection mirror  320  is not limitative thereto. For example, a free curved-face mirror may be employed as the reflection mirror  320 . A spherical mirror may be employed as the reflection mirror  320  as long as contrivance is made as to aberration or resolution. 
     While the foregoing embodiments illustrated a case (triple-plate system) in which a plurality of display elements  40  are employed as constituent elements of the image light generating unit  200 , the constituent elements of the image light generating unit  200  are not limitative thereto. A single display element  40  may be employed as a constituent element of the image light generating unit  200  (single-plate system). 
     According to each of the embodiments, as described above, a distance between a projection display apparatus and a projection plane is shortened by providing the reflection mirror  320 . Therefore, image light can be restrained from being interrupted by a foreign object such as a person standing between the projection display apparatus and the projection plane. In addition, in a case where a laser diode (LD) is employed as a light source  10 , a possibility that a person is irradiated with laser beams can be reduced. 
     In the fifth embodiment, a respective one of the first screen  510  and the second screen  520  is configured to transmit image light or diffuse image light in accordance with a voltage to be applied. However, the embodiment is not limitative thereto. For example, the following cases are considered. 
     (1) In a case in which a transparent state is not required, either one of the first screen  510  and the second screen  520  may be a diffusion film configured to diffuse image light irrespective of a voltage to be applied. In such a case, a state of the screen  500  can be switched between a highly directive state and a lowly directly state. 
     (2) In a case in which a highly directive state is not required, where a desired degree of diffusion is not obtained, two screens (first screen  510  and second screen  20 ) may be employed. In such a case, a state of the screen  500  can be switched between a highly directive state and a lowly directly state. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, there can be provided a projection display apparatus which is capable of readily switching display/non-display of an image, with the aim of shortening a distance between the projection display apparatus and a projection plane. The projection display apparatus can be employed in signage, amusement, catering establishment, multistory building or the like. A menu can be displayed on a screen by disposing the screen on a desk of catering establishment, for example. A screen is disposed on a floor surface of a higher floor of multistory building, whereby image display (diffusive state) and image non-display (transparent state) are switched from each other, enabling provision of a user-startling effect.