Patent Publication Number: US-2021173218-A1

Title: Image display system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a National Stage Application of PCT/JP2018/037272, filed on Oct. 4, 2018, and which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an image display system. 
     BACKGROUND ART 
     Patent Document 1 discloses a floating image display device that includes a mirror, a half mirror, and a pair of display sections disposed at respective distances different from each other with respect to the mirror. A background image displayed in one of the display sections nearer to the half mirror: passes through the half mirror; and is displayed by the mirror in a position nearer to the mirror (in a position farther from a user). A foreground image displayed in the other display section farther from the half mirror: is reflected by the half mirror; and is displayed by the mirror in a position farther from the mirror (in a position nearer to the user). 
     RELATED ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent No. 5,143,898 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the technique disclosed in Patent Document 1, usage of the half mirror may cause loss of light intensity of image light by the display section, resulting in a possible decrease in visibility of an aerially displayed image. On the other hand, in order to secure visibility of the image, it is necessary to display the image with high luminance, which may increase cost. Also, when a display which can provide such a high-luminance image is used, it is necessary to control a rise in temperature in a system of interest. 
     In light of the above-described problems, the present invention has been made in an attempt to provide an image display system that can form an aerial image in a plurality of positions different from each other, while keeping down loss of light intensity. 
     Means for Solving the Problem 
     An image display system includes: a first display device and a second display device, each of which displays an image; an optical imaging member that is disposed spaced apart from each of the first display device and the second display device and that forms respective images displayed in the first display device or the second display device, in respective positions different from each other; and a reflectance switching element that is switchable between a transmission state and a reflection state. Light of the image displayed in the first display device passes through the reflectance switching element and is then made incident on the optical imaging member, to thereby form the image of interest in the air. Light of the image displayed in the second display device is reflected by the reflectance switching element and is then incident on the optical imaging member, to thereby form the image of interest in the air. 
     Advantageous Effects of the Invention 
     In the present invention, an aerial image can be formed in a plurality of positions different from each other, while keeping down loss of light intensity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side diagram schematically illustrating an image display system according to a first embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating the image display system according to the first embodiment of the present invention. 
         FIG. 3A  to  FIG. 3D  are each a diagram for explaining an example of how the image display system works according to the first embodiment of the present invention. 
         FIG. 4  is a side diagram schematically illustrating an image display system according to a second embodiment of the present invention. 
         FIG. 5  is a block diagram illustrating the image display system according to the second embodiment of the present invention. 
         FIG. 6  is a side diagram schematically illustrating an image display system according to a third embodiment of the present invention. 
         FIG. 7  is a block diagram illustrating the image display system according to the third embodiment of the present invention. 
         FIG. 8A  to  FIG. 8C  are each a diagram for explaining an example of how the image display system works according to the third embodiment of the present invention. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention are described in detail with reference to related drawings. In the explanation, same reference numerals are given to same elements, and description thereof is omitted herefrom. 
     First Embodiment 
     As illustrated in  FIG. 1  and  FIG. 2 , an image display system  1 X according to a first embodiment of the present invention includes: a first display device  10 A; a second display device  10 B; a first reflectance switching element  20 A; an optical imaging member  30 ; an operation position detector  40 ; and a controller  50 . 
     &lt;First Display System&gt; 
     The first display device  10 A is housed in a housing  2  and displays an image  3 A under control of the controller  50 . The first display device  10 A is oriented upward and forward and is disposed below the optical imaging member  30 . In this embodiment, the first display device  10 A: is an LCD (Liquid Crystal Display); and includes a backlight  11 , an absorptive polarizer  12 , a liquid crystal cell  13 , and another absorptive polarizer  14 . 
     &lt;Backlight&gt; 
     The backlight  11  is an area light source composed of white light and is switchable between a lit state and an unlit state under control of the controller  50 . In the lit state, the backlight  11  emits white light forward and upward. 
     &lt;&lt;Absorptive Polarizer&gt;&gt; 
     The absorptive polarizer  12  is disposed directly on top of an upper surface (a light-emitting surface) of the backlight  11 . The absorptive polarizer  12 : lets light oscillating in a longitudinal direction (an up-and-down direction (a front-back direction)) pass through; and absorbs light oscillating in a transverse direction (a crosswise direction) which is perpendicular to the longitudinal direction. That is, a light transmission axis of the absorptive polarizer  12  is set in the longitudinal direction. Note that absorption of light in each of the absorptive polarizers  12 ,  14 ,  23  is not limited to a 100% absorption of light oscillating in a direction of interest. The absorption used herein may include absorption allowing, for example, an about 10% light transmittance. 
     &lt;&lt;Liquid Crystal Cell&gt;&gt; 
     The liquid crystal cell  13  is disposed directly on a top surface of the absorptive polarizer  12 . The liquid crystal cell  13 : is made up of a plurality of pixels; and emits an image light for displaying an image, using the white light emitted from the backlight  11 . The first display device  10 A can switch each of the pixels between: a transmittance state in which light oscillating in the longitudinal direction is passed therethrough; and a blocking state in which the light oscillating in the longitudinal direction is blocked, under control by the controller  50 . 
     The liquid crystal cell  13  is suitably realized by, for example, an IPS (In-Plane-Switching) liquid crystal cell. If the liquid crystal cell  13  is of IPS type, the liquid crystal cell  13 : blocks light when no voltage is applied; and passes light therethrough when voltage is applied. Unlike a liquid crystal cell  22  of type TN (Twisted Nematic) to be described later, the IPS liquid crystal cell  13  can realize a suitable light transmittance property in any visually recognizable directions. 
     &lt;&lt;Another Absorptive Polarizer&gt;  
     Another absorptive polarizer  14  is disposed directly on top of an upper surface (a light-emitting surface) of the liquid crystal cell  13 . The absorptive polarizer  14 : lets light oscillating in the longitudinal direction pass through; and absorbs light oscillating in the transverse direction which is perpendicular to the longitudinal direction. That is, a light transmission axis of the absorptive polarizer  14  is set in the longitudinal direction same as that of the absorptive polarizer  12 . 
     &lt;Second Display System&gt; 
     The second display device  10 B is housed in the housing  2  and displays an image  3 B under control of the controller  50 . The second display device  10 B is oriented downward and backward and is disposed in front of the first reflectance switching element  20 A. 
     In this embodiment, the second display device  10 B; is an LCD (Liquid Crystal Display); and, similarly to those of the first display device  10 A, includes a backlight  11 , an absorptive polarizer  12 , a liquid crystal cell  13 , and another absorptive polarizer  14 . 
     &lt;First Reflectance Switching Element&gt; 
     A first reflectance switching element (a mirror optical element)  20 A is housed in the housing  2  and, in this embodiment, is disposed on a side nearer to a display surface (a top surface) of the first display device  10 A. The first reflectance switching element  20 A is an element which can electrically switch a state thereof between a reflection state (reflectance: high) and a transmission state (reflectance: low) to be described hereinafter, under control of the controller  50 . The first reflectance switching element  20 A may be firmly attached to the first display device  10 A, using optical coupling resin, tape, or the like. Alternatively, the first reflectance switching element  20 A may be disposed spaced apart from the first display device  10 A. The first reflectance switching element  20 A includes a reflective polarizer  21 , a liquid crystal cell  22 , and an absorptive polarizer  23 , in this order from lower to upper. 
     &lt;&lt;Reflective Polarizer&gt;&gt; 
     The reflective polarizer  21  is disposed on a side nearer to the display surface of the first display device  10 A, that is, on a side nearer to a top surface of the absorptive polarizer  14 . The reflective polarizer  21  lets light oscillating in the longitudinal direction pass through; and reflects light oscillating in the transverse direction which is perpendicular to the longitudinal direction. That is, a light transmission axis of the reflective polarizer  21  is set in the longitudinal direction. Note that reflection of light on the reflective polarizer  21  is not limited to a 100% reflection of light oscillating in a direction of interest. The reflection used herein may include reflection allowing, for example, an about 10% transmittance and absorbance. 
     &lt;&lt;Liquid Crystal Cell&gt;&gt; 
     The liquid crystal cell  22  is disposed directly on top of an upper surface (on a display surface side) of the reflective polarizer  21 . The liquid crystal cell  22  is of TN (Twisted Nematic) type. The liquid crystal cell  22  includes: a pair of transparent substrates (for example, glass) disposed back and front; an oriented film disposed on each of the transparent substrates; and liquid crystal sealed between the transparent substrates with the respective oriented films disposed thereon. Liquid crystal is disposed between a pair of the oriented films having been subjected to so-called rubbing, and molecules of the liquid crystal arrange themselves in a 90-degrees twisted helical structure from one transparent substrate to the other transparent substrate. 
     Liquid crystal has optical rotation when no voltage is applied thereto. That is, in the voltage-off state, the liquid crystal converts light oscillating in the longitudinal direction which passes from a side nearer to the absorptive polarizer  23  to a side nearer to the reflective polarizer  21 , into light oscillating in the transverse direction. Also, in the voltage-off state, the liquid crystal converts light oscillating in the transverse direction which has been reflected by the reflective polarizer  21 , into light oscillating in the longitudinal direction, when the light passes from the side nearer to the reflective polarizer  21  to the side nearer to the absorptive polarizer  23 . 
     When voltage is applied, the liquid crystal loses the nature of optical rotation (lets light travel straight) due to a change in arrangement of molecules of the liquid crystal. That is, in the voltage-on state, the liquid crystal lets light oscillating in the longitudinal direction pass through, keeping the light oscillating in the longitudinal direction as it is. 
     &lt;&lt;Absorptive Polarizer&gt;&gt; 
     The absorptive polarizer  23  is disposed directly on top of an upper surface (on a display surface side) of the liquid crystal cell  22 . The absorptive polarizer  23  lets light oscillating in the longitudinal direction pass through; and absorbs light oscillating in the transverse direction which is perpendicular to the longitudinal direction. That is, a light transmission axis of the absorptive polarizer  23  is set in the longitudinal direction. 
     &lt;Switching Between Reflection State and Transmission State of First Reflectance Switching Element&gt; 
     The first reflectance switching element  20 A takes a reflection state under normal conditions (liquid crystal cell  22 : in the voltage-off state). In the reflection state, the liquid crystal cell  22  converts light oscillating in the longitudinal direction from the side nearer to the absorptive polarizer  23 , into light oscillating in the transverse direction, which is then reflected by the reflective polarizer  21 . The liquid crystal cell  22  convers the light oscillating in the transverse direction reflected by the reflective polarizer  21 , into light oscillating in the longitudinal direction, which exits from the absorptive polarizer  23 . In the reflection state, the absorptive polarizer  23  absorbs light oscillating in the transverse direction from the side nearer to the absorptive polarizer  23 . Also in the reflection state, light oscillating in the longitudinal direction from the side nearer to the reflective polarizer  21 ; passes through the reflective polarizer  21 ; is converted into light oscillating in the transverse direction by the liquid crystal cell  22 ; and is absorbed by the absorptive polarizer  23 . As described above, in the reflection state, the light from the side nearer to the reflective polarizer  21  will not pass through the first reflectance switching element  20 A and, obviously, will not exit upward. Therefore, even when the first display device  10 A emits image light, the first reflectance switching element  20 A can suitably serve as a mirror. 
     When the liquid crystal cell  22  is supplied with voltage, the first reflectance switching element  20 A takes a light transmission state. In the transmission state, light oscillating in the longitudinal direction passes the first reflectance switching element  20 A in both directions (from and to the side nearer to the reflective polarizer  21  to and from the side nearer to the absorptive polarizer  23 ). Also in the transmission state, the absorptive polarizer  23  absorbs light oscillating in the transverse direction from the side nearer to the absorptive polarizer  23 . 
     &lt;Optical Imaging Member&gt; 
     The optical imaging member  30  is a plate-shaped member; is housed in the housing  2 ; and forms an aerial image of the image  3 A displayed in the first display device  10 A or the image  3 B displayed in the second display device  10 B. The optical imaging member  30  is disposed spaced apart from the first display device  10 A and the second display device  10 B. The optical imaging member  30  can be suitably realized by using AI (Aerial Imaging) Plate (registered trademark; manufactured by Asukanet Co., Ltd., Japanese Patent No. 4865088), or the like. The optical imaging member  30  forms the image  3 A displayed in the first display device  10 A disposed on one side of the optical imaging member  30 , on the other side thereof. Herein; a distance which an image light travels between the optical imaging member  30  and the formed image  3 A is equal to a distance which an image light travels between the first display device  10 A and the optical imaging member  30  (a first distance L1). A size of the formed image  3 A is equal to a size displayed in the first display device  10 A. Also, the optical imaging member  30  forms the image  3 B displayed in the second display device  10 B disposed on one side of the optical imaging member  30 , at a position not corresponding to that of the image  3 A, on the other side of the optical imaging member  30  of interest. Herein, a distance which an image light travels between the optical imaging member  30  and the formed image  3 B is equal to a sum of the first distance L1, and a distance between the first reflectance switching element  20 A and the second display device  10 B, which is referred to as a distance L2 (a second distance L1+L2). A size of the formed image  3 B is equal to that displayed in the second display device  10 B. An attitude (a setting angle) of each of the first display device  10 A, the second display device  10 B, the first reflectance switching element  20 A, and the optical imaging member  30  is set such that a user can visually recognize the formed images  3 A,  3 B in good condition. For example, the formed images  3 A,  3 B are displayed on an imaginary plane which is substantially perpendicular to the front-back direction. 
     &lt;Operation Position Detector&gt; 
     The operation position detector  40 : detects a position of an operation by a user (for example, a position of a user&#39;s finger); and includes an infrared irradiation part  41  and an infrared photographing part  42 . 
     &lt;&lt;Infrared Irradiation Part&gt;&gt; 
     The infrared irradiation part  41  irradiates an area in which the images  3 A,  3 B are formed, with infrared rays. 
     &lt;&lt;Infrared Photographing Part&gt;&gt; 
     The infrared photographing part  42 : is a stereo camera; and photographs the area in which the images  3 A,  3 B are formed, using the infrared rays irradiated by the infrared irradiation part  41 . The infrared photographing part  42  outputs the photographed result to the controller  50 . 
     &lt;Controller&gt; 
     The controller  50  includes a CPU (Central Processing Unit), a ROM (Read-Only Memory), and a RAM (Random Access Memory). The controller  50  provides control over the first display device  10 A, the second display device  10 B, the first reflectance switching element  20 A, and the infrared irradiation part  41 , based on the result photographed by the infrared photographing part  42 . 
     &lt;Example of how System Works&gt; 
     Next is described an example of how the image display system  1 X works regarding: forming and displaying the image  3 A; forming and displaying the image  3 B; and operations of displays, in this order. 
     &lt;&lt;Forming and Displaying Image  3 A&gt;&gt; 
     As illustrated in  FIG. 3A , when the image  3 A is formed and displayed, the controller  50 : turns on the backlight  11  of the first display device  10 A; and applies voltage to the liquid crystal cell  13  of the first display device  10 A and the liquid crystal cell  22  of the first reflectance switching element  20 A. Note that control of whether or not voltage is applied is actually provided not to the liquid crystal cell  13  itself but rather to each of pixels thereof. Description below is thus made regarding a state of a given pixel to which voltage is applied. 
     In the first display device  10 A, from among light emitted from the backlight  11 , the absorptive polarizer  12 : absorbs light oscillating in the transverse direction; and lets light oscillating in the longitudinal direction pass therethrough. The light oscillating in the longitudinal direction having passed through the absorptive polarizer  12  passes through the liquid crystal cell  13  as it is (as the light oscillating in the longitudinal direction). The light oscillating in the longitudinal direction having passed through the liquid crystal cell  13  passes through the absorptive polarizer  14 . 
     The light oscillating in the longitudinal direction having passed through the absorptive polarizer  14  passes through the reflective polarizer  21  of the first reflectance switching element  20 A. The light oscillating in the longitudinal direction having passed through the reflective polarizer  21  passes through the liquid crystal cell  22  as it is (as the light oscillating in the longitudinal direction), The light oscillating in the longitudinal direction having passed through the liquid crystal cell  22 : passes through the absorptive polarizer  23 ; and exits to the optical imaging member  30 . 
     That is, in a state where voltage is applied, the first reflectance switching element  20 A of the image display system  1 X serves as a light transmission layer which lets light of the image  3 A displayed in the first display device  10 A pass through. 
     The optical imaging member  30  makes the image  3 A via the first reflectance switching element  20 A refracted at a refracting angle α; and forms the refracted image  3 A at a distance L1 (a distance which an image light of interest travels) from the optical imaging member  30  in the air. 
     Note that, in forming and displaying the image  3 A, the controller  50  may leave the image  3 B displayed in the second display device  10 B as it is or may turn off the second display device  10 B. 
     &lt;&lt;Forming and Displaying Image  3 B&gt;&gt; 
     As illustrated in  FIG. 3B , when the image  3 B is formed and displayed, the controller  50 : turns on the backlight  11  of the second display device  10 B; applies voltage to the liquid crystal cell  13  of the second display device  10 B; and applies no voltage to the liquid crystal cell  22  of the first reflectance switching element  20 A. 
     In the second display device  10 B, from among light emitted from the backlight  11 , the absorptive polarizer  12 : absorbs light oscillating in the transverse direction; and lets light oscillating in the longitudinal direction pass therethrough. The light oscillating in the longitudinal direction having passed through the absorptive polarizer  12  passes through the liquid crystal cell  13  as it is (as the light oscillating in the longitudinal direction). The light oscillating in the longitudinal direction having passed through the liquid crystal cell  13  passes through the absorptive polarizer  14 . 
     The light oscillating in the longitudinal direction having passed through the absorptive polarizer  14  passes through the absorptive polarizer  23  of the first reflectance switching element  20 A. The light oscillating in the longitudinal direction having passed through the absorptive polarizer  23  is, when passing downward through the liquid crystal cell  22 , converted into light oscillating in the transverse direction. The light oscillating in the transverse direction having been converted by the liquid crystal cell  22  is reflected by the reflective polarizer  21  at a reflection angle β. The light having been reflected by the reflective polarizer  21  is, when passing upward through the liquid crystal cell  22 , converted into light oscillating in the longitudinal direction by the liquid crystal cell  22 . The light oscillating in the longitudinal direction having been converted by the liquid crystal cell  22 : passes through the absorptive polarizer  23 ; and exits to the optical imaging member  30 . 
     That is, in a state where no voltage is applied, the first reflectance switching element  20 A of the image display system  1 X serves as a mirror which reflects light of the image  3 B displayed in the second display device  10 B. 
     The optical imaging member  30  makes the image  3 B via the first reflectance switching element  20 A refracted at a refracting angle α; and forms the refracted image  3 B at a distance L1+L2 (a distance which an image light of interest travels) from the optical imaging member  30  in the air. 
     Note that, in forming and displaying the image  3 B, the controller  50  may leave the image  3 A displayed in the first display device  10 A as it is or may turn off the first display device  10 A. 
     When the first reflectance switching element  20 A serves as a mirror in a voltage-on state, operations as illustrated in  FIGS. 3C and 3D  as examples are performed, though detailed description is omitted herein.  FIG. 3C  illustrates an example of operations when the image  3 A is formed and displayed.  FIG. 3D  illustrates an example of operations when the image  3 B is formed and displayed. 
     &lt;&lt;Operations of Images  3 A,  3 B&gt;&gt; 
     The controller  50 : performs an image recognition processing to the result photographed by the infrared photographing part  42 ; and thereby recognizes a finger of a user (for example, an index finger). The controller  50  detects, based on the recognized result of the users finger, a position of the user&#39;s finger (a distance thereof from the optical imaging member  30  and a two-dimensional position in the formed image  3 A (or  3 B)). When the distance from the optical imaging member  30  to the user&#39;s finger is equal to a distance from the optical imaging member  30  to the formed image  3 A (or  3 B), the controller  50  provides control of modifying the image  3 A (or  3 B). For example, the controller  50  can change contents of the image  3 A, based on a two-dimensional position of a user&#39;s finger in the formed image  3 A. Similarly, the controller  50  can change contents of the image  3 B, based on a two-dimensional position of a user&#39;s finger in the formed image  3 B. Also, the controller  50  can form and display the image  3 B having contents same as those of the image  3 A and then discontinue displaying the image  3 A, based on the two-dimensional position of the user&#39;s finger in the formed image  3 A. Similarly, the controller  50  can form and display the image  3 A having contents same as those of the image  3 B and then discontinue displaying the image  3 B, based on a two-dimensional position of the user&#39;s finger in the formed image  3 B. In the above-described display changing technique, the controller  50  previously stores therein a relationship between a two-dimensional position of a user&#39;s finger and contents of switched images. The controller  50  can form an image having contents desired by a user at a position desired by the user, using the detected two-dimensional position of the user&#39;s finger and the stored relationship. 
     The image display system  1 X can be installed in a front end portion in a vehicle length direction of a vehicle compartment and a middle portion in a vehicle width direction thereof. In this case, the image display system  1 X: can form and display the image  3 A in such a position that can be operated by a driver sitting in a driver&#39;s seat or an occupant sitting in a front passenger seat; and can form and display the image  3 B in such a position that can be operated by an occupant sitting in a back passenger seat. 
     The image display system  1 X according to the first embodiment of the present invention uses not a half mirror but the first reflectance switching element  20 A. This makes it possible to form an image in aerial positions different from each other, while keeping down loss of light intensity. In other words, the image display system  1 X can switch image forming and displaying positions from among a plurality of positions having distances different from each other with respect to the optical imaging member  30  (in this embodiment, two different positions). Also, the image display system  1 X can reduce a rise in temperature in the system  1 X, because there is no need to use a high-luminance display device. The image display system  1 X: can thus eliminate need for space, a device, or the like to reduce a rise in temperature; and can realize reduction in size and cost and improvement of reliability. 
     The system  1 X includes the operation position detector  40 , and thus, an aerially formed image can be used as a touch panel. 
     A vehicle driver or the like may wear anti-glare sunglasses using polarized lenses which let light oscillating in the longitudinal direction pass through and block light oscillating in the transverse direction. In the image display system  1 X, meanwhile, a formed image is composed of light oscillating in the longitudinal direction (in an up-and-down direction). Thus, the image display system  1 X can provide a user even wearing such sunglasses with a formed image having good visibility. 
     In the image display system  1 X, an image is formed in a compartment of a vehicle. That is, the image display system  1 X can form and display an image in a position suitable for each of one or more vehicle occupants. 
     Second Embodiment 
     Next is described an image display system according to a second embodiment of the present invention, focusing on differences from the image display system  1 X according to the first embodiment of the present invention. As illustrated in each of  FIG. 4  and  FIG. 5 , an image display system  1 Y according to the second embodiment has a structure similar to that of the first embodiment, except that the system  1 Y further includes a transfer mechanism  60 . 
     &lt;Transfer Mechanism&gt; 
     The transfer mechanism  60  transfers, under control by the controller  50 , the second display device  10 B between a position at a distance L2 (a distance which an image light of interest travels) from the first reflectance switching element  20 A and a position at a distance L2+L3 (a distance which an image light of interest travels) from the first reflectance switching element  20 A. 
     &lt;Example of how System Works&gt; 
     Next is described a change in an image forming position when the image  3 B is formed and displayed, in an example of how the image display system  1 Y works. 
     &lt;&lt;Forming and Displaying Image  3 B&gt;&gt; 
     When the image  3 B is formed and displayed, the controller  50  controls the transfer mechanism  60 , based on, for example, a result detected by the operation position detector  40 , such that: the second display device  10 B is transferred to a position desired by a user; and is then stopped at the desired position. The optical imaging member  30  forms the image  3 B via the first reflectance switching element  20 A in an aerial position at a distance not shorter than L1+L2 and not longer than L1+L2+L3 (a distance which an image light travels) from the optical imaging member  30 . 
     The image display system  1 Y can be installed in a front end portion in a vehicle length direction of a three-row seat compartment of a vehicle and a middle portion in a vehicle width direction thereof. In this case, the image display system  1 Y: can form and display the image  3 A in such a position that can be operated by a driver sitting in a driver&#39;s seat or an occupant sitting in a front passenger seat; and can form and display the image  3 B in such a position that can be operated by an occupant sitting in a middle and a back passenger seat. 
     The image display system  1 Y according to the second embodiment of the present invention can suitably change an image forming position of the image  3 B. That is, the image display system  1 Y can change an image forming and displaying position to any of different positions having different distances from the optical imaging member  30  (in this embodiment; any of a position at a distance L1, and a position between a distance L1+L2 and a distance L1+L2+L3). 
     Third Embodiment 
     Next is described an image display system according to a third embodiment of the present invention, focusing on differences from the image display system  1 X according to the first embodiment of the present invention. As illustrated in each of  FIG. 6  and  FIG. 7 , an image display system  1 Z according to the third embodiment has a structure similar to that of the first embodiment, except that the system  1 Z further includes a third display device  10 C, a second reflectance switching element  20 B, and a rotation mechanism  70 . 
     &lt;Third Display Device&gt; 
     The third display device  100  is housed in the housing  2  and displays an image under control by the controller  50 . The third display device  10 C is oriented upward and is disposed below the second reflectance switching element  20 B. A distance which an image light travels between the third display device  10 C and the second reflectance switching element  20 B is set to a distance L4. In this embodiment, the third display device  10 C is an LCD (Liquid Crystal Display); and, similarly to the first display device  10 A, includes a backlight  11 , an absorptive polarizer  12 , a liquid crystal cell  13 , and an absorptive polarizer  14 . 
     &lt;Second Reflectance Switching Element&gt; 
     The second reflectance switching element  20 B is housed in the housing  2  and, in this embodiment, is disposed on a side nearer to a display surface (a rear surface) of the second display device  10 B. The second reflectance switching element  20 B is an element which can electrically switch a state thereof between the reflection state and the transmission state as described above, under control of the controller  50 . The second reflectance switching element  20 B may be firmly attached to the second display device  10 B, using optical coupling resin, tape, or the like. Alternatively, the second reflectance switching element  20 B may be disposed spaced apart from the second display device  10 B. The second reflectance switching element  20 B includes a reflective polarizer  21 , a liquid crystal cell  22 , and an absorptive polarizer  23 , in this order from front to back. 
     &lt;Rotation Mechanism&gt; 
     The rotation mechanism  70  rotates, under control by the controller  50 , the second display device  10 B together with the second reflectance switching element  20 B so as to take an appropriate position thereof between an attitude for forming and displaying the image  3 B and an attitude for forming and displaying the image  3 C. Herein, the image  3 B is an image displayed by the second display device  10 B; and the image  3 C, by the third display device  10 C. 
     &lt;Example of how System Works&gt; 
     Next is described how the image display system  1 Z works regarding: forming and displaying the image  3 B; and forming and displaying the image  30 . Description of forming and displaying the image  3 A illustrated in  FIG. 8A  is substantially same as that in the example of how the image display system  1 X works and is thus omitted herefrom. 
     &lt;&lt;Forming and Displaying Image  3 B&gt;&gt; 
     As illustrated in  FIG. 8B , when the image  3 B is formed and displayed, the controller  50  controls the rotation mechanism  70  such that the second display device  10 B together with the second reflectance switching element  20 B are rotated to take an appropriate attitude position thereof for forming and displaying the image  3 B. Also, the controller  50 : turns on the backlight  11  of the second display device  10 B; applies voltage to the liquid crystal cell  13  of the second display device  10 B and the liquid crystal cell  22  of the second reflectance switching element  20 B. The controller  50  applies, however, no voltage to the liquid crystal cell  22  of the first reflectance switching element  20 A. 
     In the second display device  10 B, from among light emitted from the backlight  11 , the absorptive polarizer  12 ; absorbs light oscillating in the transverse direction; and lets light oscillating in the longitudinal direction pass therethrough. The light oscillating in the longitudinal direction having passed through the absorptive polarizer  12  passes through the liquid crystal cell  13  as it is (as the light oscillating in the longitudinal direction). The light oscillating in the longitudinal direction having passed through the liquid crystal cell  13  passes through the absorptive polarizer  14 . 
     The light oscillating in the longitudinal direction having passed through the absorptive polarizer  14  passes through the reflective polarizer  21  of the second reflectance switching element  20 B. The light oscillating in the longitudinal direction having passed through the reflective polarizer  21  passes through the liquid crystal cell  22  as it is (as the light oscillating in the longitudinal direction). The light oscillating in the longitudinal direction having passed through the liquid crystal cell  22 : passes through the absorptive polarizer  23 ; and exits to the first reflectance switching element  20 A. 
     That is, in a state where voltage is applied, the second reflectance switching element  20 B of the image display system  1 X serves as a light transmission layer which lets light of the image  3 A displayed in the first display device  10 A pass through. 
     The light oscillating in the longitudinal direction having exited to the first reflectance switching element  20 A passes through the absorptive polarizer  23  the first reflectance switching element  20 A. The light oscillating in the longitudinal direction having passed through the absorptive polarizer  23  is, when passing downward through the liquid crystal cell  22 , converted into light oscillating in the transverse direction. The light oscillating in the transverse direction having been converted by the liquid crystal cell  22  is reflected by the reflective polarizer  21  at a reflection angle  3 . The light having been reflected by the reflective polarizer  21  is, when passing upward through the liquid crystal cell  22 , converted into light oscillating in the longitudinal direction by the liquid crystal cell  22 . The light oscillating in the longitudinal direction having been converted by the liquid crystal cell  22 : passes through the absorptive polarizer  23 : and exits to the optical imaging member  30 . 
     That is, in a state where no voltage is applied, the first reflectance switching element  20 A of the image display system  1 Z serves as a mirror which reflects light of the image  3 B displayed in the second display device  10 B. 
     The optical imaging member  30  makes the image  3 B via the second reflectance switching element  20 B and the first reflectance switching element  20 A refracted at the refracting angle α; and forms the refracted image  3 B at a distance L1+L2 (a distance which an image light of interest travels) from the optical imaging member  30  in the air. 
     Note that, in forming and displaying the image  3 B, the controller  50  may leave the image  3 A displayed in the first display device  10 A or the image  3 C displayed in the third display device  10 C, as it is. Alternatively, in forming and displaying the image  3 B, the controller  50  may turn off the first display device  10 A and/or the third display device  10 C. 
     &lt;&lt;Forming and Displaying Image  3 C&gt;&gt; 
     As illustrated in  FIG. 8C , when the image  3 C is formed and displayed, the controller  50  controls the rotation mechanism  70  such that the second display device  10 B together with the second reflectance switching element  20 B are rotated to take an attitude position thereof for forming and displaying the image  30 . Also, the controller  50 : turns on the backlight  11  of the third display device  100 ; and applies voltage to the liquid crystal cell  13  of the third display device  10 C. The controller  50  applies, however, no voltage to the respective liquid crystal cells  22  of the first reflectance switching element  20 A and the second reflectance switching element  20 B. 
     In the third display device  100 , from among light emitted from the backlight  11 , the absorptive polarizer  12 : absorbs light oscillating in the transverse direction; and lets light oscillating in the longitudinal direction pass therethrough. The light oscillating in the longitudinal direction having passed through the absorptive polarizer  12  passes through the liquid crystal cell  13  as it is (as the light oscillating in the longitudinal direction). The light oscillating in the longitudinal direction having passed through the liquid crystal cell  13  passes through the absorptive polarizer  14 . 
     The light oscillating in the longitudinal direction having passed through the absorptive polarizer  14  passes through the absorptive polarizer  23  of the second reflectance switching element  20 B. The light oscillating in the longitudinal direction having passed through the absorptive polarizer  23  is, when passing upward through the liquid crystal cell  22 , converted into light oscillating in the transverse direction. The light oscillating in the transverse direction having been converted by the liquid crystal cell  22  is reflected by the reflective polarizer  21  at a reflection angle γ. The light having been reflected by the reflective polarizer  21  is, when passing downward through the liquid crystal cell  22 , converted into light oscillating in the longitudinal direction by the liquid crystal cell  22 . The light oscillating in the longitudinal direction having been converted by the liquid crystal cell  22 : passes through the absorptive polarizer  23 ; and exits to the first reflectance switching element  20 A. 
     That is, in a state where voltage is applied, the second reflectance switching element  20 B of the image display system  1 Z serves as a mirror which reflects light of the image  3 C displayed in the third display device  100 . 
     Then, the light oscillating in the longitudinal direction having exited to the first reflectance switching element  20 A passes through the absorptive polarizer  23  of the first reflectance switching element  20 A. The light oscillating in the longitudinal direction having passed through the absorptive polarizer  23  is, when passing downward through the liquid crystal cell  22 , converted into light oscillating in the transverse direction. The light oscillating in the transverse direction having been converted by the liquid crystal cell  22  is reflected by the reflective polarizer  21  at a reflection angle β. The light having been reflected by the reflective polarizer  21  is, when passing upward through the liquid crystal cell  22 , converted into light oscillating in the longitudinal direction by the liquid crystal cell  22 . The light oscillating in the longitudinal direction having been converted by the liquid crystal cell  22 ; passes through the absorptive polarizer  23 ; and exits to the optical imaging member  30 . 
     That is, in the state where no voltage is applied, the first reflectance switching element  20 A of the image display system  1 Z serves as a mirror which reflects light of the image  3 C displayed in the third display device  100 . 
     The optical imaging member  30  makes the image  3 C via the second reflectance switching element  20 B and the first reflectance switching element  20 A, refracted at the refracting angle α; and forms the refracted image  3 B at a distance L1+L2+L4 (a distance which an image light of interest travels) from the optical imaging member  30  in the air. 
     Note that, in forming and displaying the image  30 , the controller  50  may leave the image  3 A displayed in the first display device  10 A or the image  3 B displayed in the second display device  10 B, as it is. Alternatively, in forming and displaying the image  3 C, the controller  50  may turn off the first display device  10 A and/or the second display device  10 B. 
     The image display system  1 Z can be installed in a front end portion in a vehicle length direction of a three-row seat compartment of a vehicle and a middle portion in a vehicle width direction thereof. In this case, the image display system  1 Z can form and display: the image  3 A in such a position that can be operated by a driver sitting in a driver&#39;s seat or an occupant sitting in a front passenger seat; the image  3 B, by an occupant sitting in a middle passenger seat; and, the image  3 C, by an occupant sitting in a back passenger seat. 
     The image display system  1 Z according to the third embodiment of the present invention can suitably form an image in three different positions having different distances from the optical imaging member  30 . In other words, the image display system  1 Z can change a position in which an image is formed and displayed, to any of a plurality of different positions having distances different from each other with respect to the optical imaging member  30  (in this embodiment, three different positions). 
     The present invention has been described above with reference to the embodiments thereof, though the present invention is not limited to those embodiments, and various changes are possible within a scope not departing from the gist of the present invention. For example, an image display system of the present invention may include a manipulation part by which a driver can manipulate an image and may have a configuration such that the controller makes one or more display devices display an image created based on a result of manipulation by the manipulation part. 
     As an embodiment for reference of the present invention, a display device can be realized by combining a light source and a celluloid picture. An image display system of the present invention can be applied not only to a vehicle but also to a game console, a poster, a guideboard, touch panels of various types, and the like. 
     A structure of each of the first reflectance switching element  20 A and the second reflectance switching element  20 B is not limited to that described above. That is, a variety of elements which are switchable between a reflection state in which light is reflected thereby and a transmission state in which light passes therethrough (for example, a variable reflectance element described in WO 2015/093298) can be used as the first reflectance switching element  20 A and the second reflectance switching element  20 B. 
     The operation position detector  40  is not limited to the one which detects a position of a user&#39;s finger by means of infrared rays. The operation position detector  40  may be a detector which detects a position of the user&#39;s finger by using, for example, a visible light, a sound wave, or the like. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           1 X,  1 Y,  1 Z image display system 
           10 A first display device 
           10 B second display device 
           10 C third display device 
           20 A first reflectance switching element 
           20 B second reflectance switching element 
           30  optical imaging member 
           40  operation position detector 
           50  controller