Abstract:
A head mounted display uses an image projection device comprising: an image generation unit for generating an image; a projection unit for guiding the image generated by the image generation unit to an observer&#39;s eyes; and a support for linking the projection unit and the image generation unit. The projection unit has a lens function which makes it easiest to see an image generated by the projection unit at a distance (Lobj) within a range between 30 cm and 3 m. Thereby, the image projection device operates at high resolution, has reduced size and weight, and reduces energy consumption.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an image projection device projecting an image on observer&#39; eyes and a head mounted display using the same. 
       BACKGROUND ART 
       [0002]    As a projection optical system having a see-through function, Patent Literature 1 or the like has been proposed. 
       CITATION LIST 
     Patent Literature 
       [0003]    PTL 1: Japanese Patent Application Laid-Open No. 2006-3879 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    A head mounted display serving as a next-generation wearable device is expected because network information on the Internet is always obtained from a part of a field of vision. 
         [0005]    In order to always display an image on a part of a field of vision, a low power consumption and an increase in area of a field of vision except for the image are important. For example, Patent Literature 1 describes an ocular window through which light is emitted to user&#39;s eye and an ocular window holding unit which holds the ocular window. In the ocular window, the width of a projection section in a visual axis direction of the user is set to 4 mm which is equal to the pupil diameter, and in a member constituting the ocular window holding unit, the width of the projection section in the visual axis direction is set to 4 mm or less in a range of 10 mm or more to obtain a see-through function. Further, the patent Literature 1 describes contribution to high efficiency and power saving by using a total reflection optical element in which an optical axis is bent toward user&#39;s eye. 
         [0006]    A person changes her/his focal points. For example, the person sees a distant place 10 m far away from her/his position when she/he ordinarily sees a landscape, the person sees a place 2 to 10 m away from her/his position when she/he is walking, the person looks at the other person at a distance of approximately 1 m when she/he talks with her/him, or the person holds her/his magazine or the like at a distance of approximately 50 cm when she/he reads it. 
         [0007]    Observer&#39;s eyes cannot simultaneously focus on far and near places. More specifically, in a head mounted display, when the observer looks at a distant place, the image which she/he looks at is desirably far away from her/his position. In contrast to this, when the observer looks at a near place, the image which she/he looks at is desirably near her/his position. 
         [0008]    According to Patent Literature 1, the head mounted display has a see-through function when a projection section has a size equal to a pupil diameter of an ocular window unit. At infinity, the display has the see-through function. However, when an observer looks at an object at a distance of less than 5 m, the object is partially out of view to lose the see-through function. 
         [0009]    It is an object of the present invention to provide an image projection device and a head mounted display each of which has a see-through function at far and near places, can achieve a low power consumption and a large field of vision, and can visually check images and fields of vision at both far and near places. 
       Solution to Problems 
       [0010]    The object can be achieved by the invention described in the scope of claims as an example. 
       Advantageous Effects of Invention 
       [0011]    A head mounted display which can visually check images at both far and near places and has a low power consumption and a large field of vision can be achieved. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIGS. 1A and 1B  are schematic views showing an image projection device  1  according to a first embodiment. 
           [0013]      FIGS. 2A and 2B  are diagrams for explaining a see-through function. 
           [0014]      FIG. 3  shows a calculation result for explaining the see-through function. 
           [0015]      FIG. 4  is a diagram for explaining an appearance of an image. 
           [0016]      FIG. 5  is a diagram for explaining a resolution. 
           [0017]      FIG. 6  is a diagram for explaining a field of view. 
           [0018]      FIGS. 7A and 7B  are schematic views showing an image projection device  301  according to a second embodiment. 
           [0019]      FIGS. 8A and 8B  are schematic views showing an image projection device  351  according to a third embodiment. 
           [0020]      FIGS. 9A and 9B  are schematic views showing an image projection device  41  according to a fourth embodiment. 
           [0021]      FIGS. 10A and 10B  are schematic views showing an image projection device  51  according to a fifth embodiment. 
           [0022]      FIGS. 11A and 11B  are schematic views showing an image projection device  61  according to a sixth embodiment. 
           [0023]      FIG. 12  is a schematic view for explaining a ghost preventing function according to the sixth embodiment. 
           [0024]      FIG. 13  is a schematic view showing an image projection device  81  according to a seventh embodiment. 
           [0025]      FIGS. 14A and 14B  are schematic views showing an image projection device  91  according to an eighth embodiment. 
           [0026]      FIG. 15  is a schematic view showing an image projection device  101  according to a ninth embodiment. 
           [0027]      FIGS. 16A and 16B  are schematic views showing an image projection device  111  according to a tenth embodiment. 
           [0028]      FIGS. 17A and 17B  are schematic views showing an image projection device  121  according to an eleventh embodiment. 
           [0029]      FIG. 18  is an explanatory view showing a head mounted display  131  according to a twelfth embodiment. 
           [0030]      FIG. 19  is a schematic view showing a system configuration of the head mounted display  131  according to the twelfth embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    Modes to execute the present invention will be described below with reference to embodiments shown in the drawings, and the present invention is not limited to the modes. 
       First Embodiment 
       [0032]    A first embodiment of the present invention will be described below with reference to the accompanying drawings. 
         [0033]      FIGS. 1A and 1B  are schematic views showing an image projection device  1 , in which  FIG. 1A  is a side view when viewing from observer&#39;s eye side and  FIG. 1B  is an upper view when viewing from above the eye. The upside of paper in  FIG. 1A  is a direction corresponding to the upside of the eye. 
         [0034]    An image projection device  1  includes an image generation unit  211 , a projection unit  213  guiding an image to observer&#39;s eyes, and a support unit  212  coupling the image generation unit  211  and the projection unit  213  to each other. 
         [0035]    The image generation unit  211  includes an image generation element  7  generating an image. As the image generation element  7  mentioned here, a liquid-crystal element having red, blue, and green color filters for each pixel is supposed. Since the liquid-crystal element having the color filters is an ordinary device, the details of the element will not be described. 
         [0036]    The image generation element  7  includes a light source  8 . As the light source  8  mentioned here, a white backlight LED having a light-emitting surface larger than a region in which an image of the image generation element  7  is supposed. Since the white backlight LED is an ordinary device, the element will not be described. 
         [0037]    The image generation unit  211  includes a protecting element  6  preventing dust, drops of water, and the like from being entered from the outside. The protecting element  6  is an optically transparent flat plate, and desirably forms an anti-reflection film in red to blue regions (range from wavelengths 430 nm to 670 nm) to reduce efficiency loss. The anti-reflection film is devised to inversely reflect light having a wavelength of 430 nm or less because the anti-reflection film is supposed to be used in the open air so as to make it possible to suppress the image generation unit  211  from internally deteriorated. 
         [0038]    In the image generation unit  211 , light emitted from the light source  8  passes through the image generation element  7  to generate an image, and the image is emitted by using the protecting element  9  as an emitting surface. 
         [0039]    The image generation unit  211  includes an image-pickup element  9 , and can also pick up an outside as an image. As the image pickup element  9 , a compact camera is supposed. 
         [0040]    The image picked up by the image pickup element  9  can be utilized such that a person is specified by, for example, a face scanning process or the like and information of the person is associated with the generated image. 
         [0041]    An image generated by the image generation unit  211  is propagated to the projection unit  213  through air. The projection unit  213  includes a lens unit  3  and a total reflection surface  4 . The lens unit  3  corresponds to an incidence unit receiving an image generated by the image generation unit  211 . An arrow  10  illustrates a gaze direction. 
         [0042]    The lens unit  3  is a so-called lens having a focal length F, and can make an image projected on observer&#39;s eyes virtual such that a distance between the image generation element  7  and the lens unit  3  is made shorter than the focal length F. A position Li of observer&#39;s eyes and the virtual image can be approximately calculated by the formula of an ordinary lens expressed by numerical expression  1  based on the focal length F of the lens unit  3  and an optical distance A between the image generation element  7  and the lens unit  3 . A distance between observer&#39;s eyes and the virtual image has a negative sign because the corresponding image is virtual. 
         [0000]      1 /F= 1 /A+ 1/ Li    (Numerical Expression 1)
 
         [0043]    A mirror is generally supposed as the total reflection surface  4 , and the total reflection surface  4  has a function of bending a traveling direction of an image traveling through the lens unit  3  to project the image to observer&#39;s eyes. 
         [0044]    A projection unit  213  includes an upper wall  295  and a side-surface wall  296  and fixes the lens unit  3  and the total reflection unit  4  thereto. The lens unit  3 , the total reflection unit  4 , and the protecting element  6  are desirably hard-coated to prevent dust, drops of water, and finger marks from adhering to and being fixed thereto. 
         [0045]    A support unit  212  is a mechanism coupling the image generation unit  211  and the projection unit  213 , and is configured by a support mechanism  2  and a support mechanism  5  to avoid a region in which an image is propagated between the projection unit  213  and the image generation unit  211 . 
         [0046]    The support mechanism  2  is a mechanism supporting a side surface, and the support mechanism  5  is a mechanism coupling an incidence portion of the projection unit  213  and an upper side of an emitting portion of the image generation unit  211 . 
         [0047]    The support mechanism  2  has a width Hs smaller than that of the projection unit  213  when viewing from observer&#39;s eyes. This is to improve a see-through function (will be described later). The support unit  212  is preferably set such that a distance Ls in the eye gaze direction is larger than the Hs. The Ls is made larger than the Hs without simply narrow the width Hs to make it possible to secure necessary strength with, for example, a resin molded piece. 
         [0048]    When the Ls is desired to be small in terms of design, for example, metal may be used, or a resin mold or the like into which metal is inserted may be used. 
         [0049]    The support mechanism  5  is coupled to the support mechanism  2  to contribute to enhancement of its strength. When external light is incident on the image generation element  7 , the incident light is reflected by the image generation element  7  and reflected on observer&#39;s eyes as unnecessary light. For this reason, the support mechanism  2  and the support mechanism  5  have a function of shielding light to prevent external light from being incident on the image generation element  7  and reflected on the observer&#39;s eyes as unnecessary light. The support unit  212  does not only simply couples the projection unit  213  and the image generation unit  211  to each other but also gives the light-shielding function, so as to advantageously secure confidence to prevent an image viewed by a user from being viewed by other persons. 
         [0050]    A see-through function will be described below with reference to  FIG. 2 . 
         [0051]      FIGS. 2A and 2B  illustrate an appearance of an object  201  placed at a distance Lobj when the projection unit  213  is disposed at a place at a distance Ld from a pupil  203  of observer&#39;s eyes. 
         [0052]      FIG. 2A  shows a case in which a width Hp of a pupil  203  is equal to the width Hd of the projection unit  213 , and  FIG. 2B  shows a case in which the width Hd of the projection unit  213  is smaller than the width Hp of the pupil  203 . 
         [0053]    A beam emitted from a light source serving as an object is incident on observer&#39;s eyes, the person can recognize the object with her/his eyes. 
         [0054]    When the width Hp and the width Hd are equal to each other, as shown in  FIG. 1A , since the beam traveling from the object is completely shielded by the projection unit  213  (hatched region  204  in the drawing), the person cannot recognize the object. For this reason, the position of the object  201  must be dislocated, or the projection unit  213  must be dislocated. 
         [0055]    In contrast to this, when the width Hd of the projection unit  213  is smaller than the width Hp, as shown in  FIG. 1B , a beam traveling from the object is partially shielded by the projection unit  213  (hatched region  206  in the drawing). However, the beam (indicated by  207  in the drawing) is partially incident on a pupil  206 . For this reason, the person can recognize the object. More specifically, an angle θd between the width Hd and the object  201  need only be smaller than an angle θp between the width Hp and the object  201 . 
         [0056]    This can be collected into numerical expression  2  based on a simple similarity relation. 
         [0000]      Hp/Lobj&gt;Hd/(Lobj−Ld)   (Numerical Expression 2)
 
         [0057]      FIG. 3  is a graph obtained when the width Hp of the pupil is set to a general size of 4 mm, the distance Ld from the pupil of the projection unit  213  is fixed as 30 mm, and when the width Hd of the projection unit  213  changes, a transparent region ratio of a beam emitted from the object  201  and reaching the pupil without being shielded by the projection unit  213 . The abscissa indicates the width Hd, and the ordinate indicates a ratio of a beam reaching the pupil. The ratio of the beam is expressed such that a transparent region ratio of a beam reaching the pupil without being shielded when the object  201  is defined as a point and a beam reaching the pupil in the absence of the projection unit  213  is used as a reference. A line  261 ,  262  and  263  which is a calculation result in the graph is drawn on the assumption that the distance Lobj from the pupil to the object is 50 cm, 100 cm, and 300 cm, respectively. 
         [0058]    A person cannot accurately recognize a small object located at a distance of approximately 30 mm or less and having a size equal to that of her/his pupil. In addition, when the person wears glasses, the glasses are generally placed at a distance of 10 to 15 mm from her/his pupil. For this reason, a distance Ld between the projection unit  213  and the pupil is desirably set within the range of 15 mm to 30 mm or less such that even a person wearing glasses can dispose the projection unit  213 . As an example, the distance Ld which is a condition under which a see-through function becomes most strict is set to 30 mm. 
         [0059]    As is apparent from the calculation result, when the distance Lobj from the pupil to the object is 50 cm, the line  262  has a length of zero when the Hd exceeds 3.7 mm. 
         [0060]    When the distance Lobj from the pupil to the object is 100 cm, a line  263  has a length of zero when the Hd exceeds 3.8 mm. 
         [0061]    When the distance Lobj from the pupil to the object is 300 cm, a line  264  has a length of zero when the Hd exceeds 3.9 mm. 
         [0062]    According to the graph, when the object is near the person, the transparent region ratio becomes small. It is true that, in order to make the near object visible, the equation 1 must be satisfied to cause a beam to be incident on the pupil. 
         [0063]    When Ld=30 mm, Hp=4 mm, and Lobj=50 cm, a condition given by the width Hd of the projection unit 213&lt;3.76 is a necessary condition. Thus, the width Hd of the projection unit  213  is desirably made smaller than 3.7 mm. 
         [0064]    When the pupil diameter Hp and the width Hd of the projection unit  213  are set to be equal to each other, the equation 1 is not satisfied. Thus, an object located at a distance of 300 cm becomes invisible. 
         [0065]    As a matter of course, the width Hs of the support unit  212  has the same relationship as described above. For this reason, the width Hs is desirably made smaller than the Hd, and, in the image projection device  1 , an image is transmitted through air as described above to make it possible to make the support unit Hs smaller than the Hd. For example, it is true that, when the Hs is given as approximately 1.8 mm, even though the distance Lobj is 50 cm, the transparent region ratio becomes 50% to obtain a preferable see-through function. 
         [0066]      FIG. 4  is a schematic view showing a relationship between a size and a position of an image projected from the projection unit  212  to observer&#39;s eyes and reflected as a virtual image. 
         [0067]    The image projected on observer&#39;s eye  31  increases in size depending on the distance. For example, as shown in the drawing, a size of an image  33  at a distance of Li (near) and a size of an image  32  at a long distance Li (far) are in proportion to the distance Li. 
         [0068]    More specifically, it is true that when the distance increases, the size of each pixel of the image also increases. 
         [0069]      FIG. 5  shows a result obtained by calculating a relationship between the size of the pixel and a spot size of the pixel. The abscissa indicates the distance Li to the image, and the ordinate indicates the spot size. A broken line  251  indicates a spot size (1.5 pixels) which can be allowed to resolve the size of one pixel. A line  253  is obtained such that a focal position of each of the lens units  3  is set to minimize the spot size when the distance Li is 0.65 m, and a line  252  is obtained such that a focal position of each of the lens units  3  is set to minimize the spot size when the distance Li is 2.5 m. In this case, as an example, the relationship is calculated when a screen size located at a distance of 50 cm is 4 inches and a resolution is QVGA (360×240). 
         [0070]    The beam has the minimum spot size at a predetermined focal position, and has large spot sizes before and after the focal position. Like the line  252 , when the distance Li to the focal point is small, the spot size sharply increases after and before the focal point. In contrast to this, like the line  252 , when the distance Li to the focal point is larger than the length of the line  252 , an inclination of the spot size changing before and after the focal point becomes low. When the spot size is smaller than the broken line  251 , an optical resolution can be obtained. For this reason, when it is assumed that a person works while viewing the object at an extremely short distance of 50 cm to 1 m and watching an image, the focal point must be close to her/him as indicated by the line  253 . When it is assumed that the person works while viewing the object at a distance of 1 m or more and watching the image, the focal position must be far from her/him as indicated by the line  252 . 
         [0071]    As a matter of course, when the distance is 1 m, even a far image may be seen at a low resolution without making the focal point far from the person. In this case, as the head mounted display, a function of detecting a distance between a wearer and an object and changing an image into a low-resolution image is preferably given. 
         [0072]      FIG. 6  is a schematic view illustrating a projection of the image projection device  1  when viewing from observer&#39;s eye. A crossing point of a cross is set as a center  260  of the observer&#39;s eye. 
         [0073]    When the projection unit  213  is disposed at the center of the center  260  of observer&#39;s eye, the support unit  212  and the image generation unit  211  are projected as shown in the drawing. The width Hs of the support unit  212  and the width Hd of the projection unit  213  are set to satisfy the relationship expressed by numerical expression  2  as described above. In contrast to, the image generation unit  211  is very difficult to satisfy numerical expression  2  in consideration of mounting of the image generation element  7 , the light source  8 , and the mechanical mechanism. As an extreme example, when it is assumed that a person watches a 30-inch monitor (aspect ratio of 16:9) at a distance of 50 cm, a necessary angle of a field of vision is ±35°. 
         [0074]    When the angle is larger than the given described above, a person may generally gaze the object while inclining her/his face. When the angle is considered as a reference, when a distance Ld=30 mm from observer&#39;s eye is set, it may be desired that a person checks an object without inclining her/his face in a range of the center of observer&#39;s eye to a position at a distance of approximately 21 mm (range indicated by a broken-line circle  24  in the drawing). 
         [0075]    For this reason, as shown in  FIG. 6 , in the image projection device  1 , the image generation unit  211  having the increasing width Hb is disposed out of the range of the center of observer&#39;s eye to a position at a distance of approximately 21 mm (out of the range indicated by a broken-line circle  24  in the drawing). When an image is transmitted through air, an optical distance becomes longer than that obtained when a transparent material having a refractive index. 
         [0076]    In the image projection device  1  transmitting an image through air is devised to obtain a great advantage which can make the image generation unit  211  far from observer&#39;s eye. 
         [0077]    As described above, in the image projection device  1  according to the first embodiment, a person can work while viewing an object located at an extremely short distance of approximately 50 cm and watching an image. 
       Second Embodiment 
       [0078]    A second embodiment according to the present invention will be described below with reference to  FIGS. 7A and 7B . 
         [0079]    An image projection device  301  will be described below. 
         [0080]      FIGS. 7A and 7B  are schematic views showing the image projection device  301 , in which, like  FIGS. 1A and 1B , in which  FIG. 7A  is a side view when viewing from observer&#39;s eye side and  FIG. 7B  is an upper view when viewing from above observer&#39;s eye. The upside of paper in  FIG. 7A  is a direction corresponding to the upside of the eye. 
         [0081]    The image projection device  301  is different from the image projection device  1  according to the first embodiment in that a focus mechanism is added. The same reference numerals as in the image projection device  1  denote the same parts in the image projection device  301 . In this case, a support unit  302  and an image generation unit  308  including the focus mechanism which is not included in the image projection device  1  will be described below. 
         [0082]    The focus mechanism uses the fact that, when a distance A between the lens unit  3  and the image generation element  7  changes, a distance Li of a virtual image changes according to numerical expression 1. 
         [0083]    For this reason, at a position where an image generation unit  308  and the support unit  302  are coupled to each other, a mechanism  307  is disposed. Movement of the mechanism  307  in a direction of an arrow  303  allows a distance A to physically change. 
         [0084]    In the mechanism  307 , column supports  305  and  306  are fixed to the support unit  302 , and the column supports  305  and  306  are fitted in a mechanism unit  309  of the image generation unit  308 . In this case, the column supports  305  and  306  can be moved in a direction of the arrow  303 . The image generation unit  308  includes a stopper  304 , and the support unit  302  has a fitting portion  310  of the stopper to move the support columns  305  and  306  at only predetermined intervals. 
         [0085]    This, as shown in  FIG. 5 , gives two regions including a region extending from a position at a distance of 50 cm to a position at a distance of 1 m and a region extending from a position at a distance 1 m or more. When such two focal points are given, an image and an object can be recognized in a region extending from a position at an extremely short distance of 50 cm to a position at a long distance of 5 m or more. 
         [0086]    In the embodiment, in order to change a distance A, the lens unit  3  is explained as a moving mechanism. However, as a matter of course, a mechanism moving the image generation element  7  may be used. 
       Third Embodiment 
       [0087]    A third embodiment of the present invention will be described below with reference to  FIG. 8 . 
         [0088]    An image projection device  351  will be described below. 
         [0089]      FIGS. 8A and 8B  are schematic views showing the image projection device  351 , in which, like  FIGS. 1A and 1B , in which  FIG. 8A  is a side view when viewing from observer&#39;s eye side and  FIG. 8B  is an upper view when viewing from above observer&#39;s eye. The upside of paper in  FIG. 8A  is a direction corresponding to the upside of the eye. 
         [0090]    The image projection device  351  is different from the image projection device  1  according to the first embodiment in that a focus mechanism is added. The same reference numerals as in the image projection device  1  denote the same parts in the image projection device  351 . In the image projection device  351 , a liquid-crystal lens element  352  is disposed in place of the protecting element  6 . The liquid-crystal lens element  352  having a focus function unlike in the image projection device  1  will be described below. 
         [0091]    The liquid-crystal lens element  352  includes a liquid-crystal layer  352  and a Fresnel lens layer  354 . The Fresnel lens layer  354  is equipped with a Fresnel lens. The liquid-crystal layer  353  is obtained such that a liquid crystal is sealed between a surface having a Fresnel lens shape and a surface adjacent thereto. When the liquid-crystal layer  353  is in an OFF state, since the liquid-crystal layer  353  and the Fresnel lens layer  354  have equal refractive indexes, the liquid-crystal layer  353  has the same function as that of a flat plate with respect to a beam. In an ON state, since the refractive index of the liquid-crystal layer  353  is different from that of the Fresnel lens layer  354 , a beam is influenced by the Fresnel lens. In this manner, the power supply is turned ON/OFF to give the presence/absence of the lens function. 
         [0092]    In order to give a focus function, there is a choice to change a focal length of the lens unit  3 . For this reason, when the liquid-crystal lens element  352  is in an ON state, a combination lens between the lens unit  3  and the Fresnel lens gives a function of changing a focal length. 
         [0093]    This, as shown in  FIG. 5 , also gives two regions including a region extending from a position at a distance of 50 cm to a position at a distance of 1 m and a region extending from a position at a distance 1 m or more. When such two focal points are given, an image and an object can be recognized in a region extending from a position at an extremely short distance of 50 cm to a position at a long distance of 5 m or more. 
       Fourth Embodiment 
       [0094]    A fourth embodiment of the present invention will be described below with reference to  FIGS. 9A and 9B . 
         [0095]    An image projection device  41  will be described below. 
         [0096]      FIGS. 9A and 9B  are schematic views showing the image projection device  41 , like  FIGS. 1A and 1B , in which  FIG. 9A  is a side view when viewing from observer&#39;s eye side and  FIG. 9B  is an upper view when viewing from above observer&#39;s eye. The upside of paper in  FIG. 9A  is a direction corresponding to the upside of the eye. 
         [0097]    In the image projection device  41 , a support unit  501  has a configuration different from that in the image projection device  1  according to the first embodiment. 
         [0098]    The support unit  501  includes support mechanisms  502  and  503 . In the image projection device described above can cope with only one eye, i.e., a right eye or a left eye. As shown in  FIGS. 9A and 9B , when the support mechanism  503  is disposed in addition to the support mechanism  502 , the device can be vertically symmetrical approximately regardless of a left-to-right relationship. 
         [0099]    When an additional value of the widths of the support mechanism  502  and the support mechanism  503  is made equal to or smaller than the width Hs of the support unit  212 , the image projection device  41  can achieve the same see-through function as that of the image projection device  1 . 
       Fifth Embodiment 
       [0100]    A fifth embodiment of the present invention will be described below with reference to  FIG. 10 . 
         [0101]    An image projection device  51  will be described below. 
         [0102]      FIGS. 10A and 10B  are schematic views showing the image projection device  51 , like  FIGS. 1A and 1B , in which  FIG. 10A  is a side view when viewing from observer&#39;s eye side and  FIG. 10B  is an upper view when viewing from above observer&#39;s eye. The upside of paper in  FIG. 10A  is a direction corresponding to the upside of the eye. 
         [0103]    In the image projection device  51 , a projection unit  53  is different from that in the image projection device  1  according to the first embodiment. 
         [0104]    The projection unit  53  has a free reflection unit  52 . The free reflection unit  52  gives both the functions of the lens unit  3  and the total reflection unit  4  of the image projection device  1  according to the first embodiment to one component and has two functions including a function of lens and a function of reflecting a beam and causing the beam to travel to observer&#39;s eye. 
         [0105]    In the configuration of the image projection device  1  according to the first embodiment, the shape of the free reflection unit  52  is preferably determined such that a wave front of a beam emitted to observer&#39;s eye is almost matched with a wave front obtained as a result of ray tracing. 
         [0106]    The shape can be achieved by an inexpensive resin molded piece having a beam-receiving surface coated with metal such as aluminum. 
         [0107]    When the two components are combined into one component to obtain advantages in productivity and cost. 
         [0108]    The free reflection unit  52  is molded as a part of a mechanism component and metal-coated with respect to only its surface to obtain advantages such as high productivity and a cost advantage. 
       Sixth Embodiment 
       [0109]    A sixth embodiment of the present invention will be described below with reference to  FIGS. 11A and 11B . 
         [0110]    An image projection device  61  will be described below. 
         [0111]      FIGS. 11A and 11B  are schematic views showing the image projection device  61 , like  FIGS. 1A and 1B , in which  FIG. 11A  is a side view when viewing from observer&#39;s eye side and  FIG. 11B  is an upper view when viewing from above observer&#39;s eye. The upside of paper in  FIG. 11A  is a direction corresponding to the upside of the eye. 
         [0112]    The image projection device  61  is a modification of the image projection device  51  according to the fifth embodiment. 
         [0113]    The projection unit  63  has a prism lens unit  62 . The prism lens unit  62 , like the free reflection unit  52 , gives both the functions of the lens unit  3  and the total reflection unit  4  of the image projection device  1  to one component and has two functions including a function of lens and a function of reflecting a beam and causing the beam to travel to observer&#39;s eye. 
         [0114]    The prism lens unit  62  has a total reflection surface  63  and a lens surface  64 . A portion between the total reflection surface  63  and the lens surface  64  is made of a material having a refractive index. For example, the prism lens unit  62  is achieved such that the total reflection surface  63  and the lens surface  64  are resin-molded and the total reflection surface  63  is metal-coated. 
         [0115]    As shown in the drawings, when an emitting surface  66  is a flat plane, a beam reflected by the surface returns to the image generation element  7  and travels to the observer&#39;s eye again so as to generate an optical path of stray light. For this reason, a stray light removing element  65  is mounted in place of the protecting element  6 . The stray light removing element  65  is obtained by adding a ¼ wavelength plate function to a protecting element, and can be easily achieved by sticking a ¼ wavelength plate which is an inexpensive film to the protecting element  6 . 
         [0116]    As the image generation element  7 , as described above, a liquid-crystal element is supposed. An ordinary liquid-crystal element includes a polarization film. In use of the ¼ wavelength plate, polarized light traveling from the image generation element  7  and polarized light returning to the image generation element  7  can be made orthogonal to each other. For this reason, stray light can be removed with a polarization film included in the image generation element  7 . 
         [0117]    When a configuration like the prism lens unit  62  is used, light reflected by the upper surface or the lower surface of the prism lens unit  62  to generate stray light. In order to prevent the stray light, as shown in  FIG. 12 , a light-shielding opening  67  is preferably formed around the emitting surface  66  or the lens surface  64  of the prism lens unit  62  to remove stray light. 
         [0118]    As described above, in use of the prism lens unit  62 , two components in the image projection device  1  are combined into one component to obtain advantages in productivity and cost. 
       Seventh Embodiment 
       [0119]    A seventh embodiment of the present invention will be described below with reference to  FIG. 13 . 
         [0120]    An image projection device  81  will be described below. 
         [0121]      FIG. 13  is a schematic view showing the image projection device  81 . The drawing is an upper view when viewing from above observer&#39;s eye, and the upside of paper in  FIG. 13  is a direction corresponding to the upside of the eye. 
         [0122]    In the image projection device  81 , the configuration of an image generation unit  89  is different from that in the image projection device  1  according to the first embodiment. 
         [0123]    The image generation unit  89  includes a light source  82 , a polarization beam splinter  83 , and an image generation element  84 . The light source  82  is a light source emitting lights of three colors, i.e., red, blue, and the light source  82  is achieved such that green, includes red, blue, and green LEDs are disposed and a diffusion plate is disposed on the surface of the light source. Only polarized light of light emitted from the light source  82  is reflected by the polarization beam splitter  83  and travels to the image generation element  84 . Since the polarization beam splitter  83  is a conventional product, the polarization beam splitter  83  will not be described below. 
         [0124]    As the image projection element  84 , a reflection type liquid-crystal element free from color filter is supposed. The liquid-crystal element uses a conventional technique as an LCOS, and the details of the liquid-crystal element will not be described. Since the reflection type liquid-crystal element free from color filter can achieve pixels smaller than those of a liquid-crystal element with color filter, a high resolution can be achieved. 
         [0125]    Of a beam, only a beam serving as an image is polarized and orthogonally transformed by the image generation element  84 . For this reason, the image is incident on the polarization beam splitter  83  again. However, at this time, the image is reflected by the polarization beam splitter and directly travels. 
         [0126]    The image traveling through the polarization beam splitter, as described above, is reflected on observer&#39;s eye through the protecting element  6 , the lens unit  3 , and the total reflection unit  4 . 
         [0127]    Coloring can be achieved by using a conventional light-emission control method of the light source  82  which is called a field sequential color. 
         [0128]    As described above, the image projection device  81  can obtain an advantage, i.e., a high resolution by using a reflection type liquid-crystal element free from color filter as the image generation element  84 . 
       Eighth Embodiment 
       [0129]    An eighth embodiment of the present invention will be described below with reference to  FIGS. 14A and 14B . 
         [0130]    An image projection device  91  will be described below. 
         [0131]      FIGS. 14A and 14B  are schematic views showing the image projection device  91 , like  FIGS. 1A and 1B , in which  FIG. 14A  is a side view when viewing from observer&#39;s eye side and  FIG. 14B  is an upper view when viewing from above observer&#39;s eye. The upside of paper in  FIG. 11A  is a direction corresponding to the upside of the eye. 
         [0132]    The image projection device  91  is a modification of the image projection device  61  according to the sixth embodiment. The image projection device  91  is different from the image projection device  61  in the shape of a support unit  92 . 
         [0133]    The support unit  92  has a lower part which is not straight unlike a support mechanism  93  and which is curved. When the curved lower part is used, the strengths of the projection unit  213  on which stress is concentrated and the root of the image generation unit  211  can be advantageously improved. 
       Ninth Embodiment 
       [0134]    A ninth embodiment of the present invention will be described below with reference to  FIG. 15 . 
         [0135]    An image projection device  101  will be described below. 
         [0136]      FIGS. 15(A) to 15(C)  are schematic views showing the image projection device  101 , like  FIGS. 1A and 1B , in which  FIG. 15(A)  is a side view when viewing from observer&#39;s eye side,  FIG. 15(B)  is an upper view when viewing from above observer&#39;s eye, and  FIG. 15(C)  is a view when viewing from the left side of paper in  FIG. 15(B) . The upside of paper in  FIG. 15(A)  is a direction corresponding to the upside of the eye. 
         [0137]    The image projection device  101  is a modification of the image projection device  91  according to the eighth embodiment. The image projection device  101  is different from the image projection device  91  in the shape of a support unit  102 . 
         [0138]    The shape of the support unit  102  on a side far from observer&#39;s eye is not straight unlike a support mechanism  103  and is curved. When the support unit  102  is curved, the strength of the support unit can be more improved. 
         [0139]    In this case, when the width of the support unit is reduced in a direction away from observer&#39;s eye as shown in  FIG. 15(C) , the strength of the support unit  102  can be improved without losing a see-through function. 
       Tenth Embodiment 
       [0140]    A tenth embodiment of the present invention will be described below with reference to  FIG. 16 . 
         [0141]    An image projection device  111  will be described below. 
         [0142]      FIGS. 16A and 16B  are schematic views showing the image projection device  111 , like  FIGS. 1A and 1B ,  FIG. 16A  is a side view when viewing from observer&#39;s eye side,  FIG. 16B  is an upper view when viewing from above observer&#39;s eye. The upside of paper in  FIG. 16A  is a direction corresponding to the upside of the eye. 
         [0143]    The image projection device  111  is a modification of the image projection device  101  according to the ninth embodiment. The image projection device  111  is different from the image projection device  101  in the shape of the projection unit  213 . 
         [0144]    The projection unit  213  includes a protecting unit  113 . The protecting unit  113  is disposed to prevent the projection unit  213  from sticking in observer&#39;s eye when a user slips and bumps into something, or the support unit  102  is broken by some chance. For this reason, the protecting unit  113  is desirably made of a flexible material such as rubber. As a matter of course, in order to prevent a see-through function from being deteriorated, the protecting unit  113  is desirably devised to have a narrow width. 
       Eleventh Embodiment 
       [0145]    An eleventh embodiment of the present invention will be described below with reference to  FIG. 17 . 
         [0146]    An image projection device  121  will be described below. 
         [0147]      FIGS. 17A and 17B  are schematic views showing the image projection device  121 , like  FIGS. 1A and 1B ,  FIG. 17A  is a side view when viewing from observer&#39;s eye side, and  FIG. 17B  is an upper view when viewing from above observer&#39;s eye. The upside of paper in  FIG. 17A  is a direction corresponding to the upside of the eye. 
         [0148]    The image projection device  121  is a modification of the image projection device  111  according to the tenth embodiment. In the image projection device  121 , in comparison with the image projection device  111 , a beam traveling path extending from an image generation unit  122  to a projection unit  124  bent. 
         [0149]    For this reason, the shape of the prism lens unit  125  is devised. An emitting surface  127  is orthogonal to an arrow  10  which is an eye gaze direction like the emitting surface  66 . A lens unit  126  is orthogonal to an image traveling direction. At this time, the angle of a total reflection unit  128  is adjusted such that a beam is orthogonal to the lens unit  126  and the emitting surface  127  to make it possible to achieve the configuration. 
         [0150]    As described above, when the traveling path is bent, the image projection device  121  is formed along the shape of a head. Improvement in design can be obtained as an advantage. Furthermore, since the angle is adjusted to cause the image generation unit  122  to be close to a person, a wide field of view can also be advantageously secured. 
         [0151]    When an angle between a direction of a beam from the image generation unit  122  to the projection unit  124  and the arrow  10  exceeds 45°, the image projection device  121  hits at the wearer. For this reason, the angle is preferably set within the range of 45° to 90°. 
       Twelfth Embodiment 
       [0152]    A twelfth embodiment of the present invention will be described below with reference to  FIG. 18 . 
         [0153]    A head mounted display  131  will be described below. 
         [0154]      FIG. 18  shows a state in which a person wears the head mounted display  131 , and  FIG. 19  shows a system block of the head mounted display  131 . 
         [0155]    The head mounted display  131  includes the image projection device  121 , image pickup means  148  such as image pickup elements  9  and  136 , a power supply unit  135 , a communication unit  133 , a control unit  134  such as a voice sensing element  139  and a touch sensing element  158 , a controller  140 , sensing means  147  such as an acceleration sensing element  145  and a position sensing element  146 , a distance measurement unit  149 , and the like. 
         [0156]    As the power supply unit  135 , a rechargeable power supply like a battery is mainly supposed. As the communication unit, a communication device such as a Wi-Fi device or a Bluetooth (tradename) device which can access information on the Internet or an electronic device held by a wearer  130 . The touch sensing element  158  is a sensing element such as a touch panel. The voice sensing element  139  is a device such as a microphone sensing words of a wearer. As the control unit  134 , a processing means to operate the head mounted display  131  by the wearer  130  on the basis of voice recognition using the voice sensing element  139 , finger position information using the touch sensing element, or the like is supposed. The acceleration sensing element  145  is an element which detects an acceleration by using a principle of a piezoelectric element, an electric capacitance, or the like. The position sensing element  146  is an element such as a GPS which can sense a position. As the distance measurement unit  149 , a device which can measure a distance by using the Time-of-Flight principle is supposed. The controller  140  is a main chip controlling the devices and the means. 
         [0157]    In the head mounted display  131 , an image  159  formed by the image projection device  121  can be observed in a field of vision  137  of the wearer  130 . The head mounted display  131  includes an angle adjustment mechanism  132  which can adjust an angle such that the image  159  can be observed in the field of vision  137 . The wearer  130  can preferably adjust the position of the image  159 . The angle adjustment mechanism  132  as described above can be easily achieved by, for example, a hinge or the like. 
         [0158]    In  FIG. 18 , it is supposed that the image projection device  121  is loaded on a right eye  132 . However, for example, when the image projection device  41  is used, the image projection device  41  can also be loaded on a left eye  142 . 
         [0159]    Since the image projection device  121  is shaped such that a traveling path of a beam from the image generation unit  122  to the projection unit  124  is bent, it can be confirmed that the image projection device  121  is formed along the shape of the head of the wearer  130 . 
         [0160]    Since the head mounted display  131  is used to be fixed to a head such that the head mounted display  131  is put on ears  143  and  144 , temporal portions, back of the head, or the like, both the hands become free. 
         [0161]    A method of using the image projection device  121  will be described below. For example, when a pathway has a small step when the wearer  130  is walking, the controller  140  processes an image signal acquired by the image pickup means  148 , recognizes the presence of the step, and can inform the wearer of information such as “caution about step” on the image projection device  12 . At this time, the controller  140  also has a function of causing the light source  8  to emit light and sending a predetermined image signal to the image generation element  7 . 
         [0162]    The power supply unit  135  supplies a necessary electric power to a necessary means or device through the controller  140 . At this time, the controller  140  also has a function of supplying an electric power to the device as needed. 
         [0163]    When social network information related to the wearer  130 , for example, information representing that a train used in commute has been stopped by an accident is generated, the communication unit  133  transmits the information to the controller  140  to make it possible to inform the wearer of information representing “delay of the commuter train by accident” through the image projection device  121 . At this time, the controller  140  has a function of always monitoring information on the Internet in response to requests from the wearer  130 . 
         [0164]    When the wearer  130  begins to read her/his newspaper or magazine, the distance measurement unit  149  transmits distance information of an object in front of the wearer  130  to the controller  140  and ON/OFF-controls the power supply to the liquid-crystal lens element  352  included in the image projection device  351  to make it possible to change the liquid-crystal lens element  352  to cause the liquid-crystal lens element to focus on a place near the object. At this time, the controller  140  has a function of capable of driving the liquid-crystal lens element  352  or the like included in the image projection device  351 . The controller  140  also has a function of monitoring information of the distance measurement unit  149 . 
         [0165]    When the wearer wants to take a picture through the image pickup means  148 , the controller  140  uses voice recognition using the voice sensing element  139  or detects a request from the wearer  130  from the control unit  134  such as position information of a finger obtained by using the touch sensing element to drive the image pickup means  148  to make it possible to take a picture. In this case, the information of the taken picture can be moved by using the communication unit  133  onto a cloud network held by wearer  130  on the Internet. 
         [0166]    The controller  140  is desired to always preferentially process a signal from the control unit  134 . 
         [0167]    When the wearer  130  is sleeping in a train, the controller  140  can also perform power saving such as turning-OFF control of the image projection device  121  on the basis of pieces of information obtained from the acceleration sensing element  145  sensing swing of her/his head and the image pickup means  148  sensing being in the train. 
         [0168]    When the wearer  130  is in a region different from a region she/he is always in, the controller  140  detects a state in which the place is different from the place she/he is always in to determine whether she/he takes a private trip or a business trip and obtains a guidance of the trip, food information about the place she/he is staying, or the like from the communication unit  133  to make it possible to inform the wearer of the pieces of information. 
         [0169]    As described above, the controller  140  also has a function of determining contents to be processed on the basis of pieces of information. 
         [0170]    The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments have been described in detail to understandably explain the present invention, and are not always limited to embodiments including all the configurations described above. Some of the configurations of a certain embodiment can be replaced with configurations of another embodiment, and, to the configurations of a certain embodiment, the configurations of another embodiment can also be added. With respect to some of the configurations of each of the embodiments, addition, deletion, and replacement of other configurations can be performed. 
         [0171]    Some or all of the configurations, the functions, the processing units, the processing means, and the like described above may be achieved by hardware such that, for example, integrated circuits are designed. The configurations, the functions, and the like may be achieved by software such that a processor interprets and executes programs achieving these functions. Information such as programs, tables, and files achieving the functions can be stored in a recording device such as a memory, a hard disk device, or an SSD or a recording medium such as an IC card or an SD card. 
         [0172]    Control lines and information lines which are required for the explanations are described, and all the control lines and the information lines are not always described in the product. Actually, almost all the configurations may be regarded to be connected to each other. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  . . . image projection device 
           3  . . . lens unit 
           4  . . . total reflection surface 
           6  . . . protecting element 
           7  . . . image generation element 
           8  . . . light source 
           9  . . . image pickup element 
           130  . . . wearer 
           131  . . . head mounted display 
           133  . . . communication unit 
           134  . . . control unit 
           135  . . . power supply unit 
           139  . . . voice sensing element 
           140  . . . controller 
           145  . . . acceleration sensing element 
           146  . . . position sensing element 
           147  . . . sensing means 
           149  . . . distance measurement unit 
           158  . . . touch sensing element 
           211  . . . image generation unit 
           212  . . . support unit 
           213  . . . projection unit