Patent Publication Number: US-2022236579-A1

Title: Image display device

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-011760, filed Jan. 28, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an image display device that enables observation of a virtual image, and particularly relates to an image display device including a display unit for both eyes. 
     2. Related Art 
     An eyeglass virtual image display device is known in which an optical system for the left eye from a first display element to a light-guiding member and an optical system for the right eye from a second display element to the light-guiding member are assembled with a frame extending in a lateral direction by screwing, etc. to arrange the left and right optical systems in front of the eyes (JP-A-2017-211674). Note that, in this virtual display device, in order to reduce the effects of manufacturing tolerances and assembly tolerances, the display element is aligned with the optical system using a convex portion provided at one of a holding member of the display element and a lens barrel of a projection lens, and a concave portion provided at the other. 
     In the device of JP-A-2017-211674 described above, the final arrangement is determined by assembling the optical system for the left eye and the optical system for the right eye to the frame, therefore, there is a possibility of being affected by manufacturing tolerances of the frame and assembly tolerances of the frame. 
     SUMMARY 
     An image display device according to one aspect of the present disclosure includes a first display unit that includes a first frame, a second display unit that includes a second frame, and a fixing member that fixes a first position of the first display unit with respect to a second position the second display unit, wherein the fixing member rotates the second display unit with respect to the first display unit system in rotational directions around two or more axes. 
     A manufacturing method for an image display device according to one aspect of the present disclosure is a manufacturing method for an image display device including a first display unit including a first frame and a first optical system, a second display unit including a second frame and a second optical system, and a fixing member configured to fix the first display unit and the second display unit relative to each other, wherein the fixing member has a shape configured to rotate the first optical system and the second optical system in rotational directions around two or more axes, the fixing member being configured to, after alignment, stop rotation of the first optical system and the second optical system with respect to the fixing member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external perspective view illustrating a wearing state of an image display device according to a first exemplary embodiment. 
         FIG. 2  is a plan view, front view, side view, and bottom view of the image display device. 
         FIG. 3  is a front view, side view, perspective view, etc. illustrating an interior of the image display device with an exterior member removed. 
         FIG. 4  is an exploded perspective view of the remainder of the portion where the exterior member is removed from the image display device. 
         FIG. 5  is a plan view and a bottom view of an optical unit at which left and right display units are combined. 
         FIG. 6  illustrates a perspective view describing a coupling between a first frame and a fixing member, a perspective view describing a positional relationship between the fixing member and a first cover member, and a perspective view describing a positional relationship between the first frame, the fixing member, and the first cover member. 
         FIG. 7  illustrates a bottom view of an upper exterior member and a plan view of a lower exterior member. 
         FIG. 8  is a conceptual side cross-sectional view illustrating an optical system inside the image display device. 
         FIG. 9  is a diagram illustrating distortion correction of a display image. 
         FIG. 10A  is a front view, a plan view, and a perspective view of the fixing member. 
         FIG. 10B  is a conceptual cross-sectional view illustrating a fixed state of the fixing member to a frame. 
         FIG. 11  is a partially broken perspective view illustrating a coupling, etc. between a first display unit and the fixing member. 
         FIG. 12A  is an enlarged cross-sectional view illustrating fixing of the first frame by a first fixing portion. 
         FIG. 12B  is an enlarged cross-sectional view illustrating fixing of a second frame by a second fixing portion. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, a structure, operation, manufacturing method, etc. of an image display device according to the present disclosure will be described with reference to  FIGS. 1 to 3 , etc. 
       FIG. 1  is a diagram illustrating a wearing state of an image display device  200 . The image display device  200  is a head-mounted display (hereinafter, also referred to as HMD)  201 , and causes an observer or a wearer US who wears the head-mounted display  201  to recognize an image as a virtual image. In  FIG. 1 , etc., X, Y, and Z correspond to an orthogonal coordinate system, a +X direction corresponds to a lateral direction in which the two eyes EY of the observer or wearer US who is wearing the image display device  200  or HMD  201  are arranged, a +Y direction corresponds to an upward direction orthogonal to the lateral direction in which the two eyes EY of the wearer US are arranged, and a +Z direction corresponds to a direction to the front or a forward direction for the wearer US. A ±Y direction is parallel to a vertical axis or a vertical direction. 
     The image display device  200  includes a main body  200   a  disposed to cover the front of the wearer US and a pair of temple support devices  200   b  that support the main body  200   a . The main body  200   a , when functionally viewed, includes a first display device  100 A for the right eye and a second display device  100 B for the left eye. The first display device  100 A includes a display driving unit  102  disposed at an upper portion thereof, and a combiner  103   a  that is shaped like a spectacle lens and covers the front of the eye. Similarly, the second display device  100 B includes a display driving unit  102  disposed at an upper portion thereof, and a combiner  103   b  that is shaped like a spectacle lens and covers the front of the eye. 
     The appearance of the main body  200   a  of the image display device  200  will be described with reference to  FIG. 2 . In  FIG. 2 , a region AR 1  is a plan view of the main body  200   a , a region AR 2  is a front view of the main body  200   a , a region AR 3  is a right side view of the main body  200   a , and a region AR 4  is a bottom view of the main body  200   a . A pair of the display driving units  102  disposed on the +Y side or the upper side of the main body  200   a  are coupled and integrated, and are covered by a dome-shaped upper exterior member  107   a  elongated in the lateral direction and a flat plate-shaped lower exterior member  107   b . The first combiner  103   a  and the second combiner  103   b  have a shape such that an upper portion of a hemisphere protruding in the forward or the +Z direction is cut, and is disposed so as to protrude downward from the lower exterior member  107   b.    
     With reference to  FIG. 3 , an overview of an internal structure in which the upper exterior member  107   a  and the lower exterior member  107   b  have been removed from the main body  200   a  illustrated in  FIG. 2  will be described. In  FIG. 3 , a region BR 1  is a front view with an upper portion of the main body  200   a  exposed, a region BR 2  is a right side view with the upper portion of the main body  200   a  exposed, a region BR 3  is a perspective view with the upper portion of the main body  200   a  exposed, and a region BR 4  is a perspective view with an internal optical system of the main body  200   a  exposed. The first display device  100 A for the right eye includes a first display element  11   a , a first optical system  12   a , and the first combiner  103   a , as the first display unit  100   a . A first frame  61   a  described below is also an element of the first display unit  100   a . The first optical system  12   a  is covered with a first cover member  71   a , which is an inner cover. The first display element  11   a  is disposed so as to close an opening  710  of the first cover member  71   a , and is fixed to an outer frame of the first optical system  12   a  via a first holder  72   a  having a rectangular frame shape. 
     As illustrated in  FIG. 4 , the first optical system  12   a  is fixed to an upper surface of the plate-shaped first frame  61   a  by adhesion, etc., and the first combiner  103   a  is fixed to the front half of the periphery of the first frame  61   a  by adhesion, etc. at an upper end thereof. 
     Referring back to  FIG. 3 , the second display device  100 B includes a second display element  11   b , a second optical system  12   b , and the second combiner  103   b , as the second display unit  100   b . A second frame  61   b  described below is also an element of the second display unit  100   b . The second optical system  12   b  is covered with a second cover member  71   b , which is an inner cover. The second display element  11   b  is disposed so as to close the opening  710  of the second cover member  71   b , and is fixed to an outer frame of the second optical system  12   b  via the second holder  72   b  having a rectangular frame shape. The second display device  100 B for the left eye has the same structure and function as the first display device  100 A for the right eye. In other words, the second display element  11   b  is the same as the first display element  11   a , the second optical system  12   b  is the same as the first optical system  12   a , and the second combiner  103   b  is the same as the first combiner  103   a . However, in a case where the first optical system  12   a , the first combiner  103   a , etc. have asymmetry with respect to the left and right X direction, the second optical system  12   b , the second combiner  103   b , etc. are obtained by laterally inverting the first optical system  12   a , the first combiner  103   a , etc. 
     As illustrated in  FIG. 4 , the second optical system  12   b  is fixed to an upper surface of the plate-shaped second frame  61   b  by adhesion, etc., and the second combiner  103   b  is fixed to the front half of the periphery of the second frame  61   b  by adhesion, etc. at an upper end thereof. 
     Referring back to  FIG. 3 , the first display device  100 A and the second display device  100 B are coupled via a fixing member  78  therein. The fixing member  78  is a rod-shaped metal member, and is formed from, for example, a magnesium alloy. By forming the fixing member  78  from the magnesium alloy, the first frame  61   a  and the second frame  61   b  can be cooled by heat dissipation. The fixing member  78  fixes the first display unit  100   a  and the second display unit  100   b  relative to each other at both ends thereof. The fixing member  78  is a member corresponding to an arm of a balance, and supports a pair of the display units  100   a ,  100   b  corresponding to a pair of plates in the center. The fixing member  78  has a shape that allows the first optical system  12   a  and the second optical system  12   b  to rotate in rotational directions around two or more axes when the first display unit  100   a  and the second display unit  100   b  are aligned prior to fixing. 
     The support of the first display unit  100   a  and the second display unit  100   b  by the fixing member  78  will be described with reference to  FIGS. 4 to 6 . In  FIG. 5 , a region CR 1  is a plan view of an optical unit OU coupled to the left and right display units  100   a ,  100   b , and a region CR 2  is a bottom view of the optical unit OU. In  FIG. 6 , a region DR 1  is a perspective view describing a coupling between the first frame  61   a  and the fixing member  78 , a region DR 2  is a perspective view describing a positional relationship between the fixing member  78  and the first cover member  71   a , and a region DR 3  is a perspective view describing a positional relationship between the first frame  61   a , the fixing member  78 , and the first cover member  71   a . Fixing portions  81   a ,  82   a , which are spherical members similar to those of the ball joint components, are formed at both ends of the fixing member  78 . After the first display unit  100   a  and the second display unit  100   b  are aligned, these fixing portions  81   a ,  82   a  are adhered to concave portions  81   b ,  82   b , which are hemispherical indentation members provided at the inner ends of the display units  100   a ,  100   b  or the frame  61   a ,  61   b  by an adhesive material, etc., whereby the rotation is stopped. A photocurable resin material can be used as the adhesive material for fixing the fixing portions  81   a ,  82   a  to the concave portions  81   b ,  82   b , however, without being limited thereto, a thermosetting or room temperature curing resin material, etc. can be used. A coupling member  81  that combines the fixing portion  81   a  and the concave portion  81   b  is covered by an extending portion  71   c  of the first cover member  71   a . A coupling member  82  that combines the fixing portion  82   a  and the concave portion  82   b  is also covered by an extending portion  71   c  of the second cover member  71   b.    
     The first frame  61   a  is a semi-circular plate-shaped metal member, and is formed, for example, from a magnesium alloy. By forming the first frame  61   a  from the magnesium alloy, heat dissipation efficiency of heat generated by the display element  11   a , etc. can be increased. The concave portions  81   b  are formed at both the left and right ends of the first frame  61   a , but only one of the concave portions  81   b  is used for coupling with the fixing member  78 . An optical aperture OA is formed at the first frame  61   a , and a plate-shaped optical element  28  that seals the optical aperture OA is disposed. The plate-shaped optical element  28  is part of the first optical system  12   a . The second frame  61   b  is a semi-circular metal member, and is formed, for example, from a magnesium alloy. By forming the second frame  61   b  from the magnesium alloy, heat dissipation efficiency of heat generated by the display element  11   b , etc. can be increased. The concave portions  82   b  are formed at both the left and right ends of the second frame  61   b , but only one of the concave portions  82   b  is used for coupling with the fixing member  78 . An optical aperture OA is also formed at the second frame  61   b , and a plate-shaped optical element  28  that seals the optical aperture OA is disposed. 
     The upper exterior member  107   a  and the lower exterior member  107   b  will be described with reference to  FIG. 7 . In  FIG. 7 , a region ER 1  is a bottom view illustrating the inside of the upper exterior member  107   a , and a region ER 2  is a plan view illustrating the inside of the lower exterior member  107   b . The upper exterior member  107   a  and the lower exterior member  107   b  are formed from a resin material. An outer edge  7   a  of the upper exterior member  107   a  and an outer edge  7   b  of the lower exterior member  107   b  have the same shape. By abutting them, a space for accommodating the first optical system  12   a  and the second optical system  12   b  illustrated in  FIG. 3  can be formed. The upper exterior member  107   a  and the lower exterior member  107   b  are fixed using fastening portions  7   f ,  7   g , which are screw holes, etc. The lower exterior member  107   b  has a pair of openings OP 1 , and the first frame  61   a  and the second frame  61   b  can be disposed at the openings OP 1 , as indicated by a dotted lines. Gaps GP are provided between the openings OP 1  and the frames  61   a ,  61   b , and allows the frames  61   a ,  61   b  to shift in position with respect to the X-Y plane or the Y direction within the openings OP 1 . That is, the first display unit  100   a  and the second display unit  100   b  illustrated in  FIG. 3 , etc. are fixed to the lower exterior member  107   b  while remaining aligned with each other, and even in a state of being accommodated in the upper exterior member  107   a  and the lower exterior member  107   b , the positional relationship between the display units  100   a ,  100   b  upon completion of positioning is maintained. Screwing hole  7   j  are formed at the lower exterior member  107   b  and can be fixed by screwing to a pair of fastening portions  78   z  provided at a bridge  78   a  of the fixing member  78 . 
     Referring to  FIGS. 3 and 4 , an elastic sheet  75  is disposed above the first frame  61   a  and the second frame  61   b . An outer circumferential portion  75   a  of the elastic sheet  75  is sandwiched between the outer edge  7   a  of the upper exterior member  107   a  illustrated in  FIG. 7  and the outer edge  7   b  of the lower exterior member  107   b  to allow hermetic or liquid-tight sealing between the outer exterior members  107   a ,  107   b . A pair of openings OP 21  and OP 22  are formed at the elastic sheet  75 . An inner circumferential portion  75   b  around one opening OP 21  is disposed so as to be sandwiched between the upper surface of the first frame  61   a  and the lower end of the first cover member  71   a  at the inner end, and is adhered to the upper surface of the first frame  61   a  at a position corresponding to the outer edge of the first frame  61   a , to allow hermetic or liquid-tight sealing between the first frame  61   a  and the first cover member  71   a . An inner circumferential portion  75   c  around the other opening OP 22  is disposed so as to be sandwiched between the upper surface of the second frame  61   b  and the lower end of the second cover member  71   b  at the inner end, and is adhered to the upper surface of the second frame  61   b  at a position corresponding to the outer edge of the second frame  61   b , to allow hermetic or liquid-tight sealing between the second frame  61   b  and the second cover member  71   b.    
     With reference to  FIG. 3 , a rectangular plate-shaped circuit board  91  is disposed above the fixing member  78  between the left and right display units  100   a ,  100   b . The circuit board  91  includes a control device  92  that controls display operation of the first display element  11   a  and the second display element  11   b . The control device  92  outputs a drive signal corresponding to the display image to the left and right display elements  11   a ,  11   b  to control the display operation of the left and right display elements  11   a ,  11   b . The control device  92  includes, for example, an IF circuit, a signal processing circuit, etc., and causes the left and right display elements  11   a ,  11   b  to display a two-dimensional image according to the image data or the image signal received from the outside. Although not shown, the control device  92  includes a main board that controls the operation of the first display device  100 A and the operation of the second display device  100 B. The main substrate may have, for example, an interface function that communicates with an external device (not shown) and performs signal conversion on a signal received from the external device, and an integrated function that links between the display operation of the first display device  100 A and the display operation of the second display device  100 B. 
     The circuit board  91  is supported on the fixing member  78  by a substrate support portion  74 . The circuit board  91  is fixed at the substrate support portion  74 . The substrate support portion  74  is a member made of resin covering the fixing member  78  from the upper, front, and rear, and is detachable from the fixing member  78  together with the circuit board  91  by a snap fit using a fitting portion  51 . 
       FIG. 8  is a side cross-sectional view illustrating an optical structure of the first display unit  100   a . The first display unit  100   a  includes the first display element  11   a  and an imaging optical system  20 . The imaging optical system  20  is also referred to as a light guide optical device. The imaging optical system  20  includes a projection lens  21 , a prism mirror  22 , the plate-shaped optical element  28 , and a see-through mirror  23 . The projection lens  21 , the prism mirror  22 , and the plate-shaped optical element  28  of the imaging optical system  20  correspond to the first optical system  12   a  illustrated in  FIG. 3 , etc., and the see-through mirror  23  corresponds to the first combiner  103   a . The first display element  11   a , the projection lens  21 , and the prism mirror  22  are fixed to the first frame  61   a  in a state of being aligned with each other by a frame body (not illustrated), and is accommodated in a space SP 1  sandwiched between the first cover member  71   a  and the first frame  61   a . The plate-shaped optical element  28  is disposed so as to be fitted into a step formed at the optical aperture OA of the first frame  61   a , and the periphery of the optical aperture OA is kept airtight state. 
     The first display element  11   a  is a spontaneous light emission type display device. The first display element  11   a  is, for example, an organic EL (Organic Electro-luminescence) display, and forms a color still image or moving image on a two-dimensional display surface  11   d . The first display element  11   a  is disposed along the X-Y plane that is inclined by being rotated about the X-axis with respect to an X-Y plane. The first display element  11   a  is driven by the control device  92  provided at the circuit board  91  to perform display operation. The first display element  11   a  is not limited to the organic EL display, and can be replaced with a micro LED display or a display device using an inorganic EL, an organic LED, a laser array, a quantum dot light emitting element, etc. The first display element  11   a  is not limited to a spontaneous light emission type imaging light generation device, and may include an LCD and another light modulation element, and may form an image by illuminating the light modulation element with a light source such as a backlight. As the first display element  11   a , a LCOS (Liquid crystal on silicon, LCoS is a registered trademark), a digital micro-mirror device, etc. may be used instead of an LCD. 
     The projection lens  21  causes the imaging light ML emitted from the first display element  11   a  to pass therethrough and then to be incident on the prism mirror  22 . The projection lens  21  focuses the imaging light ML emitted from the first display element  11   a  into a state close to a parallel luminous flux. The projection lens  21  includes a first lens  21   p  and a second lens  21   q . The prism mirror  22  has an inner reflection surface  22   b , and causes the imaging light ML emitted from the projection lens  21  to be incident on a light incident surface  22   a , to be totally reflected by the inner reflection surface  22   b , and to be emitted from a light emission surface  22   c . At this time, the prism mirror  22  emits the imaging light ML incident from the front such that it is bent in a direction inclined with respect to a direction in which an incident direction is reversed (a direction of the light source seen from the prism mirror  22 ). The plate-shaped optical element  28  causes the imaging light ML from the prism mirror  22  to pass therethrough while refracting it, and then to be incident on the see-through mirror  23 . 
     The see-through mirror  23  is a curved plate-shaped optical member that serves as a concave surface mirror, and reflects the imaging light ML incident from the prism mirror  22  via the plate-shaped optical element  28  toward a pupil position PP. The pupil position PP is a position at which the imaging light ML from each of points on the display surface  11   d  is incident so as to be overlapped from an angular direction corresponding to a position of each of points on the display surface  11   d  in a predetermined divergent state or a parallel state. The see-through mirror  23  covers the pupil position PP at which the eye EY or the pupil is disposed, has a concave shape toward the pupil position PP, and has a convex shape toward the outside. The see-through mirror  23  is a mirror plate having a structure in which a mirror film  23   c  is formed at a front surface or a back surface of a plate-shaped body  23   b . The reflection surface  23   a  of the see-through mirror  23  has transmissive properties. The external light OL that has passed through the see-through mirror  23  and a support plate  41  therearound is also incident on the pupil position PP. In other words, the wearer US wearing the image display device  200  can observe a virtual image of the imaging light ML in a state in which the imaging light ML overlaps with the external image. 
     In the above, optical surfaces constituting the projection lens  21 , the prism mirror  22 , the plate-shaped optical element  28 , and the see-through mirror  23  includes a free-form surface, and at least some of the optical surfaces may be replaced with an aspheric surface or a spherical surface. 
     The imaging optical system  20  is an off-axis optical system OS due to the see-through mirror  23  being a concave mirror, etc. In the case of the present exemplary embodiment, the projection lens  21 , the prism mirror  22 , the plate-shaped optical element  28 , and the see-through mirror  23  are disposed non-axisymmetric and have a non-axisymmetric optical surface. In the imaging optical system  20 , that is, the off-axis optical system OS, an optical axis AX is bent so that the optical axis AX extends along an off-axis surface (a surface parallel to the Y-Z surface) corresponding to a plane of the drawing. In the imaging optical system  20 , the optical elements  21 ,  22 , and  23  are arranged along the off-axis surface by bending the optical axis AX in the off-axis plane parallel to the Y-Z plane. The imaging optical system  20  includes optical axis portions AX 1 , AX 2 , and AX 3  that are disposed along the off-axis surface (a surface parallel to the Y-Z plane) which is a reference surface extending in the longitudinal direction and are inclined with respect to each other before and after the reflection surface. The optical axis AX as a whole extends along an optical path of the main rays emitted from the center of the display element  11   a  and passes through the center of the eye ring ER or the pupil corresponding to an eye point. The optical axis AX is disposed in a Z shape by the plurality of optical axis portions AX 1 , AX 2 , and AX 3  when seen in a transverse cross section parallel to the Y-Z plane. In other words, in the off-axis surface parallel to the Y-Z plane, an optical path P 1  from the projection lens  21  to an inner reflection surface  22   b , an optical path P 2  from the inner reflection surface  22   b  to the see-through mirror  23 , and an optical path P 3  from the see-through mirror  23  to the pupil position PP are arranged to be bent in a Z shape in two stages. 
     As illustrated in  FIG. 9 , the display image formed at the display surface  11   d  of the first display element  11   a  is set to a modified image DA 1  having a distortion such as trapezoidal distortion. That is, since the imaging optical system  20  is the off-axis optical system OS, it is not easy for the optical system itself to remove distortion such as trapezoidal distortion. In this way, a pixel array of a projected image IG 1  of the virtual image observed at the pupil position PP via the imaging optical system  20  can be made into a grid pattern corresponding to an original display image DA 0 , and the outline thereof can be made rectangular by causing the image displayed on the first display element  11   a  to have reverse distortion that cancels out the distortion formed by the projection lens  21 , the prism mirror  22 , the plate-shaped optical element  28 , and the see-through mirror  23 . In other words, the first display element  11   a  corrects the distortion formed by the projection lens  21 , the prism mirror  22 , the plate-shaped optical element  28 , and the see-through mirror  23 . As a result, aberrations can be suppressed as a whole including the first display element  11   a  while allowing the distortion generated by the see-through mirror  23 , etc. Thus, the degree of freedom in the arrangement and size of optical elements such as the prism mirror  22  is increased, and it is possible to easily secure the optical performance of the first display unit  100   a  while achieving miniaturization of the first display unit  100   a.    
     Although the first display unit  100   a  has been described above, the second display unit  100   b  has a similar structure to that of the first display unit  100   a , and thus a description of the specific structure thereof will be omitted. 
     Hereinafter, the fixing member  78  will be described with reference to  FIG. 10A . In  FIG. 10A , a region FR1 is a front view illustrating the fixing member  78 , a region FR2 is a plan view of the fixing member  78 , and a region FR3 is a perspective view of the fixing member  78 . The fixing member  78  is a dumbbell-shaped member provided with a pair of spherical first fixing portion  81   a  and second fixing portion  82   a  on both ends of the bridge  78   a . The bridge (coupling portion)  78   a  is a coupling portion that couples the first fixing portion  81   a  and the second fixing portion  82   a . The bridge  78   a  has a shape in which both ends of an elongate web  78   j  extending along the X-Z plane are sandwiched between a pair of elongated flanges  78   i  extending along the X-Y plane. That is, the bridge  78   a  is a bar having an H-shape cross-section (see  FIG. 10B ). By configuring the bridge  78   a  as a member having a cross section H, the strength of the bridge  78   a  can be ensured and weight reduction can be achieved. 
     Referring to  FIGS. 10A and 10B , the coupling member  81 ,  82  will be described. The first fixing portion  81   a , which is a spherical member formed at one end of the bridge  78   a  of the fixing member  78 , is rotatably fitted into the first concave portion  81   b , which is a hemispherical indentation member formed at the first frame  61   a . A combination of the first fixing portion  81   a  and the first concave portion  81   b  is referred to as a first coupling member  81 . A spherical convex surface of the first fixing portion  81   a  is referred to as an opposing surface  78   s , and the spherical concave surface of the first concave portion  81   b  is referred to as an opposing surface  61   s . The curvature of the opposing surface  78   s  of the first fixing portion  81   a  is set to be greater than the curvature of the opposing surface  61   s  of the first concave portion  81   b . As a result, the adhesive material can be injected between the opposing surface  78   s  and the opposing surface  61   s  to form an adhesive layer  88  having sufficient thickness, and the adhesive strength between the first fixing portion  81   a  and the first concave portion  81   b  can be increased. The second fixing portion  82   a , which is a spherical member formed at the other end of the bridge  78   a  of the fixing member  78 , is rotatably fitted into the second concave portion  82   b , which is a hemispherical indentation member formed in the second frame  61   b . A combination of the second fixing portion  82   a  and the second concave portion  82   b  is referred to as a second coupling member  82 . The curvature of the spherical opposing surface  78   s  of the second fixing portion  82   a  is set to be greater than the curvature of the spherical opposing surface  61   s  of the second concave portion  82   b . As a result, the adhesive material can be injected between the opposing surface  78   s  and the opposing surface  61   s  to form an adhesive layer  88  having sufficient thickness, and the adhesive strength between the second fixing portion  82   a  and the second concave portion  82   b  can be increased. 
     A bottom surface  78   u  of the bridge (coupling portion)  78   a  is disposed at substantially the same position as a reference line SL extending through the center of symmetry of the first fixing portion  81   a , or on the upper side or the +Y side of the reference line SL. In other words, the bridge  78   a  is coupled to the first fixing portion  81   a  and the second fixing portion  82   a  on the upper side away from the first frame  61   a  and the second frame  61   b  with respect to the center of the first fixing portion  81   a  and the center of the second fixing portion  82   a . Furthermore, a gap GR is secured between the lower surface  78   u  of the bridge  78   a , and the surface  61   f  of the first frame  61   a  and the second frame  61   b . As a result, while ensuring a posture change in which the first frame  61   a  and the second frame  61   b  rotate around the X-axis parallel to the extending direction of the bridge  78   a  and the Z-axis perpendicular to the X-axis and parallel to the extending direction of the first frame  61   a , the fitting between the first fixing portion  81   a  and the first concave portion  81   b  and the fitting between the second fixing portion  82   a  and the second concave portion  82   b  can be deepened to stabilize the coupling between the first frame  61   a  and the second frame  61   b  by the fixing member  78 . Note that, when the size of the first fixing portion  81   a  and the second fixing portion  82   a  is increased, the adhesive area can be increased, making it easier to stabilize the fixing. 
       FIG. 11  is a partially broken perspective view illustrating a state in which the fixing member  78  is fixed to the first display unit  100   a . A first hole  81   k , which passes a screw that screws the first frame  61   a  to the first fixing portion  81   a , is formed at the first fixing portion  81   a . A cylindrical boss  81   m , formed in the center of the first concave portion  81   b  of the first frame  61   a  and extending in the Y direction, is inserted into the first hole  81   k  from below. 
     As illustrated in enlarged detail in  FIG. 12A , the first fixing portion  81   a  of the fixing member  78  is fitted into the first concave portion  81   b  formed at the first frame  61   a . A combination of the first fixing portion  81   a  and the first concave portion  81   b  is the bearing-shaped coupling member  81  that allows relative rotation in the three axial directions within a range of small angles. That is, the coupling member  81  has rotational degrees of freedom along three axes. The extending portion  71   c  of the first cover member  71   a  is disposed covering the coupling member  81 . A hemispherical third concave portion  71   j  into which the first fixing portion  81   a  is inserted is formed at the extending portion  71   c . A concave surface of the third concave portion  71   j  is referred to as an opposing surface  71   s . The opposing surface  71   s  of the third concave portion  71   j  is disposed in the vicinity of the opposing surface  78   s  of the first fixing portion  81   a . Here, the curvature of the spherical opposing surface  71   s  of the third concave portion  71   j  is set to be substantially equal to the curvature of the spherical opposing surface  78   s  of the first fixing portion  81   a , unlike in the case of the first concave portion  81   b . A cylindrical boss  71   m  extending in the vertical Y direction is formed in the center of the third concave portion  71   j , and is inserted into the first hole  81   k  for screwing formed at the first fixing portion  81   a . A screw SB is passed through the hole in the boss  71   m , and a tip SBa of the screw SB is screwed into the boss  81   m  on a side of the first frame  61   a . As a result, the first cover member  71   a  can be fixed to the first frame  61   a  so as to sandwich the fixing member  78  therebetween, and it is possible to reinforce the adhesion of the first fixing portion  81   a  with respect to the first frame  61   a . An adhesive layer can also be provided between the opposing surface  78   s  of the first fixing portion  81   a  and the opposing surface  71   s  of the third concave portion  71   j  to strengthen the fixing. 
     As illustrated in enlarged detail in  FIG. 12B , the second fixing portion  82   a  of the fixing member  78  is fitted into the second concave portion  82   b  formed at the second frame  61   b . A combination of the second fixing portion  82   a  and the second concave portion  82   b  is the bearing-shaped coupling member  82  that allows relative rotation in the three axial directions within a range of small angles. That is, the coupling member  82  has rotational degrees of freedom along three axes. The extending portion  71   c  of the second cover member  71   b  is disposed covering the coupling member  82 . A hemispherical fourth concave portion  71   k  into which the second fixing portion  82   a  is inserted is formed at the extending portion  71   c . A concave surface of the fourth concave portion  71   k  is referred to as an opposing surface  71   s . The opposing surface  71   s  of the fourth concave portion  71   k  is disposed in the vicinity of the opposing surface  78   s  of the second fixing portion  82   a . Here, the curvature of the spherical opposing surface  71   s  of the fourth concave portion  71   k  is set to be substantially equal to the curvature of the spherical opposing surface  78   s  of the second fixing portion  82   a , unlike in the case of the second concave portion  82   b . A cylindrical boss  71   m  extending in the vertical Y direction is formed in the center of the fourth concave portion  71   k , and is inserted into the second hole  82   k  for screwing formed in the second fixing portion  82   a . A screw SB is passed through the hole in the boss  71   m , and a tip SBa of the screw SB is screwed into the boss  82   m  on a side of the second frame  61   b . As a result, the second cover member  71   b  can be fixed to the second frame  61   b  so as to sandwich the fixing member  78  therebetween, and it is possible to reinforce the adhesion of the second fixing portion  82   a  with respect to the second frame  61   b . An adhesive layer can also be provided between the opposing surface  78   s  of the second fixing portion  82   a  and the opposing surface  71   s  of the fourth concave portion  71   k  to strengthen the fixing. 
     Hereinafter, the manufacturing or assembling of the image display device  200  will be described. First, the first optical system  12   a  and the first combiner  103   a  are fixed to the first frame  61   a , and the display element  11   a  is fixed while being positioned with respect to the first optical system  12   a  using the first holder  72   a , etc. This results in a right eye unit RU including the first display unit  100   a  (see  FIG. 4 ). In parallel, the second optical system  12   b  and the second combiner  103   b  are fixed to the second frame  61   b , and the display element  11   b  is fixed while being positioned with respect to the second optical system  12   b  using the second holder  72   b , etc. This results in a left eye unit LU including the second display unit  100   b  is obtained (see  FIG. 4 ). Thereafter, the right eye unit RU and the left eye unit LU are set in a two-lineage measurement device, and the elastic sheet  75  is fixed on the first frame  61   a  and the second frame  61   b  by adhesion. At this time, the inner openings OP 21 , OP 22  of the elastic sheet  75  are sealed by the first frame  61   a  and the second frame  61   b . Furthermore, the fixing member  78  is moved so as to descend, and the first fixing portion  81   a  of the fixing member  78  is fitted into the first concave portion  81   b  of the first frame  61   a , and the second fixing portion  82   a  of the fixing member  78  is fitted into the second concave portion  82   b  of the second frame  61   b . The stage of the two-lineage measurement device is then utilized to precisely adjust the angle and arrangement of the right eye unit RU and the left eye unit LU. At this time, the right eye unit RU and the left eye unit LU can independently rotate in the R 1  direction about the X-axis, the R 2  direction about the Y-axis, and the R 3  direction about the Z-axis, in a state where the right eye unit RU and the left eye unit LU are coupled by the fixing member  78  (see  FIG. 4 , etc.). After the position adjustment is complete, the adhesive supplied in advance between the first fixing portion  81   a  and the first concave portion  81   b  is cured, and the adhesive supplied in advance between the second fixing portion  82   a  and the second concave portion  82   b  is cured. This completes alignment of the right eye unit RU and the left eye unit LU. Thereafter, the first cover member  71   a  is covered so as to cover the first optical system  12   a  from above the first frame  61   a , the inner circumferential portion  75   b  of the elastic sheet  75  is sandwiched between the first frame  61   a  and the first cover member  71   a , and the boss  71   m  provided at the third concave portion  71   j  of the first cover member  71   a  is inserted into the first hole  81   k  of the first fixing portion  81   a  (see  FIG. 12A ). Thereafter, the screw SB is passed through the hole in the boss  71   m  and screwed into the boss  81   m  on the first frame  61   a  side facing the first hole  81   k  of the first fixing portion  81   a . As a result, the fixing of the first cover member  71   a  with respect to the first frame  61   a  is completed. The method of fixing the second cover member  71   b  to the second frame  61   b  is the same as the method of fixing the first cover member  71   a  to the first frame  61   a , so that description thereof is omitted. Next, the circuit board  91  is attached to the fixing member  78  using the substrate support portion  74 , and the FPC extending from the display elements  11   a ,  11   b  is coupled to the circuit board  91 . Finally, the lower exterior member  107   b  is fixed to the fixing member  78  using the pair of fastening portions  78   z  provided at the fixing member  78 , and then the upper exterior member  107   a  is fixed to the lower exterior member  107   b . At this time, the first frame  61   a  and the second frame  61   b  are allowed to shift slightly with respect to the lower exterior member  107   b , and the positioning of the first display unit  100   a  and the first display unit  100   b  with respect to the fixing member  78  is maintained. Furthermore, by sandwiching the outer circumferential portion  75   a  of the elastic sheet  75  between the outer edge  7   a  of the upper exterior member  107   a  and the outer edge  7   b  of the lower exterior member  107   b , sealing is achieved therebetween, and the interior space of the exterior member  107  is sealed. 
     The image display device  200  according to the above-described exemplary embodiment includes the first display unit  100   a  including the first frame  61   a  and the first optical system  12   a , the second display unit  100   b  including the second frame  61   b  and the second optical system  12   b , and the fixing member  78  configured to fix the first display unit  100   a  and the second display unit  100   b  relative to each other, wherein the fixing member  78  has a shape configured to rotate the first optical system  12   a  and the second optical system  12   b  in rotational directions around two or more axes when the first display unit  100   a  and the second display unit  100   b  are aligned prior to fixing. As a result, prior to fixing, the first display unit  100   a  and the second display unit  100   b  can be disposed and aligned at a high degree of freedom with respect to the fixing member  78 . 
     A manufacturing method for the image display device  200  according to the above-described exemplary embodiment includes the first display unit  100   a  including the first frame  61   a  and the first optical system  12   a , the second display unit  100   b  including the second frame and the second optical system  12   b , and the fixing member  78  configured to fix the first display unit  100   a  and the second display unit  100   b  relative to each other, wherein the fixing member  78  has a shape configured to rotate the first optical system  12   a  and the second optical system  12   b  in rotational directions around two or more axes, and stops rotation of the first optical system  12   a  and the second optical system  12   b  with respect to the fixing member  78  after alignment. In this case, prior to fixing, the first display unit  100   a  and the second display unit  100   b  can be disposed and aligned at a high degree of freedom with respect to the fixing member  78 . Furthermore, since the rotation of the first optical system  12   a  and the second optical system  12   b  with respect to the fixing member  78  is stopped after alignment, the relative positional relationship of the first display unit  100   a  and the second display unit  100   b  with respect to the fixing member  78  can be stably maintained. 
     MODIFIED EXAMPLES AND OTHERS 
     The present disclosure is described according to the above-described embodiments, but the present exemplary disclosure is not limited to the above-described embodiments. The present exemplary disclosure may be carried out in various modes without departing from the gist of the present disclosure, and, for example, the following modifications may be carried out. 
     The imaging optical system  20  incorporated into the first display unit  100   a  is not limited to that illustrated, and may have various configurations. Specifically, the imaging optical system  20  described above is the off-axis optical system OS that is asymmetric in the Y direction or the longitudinal direction, but may also be an off-axis optical system that is asymmetric in the X direction or the lateral direction. The optical elements constituting the imaging optical system  20  are merely exemplary in  FIG. 8 , and changes can be made, such as increasing or decreasing the number of lenses, adding a light-guiding member, etc. 
     A light control device that controls light by limiting the transmitted light of the combiners  103   a ,  103   b  can be attached on an external side of the combiners  103   a ,  103   b . The light control device adjusts a transmittance, for example, electrically. Mirror liquid crystals, electronic shades, etc. may be used as the light control device. The light control device may adjust a transmittance according to outside light brightness. 
     The combiner  103   a ,  103   b  may be replaced with a mirror having light blocking properties. In this case, the optical system is a non-see-through type optical system that does not assume direct observation of an external image. 
     The first frame  61   a , the second frame  61   b , and the fixing member  78  are not limited to being formed from a metal material, and may be formed from fiber-reinforced plastic (FRP). 
     The structure of the coupling members  81 ,  82  is not limited to one having a ball joint shape, and can be replaced with various mechanisms having increased rotational degrees of freedom along two or more axes. 
     In the description above, although it was assumed that the image display device  100  was worn on the head and is used, the image display device  100  may also be used as a handheld display that is not worn on the head and is to be looked into like binoculars. In other words, the head-mounted display also includes a hand-held display in the present disclosure. 
     An image display device according to a specific aspect includes a first display unit including a first frame and a first optical system, a second display unit including a second frame and a second optical system, and a fixing member configured to fix the first display unit and the second display unit relative to each other, wherein the fixing member has a shape configured to rotate the first optical system and the second optical system in rotational directions around two or more axes when the first display unit and the second display unit are aligned prior to fixing. 
     In the image display device described above, the fixing member has a shape configured to rotate the first optical system and the second optical system in rotational directions around two or more axes, thus, prior to fixing, the first display unit and the second display unit can be disposed and aligned at a high degree of freedom with respect to the fixing member. Note that after alignment, the first display unit and the second display unit are fixed to the fixing member using an adhesive material or a fastener, so that these relative positional relationships can be stably maintained. 
     In a specific aspect, bearing-shaped coupling members are provided between the fixing member and the first display unit, and between the fixing member and the second display unit, respectively, each of the bearing-shaped coupling members having rotational degrees of freedom along three axes. In this case, the first display unit and the second display unit can be freely disposed with respect to the fixing member. 
     In a specific aspect, the coupling member is brought into a state where rotation is stopped after alignment. As a result, positional maintenance after alignment is ensured while maintaining free posture adjustment prior to alignment. 
     In a specific aspect, the fixing member includes a spherical first fixing portion provided on a side of the first frame and a spherical second fixing portion provided on a side of the second frame side, the first frame includes a hemispherical first concave portion into which the first fixing portion is inserted, the second frame includes a hemispherical second concave portion into which the second fixing portion is inserted, and the first fixing portion and the first concave portion serving as the coupling member and the second fixing portion and the second concave portion serving as the coupling member are joined together in an aligned state with an adhesive layer formed therebetween. In this case, posture adjustment can be performed by freely rotating the first frame and the second frame with respect to the fixing member by a simple fitting structure. 
     In a specific aspect, the first display unit includes a first cover member configured to cover the first fixing portion and the first optical system from an opposite side of the first frame, the first cover member includes a hemispherical third concave portion into which the first fixing portion is inserted, the second display unit includes a second cover member configured to cover the second fixing portion and the second optical system from an opposite side of the second frame, the second cover member includes a hemispherical fourth concave portion into which the second fixing portion is inserted, and the first fixing portion and the third concave portion are fixed to the second fixing portion and the fourth concave portion by screwing. In this case, the first cover member and the second cover member can be attached to the first frame and the second frame via the first fixing portion and the second fixing portion. 
     In a specific aspect, the first fixing portion and the first concave portion have spherical opposing surfaces having mutually different curvatures, and the second fixing portion and the second concave portion have spherical opposing surfaces having mutually different curvatures. In this case, it is easy to form an adhesive layer having sufficient thickness by injecting the adhesive material. 
     In a specific aspect, the first fixing portion and the third concave portion have spherical opposing surfaces having the same curvature, and the second fixing portion and the fourth concave portion have spherical opposing surfaces having the same curvature. 
     In a specific aspect, the first fixing portion includes the first hole through which a screw configured to screw the first frame to the first fixing portion is passed, and the second fixing portion includes the second hole through which a screw configured to screw the second frame to the second fixing portion is passed. In this case, the first frame can be reliably fixed with respect to the first fixing portion, whereby fixing strength can be ensured. 
     In a specific aspect, the fixing member includes a coupling portion configured to couple the first fixing portion and the second fixing portion, and the coupling portion is coupled to the first fixing portion and the second fixing portion on a side away from the first frame and the second frame with respect to a center of the first fixing portion and a center of the second fixing portion. As a result, while ensuring a posture change in which the first frame and the second frame rotate around an axis perpendicular to the extending direction of the coupling portion, the fitting between the first fixing portion and the first concave portion and the fitting between the second fixing portion and the second concave portion can be deepened to stabilize the coupling. 
     In a specific aspect, the fixing member includes a substrate support portion configured to support a circuit board. In this case, the circuit board can be supported with respect to the first frame or the second frame, whereby various members can be supported collectively with reference to the fixing member. 
     A manufacturing method for an image display device according to a specific aspect is a manufacturing method for an image display device including a first display unit including a first frame and a first optical system, a second display unit including a second frame and a second optical system, and a fixing member configured to fix the first display unit and the second display unit relative to each other, wherein the fixing member has a shape configured to rotate the first optical system and the second optical system in rotational directions around two or more axes, the fixing member being configured to, after alignment, stop rotation of the first optical system and the second optical system with respect to the fixing member. 
     In the manufacturing method described above, the fixing member has a shape configured to rotate the first optical system and the second optical system in rotational directions around two or more axes, thus, prior to fixing, the first display unit and the second display unit can be disposed and aligned at a high degree of freedom with respect to the fixing member. Furthermore, since the rotation of the first optical system and the second optical system with respect to the fixing member is stopped after alignment, the relative positional relationship of the first display unit and the second display unit with respect to the fixing member can be stably maintained.