Abstract:
An image display apparatus is provided for providing a virtual image to an observer. The image display apparatus includes an image display unit, an eyepiece optical system, and a container. The image display unit is for providing modulated light corresponding to the virtual image. The eyepiece optical system is for directing the modulated light from the image display unit to one or both of the observer&#39;s eyes. The container is for supporting the image display unit on an edge portion of the eyepiece optical assembly.

Description:
RELATED APPLICATION 
     This application is based on application No. 2000-127213 filed in Japan, the content of which is hereby incorporated by reference. 
     1. Field of the Invention 
     The present invention relates to an image display apparatus that is used in front of a user&#39;s face and that provides images that are superimposed over external images. 
     2. Description of the Prior Art 
     As information-providing means for personal use, image display apparatuses have been proposed that are mounted in front of a user&#39;s face and lead light from a displayed image to the user&#39;s eye together with external light so that the displayed image is superimposed over external images. A user can use such an apparatus in a variety of everyday situations, such as observing displayed images while walking. 
     An apparatus of this kind generally has the configuration of glasses having a frame, a pair of lenses, nose pads and a pair of temples The display device that displays images is housed in a container mounted around the frame. In order for the displayed image to be superimposed on external images, light from the display device, which is located at the side, must be led to a location immediately in front of the eye and the light path must be changed there such that the light strikes the eye from the front. It is also preferred that the images displayed in a small display device be enlarged for observation. For this purpose, a hologram element is used. 
     For example, Japanese Laid-Open Patent Application Hei 11-64781 discloses an apparatus having a hologram element on a front surface of a lens (i.e., a surface located farther away from the eye). Light from a display device is led into the lens from an edge area of the lens, directly striking the hologram element, and after it is diffracted, it is led to the eye. On the other hand, Japanese Laid-Open Patent Application Hei 11-64782 discloses an apparatus having a hologram element on a rear surface of a lens (i.e., a surface closer to the eye). Here, light from a display device is led to the hologram element from the rear surface of the lens, where it is diffracted without striking the lens and led to the eye. 
     In these examples, a user observes actual external images together with an enlarged virtual image of the displayed image. However, a part of the external light is blocked by a container or a frame such that an eclipse occurs in the field of view. 
     The fact that external light is blocked by a container or a frame does not pose a problem for the purpose of providing displayed images. Nevertheless, for safety purposes, as large a field of view as possible must be maintained by reducing the range over which the light is blocked by a container or a frame since the apparatus may be used in a variety of everyday situations. 
     However, in conventional apparatuses, containers and frames are designed with a principal focus on ease of arrangement of the optical system or increased strength of the apparatus, and their sizes and configurations are not suitable for the purpose of ensuring a large field of view. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to overcome these and other shortcomings in the prior art designs. 
     Another object of the present invention is to provide an improved image display apparatus. 
     Another object of the present invention is to provide an image display apparatus in which the range of the field of view blocked by the container for housing the display device or blocked by the frame is small. 
     These objects are attained by an image display apparatus comprising nose pads that come into contact with a user&#39;s nose and a pair of temples that come into contact with a user&#39;s ears, sides of head, or rear area of head. The image display apparatus is worn in front of a user&#39;s face, such that (i) the apparatus leads light from a displayed image to a user&#39;s eye together with external light so that the displayed image is superimposed on external images, (ii) wherein the apparatus includes one or two display units including a display device that displays images, a container that supports the display device, and an eyepiece optical system that leads the light from the display device to the eye and provides a virtual image of the displayed image, and (iii) wherein at least one length of the container that extends in a direction perpendicular to a direction connecting the container and the eye is shorter than the length of the container that extends in the direction connecting the container and the eye. 
     The display device provides displayed images to at least one eye, and depending on whether one or two display devices are included, the image display apparatus may be an apparatus for one-eyed observation or two-eyed observation. The configuration of the container is such that it is thin in the direction perpendicular to the line of sight when the user looks toward the container. Therefore, the range of field of view that is blocked by the container is small. At the same time, because the container is long in the direction along the above line of view, even when a light source and optical system to illuminate the display device are included in the container, they can be easily arranged therein. 
     Here, the container should support the display device such that the display surface thereof is essentially perpendicular to the direction connecting the center thereof to the eye. In this way, when a transmission-type display device, which allows the illuminating light to pass through, is used for the display device, the illuminating light source and optical system may be placed along an extension of the straight line connecting the eye and the center of the display surface, so that the light source and optical system may have simple and lightweight constructions without increasing the width of the container. 
     The above objects are further attained by an image display apparatus comprising nose pads that come into contact with a user&#39;s nose and a pair of temples that come into contact with a user&#39;s ears, sides of head, or rear area of head. The image display apparatus is worn in front of a user&#39;s face, wherein (i) the apparatus leads light from a displayed image to a user&#39;s eye together with external light such that the displayed image is superimposed on external images, (ii) the apparatus includes one or two display units including a display device that displays images, a container that supports the display device, and an eyepiece optical system that leads light from the display device to the eye and provides a virtual image of the displayed image, and (iii) the container is configured such that an angle over which a user&#39;s field of view is blocked is determined by a part of the container closer than the center thereof to the eye in a direction connecting the container and the eye. 
     When the container has this configuration, a range of the blocked field of view may be reduced relative to a different configuration, and the container itself may be reduced in size, making the apparatus more lightweight. For example, if the angle over which the field of view is blocked is determined by a part of the container that is closer than the center thereof to the eye and a part of the container that is farther than the center thereof away from the eye, the range of the blocked field of view increases; if the angle over which the field of view is blocked is determined by a part of the container that is farther than the center thereof away from the eyes, the container increases in size. 
     A prism may be included in each of the above image display apparatuses, wherein such prism is located in front of the eye, allows external light pass through, and leads the external light to the eye; a part thereof also operates as an eyepiece optical system that leads light from the display device to the eye. 
     When at least a part of the eyepiece optical system is located in the field of view, it may affect the external light that passes therethrough in some way and may cause distortion or discontinuity in external images provided to the user. By including a prism that also operates as an eyepiece optical system, so that the prism has the same effect as an eyepiece optical system with regard to the external light that does not pass through an eyepiece optical system, or so that the effect of an eyepiece optical system is offset by the prism, the occurrence of distortion and discontinuity in the external images may be avoided. In addition, by mounting the container, nose pads, and temples to the prisms, a connecting member such as a frame to integrate these members may no longer be needed. 
     The above objects are also attained by an image display apparatus comprising nose pads that come into contact with a user&#39;s nose and a pair of temples that come into contact with a user&#39;s ears, sides of head, or rear area of head. The image display apparatus is worn in front of a user&#39;s face, wherein (i) the apparatus leads light of a displayed image to a user&#39;s eye together with external light such that the displayed image is superimposed on external images, (ii) the apparatus includes one or two display units including a display device that displays images, a container that supports the display device, and an eyepiece optical system that leads light from the display device to the eye and provides a virtual image of the displayed image, and (iii) because the prisms are mounted to the nose pad assembly and the temples and the container or containers are mounted to the prisms, a connecting member such as a frame to integrate the container or containers, nose pad assembly and temples is not needed. 
     In this apparatus, a connecting member such as a frame to integrate the container, nose pads and temples is not needed, such that the field of view is not blocked by a connecting member. 
     A part of each prism of this apparatus should also operate as an eyepiece optical system such that light from the display device is led to the eye. In doing so, as described above, the occurrence of distortion and discontinuity in external images may be avoided. 
     In the image display apparatus having the above prisms, the container or containers are located around the prism or prisms and each prism may have a construction in which it has, as an eyepiece optical system, a surface that leads light from the display device to the interior of the prism, a surface that reflects several times inside the prism the light thus led to the interior of the prism and leads it close to the eye, and a surface that directs the light led to a location immediately in front of the eye toward the eye. Because light from the display device is reflected inside the prism and is led to a location immediately in front of the eye, the container may be located around or outside of the field of view, resulting in a larger field of view. In addition, the prism may be made thinner. 
     The surface that directs the light led to a location immediately in front of the eye should comprise a hologram element. In doing so, the prism can lead both the light from the display device and the external light to the eye without light loss, and the display image or external images superimposed on the display image do not become dark, even while the apparatus maintains a simple construction. 
     The prisms should have magnification powers by which to correct a diopter. In this way, a user with weak vision can also clearly observe the external world without using other correcting means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of this invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanied drawings in which: 
     FIG. 1 is a perspective view of an image display apparatus of a first embodiment; 
     FIG. 2 is a cross-sectional view including the display device of the image display apparatus of the first embodiment; 
     FIG. 3 is a cross-sectional view of an example of a user&#39;s field of view and a range of the field of view blocked by the container in the image display apparatus of the first embodiment; 
     FIG. 4 is a perspective view of an image display apparatus of a second embodiment; 
     FIG. 5 is a cross-sectional view including the display device of the image display apparatus of the second embodiment; and 
     FIG. 6 is a perspective view of an image display apparatus of a third embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the image display apparatus of the present invention are explained below with reference to the drawings. FIG. 1 shows the external view of an image display apparatus  1  of a first embodiment. The image display apparatus  1  comprises a display unit  10 , a pair of left and right prisms  20 L and  20 R, a nose pad assembly  31 , and a pair of left and right temples  32 L and  32 R, and is worn in front of the face of a user such that the prisms  20 L and  20 R are located in front of the left and right eyes, respectively. 
     The nose pad assembly  31  is mounted to the prisms  20 L and  20 R and connect them. The temples  32 L and  32 R are mounted to the end areas of the prisms  20 L and  20 R, respectively. When the apparatus is worn, the nose pad assembly  31  rests on the nose, and the temples  32 L and  32 R rest on the ears, the sides of the head, or the rear area of the head, such that the image display apparatus  1  is supported by these three members. The temples  32 L and  32 R may be rotated around vertical axes (not shown in the drawing) located near the prisms  20 L and  20 R, respectively, such that they may be folded inward during non-use. 
     The display unit  10  is mounted to the right prism  20 R. FIG. 2 shows the cross-section thereof including the display unit  10 . The display unit  10  comprises a transmission-type liquid crystal display device (LCD)  11 , a container  12 , a prism  13 , a light emitting diode (LED)  14 , and a lens  15 . The LCD  11  displays an image to be provided to the user and the illuminating light is modulated by the displayed image The container  12  houses and supports the LCD  11 , the LED  14 , and the lens  15 . The LED  14  is a light source to illuminate the LCD  11 , and the lens  15  is an illuminating optical system to lead in a uniform fashion the light emitted by the LED  14  to the entire surface of the LCD  11 . 
     The image displayed by the LCD  11  and the light emitted by the LED  14  are controlled by a controller (not shown in the drawings) located outside the image display apparatus  1 . The controller is connected to the container  12  by a cable  40 , as shown in FIG. 1, and supplies power and image signals through the cable  40 . 
     The prism  13  has a flat plate configuration, and is made of clear glass or resin. The prism  13  leads light from the LCD  11  to the eye E of the user, and provides a virtual image of the image displayed on the LCD  11 . The upper end area of the prism  13  has a wedge configuration in which the end area is thicker than the inner side, and the container  12  is mounted to the prism  13  such that it sandwiches the wedge-shaped upper end area. The prism  20 L has a flat plate configuration and comprises a single member. The prism  20 R also has a flat plate configuration, but comprises the prism  13  and a prism  21 , instead of just a single member. The prisms  20 L and  21  are made of the same material as the prism  13 , and there is no difference in the index of refraction among these three prisms. The prisms  13  and  21  that comprise the prism  20 R have mutually compensating configurations and are glued together such that they have no substantial gap in between and their surfaces are contiguous. Except for a wedge-shaped upper end area of the prism  13 , the prisms  20 L and  20 R are symmetrical. The user wearing the image display apparatus  1  in front of his or her face observes the external world through the prisms  20 L and  20 R. 
     The lower end area of the prism  13  is constructed such that it has a wedge configuration wherein the front surface (the surface farther away from the eye E) approaches the rear surface (the surface closer to the eye E) toward the lower end. The front surface of this wedge-shaped part, i.e., the surface that connects to the prism  21 , is a flat surface, and a hologram element  22  is formed on this surface. The hologram element  22  becomes located immediately in front of the eye E when the apparatus is worn. The prism  13  and the hologram element  22  comprise an eyepiece optical system  16 . 
     The prism  13  leads light located in the interior thereof from the LCD  11  via an end surface of the upper end area of the prism  13  to the hologram element  22  while conducting total reflection via the front and rear surfaces of the prism  13  several times. The hologram element  22  diffracts the thus led light, converts it to essentially parallel light, and causes it to strike the eye E. As a result, a virtual image of the image displayed on the LCD  11  is provided to the user. The hologram element  22  operates only minimally on external light, so that the virtual image is observed to be superimposed over the center of external images. 
     The hologram element  22  is designed such that the distance from the eye E to the virtual image will appear to be one to three meters and the size of the virtual image will appear to be several times to several tens of times larger than the real image displayed on the LCD  11 . Therefore, the image provided to the user is easy to observe. The user can clearly observe the displayed image and external images through a simple slight adjustment of the focal point of the eye E. 
     In the image display apparatus  1 , light from the LCD  11  is led to the hologram element  22  while it is reflected inside the prism  13 , and therefore the prism  20 R may be made large in size. As a result, the container  12  may be located around or outside the field of view of the eye E, minimizing the range of the field of view blocked by the container  12 . In addition, because most of the external light passes through the prism  20 R and strikes the eye E, image distortion or color bleeding does not occur in the external images except for extreme edge areas. Moreover, since the width of the prism  20 R may be made small, around three millimeters for example, the entire apparatus becomes lightweight. 
     The lower end area of the prism  13  has a wedge configuration, but because it is connected to the prism  21 , which is made of the same material as the prism  13 , no refraction occurs with regard to the external light that passes through the lower end area of the prism  13 . Therefore, the center area of the external images does not experience distortion or discontinuity, and the image display apparatus  1  can provide high quality images. 
     The LCD  11  has a rectangular configuration that is horizontally long, and is capable of displaying one to several lines of character strings comprising less than 20 characters aligned horizontally. Consequently, the user can obtain a large amount of information from the displayed image at once. 
     The container  12  is designed such that its length A that extends in the direction that connects the eye E and the container  12  is approximately twice as long as the length B that extends in the direction perpendicular to the above direction and the horizontal direction. Therefore, the container  12  is thin and the range of the field of view blocked by the container  12  is small. The LCD  11  is located such that its display surface becomes perpendicular to a straight line that connects the eye E and the center of the display surface thereof, and the lens  15  and LED  14  are located along a line extending from the above straight line. Based on this construction, while the container  12  is thin, the LCD  11 , the lens  15 , and the LED  14  may be easily arranged inside of it, and an illuminating optical system may be constructed in a simple fashion using the lens  15  only. 
     FIG. 3 shows an example of the field of view of the eye E and the range of the field of view blocked by the container  12 . This example shows a case in which the entire container  12  is located within a field of view V 0 . The range of the field of view V 1 , which is a portion of the field of view V 0  blocked by the container  12 , is small. As described above, it is also possible to locate a part of the container  12  outside the field of view V 0 , so that is possible to further reduce the range of field of view blocked by the container  12 . 
     The container  12  has a configuration such that an angle α over which the field of view is blocked is determined only by a part of the container that is closer to the eye E than the center thereof in terms of a direction connecting the eye E and the container  12 . Because the container  12  is thin, the range of field of view blocked by the container  12  is small; thus, this configuration enables the range of the blocked field of view to be further reduced and the container  12  to be made lightweight. If the angle over which the field of view is blocked were to be determined by a part of the container closer to the eye E than the above center and a part of the container farther away from the eye E than the above center, even if the container has a similar configuration, the range of the blocked field of view would increase. If the angle over which the field of view is blocked were to be determined only by a part of the container farther away from the eye E than the above center, the container  12  would increase in size and weight. 
     In this embodiment, the displayed image is provided to the right eye, but naturally it is acceptable if the displayed image is provided to the left eye instead. 
     FIG. 4 shows the external view of an image display apparatus  2  of a second embodiment. The image display apparatus  2  comprises the above image display device  1  plus a frame  50 , such that the container  12 , the prisms  20 L and  20 R, the nose pad assembly  31  and the temples  32 L and  32 R are mounted to the frame  50 . While the width (the horizontal length) of the prism  13  was approximately one-third that of the prism  21  in the image display apparatus  1 , in the image display apparatus  2 , the width of the prism  13  is the same as the width of the prism  21 . 
     Using this construction, while the range of the blocked field of view increases due to the existence of the frame  50 , a wide image may be provided. The configuration of the container  12  and the constructions and functions of the prism  13  and hologram element  22  comprising an eyepiece optical system  16 , and of the prism  21 , are the same as in the image display apparatus  1 , as shown in the cross-sectional view of FIG.  5 . The cable  40  that connects the apparatus with the controller is attached to the rear end of the temple  32 L, and is connected to the container  12  through the inside of the temple  32 L and the frame  50 . 
     FIG. 6 shows an external view of an image display apparatus  3  of a third embodiment. The image display apparatus  3  includes a pair of display units  10 L and  10 R such that an image may be provided to both eyes, and includes prisms  20 L and  20 R provided with magnification powers such that the apparatus can correct the vision of the user. The construction of each of the display units  10 L and  10 R is the same as the construction of the display unit  10  of the image display apparatus  1  of the first embodiment, except that the prisms  13 L and  13 R are curved. The container  12 R is connected to the controller via the cable  40 , and the container  12 L is connected to the controller via the cable  40   a , the container  12 R and the cable  40 . 
     The magnification powers of the prisms  20 L and  20 R are set in accordance with the vision of the user. By providing the prisms  20 L and  20 R with negative magnification powers, the apparatus can correct nearsightedness, and by providing them with positive magnification powers, the apparatus can correct farsightedness. The lower end surfaces of the prisms  13 L and  13 R that connect with the prisms  21 L and  21 R, respectively, are flat surfaces, so that hologram elements  22 L and  22 R may be easily formed thereon. 
     In the image display apparatus of an embodiment that includes one or two display units each including a display device that displays images, a container that supports the display device, and an eyepiece optical system that leads the light from the display device to the eye and provides a virtual image of the displayed image, wherein at least one length of the container that extends in the direction perpendicular to the direction connecting the container and the eye is smaller than the length of the container that extends in the direction connecting the container and the eye, the container may be made small, so that the range of field of view blocked by the container is small. Therefore, a highly safe apparatus may be obtained. In addition, a light source and optical system to illuminate the display device may be easily incorporated in the container. 
     Where the container supports the display device such that the display surface thereof is essentially perpendicular to the direction that connects the center of the display surface and the eye, even if a simple and relatively inexpensive transmission-type display device is used, the illuminating light source and optical system may be arranged with few limitations, and the container may be reliably made thin. Moreover, because the illuminating light source and optical system can be simple and lightweight in construction, the resulting apparatus may be small, lightweight and comfortable to use. 
     In the image display apparatus of the present invention that includes one or two display units including a display device that displays images, a container that supports the display device, and an eyepiece optical system that leads light from the display device to the eye and provides a virtual image of the displayed image, wherein the container has a configuration such that the angle over which the field of view is blocked is determined only by a part of the container closer than the center thereof to the eye in the direction connecting the container and the eye, the field of view blocked by the container is small, resulting in a highly safe apparatus as well. 
     Where the apparatus includes a prism that allows external light to pass through and leads it to the eye, and part of the prism operates as an eyepiece optical system and leads light from the display device to the eye, the occurrence of distortion and discontinuity in the external images caused by the eyepiece optical system may be avoided, and the user feels no discomfort. Moreover, because the container, nose pads, and temples may be mounted to the prism, a connecting member such as a frame used to integrate these members is no longer necessary, and the range of the blocked field of view may be further reduced. 
     In the image display apparatus of an embodiment that includes one or two display units including a display device that displays images, a container that supports the display device, and an eyepiece optical system that leads light from the display device to the eye and provides a virtual image of the displayed image, and a pair of prisms that are located in front of the eyes allow external light to pass through and lead it to the left and right eyes, wherein the prisms are mounted to the nose pad assembly and the temples and the container or containers are mounted to the prisms, a connecting member such as a frame used to integrate the container or containers, nose pad assembly and temples is not needed. Therefore, the field of view is not blocked by a connecting member, resulting in a highly safe apparatus. In addition, the apparatus becomes lightweight and is comfortable to use. 
     Because a part of each prism works as an eyepiece optical system and leads light from the display device to the eye, the occurrence of distortion and discontinuity in external images due to the effect of the eyepiece optical system may be avoided in this apparatus as well, and natural images may be provided to the user. 
     Where the container is mounted around the prism, and the prism has surfaces which include a surface that leads light from the display device to the interior thereof, a surface that reflects several times inside the prism the light thus led to the interior thereof and leads it close to the eye, and a surface that directs the light thus led to a location immediately in front of the eye, and these surfaces comprise an eyepiece optical system, the container may be located around or outside the field of view, resulting in a larger field of view and higher safety. Moreover, the prism may be made thin, resulting in a lightweight apparatus. 
     Where the surface that directs toward the eye the light led to a location immediately in front of the eye comprises a hologram element, both the light from the display device and the external light may be led to the eye without light loss, so that all of the displayed image and external images may be viewed with sufficient brightness. In addition, the construction is simple and easy to manufacture. 
     Where the prisms are given magnification powers to correct the diopter, the apparatus can function as vision-correcting glasses, and a user with weak vision can clearly observe the external world. 
     Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.