Abstract:
A mechanism for adjusting an apparatus for the inter-pupilar distance of a user is disclosed. Example embodiments of the disclosed mechanism use gears that link the movements of eye-optics and reflectors placed along the optical path. When the eye-optics are adjusted, this movement causes a movement in the linked reflectors that maintains a constant length for the optical path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 10/715,911 entitled “OPTICAL ARRANGEMENTS FOR HEAD MOUNTED DISPLAYS,” filed Nov. 18, 2003 now U.S. Pat. No. 6,989,935, the disclosure of which is hereby incorporated herein by reference. 
    
    
     PRIORITY 
     The present application claims priority to Hungarian Patent Application, Serial No. P 02 03993, Filed, Nov. 19, 2002, entitled “OPTICAL SYSTEM FOR A BINOCULAR VIDEO SPECTACLE,” the disclosure of which is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The invention relates generally to visual displays and more specifically to optical arrangements for head mounted systems that use a single display. 
     BACKGROUND OF THE INVENTION 
     Head Mounted Displays (HMDs) are a class of image display devices that can be used to display images from television, digital versatile discs (DVDs), computer applications, game consoles, or other similar applications. A HMD can be monocular ( a single image viewed by one eye), biocular (a single image viewed by both eyes), or binocular (a different image viewed by each eye). Further, the image projected to the eye(s) may be viewed by the user as complete, or as superimposed on the user&#39;s view of the outside world. HMD designs must account for parameters such as image resolution, the distance of the virtual image from the eye, the size of the virtual image (or the angle of the virtual image), the distortions of the virtual image, the distance between the left and the right pupil of the user (inter pupillar distance (IPD)), diopter correction, loss of light from image splitting and transmission, power consumption, weight, and price. Ideally, a single HMD would account for these parameters over a variety of users and be able to display an image regardless of whether it was a stereo binocular image or a simple monoscopic image. 
     If the resolution of a picture on the HMD&#39;s internal display is 800×600 pixels, an acceptable size for the virtual image produced by the HMD&#39;s optics is a virtual image diameter of approximately 1.5 m (52″-56″) at 2 m distance which corresponds to approximately a 36° angle of view. To properly conform to the human head and eyes, the IPD should be variable between 45 mm and 75 mm. In order to compensate for near- and farsightedness, at least a ±3 diopter correction is necessary. 
     The use of only one microdisplay in the HMD (instead of using one for each eye) drastically reduces the price of the device. Typically, an arrangement for such a unit positions a microdisplay between the user&#39;s eyes. The image produced is then split, enlarged, and separately transmitted to each eye. There are numerous designs known in the art for beam splitting in single display HMDs with a center mounted display, but none are known that provide a solution that is cheap, light weight, small in size, and capable of displaying all varieties of images. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention present images produced by head mounted displays to a user by producing separate sub-images that are propagated through a plurality of optical sub-paths delivering the image to separate locations. Embodiments of the present invention hold constant the length of each optical sub-path during adjustments by coordinated the movements of the optical elements placed along the sub-paths. 
     Some embodiments utilize diffusers places in the optical sub-path onto which real images of the display are formed. By coordinating the lateral movement of eyepiece optics necessary to correct for inter-pupilar distances with proportional movement of the diffusers, embodiments of the present invention are thus capable of maintaining a constant length for the optical sub-paths. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  illustrates a top view of a head mounted display arranged according to an embodiment of the present invention; 
         FIG. 2  illustrates a prospective view of a head mounted display arranged according to an embodiment of the present invention; 
         FIG. 3A  illustrates a prospective view of a head mounted display arranged according to an embodiment the present invention showing diopter correction; 
         FIG. 3B  illustrates a prospective view of the head mounted display of  FIG. 3A  showing the simultaneous movements utilized to make the IPD adjustment; and 
         FIGS. 3C and 3D  illustrate a prospective view of the head mounted display of  FIG. 3A  showing the specific gear arrangements that can perform the linked movements of  FIG. 3A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a top view of head mounted device  100  arranged according to an embodiment of the present invention. Sub-image creation section  101 , within device  100 , creates a plurality of sub-images from a single image source into a plurality of optical sub-paths. Display  110  can be any suitable apparatus or screen operable to display a visual image of data, such as a liquid crystal display (LCD) screen. Display  110  is situated along a display axis  111 , which, in the embodiment shown, is normal to the screen of display  110  and perpendicular to facial plane  170  of a user. Display  110  is designed to project a display image along optical path  112 . In the arrangement of section  101 , optical path  112  lies along display axis  111 . Display lens  115  is located along, and perpendicular to, optical path  112 , and has display lens focal point  124 . Display lens focal point  124  lies on optical path  112 , and section  101  is arranged such that display lens focal point  124  lies within splitter  120 . By focusing the display image before it is split, the splitting of volume of sub-image creation section  101  can be greatly reduced. A small splitting volume allows an embodiment to use small, light-weight splitting elements and allows HMD designs to include advantageous arrangements and additional optical elements that improve image quality and can increase the size of the image viewed by a user. The embodiment of  FIG. 1  is arranged to produce an image through (approximately) collimated light emanated by (or being reflected from) display  110 , thus splitter  120  is placed proximate to display lens focal point  124 . The embodiments are not limited to this arrangement however, as splitter  120  should be arranged in the position most appropriate to the focused image. For example, if display  110  emits, transmits, or reflects non collimated light, the display image will be focused to a “point” that is not display lens focal point  124 , and embodiments will arrange splitter  120  in a position proximate to this focal area. 
     In embodiments using the arrangement of section  101 , splitter  120  is an asymmetric V-mirror splitter composed of a partially reflective surface  121  and a fully reflective surface  122 . The proximity of surfaces  121 ,  122  will be dependent upon the size of splitter  120  and the amount of splitter volume reduction section  101  is arranged to produce. Section  101  is further arranged so that surface  121  and surface  122  share a common edge, and are arranged asymmetrically about display axis  111 . Section  101  can thus split a display image of display  110  into two separate display sub-images. The term sub-image is used to describe the multiple images of a display created by the various embodiments of the present invention. The sub-images of  FIG. 1  contain all of the information of a display, but embodiments may use sub-images that contain only a portion of an image. 
     Upon striking partially reflective surface  121 , a portion of a display image is reflected along left-eye optical sub-path  140 , and becomes a left-eye sub-image. The portion of a display image not reflected by partially reflective surface  121  passes through and strikes fully reflective surface  122 , becoming a right-eye sub-image, which is reflected along right-eye optical sub-path  130 . The result is an identical left-eye sub-image and right-eye sub-image traveling in opposite directions and containing identical image information. 
     Left-eye sub-image will follow optical sub-path  140  and be channeled to left eye  146  of a user. Placed along optical sub-path  140  is left-eye reflector  142 , which is a fully reflective surface arranged to redirect left-eye optical sub-path  140  by 90° and into left eyepiece optics  145 . The right-eye sub-image will follow optical sub-path  130  and be channeled to right eye  136  of a user. Placed along optical sub-path  130  is right-eye reflector  132 , which is a fully reflective surface arranged to redirect right-eye optical sub-path  130  by 90° and into right eyepiece optics  135 . Right eyepiece optics  135  and left eyepiece optics  145  can be a single lens or a combination of several lenses designed to appropriately magnify a right-eye sub-image for viewing by right eye  136  of the user and a left-eye sub-image for viewing by left eye  146  of the user, respectively. 
     Eyepiece optics  135  and  145  are adjustable single lenses, but other embodiments may use multiple lenses or any other arrangement that appropriately focuses a right-eye sub-image and a left-eye sub-image for viewing by right eye  136  and left eye  146 , respectively. Further, although reflectors  142 ,  132  of device  100  are depicted as mirrors, embodiments are not limited to the use of mirrors for redirecting an optical sub-path. Rather, prisms, partially reflective surfaces, polarizing beam splitters, or any other suitable arrangements can be used for redirecting an optical sub-path. 
     Device  100  is also capable of adjusting for the varying IPDs of different users through the synchronized movements of optical elements. Right eyepiece optics  135  and left eyepiece optics  145  can shift through movements  152  and  151  respectively to create IPD  150   a  and IPD  150   b , when section  101  shifts through movement  155 . When IPD distance  150   a  is changed to IPD  150   b , section  101  is simultaneously shifted toward facial plane  170  in movement  155  (downwards in the view of  FIG. 1 ). When IPD  150   b  is changed to  150   a , section  101  is simultaneously shifted away from plane  170  (upwards in the view of  FIG. 1 ). These synchronized movements allow device  100  to adjust to accommodate for the entire range between IPD  150   a  and  150   b  while maintaining constant distances between surfaces  122 ,  121  and eyepiece optics  135 ,  145  along sub-paths  130  and  140 , respectively. Device  100  is also capable of diopter correction through additional adjustments of movement  153  of left eyepiece optics  145  and movement  154  of right eyepiece optics  135 . 
       FIG. 2  illustrates a prospective view of head mounted device  200  arranged according to an embodiment of the present invention. Head mounted device  200  includes section  101 , as described in relation to  FIG. 1 , which operates to split a display image of display  110  into a left-eye sub-image traveling along left-eye optical sub-path  140  and a right-eye sub-image traveling along right-eye optical sub-path  130 . For device  200 , left-eye transition optics  243  are placed along left-eye optical sub-path  140  to adjust the left-eye sub-image for reflection by left-eye reflector  142  onto left-eye diffuser  244 . The left-eye sub-image strikes the left-eye diffuser  244  and creates a real image of the display on the diffuser surface. The left eyepiece compound optics  245  then magnifies this real image appropriately for left eye  146 . 
     The embodiment depicted in  FIG. 2  is described using diffusers onto which real images are projected in order to prepare the image. Transition optics, having a small numerical aperture, project a real image onto the diffuser surface, and eyepiece optics having a large numerical aperture transport the image to the eyes of a user. Rather, any appropriate means may be used including microlens arrays, diffraction gratings, or other diffractive surfaces. For the purposes of the present invention, it will be understood that “diffuser” as used to describe the embodiments of the present invention, refers to all such means used to convert incident angular power density into an appropriate exiting angular power density. 
     In  FIG. 2 , a right-eye sub-image follows the right-eye optical sub-path  130  into right eye transition optics  233 . The right eye transition optics  233  adjusts the right-eye display sub-image appropriately for reflection by right-eye reflector  132  onto right-eye diffuser  234 . The right-eye sub-image strikes right-eye diffuser  234  and creates a real image. This real image is adjusted by right eyepiece compound optics  235  appropriately for right eye  136 . Device  200  is capable of diopter correction through movement  253  of left-eye compound optics  245  and of movement  254  of right-eye compound optics  235 . 
     Device  200  is also capable of IPD adjustment through multiple synchronous movements. IPD  150  can be shortened by shifting left-eye compound optics  234  to the right with movement  251 , and right-eye compound optics  235  to the left with movement  252 . For the embodiment of  FIG. 2 , segment  240  of optical sub-path  140  lies between transition optics  243  and diffuser  244 , and segment  230  of optical sub-path  130  lies between transition optics  233  and diffuser  234 . Thus, as compound optics  235  and  245  are shifted in movement  252  and  251  to shorten distance  150 , center section  201  should be shifted away from the facial plane  170 . The embodiment of  FIG. 2  describes one combination of synchronous movements that result in IPD adjustment, but embodiments of the present invention are not limited to the synchronous movements of  FIG. 2 . 
       FIG. 3  illustrates a prospective view of a head mounted device arranged according to an embodiment of the present invention. Head mounted device  300  includes section  101 , as described in relation to  FIG. 1 , to split a display image of display  110  into a left-eye sub-image traveling along left-eye optical sub-path  140  and a right-eye sub-image traveling along right-eye optical sub-path  130 . In the embodiment depicted in  FIG. 3 , a left-eye display sub-image follows left-eye optical sub-path  140  and passes through a left-eye real image reflector  342  to strike left-eye reflective diffuser  343 , thus creating a real image. This real image is then reflected by left-eye real image reflector  342  into left eyepiece optics  145 . Left eyepiece optics  145  adjusts a reflected real image appropriately for left-eye  146 . A right-eye display sub-image will follow right-eye optical sub-path  130  passing through right-eye real-image reflector  332  to strike right-eye reflective diffuser  333 , thus creating a real image. This real image is reflected by right-eye real-image reflector  332  into right eyepiece optics  135  which will adjust a reflected real-image appropriately for right-eye  136 . 
     The embodiment depicted in  FIGS. 3A and 3B  is described as using reflective diffusers on which real images are formed. The present invention is not limited to the use of any one type of diffuser. Rather, the embodiments may use any appropriate diffuser, as previously described, and may be any appropriate shape such as spherical, flat, or aspheric. 
     The embodiment in  FIG. 3A  is also capable of diopter correction through movement  153  of left eyepiece optics  145  and movement  154  of right eyepiece optics  135 . Left-eye real-image reflector  342  and left eyepiece optics  145  collectively make up left eyepiece  360 . Right-eye real-image reflector  332  and right eyepiece optics  135  collectively make up right eyepiece  361 . 
     Device  300  is capable of IPD adjustment through multiple simultaneous movements. The embodiment of  FIG. 3  simultaneously moves left eyepiece  360  and right eyepiece  361  through movements  351  and  352  respectively to set the correct IPD. At the same time, movement  153  of left eyepiece optics  145  and movement  154  of right eyepiece optics  135  are moved to maintain the optical path lengths between eyepiece optics  145 ,  135  and reflective diffusers  343 ,  333 . 
       FIG. 3B  illustrates the simultaneous movements one embodiment of the present invention utilizes to make the IPD adjustment described for  FIG. 3A . As described above, IPD correction involves lateral movements  351  and  352  (of length d in  FIG. 3A ) of eyepieces  360  and  361 . When such movements are made, however, the optical sub-paths  140  and  130  become longer. In order to maintain a constant length for optical sub-paths  140  and  130 , diffusers  343  and  333  are simultaneously perform lateral movements  371  and  372  (of length ½d in  FIG. 3A ). In preferred embodiments, movement  351  is linked with movement  371  and movement  352 , but movements  352  and  351  are independent of each other. 
       FIGS. 3C and 3D  illustrate one embodiment specific gear arrangements that can perform the linked movements described. The user adjusts IPD by sliding button  381  which is fixed directly to eye-piece  362 . As eyepiece  362  moves left and right, gear rack  382  drives idler gear  383  mated with ‘baseline’ rack  384 . Diffuser  333  (represented in the embodiment of  FIGS. 3C and 3D  as a mirror) is mounted onto idler gear  383 , which ensures that when the eyepiece  362  moves a certain distance, diffuser moves exactly half that distance. This linkage ensures that the optical sub-path  130  is a constant distance for all IPD values. 
     To allow for diopter correction, ‘baseline’ rack  384  is moved in direction  385  (towards optical axis  111 ), which in turn moves idler gear  383  and diffuser  333  towards beam splitter  120  (not shown), there by shortening optical sub-path  130  and moving the virtual image closer to the viewer. Rather than focusing the system, the virtual image is moved to the view where a user can see the image within their ‘diopter limits’. The mechanical of  FIGS. 3C and 3D  allows for a very flexible system that ensures that diffuser  333  is synchronized to eyepiece  362  and maintains a constant length for optical sub-path  362  for all IPD adjustments while maintaining any given ‘baseline’ diopter adjustment value. A similar system may be used for eyepiece  361  to ensure a constant length for optical sub-path  140 . Together, such systems provide independent left and right diopter correction. 
     In device  300 , left-eye real-image reflector  342  and right-eye real-image reflector  332  are partially reflective surfaces, but embodiments are not limited to the arrangement depicted. Rather, embodiments may easily be adapted to any arrangement, such as those using prisms, or polarizing beam splitters, that appropriately reflect light into eyepiece optics  135  and  145  and transmit light from optical paths  130 ,  140  towards reflective diffusers  333 ,  343 , respectively. 
     The embodiments of the present invention are not limited to arrangements that place an image splitter proximate to the focal point of a focusing optic. Rather, embodiments of the present invention are able to reduce the splitting volume of various applications, by positioning the image splitter to split a display image focused in a small area. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.