Abstract:
A method is provided for aligning, without user interaction, the two images of a binocular eyewear display ( 100 ) with respect to their vertical, horizontal, and rotational orientation, and with respect to magnification. The method for aligning images comprise generating a signal from a display modification system ( 108 ) based on stored values indicative of misalignment of the binocular eyewear display ( 100 ); and adjusting, in accordance with the signal, an image or images to be displayed by an optics system ( 106 ). The stored values may include values for a plurality of temperatures and humidity.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to binocular eyewear displays and more particularly to a method of aligning, without user interaction, the two images of a binocular eyewear display with respect to their vertical, horizontal, and rotational orientation, and with respect to magnification. 
     BACKGROUND OF THE INVENTION 
     Binocular displays include head mounted displays such as glasses and helmet mounted displays wherein a virtual image is presented to each eye. The image, usually created by a microdisplay, for example an LCD screen, may be presented to the eye by means of refractive or reflective optics, for example, through a lens system. Ideally the virtual images presented to each eye are perfectly aligned and the user perceives a single image similar to their perception of real images. If the virtual images are misaligned, the user may experience discomfort, for example, eye strain, headache, and nausea. 
     Commercial binocular eyewear are aligned mechanically during manufacture and some misalignment is common. Furthermore, misalignment of binocular eyewear may occur during use due to physical shock or exposure to temperature or humidity. Although there are no widely accepted standards for alignment, there have been several studies to determine acceptable values of binocular image alignment. A compilation of the desired alignment tolerances to avoid user discomfort is as shown in the following table as disclosed in Melzer &amp; Moffitt,  Head Mounted Displays-Designing for the User , New York: McGraw-Hill, 1997 (ISBN 0070418195). 
                                         REQUIREMENT   REQUIREMENT       PARAMETER   (see-through)   (immersive)                   VERTICAL   3 minutes of arc   5 minutes of arc       HORIZONTAL   3 minutes divergent;   ¼ diopter of           8 minutes convergent   focus distance       IMAGE ROTATION   1 degree   1 degree       MAGNIFICATION   1 percent   1 percent                    
Although vendors of commercial eyewear displays are aware of the need for binocular image alignment, products today are not shipped with any alignment specifications.
 
     Systems have been disclosed wherein a user of the binocular eyewear may take corrective steps to bring the misalignment within certain tolerances. See for example, in US 2003/0184860, the user operates a device to move a dot until it is aligned with another dot, and in WO 2006/058188, the user adjusts first and second display panels until images of display panel indicia shown on the viewing screen are located relative to baseline indicia. 
     However, users of systems requiring user intervention to properly align the system may find it burdensome to perform such intervention, especially when it may be required each time the system is turned on. 
     Accordingly, it is desirable to provide a method of aligning, without user interaction, the two images of a binocular eyewear display with respect to their vertical, horizontal, and rotational orientation, and with respect to magnification. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     BRIEF SUMMARY OF THE INVENTION 
     A method is provided for aligning, without user interaction, the two images of a binocular eyewear display with respect to their vertical, horizontal, and rotational orientation, and with respect to magnification. The method for aligning images comprise generating a signal from a display modification system based on stored values indicative of misalignment of the binocular eyewear display; and adjusting, in accordance with the signal, an image or images to be displayed by an optics system. The stored values may include values for a plurality of temperatures and humidity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a top schematic view of an exemplary embodiment of a binocular display device; 
         FIG. 2  is a projected image free from misalignment; 
         FIG. 3  is a projected image having horizontal misalignment; 
         FIG. 4  is a projected image having vertical misalignment; 
         FIG. 5  is a projected image having rotational misalignment; 
         FIG. 6  is a projected image having magnification misalignment; and 
         FIG. 7  is a flow chart of steps of the exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
     Commercial binocular eyewear are aligned mechanically at manufacture and some misalignment is common. By measuring the optical misalignment, e.g., at the factory or subsequently at a sales or repair facility, and storing misalignment parameters such as vertical, horizontal, rotation, and magnification, in memory integral to the eyewear, correction may be made automatically without user interaction to bring the alignment within desired limits. A first image is presented to a first eye and a second image is presented to a second eye. A microcomputer may adjust at least one of the first and second images, e.g., by shifting or rotating pixels, in accordance with the stored parameters. Additionally, the optical misalignment may be measured at a plurality of temperatures and humidity with the misalignment at each temperature and humidity stored. Subsequently, the misalignment at a current temperature and/or humidity may be adjusted in accordance with the stored values. 
     Referring to  FIG. 1 , a binocular display device  100  in accordance with an exemplary embodiment comprises a housing  102  including an image receiving device  104 , optics system  106 , and display modification system  108 . The image receiving device  104  may, for example, comprise an input (not shown) for wired or wireless coupling or an electronic device for receiving and reading video data from a DVD or the like. The optics system  106  includes a first microdisplay  112  and a first lens  114  for displaying an image for an eye, and a second microdisplay  116  and a second lens  118  for displaying the image to the other eye. The optical system  106  may also include backlights  122  and  124  for lighting the microdisplays  112  and  116 . It should be understood that there are many types of optical systems that may include, for example, mirrors and/or waveguides. It should be understood the present invention should not be limited by the type of image receiving device  104  or the type of optics system  106  described herein. The display modification system  108  includes a microcomputer  126  and memory  128  coupled to the image receiving device  104 , and a display driver  130  coupled between the microcomputer  126  and the microdisplays  112  and  116 . The display modification system  108  may further include an environmental sensor  120  for sensing, for example, the temperature and/or humidity. The microcomputer  126  and/or the memory  128  may be integrated into the binocular display device  100  or may reside elsewhere and be coupled electronically to the binocular display device  100 . 
     When an image, which typically would comprise a video stream, is received by the image receiving device  104 , it is transmitted to the microcomputer  126  via first connector  132 . The image is then transmitted to the display driver  130  via second connector  134 , and to first and second microdrivers  112  and  116  via third connector  136  and fourth connector  138 , respectively, for viewing. 
     When the binocular display device  100  is fabricated, misalignment parameters are stored in the memory  128 . When an image is to be displayed, the microcomputer  126  retrieves these misalignment parameters from the memory  128  and instructs the display driver  130  as appropriate to modify the image for display by the first microdisplay  112  and/or the second microdisplay  116  to compensate for the misalignment of the binocular display device  100 . 
     The illustration shown in  FIG. 2  is representative of an aligned image. Types of image misalignment that may be encountered by the binocular display device  100  included horizontal misalignment ( FIG. 3 ), vertical misalignment ( FIG. 4 ), rotational misalignment ( FIG. 5 ), and magnification misalignment ( FIG. 6 ). The image misalignment can be corrected either by mechanical or electronic means. 
     Mechanical means of alignment may involve mechanical adjustment of either the image source, for example a microdisplay, or by adjustment of optical components between the image source and the eye, for example a lens. Because of the very small image alignment tolerances, the required mechanical adjustment may be prohibitively expensive to execute during or after manufacture of the device. The mechanical precision required may be on the order of 1 micron to 1 mm depending on the mechanism used to make the adjustment. Utilizing only mechanical alignment has limitations. One limitation is that it can be difficult or expensive to realign the images after the device is manufactured because it may require disassembly and of the eyewear display and for some components to be debonded. Also, it is not possible to correct for misalignment that may result from changes in temperature at which the device operates. 
     Electronic image alignment can overcome some of the limitations of mechanical image alignment. Horizontal or vertical image alignment of the image presented to both eyes is accomplished by shifting pixels in one or both of the images presented by the display drivers  130 . In the chart below, it is shown that by shifting an image by one pixel shifts results in an angular change of 1.5 to 3.75 minutes of arc for the selected resolutions. This enables the very tight vertical and horizontal image alignment tolerances to be met simply through the electronic image adjustment. This chart uses values for a typical eyewear display with a 25 degree diagonal field of view with a 4:3 aspect ratio for the image. 
                                                 One pixel shift           Field of view   Resolution   corresponds to:   Alignment tolerance                   15 degrees   QVGA (240 vertical pixels)   3.75 minutes   3 minutes (see-through)       vertical   VGA (480 vertical pixels)   1.875 minutes   5 minutes (immersive)           SVGA (600 vertical pixels)   1.5 minutes       20 degrees   QVGA (320 horizontal pixels)   3.75 minutes   3 to 8 minutes (see       horizontal   VGA (640 horizontal pixels)   1.875 minutes   through           SVGA (800 horizontal pixels)   1.5 minutes                    
Although adjustments for vertical and horizontal image alignment can be accomplished by shifting the image on a microdisplay, obtaining proper alignment with respect to rotation and magnification may be more complex manipulation of the initial image. A microcomputer may be required to calculate the corrected image.
 
     A flow chart of the steps implemented by the microcomputer  126  is shown in  FIG. 7 . First, the misalignment of a test image viewed from the display driver  130  of the binocular device  100  is measured  142 . The measured misalignment is stored  144  in memory  128 . Optionally, misalignment of the viewed test image is measured  146  for a plurality of temperatures and/or humidity and stored  148 . The temperature and humidity is sensed by the environmental sensor  120 . When the user turns on the binocular display device  100  and an actual image is received for display by the microdisplays  112 ,  116 , the microcomputer  126  generates  150  a signal to the display driver  130 . The actual image to be displayed by the microdisplays  112  and  116  is adjusted  152  to improve any misalignment between the images presented to each eye. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.