Abstract:
A head mounted projection display includes an optical path to support near eye projection of the projected images. That is, the projection aperture is placed close to the user&#39;s eye. In one implementation, image projectors are located in an image projector compartment located above left and right observation lenses. The projected images are directed down and behind respective observation lenses. Additional optics then redirect the projected images out of the observation lenses. This arrangement provides various advantages. One advantage is that it that allows for reduced forward protrusion of the projector compartment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit and priority to provisional application 62/190,207, the contents of which are hereby incorporated by reference. 
       U.S. PATENT DOCUMENTS INCORPORATED BY REFERENCE 
       [0002]    The following U.S. Patent Publications and Patent Applications are hereby incorporated by reference, US2014/0340424, Ellsworth and U.S. Ser. No. 14/272,054, Ellsworth. 
     
    
     FIELD OF THE INVENTION 
       [0003]    An embodiment of the current invention is directed to a head mounted projection display (HMPD) in which images are projected from points near the eyes of a user. 
       DESCRIPTION OF THE RELATED ART 
       [0004]    The HMPD is a special form of the well known head mounted display in which projectors are mounted to a frame or headset worn by a user. Images from the projectors are then reflected from a special screen back into the user&#39;s eyes. Conventional HMPD design employs beam splitters in front of the user&#39;s eyes to allow the viewing of returning light in a coaxial relation to the projected light. The beam splitters pose a disadvantage, however, in that their position and angle in front of the user&#39;s eyes require a headset that protrudes farther forward than conventional glasses. To reduce this bulk and simplify manufacturing, the projectors may be mounted, without beam splitters, close to the user&#39;s eyes as taught in Ellsworth, U.S. Patent Publication 2014/0340424. However, projectors with projection lens systems co-linear relative to the spatial light modulator require a distance to the lenses that, again, adds protrusion. 
       SUMMARY 
       [0005]    Embodiments of the present invention are directed to head mounted projection displays (HMPDs) having near eye projection. In one embodiment, the HMPD has a glasses frame, first and second observation lenses, and an image projector compartment. Optics support initially directing the projected images down behind the observation lenses and then redirecting the projected image out through the observation lenses. In one embodiment, the image projector compartment includes light sources and spatial optical modulators. 
         [0006]    One embodiment of the HMPD of the current invention comprises an arrangement of optical components that reduces a protrusion of the projector compartment compared with directly projecting images from the projector compartment. In one embodiment, images from projection system located on the headset frame are reoriented so as to project downward into the space just behind the top rim over the observation lenses, where a mirror, right angle prism, or other optical components are positioned to redirect the projection light forward through said observation lenses. In one embodiment, the HMPD uses any filtering that is available in said observation lenses when placed in the outgoing projection light path. 
         [0007]    The HMPD may also be utilized to achieve other benefits via near eye projection. In one embodiment the near eye projection supports receiving a brighter returned image. In one embodiment, the near eye projection allows for projection rays to originate closer to the eyes of the user compared with HMPDs in which the projection rays originated from the image projector compartment. This is turn, may result in some applications in brighter returned image. For example, having the projection rays originated closer to the eyes of the user may result in the return a brighter image when reflected by a commercially available retroreflective sheeting, wherein the sheeting has a low observation angle that returns light very close to the projection origin. 
         [0008]    It will also he understood that embodiments of the present invention include methods of operating the HMPD. In one embodiment this includes the HMPD receiving images to be projected and projecting the images via near eye projection. 
         [0009]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The foregoing summary, as well as the following detailed description of illustrative implementations, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the implementations, there is shown in the drawings example constructions of the implementations; however, the implementations are not limited to the specific methods and instrumentalities disclosed. In the drawings: 
           [0011]      FIG. 1  illustrates a prior art head mounted projection display device. 
           [0012]      FIG. 2  illustrates a head mounted projection display device in accordance with an embodiment of the current invention. 
           [0013]      FIG. 3  illustrates the prior art projector optical path of  FIG. 1 . 
           [0014]      FIG. 4  illustrates a top view of the projector optical path of an embodiment of the current invention. 
           [0015]      FIG. 5  illustrates a front view of the projector optical path of an embodiment of the current invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  shows a HMPD unit of the prior art. There are two observation lenses  105 . A projector compartment  107  is located above the viewing lenses  105  in a brow region. The projector compartment  107  protrudes out relative to the viewing lenses  105 . This projector compartment  107  has image projectors located behind brow windows  101  and  102 , and tracking cameras located behind window  103 . Although the image projectors have been designed to have a small vertical thickness, the brow of the projection compartment  107  of the headset must be extended forward to accommodate the optical length necessary for the projection lenses. 
         [0017]    The configuration of an embodiment of the current invention is shown in  FIG. 2 . Some conventional HMPD components are omitted for the purposes of clarity. For example, the HMPD of  FIG. 2  may include a compact power source (e.g., a battery or a power connector), a microprocessor controller, and a communications interface to receive graphical images to be projected that are generated by a computing system (not shown in  FIG. 2 ). If the HMPD of  FIG. 2  includes a tracking module to track a user&#39;s head and/or eye movement, the HMPD may include an interface to transmit tracking information to the computing system. 
         [0018]    A glasses frame  220  is provided. An image projector compartment  225  is disposed above a lens portion  230  that includes a first observation lens  235 -A and a second observation lens  235 -B. Here the top of the projector compartment has been removed, for illustration purposes, to show the internal parts  201 . The right observation lens  203  is shown while the corresponding lens on the other side has been removed for the purposes of illustration. Likewise, the final projection lens  202  is shown while the corresponding lens of the other side has also been removed revealing the projection exit aperture  204  on the right angle mirror assembly  205 . As can be seen in  FIG. 2 , the projection exit aperture  204  may be located in an upper region of an observation lens. In this example, the projection exit aperture  204  is not coaxial with a center eye position but is near the eye of a user. The projection of images through each observation lens is thus near eye projection. It is noted that in some applications, having the projection rays originate closer to the eyes of the user may result in the return of a brighter image returned to the user&#39;s eye. 
         [0019]    In one embodiment, a complete system would include a retroreflective screen to return projected images back to the eyes of the user. Thus images projected out from the left observation lens would be retroreflected back to the user and images projected out from the right observation lens would be retroreflected back to the user. In one embodiment, the HMPD may include filtering techniques known in the art to prevent cross-talk of images by isolating the returning left and right projected images to their respective eyes. This may include, for example, polarizing filters, although it will be understood that other types of filters could be used. 
         [0020]    The optical path diagram for the prior art device of  FIG. 1  is shown in top view in  FIG. 3 . Light originates in an illumination source (typically LED based)  301  and is then collected and focused by lens means  302  and directed by beam splitter/combiner cube  303  to be spatially modulated by a spatial modulator  304 , such as Liquid Crystal on Silicon (LCOS) reflective matrix panel. The image formed and reflected by spatial modulator  304  then travels through  303  to be projected out ( 101  in  FIG. 1 ) by the lens system  305 . The left and right projection sections are separated by a pair of infrared tracking cameras  306 . 
         [0021]    In an embodiment of the current invention, the optical path can be made to cause less forward protrusion of the projector compartment  225  by rotating the horizontal axis of the projector configuration ninety degrees such that the path of generated images out of the projector compartment  225  initially goes down (vertically) instead of forward directly out through the front of projector compartment  225 . That is, the images that are generated for each eye are initially directed vertically down behind the observation lenses and then are directed out perpendicularly through the observation lenses  235 -A,  235 -B. This rotation is shown in  FIG. 4  which is, again, a view from the top looking down. Each individual left/right image projector includes the components to generate a sequence of optical images in response to computer commands (e.g., via an illumination source and spatial light modulator), direct the light of the optical images down behind an observation lens, and then redirect the light through a portion of an observation lens. 
         [0022]    Each respective spatial light modulator panel  404  is illuminated by a light source  401  to generate a set of optical images. Each respective spatial light modulator panel  404  is now located above a respective splitter/combiner cube  403 . Each splitter/combiner cube  403  directs the light from its associated spatial modulator panel  404  down. The windows  101  and  102  have been eliminated in the front brow plate  407 , which still has a window  408  for the infrared tracking cameras  406 . 
         [0023]      FIG. 5  shows how the arrangement of the image generators and associated optics direct the light from each image projector separately down vertically and then perpendicularly out through separate observation lenses would be positioned with respect to a glasses housing  501 . As in  FIG. 4  the optical path (for an individual image projector) begins with an illuminator  502  that is focused at  503  and is then directed by splitter/combiner  504  to be modulated at spatial modulator panel  505 . However, in  FIG. 5  it can be seen that the optical path drops through the housing to be directed forward by a mirror or prism of an optical component  506  and then projected by lens or lens system  507  (corresponding to  202  in  FIG. 2 ). 
         [0024]    Those skilled in the art will understand that the invention could be practiced with the projection lens or lens system  507  located above optical component  506  such that  506  turns the final projection rays. Also, those skilled in the art will understand that curvature may be introduced in the surface of optical component  506  so as to provide part or all of the function of the projection lens or lens system. 
         [0025]    In the prior art such as Ellsworth US Patent Publication 2014/0340424, polarizing filters have been applied to the projection means so as to reduce light entering the opposite eye when matched to filters in or on the observation lenses. A goal of the current invention is achieved by eliminating the need for filters at the projectors through the mounting of projector apertures behind the observation lenses, such that the filters at or in those lenses filter the image light going both forward and reflected. Ellsworth US 2014/0340424 teaches several means of filtering for the purpose of isolating the left and right images to their respective eyes, and those skilled in the art will understand that said means may also be used with the current invention. 
         [0026]    Those skilled in the art will understand that, as also disclosed in Ellsworth US 2014/0340424, the observation lenses and filtering may be eliminated by close placement said projector apertures to their respective eyes and the use of retroreflective sheeting with sufficiently low observation angle as to segregate the reflected images to their respective eyes. 
         [0027]    While examples have been provided of components to generate images, it will be understood that the invention is not limited to a particular image generation techniques. 
         [0028]    An illustrative embodiment has been described by way of example herein. Those skilled in the art will understand, however, that change and modifications may be made to this embodiment without departing from the true scope and spirit of the elements, products, and methods to which the embodiment is directed, which is defined by my claims.