Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2001-04-20
2003-03-04
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C345S009000, C349S013000
Reexamination Certificate
active
06529331
ABSTRACT:
FIELD OF INVENTION
The present invention relates to head mounted video displays for presenting virtual environments, and more particularly to a binocular head-mounted video display with full field of view and high resolution video images.
BACKGROUND OF THE INVENTION
Traditionally, displays of virtual environments have been used for entertainment purposes, such as presenting the environments for the playing of various video games. More recently, such displays have been considered for other applications, such as possible tools in the process of designing, developing, and evaluating various structures and products before they are actually built. The advantages of using virtual displays as design and development tools include flexibility in modifying designs before they are actually built and savings in the costs of actually building designs before they are finalized.
To be a useful and valid design and development tool, however, a virtual display system must be capable of generating high fidelity, interactive, virtual environments that provide correct “feelings of space” (FOS) and “feelings of mass” (FOM). Such a system must also allow users to function “naturally” within the virtual environment and not experience physical or emotional discomfort. It must also be capable of displaying a virtual environment with dynamics matched to the dynamics of human vision and motor behavior so there is no perceptible lag or loss of fidelity.
FOS and FOM are personal perceptual experiences that are highly individual. No two people are likely to agree on FOS and FOM for every environment. Also, there are likely to be variations between people in their judgments of FOS and FOM within a virtual environment, as compared to FOS and FOM in the duplicated real environment. Thus, preferably a virtual display system will provide feelings of space and mass that are based on a more objective method of measuring FOS and FOM that does not rely on personal judgments of a particular user or a group of users.
With regard to human vision, typically there are “natural behaviors” in head and eye movements related to viewing and searching a given environment. One would expect, and a few studies confirm, that visual field restrictions (e.g., with head mounted telescopes) result in a limited range of eye movements and increased head movements to scan a visual environment. Forcing a user of a virtual display system used as a design and development tool to adapt his or her behavior when working in a particular virtual environment could lead to distortions of visual perception and misjudgment on important design decisions. Thus, the ideal virtual display system will have sufficient field-of-view to allow normal and unrestricted head and eye movements.
Simulator sickness is a serious problem that has limited the acceptance of virtual reality systems. In its broadest sense, simulator sickness not only refers to feelings of dizziness and nausea, but also to feelings of disorientation, detachment from reality, eye strain, and perceptual distortion. Many of these feelings persist for several hours after use of a system has been discontinued. Most of the symptoms of simulator sickness can be attributed to optical distortions or unusual oculomotor demands placed on the user, and to perceptual lag between head and body movements and compensating movements of the virtual environment. Thus, preferably a virtual display system will eliminate simulator sickness.
One technology commonly used to present virtual environments are head mounted video displays. A head mounted display (“HMD”) is a small video display mounted on a viewer's head that is viewed through a magnifier. The magnifier can be as simple as a single convex lens, or as complicated as an off-axis reflecting telescope. Most HMDs have one video display per eye that is magnified by the display optics to fill a desired portion of the visual field.
Since the first HMD developed by Ivan Sutherland at Harvard University in 1968, there has always been a trade-off between resolution and field of view. To increase field of view, it is necessary to increase the magnification of the display. However, because video displays have a fixed number of pixels, magnification of the display to increase field of view is done at the expense of visual resolution (i.e., visual angle of the display pixels). This is because magnification of the display also increases magnification of individual display pixels, which results in a trade-off between angular resolution and field of view for HMDs that use single displays. Normal visual acuity is 1 minute of arc (20/20). Legal blindness is a visual acuity of 10 minutes of arc (20/200). The horizontal extent of the normal visual field is 140° for each eye (90° temporal and 50° nasal). Thus, to fill the entire visual field with a standard SVGA image, one must settle for visual resolution that is worse than legal blindness.
One attempt to develop an HMD with both high visual resolution and a large monocular field of view was made by Kaiser Electro-Optic, Inc. (“KEO”) under a contract with the Defense Advanced Research Projects Agency (“DARPA”). KEO developed an HMD that employed a multi-panel “video wall” design to achieve both high resolution with relatively low display magnification and wide field of view. The HMD developed by KEO, called the Full Immersion Head Mounted Display (“FIHMD”), had six displays per eye. Each display of the multiple displays forming the video wall was imaged by a separate lens that formed a 3×2 array in front of each eye. The horizontal binocular field of view of the FIHMD was 156° and the vertical was 50°. Angular resolution depended on the number of pixels per display. The FIHMD had 4 minarc per pixel resolution.
FIG. 1
is a plan view of the FIHMD, while
FIG. 2
shows the optics
10
of the FIHMD. These optics included a continuous meniscus lens
12
(“monolens”) between the eye (not shown) and the six displays
14
and a cholesteric liquid crystal (“CLC”) filter
16
for each display
14
. The meniscus lens
12
served as both a positive refracting lens and as a positive curved mirror. The CLC
16
reflected light from the displays
14
that passed through the meniscus lens
12
back onto the lens
12
and then selectively transmitted the light that was reflected from the lens' curved surface. Some versions of the FIHMD optical design employed Fresnel lenses as part of the CLC panel to increase optical power. This so-called “pancake window” (also called “visual immersion module”
18
or “VIM”), shown in
FIG. 3
, provided a large field of view that was achieved with reflective optics while folding the optical paths into a very thin package.
The FIHMD
20
, shown in
FIG. 1
, could not provide a satisfactory full field of view. The FIHMD had limitations imposed by its use of the VIM optics and the requirement for adequate eye relief to accommodate spectacles
22
. The radius of curvature of the meniscus lens
12
dictated the dimensions of the VIM
18
and, coupled with the eye relief requirement, determined the location of the center of curvature of display object space. Although no documentation is available that discusses the rationale for the design, as illustrated in
FIG. 1
, it appears that the centers of VIM field curvature
24
for the FIHMD
20
were set in the plane of a user's corneas. If the centers of the two VIM fields are separated by the typical interpupillary distance (68 mm), then the centers are located 12 mm behind the lens
23
of spectacles
22
. This is the usual distance from a spectacle lens to the surface of the cornea. Because of this choice of centers, the FIHMD
20
had problems with visibility of seams between the displays
14
and with display alignment.
Normally, when the visual angle subtended by an object is measured, the apex of the cornea is used as the reference. Technically, for paraxial rays, the anterior nodal point of the eye, which is 7.2 mm posterior to the cornea, should be used as the reference. However, most object distances are large enough that a 7.2
Brown Lawrence G.
Massof Robert W.
Shapiro Marc D.
Corless Peter F.
Edwards & Angell LLP
Epps Georgia
Jensen Steven M.
Johns Hopkins University
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