Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2003-01-02
2004-08-03
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
C345S008000
Reexamination Certificate
active
06771423
ABSTRACT:
BACKGROUND OF INVENTION
a) Field of the Invention
The present invention relates to a head-mounted virtual display apparatus (VDA) based on a cross-cavity optical configuration with an unobstructed forward field of view. More particularly, a near-eye light deflecting element (LDE) located in the peripheral field of view provides “look toward” access to an inset magnified image of a miniature display. Active and passive alignment means, including articulating connections and image warping electronics, allow correction of geometric distortion arising from folding of the optical train and/or embodiments based on off-axis optical configurations.
b) Description of the Prior Art
The head-mounted display (HMD) field has evolved on a number of fronts over the past 20 years. The earliest development by the military focused on wide field of view (FOV), see-through helmet-mounted displays for aircraft guidance and weapon aiming applications, in which the virtual image overlies the ambient environment. Since then development has included lightweight monocular HMDs for workplace wearable computer systems, binocular HMDs for full-immersion viewing of video and virtual reality applications, and various types of see-through displays for augmented reality applications.
Monocular HMDs are designed to provide access to electronic information while obscuring only a portion of the forward and peripheral fields of view. A typical monocular HMD approach places the display and optics directly in front of one eye, such that the forward FOV of that eye is partially or fully occluded and the peripheral FOVs of one or both eyes is partially occluded. The most common example of this type of monocular HMD is a boom style HMD, in which the viewable element (and often the display) is positioned in front of the face at the end of a cantilever arm. The main advantages of a boom style HMD include its relative simplicity (i.e., its one size fits all nature and minimal number of adjustments) and its construction flexibility, in that it can be added to a pair of spectacles or any head-borne structure, or can be constructed as a stand-alone headset. The disadvantages of a boom style HMD include a physical boundary that extends a distance from the face, occlusion of a portion of the forward FOV, and its suitability primarily for stationary activities due to vibration of the cantilever arm during user motion.
A second monocular HMD approach integrates the virtual display elements, in part or in full, into a pair of spectacles, with the aim of not significantly altering its form or weight. This approach allows the display and optics to be kept closer to the face, thus making it possible to limit the occluded FOV to one eye and, in some cases, to only a small portion of the peripheral FOV. The compact nature of a glasses-mounted display (GMD), however, generally requires a folding of the optical train, which increases the complexity of the construction.
In general, monocular HMDs can be categorized according to whether the optical train is an on-or off-axis configuration. In an on-axis optical configuration, the optical axis of each powered optical element is coincident with the optical train axis or illumination path (with the exception of unpowered LDEs used to “turn corners”). No optics are “tilted” with respect to the optical train axis. Off-axis optical configurations, on the other hand, generally include at least one powered optical element whose optical axis is tilted with respect to the optical train axis. Off-axis optical configurations allow more compact constructions but suffer from higher levels of aberrations.
Monocular HMDs can be further categorized according to the nature of the magnification system, of which there are two basic types: simple and compound magnification systems. A simple magnification system (or simple magnifier) is a single stage, non-pupil forming magnification system (i.e., a magnification system that does not form a real exit pupil), which is composed of either a positive refractive or reflective element, or multiple adjacent refractive elements with no spacing between them. A compound magnification system, on the other hand, is a pupil forming magnification system typically composed of two or more distinct stages. In a compound magnification system, the stage closest to the object is termed the objective or relay, while the stage viewed by the eye is termed the eyepiece or ocular. In a two stage compound magnification system, the objective forms an “intermediate” image (either real or virtual) that is the “object” projected virtually by the eyepiece. For the purposes of this invention, a third type of magnification system—termed a compound eyepiece—is defined as one in which multiple refractive and reflective elements (including the eyepiece) are in close proximity to one another with spacing between at least two of the elements. A compound eyepiece is effectively a single stage (pupil-forming) magnification system, which is typically located closer to the eye than it is to the display. Put another way, the distance between the display and the first magnifying element (or the “objective”) of the system is typically greater than the distance between the first magnifying element and the eyepiece. For a compound magnification system the converse typically holds. For example, consider an HMD with a display located above the eye and a compound eyepiece located below the eye, which is formed from a single block of material and includes three magnifying surfaces: a refractive entrance surface, a reflective intermediate surface and a refractive exit surface. This device includes multiple spaced magnifying elements (so it cannot be categorized as a simple magnification system) and the distance between the entrance and exit surfaces (or the “objective” and “eyepiece” for comparison purposes) is less than the distance between the display and the “objective”. Thus, the magnifying power is not distributed throughout the optical train like a two stage, compound magnification system.
The design of an HMD involves two generally conflicting aims: (i) achieving a high quality, computer monitor sized virtual image (i.e., a virtual image with a diagonal dimension of at least 10 inches and preferably 15 inches or greater) at a desired apparent image distance (such as a workstation distance of about 24 inches) and (ii) the desire for a compact, lightweight format. One method of balancing these aims is through the use of lightweight, reflective or light deflecting elements (LDEs), such as a mirror constructed from a plastic substrate and a reflective film. In addition, powered and unpowered LDEs may be used to increase magnification (the latter by increasing the optical train path length) and to distribute the weight of the optics more evenly about the head.
A monocular HMD for mobile activities must present a stationary virtual image to the eye during user motion. This requires that the support frame be stably secured to the head and that the display and optics be stably secured to the frame. Taking user comfort into account, the former requirement is best satisfied by a support frame in contact with both ears and the bridge of the nose; while the latter requirement negates the use of a relatively long, thin cantilever arm as the support structure for attaching the eyepiece to the frame, since this type of structure is susceptible to vibration during user motion. For safety and performance reasons, another key requirement for a mobile activity HMD is unobstructed forward vision.
For the purposes of the present invention, the head-mounted display field is further categorized according to: (i) whether the device is suitable for mobile activities; (ii) the optical configuration obstructs normal forward vision; and (iii) whether the optical configuration is a cross-cavity optical configuration (CCOC) or a non-cross-cavity configuration (non-CCOC).
As defined by Geist in U.S. patent application Ser. No. 10/216,958, incorporated herein by reference in its entirety, a cross-cavity optical configuration is an op
Epps Georgia
Geist Richard
Harrington Alicia M.
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