Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Patent
1997-02-10
1998-04-14
Nelms, David C.
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
359633, G02B 2714
Patent
active
057399557
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an optics system suitable for a head mounted display apparatus generally and more particularly, but not exclusively, to a head mounted display apparatus comprising an optics system facilitating the binocular viewing of a single LCD screen image.
BACKGROUND OF THE INVENTION
The development of head mounted display apparatus for viewing computer generated imagery has its roots in military aircraft weapons and flight simulation systems. Typically, such systems have required that a computer generated image is projected by means of an optical combiner on to a projection plane or surface overlapping the line of sight of a user, such as for example the curved visor of a helmet. One such example is illustrated in FIG. 8 of U.S. Pat. No. 5,050,966 in which a single cathode ray tube (CRT) mounted in the helmet rearwardly of the user's head feeds a mirrored optical path to a beamsplitting arrangement in the user's line of sight. The beamsplitter enables the user to view with both eyes the projected CRT image and the environment external of the helmet and in his line of sight. It will be understood that the aircraft helmet design can accommodate the described optical apparatus.
However, in many virtual reality applications a helmet of such size would inhibit the movement of a user in the real world when such movement is an integral part of most virtual reality experiences. In addition such designs are inherently complicated by the need to superimpose reasonable images projected from the CRT on to the user's view of the external environment. The design of combiner disclosed in that Specification is constrained by the requirement that the user should be able to view the external environment without eyestrain. As a consequence of this requirement, the design of the associated optics must provide the right performance after allowing for the combiner configuration. Virtual reality applications generally require the widest field of view that is feasible at low cost. If the field of view of the device shown in U.S. Pat. No. 5,050,966 were to be extended above approximately 40 degrees, the optical design would become overly complex due to the necessary first order properties required to illuminate the eye, and the third and higher order properties needed to compensate aberrations.
In virtual reality arcade games applications it has been usual to provide a head mounted display apparatus (HMD) in which a wide field of view is provided by two optical systems each comprising a plurality of lenses and a miniature liquid crystal display screen (LCD) to provide a binocular image to the user. Now that virtual reality games applications are being developed for the home market it is desirable that the unit cost of the HMD is kept to a minimum. LCD's are expensive components and it is desirable that a low-cost HMD comprises only a single LCD feeding a binocular image to the eyes of the user. One such solution is suggested in European Patent Specification No. EP 0 539 907 A2. This specification discloses an HMD shown in FIGS. 2 and 3 which comprises an LCD and magnifying lens mounted forwardly of the nose of a user, a beamsplitter feeding a separate complete image of the LCD respectively to two mirrors each mounted respectively in the line of sight of the user, and further magnifying lenses each mounted intermediate one of the mirrors and its respective eye of the user. It is understood that the arrangement described provides a construction wherein the bulk of optical apparatus disposed forwardly of the eyes is cumbersome.
The arrangement described in European Patent Specification No. 0 539 907 is understood to be fundamentally limited in the field of view that can be projected with adequate performance, by the non-rotationally symmetrical nature of the beamsplitting prism. As a consequence the two eyes of a user perceive images that are projected with different perspectives and the user looking toward the extremities of the field of view will see vertical disparities between the relati
REFERENCES:
patent: 2973683 (1961-03-01), Rowe et al.
patent: 5583695 (1996-12-01), Dobrusskin
Mack Ricky
Nelms David C.
Virtuality (IP) Limited
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