Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Reexamination Certificate
1998-03-31
2001-01-23
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
C349S011000, C349S015000, C359S458000, C345S007000
Reexamination Certificate
active
06177966
ABSTRACT:
RELATED APPLICATION
This application is based on Japanese Patent Application 09-086245, filed in Japan on Apr. 4, 1997, the content of which is hereby incorporated herein in its entirety by reference.
FIELD OF THE INVENTION
The present invention relates to a display suitable for use in a virtual reality device in order to observe a projected image as a virtual image.
BACKGROUND OF THE INVENTION
FIG. 1
shows an example of the construction of a conventional head-mounted display (HMD), which is one type of virtual reality device. In order for an eye
3
of an observer to view a virtual image, an actual image is displayed on a liquid crystal panel
1
, which is illuminated by a backlight
4
. In
FIG. 1
the virtual image is viewed at infinity by the observer's eye
3
because the liquid crystal panel
1
is disposed at the focal point position of the lens
2
. In general, head-mounted devices are constructed so as to form an image at a distance in the range of 25 cm to infinity.
It has been proposed to allow a changing of the positions of the liquid crystal panel
1
and the lens
2
so as to adjust the position of the image to match the diopter of the observer
3
(first conventional example). Japanese Laid-Open Patent Application No. 7-30928 discloses an arrangement wherein the diopter is changed by moving the focal point in conjunction with the perspective of an image so as to controllably move the image display device (i.e., liquid crystal panel
1
) forwarde and backwarde in accordance with the parallax of the displayed image (second conventional example).
However, the first conventional example normally provides that an observer continues to view the image at a fixed position insofar as the observer cannot himself optionally change the position of the image. Particularly when this viewing state continues over a long period of time, the observer's eyes become fatigued so as to cause a concern as to possible vision impairment. The second conventional example of a display described above is capable of reducing eye fatigue to some degree, but requires a complex construction which is necessary to control the position of the image display device in accordance with the displayed image. Furthermore, when the image parallax does not change, the image continues to be viewed at the same image position. In this situation, the resulting eye fatigue is similar to that of the first conventional example.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a display having a simple construction. Another object of the present invention is to provide a display which prevents eye fatigue. Another object of the present invention is to provide an improved display which is suitable for use in virtual reality devices in order to observe a projected image as a virtual image.
The present invention attains the aforesaid objects by providing a construction comprising:
an image display device for displaying an image;
an optical system for projecting, as a virtual image, an image displayed by the image display device; and
a control system for controlling at least one of the image display device and the optical system so as to periodically effect a changing of the position of the virtual image, which is projected by the optical system, each changing occurring over a predetermined time period.
According to this construction, an observer views a projected image which normally changes position during viewing. That is, the virtual image is not viewed continuously at only one point even when the viewing by the observer continues over a long period of time.
In a presently preferred embodiment, the position of the liquid crystal panel or of a lens in the optical system is moved along the optical axis at a speed of less than 0.1 mm/sec so as to avoid burdening the eye of the observer. The motion can be at a substantially uniform speed through most of the range of the motion, while permitting a slowing down to a full stop at each end of the range and then an acceleration to the uniform speed in the opposite direction. In one embodiment, a rest period (i.e., a full stop for a period of time) can be provided at one or both ends of the motion range, either for each cycle of motion or after the occurrence of a plurality of such cycles.
When the display of the present invention is used in a situation in which the size of the viewed image is of particular importance, the size of the display region can be changed so that the apparent image size remains constant with a change in the position of liquid crystal panel
1
.
REFERENCES:
patent: 3923370 (1975-12-01), Mostrom
patent: 4902083 (1990-02-01), Wells
patent: 5421589 (1995-06-01), Monroe
patent: 5579026 (1996-11-01), Tabata
patent: 5684497 (1997-11-01), Hildebrand et al.
patent: 5701132 (1997-12-01), Kollin et al.
patent: 5739797 (1998-04-01), Karasawa et al.
patent: 5896226 (1999-04-01), Peuchot et al.
patent: 5917460 (1999-06-01), Kodama
patent: 5973845 (1999-10-01), Hidebrand et al.
patent: 7-30928 (1995-01-01), None
patent: 8-257077 (1996-10-01), None
Kamoda Yuji
Masuda Tomohiko
Wada Kenichi
Chowdhury Tarifur R.
Minolta Co. , Ltd.
Sidley & Austin
Sikes William L.
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