Head-mounted display apparatus with a single image display device

A head-mounted display apparatus comprises an image display device for displaying images, a first beam splitter for partially transmitting and partially reflecting light from the image display device, a second beam splitter for partially transmitting and partially reflecting the light transmitted by the first beam splitter, and a first and a second concave reflection mirrors. The image display device, disposed on the right side of an observer, displays images on the basis of video signals from a video signal source. The first and the second beam splitters are disposed in front of the right and the left eyes of the observer, respectively. The first and the second concave reflection mirrors are disposed on the reflection side of the first and the second beam splitter, and reflect the light therefrom to the right and the left eyes of the observer, respectively. The head-mounted display apparatus of the present invention can also provide a stereoscopic vision by displaying images on the image display device on the basis of the principle of binocular parallax.

FIELD OF THE INVENTION 
The present invention relates to a head-mounted display apparatus; and, 
more particularly, to a head-mounted display apparatus incorporating 
therein a single image display device. 
DESCRIPTION OF THE PRIOR ART 
There is shown in FIG. 1 a schematic diagram of a conventional head-mounted 
display apparatus comprising a pair of image display devices 1, 2, e.g., 
liquid crystal displays, and a pair of magnifying lenses 3, 4. 
The image display devices 1, 2, disposed in front of left and right eyes 5, 
6 of an observer, respectively, are connected to a video signal source 
(not shown) and display images on the basis of video signals therefrom. 
The magnifying lenses 3, 4 are positioned between the left image display 
device 1 and the left eye 5 and between the right image display device 2 
and the right eye 6, respectively, thereby enabling the observer to see 
enlarged virtual images formed at a certain distance from the eyes 5, 6. 
However, such a conventional head-mounted display apparatus is fairly 
heavy, making it burdensome on the observer's head, as a result of the 
presence of two image display devices. In addition, there exists a 
complicated circuit for transmitting the video signals to the individual 
image display device. 
SUMMARY OF THE INVENTION 
It is, therefore, a primary object of the invention to provide a 
head-mounted display apparatus having a reduced weight and a simplified 
circuit network by incorporating therein a single image display device. 
In accordance with an aspect of the present invention, there is provided a 
head-mounted display apparatus comprising: an image display device for 
displaying images; a first beam splitter for partially transmitting and 
partially reflecting light from the image display device; a second beam 
splitter for partially transmitting and partially reflecting the light 
transmitted by the first beam splitter; and a first and a second concave 
reflection mirrors for reflecting the light reflected by the first and the 
second beam splitters to one eye and the other eye of an observer, 
respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
There are respectively shown in FIGS. 2 and 3 a schematic diagram and a 
schematic perspective view of a head-mounted display apparatus in 
accordance with a preferred embodiment of the present invention. The 
head-mounted display apparatus of the first preferred embodiment comprises 
an image display device 11, e.g., a liquid crystal display or cathode ray 
tube, a first beam splitter 12 for partially transmitting and partially 
reflecting light from the image display device 11 in proportion of 3:1, a 
second beam splitter 13 for partially transmitting and partially 
reflecting the light transmitted by the first beam splitter 12 in 
proportion of 1:1, and a first and a second concave reflection mirrors 14, 
15. 
The image display device 11, disposed on, e.g., the right side of an 
observer, is connected to a video signal source (not shown) such as a 
personal computer, a video cassette recorder, a laser disc player, etc., 
and displays images on the basis of video signals therefrom. 
The first and the second beam splitters 12, 13 are disposed in front of 
right and left eyes 16, 17 of the observer, respectively. The first beam 
splitter 12 transmits 75% of the light from the image display device 11 to 
the second beam splitter 13 and reflects 25% of the light from the image 
display device 11 to the first concave reflection mirror 14. Then, 75% of 
the light from the first concave reflection mirror 14, i.e., 18.75% of the 
light from the image display device 11, is transmitted through the first 
beam splitter 12 to the right eye 16. On the other hand, the second beam 
splitter 13 reflects 50% of the light from the first beam splitter 12 to 
the second concave reflection mirror 15 and transmits the rest of the 
light. Then, 50% of the light from the second concave reflection mirror 
15, i.e., 18.75% of the light from the image display device 11, is 
transmitted through the second beam splitter 13 to the left eye 17. In 
this way, the same amount of light enters both eyes 16, 17. 
Disposed on the opposite side of the image display device 11 is a convex 
lens 21 which transmits the light from the second beam splitter 13 to 
outside, thereby allowing the images displayed on the image display device 
11 to be viewed from the outside. In addition, a shutter 22 is disposed in 
front of the convex lens 21 in the direction of transmission through the 
second beam splitter 13 so that the images displayed on the image display 
device 11 are selectively viewed from the outside by opening or closing 
the shutter 22. It is appreciated that the shutter 22 may be disposed 
behind the convex lens 21. 
The head-mounted display apparatus of the present invention can also 
provide a stereoscopic vision by displaying images on the image display 
device on the basis of the principle of binocular parallax. 
There are respectively shown in FIGS. 4 and 5 a schematic diagram and a 
schematic perspective view of a head-mounted display apparatus in 
accordance with another preferred embodiment of the present invention, 
which provides a stereoscopic vision. The head-mounted display apparatus 
of the second preferred embodiment, as compared with the first, further 
comprises a first and a second shutter glasses 218, 219 disposed between 
the first beam splitter 12 and the right eye 16 and between the second 
beam splitter 13 and the left eye 17, respectively, wherein the image 
display device 11 alternately displays right-eye and left-eye images 
photographed from two different directions or angles. 
The first and the second shutter glasses 218, 219, synchronized with the 
right-eye and the left-eye images displayed on the image display device 
11, become alternately clear and cloudy so that the observer is able to 
see three dimensional images. The shutter glasses 218, 219 are made of a 
liquid crystal material, and disclosed in detail in U.S. Pat. Nos. 
4,907,860 and 5,539,423, which are incorporated herein by reference. 
In such head-mounted display apparatus of the present invention, since only 
one image display device is required, the weight thereof is decreased, 
thereby reducing the degree of burden on the observer's head. In addition, 
the circuit for transmitting the image signals becomes simplified. 
Although the invention has been shown and described with respect to the 
preferred embodiments, it will be understood by those skilled in the art 
that various changes and modifications may be made without departing from 
the spirit and scope of the invention as defined in the following claims.