Optical prism for projecting image

Optical: systems and elements – Prism – With reflecting surface

Reexamination Certificate

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Details

C359S631000

Reexamination Certificate

active

06690522

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an optical prism which is used in an optical system for projecting image, produced on a liquid crystal or like image display, onto a viewer's eye ball retina. Such an optical prism is a main optical element in an image display unit in a head mounted display (abbreviated HMD), in which the image display unit is held at a predetermined position by a frame member mounted on the viewer's head for single- or double-eye image viewing.
Recently, development of such HMDs is in progress, and these devices are finding increasing applications in various fields, such as medical, construction and educational fields and also amusement field such as various game machines.
Meanwhile, there is a trend for developing VGA purpose devices which can display high quality images and also displays of data systems as a version of OA (office automation) systems.
Many HMDs having been developed or proposed up to date, are of double-eye viewing type having a left and right image display for the left and right eyes for viewing these image displays with both eyes. For OA purposes, on the other hand, HDMs of single-eye viewing type also have been proposed. Such an HMD permits a single eye to view an image display, while permitting a keyboard and other operating sections to be operated simultaneously using the other eye, forward and at-hand visual field thereof being ensured to this end.
The OA and like purpose HMDs are desirably compact and handy in construction, so that they can be worn for use in a sense just like wearing glasses.
However, HMDs for general home applications are stage of development, and no proposal has been made for a product, which is not only handy but also can sufficiently solve various specific technical problems posed in its manufacture.
Japanese Laid-Open Patent Publication No. 8-234147, for instance, shows an optical prism, which reflects reflected light from an incidence surface, having been incident from a display face of an LCD or like display, at least twice in itself before emitting the light from a predetermined emission surface to the outside such that the emitted light is led to a viewer's pupil.
This optical prism is a one-piece member having a plurality of non-spherical reflecting surfaces, and satisfies various optical requirements even when constructed as a viewing system.
When constructing an HMD or the like by employing this optical prism, however, it is necessary to hold the optical prism and a liquid crystal display in a regular positional relation with high accuracy in order to obtain an accurate projection liquid crystal display image onto the viewer's retina. It is an unsolved technical problem to ensure the positioning accuracy and also facilitate the manufacture.
SUMMARY OF THE INVENTION
The present invention was made in view of the above circumstances, and its object is to provide an optical system of the type as described, which can ensure necessary accuracy of the positioning of it and an image display to each other and also facilitate manufacture when it is employed as an optical element of OA and various other systems.
Features and advantages over the prior art of the present invention will be described in the following:
(1) According to a first aspect of the present invention, there is provided an optical prism for reflecting incident light from an incidence surface suited for incidence of light from a predetermined display or like light source for at least twice before emitting the reflected light as emission light through a predetermined emission surface. The optical prism has side surfaces crossing the incidence and emission surfaces and including receded surfaces formed such as not to impede an optical path of an effective size, the incident light being led along the optical path from the incidence surface to the emission surface.
Heretofore, no optical prism of this type has been proposed, which has a specific shape such as to permit size reduction of its entirety, including portions for positioning it and a display or the like relative to each other and also maintaining the relative positions of it and the display.
According to the present invention as in (1) above, the receded surfaces do not impede the optical path of the effective size, along which light from the display or like light source is led, and can be utilized for providing portions for positioning the optical prism and the display or the like to each other and maintaining the relative positions of these components. Besides, it is possible to provide portions which do not impede size reduction of the overall structure.
(2) According to a second aspect of the present invention, there is provided the optical prism according to (1), which is fabricated by an injection molding process, and in which the side surfaces have a die removal slope of 1 to 10 degrees with respect to a die removal direction in the injection molding process.
Heretofore, no optical prism of this type has been proposed, which has a specific shape suited for mass production.
According to the present invention as in (2) above, the optical prism has a specific shape which, in addition to the effect obtainable according to the present invention as in (1) above, is suited for mass production by an injection molding process.
(3) According to a third aspect of the present invention, the optical prism according to (1) is provided having projections outwardly projecting from the receded surfaces at a predetermined position thereof.
Heretofore, no optical prism of this type has been proposed, which has a specific shape which permits size reduction of its entirety even in the case where projections are provided as portions for positioning it and the display or the like and also maintaining the relative positions of these components.
According to the present invention as in (3) above, the receded surfaces do not impede the effective size optical path of light from the display or like light source, and can be utilized for providing projections serving as portions for positioning the optical prism and the display or the like relative to each other and also maintaining the relative positions of these components. Besides, the size reduction is less impeded by the projections even though these projections outwardly project from the receded surfaces.
(4) According to a fourth aspect of the present invention, there is provided the optical prism according to (3), which is fabricated by an injection molding process, and the projections of which have predetermined outer surface portions serving as eject pin contact surfaces in the injection molding process.
Heretofore, no specific means in the optical prism has been proposed that sets eject pin contact surfaces when fabricating the optical prism of this type in an injection molding process.
According to the present invention as in (4) above, in addition to the effect obtainable according to the present invention as in (3) above, the eject pin contact surfaces concerning the pertinent injection molding process are set on predetermined portions of the projection surfaces. Thus, any push flaw by the eject pin in forced contact will not deteriorate the performance of the optical prism utilizing the optical properties thereof.
(5) According to a fifth aspect of the present invention, there is provided the optical prism according to (3), wherein the projections include frame portions for holding the display or the like and positioning portions for determining the position of the display or the like relative to the optical prism.
Heretofore, no optical prism of this type has been proposed, in which the projections do not impede the size reduction of its entirety even if they are utilized as positioning portions for determining the positions of a frame member supporting the display or the like and relative to each other.
According to the present invention as in (5) above, the projections which are provided by utilizing the receded surfaces, in addition to the effect obtainable according to the present invention as in (

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