Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2000-03-02
2002-10-08
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S119000, C349S058000
Reexamination Certificate
active
06460998
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projector which includes a light source, an electrooptic device which forms, with an optical modulation element, an optical image from light emitted from the light source in accordance with image information, a projection lens for enlarging and projecting the image formed by the electrooptic device, and an optical polarizing element. More particularly, the present invention relates to an adjustment mechanism for adjusting a mounting angle of the optical polarizing element and a projector including the adjustment mechanism.
2. Description of Related Art
Projectors are conventionally known which include a light source, an electrooptic device for forming an optical image from light emitted from the light source in accordance with image information, and a projection lens for enlarging and projecting the image formed by the electrooptic device.
Such a projector finds widespread use in a multi-media presentation in conferences, meetings of academic societies, exhibitions, etc.
In a multi-media presentation, a vast quantity of information needs to be conveyed to an audience in a short period of time, and easy-to-see and fine video information needs to be presented at the same time.
In connection with the quality of images presented, preciseness is required of the images so as not to create discontinuities and deformation in presented symbols and drawings, while high contrast and high luminance are required at the same time to achieve an easy-to-see and nice image.
To this end, a projector using polarized light has to precisely control the direction of polarization of the light. For example, it is necessary to set the angle formed by the polarization axes of both an input-side polarizer and an output-side polarizer which are disposed so as to sandwich an electrooptic device (for instance, a liquid-crystal panel) therebetween, to set the angle of the polarization axis of each of the input-side and output-side polarizers, or to set the angle of an optical axis of a wavelength plate to an optimal angle for the thickness of a layer and an orientation of electrooptic material (for instance, a liquid crystal), of the electrooptic device, which controls optical modulation.
The polarizers and wavelength plates are typically designed so that their polarization axes and optical axes are precisely set as long as they are mounted referring to their external shapes. When they are bonded onto the surface of a glass substrate or a prism, their external shapes serve as a reference. However, there are times when the relationship between the external shape of a polarizer or a wavelength plate and its polarization axis or optical axis is in error. In such a case, even if the polarizer or the wavelength plate is most accurately mounted, there will occur a deviation in the polarization axis or the optical axis, and no optimum angle will be set.
As a result, a display image transmitted through a projection lens is subject to a subtle blur or bleeding, and high contrast and high luminance are not achieved.
SUMMARY OF THE INVENTION
The invention provides a projector which fine-adjusts the mounting position of a polarizer or a wavelength plate to achieve high contrast and high luminance. The projector includes an adjustment mechanism for adjusting a mounting angle of an optical polarizing element and includes two frames and an adjustment member. The optical polarizing element may be supported by one of the two frames. The one of the two frames is pivotally supported on an axis of pivot so that it can turn with respect to the other of the two frames. The adjustment member secures the two frames, and one of the two frames is pivoted about the axis of pivot with respect to the other of the two frames through the adjustment operation of the adjustment member. In accordance with the adjustment mechanism of the present invention, the angle of the polarization axis or the optical axis is optimumly adjusted by adjusting a mounting angle of the optical polarizing element, such as the polarizer or the wavelength plate. By properly adjusting the adjustment member, the angle of the polarization axis or the optical axis of the optical polarizing element such as the polarizer is adjusted to an optimum angle.
In a projector having a light source, an electrooptic device for forming an optical image from light emitted from the light source in accordance with image information, and a projection lens for enlarging and projecting the image formed by the electrooptic device may be provided. An adjustment mechanism of the present invention serves as an adjustment mechanism to adjust the mounting angle of an optical polarizing element interposed between the light source and the electrooptic device, or to adjust the mounting angle of an optical polarizing element interposed between the electrooptic device and the projection lens.
In accordance with the projector employing the adjustment mechanism of the present invention, the angle of the polarization axis or the optical axis is adjusted to an optimum angle by adjusting the mounting angle of the optical polarizing element, such as the polarizer or the wavelength plate, and a high-contrast and high-luminance image is thus presented.
Preferably, the adjustment member is a screw, and the screw is screwed into one of the two frames while being loosely inserted through the other of the two frames. Through a simple operation, such as rotating the screw, the angle adjustment of the optical polarizing element is properly performed.
Preferably, the frame through which the screw is inserted includes a loose engagement portion, and the screw has a shoulder portion that is provided to hold the loose engagement portion between a head of the screw and the shoulder portion of the screw. With this arrangement, a displacement of the screw is absorbed by the loose engagement portion. Specifically, no mutual distortion takes place between the screw and the frame through which the screw is inserted, and the screw smoothly rotates. Since the axial motion of the screw is restrained by the head and the shoulder portion of the screw, the screw is prevented from coming off.
When the direction of the axis of the screw which is an adjustment member is aligned with the tangential direction of the trajectory of the pivotal motion of the second frame, the reciprocal movement of the screw is directly converted into a rotary motion of the second frame without any component that conveys the stroke of the screw, and the construction surrounding the adjustment member is thus simplified.
In the adjustment mechanism thus constructed, preferably, one of the first and second frames has a projection toward the other of the two frames, the other of the two frames has a recess formed in order for the projection to engage there, and the one of the two frames is pivotally supported by the other of the two frames through the engagement of the recess and the projection. This is because a simple structure of the projection and the recess presents a mechanism in which the second frame is pivotally supported, and the parts are easily machined.
Preferably, the one of the two frames has flange portions, and elastic members for pressing the optical polarizing element with elasticity is interposed between the flange portions and the end faces of the optical polarizing element. With this arrangement, the optical polarizing element is affixed to the frame without using any adhesive agent. Therefore, there is no fear of an adhesive agent flowing out onto and sticking to a light incident surface of the optical polarizing element, and no fear of light incident on the optical polarizing element being disturbed.
The adjustment mechanism having the above structure preferably includes a clamping member for clamping the first and second frames together. With this arrangement, the two frames are affixed together so that they are not separated.
Preferably, the projector having the above adjustment mechanism includes a case for covering the adjustment mechanism p
Adams Russell
Koval Melissa
Oliff & Berridg,e PLC
Seiko Epson Corporation
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