Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2002-01-11
2003-08-26
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
Reexamination Certificate
active
06609796
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection type display apparatus using a plurality of light valves and, more particularly, to a constituent part mainly including a synthesizing optical system for synthesizing beams projected from respective light valves in the projection type display apparatus.
2. Related Background Art
Such projection type display apparatus as a color projector are used as large-screen image display apparatus and the projection type display apparatus of this type are classified under a method called a single plate method for directly magnifying and projecting a color image and a method called a three plate method for synthesizing images of the three primary colors R (red), G (green), B (blue) and projecting the synthesized image. The three plate method requires more complex apparatus structure than the single plate method, but is easier in color adjustment and more advantageous in color reproduction, resolution, and so on than the single plate type. The three plate method is thus popularly employed in imagery equipment or the like.
An example of such three plate method projection type display apparatus is shown in FIG.
18
. White source light including the respective colors R, G, B, emitted from a light source not illustrated, is split into two directions of respective polarization components by polarization beam splitter
11
′. Only R light in the component reflected by the polarization beam splitter
11
′ is transmitted by red transmitting dichroic filter
52
to enter light valve
12
R for R signal. The R light is modulated to light having an image signal of R signal and this light travels again through the red transmitting dichroic filter
52
to enter the polarization beam splitter
11
′. Only the signal component is extracted from the light in the polarization beam splitter
11
′ to be outputted. On the other hand, the G light component of the polarized light component transmitted by the polarization beam splitter
11
′ is reflected to branch off by green reflecting dichroic mirror
51
to enter light valve
12
G for G signal. The G light is modulated to light having an image signal of G signal to be reflected. Then the light is again reflected by the green reflecting dichroic mirror
51
to enter the polarization beam splitter
11
′, in which only the signal component is extracted to be outputted. The B light component in the light transmitted by the green reflecting dichroic mirror
51
is extracted by blue transmitting dichroic filter
53
to enter the light valve for B signal. The B light is modulated to light having an image signal of B signal to be reflected. Then the light travels again through the blue transmitting dichroic filter
53
and then through the green reflecting dichroic mirror
51
to enter the polarization beam splitter
11
′, in which only the signal component is extracted to be outputted. As a result, the signal components R, G, B are synthesized by the polarization beam splitter
11
′ and the synthetic light is outputted to be enlarged and projected through projection lens
14
onto a screen not illustrated. Unwanted light components are outputted along the direction of the source light, so that they are not mixed in the synthetic light.
The components of the optical system including these reflection type light valves and polarization beam splitter were mounted individually on a mounting base, e.g. on a mounting base forming a floor member of a housing of the apparatus, thereby achieving the desired placement among the components. In other words, this conventional projection type display apparatus had the structure in which the components were fixed to each other through the mounting base and in which the positional relation among the components was determined through the mounting base. Materials for this mounting base were aluminum alloys, fiber reinforced resins, and so on, which were light in weight and had high workability.
SUMMARY OF THE INVENTION
This structure, however, had the problem of occurrence of so-called registration deviation that the base experienced elongation or distortion with change in the ambient temperature during operation to cause deviation of positional relation among the optical members, so as to alter positions of respective color pixels relative to each other on the screen. Particularly, in the case of the recent projection type display apparatus for projection onto a large screen, the registration deviation heavily degraded the projected image, which was a serious problem.
The present invention has been accomplished under the above-described circumstances and an object of the present invention is to provide an optical system for projection type display apparatus that can reduce the registration deviation, thereby improving the quality of projected image.
The inventors contemplated that the above registration deviation occurred as follows; the floor member on which the above-stated light valves, analyzing optical system, and color synthesizing optical system were fixedly mounted experienced expansion and contraction with change in the ambient temperature to change the positions of the components mounted thereon, so that the pixels of the respective colors deviated from their original positions achieved by initial positioning.
First of all, in order to decrease the expansion and contraction of the floor member due to the temperature change, a conceivable way is to select a material having a small thermal expansion coefficient for the floor member. In general, iron-based materials as a typical example of such material have a drawback of large weight and thus are not used easily. Further, nickel alloys typified by invar with small thermal expansion coefficient reveal poor workability and are very expensive.
The inventors considered that the above problem could be solved while using the conventional aluminum alloys or fiber reinforced resins as the material for the floor member, and accomplished the present invention.
As a result, the inventors found that the aforementioned registration deviation was reduced by integrally forming the optical system through which the modulated light beams emitted from the respective light valves traveled to be color-synthesized and outputted and that, further by fixing a member closest to the projection lens out of the thus integrated members to the floor member, focus deviation of projected image was also reduced in combination with the integration effect. This is because the change in distance with temperature change becomes ignorable when the distance is small between the fixed member and the projection lens fixed to the floor member.
The present invention provides an analyzing-synthesizing optical system unit for projection image display apparatus in which beams of the three primary colors of R, G, and B are modulated by respective, dedicated polarization beam splitters and light valves, the modulated beams are extracted, and a synthesizing optical system synthesizes the three color beams to output synthetic light, wherein the light valves and the polarization beam splitters are fixed as integrated with the synthesizing optical system and wherein optical path lengths of optical paths for the respective colors, established by each light valve, each polarization beam splitter, and the synthesizing optical system, are approximately equal to each other.
In this structure, the members constituting each optical path are integrated without intervention of the mounting base, so that the positional relation among the components is independent of the mounting base. With change in the ambient temperature, the relative positional deviation between the light valves will result from only deviation caused by dimensional change of the members including the light valves, polarization beam splitters, and so on, and is completely free of the expansion and contraction of the mounting base accordingly. Therefore, amounts of the deviation can be reduced remarkably when compared with t
Hattori Tetsuo
Kusano Masaaki
Maki Hiroshi
Numazaki Kiyoshi
Sekine Atsushi
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