Abstract:
A projection type image display device superior in reliability and also superior in both repairability and maintainability is to be provided at a low cost. Support members disposed between liquid crystal panels and a prism are made of a thermoplastic polymer material, and the liquid crystal panels and the support members are fixed to each other by heat-fusion of the support members. When it is necessary to remove a liquid crystal panel which is at fault for example from the corresponding support member, the fused portion on the support member side which less expensive is cut off, thereby permitting the liquid crystal panel which is expensive to be taken out re-utilizably without any damage thereto.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a display device which projects an image onto a screen with use of light valve elements such as liquid crystal panels. In particular, the present invention is concerned with a projection type image display device such as an LCD projector or a rear projection type display device. 
   A projection type image display device such as an LCD projector or a rear projection type display device has heretofore been known. In such a projection type image display device, light emitted from a light source such as an electric bulb is subjected to light intensity modulation for conversion of the light into light and shade for each image in accordance with an image signal by means of light valve means such as liquid crystal panels to form an optical image and the optical image is projected as image on a larger scale onto a screen or the like. 
   Many of the projection type image display devices available recently operate as follows. Light emitted from a light source is split into light rays of plural colors (e.g., three colors) by a light splitting means, and the light rays are then modulated by light valve means taking charge of the respective colors (in the following description the light valve means are assumed to be liquid crystal panels for convenience&#39; sake). The modulated light rays are passed through a synthesizing prism so that light having plural color components is obtained, the light obtained thus is then projected through a projection lens to the exterior of the device and is displayed as image. 
   In this case, it is necessary for the synthesizing prism and the liquid crystal panels to be in a positional relation such that the plural components, e.g., three-color components, are all fixed. If even one of the three liquid crystal panels is displaced, a color shift or a focal shift will occur in the synthesized display image, with the result that the quality of the image is impaired. 
   In a conventional manufacturing process for a projection type image display device using liquid crystal panels as light valve means, when the liquid crystal panels are to be mounted around a synthesizing prism, a so-called convergence adjustment is performed. This convergence adjustment involves adjusting the posture and position of the liquid crystal panels and making sure that three-color components&#39; images are coincident in the projected image. After the convergence adjustment, the liquid crystal panel is fixed at the respective positions relative to the synthesizing prism by bonding for example. 
   A conventional method wherein liquid crystal panels are fixed after adjusting their postures and positions relative to a synthesizing prism is disclosed, for example, in Japanese Patent laid-open No. 2002-372750. This publication describes a method wherein liquid crystal panels are mounted through a mounting member around a cross dichroic prism (hereinafter referred to simply as “prism” unless there arise any doubt) which serves as a synthesizing prism for synthesizing three-color components. Japanese Patent laid-open No. 2002-268032 discloses a construction wherein liquid crystal panels are screwed to sheet metal members and the screw portions are fused to molded members mounted in upper and lower positions of a prism. Japanese Patent Laid-open No. Hei 11-84196 discloses a construction wherein liquid crystal panels are secured to sheet metal members as support members and are thereafter bonded to a prism and a base which supports the prism. Japanese Patent Laid-open No. 2000-105434 discloses a construction wherein metallic frames attached to liquid crystal panels and a support frame attached to a prism are fused using a heat-fusing material and are mounted thereby. 
   SUMMARY OF THE INVENTION 
   In the conventional method disclosed in Japanese Patent laid-open No. 2002-372750, the mounting members and the prism are bonded together after adjusting the postures and positions of the liquid crystal panels. As a result, a system for performing convergence adjustment and fixing of the liquid crystal panels can be realized by a simple construction without relying on a complicated construction of an adjusting mechanism or the like. 
   In the above conventional method, however, the liquid crystal panels, which are expensive, are bonded to mounting members. In the event of failure in assembly or in the event of occurrence of any inconvenience in one of the three liquid crystal panels, for example in the event of failure of any one of the three liquid crystal panels as a result of use of the panels, the failed liquid crystal panel cannot be removed without destruction from around the prism. Therefore even the nondefective liquid crystal panels are compelled to be discarded as wastes. Also the expensive prism is often subjected to an optical coating such as anti-reflection coating on its light incidence sides. In the case where a mounting member is bonded to such a coated light incidence side and when the mounting member is to be removed upon occurrence of any inconvenience, the coated surface is damaged and eventually the expensive prism is compelled to be discarded as waste. Thus, in the conventional method in question, a thorough consideration is not given from the standpoint of re-utilization. 
   In the conventional method disclosed in Japanese Patent Laid-open No. 2002-268032, even in the event of occurrence of any inconvenience after assembly, the liquid crystal panels can be removed by removing screws from the sheet metal members and hence the nondefective liquid crystal panels can be re-utilized. Also, since no mounting member is bonded to the light incidence sides of the prism, the upper and lower molded members as support members can be removed without causing any optical damage to the prism and hence it is possible to re-utilize the prism. 
   In this conventional method, however, the liquid crystal panels are mounted with screws to the sheet metal members and a thorough consideration is not given to the point that the liquid crystal panels are apt to undergo positional deviations due to loosening of the screws. 
   In the conventional method disclosed in Japanese Patent Laid-open No. Hei 11-84196, even in the event the bonding of the sheet metal members as support member and the liquid crystal panels to the prism and the base should have failed, the prism can be re-utilized by removing the prism and the sheet metal members as support members. 
   In this conventional method, however, no clear description is found about the mounting between the sheet metal members as support members and the liquid crystal panels. In particular, the conventional method in question is deficient in recognition about the point that the mounting of liquid crystal panels is important for the stability of a three-color synthesized position after assembly. Besides, the places where the sheet metal members as support members are bonded span both an upper surface of the prism and the prism supporting base, and thus a thorough consideration is not given, either, about the stability of a long-period support for the liquid crystal panels. 
   In the conventional method disclosed in Japanese Patent Laid-open No. 2000-105434, it is possible to effect both posture and position adjustment for the liquid crystal panels and re-utilization of the expensive prism and liquid crystal panel components in the event of occurrence of any inconvenience. 
   This conventional method lacks a description on a method for fixing the liquid crystal panels and the supporting frames to each other. That is, the conventional method in question is deficient in recognition about the point that the mounting of liquid crystal panels is important for the stability of a three-color synthesized position after assembly. 
   The above-mentioned problems involved in the prior art are summarized as follows. 
   1. The position fixing method after the adjustment between liquid crystal panels and prism should ensure such a degree of stability as prevents a positional deviation after the adjustment. 
   2. In fixing liquid crystal panels and prism to each other, it is necessary to give consideration so that in the event of failure of any of the expensive liquid crystal panels and prism, the remaining expensive nondefective parts can be re-utilized. 
   The present invention has been accomplished in view of the above-mentioned problems encountered in the prior art and it is an object of the invention to solve those problems and provide at low cost a projection type image display device superior in reliability and also superior in both repairability and maintainability. In particular, in connection with adjustment and fixing between liquid crystal panels and a prism, the present invention aims at attaining the re-utilization of expensive parts and high reliability. 
   According to means adopted by the present invention for solving the above-mentioned problems, a thermoplastic polymer material is used as the material of support members which are disposed between liquid crystal panels and a prism, allowing the liquid crystal panels and the support members to be fixed together by heat-fusion of the support members. In the case where it is necessary to remove a faulty liquid crystal panel from its support member, the fused portion on the support member side which is less expensive is cut off and thus serves as means for taking out the liquid crystal panel re-utilizably without damage to the expensive liquid crystal panel. Bonding between the prism and the support members is done at portions of the prism other than light incidence/exit sides. When it is required to remove a liquid crystal panel from its support member due to failure for example, the bonded portion on the support member side which is less expensive is removed and thus serves as means for taking out the liquid crystal panel re-utilizably without damage to the expensive prism. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  are perspective views showing an appearance of a projection type image display device according to a first embodiment of the present invention; 
       FIG. 2  is a perspective view showing an interior construction of the projection type image display device, according to the first embodiment of the present invention; 
       FIG. 3  is a perspective view showing the construction of an optical engine section in the interior of the projection type image display device, according to the first embodiment of the present invention; 
       FIG. 4  is a perspective view showing the construction of a projection lens prism unit in the projection type image display device, according to the first embodiment of the present invention; 
       FIGS. 5A and 5B  are perspective views showing the construction of a prism and liquid crystal panel portions in the projection type image display device, according to the first embodiment of the present invention; 
       FIG. 6  is a sectional view showing the construction of the prism and a liquid crystal panel portion in the projection type image display device, according to the first embodiment of the present invention; 
       FIGS. 7A and 7B  are detailed explanatory diagrams of a fused portion of a liquid crystal panel portion in the projection type image display device, according to the first embodiment of the present invention; 
       FIG. 8  is a diagram explanatory of a work for removing a liquid crystal panel portion from the projection type image display device, according to the first embodiment of the present invention; 
       FIGS. 9A and 9B  are sectional views showing the construction of a prism and a liquid crystal panel portion in a projection type image display device according to a second embodiment of the present invention; 
       FIG. 10  is a sectional view showing the construction of a prism and a liquid crystal panel portion in a projection type image display device according to a third embodiment of the present invention; and 
       FIG. 11  is an enlarged detail view of portion H located near a fused portion in  FIG. 9B . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described hereinunder with reference to the accompanying drawings. In all the drawings, components having common functions are identified by like reference numerals, and explanations thereof once given will not be repeated for avoiding complexity. 
     FIGS. 1 to 8  are explanatory diagrams of a first embodiment according to the present invention. Explanations will be given with reference to those figures successively, beginning with  FIG. 1 . 
     FIG. 1  is a perspective view showing an appearance of a projection type image display device according to a first embodiment of the present invention, in which  FIG. 1A  is a front view of the projection type image display device indicated at  1  and  FIG. 1B  is a back view of thereof. 
   In the projection type image display device  1 , as shown in  FIG. 1A , an intake/exhaust port  2  faces in the same direction as a projection lens  10 , i.e., on a front side, and as shown in  FIG. 1B , an intake/exhaust port  3  is formed on a rear side. Further, an operating button  5  and a panel intake port  4  are disposed so as to face the exterior of the device  1 . 
   The projection type image display device  1  is operated by operating the operating button  5  from the exterior of the device. In operation, an image is projected and displayed onto a screen or the like (not shown) from the projection lens  10 . 
     FIG. 2  is a perspective view showing an interior construction of the projection type image display device  1 . 
   In  FIG. 2 , an optical engine section- 300  is provided in the interior of the projection type image display device  1 . An illumination means  100  is disposed in the optical engine section  300 . In the optical engine section  300 , light emitted from the illumination means  100  is split into three colors by a light splitting means (not shown), then the three-color light rays are modulated by liquid crystal panels (not shown) which are light valve means, and the thus-modulated light rays are synthesized by a prism (not shown). Lastly, the modulated light after the synthesis is projected and displayed as image onto a screen (not shown) which is disposed outside the device, by the projection lens  10  as projection means. A prism unit  310 , which is disposed in the optical engine section  300 , is provided with liquid crystal panels corresponding to the three colors are attached respectively to three faces of a prism (the details will be described later). The projection lens  10  is attached to the prism unit  310 . 
     FIG. 3  is an explanatory diagram of the optical engine section  300  installed in the interior of the projection type image display device  1 . 
   In  FIG. 3 , the optical engine section  300  includes an illumination means  100 , a light splitting means (not shown), liquid crystal panels (not shown) as light valve means, a prism (not shown) as a light synthesizing means, and a projection lens  10 . The prism unit  310  includes the liquid crystal panels (not shown), the prism (not shown) and the projection lens  10 . 
     FIG. 4  illustrates a detailed construction of the prism unit in the projection type image display device  1 . 
   In  FIG. 4 , a liquid crystal panel  320  as light valve means is attached to a light valve holder  330  and is supported by a prism holder  380  through the prism (not shown). The projection lens  10  is attached to an exit side of the prism holder  380 . 
   In the prism unit  310 , the prism (not shown) is mounted to the prism holder  380  and light valve holders  330 ,  340  and  360  are mounted so as to surround the prism. The light valve holders are formed of a thermoplastic polymer material such as a polycarbonate material. Liquid crystal panels  320 ,  350 , and  370  are mounted to the light valve holders  330 ,  340 , and  360 , respectively. While the projection type image display device is in operation, light rays of split color components, e.g., red, green, and blue, are incident on the liquid crystal panels respectively. The incident light rays are modulated by the liquid crystal panels  320 ,  350 , and  370  and are synthesized by the prism, followed by projection and output to the exterior of the device through the projection lens  10 . 
     FIG. 5  illustrates in what state liquid crystal panels are mounted around the prism in the projection type image display device  1 . 
     FIG. 5A  shows a state in which liquid crystal panels for three-color components are mounted and  FIG. 5B  shows a state in which, out of the liquid crystal panels shown in  FIG. 5A , only a liquid crystal panel for one color component is mounted for ease of understanding. 
   In  FIG. 5 , liquid crystal panels taking charge of color components respectively are mounted around a prism  600 . Light valve holders  330 ,  340 , and  360  are attached to an upper surface  610  and a lower surface  620  of the prism  600 , and liquid crystal panels  320 ,  350 , and  370 , which are light valve means, are attached to those light valve holders respectively. 
   As shown in  FIG. 5B , a polarizing plate  410  is disposed between the liquid crystal panel  320  and the prism  600 . It goes without saying that the polarizing plate is disposed also between each of the other liquid crystal panels and the prism. 
   A description will now be given of a mechanism for displaying an image with use of the liquid crystal panels. Light incident on the liquid crystal panel  320  is made beforehand into light (e.g., S polarized light) having a uniform polarization direction by polarization changing means (not shown). At a liquid crystal portion corresponding to a set pixel, a control is made for rotating or not rotating the polarization direction in the liquid crystal panel  320  to effect modulation of incident light. Then, light from the portion corresponding to the polarization direction-rotated pixel turns to, say, P polarized light relative to the incident, say, S polarized light and the so-rotated light is outputted. In this connection, a layout is made so that the polarization direction which is set at a transmission direction of the polarizing plate  410  and the P polarization corresponding to the polarization direction of light at the above rotated pixel coincide with each other. The light of the pixel portion after the rotation of polarization in the liquid crystal panel  320  then passes through the polarizing plate  410 . The unrotated S polarized light component emerging from the liquid crystal panel  320  is absorbed by the polarizing plate  410 . 
   In this way, by the combination of the polarizing plate and the liquid crystal panel, on-off control for each pixel in the liquid crystal panel is effected, and by combining such pixel by pixel controls it becomes possible to make display as a single optical image. 
   Light rays outputted from the liquid crystal panels of three-color components are synthesized by the prism  600 . The synthesis of three-color components is effected by a cross dichroic mirror surface (not shown) in the interior of the prism  600 . For example, green light of P polarization is outputted from the liquid crystal panel  320 , then passes through the prism  600  and travels straight ahead. Further, red light and blue light of S polarization are outputted from the corresponding liquid crystal panels  350  and  370 , then are each reflected at right angles by the cross dichroic mirror surface (not shown) within the prism  600  and advance toward the projection lens  10 . In this way, the prism  600  can synthesize images outputted from the liquid crystal panels which take charge of the three-color components respectively. 
   To make display positions of the three-color components coincident completely with one another, it is necessary that the three liquid crystal panels be at the same focal position and at the same screen position when looking from the projection lens  10  side. Therefore, in case of fixing the liquid crystal panels around the prism  600 , alignment adjustment (convergence adjustment) for the liquid crystal panels is usually performed as in the foregoing patent literatures. If displacement of the liquid crystal panels occurs after convergence adjustment, the synthesized image will be disturbed. Therefore the position after the adjustment is fixed firmly. 
   In the first embodiment of the present invention, first, prior to convergence adjustment, the liquid crystal panels are fixed by fusion to the light valve holders. Then, as shown in  FIG. 5 , the light valve holders  330 ,  340  and  360  with the liquid crystal panels fused thereto are subjected to convergence adjustment relative to the prism  600 . Further, after the convergence adjustment, the prism  600  and the light valve holders  330 ,  340  and  360  are bonded together at the upper and lower surfaces  610 ,  620 . Thus, since the liquid crystal panels have been already fixed by fusion to the light valve holders before convergence adjustment, the liquid crystal panels after convergence adjustment are fixed in place firmly. 
   A mounting method for the light valve holders and the liquid crystal panels will here be described typically in terms of a method for mounting the liquid crystal panel  320  to the light valve holder  330  as in  FIG. 5B . In  FIG. 5B , the liquid crystal panel  320  is mounted to the light valve holder  330 . As will be described later, this mounting method utilizes fusion. Mounting holes formed in the liquid crystal panel  320  are brought into engagement with projecting portions (not shown) of the light valve holder  330  formed of a thermoplastic polymer material to secure the liquid crystal panel to the light valve holder. Then tips (not shown) of the projecting portions of the light valve holder  330  are heat-melted into the shape of the mounting portion of the liquid crystal panel made of a magnesium alloy for example, whereupon cooling is performed for solidification and fixing. Thus, the liquid crystal panel is mounted by fusion. Numeral  500  indicates the fused portions. At least plural such fused portions are present. It goes without saying that the other light valves and liquid crystal panels are also mounted by fusion in the same manner. 
   In this case, the light valve holders  330 ,  340  and  360  are made of polycarbonate for example and have a melting point of, say, 160° C., while the outer frames of the liquid crystal panels  320 ,  350  and  370  are made of a magnesium alloy for example and have a melting point of, say, 650° C. Thus, this is a combined construction of both components different in melting point. 
   The fused portions  500  thus fixed after fusion is in a solidified state having a shape conforming to the shape of each mounting hole in the liquid crystal panel  320 , as will be described later. In this state, the liquid crystal panel  320  cannot be removed unless the light valve holder  330  is destroyed. 
     FIG. 6  is a sectional view showing a mounted state of the prism and a liquid crystal panel in the first embodiment. In  FIG. 6 , the mounted state is shown typically in terms of a mounted state of the prism  600  and the liquid crystal panel  320 . It goes without saying that the other liquid crystal panels are also mounted in the same manner. 
   In  FIG. 6 , projecting portions of the light valve holder  330  are fitted in mounting holes  322   a  of the liquid crystal panel  320 . Further, in each of the tip fused portions  500 , a part of the light valve holder  330  melts in the fusing process and is cooled and solidifies in a tapered portion (conical hole)  321  of the liquid crystal panel  320  in a shape conforming to the shape of the tapered portion  321 . In such a construction, the light valve holders  330 ,  340 ,  360  and the liquid crystal panels  320 ,  350 ,  370  are fixed integrally and their mounted positions do not shift easily. 
   The polarizing plate  410  disposed between the liquid crystal panel  320  and the prism  600  is held by a fixing groove  411  formed in the light valve holder  330 . The light valve holder  330  and the prism  600  are fixed together using an adhesive  700 . 
   Light incident on the liquid crystal panel  320  travels in the direction of arrow  220  along an optical axis  210 . After being modulated by the liquid crystal panel  320 , the light passes through the polarizing plate  410  and travels toward the prism  600 . 
   As described above in connection with  FIG. 5  there are three such constructions of one-color component, and light rays modulated in the liquid crystal panels advance to the prism  600  and are synthesized therein. 
     FIG. 7  is a detailed explanatory diagram of the fused portion shown in  FIG. 6  in this first embodiment, in which  FIG. 7A  shows a state before fusion and  FIG. 7B  shows a state after fusion. In  FIG. 7A , a fusion allowance  331  of a projecting portion in the light valve holder  330  is fitted in a mounting hole  322   a  of the liquid crystal panel  320 . The fusion allowance  331  is smaller than the diameter of a straight portion  324  of the mounting hole  322   a  in the liquid crystal panel  320 , leaving a clearance. The opening portion of the mounting hole  322   a  in the liquid crystal panel  320  is tapered at  321 . 
   As shown in  FIG. 7B , a fused portion  500  is formed after fusion. In the fused portion  500 , a fusion-side tapered portion  510  is formed following the tapered portion  321  of the liquid crystal panel  320 . At a part of the fused portion  500 , there also is formed a fusion-side-straight portion  520  following the straight portion  324  of the mounting hole  322   a  in the liquid crystal panel  320 . The fusing process is carried out by heating and melting a part of the fusion allowance  331  of the light valve holder  330  formed of a heat-melting polymer material. When the heat-melting polymer material melts, an internal stress is released and the material is transformed into a shape conforming to the surrounding shape. The deformed state is retained even after cooling and subsequent solidifying. In the deformed state, an internal stress is released, so that any special stress is developed between the liquid crystal panel and the light valve holder. Therefore, even if the liquid crystal panel is attached to the light valve holder, any internal stress results from the mounting, but an internal stress is released gradually after the mounting and the liquid crystal panel is not displaced from its mounted position. 
   Moreover, since the shape of the light valve holder is melt-deformed following the shape of the liquid crystal panel, the liquid crystal panel does not move relative to the light valve holder after the fusion process. More specifically, in the direction of arrow  250  which is an axial direction of the fused portion  500  in  FIG. 7 , the fusion-side tapered portion  510  is opposed to the tapered portion  321  of the liquid crystal panel  320 , so that the positional relation of the liquid crystal panel  320  to the light valve holder  330  does not change. In the opposite direction, the displacement of the liquid crystal panel  320  is inhibited by the light valve holder  330 . In the direction of arrow  260  which is perpendicular to the fused portion  500  in  FIG. 7 , the fusion-side straight portion  520  is opposed to the hole  322   a  formed in the liquid crystal panel  320  and thus the positional relation between the liquid crystal panel  320  and the light valve holder  330  does not change. 
   Only one fused portion is illustrated in  FIG. 7 , but as described above in connection with  FIGS. 5 and 6 , the plural fused portions (four in this embodiment) for mounting the liquid crystal panel are all subjected to the same fusion process, and the positional relation between the liquid crystal panel and the light valve holder is restricted not only in the arrow  250 ,  260  directions but also in the rotational direction. To restrict the movement in the rotational direction, at least two fused portions suffice, and in this case it is preferable that the fused portions be in a diagonal positional relation. 
   In this way the light valve holders  330 ,  340 ,  360  and the liquid crystal panels  320 ,  350 ,  370  can be fixed together without stress. 
     FIG. 8  shows in what state a liquid crystal panel is removed in the first embodiment. 
   If one of the plural liquid crystal panels disposed around the prism  600  is defective or faulty, it is necessary that such a liquid crystal panel be removed for repair or replacement. Likewise, also in the event of failure of the prism  600 , it is necessary that the liquid crystal panels disposed around the prism be-removed and mounted to another prism. 
   In such a case, as shown in  FIG. 8 , the fused portion  500  is cut with a drill or the like to let the tapered portion  321  of the liquid crystal panel  320  be exposed, whereby the liquid crystal panel- 320  can be removed in the direction of arrow  240 . By so doing, the liquid crystal panel  320  can be removed from the prism  600  without being damaged. Further, the light valve holder  330  formed of a heat-melting polymer material is fixed to the prism  600  through the adhesive  700  and therefore can be removed from the prism  600  easily by destroying the portion of the adhesive  700 . At this time, the treated incidence surface such as a coated incidence surface of the prism  600  is not damaged because the adhesive is not applied thereto. Consequently, it is possible to re-utilize the prism  600 . 
   Thus, according to the first embodiment of the present invention, in the event of failure of any of the expensive liquid crystal panels and prism, the replacement can be done easily by removing nondefective parts and it is possible to re-utilize the expensive nondefective parts and hence possible to provide a high quality projection type image display device at low cost. 
   Besides, since the liquid crystal panels are fixed by fusion, no stress is imposed on the liquid crystal panels and it is possible to effect mounting of the liquid crystal panels in a highly accurate and highly reliable state. 
     FIGS. 9A and 9B  are explanatory diagrams showing the construction of a second embodiment of the present invention.  FIG. 9A  illustrates a light valve holder and thereabouts and  FIG. 9B  illustrates a state after fusion of a liquid crystal panel to the light valve holder. In the figures, for ease of illustration of this embodiment, there are shown only one of three light valve holders and only one of three liquid crystal panels which holders and panels are installed around a prism, provided it goes without saying that the illustrated construction is also true of the other two light valve holders and the other two liquid crystal panels.  FIG. 11  is an enlarged detail view of portion H located near a fused portion in  FIG. 9B . 
   In  FIG. 9A , a light valve holder  800  formed by integral molding, so-called outsert molding, of a heat-melting polymer material is disposed in a surrounding relation to a prism  600 . The light valve holder  800  is fixed to an upper surface  610  and a lower surface  620  of the prism  600 . In the second embodiment, unlike the first embodiment, since the light valve holder  800  is formed by outsert molding, there is no fear of displacement of the light valve holder  800  relative to the prism  600 . In the event the necessity of removal of the light valve holder  800  should occur due to failure for example, the outsert-molded light valve holder is peeled off from both upper and lower surfaces of the prism. That is, a light incidence surface  630  of the prism having been subject to an expensive surface treatment is not damaged and it is possible to re-utilize the prism  600 . 
   In this embodiment, mounting holes  322   b  are formed in a liquid crystal panel  320 ′ for insertion therein of fusion allowances  810  of projecting portions of the light valve holder  800 . On an inner wall of each of the mounting holes  322   b  there is formed a projecting portion  326  having a tapered portion  321  and a tapered portion  323 . When the fusion allowance  810  is melted after insertion of the fusion allowance  810  of each projecting portion of the light valve holder  800  into the corresponding mounting hole  322   b  formed in the liquid crystal panel  320 ′, the projecting portion  326  is sandwiched in between fusion-side tapered portions  840  and  850  which are opposed to the tapered portions  321  and  323 , respectively. This state is shown in  FIG. 9B  and  FIG. 11 . 
   In  FIG. 9B  showing a fused state of the liquid crystal panel  320 ′, as is apparent from the enlarged detail view of  FIG. 11  showing portion H in  FIG. 9B , the fusion-side tapered portions  840 ,  830 , and  850  are in close contact, in a fused portion  820 , with the tapered portion  321 , a straight portion  325 , and the tapered portion  323 , respectively, of the mounting hole  322   b  formed in the liquid crystal panel  320 ′. In this embodiment illustrated in  FIG. 9 , fusion is performed after adjustment of the posture (convergence adjustment) of the liquid crystal panel  320 ′. 
   To illustrate a state in which the posture of the liquid crystal panel  320 ′ has been adjusted relative to the prism  600 ,  FIG. 9B  shows a state in which the light valve holder  800  and the liquid crystal panel  320 ′ are mounted in an inclined and floating condition. Thus, when the liquid crystal panel  320 ′ is mounted in an inclined and floating state relative to the light valve holder  800  by adjustment of its posture, the liquid crystal panel is held in a fixed stated under the action of the fused portion  820 . That is, when the liquid crystal panel tends to move in the direction of arrow  250 , this movement cannot-be effected because the fusion-side tapered portion  840  is in opposition to the tapered portion  321  of the liquid crystal panel  320 ′. When the liquid crystal panel tends to move in the direction of arrow  260 , the movement is inhibited by the fusion-side straight portion  830  which is in opposition to the straight portion  325  of the liquid crystal panel  320 ′. When the liquid crystal panel tends to move in the direction of arrow  270 , the movement is inhibited by the fusion-side tapered portion  850  which is in opposition to the tapered portion  323  of the liquid crystal panel  320 ′. The rotational direction of the liquid crystal panel can be inhibited by forming plural fused portions. 
   Thus, according to the construction of this embodiment, light valve holders are formed by outsert molding around the prism, a projecting portion having tapered portions is formed on an inner wall of each mounting hole in each liquid crystal panel, and the liquid crystal panel is fixed by fusion to the corresponding light valve holder after positioning. With this construction, the position of each liquid crystal panel relative to the prism is fixed without displacement and therefore it is possible to provide a high quality image display device. Further, in the event of failure of any of plural liquid crystal panels, the light valve holders are destroyed and the prism and the nondefective liquid crystal panels are removed and can be re-utilized. 
     FIG. 10  is an explanatory diagram illustrating a third embodiment of the present invention. In this third embodiment, reflection type liquid crystal panels are used as light valve means instead of the transmission type liquid crystal panels used in the first and second embodiments. 
   A light valve holder  330  is attached with an adhesive  700  to other surfaces than a light incidence surface  640  of a PBS prism  600 ′. Moreover, a quarter wave plate  410 ′ and a reflection type liquid crystal panel  900  are attached to the light valve holder  330 , the panel  900  being fixed by a fused portion  900 . Further, a heat radiation board  910  is attached to a rear side of the reflection type liquid crystal panel  900 . 
   Thus, also in the construction of the reflection type liquid crystal panel, the positions of liquid crystal panels are fixed without displacement and hence it is possible to provide a high quality projection type image display device. Further, in the event of failure of any of plural liquid crystal panels, it is possible to destroy the light valve holders, take out the prism and the nondefective liquid crystal panels and re-utilize them. 
   Although liquid crystal panels (transmission type) or reflection type liquid crystal panels are used as light valve means in the above embodiments, it goes without saying that the same constructions and effects as above can also be attained by using other light valve means, e.g., micromirror rotation means. 
   Although a three-color synthesizing cross dichroic mirror or PBS prism is used as the prism, it goes without saying that even a synthesizing system or a two-color synthesizing system using another prism, e.g., a triangular prism (a total reflection prism), can attain the same constructions and effects as above. 
   In the above embodiments the external member of each liquid crystal panel is made of a magnesium alloy and each light valve holder is made of a polycarbonate. However, it goes without saying that no limitation is made thereto and that a combination of other polymer materials may be used, such as a polycarbonate as the outer member of each liquid crystal panel and ABS resin as the material of each light valve holder, insofar as the difference between the respective melting points is 40° or more, whereby the same constructions and effects as above can be obtained. 
   Further, in the above embodiments heat-fusion is used as liquid crystal panel fixing means. However, it goes without saying that no limitation is made thereto, but another means may be adopted, e.g., ultrasonic fusion, insofar as a part of each light valve holder made of a thermoplastic material is eventually melted and cooled to solidify and fixed following the shape of the corresponding liquid crystal panel, whereby the same constructions and effects as above can be obtained. 
   According to the present invention, as set forth above, a projection type image display device can be provided in which mounted positions of a prism and light valves can be maintained in a stable state relative to each other, and it is possible to ensure a high quality image. Further, in the event of failure of a part of such expensive parts as a prism and light valves, it is possible to remove and re-utilize the other nondefective expensive parts. 
   Thus, according to the present invention it is possible to reduce the cost of a projection type image display device.