Patent Publication Number: US-6908198-B2

Title: Image display mechanism and image display device

Description:
This is a continuation application of U.S. Ser. No. 10/718,551, filed Nov. 24, 2003 now U.S. Pat. No. 6,817,720 (now allowed), which is a continuation application of U.S. Ser. No. 10/442,257, filed May 21, 2003 (now U.S. Pat. No. 6,682,197), which is a continuation application of U.S. Ser. No. 09/817,027, filed Mar. 27, 2001 (now U.S. Pat. No. 6,588,910), which is a divisional application of U.S. Ser. No. 09/170,773, filed Oct. 13, 1998 (now U.S. Pat. No. 6,231,191) 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a projection type image display mechanism and a projection type image display device for enlarging an image and projecting the image on a screen by utilizing a light valve element such as a LCD panel. 
   2. Description of Related Art 
   A projection type image display device epitomized by a LCD projector, a liquid crystal television, and a projection type display device has been known as a device for enlarging an image on a light valve element and for projecting it on a screen by projecting light irradiated by a light source (lamp and the like) on the light valve element (for example, LCD panel and the like). 
   As for the projection type image display device, there have been raised problems that a LCD panel and the parts thereof are heated by absorbing light irradiated by the light source and that dust floats in the vicinity of the LCD panel. The extreme heating of the LCD panel and the parts thereof causes a malfunction (in the worst case, broken LCD panel) to the LCD panel, and floating dust in the vicinity of the light incidence/reflection plane of the LCD panel or in particular, the dust stuck to the LCD panel causes the deteriorated quality of the image enlarged and projected on the screen (hereinafter referred to as screen image). 
   Therefore, in many projection type image display devices, measures have been taken to solve these two problems. 
   For example, a certain projection type image display device has a cooling unit designed specifically for the LCD panel to prevent the LCD panel from being heated over a predetermined temperature (for example, about 60° C.). This can ensure a normal operation of the LCD panel constituted by optical functional members such as semiconductor drive element, liquid crystal and the like. Further, for example, a light source which produces heat of about 30 percent of the input energy and radiates a large amount of input energy as thermal energy so as to remove light other than visible light (for example, light having a wavelength of 400 nm to 700 nm), that is, ultraviolet light (for example, light having a wavelength of less than 400 nm), or ultrared ray (for example, light having a wavelength of more than 700 nm), usually has a cooling unit designed specifically for the light source, too. The light source produces heat of more than half of the total input energy. In this respect, an air-cooled unit such as an air blowing fan is generally used as the cooling unit because it can be easily operated. 
   Further, in the image display device disclosed in the Japanese Unexamined Patent Publication No. 7-152009, a transmittance type LCD panel is housed in a hermetically closed space so as to prevent dust from entering the vicinity of the LCD panel. Further, to prevent the LCD panel from being heated, air is circulated in the hermetically closed space. 
   In the image display device disclosed in the Japanese Unexamined Patent Publication No. 64-5174, to improve utilization efficiency of light in a high definition image, a reflection type LCD panel is employed and a reverse plane of the incidence/reflection plane thereof (hereinafter referred to as reverse plane”) can be utilized as a radiation plane. 
   In the image display device disclosed in the Japanese Unexamined Patent Publication No. 62-294230, to more effectively utilize a reverse plane of the reflection type LCD panel as a radiation plane, a cooling unit is provided on the back side of the reflection type LCD panel. 
   However, since the conventional projection type image display device is provided with an air blowing fan designed specifically for each heating body (a light source and a LCD panel), a sufficient improvement has not been produced in reliability and costs of the device. Therefore, a structure of a cooling mechanism is required to be simplified. Further, the conventional projection type image display device has the problems: if an exhaust port faces a wrong direction, warm air exhausted from the exhaust port is blown over the audience and the screen image become unstable by the unstable air produced in the optical path of the light projected on the screen. 
   Any of image display devices can not solve both problems that the LCD panel and parts thereof are heated and that the dust floats in the vicinity of the light incidence/reflection plane of the LCD panel. That is, ensuring the reliability of the device and improving the quality of the image can not consist together. 
   For example, in the image display device disclosed in the Japanese Unexamined Patent Publication No. 62-294230 and in the image display device disclosed in the Japanese Unexamined Patent Publication No. 64-5174, as described above, measures have been taken to prevent the LCD panel from being heated but special measures have not been taken to prevent the dust from floating in the vicinity of the light incidence/reflection plane of the LCD panel. Therefore, there is an extremely high possibility that the shadow of the dust is seen in the screen image. Further, in the image display device disclosed in the Japanese Unexamined Patent Publication No. 62-294230, the whole device is heated but only the LCD panel is locally cooled, which does not produce a sufficient cooling effect. Therefore, the reliability of the whole device can not be ensured. 
   On the other hand, although the image display device disclosed in the Japanese Unexamined Patent Publication No. 7-152009 intends both to prevent the dust from floating in the vicinity of the light incidence/reflection plane of the LCD panel and to prevent the LCD panel and parts thereof from being heated, it employs a cooling system using air in the hermetically closed space and hence it can not be expected to produce a sufficient cooling effect because in recent years a demand for the intensity of the screen image has increased the amount of heat generated by the LCD panel. Therefore, the reliability of the device is not necessarily ensured. 
   Further, in many devices of color display type among the projection type image display devices epitomized by a LCD projector, a liquid crystal television, and a projection type display device, the images of color components formed by the light valve means like the liquid crystal are often combined together to make a multicolored image. Therefore, the quality of the colored image enlarged and projected on the screen (hereinafter referred to as screen image”) depends to a large degree on convergence performance (convergence adjustment) of converging the positions of the images of color components modulated by the light valves. Therefore, many kinds of techniques relating to a convergence adjustment have been proposed. For example, Japanese Unexamined Patent Publication No. 3-51881 discloses a technique of converging the images by using the convergence adjusting mechanisms provided on the LCD panels of color components. However, in the Japanese Unexamined Patent Publication No. 3-51881, it is not recognized that it is necessary to prevent the dust from floating in the vicinity of the LCD panel and to prevent the LCD panel and parts thereof from being heated. 
   SUMMARY OF THE INVENTION 
   It is the first object of the present invention to simplify the inside structure of the device and to improve the environment of the audience without reducing the reliability of a projection type image display device. Further, it is the second object of the present invention to improve the quality of the screen image projected by the projection type image display device. Still further, it is the third object of the present invention to provide a technology for suitably converging the light valve elements. 
   To accomplish the first and second objects, an image display mechanism according to the present invention is provided with illuminating means, projecting means, reflection type light valve means having a light incidence/reflection plane, and cooling means, wherein the reflection type light valve means and the illuminating means share a part of the cooling means. 
   In the constitution described above, it is not necessary to provide the light valve and the light source with each air blowing fan as shown in prior art. Therefore, the inside structure of the image display mechanism can be simplified without reducing the reliability thereof. Further, since it is not necessary to provide each heating body with an air blowing fan, the environment of the audience can be improved. 
   To accomplish the third object, an image display mechanism according to the present invention is provided with illuminating means, projecting means, reflection type light valve means having a light incidence/reflection plane, and almost hermetically closed space shut off from the outside air, wherein the illuminating means illuminates the reflection type light valve means to project light reflected by the reflection type light valve means by the projecting means, and wherein the almost hermetically closed space is constituted by a plurality of structural members and the light incidence/reflection plane of the reflection type light valve means contacts the joints of the plurality of structural members. 
   Since the LCD panel placed in the almost hermetically closed space is not exposed to the dust of the outside air in the constitution like this, the shadow of the dust is not produced on the screen image. 
   Further, an image display mechanism according to the present invention is provided with positioning means for supporting the light valve means to position the projected images of color components. Furthermore, the joints of the plurality of structural members constituting the almost hermetically closed space are joined to the light valve means and the almost hermetically closed space. 
   Still further, the light valve means and the positioning means are disposed outside the almost hermetically closed space shut off from the outside air. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an external view of a projection type image display device of the first embodiment according to the present invention. 
       FIG. 2  is an external view of a projection type image display device of the first embodiment according to the present invention when it is used. 
       FIG. 3  is a conceptional view of the optical path of light projected from a projection type image display device of the first embodiment according to the present invention. 
       FIG. 4  shows a schematic constitution of an optical system of a projection type image display device of the first embodiment according to the present invention. 
       FIG. 5A  is an external view of an optical unit of the first embodiment according to the present invention, and  FIG. 5B  is an external view of the optical unit when viewed from the opposite side. 
       FIG. 6  shows a basic structure of an optical unit of the first embodiment according to the present invention. 
       FIG. 7  is a cross sectional view of the optical unit shown in FIG.  5 . 
       FIG. 8  shows a basic structure of an optical unit of the second embodiment according to the present invention. 
       FIG. 9  is a cross sectional view of the optical unit shown in FIG.  8 . 
       FIG. 10  shows the third embodiment according to the present invention. 
       FIG. 11  illustrates a position relationship between an optical path of a flux of light projected on a screen and a direction of exhaust from an exhaust port of the fourth embodiment according to the present invention. 
       FIG. 12  is a cross sectional view of the fifth embodiment according to the present invention, in which a fan is disposed in a duct. 
       FIG. 13  is an exploded view of the sixth embodiment according to the present invention. 
       FIG. 14  is an enlarged view of a reflection type LCD panel shown in FIG.  8 . 
       FIG. 15  illustrates a position relationship between an optical path of a light pencil modulated by a reflection type LCD panel and a drive circuit substrate. 
       FIG. 16  is an exploded view of a position adjusting mechanism of one embodiment according to the present invention. 
       FIG. 17  is an external view of a position adjusting mechanism of one embodiment according to the present invention. 
       FIG. 18  illustrates a method for mounting a position adjusting mechanism on an optical unit. 
       FIG. 19  illustrates a lamp house positioned to a lower unit case. 
       FIG. 20  is an external view of a lamp case of one embodiment according to the present invention. 
       FIG. 21  is a cross sectional view of an optical unit of one embodiment according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments according to the present invention will be described below with reference to the drawings. 
   First, a schematic constitution of a projection type image display device according to the present embodiment will be described with reference to FIG.  1 . 
   In the outer cases  1   a  and  1   b  of the present projection type image display device  100 , a light source (a lamp in the present embodiment), a reflection type LCD panel and the other optical elements are housed. When the device  100  is used, as shown in  FIG. 2 , a cover  11  mounted on the upper outer case  1   a  is opened and only a third mirror lens  21  constituting an optical system is taken out from the outer cases  1   a  and  1   b . In this respect, each of the mirror lenses employed in the present projection type image display device  100  is an optical part having a curved mirror plane (spherical plane or non-spherical plane) for forming an image. Therefore, each of the mirror lenses may be replaced by the other optical element having the same function such as a refractive lens, a combination of a refractive lens and a mirror and the like. 
   When the light source is lighted up in this state, as shown in  FIG. 3 , a light pencil  3  containing image information written in the reflection type LCD panel is reflected by the third mirror lens  21  (see  FIG. 2 ) and is projected on a screen. The optical path of the light pencil  3  at this time will be described in detail as follows. 
   As shown in  FIG. 4 , the light pencil projected from the light source  71  and having a suitable amount of light passes first through an integrator  63  and then is reflected by a mirror  64  and passes through an integrator  65  and is reflected by a mirror  31  and is introduced to two dichroic mirrors  32  and  33 . The light pencil separated into color components (for example, red, green and blue color components) by these dichroic mirrors  32  and  33  enters the light incidence/reflection planes of reflection type LCD panels  91 A,  91 B and  91 C for displaying colors at predetermined incidence angles (not zero) and is modulated every picture element by the reflection type LCD panels  91 A,  91 B and  91 C for displaying colors. In this regard, to separate the light pencil advancing from the mirror  31  from the modulated light pencil advancing to the first mirror  25  described below by the reflection by the light incidence/reflection planes of the reflection type LCD panels  91 A,  91 B and  91 C, the light pencil is let on the light incidence/reflection planes of the reflection type LCD panels  91 A,  91 B and  91 C at predetermined incidence angles. 
   Then, the modulated light pencils reflected by the reflection type LCD panels  91 A,  91 B and  91 C for displaying colors are introduced again to two dichroic mirrors  32  and  33  and are converged into one light pencil by these two dichroic mirrors  32  and  33  and then is reflected by the first mirror lens  25  and then is reflected by the second mirror lens  22  and then is introduced to the third mirror lens  21  taken out outside the outer cases  1   a  and  1   b.    
   This enlarges the color images written on the reflection type LCD panels  91 A,  91 B and  91 C for displaying colors and displays them on a screen (not shown). In the following description, an optical path A 1 →A 2 →A 3  from the light source  71  to the reflection type LCD panels  91 A,  91 B and  91 C for displaying colors is referred to as an illumination-side optical path and an optical path A 4 →A 5 →A 6 →A 7  from the reflection type LCD panels  91 A,  91 B and  91 C for displaying colors to the screen is referred to as a projection-side optical path. 
   Further, as shown in  FIG. 1  the outer cases  1   a  and  1   b  have an intake port  12  and an exhaust port  13  in predetermined regions. In the outer cases  1   a  and  1   b , an exhaust fan is housed opposite to the exhaust port  13 . The outside air from the intake port  12  passes through the inside of the outer cases  1   a  and  1   b  and goes to the intake port of an optical unit. 
   In  FIGS. 5A and 5B , a focusing dial knob for finely adjusting the second mirror lens  22  at a suitable position is provided on the outer cases  1   a  as shown in  FIGS. 1 and 1   b  and an operator can easily bring an image enlarged and projected on the screen (hereinafter referred to as screen image”) into focus. 
   On the premise of the constitution briefly described above, the inner structure of the projection type image display device  100  as shown in  FIG. 1  will be hereinafter described in the concrete. 
   In the outer cases  1   a  and  1   b  of the projection type image display device  100 , an optical unit  500  shown in  FIG. 5  is assembled just as it is. The optical unit  500  is provided with the optical elements according to a predetermined layout. For example, the third mirror lens  21  is rotatably supported by an opening/closing mechanism  23  provided on an upper unit case  4   b  and the second mirror lens  22  is fixed to the movable part of a focusing mechanism  8  provided on the upper unit case  4   b . The movable part of the focusing mechanism  8  is moved back and forth when the focusing dial knob  14  is turned. 
   Further, the reflection type LCD panels  91 A,  91 B and  91 C, as shown in  FIG. 6 , are supported by the position adjusting mechanisms  9 A,  9 B and  9 C fixed to a lower unit case  4   a . If the upper unit case  4   b  is mounted on the lower unit case  4   a , the wall planes of these two unit cases  4   a  and  4   b  form a hermetically closed room (corresponding to the inside of  4   g  in  FIG. 5 ) is formed which shields a light pencil A 2 →A 3 →A 4 →A 5  from the integrator lens  65  to the first mirror lens  25 . Furthermore, the upper unit case  4   b  has a window through which the light pencil reflected by the first mirror lens  25  is projected toward the second mirror lens  22  and in which an aperture  24  formed of a transparent material is fitted. Therefore, the inside of the hermetically closed room is completely shutoff from the outside air containing dust. That is, such a hermetically closed room can almost completely prevent the dust having a detrimental effect on the quality of the screen image from entering the vicinities of the light incidence/reflection planes of the reflection type LCD panels  91 A,  91 B and  91 C, that is, the vicinities of focusing planes of mirror lenses. 
   Still further, the lower unit case  4   a  in  FIG. 6  is provided with an air blowing fan  45 C by a mounting plate  98 . Heat radiating fins  92 C for increasing the area of a heat radiating plane are provided on the surface opposite to the light incidence/reflection plane of the reflection type LCD panel  91 C as shown in FIG.  7 . 
   The light source  71 , as shown in  FIG. 7 , is housed in a lamp case  7  fixed to the lower unit case  4   a  in which the exhaust fan  41  is fitted in such a manner that it faces the inside of the lamp case  7 . Therefore, if the exhaust fan  41  is operated, the air in the lamp case  7  is actively exhausted from the exhaust port  13  of the outer cases  1   a  and  1   b.    
   The outer wall of the hermetically closed room and an air guiding plate ( 42  in  FIG. 6 ) fixed to the lower unit case  4   a  form a duct  49 B for guiding an air flow B 4  from the vicinity of the position adjusting mechanism  9 B for supporting the reflection type LCD panel  91 C, one of the reflection type LCD panels  91 A,  91 B and  91 C, into the lamp case  7 . Similarly, the outer wall of the hermetically closed room and the side wall of the lower unit case  4   a  form a duct  49 A for guiding an air flow B 2  from the vicinity of the position adjusting mechanism  9 A for supporting the reflection type LCD panel  91 A into the lamp case  7 . In this regard, the directions of the air flows. B 2  and B 4  are regulated by fins  42   a  provided on an air directing guide  47  and the air guiding plate  42   a  such that the air B 2  and B 4  can be reliably guided into the lamp case  7  heated by absorbing light radiated from the light source  71 . 
   When the exhaust fan  41  is operated to exhaust the air B 3  and B 6  from the exhaust port  13 , the pressure in the lamp case  7  is reduced and the air B 4  near the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91 B flows into the duct  49 B from gaps above and below the position adjusting mechanism  9 B and passes through the duct  49 B and then flows into the lamp case  7 . Similarly, the air B 2  near the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91 A flows into the duct  49 A from gaps at the top and the bottom of the position adjusting mechanism  9 A and passes through the duct  49 A and then flows into the lamp case  7 . Further, fresh air outside the optical unit  500  goes around the outer periphery of the optical unit  500  and reaches the intake port. In this respect, the planes opposite to the light incidence/reflection planes of two reflection type LCD panels  91 A and  91 B are provided with heat radiating fins  92 A and  92 B. 
   In this way, two ducts  49 A and  49 B share only one exhaust fan  41  and can constantly introduce fresh outside air into two reflection type LCD panels  91 A and  91 B and a lamp reflector  71   a . Therefore, the whole optical unit  500 , two reflection type LCD panels  91 A and  91 B, and the lamp reflector  71   a  heated by absorbing light beams in the range of infrared rays and in the range of ultraviolet rays can be cooled by the constantly flowing fresh outside air. Further, the heat of the light source  71  can be radiated sufficiently via the part where the light emitting tube of the light source  71  is put into contact with the lamp reflector  71   a . Furthermore, since the fresh outside air is brought around the outer periphery of the optical unit  500  in this constitution, the heat stored in the whole optical unit  500  can be sufficiently radiated. 
   In this respect, there is a fear that the cooling efficiency of the lamp reflector  71   a  is reduced because the air flows B 2  and B 4  flowing into the lamp case  7  receive heat from the reflection type LCD panels  91 A and  91 B, but there is no fear of this kind because the air is introduced from a low temperature side to a high temperature side. For example, the air introduced from the intake port and having ordinary temperatures (for example, about 25° C.) is heated to about 30° C. at the maximum by the heat radiation from the reflection type LCD panels  91 A and  91 B whose operating temperatures are, for example, about 60° C. at the most. Therefore, it is obvious that the cooling efficiency of the lamp reflector  71   a  disposed near the lamp  71  having an extremely higher operating temperature (for example, 300° C.) than is this operating temperature might not be reduced. 
   That is, the incidence of failure of the LCD panel, such as a breakdown caused by heat generated while it is used, can be reduced by using the duct structure described above. Further, since the exhaust fan producing noises is not required to be provided on each heat generating body, the duct structure described above also has other merits that it does not give the audience an unpleasant feeling and that it can simplify the inside structure of the device. Even in a case in which all three LCD panels are not cooled by the exhaust fan  41 , the constitution of the whole set can be simplified to produce the same effects of improving reliability and reduction in the parts thereof. 
   In this embodiment, although two of three LCD panels share a part of cooling means with the illumination side and one remaining LCD panel has a cooling fan intended therefor, it is needless to say that the same effects can be produced even if all three fans are shared or two fans are intended for the purpose and one remaining fan is shared. 
     FIG. 8  is an exploded view of an inner structure of the second embodiment according to the present invention. The image display mechanism is divided into the lower unit case  4   a  and the upper unit case  4   b  and these cases constitute the main part of the hermetically closed space. Further, an air introducing passage (duct) extending toward the lamp case is joined to the position adjusting mechanism  9 A, 9 B, 9 C for supporting the LCD panels which needs to be cooled. The air introducing plate  42  forming a part of the duct acts as a cover. Furthermore, the suction fan  45 A, 45 B, 45 C is provided in the vicinity of the position adjusting mechanism  9 A, 9 B, 9 C of the LCD panels. Each of three LCD panels is provided with one fan, respectively. 
   Further, it is recommended that the air blowing fan  45 B intended for the reflection type LCD panel  91 B near the center of the lower unit case  4   a  be fixed by a fixing plate to the window formed in the bottom surface of the lower unit case  4   a.    
   If such a constitution is employed, the fans can be used flexibly according to usage conditions; for example, when the operating temperature is considerably low, the exhaust fan  41  is stopped and a part of or all of three air blowing fans  45 A,  45 B and  45 C is operated. Further, although it is disadvantageous from the viewpoint of reducing noises that all air blowing fans  45 A,  45 B and  45 C are operated with the exhaust fan  41 , as shown in  FIG. 9 , such an operation is very advantageous when a large amount of air flow is required or when a pressure drop in the duct is large (resistance of air flow is large) because air is forcibly introduced on the planes opposite to the light incidence/reflection planes of all reflection type LCD panels  91 A,  91 B and  91 C and is pulled by the exhaust fan  41 . 
   Even if the device is constituted in this way, it can be easily modified to the embodiment shown in FIG.  5  and  FIG. 6  only by removing two air blowing fans  45 A and  45 B and by replacing the fixing plates  98  for fixing these air blowing fans  45 A and  45 B to the lower unit case  4   a  with partition plates (shown by  99  in FIG.  6 ). Therefore, the number of air blowing fans mounted in addition to the air blowing fan  45 C can be selected according to usage conditions such as input of the light source or the like; for example, when the ordinary light source of about 120 watt is used, the embodiment shown in FIG.  5  and  FIG. 6  is employed, and when the light source is 300 watt, that is, 2.5 times larger than the ordinary light source, the embodiment shown in FIG.  8  and  FIG. 9  is employed. Further, when the light source is small enough to be cooled by only three air blowing fans  45 A,  45 B and  45 C, for example, when the light source of a considerably small input (for example, about 50 watt) is used, as shown in  FIG. 10 , it is also recommended that three air blowing fans  45 A,  45 B and  45 C be not removed but that the exhaust fan  41  disposed at the position where noises are liable to leak outside be removed. 
     FIG. 10  is a perspective view of the third embodiment according to the present invention. 
   In this constitution, if the power of the illumination lamp is small, for example, 50 watt, the whole device can be cooled only by the small fans of the intake sides without using the exhaust fan. In this case, as shown in  FIG. 12 , the device can be cooled only by the fan of the intake side. That is, the air sucked like a streamline B 1  by the intake side fan  45 A exchanges heat with the heat radiating fin  92 A and advances to the lamp case side  7  through the duct  49 A. The air advancing along the outer periphery of the lamp and exchanging heat with the lamp  71  is exhausted outside through exhaust port  13 . In this constitution, noises of the fans leaking outside from the exhaust port can be reduced because the exhaust fan can be removed. 
     FIG. 11  shows the fourth embodiment according to the present invention. The most suitable position relationship between the direction in which exhaust air from the exhaust port  13  of the outer cases  1   a  and  1   b  advances and the optical path of the light pencil  3  projected on the screen will be described with reference to FIG.  11 . It is verified by experiment that, if an angle θ formed by the central axis of the exhaust port  13  of the outer cases  1   a  and  1   b , that is, the direction  17  in which the exhaust air from the exhaust port  13  advances and the optical axis of the light pencil  3  projected on the screen is smaller than 30 degrees, a problem is produced that warmed air exhausted from the exhaust port  13  of the outer cases  1   a  and  1   b  unstable air in the optical path of the light pencil  3  reflected by the third mirror lens  21  to flicker the screen image. Further, it is also verified by experiment that, if the angle θ is in the range of larger than 90 degrees, for example, as in the case in which the exhaust port  13  is in the side which does not face the screen, the warmed air is scattered beside and behind the projection type image display device  100  to make the audience feel unpleasant. 
   Therefore, it is desirable to design a position of the third mirror lens  21  when used, that is, a position relationship between the third mirror lens  21  when used and the exhaust port  13 , while bearing in mind that this angle θ is in the range of 30 to 90 degrees, in other words, that the exhaust air is blown off along the path which is different in height from the optical axis  3   a  of the light pencil  3  projected on the screen. In this regard, the angle θ is actually about 50 degrees. 
     FIG. 12  is across sectional view of the inner constitution of the fifth embodiment according to the present invention. That is, the fourth embodiment has a constitution in which the fan is provided on the intake port side of the LCD panel side and is not provided on the exhaust port side. 
   In this constitution, a middle fan  600  is disposed in the middle of the intake port of the LCD panel side and the exhaust port of the illumination means side. The middle fan  600  sucks air at the intake side and exhausts the air at the exhaust side. Therefore, the air sucked like a streamline B 1  from the intake port side by the middle fan  600  exchanges heat with the heat radiating fin  92 A and advances like a streamline B 2  to the lamp case side  7  through the duct  49 A and the middle fan  600 . The air like a streamline B 2  advancing along the outer periphery of the lamp  71  and exchanging heat with the lamp  71  in the lamp case  7  is exhausted outside like the streamlines B 5  and B 3 . In this constitution, since the air is not blown off directly from the exhaust port by the fan, noises can be reduced and since the fan is disposed not in the intake port side but in the middle, the amount of wind might not be reduced by a pressure drop by the fan. 
   Although the light valve of reflection LCD panel type has been described as the light valve means in the embodiments described above, the light bulb element of the other type such as transmittance type LCD panel, micro mirror (micro mirror driving) type, laser liquid writing type may be employed. Further, although a reflection mirror lens has been described as the optical system, the optical element other than the reflection mirror lens such as refraction lens, a combination of a refraction lens and the reflection mirror lens can also produce the same effect. 
   In the description, the image display mechanism and the image display device in which the image display mechanism is built are described together, but only the image display mechanism or only the image display device in which the image display mechanism is built can also produce the same effect. That is, even if the image display mechanism is built directly in a building and the exterior thereof is integrated with the building, or even if the image display mechanism is housed in a big cabinet and projects the image on a transmittance type screen fixed to the outer wall of the cabinet, the image display mechanism can produce the same effect. 
   Next, the schematic constitution of the projection type image display device of the sixth embodiment according to the present invention will be described with reference to FIG.  1 . In the outer cases  1   a  and  1   b  of the projection type image display device  100 , the light source, the reflection type LCD panel and the other optical elements constituting the optical system are housed. Further, the outer cases  1   a  and  1   b  have in the predetermined regions the intake port  12  for introducing the outside air thereinto and the exhaust port  13  for exhausting the air while the device is used. The exhaust fan is housed in the outer cases  1   a  and  1   b  in such a way that it faces the exhaust port  13 . The outside air introduced from the intake port  12  passes through the outer cases  1   a  and  1   b  to the intake port of the optical unit. 
   When the device is used, as shown in  FIG. 2 , the cover  11  mounted on the outer case  1   a  is opened and only the third mirror lens  21  is taken out from within the outer cases  1   a  and  1   b . In this respect, the mirror lens employed in the present projection type image display device  100  is an optical part having a curved mirror plane (spherical plane or non-spherical plane) for forming an image. Therefore, these mirror lens may be replaced by the other optical elements having the same function such as a refractive lens, a combination of a refractive lens and a mirror. 
   When the light source is lit on in the state in which the third mirror  21  is erected, as shown in  FIG. 3 , a light pencil  3  containing image information written in the reflection type LCD panel is reflected by the third mirror lens  21  and is projected on the screen. The optical path of the light pencil  3  at this time will be described in detail as follows. 
   As shown in  FIG. 4 , a light pencil having a suitable amount of light radiated from the light source  71  (lamp in the present embodiment) passes first through the integrator  63  and then is reflected by the mirror  64  and passes through the integrator  65  and is reflected by the mirror  31  and then is introduced to two dichroic mirrors  32  and  33 . The light pencil separated by these dichroic mirrors  32  and  33  into color components (for example, red, green and blue color components) enters the light incidence/reflection planes of reflection type LCD panels  91 A,  91 B and  91 C at predetermined incidence angles (not zero) via field lenses (not shown) and is modulated every picture element by the reflection type LCD panels  91 A,  91 B and  91 C for displaying colors. In this regard, to separate the light pencil advancing from the mirror  31  from the modulated light pencil advancing to the first mirror lens  25  described below by the reflection by the light incidence/reflection planes of the reflection type LCD panels  91 A,  91 B and  91 C, the light pencil is let on the light incidence/reflection planes of the reflection type LCD panels  91 A,  91 B and  91 C at predetermined incidence angles. The optical path A 1 →A 2 →A 3  will be hereinafter referred to as an illumination path. 
   Then, the modulated light pencils reflected by the reflection type LCD panels  91 A,  91 B and  91 C for displaying colors are introduced again to two dichroic mirrors  32  and  33  via the field lenses (not shown) and are converged into one light pencil by these two dichroic mirrors  32  and  33  and then is reflected by the first mirror lens  25  and is reflected by the second mirror lens  22  and is introduced to the third mirror lens  21  taken out outside the outer cases  1   a  and  1   b . The optical path A 4 →A 5 →A 6 →A 7  will be referred to as a projection path. 
   This enlarges the color image written on the reflection type LCD panels  91 A,  91 B and  91 C for displaying colors and displays it on the screen (not shown). In this regard, the image enlarged and projected on the screen (hereinafter referred to as screen image”) is brought into focus by the focusing dial knob  14  protruding from the outer cases  1   a  and  1   b.    
   On the premise of the constitution briefly described above, the inner structure of the present projection type image display device  100  will be hereinafter described in the concrete. 
   In the outer cases  1   a  and  1   b  of the projection type image display device  100 , the optical unit  500  shown in  FIG. 5  is assembled just as it is. The optical unit  500  is provided with the optical elements and the like according to a predetermined layout. For example, the third mirror lens  21  is rotatably supported by the opening/closing mechanism  23  provided on the upper unit case  4   b  and the second mirror lens  22  is fixed to the movable part of a focusing mechanism  8  provided on the upper unit case  4   b . The movable part of the focusing mechanism  8  is moved when the focusing dial knob  14  is turned. 
   Further, the reflection type LCD panels  91 A,  91 B and  91 C, as shown in  FIG. 13 , are fixed to the guide part of the lower unit case  4   a  by the position adjusting mechanisms  9 A,  9 B and  9 C. The structure of the position adjusting mechanisms  9 A,  9 B and  9 C will be described below. 
   If the upper unit case  4   b  is mounted on the lower unit case  4   a , a hermetically closed room (corresponding to a space  52  in  FIG. 9 ) is formed, which is surrounded by the inner wall planes of these two unit cases  4   a  and  4   b , the integrator  65  and the light incidence/projection planes of the reflection type LCD panels  91 A,  91 B and  91 C. That is, the hermetically closed room  52  is formed which can shield, almost from the outside air, the optical path according to the  FIG. 5  A 2 →A 3 →A 4 →A 5  from the integrator lens  65  to the light incidence/projection planes of the reflection type LCD panels  91 A,  91 B and  91 C via the mirror  31  and the like. In this regard, the position adjusting mechanisms  9 A,  9 B and  9 C are not housed in the hermetically closed room  52  so as to easily handle the adjusting screws described below provided on the position adjusting mechanisms  9 A,  9 B and  9 C. Further, the reflection type LCD panels  91 A,  91 B and  91 C are provided across two unit cases  4   a  and  4   b  and are used as parts of the partition walls of the hermetically closed room  52  so as to improve workability in assembling the device and to simplify a maintenance/inspection work and an adjusting work. In this respect, the inside of the hermetically closed room  52  can be repaired and inspected by removing the upper unit case  4   a . To prevent the light scattered in the vicinity of the reflection type LCD panels  91 A,  91 B and  91 C from leaking outside the hermetically closed room  52 , as shown in  FIG. 14 , a packing  95  formed of a shading material is fitted in each joint of a field lens frame  94  described below and two unit cases  4   a  and  4   b . Further, the material forming the packing  95  is not only shading but also elastic lest should the hermetically closed room  52  loses hermetic property even when the positions of the reflection type LCD panels are adjusted. 
   In this constitution, when the hermetically closed room  52  is opened or closed so as to assemble, adjust, repair or inspect the device, the upper unit case  4   a  is removed, and hence the positions where the position adjusting mechanism  9  and the reflection type LCD panel  91  are supported by the lower unit case  4   b  are not affected. That is, when the hermetically closed room  52  is opened or closed, it is not necessary to again adjust the positions of the position adjusting mechanism  9  and the reflection type LCD panel  91 . 
   The hermetically closed room described above can almost completely prevent dust having a detrimental effect on the quality of the screen image from entering the light incidence/reflection planes of the reflection type LCD panels  91 A,  91 B and  91 C, that is, the vicinities of focusing planes of the mirror lenses of projection system. 
   As shown in FIG.  6  and  FIG. 7 , further, the lower unit case  4   a  is provided with the air blowing fan  45 C by a mounting plate  98 C. Furthermore, another air blowing fan  45 A is mounted on the side opposite to the light incidence/reflection plane of the reflection type LCD panel  91 A by the mounting plate  98 A. Still further, the exhaust fan  41  is fitted in the lower unit case  4   a  in such a way that it faces the inside of the lamp case  7  in which the light source  71  is housed. Therefore, as shown in  FIG. 9 , if the exhaust fan  41  is operated to forcibly exhaust the air B 3 , B 6  in the lamp case  7 , the pressure in the lamp case  7  is reduced and the air B 4  near the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91 C passes through gaps above and below the position adjusting mechanism  93 B and flows into the lamp case  7 . Similarly, the air B 2  near the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91 A passes through gaps above and below the position adjusting mechanism  93 A and flows into the lamp case  7 . Further, the outside air B 7  introduced from the intake port  12  passes along the outer periphery of the unit cases  4   a  and  4   b  and the outer wall of the hermetically closed room and flows into near the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91 A. 
   Since the whole optical unit  500  exchanges heat with the fresh outside air constantly introduced thereinto in this constitution, the incidence of failure caused by heat while it is used can be reduced. 
   In this respect, there is a fear that the cooling efficiency of the light source is reduced because the air flowing into the lamp case  7  receives heat from the reflection type LCD panels  91 C, but there is never a fear of this kind because the air is introduced, in particular, from a low temperature side to a high temperature side. For example, the air introduced from the intake port  12  as shown in FIG.  7  and having ordinary temperatures (for example, about 25° C.) is heated to about 30° C. at the maximum by the heat dissipated from the reflection type LCD panels  91 A and  91 B whose operating temperature is, for example, about 60° C. Therefore, it is obvious that the cooling efficiency of the light source having an extremely higher operating temperature (for example, 300° C.) than is this operating temperature might not be reduced. 
   Further, as shown in  FIG. 15 , a drive circuit substrate  43  for giving a drive signal to the reflection type LCD panels  91  is disposed opposite to the optical path A 2  of the projection system across the optical path A 3  of the illumination system. In  FIG. 5 , LCD panel  91  represents three crystal panels  91 A, 91 B and  91 C. Furthermore, signal cables  96  connected to the connectors  44  of these drive circuit substrates  43  are taken out from the sides near the drive circuit substrates of the reflection type LCD panel  91  so as to shorten the length of the cable. This structure can reduce noises and prevent unnecessary radiation. 
   Next, the position adjusting mechanism of the LCD panel will be described. 
   As shown in  FIG. 16 , mounting seats  905   a ,  905   b  and  905   c  having threaded holes are fixed to the front plane  901   a  of a support base  901  at a plurality of positions (for example, three positions in the present embodiment). In the center of the support base  901 , a ventilating opening  906  is formed in which heat radiating fins provided on the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91  are loosely inserted. Further, on the upper plane and the bottom plane of the position adjusting mechanism, fixing plates  40   a  and  40   b  are mounted which have through holes for passing fixing screws and positioning holes. The reflection type LCD panel  91  has through holes  46   a ,  46   b  and  46   c  of suitable diameters at the positions corresponding to the screw holes of these mounting seats  905   a ,  905   b  and  905   c.    
   Therefore, if the adjusting screws  903   a ,  903   b  and  903   c  are inserted into the through holes  46   a ,  46   b  and  46   c  in a state in which the front plane  901   a  faces the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91 , and are screwed in the threaded holes of the mounting seats  905   a ,  905   b  and  905   c , the reflection type LCD panel  91  can be fixed to the front plane  901   a  of the support base  901 . In this respect, O-rings  902   a ,  902   b  and  902   c  are sandwiched between the mounting seats  905   a ,  905   b  and  905   c  and the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91 . If the field lens frame  94  is fixed to the LCD panel  91  such that it presses the field lens  93  on the light incidence/reflection plane  91   a  of the LCD panel  91 , as shown in  FIG. 17 , the position adjusting mechanism which can be mounted on the lower unit case  4   a  is completed. 
   The position adjusting mechanism  9  is finally mounted on the lower unit case  4   a  with extreme ease, as shown in  FIG. 18 , by the following steps: the position adjusting mechanism  9  is slipped into the guide  4   c  formed in the lower unit case  4   a  from a predetermined direction and then the fixing plates  40   a  and  40   b  are fixed to the lower unit case  4   a  by the fixing screws  908 A and  908 B. Further, the mounting position of the position adjusting mechanism  9  is determined by the clearance fit of the positioning pins  907 A,  907 B and  907 C fitted in the holes  401 A,  401 B and  401 C made in the lower unit case  4   a  with the positioning holes of two fixing plates  4   a  and  40   b  of the position adjusting mechanism  9 . Therefore, the position adjusting mechanism  9  can be easily mounted or dismounted when the inside of the hermetically closed room  52  needs to be repaired. 
   As described above and as shown in  FIG. 16 , the O-rings  902   a ,  902   b  and  902   c  are sandwiched between the mounting seats.  905 A,  905 B and  905 C and the plane opposite to the light incidence/reflection plane of the reflection type LCD panel  91 . Therefore, a distance between the front plane  901   a  of the support base  901  and the reflection type LCD panel  91  and a slant angle of the reflection type LCD panel  91  with the front plane  901   a  of the support base  901  can be controlled by adjusting the screwing amount of the adjusting screws  903   a ,  903   b  and  903   c . For example, if all adjusting screws  903   a ,  903   b  and  903   c  are uniformly screwed, the reflection type LCD panel  91  can be moved back and forth with respect to the front plane  901   a  of the support base  901  (in the direction of Z axis in FIG.  17 ). Further, if the screwing amount of the adjusting screws  903   a ,  903   b  and  903   c  is different from each other, the reflection type LCD panel  91  can be turned in two predetermined direction with respect to the front plane  901   a  of the support base  901  (in the directions of α and β in FIG.  17 ). 
   Further, the amount of movement of the reflection type LCD panel  91  in the up-and-down direction with respect to the front plane  901   a  of the support base  901  (in the direction of Y axis in  FIG. 17 ) and the amount of movement of the reflection type LCD panel  91  in the right-left direction with respect to the front plane  901   a  of the support base  901  (in the direction of X axis in  FIG. 17 ) can be controlled by the other adjusting screws  904 A and  904 B jointed to a drive mechanism generally referred to as a parallel moving mechanism. Furthermore, the amount of turning of the reflection type LCD panel  91  in a plane parallel to the front plane  901   a  of the support base  901  (in the direction of γ in  FIG. 17 ) can be controlled by the other adjusting screw  904 C joined to the drive mechanism generally referred to as a turning mechanism. 
   As shown in  FIG. 17 , the position and posture of each reflection type LCD panel  91  can be freely adjusted by the position adjusting mechanism  9  having 6 degrees of freedom (X, Y, Z, α, β, γ) described above. 
   Next, a basic structure of the lamp case  7  will be described with reference to FIG.  19  and FIG.  20 . 
   As shown in  FIG. 19 , the lamp case  7  is assembled in the lower unit case  4   a  from the bottom plane side thereof. Connectors  72  and  74  are connected to each other in a state in which the lamp case  7  is assembled in the lower unit case  4   a . That is, when the lamp case  7  is positioned with respect to the lower unit case  4   a , the connector electrodes  72   a  and  72   b  of the connector  72  of the lamp case  7  are also positioned with respect to the connector electrodes  74   a  and  74   b  of the connector  74  of the lower unit case  4   a . The lamp case  7 , as shown in  FIG. 20 , is provided with a grip  73  along the line of two connector electrodes  72   a  and  72   b . That is, the direction of length L 1  of the grip  73  is nearly parallel to the line L 2  of the connector electrodes  74   a  and  74   b . Therefore, if the grip  73  is pulled in the direction orthogonal to the bottom plane of the lower unit case  4   a , the connector electrodes  72   a  and  72   b  of the connector  72  of the lamp case  7  are pulled out from the connector electrodes  74   a  and  74   b  of the connector  74  of the lower unit case  4   a  without applying additional momentum. The grip  73  fixed to the lamp case  71  can make the force for mounting or dismounting the lamp case  71  minimum and in addition can prevent the deteriorated performance of the connectors  72  and  74  which is prone to happen when the lamp case  71  is mounted and dismounted many times. 
     FIG. 21  is a cross sectional view of the other embodiment of the optical unit according to the present invention. 
   The constitution shown in  FIG. 21  shows a projection type image display mechanism of single panel type in which a single LCD panel is employed. Some light valve means can display an image in a plurality of colors by a single liquid crystal and the other light valve means can display the image in monochrome. If a single light valve means is employed, it is not necessary to position the images of a plurality of colors, but it is sometimes necessary to adjust the focusing position of the projected image, the inclination of the screen, or a position of the device in the up-down direction and in the right-left direction. In these cases, the light bulb means needs to be adjusted and if the same position adjusting mechanism as the embodiment is employed, it can produce the same effects as the embodiment. 
   In this respect, for example, (1) even if only the inside of the optical unit (that is, image display mechanism) is built in the wall plane of the building, or (2) even if only the image display mechanism is housed in a large cabinet having a transmittance type screen and an image is projected on the transmittance type screen from the opposite side thereof, the effects are obtained. 
   As described above, according to the present invention, the number of fans provided in the whole device can be reduced and hence the constitution of the device can be simplified and reliability can be improved. Further, noises can be reduced because the number of fans is reduced. Further, it is possible to prevent dust near the light valve and to simplify the constitution of cooling means for cooling the device at the same time. Furthermore, since the duct is provided between the illumination means and the light valve means, one or two fans for cooling both means can be selectively operated according to the operational conditions of the device and the environmental conditions. 
   Further, since the number of fan to be mounted for cooling the device can be selected in this constitution, the most suitable cooling performance can be realized according to the operational conditions such as the kind of employed elements, the intensity of illumination and usage. 
   Still further, the constitution in which an angle formed by the optical axis of the projected light pencil and the direction of exhaust is in a predetermined region can improve the environment of the audience. 
   Still further, in the constitution in which a plurality of structural members constituting the image display mechanism constitutes the almost hermetically closed space and in which the light incidence/reflection plane of the light valve means contacts the plurality of structural members, the LCD panel does not need to be removed when the hermetically closed space is opened or closed and hence the position adjusting means does not need to be readjusted, which can provide the image display mechanism which can be easily assembled and has good maintainability. 
   Still further, when the light valve means is moved by the position adjusting means, the shading elastic body sandwiched between itself and the almost hermetically closed space can realize positioning the light valve means, preventing dust and shielding light at the same time. 
   Still further, since the position adjusting mechanism of the LCD panel can be positioned and mounted on the image display mechanism in a single direction, it can be easily assembled and adjusted. 
   Still further, since the light valve means and the drive circuit means are arranged in the minimum interval, it is possible to ensure stability in the movement of the light valve means and to reduce unnecessary radiation. 
   In addition, in the constitution in which the grip is provided in parallel to the line of connector electrodes of the lamp case, the lamp case can be removed by the minimum force without applying momentum to the lamp case, which can improve reliability of the lamp case and the device. 
   Although the present invention has been described in conjunction with the embodiments thereof, it is evident that the present invention can be also used in the embodiments that are different from the embodiments and that fall within the spirit and main features of the present invention. Therefore, the embodiments are merely illustrative in all points and should not be understood in the limited scope. The scope of the present invention will be described by the appended claims. Further, all alternatives, modifications, and variations that fall within the equivalents of the appended claims are included within the present invention.