Patent Publication Number: US-6986582-B2

Title: projector

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     An aspect of the invention relates to a duct used for a projector including, for example, plural optical modulation systems for modulating plural color lights with respect to each color light according to image information to form optical images, a color composition optical system for combining the optical images modulated in the respective optical modulation systems, and a projection optical system for magnification projection of the composite optical image, and for introducing cooling air to the optical modulation systems, a cooling device, and a projector. 
     2. Description of Related Art 
     Conventionally, using a projector for a presentation in a conference, an academic conference, an exhibition, and the like is well known. Some of such projectors adopt the so-called three-plate system in which luminous flux emitted from a light source device is separated into light of three primary colors of red, green, and blue by a dichroic mirror, and the light is modulated with respect to each color light according to image information by three liquid crystal panels, and then the respective color lights after image modulation is combined by a cross dichroic prism and a color image is magnification projected via a projection lens. In the three-plate system projector, optical conversion elements, such as polarization plates for aligning polarized direction of the respective color lights to be modulated in the liquid crystal panels are provided on the luminous flux entrance side and the luminous flux exit side of the liquid crystal panel. 
     By the way, in the above described projector, the respective polarization plates generate heat due to application of the luminous flux from the light source device. Accordingly, in order to cool these liquid crystal panels and respective polarization plates, for example, the cooling structure as below is adopted. In other words, a cooling fan and a duct connected to the cooling fan are provided in the projector. In the duct, an entrance side air outlet for discharging cooling air to the luminous flux entrance sides of the liquid crystal panels and an exit side air outlet for discharging cooling air to the luminous flux exit sides of the liquid crystal panels are formed. By the structure, the cooling air from the cooling fan is discharged while being divided appropriately from the entrance side air outlet and the exit side air outlet, and thereby, the liquid crystal panels and the respective polarization plates can be forcibly cooled. See, for example, Publication of Japanese Patent Application No. Hei-11-295814. 
     SUMMARY OF THE INVENTION 
     Normally, since optical properties of polarization plates are different between luminous flux exit side and the luminous flux entrance side, the polarization plate on the luminous flux exit side generates a larger amount of heat than that of the polarization plate on the luminous flux entrance side. In addition, recently, a projector of higher intensity is requested, however, by the above described structure, there is a possibility that the amount of heat generated in the polarization plate on the exit side is especially increased, and the heat cannot be dissipated quickly. 
     In order to solve the problems, it is conceivable that improvement in cooling efficiency is facilitated by increasing the number of rotation of the cooling fan and the mounted number of cooling fans. However, it is necessary to make the size and the mounted number of cooling fans as small as possible for realizing miniaturization and lower noise of the projector. 
     The invention can provide a duct, a cooling device, and a projector capable of cooling optical modulation systems with high efficiency while realizing miniaturization and reduction of the mounted number of cooling fans. 
     An exemplary duct of the invention can be a duct used for a projector including plural optical modulation systems for modulating plural color lights with respect to each color light according to image information to form optical images, a color composition optical system for combining the optical images modulated in the respective optical modulation systems, and a projection optical system for magnification projection of the composite optical image, and for introducing cooling air to the optical modulation systems, In the duct, each of the optical modulation systems can include an optical modulation device, an entrance side optical conversion element disposed on the luminous flux entrance side of the optical modulation device, and an exit side optical conversion element disposed on the luminous flux exit side of the optical modulation device, the duct has plural air guide paths through which cooling air passes, entrance side discharge openings for discharging cooling air to the luminous flux entrance sides of the optical modulation devices, and/or exit side discharge openings for discharging cooling air to the luminous flux exit sides of the optical modulation devices, which are formed in these air guide paths, and at least one of the plural optical modulation systems is set as a target of independent cooling, and the entrance side discharge opening and the exit side discharge opening with respect to the target of independent cooling are formed in different air guide paths. 
     Here, as the optical modulation device, a device that includes an optical modulation element, such as a liquid crystal panel having a construction in which a drive substrate and an counter substrate formed from glass and the like are bonded with a predetermined space therebetween via a sealing material, and liquid crystal is enclosed between both substrates can be adopted. 
     Further, as the optical conversion element, the construction including a substrate and an optical conversion film provided on the substrate can be adopted. As the substrate, sapphire, silica glass, quartz crystal, fluorite, and the like can be used. As the optical conversion film, a polarization film, a viewing angle correction film, a phase difference film, and the like can be used. 
     According to an aspect of the invention, since the construction in which the luminous flux entrance side and the luminous flux exit side of the optical modulation device are cooled with cooling air that has passed through different paths, the wind speed and the air flow of the cooling air may be adjusted in response to the respective generated amounts of heat. Thereby, the luminous flux entrance side and the luminous flux exit side of the optical modulation device can be cooled on more suitable conditions, respectively, compared to the case of applying cooling air from the same path, and thus, the optical modulation systems can be cooled with high efficiency while realizing miniaturization and reduction of the mounted number of cooling fans. 
     Specifically, in the case of a projector that adopts the three-plate system for separating luminous flux from a light source lamp into respective color lights of R (red), G (green), and B (blue) and perform modulation with respect to each color light by three optical modulation devices, the optical modulation systems of G and B especially generate larger amounts of heat than the optical modulation system of R due to characteristics of the light source lamp. On this account, as the target of independent cooling, optical modulation systems of G and B are preferable. 
     In the invention, it is preferred that the exit side discharge opening is formed in a position for cooling the optical modulation device and the exit side optical conversion element. 
     According to an aspect of the invention, not only the optical modulation device, but also the exit side optical conversion elements that generate a larger amount of heat can be cooled by the cooling air discharged from the exit side discharge opening, and thereby, cooling efficiency can be made better. 
     In the invention, it is preferred that the entrance side discharge opening and the exit side discharge opening with respect to at least one of optical modulation systems other than the target of independent cooling are formed in the same air guide path. 
     As described above, according to an aspect of the invention, the structure of the duct can be simplified by providing the entrance side discharge opening and the exit side discharge opening with respect to the optical modulation system that generates a smaller amount of heat than the target of independent cooling in the same air guide path. For example, in the case of the above described three-plate system projector, it is preferred that the entrance side discharge opening and the exit side discharge opening with respect to the optical modulation system of R that generates a smaller amount of heat than the optical modulation systems of G and B are provided in the same air guide path. 
     In an aspect of the invention, it is preferred that an extending direction of the optical modulation system is disposed substantially orthogonal to an extending direction of the air guide path, and at least one of the respective discharge openings is formed on a plane along the extending direction of the air guide path in a position offset to an upstream side of an intersection of the extending direction of the optical modulation system and the air guide path so that the optical modulation system may be located in a discharge direction of cooling air from the discharge opening. 
     The cooling air that has traveled in the air guide path along the extending direction is discharged from the discharge opening. However, according to the law of inertia, discharged not in a direction substantially orthogonal to the discharge opening, but in a direction rather near the downstream side in the air guide path. Therefore, according to the invention, since the discharge opening is formed offset to the upstream side of the air guide path, the cooling air from the discharge opening is assured in contact with the optical modulation system, and thereby, the optical modulation system can be cooled smoothly. 
     An exemplary cooling device of the invention can include any one of above described ducts and plural cooling fans for sending cooling air to the respective air guide paths of the duct. According to the invention, the operation and effect substantially the same as those of the above described ducts can be exerted. 
     In an aspect of the invention, it is preferred that an exit side cooling fan of the cooling fans for sending cooling air to the air guide path in which the exit side discharge opening of the target of independent cooling is formed sends a larger amount of air than that of an entrance side cooling fan for sending cooling air to the air guide path in which the entrance side discharge opening of the target of independent cooling is formed. As described above, normally, the exit side optical conversion element generates a larger amount of heat than the entrance side optical conversion element. On this account, according to the invention, the exit side cooling fan with higher cooling capability than the entrance side cooling fan is used, and thereby, each optical conversion element can quickly be cooled. 
     An exemplary projector of the invention can include plural optical modulation systems for modulating plural color lights with respect to each color light according to image information to form optical images, a color composition optical system for combining the optical images modulated in the respective optical modulation systems, and a projection optical system for magnification projection of the composite optical image. The projector can include any one of the above described cooling devices. According to the invention, the operation and effect substantially the same as those of the above described ducts can be exerted. 
     In an aspect of the invention, it is preferred that the projector further includes an exterior housing for accommodating the optical modulation systems, the color composition optical system, and the projection optical system, wherein the number of the cooling fans is set to two, and air intake ports of these cooling fans are formed on two different surfaces of the exterior housing. According to the invention, since the cooling air outside the projector is introduced into the respective cooling fans from the two different surfaces of the exterior housing, the cooling air can be introduced into the optical modulation systems smoothly to further improve cooling efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numerals reference like elements, and wherein: 
         FIG. 1  shows a perspective view showing the interior of a projector according to one embodiment of the invention; 
         FIG. 2  shows a front view of the projector in the condition of  FIG. 1 ; 
         FIG. 3  shows a plan view schematically showing an optical system within an optical unit according to the embodiment; 
         FIG. 4  shows a perspective view showing the positional relationship between a cooling device and an optical device according to the embodiment; 
         FIG. 5  shows a plan view showing the positional relationship between the cooling device and the optical device according to the embodiment; and 
         FIG. 6  shows a plan view of the cooling device according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, one exemplary embodiment of the invention will be described by referring to the drawings. 
       FIG. 1  is a perspective view from below of a projector  1  according to the exemplary embodiment. Specifically, the drawing shows that a projection lens  46  and an internal cooling unit  5  are mounted to a lower case  23  of the projector  1 .  FIG. 2  is a front view of the projector  1  in the condition of FIG.  1 .  FIG. 3  is a plan view schematically showing an optical system within an optical unit  4 . Note that these components  4 ,  5 ,  23 , and  46  constituting the projector will be described later in detail. 
     In  FIGS. 1  to  3 , the projector  1  can include an exterior case  2  as an exterior housing, a power supply unit (not shown) accommodated within the exterior case  2 , the optical unit  4  arranged in the U-shape similarly disposed within the exterior case  2 , and the internal cooling unit  5  similarly disposed within the exterior case  2 , and has the form of a substantially rectangular parallelepiped as a whole. 
     Here, the power supply unit can include a power supply for supplying power to a lamp drive circuit, a driver board, etc. and the lamp drive circuit (ballast) for supplying power to a light source lamp  411  of the optical unit  4 . Further, the driver board is for controlling to drive liquid crystal panels  441 , which will be described later, according to image information. 
     The exterior case  2  includes an upper case (not shown) and the lower case  23 , which are made of resin, respectively, and they are fixed to each other with screws. Note that the lower case  23  is not necessarily made of resin, but may be made of metal. 
     The lower case  23  is for mounting and fixing the above described power supply unit, the optical unit  4 , and the internal cooling unit  5  thereto, and formed by a bottom face  231 , side faces  232  provided on the circumference thereof, a rear face  233 , and a front face  234 . 
     Substantially at the forward center of the bottom face  231 , a position adjustment mechanism mounting portion  231 A for mounting a position adjustment mechanism for registration of projected images by adjusting the entire tilt of the projector  1  is provided. In addition, on the forward left side of the bottom face  231  in  FIG. 1 , an opening for lamp cover  231 B to which a lamp cover is detachably attached is formed. Moreover, on the forward right side of the bottom face  231  in  FIG. 1 , an air intake port  231 C for cooling air is formed. Further, on two corners rearward of the bottom face  231 , rear foot mounting portions  231 D for fitting rear feet are formed. 
     In the front face  234 , a notch portion  234 A for supporting the projection lens  46  as a projection optical system is formed. This projection lens  46  has a top face portion exposed from the upper case, and the zoom operation and focusing operation of the projection lens  46  can be manually performed via a lever. 
     In the front face  234 , on the opposite side to the notch portion  234 A, an exhaust port mounting portion  234 B for mounting an exhaust port for exhausting air via the internal cooling unit  5  is formed. The exhaust port mounting portion  234 B is located forward of the internal power supply unit. 
     In the side faces  232 , a handle mounting portion  232 A for mounting a C-shaped handle rotatably on one side face (on the right side in FIG.  1 ). Further, on the other side face (on the left side in FIG.  1 ), side feet  2 A (see  FIG. 2 ) as feet in the case the projector  1  is stood vertically with the handle on the upper side. 
     In addition, in the part surrounded by the handle mounting portion  232 A, an air intake port  232 B for cooling air is formed. That is, the air intake port  231 C and the air intake port  232 B are formed on the bottom face  231  and the side face  232  as two different surfaces of the exterior case  2 . 
     The rear face  233  has an interface portion  2 B for mounting an interface cover formed therein, as shown in FIG.  2 . On the left side in  FIG. 2  of the interface portion  2 B, an air intake port  233 A located rearward of the internal power supply unit is formed. 
     The optical unit  4  is a unit that forms an optical image corresponding to image information by optically processing the luminous flux emitted from the light source lamp  411  as shown in FIG.  3 . This optical unit  4  can include an integrator illumination optical system  41 , a color separation optical system  42 , a relay optical system  43 , an optical device  44 , and a projection lens  46 . 
     The internal cooling unit  5  intakes external cooling air and introduces the air into the projector  1  to cool the internal heat generating members and exhaust warmed air to the outside. 
     This interior cooling unit  5  can include, other than a panel cooling device  50  as a cooling unit for cooling mainly the optical device  44  of the optical unit  4 , though not shown in the drawing, a lamp cooling sirocco fan for cooling mainly the light source lamp  411 , an axial-flow fan for intaking external cooling air and sending air to the power supply unit, and an exhaust sirocco fan for exhausting the air within the projector  1  to the outside. 
     These power supply unit, optical unit  4 , and internal cooling unit  5  have their surroundings including top and bottom covered by a shield plate of aluminum (not shown), and thereby, the leakage of electromagnetic noise from the power supply unit etc. to the outside is prevented. 
     In  FIG. 3 , the integrator illumination optical system  41  is an optical system for illuminating image forming regions of the three liquid crystal panels  441  (represented by liquid panels  441 R,  441 G, and  441 B for each color light of red, green, and blue, respectively) configuring the optical device  44  nearly uniformly, and includes a light source device  413 , a first lens array  418 , a second lens array  414  including a UV filter, a polarization conversion element  415 , a superposition lens  416 , and a reflecting mirror  424 . 
     Of these, the light source device  413  has the light source lamp  411  as a light radiation source that emits a radial ray and a reflector  412  for reflecting radiated light emitted from the light source lamp  411 . As the light source lamp  411 , a halogen lamp, a metal halide lamp, or a high-pressure mercury lamp is often used. As the reflector  412 , a parabolic mirror is used. Other than the parabolic mirror, an ellipsoidal mirror may be used with a collimator lens (concave lens). 
     The first lens array  418  has a construction in which small lenses having nearly rectangular outlines seen from an optical axis direction are arranged in a matrix form. The respective small lenses divide luminous flux emitted from the light source lamp  411  into plural pieces of partial luminous flux. The outline form of the small lens is set so as to be a nearly similar form to the form of image forming region of the liquid crystal panels  441 . 
     The second lens array  414  has a construction substantially similar to the first lens array  418 , in which small lenses are arranged in a matrix form. The second lens array  414  has a function of forming images of the respective small lenses of the first lens array  418  on the liquid crystal panels  441 R,  441 G, and  441 B together with the superposition lens  416 . 
     The polarization conversion element  415  is disposed between the second lens array  414  and the superposition lens  416 , and integrated with the second lens array  414  into a unit. Such polarization conversion element  415  is for converting the light from the second lens array  414  into one kind of polarized light, and thereby, utilization efficiency of light in the optical device  44  is improved. 
     Specifically, the respective pieces of partial light converted into one kind of polarized light by the polarization conversion element  415  are nearly superposed on the liquid crystal panels  441 R,  441 G, and  441 B of the optical device  44  finally by the superposition lens  416 . In the projector using liquid crystal panels of type of modulating polarized light, only one kind of polarized light can be used, and thus, nearly the half of light from the light source lamp  411  for emitting random polarized light can not be used. 
     Accordingly, by using the polarization conversion element  415 , emitted light from the light source lamp  411  is converted into nearly one kind of polarized light to improve utilization efficiency of light in the optical device  44 . By the way, such polarization conversion element  415  is referred to, for example, in Publication of JP-A-8-304739. 
     The color separation optical system  42  can include two dichroic mirrors  421  and  422  and reflecting mirrors  423  and  424 , and can separate the plural pieces of partial luminous flux emitted from the integrator illumination optical system  41  into color light of three colors of red, green, and blue by the dichroic mirrors  421  and  422 . 
     The relay optical system  43  includes an entrance side lens  431 , a relay lens  433 , and reflecting mirrors  432  and  434 , and has a function of guiding the separated color light in the color separation optical system  42  and the red light to the liquid crystal panel  441 R. 
     At that time, in the dichroic mirror  421  of the color separation optical system  42 , a red light component and a green light component of the luminous flux emitted from the integrator illumination optical system  41  are transmitted, and a blue light component is reflected. The blue light component reflected by the dichroic mirror  421  is reflected by the reflecting mirror  423 , passes through a field lens  417 , and, after a polarized direction thereof is aligned by an entrance side polarization plate  442 , reaches the liquid crystal panel  441 B for blue. This field lens  417  converts the respective pieces of partial luminous flux emitted from the second lens array  414  into luminous flux parallel to the central axis (principal ray) thereof. Field lenses  417  provided on the light entrance sides of other liquid crystal panels  441 R and  441 G are the same. 
     Of the red light and the green light transmitted through the dichroic mirror  421 , the green light is reflected by the dichroic mirror  422 , passes through the field lens  417 , and, after a polarized direction thereof is aligned by the entrance side polarization plate  442 , reaches the liquid crystal panel  441 G for green. On the other hand, the red light is transmitted through the dichroic mirror  422 , passes through the relay optical system  43 , and further passes the field lens  417 , and, after a polarized direction thereof is aligned by the entrance side polarization plate  442 , reaches the liquid crystal panel  441 R for red. 
     Note that the relay optical system  43  is used for red light in order to prevent the reduction of the utilization efficiency of light due to diffusion of light and the like because the length of the optical path of the red light is longer than the optical path lengths of other color light. That is, so that the partial luminous flux that has entered the entrance side lens  431  may be sent to the field lens  417  without change. By the way, the construction for transmitting red light of the three color lights is adopted to the relay optical system  43 , however, not limited to that, for example, a construction for transmitting blue light may be adopted. 
     The optical device  44  is for forming a color image by modulating the entering luminous flux according to image information, and includes three optical modulation systems  44 R,  44 G, and  44 B into which the respective color lights separated in the color separation optical system  42  enters and a cross dichroic prism  445  as a color composition optical system for combining optical images modulated in the respective optical modulation systems  44 R,  44 G, and  44 B. 
     The respective optical modulation systems  44 R,  44 G, and  44 B include the liquid crystal panels  441 R,  441 G, and  441 B as optical modulation devices, the entrance side polarization plates  442  and viewing angle correction plates  443  as entrance side optical conversion elements disposed on the luminous flux entrance sides of these liquid crystal panels  441 R,  441 G, and  441 B, and exit side polarized plates  444  as exit side optical conversion elements disposed on the luminous flux exit sides of these liquid crystal panels  441 R,  441 G, and  441 B. 
     The liquid crystal panels  441 R,  441 G, and  441 B use polysilicon TFTs as switching elements, and, though omitted to be shown, constructed by enclosing and sealing liquid crystal within a pair of oppositely disposed transparent substrates. 
     The entrance side polarization plates  442  disposed in front stages of such liquid crystal panels  441 R,  441 G, and  441 B arc for transmitting the polarized light in a fixed direction of the respective color lights separated in the color separation optical system  42  and absorbing other luminous flux, and has substrates of sapphire glass etc. to which polarization films are attached. Alternatively, without using substrates, the polarization films may be attached to the field lenses  417 . 
     The viewing angle correction plate  443  has an optical conversion film having a function of correcting viewing angles of the optical images formed in the liquid crystal panels  441 R,  441 G, and  441 B of the optical modulation systems  44 R,  44 G, and  44 B formed on substrates, and by disposing such viewing angle correction plates  443 , the viewing angle of a projected image is enlarged and the contrast of the projected image is largely improved. 
     The exit side polarization plate  444  is for transmitting only the polarized light in a predetermined direction of the luminous flux optically modulated in the liquid crystal panels  441 R,  441 G, and  441 B and absorbing other luminous flux, and, in the example, the plate includes two plates of a first polarization plate (pre-polarizer)  444 P and a second polarization plate (analyzer)  444 A. The exit side polarization plate  444  is thus constituted by two plates because the entering polarized light is absorbed by the respective first polarization plate  444 P and second polarization plate  444 A while being divided appropriately, and thereby, the heat generated by the polarized light is divided appropriately by both polarization plates  444 P and  444 A to prevent overheating of the respective plates. 
     The cross dichroic prism  445  is for forming a color image by combining optical images emitted from the exit side polarization plates  444 . In the cross dichroic prism  445 , a dielectric multi-layer film for reflecting red light and a dielectric multi-layer film for reflecting blue light are provided substantially in an X-shape along the interfaces of four rectangular prisms, and the three color lights are combined by these dielectric multi-layer films. Then, the color image combined in the cross dichroic prism  445  is emitted from the projection lens  46  and magnification projected onto a screen. 
     The above described liquid crystal panels  441 R,  441 G, and  441 B, the viewing angle correction plates  443 , the first polarization plates  444 P and the second polarization plates  444 A are fixed to luminous flux entrance end surfaces of the cross dichroic prism  445  via panel fixing plates, which are not shown. 
     The above described respective optical systems  41  to  44  and  46  are accommodated in a housing for optical components (not shown) made of synthetic resin as a housing for optical components arranged substantially in the U-shape in a plan view. 
       FIGS. 4 and 5  are a perspective view and a plan view showing the positional relationship between a panel cooling device  50  and the optical device  44 .  FIG. 6  is a plan view of the panel cooling device  50 . The panel cooling device  50  is for introducing cooling air into the optical modulation systems  44 R,  44 G, and  44 B, and includes a duct  53  having two air guide paths  51  and  52  through which cooling air passes and sirocco fans  54  and  55  as two cooling fans for sending cooling air to the respective air guide paths  51  and  52 . 
     The duct  53  is integrally formed from synthetic resin substantially in the U-shape extending along the bottom face  231  of the lower case  23  and disposed below the optical unit  4 . This duct  53  is divided into the air guide path  51  and the air guide path  52  substantially at the center thereof as shown in  FIG. 6  by a dashed line. That is, the air guide path  51  extends from below the dichroic prism  445  constituting the optical unit to the right side of the projection lens  46  in  FIG. 6  substantially in the L-shape. The air guide path  52  extends from below the dichroic prism  445  to the left side of the projection lens  46  in  FIG. 6  substantially in the L-shape. Thereby, the extending directions of the air guide paths  51  and  52  are substantially orthogonal to the extending directions of the optical modulation systems  44 R,  44 G, and  44 B. 
     Here, in the air guide path  51 , entrance side discharge openings  61 G and  61 B that discharge cooling air to the luminous flux entrance sides of the liquid crystal panels  441 G and  441 B of the light modulation systems  44 G and  44 B are formed. Further, in the air guide path  52 , exit side discharge openings  62 G and  62 B for discharging cooling air to the luminous flux exit sides of the liquid crystal panels  441 G and  441 B of the light modulation systems  44 G and  44 B are formed. 
     Thereby, in the light modulation systems  44 G and  44 B, the entrance side discharge openings  61 G and  61 B and the exit side discharge openings  62 G and  62 B are formed in the different air guide paths  51  and  52 , and the luminous flux entrance sides and the luminous flux exit sides of the liquid crystal panels  441 G and  441 B are set as the targets of independent cooling to be independently cooled, respectively. 
     In addition, in the air guide path  52 , a discharge opening  61 R can be formed in which an entrance side discharge opening for discharging cooling air to the luminous flux entrance side of the liquid crystal panel  441 R of the optical modulation system  44 R and an exit side discharge opening for discharging cooling air to the luminous flux exit side thereof are integrated. Thereby, in the optical modulation system  44 R, the entrance side discharge opening and the exit side discharge opening thereof (i.e., the discharge opening  61 R) are formed in the same air guide path  52  and not set as the targets of independent cooling. 
     The respective entrance side discharge openings  61 G and  61 B are formed in positions for cooling luminous flux entrance surfaces of the liquid crystal panels  441 G and  441 B, the viewing angle correction plates  443 , and the entrance side polarization plates  442 . 
     Specifically, the entrance side discharge opening  61 G can be formed in a position offset to the upstream side of the air guide path  51  than the intersection of the extending direction of the optical components  441 G,  443 , and  442  and the air guide path  51  on a plane along the extending direction of the air guide path  51 . This is because, since the cooling air within the air guide path  51  is discharged in a direction rather near the downstream side from the entrance side discharge opening  61 G according to the law of inertia, the optical components  441 G,  443 , and  442  are located in the discharge direction of the cooling air. 
     The entrance side discharge opening  61 B is formed at the intersection of the extending direction of the optical components  441 B,  443 , and  442  and the air guide path  51  on a plane along the extending direction of the air guide path  51 . 
     The respective exit side discharge openings  62 G and  62 B are formed in positions for cooling luminous flux exit surfaces of the liquid crystal panels  441 G and  441 B and the exit side polarization plates  444 . 
     Specifically, the exit side discharge opening  62 G is formed in a position offset to the upstream side of the air guide path  52  than the intersection of the extending direction of the optical components  441 G and  444  and the air guide path  52  on a plane along the extending direction of the air guide path  52  for the same reason as that for the entrance side discharge opening  61 G. 
     The exit side discharge opening  62 B is formed at the intersection of the extending direction of the optical components  441 B and  444  and the air guide path  52  on a plane along the extending direction of the air guide path  52 . 
     The discharge opening  61 R is formed in a position for cooling a luminous flux entrance surface of the liquid crystal panel  441 R, the viewing angle correction plate  443 , and the entrance side polarization plate  442  on its luminous flux entrance side, and a luminous flux exit surface of the liquid crystal panel  441 R and the exit side polarization plate  444  on its luminous flux exit side. 
     Specifically, the discharge opening  61 R is formed at the intersection of the extending directions of the optical components  441 R,  442 , and  444  and the air guide path  52  on a plane along the extending direction of the air guide path  52 . 
     The sirocco fan  54  is disposed on the right side of the projection lens in  FIG. 6 , and introduces cooling air from the air intake port  231 C formed on the bottom face  231  of the lower case  23  through the lower surface and the side surfaces of the projection lens  46  into the air guide path  51 . The sirocco fan  54  is used as an entrance side cooling fan for sending cooling air to the air guide path  51  in which the entrance side discharge openings  61 G and  61 B of the optical modulation systems  44 G and  44 B as the targets of independent cooling are formed. 
     The sirocco fan  55  is larger scaled and sends a larger amount of air than the sirocco fan  54 , disposed on the left side of the projection lens in  FIG. 6  along the side face  232  of the lower case  23 , and introduces cooling air from the air intake port  232 B formed on this side face  232  into the air guide path  52 . The sirocco fan  55  is used as an exit side cooling fan for sending cooling air to the air guide path  52  in which the exit side discharge openings  62 G and  62 B of the optical modulation systems  44 G and  44 B as the targets of independent cooling are formed. 
     Next, the operation of the above panel cooling device  50  will be described. 
     The cooling air introduced from the air intake port  231 C by the sirocco fan  54  passes through the air guide path  51  and is discharged from the entrance side discharge openings  61 G and  61 B. The cooling air discharged from the entrance side discharge openings  61 G and  61 B cools the luminous flux entrance surfaces of the liquid crystal panels  441 G and  441 B, the viewing angle correction plates  443 , and the entrance side polarization plates  442 . 
     The cooling air introduced from the air intake port  232 B by the sirocco fan  55  passes through the air guide path  52  and is discharged from the exit side discharge openings  62 G and  62 B and the discharge opening  61 R. Of the air, the cooling air discharged from the exit side discharge openings  62 G and  62 B cools the luminous flux exit surfaces of the liquid crystal panels  441 G and  441 B and the exit side polarization plate  444 . The air discharged from the discharge opening  61 R cools the luminous flux entrance surface and the luminous flux exit surface of the liquid crystal panel  441 R, the entrance side polarization plate  442 , the viewing angle correction plate  443 , and the exit side polarization plate  444 . 
     The cooling air that has cooled the above optical components is collected by the exhaust sirocco fan, which is not shown, and exhausted from the exhaust port formed on the front face of the projector  1 . 
     According to the embodiment, the following effects can be obtained. Since the construction in which the luminous flux entrance sides and the luminous flux exit sides of the liquid crystal panels  441 G and  441 B are cooled with cooling air that has passed through different paths, the wind speed and the air flow of the cooling air may be adjusted in response to the respective generated amounts of heat. Thereby, the luminous flux entrance sides and the luminous flux exit sides of the liquid crystal panels  441 G and  441 B can be cooled on more suitable conditions, respectively, compared to the case of applying cooling air from the same path, and thus, the optical modulation systems  44 G and  44 B can be cooled with high efficiency while realizing miniaturization and reduction of the mounted number of cooling fans. 
     Since the discharge opening  61 R and the exit side discharge openings  62 G and  62 B are formed in the positions for cooling the liquid crystal panels  441 R,  441 G, and  441 B and the exit side polarization plates  444 , not only the liquid crystal panels  441 R,  441 G, and  441 B, but also the exit side polarization plates  444  which generates a larger amount of heat can be cooled by the discharged cooling air, and thereby, cooling efficiency can be made better. 
     Since the discharge opening  61 R with respect to the optical modulation system  44 R other than the target of independent cooling is formed in the air guide path  52 , the entrance side discharge opening and the exit side discharge opening can be provided in the same the air guide path  52 , and thereby the structure of the duct  53  can be simplified. 
     Since the entrance side discharge opening  61 G and the exit side discharge opening  62 G are formed on the positions offset to the upstream side of the intersections of the extending direction of the optical modulation system  44 G and the air guide paths  51  and  52 , the cooling air from the discharge openings  61 G and  62 G can be assured to be in contact with the optical modulation system  44 G, and thereby, the optical modulation system  44 G can be cooled smoothly. 
     Since, normally, the exit side polarization plate  444  generates a larger amount of heat than the entrance side polarization plate  442 , the sirocco fan  55  with higher cooling capability than the sirocco fan  54  is used, and thereby, the exit side polarization plate  444  and the entrance side polarization plate  442  can quickly be cooled, respectively. 
     Since the air intake ports  231 C and  232 B of the cooling fans  54  and  55  are formed on the two different faces of the exterior case  2 , respectively, cooling air outside the projector  1  can be introduced into the optical modulation systems  44 R,  44 G, and  44 B smoothly to further improve cooling efficiency. 
     As described above, the invention has been described by citing the preferable embodiment, however, it should be understood that the invention is not limited to the exemplary embodiment, and various improvements and design changes can be made without departing from the content of the invention. 
     For example, in the above embodiment, only the optical modulation systems  44 G and  44 B are set as the targets of independent cooling, however, not limited to that. That is, all of optical modulation systems  44 R,  44 G, and  44 B may be set as the targets of independent cooling, or any one of these optical modulation systems  44 R,  44 G, and  44 B may be set as the target of independent cooling. 
     Further, the size, performance, etc. of the sirocco fans  54  and  55  may be determined suitably according to the generated amounts of heat of the optical modulation systems  44 R,  44 G, and  44 B.