Abstract:
The projector apparatus of the invention constructs colored imaging light by splitting a beam of light received from a light source into beams of three primary colors and inputting the beams of three primary colors in an image synthesizing device via light adjusting means. The image synthesizing device includes a prism, a prism mount for fixing the prism, LCPs, and LCP holders integral with the prism mounts for fixing the LCPs. The prism mount has a central area and multiple peripheral areas, each area in contact with the prism. The invention provides effective means for solving reliability problems encountered in a cost reduction strategy for miniaturization of a prism and for using inexpensive plastic prism fixation members

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a projector apparatus for constructing imaging light to be projected onto a front screen by leading a beam of light from a light source to an optical system, and more particularly, to a projector apparatus adapted to construct colored imaging light by splitting a beam of light received from a light source into beams of three primary colors and inputting the beams of three primary colors in an image synthesizing device via light adjusting means. 
       BACKGROUND OF THE INVENTION 
       [0002]    A typical projector apparatus of this type is a liquid crystal (LC) projector having the following configuration. White light emitted from a light source is split into three beams of primary colors, blue (B), green (G), and red (R), which are used to illuminate three liquid crystal panels (LCPs). The light beams emerging from the respective LCPs are synthesized by a color synthesizing prism of an image synthesizing device to form a trichromatic imaging light, which is projected by projection mirrors onto a front screen. 
         [0003]    Since low-cost competition is very severe in the market of compact projector apparatuses, cost reduction effort for peripheral parts of an image synthesizing device is important. That is also the case with a prism alone. 
         [0004]    For example, although aluminum die-casting of a prism fixing member is customary, use of a resin material has emerged in recent years to reduce the cost of the prism fixing member. However, in order to ensure the same reliability of such plastic fixation member as that of conventional one, an appropriate fixation method must be invented. 
       SUMMARY OF THE INVENTION 
       [0005]    In view of the pending problem as stated above, it is an object of the invention to provide a cost-effective means for fixing a plastic fixation member for fixing a small-sized prism, and, at the same time, provide newly-designs peripherals of the prism. It is also an object of the invention to provide a projector apparatus equipped with such image synthesizing device having at least the same reliability as that of prior and existing device. 
         [0006]    A projector apparatus of the invention constructs colored imaging light by splitting a beam of light received from a light source into beams of three primary colors and inputting the beams of three primary colors in an image synthesizing device via light adjusting means, the image synthesizing device comprising: 
         [0007]    a prism; 
         [0008]    a prism mount for fixing the prism; 
         [0009]    LCPs; and 
         [0010]    LCP holders formed integral with the prism mount and adapted to fix the LCPs. 
         [0011]    In one embodiment, the prism mount has a central area and multiple small peripheral joint areas, each area in contact with the prism, thereby providing increased peel strength between the prism and prism mount in the range of 17-20 kgf. 
         [0012]    Specifically, the prism mount provides face-to-face contact to each of the LCP holders to effect positioning of the LCP holders on the prism mount at the time of assembly. Since each LCP holder is positioned under the face-to-face contact between the entire area of an associate side of the prism mount and the LCP holder, condensing (CG) displacement problem that arises from stress concentration in a conventional prism mount is prevented. 
         [0013]    In the embodiment shown herein, the prism mount and the LCP holders are fixed with screws that engage tapped holes formed in the prism mount at vertically offset positions. 
         [0014]    By vertically offsetting the tapped holes in this way, wear of the screws caused by unbalanced torsional moments of forces acting on the prism mount can be prevented. 
         [0015]    In the example shown herein, the prism mount is made of a resin material. This leads to cost reduction of the projector apparatus. 
         [0016]    Environment tests performed in a warehouse under a condition of 40° C./90% reveal the displacement of an image is in the range 0.8 to 1 pixel at the center of a projected image if the conventional image synthesizing device is used (i.e. without using the improved prism mount of the invention). However, if the invention is applied to the prism mount, the displacement of the image can be suppressed to 0.3 pixels or less. 
         [0017]    Thus, the invention provides an effective means for solving reliability problems encountered in a cost reduction strategy for miniaturization of a prism and fixation of the prism by inexpensive plastic prism fixation members. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view of an LC (liquid crystal) projector apparatus in accordance with the present invention. 
           [0019]      FIG. 2  is a perspective view of the LC projector apparatus shown in  FIG. 1 , with the upper half section of its casing removed. 
           [0020]      FIG. 3  is an exploded perspective view of the LC projector apparatus of  FIG. 1 , with the upper half section of the casing removed.  FIG. 4  is a perspective diagram in which showing the upper half section of the LC projector apparatus, and with the optical system of the projector apparatus were partially removed together with the power supply unit. 
           [0021]      FIG. 5  is a diagram showing the arrangement of the optical system of the LC projector apparatus. 
           [0022]      FIGS. 6 and 7  are perspective views of an image synthesizing device of the LC projector apparatus. 
           [0023]      FIG. 8  is an exploded perspective view of the image synthesizing device of the LC projector apparatus. 
           [0024]      FIGS. 9 and 10  are exploded perspective views of a prism, a prism mount, and LCP holders. 
           [0025]      FIG. 11  is a bird&#39;s eye view of the LC projector apparatus with its upper half section of the casing removed to show the internal arrangement of the LC projector apparatus. 
           [0026]      FIG. 12  is an exploded perspective view of the LC projector apparatus as seen from a lateral backward position, showing a cooling unit below the image synthesizing device. 
           [0027]      FIG. 13  is a perspective view of an exhaust duct associated with a first fan below a light source, showing air streams in the exhaust duct. 
           [0028]      FIG. 14  is a plan view of the cooling ducts for a fourth fan, distributed in the central region of the projector apparatus. 
           [0029]      FIG. 15  is a perspective view of a metal plate structure that extends above the light source. 
           [0030]      FIG. 16  is a top perspective view of a circuit board of the power supply circuit and an upper frame of a power supply unit as viewed from one side of the upper frame (the circuit board hereinafter referred to as power supply circuit board). 
           [0031]      FIG. 17  is a perspective view of the power supply circuit board having board fixation structures. 
           [0032]      FIG. 18  is a perspective view of the frame of the power supply unit as viewed upward from a lower lateral position. 
           [0033]      FIG. 19  is an enlarged view of a fixation member illustrated in  FIG. 18 . 
           [0034]      FIG. 20  shows the power supply circuit board mounted on the frame and fixed by elastic fixation members. 
           [0035]      FIG. 21  is a perspective diagram showing the internal structure of the projector apparatus, particularly elements associated with a light source protective cover of the invention. 
           [0036]      FIG. 22  is a front view of the side panel of the protective cover installed on one side of the light source of the projector apparatus, the figure showing the first fan and the light source located on the opposite sides of the side panel. 
           [0037]      FIG. 23  is a perspective view showing the protective cover and the light source assembled. 
           [0038]      FIG. 24  is an exploded perspective view of the protective cover and the first fan. 
           [0039]      FIG. 25  is an exploded perspective view of the protective cover and the light source. 
           [0040]      FIG. 26  is a partial projection view of the first fan. 
           [0041]      FIG. 27  shows an exhaust associated with the light source of the projector apparatus. 
           [0042]      FIG. 28  is an exploded perspective view of the protective cover and the first fan. 
           [0043]      FIG. 29  is an orthographic diagram of the light source protective cover. 
           [0044]      FIG. 30  is an exploded perspective view of a lamp fixation structure for fixing a lamp, showing its various components along with a lamp and a lens. 
           [0045]      FIG. 31  is another perspective view of the lamp fixation structure as viewed from an angle. 
           [0046]      FIG. 32  is a diagram showing a horizontal cross section of the lamp fixation structure. 
           [0047]      FIG. 33  is another diagram showing a horizontal cross section of the lamp fixation structure as viewed from another angle. 
           [0048]      FIG. 34  is a still another diagram showing another horizontal cross section of the lamp fixation structure as viewed from a still another angle. 
           [0049]      FIG. 35  is a perspective view of the LC projector apparatus as viewed backward. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0050]    The invention will now be described in detail by way of example, particularly an LC projector apparatus and related parts, with reference to the accompanying drawings. In what follows, the “front” side of the projector apparatus refers to the side thereof having its projection lens ( FIG. 1 ), and the “right” and “left” of the LC projector apparatus refer to the directions to the “right” and “left” relative to the front side, respectively. It should be understood that terms indicating relative positions of elements such as “bottom”, “side”, “oblique”, and “directly below” are illustrative, and that the relative positions can be conveniently altered as needed. 
       Overall Arrangement  
       [0051]    The LC projector apparatus is provided with a generally flat casing  1  which consists of an upper half section  11  and a lower half section  12 , as shown in  FIG. 1 . Provided on the upper end of the casing  1  is a controller  15  having a multiplicity of buttons for manual operation of the projector apparatus. Formed in the front end is a projection window  13 . Provided on the rear end of the casing  1  are exhausts, a power supply socket, and signal I/O device (not shown). 
         [0052]      FIG. 35  is a perspective view of the LC projector apparatus as viewed backward, showing a compound unit  251  provided on the rear end, which includes a D-SUB terminal to be connected with a computer and various external input terminals. Input terminals of the unit  251  can be molded. Each of them can be easily identified by the name, e.g. “AUDIO”, of the terminal engraved on the surface of the terminal. Thus, it is not necessary to print characters on the exterior of the casing, which enhances manufacturing efficiency and lowers the cost of the projector apparatus. 
         [0053]    As shown in  FIGS. 2 and 3 , the casing  1  accommodates therein a generally L-shaped plastic optical engine  7  that includes a lamp unit  4  serving as a light source, an optical system  2  ( FIG. 5 ) for splitting the white light received from the lamp unit into three beams of three primary colors (R, G, B beams); and an image synthesizing device  3  adapted to illuminate three LCPs (B-, G-, and R-LCP) with the B, G, and R beams to obtain imaging lights of three primary colors (B, G, and R imaging light) and synthesize them into a beam of tricolor imaging light. The lamp unit is arranged at the right end of the optical engine  7 , and the image synthesizing device  3  in the front end of the optical engine  7 . The optical system  2  is arranged on the optical path starting from the lamp unit to the image synthesizing device  3  of the optical engine  7 . 
         [0054]    There is provided in the casing  1  a cylindrical body  39   a  for holding a projection lens  39 , the base of which cylindrical body  39   a  is connected to the front end of the optical engine  7 , and a power supply unit  9  installed in front of the optical engine  7 . 
         [0055]    A cooling unit is mounted on the lower half section  12 , as shown in  FIGS. 3 and 4 . The cooling unit has a third fan  52  and a fourth fan  53  in the left area of the projector apparatus, a second fan  10  in the central area, and a first fan  6  in the right area. The third fan  52  and the fourth fan  53  are located below the image synthesizing device  3  to cool the image synthesizing device  3 . Formed in the bottom wall of the lower half section  12  is a bottom air intake window (not shown) for use with the first exhaust fan  52  and the fourth fan  53 . 
         [0056]    The structures of the components of the LC projector apparatus of the present invention will now be described in detail below. 
       Optical System  2   
       [0057]    The white light received from the lamp unit is led to a first dichroic mirror  26  via a first integrator lens  21 , a pre-stage light shielding lattice  23 , a second integrator lens  22 , a post-stage light shielding lattice  24 , a polarization prism substrate  25 , and a condenser lens  20 , as shown in  FIG. 5 . 
         [0058]    The first integrator lens  21  and second integrator lens  22  are fly-eye lenses made of a heat resistive glass, adapted to uniformize the illumination distribution of the while light emitted from the lamp unit. The pre-stage light shielding lattice  23  and the post-stage light shielding lattice  24  are thin aluminum films adapted to block incident light that is not wanted by the polarization prism substrate  25 . 
         [0059]    As shown in  FIG. 5 , the light that has passed through the polarization prism substrate  25  is collected onto the first dichroic mirror  26  by a condenser lens  20 . The first dichroic mirror  26  reflects only a blue component of light, letting red and green components of light pass through it, while a second dichroic mirror  27  reflects green component of light, and allows red component of light to pass through it. A field mirror  28  reflects green light. Thus, the white light emitted from the lamp unit is split by the first and second dichroic mirrors  26  and  27  into blue (B), green (G), and red (R) light, which are respectively led to the image synthesizing device  3 . 
       Image Synthesizing Device  3   
       [0060]    As shown in  FIGS. 6 and 7 , the image synthesizing device  3  includes a cubic color synthesizing prism  31 , a prism mount  30  having an upper prism mount  301  and a lower prism mount  302 , for fixing the prism, an LCP  33   b  for blue light, an LCP  33   g  for green light and an LCP  33   r  for red right (the three LCPs hereinafter referred to as B-, G-, and R-LCP, respectively) which are arranged on the respective three faces of the color synthesizing prism  31 , LCP holders  38   b ,  38   g , and  38   r  for securely fixing the respective B-, G-, and R-LCP. The LCP holders  38   b ,  38   g , and  38   r  are jointed to the prism mount  30  to form an integrated image synthesizing device. 
         [0061]    The image synthesizing device  3  is placed in the optical engine  7  through an opening  172  formed in the lid  7   a  of the optical engine  7 . 
         [0062]    The blue light reflected by the first dichroic mirror  26  and a field mirror  29   a  is led to a condenser lens  35   b , as shown in  FIG. 5 , and then to the color synthesizing prism  31 , via a blue incidence polarization plate  32   b , the B-LCP  33   b , and a blue emergence polarization plate  34   b.    
         [0063]    Similarly, the green light beam reflected by the second dichroic mirror  27  is directed to a condenser lens  35   g , and then led to the color synthesizing prism  31  via a green incidence polarization plate  32   g , the G-LCP  33   g , and a green emergence polarization plate  34   g.    
         [0064]    Similarly, the red light reflected by two field mirrors  28  and  29   b  are led to a condenser lens  35   r , and then to the color synthesizing prism  31  via a red incidence polarization plate  32   r , R-LCP  33   r , and a red emergence polarization plate  34   r.    
         [0065]    The three B, G, R beams led to the color synthesizing prism  31  are synthesized by the color synthesizing prism  31  into a beam of tricolor imaging light, which is projected by the projection lens  39  onto a front screen. 
         [0066]    As shown in  FIGS. 6 ,  7 , and  8 , the prism  31  is securely fixed by the upper and lower prism mount  301  and  302 , respectively. The LCP holders  38   b ,  38   g , and  38   r  are securely fixed to the upper prism mount  301  and the lower prism mount  302 . The B-LCP  33   b , G-LCP  33   g , and R-LCP  33   r  are securely fixed on the respective LCP holders  33   b ,  33   g , and  33   r . Normally, the B-LCP  33   b , G-LCP  33   g , and R-LCP  33   r  and LCP holders  33   b ,  33   g , and  33   r  are adjusted for correct condensation and focusing of the B-, G, R-light, and firmly fixed by soldering. 
         [0067]    As shown in  FIGS. 9 and 10 , the prism  31  is jointed to the prism mount  30  such that the upper and lower ends of the prism  31  are jointed to the corresponding joint surfaces  301 A,  301 B of the upper prism mount  301  and to the joint surfaces  302 A and  302 B of the lower prism mount  302 , respectively. The joint surfaces  301 A and  302 A correspond to the upper and lower central areas of the prism  31 , and the joint surfaces  301 B and  302 B correspond to the peripheral areas of the prism  31 . 
         [0068]    In conventional image synthesizing devices joint surfaces  301 A and  302 A are provided only in the central area of a prism mount, so that they have low peel strength. The image synthesizing devices  3 , now provided with additional small joint surfaces  301 B and  302 B on the periphery of the prism mount  30  near the prism  31  in accordance with the invention, has an improved peel strength of 20 Kgf or greater as compared with the original peel strength of 17 Kgf. In the example shown herein, a UV adhesive was used to bond the prism  31  to the joint surfaces  301 A,  301 B,  302 A, and  302 B. It is noted here that the dimensions and the distribution of the small joint surfaces  301 B and  302 B can be adjusted depending on the conditions of the joint surfaces. 
         [0069]    Referring again to  FIGS. 9 and 10 , it is seen that the prism  30  jointed to the LCP holders  38   b ,  38   g , and  38   r  by the threads of screws  3801 ,  3802 ,  3803 , and  3804  engaging corresponding threads of bores  301 E,  301 F,  302 E, and  302 F. Screws  3801  and  3802  are provided at suitable positions in the lower sections of the LCP holders  38   b ,  38   g , and  38   r . The threaded bores  301 E and  301 F are formed in the side of the upper prism mount  301 , and the threaded bores  302 E and  302 F are formed in the side of the lower prism mount, respectively. The threaded bores  301 E and  301 F are mutually offset in the vertical direction, so that they do conflict each other. 
         [0070]    When the prism mount  30  is made of a resin, if the lengths of the screws are not sufficiently long (for example, when the length is less than 6 mm for a 20 mm prism), unbalanced torsional moments of forces appear in the prism mount  30 , which moments can easily cause wear of the screws. Such wear advertently affects the production of the prism mount. In the invention, therefore, positions of the upper and lower threaded bores are offset from each other so that longer screws can be used. Although only a few of the threaded bores are shown in  FIGS. 9 and 10 , threaded bores are formed in all of the sides of the prism mount  30  and of the LCP holders  38   b ,  38   g , and  38   r  that are associated with each other. The number of the threaded bores can be changed depending on particular use conditions. 
         [0071]    Referring to  FIGS. 7 and 10 , positioning of the LCP holders  38   b ,  38   g , and  38   r  on the prism mount  30  will be described. Since three LCP holders  38   b ,  38   g , and  38   r  have a similar positioning structure, only the LCP holder  38   b  will be described below. It should be understood, however, that the remaining LCP holders  38   g  and  38   r  could have a similar positioning structure. The upper prism mount  301  and the lower prism mount  302  are provided with respective side  301 Z and side  302 Z that correspond to the respective sides  3905  and  3806  of the LCP holder  38   b , as shown. As seen in  FIG. 10 , when assembled, the side  301 Z is in contact with the mating side  3805 , and the side  302 Z in contact with the mating side  3806 . 
         [0072]    It is noted that in conventional structures, only the fixing screws fixed to the screw pillars of the prism mount are in contact with the LCP holders, so that the stresses created by the fixing screws concentrate in the screw pillars of the prism mount, thereby deforming the screw pillars. This deformation causes inadvertent effects in condensation of light by the optical system. In contrast, in the present invention, all the sides of the prism mount are in contact with the corresponding sides of the LCP holders, so that the stresses created by the fixing screws are distributed over all the sides, thereby reducing the concentration of the stresses. 
         [0073]    Utilizing this improved fixing configuration, the prism mount can be made of a resin to reduce the cost of the projector apparatus. 
         [0074]    Environment tests performed in a warehouse under a condition of 40° C./90% reveal the displacement of an image is in the range 0.8 to 1 pixel at the center of a projected image if the conventional image synthesizing device is used (i.e. without using the improved prism mount of the invention). However, if the invention is applied to the prism mount, the displacements of the condensed light can be suppressed to 0.3 pixels or less. 
       Cooling Unit  
       [0075]    As described previously, the cooling unit of the projector apparatus of the invention has the third fan  52  and fourth fan  53  in the left area of the projector apparatus, second fan  10  in the central area, and first fan  6  in the right area. Further details of the cooling unit will be given below. 
         [0076]      FIG. 2  shows the arrangement of a lamp unit  4  serving as the light source in proximity to the right wall of the lower half section  12  of the casing  1  of the projector apparatus, and a power supply unit  9  located away from the light source. The first fan  6  is installed between the lamp unit  4  and the power supply unit  9  with its inspiration face oriented to the power supply unit  9  and its expiration face to the lamp unit  4 . The expiration face of the first fan  6  is set at a predetermined angle with respect to the optical axis of the light source. The angle is most preferably 12 degrees. Further, the inspiration face of the first fan  6  is installed at an oblique angle relative to the power supply unit  9 . The oblique angle can be in the range from 5 to 30 degrees, and is preferably 12 degrees. 
         [0077]    As seen in  FIG. 2 , there are provided on the air expiration side of the first fan  6  vertical panels  61 ,  62 , and  63 , and a top panel  64 . The space surrounded by these panels and the bottom wall and the sidewalls of the casing serves as an exhaust duct. Air outlet sections of the sidewalls of the casing define two elongate exhausts  611  and  631 . (Similar exhausts are also defined in a corresponding section of the upper half section  11 .) The top panel  64  located above the exhaust duct serves as a baffle ( FIG. 2 ). The rear section of the baffle will be described in detail later. As will be clear from  FIG. 11 , the expiration face of the first fan  6  and the lamp unit  4  do not wholly overlap with each other, i.e. they are offset at a predetermined distance. That is, the first fan  6  is displaced relative to the lamp unit  4  towards the sidewall of the casing by a predetermined distance, so that only a portion of the air expired from the first fan  6  is blown to the lamp unit  4 . The rest of the air is blown to circumvent the lamp unit  4  and discharged from the exhaust duct. Formed on the opposite sides of the lamp unit  4  are openings  41  and  42  to introduce into the lamp unit  4  a portion of the air expired from the first fan  6  through the opening  41 . The air flows out of the lamp unit  4  through the opening  42 . In order to smoothly discharge the cooling air from the lamp unit  4 , it is necessary to set the angle of the exhaust duct in the range from 5 to 30 degrees. The angle of 12 degrees is particularly preferable. The angle of the exhaust duct can be defined to be the angle between the vertical plate  63  of the exhaust duct and the optical axis of the light source. Since the air expired from the first fan  6  is not totally passed through the high-temperature lamp unit  4 , the temperature of the exhaust air flowing out of the exhausts  611  and  631  of the casing is sufficiently low that it does not hurt the user of the projector apparatus. In this instance, the proportion of the air that is expired from the first fan  6  to the air allocated to the lamp unit  4  is about one half. 
         [0078]    In order to cool the power supply unit  9  through ventilation thereof, the air inspiration face of the first fan  6  is communicated with the hole  94  formed in the sidewall of the frame of the power supply unit  9 . Referring to  FIG. 4 , it is seen that the power supply unit is installed at a predetermined oblique angle with respect to the first fan  6 . The optimal oblique angle is 10 degrees. 
         [0079]    In order not to cause hot air to stagnate in the upper section of the first fan  6 , it is necessary to set up the first fan  6  higher than the lamp unit  4 . But in doing so, the overall height of the projector apparatus must be taken into account. As an example, the first fan  6  is raised by 5 mm. To do so, a mount structure for raising the lamp unit  4  may be provided to the exhaust duct under the lamp unit  4 . For example, a generally U-shaped pedestal  645  for raising the lamp unit  4  may be provided on the bottom of the casing, as shown in  FIGS. 12 and 13 . In the example shown herein, the height of the pedestal is set to 5 mm. The pedestal  645  is provided with openings  646  and  647  formed in the bottom wall of the exhaust duct and along the route of the exhaust duct for the first fan  6  so as to allow the exhaust air expired from the first fan  6  to be discharged through these openings towards the underside of the lamp unit  4 . In this way, if heat accumulates in the bottom section of the projector apparatus held upside down or hung during its use, the heat is easily and successfully discharged. 
         [0080]    Referring to  FIGS. 3 ,  4 , and  11 , it is seen that the second fan  10  is installed in the central area of the projector apparatus to inspire air inside the projector apparatus. Although the air in this area tends to stagnate, the second fan  10  facilitates exhaustion of the air by decreasing the inner pressure in this area. Referring particularly to  FIG. 11 , there are shown a cooling duct  101  that includes a multiplicity of bifurcating cooling ducts, provided on the air expiration side of the second fan  10 . Of these cooling ducts, a first bifurcating cooling duct  102  communicates mainly with the lamp unit  4 , and a second bifurcating cooling duct  103  communicates with the polarization prism substrate  25  of the optical system. Additional bifurcating cooling ducts that communicate with other components (including other optical elements) may be provided as needed, as shown in  FIG. 11 . For example, a third bifurcating cooling duct  104  communicates with the area between the light source and the polarization prism substrate  25  where the lens unit is arranged. 
         [0081]    As a result of the exhaustion of air by the first bifurcating cooling duct  102  and the first fan  6 , the lamp unit  4  is cooled that the exhaust air temperature will be low. The outlet of the second bifurcating cooling duct  103  has a shape adequate to cool the polarization prism substrate  25 . When the outlet is elongate, the air discharged therefrom flows along the bottom of the projector apparatus and across the polarization prism substrate  25 . The cooling air that has passed across the polarization prism substrate  25  can be used by the cooling unit placed near a power supply socket  205  ( FIG. 12 ). 
         [0082]    The exhaust ends of the first bifurcating cooling duct  102 , second bifurcating cooling duct  103 , and the third bifurcating cooling duct  104  have predetermined a real ratios and configurations according to the requirements of the elements to be cooled. 
         [0083]    Referring to  FIG. 12 , there is shown under the image synthesizing device  3  a cooling unit  5  for cooling the image synthesizing device  3 . The cooling unit  5  includes a third fan  52  and a fourth fan  53 . The ambient air inspired by the third and fourth fans  52  and  5 , respectively, is lead to the three LCP boards  33   b ,  33   g , and  33   r  and three polarization plates  32   b ,  32   g , and  32   r  shown in  FIG. 5  through associated ducts. The third fan  52  and the fourth fan  53  are installed such that the streams of air expired from them intersect each other. 
         [0084]    In the embodiment shown herein, the air sent from the third fan  52  is partly blown to the blue incidence polarization plate  32   b  and B-LCP  33   b , and partly to the red incidence polarization plate  32   r  and R-LCP  33   r . The air sent from the fourth fan  53  is partly blown to the green incidence polarization plate  32   g , and G-LCPs  33   g , and partly to the red incidence polarization plate  32   r  and R-LCP  33   r.    
         [0085]    In conventional projector apparatuses, a cooling unit has three dedicated cooling fans one for each of the R-, G-, B-LCPs. In the inventive LC projector apparatus, the cooling unit has only two cooling fans  52  and  53 , which suffice to cool the incidence polarization plates  32   r ,  32   g , and  32   b  and the LCPs  33   r ,  33   g , and  33   b . In this way, a space for one cooling fan is cut down, which can be advantageously utilized for minimization of the projector apparatus. Further, the total operating power consumption of the projector apparatus can be also reduced by the amount that would be otherwise consumed by the cooling fan. 
         [0086]    In addition, the LCP projector apparatus of invention has a low power consumption mode where the intensity of light of the lamp unit  4  is reduced to a lower level. In the low power consumption mode, the rotational speeds of the first and second exhaust fans  52  and  53 , respectively, can be reduced to further reduce the noise level of the exhaust unit. 
       Upper Metal Panel Structure Above Light Source  
       [0087]    Referring to  FIGS. 2 and 3 , the projector apparatus of the invention has a metal plate structure in the form of a top panel  64  extending over the light source. The top panel  64  covers the upper part of the lamp unit  4  serving as the light source. The top panel  64  is located adjacent the upper section of the expiration face of the first fan  6 , and forms the baffle of the exhaust duct for the first fan  5 . 
         [0088]    The top panel  64  is configured to exactly fit the top end of the lamp unit  4 , and has a multiplicity of cut sections in the two edges thereof adjacent to the casing. The top panel  64  also has a multiplicity of ribs  641  and  641  of different widths. The top panel  64  is made of copper or aluminum, so that it has good heat radiation performance. It can be made of any alternative metal having good heat radiation performance. It radiates heat generated by the light source during operation, and, particularly afterheat of the light source after the cooling fans are stopped. 
         [0089]    Provided at the periphery of the top panel  64  are curved pawls  644  for positioning the top plate  64 . In the example shown herein, the top panel  64  is assembled on top of the frame of the first fan (i.e. on the vertical plate  61  of the exhaust duct) by pawls  644  and projections. (See also  FIGS. 11 and 15 .) 
         [0090]    In addition to radiating heat generated by the light source, the metal plate structure shields the electromagnetic radiation from the lamp of the light source. Owing to the metal plate structure, the casing of the projector apparatus can be made of a resin, without coating it with an electroplated metal layer. When the metal plate structure is used as a shield plate, it is necessary to connect it with a grounded metal member. It is noted that the top plate can be formed of a non-metallic material and coated with an electroplated metal layer when it is used as a shield plate. Referring to  FIG. 2  again, there is shown on top of the top panel  64  a further top shield plate  643 , which is jointed to a power supply shield case  924  located on the air inspiration side of the first fan and the vertical metal plate  63  of the exhaust duct for the lamp unit  4 . (See also  FIG. 11 .) The vertical metal plate  63  and the grounded metal member  206  of the power supply socket  205  are jointed to serve as the shield plate. (See also  FIGS. 11 and 15 .) 
         [0091]    In addition to the top panel  64 , the metal plate structure may include a latticed lateral panel  60 a, which is perpendicular to the top panel  64  and extends to above the air expiration face of the first fan  6 , all integrated together. (See also  FIGS. 24 and 25 .) The lateral panel  60   a  constitutes a part of the exhaust duct for the first fan  6 , facilitating exhaustion of air and protection of the first fan  6 . 
       Fixation Structure of Power Supply Circuit Board  
       [0092]    Referring to  FIG. 3 , the frame of the power supply unit  9  in accordance with one embodiment consists of a lower frame  91  in contact with the bottom of the casing and an upper frame  92  located above the lower frame  91 . Each of the lower and upper frames  91  and  92 , respectively, is substantially rectangular in shape. 
         [0093]      FIGS. 14 and 16  are bird&#39;s eye views of the respective frames as viewed from above and one side of the frame, respectively.  FIG. 17  is an oblique perspective view, of the entire power supply unit  9 . As seen in this figure, the power supply circuit board includes a bottom power supply board  111  ( FIGS. 14 and 16 ) mounted on the lower frame  91 , and a top power supply board  112  ( FIG. 17 ) mounted on the upper frame  92 . In the embodiment shown herein, the bottom power supply board  111  is used as a power supply board for the light source. The top power supply board  112  is used to supply electricity to various components of the projector apparatus. The lower frame  91  is provided on each of the longer sidewalls  911  and  912  thereof with two fixation members  913 . The fixation members  913  are connected at the top end thereof to the surface of the bottom power supply board  111 , and securely fix the bottom power supply board  111  to the lower frame  91 . 
         [0094]      FIG. 18  is a perspective view of the frame as viewed upward from one side thereof. As seen clearly in  FIG. 17 , the fixation members  913  are formed on the sidewalls  911  and  912 , near the bottom of the lower frame  91 . 
         [0095]    Referring to  FIGS. 16 through 18 , the area of the upper opening of the lower frame  91  is smaller than the bottom area of the upper frame  92 . To securely fix the top power supply board  112  ( FIG. 17 ) in proximity to the upper opening of the upper frame  92 , two elastic fixation members  920  are formed on each of the shorter side walls  918  and  919  of the upper frame  92 . These fixation members  920  are the same in structure as the fixation members  913  formed on the lower frame  91 . Alternatively, fixation members in the form of inclined protrusions  920  as shown in  FIG. 17  are engaged with the top power supply board  112  to fix it near the top end of the upper opening of the upper frame  92 . 
         [0096]    In this embodiment, the lower frame  91  and the upper frames  92  are resin parts that can be integrated. The fixation members  913  and  920  are integrally formed on the respective sidewalls  911  and  912  and on the sidewalls  918  and  919 , extending therefrom in oblique directions toward the bottom of the casing.  FIG. 17  shows openings  914  formed in the sidewalls  911  and  912 , which is shaped to match the shape of the fixation members  913  and allows the fixation members  913  to depend in the openings  914  (See also  FIG. 18 ).  FIG. 19  is an enlarged view of a fixation member  913 , showing that the fixation member  913  extends downward and that its thickness increases downward. It is seen in  FIG. 19  that the thickness of each fixation member  913  becomes largest at the lowest end  916  thereof and that the fixation member  913  has a generally L-shaped upward step  917  formed on the lowest end  916 . 
         [0097]    Referring to  FIGS. 16 and 17 , there are shown projections  922  and  923  for joining the power supply unit to the casing, formed on the outer surfaces of the opposite sides of the upper frame  92 . 
         [0098]    To mount the bottom power supply board  111 , it is inserted into the lower frame  91  through the upper opening of the lower frame  91 . As it is pushed inward past the resilient fixation members  913 , the fixation members  913  are compressed outward by the edges of the bottom power supply board  111 . When the bottom power supply board  111  reaches the bottom of the casing past the fixation members  913 , the fixation members  913  will restore their original configurations. Thus, the L-shaped upward steps  917  of the lower ends  916  of the four fixation members  913  resiliently engage the edge of the bottom power supply board  111 , thereby securely fixing the bottom power supply board  111  to the lower frame  91 . In the event that the bottom power supply board  111  needs to be removed for repair, for example, the bottom power supply board  111  may be pushed against the side walls having the fixation members  913 , until the bottom power supply board  111  is released from the fixation members  913 . The top power supply board  112  can be mounted on, and dismounted from, the lower frame  91  in the same manner. 
       Lamp Fixation Structure  
       [0099]    First, the lamp fixation structure of the invention will be overviewed. 
         [0100]      FIG. 30  is an exploded perspective view of a lamp fixation structure, illustrating how its various components, the lamp  100  of the lamp unit  4 , and a lens  40  are assembled together. Referring to  FIGS. 30 through 34 , the lamp fixation structure has a metal holder  50 , a lower holder  70 , and an upper holder  80 . The lower holder  70  has a lower holder lens section  710  and a lower holder lamp section  720  which are integrally formed. The lower holder lamp section  720  is provided with a lamp fitting slot  720 A for fitting therein a lamp. The lower holder lens section  710  is provided with a lens fixing slot  710 A for fitting therein a lens. The upper holder  80  is located above the lamp  100  and fixed together with the lower holder  70 . The upper holder  80  has a top end section  81  and a lateral section  82 . As shown in  FIG. 30 , the lamp  100  does not have a lamp case but is accommodated in the metal holder  50 , which exerts elastic forces on the lamp to firmly hold it in position. As is clearly shown in  FIG. 30 , the front portion of the lamp case  110  oriented to the lens  40  is fitted in the metal holder  50 . The upper holder  80  is located above the metal holder  50  and the lower holder  70 , without being fixed to the lower holder  70 .  FIG. 30  shows the metal holder  50 , lamp  100 , and lens  40  prior to assembly on the lower holder lamp section  720  and on the lower holder lens section  710 . 
         [0101]    The lower holder lens section  710  will now be described in detail with reference to  FIG. 30  and  FIGS. 32 through 34 . These figures clearly show details of the lower holder lens section  710 . 
         [0102]    A lens fixing slot  710 A is provided in the lower holder lens section  710 , in which slot the lens  40  is fitted in the process of assembly. As shown in  FIGS. 32 through 34 , each side of the lower holder lens section  710  has at least one thin protrusion  715  adapted to form an annular rim that intimately fits the lens  40 . The protrusions  715  can be omitted or replaced by other forms of fixation members for firmly fitting the lens  40  in the lens fixing slot  710 A. Each side of the lower holder lens section  710  is further provided with an inwardly protruding rib  716 . The rib  716  protrudes further than the protrusions  715  to facilitate fitting the lens  40  in the lens fixing slot  710 A in placing the lens  40  in the groove  710 A. The protruding rib  716  is useful in assembling the metal holder  50 , as described below. 
         [0103]    As shown in  FIG. 32 , an opening  713  facing the lens  40  is formed in the front end  712  of the lower holder lens section  710 . Since the lens  40  is substantially circular in shape, so is the opening  713 . Obviously, if the lens has a different shape, correspondingly so does the opening  713  also a different shape. Further, the diameter of the opening  713  is smaller than that of the lens  40  so that the lens  40  is firmly fixed by the inner surface of the opening  713 , protrusions  715 , and protruding rib  716  in the fitting groove  719 A. 
         [0104]    The lower holder lamp section  720  will now be described below. 
         [0105]    Referring to  FIG. 30  and  FIG. 32 through 34 , the lower holder lamp section  720  and the lower holder lens section  710  are integrally formed. In the most preferred mode of the invention, the lower holder  70  is made of a polymer material (synthetic resin). The lower holder lamp section  720  and the lower holder lens section  710  of the lower holder  70  are integrally formed by pouring a melt plastic into a mold. Alternatively, they can be formed by other processes such as machining, soldering, and welding. The lower holder lamp section  720  is used only as the slot for receiving a lamp as shown. The lower holder  70  is most preferably molded using a resin such as a polyethylene compound, but it can be also fabricated by any other material such as a metal, alloy, and non-organic material. 
         [0106]    An opening  722  is formed in each of the opposite side walls facing the lower holder lamp section  720  to send cooling air to the lamp  100 . The size, shape, and location of each opening  722  are arbitrary so long as the opening facilitates airing of the lamp  100  while providing the lower holder lamp section  720  with sufficient strength. Obviously, the number of the openings  722  is not limited to two. For example, such opening  722  can be provided in each of the sidewalls. 
         [0107]    Referring to  FIGS. 30 and 31 , the upper holder  80  will now be described below. 
         [0108]    The upper holder  80  is provided with the top end section  81  and a lateral section  82  covering the lamp  100  as shown. When assembled, the upper holder  80  is jointed to the lower holder  70 . The top end section of the upper holder  80  is located above the lamp  100 . The lateral section  82  is arranged on one side of the lamp  100 . The upper holder  80  is most preferably made of a plastic material. The top end section  81  and the lateral section  82  are integrally formed by molding, but they can be alternatively jointed by other means such as welding. The top end sections have holes  811  and struts  812 . The role of the struts  812  is to fasten corresponding portions of the top end section  81  and the lower holder  70  by means of screws or other fixation members. The lateral section  82  is also provided with a multiplicity of holes  821 . The holes  811  and  821  are used to fit corresponding portions of the upper protective cover and the top panel  64 . 
         [0109]    The metal holder  50  of the invention will now be described in detail with reference to  FIGS. 30 through 34 . Since the lens  40  and the light source have dimensional tolerances, they need to be fixed using resilient metal frames. 
         [0110]      FIG. 30  clearly shows the entire metal holder  50 . The metal holder  50  is fabricated from a machinable thin sheet metal of, for example, stainless steel, aluminum, and copper or an alloy. The metal holder  50  has an elastic top plate  50   a , two facing elastic lateral plates  50   b , a front plate  50   c , an elastic bottom piece  50   e , and two pieces of elastic jointing plate  50   d . The front plate  50   c  is provided with an opening  55  for allowing the light emitted from the lamp  100  to pass through it to the lens  40 . 
         [0111]    Although the top piece elastic piece  50   a , two elastic lateral plates  50   b , and the bottom elastic plate  50   e  are separate pieces, they are integrated with the front plate  50   c , advantageously jointed thereto at an angle, e.g. at about a right angle. In this way, an elastic frame for the lamp case  110  is formed. The shape and dimensions of the elastic frame described above should basically match those of the lamp case  110  of the lamp  100 . However, the dimensions of the elastic frame are preferably slightly larger than those of the lamp case  110  near the opening of the lamp case  110 , but slightly smaller near the front plate  50   c . Therefore, as the lamp case  110  of the lamp  100  is inserted into the elastic frame towards the front plate  50   c , the four elastic plates  50   a ,  50   b , and  50   e  are deformed so as to firmly fix the lamp case  110  in position. 
         [0112]    Referring to  FIG. 30 , the two elastic jointing plate  50   d  are integrally formed on the metal holder  50 . They are jointed to the front plate  50   c . These elastic jointing metal pieces  50   d  are simultaneously inserted in the lens fixing slot  710 A, and along the ribs  716 , together with the metal holder  50  into the lamp fitting slot  710 A. Then the elastic jointing plate  50   d  are slightly deformed, pressed against the lens  40 , and in intimate contact with the lens  40 . 
         [0113]    A multiplicity of venting holes  520  are formed in the two elastic lateral plates  50   b  of the metal holder  50  such that the venting holes  520  face the opening  722  when assembled. These venting holes  520  allows air that has passed through the opening  722  to further pass through them to the lamp unit  4 , thereby facilitating ventilation and heat dissipation of the lamp unit  4 . There is no restriction to the number, dimensions, or shapes of the venting holes  520 . They can be circular, polygonal, oval, or slit. In one preferred mode of the invention, the venting holes  520  have circular shapes. As is well known to persons skilled in the art, additional vents can be advantageously provided as needed not only in the lamp unit region but also in other regions of, for example, the metal holder  50  for enhanced ventilation and heat dissipation. 
         [0114]    As shown in  FIG. 30 , the metal holder  50  also functions as a shield for blocking light from the light source, in addition to fixing the lens  40  and the light source and effectively venting and cooling them. Thus, the metal holder  50  prevents the upper and lower frames  80  and  70  from being directly heated by light to a high temperature, thereby preventing the light from destroying cooling effect of the ventilation. 
         [0115]    The assembly of the lamp fixation structure of the invention will now be described. The lamp fixation structure can be assembled in the following order. First, the lens  40  is inserted in the lens fixing slot  710 A of the lower holder  70 . Second, the metal holder  50  is forced, along the protruding rib  716  formed on the opposite sides of the lens fixing slot  710 A, into the lower holder  70 , thereby fringing the elastic jointing plate  50   d  of the metal holder  50  in the lens fixing slot  710 A and in intimate contact with the lens  40  to firmly fix the lens  40  in position. Third, the lamp case  110  for the lamp  100  is inserted in the metal holder  50  and then pushed into the lamp fitting slot  20 A of the lower holder  70  together with the metal holder  50 . Next, a cover is placed over the upper holder  80 . The covered upper holder  80  is then firmly fixed with screws or any other convenient fixation members to the lower frame. Assembly of the lamp fixation structure of the invention is completed in this way. 
         [0116]    The lamp fixation structure of the invention has many distinct advantages. For example, the lamp fixation structure of the invention can not only simplify fabrication and assembly thereof but also reduce the fabrication and assembly cost as well as assembly time of the lamp fixation structure. Particularly, integral formation of the metal frame can no only simplify fabrication and assembly of the lamp fixation structure but also reduce the fabrication and assembly cost as well as assembly time, as compared with conventional lamp fixation structures. Further, lamp replacement and the general maintenance of the lamp fixation structure require less time. Still further, the lamp and the lens can be securely fixed in position. 
         [0117]    In short, the inventive lamp fixation structure of the projector apparatus consists of a fewer components and can be assembled in a simple manner. Furthermore, it is highly wrought. The components are designed with consideration especially to better fixation of the lamp and the lens. This point is an advantage of the inventive lamp fixation structure over conventional lamp fixation structures. 
       Light Source Protective Cover  
       [0118]    Referring to  FIG. 21 , there is shown the internal structure of the projector apparatus equipped with the power supply unit  9  and the light source  4 . To cool the lamp, the first fan  6  first blows air to the power supply unit  9 , from where the air is blown into the light source  4 , from where the air is exhausted by exhausts  631  and  611 , as shown in  FIGS. 21 and 27 . In order to better cool the light source, the light source  4  is exposed in the exhaust duct for the first fan  6 . 
         [0119]    Referring to  FIGS. 21 through 23 , and  FIG. 29 , the top area and one lateral side of the light source  4  are covered with an L-shaped protective cover  60 . The L-shaped protective cover  60  has an integral structure consisting of a lateral panel  60   a  and a top panel  64 . The lateral panel  60   a  is installed between the light source  4  and the first fan  6 . The top panel  64  covers upper end of the light source  4 . Preferably, the lateral panel  60   a  and the top panel  64  are substantially perpendicular to each other, so that the protective cover  60  has a substantially L-shaped transverse cross section. 
         [0120]    First, the lateral panel  60   a  of the protective cover  60  will be described below. 
         [0121]    Referring to  FIGS. 24 and 25  and  FIGS. 28 and 29 , details of the arrangement of the protective cover  60 , first fan  6 , and light source  4  are shown. In operation the light source  4  generates a large amount of light and radiant heat. In order to ensure normal operation of the light source  4 , the first fan  6  is oriented such that the air expired therefrom is passed through the exhaust duct for the light source  4 . The lateral panel  60   a  is provided between the first fan  6  and the light source  4 , that is, it is installed at a location where light from the light source passes through the duct for the light source  4  if not blocked by the lateral panel  60   a . The lateral panel  60   a  has a multiplicity of vertical openings  600   a . As shown in  FIG. 24 , the openings  600   a  are separated by vertical strip  601   a  and the horizontal strips  602   a . The lateral panel  60   a  is formed as a latticed structure. The widths of the openings  600   a  is sufficiently narrow so that, should a worker who is assembling, disintegrating, or doing maintenance put his finger unintentionally in between the light source  4  and the lateral panel  60   a , the finger will not enter the opening  600   a  and touch the fins of the first fan to get hurt. The width d 1  of each opening  600   a  is usually set in the range from 6 to 8 mm, and most preferably, set to 8 mm. The width d 2  of each vertical strip  601   a  is usually set to 3 mm. 
         [0122]    Referring to  FIGS. 24 through 26 , and  FIG. 34 , a central light shield  603   a  is provided at the center of the lateral panel  60   a . The central light shield  603   a  is substantially circular in shape. When assembled, the central light shield  603   a  faces the first fan  6  to completely blot out the motor  6   a  of the first fan  6 . Mounted on the central light shield  603   a  is a light shielding piece  604   a  having the same size and the same shape as the central light shield  603   a . The light shielding piece  604   a  is preferably colored black to absorb light impinging thereon from the light source. One of the purposes of providing the black central light shield  603   a  is to absorb the light that has leaked from the light source  4  and would otherwise directly impinge on the motor  6   a  of the first fan, to thereby prevent the motor  6   a  of the first fan from being heated to an inoperably high temperature by the light. It would be obvious to a person skilled in the art that, to blot out the motor  6   a  of the first fan, the central light shield  603   a  can be of any size and any shape. It would be also obvious to a person skilled in the art that the openings  600   a  can also be of any shape, e.g. circular, polygonal, slit, etc. or elongate in the horizontal direction. The manners of installation of the openings  600   a  can be also modified. That is, the openings can be arbitrarily modified in shape and/or manner of installation to protect fingers from the openings, so long as the modified openings permit good ventilation by the first fan. 
         [0123]    The top panel  64  of the protective cover  60  will now be described below. Referring to  FIGS. 23  though  25 , details of the top panel  64  of the protective cover  60  are shown. 
         [0124]    The top panel  64  is installed above the upper end of the light source  4 . The top panel  64  has ribs  641  and  642 , which are jointed to surrounding structures to firmly fix the top panel  64  in position. One of the purposes to provide the top panel  64  is to shield light that has leaked from the light source  4  and directly impinges on the exterior of the projector apparatus. Further, since the top panel  64  is metallic, it is capable of shielding ambient electromagnetic radiation. Thus, the projector apparatus of the invention complies with the EMC regulations. 
         [0125]    The top panel  64  and the lateral panel  60   a  of the protective cover  60  are preferably integrally formed from a sheet metal using a press machine. Thus, not only the fabrication but also assembly of the protective cover  60  is achieved in a simple manner with a reduced manufacturing cost. Of course, the top panel  64  and the lateral panel  60   a  can be formed as independent parts that can be jointed or assembled later to form the protective cover  60 . The protective cover is typically manufactured from a sheet metal of, e.g. steel, aluminum, stainless steel, or alloy, but it may be manufactured from other materials including heat-resistive polymers and non-organic materials covered with a heat-conductive and radiation-shielding metal layer formed by electroplating, chemical plating, brushing, etc. 
         [0126]    By applying the invention, it is possible to protect relevant components such as a motor of a first fan from light that has leaked from the light source, and at the same time establish an open cooling system, thereby preventing the relevant components from being heated to a high temperature. In this way, the invention can provide durable and cost effective exhaust fans, avoiding use of expensive high-temperature-tolerant exhaust fans. 
         [0127]    Based on the description above, a person skilled in the art can provide a protective cover  60  capable of effectively shielding and absorbing light (or heat) radiated from the light source  4  and dissipating the heat, thereby providing a projection apparatus that complies with the EMC regulations.