Abstract:
It is proposed to provide a projection apparatus capable of displaying an image by eliminating or reducing the influence of dust. The projection apparatus for projecting image information on a display surface such as a screen, comprises a dust preventive structure (prevention from attaching a foreign substance) of dusting main apparatus members such as an optical modulation device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a projection apparatus and, more particularly, to a projection liquid crystal projector for enlarging and projecting, on a screen or the like, image information displayed on an optical modulation device such as a color liquid crystal panel. 
     2. Related Background Art 
     A variety of conventional color liquid crystal projectors have been proposed as optical modulation devices to display image information on liquid crystal panels and enlarge and project the image information on screens. 
     FIGS. 9 and 10 show a projection liquid crystal projector described in Japanese Utility Model Publication No. 5-950. 
     Referring to FIGS. 9 and 10, a case  1  is divided into two chambers through side walls  4  and  5 . A light source  9  is arranged in a rear-side chamber  2 , and a liquid crystal display drive unit is arranged in a front-side chamber  3 . Openings  6  and  7  are formed at the central portions of the side walls  4  and  5 . Transparent plates  6   a  and  7   a  made of heat-resistant glass are fitted in the openings  6  and  7 . A plurality of vent holes  8  are formed in the outer surface of the case between the side walls  4  and  5 . 
     The light source  9  is located at a position opposing the openings  6  and  7  of the side walls  4  and  5  and comprises a lamp  10  and a reflecting mirror  11 . The lamp  10  is connected to a power circuit board  12  having a power transformer  13  and a transformer coil  14  through lead wires  15 . A polarizing separation prism  16  is arranged in front of the light source  9  to separate light reflected by the reflecting mirror  11  into S- and P-polarized light components. The P-polarized light component passes through the polarizing separation prism  16  and enters a liquid crystal panel  19  of a liquid crystal display drive unit in the front-side chamber  3 . The S-polarized light component is guided to the side surface of the polarizing separation prism  16  and emerges from an exit port  17 . 
     Heat dissipation slits  18  are formed in the upper, lower, and side surfaces of the rear-side chamber  2  containing the light source  9 . Heat from the lamp  10  is dissipated through the heat dissipation slits  18  and the exit port  17 . 
     A display panel cooler  20  through which the P-polarized light component pass is located at a position opposing the opening  7  in the front-side chamber  3  which accommodates the liquid crystal display drive unit. The P-polarized light component of the beam from the lamp  10  in the light source  9  passes through the display panel cooler  20  and is incident on the liquid crystal panel  19 . The liquid crystal panel  19  is connected to a main circuit board  23  through a panel drive circuit board  24  made of a flexible board. A Fresnel lens  21  is spaced apart from the front surface of the liquid crystal panel  19 . A projection lens  22  for projecting the beam focused by the Fresnel lens  21  is hold on the front surface side of the case  1  at a position in front of the Fresnel lens  21 . Heat dissipation slits  25  are formed in the front and upper surfaces of the front-side chamber  3  incorporating the above components, as in the rear-side chamber  2 . 
     An open space is formed between the liquid crystal panel  19  and the Fresnel lens  21  in the conventional liquid crystal projector described above. The heat dissipation slits  25  formed in the case  1  prevent dust from entering into the apparatus. Since the drive voltage generates static electricity on the surface of the liquid crystal panel  19  driven by the panel drive circuit board  24 , the dust is attracted to the surface of the liquid crystal panel  19 . As a result, an image enlarged and projected by the projection lens  22  through the Fresnel lens  21  contains an enlarged image of dust, so a high-quality image cannot be obtained. 
     The heat dissipation slits  18  are also formed in the rear-side chamber  2  for the light source  9  as in the heat dissipation slits  18 , and dust enters through the heat dissipation slits  18 . The dust attaches to the reflecting mirror  11 , the polarizing separation prism  16 , and the like to greatly decrease the brightness of the projector. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the conventional problems described above, and has as its object to provide a projection apparatus capable of displaying an image by eliminating or reducing the influence of dust. 
     In order to achieve the above object, there is provided a projection apparatus for projecting image information on a display surface such as a screen, comprising a dust preventive structure (prevention from attaching a foreign substance) of dusting main apparatus members such as an optical modulation device. 
     According to an aspect of the present invention, there is provided a projection apparatus comprising a display device, a projection optical system for projecting, on a display surface, an image obtained by the display device, and preventive means for preventing a foreign substance from attaching to a surface of the display device. 
     This projection apparatus is a single-plate monochrome or three-plate full-color image projection apparatus in which the projection optical system comprises a field lens and a projection lens in the order named from the display. device side, and the preventive means comprises sealing means for sealing a space formed between the field lens and the display device. 
     The present invention discloses the following arrangement. The preventive means comprises the field lens, a lens barrel for holding the field lens, and a seal ring. 
     The present invention discloses the following arrangements. The display device comprises three liquid crystal panels for forming red, green, and blue images. The projection optical system comprises a projection lens and three field lenses located in front of one of the three liquid crystal panels. The projection lens is one lens system shared by three pairs of liquid crystal panels and field lenses. The preventive means has sealing structures for sealing the spaces between the field lenses and the display device. Each sealing structure comprises the field lens, a lens barrel for holding the field lens, and a seal ring. 
     The present invention further comprises an illumination optical system for supplying red, green, and blue beams which illuminate the three liquid crystal panels. The illumination optical system comprises a trimming filter for each of red, green, and blue. 
     The present invention discloses the following arrangement. The trimming filter is located to seal the space between the field lens and itself. 
     According to another aspect of the present invention, there is provided a projection apparatus in which color separation means color-separates a beam from light source means into a plurality of color beams, lens means focuses the color-separated beams, first deflection means is arranged near-the focal position to irradiate optical modulation devices with the focused beams through field lenses, and second deflection means and a projection optical system project image information based on each optical modulation device to a desired position, wherein dusting structures are respectively arranged between the optical modulation devices corresponding to the plurality of color beams and the field lens opposing the optical modulation devices. Dust can be prevented from attaching to the optical modulation devices, and therefore a high-quality image free from the influence of dust can be projected. 
     According to still another aspect of the present invention, there is provided a projection apparatus in which color separation means color-separates a beam from light source means into a plurality of color beams, lens means focuses the color-separated beams, first deflection means is arranged near the focal position to irradiate optical modulation devices with the focused beams through field lenses, and second deflection means and a projection optical system project image information based on each optical modulation device to a desired position, wherein the deflection means, the field lenses, and the optical modulation devices are mounted and fixed respectively at predetermined positions in a substantially box-like structure, a light guide opening is formed near the deflection means located at substantially the center of the box-like structure, and the opening is closed with a trimming filter of each color beam to obtain a dusting structure. Even if duct enters from the vent holes due to heat dissipation from the optical modulation devices and light source serving as heat sources, the dust can be prevented from attaching to the optical modulation devices and the like. Therefore, a high-quality image free from the influence of dust can be projected. 
     The projection apparatus described above may further comprise cooling means having a plurality of vent holes and a fan to cool the interior of the apparatus. 
     An arrangement for driving, e.g., a scattering type liquid crystal is used as the liquid crystal panel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing the schematic optical mode of an optical system of a color liquid crystal projector using a liquid crystal panel according to an embodiment of the present invention; 
     FIG. 2 is a view showing the schematic optical mode for explaining a main optical system; 
     FIG. 3 is a view for explaining the main optical system; 
     FIG. 4 is a view for explaining a state of projection by the main optical system; 
     FIG. 5 is a perspective view showing the state of projection by the main optical system; 
     FIG. 6 is an exploded perspective view showing the structure of the main optical system; 
     FIG. 7 is a perspective view of the main part of the main optical system; 
     FIG. 8 is a perspective view of the main part of the main optical system; 
     FIG. 9 is a cross-sectional view of a liquid crystal projector using a conventional transmission liquid crystal panel; and 
     FIG. 10 is a perspective view showing the outer appearance of the projector shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described with reference to FIGS. 1 to  8 . 
     FIGS. 1 to  5  show the schematic modes of an optical system of a color liquid crystal projector using a liquid crystal panel according to an embodiment. FIG. 6 is an exploded perspective view of this optical system, FIG. 7 is a perspective view of the main part when this optical system is assembled in a lens barrel, and FIG. 8 is a sectional view of the main part shown in FIG.  7 . The projector of this embodiment has a plurality of vent holes in a case (not shown) as in the conventional case, and the interior of the case is cooled by a cooling fan. 
     Referring to FIGS. 1 and 2, white light emitted by a light source (light source means)  31  is collimated into almost parallel light by a reflecting mirror (parabolic mirror)  32  and separated by a transmission diffraction grating (color separation means)  33  into three beams (color beams) corresponding to the wavelength ranges of red light (R), green light (G), and blue light (B). The transmission diffraction grating  33  is located in almost the parallel light obtained by the reflecting mirror  32  to prevent color and brightness irregularities in illuminating the liquid crystal panel. 
     The color beams (R, G, and B beams) from the transmission diffraction grating  33  are incident on a condenser lens (lens means)  34  at different angles within the plane perpendicular to the drawing surface of FIG.  1  and focused by the condenser lens  34  to form light source images near mirrors  54 ,  35 , and  36  inclined with each other and spaced apart from each other near a stop  58  of a projection optical system  52 . 
     The G beam is present on the section of FIG.  1 . The G beam is reflected by the mirror  54  and collimated to an almost parallel beam by a field lens  47 . The G beam illuminates a reflection liquid crystal panel  55  obliquely downward with respect to the above section. The beam modulated with image information from the reflection liquid crystal panel  55  is reflected obliquely upward with respect to the above section. The field lens  47  focuses the reflected beam so as to form a light source (image) again between mirrors  50  and  51  located near the stop  58  of the projection optical system  52 . 
     The R and B beams will be described with reference to FIGS. 2 to  4 . 
     The R beam is sequentially reflected by the mirror  35  and a mirror  59  and collimated to an almost parallel beam by a field lens  48 . This parallel beam illuminates a reflection liquid crystal panel  56 . The liquid crystal illumination direction is obliquely downward with respect to the section in FIG. 2 as in the G beam and obliquely upward with respect to the section in FIG.  3 . 
     The beam modulated with the image information by the reflection liquid crystal panel  56  is reflected by the reflection liquid crystal panel  56  in a direction opposite to the incident illumination direction. The field lens  48  focuses the reflected light so as to form a light source (image) again on the mirror  50  located near the stop  58  of the projection optical system  52 . 
     Similarly, the B beam is sequentially reflected by the mirror  36  and a mirror  60  and collimated to an almost parallel beam by a field lens  49 . This parallel beam illuminates a reflection liquid crystal panel  57 . The liquid crystal illumination direction is obliquely downward with respect to the section in FIG. 2 as in the G beam and obliquely upward with respect to the section in FIG.  3 . 
     The beam modulated with the image information by the reflection liquid crystal panel  57  is reflected by the reflection liquid crystal panel  57  in a direction opposite to the incident illumination direction. The field lens  49  focuses the reflected light so as to form a light source (image) again on the mirror  51  located near the stop  58  of the projection optical system  52 . 
     The G beam passes between the mirrors  50  and  51 , while the R and B beams are respectively reflected by the mirrors  50  and  51 . These three beams are incident on the projection optical system  52 . The projection optical system  52  superposes the pieces of image information of the respective colors from the liquid crystal panels  55 ,  56 , and  57  on a screen  53  and forms a full-color image on the screen  53 . 
     The field lenses  48  and  49  respectively have common optical axes  48 ′ and  49 ′ perpendicular to an optical axis  47 ′ of the field lens  47 . When the field lens  48  and the reflection liquid crystal panel  56  are folded with respect to the mirror  50 , they overlap the field lens  47  and the reflection liquid crystal panel  55 , respectively. Similarly, when the field lens  49  and the reflection liquid crystal panel  57  are folded with respect to the mirror  51 , they respectively overlap the field lens  47  and the reflection liquid crystal panel  55 , respectively. That is, the respective liquid crystal panels are located at optically identical positions with respect to the projection optical system  52 . For this reason, the beams from the liquid crystal panels  55 ,  56 , and  57  pass through the different portions of the aperture of the stop  58  of the projection optical system  52  to project enlarged images of the corresponding colors at the same position on the screen, thereby forming a full-color image. To satisfy this relationship, the liquid crystal panels  55 ,  56 , and  57  are located on the optical axes of the corresponding field lenses  47 ,  48 , and  49 . The liquid crystal panels  56  and  57  are illuminated with the light beams inclined with respect to the optical axes on the sections shown in FIGS. 3 and  8 . The light source images of R, G, and B beams respectively focused by the field lenses  47 ,  48 , and  49  are set to have sizes to fall within the aperture of the stop  58  of the projection optical system  52 . The field lenses are arranged to efficiently use the light beams. The liquid crystal panels  55 ,  56 , and  57  drive a scattering type liquid crystal and are disclosed in U.S. Pat. No. 4,613,207. 
     The mirrors  35 ,  36 ,  54 ,  59 , and  60  constitute elements of the first deflection means (mirror means), and the mirrors  50  and  51  constitute the elements of the second deflection means. 
     Since the white light beam is incident almost vertically on the transmission diffraction grating  33  serving as a transmission color separation device, a diffraction angle of the ±1st-order diffracted beams with respect to the 0th-order diffracted beam is given by equation (1) as follows: 
     
       
         sin θ=λ/ p   (1) 
       
     
     where p is the patch of the step grating, and λ is the peak wavelength of diffracted light from the step grating. 
     Since the R beam as the +1st-order diffracted beam is asymmetrical about the B beam as the −1st-order diffracted beam, the inclinations of the mirrors  59  and  60  may be set so as to illuminate the liquid crystal panels  56  and  57  at equal tilt angles. 
     FIG. 5 stereoscopically shows the mirrors  54 ,  35 ,  36 ,  59 , and  60  arranged in the color separation illumination optical system and the mirrors  50  and  51  arranged in the color synthesis optical system. 
     The positional relationship between the mirror positions can be readily understood from FIG.  5 . Optical components from the light source  31  to the condenser lens  34  are not illustrated in FIG.  5 . 
     A light-shielding plate  61  located at the upper half of a rear element  52 R of the projection optical system  52  prevents stray light from the color separation illumination optical system from directly entering into the projection optical system  52 . This light-shielding plate  61  allows to obtain a high-contrast projection image free from stray light. 
     The mirrors  35 ,  36 ,  54 ,  59 , and  60  constituting the first deflection means and the mirrors  50  and  51  constituting the second deflection means are respectively located in areas obtained by dividing the aperture (see FIGS. 1 and 4) of the stop  58  of the projection optical system  52  two separate areas including an optical axis  52 ′. 
     Note that the color separation optical system and the color synthesis optical system are preferably arranged to pass the G beam at the central portion of the aperture of the stop  58  of the projection optical system  52  and the B and R beams at the peripheral portions of the aperture of the stop  58 . With this arrangement, a projection image having a high resolution can be obtained. 
     A structure in which the above-mentioned plurality of optical components constituting the above optical systems are assembled will be described with reference to FIGS. 6 to  8 . 
     Referring to FIG. 6, an optical housing  70  for accommodating the optical components (plurality) is formed into an almost box-like shape and has a side wall  70 G formed along the optical axis “X” and side walls  70 R and  70 B formed along the optical axis “Y”. The side walls  70 R and  70 B are perpendicular to the side wall  70 G. Openings  70   r,    70   g,  and  70   b  are respectively formed in the side walls  70 R,  70 G, and  70 B to transmit the light beams centered on their optical axes. A mirror holding frame  71  which holds the mirrors  35 ,  36 ,  54 ,  59 , and  60  constituting the first deflection means described with reference to the optical systems shown in FIGS. 1 to  5  is located at almost the central portion of the optical housing  70  and supported and fixed in the optical housing  70 . The optical axis “Y” corresponds to the optical axis  52 ′ in FIGS. 1 to  5 . 
     As shown in FIG. 7, the reflecting mirrors  35  and  36 , the reflecting mirrors  36  and  60 , and the reflecting mirror  54  are fixed in the mirror holding frame  71  at desired tilt angles. 
     The mirror holding frame  71  has a shape open along the optical axes “X” and “Y” in FIG. 6 so as to prevent an eclipse on the optical paths of the R, G, and B color beams described above. 
     Near the stop  58  of the projection optical system  52 , the synthesis mirrors  50  and  51  constituting the second deflection means are supported and fixed on an almost inverted V-shaped Z-direction wall perpendicular to the “A” surface serving as the inner surface of the optical housing  70 . The synthesis mirrors  50  and  51  are spaced apart from each other by a desired distance near the stop  58 . 
     As shown in FIG. 7, an engaging hole  70   a  for positioning the mirror holding frame  71  and a mounting screw hole  70   a ′ are formed in the “A” surface. The mirror holding frame  71  is positioned by fitting its projecting pin in the engaging hole  70   a,  and a screw is threadably engaged with the mounting screw hole  70   a′,  thereby fixing and supporting the mirror holding frame  71  on the optical housing  70 . 
     The optical housing  70  has the other open end face so as to insert and arrange the synthesis mirrors  50  and  51  in the mirror holding frame  71 . Therefore, the first and second deflection means are located near the stop  58  of the projection optical system  52  described above. 
     As shown in FIG. 6, in the optical housing  70 , a lens barrel  49   a  which supports the field lens  49  is engaged with the opening  70   b  at a desired position in one direction along the optical axis “X” from an intersection P between the optical axes “X” and “Y” and is movable along the optical axis “X”. Similarly, a lens barrel  48   a  which supports the field lens  48  is engaged with the opening  70   r  at a desired position in the other direction along the optical axis “X” and is movable along the optical axis “X”. 
     The opening  70   g  is formed at a desired position in one direction along the optical axis “Y” from the intersection P in the optical housing as in the optical axis “X”. A lens barrel  47   a  having the field lens  47  is engaged and held in the opening  70   g.  An opening  70   f  for supporting and fixing a lens barrel  52   a  for the projection optical system  52  along the optical axis “Y” is formed at a desired position in the other direction along the optical axis “Y”. The lens barrel  52   a  is held movable along the optical axis “Y”. Although not shown in this embodiment, the lens barrel  52   a  is held and fixed to be movable by threadable engagement or a helicoid. 
     The R, G, and B color beams are focused on the corresponding liquid crystal panels  55 ,  56 , and  57  by the field lenses  47 ,  48 , and  49 . A system associated with the G beam is taken as an example. An almost rectangular holding plate  72  integrally formed with the liquid crystal panel  55 , and an almost rectangular support plate  82  made of a heat conductive material almost identical to the holding plate  72  are fixed with positioning screws  85  at at least two threaded portions with positioning holes formed in the projections on the side wall  70 G of the optical housing  70 . In the embodiment shown in FIG. 6, the holding plate  72  of the liquid crystal panel  55  is located on the support plate  82  at an optically appropriate position by an external adjusting unit (not shown) and fixed at this position with a bonding material such as solder or adhesive resin. The external adjusting unit can perform rotation (θ) and movement (“aori” in Japanese) with respect to the optical axes “X”, “Y”, and “Z”. For a system associated with the R beam, a holding plate  73  with the reflection liquid crystal panel  56  is located at a desired position so as to register the reflection liquid crystal panel  56  fixed in the optical housing  70 , and the holding plate  73  is fixed. 
     For the B beam, a holding plate  74  with the reflection liquid crystal panel  57  is located at a desired position so as to register the reflection liquid crystal panel  57  in the same manner as described above, and the holding plate  74  is fixed to a support plate  84 . 
     Almost rectangular dust covers  86  are disposed on the R, G, and B liquid crystal panels from the outer side (rear side) of the fixed liquid crystal panels  55 ,  56 , and  57 . 
     Outer walls  70   h  are formed on the edges of the side walls  70 R,  70 G, and  70 B of the optical housing  70 , respectively, as shown in FIG.  6 . The outer walls  70   h  are engaged with the dust covers  86  and are fixed to each other with screws. Although the inner sides of the dust covers  86  are not illustrated, openings are formed in the dust covers  86  to partially expose the. flexible drive circuit boards of the liquid crystal panels  55 ,  56 , and  57  outside. An elastic member seals the edge of each opening to prevent external dust from entering into the housing in extracting the corresponding flexible drive circuit board. 
     In the embodiment having the above structure, dust can be prevented from entering into the liquid crystal panels  55 ,  56 , and  57  between the dust covers  86  and the lens barrels  47   a,    48   a,    49   a  of the field lenses  47 ,  48 , and  49 . 
     The sealing structure of the optical housing  70  will be described in detail with reference to FIG.  8 . FIG. 8 shows the mounting structure of the lens barrels  47   a,    48   a,  and  49   a  accommodating the field lenses  47 ,  48 , and  49 , the liquid crystal panels  55 ,  56 , and  57 , and their holding plates  72 ,  73 , and  74 , and support plates  82 ,  83 , and  84 , all of which are disposed on the side walls  70 R,  70 G, and  70 B of the optical housing  70 . 
     Common parts can be used for R, G, and B, and an example will be described below. A lead screw to engage with the threaded portion of the opening  70   g  of the optical housing  70  is formed on the outer surface of the forward end side of the lens barrel  47   a  of the field lens  47 . A seal ring  90  is disposed at the stepped portion at almost the center between the forward end side and the rear end side. The peripheral portion of the seal ring  90  and the edge portion of the opening  70   g  on the optical housing  70  side achieve excellent sealing. 
     A seal member  91  made of a funnel-like elastic member is disposed on the outer surface of the rear end side of the lens barrel  47   a.  The seal member  91  is in contact with the holding plate  72  of the liquid crystal panel  55 . The elastic force of the funnel-like portion is used to achieve contact with a sufficient adjustment margin in the optical axis in the above-mentioned positioning. Therefore, the liquid crystal panel  55  can be kept sealed by the seal members  90  and  91 . 
     In positioning, an external adjusting unit is used to position the G liquid crystal panel in the same manner as described above. The R and B liquid crystal panels are positioned in the same manner as the G liquid crystal panel. These liquid crystal panels are fixed with a bonding member (solder or resin adhesive). The support plate  82  and holding plate  72 , the support plate  83  and holding plate  73 , and the support plate  84  and holding plate  74  are disposed to obtain a desired gap in the optical axis in bonding. 
     In this embodiment, the external adjusting unit is used as a positioning means for the liquid crystal panels  55 ,  56 , and  57 . However, the liquid crystal panels may be fixed on a general X-Y-Z-θ stage, and the stage with the liquid panels may be supported and fixed in the optical housing  70 . 
     In this embodiment, the spaces around the display surfaces of the liquid crystal panels  55 ,  56 , and  57  are closed to obtain a dusting structure. At the same time, the opening in the Z-direction side surface of the optical housing  70  is covered from the Z direction (see FIG. 6) of the box-like optical housing  70  with a trimming filter mounting plate  93  formed to dispose a trimming filter  92  (R, G, and B) corresponding to the R, G, and B color beams near the Z-direction upper surfaces of the mirrors of the mirror holding frame  71 . Almost the central portion of the mounting plate  93  projects toward the mirror holding frame  71 . The mounting plate  93  has a trimming filter opening and a bonding margin at almost its center. The trimming filter  92  (R, G, and B) is adhered to the opening, thereby preventing dust from entering into the housing. 
     In the embodiment having the above structure, the main optical members in the integral optical housing  70  are covered with the trimming filter  92  and its mounting plate  93 . At the same time, the liquid crystal panels  55 ,  56 , and  57  are kept sealed by the funnel-like seal members  91  provided in the lens barrels  47   a,    48   a,  and  49   a  contacting with the holding plates  72 ,  73 , and  74  for the liquid crystal panels  55 ,  56 , and  57 , and by the seal rings  90  engaged with the openings  80   g,    70   b,  and  70   r  of the optical housing  70  together with the lens barrels  47   a,    48   a,  and  49   a,  thereby preventing dust from attaching the surfaces of liquid crystal panels  55 ,  56 , and  57 . 
     In the projection apparatus of the above embodiment, there is provided a projection apparatus in which color separation means color-separates a beam from light source means into a plurality of color beams, lens means focuses the color-separated beams, first deflection means is arranged near the focal position to irradiate optical modulation devices with the focused beams through field lenses, and second deflection means and a projection optical system project image information based on each optical modulation device to a desired position, wherein dusting structures are respectively arranged between the optical modulation devices corresponding to the plurality of color beams and the field lens opposing the optical modulation devices, or there is provided a projection apparatus in which color separation means color-separates a beam from light source means into a plurality of color beams, lens means focuses the color-separated beams, first deflection means is arranged near the focal position to irradiate optical modulation devices with the focused beams through field lenses, and second deflection means and a projection optical system project image information based on each optical modulation device to a desired position, wherein the deflection means, the field lenses, and the optical modulation devices are mounted and fixed respectively at predetermined positions in a substantially box-like structure, a light guide opening is formed near the deflection means located at substantially the center of the box-like structure, and the opening is closed with a trimming filter of each color beam to obtain a dusting structure. A cooling fan can cool a light source and an optical modulation device or drive power source serving as a heat source with wind (air) without considering the influence of dust. Vent holes communicating with the outer air can be formed at desired positions, thereby facilitating the arbitrary apparatus layout and obtaining a high-quality image free from the influence of dust. 
     Since the main optical members are accommodated in a sealing structure, the optical modulation device or the like serving as a main optical member can be disconnected from a light source means and mounted on a dedicated positioning adjusting illumination unit, thereby improving productivity.