Abstract:
The projection type image display apparatus is equipped with a lamp unit ( 22 ), an optical block ( 21 ) which modulates light from the lamp unit and projects an image signal, a circuit board ( 24 ) having via holes and on which an external connector ( 25 ) is mounted, and a cabinet ( 2 ) for housing the aforementioned elements. The display apparatus is equipped with a back cover ( 26 ) provided to cover around the external connector from the outside and a dustproof cover ( 29 ) provided to cover around the external connector from the inside. A closed space is formed by the circuit board, the back cover ( 26 ) and the dustproof cover ( 29 ), and the dustproof cover closely shields at least a space below the circuit board from the exterior. Excellent dustproof characteristics enabling use even in installation environments with a large amount of dust and dirt can be obtained.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a projection type image display apparatus, and particularly, a multipurpose projection type image display apparatus that can be used in a severe environment subjected to a dust and dirt. 
       BACKGROUND ART 
       [0002]    Recently, projection type image display apparatuses (hereinafter, described also as projectors) have been widespread, and such projection type image display apparatuses often have been used in various locations indoors and outdoors, in addition to the conventional application in an environment with relatively clean air, such as a meeting room of an enterprise. The increased scope of the use location results in variation in the use environments, and thus the conditions for temperature, humidity and air cleanliness become more severe. As a result, with the expanding use, new problems have occurred with respect to the quality of the projector. 
         [0003]    In particular, when the projection type image display apparatus is used in an environment with an inferior air cleanliness, dust and dirt enter the interior of the cabinet of the projector and adhere to elements and components of the optical system, thereby degrading drastically the illuminance of the projector. For solving the problem, a dustproof measure for a projector is an urgent and important technical object. 
         [0004]    For a conventional dustproof measure in a projection type image display apparatus, an air filter is provided at an opening, and concurrently, a wall is provided on the interior of the display apparatus so as to configure a dustproof space in which optical components (prism unit) are housed (see Patent Document 1 for example). In this example, a buffer material as a dustproof member is inserted in the clearance of a dustproof space. 
         [0005]    Dustproof measures for circuit boards are disclosed in Patent Documents 2 and 3, for example. The methods include: filling through holes of a printed wiring board for IC cards with plated metal so as to prevent dust and dirt from entering the substrate at the side where electronic components are mounted; or attaching a shield case to a substrate, thereby enveloping the substrate with the shield case and a metal case so as to prevent adherence of dust. 
       PRIOR ART DOCUMENT 
     Patent Documents 
       [0000]    
       
         Patent document 1: JP H10-186513 A 
         Patent document 2: JP H01-171992 A 
         Patent document 3: JP H04-372205 A 
       
     
       DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
       [0009]    However, the conventional measures as described above were insufficient for dustproof of a general-purpose projector to be used under an environment with a large amount of dust and dirt. In particular, the conventional method of taking dustproof measures with respect to some partial areas inside a projection type image display apparatus is insufficient to prevent dust and dirt from entering the interior of the display apparatus. Therefore, in a case of using the display apparatus in an environment with a large amount of dust and dirt, the circuit board and the other elements and components may be affected seriously, which results in problems for the display apparatus, such as degradation of function, failures, degradation in the durability and the like. 
         [0010]    As mentioned above, there has not been any example of clarifying dustproof characteristics required for the respective areas of the display apparatus so as to take a comprehensive dustproof measure. 
         [0011]    Therefore, with the foregoing in mind, it is an object of the present invention to provide a projection type image display apparatus configured to take comprehensive dustproof measures corresponding to the dustproof characteristics required for the respective areas of the display apparatus, and thus can be installed in environments with various levels of dust and dirt indoors and outdoors. 
       Means for Solving Problem 
       [0012]    For achieving the above-described object, a projection type image display apparatus of the present invention includes: a light source; an optical component that modulates light coming from the light source and projects an image signal; a circuit board formed with via holes, on which an external connector is mounted; and a cabinet for housing these components. The projection type image display apparatus includes further a connector cover provided to cover around the external connector from the outside, and a dustproof cover provided to cover around the external connector from the inside. A closed space is formed by the circuit board, the connector cover and the dustproof cover, and the dustproof cover hermitically shields to at least the space below the circuit board from the exterior. 
       Effects of the Invention 
       [0013]    The projection type image display apparatus of the present invention is capable of preventing effectively dust and dirt from entering through the clearance between the connector cover and the external connector and also through the pinholes formed on the external connector. Further, a comprehensive dustproof measure is taken, particularly for the area for providing the external connector that is susceptible to entrance of dust and dirt. Therefore, the weather durability of the projection type image display apparatus can be improved suitably and effectively, and thus a convenient projection type image display apparatus, which can be installed in environments with various levels of dust and dirt indoors and outdoors, can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a perspective view showing an appearance of a projection type image display apparatus according to an embodiment of the present invention. 
           [0015]      FIG. 2  is a perspective view showing main components and the arrangement inside the display apparatus. 
           [0016]      FIG. 3  is a perspective view showing an optical block area of the display apparatus. 
           [0017]      FIG. 4  is a perspective view showing a configuration of a circuit board unit of the display apparatus. 
           [0018]      FIG. 5  is a perspective view showing a configuration of a circuit board unit of the display apparatus. 
           [0019]      FIG. 6  is a perspective view showing a shape of a dustproof cover included in the circuit board unit of the display apparatus. 
           [0020]      FIG. 7  is a plan view showing the upper side of the circuit board unit of the display apparatus. 
           [0021]      FIG. 8  is a perspective view showing a dustproof structure on the back face of the display apparatus. 
           [0022]      FIG. 9  is a perspective view showing a dustproof structure at another location on the back face of the display apparatus. 
           [0023]      FIG. 10A  is a plan view showing an example of a printed wiring board as the circuit board of the display apparatus. 
           [0024]      FIG. 10B  is a plan view for explaining a process of forming via holes on a circuit board by using an ordinary metal mask. 
           [0025]      FIG. 10C  is a plan view for explaining a process of clogging via holes on a circuit board in an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0026]    A projection type image display apparatus of the present invention can be modified as described below without departing from the above-described configurations. 
         [0027]    That is, as a preferred configuration, an elastic dustproof sheet is provided further between the circuit board and the outer cover that composes a part of the cabinet and that covers the circuit board, for the purpose of shielding through holes other than the via holes on the circuit board and shielding the clearance between the circuit board and the connector cover. 
         [0028]    With this configuration, it is possible to prevent effectively entrance of dust and dirt from the through holes such as attachment holes other than the via holes on the circuit board and from the clearance between the circuit board and the connector cover. 
         [0029]    It is further preferable that the via holes formed in an area of the circuit board corresponding to the closed space are clogged. 
         [0030]    The configuration effectively serves to prevent the entrance of dust and dirt from the via holes. Further, since there is no necessity of covering the via holes with the dustproof sheet, the surface area of the dustproof sheet can be decreased. 
         [0031]    The dustproof cover can be formed of a resin material. By use of the resin dustproof cover, the shape of the dustproof member can be optimized easily. 
         [0032]    Further, the circuit board can be configured with dogged via holes as a result of solder application conducted using a solder application mask having a pattern of the solder application including the position of the via holes. 
         [0033]    According to the configuration, the via holes can be clogged in a simple manner. 
         [0034]    Hereinafter, a preferred embodiment of the present invention will be specified with reference to the attached drawings. 
       Embodiment 
       [0035]    The basic configuration and the function of the image display apparatus according to an embodiment of the present invention will be described below with reference to  FIGS. 1 and 2 .  FIG. 1  is a perspective view showing an appearance of a projection type image display apparatus (hereinafter, this will be described as the apparatus)  1  according to the present embodiment.  FIG. 2  is a perspective view showing main components and the arrangement inside the apparatus  1 . 
         [0036]    In the apparatus  1 , a projection type projector unit (not shown, hereinafter, this will be described simply as projector) is housed in a cabinet  2 . The cabinet  2  includes a front panel  3 , an outer cover  4  and a bottom plate (not shown). A projection window  5  for the projector is formed on the front panel  3 , air vents  6  are formed on the side faces, and legs  7  are provided to the bottom face. The projector has a capability of projecting an image of a certain dimension and a certain illuminance from a certain projection distance. By projecting image information outputted by the projector on a screen (not shown) through the projection window  5 , an image can be displayed at a large scale. It should be noted that the projector can be connected to an information processing device such as a personal computer (not shown), thereby storing information necessary for information delivery service, or acquiring information from the exterior through a communication line. 
         [0037]    The main configuration inside the apparatus  1  will be described below with reference to  FIGS. 2 and 3 . 
         [0038]    As shown in  FIG. 2 , a lamp unit  22 , a power source unit  23 , a circuit board  24  and an optical block  21  disposed below the circuit board  24  are housed as a projector unit inside the cabinet  2  of the apparatus  1 .  FIG. 3  shows the projector unit from which the circuit board  24  in  FIG. 2  has been removed. An area enclosed by a dotted line  20  indicates the optical block  21 , and the area includes optical components such as a condensing lens, a prism, a liquid crystal display element and a projection lens. When dust and dirt enter this area, the dust and dirt will adhere to the optical components, thereby degrading drastically the illuminance of the projector. For this reason, a special emphasis is placed on measures for protecting this area from dust and dirt. 
         [0039]    As shown in  FIG. 2 , an external connector (hereinafter, this will be described simply as connector)  25  is mounted on the circuit board  24 . The connector  25  is disposed on the back face of the apparatus  1 , on which a back cover  26  as a connector cover is disposed to cover from the outside. 
         [0040]    Further, two air routes are provided to the apparatus  1 . A first air route is a path for cooling the optical block  21  and the lamp unit  22 . Namely, an intake A is conducted by a fan (not shown) from an air intake port  27  provided on a side face. The air flow passes between the circuit board  24  and the bottom plate and an exhaust B is conducted from an exhaust port (not shown) formed on the other side face. A second air route is a path for cooling the power source unit  23 . An air intake port and an exhaust port (either not shown) are formed on either of the side faces, for conducting an intake C and an exhaust D. 
         [0041]    On the air intake port  27  of the display apparatus  1 , a dustproof filter (not shown) is disposed in an exchangeable manner. Such a dustproof filter is not disposed at the air intake port (not shown) for the air intake C, since there is a necessity of reducing air resistance and feeding as much air as possible to the power source unit  23  for the purpose of cooling. Instead, a partition board  28  serves to prevent dust and dirt from entering the optical block  21 . Since the exhaust ports exhaust dust and dirt during operations of the display apparatus  1 , such a dustproof filter is not an essential element. However, by providing the dustproof filter also at the exhaust port, the dustproof system at the air intake ports and the exhaust ports will be more reliable. All of the openings except for the air intake ports and the exhaust ports formed on the outer cover  4  are provided with a dustproof member. 
         [0042]    Next, the dustproof structure on the back face, which characterizes the configuration of the display apparatus  1 , will be described. 
         [0043]    As shown in  FIG. 2 , the connector  25  mounted on the circuit board  24  is exposed on the back face of the display apparatus  1 . This structure may permit the entrance of dust and dirt from the clearance (part E) between the back cover  26  and the connector  25 . Further, each pinhole (not shown) of the connector  25  forms a via hole opening (part F), through which dust and dirt may enter. In light of preventing the entrance of dust and dirt through these parts on the back face, the display apparatus  1  is configured to have a dustproof system. 
         [0044]    Hereinafter, the dustproof structures on the back face of the display apparatus  1  will be specified with reference to  FIGS. 4 to 9 . 
         [0045]      FIGS. 4 and 5  are perspective views showing the configuration of a circuit board unit. As shown in  FIG. 4 , the connector  25  is mounted on the circuit board  24 , and a back cover  26  is attached for covering the connecter  25  from the outside.  FIG. 5  shows the circuit board unit from which the back cover  26  as shown in  FIG. 4  has been removed. In the circuit board unit, a resin dustproof cover  29  is provided as a dustproof outer component on the inner surface of the back cover  26 .  FIG. 6  is a perspective view showing the shape of the dustproof cover  29 . 
         [0046]    The dustproof cover  29  covers around the backside of the connector  25  in the space below the circuit board  24 , and the upper end part is in close contact with the circuit board  24 . The back face cover  26 , the circuit board  24  and the dustproof cover  29  form a closed space for blocking the area communicating with the space below the circuit board  24  from outside the cabinet  2 , thereby preventing entrance of dust and dirt. It should be noted that the closed space is not necessarily a hermetically-shielded space but a space substantially shielded from the exterior though including some leakages as the parts indicated with the arrows E and F in  FIG. 2 . However, the dustproof cover  29  hermetically shields at least the space below the circuit board  24  from the exterior, thereby preventing entrance of dust and dirt via the space below the circuit board  24 . 
         [0047]    On the circuit board  24 , a number of via holes  32  that penetrate the substrate are formed. Each of the via holes  32  is plated with a conductive material on the inner surface in order to connect electrically the surface and the back face of the circuit board  24 , thereby making the wiring pattern on the back face of the package face available. When the packaging density of the components is raised further, the packaging surface and the back face alone will be insufficient for ensuring the area for the wiring pattern. In such a case, the circuit board  24  is made as a multilayer, and a power source layer, a ground layer and a wiring layer are formed on the inner layer. And by the interlayer connection with the via holes  32 , high-density packaging on the circuit board  24  can be provided. As described below, the via holes  32  need a dustproof system. 
         [0048]    As mentioned above, the thus provided dustproof cover  29  can block dust and dirt entering from the clearance between the back cover  26  and the connector  25  ( FIG. 2 , arrow E) and from the pinhole ( FIG. 2 , arrow F) of the connector  25 . 
         [0049]    However, it is preferable to provide an additional dustproof structure. Namely, as shown in  FIG. 7  of a top plan view of the circuit board unit, not only the via holes  32  but attachment holes  33  for attaching the connector  25  and other components are formed on the circuit board  24 . Further, there is a small clearance  34  between the circuit board  24  and the back cover  26 . Dust and dirt that are blocked by the dustproof cover  29  so as not to enter the space below the circuit board  24  may enter above the circuit board  24  through the attachment holes  33  and the clearance  34  so as to reach the optical block  21 . 
         [0050]    In view of this problem, as shown in  FIG. 8  the display apparatus  1  has further an elastic dustproof sheet  30  interposed between the circuit board  24  and the outer cover  4 . Further, as shown in  FIG. 9 , a dustproof member  31  is inserted between the circuit board  24  and the dustproof cover  29  to fill the clearance between the joint surfaces. 
         [0051]    In addition, in the display apparatus  1 , among the via holes  32  formed on the circuit board  24 , at least all of the via holes in an area surrounded by the dustproof cover  29  are clogged. Here, the via hole in the area surrounded by the dustproof cover  29  denotes the via hole formed in the area closer to the connector  25  in comparison with the position at which the upper end of the dustproof cover  29  contacts. When the via holes are clogged in this manner, the surface area of the dustproof sheet  30  can be decreased in comparison with a case where the via holes are not clogged, and thus the cost for the components can be reduced. 
         [0052]    An example of a process for clogging the via holes  32  on the circuit board  24  will be described below. In the case of the display apparatus  1 , a solder application mask used to process the circuit board  24  (hereinafter, this will be described as metal mask) has a pattern for solder application including the positions of the via holes to be formed on the circuit board  24 . Thereby, the via holes  32  on the circuit board  24  can be clogged during the process of solder application.  FIGS. 10A-10C  show a process of clogging the via holes  32  on the circuit board  24 . 
         [0053]      FIG. 10A  is a plan view showing an example of a printed wiring board  41 , where via holes  44  are formed.  FIG. 10B  shows a process of forming via holes by use of an ordinary metal mask  42  at the time of soldering the printed wiring board  41 .  FIG. 10C  shows a process of soldering by use of a metal mask  43  prepared for clogging the via holes, during production of the apparatus  1 . 
         [0054]    For clogging the via holes  44  for example, openings  45  are formed on the metal mask  43  as shown in  FIG. 10C  at positions corresponding to the via holes  44  so as to form clogged via holes  46 . In this manner, the via holes formed at arbitrary positions on the circuit board  24  can be clogged by use of the metal mask  43 , and thus the via holes can be clogged in a simple manner. 
         [0055]    As described above, the display apparatus  1  has a dustproof filter at openings formed on the outer cover  4 , and furthermore, a dustproof cover  29  on the inner surface of the back cover  26 , and an elastic dustproof sheet  30  interposed between the circuit board  24  and the outer cover  4 . In the display apparatus  1 , among the via holes  32  on the circuit board  24 , the via holes in an area surrounded by the dustproof cover  29  are clogged. 
         [0056]    The above-described configuration serves to dustproof measures for the back face of the display apparatus  1  on which the connector  25  is mounted, and the configuration is effective in preventing entrance of dust and dirt from the position at which the connector is provided, such as the pinholes at the terminal of the connector and the clearance between the connector and the outer cover. Therefore, it is possible to have comprehensive and effective dustproof measures, and the entrance of dust and dirt inside the display apparatus can be prevented reliably. As a result, a projection type image display apparatus that can be installed in any environments with various levels of dust and dirt level indoors and outdoors can be provided. Furthermore, the numbers of components, the numbers of process steps and the numbers of repairs can be decreased to improve the cost effect. 
         [0057]    Though the above-described embodiment refers to an example where the connector  25  is provided on the back face, the configuration of the present embodiment can be applied similarly to a case where the connector  25  is provided not on the back face but on a side face or the like. 
       INDUSTRIAL APPLICABILITY 
       [0058]    The present invention can provide a projection type image display apparatus with excellent dustproof performance. Such a projection type image display apparatus can be used preferably in installation environments with a large amount of dust and dirt indoors and outdoors. 
       EXPLANATION OF LETTERS AND NUMERALS 
       [0000]    
       
         
           
               1  Projection type image display apparatus (the apparatus) 
               2  Cabinet 
               3  Front panel 
               4  Outer cover 
               5  Projection window 
               6  Air vent 
               7  Leg 
               20  Optical block area 
               21  Optical block 
               22  Lamp unit 
               23  Power source unit 
               24 , 41  Circuit board 
               25  External connector (connector) 
               26  Back cover (connector cover) 
               27  Air intake port 
               28  Partition panel 
               29  Dustproof cover 
               30  Dustproof sheet 
               31  Dustproof member 
               32 , 44  Via hole 
               33  Attachment hole 
               34  Clearance 
               41  Printed wiring board 
               42 , 43  Solder application mask (metal mask) 
               45  Opening for solder application 
               46  Clogged via hole