Patent Publication Number: US-2013242271-A1

Title: Projection display device

Description:
TECHNICAL FIELD  
     The present invention relates to a projection display device. More specifically, the invention relates to an image forming element included in the projection display device and the cooling mechanism of a member disposed around it. 
     BACKGROUND ART  
     The projection display device includes the image forming element that modulates illumination light based on an image signal to form image light. The projection display device has a cooling mechanism to maintain the temperature of the image forming element within a predetermined range. A typical cooling mechanism includes an inlet formed in the case and a fan for introducing outside air through the inlet. Further, in the inlet, a filter is disposed to remove dust from the outside air introduced through the inlet. However, because the dust resistance performance of the filter is high, the maintenance frequency of the filter is large. 
     As a cooling mechanism to solve the problem, there is known a cyclical cooling mechanism. For example, Patent Literature 1 describes a cooling mechanism that includes an airtight container housing a liquid crystal panel, a fan disposed in the airtight container, and a cooling unit disposed on the side face of the airtight container. The fan causes air (refrigerant) in the airtight container to convectively flow therein. The refrigerant cools the liquid crystal panel by the process of exchanging heat with the liquid crystal panel. The refrigerant whose temperature has increased due to the process of heat exchange with the liquid crystal panel is cooled by the cooling unit to cool the liquid crystal panel again. 
     CITATION LIST  
     Patent Literature 1: Japanese Utility Model Application Laid-Open No. 1994-002337 
     SUMMARY OF INVENTION  
     Problems to be Solved by Invention 
     The aforementioned cyclical cooling mechanism has had the following problem. That is, the refrigerant circulating in the container or a duct is cooled equal to or lower than the ambient temperature of the container or the duct. As a result, the surface temperature of the container or the duct also drops to become equal to or lower than the ambient temperature, thereby causing dew condensation on the surface of the container or the duct. 
     Solution to Problem 
     The present invention provides a projection display device that magnifies and projects an image via a projection lens. The projection display device of the present invention includes, in a case, a flow path forming member for forming a flow path through which cooling air circulates, an image forming element disposed in the flow path, a fan disposed in the flow path, a cooling element for cooling the cooling air circulated in the flow path via the flow path forming member, a first temperature detection element for detecting the surface temperature of the flow path forming member, a second temperature detection element for detecting the temperature of a space in the case, and a control unit for controlling the cooling element based on the detection results of the first temperature detection element and the second temperature detection element. The control unit controls the cooling element so that inputs from the first temperature detection element and the second temperature detection element can be identical. 
     Effect of Invention 
     According to the present invention, a projection display device including a cyclical cooling mechanism where no dew condensation occurs can be realized. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       [ FIG. 1 ] A plan view showing the internal structure of a projection display device according to the present invention. 
       [ FIG. 2 ] An upper perspective view showing a projection lens, a lens holder, and a box. 
       [ FIG. 3A ] An exploded perspective view showing the box. 
       [ FIG. 3B ] An exploded perspective view showing the box. 
       [ FIG. 4 ] An upper perspective view showing the box from which a cover member and the top board of a second box have been removed. 
       [ FIG. 5 ] A lower perspective view showing the projection lens, the lens holder, and the box. 
       [ FIG. 6 ] A control block diagram showing a Pertier element. 
     
    
    
     DESCRIPTION OF EMBODIMENTS  
     Next, the embodiment of the present invention will be described with reference to the drawings.  FIG. 1  is a schematic plan view showing the internal structure of a projection display device according to the embodiment. The projection display device according to the embodiment includes a case divided into a lower case and an upper case. However, in  FIG. 1 , the upper case is omitted to show the internal structure. 
     As shown in  FIG. 1 , projection lens  2  is disposed roughly in the center of case  1 . First power source  3  and first light source  4  are arranged on the left side of projection lens  2 . Second power source  5  and second light source  6  are arranged on the right side of projection lens  2 . Further, axial fans  7  and  8  are respectively arranged between first power source  3  and second power source  5  and the back panel of case  1 . Axial fans  9  and  10  are respectively arranged between first light source  4  and second light source  6  and the back panel of case  1 . Axial fan  7  mainly cools first power source  3 , and axial fan  8  mainly cools second power source  5 . Axial fan  9  mainly cools first light source  4 , and axial fan  10  mainly cools second light source  6 . 
     Lens holder  20  for holding the rear end of projection lens  2  is disposed behind projection lens  2 , and box  30  is disposed behind lens holder  20 . 
       FIG. 2  is an enlarged perspective view showing projection lens  2 , lens holder  20 , and box  30 .  FIGS. 3A and 3B  are exploded perspective views showing the box. As shown in  FIG. 2 , box  30  includes first box  31 , second box  32  stacked on first box  31 , and cover member  33  disposed over first box  31  and second box  32 . 
     As shown in  FIGS. 3A and 3B , first box  31  includes bottom plate  40 , side plate  41 , and top plate  42 . Bottom plate  40  is made of metal while side plate  41  and top plate  42  are made of resins. Side plate  41  and top plate  42  are integrally formed. 
     As shown in  FIG. 4 , first box  31  includes sirocco fan  50 . Specifically, as shown in  FIGS. 3A and 3B , sirocco fan  50  is disposed on bottom plate  40  of first box  31  and covered with side plate  41  and top plate  42 . Top plate  42  partially covers the top of first box  31 . In other words, opening  43  is formed in the top of first box  31 , and the inlet of sirocco fan  50  is exposed from opening  43  (refer to  FIG. 4 ). Top plate  42  includes three outlets  44  ( FIG. 3A  shows only two outlets, while  FIG. 3B  shows only one outlet) formed to blow out air (cooling air) sent from sirocco fan  50 . Further, as shown in  FIG. 3A , many metal plates (aluminum plates  51 ) are arranged before the exhaust port of sirocco fan  50 . Aluminum plates  51  are arranged at fixed intervals. The end surface of each aluminum plate  51  is in contact with the bottom plate inner surface of first box  31 . The cooing air sent from sirocco fan  50  passes through adjacent aluminum plates  51  to be blown out from each outlet  44 . 
     As shown in  FIGS. 3A and 3B , second box  32  also includes bottom plate  60 , side plate  61 , and top plate  62 . However, bottom plate  60 , side plate  61  and top plate  62  of second box  32  are all made of resins. Bottom plate  60  and side plate  61  are integrally formed. Side plate  61  includes a plurality of rectangular windows  67  through which lights emitted from light sources  4  and  6  shown in  FIG. 1  enter. 
     Second box  32  houses a plurality of optical elements (not shown) constituting a lighting optical system. As shown in  FIG. 4 , second box  32  is installed on first box  31 . The region of side plate  61  of second box  32  facing lens holder  20  is recessed to be away from lens holder  20 . As a result, installation space  63  is formed behind lens holder  20 , the lower portion of installation space  63  is covered with top plate  42  ( FIG. 3A ) of first box  31  and the upper portion of installation space  63  is opened. 
     Cross dichroic prism (XDP  70 ) is installed in installation space  63 . Further, a liquid crystal panel or a polarization plate is disposed in a gap between XDP  70  and side plate  61  of second box  32 . Specifically, a red-color liquid crystal panel or the like is disposed in the gap (first gap  71 ) between the first incident surface of XDP  70  and the first region of side plate  61  facing the first incident surface. A green-color liquid crystal panel or the like is disposed in a gap (second gap  72 ) between the second incident surface of XDP  70  and the second region of side plate  61  facing the second incident surface. A blue-color liquid crystal panel is disposed in the gap (third gap  73 ) between the third incident surface of XDP  70  and the third region of side plate  61  facing the third incident surface. In each region of side plate  61 , a circular window through which light enters from corresponding window  67 , and convex lens  68  is fitted in the circular window. Further, a polarization plate is disposed on the incident side of each liquid crystal panel. On the other hand, a compensating plate and an analyzer are arranged on the exit side of each liquid crystal panel. 
     Installation space  63  is located above outlet  44  formed in top plate  42  of first box  31  ( FIG. 3A ). Accordingly, the cooling air blown out of each outlet  44  flows into installation place  63 . More specifically, first gap  71  is located above first outlet  44 , second gap  72  is located above second outlet  44 , and third gap  73  is located above third outlet  44 . Accordingly, the cooling air blown out of first outlet  44  mainly flows into first gap  71 , the cooling air blown out of second outlet  44  mainly flows into second gap  72 , and the cooling air blown out of third outlet  44  mainly flows into third gap  73 . 
     Further, as shown in  FIGS. 2 and 4 , the upper portion of installation space  63  and opening  43  of first box  31  are connected by cover member  33 . In other words, a duct constituting a part of the flow path of the cooling air is formed between installation space  63  and opening  43 . 
     That is, the cooling air sent from sirocco fan  50  flows out of each outlet  44 , and flows into installation space  63 . The cooling air that flew into installation space  63  passes through installation space  63  to flow into the duct. The cooling air that flew into the duct is sucked into sirocco fan  50  via opening  43 . The cooling air sucked into sirocco fan  50  is blown out again from sirocco fan  50 . 
     As described above, in the projection display device of the embodiment, the flow path through which the cooling air circulates is formed, and a cooling target such as the liquid crystal panel or the polarization plate is formed in the midway of the flow path. Further, the flow path includes first box  31 , second box  32 , lens holder  20 , and cover member  33 . In other words, first box  31 , second box  32 , lens holder  20 , and cover member  33  are flow path forming members constituting the flow path of the cooling air. 
     As shown in  FIG. 5 , a cooling element (Pertier element  80 ) and a first temperature detection element (first thermistor  81 ) are arranged on the outer surface of bottom plate  40  of first box  31 . Heat sink  82  is disposed laterally to first box  31 . Pertier element  80  and heat sink  82  are connected via heat pipe  83 . However, heat sink  82  can be directly mounted on Pertier element  80 . A second temperature detection element (second thermistor  84 ) is disposed laterally to projection lens  2 . 
     As described above, many aluminum plates  51  are arranged before the exhaust port of sirocco fan  50  in first box  31 , and the end surface of each aluminum plate  51  is in contact with the bottom plate inner surface of first box  31  ( FIG. 3A ). On the other hand, Pertier element  80  is in contact with the bottom plate outer surface of first box  31 . In other words, aluminum plate  51  and Pertier element  80  face each other via bottom plate  40  of first box  31 , and are thermally connected via bottom plate  40 . Accordingly, when bottom plate  40  of first box  31  is cooled by Pertier element  80 , aluminum plate  51  is cooled. When aluminum plate  51  is cooled, the cooling air that passed between adjacent aluminum plates  51  is cooled. 
     Next, the thermistor will be described. First thermistor  81  is in contact with the bottom plate outer surface of first box  31 . Accordingly, the temperature of bottom plate  40  of first box  31  is detected by first thermistor  81 . On the other hand, second thermistor  84  is not in contact with box  30 . Accordingly, the ambient temperature of box  30  is detected by second thermistor  84 . In the projection display device of the embodiment, Pertier element  80  is controlled based on the temperatures detected by two thermistors  81  and  84 . 
       FIG. 6  is a control block diagram showing Pertier element  80 . The projection display device of the embodiment includes control unit  85  for controlling Pertier element  80 . The outputs of first thermistor  81  and second thermistor  84  are input to control unit  85 . Control unit  85  controls Pertier element  80  so that the input from first thermistor  81  and the input from second thermistor  84  can be identical. In other words, Pertier element  80  is controlled so that the temperature of bottom plate  40  of first box  31  and the ambient temperature can be equal. 
     By controlling Pertier element  80  as described above, the temperature of bottom plate  40  of first box  31  is maintained roughly equal to the ambient temperature (e.g., ambient temperature +5° C.), thereby preventing dew condensation. 
     As described above, first box  31 , second box  32 , lens holder  20 , and cover member  33  are flow path forming members constituting the flow path of the cooling air. Among the flow path forming members, only bottom plate  40  of first box  31  is made of metal. Pertier element  80  is disposed on bottom plate  40  of first box  31 . In other words, among the flow path forming members, the temperature of bottom plate  40  of first box  31  is lowest. Thus, as long as the temperature of bottom plate  40  of first box  31  is maintained roughly equal to the ambient temperature, dew condensation in the entire flow path forming members is prevented. 
     Since Pertier element  80  is disposed on bottom plate  40  of first box  31 , even when the flow path forming members other than the bottom plate of first box  31  are made of metal, the temperature of bottom plate  40  is lowest. Thus, the aforementioned effects can be provided even when the members other than the bottom plate of first box  31  are made of metal. Further, when many portions of the flow path forming members are made of metal, the improvement of cooling effects can be expected. 
     The exemplary embodiment of the present invention has been described. However, the present invention is not limited to the embodiment. For example, the cooling element is not limited to the Pertier element, and the temperature detection element is not limited to the thermistor. The first temperature detection element only needs to be installed at a position where the surface temperature of the flow path forming member can be detected. The second temperature detection element only needs to be installed at a position where the temperature of the space in the case can be detected. For example, when a temperature sensor having a sensing unit and a body separated from each other is used as a first temperature detection element, the sensing unit only needs to be disposed on the surface of the flow path forming member. When a similar temperature sensor is used as a second temperature detection element, a body can be in contact with the flow path forming member as long as a sensing unit is not in contact with the flow path forming member.