Patent Publication Number: US-2011075111-A1

Title: Video projector

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2009-226252, filed on Sep. 30, 2009, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a video projector, and more particularly to a video projector that cools an optical component with a cooling current. 
     In the prior art, a video projector includes optical systems that are arranged in a housing. The optical systems include an illumination optical system having a light source or the like, a splitting optical system that splits illumination light into a red light, green light, and blue light, light valves modulating the colored lights in accordance with video information, a combining optical system that combines the modulated lights, and a projector lens enlarging and projecting the combined light. Due to the increased illuminance of images, recent projectors use light sources that emit a large amount of light. Further, recent projectors have become more compact. This has resulted in a tendency for heat to build up inside the projectors. It is thus important for optical components vulnerable to heat to be cooled, such as an emission side polarizing plate of a light valve and a polarizing beam splitter (PBS) of the illumination optical system. 
     These optical components are generally cooled by delivering a flow of air from a blower to a subject to be cooled (cooling subject) through a duct and supplying a predetermined amount of air to a predetermined location with a deflection plate and a nozzle. Japanese Laid Open Patent Publication Nos. 2007-298890 and 2000-81667 describe prior art examples of such a cooling scheme. 
     In the prior art cooling scheme described above, the amount of air and blowing location of a nozzle are selected in accordance with the cooled optical component. This is because the optical components that are cooled have different temperature rising rates and different tolerable temperature limits. However, in an optical component that is vulnerable to heat such as those described above, the temperature does not rise evenly in the entire optical component. Thus, the temperature distribution is not uniform. More specifically, as shown in  FIG. 1 , there is a tendency for the temperature to be higher at a central portion in which a large amount of light is concentrated, and there is a tendency for the temperature to be lower as a peripheral portion becomes closer. However, in the prior art cooling scheme, the blower cools such an optical component entirely by blowing air against the optical component. Such a cooling scheme does not take into consideration the temperature distribution of the cooled optical component. Since a temperature rise in part of an optical component would be dealt with by increasing the entire amount of air, when a projector uses a light source emitting an increased amount of light and has a smaller size, the amount of air would be significantly increased. This would lower efficiency and increase noise. 
     SUMMARY OF THE INVENTION 
     The present invention provides a video projector that efficiently cools an optical component, while taking into consideration the temperature distribution of the optical component. 
     One aspect of the present invention is a video projector provided with an optical system, which includes an optical component, and a cooling current discharging structure, which is capable of providing a high-speed cooling current and a low-speed cooling current to the optical component of the optical system. The optical component serves as a cooling subject. The cooling current discharging structure discharges the high-speed cooling current toward a high-temperature region of the optical component and discharges the low-speed cooling current toward a low-temperature region having a relatively low temperature. 
     A further aspect of the present invention is a video projector provided with an optical system, which includes an optical component, and a cooling current discharging structure, which provides first and second airflow cooling currents to the optical component of the optical system in which one of the airflow cooling currents has a higher flow speed than the other of the airflow cooling currents. The optical component serves as a cooling subject. The cooling current discharging structure discharges the one of the airflow cooling currents having a higher flow speed toward a first region of the optical component and discharges the other of the airflow cooling currents toward a second region of the optical component in which the first region when the optical system is operating has a higher temperature than the second region. 
     Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. In the drawings, like numerals are used for like elements throughout: 
         FIG. 1  is a chart showing the general temperature distribution in an optical component; 
         FIG. 2  is a schematic view showing optical systems of a representative video projector according to one embodiment of the present invention; 
         FIG. 3  is a plan view showing a light valve for a red light and its surroundings in the video projector of  FIG. 1 . 
         FIG. 4  is a cross-sectional view taken along line A-A in  FIG. 3 ; 
         FIG. 5  is a cross-sectional view taken along line B-B in 
         FIG. 3 ; 
         FIG. 6  is a cross-sectional view of a blower chamber for a low-speed air passage in a modification of the video projector; 
         FIG. 7  is a cross-sectional plan view of a high-speed air passage in a modification of the video projector; and 
         FIG. 8  is a perspective view showing an engaging portion formed at a distal portion of the high-speed air passage in a modification of the video projector. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Optical systems in a video projector according to the present invention will first be described with reference to  FIG. 2 . 
     The video projector is a liquid crystal display (LCD) video projector and is of a three-panel type in this example. Optical systems of the projector include an illumination optical system  10 , which emits illumination light, and a color splitting optical system  20 , which splits the illumination light emitted from the illumination optical system  10  into a red light, green light, and blue light. The optical systems further include a red light valve  30 , a green light valve  40 , and a blue light valve  50  respectively modulating the red light, green light, and blue light split by the color splitting optical system  20 . The optical systems also include a color combining optical system  60 , which combines the modulation lights modulated by the light valves  30 ,  40 , and  50 , and a projection optical system  70 , which enlarges and projects the combined light emitted from the color combining optical system  60  as a colored image light onto a screen or the like. 
     The illumination optical system  10  includes a light source lamp  11 , an integrator lens  12 , a polarizing beam splitter  13 , a condenser lens  14 , a reflection mirror  15 , and a relay lens  16 . A light beam is emitted from the light source lamp  11  toward the integrator lens  12 , which includes a first lens array arranged at an entry side and a second lens array arranged at an emission side. A plurality of cell lenses in the first lens array divides the light beam emitted to the integrator lens  12  into a plurality of fine partial light beams. Then, each of the partial light beams emitted from the first lens array is converged on a corresponding cell lens in the second lens array. Further, the polarizing beam splitter  13  gathers the light beams emitted from the integrator lens  12  and forms predetermined polarized light, which is emitted via the condenser lens  14 , reflection mirror  15 , and relay lens  16  to the color splitting optical system  20 . 
     The color splitting optical system  20  includes dichroic mirrors  21  and  22 , reflection mirrors  23 ,  24 , and  25 , relay lenses  26  and  27 , condenser lenses  28   r ,  28   g , and  28   b  and function to split the illumination light emitted from the illumination optical system  10  into a red light, a green light, and a blue light. 
     The first dichroic mirror  21  transmits red light and reflects green light and blue light. The red light transmitted through the first dichroic mirror  21  is reflected by the reflection mirror  23  and transmitted through the condenser lens  28   r  to illuminate the red light valve  30 . The condenser lens  28   r  converges the partial light beams from the illumination optical system  10  at the red light valve  30  to form a light beam in which the partial light beams are substantially parallel to one another. The condenser lenses  28   g  and  28   b  respectively arranged at the entry sides of the green light valve  40  and the blue light valve  50  are formed in a manner similar to the condenser lens  28   r.    
     Among the green light and blue light reflected by the first dichroic mirror  21 , the green light is reflected by the second dichroic mirror  22  and transmitted through the condenser lens  28   g  to illuminate the green light valve  40 . In contrast, the blue light is transmitted through the second dichroic mirror  22  and sequentially travels to the relay lens  26 , the reflection mirror  24 , the relay lens  27 , the reflection mirror  25 , and the condenser lens  28   b  to illuminate the blue light valve  50 . 
     The red light valve  30  includes an entry side polarizing plate  31  arranged at the entry side, an optical compensation plate  32 , a transmissive liquid crystal panel  33 , a pre-polarizing plate  34 , and an emission side polarizing plate  35  in a manner similar to the structure of the prior art. The green light valve  40  includes an entry side polarizing plate  41  arranged on the entry side, an optical compensation plate  42 , a transmissive liquid crystal panel  43 , a pre-polarizing plate  44 , and an emission side polarizing plate  45  arranged on the emission side. The blue light valve  50  includes an entry side polarizing plate  51  arranged on the entry side, an optical compensation plate  52 , a transmissive liquid crystal panel  53 , a pre-polarizing plate  54 , and an emission side polarizing plate  55  arranged on the emission side. 
     The color combining optical system  60  includes a cross dichroic prism  61 . The cross dichroic prism  61  has a reflection surface  61   a , which reflects the red light modulated by and emitted from the red light valve  30 , and a reflection surface  61   b , which reflects the blue light modulated by and emitted from the blue light valve  50 . The red and blue lights, which enter the cross dichroic prism  61  and are reflected by the reflection surfaces  61   a  and  61   b , are combined with the green light, which enters and transmits straight through the cross dichroic prism  61 . The combined light is emitted from the cross dichroic prism  61  as a colored image. 
     The projection optical system  70  is arranged at the emission side of the cross dichroic prism  61  and includes a projector lens unit. 
     In such optical systems, the light source increases the temperature. Further, the polarizing beam splitter  13  and the light valves  30 ,  40 , and  50  are formed by optical components having a relatively low tolerable temperature limits. In this case, the temperature increases is highest at the emission side polarizing plates  35 ,  45 , and  55 , which regulate the amount of emitted light. Further, the central portion of each of these optical components receives a larger amount of light from the light source. Thus, there is a tendency for the temperature to be higher at the central portion and lower as the peripheral portion becomes lower as shown in  FIG. 1 . 
     A cooling structure for optical components according to the present invention will now be discussed with reference to  FIGS. 3 to 5 . Here, the red light valve  30  will be used as an example for describing the cooling structure.  FIG. 3  is a plan view. In the following description, the vertical direction refers to a direction perpendicular to the plane of  FIG. 3 , with the upper side of  FIG. 3  being defined as the upper side. 
       FIG. 3  is a schematic plan view showing the cooling structure for cooling the optical components of the red light valve  30  with a cooling current. As viewed in the drawing, a double duct type air conduit is formed below the optical components of the red light valve  30 . More specifically, the air conduit includes an outer air passage and an inner air passage. The outer air passage is a low-speed air passage  80  through which air flows at a low speed, and the inner air passage is a high-speed air passage  90  through which air flows at a high speed. 
     The low-speed air passage  80  includes a blower  81 , a blower duct  82  connected to the outlet side of the blower  81 , a blower port  83  that discharges a cooling current toward the optical components of the red light valve  30  from below (refer to  FIG. 4 ), and a blower chamber  84  formed ahead of the blower port  83 . 
     A normal low pressure fan, such as a sirocco fan, of which the specifications are suitable for discharging an air current from the blower port  83  at a low speed, is used as the blower  81 . The blower duct  82  provides a cooling current airway to the blower chamber  84  through a side wall thereof. In the present embodiment, the blower port  83  is formed with a shape that opens upwardly from the blower chamber  84 . The dimension of the blower port  83  in the lateral direction of  FIG. 3  (direction perpendicular to the light axis) is set to be slightly greater than the lateral dimensions of the optical components (light valve  30  in this case). The dimension of the blower port  83  in the light axis direction is set to be large enough to include the entry side polarizing plate  31  to the emission side polarizing plate  35  (refer to  FIG. 4 ). In this manner, the blower port  83  is formed so as to discharge a predetermined amount of cooling current airflow at predetermined speed over the entire range of optical components in the light valve  30  excluding the portion in which a high-speed cooling current is discharged from a nozzle  94  of the high-speed air passage  90 . The cooling current discharged from the blower port  83  is slower than the cooling current discharged from the nozzle  94 . Thus, in this specification, the cooling current discharged from the blower port  83  is referred to as a low-speed current, and the cooling current discharged from the nozzle  94  is referred to as a high-speed current. 
     The high-speed air passage  90  includes a blower  91 , a blower duct  92  connected to the outlet side of the blower  91 , an inner duct  93  inserted inside the blower chamber  84 , and a nozzle  94  formed at the distal portion of the high-speed air passage  90 , that is, at the distal portion of the inner duct  93  in the present embodiment. 
     A high pressure fan, such as a turbo fan, of which the specifications are suitable for discharging an air current from the nozzle  94  at a high speed, is used as the blower  91 . The blower duct  92  extends upward from the lower surface of the blower chamber  84 . The inner duct  93 , which is a duct portion arranged in the blower chamber  84 , is supported in the blower chamber  84  by a portion connected to the blower duct  92 . The inner duct  93  includes a side surface  93   a  formed to have a horizontal cross-section that is tapered (triangular in the present embodiment) toward the air current flowing from the sideward blower duct  82  (refer to  FIGS. 3 and 5 ). The side surface  93   a  allows for the air current drawn in from the blower duct  82  to flow smoothly to the rear of the inner duct  93 , that is, to the right as viewed in  FIG. 3 . 
     As shown in  FIG. 3 , the nozzle  94  is arranged to cool the central portions of the pre-polarizing plate  34  and the emission side polarizing plate  35 , which are located at the light emission side where there is a tendency for the temperature to easily increase. As apparent from  FIG. 3 , the nozzle  94  is formed with a dimension that covers the liquid crystal panel  33 , the pre-polarizing plate  34 , and the emission side polarizing plate  35  of the red light valve  30  in the light axis direction. Further, in the lateral direction perpendicular to the light axis, the size and location of the nozzle  94  are set to discharge a high-speed cooling current at predetermined speed to the central portion of the optical component (light valve  30 ). Further, as shown in  FIGS. 4 and 5 , the nozzle  94  has tapered portions  94   a  that are sloped so that its dimensions become smaller as the distal end (i.e., top end) becomes closer. 
     The structure for strongly cooling the central portions of the pre-polarizing plate  34  and the emission side polarizing plate  35  has been described above. In the video projector according to the present embodiment, the pre-polarizing plate  44  and emission side polarizing plate  45  in the green light valve  40  and the pre-polarizing plate  54  and emission side polarizing plate  55  in the blue light valve  50  are also cooled in the same manner. 
     In the video projector, the optical components are cooled as described below. 
     Some of the optical components in the optical systems are vulnerable to heat, for example, the entry side polarizing plates  31 ,  41 , and  51 , the optical compensation plates  32 ,  42 , and  52 , the liquid crystal panels  33 ,  43 , and  53 , the pre-polarizing plates  34 ,  44 , and  54 , and the emission side polarizing plates  35 ,  45 , and  55  of the light valves  30 ,  40 , and  50 . The polarizing beam splitter  13  is also vulnerable to heat. Further, the temperature distribution is not uniform in such optical components as shown in  FIG. 1 , and the temperature has a tendency of being higher at the central portions of such optical components in surfaces perpendicular to the light axis. That is, in each of such optical components, the central portion forms a high-temperature region, and the peripheral portion forms a low-temperature region having relatively low temperature. Among these optical components, the rise in temperature is highest in the pre-polarizing plates  34 ,  44 , and  54  and the emission side polarizing plates  35 ,  45 , and  55 . In the present embodiment, in order to strongly cool the high-temperature region in the central portion of each of these optical components especially at the emission side, cooling current is discharged at a high speed from the nozzle  94  by the high-speed, high-pressure blower  91 . This lowers the temperature of the high-temperature regions in these optical components and decreases temperature variations. Further, the low-temperature region surrounding the high-temperature region, that is, the peripheral portion of each optical component, is cooled by discharging air from the normal blower  81 . The peripheral portion of the optical component is also cooled by a swirling air current generated by the speed difference between the air currents. In this manner, cooling currents of two or more speeds are used. This efficiently cools the optical components. Further, such a structure decreases temperature variations in the optical component and allows for a uniform temperature distribution. 
     The video projector according to the present embodiment has the advantages described below. 
     (1) The video projector includes a cooling current discharge structure that discharges high-speed cooling current to the high-temperature region of an optical component and discharges a low-speed cooling current to the low-temperature region at which the temperature is relatively low. By using such a finely regulated cooling means, cooling is performed without using unnecessary amounts of air and unnecessary current speeds. This improves the cooling effect and efficiency, while reducing noise. Further, temperature variations are decreased in the optical components and the cooling capacity is increased. Thus, the reliability and durability of the optical components are improved. 
     (2) The nozzle  94  that discharges the cooling current is formed at the distal end of the high-speed air passage  90 . This efficiently discharges cooling current to the high-temperature regions of the optical components and thereby increases the cooling capacity. 
     (3) The nozzle  94 , which discharges the high-speed cooling current, is located inside the blower port  83 , which discharges the low-speed cooling current. Further, the periphery of the nozzle  94  is surrounded by the low-speed cooling current. Accordingly, a cooling current optimal for the temperature distribution of the cooled optical component is discharged from the nozzle  94 . Further, the cooling current directed to the peripheral portion of the optical component draws in surrounding air due to the pressure difference corresponding to the current speed difference. This reduces the amount of air used to cool the peripheral portion and further improves efficiency. 
     (4) The nozzle  94  formed at the distal end of the high-speed air passage  90  is arranged in the blower port  83  formed at the distal end of the low-speed air passage  80 . Accordingly, the high-speed air passage  90  and the low-speed air passage  80  form a double duct at least at a location just ahead of the blower port  83 . This simplifies the structures for a cooling current passage for a cooling subject. 
     (5) The blower chamber  84  is provided ahead of the blower port  83  in the low-speed air passage  80 , and the blower duct  92  connected to the blower  91  in the high-speed air passage  90  is inserted in the blower chamber  84 . This forms a double duct. Accordingly, the inner duct  93  in the high-speed air passage  90  is supported by the low-speed air passage  80 . This facilitates the mounting of the high-speed air passage  90 . 
     (6) The blower duct  82  in the low-speed air passage  80  is connected to the side wall of the blower chamber  84 , and the high-speed air passage  90  includes the side surface  93   a , which has a horizontal cross-section tapered toward the air current from the blower duct  82 . Accordingly, the flow of air drawn from the blower duct  82  into the low-speed air passage  80  is smoothly guided to the rear of the high-speed air passage (inner duct  93 ), that is, toward the right as viewed in  FIG. 3 . This forms a uniform low-speed air current around the high-speed air passage  90 . 
     (7) The blower  91  for generating the high-speed cooling current and the blower  81  for generating the low-speed cooling current are different types of blowers, and the blower  91  is more suitable for generating high-pressure air current than the blower  81 . Accordingly, air currents are generated at speeds optimal for their applications (i.e., temperature regions). 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
     The cooling structure of the above-discussed embodiment cools the pre-polarizing plates  34 ,  44 , and  54  and the emission side polarizing plates  35 ,  45 , and  55  with cooling currents of two speeds. In the same manner, any component having a temperature distribution variation such as the other optical components in the light valves  30 ,  40 , and  50 , the polarizing beam splitter  13 , and the light source may also be cooled by cooling currents of two speeds. 
     As shown in  FIG. 6 , the blower port  83  discharging the low-speed cooling current may have an opening area that is smaller than the cross-sectional area of the blower chamber  84 . More specifically, the upper end of the blower chamber  84  may be bent inward and then upward to form an upright wall  84   b  that defines the blower port  83 . In this structure, the blower port  83  is narrower than the blower chamber  84 . This moderates the effect of dynamic pressure produced by the air current drawn into the blower duct  82  and uniformly distributes the speed of the air current discharged from the blower port  83 . Further, the upright wall  84   b  may function as a deflection plate. 
     The side surface  93   a  of the inner duct  93  located at the outlet side of the blower duct  82  is not required to have a tapered triangular shape and may be, for example, semicircular in shape (refer to  FIG. 7 ) or semielliptical. Such forms would also allow for air to smoothly flow from the low-speed air passage  80  toward the rear of the inner duct  93  (toward the right in  FIG. 3 ). 
     An engaging portion for positioning the high-speed air passage  90  relative to the low-speed air passage  80  may be arranged at the distal portion of the high-speed air passage  90 , which includes the nozzle  94 . In this case, in addition to fixing the inner duct  93  to an insertion portion  84   a , but the nozzle  94  may be positioned with further accuracy. This accurately discharges cooling current to the region subject to cooling.  FIG. 8  shows an example of an engaging portion. Arms  95  extend from near the nozzle  94  toward the top end of the blower chamber  84 . Each arm  95  has a distal portion forming an engaging portion  95   a , which is rod-shaped and curved and thereby has a circular cross-section. The blower chamber  84  includes supports  85 , each having an engaging portion  85   a  formed by a hole for insertion of the corresponding engaging portion  95   a . Accordingly, insertion of the rod-shaped curved engaging portions  95   a  into the holes of the engaging portions  85   a  stabilizes the position and direction of the nozzle  94  and accurately adjusts the direction of the cooling current. 
     In the above-discussed embodiment, as apparent from  FIG. 3 , the low-speed air passage  80  is formed so that the blower duct  82  has a cross-sectional area smaller than that of the blower chamber  84  the low-speed air passage  80 . However, the low-speed air passage  80  is not limited to such a structure, and the cross-sectional area of the blower duct  82  may be larger depending on available space. In the same manner, it is obvious that the blower duct  92  of the high-speed air passage  90  may have a larger cross-section. 
     The blower port  83  formed in the distal portion of the low-speed air passage  80  may include deflection to further finely adjust the amount and speed of the air current directed to a region subject to cooling. In the same manner, the nozzle  94  in the high-speed air passage  90  may also include such a mechanism. 
     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.