Patent Publication Number: US-2006001840-A1

Title: Projection image display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-192937, filed Jun. 30, 2004, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a projection image display apparatus using an optical space modulation element such as a digital micromirror device (DMD).  
      2. Description of the Related Art  
      There is a projection image display apparatus using a digital micromirror device (DMD) as a space modulation element.  
      This image display apparatus selectively generates R, G and B video light by turning red (R), green (G) and blue (B) filters of a color wheel provided in a front stage of a light source, and obtains a projection image by reflecting the light for each color on the DMD.  
      The R, G and B light transmitted through the R, G and B filters is applied to the respective reflection surfaces of DMD. The DMD is driven by the R, G and B video signals in synchronization with the application of the R, G and B light. The R, G and B video light reflected from the DMD is magnified and projected onto a screen through a projection lens.  
      In such a projection image display apparatus, a discharge lamp is often used as a light source. Thus, when a power supply is turned on again after once turned off, it takes certain time (waiting time) for the lamp to stabilize the illuminance of light and color temperature.  
      As a well-known means of reducing the waiting time, there is a backup lighting system (a residual heat system) which supplies a lamp with certain power (a heater current (ballast)) even in a standby state. This state is generally called low-power shutdown (LPS). When a main power supply is turned on from this waiting state, the lamp restart speed is increased. U.S. Pat. No. 5,134,491 describes an example of stopping a ballast lamp lighting circuit with a certain time delay after a main power supply is turned off.  
      Most projection image display apparatus are not provided with a mechanism to permit the user to easily and externally confirm that power is supplied in a standby state. Thus, the user may misunderstand that power is completely turned off even in a standby state (power is not completely turned off in a backup lighting system (a residual heat system). In this case, the user may open the cover of an image display apparatus for maintenance, and may touch an energized part or a light source generating much volume of heat.  
     BRIEF SUMMARY OF THE INVENTION  
      According to an aspect of the present invention, there is provided a projection image display apparatus comprising:  
      a light source;  
      a modulation element which receives light from the light source and emits video light modulated by a video signal having a predetermined color space;  
      a screen onto which video light from the optical space modulation element is projected through a projection lens;  
      a power supply unit which controls a supply voltage of the light source in a completely on state, completely off state, and low-power standby state; and  
      an informing mechanism which informs the controlled states of the light source. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
       FIG. 1  is a schematic illustration showing an example of a projection image display apparatus applicable to an embodiment of the present invention;  
       FIG. 2  is a timing chart explaining an example of operation of the projection image display apparatus shown in  FIG. 1 ; and  
       FIG. 3  is a table explaining an example of control of a display unit of the projection image display apparatus shown in  FIG. 1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter preferred embodiments of the present invention will be explained in detail with reference to the accompanying drawings.  
       FIG. 1  shows an example of a projection image display apparatus applicable to an embodiment of the present invention.  
      The projection image display apparatus shown in  FIG. 1  uses a digital micromirror device (DMD) as an optical space modulation element.  
      While light emitted from a light source  11  passes through a lens  12  and filters R (red), G (green) and B (blue). The light source  11  uses a xenon lamp, for example.  
      A color wheel  13  is turned by a motor  14  at a predetermined speed. Therefore, light from the light source  11  is given a predetermined color when passing through respective filters R (red), G (green) and B (blue) of the color wheel  13 .  
      The light given predetermined colors after passing through the color wheel  13  is applied to an image forming surface of a digital micromirror device (DMD). The image forming surface is provided with micromirrors arranged like a matrix, for example.  
      The micromirrors can reflect the light given the colors R, G and B in the color wheel  13  at a predetermined timing in the direction toward or away from a projection lens system  17 , by controlling the inclination of each mirror. Therefore, when each micromirror is given a reflecting direction toward the lens system  17  according to a video signal, video light (R, G and B) corresponding to a video signal sequentially enters the lens system  17 . The R, G and B video light emitted from the projection lens system  17  is projected onto a screen  18 .  
      A signal processing circuit  19  supplies a DMD  16  with video signals corresponding to R, G and B at certain time intervals. In this time, a motor  14  is controlled so that the R, G and B color filters of the color wheel  13  are placed in the optical path in synchronization with the video signal corresponding to R, G and B. Therefore, the micromirrors of the DMD  16  output video light for R, G and B at certain time intervals.  
      In this image display apparatus, there are two fans  21  and  22  for cooling the light source  11  and DMD  16 , respectively. The fans  21  and  22  are controlled by fan driving circuits  23  and  24 , respectively. The fan driving circuits  23  and  24  control the rotation speed and time of the fans  21  and  22 , based on the control information (instructions) from a main control unit  50 .  
      The main control unit  50  sets the on/off states and standby state of the light source  11  for a lamp driving circuit  30 . This control will be described later.  
      The main control unit  50  gives the motor driving circuit  41  instructions to set the rotation frequency (rotational speed) and phase of the motor  14  to drive and turn the color wheel  13 . The rotation of the motor  14  is detected by a rotation detector  42 , and the detected information is fed back to the main control unit  50 .  
      The main control unit  50  also controls the output timing of a video output signal output from the signal processing circuit  19 , so that the positions of the color filters R, G and B of the color wheel  13  (which color is given to the light from the lamp  11 ) are synchronized with the R, G and B video signals output from the signal processing circuit  19  at certain time intervals.  
      The main control unit  50  can control the operations (power output state) of a main power supply circuit  601  of a power supply unit  60  and an auxiliary power supply circuit  602 . The power supply unit  60  is connected to the commercial power supply.  
      The state of the image display apparatus is determined by a switching operation of an operation unit  70  connected to the main control unit  50 , or by a signal input from a not-shown remote control terminal and received by a remote control receiver  80 .  
      The main control unit  50  is connected with display elements  91  and  92 , which enable the user to determine whether the user can recognize the states, standby or completely off, of the image display apparatus, especially the light source (lamp)  11 . The display elements  91  and  92  are lit by the main control unit  50  in several patterns explained later with reference to  FIG. 3 .  
       FIG. 2  shows the relationship between the power supplied to the light source (lamp) and time. The horizontal axis indicates the time, and the vertical axis indicates the power applied to the lamp.  
      The main control unit has a power supply controller  501 , which controls the supply voltage applied to the light source  11  through the lamp driving circuit  30 . This includes whether the light source is completely turned on/off or in the standby state (low-power state or residual heat mode (or backup lighting).  
      In the completely on state, power applied to the lamp (input voltage) is usually a rated value.  
      For example, when the power is turned off by the user, a low-power state or a residual heat mode (or backup lighting) is set for a period from time T 1  to T 2 . This state is called a low-power shutdown (LPS) mode. The standby state (LPS) turns to the completely off state after a predetermined period X 1  (at time T 2 ).  
      Conversely, when the main power supply is turned on again by the user within the period X 1 , the light from the light source  11  rises smoothly, and the light source is completely turned on within a very short time (indicated by a dotted line in  FIG. 2 ).  
      During the LPS mode, the fan  21  for cooling the light source  11  is held on. Therefore, after the period X 1  elapses, the light source  11  is sufficiently cooled. The length of the LPS mode is optionally set by the power supply controller  501  of the main control unit  50 .  
      In the above case, the rotation speed of the fan  21  is optimized based on the length of the period X 1 . The length of the period X 1  may also be changed according to a time frame of a day, or set to a desired length by the user.  
       FIG. 3  shows the relationship between the lighting timing of two (red and green) light-emitting elements and the operation states of the image display apparatus. The light-emitting element lighting timing (the lighting pattern) shown in  FIG. 3  is just an example, and any patterns can be used at least if the LPS period can be informed to the user.  
      The lighting patterns (lighting time) of the light-emitting elements  91  and  92  are controlled by the light-emitting element controller  502 . Hereinafter an example of lighting pattern will be explained with reference to  FIG. 3 .  
      When the main power supply of the power supply unit  60  is turned off and the light source  11  is completely turned off, the light-emitting elements  91  and  92  are also turned off. When the main power supply is turned on and the light source  11  is completely turned on, only the light-emitting element  91  is turned on.  
      During the LPS mode, the light-emitting element  91  turns off, but the light-emitting element  92  blinks at one-second intervals. Therefore, the user can easily recognize that the image display apparatus is in the standby state.  
      When the main power supply is turned on during the LPS mode (the main power supply is turned on at the time t 1  in  FIG. 2 ), the light-emitting element  91  lights continuously and the light-emitting element  92  turns on at every predetermined period (0.3 seconds) (the light-emitting element  92  blinks).  
      When the light from the light source  11  is stabilized, the light source is completely turned on and only the light-emitting element  91  turns on.  
      In the above informing mechanism (display means), the red light-emitting element  91  indicates on/off of the main power supply, and the blue light-emitting element  92  warns of the LPS mode (standby state) and lighting again in the LPS mode.  
      As described above, the informing mechanism of the present invention can inform the user of the states of the image display apparatus, especially the state of the light source heated to a high temperature while being energized in the standby state, by combining the lighting and blinking of the least necessary number of light-emitting elements.  
      A projection image display apparatus using a color wheel and DMD has been described hereinabove. The invention is applicable also to a projection image display apparatus using a liquid crystal. Namely, in an apparatus which applies light from a light source to a liquid crystal panel, and projects reflected light from a liquid crystal panel onto a screen through a projection lens, the above-mentioned lamp can be applied to a member driving in LPS or normal mode.  
      According to the present invention, the power control states of a light source of an apparatus can be easily and externally recognized, increasing safety and reliability.  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.