Patent Publication Number: US-2009219493-A1

Title: Projection type display apparatus and method of controlling the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-050569, filed Feb. 29, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     One embodiment of the invention relates to a projection type display apparatus which projects a laser beam onto a screen so as to display a video and a method of controlling the apparatus. 
     2. Description of the Related Art 
     As is well known, projection type display apparatuses represented by, for example, color projectors project an optical image, in which an emitted light from a light source is modulated by a video signal, onto a screen so as to display a video. As the light source in the projection type display apparatuses, attention was paid to a lamp and LED (light emitting diode) and is currently paid to a laser element. 
     International safety standards relating to a light quantity of a laser beam is defined for devices using laser beam. In the projection type display apparatuses using the laser element as the light source, the light quantity of a laser beam emitted onto the screens should be limited based on the safety standards. 
     That is, in the safety standards, maximum permissible exposure (MPE) is defined as a safe level of a laser beam which can be permitted when the laser beam enters an eye or is emitted to a skin. The MPE value is set based on 1/10 of an exposure amount (level) in which a fault incidence becomes 50%. The MPE value is obtained by power density (W/m 2 ) or energy density (J/m 2 ) of the laser beam per unit area. 
     For this reason, when a radiation level of the laser beam is set so as to be smaller than the MPE value, a problem of safety does not arise. However, sufficient brightness of the laser beam cannot be secured on a screen only by setting the radiation level of the laser beam to a smaller value than the MPE value. For this reason, such projection type display apparatuses lack in practicality. 
     Jpn. Pat. Appln. KOKAI Publication No. 2005-091610 discloses a constitution of an image display apparatus. This apparatus has a first image display system which displays an image using a laser beam as a light source, and a second image display system which displays an image using a light source other than the laser beam. The same image is projected to be displayed by the first and second image display systems so that the brightness of the laser beam is reduced and the displayed image is made to be bright. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. 
         FIG. 1  is a perspective view illustrating an appearance of a laser projector according to one embodiment of the present invention; 
         FIG. 2  is a block constitutional diagram illustrating a signal processing system of the laser projector according to the embodiment of present invention; 
         FIG. 3  is a block constitutional diagram illustrating a constitution of a video projecting module in the laser projector according to the embodiment; 
         FIG. 4  is a diagram illustrating a relationship between a screen size of the laser projector and an optical power per unit area on the screen according to the embodiment of the present invention; 
         FIG. 5  is a diagram illustrating a relationship between a screen position of the laser projector and the optical power per unit area on the screen according to the embodiment of the present invention; 
         FIG. 6  is a diagram illustrating a safety countermeasure in the case where a person is in front of the screen of the laser projector according to the embodiment of the present invention; 
         FIG. 7  is a flow chart describing a main processing operation of the laser projector according to the embodiment of the present invention; and 
         FIG. 8  is a diagram illustrating one example of the relationship between the screen size of the laser projector and the optical power per unit area on the screen according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION  
     Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, a projection type display apparatus, which modulates a laser beam generated from a laser beam generating element according to an input video signal and projects the modulated laser beam onto a screen via a projection lens so as to display a video, sets a light quantity of the laser beam based on information representing a size of the screen so that an optical power of the laser beam per unit area on the screen falls within a range conforming to predetermined safety standards and brightness on the screen can be secured at a maximum, and controls the laser beam generating element so that the laser beam of the set light quantity is generated. 
       FIG. 1  illustrates an appearance of a laser projector  11  described in this embodiment. That is, the laser projector  11  has a stationary cabinet  12  which becomes a projector main body and is formed into an approximately thin box shape. 
     A projection lens  13  and a distance measuring module  14  are arranged proximately on one end of a front panel  12   a  of the cabinet  12 . The projection lens  13  is for enlarging and projecting so as to display imaged information onto a screen, described later, which becomes a video projection surface provided on the front surface of the cabinet  12 . 
     The distance measuring module  14  normally measures a distance from the projection lens  13  to the screen. When a person enters between the projection lens  13  and the screen, the distance measuring module  14  measures a distance from the projection lens  13  to the person. 
     A display module  15  and an operating module  16  are arranged on an upper panel  12   b  of the cabinet  12 . The display module  15  displays a current state of the laser projector  11 , or a menu for setting various modes of the laser projector  11 . 
     The operating module  16  has a power supply key, and various keys which control various operating states or a halt state of the laser projector  11 , or sets various modes of the laser projector  11 . These keys are provided to be exposed from the upper panel  12   b  so as to be operated by a user. 
       FIG. 2  illustrates a signal processing system of the laser projector  11 . That is, a video signal supplied to an input terminal  17  is subject to a predetermined signal process necessary when the signal is supplied to a video signal processing module  18  so as to be projected. The video signal output from the video signal processing module  18  is supplied to a video projecting module  19  so as to be converted into an optical image. Thereafter, an optical image is enlarged and projected onto a screen  20  via the projection lens  13 , and then a video is displayed. 
     The video display operation of the laser projector  11  is controlled by a control module  21  in an integrated manner. The control module  21  contains a CPU (central processing unit)  21   a,  for example, and controls the respective modules based on operating information acquired from the operating module  16  or operating information transmitted from a remote controller  22  and received by a receiving module  23  so that operating contents are reflected. 
     In this case, the control module  21  utilizes a memory module  21   b.  The memory module  21   b  mainly has a ROM (read only memory), a RAM (random access memory) and a nonvolatile memory. The ROM stores a control program executed by the CPU  21   a  therein. The RAM provides an operating area to the CPU  21   a.  The nonvolatile memory stores various setting information and control information therein. 
     The control module  21  is connected to the distance measuring module  14 , and acquires distance information measured by the distance measuring module  14 . When the control module  21  controls the video projecting module  19 , it outputs the distance information acquired from the distance measuring module  14  to the video projecting module  19 . 
       FIG. 3  illustrates a constitution of the video projecting module  19 . That is, the video signal output from the video signal processing module  18  is supplied to a video optical converting module  25  via an input terminal  24 . An R (red) laser beam, a B (blue) laser beam and a G (green) Laser beam are allowed to enter the video optical converting module  25  via a mirror  26  at a constant cycle in a time-division manner. 
     The R, B and G laser beams are generated from an R laser beam generating element  27 , a B laser beam generating element  28  and a G laser beam generating element  29 , respectively. The respective generating elements  27  to  29  are selectively driven based on control of a laser beam control module  30 , so that the R laser beam, the B laser beam and the G laser beam are generated at a constant cycle in time-division manner. The R, B and G laser beams are allowed to enter the video optical converting module  25  via dichroic filters  31 ,  32  and  33 , and the mirror  26 . 
     The video optical converting module  25  modulates the R, B and G laser beams, which enter in the time-division manner, according to color component signals corresponding to the incident laser beams in the input video signal in each horizontal line. The laser beams are allowed to scan the screen  20  via the projection lens  13 , so that a video is displayed. 
     The laser beam control module  30  controls the R, B and G laser beam generating elements  27  to  29  based on a control signal supplied from the control module  21  via an input terminal  34 . In this case, the control signal supplied from the control module  21  includes the distance information measured by the distance measuring module  14  and information showing a size of the screen  20  to be used. The size of the screen  20  is expressed by a size ratio between a longitudinal direction and a lateral direction with respect to the screen  20  with a basic size. 
     The laser beam control module  30  sets a light quantity of laser beams based on the size of the screen  20  to be used so that an optical power of the laser beams per unit area on the screen  20  falls within a range (within MPE value) conforming to safety standards and brightness on the screen  20  is secured at a maximum. The laser beam control module  30  controls the R, B and G Laser beam generating elements  27  to  29  so that the laser beams of the set light quantity are generated. 
     That is, as shown in  FIG. 4 , a case where a screen  20   a  or a size S 1  and a screen  20   b  of a smaller size S 2  are provided on a position separated from the projection lens  13  by a distance L, is considered. In this case, when the light quantity of the laser beams emitted from the laser projector  11  is constant, the optical power of the laser beam per unit area on the screen  20   b  becomes stronger than optical power of the laser beam per unit area on the screen  20   a.    
     As shown in  FIG. 5 , however, a case where the screen  20  of the screen size S 1  is installed on a position separated from the projection lens  13  by a distance L 1  and a position separated by a longer distance L 2 , is descried. When the light quantity of the laser beam emitted from the laser projector  11  is constant, the optical powers of the laser beam on the display surfaces of the screens  20  on the positions of the distances L 1  and L 2  become equal to each other. 
     As a result, when the light quantity of the laser beam emitted from the laser projector  11  is constant, the optical power of the laser beam per unit area on the screen changes according to the size of the screen  20  regardless of the distance from the projection lens  13  to the screen  20 . 
     For this reason, the laser beam control module  30  sets the light quantity of the laser beam based on the size of the screen  20  to be used so that the optical power of the laser beam per unit area on the screen  20  falls within the range (within MPE value) conforming to the safety standards and the brightness on the screen  20  becomes maximum. Further, the laser beam control module  30  controls the R, B and G laser beam generating elements  27  to  29 . 
     In  FIG. 5 , assume that in a state that a video is projected onto the screen  20  on the position separated from the projection lens  13  by the distance L 2 , a person enters an emitting range of the laser beam (range shown by hatching in the drawing) between the projection lens  13  and the screen  20 , such as the position separated from the projection lens  13  by the distance L 1 . 
     Since the emitting range of the laser beam is smaller than the size S 1  of the screen  20 , as shown in  FIG. 4 , the optical power of the laser beam per unit area within that range becomes stronger than the optical power of the laser beam per unit area on the screen  20 . That optical power possibly exceeds the safety standards. 
     For this reason, when the measured result in the distance measuring module  14  is changed suddenly from the distance L 2  to the distance L 1 , the laser beam control module  30  determines that a person enters. In this case, the laser beam control module  30  assumes that a screen  20   c  having a size S 3  corresponding to the emitting range of the laser beam in the state that a video is projected onto the screen  20  on the position separated from the projection lens  13  by the distance L 2  is provided on the position separated from the projection lens  13  by the distance L 1  as shown in  FIG. 6 . The laser beam control module  30  sets the light quantity of the laser beam so that the optical power of the laser beam per unit area on the screen  20   c  falls within the range (within MPE value) conforming to the safety standards, and controls the R, B and G laser beam generating elements  27  to  29 . 
     In this case, since a person is likely to enter there, the laser beam control module  30  has only to control the light quantity of the laser beam within the range conforming to the safety standards. It is not always necessary to control the light quantity so that the brightness on the screen  20   c  becomes maximum within the range conforming to the safety standards. 
       FIG. 7  illustrates a flow chart of the processing operation for controlling the light quantity of the laser beam using the laser beam control module  30 . That is, this process is started by requesting video display on the screen  20  (step S 11 ). 
     As a result, the laser beam control module  30  acquires size information about the screen  20  to be used at step S 12 . The size information about the screen  20  is defined by a video signal to be input, setting according to a user&#39;s operation, or a specification of the video optical converting module  25 . The laser beam control module  30  acquires distance information measured by the distance measuring module  14  at step S 13 . 
     Thereafter, the laser beam control module  30  calculates the light quantity of the laser beam based on the acquired size information about the screen  20  at step S 34  so that the optical power of the laser beam per unit area on the screen  20  falls within the range (within MPE value) confirming to the safety standards and the brightness on the screen  20  is secured at a maximum. The laser beam control module  30  controls the R, B and G laser beam generating elements  27  to  29  at step S 15  so that the laser beams of the calculated light quantity are generated. 
     The laser beam control module  30  determines at step S 16  whether the distance measured by the distance measuring module  14  changes so as to be short. When it is determined that it has changed (YES), the process goes to step  314 . In this case, the laser beam control module  30  determines that the person has entered the current emitting range of the laser beams on the changed distance position. The laser beam control module  30  assumes a screen with size according to the current emitting range of the laser beams on the changed distance position, and calculates the light quantity of the laser beam so that the optical power per unit area on the assumed screen falls within the range (within MPE value) confirming to the safety standards at step S 14 . 
     When the determination is made that the distance does not change at step S 16  (NO), the laser beam control module  30  determines whether stopping of video display on the screen  20  is requested at step S 17 . When the determination is made that the stopping is not requested (NO), the process goes to step S 13  so that the distance information is acquired from the distance measuring module  14 . When the determination is made that the stopping is requested (YES), the process is ended (step S 18 ). 
     According to the above embodiment, the light quantity of the laser beam is set according to the size of the screen  20  to be used so that the optical power of the laser beam on the screen  20  per unit area falls within the range (within MPE value) conforming to the safety standards and the brightness of the screen  20  becomes maximum. For this reason, user&#39;s convenience is improved, and thus the embodiment is suitable sufficiently for actual use. 
     The distance between the projection lens  13  and the screen  20  is measured, and when the distance changes abruptly, the determination is made that a person has entered. The light quantity of the laser beam is set so that the optical power per unit area on the assumed screen with size conforming to the current emitting range of the laser beam falls within the range (within MPE value) conforming to the safety standards on the changed distance position. For this reason, sufficient safety can be secured. 
       FIG. 8  illustrates one example of a relationship among the distance to the screen  20 , the longitudinal length of the screen  20 , the lateral length of the screen  20 , the area of the screen  20  and the optical power per unit area. 
     That is, the case where the light quantity of the laser beam emitted from the laser projector  11  is constant is assumed. The optical power of the laser beam per unit area, at which the brightness on the screen  20  becomes maximum with longitudinal length of A and lateral length of B within the range (within MPE value) conforming to the safety standards, is C. When the longitudinal and lateral lengths of the screen  20  are doubled, the optical power is reduced to ¼, and when the longitudinal and lateral lengths of the screen  20  are tripled, the optical power is reduced to 1/9. When the longitudinal and lateral lengths of the screen  20  becomes fourfold, the optical power is reduced to 1/16. 
     In other words, when the longitudinal and lateral lengths of the screen  20  are doubled, the optical power per unit area on the screen  20  can be increased fourfold. When the longitudinal and lateral lengths of the screen  20  are tripled, the optical power can be increased ninefold. When the longitudinal and lateral lengths of the screen  20  are quadrupled, the optical power can be increased sixteenfold. 
     Before the laser beam is projected onto the screen  20 , it is desirable that the light quantity of the laser beam is preset according to the size of the screen  20  to be used, and the laser beam with the set light quantity is generated. Before the laser beam is projected onto the screen  20 , an infrared ray is projected and it is confirmed that no obstruction is present through the distance up to the screen  20 , and the laser beam of the set light quantity is generated. As a result, safety is further ensured. 
     The various modules of the systems described herein can be implemented as software applications, hardware and/or software modules, or components on one or more computers, such as servers. While the various modules are illustrated separately, they may share some or all of the same underlying logic or code. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.