Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to control of an image display device, and particularly relates to control of an image display device having a plurality of light sources. 
     2. Description of the Background Art 
     As to image display devices such as laser projectors, Japanese Patent Laying-Open No. 06-342126, for example, discloses “a projection display device, more specifically, a projection display device in which an optical signal emitted from an optical shutter array having multiple optical shutter elements arranged in a one-dimensional manner, based on image data, is scanned with a deflection mirror to project a two-dimensional image” (Paragraph 0001). 
     Japanese Patent Laying-Open No. 2004-184852 discloses a technique for “adjusting a color balance including a white balance in a display device enabling white display with use of light from RGB light emitters” (“Problems to be Solved” in “Abstract”). 
     Japanese Patent Laying-Open No. 2007-065012 discloses “a projection display device capable of maintaining an optimal white balance of a displayed image and obtaining high image quality even if quantities of light of a plurality of colors in light-emitting elements of the relevant colors are changed owing to degradation or failure of the light-emitting elements” (“Problems to be Solved” in “Abstract”). 
     Japanese Patent Laying-Open No. 2005-236650 discloses “a projector capable of quickly and easily creating a color correction table for projecting an easily-viewable image of a desired color onto a screen” (“Problems to be Solved” in “Abstract”). 
     Japanese Patent Laying-Open No. 2002-244206 discloses “a system for adjusting a position of a light modulation device, even capable of addressing a decrease in illumination margin associated with downsizing of a projector” (“Problems to be Solved” in “Abstract”). 
     In a so-called beam-scanning display device such as a laser projector, if optic axes of RGB (Red, Green, Blue) do not coincide with one another, colors to be projected cannot be reproduced accurately. Therefore, precise adjustment for allowing the optic axes to coincide with one another, and accordingly, an ability to easily adjust the optic axes are demanded. Furthermore, an ability to add a function of adjusting the optic axes without increasing the number of components is also demanded. 
     SUMMARY OF THE INVENTION 
     In brief, according to an embodiment, a device for displaying an image is provided. The device includes: a first light source for emitting first light; and a second light source for emitting second light. A color of the first light differs from a color of the second light. The device further includes: a mirror for reflecting the first light and the second light; an actuator configured to drive the mirror in a scan direction; and a photoreceptor for receiving the first light and the second light. The photoreceptor includes a first light-receiving region and a second light-receiving region. A boundary between the first light-receiving region and the second light-receiving region is orthogonal to the scan direction. The device further includes: a controller configured to control light emission and shut off of the first light source, and light emission and shutoff of the second light source; a detector configured to detect a deviation between an optic axis of the first light source and an optic axis of the second light source, based on a timing at which the first light is received in the second light-receiving region and a timing at which the second light is received in the second light-receiving region; and a corrector configured to correct a light emission timing of the second light source based on the deviation detected by the detector. 
     In accordance with another embodiment, a method for displaying an image is provided. The method includes the steps of: emitting first light; and emitting second light. A color of the first light differs from a color of the second light. The method further includes the steps of reflecting the first light and the second light at a mirror; driving the mirror in a scan direction; and receiving the first light and the second light. A region for receiving includes a first light-receiving region and a second light-receiving region. A boundary between the first light-receiving region and the second light-receiving region is orthogonal to the scan direction. The method further includes the steps of: controlling light emission and shut off of the first light, and light emission and shut off of the second light; detecting a deviation between an optic axis of the first light and an optic axis of the second light, based on a timing at which the first light is received in the second light-receiving region and a timing at which the second light is received in the second light-receiving region; and correcting a light emission timing of the second light based on the detected deviation. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram that represents a hardware configuration of a laser projector  10  serving as a mode of an image display device according to an embodiment of the present invention. 
         FIG. 2  is a diagram that schematically represents a light-receiving region in a photoreceptor  126  of an optical system  100 . 
         FIG. 3  is a block diagram that represents a configuration of functions implemented by a CPU  160  that implements laser projector  10 . 
         FIG. 4  is a flowchart that represents a part of a series of operations executed by CPU  160 . 
         FIG. 5  is a diagram that represents the relation between a timing of each of light emission and light-up of a laser of each color and an output of photoreceptor  126 . 
         FIG. 6  is a diagram that represents the relation between drive of scanner mirror  120  in a vertical direction and an output based on irradiation by a green laser  112  or red/blue lasers  110 . 
         FIG. 7  is a diagram for describing correction to irradiation timings of green laser  112  and red/blue lasers  110 . 
         FIG. 8A  and  FIG. 8B  are a diagram that represents a pattern of drive of scanner mirror  120  in a horizontal direction, and a diagram that represents the relation between a scan angle and a scan speed in a light-receiving region, respectively. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will hereinafter be described with reference to the drawings. In the following description, the same parts are provided with the same reference characters, and have the same names and functions. Therefore, the detailed description thereof will not be repeated. 
     [Hardware Configuration] 
     With reference to  FIG. 1 , description will be made on an image display device according to an embodiment of the present invention. Laser projector  10  includes an optical system  100 , a system controller  150 , an X driver  130 , and a Y driver  132 . 
     Optical system  100  includes red/blue lasers  110 , a green laser  112 , a polarization beam splitter  114 , a collimator lens  116 , a scanner mirror  120 , a half mirror  124 , a photoreceptor  126 , and a position detector  122 . System controller  150  includes a laser controller  152 , a drive frequency controller  154 , a position detection controller  156 , a memory  158 , and a CPU (Central Processing Unit)  160 . Laser projector  10  projects an image onto a screen  170  provided in front of optical system  100 . 
     A red laser beam and a blue laser beam delivered by red/blue lasers  110  are reflected by polarization beam splitter  114 , and the reflected lights are directed to collimator lens  116 . A laser beam delivered by green laser  112  passes through polarization beam splitter  114  and is directed to collimator lens  116 . 
     Scanner mirror  120  reflects the laser beams of respective colors, which have passed through collimator lens  116 , toward a range predefined as a scan range. Scanner mirror  120  is driven by X driver  130  and Y driver  132  in a horizontal direction and a vertical direction, respectively. 
     Half mirror  124  allows a part of the laser beams reflected by scanner mirror  124  to pass therethrough, and reflects another part of the laser beams. The light reflected by half mirror  124  is received by photoreceptor  126 . In contrast, the part of the laser beams that has passed through half mirror  124  is projected onto screen  170  via a lens (not shown). 
     Photoreceptor  126  is configured with, for example, a plurality of photodiodes. An output of photoreceptor  126  is inputted to position detector  122 . Position detector  122  scans an output obtained from photoreceptor  126  in a horizontal direction and a vertical direction, and delivers data obtained through the scanning to system controller  150 . 
     In system controller  150 , CPU  160  is configured to control laser controller  152  and drive frequency controller  154  based on an output from position detection controller  156 . Furthermore, CPU  160  stores in memory  158  positional information of scanner mirror  120 , which has been calculated based on the output from position detection controller  156 . The positional information includes, for example, a scan angle, a signal value outputted for providing the scan angle (e.g. a voltage value), and the like. Memory  158  is implemented as a nonvolatile memory such as a flash memory in a certain aspect, or as a volatile memory in another aspect. 
     Laser controller  152  is configured to control red/blue lasers  10  and green laser  112  based on an output from CPU  160  and an output from a laser power detector  118 . Further, laser controller  152  can deliver to CPU  160  an output obtained from laser power detector  118 . 
     Drive frequency controller  154  is configured to control X driver  130  and Y driver  132  based on an output from CPU  160 . More specifically, drive frequency band controller  154  delivers to X driver  130  a signal having a frequency that defines drive in a horizontal direction such that scanner mirror  120  is driven in the horizontal direction (hereinafter also referred to as a “horizontal drive signal”), in response to a command from CPU  160 . Furthermore, drive frequency controller  154  delivers to Y driver  132  a signal having a frequency that defines drive in a vertical direction such that scanner mirror  120  is driven in the vertical direction (hereinafter also referred to as a “vertical drive signal”), in response to a command from CPU  160 . Based on the horizontal drive signal, X driver  130  drives scanner mirror  120  in the horizontal direction. Based on the vertical drive signal, Y driver  132  drives scanner mirror  120  in the vertical direction. 
     Based on an output from position detector  122 , position detection controller  156  A/D (Analog to Digital)-converts positional information of scanner mirror  120  (scan range), which is defined by the output of photoreceptor  126 , and delivers the converted digital data to CPU  160 . Based on the digital data, CPU  160  detects the position of scanner mirror  120 , and in accordance with the detection result, controls laser controller  152  or drive frequency controller  154 . 
     A vertical drive frequency and a horizontal drive frequency are predefined based on the size of scanner mirror  120 , the scan direction, and drive characteristics of X driver  130  or Y driver  132 . In a certain aspect, data that provides the vertical drive frequency and data that provides the horizontal drive frequency are stored in advance in memory  158 . 
     In the present embodiment, a part or a whole of system controller  150  may also be implemented by a combination of hardware such as circuit elements. In another aspect, system controller  150  may also be implemented as a configuration that controls an operation of the hardware by software, by means of CPU  160  executing a program stored in memory  158 . 
     With reference to  FIG. 2 , description will be made on a configuration of photoreceptor  126  that configures optical system  100  according to the present embodiment.  FIG. 2  is a diagram that schematically represents a light-receiving region in photoreceptor  126 . Photoreceptor  126  is configured with a plurality of light-receiving elements. Photoreceptor  126  includes a region for receiving a laser beam for projecting an image, and other regions. More specifically, photoreceptor  126  includes a peripheral region  200 , which differs from a region for projecting an image, and regions  210 ,  220 ,  230 , and  240  for projecting an image. 
     Portions of a laser beam reflected by scanner mirror  120  which correspond to light-receiving regions  210 ,  220 ,  230 , and  240  are projected onto screen  170  as an image. Peripheral region  200  is defined as a region that does not relate to image projection, and is intended for switching a scan direction of scanner mirror  120 . 
     In photoreceptor  126 , a boundary between light-receiving regions  210 ,  240  and light-receiving regions  220 ,  230  is orthogonal to a horizontal scan direction of scanner mirror  120 . Further, a boundary between light-receiving regions  210 ,  220  and light-receiving regions  230 ,  240  is defined to be parallel with a horizontal direction of scanner mirror  120 . 
     In the example shown in  FIG. 2 , the light-receiving region is defined as four regions  210 ,  220 ,  230 , and  240 . However, the number of light-receiving regions is not limited to the one specified by  FIG. 2 . For example, three or more light-receiving regions may be defined in a horizontal direction, or three or more light-receiving regions may be defined in a vertical direction. 
     [Functional Configuration] 
     With reference to  FIG. 3 , description will be made on a configuration of CPU  160  that implements laser projector  10  according to the present embodiment.  FIG. 3  is a block diagram that represents a configuration of functions implemented by CPU  160 . CPU  160  includes a laser light emission control unit  310 , a detection unit  320 , and a timing correction unit  330 . These functions are implemented by CPU  160  executing an executable program stored in memory  158 . 
     Laser light emission control unit  310  controls light emission and shut off of each of red/blue lasers  110  and green laser  112 . In another aspect, laser light emission control unit  310  is configured to shut off a light-emitting first light source (e.g. a laser beam source of any color in red/blue lasers  110 , or green laser  112 ) when sensing that a laser beam emitted from the first light source is received in light-receiving regions  210 ,  240  (hereinafter also referred to as a “first light-receiving region”). In this case, laser light emission control unit  310  allows the first light source to emit light again at an elapse of predetermined time from the shut off of the first light source. The predetermined time is defined as one piece of design information on laser projector  10 . This time is defined in accordance with a scan speed of scanner mirror  120  and a size of the light-receiving region in photoreceptor  126 . 
     In another aspect, when laser light emission control unit  310  senses that a laser beam emitted from a light-emitting second light source (e.g. a laser beam source different from a laser beam source corresponding to the above-described first light source) is received in light-receiving regions  210 ,  240 , laser light emission control unit  310  terminates the light emission caused by the second light source. Furthermore, laser light emission control unit  310  allows the second light source to emit light again at an elapse of predetermined time from the shut off of the second light source. 
     Detection unit  320  detects a deviation between an optic axis of the first light source and an optic axis of the second light source, based on a timing at which a laser beam emitted from the first light source is received in light-receiving regions  220 ,  230  (hereinafter also referred to as a “second light-receiving region”), and a timing at which a laser beam emitted from the second light source is received in the second light-receiving region. Timing correction unit  330  corrects the light emission timing of a laser beam source corresponding to the second light source, based on the “deviation” detected by detection unit  320 . 
     In another aspect, detection unit  320  includes a first calculation unit, a second calculation unit, and a third calculation unit. The first calculation unit calculates time that starts at a timing when reception of the laser beam emitted from a laser beam source serving as the first light source is sensed in the first light-receiving region (i.e. light-receiving regions  210 ,  240 ) and ends at a timing when the reception of the laser beam emitted from that laser beam source is sensed in the second light-receiving region (i.e. light-receiving regions  220 ,  230 ) (hereinafter also referred to as “first time”). 
     The second calculation unit calculates time that starts when the laser beam emitted from the first light source is received in the first light-receiving region and ends when the laser beam emitted from another laser beam source corresponding to the “second light source” is received in the second light-receiving region (hereinafter also referred to as “second time”). For example, the second time is calculated as time between the timing at which reception of a laser beam of one color is sensed in one light-receiving region and the timing at which reception of a laser beam of another color is sensed in another light-receiving region. 
     The third calculation unit calculates a difference between the first time and the second time. Timing correction unit  330  corrects the light emission timing of a laser beam source corresponding to the second light source, based on the difference calculated by the third calculation unit. 
     In an aspect, the scan direction includes a direction along which scanner mirror  120  is driven horizontally. In another aspect, the scan direction includes a direction along which scanner mirror  120  is driven vertically. 
     In another aspect, detection unit  320  detects the above-described deviation when laser projector  10  is started up. In still another aspect, detection unit  320  may also detect the above-described deviation in response to an input of a correction instruction to laser projector  10 . This input can be accepted, for example, via a switch provided at a housing of laser projector  10 . 
     In a further aspect, memory  158  stores data representing the relation between a scan angle of scanner mirror  120  and a scan speed predetermined in accordance with the relevant scan angle. Timing correction unit  330  corrects the “deviation” detected by detection unit  320 , based on the data. 
     [Control Structure] 
     With reference to  FIG. 4 , description will be made on a control structure of laser projector  10  according to the present embodiment.  FIG. 4  is a flowchart that represents a part of a series of operations executed by CPU  160  provided at laser projector  10 . 
     In step S 410 , CPU  160  delivers a command to laser controller  152  to thereby command a laser beam source of any one color, out of the laser beam sources of three colors, to emit a laser beam. The laser beam source of any one color is used as a reference for detecting a deviation of an optic axis. 
     In step S 420 , when CPU  160  senses that the laser beam is received in light-receiving regions  210 ,  240  in photoreceptor  126 , based on an output from position detection controller  156 , CPU  160  causes the relevant laser to be shut off. 
     In step S 430 , CPU  160  causes a laser of a color, which is to be detected as to the presence or absence of a deviation of an optic axis, to be applied until the reception thereof is sensed in light-receiving regions  220 ,  230 . The laser beam source lit at this time differs from the laser beam source lit in step S 410 . 
     In step S 440 , CPU  160  keeps time that starts when light reception is sensed in light-receiving regions  210 ,  240  and ends when light reception is sensed in light-receiving regions  220 ,  230 . 
     In step S 450 , CPU  160  determines whether or not the lasers of all colors, namely, red, blue and green, have been lit and shut off. For example, whenever CPU  160  delivers to laser controller  152  a command to allow a laser of any color to be emitted, CPU  160  sets a flag indicating that a laser beam of the relevant color has been lit. CPU  160  determines whether or not the lasers of all colors have been lit and shut off, based on a set state of the flags. If CPU  160  determines that the lasers of all colors have been lit and shut off (YES in step S 450 ), CPU  160  switches the control to step S 460 . If not so (NO in step S 450 ), CPU  160  returns the control to step S 420 , and allows a laser beam source of another color to be lit and shut off. 
     In step S 460 , CPU  160  calculates a relative time difference as to each color with respect to the reference color. 
     In step S 470 , CPU  160  corrects the light emission timing of the laser beam source of each color, based on the time calculated in step S 460 . More specifically, CPU  160  delivers to drive frequency controller  154  a command in which a light emission timing is corrected. Drive frequency controller  154  drives X driver  130  or Y driver  132  based on the command in which the light emission timing is corrected. 
     [Detection of a Deviation of an Optic Axis in a Horizontal Direction] 
     With reference to  FIG. 5 , description will be made on a deviation of an optic axis of a laser beam source in laser projector  10  in a horizontal direction.  FIG. 5  is a diagram that represents the relation between a timing of each of light emission and light-up of a laser of each color and an output of photoreceptor  126 . As an example, description will be made on the case that a red laser beam source in red/blue lasers  110  is used as a reference laser beam source. However, a laser beam of another color may also be used. 
     In  FIG. 5 , with reference to graph (A), a red laser beam source in red/blue lasers  110  performs irradiation based on a command from laser controller  152 . Specifically, the red laser beam source is lit at time point t( 0 ) (a sign of “R”). When the light reflected from half mirror  124  reaches the first light-receiving region (light-receiving regions  210 ,  240 ) by the drive of scanner mirror  120  in a horizontal direction, the laser beam from the red laser beam source is received in light-receiving regions  210 ,  240  at time point t( 1 ) (see timing chart A+D). 
     At time point t( 2 ), the red laser beam source is shut off based on a command from laser controller  152 . As a result, no laser beam is received in light-receiving regions  210 ,  240  after time point t( 2 ) (see timing chart A+D). 
     Subsequently, at time point t( 3 ), the red laser beam source is lit again based on a command from laser controller  152 . An output from the first light-receiving region appears again (see timing chart A+D). Note that time from time point t( 2 ) to time point t( 3 ) is predefined as design information, based on a width of the first light-receiving region and a scan speed of scanner mirror  120 . When scanner mirror  120  scans in a horizontal direction while the red laser beam source is being lit, the sensing of light reception in light-receiving regions  210 ,  240  continues from time point t( 3 ) to time point t( 4 ). 
     At time point t( 4 ), an output of the laser beam in photoreceptor  126  is sensed as light reception in light-receiving regions  220 ,  230  (see timing chart B+C). At time point t( 5 ), the red laser beam source is shut off in accordance with a command from laser controller  152 . As a result, the output from light-receiving regions  220 ,  230  also disappears (see timing chart B+C). 
     CPU  160  calculates a difference between the timing (time point t( 1 )) at which light reception in light-receiving regions  210 ,  240  is sensed, and the timing (time point t( 4 )) at which reception of the laser beam in light-receiving regions  220 ,  230  is sensed, as reference time T HR . Reference time T HR  is used for comparison with corresponding time of a laser beam of another color. 
     In  FIG. 5 , with reference to graph (B), after the red laser beam source selected as a reference laser beam source is lit and shut off, similar processing is executed on the laser beam sources of other colors. For example, processing for detecting a deviation of an optic axis of green laser  112  is initiated. 
     More specifically, laser controller  152  initially provides a command to the red laser beam source and allows it to be lit at time point t( 10 ) and shut off at time point t( 12 ). In this case, an output from light-receiving regions  210 ,  240  continues from time point t( 11 ) to time point t( 12 ) (timing chart A+D). 
     At time point t( 13 ), laser controller  152  provides a command to green laser  112  and allows it to be lit. The light-up of green laser  112  continues from time point t( 13 ) to time point t( 15 ). Reception of the green laser beam in light-receiving regions  210 ,  240  is sensed from time point t( 13 ). When scanner mirror  120  is kept driven in a horizontal direction, an output indicating the reception of the laser beam from green laser  112  is switched at time point t( 14 ) from light-receiving regions  210 ,  240  (timing chart A+D) to light-receiving regions  220 ,  230  (timing chart B+C). 
     CPU  160  calculates time that starts at the light emission timing (time point t( 10 )) of the reference laser beam source (the red laser beam source) and ends at time point t( 14 ), as determination target time T HG . CPU  160  compares determination target time T HG  with reference time T HR , and determines the presence or absence of the difference therebetween. 
     In  FIG. 5 , with reference to graph (C), laser controller  152  executes processing for detecting a deviation of an optic axis of a laser beam source of still another color. For example, laser controller  152  provides a command to a blue laser beam source in red/blue lasers  110 . 
     More specifically, laser controller  152  allows the red laser beam source to be lit at time point t( 20 ). When scanner mirror  120  is kept driven in a horizontal direction, an output indicating the reception of the red laser beam in light-receiving regions  210 ,  240  appears at time point t( 21 ) (timing chart A+D). Subsequently, at time point t( 22 ), laser controller  152  allows the red laser beam source to be shut off. The output from light-receiving regions  210 ,  240  disappears (see timing chart A+D). 
     At time point t( 23 ), laser controller  152  allows the blue laser beam source in red/blue lasers  110  to be lit. The light-up of the blue laser beam source continues until time point t( 25 ). The reception of the blue laser beam in light-receiving regions  210 ,  240  continues, for example, from time point t( 23 ) to time point t( 24 ). After time point t( 24 ), the reception of the blue laser beam is sensed as an output from the second light-receiving region. 
     CPU  160  calculates a difference between time point t( 21 ) and time point t( 24 ) as determination target time T HB . CPU  160  compares the calculated determination target time T HB  with reference time T HR , and determines the presence or absence of a deviation of an optic axis of the blue laser beam source. 
     [Detection of a Deviation of an Optic Axis in a Vertical Direction] 
     With reference to  FIG. 6 , description will be made on detection of the presence or absence of a deviation of an optic axis in a vertical direction in optical system  100 .  FIG. 6  is a diagram that represents the relation between drive of scanner mirror  120  in a vertical direction and an output based on irradiation by a green laser  112  and red/blue lasers  110 . The red laser beam source in red/blue lasers  110  is used as a reference. 
     In  FIG. 6 , with reference to graph (A), the drive of scanner mirror  120  is started at time point t( 30 ) based on a command from Y driver  132 , and scanner mirror  120  is vertically driven until time point t( 35 ). Scanner mirror  120  is returned to the initial position between time point t( 35 ) and time point t( 36 ). 
     With reference to graph (B), the red laser beam source is lit based on a command from laser controller  152  at time point t( 31 ). The output of the red laser beam continues from time point t( 31 ) to time point t( 34 ). 
     The light reflected from half mirror  124  is directed to light-receiving regions  210 ,  220 , and at time point t( 32 ), directed to light-receiving regions  230 ,  240  (second light-receiving region). Accordingly, the output from light-receiving regions  230 ,  240  starts at time point t( 32 ). At time point t( 33 ), when the light reflected from half mirror  124  deviates from light-receiving regions  230 ,  240 , the output in light-receiving regions  230 ,  240  is terminated (see timing chart C+D). Subsequently, at time point t( 34 ), the red laser beam source terminates irradiation of the laser beam based on a command from laser controller  152 . 
     CPU  160  calculates reference time T VR  from time point t( 31 ) to time point t( 32 ), as reference time. Reference time T VR  is used for determining the presence or absence of a deviation of an optic axis of the laser beam of another color. 
     With reference to graph (C), at time point t( 41 ), laser controller  152  allows green laser  112  to be lit (see LD irradiation (G)). When scanner mirror  120  is driven in a vertical direction, the light reception in light-receiving regions  230 ,  240  is sensed at time point t( 42 ). The light reception in light-receiving regions  230 ,  240  continues from time point t( 42 ) to time point t( 43 ). At time point t( 44 ), laser controller  152  terminates the light-up caused by green laser  112 . CPU  160  calculates a difference between time point t( 41 ) and time point t( 42 ) as determination target time T VG . 
     With reference to graph (D), at time point t( 51 ), laser controller  152  allows the blue laser beam source in red/blue lasers  110  to be lit (see LD irradiation (B)). When scanner mirror  120  is driven in a vertical direction, the light reception in light-receiving regions  230 ,  240  is sensed at time point t( 52 ). The light reception in light-receiving regions  230 ,  240  continues from time point t( 52 ) to time point t( 53 ). At time point t( 54 ), laser controller  152  terminates the light-up caused by the blue laser beam source. CPU  160  calculates a difference between time point t( 51 ) and time point t( 52 ) as determination target time T VB . 
     [Correction to the Timing] 
     With reference to  FIG. 7 , description will be made on the correction to irradiation timings of green laser  112  and red/blue lasers  110 . In  FIG. 7 , timing chart (A) represents a timing at which laser controller  152  provides a command to emit light to a light source of any of the colors selected as a reference color. Specifically, the red laser beam source is selected as a reference laser beam source. A laser beam source of another color may also be selected. 
     The red laser beam source is applied from time point t( 60 ) to time point t( 61 ), from time point t( 62 ) to time point( 63 ), from time point t( 64 ) to time point t( 65 ), and from time point t( 66 ) to time point t( 67 ), so as to determine the presence or absence of a deviation of an optic axis. 
     With reference to timing chart (B), the red laser beam is lit based on the command from laser controller  152 , at the same interval as the interval between the starts of irradiation defined in timing chart (A). 
     With reference to timing chart (C), green laser  112  is lit in accordance with a corrected timing calculated based on the examples shown in  FIGS. 5 and 6 . Specifically, green laser  112  is lit at time point t( 71 ). Time point t( 71 ) is delayed with respect to time point t( 60 ) at which the red laser is lit, by corrected time (T VG −T VR )+(T HG −T HR ). 
     With reference to timing chart (D), the blue laser source in red/blue lasers  110  is lit in accordance with the corrected timing calculated based on the examples shown in  FIGS. 5 and 6 . Specifically, the blue laser beam source is lit at time point t( 81 ). Time point t( 81 ) is advanced with respect to time point t( 60 ) at which the red laser is lit, by corrected time (T VB −T VR )+(T HB −T HR ). 
     Effects of the Embodiment  
     As described above, laser projector  10  according to the embodiment of the present invention detects the presence or absence of a deviation of an optic axis of a light source of each of the colors of R, G and B at start-up, and based on the detection results, corrects the emission timing of a laser beam to be emitted from the light source in which a deviation is detected. 
     Before projecting an image, laser projector  10  drives scanner mirror  120  in a horizontal direction or a vertical direction, while applying a laser beam of a single specific color. The laser beam is received in the two light-receiving regions in photoreceptor  126 , the two light-receiving regions being defined by a boundary orthogonal to the moving direction of scanner mirror  120 . Laser projector  10  calculates each output time from each of the light-receiving regions, each output time being based on the emission of the laser beam of the single specific color. 
     Subsequently, laser projector  10  applies laser beams of other colors one by one, and drives scanner mirror  120  in the same direction. Laser projector  10  calculates each output time from each of the light-receiving regions, each output time being based on the emission of the laser beam of the single color, as to each of the colors. 
     Laser projector  10  further calculates a difference between the time calculated as to the single specific color and the time calculated as to one of the other colors, so as to check whether or not there is a difference. The existence of the difference means that the emission timing of that color deviates, so that laser projector  10  corrects the deviation. For example, laser projector  10  calculates the time to be corrected, based on the time calculated as a difference and a movement speed of scanner mirror  120 . 
     For example, if the interval between when the reception in one light-receiving region is sensed and when the reception in another light-receiving region is sensed, as to the color to be compared, is shorter than the corresponding interval as to the specific color serving as a reference, laser projector  10  makes a correction to delay the irradiation timing of the laser beam. In contrast, if the interval between when the reception in one light-receiving region is sensed and when the reception in another light-receiving region is sensed, as to the color to be compared, is longer than the corresponding interval as to the specific color serving as a reference, laser projector  10  makes a correction to advance the irradiation timing of the laser beam. By doing so, the optic axes of respective laser beam sources coincide with one another when an image is projected, so that each of the colors is accurately reproduced. Consequently, adjustment of the optic axes can readily be achieved without an increase in number of components. 
     Although the timing of correction is set at the start-up of laser projector  10 , the timing is not limited thereto. For example, the switch that accepts an instruction of adjustment is provided at a housing of laser projector  10 , and a deviation of the optic axes may be corrected in response to a manipulation on the relevant switch. Alternatively, the correction may also be made at a timing at which the data to be projected is inputted to laser projector  10 . 
     &lt;Modification&gt; 
     With reference to  FIG. 8A  and  FIG. 8B , description will be made on a modification of the present embodiment. Scanner mirror  120  has a scan speed that varies depending on a scan angle, and hence laser projector  10  according to the present modification may have a configuration in which a lookup table of a scan speed of scanner mirror  120  is included and CPU  160  corrects the detected time difference by referring to the table. It is noted that laser projector  10  according to the present modification has a hardware configuration similar to that of laser projector  10  shown in  FIG. 1 , and has the same functions. Accordingly, the detailed description of the hardware configuration is not repeated. 
       FIG. 8A  is a diagram that shows a pattern of the drive of scanner mirror  120  in a horizontal direction.  FIG. 8B  is a diagram that shows the relation between a scan angle and a scan speed at each location shown in  FIG. 8A . 
     More specifically, when scanner mirror  120  is positioned at opposite ends of the scan range in the horizontal direction (specifically, at locations  810 ,  820 , and  830 ), the scan speed is 0. In contrast, in proximity to the center of photoreceptor  126  in the horizontal direction, the scan speed of scanner mirror  120  has local maximum. Therefore, the timing at which each of the laser beams is lit for correcting a deviation of the optic axes may be calculated based on the relation between the scan angle and the scan speed as shown in  FIG. 8B  (e.g. the relation expressed as a sine curve). Such a relation is retained in memory  158 , for example, as a mapped data table or a function. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by the terms of the appended claims.

Technology Category: 5