Abstract:
A single-plate color projector includes a color wheel for chromatically separating light emitted from a light source in time series. An image forming device optically modulates each separated color light in sequence. A driving mechanism rotates the color wheel in a circumferential direction. A reflective marker is rotated together with the color wheel. A detector circuit detects movement of the reflective marker to generate a signal. A driving mechanism control circuit drives the driving mechanism in synchronization with the signal generated by the detector circuit. An image forming device control circuit drives the image forming device in synchronization with the signal generated by the detector circuit; and a time adjusting mechanism moves either the reflective marker or the detector circuit or both the reflective marker and the detector circuit to change a relative positional relationship therebetween.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a single-plate color projector and a method to adjust synchronization of a color wheel and an image forming device.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 1  illustrates the basic configuration of a conventional single-plate color projector (also referred to as “color projector”) using a color wheel. In color projector  10  illustrated in  FIG. 1 , white light emitted from light source  11  is converged by reflective mirror  12 , and irradiated to color wheel  13 . Color wheel  13  comprises a disk which is formed with an optical filter (red filter) for transmitting only red light and reflecting or absorbing the remaining color light, an optical filter (green filter) for transmitting only green light and reflecting or absorbing the remaining color light, and an optical filter (blue filter) for transmitting only blue light and reflecting or absorbing the remaining color light. These filters are arranged along the circumferential direction of the disk. Color wheel  13  is driven by driving motor  23 , controlled by motor control circuit  22 , at high speeds. The filters in respective colors are sequentially inserted into a light path of the light emitted from light source  11  in association with the rotation of color wheel  13 , so that white light irradiated to color wheel  13  is separated into red light, green light, and blue light in time series. Each of the separated red, green, and blue light is sent to light valve  14  then to reflective minor  15  for irradiation to image forming device  16  such as a liquid crystal panel, DMD (registered trademark), etc. On the other hand, image forming device  16  is driven under the control of image forming device control circuit  17 . Image forming device control circuit  17  drives image forming device  16  in accordance with a video signal applied thereto. Image forming device control circuit  17  turns ON or OFF each of the cells or miniature mirrors of image forming device  16  in accordance with a video signal applied thereto to reflect the irradiated single-color light pixel by pixel for optical modulation to form image light. The formed image light is directed into projection lens  18  which projects the image light onto a screen etc., not shown, in an enlarged view.  
         [0005]     The color projector having the configuration described above must synchronize a color separation performed by color wheel  13  with an optical modulation performed by image forming device  16 . In color projector  10  illustrated in  FIG. 1 , highly reflective marker  19  is attached onto color wheel  13 , and reflection-type photo-interrupter  20  is disposed near color wheel  13 . Reflection-type photo-interrupter  20  is a sensor having a light emitting element integrated with a light receiving element. Light emitted from the light emitting element impinges on and is reflected by reflective marker  19  each time color wheel  13  rotates once. The reflected light is then received by the light receiving element, and the light receiving element generates a signal. The signal generated by the light receiving element is detected by detector circuit  21 , and is applied to motor control circuit  22  and image forming device control circuit  17  as a synchronizing signal. Motor control circuit  22  and image forming device control circuit  17  drive driving motor  23  and image forming device  16  respectively in accordance with the synchronizing signal applied thereto. The foregoing operation accomplishes the synchronization of the color separation performed by color wheel  13  with the optical modulation performed by image forming device  16 . Details on a color projector which accomplishes the synchronization in the foregoing manner are described in the specification etc. of Japanese Patent Laid-open Publication No. 2001-337390 (reference document No. 1).  
         [0006]     Another technique for accomplishing the synchronization of the color separation performed by the color wheel with the optical modulation performed by the image forming device may involve detecting a light color transmitted by the color wheel with a pair of sensors each detecting different color light, and detecting a time at which light beam from a light source passes through the boundary between the two color filters. For example, a pair of sensors may be composed of a photodiode for detecting blue light and a photodiode for detecting red light, and the beam spot is determined to have passed the boundary between the red filter and blue filter, when the outputs of the respective photodiodes become equal to each other, i.e., when a magenta color is detected. In this way, the boundary between the red filter and blue filter is detected as a reference position for the rotation of the color wheel, and the image forming device is driven based on the result of the detection, thereby accomplishing the synchronization of the color separation performed by the color wheel with the optical modulation performed by the image forming device. Details on a projector which accomplishes the synchronization in this manner are described in the specification etc. of Japanese Patent Laid-open Publication No. 127437/97 (reference document No. 2).  
         [0007]     However, there will be errors in the position to which the reflective marker is attached, and the position at which the sensor is disposed. Further, the boundary between the respective color filters includes errors associated with manufacturing. When these errors exist, the technique described in reference document No. 1 fails to fully accomplish the synchronization of the color separation performed by the color wheel with the optical modulation performed by the image forming device, resulting in a failure in to correctly to reproduce the colors.  
         [0008]     The technique described in reference document No. 2 cannot accurately detect a magenta color unless the pair of sensors (photodiodes) match each other in characteristics and are equal in detection sensitivity to each other, thus experiencing difficulties in detecting the reference position for the rotation with a high accuracy. Further, since the pair of sensors must detect color light under equal conditions, the pair of sensors are required to be disposed at optically equivalent positions. It is therefore difficult to detect the reference position for the color wheel with high accuracy in a simple configuration to control the rotation time. Consequently, colors are not correctly reproduced as is the technique described in the reference document No. 1.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the present invention to provide a color projector which accurately accomplishes synchronization of color separation performed by a color wheel with an optical modulation performed by an image forming device in a simple configuration, as well as a synchronization adjusting method for the color projector.  
         [0010]     A single-plate color projector according to an embodiment of the present invention comprises a color wheel for chromatically separating light emitted from a light source in time series; an image forming device for optically modulating each separated color light in sequence; a driving mechanism for rotating the color wheel in a circumferential direction; a reflective marker rotated together with the color wheel; a detector circuit for detecting movement of the reflective marker to generate a signal; a driving mechanism control circuit for driving the driving mechanism in synchronization with the signal generated by the detector circuit; an image forming device control circuit for driving the image forming device in synchronization with the signal generated by the detector circuit; and a time adjusting mechanism for moving either the reflective marker or the detector circuit or both the reflective marker and the detection circuit to change a relative positional relationship therebetween.  
         [0011]     A method of adjusting synchronization of a single-plate color projector according to another embodiment of the present invention relates to a single-plate color projector comprising a light source, a color wheel comprising two or more optical filters for chromatically separating light emitted from the light source in time series, an image forming device for optically modulating each separated color light in sequence, a driving mechanism for rotating the color wheel in a circumferential direction, a reflective marker rotated together with the color wheel, a detector circuit for detecting movement of the reflective marker to generate a signal, a driving mechanism control circuit for driving the driving mechanism in synchronization with the signal generated by the detector circuit, an image forming device control circuit for driving the image forming device in synchronization with the signal generated by the detector circuit. The method comprising the steps of: operating the color projector such that the image forming device, is driven only when a particular one of the two or more optical filters is inserted in a light path; detecting a chromaticity value of light projected from the color projector while moving either the reflective marker or the detector circuit or both the reflective marker and the detection circuit; and adjusting a positional relationship between the reflective marker and the detector circuit such that the detected chromaticity value reaches a maximum.  
         [0012]     Thus, according to the present invention, an error in synchronization caused by a positional relationship between the reflective marker and the detector circuit can be corrected by physically shifting the reflective marker or detector circuit. Since a chromaticity value of actual projected light is utilized to determine the moving direction and the moving distance, an accurate synchronization adjustment can be accomplished. In addition, since the chromaticity value of projected light can be detected by a conventional detector or measuring device, no special device needs to be provided for adjusting the synchronization. It is therefore possible to accurately adjust the synchronization time in a simple configuration and accordingly reproduce correct colors in accordance with a video signal.  
         [0013]     The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a block diagram illustrating an example of a prior art color projector;  
         [0015]      FIG. 2  is a block diagram illustrating one embodiment of a color projector according to the present invention;  
         [0016]      FIG. 3  is a diagram showing a single-color spectrum locus, and a chromaticity diagram representing a range of colors which can be reproduced by the color projector; and  
         [0017]      FIG. 4  is a block diagram illustrating another embodiment of a color projector according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring to  FIG. 2 , color projectors has time adjuster  2  in addition to the same components as those in color projector  10  illustrated in  FIG. 1 . Components identical to those illustrated in  FIG. 1  are designated the same reference numerals, and repetitive description is omitted. The following description will focus on the features of the color projector according to this embodiment, especially on time adjuster  2 .  
         [0019]     Time adjuster  2  illustrated in  FIG. 2  comprises a movable table, not shown, on which a reflective photo-interrupter  20  is mounted; and a driving mechanism, not shown, for moving the movable table by a distance and in a direction determined by external color determination unit  3 . Color determination unit  3  determines a moving direction and a moving distance of the movable table based on the detection result of chromaticity detector  4  which detects colors of light emitted from color projector  1  as chromaticity values. Color determination unit  3  sends the result to the driving mechanism.  
         [0020]      FIG. 3  shows colors of light emitted from color projector  1  in an xy chromaticity diagram. Curve (a) shown in  FIG. 3  represents a single-color spectrum locus, and all chromaticity values (chromaticity coordinates) of actual objects exist within this area. On the other hand, in single-plate color projector  1  which chromatically separates white light by color wheel  13  composed of a red, a green, and a blue filter, a color image is reproduced by a combination of light in three primary colors, i.e., red, green, blue, so that a color reproducible range exists within triangle (b) shown in  FIG. 3 . In other words, the chromaticity value of a color reproduced by color projector  1  exists within triangle (b) which has apexes at chromaticity value R of color light which is transmitted by a red filter, chromatcity value G of color light which is transmitted by a green filter, and chromaticity value B of color light which is transmitted by a blue filter. For example, when color projector  1  is operated to emit color light which is transmitted by the red filter only (image forming device  16  is driven to reflect light emitted from light source  11  only when the red filter of color wheel  13  is inserted in the light path of the light emitted from light source  11 ), the chromaticity value at point R in  FIG. 3  will be found by chromaticity detector  4 . However, if the time at which a color filter inserted in the light path of the light emitted from light source  11  is switched to the next filter deviates from the time at which image forming device  16  is driven, image forming device  16  continues the reflecting operation even after the next color filter is inserted into the light path. For example, if the time at which the red filter is switched to the blue filter for insertion into the light path is not synchronized with the time at which image forming device  16  is driven, the chromaticity value detected by chromaticity detector  4  will be shifted from point R towards point B along a straight line which connects point R to point B shown in  FIG. 3  in accordance with the amount of the deviation between the times. Also, if the time at which the green filter is inserted into the light path instead of the red filter is not synchronized with the time at which the image forming device  16  is driven, the chromaticity value detected by chromaticity detector  4  will be shifted from point R towards point G along a straight line which connects point R to point G shown in  FIG. 3  in accordance with the amount of the deviation between the times.  
         [0021]     Color projector  1  of the present invention accomplishes the synchronization of time at which a color filter is inserted into the light path instead of a currently inserted color filter with the time at which image forming device  16  is driven by similar principles to color projector  10  illustrated in  FIG. 1 . Therefore, the error in synchronization as mentioned above is mainly caused by a deviation from, an expected positional relationship of the position of reflective marker  19 , which serves as a reference position for rotation of color wheel  13 , and the position of reflective photo-interrupter  20 .  
         [0022]     However, color projector  1  of the present invention which comprises time adjuster  2 , that can shift reflective photo-interrupter  20 , adjusts (calibrates) the synchronization by correcting a relative positional relationship between reflective marker  19  and reflective photo-interrupter  20  in the following procedure.  
         [0023]     A computer is provided outside color projector  1  for functioning as color determination unit  3  described above and later again. Color projector  1  is provided with an input port for providing time adjuster  2  with a signal delivered from color determination unit  3 . An output port of color determination unit  3  is connected to the input port of color projector  1  through a coaxial cable or the like, so that a signal indicative of a moving direction and a moving distance of the movable table is input to time adjuster  2 . Color projector  1  is operated with its input port connected to the output port of color determination unit  3  through the coaxial cable, such that image forming device  16  is driven only when the read filter of color wheel  13  is inserted in the light path of the light emitted from light source  11 . As will be apparent from the foregoing description, color wheel  13  is synchronized with image forming device  16  by a synchronizing signal based on the result of the detection made by current reflective photo-interrupter  20 . Color projector  1  is provided with a synchronization adjusting mode, and automatically performs the operation as described above in response to a selection of this mode.  
         [0024]     Next, the projected light from color projector  1  is incident on chromaticity detector  4 . Chromaticity detector  4  detects the chromaticity value of the projected light incident thereon, and sends the detected chromaticity value to color determination unit  3 . If reflective marker  19  and reflective photo-interrupter  20  are in a correct relative positional relationship, the chromaticity value detected by chromaticity detector  4  will be found on point R shown in  FIG. 3 . If there is an error in the relative positional relationship, the chromaticity value detected by chromaticity detector  4  is shifted from point R towards point B along the straight line which connects point R to point B, shown in  FIG. 3 , or from point R towards point G along the straight line which connects point R to point G. The movable table of time adjuster  2  is moved in a continuous or a step-by-step manner to change the relative positional relationship between reflective marker  19  and reflective photo-interrupter  20 . Color determination unit  3  monitors the chromaticity value detected by chromaticity detector  4  simultaneously and directs time adjuster  2  to move reflective photo-interrupter  20  to a position at which the chromaticity value (x-value) reaches a maximum.  
         [0025]     With the foregoing procedure, a proper relative positional relationship can be achieved between reflective marker  19  and reflective photo-interrupter  20 . As a result, the time at which a color wheel is inserted is correctly synchronized with the time at which image forming device  16  is driven by the synchronizing signal based on the result of the detection by reflective photo-interrupter  20 .  
         [0026]     Next, another embodiment of the color projector according to the present invention will be described in detail with reference to  FIG. 4 .  FIG. 4  is a block diagram schematically illustrating the configuration of a color projector according to a second embodiment. Color projector  5  is identical in basic configuration to color projector  1  illustrated in  FIG. 2 . The illustration of light source  1  and reflective mirror  12  is omitted in  FIG. 4 . A difference is that color projector  1  accomplishes the adjustment of synchronization by physically shifting the position of reflective photo-interrupter  20  through time adjuster  2 , whereas color projector  5  of the second embodiment accomplishes a similar adjustment of synchronization by signal processing using delay circuit  28 . Components common to color projector  1  illustrated in  FIG. 2  are designated the same reference numerals, and are omitted in the following description. The following description will focus on the features of color projector  5  of the second embodiment, especially on delay circuit  28 .  
         [0027]     Color projector  5  accomplishes the synchronization of the time at which a filter is inserted next with the time of light modulation performed by image forming device  16  by similar principles to color projector  10  illustrated in  FIG. 1 . Specifically, the time at which a filter is inserted next is synchronized with the time of light modulation performed by image forming device  16  using a synchronizing signal which is delivered from reflective photo-interrupter  20  and detected by detector circuit  21 . However, one of two synchronizing signals divided from the signal delivered from detector circuit  21 , and which is a synchronizing signal applied to motor circuit  22 , is delayed by delay circuit  28  before it is input to motor control circuit  22 . On the other hand, image forming device control circuit  17  is provided with a synchronizing signal as delivered from detector circuit  21  without delay.  
         [0028]     Color projector  5  correctly synchronizes the time at which a filter is inserted next with the time of light modulation performed by image forming device  16  by adjusting the timing at which color wheel  13  is rotated in the following procedure.  
         [0029]     First, as described in connection with the first embodiment, color projector  5  is operated in the synchronization adjusting mode to project only red light. Next, the projected light of color projector  5  is incident on chromaticity detector  4  to detect a chromaticity value of the light. A predetermined output port of chromaticity detector  4  is connected to a predetermined input port of color projector  5  through a coaxial cable or the like. The chromaticity value detected by chromaticity detector  4  is input to CPU (Central Processing Unit)  30 . CPU  30  monitors the chromaticity value applied thereto. If reflective marker  19  and reflective photo-interrupter  20  are in a correct relative positional relationship, the chromaticity value input to CPU  30  will be found on point R shown in  FIG. 3 . However, if there is an error in the relative positional relationship, the applied chromaticity value is shifted from point R towards point B along the straight line which connects point R to point B shown in  FIG. 3 , or shifted from point R towards point G along the line which connects point R to point G.  
         [0030]     CPU  30  monitors the chromaticity value applied thereto, while changing the amount of delay in delay circuit  28  in a continuous or a step-by-step manner, to set the amount of delay which results in a maximum chromaticity value (x-value), and stores the set amount of delay in memory  29 . Once stored in memory  29 , CPU  30  can read the amount of delay from memory  29  to control the amount of delay in delay circuit  28 .  
         [0031]     Thus, color projector  5  of the second embodiment correctly synchronizes the time at which a filter is inserted next with the time of light modulation performed by image forming device  16  by adjusting the time at which a filter is inserted next to the time at which image forming device  16  is driven in accordance with a reference synchronizing signal which is not delayed.  
         [0032]     Alternatively, one of the two synchronizing signals divided from the signal delivered from detector circuit  21 , and which is a synchronizing signal input to image forming device control circuit  17 , may be delayed by delay circuit  28 , while motor control circuit  22  may be applied with a synchronizing signal which is not delayed. This also correctly synchronizes the time at which a filter is inserted next with the time of light modulation performed by image forming device  16 .  
         [0033]     While the first and second embodiments have been described in connection with the synchronization adjustment by utilizing red light transmitted by the red filter of color wheel  13 , the synchronization adjustment also may be made by utilizing color light which is transmitted by the green filter or blue filter of color wheel  13 . The relative positional relationship between reflective marker  19  and reflective photo-interrupter  20  or the amount of delay caused by delay circuit  28  may be adjusted such that a chromaticity value detected by chromaticity detector  4  reaches that of a maximum green color or a maximum blue color. Specifically, the maximum green color is determined when the y-value of the chromaticity value reaches a maximum, and the maximum blue color is determined when the x-value or y-value of the chromaticity value reaches a minimum. Further, the xy-chromaticity coordinate may be rotated in an appropriate manner to detect the maximum or minimum x-value or y-value more accurately.  
         [0034]     In certain embodiments, color wheel  13  may comprise a white filter, which is an optical filter which has characteristics of transmitting incident light as it is, in addition to the red filter, green filter, and blue filter, to increase the amount of light emitted from projection lens  18 . Since the color reproducible range remains within the area of triangle (b) shown in  FIG. 3 , the synchronization adjustment may be made by the procedure described above.  
         [0035]     Chromaticity detector  4  used in the present invention may be a conventional color meter used for color adjusting for a color projector. It is therefore possible to accurately synchronize the time of color separation performed by the color wheel and the time of light modulation performed by the image forming device without the need of a special device. This is particularly effective when the synchronization is adjusted in a manufacturing factory or a repair site.  
         [0036]     Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims.