JP4810941B2 - projector - Google Patents

Description

  The present invention relates to a projector capable of projecting a color image on a screen.

  Conventionally, small projectors using LEDs (light emitting diodes) have been proposed (see, for example, Patent Document 1). When performing color display projection by separately providing RGB LEDs, white balance adjustment becomes a problem because the light emission efficiency of the LEDs is different for each RGB and there are individual differences in the LEDs. In general, white balance adjustment is performed by actually measuring the color balance of projection light at the time of manufacture and finely adjusting the drive current value or drive duty ratio of each of RGB based on the measurement result. These adjustment values are stored in advance in the apparatus.

Japanese Patent Laid-Open No. 2005-3900

  However, the luminous efficiency of the LED has temperature dependence, and the temperature dependence differs for each of R, G, and B. Therefore, even if the adjustment as described above is performed at the shipping stage, if the environmental temperature during actual use is different from the temperature at the time of adjustment, the color balance will be lost. Also, the color balance is lost when the light emission characteristics of the LED change with time.

The projector according to the first aspect of the present invention has a plurality of light sources that generate different color lights, and can illuminate them independently, and the illumination light from the illumination means is converted into two polarized lights having different polarization directions. A polarization separation element to be separated, a spatial light modulation element that modulates the incident polarized light based on image information, and a light modulated by the spatial light modulation element. Separating and projecting means for separating the polarized light for projection and projecting it on the screen, a photoelectric conversion element for receiving the other polarized light separated by the polarization separation element and outputting a signal corresponding to the amount of received light, and a photoelectric conversion element And a control means for adjusting the color balance of the projected image projected on the screen by driving and controlling each of the plurality of light sources based on the output signal.
According to a second aspect of the present invention, in the projector according to the first aspect, the correlation between the intensity of the polarized light for projection and the amount of light received by the photoelectric conversion element or the signal output value of the photoelectric conversion element is stored in advance as data. The control means is configured to perform color balance adjustment based on data stored in the storage unit.
According to a third aspect of the present invention, in the projector according to the first or second aspect, the illuminating means includes a first light emission with a first intensity and a second with a second intensity weaker than the first intensity for each of a plurality of light sources. The light emission can be switched, and the control means performs color balance adjustment based on the output signal of the photoelectric conversion element during the second light emission.
According to a fourth aspect of the present invention, in the projector according to the third aspect, the spatial light modulation element is a reflective light valve using a ferroelectric liquid crystal, and performs normal image display during the first light emission and an inverted image during the second light emission. The display is performed.

  According to the present invention, polarized light that is not used for projection among the two polarized lights separated by the polarization separation element is received by the photoelectric conversion element, and a plurality of different colored lights are generated based on the output signal of the photoelectric conversion element. Since the light source is driven and controlled, and the color balance of the projected image projected on the screen is adjusted, it is possible to obtain a projected image with good color balance even if the light source light changes due to temperature changes or changes over time. it can.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a projector according to the present invention. The projector includes an illumination unit 1 that generates illumination light, a polarizing beam splitter (hereinafter referred to as PBS) 2, an LCOS 3 that is a kind of a reflective liquid crystal light valve, a CMOS light receiving element 4, a projection lens 5, and a controller 6. Yes. The controller 6 is provided with an LED control circuit 61, an LCOS control circuit 62, a CMOS control circuit 63, a CPU 64, and a memory 65. The memory 65 stores programs processed by the CPU 64 and various data.

  The illumination unit 1 includes a high-intensity LED 11 that is a light source, and a condenser lens 12 that makes light from the LED 11 substantially parallel light. The LED 11 is provided with LEDs of three colors, R (red), G (green), and B (blue), in one package. By switching between these LEDs, R light, G light, and B light are individually provided. Can emit light. The light emission control of the LED 11 is performed by an LED control circuit 61 provided in the controller 6. By controlling the drive current value, lighting time (duty ratio), etc. of each color LED, it is possible to control the light emission intensity of each of RGB, thereby adjusting the white balance (color balance) of the projected image. Can do.

  The unpolarized light emitted from the illumination unit 1 enters the PBS 2, and is separated into S-polarized light and P-polarized light by the separation surface 2a on which the polarization separation film is formed. The polarization separation film is configured to transmit P-polarized light and reflect S-polarized light, and the P-polarized light transmitted through the separation surface 2 a is incident on the CMOS light receiving element 4. The detection signal of the CMOS light receiving element 4 that has received the P-polarized light is input to the CMOS control circuit 63. In the present embodiment, the amount of illumination light emitted from the illumination unit 1 can be detected by receiving the P-polarized light by the CMOS light receiving element 4.

  On the other hand, the S-polarized light reflected by the separation surface 2a enters the LCOS 3. In the projector according to the present embodiment, ferroelectric liquid crystal (FLC) capable of high-speed driving is used for LCOS 3 in order to perform color display by field sequential driving.

  The LCOS control circuit 62 controls the voltage applied to each pixel of the LCOS 3 based on image information input from the CPU 64. In each pixel of the LCOS 3, the arrangement of liquid crystal molecules changes according to the applied voltage, and the liquid crystal layer serves as a phase plate. By controlling the applied voltage, it is possible to form a state in which the polarization direction of the incident polarized light is emitted by rotating by 90 degrees and a state in which the incident polarized light is emitted without changing the polarization direction. Here, a pixel whose polarization direction is rotated by 90 degrees is called a white pixel, and a pixel whose polarization direction is not changed is called a black pixel. That is, an image pattern composed of white pixels and black pixels corresponding to the image information is formed on the LCOS 3.

  S-polarized light incident on the LCOS 3 from the PBS 2 is modulated according to whether the state of each pixel is a white pixel or a black pixel. That is, the S-polarized light incident on the black pixel of the LCOS 3 is emitted in the PBS2 direction as the S-polarized light without changing the polarization state. On the other hand, the polarization direction of the S-polarized light incident on the white pixel is rotated by 90 degrees and emitted to the PBS 2 as P-polarized light. Thus, the LCOS 3 performs spatial light modulation according to the input image information and emits the incident polarized light as modulated light.

  S-polarized light included in the modulated light emitted from the LCOS 3 (that is, S-polarized light emitted from the black pixel portion of the LCOS 3) is reflected by the separation surface 2a of the PBS 2 and returns to the illumination unit 1. The polarized light that has returned to the illuminating unit 1 is reflected inside the illuminating unit 1, and a part thereof is used again as illuminating light. On the other hand, the P-polarized light emitted from the white pixel portion of the LCOS 3 is transmitted through the separation surface 2a of the PBS 2 and projected onto a screen (not shown) by the projection lens 5.

  In the case of LCOS3 using ferroelectric liquid crystal, high-speed driving is possible as described above, but in order to prevent image burn-in phenomenon, reverse image display by reverse drive in which the polarity of the liquid crystal is reversed and normal image display Need to be performed alternately. In general, when the reverse image is displayed, the illumination light is turned off to prevent the reverse image from being projected on the screen. In the present embodiment, when the inverted image is displayed, the amount of illumination light is reduced to suppress the influence of the inverted image being projected on the screen, and the illumination light is detected based on the detection value of the light receiving element 4. Sensing was performed to adjust the white balance of the illumination unit 1.

<< Explanation of control sequence >>
FIG. 2 is a diagram for explaining a first control example when image projection and illumination light sensing are performed. In FIG. 2, the first stage shows the control sequence of the LED 11, the second stage shows the control sequence of the LCOS 3, and the third stage shows the control sequence of the CMOS light receiving element 4. One frame is composed of six fields. The first and second fields relate to R image data, the third and fourth fields relate to G image data, and the fifth and sixth fields relate to B image data.

  Here, the case where the LCOS 3 is normally displayed is referred to as a first state, and the case where the LCOS 3 is reversely displayed is referred to as a second state. In the first state, the LED 11 is pulsed with high luminance, and in the second state, the LED 11 is pulsed with low luminance. That is, the LED 11 can be switched between high-intensity lighting and low-intensity lighting, and high-intensity lighting and low-intensity lighting are alternately and continuously repeated. In addition, regarding the sensing of the amount of light by the CMOS light receiving element 4, sensing is not performed in the first state where the LED 11 emits light with high luminance, but sensing is performed in the second state where the LED 11 emits light with low luminance.

  The reason why the CMOS light receiving element 4 does not perform sensing when the LED 11 emits light with high luminance is that the amount of light received during high luminance light emission is too large and the output of the CMOS light receiving element 4 is saturated, so that accurate sensing cannot be performed. Because there is a fear. If a light-receiving element that can be exposed in a short time by a function such as a high-speed shutter, sensing is possible even during high-luminance light emission, but consideration is given to using an inexpensive light-receiving element that does not have such a function. Thus, as described above, control is performed such that sensing is not performed during light emission.

  In the first field that is in the first state with respect to the R image data, the LED 11 is controlled so that the R light is pulsed with high brightness, and the LCOS 3 is controlled to display a normal display of the R image. In the second field, which is in the second state with respect to the R image data, the LED 11 pulses the R light with a low luminance, and a reverse display of the R image is displayed on the LCOS 3. Based on the output signal of the CMOS light receiving element 4 on which the P-polarized light is incident, the amount of light received at that time is calculated. Thus, by performing the reverse display of the R image in the second field, it is possible to prevent the image burn-in phenomenon in the LCOS 3. The third and fourth fields relating to the G image data and the fifth and sixth fields relating to the B image data are similarly controlled in the order of the first state and the second state. The amount of light is sensed by the element 4.

  In the control sequence shown in FIG. 2, a reverse display image at the time of low luminance emission is projected on the screen, which is not strictly preferable from the viewpoint of image quality. However, if the light amount difference from that during high-intensity projection is large, even if a small number of reversed images overlap due to the afterimage effect of the eyes, it can be suppressed to a level where it can hardly be recognized.

  FIG. 3 shows a second control example, and shows a control sequence similar to FIG. In the case of the second control example, image projection is performed in the first to third fields in the first half, and illumination light sensing is performed by the CMOS light receiving element 4 in the fourth to sixth fields in the second half. That is, in the first field, the LED 11 performs pulse lighting of the R light with high luminance, performs normal display of the R image on the LCOS 3, and performs the same control regarding the G light and the B light in the second and third fields.

  On the other hand, in the fourth field, the LED 11 pulse-lights the R light with low luminance and displays a reverse display of the R image on the LCOS 3. Then, the amount of light is sensed by the CMOS light receiving element 4. In the fifth and sixth fields, the same control for G light and B light is performed. Also in this case, inversion display is performed corresponding to normal display within one frame, and image burn-in is prevented. Also in the second control example, when looking at the LEDs of the respective colors, the high-intensity lighting and the low-intensity lighting are alternately repeated with the light-off state interposed.

  By the way, the optical path from the illuminating unit 1 to the screen is different from the optical path from the illuminating unit 1 to the CMOS light receiving element 4, and emits high luminance during image projection, but emits low luminance during light amount sensing. The change in the amount of light received by the CMOS light receiving element 4 does not always coincide with the change in the projection luminance (the luminance of the projected image). Therefore, it is necessary to obtain a correlation between the projection luminance and the output of the CMOS light receiving element 4 as shown in FIG. 4 and adjust the luminance of the LED 11 based on the correlation.

  FIG. 4 illustrates the correlation between the projection luminance at the time of high luminance light emission and the output of the CMOS light receiving element 4 at the time of low luminance light emission with respect to each light of R, G, B, and the vertical axis represents the high luminance light emission. The horizontal axis represents the output of the CMOS light receiving element 4 at the time of low luminance light emission. These correlations are measured in advance at the time of manufacturing inspection and stored in the memory 65 as a data table. For example, regarding the R light, when the CMOS output during low-luminance emission is b, the projection luminance a is obtained when high-luminance emission is performed. In order to obtain the same luminance a when G light and B light are emitted with high luminance, light emission control may be performed so that the CMOS output at low luminance emission becomes c and d.

  When the CMOS output related to R light changes to b ′ (corresponding to the projection luminance e) due to temperature change, change with time, etc., light emission control is performed so that the CMOS output related to R light becomes b in order to correct the RGB luminance balance. To do. That is, a change in RGB luminance of the projected image can be detected from the change in the CMOS output, and the white balance of the projected image can be kept optimal by feeding back the detection result and controlling the light emission luminance of the LED 11. In FIG. 4, the horizontal axis indicates CMOS output, but the amount of light received by the CMOS light receiving element 4 may be used. When the CMOS output is used, there is a correlation including the relationship between the amount of light received by the CMOS light receiving element 4 and the output.

  In the above-described embodiment, the example in which the ferroelectric liquid crystal is used for the LCOS 3 has been described. However, the present invention can be applied to the LCOS 3 using the TN type liquid crystal. In LCOS3 using TN type liquid crystal, it is not necessary to perform reverse display for preventing burn-in unlike in the case of using ferroelectric liquid crystal. As shown in the control sequence of FIG. Normal display is performed.

  Further, if a dimming means such as an ND filter is provided between the PBS 2 and the CMOS light receiving element 4 in FIG. 1, the LED 11 does not emit low luminance as shown in the control sequence in FIG. , Image projection by high luminance emission of B light and sensing of light quantity by the CMOS light receiving element 4 can be performed simultaneously. In this case, unlike in the case of FIG. 5, there is no timing at which the projected image becomes dark, and further high-speed switching is not required.

  In the above-described embodiment, the projector that performs color display by field sequential driving has been described as an example. However, the present invention is applied to any projector that includes the illumination unit 1 that can independently control R, G, and B light. Can do. For example, the present invention can also be applied to a projector in which white illumination light is incident by simultaneously emitting R light, G light, and B light from the illumination unit 1 made of RGB LEDs to an LCOS with a color filter. Further, the present invention can be applied to a projector using a transmissive LCOS instead of a reflective LCOS.

  FIG. 7 is a diagram showing an example applied to a projector using a transmissive liquid crystal display element. The same components as those in the embodiment shown in FIG. The illumination unit 1 including the RGB three-color LEDs emits light of the three RGB colors simultaneously. The light emitted from the illuminating unit 1 is reflected by the dichroic mirror D1 with the first color light of RGB, and the light of the color other than the first light is transmitted. The light transmitted through the dichroic mirror D1 is reflected by the dichroic mirror D2 and the remaining color component (third color) is transmitted.

  The lights reflected by the dichroic mirrors D1 and D2 are reflected by the mirrors M1 and M2, respectively, and enter the PBSs 2-1 and 2-2 having the same configuration as the PBS indicated by reference numeral 2 in FIG. Further, the light transmitted through the dichroic mirror D2 is reflected by the mirrors M5 and M4, and enters the PBS 2-3 having the same configuration as the PBS indicated by reference numeral 2 in FIG. Among the light incident on the PBSs 2-1, 2-2, and 2-3, P-polarized light is light receiving elements 4-1, 4-2, 4 having the same configuration as the light receiving element indicated by reference numeral 4 in FIG. -3. The S-polarized light is reflected by the polarization separation film of each PBS and guided to the transmissive liquid crystal display elements 3-1, 3-2 and 3-3. That is, the PBSs 2-1, 2-2, and 2-3 serve as a polarization separation element that separates the illumination light from the illumination unit 1 into two polarized light beams having different polarization directions.

  In FIG. 7, M2 and M6 each indicate a mirror. Each color light incident on the transmissive liquid crystal display elements 3-1, 3-2 and 3-3 is spatially modulated, and is applied to the dichroic prism D3 via the polarizing plates 7-1, 7-2 and 7-3. Incident. Here, the polarizing plates 7-1, 7-2, and 7-3 separate the projection polarized light from the transmitted light modulated by the transmissive liquid crystal display elements 3-1, 3-2, and 3-3.

  The dichroic prism D3 synthesizes each color image light that has been spatially light modulated by the transmissive liquid crystal display elements 3-1, 3-2, and 3-3 and received through the polarizing plates 7-1, 7-2, and 7-3. Then, the composite image is projected onto an external screen via the projection lens 5. The light receiving elements 4-1, 4-2 and 4-3 receive the light of each color as in the embodiment shown in FIG. 1, and control the light emission amount of each color LED of the illumination unit 1 according to the light reception amount. To do.

  In the case of the embodiment in FIG. 7, a polarization separation element (PBS 2-1, 2-2, 2-3) that separates the illumination light from the illumination unit 1 into two polarized lights having different polarization directions, and a transmission type A description will be given of a configuration in which a part of the separating projection means (polarizing plates 7-1, 7-2, 7-3) for separating and projecting the polarized polarized light for projection from the light modulated by the liquid crystal display element is used as another element. However, the same element (PBS2) may be used as in the embodiment of FIG. In FIG. 7, a ferroelectric liquid crystal display element may be used as the transmissive liquid crystal display element.

  Moreover, although the example using a CMOS light receiving element as the light receiving element 4 has been described, other light receiving elements such as a CCD light receiving element may be used. The sensing of LED light by the CMOS light receiving element 4 described in the above embodiment does not necessarily have to be performed for each frame. Even if it is performed once for a plurality of frames, it is based on an instruction from the operator. It may be performed each time. That is, even if the operation of continuously performing the high-intensity lighting and the low-intensity lighting of the LED light source is performed for a plurality of frames or once in a predetermined time, it is performed each time based on an instruction from the operator. It may be. Here, the operation of continuously performing high-intensity lighting and low-intensity lighting of the LED light source may include, for example, a light-off state between both lighting as in the control sequence of FIG.

1 is a block diagram showing an embodiment of a projector according to the present invention. It is a figure explaining the 1st control example. It is a figure explaining the 2nd control example. It is a figure which shows the relationship between the projection brightness | luminance at the time of high-intensity light emission, and the output of the CMOS light receiving element 4 at the time of low-intensity light emission. It is a figure which shows the control sequence at the time of using LCOS3 of TN type | mold liquid crystal. It is a figure which shows the control sequence at the time of using LCOS3 and ND filter of TN type | mold liquid crystal. It is a figure which shows an example of the projector using a transmissive liquid crystal display element.

Explanation of symbols

1: Lighting section
2, 2-1, 2-2, 2-3: Polarizing beam splitter 3: LCOS 4: CMOS light receiving element 5: Projection lens 6: Controller 61: LED control circuit 62: Polarization control circuit 63: LOS control circuit 64: CPU
65: Memory 7-1, 7-2, 7-3: Polarizing plate 3-1, 3-2, 3-3: Transmission type liquid crystal display element

Claims (4)

Illuminating means having a plurality of light sources that generate different colored lights and capable of independently emitting them;
A polarization separation element that separates the illumination light from the illumination means into two polarized lights having different polarization directions;
One of the polarized lights separated by the polarization separation element is incident, and a spatial light modulation element that modulates the incident polarized light based on image information;
Separating projection means for separating the polarized light for projection from the light modulated by the spatial light modulator and projecting it on the screen;
A photoelectric conversion element that receives the other polarized light separated by the polarization separation element and outputs a signal corresponding to the amount of received light;
A projector comprising: control means for driving and controlling each of the plurality of light sources based on an output signal of the photoelectric conversion element to adjust a color balance of a projected image projected on the screen. The projector according to claim 1, wherein
A storage unit that stores in advance the correlation between the intensity of the polarized light for projection and the amount of light received by the photoelectric conversion element or the signal output value of the photoelectric conversion element;
The projector according to claim 1, wherein the control unit performs color balance adjustment based on the data stored in the storage unit. The projector according to claim 1 or 2,
The illuminating means can switch, for each of the plurality of light sources, a first light emission with a first intensity and a second light emission with a second intensity weaker than the first intensity,
The projector according to claim 1, wherein the control unit performs color balance adjustment based on an output signal of the photoelectric conversion element during the second light emission. The projector according to claim 3, wherein
The projector is a reflection type light valve using a ferroelectric liquid crystal, and performs normal image display during the first light emission and reverse image display during the second light emission.

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