JP2016180875A - Display control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display control device that can suppress a reduction in image quality despite execution of overdrive driving.SOLUTION: A synchronization control part 31 controls switching between a transmission state and a scattering state on a screen 21 by applying, to the screen 21, a start-up driving voltage and a stable driving voltage providing the screen 21 with a difference in potential lower than the start-up driving voltage after application of the start-up driving voltage. After the application of the start-up driving voltage, the synchronization control part 31 provides a ground potential to the screen 21 for a certain period to discharge electric charges accumulated in the screen 21 from the screen 21.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a display control device that controls display of a screen or the like that displays an image.

  For example, Patent Document 1 discloses a display device that displays an image projected from a projector or the like when a transparent body such as glass is used as a screen and the screen is in a scattering state.

  In this type of screen, liquid crystal is often used as a material for an optical layer that can be in a transmission state and a scattering state.

  When liquid crystal is used for a screen as in Patent Document 1, it is necessary to increase the response of the liquid crystal in order to switch between the scattering state and the transmission state at high speed. As a technique for causing the liquid crystal to respond at high speed, a technique for providing a potential difference higher than a potential difference caused by a normal driving voltage (also referred to as overdrive driving) is well known (see, for example, Patent Document 2).

JP 2004-184979 A JP 2009-75384 A

  In order to achieve both video display and transparency on a screen as described in Patent Document 1, it is necessary to change the transmission state and the scattering state within one frame period. Therefore, when a high voltage that can be started up in about several ms is applied as the drive voltage, the scattering state is rapidly achieved, but the scattering state is lowered with the passage of time thereafter (the transmittance is increased after the transmittance is lowered). ) The phenomenon occurs. When such a phenomenon occurs, the image quality is deteriorated, for example, the displayed image becomes thin.

  Therefore, Patent Document 2 applies a voltage (maintenance voltage) that can stably maintain the scattering state after application of a drive voltage (startup voltage) for high-speed startup. However, in the case of the screen described in Patent Document 1, there is a problem that even if a sustain voltage is applied after the start-up voltage, the potential difference due to the sustain voltage is not quickly reduced due to the electrostatic capacity component of the screen.

  Since the screen described in Patent Document 1 changes the entire screen into a scattering state and a transmission state in a lump, the cell size is much larger than the liquid crystal used in normal electronic devices and televisions. One cell has a very large capacitance component.

  Accordingly, there is a problem that even if the technology for liquid crystal used in ordinary electronic devices and televisions such as Patent Document 2 is simply used, the potential difference due to the maintenance voltage does not rapidly decrease as described above. It cannot be solved.

  Therefore, in view of the above-described problems, an object of the present invention is to provide a display control device that can suppress deterioration in image quality even when overdrive driving is performed.

  In order to solve the above-mentioned problem, the invention described in claim 1 is a display control device for controlling a screen capable of switching between a transmission state and a scattering state with respect to light. And a screen control unit that applies a drive voltage including a sustain voltage that gives a potential difference lower than the startup voltage to the screen after voltage application to the screen, and the screen control unit is configured to apply the voltage after the startup voltage is applied. A display control device that discharges electric charges accumulated in the screen from the screen.

  Further, the invention described in claim 5 is a display control method for controlling a screen capable of switching between a transmission state and a scattering state with respect to light, wherein the startup voltage and the startup voltage are applied after the startup voltage is applied. A screen control step of applying to the screen a drive voltage including a sustain voltage that gives a potential difference lower than a voltage to the screen; and a charge for discharging the charge accumulated on the screen after the start-up voltage is applied from the screen. A display control method characterized by including a discharging step.

It is a schematic block diagram of the display apparatus provided with the display control apparatus concerning 1st Example of this invention. It is typical sectional drawing of the screen shown by FIG. It is explanatory drawing of the projector which projects in synchronization with the optical characteristic of the screen shown by FIG. It is explanatory drawing of the display state with which the image | video by the image light and the background of a screen overlap in the display apparatus shown by FIG. It is a functional block diagram of the synchronous control part shown by FIG. 2 is a timing chart of the operation of the synchronization control unit shown in FIG. 1. It is the graph which showed the comparison with the display control apparatus shown by FIG. 1, and the conventional display control apparatus. It is a functional block diagram of the synchronous control part concerning the 2nd Example of this invention. FIG. 9 is a timing chart of the operation of the synchronization control unit shown in FIG. 8. It is a typical front view of the structure of the screen concerning the other Example of this invention.

  Hereinafter, a display device according to an embodiment of the present invention will be described. In a display control apparatus according to an embodiment of the present invention, a screen control unit applies a drive voltage including a start-up voltage and a sustain voltage that gives a potential difference lower than the start-up voltage to the screen after the start-up voltage is applied to the screen. . Then, the screen control unit discharges the charge accumulated on the screen from the screen after the start-up voltage is applied. In this way, the charge can be discharged, so that the potential difference applied to the screen quickly decreases to the potential difference due to the sustain voltage, and the image quality increases due to the phenomenon that the transmittance increases even after overdrive driving. Can be suppressed.

  The screen control unit may apply a charge discharge voltage that applies a potential difference lower than the sustain voltage to the screen after applying the start-up voltage and before applying the sustain voltage. By doing in this way, the electric charge accumulate | stored by the starting voltage application can be discharged | emitted. Therefore, the potential difference due to the sustain voltage can be quickly reduced.

  The screen controller may apply the charge discharge voltage for a predetermined period. By doing so, the electric charge is discharged for a certain period, so that the potential difference applied to the screen can be reliably reduced.

  In addition, the screen control unit compares the potential difference of the drive voltage with the potential difference generated by the charge accumulated on the screen after applying the start-up voltage, and the potential difference generated by the charge accumulated on the screen is the drive voltage. The charge discharge voltage may be applied when the potential difference is larger. By doing so, the potential difference between the actual drive voltage and the potential difference generated by the charge accumulated on the screen is compared, so that it is possible to prevent the charge from being discharged below the drive voltage.

  Further, the display control method according to the embodiment of the present invention provides a screen with a drive voltage including a start-up voltage in the screen control step and a sustain voltage that gives the screen a potential difference lower than the start-up voltage after the start-up voltage is applied. Apply. Then, after the start-up voltage is applied in the screen control process, the charges accumulated on the screen are discharged from the screen. In this way, the charge can be discharged by the electrification discharging unit, so that the potential difference applied to the screen quickly decreases to the potential difference due to the sustain voltage, and the transmittance decreases even if overdrive driving is performed. It is possible to prevent the image quality from being lowered due to the rising phenomenon.

  A display device 1 including a display control device according to a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the display device 1 includes a screen 21 and a synchronization control unit 31 as a display control device according to the present embodiment, and a projector 11 is connected to the display device 1. The display device 1 is a transmissive projection device that transmits and scatters image light from the projector 11 through a screen 21.

  The projector 11 can use a transmission-type or reflection-type liquid crystal light valve that sequentially shifts the black state (a state in which no projection light is emitted) on the screen 21 during the scanning cycle, but other elements may be used. The projector 11 may perform raster scanning in the video scanning cycle and project video light (image light) on the display surface of the screen 21 dot-sequentially. That is, video light is projected intermittently at a predetermined cycle. As the projector 11, for example, a laser projector or the like in which the irradiation direction of the intensity-modulated light beam is reflected by a movable mirror and shaken can be used. The projector 11 can be considered in the same manner as the image light irradiation position being sequentially scanned in one direction on the screen 21.

  The projector 11 may be any projector that can project video light modulated by video information (image information) onto the screen 21. Note that the video information is obtained from a video signal input to the projector 11. Video signals include, for example, NTSC (National Television Standards Committee), analog video signals such as PAL (Phase Alternation by Line), MPEG-TS (Moving Picture Experts Group-Transport Stream) format, HDV (High -There are video signals in digital format such as Definition Video) format. The projector 11 may receive not only a moving image video signal but also a still image video signal such as JPEG (Joint Photographic Experts Group). In this case, the projector 11 may scan the screen 21 repeatedly with the same video light for displaying a still image.

  The screen 21 may be any screen that can change the optical state by applying a voltage. As for the optical state of the screen 21, a scattering state is an image state, and a transparent transmission state in which the scattering of incident light is smaller and the parallel light transmittance is higher than that is a non-image state. That is, it is possible to switch between a transmission state and a scattering state with respect to light.

  The screen 21 may be, for example, a light control screen that uses a liquid crystal material and changes a scattering state and a transparent transmission state in which scattering of incident light is small. The light control screen uses, for example, a liquid crystal element such as a polymer-dispersed liquid crystal, or an element that controls a transparent transmission state with small scattering of incident light by moving white powder in a transparent cell. There are things that use etc.

  FIG. 2 is a schematic cross-sectional view of the screen 21 that can control the optical state. The screen 21 shown in FIG. 2 has an optical layer 25 in which a composite material containing liquid crystal is sandwiched between a pair of transparent glass plates 23 and 24. A counter electrode 26 is formed on the entire surface of one glass plate 24 on the optical layer 25 side. A control electrode 27 is disposed on the entire surface of the other glass plate 23 on the optical layer 25 side. An intermediate layer made of an insulator may be formed between the electrodes 26 and 27 and the optical layer 25.

  The counter electrode 26 and the control electrode 27 are formed as transparent electrodes by using, for example, ITO (indium tin oxide). The optical layer 25 is disposed between the control electrode 27 and the counter electrode 26. Further, at least one of the counter electrode 26 and the control electrode 27 may be configured as an electrode that is a half mirror that transmits a part of incident light.

  A voltage is applied to the screen 21 so as to generate a potential difference between the counter electrode 26 as the first electrode and the control electrode 27 as the second electrode. The optical state in the optical layer 25 varies depending on the voltage applied to the counter electrode 26 and the control electrode 27.

  The screen 21 is classified into a reverse mode and a normal mode according to a state when a voltage is applied so as to generate a potential difference. The screen 21 operating in the reverse mode is in a transparent transmissive state in a normal state where no voltage is applied. When a voltage is applied, it becomes a scattering state with a scattering rate of parallel rays according to the applied voltage. In a screen operating in the normal mode, the screen is in a scattering state in a normal state where no voltage is applied. When a voltage is applied, a transparent transmission state with parallel light transmittance corresponding to the applied voltage is obtained. As for the optical state of the screen 21, a predetermined scattering state corresponds to an image state, and a transparent transmission state having a higher parallel light transmittance than that corresponds to a non-image state. In this embodiment, the reverse mode is described, but the normal mode is also applicable.

  The synchronization control unit 31 controls the screen 21 on which the video (image) is projected as light so as to scatter the projected video light, and controls the screen 21 in a transmissive state when it is not projected. That is, an image is projected from the projector 11 in the scattering state. As shown in FIG. 1, the synchronization control unit 31 is connected to the projector 11 and the screen 21. The synchronization control unit 31 controls the optical state of the screen 21 in synchronization with the projection of the image light from the projector 11.

  Next, in the display device 1 according to the present embodiment, a projection method of the projector 11 that projects in synchronization with the optical characteristics of the screen 21 will be described with reference to FIG. FIG. 3 is an explanatory diagram of a method in which the projector 11 projects image light at intervals. In this case, as shown in FIG. 3B, image light is projected on the screen 21 in a short period of time during a part of the scanning cycle. As shown in FIG. 3C, the screen 21 may be in a scattering state during the partial period.

  If the optical state of the screen 21 is controlled so that the screen 21 is in a transmissive state during a period other than the part, the see-through characteristic of the screen 21 can be obtained without causing a decrease in the luminance of the image in the scanning period. In order to obtain the same luminance as compared with the case where image light is regularly projected, projection light whose intensity is approximately the reciprocal of the duty (duty: a) in the scattering state for one scanning period is required. It becomes. Therefore, in order to obtain a high see-through characteristic, a powerful pulsed projection light output is required.

  By controlling the projector 11 and the screen 21 in this way, the screen 21 scatters image light with the same brightness as when the screen 21 is always in a scattering state while having transparency capable of recognizing the object behind the screen. And can be transmitted. That is, it is possible to achieve both a see-through property capable of recognizing a background object and a high image visibility.

  Information on the switching timing for the synchronization control between the projector 11 and the screen 21 is sent from the synchronization control unit 31 to the screen 21 based on an image periodic signal such as a vertical synchronization signal output from the projector 11. Note that the projector 11 and the screen 21 and the synchronization control unit 31 may be capable of wireless communication using electromagnetic waves such as microwaves and infrared rays, and information for obtaining these synchronizations may be exchanged by radio signals.

  In the display device 1, for example, in the installation environment of FIG. 1, an image can be visually recognized as shown in FIG. FIG. 4 is an explanatory diagram of a display state in which the image by the image light and the background of the screen 21 overlap. In FIG. 4, triangular and circular images of image light are displayed on the screen 21, and a tree 42 as a background on the other side of the screen 21 can be seen at the same time.

  Next, FIG. 5 shows a functional configuration of the synchronization control unit 31. The synchronization control unit 31 includes a power supply circuit 32, a screen control unit, and drive circuits 33 and 34 as charge discharging units.

  The power supply circuit 32 includes a startup drive voltage generation unit 321, a stable drive voltage generation unit 322, and a voltage switching circuit 323.

  The start-up drive voltage generation unit 321 generates a start-up drive voltage (start-up voltage) for overdrive driving.

The stable drive voltage generation unit 322 is an absolute value voltage smaller than the startup drive voltage,
A stable drive voltage (sustain voltage) that generates a potential difference lower than the rise drive voltage to the screen 21 after the rise drive voltage is applied is generated. This stable driving voltage is a voltage that can stably maintain the screen 21 in the scattering state.

  The voltage switching circuit 323 uses the rising drive voltage generated by the rising drive voltage generation unit 321 and the stable drive voltage generated by the stable drive voltage generation unit 322 based on, for example, an image periodic signal such as a vertical synchronization signal. Switch from the generated start signal. Therefore, the voltage output from the voltage switching circuit 323 becomes the drive voltage for the screen 21.

  The drive circuit 33 applies a drive voltage output from the power supply circuit 32 to the counter electrode 26 of the screen 21 based on a drive control signal generated inside the synchronization control unit 31.

  The drive circuit 34 applies a drive voltage output from the power supply circuit 32 to the control electrode 27 of the screen 21 based on a drive control signal generated inside the synchronization control unit 31. Accordingly, the drive circuits 33 and 34 perform switching control between the transmission state and the scattering state on the screen 21 by applying a drive voltage to the screen 21.

  Then, the drive circuits 33 and 34 connect, for example, the counter electrode 26 or the control electrode 27 to the ground potential on the screen 21 based on the charge discharge control signal generated inside the synchronization control unit 31 after applying the startup drive voltage. Discharge accumulated charge. That is, the drive circuits 33 and 34 discharge the charge accumulated on the screen 21 from the screen after the start-up voltage is applied.

  Next, the operation of the synchronization control unit 31 configured as described above will be described with reference to the timing chart of FIG.

  First, at the beginning of one video cycle T (time t1), the start signal is turned on and the drive control signal is turned on. Then, the voltage switching circuit 323 of the power supply circuit 32 switches the output voltage to the startup drive voltage V1 generated by the startup drive voltage generation unit 321 and the drive circuit 33 applies the startup drive voltage V1 to the counter electrode 26. . On the other hand, the drive circuit 34 does not apply the voltage output from the power supply circuit 32 to the control electrode 27. Therefore, the potential difference (screen applied voltage) applied to the screen 21 is the rising drive voltage V1, and the screen 21 starts to change to the scattering state at a higher speed than when the stable drive voltage is applied by overdrive drive.

  Next, at time t2 when a period necessary for raising the screen 21 to the scattering state has elapsed from time t1, the rise signal is turned off and the video projection signal and the charge discharge signal are turned on. Then, the voltage switching circuit 323 of the power supply circuit 32 switches the output voltage to the stable driving voltage V2 generated by the stable driving voltage generation unit 322. However, since the charge discharge signal is turned ON, the driving circuit 33 grounds the counter electrode 26. In order to connect to the potential, the counter electrode 26 has a ground potential (0 volt in FIG. 6). By connecting the counter electrode 26 to the ground potential, the charges accumulated in the screen 21 are discharged. Therefore, the voltage of the counter electrode 26 decreases rapidly.

  That is, the drive circuits 33 and 34 apply a ground potential (charge discharge voltage) that gives the screen 21 a potential difference lower than the stable drive voltage after applying the startup drive voltage and before applying the stable drive voltage. Yes.

  Although not shown in FIG. 5, the video control signal is a control signal for instructing the projector 11 to project video light. Therefore, the projector 11 projects the image light on the screen 21 while the image control signal is ON.

  Next, at time t3 when a predetermined period has elapsed from time t2, the charge discharge signal is turned off. Then, the drive circuit 33 applies a stable drive voltage V <b> 2 to the counter electrode 26. Therefore, the screen application voltage is the stable drive voltage V2. The period from time t2 to t3 is a period determined for discharging the electric charge accumulated in the screen 21, and is set as appropriate based on the material of the optical layer 25, the startup drive voltage V1, the stable drive voltage V2, and the like.

  In the present embodiment, it is not necessary to discharge all the charges accumulated on the screen 21, and it is sufficient if the charges can be discharged to the extent that the stable driving voltage V2 is reached.

  Next, the drive control signal is turned OFF at time t4 when a certain period has elapsed from time t3. Then, the drive circuit 34 applies a stable drive voltage V <b> 2 to the control electrode 27. For this reason, the potential difference between the counter electrode 26 and the control electrode 27 is eliminated, and the screen applied voltage is 0 volts. Accordingly, the screen 21 starts to change to the transmissive state.

  Note that the video projection signal may be turned off at any time up to time t4. That is, since the drive control signal determines the period in the scattering state of the screen 21, the image light may be projected onto the scattering state.

  At the beginning of the next one video cycle T (time t5), similarly to time t1, the start signal is turned on and the drive control signal is turned on. Then, the voltage switching circuit 323 of the power supply circuit 32 switches the output voltage to the rising drive voltage V1 generated by the rising drive voltage generation unit 321. In this cycle, the drive voltage V1 is applied from the drive circuit 34 to the control electrode 27. On the other hand, the drive circuit 33 does not apply the voltage output from the power supply circuit 32 to the counter electrode 26. Then, the startup drive voltage V1 is applied as a negative potential to the screen 21, and the screen 21 starts to change into a scattering state by overdrive driving. In this embodiment, the negative potential is applied in this cycle in the frame inversion method in which a rectangular wave is input to both the counter electrode 26 side and the control electrode 27 side, and the voltage polarity of the voltage between the screen electrodes changes every video cycle. This is because it is driven.

  Time t6 to t8 is the same as time t2 to t4. Accordingly, the charge accumulated on the screen 21 at time t6 to t7 is discharged. Thereafter, by repeatedly driving such an operation, for example, the display as shown in FIG. 4 is performed.

  As is clear from the above description, the operation described with reference to FIG. 6 is the screen control process, and the operation from time t3 to t4 (time t6 to t7) is the charge discharging process.

  Next, FIG. 7 shows a comparison between the case of the configuration of this embodiment described above and the case of the conventional configuration (without a charge discharging circuit). In FIG. 7, the left vertical axis represents drive voltage, the right vertical axis represents transmittance relative ratio, and the horizontal axis represents time. The solid line indicates the change in the drive voltage in the configuration of the present embodiment, the broken line indicates the change in the drive voltage in the conventional configuration, the alternate long and short dash line indicates the change in the transmittance relative ratio in the configuration of the present embodiment, and the alternate long and two short dashes line indicates the conventional change. The change of the transmittance | permeability structure ratio in a structure is shown. Also, t2 and t4 in the figure correspond to times t2 and t4 in FIG.

  As shown in FIG. 7, in the conventional configuration, the driving voltage gradually decreases from the rising driving voltage to the stable driving voltage. Therefore, it slightly increases after the transmittance relative ratio decreases. On the other hand, in the configuration of the present embodiment, since the electric charge accumulated in the screen 21 is discharged, the driving voltage rapidly rises from the starting driving voltage to the stable driving voltage. Therefore, it is possible to maintain a value with a reduced relative transmittance ratio.

  According to the present embodiment, the synchronization control unit 31 applies the stable drive voltage that gives the screen 21 a potential difference lower than the startup drive voltage after the startup drive voltage and the startup drive voltage are applied. Switching control between the transmission state and the scattering state in 21 is performed. Then, after applying the start-up drive voltage, a ground potential is applied to the screen 21 for a certain period, and the charges accumulated on the screen 21 are discharged from the screen 21. In this way, the charge accumulated on the screen 21 can be discharged, so that the potential difference applied to the screen 21 quickly decreases to the potential difference due to the stable driving voltage, and the transmittance is maintained even when overdrive driving is performed. The deterioration of image quality can be suppressed by the phenomenon that the image increases after the decrease.

  A display control apparatus according to a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, a charge discharging circuit 35 is provided as shown in FIG. The charge discharging circuit 35 includes a comparator 351, a switch 352, and a diode 353.

  The comparator 351 is generated by the drive voltage (potential difference between the drive voltages) output from the power supply circuit 32 and the voltage applied to the screen 21 by the drive circuit 33 or the drive circuit 34 (charge accumulated in the screen 21). Potential difference).

  The switch 352 is turned on when the voltage applied to the screen 21 is larger than the drive voltage output from the power supply circuit 32 as a result of the comparison by the comparator 351, and the drive circuit 33 or the drive circuit 34 is connected to the ground potential. Connect to. Further, as a result of comparison by the comparator 351, when the voltage applied to the screen 21 is smaller than the drive voltage output from the power supply circuit 32, the power supply circuit 32 and the drive circuit 33 or the drive circuit 34 are turned off. Connect. The switch 352 may be constituted by a transistor or the like, for example.

  The diode 353 is connected between the power supply circuit 32 and the switch 352 and functions as a protection circuit.

  In the first embodiment, a circuit such as the switch 352 is turned on for a predetermined period, and the drive circuit 33 or the drive circuit 34 is connected to the ground potential. However, in this embodiment, the comparator 351 is connected. The point where the switch 352 is turned on or off is different depending on the output result.

  Next, the operation of the synchronization control unit 31 configured as described above will be described with reference to the timing chart of FIG. The basic operation is the same as the timing chart of FIG. In FIG. 9, power supply voltage-screen applied voltage is added. This shows the comparison operation of the comparator 351. When the voltage (potential difference) applied to the screen 21 is higher (larger) than the voltage (potential difference) output from the power supply circuit 32 as a result of the comparison by the comparator 351, the comparator 351 outputs the output to a high level ( ON) and switch 352 is turned ON. That is, the output of the comparator 351 becomes a charge discharge control signal.

  As a result of comparison by the comparator 351, when the voltage applied to the screen 21 becomes lower than the voltage output from the power supply circuit 32, the comparator 351 sets the output to a low level (charge discharge control signal: OFF). Switch 352 is turned OFF.

  According to the present embodiment, the charge discharging circuit 35 compares the voltage of the power supply circuit 32 and the voltage of the driving circuit 33 or the driving circuit 34 by the comparator 351 after applying the starting driving voltage, and the driving circuit 33 or driving circuit is compared. When the voltage of the circuit 34 is larger than the potential difference of the power supply circuit 32, the switch 352 is turned on to discharge the charge from the screen 21. By doing so, the voltage of the actual power supply circuit 32 and the voltage of the drive circuit 33 or the drive circuit 34 are compared by the comparator 351, so that it is possible to prevent electric charges from being discharged to a stable drive voltage V2 or less. Can do.

  In the above-described embodiment, the screen 21 is driven by the frame inversion method. However, the present invention can also be applied to the common DC method. In the common DC system, the voltage between the screen electrodes varies as a rectangular wave in which the voltage on the counter electrode 26 side is constant at an intermediate potential (for example, 0 volts) and the voltage on the opposite control electrode 27 side is a positive or negative potential. To do.

  Further, in the first and second embodiments, the entire surface of the screen 21 is switched between the scattering state and the transmission state at once, but the screen 21 is divided into a plurality of regions as shown in FIG. The screen 21 may be in a scattering state in order from the top, and image light may be projected onto a region in the scattering state.

  In FIG. 10, the area of the screen 21 irradiated with the image light is divided into strips in one direction (for example, the scanning direction) (divided area). In FIG. 10, the control electrode 27 is divided into a plurality of regions corresponding to the divided regions and individually connected to the synchronization control unit 31 so that voltages can be individually applied.

  By configuring the screen 21 in this way, it is possible to switch between the scattering state and the transmission state for each divided region. Accordingly, the portion of the screen 21 irradiated with the scanning light is maintained in the video state. Thereby, the image light that scans the screen 21 is scattered by the screen 21 in the scattering state. Further, the portion of the screen 21 that is not irradiated with the scanning light is controlled to a non-image state. Each divided region is controlled to a transparent transmission state in a non-video state during most of the period not scanned by the scanning light. During the image light projection period, the see-through characteristic of the screen 21 is obtained while maintaining the image visibility.

  Each divided area of the screen 21 is controlled from the transparent transmission state to the scattering state before the timing when the image light starts to scan each area. Further, the divided region in the scattering state is controlled from the scattering state to the transparent transmission state after the scanning of the region is completed. That is, the control electrode 27 is divided into a plurality of regions, and the voltage application timing is sequentially switched so as to sequentially switch the timing for changing the optical state of the optical layer 25 corresponding to each region of the divided control electrode 27. It may be.

  Therefore, the screen 21 can scatter and transmit the image light with the same brightness as that in the case where the screen 21 is always in the scattering state while having transparency that can recognize the object on the back surface. That is, it is possible to achieve both a see-through property capable of recognizing a background object and a high image visibility.

  Even in such a configuration, when the divided region is viewed as one cell, the capacitance component is much larger than that of a liquid crystal display used for a television or the like. Therefore, by applying the configurations of the first and second embodiments to such a configuration, the potential difference applied to the screen is quickly reduced to the potential difference due to the sustain voltage, and even if overdrive driving is performed, it is caused by the shoot phenomenon. Degradation of image quality can be suppressed.

  In the above-described embodiment, the ground potential is connected to discharge the electric charge. However, the voltage is not limited to the ground potential, but is lower than the stable driving voltage V2 (smaller than the potential difference given to the screen 21 by the stable driving voltage V2. Potential difference).

  Further, the present invention is not limited to the above embodiment. That is, those skilled in the art can implement various modifications in accordance with conventionally known knowledge without departing from the scope of the present invention. Of course, such modifications are also included in the scope of the present invention as long as the configuration of the display control apparatus of the present invention is provided.

DESCRIPTION OF SYMBOLS 1 Display apparatus 11 Projector 21 Screen 31 Synchronization control part (display control apparatus)
32 Power supply circuit 33 Drive circuit 34 Drive circuit 35 Charge discharge circuit 351 Comparator 352 Switch V1 Startup drive voltage V2 Stable drive voltage

Claims (5)

A display control device that controls a screen capable of switching between a transmission state and a scattering state for light,
A screen control unit that applies a drive voltage to the screen, including a start-up voltage and a sustain voltage that gives the screen a potential difference lower than the start-up voltage after the start-up voltage is applied;
The screen controller discharges the charge accumulated on the screen from the screen after applying the start-up voltage.
A display control device characterized by that.   2. The screen control unit according to claim 1, wherein a charge discharge voltage that applies a potential difference lower than the sustain voltage to the screen is applied after the start-up voltage is applied and before the sustain voltage is applied. The display control apparatus described.   The display control apparatus according to claim 2, wherein the screen control unit applies the charge discharge voltage for a predetermined period.   The screen control unit compares the potential difference of the driving voltage and the potential difference generated by the charge accumulated in the screen after applying the start-up voltage, and generates a potential difference generated by the charge accumulated in the screen. The display control device according to claim 2, wherein the charge discharge voltage is applied when the voltage difference is larger than a potential difference of the drive voltage. A display control method for controlling a screen capable of switching between a transmission state and a scattering state for light,
A screen control step of applying to the screen a drive voltage including a start-up voltage and a sustain voltage that gives the screen a potential difference lower than the start-up voltage after the start-up voltage is applied;
In the screen control step, after the start-up voltage is applied, the charge accumulated in the screen is discharged from the screen.
A display control method characterized by the above.

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