JPWO2013140626A1 - Display device, driving method thereof, and display screen device - Google Patents

Abstract

With good visibility and see-through, the projected image and the background are superimposed on the screen. A plurality of control electrodes (27) are arranged side by side along the optical layer (25) on the screen (21) scanned by the image light of the projector (11). The synchronization control unit (31) applies a voltage to the plurality of control electrodes (27), and changes the screen (21) between the video state and the non-video state for each divided region (22) in the scanning period T of the video light. Switch between. The synchronization control unit (31) switches the optical state of the plurality of divided regions (22) in the scanning period T of the video light in synchronization with the scanning of the video light, and the video light on the screen (21) is projected. The optical state of a certain region is an image state held by a voltage having an amplitude of 2 or more.

Description

  The present invention relates to a display device, a driving method thereof, and a display screen device.

Some display devices project image light onto a screen to display the image on the screen.
There exists a liquid crystal light control device which can control the transmittance | permeability in the light control device (patent document 1).

JP 2007-219419 A

By the way, it is conceivable to form a dimming screen using the technology of the liquid crystal dimming device and to use this dimming screen as a screen for projecting an image.
In such a display device, when the image is projected, the dimming screen is controlled to be scattered and transmitted, for example, so that the image is projected on the dimming screen. In other cases, for example, the dimming screen scatters incident light. A small transparent transmission state can be controlled so that the other side of the dimming screen is seen through.
However, even if such a dimming screen is used as a screen for projecting an image, it is necessary to control the screen in a scattering state during the projection period of the image light.
Therefore, it is not possible to display the image projected on the screen and the scenery on the other side of the screen on the screen with good visibility and see-through.

  As described above, the display device cannot display the video and the background on the screen.

  The invention described in claim 1 includes a screen having an optical layer whose optical state changes by application of a voltage, a plurality of control electrodes arranged side by side along the optical layer in order to apply a voltage to the optical layer, and a screen. A projector for projecting image light to display an image and a voltage applied to a plurality of control electrodes, and during the image light projection period, the screen scatters image light for each divided region where each control electrode is formed. A control unit that switches between a predetermined video state and a non-video state that is an optical state different from the predetermined video state. The screen is switched in synchronization with the projection of the light, and the optical state of the portion of the screen where the image light is projected is set to the video state. To lifting a display device.

  The invention according to claim 11 is a driving method of a display device for displaying an image of image light projected from a projector on a screen having an optical layer whose optical state changes by application of a voltage, the optical state of the screen being changed. The controlling unit applies a voltage to a plurality of control electrodes arranged side by side along the optical layer, displays an image based on image light on a screen having the optical layer and the plurality of control electrodes, and projects the image light. In the period, the screen is switched between a predetermined image state in which the image light is scattered and a non-image state which is an optical state different from the predetermined image state for each divided region in which each control electrode is formed. Switching the optical state of multiple divided areas in synchronization with the projection of image light by the projector, the optical state of the part of the screen where the image light is projected And image condition, the optical state of the image state, is held by two or more of the amplitude of the voltage is a driving method of a display device.

  The invention according to claim 12 has an optical layer in which an optical state is changed by applying a voltage, and a plurality of control electrodes arranged side by side along the optical layer in order to apply a voltage to the optical layer, and is projected A screen for displaying an image by image light, a voltage applied to a plurality of control electrodes, and a predetermined image state in which image light is scattered in each divided region in which the control electrode is formed during the image light projection period A control unit that controls to switch between a non-image state that is a different optical state, and the control unit determines the optical state of the plurality of divided regions during the projection period of the image light, The display screen device is switched in synchronization with the projection so that the optical state of the portion of the screen on which the image light is projected is the image state, and the optical state of the image state is held by a voltage having an amplitude of 2 or more. It is.

FIG. 1 is a schematic configuration diagram of a display device according to the first embodiment of the present invention. FIG. 2 is an explanatory diagram of the synchronous control of screen scanning and driving. FIG. 3 is an explanatory diagram of a projector that continuously projects a plane image. FIG. 4 is an explanatory diagram of a projector that projects a plane image by time modulation. FIG. 5 is an explanatory diagram of a projector that scans the screen. FIG. 6 is a schematic cross-sectional view of the screen. FIG. 7 is a schematic front view of a screen showing the arrangement of a plurality of control electrodes. FIG. 8 is a schematic timing chart of screen scanning and driving. FIG. 9 is an explanatory diagram of a display state in which the image by the image light overlaps the screen background. FIG. 10 is a schematic timing chart showing an example of the relationship between the drive voltage waveform of a general normal mode screen, which is a conventional example, and the optical state. FIG. 11 is a timing chart showing an optical state of a plurality of divided regions where the luminance unevenness of the video occurs. FIG. 12 is a timing chart showing optical states of a plurality of divided regions in the first embodiment. FIG. 13 is a schematic timing chart showing the relationship between the two-level driving voltage waveform and the optical state in the present embodiment. FIG. 14 is a schematic timing chart showing the relationship between the two-level driving voltage waveform and the optical state for a plurality of control electrodes. FIG. 15 is a schematic timing chart showing an example of a relationship between a driving voltage waveform of a general reverse mode screen as a conventional example and an optical state. FIG. 16 is a diagram illustrating an example of optical characteristics of the screen in the reverse mode. FIG. 17 is a schematic timing chart showing two-level drive voltage waveforms in the second embodiment. FIG. 18 is a schematic timing chart showing the relationship between the two-level driving voltage waveform and the optical state for a plurality of control electrodes. FIG. 19 is a schematic timing chart showing two-level drive voltage waveforms using a half cycle in the third embodiment (for a normal mode screen). FIG. 20 is a schematic timing chart showing a two-level drive voltage waveform using a half cycle in the third embodiment (for a screen in the reverse mode). FIG. 21 is a schematic timing chart showing three-level drive voltage waveforms in the fourth embodiment. FIG. 22 is a schematic configuration diagram of a display device according to the fifth embodiment. FIG. 23 is a schematic configuration diagram of a modified example of the display device according to the second embodiment of the present invention using a reflective screen.

  Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment]
FIG. 1 is a schematic configuration diagram of a display device 1 according to the first embodiment.
The display device 1 in FIG. 1 includes a projector 11 that projects image light, a screen 21 that can control the optical state, and a synchronization control unit 31. The synchronization control unit 31 is connected to the projector 11 and the screen 21.
The display device 1 of the present embodiment is a transmissive projection device that transmits and scatters image light from the projector 11 through a screen 21.
The synchronization control unit 31 controls the screen 21 on which the image is projected to a state where the projected image light is scattered while being transmitted, and controls the screen 21 to a transmission state when it is not projected.
As for the optical state of the screen 21, the state of being scattered and transmitted is an image state, and the transparent state of being less scattered of incident light and having a high parallel light transmittance is a non-image state.
The display device 1 can be used as, for example, a sign boat that displays advertisements and the like.

Next, the basic operation principle of the display device 1 of FIG. 1 will be described.
FIG. 2 is an explanatory diagram of synchronous control of scanning and driving of the screen 21.
The projector 11 vertically scans the screen 21 from the top to the bottom with image light modulated by the image information. The projector 11 scans the screen 21 vertically from top to bottom for each scanning repetition period (hereinafter also referred to as a scanning cycle).
2A to 2E show the scanning state at each time point in one scanning cycle in the scanning order.
The screen 21 in FIG. 2 has five divided regions 22. The five divided regions 22 are arranged vertically along the scanning direction of the image light.
The synchronization control unit 31 controls the optical states of the five divided regions 22 individually in synchronization with the one-dimensional vertical scanning of the screen 21 by the projector 11. When the image light is not projected, each divided region 22 is controlled to a non-image state, that is, a transparent transmissive state with small scattering of incident light.

When the scanning of the image light is started, the scanning light of the projector 11 is first applied to the uppermost divided area 22 of the screen 21 as shown in FIG. Hereinafter, in this description, reference numeral 221 is used to distinguish the divided region 22 irradiated with the scanning light from other divided regions 22 that are not scanned. The synchronization control unit 31 specifies a period during which the uppermost divided area 221 is scanned in the scanning cycle based on the synchronization signal from the projector, and controls the uppermost divided area 221 to the video state. The image light that scans the uppermost divided area 221 is scattered by the divided area 221 in the scattering state and passes through the screen 21.
Next, the scanning of the image light moves to the second divided region 221 from the top of the screen 21 as shown in FIG. The synchronization control unit 31 specifies a period during which the second divided region 221 from the top in the scanning cycle is scanned, and controls the second divided region 221 from the top to the video state. The image light that scans the second divided region 221 from the top is scattered by the divided region 221 in the scattering state and passes through the screen 21. Further, the synchronization control unit 31 controls the second divided area 221 from the top to the video state, and then controls the uppermost divided area 22 to the non-video state.
Thereafter, as shown in FIGS. 2C to 2E, the synchronization control unit 31 controls the divided area 221 scanned by the scanning light to the video state, and sets the other divided areas 22 to the non-video state. Control.

Through the above-described synchronization control, 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 transmitted through the screen 21 in a scattered 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 22 is controlled to a transparent transmission state in a non-video state during most of the period that is 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.

The projector 11 only needs to be able to project video light modulated by video 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.

  3 to 5 are explanatory diagrams of the projection method of the projector 11. FIG. 3 is an explanatory diagram of the projector 11 that continuously projects a plane image. FIG. 4 is an explanatory diagram of the projector 11 that projects a plane image by time modulation. FIG. 5 is an explanatory diagram of the projector 11 that scans the screen 21.

FIG. 3A is an explanatory diagram of a method in which the projector 11 regularly projects image light. In this case, as shown in FIG. 3B, image light is always projected onto the screen 21 in the scanning cycle. As shown in FIG. 3C, the screen 21 must always be in a scattering state. In this case, if the optical state of the screen 21 is controlled so as to increase the parallel light transmittance, the luminance of the image decreases.
Note that the horizontal axis of FIGS. 3B and 3C is the scanning cycle (time). The same applies to FIGS. 4B, 4C, 5B, and 5C.

  FIG. 4A is an explanatory diagram of a method in which the projector 11 projects image light at intervals. In this case, as shown in FIG. 4B, 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. 4C, the screen 21 may be in a scattering state during the partial period. When the optical state of the screen 21 is controlled so as to increase the parallel light transmittance of the screen 21 in a period other than the part, the see-through characteristic of the screen 21 is not caused in the scanning cycle without causing a decrease in the luminance of the image. Is obtained. In order to obtain the same brightness compared to the case of projecting image light regularly, the projection light needs to have a strength that is approximately the reciprocal of the duty (duty: a) in the scattering state for one scanning period. It becomes. Therefore, in order to obtain a high see-through characteristic, a powerful pulsed projection light output is required.

  FIG. 5A is an explanatory diagram of a projection method in which the projector 11 scans the screen 21. In this case, video light is always projected onto the screen 21 during the scanning cycle. However, paying attention to each part of the screen 21, the image light is projected in a part of the scanning period as shown in FIG. For this reason, as shown in FIG. 5C, each part of the screen only needs to be in a scattering state in the partial scanning period TP in which each part is scanned. Further, if each part of the screen 21 is controlled so as to increase the parallel light transmittance in a period other than the partial scanning period TP, the see-through characteristic of the screen 21 can be achieved without causing a decrease in the luminance of the image in the scanning period. can get.

The projector 11 that projects the image light may be of any of the above projection methods.
However, in order to suppress the generation of image light that is not used for scattering, the method of FIG. 4 or FIG. 5 is desirable. Moreover, a response time is required for the change in the optical state of the screen 21. For this reason, the projection method of FIG. 5 in which the response time is easily secured is preferable to FIG. In the following description, a case where the projector 11 of the projection method shown in FIG. 5 is used will be described.

In the driving method of FIG. 5, a line-shaped image corresponding to a part of the screen 21 is sequentially projected onto the display surface of the screen 21 during a scanning period that is a scanning period of the image light.
The projector 11 can be a transmissive or reflective liquid crystal light valve that sequentially shifts the black state (the state in which no projection light is emitted) on the screen 21 during the scanning cycle, but other elements can also be used. Good.
Alternatively, the projector 11 may perform raster scanning in a video scanning cycle and project video light on the display surface of the screen 21 dot-sequentially. As the projector 11, for example, a laser projector that reflects and shakes the irradiation direction of the image-modulated light beam with a movable mirror 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 screen 21 may be anything that can change the optical state by an electrical signal such as voltage or current.
For example, it may be a dimming screen that uses a liquid crystal material and changes a scattering state and a transparent transmission state in which the 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 is something that uses.

In addition, the screen 21 can be switched between a transparent transmission state where the scattering of incident light is small and a scattering state when the plurality of divided regions 22 dividing the screen 21 are independent of each other. Good.
For example, the screen 21 only needs to have a plurality of divided regions divided into strips so as to correspond to the main scanning direction of the projector 11 (for example, the vertical direction in FIG. 2).
In addition, the screen 21 may be a screen in which regions divided into rectangles are arranged in a matrix so as to correspond to the scanning direction and the sub-scanning direction of the projector 11 (for example, the horizontal direction of the image).

FIG. 6 is a schematic cross-sectional view of the screen 21 that can control the optical state for each divided region 22. FIG. 6 also shows the synchronization control unit 31.
FIG. 7 is a schematic front view of a screen showing the arrangement of a plurality of control electrodes on the screen 21 of FIG.
The screen 21 in the example of FIG. 6 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 plurality of control electrodes 27 are arranged side by side on the optical layer 25 side of the other glass plate 23.
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 plurality of control electrodes 27 and the counter electrode 26.

The plurality of control electrodes 27 divide the area of the screen 21 irradiated with the image light into strips in one direction (for example, the scanning direction).
The plurality of control electrodes 27 are individually connected to the synchronization control unit 31 and applied with individual voltages.
Adjacent control electrodes 27 are arranged apart from each other.
In FIG. 6, the counter electrode 26 is grounded.
A voltage is applied so as to generate a potential difference between the control electrode 27 and the counter electrode 26. Note that the voltage of the driving waveform described below indicates a potential difference between the control electrode 27 and the counter electrode 26.
The voltage applied to the control electrode 27 is applied to the optical layer 25 in a region corresponding to the control electrode 27. The alignment state of the liquid crystal in the optical layer 25 changes depending on the voltage applied to the control electrode 27. The optical layer 25 can be adjusted for each divided region 22 between a transparent transmission state where the scattering of incident light is small and a scattering state where the incident light is scattered.
The width of the gap region in the optical layer 25 corresponding to the region where the control electrode 27 is not formed between the control electrodes 27 is about 5 to 100 micrometers, and is desirably as narrow as possible. The thickness of the optical layer 25 is several to several tens of micrometers, and is determined in consideration of optical characteristics and drive voltage.

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 of the projector 11.
As the synchronization signal input from the projector 11 to the synchronization control unit 31, for example, a synchronization signal synchronized with the scanning cycle of the projector 11 can be used.

When the screen 21 is divided into strips in one direction like the screen 21 in FIG. 7, the projection light of the projector 11 is sequentially scanned in the division direction of the screen 21.
Based on the synchronization signal from the projector 11, the synchronization control unit 31 sets the plurality of divided regions 22 so that the portion irradiated with the projection light of the projector 11 is maintained in the video state (scattering state in the present embodiment). In the scanning order, the transparent transmission state is controlled to the scattering state.
By this synchronization control, each divided region 22 of the screen 21 is in a scattering state as a video state in a period Ton including a video period in which projection light is irradiated to the region. Further, in the non-image period Toff where the projection light is not irradiated, a transparent transmission state as a non-image state is obtained.
The screen 21 has transparency that can recognize the object on the back surface, and can scatter and transmit image light with the same brightness as when the screen is always in a scattering state. That is, it is possible to achieve both a see-through property capable of recognizing a background object and a high image visibility.

FIG. 8 is a schematic timing chart of scanning and driving of the screen 21. The horizontal axis is time. The vertical axis indicates the position in the vertical direction of the screen, and corresponds to a plurality of divided regions 22 on the screen 21.
Each divided region 22 of the screen 21 is controlled from a transparent transmission state to a scattering state before the timing at which the image light starts to scan each region. Further, the divided region 22 in the scattering state is controlled from the scattering state to the transparent transmission state after the scanning of the region is completed.
The plurality of divided regions 22 are sequentially switched to the video state by shifting the time in the scanning order by controlling the video state in synchronization with the partial scanning period TP in which the image light is irradiated to each region by scanning. It is done. The image light that scans the screen 21 is efficiently scattered by the portion maintained in the image state, and it is possible to obtain bright and high visibility.

Information on the switching timing for the synchronization control is sent from the projector 11 to the synchronization control unit 31 as a synchronization signal.
The synchronization control unit 31 preferably controls the voltage applied to each control electrode 27 so that the projection light is irradiated during a period in which the optical state of each divided region 22 is stable in a predetermined scattering state. The optical state of each divided region 22 is switched according to the signal waveform of the voltage applied to the control electrode 27.
In particular, the information on the switching timing output from the projector 11 to the synchronization control unit 31 may include information on timing at which the projector 11 starts scanning each frame and a scanning speed (scanning delay / shift). Thereby, even when the frame frequency changes, it is possible to realize a good see-through display without disturbing the video.
The projector 11 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.

Through the above-described synchronization control, the synchronization control unit 31 of the present embodiment switches the optical state of the plurality of divided regions 22 in the scanning period T of the video light in synchronization with the scanning of the video light by the projector 11 and The optical state of the part where the image light is projected is defined as an image state.
Therefore, the screen 21 can display an image because the portion irradiated with the image light is maintained in the scattering state in the period Ton including the timing when the image light is irradiated.
Moreover, since the screen 21 is controlled to be in a transparent transmissive state at times other than the period Ton during the projection period of the image light, the screen 21 can be seen through. Since the light transmitted through the screen 21 appears to be averaged (integrated) to the human eye, a see-through characteristic without flicker is obtained in a sufficiently short scanning period.
Thereby, for example, in the installation environment of FIG. 1, the image of FIG. 9 can be visually recognized.
FIG. 9 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. 9, an image of a person 41 by video light is shown on the right side of the screen 21, and a tree 42 as a background on the other side of the screen 21 can be seen on the left side.

In the first embodiment, the display device 1 using the screen 21 that operates in the normal mode will be further described.
In the screen 21 operating in the normal mode, the screen 21 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.

FIG. 10 is a schematic timing chart showing an example of the relationship between the drive voltage waveform of the conventional normal mode screen 21 as a conventional example and the optical state.
FIG. 10A shows a voltage waveform applied to the control electrode 27 by the synchronization control unit 31. The horizontal axis is time. The vertical axis represents voltage.
FIG. 10B shows the optical state of the optical layer 25. The vertical axis represents the transmittance of parallel rays. Small parallel light transmittance indicates strong scattering.

As shown in FIG. 10, a voltage is applied to the optical layer 25 operating in the normal mode in a non-video state where no video is displayed. This voltage is preferably a voltage that maximizes the parallel light transmittance, for example. In FIG. 10A, the driving voltage waveform in the non-video state period controlled to the transmissive state is an example of two rectangular wave AC cycles, but is not limited thereto.
When each divided region 22 is scanned with image light, the application of voltage is stopped so that the optical layer 25 of the divided region 22 is in a scattering state. The optical layer 25 gradually shifts from the transparent transmission state to the scattering state after the voltage is removed.
In this way, by applying the one-level drive voltage waveform of FIG. 10A to each control electrode 27, the optical state of the divided region 22 corresponding to each control electrode 27 is synchronized with the scanning of the screen 21. It is possible to switch between a transparent transmission state and a scattering state.

However, when the optical state of the screen 21 operating in the normal mode is switched between application and stop and the optical state is changed, the optical layer 25 is stabilized in a constant scattering state after the application of the voltage is stopped. In general, it takes several milliseconds to several tens of milliseconds.
The screen 21 used in the present embodiment changes the optical state in response to an electrical signal such as voltage or current. For example, the screen 21 includes a light control screen that uses a liquid crystal material to change a scattering state and a transparent transmission state. The optical state of the light modulating material generally exhibits a transient response to changes in the electrical signal. If a constant electric signal (including removing the electric signal) is applied, it does not immediately converge to a certain optical state.
For example, in the case of a normal mode dimming screen that is in a scattering state when no voltage is applied to the screen 21, after the voltage is removed in order to control the scattering state, a constant characteristic inherent to the screen is obtained until the scattering is stabilized. Takes time. As a result, even if the control for switching the optical state of the divided region 22 is executed during the scanning cycle, the optical state of the screen 21 is controlled to a transmission characteristic that can scatter the image light well and can visually recognize the back surface suitably. Is not easy.

  When the optical state of the divided region 22 is not stable in a constant scattering state, luminance unevenness occurs in the image projected on the screen 21.

First, in the partial scanning period TP in which each divided region 22 is scanned with video light, when the optical state of the divided region 22 is not stable in a certain scattering state, an image obtained by scanning the divided region 22 with video light In this case, scattering unevenness corresponding to the change in the optical state during the partial scanning period TP occurs.
In the example of FIG. 10B, the image light immediately after the start of scanning of the divided region 22 is scattered at a lower scattering rate than the image light immediately before the scan of the divided region 22 is finished. . As a result, the luminance is relatively lowered.

Secondly, when the optical state of each divided region 22 is not controlled to be constant, luminance unevenness occurs between the plurality of divided regions 22 arranged adjacently and scanned in order.
In particular, light and darkness (luminance difference) that does not exist in the video signal occurs around the boundary portion of the divided region 22, and streaky luminance unevenness along the boundary occurs.
FIG. 11 is a timing chart showing the optical state of the plurality of divided regions 22 in which the luminance unevenness of the video occurs. The horizontal axis is time, and the vertical axis is drive voltage.
FIG. 11 is an example in which the driving voltage having the waveform of FIG. 10 is applied to four consecutive divided regions 22 in synchronization with the scanning of the image light. Therefore, the timings of the four drive voltage waveforms are shifted in synchronization with scanning.
As shown in FIG. 11, when the divided regions 22 are sequentially driven at a high speed in synchronization with the scanning of the image light, the divided regions 22 previously controlled in the scattering state are strongly scattered at the end of each partial scanning period TP. While the state is controlled, the divided region 22 which is controlled to the scattering state later is in a weak scattering state.
In FIG. 11, the end timing of each partial scanning period TP is illustrated so as to coincide with the end timing of the period Ton including the video period for displaying the video. It may be slightly delayed from the end timing of the partial scanning period TP.
Then, the scanning of the image light moves from the previous divided area 22 to the subsequent divided area 22 at the end of the partial scanning period TP.
Therefore, the intensity of scattering is discontinuously switched at the boundary portion of the divided region 22, and streaky luminance unevenness occurs in the video.
As described above, when the optical state of the screen 21 is sequentially switched for each divided region 22 in synchronization with the scanning of the image light, it is necessary to suppress these image quality degradations.
For this purpose, it is necessary to keep the intensity of scattering of the portion where the image light is scanned constant during the image light scanning time of the region.
For example, at the timing when the projection light crosses the divided area 22 of the screen 21, it is necessary to make the scattering states of the front and rear divided areas 22 the same.

FIG. 12 is a timing chart showing optical states of a plurality of divided regions in the present embodiment that can suppress luminance unevenness. The horizontal axis is time. The vertical axis represents the parallel light transmittance. Low parallel light transmittance means strong scattering.
In FIG. 12, curves indicating the optical states of the four continuous divided regions 22 are drawn in an overlapping manner.
When the optical state of the four consecutive divided regions 22 is sequentially switched in synchronization with the scanning of the image light and the luminance unevenness caused by the unstable parallel light transmittance is suppressed, as shown in FIG. In the partial scanning period TP, each divided region 22 may be in a certain optical state (scattering state).
Moreover, what is necessary is just to arrange | equalize the optical state (scattering state) of this adjacent division area 22 in the timing to which image light moves between adjacent division areas 22. FIG.
In this way, by controlling the optical state of the scanning part of the screen 21 to a substantially constant optical state, the luminance unevenness of the image can be suppressed.

FIG. 13 is a schematic timing chart showing the relationship between the two-level drive voltage waveform and the optical state in the present embodiment. FIG. 13A shows a drive voltage waveform applied to the screen 21 operating in the normal mode. The horizontal axis is time, and the vertical axis is voltage. FIG. 13B shows the optical state of the screen 21 operating in the normal mode. The horizontal axis is time, and the vertical axis is parallel light transmittance.
In FIG. 13, when the divided region 22 of the screen 21 is controlled from the transparent transmission state to the scattering state, first, application of the drive voltage is stopped.
Thereafter, a small second-stage driving voltage is applied.
By applying this second stage voltage, the intensity of scattering can be stabilized at a substantially constant required value.
However, the intensity of scattering is relatively reduced as compared with the case where the application of the drive voltage is simply stopped to control the divided region to the maximum scattering state.

Next, the application timing of the drive voltage waveform in FIG.
When each divided region 22 is controlled to be in a scattering state (image state) in the partial scanning period TP in which each region is scanned, the synchronization control unit 31 applies a voltage applied to the control electrode 27 in synchronization with the scanning of the image light. , Stop shortly before the projection light is applied to the area.
From the timing when the voltage application is stopped, the optical layer 25 in the divided region 22 starts to change from the transparent transmission scattering to the scattering state. The response time of the optical layer 25 is unique to the screen 21 and is affected by temperature and the like. In general, it takes several milliseconds to several tens of milliseconds to reach a stable maximum scattering state with minimum parallel light transmittance.
After the scanning of the divided region 22 controlled to the scattering state is completed, the synchronization control unit 31 resumes application of a voltage for controlling the control electrode 27 to the transmission state. From that timing, the optical layer 25 in the divided region 22 starts to change from the scattering state to the transparent transmission state.
Since these response times are required, when switching the divided region 22 between the image state and the transmission state of the minimum parallel light transmittance in synchronization with the scanning of the image light, both good see-through property and visibility are compatible. There is not enough time to make it happen.
As a result, in order to realize a good transparent display (transparent display in the non-image state) with less turbidity due to scattering (haze) in the non-image period Toff, after removing the voltage to control to the image state, It is necessary to start scanning of image light within a short time. While the optical state continues to change, it is necessary to scan with image light.
Therefore, in FIG. 13A, by applying a voltage pulse or an alternating voltage of a plurality of values, the scattering state of the divided region 22 is maintained, and the scattering state is changed before the partial scanning period TP of the divided region 22. Stabilize almost constant.

Next, an example in which drive voltages having a plurality of values are applied to the plurality of divided regions 22 will be described.
FIG. 14 is a schematic timing chart showing the relationship between the two-level drive voltage waveform and the optical state for the plurality of control electrodes 27.
14A to 14D show voltages applied to four consecutive control electrodes 27. FIG. The horizontal axis is time, and the vertical axis is voltage. FIGS. 14E to 14H show optical characteristics of four continuous divided regions 22 corresponding to FIGS. 14A to 14D. The horizontal axis is time, and the vertical axis is parallel light transmittance. In the following description, changes in the optical state are described using changes in parallel light transmittance. In the screen of the present invention, the decrease in parallel light transmittance indicates an increase in scattering.
As shown in FIGS. 14A to 14D, a high voltage for controlling the transparent transmission state is applied to the four consecutive control electrodes 27 in a period in which each of the four control electrodes 27 is not scanned. Then, the voltage application is stopped before each scanning period, and then a low voltage is applied. The applied voltage is AC. As a result, as shown in FIGS. 14E to 14H, the four continuous divided regions 22 are controlled from the transparent transmission state to the constant scattering state in synchronization with the scanning of the image light.
Further, as shown in FIGS. 14A to 14D, a high voltage for controlling the transmission state is again applied to the four consecutive control electrodes 27 after each scanning is completed. As a result, as shown in FIGS. 14E to 14H, the four continuous divided regions 22 are controlled from the scattering state to the transparent transmission state in synchronization with the scanning of the image light.
The reference timing information for the synchronization control is sent from the projector 11 to the synchronization control unit 31. The synchronization control unit 31 switches the voltage to be applied to each control electrode 27 based on the reference timing so that the projection light is not irradiated during a period in which the scattering characteristics are not constant.

As described above, the screen 21 of the present embodiment operates in the normal mode in which the parallel light transmittance is increased by applying a voltage, and scatters the projected image light.
Further, the synchronization control unit 31 switches the voltage applied to the plurality of divided regions 22 in the scanning order in the scanning period of the image light, and controls each divided region 22 to the video state in the partial scanning period TP in which each is scanned. Then, the non-video state is controlled in a period in which each is not scanned, that is, a period other than the partial scanning period TP.
In addition, when controlling the divided region 22 to the video state, the synchronization control unit 31 increases the applied voltage after stopping the voltage application to the control electrode 27, and applies voltages having a plurality of values with two amplitudes. The optical state of the divided region 22 is held in a predetermined scattering state in which the degree of scattering is lower than the maximum scattering state of the divided region 22, and the scattering state of the divided region 22 in the partial scanning period TP scanned with image light is determined. Stabilize.
As a result, the scattering characteristics of each divided region 22 in the partial scanning period TP are maintained constant. The image light irradiated on the screen 21 is scattered by a plurality of divided regions 22 controlled to a constant scattering state. In the image displayed on the screen 21, uneven brightness is suppressed when the scattering state is not controlled to be constant.
In the present embodiment, since voltages with two amplitudes are applied to each divided region 22, there is no need to delay scanning until each divided region 22 is controlled to the maximum scattering state. The optical state can be switched at high speed in synchronization with the scanning of the image light. Therefore, each divided region 22 can be controlled to be in a transparent transmissive state for a long time, and the screen 21 can be better seen through, so that the see-through characteristic of the screen 21 can be obtained while brightening the image. Although the response time for switching the optical state of the screen 21 in the normal mode is long, the parallel light transmittance of the screen 21 is kept high, and the high see-through characteristic of the screen 21 and good image visibility are obtained.
While obtaining the see-through characteristic of the screen 21, it is possible to display an image by scattering image light uniformly and without waste.
In particular, in this embodiment, the time from when the voltage is controlled to 0 V until the application of the low voltage for making the scattering constant is 5 milliseconds or less, preferably 2 milliseconds or less. Thereby, the effective scattering period of each divided region 22 can be shortened. As a result, even when the control for switching the optical state in synchronization with the scanning of the projection light is executed, the transparency of the screen 21 is kept high.
In the present embodiment, a low drive voltage applied to obtain a constant scattering state and a high drive voltage to control the transmission state are applied as substantially low-frequency AC voltages. In the liquid crystal element, in order to ensure the reliability and suppress the deterioration, it is preferable to suppress the direct current component of the voltage applied to the optical layer 25 and drive it with an alternating voltage. In the normal mode, since the non-video period Toff to be controlled to the transmission state is long, the effective AC frequency in the transmission state affects the power consumption. In this embodiment, since the AC voltage is as low as possible, the power consumption can be suppressed.

[Second Embodiment]
In the second embodiment, a display device 1 using a screen 21 that operates in the reverse mode will be described.
In the screen 21 operating in the reverse mode, the screen 21 is in a transparent transmissive state in a normal state where no voltage is applied. When a voltage is applied, a scattering state of parallel light scattering rate (transmittance) according to the applied voltage is obtained.
The configuration and basic operation of the optical device of the present embodiment are the same as those of the optical device of the first embodiment. In the screen 21, the scattering state corresponds to the video state.

FIG. 15 is a schematic timing chart showing an example of the relationship between the drive voltage waveform of the screen 21 in a general reverse mode, which is a conventional example, and the optical state.
FIG. 15A shows a voltage waveform applied to the control electrode 27. The horizontal axis is time. The vertical axis represents voltage. FIG. 15B shows the optical state of the optical layer 25. The vertical axis represents the transmittance of parallel rays. Small parallel light transmittance indicates strong scattering.
As shown in FIG. 15, a voltage is applied to the optical layer 25 operating in the reverse mode in a period Ton including a video period for displaying a video in the scanning cycle of the video light. This voltage is preferably a voltage that maximizes the parallel light transmittance, for example. In FIG. 15A, the driving voltage waveform in the period Ton controlled to the scattering state is an example of two rectangular wave AC cycles, but is not limited thereto.
When the divided region 22 is scanned, voltage application is started so that the optical layer 25 in the divided region 22 is in a scattering state. The optical layer 25 gradually transitions from a transparent transmission state to a scattering state after a voltage is applied.
Thus, by applying the drive voltage waveform of FIG. 15A to each control electrode 27, the optical state of the divided region 22 corresponding to each control electrode 27 is synchronized with the scanning of the screen 21 and transparent transmission is performed. It is possible to switch between a state and a scattering state.

Here, the optical characteristics of the screen 21 in the reverse mode will be described.
FIG. 16 is a diagram illustrating an example of optical characteristics of the screen 21 in the reverse mode.
The horizontal axis represents the amplitude of the applied voltage. The left vertical axis corresponds to the characteristic curve A and is a convergent optical state (scattering intensity). The right vertical axis corresponds to the characteristic curve B and is the response period.
Here, the response time refers to the time from the start of voltage application until the intensity of scattering reaches 90% of the maximum optical characteristic stabilized at the voltage.
The threshold voltage VTH is a voltage at which the optical characteristic starts to change from the optical state of 0V.
The first voltage V1 is a voltage that maximizes the converged optical state (scattering intensity).
The second voltage V2 is higher than the first voltage V1.

As shown in FIG. 16, when the voltage applied to the optical layer 25 of the screen 21 in the reverse mode is increased and exceeds the threshold voltage VTH, the intensity of scattering in the converged state starts to change from the 0V state. Thereafter, the intensity of the scattering changes as the applied voltage increases.
When the applied voltage reaches the first voltage V1, the intensity of the scattered scattering is maximized.
When the voltage exceeds the first voltage V1, the intensity of the scattered scattering starts to decrease. The second voltage V2 converges to a scattering intensity lower than that of V1.
Thus, the optical state may increase or decrease with the characteristic having the maximum according to the applied voltage.

On the other hand, the response time has a substantially inversely proportional characteristic that becomes shorter as the voltage applied to the screen 21 in the reverse mode is higher.
That is, the second voltage V2 has a constant optical state in a short time.
As shown in the example of FIG. 16, the response time of the screen 21 becomes longer when the applied voltage is lower.
For this reason, even if a voltage equal to or lower than the first voltage V1 is applied when the optical state is to be switched in a short time, such as when a drive voltage waveform synchronized with the scanning of the image light is applied, the predetermined voltage is applied. In many cases, a stable scattering state cannot be obtained within this time.
That is, even if the voltage V1 is applied so as to obtain an optimal scattering state in the reverse mode, the optical state of the optical layer 25 is constant during the period Ton including the video period to be controlled to the scattering state. It cannot be stabilized. As a result, in the period Ton controlled to the scattering state, the optical state of the divided region 22 cannot be flattened, and the optical state of the adjacent divided region cannot be made substantially equal at the timing when the image light is irradiated. , Luminance unevenness is visually recognized at the region boundary.

When the screen 21 in the reverse mode is controlled in synchronization with the scanning of the image light in this way, a response time is required for the divided region 22 to switch between the transparent transmission state and the maximum scattering state. In the case where the control is performed in synchronization with the scanning of the image light, it takes time for the divided region 22 to be scanned until the divided region 22 is stabilized in the maximum scattering state.
As a result, a constant scattering state cannot be obtained in the partial scanning period TP.
That is, as shown in FIG. 15B, even when the application of a voltage at which the maximum scattering state is started, the optical state of the optical layer 25 is not stable in a constant state within the period of controlling to the scattering state. The optical state is not flattened.
When the optical state of the divided region 22 is not stable in a constant scattering state, luminance unevenness occurs in the image projected on the screen 21.

Therefore, the synchronization control unit 31 applies a plurality of levels of voltage to the screen 21 in the reverse mode in a period Ton including a video period in which each divided region 22 is controlled to be in a scattering state by voltage application.
FIG. 17 is a schematic timing chart showing two-level drive voltage waveforms in the first embodiment.
Specifically, as shown in FIG. 17, the synchronization control unit 31 first applies a voltage waveform composed of the second voltage V2 to the control electrode 27 in the divided region 22 slightly before the projection light is irradiated. To start.
When the second voltage V2 is applied, the response time (rise time) is sufficiently fast. When this waveform is applied continuously, the optical characteristics gradually decrease after the scattering intensity reaches the maximum scattering state, and the scattering state converges to a constant value slightly lower than the maximum. That is, even when the second voltage V2 is continuously applied, it is necessary to irradiate the image light during the time when the optical state change continues.
Therefore, as illustrated in FIG. 17, the synchronization control unit 31 applies the first voltage V1 following the application of the second voltage V2.
The 1st voltage V1 is a voltage which can be made into the maximum scattering state in general. The first voltage V1 is a voltage that converges to the optical state when switching from the second voltage V2 to the first voltage V1.
The first voltage V1 and the second voltage V2 are applied as low-frequency AC voltages.
In addition, the first voltage V1 is switched from the second voltage V2 and applied at the timing when the scattering state that changes momentarily by the second voltage V2 becomes maximum.

As described above, in the present embodiment, the scattering rate (transmittance) of parallel rays can be maintained at a constant level during the period Ton including the video period in which the optical layer 25 is controlled to be in a scattering state by applying a plurality of values of voltage. . In the partial scanning period TP, a certain scattering state is obtained.
In particular, in the present embodiment, the maximum scattering is achieved by application of the second voltage V2 so that the scattering state immediately after the end of the application period of the second voltage V2 becomes a maximum value (a value at which the parallel light transmittance is minimized). At the timing when the state is reached, the applied voltage is switched from the second voltage V2 to the first voltage V1.

As shown in FIG. 17, after the scanning of the divided region 22 controlled to the scattering state is completed, the synchronization control unit 31 stops the voltage application to the control electrode 27. From this timing, the optical layer 25 in the divided region 22 starts to change from the scattering state to the transmission state.
Thereby, the plurality of divided regions 22 can be sequentially controlled to be in a scattering state, and each divided region 22 can be held in a transmissive state for a long period in the non-video period Toff.

Next, an example in which drive voltages having a plurality of values are applied to the plurality of divided regions 22 will be described.
FIG. 18 is a schematic timing chart showing the relationship between the two-level driving voltage waveform and the optical state for a plurality of control electrodes.
18A to 18D show voltages applied to four consecutive control electrodes 27. FIG. The horizontal axis is time, and the vertical axis is voltage. FIGS. 18E to 18H show optical characteristics of four continuous divided regions 22 corresponding to FIGS. 14A to 14D. The horizontal axis is time, and the vertical axis is parallel light transmittance.
As shown in FIGS. 18A to 18D, in the non-video period Toff in which each of the four consecutive control electrodes 27 is not scanned, voltage application is stopped in order to control the transmission state. Then, voltage application is started before the partial scanning period TP in which each is scanned, and then a low voltage is applied. The applied voltage is AC. By applying such a voltage waveform, as shown in FIGS. 18E to 18H, the four continuous divided regions 22 are controlled from the transmission state to the constant scattering state.
Further, as shown in FIGS. 18A to 18D, the application of voltage to the four consecutive control electrodes 27 is stopped in order to control the transmission state after each scanning is completed. By applying such a voltage waveform, as shown in FIGS. 18E to 18H, the four continuous divided regions 22 are controlled from the scattering state to the transmission state.
The reference timing information for the synchronization control is sent from the projector 11 to the synchronization control unit 31. The synchronization control unit 31 sequentially switches the voltage applied to the plurality of control electrodes 27 based on the reference timing so that the projection light is not irradiated during a period in which the scattering characteristics are not stable.

As described above, in the present embodiment, the screen 21 operates in the reverse mode in which the transmissivity of parallel rays is reduced by applying a voltage, and scatters the projected image light.
Further, the synchronization control unit 31 switches the voltage applied to the plurality of divided regions 22 in the scanning order in the scanning period of the image light, and controls each divided region 22 to the video state in the partial scanning period TP in which each is scanned. Then, the non-video state is controlled in a period in which each is not scanned, that is, a period other than the partial scanning period TP.
In addition, when controlling the divided region 22 to the video state, the synchronization control unit 31 decreases the applied voltage after applying a voltage to the control electrode 27 and applies voltages having a plurality of values with two amplitudes. The optical state of 22 is held in a predetermined scattering state whose degree of scattering is lower than the maximum scattering state of the divided region 22, and the scattering state of the divided region 22 in the partial scanning period TP scanned with image light is stabilized. .
As a result, the scattering characteristics of each divided region 22 in the partial scanning period TP are maintained constant. The image light irradiated on the screen 21 is scattered by a plurality of divided regions 22 controlled to a constant scattering state. In the image displayed on the screen 21, luminance unevenness when the scattering state is not controlled to be constant is suppressed.
In the present embodiment, since voltages with two amplitudes are applied to each divided region 22, there is no need to delay scanning until each divided region 22 is controlled to the maximum scattering state. The optical state can be switched at high speed in synchronization with the scanning of the image light. Therefore, each divided region 22 can be controlled to be in a transparent transmissive state for a long time, and the screen 21 can be better seen through, so that the see-through characteristic of the screen 21 can be obtained while brightening the image. In spite of the long response time for switching the optical state of the screen 21 in the reverse mode, the parallel light transmittance of the screen 21 is kept high, and the high see-through characteristic of the screen 21 and good image visibility are obtained.
While obtaining the see-through characteristic of the screen 21, it is possible to display an image by scattering image light uniformly and without waste.
In particular, the voltage initially applied to the control electrode 27 by the synchronization control unit 31 to control the divided region 22 to the video state is a second voltage V2 higher than the first voltage V1 that can bring the divided region 22 into the maximum scattering state. Then, the voltage to be applied after being lowered may be set to a voltage equal to or lower than the first voltage V1 that can achieve the maximum scattering state. Thereby, the switching time to the parallel light transmittance in a stable scattering state can be minimized.

[Third Embodiment]
In the third embodiment, a modification of the display device 1 of the above embodiment will be described.
In the third embodiment, by setting each voltage applied to the control electrode 27 to a half cycle, luminance unevenness and the like are further suppressed as compared to the above embodiment.

FIG. 19 is a schematic timing chart showing a two-level driving voltage waveform using a half cycle in the third embodiment. FIG. 19 is used for the screen 21 in the normal mode.
In the first embodiment, as shown in FIG. 19A, low voltage AC voltage of several cycles is applied to each divided region 22 of the screen 21 operating in the normal mode in the second half of the period Ton including the video period. A high voltage AC voltage of several cycles is applied in the non-video period Toff.
When an AC voltage is applied, the polarity of the applied voltage changes. The orientation of the optical layer 25 is also switched.
This may result in a dip in the parallel light transmittance, i.e., a spike in the scattering state.
When this phenomenon occurs in the partial scanning period TP where it is necessary to maintain a constant scattering state, a dip is generated, and the scattering state is changed to deteriorate the image quality.

In order to avoid this, in this embodiment, as shown in FIGS. 19B to 19D, the voltage applied in the period Ton including the video period is a unipolar square wave. The application time of the square wave voltage may be the same as that in the first embodiment.
Specifically, in FIG. 19B, the low voltage applied in the second half of the period Ton including the video period is a half wave (half cycle) square wave in which the polarity does not change during the period.
In FIG. 19C, the voltage applied during the non-video period Toff is a half-wave square wave.
In FIG. 19D, the voltage applied in the second half of the period Ton including the video period and the voltage applied in the non-video period Toff are both a half-wave square wave.
As shown in FIGS. 19B to 19D, by using a half cycle and using a unipolar voltage in the period Ton including the video period and / or the non-video period Toff, the spikes are not generated.
Moreover, power consumption can be reduced by adopting a half cycle.

However, when the half cycle is used, a DC bias is effectively applied to the optical layer 25 in each scanning period.
For this reason, in FIGS. 19B to 19D, the polarity is inverted for each frame in the odd-numbered scan cycle and the even-numbered scan cycle.
In the case of FIG. 19B, the phase of the voltage waveform in the non-video period Toff following the period Ton including the video period is also shifted by a half cycle for each scanning period. Without such a shift, the transmission state fluctuates with a double period (half frequency), and haze flicker may occur on the entire screen.

FIG. 20 is a schematic timing chart showing a two-level drive voltage waveform using a half cycle in the third embodiment. FIG. 19 is used for the screen 21 in the reverse mode.
In the second embodiment, as shown in FIG. 20A, an alternating voltage of several cycles is applied to each divided region 22 of the screen 21 operating in the reverse mode in the video state.
In this case, the polarity of the voltage is switched during the period Ton including the video period. The orientation of the optical layer 25 is also switched.
When the polarity of the applied voltage changes during the period Ton including the video period, a dip in the parallel light transmittance, that is, a spike like spike may occur in the scattering state.
When this phenomenon occurs in the partial scanning period TP that needs to be maintained in a constant scattering state, a dip is generated, and the scattering state is changed to deteriorate the image quality.

In order to avoid this, in this embodiment, as shown in FIGS. 20B to 20D, the voltage applied in the period Ton including the video period is a unipolar square wave. The application time may be the same period as in the second embodiment.
Specifically, in FIG. 20B, the high voltage applied in the first half of the period Ton including the video period is a half wave (half cycle) square wave.
In FIG. 20C, the low voltage applied in the second half of the non-video period Toff is a half-wave square wave.
In FIG. 20D, the high voltage applied in the first half of the period Ton including the video period and the low voltage applied in the second half are both formed into a half-wave square wave.
As shown in FIGS. 20B to 20D, by using a half cycle and using a unipolar voltage in a period Ton including a video period, a spike-like spike is not generated.
Moreover, power consumption can be reduced by adopting a half cycle.

However, when the half cycle is used, a DC bias is effectively applied to the optical layer 25 in each scanning period.
For this reason, in FIGS. 20B to 20D, the polarity is inverted for each scanning period between the odd-numbered scanning period and the even-numbered scanning period.
Further, as shown in FIG. 20C, in the reverse mode, it is desirable to shift the phase of the waveform in the rising period by a half cycle.

As described above, in the present embodiment, since the half-cycle voltage is applied when controlling the optical state of the divided region 22, the scattering state is less likely to fluctuate in the period Ton including the video period, and / or In the non-video period Toff, the transmission state hardly changes.
In FIG. 19C, the applied voltage that is maintained in the transmissive state in the transparent period (non-video period Toff) of the screen 21 in the normal mode is a unipolar square wave or bipolar (2m + 1) / It is a rectangular wave of 2 cycles (m is an integer). Thereby, the frequency in the application period of a high voltage can be made as low as possible, and power consumption can be reduced. The rectangular wave period of m cycles may not be constant.
In FIG. 20B, the first high voltage in the period Ton including the reverse mode video period is applied. Thereby, the following problems can be avoided.
That is, when driving a region with a large load capacity (such as a large area), the rise of the applied voltage is slow. Therefore, if a bipolar waveform is used as the high voltage at the time of start-up, the rise of optical characteristics is wasted at the time when the polarity is switched. As a result, the rise time becomes longer. As a result, the haze during operation increases.
As shown in FIG. 20B, the polarity switching time can be reduced even when driving a large load capacity region by increasing the area by making the high voltage during this startup period a unipolar square wave. Loss can be reduced, and as a result, haze can be suppressed and display quality can be improved.
In FIG. 20B, since the DC bias is effectively applied, it is preferable to reverse the polarity every scanning cycle. Further, the phase of the low voltage applied in the second half of the period Ton including the video period may be shifted by a half cycle for each scanning period. If this shift is not performed, the scattering state will fluctuate with a double period (half frequency), and flicker may occur in the display image.
Further, as shown in FIG. 19D or FIG. 20D, the effect can be further enhanced by combining the half-wave voltages. When this method is used, the voltage difference between the first voltage V1 and the second voltage V2 effectively becomes a DC bias, and therefore the polarity may be reversed every scanning period.

As described above, in the present embodiment, the synchronization control unit 31 sets the voltage applied to the control electrode 27 as a half-cycle voltage whose polarity does not change during the application period.
Therefore, in the screen 21 in the normal mode, the fluctuation in the transmittance of parallel light that occurs when an AC voltage is used is suppressed, and the luminance unevenness in the second half of the video period or the fluctuation in the parallel light transmittance in the non-video period. Can be suppressed.
In the reverse mode screen 21, fluctuations in parallel light transmittance that occur when an AC voltage is used can be suppressed, and luminance unevenness in the latter half of the video period can be suppressed.

In the present embodiment, the synchronization control unit 31 switches the polarity of the voltage applied to the control electrode 27 in the scanning period T of the plurality of image lights in units of the scanning period T.
Therefore, although a DC voltage is applied to the optical layer 25 in each scanning period T, a DC component of the voltage applied to the optical layer 25 in a plurality of scanning periods T can be suppressed.

[Fourth Embodiment]
4th Embodiment demonstrates the modification of the display apparatus 1 of the above embodiment.
In the fourth embodiment, a display device 1 in which the voltage applied to the control electrode 27 has three or more levels will be described.
FIG. 21 is a schematic timing chart showing three-level drive voltage waveforms in the fourth embodiment.

FIG. 21A shows three-level drive voltage waveforms applied to the control electrode 27 of the screen 21 in the normal mode. The horizontal axis is time, and the vertical axis is voltage.
The drive voltage in FIG. 21A is an AC voltage with three amplitudes (6 levels + 0 V). At the beginning of the non-video period Toff controlled to the transmission state, a voltage waveform having an intermediate level different from the voltage applied in the second half is applied.
Thereby, it is possible to speed up the return from the scattering state to the transmission state.

FIG. 21B shows three-level drive voltage waveforms applied to the control electrode 27 of the screen 21 in the reverse mode.
The drive voltage in FIG. 21B is an AC voltage with three amplitudes (6 levels + 0 V). As the drive voltage, an AC voltage having three amplitudes (6 levels + 0 V) is applied in a period Ton including a video period. Specifically, it is an example in which a voltage waveform at an intermediate level different from the voltage applied in each period is applied between the period of rising from the transmission state to the scattering state and the period of maintaining the constant scattering state.
Thereby, even when the response time varies among the plurality of divided regions 22 in one screen 21, the influence can be suppressed.

[Fifth Embodiment]
5th Embodiment demonstrates the modification of the display apparatus 1 of the above embodiment.
FIG. 22 is a schematic configuration diagram of a display device 1 according to the fifth embodiment of the present invention.
As shown in FIG. 22, the display device 1 of the fifth embodiment includes a temperature sensor 51.
The temperature sensor 51 is disposed on the screen 21 and detects the temperature of the screen 21.
The temperature sensor 51 is connected to the synchronization control unit 31 and outputs a signal indicating the detected temperature.

The synchronization control unit 31 adjusts the drive voltage waveform based on the panel temperature detected by the temperature sensor 51.
For example, the synchronization control unit 31 changes the voltage (amplitude) of the drive waveform based on the detected temperature.
Alternatively, the synchronization control unit 31 changes the pulse period or AC frequency of the drive waveform based on the detected temperature.
Alternatively, the synchronization control unit 31 changes the voltage of the drive waveform and the pulse period or AC frequency based on the detected temperature.
For example, the synchronization control unit 31 may determine a drive voltage or the like according to the detected temperature using a preset reference table in which the relationship between the detected temperature and the drive voltage is set.
In addition to this, for example, the synchronization control unit 31 may determine a reference voltage in which the relationship between the waveform of the drive voltage and the detected temperature is set in advance, and the drive voltage corresponding to the temperature detected by the interpolation value based on the reference table. Good.

As described above, the display device 1 according to the present embodiment functions as a drive system including the temperature detection system of the screen 21 and the drive waveform control system.
In the present embodiment, even if the response speed of the screen 21 varies depending on the temperature of the screen 21 (liquid crystal temperature), it is possible to suppress luminance variation due to this variation.

Each of the above embodiments is an example of a preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications or changes can be made without departing from the scope of the invention. .
For example, in the above-described embodiment, the screen 21 is controlled to be in the scattering state in the image state, and is scattered while transmitting the image light. In addition, for example, the screen 21 may be controlled to be in a high scattering state in the video state, and may be scattered while reflecting the video light. In this case, the screen 21 functions as a reflective screen positioned between the projector 11 and the viewer.
FIG. 23 is a schematic configuration diagram of a modified example of the display device 1 according to the second embodiment of the present invention using the reflective screen 21.
In FIG. 23, the projector is disposed on the viewer side with respect to the reflective screen 21. Even in this case, by applying the present invention, the image 41 by the image light and the background 42 of the screen 21 can be overlapped and displayed on the screen 21 as shown in FIG.

DESCRIPTION OF SYMBOLS 1 Display apparatus 11 Projector 21 Screen 22 Division | segmentation area | region 25 Optical layer 27 Control electrode 31 Synchronization control part (control part)
51 Temperature Sensor T Scanning Period TP Partial Scanning Period Ton Period Including Video Period Toff Non-Video Period

Claims (12)

An optical layer whose optical state changes by application of a voltage, and a screen having a plurality of control electrodes arranged side by side along the optical layer in order to apply a voltage to the optical layer;
A projector for projecting image light onto the screen to display an image;
A voltage is applied to the plurality of control electrodes, and in a projection period of image light, the screen is optically different from a predetermined image state in which the image light is scattered for each divided region where the control electrodes are formed. A control unit that switches between a non-video state that is a state;
Have
The controller is
The optical state of the plurality of divided regions in the projection period of the image light is switched in synchronization with the projection of the image light by the projector, and the optical state of the portion of the screen on which the image light is projected is the image state age,
The optical state of the image state is held by a voltage having an amplitude of 2 or more.
Display device. The projector scans the screen with image light,
The controller is
The voltage applied to the plurality of divided regions in the scanning period of the image light is switched in the scanning order, and each of the divided regions is controlled to the video state in the partial scanning period in which each is scanned, and each is not scanned Control to a non-video state in
The display device according to claim 1. The screen operates in a normal mode in which parallel light transmittance is increased by applying a voltage, and scatters image light projected in the previous image state,
The controller is
A voltage is applied to the control electrode of the divided area to be controlled to a non-image state, and the divided area is controlled to a transmissive state,
The voltage applied to the control electrode of the divided region to be controlled to the video state is lower than the applied voltage in the non-video state, and the divided region scanned with the video light is controlled to be in the scattering state, and the video light is scattered.
The display device according to claim 1 or 2. The controller is
When controlling the divided region to the video state, the applied voltage is increased after the voltage application to the control electrode is stopped, and the optical state of the divided region is less scattered than the maximum scattering state of the divided region. Hold in a predetermined scattering state, and stabilize the scattering state of the divided region in a partial scanning period scanned with image light,
The display device according to claim 3. The screen operates in a reverse mode in which scattering is increased when a voltage is applied, and scatters projected image light,
The controller is
Stop application of voltage to the control electrode of the divided region to be controlled to a non-image state, and control the divided region to a transparent transmission state;
A voltage is applied to the control electrode of the divided region to be controlled to the image state, the divided region scanned with the image light is controlled to the scattering state, and the image light is scattered.
The display device according to claim 1 or 2. The controller is
When the divided area is controlled to be in an image state, a voltage is applied to the control electrode and then the applied voltage is lowered, and the optical state of the divided area is held in the scattered state and scanned with image light. Stabilizing the scattering state of the divided regions in the partial scanning period;
The display device according to claim 5. The voltage initially applied to the control electrode by the control unit to control the divided region to the video state is a voltage higher than a voltage capable of bringing the divided region into a maximum scattering state.
Thereafter, the voltage applied by lowering the voltage is a voltage that can achieve the maximum scattering state.
The display device according to claim 6. The voltage initially applied to the control electrode by the control unit to control the divided region to a video state is:
It is changed at the timing when the scattering due to the voltage is maximized.
The display device according to claim 7. The controller is
The voltage applied to the control electrode is a substantially low frequency alternating voltage,
The display device according to claim 1. The controller is
The polarity of the voltage applied to the control electrode in a plurality of projection periods of video light is switched in units of the projection period, and the direct current component of the voltage applied to the optical layer in the plurality of projection periods is suppressed.
The display device according to claim 1. A display device driving method for displaying an image of image light projected from a projector on a screen having an optical layer whose optical state changes by application of a voltage,
The control unit for controlling the optical state of the screen,
A voltage is applied to a plurality of control electrodes arranged side by side along the optical layer, and an image by image light is displayed on a screen having the optical layer and the plurality of control electrodes,
During the image light projection period, the screen is switched between a predetermined image state in which the image light is scattered and a non-image state which is an optical state different from the predetermined image state for each divided region where the control electrodes are formed. ,
The optical state of the plurality of divided regions in the projection period of the video light is switched in synchronization with the projection of the video light by the projector, and the optical state of the portion of the screen on which the video light is projected is the video state age,
The optical state of the image state is held by a voltage having an amplitude of 2 or more.
A driving method of a display device. An optical layer whose optical state is changed by applying a voltage, and a plurality of control electrodes arranged side by side along the optical layer for applying a voltage to the optical layer, and displays an image based on the projected image light And a screen to
A voltage is applied to the plurality of control electrodes, and in a projection period of image light, each divided region in which the control electrode is formed has a non-image in a predetermined image state in which the image light is scattered and an optical state different from the predetermined image state A controller that controls to switch between states;
Have
The controller is
The optical state of the plurality of divided areas in the projection period of the image light is switched in synchronization with the projection of the image light onto the screen, and the optical state of the portion of the screen on which the image light is projected is changed to the image State and
The optical state of the image state is held by a voltage having an amplitude of 2 or more.
Screen device for display.