JPH04270311A - Writing device for liquid crystal light valve - Google Patents

Abstract

PURPOSE:To allow plotting with a laser beam at a high speed under any polarity and to allow partial rewriting as well while assuring the threshold characteristic of a liquid crystal. CONSTITUTION:The start of sweeping is detected by a timing signal generating circuit and the polarities of image signals are inverted by a polarity changing circuit at every time when the laser beam emitted from a laser beam source forming at least two spots is deflected and scanned in a main scanning direction by a main scanning means. The laser beam source is driven in accordance with the inverted image signals and the polarities of the impressed voltage for driving a liquid crystal light valve are inverted at every detection of the start of the scanning. The writing of the liquid crystal light valve is executed by the laser beam for writing while the respective next scanning lines are erased alternately by the laser beam for erasing by the main scanning means and auxiliary scanning means in correspondence to the above-mentioned polarities. The wasteful use of the impressed voltage of both polarities of the driving electrodes of the liquid crystal light valve is effectively used in this way and the partial rewriting is possible as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a writing device for a liquid crystal light valve that uses photoconductivity to write and display images on a bistable liquid crystal.

0002

2. Description of the Related Art FIG. 5 is a time chart for explaining the writing procedure of a liquid crystal light valve applied to a conventional image forming apparatus disclosed in, for example, Japanese Unexamined Patent Publication No. 1-241528. An image is written by condensing and scanning a beam of light and making use of the decrease in resistance of the photoconductor in the irradiated area.

FIG. 5(a) shows a timing signal generated from a scanning start signal, FIG. 5(b) shows a driving electric field for driving a liquid crystal light valve, and FIG. 5(c) shows a video signal for modulating a laser beam. be.

Next, the operation will be explained. This writing method for liquid crystal light valves uses a polygon mirror scanner and a galvanometer mirror scanner to perform raster scanning, and during the main sweep, a square wave with both positive and negative polarities is applied as shown in Figure 5(b). are doing.

Writing is performed under a specific polarity of the drive voltage, and in this example, the video signal shown in FIG. 5(c) is sent when the drive voltage is negative. The positive polarity pulse is used to cancel the DC component of the pulse during writing, and the period during which it is written is a pause period for writing.

[0006]

[0007] Since writing in the conventional liquid crystal light valve is performed as described above, there is a problem in that writing must be stopped during the application period of pulses of opposite polarity.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a writing device for a liquid crystal light valve that is capable of writing under any polarity and also allows partial rewriting. With the goal.

[0008]

[Means for Solving the Problems] A writing device for a liquid crystal light valve according to the present invention includes a liquid crystal light valve made of a photoconductor layer and a liquid crystal that is bistable with respect to an electric field, and a recording pixel of this liquid crystal light valve. a laser light source that emits at least two laser beams for erasing and recording; a scanning device that alternately and repeatedly deflects and scans each of the at least two laser beams by a main scanning device and a sub scanning device; and a laser beam of the main scanning device. A timing signal generation circuit detects the start of beam sweep, and each time the timing signal generation circuit detects the start of sweep, the polarity of the image signal is reversed to drive the laser light source and the polarity of the voltage applied to the liquid crystal light valve is reversed. The means are provided.

[0009]

[Operation] At least two laser beams generated from the laser light source of the present invention are deflected and scanned by the main scanning means, and the timing signal generation circuit detects each time the sweep starts, and each time the start of the sweep is detected, the polarity of the image signal is inverted. At the same time as driving the laser light source, the polarity of the applied voltage that drives the liquid crystal light valve is reversed, and when the applied voltage of one polarity of the liquid crystal light valve is applied, the erasing laser beam deflected and scanned by the main scanning means is used to scan the next scanning line. When the voltage of the other polarity is applied, the next scanning line is erased by the erasing laser beam deflected and scanned by the sub-scanning means, while the writing laser beam is used to erase the next scanning line. Writing is performed and sweeping is performed without providing a writing pause period to cancel the DC component of the drive voltage, reducing the writing time for one frame and erasing only the adjacent scanning lines. Therefore, it is also possible to rewrite part of the image.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a writing device for a liquid crystal light valve according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of one embodiment. In this Figure 1,
101 is a laser light source that generates two spots, 102
103 is a main scanning means for deflecting the laser beam emitted from the laser light source 101 in the main scanning direction, 103 is a sub-scanning means, and 104 is a main scanning means 102, and a laser beam deflected by the sub-scanning means 103 is condensed.・It is a scanning optical system for scanning. 105 is a liquid crystal light valve;
The area illuminated by light is stored in a dark state.

On the other hand, 106 is an image signal generation circuit,
The image signal generated from the image signal generation circuit 106 is input to the polarity switching circuit 107, and the image signal input to the polarity switching circuit 107 is transferred from the timing signal generation circuit 110 to the polarity switching circuit 107. The polarity of the image signal is switched every scan by the timing signal.

The image signal whose polarity has been switched by the polarity switching circuit 107 is input to a laser drive circuit 108. This laser drive circuit 108 is configured to drive the laser light source 101.

Further, the liquid crystal light valve driving circuit 109 applies a bipolar square wave to the liquid crystal light valve 105 in response to a timing signal from a timing signal generating circuit 110. Then, the timing signal generation circuit 110 detects the start of the sweep of the main scanning means 102 and outputs the timing signal to the polarity switching circuit 10 as described above.
7 and the liquid crystal light valve drive circuit 109.

Furthermore, the light source 111 is a liquid crystal light valve 1.
A light beam is generated in order to project and display the image of
5, the image on the liquid crystal light valve 105 is read out and projected onto the screen 113.

Generally, the liquid crystal light valve 105 is constructed as shown in FIG. This FIG. 2 is shown as an enlarged sectional view, and shows a pair of opposing glass substrates 20.
A transparent electrode 20 is provided on the inner surface of each of 1a and 201b.
2a and 202b are formed. Among these, on the transparent electrode 202b side, a photoconductor 207, a dielectric layer film mirror 2
06 is connected. A liquid crystal alignment film 203a is provided between the dielectric layer mirror 206 and the transparent electrode 202a, respectively.
, 203b, the liquid crystal 205 is sandwiched between them. The upper and lower ends of this liquid crystal 204 are held between spacers 204a and 204b.

Next, the operation will be explained. In this embodiment, the liquid crystal 205 is made of, for example, a ferroelectric liquid crystal which has bistability with respect to an electric field. The photoconductor 207 has a property that it has a high resistance when not irradiated with light, but its resistance decreases when irradiated with light. ,
If a part of the photoconductor 207 is irradiated with laser light 208,
As the resistance of the photoconductor 207 in the irradiated area decreases, the liquid crystal 20
The electric field applied to 5 increases, and only the irradiated portion of the liquid crystal is driven.

In this embodiment, since the liquid crystal 205 has bistability with respect to the electric field, the liquid crystal once driven beyond the threshold will not remain in the written state even after the light irradiation is finished and the applied voltage is reduced. will be maintained. Therefore, the laser beam 208 is raster-swept, image information is recorded on the liquid crystal, and the image can be displayed on the screen using the illumination/projection light 209. As mentioned above, the ferroelectric liquid crystal has bistability and takes on two values of brightness and darkness during display.

The correspondence between the stable state of the liquid crystal and the brightness and darkness of the display changes depending on the configuration of the projection optical system 112, but here, for the sake of simplicity, the transparent electrode 20 on the photoconductor 207 side is
Assume that when a positive voltage is applied to 2b, a bright display is performed, and when a negative voltage is applied, a dark display is performed.

Now, FIG. 3 shows the state of writing to the liquid crystal light valve 105 in this embodiment.
Figure 3(a) shows the writing of the n-th scanning line, and Figure 3(b) shows the writing of the n-th scanning line.
represents writing of the (n+1)th scanning line. The diagonal lines in FIGS. 3(a) and 3(b) are laser spots, 301a is a writing spot, and 302a is an erasing spot, which are scanned from left to right in the figure by the main scanning means 102.

In FIG. 3A, a negative voltage is applied to the liquid crystal light valve 105 by the liquid crystal light valve drive circuit 109, and the portion irradiated with light is recorded in a dark state. The writing spot 301a irradiates light at an image position corresponding to the black portion of the image signal, recording black pixels on a white background.

Furthermore, the erase spot 302a is located at the next n+
The first scanning line is scanned while constantly irradiating light,
The n+1st scanning line is all changed to black.

In the next scan, the writing spot 301b is scanning the (n+1)th writing spot 301b by the sub-scanning means 103, but at this time, the liquid crystal light valve driving circuit 109 changes the applied voltage by the sweep start signal from the timing signal generating circuit 110. The polarity of the liquid crystal light valve 105 is reversed, and a positive voltage is applied to the liquid crystal light valve 105.

As described above, the n+1th scanning line is entirely black due to the erase spot 302a, so the light irradiated portion of the write spot 301b records white on a black background.

In this manner, in the scanning shown in FIG. 3(b), the correspondence between light irradiation and display brightness is reversed from that in FIG. The polarity is reversed by the circuit 107 and the laser drive circuit 1
08, and light is irradiated at the white position of the image signal.

FIG. 4 illustrates the state of this drive signal.
In FIG. 4, the liquid crystal light valve driving voltage diagram 4(a), the image signal diagram 4(b), and the laser driving signal diagram 4(c) are shown on the horizontal axis with the time axis. Figure 4(b)
The image signal has a periodic waveform of one white (W) pixel and two black (B) pixels, and when the liquid crystal light valve drive signal in Fig. 4(a) is negative, the image signal in Fig. 4(b) When the laser drive signal in FIG. 4(c) is turned on for the black of the image signal of FIG.
(c) The laser drive signal is turned on.

Further, in FIG. 3(b), the erasing spot 302b is constantly irradiated with light as in FIG. 3(a), and the (n+2)th scanning line is entirely erased to white. By repeating this operation for all scanning lines, image rewriting in which erasing and writing are performed simultaneously is performed.

It should be noted that the polarities of the image signal, liquid crystal light valve drive voltage, and laser drive signal in the above embodiment can be combined differently from the above example depending on the configuration of the projection optical system, and even in that case, The basic operation remains unchanged.

Further, in the above embodiment, one erase/write spot is used, but a plurality of spots may be used. In that case, writing is performed on the same number of scanning lines as the number of spots in one main scan. In sub-scanning, it is necessary to perform interlaced scanning corresponding to the number of spots.

Furthermore, since erasing and writing are limited to the irradiation position of the laser spot, if scanning is limited to a portion,
Partial rewriting is also possible.

[0030]

As described above, according to the present invention, writing is performed while erasing the next scanning line in both polarities of the drive voltage of the liquid crystal light valve, so that the threshold performance of the liquid crystal is ensured and high speed is achieved. It is possible to realize laser beam drawing of 200 degrees, use applied voltages of both polarities without waste, and also enable partial rewriting.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a writing device for a liquid crystal light valve according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing the structure of the liquid crystal light valve in the embodiment of FIG. 1;

FIG. 3 is an explanatory diagram showing a writing state of the liquid crystal light valve in the embodiment of FIG. 1;

FIG. 4 is a timing chart of a drive signal for a laser light source in the embodiment of FIG. 1;

FIG. 5 is a timing chart showing a writing procedure of a conventional liquid crystal light valve.

[Explanation of symbols]

101 Laser light source 102 Main scanning means 103 Sub-scanning means 104 Scanning optical system 105 LCD light valve 106 Image signal generation circuit 107 Polarity switching circuit 108 Laser drive circuit 109 Liquid crystal light valve drive circuit 110 Timing signal generation circuit 111 Light source 112 Projection optical system 113 Screen 201a, 201b Glass substrate 202a, 202b Transparent electrode 203a, 203b Liquid crystal alignment film 205 LCD 206 Dielectric multilayer film 207 Photoconductor

Claims (1)

[Claims] 1. A liquid crystal light valve comprising a photoconductor layer and a liquid crystal that is bistable with respect to an electric field, and at least two beams for erasing a previously recorded pixel of the liquid crystal light valve and for image recording. a laser light source that generates a laser beam; and at least two laser beams that write on the liquid crystal light valve with a writing laser beam while erasing the next scanning line with an erasing laser beam emitted from this laser light source. a main scanning means for deflection scanning; a timing signal generation circuit for detecting the start of the sweep of the laser beam of the main scanning means; and a timing signal generation circuit for detecting the start of the sweep of the main scanning means; A polarity switching circuit that switches the polarity, a laser drive circuit that drives the laser light source to emit the laser beam based on the image signal whose polarity has been switched by the polarity switching circuit, and a timing generation circuit that starts the sweep. a liquid crystal light valve drive circuit that inverts the polarity of the voltage applied to the liquid crystal light valve each time the liquid crystal light valve is detected; and a laser light source that alternately operates with the main scanning means in response to each reversal of the polarity of the voltage applied to drive the liquid crystal light valve. and sub-scanning means for deflecting and scanning in the scanning direction of the liquid crystal light valve so that the next scanning line is erased by the erasing laser beam emitted from the laser beam and the writing laser beam is used for writing. writing device.