JPH07111517B2 - Liquid crystal light valve, printer using the same, and optical logic operator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal light valve having a ferroelectric liquid crystal as a liquid crystal layer, a display device, a printing device, and an optical logic operator using the ferroelectric liquid crystal light valve. Is.

2. Description of the Related Art As a conventional ferroelectric liquid crystal light valve, for example,
It is composed of a liquid crystal panel having the structure shown in the figure and a drive circuit. A pair of substrates equipped with a transparent electrode, an electric insulating film, and an alignment film on glass are placed with a spacer between 1.5 μm and 5 μm.
The ferroelectric liquid crystals are injected and aligned in the interval while facing each other with a certain interval between them. As the orientation film, a rubbing treatment may be performed after a thin film made of an organic material is formed, or an inorganic material such as SiO may be vapor-deposited from an oblique direction. As described above, when the thickness of the liquid crystal layer is thinned, the ferroelectric liquid crystal has its original helical structure and the several states shown in the schematic diagram of FIG. 6 are stabilized. The hatched liquid crystal molecules 60 move on the side surface of the cone 61. Figure 6 (a), (b)
Indicates that the directions of the liquid crystal molecules are substantially aligned, and at this time, the spontaneous polarization is directed in the upward and downward directions of the substrate normal. FIG. 6 (c) shows a state in which the liquid crystal molecules are twisted in the direction normal to the substrate, and there is also a state in which the twist direction is reversed. Depending on the type of alignment film, it may differ from that shown in FIG. 6 depending on the tilt angle of the liquid crystal molecules on the substrate and the bending of the liquid crystal layer.
Basically, this schematic diagram shows the stable state of liquid crystal molecules. Words 7 (a), (b), and (c) are plan views of the liquid crystal shown in FIGS. 6 (a), (b), and (c) as seen from the upper substrate, respectively, but the polarizers are made orthogonal to each other. If a liquid crystal cell is sandwiched between 71 and 72, it is possible to add light and dark using a uniform state as shown in FIGS. 7 (a) and 7 (b). When the liquid crystal molecule has a twisted structure as shown in FIG. 7 (c), it is displayed in gray. The thin-film ferroelectric liquid crystal panel has such stable states, and the transition between these states occurs very rapidly in response to the applied voltage, and the applied voltage and transmitted light quantity characteristics show steep threshold characteristics. Show. Therefore, without providing a non-linear element such as a thin film transistor, it is possible to obtain a large-capacity and high-contrast display only with electrodes having a simple matrix structure.

Scan and signal side drivers are connected to this liquid crystal panel, and information is written to the panel by a voltage / timing control circuit and a line memory.

Problems to be Solved by the Invention When a ferroelectric liquid crystal panel is left in a stable state, the stability of the left state gradually increases, and other states become unstable, and writing of a display by matrix drive is performed. Our experiments have revealed that the The time when display was impossible was about 1,000 hours, although it varied depending on the configuration of the panel, that is, the liquid crystal material and the alignment film. Such changes in characteristics over time are not limited to our experiments, for example, Tanaka, Horiguchi, Kobayashi, et al .; "Electro-optical characteristics of ferroelectric liquid crystal devices that have been subjected to electrical current orientation treatment," 14th Liquid Crystal Conference There are also some reports in the Preliminary Collection, page 133.

When the above-mentioned change over time occurs, it cannot be easily restored,
Lack of reliability as a product.

Means for Solving the Problems In order to solve the above-mentioned problems, the liquid crystal light valve of the present invention sandwiches a ferroelectric liquid crystal between substrates having electrodes on opposite surfaces, and a predetermined voltage is applied via the electrodes. In a liquid crystal light valve having means for applying to a ferroelectric liquid crystal, the state of the liquid crystal when a driving device for writing an image in the liquid crystal light valve is stopped is alternately switched by the means at predetermined time intervals. As a result, only the stability of the state of the characteristics is increased, and the writing of the display is prevented from becoming impossible.

Action According to our experiments, the change in characteristics of the ferroelectric liquid crystal panel begins to occur in about 300 hours, and matrix drive becomes impossible in 1000 hours. When the stable state is switched every 300 hours, the change in characteristics is small and there is no effect on the display. In particular, in order to obtain a high-contrast display, it is preferable to switch between the states shown in FIGS. 6A and 6B in which the directions of the liquid crystal molecules in the substrate normal direction are substantially uniform. Also,
If a specific pattern is left as it is written, the pattern may be fixed due to changes over time, so it is desirable to keep the state of all pixels constant.

EXAMPLE A liquid crystal light valve according to an example of the present invention will be described below with reference to the drawings.

2 and 3 are optical characteristic diagrams of the ferroelectric liquid crystal panel. The panel used is a surface-stabilized ferroelectric liquid crystal matrix panel with a liquid crystal layer of 2.5 μm thick that uses an ester-based ferroelectric liquid crystal. SiO is vapor-deposited from a direction tilted by 82 degrees from the substrate normal and aligned. A film was formed. The voltage is applied to the panel with the pulse width fixed to 100 μs, and the brightness of the holding state after the voltage application is measured. Figure 2 shows the panel immediately after it was made, and Figure 3 shows the same panel as a dark display. It is a characteristic view after leaving for 500 hours. In FIG. 2, from bright display to dark display,
Threshold voltage for both dark and bright display is about 15 volts,
At 14 volts, it becomes a twisted state as shown in FIGS. 7 (c) and (d), and takes an intermediate luminance. At this time, when the panel was driven using the matrix drive waveform as shown in FIG. 4, a display with contrast 20 was obtained. In FIG. 4, the horizontal axis is time, (a) scanning waveform of FIG. 4, (b) of FIG. 4 shows a signal voltage waveform, (c) of FIG. 4 shows a voltage waveform applied to a pixel, FIG. 4 (d) shows the luminance of the picture element. Looking at the optical characteristic diagram of FIG. 3 when left in the dark display for 500 hours, the threshold voltage for dark display rises and the threshold voltage for bright display falls.
At this time, when driven by the driving method shown in FIG. 4, the bright display written in the selection period was twisted due to the crosstalk voltage, and the contrast was reduced to about 10. Furthermore,
The panel that was left for 1000 hours in the dark display had only dark display in the stable state, and had no contrast.

However, the same state of the ferroelectric liquid crystal panel
When switching between bright and dark within 300 hours, the threshold voltage changed only slightly when the panel was made, and after 3000 hours, the contrast in the matrix drive was about 20.

Therefore, in the liquid crystal light valve of the present invention, by changing the left state of the liquid crystal panel within a predetermined period of 300 hours or less by the configuration as shown in FIG. 1, the change of the liquid crystal panel over time is suppressed and the reliability is improved. Was successful. When the switch 9 is on, data is supplied from the outside through the line memory 7 by supplying power from the external power source or the storage battery 10 to drive circuits 5, 6
To write on the liquid crystal panel. Flag memory when the switch 9 is turned off after the use of the liquid crystal light valve is completed
After seeing the contents of 12, set the screen to either light or dark,
The power supply to the driving device that writes an image in the liquid crystal light valve such as the line memory or the driving circuit is stopped, and the driving device is stopped. The timer counts the time or the elapsed time after switching the neglected state, and when the predetermined time is exceeded, the output 13 is turned on, and when the logical product 14 with the negative logic of the switch 9 is 1, the timing The voltage control circuit 8 activates the drive circuit so that the liquid crystal panel is displayed as either bright or dark according to the data in the flag memory 12, and after the rewriting is finished, the drive circuit is stopped and the flag memory 12 is inverted. Since the response speed of ferroelectric liquid crystal changes with temperature, the panel temperature is measured and the pulse width is optimized according to the temperature. With such a configuration, even when the light valve was not used for a long time, the display was not deteriorated even under various environmental conditions of 10,000 hours or more with only the electric power of the storage battery.

If a highly reliable light valve as described above is used, a high-speed and inexpensive printing device other than the display device and a large-capacity parallel optical logical operator can be realized by stacking the light valves.

EFFECTS OF THE INVENTION The liquid crystal light valve of the present invention changes the state of the ferroelectric liquid crystal at every predetermined time when the driving device for writing an image is stopped, and thus has a highly reliable and highly reliable change over time. A dielectric liquid crystal light valve is provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIGS. 2 and 3 are optical characteristic diagrams of a ferroelectric liquid crystal panel, FIG. 4 is a matrix drive waveform diagram, and FIG. 5 is a ferroelectric characteristic of a conventional example. 6 and 7 are schematic diagrams of the stable state of the ferroelectric liquid crystal. 3 ... Signal electrode, 4 ... Scan electrode, 5 ... Scan side drive circuit, 6 ... Signal side drive circuit, 8 ... Timing voltage control circuit, 9 ... Switch, 10 ... Storage battery, 11 ...
Timer, 12 ... Flag memory, 13 ... Temperature sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Iwai 1006, Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kazuhiro Uaten, 1006, Kadoma, Kadoma, Osaka Prefecture 72) Inventor Satoshi Kimura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-62-165630 (JP, A) JP-A-57-136689 (JP, A)

Claims (8)

[Claims] 1. A liquid crystal light valve comprising a voltage applying means for sandwiching a ferroelectric liquid crystal between substrates having electrodes on opposite surfaces and applying a predetermined voltage to the ferroelectric liquid crystal through the electrodes. A liquid crystal light valve, comprising: switching means for alternately switching the state of the liquid crystal when the driving device for writing an image to the liquid crystal light valve is stopped by the voltage applying means at predetermined time intervals. 2. A storage battery and a timer or a counter are provided, and when the driving device for writing an image in the liquid crystal light valve is stopped by measuring the predetermined time by the timer or counter, the voltage is applied only when the state of the liquid crystal is switched. The liquid crystal light valve according to claim 1, wherein electric power is supplied to the means from the storage battery. 3. A liquid crystal state when a driving device for writing an image to a liquid crystal light valve is stopped is a memory state in which the directions of liquid crystal molecules are aligned substantially uniformly, and all pixels are set to the same state. The liquid crystal light valve according to claim 1, wherein 4. The liquid crystal light valve according to claim 2, wherein the electrodes on the opposite surface form pixels in a matrix. 5. The liquid crystal light valve according to claim 1, wherein the predetermined time is 1000 hours or less. 6. The liquid crystal light valve according to claim 1, wherein the predetermined time is 300 hours or less. 7. A liquid crystal light valve comprising a voltage applying means for sandwiching a ferroelectric liquid crystal between substrates having electrodes on opposite surfaces, and applying a predetermined voltage to the ferroelectric liquid crystal via the electrodes, The liquid crystal light valve includes a liquid crystal light valve having a switching unit that alternately switches the state of the liquid crystal when the drive device for writing an image to the liquid crystal light valve is stopped by the voltage applying unit. A printing device equipped with means for converting the image on the bulb into a latent image on paper or resin film. 8. A liquid crystal light valve comprising a voltage applying means for sandwiching a ferroelectric liquid crystal between substrates having electrodes on opposite surfaces, and applying a predetermined voltage to the ferroelectric liquid crystal via the electrodes, Optical logic operation provided with a liquid crystal light valve having switching means for alternately switching the state of the liquid crystal when the driving device for writing an image to the liquid crystal light valve is stopped by the voltage applying means at predetermined time intervals. Child.