JPH0442660B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for driving a liquid crystal shutter for an optical printer.

(Prior Art) Recently, ferroelectric liquid crystals with high-speed response have been developed as liquid crystal shutters for optical printers, for example.

The optical modes of ferroelectric liquid crystals include birefringent optical mode and guest-host optical mode. When driving these, unlike conventional TN-type liquid crystals, the opening/closing state is controlled by the direction of electric field application, so the driving method used for TN-type liquid crystals cannot be used and a special driving method is required. It is something to do.

Furthermore, considering the lifespan of the liquid crystal shutter, it is undesirable for a direct current component to be continuously applied to the shutter element, and a driving method that takes this point into account is required.

Therefore, as a method of not continuously applying direct current to the shutter element, a two-pulse method is used in which open and close signals are written using alternating current pulses of voltages -V/+V and +V/-V, respectively. Alternatively, it is considered to use a method of writing open and closed states using voltages +V and -V.

(Problem to be Solved by the Invention) However, when the former driving method is used for a liquid crystal shutter for an optical printer, the voltage -V/+V and the voltage +V/-V are respectively closed/open and open/closed. This is not practical because the contrast cannot be maintained. On the other hand, if the latter driving method is used, contrast can be obtained, but +V or -V may be continuously applied, which causes problems such as reduction of the transparent electrode and darkening, and deterioration of the liquid crystal. It was hot.

The purpose of the present invention is to eliminate blackening of transparent electrodes, deterioration of liquid crystal, etc. even when driven for a long time,
The purpose is to increase contrast.

(Means for Solving the Problems) The present invention is characterized by a liquid crystal that changes the orientation state of molecules depending on the direction of application of an electric field, has two different optically stable states, and has an AC stabilizing effect. is used to form a shutter element, and the previous open/close state designation data of the shutter element is compared with the current open/close state designation data, and if the two do not match, the first or second DC pulse is applied to the shutter element. The first and second DC pulses have opposite polarities and have symmetrical waveforms. achieves the above object by alternately generating pulses of positive polarity and pulses of negative polarity whose waveforms are symmetrical.

(Example) An embodiment of the present invention will be described based on the drawings.

Figures 1 and 2 show an example of a liquid crystal cell, in which a common electrode 11 made of a transparent electrode is mounted on one of the opposing surfaces of two glasses 1 and 2 facing each other with a predetermined gap. It is formed. The entire surface of the common electrode 11 is covered with a metal film, for example, a chromium film 12, and windows 12a serving as shutters are formed in the chrome film in two rows arranged in a staggered manner. On the other opposing surface, segment electrodes 21 made of transparent electrodes are formed at positions facing the windows 12a. A ferroelectric liquid crystal 3 is sealed in the gap between the glasses 1 and 2, which has two different optically stable states and whose molecular orientation changes depending on the direction of electric field application, and which has an AC stabilizing effect. has been done. 4 and 5 are polarizing plates. As a result, a large number of shutter elements are arranged in two rows in a staggered manner, sandwiched between each segment electrode and a common electrode facing each other through a window. C is a common terminal, and S1 to Sn are segment terminals.

FIG. 3 shows voltage waveforms for writing open and closed states into the shutter element, and the common terminal C is constantly supplied with voltage O. On the other hand, only when changing the opening/closing state of the shutter element, the segment terminals S1 to Sn receive the first signal of voltage V or the voltage - of the opposite polarity and symmetrical waveform.
V, and otherwise supplies a high frequency alternating current pulse F that maintains the desired open/closed state.

In other words, the output of a memory circuit (not shown) that stores the previous open/close state designation data of the shutter element is compared with the open/close state designation data that designates the current open/close state, and only when the two do not match, the current open/close state is determined. The first signal or the second signal based on the open/close state designation data.
It supplies the signal.

Therefore, the first DC pulse P1 of voltage V is applied to the shutter element to be changed from the closed state to the open state, and the shutter element is written into the open state. A second DC pulse P2 of voltage -V is applied to the shutter element to be changed from the open state to the closed state, and the shutter element is written into the open state.

After this writing is completed, a high frequency alternating current pulse F is applied to maintain the open/closed state.

Further, by applying a high frequency alternating current pulse F to a shutter element whose open/closed state does not change, its open/closed state is maintained.

In this way, only when changing the open/close state,
Since a DC pulse is applied to bring the pixel into the desired open/close state, and a high-frequency AC pulse is applied otherwise, the voltage applied to the shutter element is
As shown in the figure, the first and second DC pulses have opposite polarities and symmetrical waveforms, and the frequency AC pulses alternate between positive polarity pulses and negative polarity pulses whose waveforms are symmetrical. A biased DC pulse is not applied.

Furthermore, since a high-frequency AC pulse is applied during non-writing, high contrast can be obtained due to the AC smoothing effect in a ferroelectric liquid crystal with dielectric anisotropy of Δε<O.

The frequency of the high-frequency AC pulse is preferably such that the pulse width is less than or equal to 1/4 of the DC pulse and is a fraction of an integer. Set to remain stable.

Further, the pulse width and pulse height of the DC pulse are appropriately set in relation to the magnitude of spontaneous polarization of the ferroelectric liquid crystal and the thickness of the liquid crystal cell so as to obtain an open state or a closed state.

Also, in the above explanation, the positive voltage causes the open state, and the negative voltage causes the closed state.
Conversely, a voltage on the + side may cause the cap to be in the closed state, and a voltage on the minus side may cause the cap to be in the open state.

By the way, the signals supplied to each electrode are not limited to those described above, and various changes can be made, and a bias voltage may be applied as necessary.

The liquid crystal in the present invention is not limited to bistable uniform alignment, but can also be applied to bistable twisted alignment or monostable uniform alignment.

However, in the case of monostable uniform orientation, the stable orientation state is set to be a closed state.

(Effects of the Invention) According to the present invention, only when changing the open/close state, the first or second DC pulses with opposite polarities and symmetrical waveforms are applied to bring the pixel into the desired open/close state; Sometimes, high-frequency alternating current pulses are applied that alternate between positive pulses and negative pulses whose waveforms are symmetrical.
The transparent electrode will not darken or the liquid crystal will deteriorate even after long-term operation. Moreover, since it can achieve high contrast, it can be realized as a high-performance liquid crystal shutter.

Furthermore, since the desired open/closed state is maintained by the AC stabilization effect, it can be applied to liquid crystals with various orientation states, including not only bistable uniform orientation, but also bistable twisted orientation, monostable uniform orientation, and non-memory orientation such as helical state. It is easy to manufacture, and the contrast can be improved.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view showing an example of a liquid crystal cell, FIG. 2 is a sectional view taken along the line shown in FIG. 1, and FIG. 3 is an explanatory diagram showing voltage waveforms for realizing the present invention.
FIG. 4 is a time chart showing an example of a voltage waveform applied to one shutter element. 3...Liquid crystal, 11...Common electrode, 12a...
Window, 21...Segment electrode, P1...First DC pulse, P2...Second DC pulse, F...High frequency AC pulse.

Claims (1)

[Claims] 1. A liquid crystal that has different orientation states of molecules depending on the direction of electric field application, has two different optically stable states, and has an AC stabilizing effect.
In a method of driving a liquid crystal shutter for an optical printer in which a plurality of shutter elements are formed by interposing one common electrode and a plurality of segment electrodes, a desired signal is always supplied to the common electrode and the signal is stored in a storage means. The comparison means compares the previous opening/closing state designation data of each shutter element with the current opening/closing state designation data of each shutter element, and the segment electrode of the shutter element with which the two do not match receives the first signal or the current opening/closing state designation data. By selectively supplying either the second signal, either the first DC pulse or the second DC pulse is applied to the shutter element to bring it into a designated open/close state; After applying the second DC pulse,
A state-holding signal is supplied to the segment electrode, and a high-frequency AC pulse is applied to the shutter element to maintain the open/closed state based on the potential difference between the state-holding signal and the desired signal, and the first DC pulse and the second DC pulse is
Drive of a liquid crystal shutter for an optical printer, characterized in that the high-frequency alternating current pulses have opposite polarities and symmetrical waveforms, and the high-frequency alternating current pulses alternately generate positive-polarity pulses and negative-polarity pulses whose waveforms are symmetrical. Method. 2. The method of driving a liquid crystal shutter for an optical printer according to claim 1, wherein the liquid crystal exhibits negative dielectric anisotropy in the frequency range of the high-frequency AC pulse.