JPH0442661B2 - - 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.

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 an open state and a closed state 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, the contrast can be maintained, but +V or -V may be continuously applied, which may reduce the transparent electrode for driving and darken it, or cause deterioration of the liquid crystal. There was a problem with causing it.

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 objective is to increase the contrast and improve the performance of the shutter.

(Means for Solving the Problems) The present invention forms two rows of shutter elements using a liquid crystal having an AC stabilizing effect, and each row of shutter elements has a length in the column direction that is longer than that of the adjacent shutter element. The first DC pulse is applied to the shutter elements that are sufficiently longer than the spacing between the elements and that are to be brought into an open state by continuously moving the photoreceptor in a direction perpendicular to the direction in which the shutter elements are lined up. After applying a second DC pulse with a symmetrical waveform and a polarity opposite to the first DC pulse to create an open state, the closed state is maintained by an AC pulse at a frequency that exhibits an AC stabilizing effect. When continuous optical writing is performed on the photoconductor in the direction of movement, a second direct current pulse is applied to the shutter elements of one row, and at a location where optical writing is disabled, the shutter elements of the other row are The above object is achieved by performing optical writing using shutter elements arranged in rows.

(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 having an AC stabilizing effect is sealed in the gap between the glasses 1 and 2. One optical response state (saturated reverse response state) of this liquid crystal is set to a closed state by polarizing plates 4 and 5 disposed on the outside of the two glasses 1 and 2. As a result, a large number of shutter elements 13 to 13 are arranged in two rows in a staggered manner, sandwiched between each segment electrode and a common electrode facing each other via a window. The length of each of the shutter elements 13 to 13 in the column direction is set to be sufficiently longer than the interval between adjacent shutter elements. In other words, the distance between adjacent shutter elements is made as small as possible. 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 a common signal consisting of a voltage O is constantly supplied to the common terminal C. In contrast, segment terminals S1 to Sn
In order to once open the shutter element, a first data signal D1 consisting of voltage V1 and voltage -V1 is supplied, and in order to maintain the shutter element in a closed state, a high frequency alternating current signal, which is a second data signal, is supplied. Supply F.

For this purpose, a pulse group P1 generated by the common signal and the signal D1 is applied to the shutter element to which the open state is to be written. That is, the first DC pulse P11 that brings the shutter element of voltage V1 into a saturated response state (open state) is applied, an open state is written, and the shutter is opened. Immediately thereafter, a voltage -V1, which is a second DC pulse of opposite polarity and symmetrical to this DC pulse, is applied to return the shutter element to a saturated reverse response state (closed state).

A high-frequency AC pulse P generated by a common signal and a signal F is applied to the shutter element which is to be kept in a closed state.
2 is applied. Therefore, the response state does not change and the closed state is maintained.

The pulses thus applied to the shutter element are complete alternating current pulses, with negative polarity pulses having a symmetrical waveform to the positive polarity pulses.

In addition, in a ferroelectric liquid crystal with dielectric anisotropy Δε<O,
Since the closed state is stably maintained by the high-frequency AC pulse due to the AC stabilizing effect, high contrast can be obtained.

The frequency of the high-frequency AC pulse is preferably such that the pulse width is 1/4 or less of the DC pulse width and is a fraction of an integer, and the pulse height H is related to the dielectric anisotropy of the ferroelectric liquid crystal, so that the closed state is stable. It is set appropriately so that it can be maintained.

In addition, the pulse width and pulse height of the DC pulse are adjusted to obtain a saturated response state (open state) or a saturated reverse response state (closed state) depending on the magnitude of the spontaneous polarization of the ferroelectric liquid crystal and the thickness of the liquid crystal cell. Set as appropriate.

By the way, when the one shown in the first figure is used as a liquid crystal shutter for writing on a photoreceptor that continuously moves in a direction perpendicular to the direction in which the shutter elements are arranged in an optical printer, for example, when writing a straight line, When using the electrical signals shown in Fig. 3, voltage -V1 is applied by the second DC pulse in the latter half of the pulse group P1 applied to the shutter element by the signal D1 and the common signal, so that the shutter element becomes in the closed state. A portion remains as a non-writable portion, resulting in a low exposure density.

Therefore, in order to improve the printing quality, the interval between the adjacent window parts 12a, 12a is reduced, and the segment electrode 21 is formed opposite to this, so that the shutter elements in the first row and the shutter elements in the second row are Most of the shutter elements are located opposite to each other, and the portions that cannot be written to by the shutter elements in the first row are written by the shutter elements in the second row. For this purpose, the first and second columns
Since the exposure density can be increased depending on the row, clear straight lines can be written.

Note that in the above example, the shutter elements in the first row and the shutter elements in the second row are arranged to be shifted by a half pitch, but the arrangement is not limited to this.
It is also possible to arrange the entire parts facing each other.

FIG. 4 shows another example of the voltage waveform, in which the pulse width of the DC pulse is half that of the example shown in FIG. 3, and the voltage is doubled. That is, the common signal consists of a voltage O, and the first signal for writing an open state.
The data signal D2 consists of a quarter of the DC pulse of the voltage V2, followed by a half of the high frequency AC pulse, and then a quarter of the DC pulse of the voltage -V2. The second data signal F that maintains the closed state is the third
Same as the figure.

For this reason, when maintaining the closed state, a high frequency AC pulse P2 is applied, which is exactly the same as shown in the third diagram, but when writing the open state, a pulse group P3 generated by the common signal and signal D2 is applied to the shutter element. be done. That is, the voltage V2,
First DC pulse P that opens the shutter element
31 is applied to write an open state, after which this open state is maintained during the high frequency AC pulse by the AC stabilizing effect. Therefore, the exposure density can be increased to 1.5 times that of the example shown in FIG. 3, and the printing quality can be improved.
Next, a voltage -V2, which is a second DC pulse having a symmetrical waveform and opposite polarity to the first DC pulse, is applied to return the shutter element to the closed state. In this example as well, the pulse applied to the shutter element is a complete alternating current pulse because there is a pulse of negative polarity with a symmetrical waveform to the pulse of positive polarity.

In the above explanation, the response depends on the voltage on the + side.
Although it has been referred to as a reverse response due to a voltage on the − side, since the response and reverse response are two sides of the same coin, it may also be referred to as a reverse response due to a voltage on the + side and a response due to a voltage on the − side.

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 ferroelectric liquid crystal in the present invention is not limited to bistable uniform alignment, but can also be applied to bistable switch 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, since the pulse applied to the shutter element has a negative polarity pulse with a symmetrical waveform to the positive polarity pulse, the transparent electrode does not darken even when driven for a long time. , the liquid crystal will not deteriorate. Furthermore, since the closed state is maintained by the alternating current slabilizing effect, it can be applied to shutter elements in various orientation states, including not only bistable uniform orientation, but also bistable Swiss orientation, monostable uniform orientation, and non-memory orientation such as helical state. In particular, monostable uniform orientation is easy to manufacture and can provide high contrast. Furthermore, with a two-row shutter element configuration, the unexposed areas in the first row are exposed in the second row, so even if the photoreceptor is moved continuously, the exposure density can be increased, making it possible to realize an optical printer with high printing quality. .

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view showing a row of liquid crystal cells, 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 an explanatory diagram showing other voltage waveforms for realizing the present invention. 3... Ferroelectric liquid crystal, 11... Common electrode, 21
...Segment electrode, 13...Shutter element, D
1, D2...First data signal, F...Second data signal, P11, P31...First DC pulse, P12, P32...Second DC pulse, P2
...AC pulse.

Claims (1)

[Claims] 1. Two rows of shutter elements are formed by interposing a liquid crystal that changes the orientation of molecules depending on the direction of electric field application and has an AC stabilizing effect between one common electrode and a plurality of segment electrodes. The shutter elements in each row have a length in the row direction that is sufficiently longer than the interval between adjacent shutter elements, and are arranged opposite to the shutter elements in each row and perpendicular to the direction in which the shutter elements are arranged. A desired signal is constantly supplied to the common electrode, and a first data signal is supplied to the segment electrode of the shutter element that should be in the open state, so that the shutter element is in the closed state. A second data signal is supplied to the segment electrode of the shutter element to be shuttered, and a first DC pulse is applied to the shutter element according to the potential difference between the first data signal and the desired signal to bring the shutter element into an open state. After that, a second DC pulse with a symmetrical waveform and a polarity opposite to that of the first DC pulse is applied to create a closed state, and the AC stabilizing effect is produced by the potential difference between the second data signal and the desired signal. The shutter element is maintained in a closed state by applying an alternating current pulse at a frequency corresponding to the shutter element, and when performing continuous optical writing on the photoreceptor in the direction of movement, a second direct current is applied to the shutter element in one row. 1. A method for driving a liquid crystal shutter for an optical printer, characterized in that a shutter element in the other row performs optical writing at a location where optical writing becomes impossible due to the application of a pulse.