JPH0442656B2 - - 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 optical response state (brightness and darkness) is controlled by the direction of electric field application, so the driving method used for TN-type liquid crystals cannot be used, and special driving methods are required. It requires a method.

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 DC to the shutter element, a two-pulse method is used in which a response (for example, an open state) and a reverse response (for example, a closed state) are written using AC pulses of voltages -V/+V and +V/-V, respectively. Use. Alternatively, it is considered to use a method of writing a response and an inverse response 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. As a result, the contrast cannot be maintained, making it impractical. 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,
Another object of the present invention is to enable continuous optical writing and improve performance as a shutter.

(Means for Solving the Problems) The present invention provides liquid crystals having different orientation states of molecules depending on the direction of application of an electric field and two different optically stable states, which are connected to one common electrode and a plurality of segment electrodes. Two rows of shutter elements are interposed between the shutter elements, and the length of the shutter elements in each row in the row direction is sufficiently longer than the distance between adjacent shutter elements, so that the photoreceptor can be moved between the shutter elements. The shutter element is moved continuously in a direction perpendicular to the arrangement direction, and when opening the shutter element, after opening the shutter element with the first DC pulse,
A second DC pulse having a symmetrical waveform and a polarity opposite to that of the first DC pulse is used to close the shutter element, and when continuous optical writing is performed on the photoconductor in the direction of its movement, the second DC pulse is applied to the shutter elements in one row. The above object is achieved by performing optical writing using the shutter elements of the other row at a location where optical writing becomes impossible due to the application of a pulse.

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

Figures 1 and 2 show a row of liquid crystal cells, in which a common electrode 11 made of a transparent electrode is formed on one of the opposing surfaces of two glasses 1 and 2 facing each other with a predetermined gap. has been done. Common electrode 1
1 has a front surface covered with a metal film, for example, a chrome 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 at least one stable alignment state is sealed in the gap between the glasses 1 and 2. The stable orientation state of this liquid crystal is 2
A polarizing plate 4 arranged on the outside of the glass sheets 1 and 2,
5, it is set to the closed state. 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 the common terminal C is constantly supplied with a common signal consisting of DC pulses of voltage O and voltage V1. On the other hand, a first data signal D1 consisting of a DC pulse of voltage V1 and a voltage O is supplied to the segment terminals S1 to Sn in order to write an open state to the shutter element, and a common signal D1 is supplied to write a closed state in the shutter element. A second data signal RD1 consisting of a DC pulse of the same voltage O and voltage V1 is supplied. 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 P that brings the shutter element into a saturated response state (open state) by voltage V1.
11 is applied to write an open state, and immediately thereafter, a voltage -V1, which is a second DC pulse 12 of opposite polarity symmetrical to this DC pulse, is applied to return the shutter element to a saturated reverse response state (closed state). . A voltage O generated by the common signal and signal RD1 is then applied to the shutter element to which the closed state is to be written. For this reason, a closed state, which is a stable orientation state, is written into the shutter element. 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.

By the way, when the one shown in the first figure is used as a liquid crystal shutter for writing on a photoreceptor that moves continuously in a direction perpendicular to the direction in which the shutter elements are arranged, for example when writing a straight line, the third
Using the electrical signals in the figure, the second half of the pulse group P1 applied to the shutter element by the signal D1 and the common signal is the second DC pulse P1 of voltage -V1.
2 is applied and becomes a closed state, that 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 windows 12a is reduced, and the segment electrodes 21 are formed opposite to the adjacent windows 12a.
Most of the shutter elements in the column and the shutter elements in the second column are located opposite each other, and the portions which cannot be written by the shutter elements in the first column are written by the shutter elements in the second column. For this reason, the exposure density can be increased by the first and second rows, so
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 three quarters of the voltage O, followed by one quarter of the DC pulse of the voltage V2, and the first data signal D2
consists of a DC pulse of voltage V2 of 1/4, followed by 3/4 of voltage O, and the second data signal RD
2 is the same as the common signal. For this reason, when writing a closed state, since the common signal and signal RD2 are the same, voltage O is applied to the shutter element, which is exactly the same as shown in Figure 3. However, when writing an open state, the common signal and signal A pulse group P2 generated by D2 is applied to the shutter element. That is, the first DC pulse P that brings the shutter element into a saturated response state (open state) by voltage V2.
21 is applied to write an open state, and thereafter this open state is maintained during the voltage O. 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. Then, a second DC pulse P22 having a voltage -V2 of opposite polarity and symmetrical to the DC pulse is applied to return the shutter element to a saturated reverse response state (closed state). In this example as well, the pulse applied to the shutter element is a complete alternating current pulse, with a negative polarity pulse having a symmetrical waveform to the positive polarity pulse.

In addition, the pulse width and pulse height V of the DC pulse are
It is appropriately determined in relation to the magnitude of spontaneous polarization of the ferroelectric liquid crystal and the thickness of the liquid crystal cell so that a saturated reverse response state and a saturated response state can be obtained.

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 appropriate.

The ferroelectric 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, 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. In particular, monostable uniform alignment is easy to manufacture and can provide high contrast, so even if the photoreceptor is moved continuously, the exposure density can be increased, and an optical printer with high printing quality can be realized.

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 the drawing]

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 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, RD1, RD2
...Second data signal, P11, P21...First
DC pulses, P12, P22... second DC pulses.

Claims (1)

[Claims] 1. Two rows of liquid crystals having different orientation states of molecules depending on the direction of electric field application and having two different optically stable states interposed 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 the shutter elements in each row are opposite to each other in the direction in which the shutter elements are arranged. The photoreceptor is continuously moved in a direction perpendicular to the shutter element, a desired signal is always supplied to the common electrode, and a first data signal is supplied to the segment electrode of the shutter element that is to be in an open state. , supplying a second data signal to the segment electrode of the shutter element to be in the closed state, and applying a first DC pulse to the shutter element based on the potential difference between the first data signal and the desired signal; After applying a second DC pulse of opposite polarity and symmetrical waveform to the first DC pulse to create an open state, the voltage difference between the second data signal and the desired signal causes The shutter element is maintained in a closed state by setting the voltage applied to the shutter element to O, and when performing continuous optical writing on the photoreceptor in the direction of movement thereof, a second DC pulse 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 application of a voltage.