JPH0915553A - Method and circuit for driving liquid crystal shutter - Google Patents

Abstract

PURPOSE: To enable a liquid crystal shutter to drive with low voltage by impressing a square- wave signal having different phases between selective and nonselective electrodes on a scanning electrode and impressing a specific square-wave signal on a signal electrode corresponding to translucent and shielding states of a liquid crystal pixel. CONSTITUTION: A square-wave generating circuit for scanning 13 generates plural square-waves having different phases and a scanning signal switching circuit 15 selects a signal which is outputted to the scanning electrode of a liquid crystal panel 5 from the square-waves corresponding to picture data 29. A square-wave generating circuit for data 19 generates square-waves for making liquid crystals in a translucent state or a shielding state and a data signal selecting circuit 21 selects a signal which is outputted to the signal electrode of the liquid crystal panel 5 from the square-waves corresponding to picture data 29. In order to make the liquid crystal pixel in the translucent state, the liquid crystal pixel is driven by impressing the square-wave signal the phase of which is adjusted so that a period in which both ends of the liquid crystal pixel are at zero-potential is longer than a response period of the liquid crystal on the signal electrode. In order to make the liquid crystal pixel in the shielding state, liquid crystal pixel is driven by impressing the square-wave signal the phase of which is adjusted so that a period in which both ends of the liquid crystal pixel are at zero-potential is shorter than the response period of the liquid crystal on the signal electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer for optically writing an image on a photosensitive member by using a liquid crystal shutter, and more particularly to a driving method and a driving circuit of a matrix type liquid crystal shutter for forming a color image.

[0002]

2. Description of the Related Art Conventionally, a technique has been developed in which color image data is optically written on a photosensitive member by a liquid crystal shutter having a plurality of pixel rows and the image is recorded on paper by an electrophotographic process. FIG. 5 is a schematic diagram of a color optical printer using such a technique. The light emitted from the exposure light source 1 is modulated by the first optical system 3, the color filter 4, the liquid crystal shutter 5, and the second optical system 7 in accordance with the image data, and the photosensitive member 9 is irradiated with the colored light. Exposure is performed by time-divided irradiation. Here, the color filter 4 includes a red filter 41, a green filter 42, and a blue filter 4.
3 is comprised. The liquid crystal shutter 5 is composed of a plurality of red pixels 51 for optically writing red image information, and a green pixel 52 and a blue pixel 53 for optically writing green and blue image information, respectively.

When a liquid crystal panel having a plurality of pixel rows is adopted as the liquid crystal shutter 5, the electrode configuration is as follows.
A method having a common electrode for each pixel column and an electrode for applying a signal extracted from all pixels, and a method using a crossing portion of a plurality of scanning electrodes and a plurality of signal electrodes as a shutter can be considered. The former can easily obtain a high contrast ratio, but has problems such as a decrease in aperture ratio and a large number of driving ICs due to the large number of extraction electrodes. On the other hand, in the latter, since the liquid crystal shutter is composed of a plurality of scanning electrodes and a plurality of signal electrodes, the number of extraction electrodes is small, and there are many advantages such as an increase in aperture ratio, a reduction in manufacturing cost, and a reduction in the number of driving ICs. have. By the way, in the following description, the liquid crystal panel having the latter electrode configuration will be referred to as a matrix liquid crystal panel, and the liquid crystal shutter having the liquid crystal panel as a constituent element will be referred to as a matrix liquid crystal shutter.

The structure of a matrix type liquid crystal panel and its driving method are disclosed in Japanese Patent Laid-Open No. 7-43669, which will be described with reference to FIGS. 6 and 7. Scan electrode T1 of FIG.
~ T3 and signal electrodes S1 to S7 are formed on the opposite surfaces of two glass plates, and a liquid crystal is sandwiched between the two glass substrates. Further, the two glass substrates are sandwiched by two polarizing plates (not shown). For example, as in the case of crossed nicols super twisted nematic liquid crystal, transmission and application of voltage between both electrodes of liquid crystal are applied. The shielded state is obtained in the opened state.

In order to optically write color image information on the photosensitive member with the liquid crystal shutter having this structure, for example, as shown in FIG. 5, red light is emitted from the pixel on the scanning electrode T1, and red light is emitted from the scanning electrodes T2 and T3. An exposure optical system is configured so that green light and blue light are respectively emitted, and the photosensitive member is exposed by the modulated red, green, and blue lights while selecting the scanning electrodes in a time division manner. Further, each scan electrode needs to be sufficiently shielded so as not to transmit light while the other scan electrodes are selected. Appropriate signals must be applied to the signal electrodes so as to obtain an exposure state according to the image data of the pixels on the selected scanning electrodes.

Based on the method disclosed in the above publication,
Considering the case of optically writing to the liquid crystal pixel on the scanning electrode T2 in FIG. 6, the liquid crystal pixel is driven by the drive signal as shown in FIG. That is, as shown in FIG.
As shown in (a), a square wave having an amplitude of 24 V is applied to the scanning electrode T.
To T1 and T3, a square wave having an amplitude of 72 V shown in FIG. 7B is applied so that the signal applied to the signal electrode can be sufficiently canceled. Signal electrodes S1 to S7 are supplied with signals of amplitude 24V, which have the same phase as in FIG. 7A during the transmission period and the opposite phase during the shielding period, as shown in FIG.
It is created from the image data on 2 and applied. For example, when the signal of FIG. 7C is applied to the signal electrode S3, the potential difference shown in FIG. 7D is generated at both ends of the pixel 33, and the potential difference shown in FIG. 7E is generated at both ends of the pixels 31 and 35. become. That is, the potential difference between both ends of the pixel on the scanning electrode T2 is 0 in the transmissive state and ± 24 V in the shielding state, and the potential difference between both ends of the pixels on the scanning electrodes T1 and T3 is ± 24 depending on the image data of the pixel on T2.
It becomes V to ± 48V, and the shielded state is always maintained.

[0007]

The liquid crystal shutter having the above matrix structure can obtain a sufficient contrast ratio with a small number of extraction electrodes. However, when it is intended to be incorporated in a small device, a high voltage signal is used for driving, so there are problems such as heat generation, power consumption, and power source size. That is, in the example of FIG. 7, the scan electrode T not selected is compared with the amplitude of the signal of the scan electrode T2 selected.
The amplitude of the signals of T1 and T3 requires a high voltage three times higher.

The present invention provides a driving method of a matrix type liquid crystal shutter which does not have the above-mentioned problems caused when it is incorporated in a small device, that is, a driving method which can be driven with a low voltage and can obtain a sufficient contrast ratio. The purpose is to do.

[0009]

In order to achieve the above object, a driving method of a liquid crystal shutter according to the present invention is to apply a square wave for selection to a scan electrode selected from a plurality of scan electrodes for image formation. Then, a non-selection square wave having a phase different from that of the selection square wave is applied to the non-selection scan electrode. Further, when the liquid crystal pixel on the selected scanning electrode is set in the transmission state to the signal electrode, the time at which the both ends become zero potential is longer than the response time of the liquid crystal, and the liquid crystal on the unselected scanning electrode is set. A liquid crystal pixel on the selected scan electrode is shielded by applying a signal whose phase is adjusted with respect to the signal applied to the scan electrode so that the time at which both ends of the pixel become zero potential is shorter than the response time of the liquid crystal. When the liquid crystal pixel and the liquid crystal pixel on the non-selected scanning electrode are brought into the state, the time when the both ends of the liquid crystal pixel become zero potential is shorter than the response time of the liquid crystal, with respect to the signal applied to the scanning electrode. It is characterized in that a signal whose phase is adjusted is applied and driven.

Further, the liquid crystal shutter drive circuit of the present invention has a scanning signal generating circuit and a data signal generating circuit, and applies a scanning signal and a data signal to the scanning electrodes and the signal electrodes of the liquid crystal panel, respectively, to form liquid crystal pixels. In a drive circuit of a liquid crystal shutter for controlling light passing through the scanning signal generation circuit, the scanning signal generation circuit generates a selection square wave and a non-selection square wave having a phase different from that of the selection square wave. The circuit and a scanning signal switching circuit for sequentially switching the selection square wave and applying it to each scanning electrode, the data signal generating circuit is configured such that the time during which the potential is the same as that of the selection square wave is the response of the liquid crystal. It is longer than the time and the same potential as the non-selection square wave is shorter than the response time of the liquid crystal, and the transmission signal and each square wave of the scanning square wave generation circuit are the same potential as the response time of the liquid crystal. Shorter A data square wave generating circuit for generating a shielding signal, and having a data signal selection circuit for applying select a shielding signals and transmitting signals to the signal electrodes in accordance with image data.

[0011]

By applying the above signals to the scan electrodes and signal electrodes of the liquid crystal shutter, the liquid crystal pixels on the selected scan electrodes have the same potential as the scan electrode signal and the signal electrode signal. When the time is longer than the response time of the liquid crystal, the transmission state is set, and when the time is shorter than the response time of the liquid crystal, the shield state is set. Further, the voltage of the signal electrode of the liquid crystal pixel on the unselected scanning electrode is always in the shielded state regardless of the signal applied to the signal electrode, because the time when the potential is zero is always shorter than the response time of the liquid crystal.

[0012]

【Example】

(Embodiment 1) Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a first example of a waveform for driving the liquid crystal shutter shown in FIG. In this embodiment, the liquid crystal pixel on the scanning electrode T2 in FIG.
The liquid crystal elements on the scanning electrodes T1 and T3 show signal waveforms applied to the respective electrodes when they are shielded. FIG. 1A shows a continuous square wave serving as a reference applied to the scan electrode selected for image formation, which is applied to the scan electrode T2. In the same figure, (b) is a continuous square wave whose phase is different from the reference square wave by 90 degrees and is applied to the scan electrodes T1 and T3 not selected for image formation. As shown in FIG. 1C, the signal electrode has the same phase as that shown in FIG. 1A in the transmission state and the phase opposite to that shown in FIG. Apply a signal.

When such a signal is applied, the pixel 3
The voltage across 3 is as shown in (d). The period of zero potential is in the transmission state, and the period in which the square wave voltage is applied is in the shielding state. Pixels 31, 35 on non-selected scan electrodes
A voltage as shown in (c) is applied to. That is,
Regardless of the state of the signal waveform in (c), a voltage is always applied to both ends of the pixel, and the pixel is in the shielded state. By the way, in the case of optically writing data with gradation, it can be achieved by changing the time of the transmission period of (c) according to the gradation.

(Second Embodiment) FIG. 2 is a waveform diagram of a second embodiment of the waveform for driving the liquid crystal shutter shown in FIG. Comparing the present embodiment with the first embodiment, the phase shift amount is different. FIG. 2A shows a continuous square wave serving as a reference applied to the scan electrode T2 selected for image formation, and FIG. 2B shows a continuous square wave having a phase difference of 120 degrees from that of the reference square wave. Is applied to the scan electrodes T1 and T3 not selected for image formation. As shown in FIG. 2C, the signal electrode has the same phase as in FIG. 2A in the transmitting state and the phase of 240 ° in the shielding state as shown in FIG. 2A, depending on the data of the pixel on the selected scanning electrode. Apply different signals.

Similar to the first embodiment, the pixels 31 to 3 are
Focusing on FIG. 5, the signal applied to the signal electrode S3 is
In the signal shown in (c), the time of the transmission period is a signal determined according to the gradation information of the pixel 33. As a result, the voltage shown in FIG.
The voltage shown in (e) of FIG.

(Embodiment 3) This embodiment is an embodiment of a drive circuit for generating drive signals as shown in Embodiments 1 and 2. It can be realized by the circuit shown in FIG. The scanning signal generation circuit 11 selects a scanning square wave generation circuit 13 that generates a plurality of square waves having different phases and a signal that is output to the scan electrode from the plurality of input square waves according to the image data 29. The scanning signal switching circuit 15 is provided, and the scanning signal generating circuit 11 outputs the scanning electrodes T1 to T1 of the liquid crystal panel 5.
Applied to T3. The data signal generating circuit 17 includes a data square wave generating circuit 19 for generating a square wave for bringing the liquid crystal into a transparent state and a square wave for bringing the liquid crystal into a shielding state, and image data 29 from a plurality of input square waves. The data signal selection circuit 21 selects a signal to be output to the signal electrode according to the data signal generation circuit 15.
Is applied to the signal electrode of.

In order for the liquid crystal pixel to have the highest transmittance, the potential difference between the electrodes at both ends must be zero. To achieve this, the phase of the square wave applied to the selected scan electrode and the signal It is necessary that the transmission signals applied from the electrodes have the same phase. Therefore, in the scanning square wave generating circuit 13 and the data square wave generating circuit 19 of FIG. 3 which can be configured by the circuit whose block diagram is shown in FIG. 4, the phases of the clock generating circuits 25 need to be the same. is there. Also, instead of each clock generation circuit, a common clock can be input from the outside.

Although three scan electrodes are described in the above embodiment for simplicity, it is obvious that any number of scan electrodes and signal electrodes can be driven by the method of the present invention. Further, in the present embodiment, the phase of the continuous square wave applied to the unselected scan electrodes is set to 90 degrees and 120 degrees for convenience of the signal applied to the selected scan electrodes, but it may be other than that. There is no problem if they are not in the same phase, and the phase of the signal applied to the signal electrode at the time of blocking is different from the two signals applied to the scanning electrode and is intermittent even if it is other than 180 degrees and 240 degrees shown in the embodiment. There is no problem if the zero potential period of the drive waveform is shorter than the response time of the liquid crystal.
In the present embodiment, when the scanning signal and the data signal are driven at amplitudes of 20 Vpp or more, respectively, the clock generation circuit 25
When the transmission frequency is 1.6 kHz, a good contrast ratio was obtained in Example 2, but in Example 1, the zero potential period in the non-selection period and the shielding period was long, so the shielding state became insufficient. , The black image became whitish. Further, at 2.5 kHz or higher, good contrast ratios could be obtained in both Examples 1 and 2.

[0019]

As described in the above embodiments, in driving a matrix type liquid crystal shutter composed of a scanning electrode and a signal electrode, a selection is made by using a simple circuit configuration without using a high voltage. An image can be formed on the photosensitive member by the pixels on the scanning electrodes, and all the pixels on the scanning electrodes that are not selected can be shielded. Therefore, the power supply circuit for generating the drive waveform can be downsized, and the device can be downsized while maintaining the same image quality as the conventional one.
It is possible to achieve low power consumption and reduction of heat generation.

[Brief description of the drawings]

FIG. 1 is a signal waveform diagram of a first embodiment showing a driving method of the present invention.

FIG. 2 is a signal waveform diagram of a second embodiment showing the driving method of the present invention.

FIG. 3 is a block diagram of an embodiment of a drive circuit of the present invention.

FIG. 4 is a block diagram of a square wave generation circuit in the drive circuit of the present invention.

FIG. 5 is a schematic block diagram of a conventional printer that performs optical writing on a photosensitive member.

FIG. 6 is a schematic view of a liquid crystal panel that constitutes a conventional matrix liquid crystal shutter.

FIG. 7 is a drive waveform diagram of a conventional matrix liquid crystal shutter.

[Explanation of symbols]

 1 Light Source 3 First Optical System 7 Second Optical System 4 Color Filter 5 Liquid Crystal Shutter 9 Photosensitive Member 11 Scanning Signal Generation Circuit 13 Scanning Square Wave Generation Circuit 15 Scanning Signal Switching Circuit 17 Data Signal Generation Circuit 19 Data Square Wave Generating circuit 21 Data signal selecting circuit 23 Phase delay circuit 25 Clock generating circuit 26, 27 Output signal 29 Image data 31-35 Liquid crystal pixel 41-43 Color filter T1-T3 Scan electrode S1-S7 Signal electrode

Claims (4)

[Claims] 1. A liquid crystal pixel having a plurality of scanning electrodes and a plurality of signal electrodes, a drive signal being applied from the electrodes to drive liquid crystal pixels,
In a method of driving a liquid crystal shutter for optically writing image data on a photosensitive member, a square wave signal having a different phase between a selected scan electrode and an unselected scan electrode is applied to the scan electrode, When a liquid crystal pixel on the selected scan electrode is set in a transmissive state, the time when both ends of the liquid crystal pixel are zero potential is longer than the response time of the liquid crystal, and the liquid crystal pixel on the unselected scan electrode is A square wave signal whose phase is adjusted with respect to the signal applied to the scan electrodes is applied so that the time at which both ends of the liquid crystal pixel become zero potential becomes shorter than the response time of the liquid crystal, and the square wave signal is applied on the selected scan electrodes. When the liquid crystal pixel of is placed in the shielded state, the liquid crystal pixel and the liquid crystal pixel on the non-selected scanning electrode are set to the scanning electrodes so that the time at which both ends become zero potential is shorter than the response time of the liquid crystal. Method of driving a liquid crystal shutter, characterized in that driven by applying a square wave signal to adjust the phase for the signal to be pressurized. 2. When a square wave signal having a 90 ° phase difference with respect to the selected scan electrode is applied to the non-selected scan electrode to bring the liquid crystal pixel into a transmissive state, the scan electrode of the selected scan electrode is selected. When a square wave signal having the same phase as the signal is applied to the signal electrode to bring the liquid crystal pixel into a shielded state, a square wave signal having a 180 ° phase difference from the signal of the selected scan electrode is applied to the signal electrode. The method for driving a liquid crystal shutter according to claim 1. 3. A drive of a liquid crystal shutter which has a scan signal generating circuit and a data signal generating circuit, and applies a scan signal and a data signal to the scan electrode and the signal electrode of the liquid crystal panel to control the light passing through the liquid crystal pixels. In the circuit, the scanning signal generation circuit sequentially outputs one selection square wave, a scanning square wave generation circuit which generates a non-selection square wave having a phase different from that of the square wave, and a selection square wave. The data signal generating circuit has a scanning signal switching circuit for switching and applying to each scanning electrode, and the data signal generating circuit has a time in which the potential becomes the same as the selection square wave longer than the response time of the liquid crystal and a non-selection square wave. For data that generates a transmission signal whose potential is the same as that of the liquid crystal whose response time is shorter than the response time of the liquid crystal and a shielding signal whose potential of which is the same as each square wave of the scanning square wave generation circuit is shorter than the response time of the liquid crystal Square wave generation times A drive circuit for a liquid crystal shutter, comprising: a path; and a data signal selection circuit that selects a transmission signal and a shielding signal according to image data and applies the selected signal to each signal electrode. 4. A scanning square wave generating circuit and a data square wave generating circuit have a clock circuit and one or a plurality of phase delay circuits, and output a plurality of square waves having different phases. The drive circuit for the liquid crystal shutter according to claim 3.