JPH0564773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a liquid crystal element, and more particularly to a method for driving a liquid crystal element used as a light modulation element in an electrophotographic printer head or the like.

[Conventional technology]

Liquid crystal elements have been actively researched and developed as direct-view display elements, and are now widely used. On the other hand, light modulation elements using liquid crystals are also used. For example, a printer is known in which the intensity of light irradiated onto a photoreceptor is modulated using a light modulation element, and the resulting latent image on the photoreceptor is developed onto plain paper using toner. The part of the printer that includes the light source, light modulation element, and imaging optical system is called the printer head. Liquid crystal light modulators used in printer heads function as liquid crystal light shutters. In addition to this, liquid crystal light modulation elements are widely applied to optical theory elements, etc., but all of them use the function of spatially modulating the intensity of incident light. This will be explained using an example.

In recent years, high speed, high resolution,
Demand for low cost, low noise, compactness, etc. is increasing, and in response to these demands, non-impact printers such as laser beam printers are becoming widely used. Under such circumstances, liquid crystal printers using liquid crystal shutter arrays are expected to be in great demand, especially because of their low cost, and are being actively developed.

Conventionally, the response speed of liquid crystals was a few milliseconds at most, which meant that only a few sheets of A4 paper could be printed per minute, which was far from practical. In recent years, ferroelectric liquid crystals have been developed as liquid crystals with fast response speeds, and efforts are being made to increase the speed.

Here, the operation of the ferroelectric liquid crystal will be explained.
The fast response behavior of ferroelectric liquid crystals was confirmed by Noel A.Clark and Sven T.Lagerwall (Appl.Phys.rett. 36 (1980) 899).In other words, a chiral smectic liquid crystal exhibiting ferroelectricity consists of liquid crystal molecules 12 with spontaneous polarization 121, as shown in FIG.
2 has a layered structure and at the same time forms a helical structure. As it is, the spontaneous polarization 121 is the helical axis 12
3 is uniformly distributed around the helical axis and cancels each other out. However, when such a liquid crystal is
When sandwiched between two substrates and the gap between them, that is, the thickness of the liquid crystal, is made thinner to at least the pitch length of the spiral structure, the liquid crystal molecules can be in one of two orientation states where the spontaneous polarization 121 is perpendicular to the substrates. forced to be oriented.

FIG. 6 is a diagram showing this state, and region A is a state in which the spontaneous polarization 121 faces the lower substrate 131,
Region B is in a state where the spontaneous polarization 121 faces the upper substrate 132. FIG. 7 is a diagram of the state shown in FIG. 6 viewed from the top surface of the substrate 132, and the liquid crystal molecules in region A and region B have different alignment states as shown by liquid crystal molecules 141 and 142. moreover,
This state is sandwiched between two polarizing plates whose polarization directions are orthogonal to each other, and the polarization direction 1 of one polarizing plate is
When observed while aligning 43 with the direction of liquid crystal molecules 142, region A appears dark and region B appears bright.

In this way, when a chiral smectic liquid crystal exhibiting ferroelectricity is sandwiched between two substrates with a narrow gap, the liquid crystal molecules will assume one of two optically distinguishable orientation states. Moreover, the spontaneous polarization of the ferroelectric liquid crystal aligns in direct response to an external electric field. Therefore, when a direct current electric field in a direction perpendicular to the substrate is applied from the outside and its direction is reversed, the direction of spontaneous polarization is accordingly reversed. That is,
Region A and region B in FIG. 7 are electrically switched, and this can be easily realized by forming transparent electrodes or the like on the inner surfaces of the two substrates. Furthermore, since this electrical switching phenomenon is due to a direct response between spontaneous polarization and an external electric field, it is extremely fast, and according to the above-mentioned paper, a response speed on the order of microseconds has been confirmed.

Furthermore, ferroelectric liquid crystals have the property that even after the voltage is removed, the orientation state at the time of voltage application is maintained. This is commonly called bistability. The above-mentioned ferroelectric liquid crystal is used in the printer head of a light modulating element to increase the speed of the printer.

[Problem that the invention seeks to solve]

However, in order to obtain a liquid crystal device with the above-mentioned bistability and high speed, the gap between the two substrates must be thinned to about 1μ and uniform, which is extremely difficult in terms of device manufacturing technology. Have difficulty.
Therefore, the yield is poor, the manufacturing cost is high, and the product becomes expensive.

Furthermore, if ferroelectric liquid crystals are used, even if the spacing between the substrates is wide and bistability has not been achieved, its high-speed response makes it possible to operate at higher speeds than before, but there is a clear threshold. Because you haven't
It is difficult to perform time-division driving, requires driving similar to static driving, increases the number of circuits and connection terminals, and is also expensive.

The object of the present invention is to eliminate the above-mentioned drawbacks, to provide a liquid crystal element that can be used as a liquid crystal light variable element, which can be time-divisionally driven with a simple circuit configuration even in liquid crystal elements where the substrate spacing is wide and bistability has not been achieved. The object of the present invention is to provide a driving method.

[Means for solving problems]

The method for driving a liquid crystal element of the present invention includes filling a gap between two opposing electrode substrates, each of which has been subjected to an alignment process to form a fine groove structure parallel to the same direction on the inner surface, with a ferroconducting liquid crystal; In this method of driving a liquid crystal element having a structure in which the ferroelectric liquid crystal does not exhibit bistability, a first voltage is applied to a plurality of scan electrodes formed on one of the two electrode substrates during scanning, and then the first voltage is applied to the plurality of scan electrodes formed on one of the two electrode substrates.
time-division in which a rectangular waveform voltage having the same magnitude and opposite polarity as the voltage is applied, and a second voltage which is larger than the first voltage and has the same polarity as the first voltage is applied during non-scanning; a scanning means and a plurality of selection electrodes formed on the other of the two electrode substrates so as to face the scanning electrodes; and a third voltage intermediate between the first and second voltages at the time of selection; A voltage with a rectangular waveform that is a fourth voltage between the first and second voltages is applied, and when not selected, a voltage with the same magnitude and opposite polarity as the first voltage is applied next to the first voltage. time-division driving means for applying a rectangular voltage of a rectangular shape, and the direction of the liquid crystal molecules due to the voltage applied between the scanning electrode and the selection electrode when not selected is the same as that due to the alignment treatment. Features.

[Effect]

The liquid crystal molecules of a liquid crystal element made of two electrode substrates on which fine grooves parallel to each other are formed in the same direction by rubbing, oblique evaporation, etc. and liquid crystal sandwiched between them are aligned in one direction. In the present invention, this arrangement is equal to the arrangement formed by applying a voltage of one polarity, and therefore is maintained even after the voltage of one polarity is removed. When a voltage of the opposite polarity is further applied, the direction of the spontaneous polarization of the ferroelectric liquid crystal molecules is reversed, resulting in a different alignment state. This phenomenon can be used to form a liquid crystal light modulation element. In other words, a light modulation element constructed by sandwiching a liquid crystal element made of two electrode substrates between two orthogonal polarizing plates exhibits electro-optic characteristics as shown in FIG.

For example, using one of the two electrode substrates as a reference,
The alignment state when a negative voltage is applied to the liquid crystal is
This is the same as when no voltage is applied, and conversely, when a sufficient positive voltage is applied to the liquid crystal, it assumes a different alignment state. If one direction of the orthogonal polarization axes of the polarizing plate matches the light distribution direction when a negative voltage is applied, the light transmittance will be 0% when a negative voltage is applied. When a positive voltage is applied, the transmittance is 100%.
When transmitting light, a positive voltage is applied from a stable state where the liquid crystal molecules are regulated by narrow grooves formed parallel to the substrate surface.
Change the orientation state. Conversely, when blocking light, a negative voltage is applied to restore a stable state. Therefore, it exhibits electro-optical characteristics such that the fall is slow and the rise is fast.

A scanning electrode is provided on one of the two electrode substrates of this liquid crystal element, and a selection electrode is provided on the other, and a voltage having the waveform shown in FIG. 3 is applied to these electrodes. The left column of the table shown in Figure 3 shows the voltage waveforms applied to the scanning electrodes during non-scanning and during scanning, and the upper column shows the waveforms applied to the selection electrodes during selection and non-selection. , the voltage waveforms between the selection electrode and the scanning electrode are shown in the four columns at the lower right for the selection, non-selection, non-scanning, and scanning, respectively.

As shown in Figure 3, the scanning electrodes are
A rectangular voltage that is −V ₁ after V ₁ is applied during non-scanning.
If a voltage of V ₂ is applied, and a rectangular voltage that becomes V ₄ after V ₃ when selected is applied to the selection electrode, and a rectangular voltage that becomes -V ₁ after V ₁ when not selected (however, ,
V ₁ < V ₃ < V ₂ , V ₁ < V ₄ < V ₂ ), and (V ₃ −V ₁ ), then (V ₄
+V ₁ ), a voltage of 0 for non-selected pixels, and (V ₃ −V ₂ ) for selected pixels during non-scanning.
A rectangular voltage of (V ₄ -V ₂ ) is applied next to (V ₁ -V _{2 ), and a rectangular voltage of (-V 1 -V 2} ) next to (V ₁ -V ₂ ) is applied to the unselected pixel. In other words, a positive voltage is applied only to the selected pixel where the scanning electrode is in the scanning mode and the selection electrode is in the selecting mode, and light is transmitted. As a result, the photoreceptor drum of the printer is exposed to light,
Printing is performed.

In addition, as mentioned above, the falling time that blocks light is longer than the rising time that transmits light, so even after a pixel has been selected, light is transmitted only during the falling time, and during that time The photoreceptor drum is also exposed to light. Therefore, sufficient exposure is achieved even if the pixel selection time is shortened, and when pixels are time-divisionally driven, it becomes possible to drive many pixels in one frame period, increasing the duty ratio.
Time division driving becomes easy.

Furthermore, the response of a ferroelectric liquid crystal depends on the voltage value and time width applied to the liquid crystal (the higher the voltage or the longer the time width, the faster the response). Therefore, a step-like waveform is applied to the pixel during non-scanning, but
By changing the period (FIG. 3 shows the case where the scanning time and period coincide), it is possible to change the response time of the liquid crystal. By using this, it is possible to adjust the time until light is blocked after pixel selection. Thereby, the potential of the photoreceptor can be adjusted and good print quality can be obtained.

〔Example〕

Hereinafter, the present invention will be explained in detail by giving examples.

FIG. 1 is an exploded perspective view schematically showing a liquid crystal light modulation element using an embodiment of the present invention, and FIG. 2 is a cross-sectional view along AA' shown in FIG. 1. A glass substrate 11 provided with scanning electrodes 15 and coated with a polyimide alignment film 19 is rubbed in one direction, and then the substrate 1
A substrate 20, which is provided with a selective electrode 14 and coated with an alignment film 19, is rubbed in one direction, and the substrates 11 and 20 are bonded together with a spacer 18 at an interval of 5 μm so that the rubbing directions are parallel to each other. , between the substrates 11 and 20, a liquid crystal material 13 manufactured by Merck & Co., Ltd.
Filled with ZLI-3079. Scanning electrode 15 is 1mm
Since 16 electrodes are formed per electrode and driven by 1/4 duty time division driving, one selection electrode 14 faces the scanning electrode 15. The selection electrode 14 is connected to the scanning electrode 1 by the selection electrode drive circuit 16.
5 is driven by a scan electrode drive circuit 17. Further, the element is sandwiched between two polarizing plates 12.

A voltage as shown in FIG. 4 is applied to the liquid crystal light modulation device shown in FIGS. 1 and 2 to operate it. In other words, the scan electrode 15 receives a rectangular wave of voltage of 5V and then -5V during scanning by the scan drive circuit 17, the voltage of 20V during non-scanning, and the voltage of 20V and the next voltage of -5V during selection by the selection electrode drive circuit 16 for the selection electrode 14. When a rectangular wave with a voltage of 10V is applied to the pixel, and a rectangular wave with a voltage of 5V and then -5V is applied when not selected, a positive voltage of 15V is applied only to the liquid crystal of the selected pixel, allowing light to pass through. Become. However, since 0 or negative voltage is applied to pixels other than the selected pixel, light is blocked. Note that the driving voltage is a 125 μs rectangular wave, and the frame period is 1 ms. By driving as described above, a contrast of 30:1 can be obtained.

When the liquid crystal light modulation element shown in FIG. 1 is used in a printer head to construct an electrophotographic printer of a well-known configuration, it is possible to print 12 pages per minute with clear quality at 16 dots/1 mm. Since the liquid crystal light modulation element of this example has a gap between the substrates of 5 μm, it can be sufficiently handled using conventional liquid crystal element manufacturing technology and can be manufactured with a high yield. Furthermore, since the drive circuit is 1/4 duty time-division drive, the number of circuits is small and a low-cost optical modulation element can be realized.

In addition, if the drive voltage is made higher frequency, 15V
After the voltage of 0V, −10V or −15V, −
A 20V high frequency rectangular wave is applied, which increases the time it takes to block the light, making it possible to drive at 1/6 duty while keeping the frame period at 1ms, and further reducing the number of circuits. can.

〔Effect of the invention〕

As described above, the present invention enables time-division driving of a liquid crystal element filled with ferroelectric liquid crystal between two electrode substrates facing each other at a relatively wide interval by applying a rectangular waveform voltage to the electrodes. There is an effect that can be done.

Therefore, according to the present invention, it is possible to time-divisionally drive a liquid crystal element that can be easily manufactured with high yield at high speed, and it is possible to realize an inexpensive light modulation element and the like.

[Brief explanation of drawings]

Fig. 1 is a schematic perspective view of a liquid crystal light modulation element used in an embodiment of the present invention, and Fig. 2 is shown in Fig. 1.
AA′ cross-sectional view, FIG. 3 is a table showing the voltage waveform applied to the liquid crystal element according to the present invention, FIG. 4 is a table showing the voltage waveform applied to the embodiment shown in FIG. 1, and FIG. Schematic diagram showing the helical arrangement of liquid crystal molecules,
Figures 6 and 7 are a side view and a plan view schematically showing the orientation state of ferroelectric liquid crystal molecules between two substrates, and Figure 8 is a side view and a plan view schematically showing the alignment state of ferroelectric liquid crystal molecules between two substrates, and Figure 8 shows a structure in which the ferroelectric liquid crystal molecules are sandwiched between two deflection plates whose polarization axes are orthogonal to each other. 2 is a graph showing the relationship between the voltage applied to the liquid crystal light modulation element and the light transmittance. 11, 20...Glass substrate, 12...Polarizing plate,
13... Ferroelectric liquid crystal, 14... Selection electrode, 15
...Scanning electrode, 16...Selection electrode drive circuit, 17
...Scanning electrode drive circuit, 18...Spacer, 19
...Alignment film.

Claims (1)

[Claims] 1 A ferroelectric liquid crystal is filled in the gap between two opposing electrode substrates that have been subjected to alignment treatment to form a fine groove structure parallel to the same direction on the inner surface, and this ferroelectric liquid crystal is bistable. In a method for driving a liquid crystal element having a structure that does not exhibit a voltage, a first voltage is applied to a plurality of scanning electrodes formed on one of the two electrode substrates during scanning, and then a voltage of the same magnitude and opposite to the first voltage is applied. time-division scanning means for applying a rectangular waveform voltage that is a voltage of polarity, and applying a second voltage that is larger than the first voltage and has the same polarity as the first voltage during non-scanning;
A third voltage intermediate between the first and second voltages is applied to a plurality of selection electrodes formed on the other of the two electrode substrates so as to face the scanning electrodes, and then the first and second voltages are applied. A voltage with a rectangular waveform that is a fourth voltage intermediate between the two voltages is applied, and when it is not selected, a voltage with the same magnitude and opposite polarity as the first voltage is applied next to the first voltage. time-division driving means for applying a rectangular voltage, and the direction of the liquid crystal molecules due to the voltage applied between the scanning electrode and the selection electrode when not selected is the same as that due to the alignment treatment. How to drive a liquid crystal element.