JPH01193814A - Method for driving liquid crystal optical shutter array - Google Patents

Abstract

PURPOSE:To prevent degradation in a memory characteristic, etc., even if an optical shutter array is operated at a high speed and is driven for a long period of time by decreasing the voltage to be impressed to a liquid crystal in the time left when the time required for writing and erasing is subtracted from address time to 0 volt. CONSTITUTION:The erasing and writing time at the time of time sharing driving is set at the required min. pulse width in the case of writing an image by having the optical shutter array, imaging element and photosensitive body and exposing the photosensitive body by the light emitted from a light source and controlled by the optical shutter array. The zero volt is set within the time after the erasing and writing time is subtracted from the address time necessary for exposing of one dot. The deterioration in the memory characteristic is decreased by inserting the zero volt in the driving time when the sum of the erasing and writing time of the liquid crystal is small with respect to the address time at the time of the time sharing driving and, therefore, the driving of the high- speed light crystal optical shutter array is enabled with a high contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a liquid crystal optical shutter array used in an electrophotographic printer head or the like.

(Prior Art) 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 light modulation element is used to modulate the intensity of the light irradiated onto a photoreceptor, and the resulting latent image on the photoreceptor is normally converted into a latent image using toner. Printers that develop images on paper are known. The part of the printer that includes the light source, light modulation element, imaging optical system, etc. is called the printer head. The liquid crystal light modulator used in the printer head functions as a liquid crystal light shutter. In this case, liquid crystal light modulation elements are widely applied to optical logic elements, etc., but all of them use the function of spatially modulating the intensity of incident light. This will be explained by taking as an example the case where it is used in a code.

In recent years, printers have become faster, higher resolution, lower priced, and
Demand for 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 these circumstances, LCD printers using LCD shutter arrays are expected to be in high demand, especially due to their low l1fli characteristics, and are being actively developed, and LCD printers using dual-frequency drive LCDs have been developed. There is.

Furthermore, in recent years, ferroelectric liquid crystals have been developed as liquid crystals with high response speeds, and efforts are being made to increase the speed.

Ferroelectric liquid crystals have a property called bistability, in which the orientation state at the time of voltage application is maintained even after the voltage is removed, and a time-division driving method that utilizes this property has been proposed. for example,
Proceedings of the 1985 Electrical and Information Society Federation Conference 17-4
．． 359 <1985> proposes the following method.

There is a relationship between the voltage applied to the liquid crystal and the response time, below which the response time is proportional to the square of the reciprocal of the voltage, whereas above it the response time is proportional to the reciprocal of the voltage. Taking note of this, an appropriate voltage is selected as the driving voltage, and a pulsed voltage is applied to the liquid crystal to drive it, with the minimum time required for the response in that case as the pulse width. Furthermore, in order to prevent direct current voltage from being applied to the liquid crystal, one scanning time is divided into writing scanning and erasing scanning.
At the time of selection, driving voltages of opposite polarity are applied during write scanning and erasing scanning. On the other hand, a method has been proposed in which a low-voltage alternating current electric field is applied when the selection is not made. However, in this method, the time required for one scan is four times the response time of the ferroelectric liquid crystal. Therefore, as a driving method capable of higher-speed operation, the following method is proposed on page 13 of the 31st Study Group Materials of the 142nd Committee on Organic Materials for Academic Use, Subcommittee A (Liquid Crystal Subcommittee), Information 14, Japan Society for the Promotion of Science. This takes advantage of the difference in response time due to the difference in the voltage applied to the liquid crystal, and as shown in Figure 14, the scanning signal and selection signal are selected as shown in the figure, and the waveform that surrounds the voltage applied to the liquid crystal in circles is shown in Figure 14. I'm trying to make it happen. In this driving method, the previous memory state is erased in the first half of scanning, a high voltage pulse is applied during selection, and a low voltage pulse that does not cause switching is applied during non-selection. In other words, during selection, the applied voltage is low during non-scanning, and the liquid crystal does not respond sufficiently within the pulse width time that it responded sufficiently during scanning.
No switching occurs. On the other hand, in the non-selected state, OV is applied in the first half, but in the second half, a pulse with a shorter pulse width and lower voltage than in the selected state is applied to drive the liquid crystal. In this case, scanning with one scanning electrode may take twice the response time of the ferroelectric liquid crystal, but a DC component voltage is applied to the liquid crystal.

(Problem to be solved by the invention) Ferroelectric liquid crystals have a faster response than conventional TN liquid crystals, etc., but when driven in such a way that no direct current voltage is applied that would have a negative effect on the liquid crystals, the ferroelectric liquid crystals disappear. It is necessary to perform two scans, a scan and a write scan, and it takes four times the response time of the ferroelectric liquid crystal to scan one scan electrode.

On the other hand, if high-speed response is prioritized and one scanning electrode is driven so that the scanning time is 2@2 of the response time, a DC component voltage will be applied during driving, making it difficult to maintain memory properties, and this will affect the DC component voltage application time. As time passes, it becomes a crime.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for driving a liquid crystal optical shutter array that eliminates the above-mentioned drawbacks and does not cause problems such as memory loss even when operated at high speed and for a long time. .

(Means for Solving the Problem) The present invention includes a light source, a light shutter array, an imaging element, and a photoconductor, and exposes the photoconductor with light emitted from the light source and controlled by the light shutter array, In a time-division driving method for a ferroelectric liquid crystal optical shutter array used in an image writing type electrophotographic printing device, a ferroelectric liquid crystal sandwiched between a scanning electrode and a selection electrode is
<B> During scanning, a first step of applying a voltage pulse to bring the first stable state into a first stable state with a time width wider than the response time width of the ferroelectric liquid crystal, followed by a first step or a first step (2) During non-scanning, the second step is to apply a voltage pulse to bring the ferroelectric liquid crystal into a stable state. 3 steps, and for the remaining time after subtracting the first and second steps or the third step from the address time required to write an image on the photoreceptor, the applied voltage is set to ○■. A method for driving a liquid crystal optical shutter array characterized by its features is provided.

(Function) The ferroelectric liquid crystal in the liquid crystal optical shutter array formed by the two electrode substrates subjected to alignment treatment performs a so-called bistable operation in which the state at the time of voltage application is maintained even after the voltage is removed. This is usually called memory property.

In a time-division driving method that takes advantage of this memory property and produces high-speed response of ferroelectric liquid crystals, a DC component voltage is applied to the liquid crystals. It has been confirmed through experiments that when such a DC component is applied to a liquid crystal, the memory property decreases as the voltage application time elapses. The experimental results are shown below.

By continuously applying a voltage waveform such that the average voltage in one period is negative to the liquid crystal as shown in Fig. 2, and explaining the change in light transmittance over time at point A in Fig. 2, As shown in FIG. 3, it was found that the transmittance decreased with time.

In this example, the dyeing of the polarizing plate is selected so that it will be in an ON state when a negative voltage is applied.

In addition, as shown in Fig. 4, we conducted a similar experiment using a voltage waveform with a pulse width narrower than that shown in Fig. 2, but set to a pulse width that is sufficient to turn the liquid crystal ON or OFF.
When the points were observed, the results were as shown in FIG. 5, and it was confirmed that the decrease in transmittance was smaller than in FIG. 3. Therefore, it can be said that by narrowing the pulse width, the life of the liquid crystal can be extended.

However, the address time for writing data into one shutter array element during time-division driving of a liquid crystal optical shutter array cannot be determined solely by the response speed of the liquid crystal material. This is because it is related to the exposure characteristics of the photoreceptor, which is the main part of an electrophotographic printer.Finally, the address time is considered to be the time width required for the photoreceptor to be sufficiently exposed.

Therefore, when the drive pulse width is narrowed, extra time is generated when the time required for writing and erasing is subtracted from the address time. During this extra time, reduce the voltage applied to the liquid crystal.
If the voltage is set to volts, the influence on deterioration of memory properties and deterioration of contrast during driving will be reduced. This drive waveform is shown in FIG.

Therefore, the erasing and writing times during time-division driving should be set to the minimum necessary pulse width, and the lifetime will be extended by setting the erasure and writing times to O volts during the address time required for one dot exposure minus the erasing and writing times. Moreover, the liquid crystal optical shutter array can be driven by taking advantage of its high speed.

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

FIG. 6 is an exploded perspective view schematically showing a liquid crystal optical shutter array used in an embodiment of the present invention, and FIG. 7 is a cross-sectional view along line AA' shown in FIG. 6. A glass substrate 11 coated with a polyimide alignment film 19 provided with scanning electrodes 15 is rubbed in one direction, and signal electrodes 14 are formed opposite to the substrate 11.
The substrate 20 provided with the alignment film 19 and coated with the alignment film 19 is rubbed in one direction, and the substrates 11.20 are bonded via the spacer 18 at intervals of 2 μm so that the rubbing directions are parallel to each other. The liquid crystal material 13 was filled with TKF-8616 (trade name) manufactured by Teikoku Kagaku Co., Ltd. Sixteen scanning electrodes 15 are formed per 1 mm and driven by time-division driving with a 1/4 duty, so that one signal electrode 14 faces four scanning electrodes 15. The signal electrode 14 is a signal electrode drive circuit 16, and the scanning electrode 1
5 is driven by a scan electrode drive circuit 17. Furthermore, the element is sandwiched between two polarizing plates 12, and...! The total number of dots is 4096.

In the liquid crystal light shutter array shown in FIGS. 6 and 7, as shown in FIG.
It is operated by applying a voltage as shown in FIG. 8th
The waveform shown in the figure is for comparison with the present invention, and the frame period is 1.
．． Since the duty was 1/4 at 1 mS, one address time was set to 275 μs. - Erased with ■o, written with ■o.

The erase and write time is 137.5 μs, which is half of the l address time of 275 μS. Note that during non-scanning, the first half is O volts, and the second half is an alternating voltage of 0 and 12 o. The frequency of this part is 50KHz■. = 10V.

On the other hand, in the waveform of FIG. 10, the minimum necessary pulse width is set for writing and erasing, and the time obtained by subtracting the writing and erasing time from one address time is set to O volts. Here, when scanning is selected, the erase pulse and write pulse are both 100 μS.
The remaining 75 μS is 0 volt. During scanning and non-selection, the voltage is 0 volts for 175 μs other than the 100 μs erase pulse. During non-scanning/selection, the first 100 μs and the last 75 μs are O volts, and the rest is ±vo. During non-scanning/non-selection, the first half is 100 μs and the last 75 μs.
is D volts, and the rest are alternating voltages of O volts and -2Vo. Here, ra is IO volts, and the alternating voltage part is 50 K I-1z.

The waveform of the data combination in which the most DC component voltage is applied to the liquid crystal in each of Figures 8 and 10 is shown in Figure 9.
As shown in FIG. Even when the waveforms shown in FIGS. 9 and 11 were continuously applied to the liquid crystal optical shutter array, changes in memory properties were observed. Incidentally, the voltage waveform for observing the memory property is shown in FIG. The voltage waveform shown in FIG. 12 was applied to the liquid crystal optical shutter array, and changes in the zero point were observed. The light source was a He-Ne laser, and the light receiving element was a photodiode. The results are shown in FIG. a is the result of the waveform in FIG. 9, and b is the result of the waveform in FIG. 11. In the driving method in which 0 volt is inserted, the deterioration in memory performance is reduced to about 1/4.

In this way, if the sum of E during erasing and writing of the liquid crystal is small with respect to the address time during time-division driving, O during the driving period jm
By inserting bolts, it is possible to reduce memory deterioration, making it possible to drive high-contrast, high-speed liquid crystal optical shutter arrays.

(Effects of the Invention) As described above, according to the present invention, since deterioration of memory performance can be reduced, it is possible to drive a liquid crystal optical shutter array for an electrophotographic printer with high contrast and high quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows voltage waveforms applied to the liquid crystal light shutter array according to the present invention, FIGS. 2 and 4 show voltage waveforms applied to the liquid crystal, and FIGS. 3 and 5 show voltage waveforms applied to the liquid crystal light shutter array. It is a figure which shows the relationship between the light transmittance and elapsed time in each case. FIG. 6 is a schematic perspective view of a liquid crystal optical shutter array used in an embodiment of the present invention, and FIG. 7 is a cross-sectional view taken along line AA' shown in FIG. FIG. 8 is a diagram showing conventional driving waveforms, and FIG. 9 shows an example of applied voltage in the driving method of FIG. 8. FIG. 10 is a diagram showing a voltage waveform applied to the liquid crystal optical shutter array according to the present invention, and FIG. 11 is a diagram showing an example of the applied voltage in the driving method of FIG. 10.

FIG. 12(a) is a voltage waveform diagram applied to the liquid crystal,
FIG. 4B is a diagram showing the optical response waveform. 13th
The figure shows the relationship between the change in light transmittance and the passage of time for the voltage waveform in FIG. 12 when the voltage waveforms in FIGS. 9 and 11 are applied to the liquid crystal. FIG. 14 is a diagram showing conventional drive waveforms.

Claims (1)

[Scope of Claims] A light source, a light shutter array, an imaging element, and a photoreceptor are provided, and the photoreceptor is exposed to light emitted from the light source and controlled by the light shutter array to write an image. In a time-division driving method of a ferroelectric liquid crystal optical shutter array used in an electrophotographic printing apparatus, the ferroelectric liquid crystal sandwiched between a scanning electrode and a selection electrode is exposed to at least the above-mentioned conditions during scanning. A first step of applying a voltage pulse to bring the first stable state to a first stable state, respectively, with a time width wider than the response time width of the ferroelectric liquid crystal, and then applying a voltage pulse to bring the first or second stable state to the ferroelectric liquid crystal. (b) during non-scanning, a third step of applying a voltage pulse with such a low voltage or narrow pulse width that the ferroelectric liquid crystal does not respond; A method for driving a liquid crystal optical shutter array, characterized in that the applied voltage is set to OV during the remaining time after subtracting the first and second steps or the third step from the address time required to write an image on the LCD.