JPH0363624A - Method for driving liquid crystal optical shutter array - Google Patents

Abstract

PURPOSE:To allow high-quality printing with less unequal printing by previously setting the voltage values to be applied to respective electrodes in such a manner as to have the same ratios of the quantity of transmitted light at the time of opening and closing of respective shutter dots. CONSTITUTION:A liquid crystal element is formed by rubbing electrode substrates coated with polyimide as oriented films, adhering the substrates at 2mum spacing via spacer and packing 'CS-1018(R)' produced by CHISSO as a liquid crystal material 13 into the spacing between the substrates. The signal electrodes 14 are formed by 12 pieces per 1mm and the liquid crystal element is crimped by two sheets of polarizing plates 12. The voltages of the respective signal electrodes 14 are set at 10, 9.75, 9.75, 9.75, 10, 9.5 volts so as to uniformize the contrasts at the respective points of this element. The average contrast is improved from 3.7 to 5.1 in this way and further, the balance of the contrast is improved from + or -10% to + or -3%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) 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 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 including the light source, light modulation element, imaging optical system, etc. is called a printer head. A liquid crystal light modulation element used in a printer head functions as a liquid crystal light shutter. In addition to this, 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.The following describes the case where liquid crystal light modulation elements are used in printer heads. This will be explained using an example.

In recent years, demands for printers such as high speed, high resolution, low cost, low noise, and miniaturization have been increasing, and in response to these demands, non-impact printers such as laser beam printers and light emitting diode printers are becoming widely used. Under these circumstances, large demand is expected for liquid crystal printers using liquid crystal shutter arrays, especially due to their low cost, and active development is progressing, and liquid crystal printers using dual-frequency drive liquid crystals have been developed. There is.

Moreover, as reported in the Proceedings of the Society for Information Display by Naemura et al.
; PROCEEDINGS OF THE 5OCI
ETY FORINFORMATION DISPLA
Y; 489 (1987)) A printer head was developed that used ferroelectric liquid crystal as a liquid crystal with a short response time.
Efforts are being made to speed it up. Here, a pulse is applied to reset the shutter before selection, then a voltage is applied to turn the shutter on and off according to the printed signal, and when no selection is made, a high-frequency pulse train is applied. method is used. The same voltage is applied to all shutters.

(Problem to be solved by the invention) Ferroelectric liquid crystals have the characteristics of high-speed response and bistability, but in order to effectively realize these characteristics,
It is preferable for the cell to be as thin as possible, especially lpm
~5pm is suitable. A liquid crystal shutter for a printer requires a shutter array in which the layer thickness is uniform over a length corresponding to the paper sheet, and the liquid crystals are oriented in the same manner.

However, manufacturing such a liquid crystal element is difficult, and even when driven under the same driving conditions, the operation is uneven due to shutter dots, resulting in uneven printing when used as a printer head.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for driving a liquid crystal optical shutter array that reduces non-uniformity of shutter dot operation and enables high quality printing.

(Means for Solving the Problems) The present invention includes a light source, a light shutter array, an imaging element, and a photoreceptor, and an image is written by exposing the photoreceptor with light emitted from the light source and controlled by the light shutter array. A driving method for a ferroelectric liquid crystal optical shutter array used in an electrophotographic printing device of The feature is that the voltage value is set in advance for each signal electrode.

(Function) Liquid crystal shutters using ferroelectric liquid crystals must be assembled to a thickness of lpm to 5pm in order to achieve high-speed response and bistability. It is difficult to make it uniform. Further, the two electrode substrates forming the groove bottom of the liquid crystal shutter array are subjected to an alignment process, but like the thickness of the shutter array, it is difficult to make this uniform over the length corresponding to the paper sheet. Therefore, even if the same voltage is applied to each shutter dot, due to these factors, the light transmission properties of the liquid crystal shutter array differ for each shutter dot when on and off, resulting in uneven contrast and uneven density during printing. happens.

FIG. 2 shows a contrast distribution of the light amount distribution during on and off times when driven with a voltage such as -. A photodiode is used as the light receiving element. Further, FIG. 3 shows the relationship between the drive voltage, the photodiode output voltage and the contrast when the photodiode is on and off. The second and third standard drive waveforms were tested by erasing the previous memory state in the first half of scanning, applying a high voltage pulse when selected, and applying a low voltage pulse when not selected.

From FIG. 3, it can be seen that the contrast can be controlled by adjusting the driving voltage. Therefore, for example, by examining the relationship between drive voltage and contrast for each signal electrode using a light receiving element, it is possible to determine the drive voltage for each signal electrode to obtain approximately -like contrast for all shutter dots. By setting this voltage value in advance for each signal electrode, it is possible to realize a printer head that has little variation in shutter operation and forms prints with uniform print quality.

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

FIG. 1 is a diagram of a liquid crystal element driven using the driving method of the present invention. The electrode substrate coated with polyimide as an alignment film is rubbed, and the substrates 11 and 20 are bonded at intervals of 2.1m via spacers, and C8-1018 manufactured by Chisso Oil Co., Ltd. is filled as the liquid crystal material 13 to assemble. Signal electrode 1
4 is formed with 12 pieces per 1 mm. Further, the liquid crystal element is sandwiched between two polarizing plates 12.

Using this element, the scanning electrode 15 and the signal electrode 14 can be
The voltage waveform shown in the figure was set to VQ=10 volts and was driven by the signal electrode drive circuit 16 and the scan electrode drive circuit 17.

The angle of the polarizing plate was chosen so that when selected, light passes through, and when non-selected, light does not pass through.

FIG. 5 shows the contrast distribution when both the scanning electrode and the signal electrode are driven at a voltage VQ=10 volts. Note that a
-f represents the positions of points selected at equal intervals on the shutter array. Further, FIG. 6 shows the relationship between the driving voltage at point a, the output voltage of the light receiving system during on/off states, and the contrast. Point a
When examining the same characteristics as in FIG. 6 for -f, it is found that the signal electrode drive voltage at which the maximum contrast is obtained differs at each point.

Therefore, each signal electrode voltage was adjusted so that the contrast at each point was as close to the maximum as possible and even more uniform. A contrast distribution map of each point obtained as a result is shown in FIG. At this time, the set voltages o of the signal electrodes at points a-f are respectively 10.9.75.9.75.9.75.10.9.5
It became a bolt. By this method, the average contrast was improved from 3.7 to 5.1, and the variation in contrast was improved from ±10% to ±3%.

(Effects of the Invention) As described above, according to the present invention, it is possible to drive a liquid crystal optical shutter that provides high quality printing with less uneven printing.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing an embodiment of the present invention;
11.20 is a counter substrate, 12 is a polarizing plate, 13 is a ferroelectric liquid crystal, 14 is a signal electrode, 15 is a scan electrode, 16 is a signal electrode drive circuit, and 17 is a scan electrode drive circuit. FIG. 2 is a diagram showing the light amount distribution and contrast distribution when the shutter array is on and off. FIG. 3 is a diagram showing the relationship between the signal electrode voltage, the amount of light when the shutter is on and off, and the contrast. FIG. 4 is a liquid crystal drive voltage waveform diagram. 5 and 7 are diagrams showing the position and contrast of the shutter array. FIG. 6 is a diagram showing the relationship between the signal electrode voltage and the photodiode output and contrast when the shutter is on and off.

Claims (1)

[Claims] In a method of driving a liquid crystal optical shutter array in which a signal voltage is applied to each electrode of each shutter dot constituting a liquid crystal optical shutter array in which a liquid crystal material is sandwiched between electrode substrates subjected to alignment treatment, each shutter dot is opened and closed. A liquid crystal light device characterized in that the voltage value applied to each electrode is set in advance for each shutter dot so that the ratio (contrast) of the amount of transmitted light when the dot is open and closed is the same for all shutter dots. How to drive a shutter array.