JPS6347731A - Driving system for liquid crystal shutter array - Google Patents

Abstract

PURPOSE:To improve contrast with a simple circuit constitution by impressing a pulse signal with a repeating period shorter than an optical response time of a liquid crystal shutter to the other input end of an exclusive logical gate circuit at the time of transferring the ON/OFF data of respective microshutters to shift registers in the first half of a writing period. CONSTITUTION:Data DT are transferred and inputted to all shift registers SR in a driving circuit at the initial part of the writing period T11 for writing a recording image corresponding to one line, and during a period T13 slightly longer than a data transfer period T12 a high frequency pulse signal HP is applied as a gate signal GTa. When the high frequency pulse signal HP whose logical level is inverted at 1/2 period T14 is applied to one input terminals of respective exclusive OR circuits X01, X02,..., X0k, the outputs of the exclusive OR circuits can not be held at the same logical level during the period longer then the period T14. A period T15 for optically turning on a liquid crystal shutter is almost equal to the writing period T11, so that the contrast of a recording image can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a driving method for a liquid crystal shutter array constructed using a liquid crystal plate containing ferroelectric liquid crystal as a liquid crystal composition.

[Prior Art] In recent years, with the spread of so-called office automation, various information processing devices have been introduced into office environments.

Devices used in such environments are required to suppress elements such as noise and vibration that adversely affect the environment as much as possible.

By the way, dot impact printers have been widely used for printing documents created with Japanese word processors etc. as hard copies, but these dot impact printers produce a lot of printing noise and vibration. This tendency was especially strong with high-speed machines, and they often interfered with the work of those around them.

To solve this problem, non-impact printers that form images using an electrophotographic process, such as laser beam printers, liquid crystal shutter printers, or LED printers, have been put into practical use.

Unlike the above-mentioned dot-impact printers, this printer has no part where the paper is struck when forming an image, so the printing noise is very low, and it is also a page printer that basically records images on a page-by-page basis. Therefore, high-speed recording is possible.

By the way, among such page printers, laser beam printers require a high-precision optical system such as a polygon mirror for the optical writing system, so they are very costly, and LED printers require a high-precision optical system such as a polygon mirror for the optical writing system. Due to variations in the light emitting characteristics of LEDs (light emitting diodes), it is difficult to obtain stable recorded images.

On the other hand, the liquid crystal shutter used in the optical writing system of liquid crystal shutter printers can integrate the light source, liquid crystal shutter, and imaging element that make up the optical system, and the optical system can be configured easily and compactly, resulting in an inexpensive device. can do.

Now, the recording speed of such a liquid crystal shutter printer is
Naturally, this depends on the on/off characteristics of the liquid crystal shutter. In the TN (twisted nematic) liquid crystal that has been used for liquid crystal shutters up until now, even when driven at so-called dual frequency, the time required for rising and falling during on/off is relatively slow at about 0.5 milliseconds, and therefore , compared to laser beam printers, etc., the recording speed could not be increased much. Furthermore, since the TN type liquid crystal requires alternating current driving, the driving circuit is relatively complicated.

By the way, ferroelectric liquid crystal has a response time that is more than two orders of magnitude shorter than TN type liquid crystal, and can be driven with direct current, so by using this ferroelectric liquid crystal, a high-speed liquid crystal shutter with a simple peripheral circuit can be realized. can do.

This ferroelectric liquid crystal can achieve a memory effect by making its thickness smaller than the helical pitch of the liquid crystal molecules (Hideo Takezoe, Atsuo Fukuda, Sakae Kuze - "Ferroelectric liquid crystal high-speed display device" Industrial Chemistry Vol. 31 (See No. 10, 222-p25).

A conventional example of a driving device for a liquid crystal shutter array when such a ferroelectric liquid crystal is used as a liquid crystal composition is shown in FIG. It shows.

In the figure, data DT (see FIG. 9(d)) for turning on and off each micro-shutter (liquid crystal shutter) is sequentially stored in a shift register SR in synchronization with a shift clock SP (see FIG. 9(c)). The data of each digit of this shift register SR is transferred and inputted by latch pulse LP (9th
The data is stored in the latch circuit LA at the output timing shown in FIG.

The data of each digit of this latch circuit LA is stored in AND circuits ANI, AN2, . . . , are added to the other input terminals of ANk, and the AND circuits ANI, AN2 .・・・
, ANk output data is transmitted to segment electrodes SGi, SG2 . ..., S.G.
k, and each micro-shutter is turned on and off in response to the data DT.

In this case, voltage V/2 is applied to the common electrode that faces the segment electrodes and constitutes the micro shutter, and when voltage V is applied to the segment electrodes, the potential difference applied to the liquid crystal shutter is V/2. Therefore, the liquid crystal shutter is turned on, and when the voltage V is not applied to the segment electrode, the potential difference applied to the liquid crystal shutter becomes -V/2, which is the opposite polarity, so the liquid crystal shutter is turned off. In addition, in this way, the liquid crystal shutter that has turned on or turned off the star light maintains its light on/off state until the light is turned off or turned on (memory effect).

In this way, the data DT corresponding to the recorded image of the next line is transferred to the shift register SR in the first period T2 of the printing cycle T1, and the image of the transferred data is recorded in the first printing cycle. be done. But then,
In this case, the recording period T3 of data for one line almost coincides with the printing cycle TI.

By the way, since this drive device uses a shift register SR and a latch circuit LA, the number of transistors per one micro-shutter is very large, about 40, and it is necessary to configure this drive device integrally with the liquid crystal shutter array. However, if an attempt is made to realize this using a thin film circuit, the yield of the thin film circuit is poor, and the liquid crystal shutter device becomes very expensive.

In order to solve this problem, as shown in FIG. 10, the data of each digit of the shift register SR is directly transferred to AND circuits ANI, AN2 . ..., it is conceivable to add it to the other input terminal of ANk.

However, in this device, when the data DT is being transferred and input to the shift register SR, the AND circuit ANI
, AN2. . . . If the data being output to ANk fluctuates and the liquid crystal shutter responds to the fluctuation, a recorded image will not be properly obtained. Therefore, during a period τ4 which includes the period T2 required for transfer input of the data DT and is slightly longer than the period τ2, the gate signal GT is lowered and the output of the shift register SR is output from the AND circuits ANI and AN2.
．． ..., it is necessary to prevent the voltage from being applied to ANk (see FIGS. 11(a) to 11(c)).

Therefore, the liquid crystal shutter is only turned on during a period T3' excluding the period T4 of the printing period T1 (see FIGS. 11(d) to 11(g)).

This results in the disadvantage that the contrast of the recorded image decreases.

[Purpose] The present invention was made in order to solve the above-mentioned disadvantages of the conventional technology, and an object of the present invention is to provide a driving method for a liquid crystal shutter array that has a simple circuit configuration and can improve the contrast of recorded images. do.

[Configuration] The present invention includes a shift register for storing on/off data of each liquid crystal shutter, and output data of each digit of this shift register is added to one input terminal of the shift register so that the output corresponds to the liquid crystal shutter. It is equipped with an exclusive logic gate circuit that is applied to the segment electrode, and when the on/off data of each micro-shutter is being transferred to the shift register in the first half of the write cycle, the liquid crystal shutter is applied to the other input terminal of the exclusive logic gate circuit. A pulse signal with a repetition period shorter than the photoresponse time of is applied. As a result, the microshutter does not respond to light due to data that changes during the data transfer period, so the liquid crystal shutter is turned on or off during the entire writing period, and the contrast of the recorded image can be improved. Further, since the drive circuit can be configured only with a shift register and an exclusive logic gate circuit, the drive circuit can be realized with a very simple configuration.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a liquid crystal shutter printer according to an embodiment of the present invention.

In the figure, the surface of a photoreceptor 1 is uniformly charged by a charger 2, and an optical system 3 exposes a light image corresponding to a recorded image to form an electrostatic latent image corresponding to the recorded image on its surface. Ru. This electrostatic latent image is developed with toner by the developing device 4.

Further, the toner image thus formed on the surface of the photoreceptor 1 is transferred by the transfer charger 5 onto a recording sheet conveyed by a paper feeding system (not shown).

The toner image transferred to the recording paper is then thermally fixed by the fixing device 6, thereby forming a recorded image on the recording paper.

Further, residual toner and residual charges on the photoreceptor 1 are removed by a cleaner 7.

An example of the optical system 3 is shown in FIG.

In the figure, the optical system 3 includes a light source 11, a reflector 12 that reflects the light from the light source 11, and a reflector 12 that reflects the light from the light source 11. A polarizing plate 13 having a crossed Nicols polarization axis, a liquid crystal plate 14 formed by sealing ferroelectric liquid crystal in a transparent substrate with transparent electrodes forming a micro shutter array, and a polarization axis perpendicular to the polarizing plate 14. It consists of a polarizing plate 15 and an equilateral linear imaging element 16 such as a focusing fiber array.

An example of the liquid crystal plate 14 is shown in FIGS. 3(a) and 3(b).

The liquid crystal plate 14 includes transparent substrates 21 and 22, which are made of two glass substrates arranged at a predetermined interval.
A large number of segment electrodes 23 made of a strip-shaped transparent electrode material are attached to the lower surface at micro-shutter formation intervals, and the width dimension is slightly larger than that of the micro-shutters. A common electrode 2 made of a band-shaped transparent electrode material is provided on the upper surface of the transparent substrate 22 at least over an area wider than the area where the micro-shutter array is formed.
4. Aperture AP forming micro shutter array
A light mask 25. is used to block leakage light from the attached portion of the other common electrode 24, except for the portion of the common electrode 24. An alignment film 26 made of a transparent material with high resistance and laminated on the upper surface of the optical mask 25 for aligning the molecules of the ferroelectric liquid crystal 27;
It consists of a ferroelectric liquid crystal 27 sealed between a transparent substrate 21 and a transparent substrate 21.

In this case, in order to improve the recording density, the microshutters are arranged in two rows in a staggered manner at predetermined intervals. Further, the entire array of microshutters is referred to herein as a microshutter array.

Further, the thickness of the ferroelectric liquid crystal 27 to be sealed is desirably set to 10 μm or less (preferably 1 to several μm) so that the ferroelectricity of the liquid crystal composition can be strengthened.

FIG. 4 shows a driving circuit for a liquid crystal shutter according to an embodiment of the present invention.

In the figure, data DT (see Fig. 5(c)) for turning on and off each micro-shutter (liquid crystal shutter) is sequentially stored in a shift register SR in synchronization with a shift clock SP (see Fig. 5(b)). The transfer is input.

The data of each digit of this shift register SR is transmitted through exclusive OR circuits XOI, XO2, .
The output data of these exclusive OR circuits XOI, XO2, . . . ..., 23k
has been added to. In addition, exclusive OR circuits XOI,
The output logic level H of O2, . . . , There is.

Further, as in FIG. 8, the voltage V/2 is always applied to the common electrode 24 (see FIG. 5(d)), and the segment electrodes 231, 232 . . . . When a voltage V is applied to the logic level H to 23k, the potential difference applied to the corresponding liquid crystal shutter becomes V/2, so the liquid crystal shutter is turned on and the segment electrode 231.2 is turned on.
When a ground level that generates a logic level L is applied to 3zt, . Like this again.

- The liquid crystal shutter that turns on the starlight or turns off the light will maintain its light on/off state until the next light off or light on.

One shift register SR and exclusive OR circuits X
OI, XO2, . . .
X m) micro shutters are being driven. Also,
The shift register SR of each drive circuit is connected in series with the shift register SR of the drive circuits arranged before and after.

When driving the liquid crystal shutter with this drive circuit, 1
Writing cycle Tl for writing a recorded image for a line
In the first part of l, all shift registers S of the drive circuit
Data DT is transferred and input to R.

Then, this data transfer period T12 (=n x Psp
; However, during a period T13 that is slightly longer than this period T12 and includes Psp (the period of the shift clock SP), the high frequency pulse signal HP with a predetermined repetition period is applied to the gate signal G.
Added as Ta.

This high frequency pulse signal HP is, for example, shown in FIGS.
As shown in c), it is a pulse signal with a cycle T14 shorter than the optical response time of the liquid crystal shutter and a duty of 50%. In this example, high frequency pulse signal 1 (period T14 of P
is equal to 1/2 period of the shift clock SP, and the high frequency pulse signal HP and the shift clock SP are synchronized in phase. Furthermore, since the optical response time of the liquid crystal shutter changes as shown in FIG. 7 in response to the applied driving voltage, the period TI4 can be set based on this relationship. In addition, the duty of high-speed pulse signal 1 (P is 50
Not limited to %.

In this way, the high-frequency pulse signal HP whose logic level is inverted every 172 cycles of the period Ti4 is applied to one input terminal of each exclusive OR circuit XOI, XO2, ..., XOk, so that the data No matter how the data DT transferred during the transfer period T12 changes.

Exclusive OR circuit X in this data transfer period T12
The outputs of OI, XO2, . . . , XOk never maintain the same logic level for a period longer than the period T14.

That is, during this data transfer period T12, the outputs of the exclusive OR circuits XOI, XO2,...,
times) to invert the logic level.

Therefore, during this data transfer period T12, none of the liquid crystal shutters responds to light and maintains its previous state.

Therefore, when the data transfer period T12 ends and the optical response time of the liquid crystal shutters elapses, each liquid crystal shutter completes its on/off operation in response to the data DT that has been transferred to the shift register SR at that time. However, the on/off state lasts for a period T15 until the data DT of the primary line is completely transferred to the shift register SR.

Note that, as a matter of course, the period T16 from the end of the data transfer period T12 until the start of the writing cycle of the next line is set to a time during which the liquid crystal shutter can sufficiently respond to light.

Therefore, in this case, the period T15 during which the liquid crystal shutter is turned on is approximately equal to the writing period Tll,
Thereby, the contrast of the recorded image can be improved.

Note that it is sufficient to use a high-speed pulse signal that satisfies the above-mentioned conditions, but when using a high-speed pulse signal that has the same period as the shift clock and is phase-synchronized with the shift clock, depending on the data content, Since there is a possibility that the output of the exclusive OR circuit becomes DC-like, it is necessary to exclude those that satisfy this condition. Further, it is preferable that the high-speed pulse signal is not synchronized with the shift clock.

In this way, a recorded image with good contrast can be obtained with a drive circuit having a simple configuration using only a shift register and a gate circuit (exclusive OR circuit). Furthermore, when the drive circuit is implemented using a thin film circuit, the number of components is small, so yield can be improved.

In the above-mentioned embodiment, the liquid crystal shutters are arranged in a staggered manner on the liquid crystal plate, but the method of arrangement is not limited to this. The embodiment described above can also be reversed, in which case an exclusive NOR circuit can also be used.

[Effects] As explained above, according to the present invention, there is provided a shift register for storing on/off data of each liquid crystal shutter, and output data of each digit of this shift register is added to one input terminal of the shift register. The exclusive logic gate circuit is equipped with an exclusive logic gate circuit whose output is applied to the segment electrode corresponding to the liquid crystal shutter. A pulse signal with a repetition period shorter than the optical response time of the liquid crystal shutter is applied to the other input terminal. As a result, the liquid crystal shutter does not respond to light due to data that fluctuates during the data transfer period, so the liquid crystal shutter is turned on or off during the entire writing cycle, making it possible to improve the contrast of the recorded image.

Furthermore, since the drive circuit can be configured with only shift registers and exclusive logic gate circuits, the drive circuit can be realized with a very simple configuration, and the yield can be improved when realizing one circuit using thin film technology. can.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a liquid crystal shutter printer according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing an example of an optical system, and FIG. 3(a) is a sectional view showing an example of the configuration of a liquid crystal plate. , FIG. 4 is a circuit diagram showing an example of the driving circuit, FIG. 5 is a waveform diagram showing an example of driving, and FIG. 6 is for explaining an example of a high-speed pulse signal. 7 is a graph showing an actual measurement example of the drive voltage and the optical response time of the liquid crystal shutter, FIG. 8 is a circuit diagram showing a conventional example of a drive circuit, and FIG. 9 is a waveform showing an example of the drive. 10 is a circuit diagram showing another conventional example of a drive circuit, and FIG. 11 is a waveform diagram showing an example of the drive circuit. 14...Liquid crystal plate, 23,23x-23k...Segment electrode. 24... Common electrode, XOI to XOk... Exclusive OR circuit. SR...Shift register. Figure 1 Figure 2 Figure 3 23 2.3 ZJ lj Figure 4 Figure 5 Figure 6 Figure 7 Jl/initial voltage □ Figure 8 Figure 9

Claims (1)

[Claims] In the driving method of a liquid crystal shutter array constructed using a liquid crystal plate containing ferroelectric liquid crystal as a liquid crystal composition, a shift register is used to store on/off data of each liquid crystal shutter, and an output of each digit of this shift register is used. It is equipped with an exclusive logic gate circuit in which data is applied to one input terminal and its output is applied to the segment electrode corresponding to the micro shutter, and in the first half of the write cycle, on/off data of each liquid crystal shutter is sent to the shift register. A driving method for a liquid crystal shutter array, characterized in that during transfer, a pulse signal with a repetition period shorter than the optical response time of the liquid crystal shutter is applied to the other input terminal of the exclusive logic gate circuit.