JPS63135921A - Driving method of liquid crystal element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for driving a liquid crystal element using a dual-frequency driven liquid crystal.

[Technical background of the invention and its problems]

BACKGROUND ART Recently, for example, in optical writing in an optical writing printer, a liquid crystal element called a liquid crystal shutter, which has a large number of shutter parts arranged in an array to control transmission of light, is used.

This liquid crystal element consists of a transparent substrate on which a large number of signal electrodes are arranged and a transparent substrate on which a common electrode is formed opposite to the signal electrodes, with a liquid crystal interposed between them so that the electrode formation surface is on the inside. A large number of minute shutter portions are arrayed and formed by opposing signal rods and common electrodes of each of the substrates and the liquid crystal located between these two electrodes. Then, by applying a voltage between the signal electrode and the common electrode to control the behavior of the liquid crystal, each nyatta section is opened.
or "closed".

When this liquid crystal element is installed in an optical writing printer for optical writing, the liquid crystal element 1, light source 2, and lens 3 are assembled into a head cover 4 to form an optical writing head 5, as shown in FIG. , this optical writing head 5 is provided facing the photosensitive drum 6. Transmission of light from the light source 2 is controlled by opening and closing the shutter section of the liquid crystal element 1, and the light transmitted through the shutter section of the liquid crystal element 1 is irradiated onto the surface of the photosensitive drum 6, so that the light on the surface of the photosensitive drum 6 is Optical writing is performed by erasing the charge on the irradiated area. What is written on the surface of the photosensitive drum 6 under the control of the shutter section of the liquid crystal element 1 forms dots corresponding to the negative section, and the combination of these dots expresses characters such as υ. Note that the electrostatic latent image on the photosensitive drum is transferred to recording paper.

As a method for vlPIlling this liquid crystal element, a two-frequency driving method that utilizes the dielectric dispersion phenomenon of liquid crystal is adopted in order to operate the shutter section at high speed and obtain high contrast.

In this two-frequency driving method, when a high frequency electric field is applied to the liquid crystal, the liquid crystal molecules try to align perpendicular to the electric field, and when a low frequency electric field is applied, the liquid crystal molecules try to align parallel to the electric field. The TN type (twisted nematic type, in which the polarizing axes of the polarizing plates are arranged perpendicular to each other) liquid crystal element with a positive display using this driving method uses the phenomenon that the shutter part opens ( In the case of a GH type (guest-host effect type) liquid crystal element, the shutter part closes (opaque) when high frequency is applied (light transmission), and the shutter closes (opaque) when a low frequency is applied.
・・Coloring), the shutter part opens when low frequency is applied (light transmission・・
...no coloring).

When driving a liquid crystal element by such a two-frequency driving method, there is a problem that when the high frequency application time becomes long, the responsiveness of the liquid crystal to the next low frequency application deteriorates due to the hysteresis effect of the liquid crystal. For example, as shown in FIG. 8, such a drive method that performs time-division driving with two frequencies reduces one cycle (one dot writing time) TW to 1/2 for controlling the shutter section.
When the liquid crystal is divided into two parts, TW and 1/2TW, and a G, H effect type liquid crystal is used, an electric field having the waveform shown in the figure is basically applied to the liquid crystal. In other words, the shutter section is opened (
(light transmission), as shown in Figure 8 (al), the open start signal (low frequency) is applied to the first half TW, and the second half TW is
When applying a signal to maintain the open state at /2 TW, and when the shutter section is to be "closed" (no light transmittance), it is closed at the first half TW, as shown in Figure 8(b). Start signal (
This is a method of applying a signal that maintains the closed state in the latter 1/2 TW. In this way, the conventional method applies a signal to open or close the shutter part during the first half of the time when the liquid crystal element writes one dot on the photosensitive drum, and then uses the history effect of the liquid crystal in the second half to apply a signal to open or close the shutter part. Since a signal is applied to maintain the shutter open or closed, the shutter remains open or closed throughout the one-dot writing time.

However, in the conventional method of driving the liquid crystal element at two frequencies in a time-division manner, when writing dots on the photosensitive drum using the liquid crystal element, it is necessary to accurately form a single dot image to a predetermined size and write it on the photosensitive drum. There is a problem in that it is difficult to print and the print quality deteriorates.

In other words, in an optical writing printer, optical writing is performed while the photosensitive drum is continuously rotated, and as a result, each dot writing area on the surface of the photosensitive drum is continuously continuous with respect to the nying area of the liquid crystal element. pass through. On the other hand, in a liquid crystal element, a shutter section operates for a certain period of time to irradiate a light spot onto the surface of the photosensitive drum. Light transmitted through this shutter section: (Therefore, the light irradiation point on the surface of the photosensitive drum is
The length increases in the rotational direction of the photosensitive drum, and a gradient of the light irradiation light 1 occurs within the light irradiation point, and the charge in the portion irradiated with a predetermined amount of light depending on the sensitivity of the photosensitive drum is discharged, resulting in static electricity. An electrostatic latent image is formed.

In this way, one of the electrostatic latent images formed on the surface of the photosensitive drum
The length of the dot in the rotational direction of the photosensitive drum is determined by the amount of irradiated light and the sensitivity of the photosensitive member. For this reason, the size of the dot image written on the surface of the photosensitive drum by the shutter section of the liquid crystal element increases. In particular, in the conventional driving method of a liquid crystal element, since the shutter section is in the closed state a or the closed state throughout the one-dot writing time, the gradient of the amount of irradiation light is gentle, and the entire adjacent dot area is irradiated with light. Therefore, the degree of influence of the above-mentioned phenomenon on dot writing is variable.

This point will be explained with reference to FIG. 9.

FIG. 9 schematically shows the state of optical writing on the surface of the photosensitive drum by the shutter section of the liquid crystal element. 1 in the diagram
6 is a liquid crystal element having a shutter section A, and 6 is a photosensitive drum.
It rotates continuously at a constant speed in the direction of the arrow. D1～
DI is the first image sequentially written on the drum surface by the opening/closing operation of the shutter section A of the liquid crystal element 1 as the photosensitive drum 6 rotates.
This is the fourth dot writing section. 0-0' indicates the level of the sensitive light amount of the photosensitive member on the surface of the photosensitive drum 6 (hereinafter referred to as sensitivity D level 5), and the amount of light irradiated from the shutter of the liquid crystal element 1 to the surface of the photosensitive drum 60 is the sensitive level O.
If it is less than -07, electric charge remains on the drum surface and a black dot is printed on the recording medium, and if it is more than the sensitive level O-0', the electric charge is discharged and a white dot is printed on the recording medium. The amount of light irradiated to each dot writing portion D1 to D4 on the surface of the photosensitive drum 6 can be represented by a solid line, a broken line, and a dashed-dotted line in FIG. In this case, 1. 2nd and 4th dot M-containing part DJ, D, ? , D4 write dots corresponding to white, and dots corresponding to black are written in the third dot writing section D3. First, writing of a single dot will be described, focusing on point P (>K corresponding to the front edge of shutter section A) on the photosensitive drum.

Point P is reached during one writing period (2 m) by 60 rotations of the photosensitive drum.
sec), it moves at a constant speed to 23 points.

At the same time, the shutter section A of the liquid crystal element 1 is opened, and the drum surface is irradiated with light for a period of 2 ms.

As shown by the solid line in FIG. 9, the amount of light irradiated with K in this manner is a distance P which is shifted by TWK during one writing period.

It becomes a triangle with the point as the vertex and the base as p, p, and the point,
A dot corresponding to white is written in a portion of the light 11 diagram to which a light quantity greater than the sensitivity level is applied, that is, D2.

This writing operation is performed continuously, so when writing the dot writing part, the dot writing part before 2, and 1 as a dot corresponding to white, the irradiation is done in the same way as the writing operation described above. The amount of light is represented by a broken line in the figure. Incidentally, the light amount from the 28th point to the 21st point is the sum of the light amount shown by the solid line and the light amount shown by the broken line, and actually indicates the value connecting the broken line and the maximum value of the actual record. Thus, white dots are written in the first dot writing portions 1.1) and 12. When writing the third black dot from the state in which the second dot writing section D22 has written 11 times as shown in FIG. When the point moves to point 21, the photosensitive drum 6 passing through the shutter section A during this period is not irradiated with light. Then, when a white dot is written in the next writing period TW, the shutter section A becomes "open", so that the scene diagram shown by the dashed dotted line as described above is obtained.

Therefore, the third dot writing section, ? Since the amount of light has not reached the sensitive level, the charge remains and corresponds to a black dot, and the fourth dot D44 corresponds to a white dot because the amount of light has reached the sensitive level.

However, in this method of writing each dot, the light beam is irradiated over the entire area of the point on the photosensitive drum corresponding to the black dot, with the amount of light changing continuously along the direction of movement of the photosensitive drum. The area corresponding to the white dot and
The boundary with the area corresponding to the black dot is determined by the sensitivity level of the photosensitive drum. For this reason, the boundary is not clear, and since the area corresponding to the black dot is irradiated with a large area, the area corresponding to the black dot adjacent to the area corresponding to the white dot is A portion of the photosensitive drum is sensitive to light, and the area corresponding to the black dot becomes narrower, making the black dot smaller.

In this way, according to the conventional driving method, white and
When dot images are written in the order of black and white, the shutter remains open or open during the dot writing time, so light irradiates the entire area corresponding to the black dot on the photosensitive drum. As a result, the black dot image becomes chipped and the size of the dot becomes smaller.

[Purpose of the invention]

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a method for driving a liquid crystal element that can accurately represent an image of the shutter part when driving the shutter part of the liquid crystal element in a time-division manner.

[Summary of the invention]

The method for driving a liquid crystal element of the present invention includes arranging a pair of transparent substrates on which a plurality of electrodes are formed to face each other with a two-frequency liquid crystal interposed therebetween.
This is a method of driving a liquid crystal element in which a shutter part made up of opposing electrodes of each substrate and liquid crystal is arranged and formed, and one operation time of the shutter part in the liquid crystal element is N(1, 2...
・) The opening/closing operation period of the shutter section is set by dividing the operation time, and the shutter section is driven by dividing the one operation time into 2N.

In other words, when the shutter section of the liquid crystal element is time-divisionally driven using the two-frequency driving method, the drive is divided into 2N times for the number N of time divisions, and one of the shutter sections is driven in one operation time. This is a method in which the open or closed state is selected in a period of /2N, and the open or closed state is always controlled during the other (2N 1)/2N periods that follow. This allows the liquid crystal element to be operated as a shutter in a time-division manner, and when the liquid crystal element is used as a light infiltration sensor, the length of the light irradiation area due to the movement of the photosensitive drum during the opening operation time of the shutter area can be increased. By shortening the length, the degree of missing dots (shutter images) can be minimized and printing quality can be improved.

[Embodiments of the invention]

An embodiment of the present invention illustrated in the drawings will be described below.

First, seven embodiments of liquid crystal elements to which the driving method of the present invention is applied will be described with reference to FIGS. 4 to 7.

In the figure, reference numeral 11.12 denotes a substrate made of a transparent glass plate, and this substrate 11.12 is arranged opposite to a frame-shaped external sealing material 13.
and is bonded via a linear internal sealing material 14°14. Internal coil material 1 in the gap of the substrate 11.12
4.14 and both ends of the external sealing material 13 are filled with liquid crystal LC, for example, a guest-host effect type liquid crystal.

On the inner surface of one substrate 1, a large number of signal electrodes S are arranged at intervals in the longitudinal direction.

The signal electrode S... consists of a transparent electrode 15 and a metal film 16, and the transparent electrode 15 is attached to the inner surface of the substrate 11,
Two shutter electrodes 17° 17, which are light transmitting parts located inside the internal sealing material 14, and the external sealing material 1.
The terminals 18 of each signal electrode S... are formed so as to be led out alternately on the left and right sides. The metal film 16 is deposited on the surface of the transparent electrode 5 except for the shutter electrode 17.17. Note that 19 is an alignment film formed on the inner surface of the substrate 11.

On the inner surface of the other substrate 12, two strip-shaped common electrodes Cz, C2 are formed along the longitudinal direction. represents each signal electrode S of the substrate 11.
One shutter electrode 17 in . . . , terminal 18 .
. . and the other shutter electrode 17 . . . , terminal 18 .
It is facing the row of... The common electrodes C1 and C2 are composed of a band-shaped transparent electrode 20 deposited on the inner surface of the substrate 12, and a metal lI% 21 deposited on the surface of the transparent electrode 20, and this gold! The portions of the signal electrodes S of the @ film 21 facing the shutter electrodes 17..., 12... are opened, and the portions of the transparent electrode 20 facing these openings in the gold envelope 21 are opened. A large number of shutter electrodes 22 . . . , 22 . Note that 23 is an alignment film formed on the inner surface of the substrate 12.

The shutter electrode 17 of the signal electrode S...
, 17... and each of the common electrodes Cz opposite thereto.
, Cx's shutter electrodes 22..., 22... and the liquid crystal LC form a large number of shutter sections AI..., A2...
・are constructed and arranged in two columns.

Next, an embodiment of the driving method for driving the liquid crystal element described above will be described.

In order to drive the liquid crystal element, in the shutter section A1..., one shutter electrode 17 of the signal electrode S... formed on the substrate 1 and the shutter electrode 22 of the common electrode C1 formed on the substrate 12 are connected. In the meantime, a signal voltage, which will be described later, is applied to cause the liquid crystal LC between both electrodes 17 and 22 to behave and perform opening/closing operations. A signal voltage, which will be described later, is applied between the other shutter electrode 17 and the shutter electrode 22 of the common electrode C2 formed on the substrate 12, and the liquid crystal LC between the two electrodes 17 and 22 is caused to behave and open/close. Basically, a low frequency signal is applied to open the shutter sections AI, A2, and so on, and a high frequency signal is applied to the shutter sections AI to close them.

The drive signals for driving the shutter sections AI and A2 will be explained. In this embodiment, as shown in FIGS. 1 and 2, the shutter section! '1. A.? One operation cycle (one write cycle) TW (for example, 3 ms) is divided into N, that is, divided into two (1/2 TW + '/2 TW) to make the time division number N 2, and further this time division number 2 is 2N. division i.e. 2X
2 = 4 divisions (1/4 TW +1/4 TW +1/4
TW + 1/4 TW ) and supplies a drive signal for each divided period to drive the shutter units AI and A2.

FIG. 1 shows common signals CI and C2 and drive signals applied to signal electrodes S...K individually. CDMz is a common signal applied to one common electrode C1, COM, ? are common signals applied to the other common electrode C2, and these common signals C0M1. C0M2 has the same waveform, but
The phase is shifted by 1/4 TW and the voltage is applied at a period of TW. Further, 5EG1 to 5EG4 are segment signals applied to the signal electrodes S in the same way as the common signal is applied. The segment signal 5EG1 is sent to the shutter section kl, A.
Segment signal 5 is applied when both of 2 are closed.
EG2 is the shutter part AZ, II! Segment signals 8EG and y are applied when both are used as "barrels", and segment signals 8EG and y are applied to shutter section A.
Segment signal 5EG4ri is applied when the shutter section A2 is set to "open" and the shutter section A2 is set to "closed".
, is applied when the shutter section A2 is opened. In addition,
In FIG. 1, only the low frequency component H is shown by a pulse waveform, and the high frequency component H is represented by a vertical line.

Further, r and ``■'' indicate signals that are inverted and applied.

And the common signal COMJ explained so far.

A combination of COM2 and segment electrodes 5EOz to 5EG2 is applied to the liquid crystals of the shutter sections AI and A2 to open and close the shutter sections. Figure 2 shows the shutter parts AJ, A, ? shows the waveform of the signal applied to the

FIG. 2(a) shows the liquid crystal applied signal when the segment signal 5EG1 is applied to the signal electrode S1. At this time, in the shutter section A1, 1/4T of the operating frequency qTW
A closing operation signal to lay down the liquid crystal is applied during the period W, a signal to keep the liquid crystal in the lying state is applied during the following 1/4 TW period, and then the remaining 1/4 TW and 1/4
A signal for not operating the liquid crystal, specifically a signal for closing the shutter portion, is applied in each period of TW. In the shutter section A2, a signal having the same waveform as the signal applied to the liquid crystal of the shutter section A1 is applied to the liquid crystal with a period shifted by 1/4 TW. That is, here, the shutter parts kl, I',
Set both 2 to "closed".

FIG. 2(b) shows the liquid crystal applied signal when the segment signal 5EG2 is applied to the signal 1x, the pole S, . . . .

At this time, in the shutter section A2, an open start signal is applied to make the liquid crystal stand up between the 1/'4 TW,
Apply a signal to keep the liquid crystal in an upright position for a period of
Furthermore, a signal that does not operate the liquid crystal is applied during the remaining period of 1/4 TW + 1/4 TW. The shutter section A2 applies a signal equivalent to that of the shutter section AI with a period shifted by 1/4 TW. That is, here, the Nyatta part fi
l, A,? Set both to "open".

Figure 2 (C1 is the signal electrode S...K common signal 5EO
It shows the liquid crystal application signal when 3 is applied. At this time,
The signal application state in the shutter section A1 is shown in FIG.
The signal application state in the shutter part A2 is the same as in the case of the shutter part A2 in FIG. 2(a), and the period is shifted by 1/4 TW with respect to the shutter part AJI. There is. That is, here, the shutter section AI is "open" and the shutter section A2 is "closed."

Fig. 2(d) shows that the common signal 8EG is connected to the signal electrode S...
It shows the liquid crystal application signal when 4 is applied. At this time,
The signal application state in the shutter section A1 is shown in Fig. 2(a).
The signal application state in the shutter part A2 is the same as in the case of the shutter part A2 in FIG. 2(b).
/4 The period is off by TW. That is, here, the shutter-to-person 1 is "closed" and the shutter section A2 is "open".

In this way, a selection signal is supplied to the shutter units AI and A2 during a period of 1/4 TW of one operation cycle TW, a signal to maintain that state is supplied to the subsequent 1/4 TW, and further During the remaining period, it is driven by supplying a control signal to either the open or closed state. That is, while the shutter parts AI and AJ are apparently driven at an upper 174 density, they are substantially driven at 1/2 duty, and as a result, a shutter image can be formed within a time corresponding to the time division of the shutter operation time. can.

Therefore, when the present invention is applied to a liquid crystal element provided in an optical writing head of an optical writing printer, a dot image can be accurately written on a photosensitive drum by the liquid crystal element. FIG. 3 schematically shows the state of optical writing on the surface of the photosensitive drum by the shutter section of the liquid crystal element when the liquid crystal element is driven by the driving method of the present invention. The manner in which optical writing is represented in FIG. 3 is the same as that in FIG. 9. First and second dot writing portions D1 on the surface of the photosensitive drum 6. At D2, a dot image is formed as follows. That is, point P of the photosensitive drum 5 (shutter to person 1
) moves up to 21 points during one writing period +'ll. At the same time, the shutter section A1 is 1/
Since it is in the open state for a time of 2'l'W, the photosensitive drum is irradiated with light for 1/2 of the moving distance of the photosensitive drum. The amount of light irradiated onto the photosensitive drum at this time is shown by the two-dot chain line in the figure. Since the shutter section A1 is closed during the subsequent 1/2 TW, the amount of light irradiated onto the photosensitive drum during ITW is represented by a trapezoidal line as shown by the solid line in the figure. Therefore, the portion irradiated with a light amount greater than the sensitivity level of the photosensitive drum, ie, the dot writing portion D2, corresponds to a white dot. The dot writing part DJ written before the dot writing part D2 corresponding to this white dot
If it also corresponds to white, the photosensitive drum is irradiated with a light beam with the amount of light shown by the broken line in the figure, so the dot g-containing part D1
．． D2 is continuously given a light amount that is higher than the sensitive level.

Here, if the write dot D3 following the write dot D2 corresponds to a black dot, the shutter counter is closed during the write period TW, so no light is irradiated onto the photosensitive drum during this period. Subsequently, when writing dot D4 corresponds to a white dot, the photosensitive drum is irradiated with a light beam having the amount of light indicated by the dashed line in the figure, similarly to the writing dot D2 described above.

Therefore, the area of the write dot D3 has a light intensity lower than the sensitivity level of the photosensitive drum, so the electric charge is not discharged.
Corresponds to the black dot. Since the light intensity in the write driver (DJ) area is higher than the sensitive level, charges are discharged and the area corresponds to a white dot.

In this way, it is possible to provide a portion where no light is irradiated in the region of the writing dot D3 corresponding to the black dot, and also to form a white dot D3 set before and after the writing dot D30 corresponding to the black dot. By irradiating light to do this, it is possible to increase the gradient of the light intensity of the light beam irradiated to the region of the write dot D3 corresponding to the black dot, so that the difference between the write dot D3 and the write dot D, ? , the boundary between DJ and DJ becomes clear.

Therefore, in the third dot writing section D3, a dot image having a predetermined size can be accurately formed in the same way as in other parts without causing any chipping of the dot image.

Therefore, high quality printing without missing black dots can be performed.

In addition, in the above-mentioned embodiment, the case where one operation cycle of the shutter section of the liquid crystal element is divided into two and the number of time divisions is 2 will be explained.
The present invention can be applied with arbitrary settings depending on the number of bridges.

〔Effect of the invention〕

As explained above, according to the method for driving a liquid crystal element of the present invention, it is possible to accurately form a shutter image in a predetermined size by the opening/closing operation of the shutter section of the liquid crystal element. High quality printing can be achieved by applying this method when driving.

[Brief explanation of the drawing]

Figures 1 to 3 show an embodiment of the present invention, Figure 1 is a waveform diagram showing the common signal and segment signal applied to the liquid crystal element, and Figure 2-11 is a waveform diagram showing the common signal and segment signal applied to the liquid crystal of the liquid crystal element. A waveform diagram showing signals, FIG. 3 is an enlarged cross-sectional view showing the state of optical writing on a photosensitive drum by a liquid crystal element, FIG. 7 is a plan view showing an enlarged electrode, and FIGS. 8 and 9 are conventional The method of driving the liquid crystal element is shown in Figure 8 - ← is a waveform diagram showing the drive signal, Figure 9 is an explanatory diagram showing the state of optical writing on the photosensitive drum by the liquid crystal element, and Figure 10 is the light of the optical writing printer. FIG. 3 is an explanatory diagram showing a write head. 11.12...Substrate, LC...Liquid crystal, S...Signal electrode, CI, C2...Common electrode, kl, 2...Shutter electrode. Applicant's Representative Patent Attorney Takeshi Suzue Industry 1 Diagram (Shipudda Decoration A2) N2 Diagram

Claims (3)

[Claims] (1) A liquid crystal element in which a pair of transparent substrates on which a plurality of electrodes are formed are arranged facing each other with a dual-frequency liquid crystal interposed therebetween, and a shutter section formed by the opposing electrodes of each substrate and the liquid crystal is arranged. The driving method includes dividing one operation time of the shutter section in the liquid crystal element into N (2, 3...) to set the opening/closing operation cycle of the shutter section,
A method for driving a liquid crystal element, characterized in that the shutter section is driven by dividing the operating time into 2N parts. (2) 1 operation period of the liquid crystal element for the shutter section
2. The method of driving a liquid crystal element according to claim 1, wherein the selection signal is supplied only during a period of /2N, and a signal for controlling either a shutter open or shutter closed state is supplied during other periods. (3) The method for driving a liquid crystal element according to claim 1, wherein the selection period of the shutter section is varied by 1/2N.