JPS61158315A - Driving method of liquid crystal - Google Patents

Abstract

PURPOSE:To expand a temperature range in which a liquid crystal optical shutter can be exactly operated and to increase the quantity of transmitted light in case of time division driving by adopting a signal including a signal having frequency higher than a specific frequency and a non-signal as a driving waveform setting up closed status in a selection period. CONSTITUTION:Microshutters 15a-18b to which recording signals 19, 20 and a selecting signal are impressed input a ON-ON driving signal 21 and an ON- OFF driving signal 22 which are superposed signals of both the signals as shown in Fig.C. Inthe period 21 of a selecting period TL3 in the first half Tw/2, the ON-ON driving signal 21 includes a low frequency signal fL3 and the OFF-OFF driving signal 22 includes a non-signal (O). In the period of TL3, an ON-OFF driving signal includes a low frequency signal of fL3 and an OFF-ON driving signal includes a non-signal period. Thus, the insertion of the low frequency signal of fL3 in the selecting period Tw/2 of ON driving makes it possible to orientate liquid crystal molecules more strongly to the electric field direction and strengthen the ON status moreover.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for driving a liquid crystal, and particularly to a method for driving a liquid crystal in a time division manner. [Prior art] A recording device using a liquid crystal light shutter uses a control circuit to open and close a large number of microshutters provided in the liquid crystal light shutter, and performs optical writing on a recording medium by blocking or transmitting light from a light source. It is a device. In such a recording device, a high-speed response of the liquid crystal is required.2 Normally, a liquid crystal whose dielectric anisotropy is inverted depending on the frequency of the electric field is used, and a frequency higher than the frequency at which the dielectric anisotropy becomes zero (hereinafter referred to as fc) is used. It is driven by two frequencies: (hereinafter referred to as fH) and a low frequency (hereinafter referred to as f). In such a liquid crystal optical shutter, recording is performed at a density of about 10 dots per 1 mm2, and for example, in the case of A4 size, the density is about 3.0 dots per line.
00 (Requires 11 micro-shutters. Therefore, in order to prevent an increase in the number of wiring lines and mounting area, liquid crystal optical shutters are normally driven by time-division driving. This time-division driving is common to liquid crystal optical shutters. The electrode and the signal electrode are arranged perpendicularly to each other, and a micro-shutter is formed in the common part of the two electrodes, and the recording signal is input to the signal electrode, and the time-divided selection signal is input to the common electrode to drive the shutter. However, in such time-division driving (1, for example, 2-time division driving), the light can only be transmitted for half the time during the - writing period Tw, and in n-time division driving, the transmission time becomes even shorter, and the light is not transmitted to the irradiated object. Therefore, the selected period Tu of one writing cycle Tw is caused by the 1 selection signal.
Set the micro shutter open or close to +/n, and -
During the remaining period of the write cycle Tw (hereinafter referred to as a non-selection period) (1-1/n), T and JJ are driven so as to substantially maintain the set state. for example. In two-time division driving, the phases of the fH times signal, fL times signal, fH times signal, and fL times signal differ by 180 degrees as shown in Fig. 2(a).
6. Create a drive pattern signal in which the *fH signal and *fL signal are mixed during the writing cycle, apply this signal to the common electrode, and then apply the four drive pattern signals 1 to 4 shown in FIG. By selecting one of these signals and applying them to the signal electrodes, four types of superimposed signals 5 to 8 shown in FIG. Furthermore, the signal given to the other common electrode is T.
Since signals with different phases of w/2 are given, the micro shutter receives a superimposed signal similar to the signal shown in <c) in the same figure.
/2 phases are applied to open and close the corresponding micro shutters. The light transmittance characteristics of the microshutter when these superimposed signals 5 to 8 are applied are shown in FIG. 4(d). The light transmittance characteristic 9 is a characteristic based on the superimposed signal 5 created when the pattern signal 1 is applied to the signal electrode and the pattern signal shown in the same figure (al) is applied to the common electrode in order to open the paired micro-shutter. In light transmittance characteristic 10, pattern signal 2 is applied to the pair of signal electrodes to open one of the microshutters and close the other, and the pattern signal 2 is applied to the common electrode (
This is the characteristic of the superimposed signal 6 when the pattern signal of al is applied. Similarly, for light transmittance characteristics 11 and 12, one of the paired micro shutters is closed in the opposite manner as described above. This is the characteristic due to the superimposed signal 7.8 when the pattern signal 3.4 for opening the mountain man or for closing both the micro shutters is applied. here. The signal shown in Fig. 2 (C) [fL+rH] is fL times the signal f
, indicates a superimposed signal of four signals, and the -(fL+*fM) signal indicates a superposed signal of fL, signal and IfH signal. [0] indicates no signal. By driving the liquid crystal optical shutter in this way, in the case of n time division driving, the non-selection period (1-1/n) T,
The selected microshape can also be kept open during the last period of the cycle of - writing T,
When the microshutter is opened in response to the L times signal and the hysteresis effect peculiar to the liquid crystal is cut out, the liquid crystal light shutter can be opened and closed in the same way as statically driven. [Problems with the prior art] However, in the time-division driving method of the liquid crystal optical shutter as described above, even if the hysteresis effect of the liquid crystal can be cut, the appropriate temperature range is as narrow as 2 to 3 degrees. Due to quality difference. Since the appropriate temperature differs somewhat, it was necessary to set a different temperature for each recording device. In addition, a liquid crystal light shutter using a CH (guest-host) type liquid crystal agent has the disadvantage that the amount of transmitted light is small when the shutter is open. [Object of the Invention] In view of the above-mentioned conventional drawbacks, the present invention provides a driving method for a liquid crystal light shutter that expands the temperature range in which the liquid crystal light shutter operates accurately and increases the amount of transmitted light when the liquid crystal light shutter is time-divisionally driven. The purpose is to provide law. [Summary of the Invention] In order to achieve the above object, the present invention sets the open/closed state of the liquid crystal in 9 time-divided selection periods when time-divisionally driving a liquid crystal whose dielectric anisotropy is reversed at a specific driving frequency. In a driving method that provides a driving waveform that substantially continues the state set in the immediately preceding selection period during a non-selection period, the driving waveform that sets the open state during the selection period is higher than the specific frequency. The drive waveform includes a low frequency signal, a superimposed signal of a frequency signal lower than the specific frequency, and a frequency signal higher than the specific frequency, and the drive waveform that sets the closed state in the selected period is a frequency signal higher than the specific frequency. The signal is characterized in that it is a signal that includes a signal. [Embodiments of the Invention] Examples of the present invention will be described in detail below with reference to the drawings. This embodiment uses two-time division driving, and FIG. 3 shows a partial configuration of the liquid crystal optical shutter used in the present invention. In the figure, common electrodes 13, 14 and signal electrodes 15 to 18 are provided perpendicularly to each other, and the common portions of the two electrodes are micro shutters 15a, 15b to 18a, which are made of transparent electrodes.
18b is provided to input a recording signal to the signal electrodes 15 to 18, and input a selection signal to the common type +i13.14. FIG. 1(a) shows recording signals input to the signal electrodes 15 to 18, and FIG. 1(b) shows a selection signal input to the common electrode 13. Further, the common electrode 14 is provided with a signal having a phase different from that of the signal provided to the common electrode 13 by T, . . . /2. Also, among the recording signals input to the signal electrodes 15 to 18, the on-on recording signal 19 indicates the off-off recording signal 20, and the on-off and off-on recording signals are It is a combination of the first half and the second half, which is not shown in Figure 1, but is composed of the same combination as the waveform in 2.3 of Figure 2 (bl).In the same figure, the signal fL
2゜TL3 represents a frequency lower than the crossover frequency like f and the signal, but in this embodiment, the predetermined period (TL+,
The fL flaw signal uses signals of different frequencies so that an integer number of waveforms can fit in TL3). Therefore, in the microshafts 15a to 18b to which these recording signals 19, 20 and selection signals are applied,
As shown in C1, an on-on drive signal 21 and an off-off drive signal 22, which are superimposed signals of both signals, are provided. What is this on-on drive signal 21?
The conventional on-on drive signal shown in 5. Unlike the off-off drive signal 8, a low frequency signal of TL3 is included in the first half Tw/2 selection period TL, period 21 of 3, and the off-off drive signal 22 contains [0] Contains no signal. Further, the on-off drive signal (not shown) includes a low frequency signal of period f-L3 of T and 3, and the off-on drive signal includes a no-signal period. Inserting the low frequency signal of TL3 into the selection period of Tw/2 of the on drive in this way makes the liquid crystal molecules stronger (orientate in the direction of the electric field) and strengthens the on tendency. As shown in the characteristics, the light transmittance in Figure 1 (d) is
The on-on response characteristics 23 and the on-off response characteristics 24 of the micro shutters 15a to 18b improve the light transmittance during TL3. That is, by using the (fL.+rM) signal of the on-off drive signal 21, the light transmittance that has decreased to a certain level can be restored to the original level, and the amount of on-light can be further increased. In addition, by inserting a no signal of [0] in place of the fH multiplied signal during the off-drive selection period, the dielectric relaxation that shifts the liquid crystal to on is weakened, and the transition to natural relaxation occurs, resulting in an off-response. However, in reality, as shown in the same figure (dl as off-on response characteristic 25 and off-off response characteristic 26), there is not only no major change but also the balance between the two characteristics 25 and 26. As described above, by using a waveform in which the low frequency of TL3 is inserted into a part of period TL3 of one selection period TLIJ/2, the f,3 signal is , a stronger ON effect can be obtained, and the so-called high frequency hysteresis effect can be prevented by the no signal of [0] in the OFF drive signal.Therefore, in a liquid crystal optical shutter that operates repeatedly, it is possible to achieve a more efficient opening/closing effect. Drive can be performed.Also,
By reducing high-frequency components and increasing low-frequency components, temperature characteristics are significantly improved and proper operation can be performed over a wide temperature range. Figures 4(a) and (b) show the results; 27.31 is the on-on drive characteristic;
28.32 is on-off drive characteristic, 29.33 is off-
The on-drive characteristic and 30.34 indicate the off-off drive characteristic, and the amount of light transmitted through the micro-shutter by the conventional drive signal (Figure 4(a)) and the amount of transmitted light by the drive signal of the present invention (Figure 4(b)) are shown. ) shows a comparison with respect to temperature. In other words, the temperature range in which the micro-shutter as described above can be efficiently opened and closed is 45°C as shown in Figure (a).
Compared to the narrow range of ℃ to 48℃, the present invention has a wide appropriate temperature range of 40℃ to 50℃ as shown in the same figure (bl). Next, another embodiment according to the present invention will be described below using FIG. 5. Compared to FIG. 1, this embodiment shows that fL3 is It is similar in that a period for inserting a signal is provided, but T1.
The difference is that the fHv signal is inserted into the lv period. This f
The Hv signal is shown enlarged in FIG. 6 (bl). Also, the fH multiplied signal of the off-off recording signal 35 in FIG. 5(a) is partially enlarged and shown in the same figure (81).
The waveform diagram obtained by combining the V signal and the V signal becomes the waveform shown in FIG. 6(C). That is, when the drive signal 35 applied to the signal electrode shown in FIG. (The waveform of C1 is (f, -f
,,) is an enlarged version of the signal. This signal has a smaller duty than the conventional (rL"rs) signal, and therefore becomes a superimposed signal with a low effective value. Also, FIG.
The on-on drive signal 37 is created by applying the fL times the on-on drive signal 36 of FIG. The fN-) signal is also a similar signal. By inserting the fMV signal into the non-selection period in this way, the on-duration is slightly weakened in the on-drive.
In off-drive, it works to prevent it from opening too much under high temperatures. This works to somewhat delay the opening operation during the period TL3, as shown in FIG. 4(d). As described above, by adding the fL] signal to the 7.3 period of one selection period and providing the selection signal including the fH9 signal to the non-selection period in order to best match the dielectric characteristics and temperature characteristics of the liquid crystal, a wide range of It is possible to provide time-division driving of a liquid crystal optical shutter with good repeatability over a range of degrees. Furthermore, in this case as well, due to the fL3 signal effect added to the T,3 period, the on-characteristics can be significantly improved without deteriorating the off-characteristics, and a bright liquid crystal light shutter can be realized. Additionally, the operating temperature becomes less sensitive to changes in the liquid crystal material, resulting in greater flexibility. [Effects of the Invention] As explained in detail above, according to the present invention, the proper operating temperature range for accurately controlling the liquid crystal light shutter is lower than that of the conventional 2~
The beam width becomes wider than 3 degrees, and the amount of light irradiated onto the recording medium can be increased. Furthermore, since the operating temperature range has been widened, there is increased flexibility in changing the liquid crystal material, etc.

[Brief explanation of drawings]

Figures 1+8) to (C) are signal waveform diagrams according to the driving method of the present invention, and (d) is a light transmission characteristic diagram according to the driving method of the present invention. FIGS. 2(a) to 2(C) are signal waveform diagrams according to the conventional driving method. (d> is a light transmission characteristic diagram using the conventional driving method. Figure 3 is a configuration diagram showing a part of the liquid crystal optical shutter. Figures 4 (a) and (b) are temperature changes according to the present invention and the conventional driving method. FIG. 5 (al to (C) are signal waveform diagrams of other embodiments of the present invention, (d) is a light transmission characteristic diagram of the present invention. is a waveform diagram for explaining the F HX signal. 13.14... Common electrode. 15-18... Signal electrode. 15a, 15b-18a, 18b... Micro shutter. 19.20.35 .36... Recording signal. 21.22, 37.38... Drive signal. 23-26. 39-42... Response characteristics. 27-30. 31-34... Driving characteristics. Figure 1 Figure 2 Figure 2 (C) Figure 2 Figure 3 Figure 1 1 r Figure 4 Temperature: 11'C] Figure 5

Claims (1)

[Claims] When time-divisionally driving a liquid crystal whose dielectric anisotropy is reversed at a specific drive frequency, a drive waveform is applied to set the open/closed state of the liquid crystal during the time-divided selection period, and the non-selection period is set to the immediately previous selection period. In the driving method that provides a driving waveform that substantially continues the opened state, the driving waveform that sets the open state during the selection period is a frequency signal lower than the specific frequency;
A drive waveform that includes a superimposed signal of a frequency signal lower than the specific frequency and a frequency signal higher than the specific frequency, and the drive waveform that sets the closed state in the selected period is a signal that includes a frequency signal higher than the specific frequency and no signal. A liquid crystal driving method characterized by: