JPH0833533B2 - Driving method for liquid crystal optical element - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for driving a liquid crystal optical element using a liquid crystal for dual frequency driving.

[Prior Art and Problems Thereof] In recent years, optical devices that use liquid crystals to control the light transmission state have been widely used. Among these optical devices, a liquid crystal shutter that switches between a light blocking state and a light transmitting state at a high speed is used as a light control element of an electrophotographic printer. In this type of conventional liquid crystal shutter,
Since a high shutter speed is required, the liquid crystal element of the electric field control birefringence mode is used to drive at two frequencies. That is, as shown in FIGS. 13A and 13B, the high frequency electric field f _H and the low frequency electric field f _L are combined to control the on / off of the liquid crystal element. In the case of dynamically driving a plurality of shutters, one writing period is composed of a selection period and a non-selection period, and the selection period is specified by applying a high frequency electric field f _H and a low frequency electric field f _L for each 1/2 cycle. , The non-selection period is specified by applying the superposed electric field f _H / f _L and the low-frequency electric field f _L every 1/2 cycle.

As described above, in the conventional liquid crystal optical element driving method, the shutter is turned on only in the selection period in one writing period (ON period), so that the amount of light passing through the shutter is small and the shutter speed is increased. Is a problem in doing.

[Object of the Invention] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of driving a liquid crystal optical element capable of obtaining a sufficient amount of transmitted light in a shutter-on state and capable of high-speed shutter operation. .

SUMMARY OF THE INVENTION The present invention relates to a driving method for controlling a light transmission state of a liquid crystal optical element having a plurality of optical shutters of an electric field control birefringence mode using a liquid crystal for dual frequency driving, wherein the liquid crystal shutter is optically controlled. 1 sequentially controls the light transmission state of a plurality of optical shutters by operating voltage for operating in a state where 1 transmits.
In the repeating period, the voltage is applied between the opposing electrodes of the liquid crystal shutter only for a half period or a period shorter than 1/2 of the selection period assigned to control one optical shutter. It is a feature.

[Examples of the Invention] Hereinafter, a case where the present invention is applied to a liquid crystal shutter will be described. First, the structure of the liquid crystal shutter will be described with reference to FIGS. 1 and 2. In FIG. 2, 11 and 12 are a pair of substrates made of transparent glass plates, respectively.
11 and 12 are adhered to each other by a horizontally long frame-shaped sealing material 13 with a constant interval. Then, between the substrates 11 and 12, a two-frequency driving liquid crystal 16 that is sandwiched between the electrodes 14a and 14b and the alignment films 15a and 15b to form an optical shutter is sealed. Polarizing plates 17a and 17b are attached to the outer surfaces of the substrates 11 and 12, respectively.

On the inner surface of the one substrate 11 (referred to as a signal electrode substrate), as shown in FIG. 1, a large number of signal electrodes 18a ..., 18b. Strip-shaped terminals 19 ... Are alternately led out from one side and the other side of the signal electrode substrate 11 from 18a. The signal electrodes 18a, 18b, and the terminals 19 are integrally formed of a transparent conductive material such as indium oxide, and the shutter portions S ₁ ..., S ₂ of the signal electrodes 18a, 18b.
A metal film 20 of chromium or the like is deposited on the portion except the portion corresponding to ... And on the terminal 19. One of the signal electrodes 18a ... Is 1/2 of the other signal electrode 18b.
The shutter portions S ₁ ..., S ₂ ... Are arranged in two rows with a shift of 1/2 pitch.

On the inner surface of the other substrate 12 (hereinafter referred to as the common electrode substrate), a pair of strip-shaped common electrodes 21a, 21b facing the respective signal electrodes 18a, 18b, ... Of the signal electrode substrate 11 are provided. It is formed of a transparent conductive material such as indium oxide in parallel along the longitudinal direction with a minute interval, and a metal film such as chromium is formed on these common electrodes 21a and 21b except for the portions corresponding to the shutter portions S ₁ ..., S ₂ ... Twenty-two are being worn. The metal film 20 includes signal electrodes 18a ..., 18b ... And terminals 19
To reduce the electric resistance of, also, the metal film 22 is provided to regulate the order to reduce the electrical resistance of the common electrodes 21a, 21b, the shutter unit S ₁ ..., the light transmission area of S ₂ ... It is a thing.

Further, a light blocking member 23 is provided on the outer surface of the polarizing plate 17b laminated on the common electrode substrate 12 on the light emitting side by, for example, printing means. This light shielding member 23 is provided with a shutter portion S
, S ₂ are provided on the outer surface of the polarizing plate 17b so as to cover the sealing material 13 except for the portion facing the array area A of ₁ . As described above, the common electrode 21a and the signal electrodes 18a, 18a, ...
The shutter unit S _1, S ₁ consisting, ... and common electrode 21b and the signal electrode 18b, 18b, the shutter unit S _2, S ₂ consisting of ..., ... it is formed.

FIG. 3 shows the relationship between the orientation of liquid crystal molecules (rubbing direction) of the liquid crystal shutter configured as described above and the arrangement of the polarizing plates 17a and 17b. In FIG. 3, 31 is the liquid crystal molecule alignment direction, 32 is the transmission axis (or absorption axis) of the upper polarizing plate 17a, and 33 is the transmission axis (or absorption axis) of the lower polarizing plate 17b. In other words, 2
The frequency drive liquid crystal 16 is enclosed, and the polarization axis (transmission axis or absorption axis) of one of the polarizing plates 17a or 17b is inclined by 45 ° with respect to the liquid crystal molecule alignment direction (rubbing direction), and the upper and lower polarizing plates 17a and 17b are The polarization axes are orthogonal to each other. The method of this arrangement is similar to the electric field control birefringence mode.

Therefore, the transmitted light intensity I in the liquid crystal shutter is
Is calculated by the following equation (1).

I = I ₀ sin ² 2θ ・ sin ² (π ・ Δnd / λ) (1) where I ₀ : intensity of light determined by the transmittance of parallel polarizing plates θ: optical axis at initial alignment and polarizing plate Formed angle Δn: Birefringence index depending on the angle φ formed by the liquid crystal optical axis with the normal direction of the substrate surface λ: Wavelength of incident light d: Cell thickness The value of the birefringence index Δn changes depending on φ. Can be calculated by the following equation (2) if the refractive indices n ₁₁ and n _I of the liquid crystal are known.

n ₀ = n _I Δn = n _e −n _{0 Further} , FIG. 4 shows the dielectric anisotropy Δε when the liquid crystal 16 for driving two frequencies having the characteristics shown in the following Table 1 is used, and the frequency dependence is 23 ° C. and 35 ° C. , 40 ° C, 45 ° C, 50 ° C, 55 ° C.

The dual frequency driving liquid crystal 16 has a dielectric anisotropy Δε of “0”.
Which has a positive dielectric anisotropy for an electric field f _{L at a} frequency lower than the crossover frequency fc and a negative dielectric anisotropy for an electric field f _{H at a} frequency higher than the crossover frequency fc. is there. In this case, the crossover frequency gradually moves to the higher side as the temperature rises.

Therefore, the liquid crystal shutter configured as described above is driven by a signal waveform such that the shutter opens for a selection period or more during the ON operation. For example, the common signal shown in FIG.
It is driven by C1 and segment signals S1 to S4. The common signal C1 is intended for the shutter unit S _1, a shutter unit
The common signal for S ₂ is generated with a delay of half of one writing period from the case of FIG. In this case, the segment signals S1, S2 are ON signal to the shutter unit S _1, S3, S4 are OFF signals, also, the segment signal to the shutter unit S ₂
S1 and S3 are ON signals, and S2 and S4 are OFF signals. In FIG. 5 above, T1 is a selection period (1 msec), T2 is a non-selection period (1 ms).
ec), T3 is the first f _H application period, T4 is the second f _H application period,
T5 is a non-electric field application period, T6 is a holding voltage application period set in the remaining period of the selection period T1, T7 is an f _L application period provided at the end of one writing period for shutter-off, and T8 is a non-selection period. It is the remaining period in T2. In this case, the T6 period in the selection period T1 and the T8 period in the non-selection period T2 are periods in which a holding voltage is applied to keep the shutter-on or shutter-off state at that time, and the T6 period is the non-selection period. The time width is set equal to the T7 period in T2.

Then, the common signal C1 gives the high frequency voltage f _H in the selection period T1, but inverts its phase in the T5 period,
In the non-selection period T2, the superimposed wave voltage f _H / f
_L is applied and the low frequency voltage f _L is applied during the T7 period. in this case,
The superposed wave voltage f _H / f _L is obtained by alternately dividing the T8 period into eight and applying the high frequency voltage f _H. Then, the shutter parts S ₁ , S ₂
The segment signal S1 for turning on the transistor is applied with the low-frequency voltage f _L during the periods T6 and T7, and the high-frequency voltage during the other periods.
give f _H. On the shutter unit S _1, segment signal S2 for turning off the operation of the S ₂ gives the low frequency voltage f _L to the entire period of T6 period and non-selection period T2 in the selection period T1, other during the selection period T1 The high frequency voltage f _H is applied during the period. The segment signal S3 for turning on operation off, the S ₂ the shutter unit S ₁ gives the high-frequency voltage f _H to T8 period at low frequency voltage f _L, the non-selection period T2 to the entire period of the selection period T1 , Low frequency voltage f _L is applied during T7 period. In addition, the segment signal S for turning off the shutter sections S ₁ and S ₂
4 applies the low frequency voltage f _L to the entire period of the selection period T1 and the non-selection period T2.

Further, in FIG. 5, C1-S1, C1-S2, C1-S3, C1-S4
Shows a composite waveform of the common signal C1 and the segment signals S1 to S4. As shown in this composite waveform,
In the period T8 within the non-selection period T2, the holding electric field in which the superposed electric field in which the high frequency electric field f _H is superposed on the low frequency electric field f _L and the non-electric field are repeated at regular intervals is applied to the two-frequency driving liquid crystal cell 16.

FIG. 6 shows a liquid crystal shutter configured as shown in FIGS. 1 and 2 in which the liquid crystal for dual frequency driving shown in Table 1 is enclosed in a cell having a thickness of 4.36 μm and shown in FIG. The shutter characteristics at each temperature of 55 ° C, 50 ° C, 45 ° C, and 40 ° C when the signal waveform is continuously given, the horizontal axis shows time (msec), and the vertical axis shows transmitted light intensity (arbitrary unit). It is shown. Note that this shutter characteristic is the same as T4 during the T3 period.
This is the case when a period is provided and the high frequency electric field f _H is continuously applied for 0.6 msec, a fluorescent lamp having an emission peak at 543 nm is used as a light source, the high frequency electric field f _H is 200 KHz, and the T7 period is 0.4 msec. It is set and measured. 5th above
In the liquid crystal drive signal waveform shown in the figure, since the holding electric field consisting of the superimposed electric field or repetition of the superimposed electric field and no electric field is applied in the T6 period and the subsequent T8 period, the ON state in the selection period T1 is within the non-selection period T2 It has spread to the T8 period.
Then, in the last T7 period of one writing period, the low-frequency electric field f _L is applied and the shutter is turned off to complete one shutter operation, but the shutter characteristic changes depending on the temperature at that time.

That is, at the temperature of 55 ° C. shown in FIG. 6 (a), the liquid crystal molecules to which the high frequency electric field f _H is initially applied pass the tilt angle corresponding to the first peak where the transmitted light becomes maximum, Here, the first maximum value of the transmission intensity appears. Next, when a superposed electric field f _H / f _L is applied, in the case of a temperature of 55 ° C,
Since the force of tilting the liquid crystal molecules by Δε _H | is smaller than the force of standing the liquid crystal molecules by | Δε _L |
The influence of f _L appears strongly, the liquid crystal molecules start to stand up slowly,
Pass through the above angle of inclination. Here, the second maximum value of the transmitted light intensity appears. After that, the liquid crystal molecules rise slowly, and finally when the low-frequency electric field f _L is applied, the liquid crystal molecules rapidly rise and the transmitted light intensity also sharply decreases.

In the case of the temperature of 50 ° C. shown in FIG. 6 (b), it is almost the same as the case of FIG. 6 (a), but the difference between the force due to | Δε _H | and the force due to | Δε _L | becomes small. Therefore, the influence of the low-frequency electric field f _L is reduced, and the movement of the liquid crystal molecules due to the application of the superposed electric field f _H / f _L is slower. Therefore, until the low-frequency electric field f _L is applied, the transmitted light intensity is slightly reduced, and good shutter characteristics can be obtained.

In the case of the temperature of 45 ° C. shown in FIG. 6 (c), the response speed becomes slow due to the decrease in temperature, and therefore the inclination angle is reached just before the end of the high frequency electric field f _H. At this temperature | Δε _H
Since the force due to | and the force due to | Δε _L | are substantially equal to each other, the tilting speed of the liquid crystal molecules becomes extremely slow, and the peak of transmitted light intensity becomes flat. However, in this case, an unstable state may occur in which the transmitted light intensity fluctuates over time.

In the case of the temperature of 40 ° C. shown in FIG. 6 (d), | Δε _H
The force due to | becomes larger than the force due to | Δε _L |, and the average high-frequency electric field f _H is applied for a longer time, so the high-frequency hysteresis effect becomes greater. For this reason, the way the liquid crystal molecules stand when a low frequency is applied becomes different, and the behavior of the liquid crystal molecules does not operate as in (a) to (c) above. In addition, a portion that does not operate normally, that is, a domain is generated by the application of the electric field, and the transmitted light intensity is reduced. Therefore, when continuously applying the high frequency electric field f _H , it is desirable to set the operating temperature to about 50 ° C.

FIG. 7 shows T3 = T4 = 0.25 msec, T5 = 0.1 msec, T6 = T7 = 0.4 msec in the liquid crystal drive signal waveform shown in FIG.
In the case of, the shutter characteristics at respective temperatures of 55 ° C., 50 ° C., 45 ° C., and 40 ° C. when the ON signal (C1-S1 signal) is continuously given are shown. In this case, the transmitted light intensity did not drop even at a temperature of 40 ° C, and no unstable state that fluctuated with time was observed. High frequency electric field at this time
The total application time of f _H is 0.5 msec, which is preferably half the selection time. Therefore, by interposing the T5 period in which there is no electric field between the T3 and T4 periods, the alignment direction of the liquid crystal molecules becomes uniform, the temperature characteristics are improved, and the stable shutter opening / closing operation can be performed.

Next, let us examine the responsiveness to the length of the T6 and T7 periods. Fix T3 = T4 = 0.25msec, and set T6 = T7 to “0.1”,
"0.2", "0.3", "0.4" msec (At this time, T5 = "0.
4 ”,“ 0.3 ”,“ 0.2 ”,“ 0.1 ”msec) and measure the shutter characteristics. FIG. 7 shows the shutter characteristics when T6 = T7 = 0.4 msec.

Then, at T6 = T7 = 0.2 msec, when continuously turned on, at temperatures of 55 ° C., 50 ° C., and 45 ° C., as shown in FIG.
The characteristics as shown in (c) are obtained. At 45 ° C. shown in FIG. 8 (c), the liquid crystal hardly responded, and the brightness was constant. When T6 = T7 = 0.1 msec, although not shown in the figure, the state already shown in FIG. 8 (c) is reached at 50 ° C. However, as shown in Fig. 8 (d), 45 ° C for one ON signal when OFF is continuous.
But respond.

Further, at T6 = T7 = 0.3 msec, the same responsiveness as in FIG. 7 was exhibited.

As described above, the length of the T6 and T7 periods contributes to the stability of the temperature characteristics, and even if it is used while adjusting the temperature, the length is 20% or more of the T1 and T2 periods. is necessary. However, if it is too long, the application time of the high-frequency electric field f _H inevitably becomes short, and the amount of transmitted light becomes small. Therefore, it is desirable to set it to half the period of T1, T2.

A high-frequency electric field f _H is applied when the ON operation is performed. The length of the T3 period at this time was examined, and the following results were obtained. Total f _H application time during T3 + T4 period is 0.5 mse
c, T5 = 0.1 msec, T6 = T7 = 0.4 msec, and the ratio between the T3 and T4 periods was changed as shown in Table 2 below.

FIG. 9 shows the response characteristic in the case of “1” in Table 2 above. In this case, the shoulder is raised before the maximum transmitted light intensity is obtained, and the apparent responsiveness deteriorates. At this time, T5 = 0.1 msec, and the high-frequency electric field f _H is applied again after that, so that the transmitted light intensity increases. However, T5 = 0.2msec, T3 = 0.1msec, T4 = 0.4msec, T1 = T7
= 0.4 msec, when the T5 period is long and the T3 period is short until the second high-frequency electric field f _H is applied, the brightness cannot be ensured as shown in Fig. 10, so the liquid crystal response during the T3 period. Be careful when shorter than time. Incidentally, the response time at 50 ° C is about 0.15 msec. That is, when the T3 period is shorter than the response time of the liquid crystal, it is necessary to further apply the high frequency electric field f _H, and it is necessary to shorten the time until the second application. The total f _H application time is related to the amount of transmitted light.
In order to increase the amount of transmitted light, it is preferable to lengthen the f _H application time, but as shown in FIG. 6, the temperature characteristics deteriorate. In this case, the characteristics deteriorate, especially on the low temperature side. Selection period
To extend the on-state at T1 to the deselect period T2, use T4
It is better to lengthen the f _H application time of the period. When a shutter having good temperature characteristics is desired, the f _H application time should be short and the T6 and T7 periods should be long. As described above, T3, T4, T5, T6, T7, T8 in the signal waveform shown in FIG.
The period can be arbitrarily set within the range described above according to the usage conditions of the liquid crystal shutter.

The response when the total f _H application time was changed was 11th.
Fig.12. Figure 11 shows T3 = 0.25msec, T4
= 0.15msec, T5 = 0.2msec, T6 = T7 = 0.4msec, and FIG. 12 shows T3 = 0.25msec, T4 = 0.05msec,
This is the case when T5 = 0.3 msec and T6 = T7 = 0.4 msec.
That is, the T3 + T4 period is set to 0.4 msec and 0.3 msec. As is clear from FIGS. 11 and 12 above, 1 /
The amount of transmitted light is larger than that at 2 duty. T3 + T4
As the period becomes shorter, the duty becomes closer to 1/2. Therefore, the light amount can be adjusted by adjusting the T3 + T4 period. In any case, if the length of the T3 + T4 period is shorter than the response time of the liquid crystal, the transmitted light does not reach a sufficient intensity, so that it is required more.

The present invention is not limited to the above embodiment,
The open operating voltage, the holding voltage, and the closing operating voltage can be created by arbitrarily combining a high frequency voltage, a low frequency voltage, and no voltage.

[Effects of the Invention] As described in detail above, according to the present invention, light is transmitted through the liquid crystal shutter between opposing electrodes of the optical shutter for a period of 1/2 of the selection period or a period shorter than 1/2. Since the operating voltage for operating in such a state is applied, the high frequency component of the applied voltage can be minimized, the influence of the high frequency history in the dual frequency liquid crystal is reduced, and high speed, high contrast, and temperature A liquid crystal shutter with little dependence can be obtained.

[Brief description of drawings]

1 to 12 show an embodiment of the present invention,
FIG. 1 is a plan view showing the main part of a liquid crystal optical element, FIG. 2 is a cross-sectional view, FIG. 3 is a view showing the relationship between the liquid crystal alignment direction and the arrangement of polarizing plates in FIG. 2, and FIG. FIG. 5 is a diagram showing frequency dependence of dielectric anisotropy in a driving liquid crystal, FIG. 5 is a diagram showing examples of drive signal waveforms for driving a liquid crystal optical element, and FIGS. 6 to 12 are optical response characteristics to various drive signals. FIGS. 13A and 13B are diagrams showing a conventional method of driving a liquid crystal optical element and its optical response characteristic. 11, 12 …… Substrate, 12 …… Sealant, 14a, 14b …… Electrode,
16 ... Liquid crystal, 17 ... Polarizing plate, 18a, 18b ... Signal electrode, 19
...... Terminals, 20, 22 …… Metal films, 21a, 21b …… Common electrodes, 23 …… Shading member, 31 …… Liquid crystal molecule orientation direction, 32 ……
Transmission axis (or absorption axis) of upper substrate polarizing plate, 33 ... Transmission axis (or absorption axis) of upper substrate polarizing plate.

Claims (3)

[Claims] 1. A pair of substrates facing each other, one electrode arranged in a plurality on one inner surface of the pair of substrates facing each other, and the other inner surface of the pair of substrates facing the plurality of one electrodes. And the other electrode formed in multiple arrays, the dielectric anisotropy is zero at low frequency electric field lower than the crossover frequency and the dielectric anisotropy becomes negative at low frequency electric field higher than the crossover frequency. A liquid crystal material exhibiting a dielectric dispersion phenomenon, the liquid crystal layer enclosed between the pair of substrates subjected to horizontal alignment processing in a direction parallel to each other, and a polarization axis tilted by approximately 45 ° with respect to the alignment film direction of the liquid crystal layer. A polarizing plate disposed in a manner such that between the one electrode and the other electrode, an opening operation voltage for making a plurality of optical shutters formed in portions where these electrodes face each other a state in which light is transmitted, By applying the closing operation voltage to make the light cut off, In the method for driving a liquid crystal optical element for controlling the light transmission states of a plurality of optical shutters, the open operation voltage is set to one optical shutter in one repetition period for sequentially controlling the light transmission states of the plurality of optical shutters. 1/2 of the selection period allotted to control
The method for driving a liquid crystal optical element, characterized in that the liquid crystal optical element has an operating voltage applied for a period of 1 or a period shorter than 1/2 and has an operating voltage for operating the liquid crystal shutter in a state in which light is transmitted. 2. The operating voltage is composed of a combination of a high frequency voltage and a non-voltage which does not apply the voltage, and the total of the application time of the high frequency voltage is equal to or less than 1/2 of the selection period. The voltage is applied between the electrodes.
A method for driving a liquid crystal optical element according to item 1. 3. The open operating voltage is applied to a part of the selection period and part of the remaining selection period and non-selection period to keep the optical shutter in a light transmitting state. 2. The holding voltage according to claim 1, wherein the holding voltage is a combination of a superposed voltage, a no-voltage, a high frequency voltage, and a low frequency voltage at which the optical shutter is not closed. Driving method of liquid crystal optical element of.