JPH0548887B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a recording device using a liquid crystal optical shutter, and more particularly to a driving method for driving the liquid crystal optical shutter to open and close. [Prior art] A recording device using a liquid crystal optical shutter opens and closes a large number of microshutters provided on the liquid crystal optical shutter by a control circuit, and optically writes on a recording medium by blocking or transmitting light from a light source. It is a device that performs Since such recording devices require high-speed response of the liquid crystal, liquid crystal optical shutters usually use liquid crystals whose dielectric anisotropy is inverted depending on the frequency of the electric field, and are used at frequencies f higher than the frequency f _C at which the dielectric anisotropy is zero. It is driven by two frequencies: _H and low frequency f _L. For example, to record A3 size at a density of 10 dots per mm, approximately 3000 microshutters are required per line. Therefore, the normal number of wires,
The liquid crystal optical shutter, which prevents an increase in mounting area, is driven by time-division driving. As shown in FIG. 2a, time-division driving is carried out using common electrodes 1a to 1n and signal electrodes 2a to 2n of the liquid crystal light shutter.
are arranged perpendicular to each other, and a microshutter 3 is configured in the common part of both electrodes, and recording signals S ₁ to Sn are input to the signal electrodes 2a to 2n as shown in FIG. The liquid crystal light shutter is driven by inputting and inputting time-divided write selection signals C ₁ to Cn at time _n shown in FIG. For example, in two-time division driving, two common electrodes 1a and 1b are provided for one column of writing as shown in FIG. As shown, open driving is performed for half of one writing cycle Tw to transmit light. Figure b shows an example in which microshutters 3a and 3b are used to record white-black-white-white-black; the solid line shows the response of 3a, and the dotted line shows the response of 3b. Therefore, the period 0~Tw/2, 2Tw~
Open drive will be performed between 5Tw/2 and 3Tw/7Tw/2. In such two-time division drive, one write cycle Tw
In the n-time division drive, the light can pass through only half of the time, and the transmission time becomes even shorter, resulting in insufficient exposure. Therefore, the write selection signal sets the microshutter to open or close during the selected period of one write cycle Tw, and the set state of 1-Tw/n is effectively maintained for the remaining period (non-selected period) of one write cycle Tw. The drive is carried out in such a way that it lasts for a long time. For example, _* f H signal and *f _L signal whose phase is 180 degrees different from f _H signal, f _L signal, f _H signal, and f _L signal as shown in Fig. 4a.
A drive pattern signal in which the signals are mixed during one writing period is created, this signal is applied to the common electrode 1a, and the four drive pattern signals 4 to 7 shown in FIG.
By selecting one of them and applying it to the signal electrode, one of the superimposed signals 8 to 11 as shown in _C in the figure is applied to the microshutter 3a. Also,
Since the common electrode 1h is given a signal that has a different phase by Tw/2 from the signal given to the common electrode 1a, a superimposed signal similar to the signal shown in _FIG . It will be given to you. The light transmittance characteristics of the microshutter 3a when these superimposed signals 8 to 11 are applied are shown in FIG. The light transmittance characteristic 12 is based on a superimposed signal 8 created when a pattern signal 4 for opening both microshutters 3a and 3b is applied to the signal electrode, and a pattern signal shown in the figure a is applied to the common electrode. The light transmittance characteristic 13 is the superimposed signal 9 when the pattern signal 5 for opening the microshutter 3a and closing the microshutter 3b is applied to the signal electrode, and the pattern signal shown in figure a is applied to the common electrode. This is a characteristic due to
Similarly, for light transmittance characteristics 14 and 15, when pattern signal 6 is applied to the signal electrodes to close 3a and open 3b, and pattern signal 7 is applied to close both 3a and 3b, superimposed signal 10,
This is the characteristic according to No. 11. Here, the [f _L + f _H ] signal shown in c in the figure indicates a superimposed signal of the f _L signal and the f _H signal,

[0] indicates no signal. By driving the liquid crystal light shutter in this way, the non-selection period 1-
Even at Tw/n, the selected microshutter can be maintained in the open state, and the liquid crystal light shutter can be substantially statically driven. In addition, if it is necessary to change the open state maintenance time, for example due to a change in the temperature of the liquid crystal light shutter, the voltage of the [f _H + f _L ] signal applied during the non-selection period, as shown in Figure 5, may be changed. The open state maintenance time is controlled by inputting a superimposed signal with a different value. In addition, in a recording apparatus that uses such a driving method, as shown in FIGS. _4C and 5, when the f _L signal is input to the last period T _L of the non-selection period to perform essentially static driving. This eliminates the history effect of the liquid crystal used. [Problems with the prior art] Comparing the light transmittance characteristics 14 and 15 shown in FIG.
2 and 13, the average level is different, the light transmittance characteristic 15 is high between Tw/2 and Tw, and there is a difference in level between the light transmittance characteristics 14 and 15. This shows that when the micro-shutter 3a records black, the black density recorded by the micro-shutter 3a changes depending on whether the micro-shutter 3b records black or white. There is. When the temperature of the liquid crystal deviates from the optimum temperature, this difference in level becomes even larger and adversely affects the quality of recorded images. It is conceivable to change the voltage value of the above-mentioned signal in order to reduce this difference in level, but this requires multi-valued signal voltage values, which also causes the drive circuit to become complicated. [Object of the Invention] In view of the above-mentioned conventional drawbacks, the present invention provides
The purpose of this invention is to simplify the drive circuit of a liquid crystal optical shutter by providing a signal having a phase difference with the _fH signal, and to provide a method for driving a recording device that produces high quality recorded images over a wide temperature range. [Summary of the Invention] In order to achieve the above object, the present invention has n common electrodes and a plurality of signal electrodes that cross and oppose the common electrodes, and a dielectric difference is generated between the two electrodes at a specific frequency f _C. A liquid crystal agent with zero polarity is sealed, and the intersection of both electrodes forms a microshatter.The microshatter is driven to open and close according to the signal to be recorded, and the light is irradiated by a light source and passes through the microshatter. In a method of driving a recording device that performs recording by irradiating a photoreceptor with light, the n common electrodes are connected to the specific frequency f _C
A selection signal that is a combination of a signal with a higher frequency *f _H and a signal with a lower frequency f _L is sequentially applied to I/
The specific frequency f _C is supplied to the plurality of signal electrodes with a phase shift of n depending on the signal to be recorded.
A signal that is a combination of a signal with a higher frequency f _H and a signal with a lower frequency f _L is supplied, and a signal with a frequency higher than the specific frequency f _C that is supplied to the common electrode is supplied to the signal electrode. The specific frequency f _C
A signal with a phase that is inverted from the phase of the signal with a frequency higher than *f _H , and whose phase is shifted by a predetermined amount.
f _HX . [Embodiments of the Invention] Examples of the present invention will be described in detail below with reference to the drawings. FIG. 6 shows an f _HX signal in which the f _H signal and the f _H signal used in the present invention have a phase difference, and a superimposed signal of the f _H signal and the f _HX signal. T _H is the period of f _H signal
The f _HX signal is a signal whose phase is delayed by Td compared to the f _H signal, and the [f _H −f _X ] signal is a superimposed signal of the f _H signal and the f _HX signal. When such a signal is applied, the liquid crystal exhibits a stronger closing tendency than when no voltage is applied, but weaker than when an f _H or f _HX signal is applied. The strength of this closing tendency is determined by the phase difference
Determined according to Td. Also, Fig. 7a shows f _L signal and f _{HX
A superposed} signal of [ _{f L + f H} This shows that there is no difference in effectiveness when driving the liquid crystal light shutter. The present invention is capable of handling signals whose phase is shifted by Td from such _fH signal.
A pattern signal in which a superimposed signal including the f _HX signal or f _HHX is mixed in the non-selection period shown in FIG. 4c is applied to the liquid crystal light shutter, and FIG. 1a shows this pattern signal. In the same figure, a pattern signal 16 is a signal given to the common electrode 1a mentioned above, and by selecting one of the four pattern signals 4 to 7 shown in FIG. 4b and giving it to the signal electrode, the liquid crystal light shutter is Driving superimposed signals 17-20 can be obtained. By applying these superimposed signals 17 to 20 to the liquid crystal shutter, a light transmittance characteristic as shown in FIG. 1b can be obtained. Light transmittance characteristics 21, 22, 2
3 and 24 are superimposed signals 17, 18, 19, and 20, respectively.
The light transmittance characteristic 21 is the characteristic when both the microshutters 3a and 3b are open, and the light transmittance characteristic 22 is the characteristic when the microshutter 3a is opened. Open, 3
The characteristic when b is closed, the light transmittance characteristic 23 is 3a
Characteristics when 3b is closed and 3b is open, light transmittance characteristics 2
4 shows the characteristics when both 3a and 3b are closed. Comparing the light transmittance characteristics shown in FIG. 4B with the conventional light transmittance characteristics shown in FIG. 24, the light transmittance characteristics 23 and 24 using the pattern signal 16 of the present invention are different from the non-selection period Tw/2 to
In Tw, the off period is long, indicating that the LCD light shutter can be turned off reliably. Furthermore, FIG. 8a shows the microshutter when the conventional pattern signal shown in FIG. 4c is applied, and FIG. 8b shows the microshutter when the pattern signal of the present invention shown in FIG. The relationship between the amount of transmitted light and the liquid crystal temperature is shown, and 25 indicates the micro shutters 3a and 3b.
When both are open, 26 is when 3a is open and 3b is closed, 27 is when 3a is closed and 3b is open, and 28 is when 3a and 3b are both closed. It shows the amount of light transmitted through the shutter 3a. The optimal temperature range 29, in which there is almost no difference between the amounts of transmitted light 25 and 26, and at the same time there is almost no difference between 27 and 28, is wider than the conventional optimal temperature range 30 for the amount of transmitted light shown in FIG. For example, the optimal temperature range 29 is approximately 6 degrees, which is the conventional optimal temperature range 30.
Compared to 3deg, it is twice as wide on the high temperature side. As described above, according to this embodiment, the signals f _HX and f _L during the non-selection period of the pattern signal 16 shown in FIG.
By combining the position and period of , it is possible to absorb differences due to the way the time-division drive is received, balance the light response, and improve the state of the liquid crystal light shutter during the non-selection period. Furthermore, when the [f _L + f _H ] signal or the [f _L + f _HX ] signal is continuous, if the period of the f _H signal and the f _HX signal is T _H , then there is an effective value of √2 _H before and after it By inserting the [f _H −f _HXf ] signal, the balance at high temperatures can be compensated and the operating temperature range of the liquid crystal light shutter can be expanded. This means that even when the ambient temperature of the liquid crystal light shutter changes, there is no need to multi-value the voltage value of the pattern signal as in the prior art, and the control circuit can be simplified. Next, another embodiment of the present invention will be described below using FIGS. 9 to 12. Figure 9 shows one write period in two-time division drive.
A pattern signal 31 is used in which an f _L signal is inserted into the last period T _L1 of Tw/2 in the first half of Tw.
In this case as well, four superimposed signals are formed, but the combination in the non-selection period is represented by the latter half of the superimposed signals 32a and 32b. Such a superimposed signal 32
By using a and 32b in the liquid crystal light shutter, it is possible to cope with changes in the above-mentioned temperature range when the combination of recording elements such as liquid crystal agent and photoreceptor is changed. For example, changing the time of period T _L1 , or
By changing the frequency of the f _L signal, a wide optimum temperature range 29 can be secured. Figure 10 shows Tw/2 in the first half of one write period Tw.
A pattern signal 33 is used in which an f _L2 signal and an *f _L2 signal having a phase difference of 180° from the f _L2 signal are inserted into each of the last period TfL1 of TfL1 and the last period T _L2 of Tw/2 in the second half. In this case as well, four superimposed signals are formed in the two-time division drive, but the combination in the non-selection period is represented by the latter half of the superimposed signals 34 and 35. It can be used as a signal to secure the range 29. In addition, in this case, the f _L1 signal and the f _L2 signal have frequencies that fall within one write period Tw, and any signal with a frequency lower than the frequency f _C can be used.
In this embodiment, a frequency that accommodates an integer number of waveforms is used. Figure 11 shows the period T _L1 in Figure 10 from the f _L2 signal.
This uses a pattern signal 36 changed to a combination signal of the f _L2 signal and the *f _H signal. In this case as well, the first
Similar to FIG. 0, the superimposed signal during the non-selection period in the two-time division drive is represented by the latter half signals 37 and 38, and can be used as a signal to ensure the optimum temperature range 29 of the liquid crystal light shutter. Furthermore, FIG. 12 shows a pattern signal 39 in which an f _H signal is inserted in the first half of each of the drive signal periods T _L1 and T _L2 for setting the liquid crystal light shutter to an open state among the pattern signals applied to the signal electrodes, and the liquid crystal light shutter. A pattern signal 40 in which the f L signal is inserted redundantly in the first half of each of the periods T _L1 and T _L2 of the drive signal for setting the optical shutter to the closed state is used as the signal electrode, and a pattern signal 40 with the f _L signal inserted redundantly in the first half of each of the periods T L1 and T L2 of the drive signal for setting the optical shutter in the closed state is used, and the common electrode is Pattern signal 4 using f _HX signal in section 41
2, superimposed signals 43 and 44 were created and used as a liquid crystal optical shutter drive signal. In this case as well, the superimposed signals 32a, 32b,
Similar to 34, 35, 37, and 38, a wide optimum temperature range 29 of the liquid crystal light shutter can be secured. As described above, according to the driving method of the recording device according to the present invention, the optimum temperature range of the liquid crystal light shutter is 2.
9, and this optimum temperature range 29 can be secured even when the combination of recording elements etc. is changed. Furthermore, it is possible to eliminate drive unevenness during non-selection periods and perform stable opening/closing drive that appears to be similar to static drive. The embodiments of the present invention are not limited to the above, and the pattern signals in the non-selection period have been explained by fixing part of the positions of the f _HX signal and f _L signal (or f _L1 signal), but they may be freely combined. It is of course possible to change the entire superimposed signal. [Effects of the Invention] As explained in detail above, according to the present invention, f _H
By driving the LCD optical shutter using the f _HX signal, which has a different phase from the signal, the drive balance due to the difference in signal combination during the non-selection period is improved, and in particular, it is possible to ensure that the LCD optical shutter is in the closed state. It can be opened and closed in substantially the same way as a static one. Further, unlike conventional driving methods, an optimum temperature range can be secured without multi-leveling the voltage value of the signal due to temperature changes in the liquid crystal light shutter, and a highly practical method for driving a recording device can be provided. Furthermore, even if the liquid crystal temperature changes due to the ambient temperature of the printing apparatus, high-quality printing can be performed without causing a change in the printing density.

[Brief explanation of the drawing]

FIG. 1a is a waveform diagram illustrating the driving method of the present invention;
Fig. 1b is a light transmittance characteristic diagram according to the driving method of the present invention, Fig. 2a is a configuration diagram of a liquid crystal light shutter in n time division driving, and Fig. 2b is a circuit diagram of a liquid crystal light shutter in n time division driving. , Figure _2C is a time chart diagram, Figure 3a is a configuration diagram of a liquid crystal light shutter in two time division drive, Figure 3b is a configuration diagram of light transmission in two time division drive, and Figure 4a is a common electrode. FIG. 4b is a waveform diagram of the pattern signal input to the signal electrode, FIG. _4C is a waveform diagram of the superimposed signal, FIG. 4d is a conventional light transmittance characteristic diagram, and FIG. FIG. 5 is a configuration diagram and light transmittance characteristic diagram of a conventional superimposed signal, FIG. 6 is a configuration diagram explaining a phase-shifted signal, and FIGS. 7a and b are also configuration diagrams explaining a phase-shifted signal. Figures 8a and b are transmitted light quantity characteristic diagrams, Figure 9
The figure is a waveform diagram illustrating a driving method according to another embodiment of the present invention, and FIGS. 10 to 12 are also waveform diagrams illustrating a driving method according to other embodiments of the present invention. 1a, 1b~1n...common electrode, 2a, 2b~
2n...Signal electrode, 3...Micro shutter, 4
~7, 31, 33, 36, 39, 40, 42...
Pattern signal, 8-11, 16-20, 32a,
32b, 34, 35, 37, 38, 43, 44...
...Superimposed signal, 12-14, 21-24...Light transmittance characteristics, 29,30...Optimum temperature range, 41...
part.

Claims (1)

[Claims] It has 1 n common electrodes and a plurality of signal electrodes that cross and oppose the common electrodes, and has a specific frequency between the two electrodes.
A liquid crystal agent with zero dielectric anisotropy is sealed at _fC , and the intersection of both electrodes forms a microshutter.The microshutter is driven to open and close according to the signal to be recorded, and is irradiated by a light source. In a method of driving a recording device that performs recording by irradiating a photoreceptor with light that has passed through the microshutter, the n common electrodes are provided with a signal at a frequency *f _H higher than the specific frequency f _C and a signal at a lower frequency. A selection signal that is a combination of signals of f _L is sequentially supplied with a phase shift of 1/n of the writing period, and a frequency f _H higher than the specific frequency f _C is supplied to the plurality of signal electrodes according to the signal to be recorded. and a signal with a lower frequency f _L , and a signal with a frequency higher than the specific frequency f _C supplied to the common electrode is supplied to the common electrode at a frequency higher than the specific frequency f _C supplied to the signal electrode. A method for driving a recording device, characterized in that the method includes a signal f _HX which is a signal whose phase is inverted from that of a signal having a high frequency * f _H and whose phase is shifted by a predetermined amount.