JPS5993425A - Liquid crystal light valve - Google Patents

Abstract

PURPOSE:To increase the quantity of transmitted light and to speed up response by providing an opening signal and a maintaining signal within a write allotted time and a closing signal within a time other than said allotted time, and using a four-level voltage as a write selection signal. CONSTITUTION:A glass substrate having N piece of write selection electrodes and a glass substrate having M pieces of data signal electrodes are opposed to oppose and cross each other; and a nematic liquid crystal composition is enclosed between both substrates and a couple of polarizing plates are provided outside of them. Then, a signal is applied between a write selection electrode and a data signal electrode to perform N time-division driving. In this case, the valve opening signal 903 and maintaining signal 902 are provided within the write allotted time and the closing signal 901 is provided within the time other than said allotted time; and a write selection signal T1 uses a four-level voltage to realize an increase in the quantity of transmitted light and fast light transmission response.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal light valve, and more particularly to a liquid crystal light valve having high-speed response characteristics using a nematic liquid crystal composition that causes dielectric relaxation at low frequencies. This paper relates to a liquid crystal light valve that is driven in a time-division manner.

Recent advances in information processing technology have been remarkable, and along with this, printing devices, which are one of the output devices, have
High density and high speed are required. Furthermore, there is a strong demand for printing quality, and a laser beam printer (using electrophotography and optical writing) that satisfies this demand is a printing device that meets these demands.
LBp) or fiber optic tube (orT) printers are in practical use. However, despite the strong demand as described above, both LBP and OFT are extremely expensive, which is a major factor preventing their widespread use.

In view of this situation, the present invention has realized a high-speed liquid crystal light pulp that has been difficult to put into practical use due to various technical problems based on ideas alone, and can be used as an optical writing device such as the above-mentioned optical printer. This is how it was done. Furthermore, the present invention has succeeded in significantly reducing the number of liquid crystal drive circuits by improving the drive method, and has achieved a large 111i
, is a groundbreaking technology that can significantly reduce costs.

A method for realizing an optical printing device using a liquid crystal light valve is disclosed in Japanese Patent Application Laid-Open No. 56-93568. Japanese Patent Publication No. 57-64722
There is a method described in . First, the configuration of a printing apparatus using the above method and the characteristics of a liquid crystal light valve will be described.

FIG. 1 shows the configuration of the printing apparatus described above. A photosensitive drum 102 is generated by an optical signal generator 101 using a liquid crystal light valve.
Light writing is done on top. At this time, the photosensitive drum 102 is charged in advance by a corona charger 110. At this time, when printing characters, the light signal is usually generated in correspondence with the character parts. This forms an electrostatic latent image, which is developed with toner by a magnetic brush developer 106. The developing method at this time is usually reversal development. Thereafter, the toner is transferred onto plain paper 104 by a transfer corona discharger 105 and fixed by a fixing device 106 . The toner remaining on the photosensitive drum after transfer is neutralized by the blade 108, and the electrostatic latent image is neutralized by the static eliminating lamp 109, and the process ends.

FIG. 2 shows the configuration of the optical signal generator. The optical signal generator is
A light source 111 such as a fluorescent lamp and a liquid crystal light valve 150
and an imaging lens 115, and a liquid crystal light valve 15.
0 consists of a liquid crystal panel 112 and a liquid crystal drive circuit 113, and is mounted on a mounting board 114. The light emitted from the light source is modulated by a liquid crystal light valve.

This optical signal 116 is imaged onto the photosensitive drum 102 by an imaging lens 115. An erect image can be obtained by using a focusing optical fiber array as the imaging lens. Third
The structure of the liquid crystal panel is shown in FIG. The liquid crystal panel includes a glass substrate 1 having common signal electrodes 119 and 120.
17 and a glass substrate 118 having data signal electrodes 121 and 122 and a spacer 126, the liquid crystal composition 12
5 and is provided with polarizing plates 123 and 124 on both sides of a glass substrate. The common signal electrode is a transparent electrode 11
9 and an optically opaque metal electrode 120, and data signal electrodes 121 and 122 are transparent electrodes. Polarizing plate 1
23 and 124 are arranged so as to be orthogonal to each other in terms of polarization plane power 2. The light is modulated by a microshutter formed by the transparent portion 112 of the common electrode and the signal electrode. In the text below, there are parts where the shape of the transparent part of the common electrode is expressed as a microshutter, but in this case, please interpret it as forming a microshutter with the opposing signal electrode.

Next, we will discuss the characteristics of the liquid crystal composition that causes dielectric relaxation at low frequencies. Table 1 shows an example of a liquid crystal composition having the above characteristics. The descriptions and examples shown in this specification are
The liquid crystal composition shown in Table 1 was used.

Table 1 -e-:) Lance cyclohexane-0-:benzene ring FIG. 5 shows the frequency characteristics of the dielectric constant of the liquid crystal composition of Table 1. The measurement temperature is 30°C. 153 is ε soil, 15
4, ε9 causes dielectric relaxation and becomes a smaller value as the frequency becomes higher, as shown in the figure. 154 has an inflection point,
At this frequency, the imaginary permittivity 155 in the major axis direction reaches a peak, and this frequency 157 is called a relaxation frequency (abbreviated as fτ). In the case of this liquid crystal composition, it is 5.7 KHz.

The dielectric anisotropy becomes zero at a frequency (IC) 156 where ε earth and ε7 intersect. This frequency is the crossover frequency, and at frequencies lower than this, Δε>0. At high frequencies, the Δ value becomes 0. In the case of this liquid crystal composition, fc is 8
It is KHz. When a nematic liquid crystal with such dielectric constant characteristics is used and a signal with a frequency lower than lc is applied, the liquid crystal molecules are subjected to a force that aligns them perpendicularly to the glass substrate, and when a signal with a frequency higher than fc is applied, A force that aligns them in parallel acts. By arranging the polarizing plates on both sides of the panel with their polarization planes perpendicular to each other, the microshutter is in a light-blocking state with a signal of a frequency lower than fc, and becomes a light-transmitting state with a signal of a frequency higher than fc.

The basic explanation of the liquid crystal light valve of the present invention has been given above. When commercializing such a liquid crystal light valve,
The price is an important factor.

When using a liquid crystal light valve in an optical printing device, the micro shutter for A4 size is 2000 microns with a regular pitch of 100μ.
You will need about 1 piece. In order to operate this micro-shutter, if one data signal electrode is provided for each micro-shutter, the data signal generation drive circuit will also require 2000
This is extremely undesirable in terms of price. As a means to solve this problem, there is a method of performing time division driving. Regarding this, patent application No. 55-7042. Special application 1986-7
045. The patent application was filed in Japanese Patent Application No. 7047/1983. The present invention further improves the above patent application and achieves higher speed and lower cost.

First, as a conventional example, the method disclosed in Japanese Patent Application No. 55-7042 will be described.

FIGS. 6 and 7 show an example of the electrode configuration of a liquid crystal light valve. This electrode configuration is also the same in the present invention. 6th
The figure shows an example of 2 time division, and FIG. 7 shows an example of 6 time division. Here, as mentioned above, examples with the number of time divisions of 2 and 6 will be given, but it can be generalized to N time divisions [N is a positive integer]. First, FIG. 6 of N-2 will be explained. This feature is that the common electrode is divided into two, which serve as the write selection electrodes 401 and 402 and the data signal 'F! L pole 403-40
5 intersects with the two write selection electrodes, and 41
As represented by 0 and 411, one data signal electrode is provided with two microshutters. In this figure, the number of data signal electrodes is four, but hereinafter M (positive integer) will be used. In the example of FIG. 7 of N; 6, the write selection electrodes are divided into six electrodes 801 to 806, intersect with the data signal electrodes 811 to 814, and one data signal electrode has six electrodes as represented by 821 to 826. Equipped with several micro-shutters. As described above, the electrodes for N time division are composed of N write selection electrodes and M data signal electrodes each having N micro-shutters, with a total of MXM micro-shutters. . Next, a driving method for a liquid crystal light pulp having this electrode configuration will be explained using an example where N=2.

FIG. 8 shows two write selection signals for performing time division of M=2, and ON and OFF signals for opening and closing each microshutter.

501 and 502 are two write selection signals 01 and 0
It is 2. Tf in 01 is the write cycle.

Tα is the write time allocated to the write selection signal o1, which is one half of Tf. Th is C1
This is the time other than the time allocated to 02, and in the case of N=2, it is the write time allocated to 02. During Th in 01, the Fh signal is TOl and Ta2, T
A signal of Ft is applied to a2. C1 signal to T
The signal delayed by f/2 is 02. Therefore'l
Thank you for l'A=T03, and TO1=TO2.

503 and 504 are symbols for opening and closing microshutters, respectively. In Ton, a portion indicated by 507 and a portion indicated by 508 in F Off are signals of the ph frequency, and a portion indicated by 509 is a signal of the Ft frequency. High frequency 50 of write selection signals 01 and 02
5? The off high frequency 508 is in phase and FOn
The high frequency waves 507 are in opposite phase. Further, the low frequency waves 506 of the write selection signals 01 and 02 (the low frequencies of the TOl and I'020 portions) and the low frequencies 509 of 'Fon and Tr off are in opposite phase. The important parts of this drive system are that a part for applying a low frequency indicated by 506 to the write selection signals a1 and 02 is provided, and
The reason is that a portion is provided to apply a low frequency signal 509 to l'On and Foff in the opposite phase to 506.

Next, an example of the number of time divisions N will be described. FIG. 9 is an example of this. The only difference from the case of H=2 is that the allocated write time is Tα''T//N. 520 is the first write selection signal 01, and this signal The write time Tα consists of the write time Tα and the other time T6.Tα is the FA signal 510 and p
It consists of a signal 511 of t. The second write selection signal C2 is obtained by delaying ol by T//N, and is the Nth write selection signal ((N-1), /N).
It is delayed by XTf. The voltage of each signal shown in FIGS. 8 and 9 is 1, and is switched between 0 and 1.

Next, we will show the light transmission response characteristics of the liquid crystal light pulp when using this signal. Here, an example where N=2 will be described.

An example will be described in which signals 501 and 502 are applied to the write selection electrodes 401 and 4.02 in FIG. 6, respectively, and the microshutters 410 and 411 are opened and closed at timings T410 and T411 shown in FIG. 10. The white circle is open and the black circle is closed. TiO2 is applied to the electrode 405 to open and close the microshutter as shown in this figure.
As shown in (Switch the scale of Fon and F off and apply it. This signal and 01 (401) and Cl 2
The signals applied to the microshutters 410 and 411 by the combination of (402) are shown in FIG. Indicated by a dotted chain line.

601 is a high frequency FA signal, 602 is a low frequency Pi signal, 603 is a signal in which Ft and FA are superimposed, and 604 is a signal with zero applied voltage. Signals shown with similar waveforms in the figures are referred to by the same numbers.

The light transmittance of 620 will be explained. This is the response characteristic of the microshutter. 610 and 411 are signals for opening the micro shutters 410 and 411, respectively. 610 opens from the FA double signal of 601,
It is closed by the Ft times signal of 602. In other words, 610 is 01
The open and close response is completed during the write time Tα allocated to . The same applies to 611. 612
and 613 are responses to the close signal. It begins to open slightly in response to the zero voltage signal at 604, but remains closed by closing due to the Ft times signal at 602. Furthermore, the microshutter is maintained in a closed state by the superimposed signals of Ft and FA 603, and time division is performed, thereby reducing the number of data signal drive circuits. However, the above method has the following drawbacks. Since the number of time divisions (N) is increased without changing the response time of the liquid crystal light pulp, the writing cycle becomes longer.

In other words, the speed of the light pulp function is reduced. This can be prevented by increasing the voltage (1) of the signal shown in FIGS. 8 and 9 and shortening the write cycle. However, the purpose of time-division driving is to reduce costs, and increasing the drive voltage increases the unit cost of each drive circuit even if the number of drive circuits decreases, which defeats the purpose. Furthermore, the biggest drawback of the above method is that each micro-shutter only transmits light during the allotted writing time Tα of the writing cycle T/. The energy (proportional to the time integral value of transmittance: energy of optical pulse) is at most Tα/
This results in a drop of T/. In other words, when the writing cycle Tf is constant and N time-division driving is used, the light energy decreases to one-Nth. This problem can be completely resolved by improving the signal that drives the light valve.

FIG. 12 shows the liquid crystal light pulp drive signal of the present invention.

A write selection signal and a data signal for performing N time-division driving are shown. First write selection signal (TI) 700.
The second (T2) 701 and the Nth (TN) 702 are shown. T7705 is the writing period, Ta704 is the time allocated to writing, and Tα=T 7 /
It is N.

Tb705 is this remaining time, Tb='['/
−=Tα. Each write selection signal has the same shape shifted by a time Ta. (The force fTN is when TI is delayed by Ta, and the force fTN is when TI is delayed by (N-1)XTa.) Therefore, regarding the write selection signal, let us take T1 as an example and explain t! IH. 'I'770
3 is composed of N signals in units of a period of Tf/H, and the period is further divided into two parts: front and rear. Here, 706 is the front and 707 is the rear in FIG. 12.

As a result, TI is divided into 2XN pieces (70
8.

709.710,711...712,7
13°714). Here, the explanation is a little confusing, but the first
The basic signals used in FIG. 2 will be explained.

Basically, four signals are used. It is (1)
p t s (2) ''' s and each low phase, (8) F t. (4) FA.This 4
A combination of two signals opens and closes the LCD light valve.

Furthermore, the opening and closing of the liquid crystal light valve is controlled by the combination of the write selection signal and the data signal, and the former and the latter use F′h, and when they are in opposite phase, that is, the liquid crystal light valve Open when a signal is applied. It closes when the signal yt is applied to the liquid crystal light valve in the opposite phase of Ft.

If a combination of signals other than this is applied, that is, Ft or FA of the same phase (in this case, a voltage of 0 ■ to the liquid crystal light pulp; the same as no voltage applied), or
In the case of a combination of Ft and FA (in this case, the phase is irrelevant), when a superimposed signal of FA and yt is applied to the liquid crystal light valve, the liquid crystal light pulp maintains its previous state. That is, if these signals are applied in the open state, the open state is maintained, and if it is in the closed state, the closed state is maintained. The present invention effectively utilizes the characteristics of the liquid crystal light valve described above. Based on the above, two types of data signals, open and closed, are created as the open signal DN740 and the closed signal DF741 shown in FIG. DN74
0 consists of 730 and 731, 730 is FA, '7
31 is the lower t signal. DF741 is 732,73
3, 732 is an Fh signal, and 733 is an Ft signal. The difference between DN740 and D1'741 is that FA or lower k is used for 73G and 732.

Next, the write selection signal will be explained. As mentioned above, since T1 to TN are isomorphic, only TI will be explained. T (Z704 is the allocated writing time, but this first half 70B is ph, 7o9 is 7t
This is the signal.

Tα) The first half 710 of the next T f / N period is a signal of Ft in this figure, but it may be 7t, or it may be Ft.
Any signal other than t and having a frequency lower than yt may be used. The latter half 711 is an Ft signal. The remaining period of Tf other than the above is a signal of Ft. Next, the voltage levels of the signals in FIG. 12 will be explained.

Data signals DN740 and D'F741 are +■1/2
and −■1/2, and the write selection signal is +V 2 / 2 * + V 1
This signal has four levels of voltage values: /2, -v1/2, and -22/2. By using these four levels, the present invention further increases the effect of the opening/closing signal of the liquid crystal light valve. Next, the diagram showing the response characteristics of the liquid crystal light pulp when using this signal is shown in the 16th figure.
FIG.

In both cases, N=4. In both cases, Tf=2 seconds. The difference between FIG. 13 and FIG. 14 is the length of the period 902. First, FIG. 13 will be explained. T1 in FIG. 13 is the same as that in FIG. 12 where N=4.

D is a data signal obtained by switching between DN and DF in FIG. 12, where 903 is a DN and an open signal 904 is I)F, a closed signal. When these signals are applied to the liquid crystal light pulp, the 1! Between the poles, T
A 1-D signal is applied. 905 is FA, an open signal; 907 is a superimposed signal of 0 and FA and Ft, which is a maintenance signal; 906 is a close signal of Ft; 908 is a ii times signal of Ft, FA, and Ft-FA, and a close signal. and becomes a maintenance signal. Furthermore, 909 is a low voltage (7) Irh, and 91
1, '910 and 912 are respectively "907
, 'S) Same as 015 and 908. The light transmittance of the liquid crystal light valve corresponding to this is shown in the lower part of FIG. 9
Reference numeral 13 indicates the transmittance at the time of opening, which is opened by the open signal 905, maintained at 907, and closed at 906. 914
is a leaking light. 915 is leakage light due to the MO multiplied signal. 916 is the optical response of the microshutter at the electrode to which the write selection signal T2 and the D signal are applied. The light transmissions 913 and 916 due to the aperture signal have a longer aperture time than the conventional example 610 and 611 in FIG. The Cn product in the graph of the ratio is high.

FIG. 14 shows an example in which the light energy is higher than the example shown in FIG. 13. The only difference between FIG. 13 and FIG. 14 is that the period of the sustain signal 902 is longer, as described above. As a result, the light energy is further increased as shown in FIG. 14 913. This light transmittance measurement data shows that the optically active substance 4-(4
1.6% by weight of benzoic acid (alpha-2-octyl ester) was added. By adding an optically active substance, the amount of leaked light can be kept extremely low.

The light transmission response according to the present invention has been described above, but here, the features of the present invention will be summarized.

Whereas in the conventional method, the opening/closing was completed within the allotted writing time (open signal 9 close signal was provided within the allotted writing time), the present invention completes the opening/closing within the allotted writing time. The reason is that the maintain signal was killed and the close signal was set outside the allotted writing time. This resulted in a significant increase in light energy. Furthermore, the present invention provides four levels of voltage for the write selection signal, so that the sustain signal can effectively act. Furthermore, in order to speed up the light transmission response,
The solution is to increase the voltage of only the write selection signal without lowering the voltage of the data signal, which causes the price increase,
Furthermore, in order to minimize the increase in the cost of the power supply that operates each signal, the middle two levels of the four levels of the write selection signal are made the same as the voltage of the data signal.

As described above, the present invention performs time-division driving at high speed and without reducing light energy in order to reduce the cost of a liquid crystal light valve. Next, some examples will be described.

<Example 1> Using the circuit shown in FIG. 15, a write selection signal of four voltage levels was created to operate a liquid crystal light valve. 1
006 is a capacitive element, 1004 is a resistive element, 1005 is
A PNP transistor 1006 is an NPN transistor, and 1007 is a diode. 1008, -1-V 2 / 2.1009, +V1/2.1
Connect a power supply with a voltage value of -V1/2.1011 to 12/2 to 010, and connect terminals 1000.1001 and 100
2, FIG. 16 1021, 1020 and 10, respectively.
22 signals are input, and output signals 1023 are obtained from terminals 1012. Using this signal, ■1=28V, V2
When the liquid crystal light valve was operated with = 42V,
The response characteristics of light transmittance shown in FIG. 16 were obtained.

Example 2 A liquid crystal light valve having 4 write selection electrodes, 500 data signal electrodes, and 2000 microshutters was manufactured and operated using the drive signal shown in FIG. 1!1. V
2=42V, V1=28V.

Set the temperature to about 40℃~45℃, FA=130KH
z, FA+6 KHz, and Tf=2 msec. Behind this liquid crystal light valve, there is a glow with a luminance of 100,000 cd/rrl, which has an emission peak at a wavelength of 540 nm.
The light transmitted through the microshutter was imaged onto the Sθ-Tθ photoreceptor using a vehicle-collecting optical fiber array. When the photoreceptor was developed with toner, an image corresponding to the print signal was formed. Incidentally, the light energy of one pulse emitted from one microshutter at the photoreceptor position was 61 vg/cd.

As described above, the present invention uses time-division driving to reduce the cost of a liquid crystal light valve, and increases the speed without reducing the light energy.
This realizes a high-speed printing device at a very low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of a printing device using a liquid crystal light valve. FIG. 2 is a diagram showing an example of the configuration of an optical signal generating section using a liquid crystal light valve. 3 and 4 are diagrams showing the structure of a liquid crystal panel. FIG. 5 is a diagram showing the frequency characteristics of dielectric anisotropy of the liquid crystal material used in the present invention. FIG. 6 and FIG. 7 are diagrams showing the configuration of hour and minute side drive electrodes. FIGS. 8 and 9 are diagrams showing conventional time-division drive signals. FIGS. 10 and 11 are conventional examples, and are diagrams showing a time chart of an opening/closing signal, a corresponding signal waveform applied to a microshutter, and a corresponding light transmission response characteristic of the microshutter. FIG. 12 is a diagram showing signals for driving the liquid crystal light valve of the present invention. FIGS. 13 and 14 are diagrams showing drive signals and light transmission response characteristics of the liquid crystal light valve of the present invention. FIGS. 15 and 16 are diagrams showing an embodiment of a circuit and a signal for generating a write selection signal having four levels of voltage values. 401.402, 8o1-806...Write selection electrodes 403-406 and 811-814...Data signal electrode 156...Cross frequency 123.124... Polarizing plate 700.701.702...Write selection signal (700...TI, 701...T2.
702...TN) 740.741...Data signal (740...
...DN, 741...DF)708...
... TO1 709... ... '1'01 710...TO2 711...TO2 713... ... TON 714 ...... TON or more applications Person Suwa Seikosha Co., Ltd. Fig. 2 μ Go Fig. 3 11 da Fig. 4 Fig. 3

Claims (1)

[Scope of Claims] (1) A glass substrate having N writing selection ta electrodes (N is a positive integer) and a glass substrate having M data signal electrodes (M being a positive integer) The electrodes are arranged to face each other so as to cross each other, and a nematic liquid crystal composition having a crossing frequency at which the di'tM and anisotropy become zero is 1oOKHz or less at room temperature is sealed between them, and a set of polarizing plates is provided on the outside thereof. In a liquid crystal light pulp that is a liquid crystal panel and performs N time-division driving by applying a signal between the write selection electrode and the data signal electrode, the write selection signal (N types, each with TI , T2.・・・・・・・・・It is called TN and will be used hereafter) and data signal (there are two types, the signal to open the liquid crystal light pulp is called DN, the signal to close it is called I) and F is called hereafter. (used) is a signal with a frequency lower than the above crossover frequency (hereinafter referred to as Ft), and a signal with a higher frequency (hereinafter referred to as Ft).
(hereinafter referred to as FA), and signals with opposite phases of Ft and FA (7 and 7h, respectively, hereinafter referred to as FA), and each of the write selection signals described above has a cycle of the write selection signal (hereinafter referred to as FA). Each write selection signal is composed of N types of signals, and each of the N types of signals is divided into two parts: front and rear. Name each signal from the front: To-1, To-j, To-2, To-2, etc.
・・・・・・・TO-N, named TO-N, and furthermore,
The period of each data signal is T f /N, and each data signal is further divided into two parts, the front and rear.
When called FO, each of the above signals is To-1 is FA, 'l'
o-1 is Ft, To-N is Ft, write selection signals other than the above To-1, To-1, and To-N are vt or Tet, DNO is Il'A, DIrO is FA, DNO, and]
) A liquid crystal light valve characterized in that FO is vt and the write selection signal has four levels of voltage. (2) The voltage level of the data signal applied to the data signal electrode is two levels, and the voltage values of these two levels match the middle two levels of the '4 level voltage of the write selection signal. A liquid crystal light valve according to claim 1, characterized in that: (8) Change the voltage of the above four levels from the lowest to 2゜-Vl.
When e+vi, +V2, the write selection signal is
The scope of the patent Wn is characterized in that TO-1 and TO-N are at voltage levels of -V2 and -+-V2, and To-'1 is at voltage levels of -41 and +■1. The liquid crystal light valve described in item 2. (4) The liquid crystal light pulp according to claims 1, 2 and 6, wherein the nematic liquid crystal composition is optically active.