JPS62254128A - Liquid crystal optical device - Google Patents

Abstract

PURPOSE:To form a high-density liquid crystal optical device which provides gradational representation by providing an N-time-division driving device which is so constituted so to change independently respective light values constituting a liquid crystal element. CONSTITUTION:A pulse which is as high as a voltage +V and has pulse width Pw is impressed to turn on a liquid crystal light valve (light transmission state). The transmissivity draws a track shown by an arrow 502 above a hysteresis loop as the voltage +V rises, and gets saturated above a saturation voltage Vsat1 even if the voltage rises more. At this time, the voltage is held at zero V to hold the last state and the transmissivity is maximum because it has a track shown by an arrow 503 above the hysteresis loop. When a valve Vht is so selected that Vth1<V<Vsat1, the hysteresis loop of the transmissivity has a track as shown by an arrow 505, so as intermediate level is obtained for the maximum transmissivity. for the purpose, voltages are set by dividing the section between Vsat1 and Vth1 by several and gradational control over the trasmissivity becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal optical device, and more particularly, to a liquid crystal optical device having a drive device that can independently change the degree of modulation of each light valve constituting a liquid crystal element. Regarding equipment.

[Conventional technology]

Conventionally, in printing devices that combine a liquid crystal light valve as an optical writing element and an electrophotographic device, the liquid crystal light valve can only be set to two values, ON or OFF, so each pixel of the output image has two values: white or black. It appears in two concentrations. Therefore, in order to express the shading of images such as photographs, the entire pixel of the printing device is divided into submatrixes each containing a certain number of pixels.
This corresponds to one pixel of the input m image. Then, by changing the ratio of brightness and darkness of the binary state of each 118 strokes in the submatrix according to the shading of the image, it looks like the binary state of brightness and darkness of each pixel in the submatrix is Methods have been put into practical use that spatially average density ratios to express gradations.

[Problems that Masumei tries to solve]

However, in these methods, a fixed number of i[! Since the sub-matrix is constructed by II and corresponds to one pixel of the input image, the number of pixels in the sub-matrix is significantly reduced compared to the original number of pixels. For example, submatrix 54X
When configured with 4=16 pixels, there was a problem in that the number of pixels was reduced to 1/16.

Therefore, the present invention aims to solve these problems.
The purpose is to provide a liquid crystal optical device that can express gradation based on density by changing the modulation of the liquid crystal element according to the density information of the image signal, giving each light valve an independent gradation expression function. There is a particular thing.

[Another way to solve the interlacing point]

The liquid crystal optical device of the present invention includes a substrate provided with N scanning electrodes, a substrate provided with M signal electrodes, a liquid crystal layer sandwiched between the substrates, and at least one polarized light layer on the outside of the inner substrate. In the liquid crystal element comprising a plate, the modulation degree of the liquid crystal element can be independently changed for each light valve constituting the liquid crystal element according to gradation information.
It is characterized by having a time division drive device.

[Effect]

According to the above configuration of the present invention, it is possible to provide each light valve with a gradation function, and when used as a gradation unit of a printing device, a high-density gradation display image can be obtained.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Here, the application to a printing device will be described as ff1J t. Figure 1 shows the configuration of the printing device of this embodiment. The input image signal is transmitted through a light modulation element 1 using a liquid crystal light valve.
01, the signal is modulated into an optical signal and optically written on the photosensitive drum 102. At this time, the photosensitive drum 102 has been charged in advance by the corona charger 105 ◎The light modulation element 101 synchronizes with the rotation of the photosensitive drum 102.
Generates an optical signal corresponding to the input image. by this,
An electrostatic latent image is formed on the photosensitive drum 102, and the developing device 10
Toner development is performed in step 4. After that, the photosensitive drum 10
2 is transferred by a transfer corona charger 106. The plain paper 105 after toner transfer is
The image is fixed by the fixing device 107. The toner remaining on the photosensitive drum 102 after the transfer is removed by the blade 108, and the electrostatic latent image is neutralized by the neutralizing lamp 109, thereby completing the series of processes.

FIG. 2 shows the configuration of the light modulation element. Light emitted from a linear light source 110 such as a fluorescent lamp is transmitted to a liquid crystal light valve 11.
1. The liquid crystal light valve 111 includes a liquid crystal panel 112, a polarizing plate 113, and a liquid crystal drive circuit 115 mounted on a mounting board 114. The light 116 modulated by the liquid crystal light valve 111 passes through the imaging lens 117.
An image is formed on the photosensitive drum 102 by this. Imaging lens 1
17, an erect image can be obtained by using a SELFOC lens array (8LA) manufactured by Nippon Sheet Glass. 3 and 4 show the structure of the liquid crystal panel. The liquid crystal panel includes a glass substrate 1 provided with scanning electrodes 119 and 120.
18, a glass substrate 122 with signal electrodes 125 and 124, and a spacer 126, and a liquid crystal composition 127 is sealed between the glass substrate 122 and a spacer 126, and polarizing plates 128 and 1 are placed on both sides of the glass substrate.
It consists of 29 preparations. The scanning electrode consists of a transparent electrode 119 and an optically opaque metal electrode 120, and the signal electrode, like the scanning electrode, also consists of a transparent electrode 126 and a metal electrode 120.
It consists of an L pole 124. An alignment film 121 for regularly aligning the liquid crystal composition is provided on the surfaces of the scanning electrode and the signal electrode.
and 125 are formed.

The polarizing plates 128 and 129 are arranged so that their polarization axes are orthogonal to each other. The micro-shutters 150 are arranged at a rate of 10 pieces/m in order to form a high-density image, and the total number of micro-shutters is 2000 pieces because the image is formed on a width of 20 sheets of A4 paper. However, if this continues, 2000 signal electrodes will be required.
Furthermore, 2000 drive circuits and mounting terminals are required.
The manufacturing yield of liquid crystal panels decreases, and the cost also increases.The present invention uses time-division driving to significantly reduce the number of signal electrodes and simultaneously reduce the number of drive circuits. The liquid crystal panel of this embodiment has a duty of 115, thereby reducing the number of signal electrodes to 1/6.

The portion of the micro-shutter 160 of the scanning electrodes 119 and 120 is only the transparent side 119, and the hatched portion is crossed by the metal electrode 120.

As a signal electrode, a full length electrode 124 is provided on a part of a transparent electrode 123. If this metal electrode were not present, when the scanning electrode and the signal electrode were overlapped, light constantly leaking from the gap between the scanning electrodes would enter the wall, reducing the contrast ratio of the transmitted light of the microshutter.

Therefore, a part of the signal electrode was masked with a metal electrode to minimize the area of the light leakage portion 132, and it was possible to suppress the light leakage portion 132 to an extent that causes no practical problems.

In addition, by making the signal electrode 123 transparent except for the metal electrode portion 124, the alignment margin when combined with the glass substrate 118 on which the scanning electrode is configured can be increased in both the vertical and horizontal directions, and the yield can be increased. has improved.

Next, the interval t between the micro shutter arrays arranged in three rows is explained in detail in Japanese Patent Application Laid-Open No. 171578/1983, and when driven in n time divisions, L = (m +
1/n) X V X T I.

Here, mFi is an integer, V is the moving distance of the photoreceptor, Tl1k
The period includes v#. The image forming device we created this time has the following features:
The moving speed of the photoreceptor is V = 50 mm/a, the writing period T is 2 mm, and the number of time divisions n = 3. m can be any integer, but if it is small, t will be short and the electrode routing will be difficult. On the other hand, if it is large, it will be easier to route the stain pole with a long t, but the amount of data delay caused by shifting the micro shutter 7 array will increase, which will place a burden on the drive circuit. becomes larger.

Therefore, the number of m is determined by the trade-off between the two. In this liquid crystal panel, m=6, so t=sssμm.

Next, a method for driving the liquid crystal panel will be described.

In this example, the method described in Japanese Patent Application No. 60-228501 was adopted. FIG. 5 is a voltage-transmittance characteristic diagram of a ferroelectric liquid crystal and depicts a hysteresis loop. In order to turn on the liquid crystal light valve (light transmitting state), a voltage of 10 V is required.
A nollus with a pulse width Pw is applied. When the voltage +V is below the threshold voltage Vth1, the transmittance follows the locus of arrow 501 on the hysteresis loop, and the silite valve remains OFF. As the voltage of 10V is further increased, the transmittance follows the locus of the arrow 502 on the hysteresis loop, and once the saturation voltage v1'1 is exceeded, the transmittance is saturated even if the voltage is increased further. At this time, even if the voltage is zero, the previous state is maintained and the transmittance is maximized because it follows the trajectory of arrow 503 on the hysteresis loop.

If the voltage V is chosen to be a value vht that has the relationship vthl(v(vsatl), the hysteresis loop of transmittance will follow the locus of arrow 505, and an intermediate level for the maximum transmittance will be obtained. Therefore, vl”1 and Vthl
Transmittance gradation control becomes possible by setting the voltage by dividing the interval. The liquid crystal light valve can be turned OFF (light cutoff state) by setting the voltage -V, which has the opposite polarity to that when turning it ON, to a voltage that exceeds the saturation voltage Vaa12. Further, from the voltage-transmittance characteristic diagram in FIG. 5, the following two characteristics can be read which are extremely important for time-division driving. First, the = 9- voltage applied to the liquid crystal is below the threshold voltage, Vth, )VIVth21)1
-vl, the optical characteristics are not affected. Second,
The point is that 4A'l when a voltage of pulse width Pv is applied is maintained even after the voltage is reduced to zero V.

Figure s6 shows a drive waveform based on the characteristics of the ferroelectric liquid crystal and the optical response characteristics at that time. The scanning electrode waveform 200 is at 1/6 duty, where Tf is the scanning period and Ts
is the selection period. The first half pulse of Ts is an erase pulse for turning off the liquid crystal light valve, and the second half pulse of Ta is a drop pulse for modulating the transmittance of the light valve with gradation data. Reference numeral 201 denotes a signal electrode waveform, which is a pulse having an opposite phase to the selection period of the scanning electrode waveform having oscillations corresponding to each gradation level.

In this embodiment, in order to express 8 gradations, the data amplitude is divided into 8 between vtb and VaaLl.
Levels are prepared and selected according to the key data of V/. 202 is a scanning electrode waveform 200 and a signal electrode waveform 201
This shows an example of a waveform when the transmittance is increased every frame, and the voltage applied to the liquid crystal layer during the writing period Tw is V of the transmittance-applied voltage characteristic 203.
It is applied between a h 1 and Vsatl according to the floor data. Further, the absolute value of the voltage applied to the liquid crystal layer during the non-selection period Tus is always less than or equal to the threshold value Vth, , IVh21. The absolute value of the voltage of the erase pulse applied to the first half To of the selection period Ts is always equal to or higher than IVaat21,
At the beginning of each frame Tf, the light valve is always turned off. The threshold characteristics of the liquid crystal used in this example are V t
h, = 8 V, V satl = 14.4 V
V t hl=asv, Vs a tl =15. O
It was v.

Therefore, the driving conditions are V, =7.8V-V, =-
1! i2 V, V, = &4 V, and the applied voltage difference between each gray level of the signal electrode was set to α8v.

Next, FIG. 7 shows the configuration of a drive circuit that can realize the drive waveform shown in FIG. 6. 8(a) and 8(b) show waveforms of various parts of the drive circuit of FIG. 7.

By driving the liquid crystal light valve as described above, it became possible to control the transmittance at 8yfI.

Next, a method for obtaining a gradation display image using the light valve will be described. A high-intensity monochromatic fluorescent tube with an aperture is used as the light source, and the output energy of the light valve on the photosensitive drum is obtained at a maximum of 20 ert/cdl. An organic photoreceptor is used as the photoreceptor.

The surface movement speed of the photosensitive drum was 50 m/a.

FIG. 9 shows various characteristics in each image forming process. (&) The figure shows the relationship between the output energy of the light valve and the gradation level of the input image data.0 (b) The figure shows the exposure characteristics when the output light from the light valve is irradiated onto the photosensitive drum that has been initially electrified. It is. In this example, when the initial charging was 720V, the exposure amount was 20er.
A near IJ region up to f/cm was obtained. The figure (e) shows the development characteristics.

This embodiment employs reversal development. Figure (d) is a combination of the previous m15% characteristics and shows the relationship between input gradation level and image density. Here, by using a combination of linear regions of each characteristic, a good gradation display image was obtained in which the input gradation level and image density were proportional to each other.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to independently change the degree of modulation of each liquid crystal light valve according to the gradation information of the image signal, making it ideal for printing devices that produce high-density and variable gradation images. It has this effect.

The above embodiment shows an example of the present invention, and the present invention is not limited to 8 gradations, but can also be applied to 161v tone expression etc.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of the printing apparatus of this embodiment, FIG. 2 is a diagram showing the configuration of the light modulation element, FIG. 3 is a sectional view showing the configuration of the liquid crystal panel, and FIG. 4 is a diagram showing the configuration of the liquid crystal panel. , a pattern diagram of a liquid crystal panel, FIG. 5 is a voltage-transmittance characteristic diagram of ferroelectric liquid crystal, FIG. 6 is a diagram of driving waveforms and transmittance characteristics of a light valve, and FIG.
The figure is a configuration diagram of the g-dynamic circuit. 205: Gradation data 206: Gradation data Shift clock 207: Gradation data launch pulse 208 Double-launched gradation data 209: Voltage control signal 210: Scanning data 211: Scanning data Shift clock 212: Voltage control signal 213.214 ,215,216,217,218゜2
19.220, 221: Liquid crystal drive voltage 222: Signal electrode 9111 shift register 226: Signal electrode side latch 224: Signal electrode side decoder 225: ) Transmission gate 226: Inverter 227: Scanning electrode side shift register 228: Voltage follower 229: Voltage dividing resistor 230: Scanning electrode 251: Signal electrode FIG. 8 is a diagram showing waveforms of various parts of the drive circuit, and FIG. 9 is a diagram showing various properties of the image forming process. Figure 1 Figure 2 Figure 3 (pano (b) 'iff A F”A 禾 t+ ward HOx-ne 1reki ゛E [υ1に１] Ltr] at amount E [&1 /cd3 (λ 4σV nt(c4)

Claims (1)

[Claims] A substrate equipped with N scanning electrodes (N is an integer), a substrate equipped with M signal electrodes (M is an integer), a liquid crystal layer sandwiched between the two substrates, and at least one layer on the outside of both the substrates. What is claimed is: 1. A liquid crystal optical device comprising an N time-division driving device configured to independently change each light valve constituting the liquid crystal device.