JP2502317B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including a liquid crystal-optical shutter array using a ferroelectric liquid crystal.

[Prior Art] Up to now, in JP-A-56-98073, JP-A-56-98967, JP-A-57-120466, etc., by utilizing the optical modulation function of the liquid crystal, this modulator A so-called liquid crystal-optical shutter array has been proposed in which micro-shutters are arranged in an array, light is projected onto the micro-shutters, and an optical image signal is given to a photoconductor by the transmitted light.

A liquid crystal-optical shutter array utilizing the high-speed response and memory property of a ferroelectric liquid crystal is disclosed in, for example, US Pat. No. 454847.
No. 6 and Japanese Patent Laid-Open No. 60-107023.

However, there is a problem that it is difficult to obtain a halftone print by the liquid crystal-optical shutter array described above. In particular, in the case of a liquid crystal-optical shutter array using a ferroelectric liquid crystal, the ferroelectric liquid crystal adopts two optical stable states depending on the direction of the electric field, as disclosed in US Pat. No. 4,367,924. Therefore, there is a difficult problem in forming a halftone light transmission state.

[Outline of Invention]

An object of the present invention is to provide an image forming apparatus capable of forming a halftone image at high speed. A device that achieves this object includes: a light source; a photoconductor; and a plurality of pixel rows, each of which includes a plurality of liquid crystal pixels arranged in a first direction, arranged in a second direction intersecting the first direction. A liquid crystal-optical shutter for selectively transmitting light from a light source to expose the photoconductor, and an opening time of liquid crystal pixels for transmitting light are different for each pixel row and the photoconductor is the same. The liquid crystal so that the part is exposed a plurality of times by a plurality of the pixel rows.
A driving circuit for driving an optical shutter, wherein the liquid crystal pixel is a pixel configured by using a chiral smectic liquid crystal, and the driving circuit has a period in which an opening of the liquid crystal pixel is simultaneously generated in all the pixel columns. As described above, the image forming apparatus is a circuit for driving the liquid crystal-optical shutter. According to the present invention, since it is possible to drive all pixel columns without time-division driving and with a simple circuit configuration, exposure control for halftone can be performed at high speed.

[Detailed Description of Embodiments of the Invention]

FIG. 1 is a timing chart showing a drive waveform used in the apparatus of the present invention and its optical response state in time series.
FIG. 2 is a plan view of the matrix electrode structure used in the device of the present invention.

The matrix electrode structure shown in FIG. 2 is capable of expressing gradation in 16 steps of 0/15, 1/15, ... 15/15 by four shutter rows. Scan lines S ₁ °, S ₂ °, S ₃ ° and S ₄
The scan pulses S ₁ , S ₂ , S ₃ and S ₄ shown in FIG. 1 (a) are applied to each of the data lines, and the data lines I ₁ °, I ₂ °, ... As shown, the image signals I ₁ , I ₂ , ... Are applied as the open / closed binary signal divided into four timings.

At this time, four pixels A on the same data line (signal electrode),
The applied voltages of B, C, and D have the time-series waveforms shown in FIG. 1 (c), and the open / closed state is determined according to the electric field direction of the voltage exceeding the threshold voltage of the ferroelectric liquid crystal. The light transmission state of each pixel is as shown in FIG. Therefore,
The exposure amount on the photoconductor in this scanning cycle is A ′, B ′,
The ratio of 8: 4: 2: 1 is obtained at the imaging positions of C'and D '. At this time, among the scanning lines S ₁ , S ₂ , S ₃ and S ₄ , the time intervals t ₂ , t ₂ , t ₃ , t _{4 of the} scanning selection signals applied to the adjacent scanning lines are 8: 4: 2. It is set to a ratio of: 1. FIG. 3 is a diagram showing the positional relationship between the shutter 31 and the photoconductor 32. The windows of the pixels A, B, C, and D on the shutter 31 are formed by the lens array 33 of an equal-magnification inverted position on the photoconductor 32. Images are formed on A ', B', C ', and D'.

Next, the above scanning is repeated to form another image on the shutter, and at the same time, the photoconductor is moved by one line. At this time, the shutter windows of the pixels B, C, D form images at the image forming locations A ', B', C'on the photoconductor, respectively, while the image forming location D'exits outside the image forming range. The image forming location Z ′ is newly positioned to receive the transmitted light from the shutter window of the pixel A.

By repeating this operation, one point on the photoconductor will be pixel A
The whole exposure process is completed in four scanning cycles by receiving the transmitted light in the order of B → C → D. In this respect, for example,
When the exposure of 11/15 is performed, since 11 = 8 + 2 + 1, it is sufficient to give a signal of opening at pixel A, closing at pixel B, opening at pixel C, and opening at pixel D. FIG. 4 shows the scanning line voltage and the signal line voltage in that case. Table 1 shows the correspondence between the gradation signal and the opening / closing signal at each exposure timing of the pixels A, B, C and D.

Further, in a preferred embodiment of the present invention, the driving method disclosed in, for example, US Pat. No. 4,655,561 can be used in addition to the driving train shown in FIG.

In the above-described embodiment, the property that the ferroelectric liquid crystal transits between states only at a voltage equal to or higher than the threshold value and retains the state at a voltage lower than the threshold value is used. In the following reference examples, an open / closed state of the ferroelectric liquid crystal can be controlled by always applying an electric field equal to or higher than the threshold value and by controlling the direction of the electric field.

FIG. 5 shows an example of the driving, and the scanning pulses (a) of S _{1 to} S ₄ for driving the matrix shutters of four columns, I ₁ , I
₂ signal pulse (b), composite voltage applied to pixel (c),
It is a figure which shows the light transmission state (d) of each pixel at that time.
This driving method, as described in detail in U.S. Pat.No. 4,548,476, opens with a positive direction applied voltage of voltage V ₀ or more,
The property of taking a closed state by an applied voltage in the negative direction is used, and the light transmission state is as shown in FIG. 5 (d).

As shown in FIG. 5 (a), the scanning line selection time is 8: 4: 2:
Since it is set to 1, the exposure amount of each pixel of pixels A, B, C and D is also 8: 4: 2: 1, and by repeating this scanning, the same gradation printing as in the previous embodiment can be obtained. it can.

FIG. 6 is a schematic configuration diagram showing an example of an image forming apparatus using a liquid crystal-optical shutter. In the figure, the image forming apparatus is a linear light source 61 such as a fluorescent lamp and a pair of polarizing plates 62 and 63.
And a substrate 64 sandwiched between the polarizing plates 62 and 63.
, A lens array 65 and a photosensitive drum 66, and a liquid crystal-optical shutter array is mounted on the substrate 64. Accessories such as a charger are omitted in the figure. The light emitted from the light source 61 passes through the modulation systems 62, 63 and 64, is condensed by the lens array 65, and is printed on the photosensitive drum 66. Such an electrostatic recording device has advantages that it is easier to miniaturize the device than a laser printer or the like, and that there is no mechanical drive portion, so that noise is small.

FIG. 7 shows a driving device for the ferroelectric liquid crystal panel 71 in which the matrix electrodes used in the present invention are arranged. In the panel 71 of FIG. 7, the scanning lines 72 and the data lines 73 intersect each other, and the ferroelectric liquid crystal is disposed between the scanning lines 72 and the data lines 73 at the intersections. . Also, 74 in FIG.
Is a scanning circuit, 75 is a scanning side driving circuit, 76 is a signal side driving voltage generating circuit, 77 is a line memory, 78 is a shift register,
Reference numeral 79 represents a scanning side drive voltage generating power source, and 70 represents a micro processor unit (MPU).

The scanning side drive voltage generating power supply 79 is provided with voltages V ₀ , −V ₀ and O. For example, the voltages V ₀ and −V ₀ are used as the power supply for the scan selection signal described above, and the voltage O is the power supply for the scan non-selection signal. Can be

As the liquid crystal having bistability that can be used in the driving method of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable. Among them, a chiral smectic C phase (SmC ^* ) or an H phase (SmH ^* ) is used ^. A) liquid crystal is suitable. This ferroelectric liquid crystal is described in "Le Journal de
"The Letter of Le Journal de Physic lette"
r ") Volume 36 (L-69), 1975," Ferroelectric
Liquid Crystals "(" Ferroelectric Liquid C
rystals ");" Applied Physics Letters "36 (11), 198
"Submicro Second Bistable Electro-Optical Switching in Liquid Crystal"("Submicro Second Bistable Electro
optic Switching in Liquid Crystals ”);“ Solid physics
16 (141) 1981 "Liquid Crystal" U.S. Patent No. 4561726, U.S. Patent No. 4589996, U.S. Patent No. 4596667, U.S. Patent No. 4613209, U.S. Patent No. 4614609, U.S. Patent No. 4639089 And the ferroelectric liquid crystals disclosed therein can be used in the present invention.

More specifically, examples of the ferroelectric liquid crystal compound used in the method of the present invention include desiloxybenzylidene-P'-
Amino-2-methylbutyl cinnamate (DOBAMBC),
Hexyloxybenzylidene-P'-amino-2-chloropropyl cinnamate (HOBACPC) and 4-o-
(2-methyl) -butyl resorcylidene-4'-octylaniline (MBRA8) and the like can be mentioned.

When an element is formed using these materials, the element is supported by a copper block or the like in which a heater is embedded as necessary in order to maintain a temperature state in which the liquid crystal compound becomes a SmC ^* phase or an SmH ^* phase. be able to.

Further, in the present invention, in addition to SmC ^* and SmH ^* described above, it is also possible to use a ferroelectric liquid crystal represented by chiral smectic F phase, I phase, J phase, G phase or K phase.

FIG. 8 schematically illustrates an example of a ferroelectric liquid crystal cell. 81a and 81b are substrates (glass plates) coated with transparent electrodes such as In ₂ O ₃ , SnO ₂ and ITO (indium-thein-oxide). In the meantime, a liquid crystal of SmC ^* phase in which the liquid crystal molecular layer 82 is oriented perpendicular to the glass surface is enclosed. A thick line 83 represents a liquid crystal molecule, and the liquid crystal molecule 83 has a dipole moment (P⊥) 84 in a direction orthogonal to the molecule. When a voltage higher than a certain threshold is applied between the electrodes on the substrates 81a and 81b, the helical structure of the liquid crystal molecules 83 is unraveled, and all the dipole moments (P⊥) 84 are oriented in the electric field direction. Can be changed. The liquid crystal molecules 83 have an elongated shape, and exhibit refractive index anisotropy in the major axis direction and the minor axis direction thereof. Therefore, for example, if polarizers arranged in a crossed Nicols position above and below a glass surface are placed. It is easily understood that the liquid crystal optical modulation element has optical characteristics that change depending on the polarity of voltage application. Further, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1 μ), the helical structure of the liquid crystal molecules is unraveled even when no electric field is applied, as shown in FIG.
The dipole moment Pa or Pb takes either an upward (94a) or downward (94b) state. When an electric field Ea or Eb having a polarity equal to or higher than a certain threshold value is applied to such a cell for a predetermined time as shown in FIG. 9, the dipole moment is upward 94a or downward 94b with respect to the electric field vector of the electric field Ea or Eb. The orientation is changed, and the liquid crystal molecules are aligned in either the first stable state 93a or the second stable state 93b accordingly.

There are two advantages of using such a ferroelectric liquid crystal as the optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has a bistable state. The second point will be described with reference to FIG. 9, for example. When an electric field Ea is applied, the liquid crystal molecules are oriented to a first stable state 93a. This state is stable even when the electric field is turned off. When an electric field Eb in the opposite direction is applied, the liquid crystal molecules are in the second stable state 93.
The molecule is oriented to b and the direction of the molecule is changed, but it remains in this state even after the electric field is cut off. Further, unless the applied electric field Ea exceeds a certain threshold value, the respective alignment states are also maintained. In order to effectively realize such a high response speed and bistability, it is preferable that the cell is as thin as possible, generally 0.5 μ to 20 μ, and particularly 1 μ to
5μ is suitable.

〔The invention's effect〕

According to the present invention, since a halftone print can be formed by a binary drive method that controls opening and closing, it is possible to simplify the device design, particularly the design of the drive circuit.

[Brief description of drawings]

1 and 4 are timing charts showing the drive waveform and the optical response used in the present invention in time series. Second
The figure is a plan view of the matrix electrode structure used in the present invention. FIG. 3 is an explanatory diagram showing the positional relationship between the shutter section and the light irradiation section. FIG. 5 is a timing chart showing the drive waveform and the optical response used in the reference example in time series. FIG. 6 is a perspective view of an electrophotographic printer which is an example of the present invention. FIG. 7 is a block diagram of the liquid crystal-optical shutter section used in the image forming apparatus of the present invention. 8 and 9 are perspective views of the ferroelectric liquid crystal device used in the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shuzo Kaneko 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP 61-116325 (JP, A) JP 61 -103122 (JP, A) JP-A-60-153028 (JP, A)

Claims (3)

(57) [Claims] 1. A light source, a photoconductor, and a plurality of pixel rows each including a plurality of liquid crystal pixels arranged in a first direction are arranged in a second direction intersecting the first direction. A liquid crystal-optical shutter for selectively transmitting light to expose the photoconductor and an opening time of liquid crystal pixels for transmitting light are made different for each pixel row, and the same portion of the photoconductor is set to A driving circuit for driving the liquid crystal-optical shutter so as to expose a plurality of times by a plurality of pixel rows, wherein the liquid crystal pixel is a pixel configured by using a chiral smectic liquid crystal, and the driving circuit is An image forming apparatus comprising: a circuit that drives the liquid crystal-optical shutter so that an opening of liquid crystal pixels is simultaneously generated in the pixel row. 2. The liquid crystal pixel opening time set for each pixel column has a ratio of 1: 2: 4: 8: ... 2 ^N (N is the number of columns) for each column. The image forming apparatus according to claim 1, wherein the image forming apparatus is driven. 3. The respective pixel columns are connected to each other by scanning lines, and the drive circuit makes the application timing of a scanning selection signal applied to the scanning lines different for each pixel column. The image forming apparatus according to claim 1.