JPS63234220A - Optical writing device - Google Patents

Abstract

PURPOSE:To prevent degradation in the quality of a recording image by providing a light shielding region to the central part of a mask aperture forming each of microshutters of a crystal shutter array for an optical writing device, thereby flattening the distribution of quantity of light for each of dots and increasing the inclination of the quantity of light from the peripheral part to the central part. CONSTITUTION:Light from a fluorescent lamp 11 of the optical writing device 3 for a liquid crystal shutter printer is entered via a reflecting plate 12 and a deflecting plate 13 to a liquid crystal 14 constituting the liquid crystal microshutter array and the recording image for one line is projected on a photosensitive body by on/off of the shutter array. A common electrode and a photomask 24 which shields the other parts except the part of the aperture AP forming the microshutter array of the device 3 are attached to the liquid crystal 22 of the transparent electrode 20 of such array. A star-shaped exposing part 30 is formed to the central part of the aperture AP so that the light past the aperture AP has a flat distribution of the quantity of the light in the central part. A difference in the quantity of light between the central part and the peripheral part is thereby decreased and the degradation in the quality of the recording image is prevented.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to an optical writing device that turns on and off light from a light source from a liquid crystal shutter array and irradiates a photoreceptor with recording light corresponding to one line of recorded image. Regarding this.

[Prior Art] In recent years, with the spread of so-called office automation, various information processing devices have been introduced into office environments. Devices used for such environmental protection 1 are required to suppress as much as possible elements that adversely affect the environment, such as noise and vibration.

By the way, dot impact printers have been widely used for recording and outputting documents created with Japanese word processors etc. as hard copies, but such dot impact printers produce printing noise and vibration. Large, especially high-speed machines tended to be prone to this, and often interfered with the work of those around them.

To solve this problem, non-impact printers, such as laser beam printers, liquid crystal shutter printers, and LED printers, which form images using an electrophotographic process, have been put into practical use.

Unlike the above-mentioned dot-impact printer, this printer produces very low printing noise because there is no part where the paper is struck when forming an image, and it also uses a page printer that basically records an image on a page-by-page basis. Therefore, high-speed recording is possible.

By the way, among such page printers, laser beam printers require a highly accurate optical system such as a polygon mirror in the optical writing system, and are therefore extremely costly. In addition, in LED printers, L is used for optical writing system.
Due to variations in the light emitting characteristics of EDs (light emitting diodes), it is difficult to obtain stable recorded images.

On the other hand, the liquid crystal shutter used in the optical writing system of liquid crystal shutter printers can integrate the light source, liquid crystal shutter, and imaging element that make up the optical system, and the optical system can be configured easily and compactly, resulting in an inexpensive device. can do.

FIG. 5 illustrates a liquid crystal shutter printer.

In the figure, the surface of a photoreceptor 1 is uniformly charged by a charger 2, and an optical writing device 3 exposes a light image corresponding to a recorded image to form an electrostatic latent image corresponding to the recorded image on its surface. be done. This electrostatic latent image is developed with toner by a developing device 4, and the toner image thus formed on the surface of the photoreceptor l is transferred by a transfer charger 5 onto a recording sheet conveyed by a paper feeding system (not shown). .

The toner image transferred to the recording paper is then thermally fixed by the fixing device 6, thereby forming a recorded image on the recording paper.

Further, residual toner and residual charges on the photoreceptor l are removed by a cleaner 7.

An example of the optical writing device 3 is shown in FIG.

In the figure, the optical writing device 3 includes a fluorescent lamp 1, a reflecting plate 12 that reflects the light of the fluorescent lamp 11, a polarizing plate 13 having a crossed Nicol polarization axis, a liquid crystal plate 14 constituting a liquid crystal micro shutter array, and a polarizing plate 12 that reflects the light of the fluorescent lamp 11. It consists of a polarizing plate 15 having a polarization axis perpendicular to the plate 13, and a same-magnification linear imaging element 16 such as a focusing fiber array.

The liquid crystal plate 14 includes a pair of transparent substrates 20, 21 and a liquid crystal 22.
It is composed of enclosed. Liquid crystal 22 on one transparent substrate 20
As shown in FIG. 7(, ), the common electrode 2 made of a band-shaped transparent electrode material covers an area wider than the area where the micro-shutter array is formed.
3, and as shown in FIG. 7(b), an optical mask 24 is attached for shielding light from the other parts except for the part of the opening AP forming the micro-shutter array. The opening AP is one of the images generated by this optical writing device 3.
They are formed in dimensions corresponding to the pixels, and all have the same shape 4 Also, on the surface of the other transparent substrate 21 that contacts the liquid crystal 22, as shown in FIGS. 7(C) and (d), , a segment electrode 25 made of a strip-shaped transparent electrode material and set to have a width slightly larger than the opening AP is attached.

Note that an ITO film or the like can be used as the transparent electrode material constituting the segment electrodes 25 and the common electrode 23. Further, the material of the optical mask 24 can be a metal such as nickel or molybdenum, and is formed by etching, vapor deposition, plating, or the like.

Now, due to the MTF (spatial frequency) characteristics of the optical system, the light that has passed through the aperture AP that forms the micro-shutter has a light intensity distribution in which the light intensity peaks at the center, as shown in Figure 8. Become.

Therefore, as shown in FIG. 9, the voltage distribution of the electrostatic latent image formed on the photoreceptor 1 has an inverse peak shape with a slope such that the level at the center of the dot is the lowest.

Then, the toner supplied from the developing device 4 adheres to the portion where the voltage is lower than the development threshold Td, so that the electrostatic latent image is visualized.

Here, the voltage vb is a precharge voltage applied to the photoreceptor 1 by the charger 2.

This precharge voltage vb varies due to variations in the characteristics of the photoconductor 1 (especially in the circumferential direction) and variations in humidity and temperature. The image voltage varies depending on the variation.

On the other hand, since the development threshold Td takes a value specific to the image forming system, if the voltage of the electrostatic latent image changes in this way, the threshold Td will relatively change.

Further, as described above, since the voltage distribution of the electrostatic latent image of one dot has a slope, when the threshold value Td changes in this way, the adhesion area of toner per dot changes.

Therefore, conventionally, the density of recorded images is uneven.

This has caused the inconvenience of deteriorating image quality.

[Objective] The present invention was made in order to eliminate the disadvantages of the prior art, and an object of the present invention is to provide an optical writing device that can prevent deterioration in the quality of recorded images.

[Structure] In order to achieve this object, the present invention provides a light-shielding region in the center of each mask opening for forming each micro-shutter.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an optical mask according to an embodiment of the present invention. The present invention is applied to an optical writing device used in a device similar to the above-mentioned liquid crystal shutter printer, and in the following description, corresponding parts in FIGS. 5 to 9 will be referred to. are given the same symbol.

A star-shaped light shielding part 30 is formed in the center of the opening AP formed in the optical mask 24.

Therefore, as shown in FIG. 2, the light passing through the aperture AP has a flat light intensity distribution in the center, and the difference in light intensity between the center and the periphery is different from the conventional one shown in FIG. smaller than that of the device. Furthermore, the slope of the amount of light from the periphery to the center is larger than in the conventional case.

Therefore, as shown in Fig. 3, the voltage distribution of the electrostatic latent image formed on the photoreceptor 1 by the light passing through the aperture AP is large at the center of the dot where the level is minimum, and from the periphery to the center. The voltage gradient becomes very large.

Therefore, as described above, even if the development threshold Td changes relatively, the area of the portion to which the toner adheres hardly changes.

As a result, the density of the recorded image becomes uniform, and the quality of the recorded image can be significantly improved.

Incidentally, in the above-described embodiment, the shape of the light shielding part 30 formed at the center of the opening AP is star-shaped, but the shape is not limited to this.

For example, as shown in FIG. 4(a''), a square light shielding part 31 having a similar shape to the opening AP is provided, or as shown in FIG. 4(b), the light shielding part 31 is rotated by 45 degrees. Even if the light shielding part 32 is provided, the same effect as that of the above-mentioned embodiment can be obtained.

In the embodiments described above, the shape of the opening is square, but the present invention can be similarly applied to an opening having a rectangular shape.

[Effects] As explained above, according to the present invention, since a sparse light region is provided in the center of the mask opening for forming each micro-shutter, the light intensity distribution for each dot becomes flat and The gradient of the amount of light from the periphery to the center becomes very large, resulting in the effect that deterioration in the quality of recorded images can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an optical mask according to an embodiment of the present invention, FIG. 2 is a graph diagram showing a light amount distribution due to the opening formed in the optical mask of FIG. 1, and FIG. A waveform diagram showing the voltage distribution of the electrostatic latent image formed by the aperture of the light intensity distribution shown in the figure, Figure 4 (a) is a schematic diagram showing another example of the light shielding part, and Figure 4 (b) is a schematic diagram showing the light shielding part. 5 is a schematic diagram showing another example, FIG. 5 is a schematic configuration diagram of a liquid crystal shutter printer, FIG. 6 is a schematic diagram of an optical writing device, and FIG. 7(a) is a schematic diagram showing an example of a common electrode. Figure (b) is a schematic diagram showing a conventional example of an optical mask, Figure (c) is a schematic diagram showing an example of segment electrodes, Figure (d is a schematic diagram for explaining the positional relationship of each electrode, Fig. 8 is a graph showing the light quantity distribution due to the aperture formed in the optical mask of Fig. 7(b), and Fig. 9 is a voltage distribution of the electrostatic latent image formed by the aperture of the light quantity distribution of Fig. 8. It is a waveform diagram showing 24... optical mask, 30, 31, 32... light shielding part,
AP...open['' section. Agent Patent Attorney Makoto Hijiri Figure 1 Figure 2 Figure 4 (a) (b) Figure 5 Figure 6 Figure 7 Figure 7 Figure 8 25 Figure 9

Claims (1)

[Claims] The light source is turned on and off by the liquid crystal shutter array.
An optical writing device that irradiates a photoreceptor with recording light corresponding to a recorded image for a line, characterized in that a light-blocking area is provided in the center of a mask opening for forming each micro-shutter of the liquid crystal shutter array. An optical writing device.