JPH07108574B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus using a liquid crystal shutter array as a printer bed.

(Prior Art) Conventionally, in a liquid crystal display element or a liquid crystal shutter array, n scanning electrodes and m signal electrodes are formed in a matrix, and a large number of pixels and shutter openings are formed of liquid crystal which is a capacitive load element. There is something I did. As a driving method of the liquid crystal element, time division drive is employed in which address signals are sequentially and selectively applied to the scanning electrode groups, and predetermined information is selectively applied to the signal electrode groups in parallel in synchronization with the address signals. Has been done. Particularly in a well-known TN (Twisted Nematic) type liquid crystal element, V _ON (on signal) / V _OFF (off signal) becomes 1 as the number of time divisions increases as shown in the following formula (1) in the above driving method. As a result, the opening and closing efficiency of the liquid crystal element forming the pixel becomes poor. Therefore, especially in the case of a liquid crystal shutter array, it is not possible to give an optical signal having a sufficient S / N ratio, and when this is used in the image exposure unit (printer head) of an electrophotographic copying machine, it is possible to obtain a good optical signal. There is a problem that an image cannot be formed.

(In the formula, 1 / N; duty ratio, 1 / a; bias ratio, V ₀ ; applied voltage) That is, the best driving condition is / 1 duty, that is, stack driving, but in this driving method, each pixel is It needs to be controlled by the driver circuit. For example, A4
In the case of a liquid crystal shutter array capable of generating a light spot with a pixel density of 16 dots / mm in the short width of (Japanese Industrial Standards), 3360 drive circuits are required, and 32 ICs per IC.
If the drive circuits are integrated, 105 ICs will be required. Therefore, the static driving method is not suitable for driving a high-density pixel or a liquid crystal shutter array having a shutter opening.

Further, US Pat. No. 4,367,924 discloses a ferroelectric liquid crystal shutter having a high-speed response and a memory property, and this liquid crystal shutter can improve the S / N ratio in principle. It is said that.

(Problems to be Solved by the Invention) However, although such a conventional example has excellent characteristics in terms of memory property, threshold value characteristic, and cell reliability, the alignment of the ferroelectric liquid crystal Due to the state, the opening / closing efficiency (contrast) when the panel surface of the liquid crystal shutter array is oriented perpendicular to the optical path cannot be obtained, and an optical signal having a sufficient S / N ratio cannot be given after all. However, there was a problem that a good image could not be formed when used in the image exposure section of an electrophotographic copying machine.

Therefore, the present invention has been made to solve the above-mentioned problems of the conventional example, and an object thereof is to provide an image forming apparatus capable of obtaining a high-quality image.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, a photosensitive drum, a light source, and a liquid crystal whose longitudinal direction is arranged parallel to the rotation axis of the photosensitive drum. A shutter array,
In an image forming apparatus that forms an image on the surface of the photosensitive drum by exposing the surface of the photosensitive drum with light emitted from the light source and passing through a liquid crystal shutter array, the liquid crystal shutter array is arranged in a direction intersecting a longitudinal direction. A glass surface of the liquid crystal shutter array having a pair of rubbed glass plates and a ferroelectric liquid crystal sandwiched between the pair of glass plates so that the downstream side in the rubbing direction of the glass plates is closer to the light source than the upstream side. Is inclined with respect to a plane perpendicular to the exposure optical path.

(Operation) In the present invention having the above configuration, the panel surface of the liquid crystal shutter array is arranged so as to be inclined with respect to the exposure light path, so that the opening / closing efficiency (contrast) and S / N ratio of the liquid crystal shutter array can be improved. It is an improvement.

(Example) Below, this invention is demonstrated based on the Example shown in figure. First
FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention, in which 1 is a liquid crystal shutter array,
2 is a photosensitive drum made of amorphous silicon (a-Si), an organic photoconductive photosensitive member, 3 is a fluorescent lamp as a light source, 4
Is a Selfoc lens array (SLA) as an imaging means
The surface of the photosensitive drum 2 is uniformly charged in advance by the charger 5, and the light generated from the printer head unit 10 including the fluorescent lamp 3 and the liquid crystal shutter array 1 is formed on the surface of the photosensitive drum 2. By irradiating the signal, an electrostatic latent image roughly equivalent to the information signal can be formed. This electrostatic latent image is developed by a developing device 6 through a normal electrophotographic process and is transferred by a transfer charging device 7 to a transfer paper which is transferred in the direction of arrow B. The transfer image is fixed by a fixing device 9 to form an image. To be done. Reference numeral 8 is a cleaning device for cleaning the surface of the photosensitive drum 2, and 15 is a light collecting cover for the fluorescent lamp 3.

Here, in the present invention, the liquid crystal shutter array 1 includes the substrate glass 22 as a pair of glass plates rubbed in a direction intersecting the longitudinal direction, and the ferroelectric material sandwiched between the upper and lower substrate glasses 22, 22. With the liquid crystal 26, the surface of the substrate glass 22 of the liquid crystal shutter array 1 is inclined with respect to the surface perpendicular to the exposure light path so that the downstream side of the substrate glass 22 in the rubbing direction is closer to the fluorescent lamp 3 than the upstream side. By being arranged, the opening / closing efficiency (contrast (brightness)) of the liquid crystal shutter array 1 is improved, and it becomes possible to irradiate the photosensitive drum 2 with an optical signal having a sufficient S / N ratio, thereby forming a good image. be able to.

In addition, what angle of the liquid crystal shutter array 1 is set to the exposure optical path.
Whether to incline with respect to 12 differs depending on the liquid crystal material and the alignment film used and the alignment state of the liquid crystal associated therewith, or the position of the polarizing plate and the rubbing direction. For example, the third
As shown in the figure, an analyzer for a ferroelectric liquid crystal cell in which a ferroelectric liquid crystal 26 is sandwiched from both sides by a substrate glass 22 having an ITO (InTiO ₃ ) electrode 23 and a PVA (polyvinyl alcohol) alignment film 25 containing a Ti-based chelating material 21 and Polarizer
The case of using the ferroelectric liquid crystal shutter array 1 arranged between 27 will be described. In this case, an insulating film of SiO ₂ film 24 is particularly used between the bead spacer 28 and the substrate glass 22. The configuration is shown. Further, the fine matrix wiring of the liquid crystal shutter array is omitted, and the analyzer 21 and the polarizer 27 are arranged in parallel with the ferroelectric liquid crystal cell, but it is also possible to arrange them apart from the cell and inclined with respect to the cell. is there.

In the liquid crystal shutter array 1 having the configuration shown in FIGS. 4 (a) and 4 (b), X of FIG.
The rubbing is performed in the a direction, which is tilted approximately 60 ° with respect to the direction (main scanning direction), and the polarizer 27 is arranged so that the polarization axis of the electric vector is in the b direction. The vector was arranged in the C direction where the polarization axis was perpendicular. At this time, the angle between the normal direction (Z direction) of the panel surface 13 of the liquid crystal shutter array 1 and the exposure light path 12, that is, the tilt angle θp of the panel surface 13 is tilted by about 30 °, so that the openings of the liquid crystal shutter array 1 are formed. It is possible to improve efficiency (contrast) and form a good image.
In FIG. 2B, 30 is a pixel.

FIG. 5 is a graph showing the dependence of the transmitted light amount in each of the bright state and the dark state on the inclination angle θp of the panel surface 13,
According to the figure, when the panel surface 13 is not tilted so that the downstream side of the substrate glass 22 in the rubbing direction is closer to the fluorescent lamp 3 than the upstream side with respect to the exposure optical path 12, that is, the contrast when θp = 0 °. In contrast to 2.1, the contrast is improved to about 2.6 when the panel surface 13 is tilted about 30 ° with respect to the exposure light path 12, that is, when θp = 30 °. Also, the brightness in the bright state is more than that in the case of θp = 0 °.
It can be seen that the image quality is increased 1.1 times and the image quality is improved from θp = 0 °.

Incidentally, regarding the alignment state of the ferroelectric liquid crystal, the panel surface of the liquid crystal shutter array 1 with respect to the exposure optical path 12 as described above.
It is possible to improve the opening and closing efficiency by tilting 13.
It is believed that the molecules have a twisted structure from bottom to top of the substrate glass.

(Effects of the Invention) The image forming apparatus according to the present invention has the above-described configuration and operation, and it is said that a favorable image can be formed by improving the opening / closing efficiency (contrast) and the S / N ratio. Produce an effect.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a view from the direction of arrow A in FIG. 1, and FIG.
FIG. 4 is a partial sectional view showing a liquid crystal shutter array in the same embodiment, FIGS. 4 (a) and 4 (b) are explanatory views of a tilt angle of a panel surface of the liquid crystal shutter array, and FIG. 5 is a panel of the liquid crystal shutter array. It is a graph which shows the relationship between the inclination angle of a surface and the amount of transmitted light. Explanation of symbols 1 ... Liquid crystal shutter array 2 ... Photosensitive drum (image carrier) 3 ... Fluorescent lamp (light source) 12 ... Exposure optical path, 13 ... Panel surface 22 ... Substrate glass (glass plate), 26 ... … Ferroelectric liquid crystal

Claims (1)

[Claims] 1. A light which has a photosensitive drum, a light source, and a liquid crystal shutter array whose longitudinal direction is arranged in parallel with a rotation axis of the photosensitive drum, and which is emitted from the light source and passed through the liquid crystal shutter array. In the image forming apparatus that exposes the surface of the photosensitive drum to form an image on the surface of the photosensitive drum, the liquid crystal shutter array includes a pair of glass plates rubbed in a direction intersecting the longitudinal direction, and a space between the pair of glass plates. The glass surface of the liquid crystal shutter array is inclined with respect to the surface perpendicular to the exposure light path so that the liquid crystal has a ferroelectric liquid crystal sandwiched between the glass plate and the downstream side in the rubbing direction of the glass plate is closer to the light source than the upstream side. An image forming apparatus characterized by being arranged.