JPH1052940A - Image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve high print quality by forming a high-density head and a high-resolution optical system of a solid scanning type exceeding 1200DPI in a simple constitution. SOLUTION: A prism type half mirror 10 is a quadrangular prism type half mirror 1 obtained by bonding two prisms 2A, 2B of triangular prisms of a right triangular cross section at respective inclined faces. The bonded face is a half mirror face. Two heads 3A, 3B are set at two side faces adjacent to each other via the half mirror face. Lights from the heads 3A, 3B are combined thereby to make double a density of light-emitting elements. An image is formed on a photosensitive body 5 through one aspheric lens 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus in which light from a light emitting element array head such as a light emitting diode array is focused on a photosensitive member by a lens.

[0002]

2. Description of the Related Art Conventionally, in the field of image forming apparatuses such as electrophotographic printers, the light emitting element density of a light emitting element array head (hereinafter abbreviated as head) of a light source section is 300 DPI.
(Dots / inch) and 600 DPI, however, a demand for higher printing quality requires a light emitting element density of 1200 DPI. A light-emitting diode (hereinafter, referred to as LED) array head used as a printing head of this image forming apparatus is a solid-scanning head, and has a larger number of light-emitting elements (light-emitting dots) of several mm to several It is necessary to arrange between 10 mm.
Therefore, the size of the light emitting element must be several μm to several tens μm. Specifically, the pitch between the light emitting elements and the light emitting element size are as shown in Table 1 below.

[0003]

[Table 1]

[0004]

However, in the case of 2400 DPI as shown in Table 1, the light emitting element size is 0.58
It is necessary to set the width of the electrode for the light emitting element to about 5 μm at about μm, and it is difficult to form such an electrode width, so that it is impossible to provide a light emitting portion. Therefore, the size of the light emitting element itself cannot be reduced, and it is very difficult to increase the density.

[0005] In addition, when 1200 DPI is exceeded, LED
Wire bonding between the electrode and an external drive circuit or a drive IC chip has been difficult. For example, a wire bonding pad needs to have a size of about 40 μm,
At 0 DPI, it is a size that can be placed just barely.
At 0 DPI, it was impossible to arrange. In addition, if it is attempted to arrange driving IC chips close to both sides of a plurality of LED array chips in order to simplify wire bonding, the number of driving IC chips doubles, resulting in a significant increase in cost. Become. Therefore, when the driving IC chips are arranged on one side of the LED array chip to reduce the number of driving IC chips, the length of the wires is increased, the arrangement of the wires is complicated, and the yield is reduced. .

Further, in a solid-scanning head, a gradient index cylindrical lens array (also referred to as a SELFOC lens array, SELFOC is a registered trademark of Nippon Sheet Glass Co., Ltd.) is used to magnify and form light. However, the gradient index type cylindrical lens had low resolution and poor print quality. In addition, the refractive index distribution type cylindrical lens array requires a large number of lenses to be arranged at a high density. As a result, it is difficult to increase the yield, and therefore, there is a problem that productivity is low. For this reason, a high-resolution optical system that is easy to manufacture has been desired.

[0007] Accordingly, the present invention has been completed in view of the above circumstances, and its object is to provide a 1200 DP with a simple configuration.
An object of the present invention is to provide a high-density head and a high-resolution optical system of a solid-state scanning method exceeding I.

[0008]

According to an image forming apparatus of the present invention, a plurality of light emitting element array heads in which a large number of light emitting elements are linearly arranged at predetermined intervals and a light emitting dot of one of the light emitting element array heads. A prism disposed in the optical path of these light emitting element array heads in order to position the light emitting dots of the other light emitting element array head or to superimpose the light emitting dots of a plurality of light emitting element array heads to form one line. A half mirror, and the light emitted from the prism half mirror is formed on the photoreceptor through an aspheric lens.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIGS. FIG. 1 is a perspective view of a basic configuration of an image forming apparatus, FIGS. 2 and 3 are side views of a light source unit, and FIG. 4 is a side view of a basic configuration of another example of an image forming apparatus.

In FIG. 1, light from the heads 3A and 3B is synthesized by a prism type half mirror 10, which is magnified by an aspherical lens 4 and irradiated on a photoreceptor 5 to form a latent image with electric charges. Then, for example, no charge is formed in the portion corresponding to the emitted dot, and a positive charge is formed in the other portion.Then, the positively charged toner is attracted to the portion where no charge is formed by electrostatic force, and the toner is absorbed. An image is transferred to a printing material such as paper or a substrate.

In this case, as shown in FIG. 2 (a), a prism type half mirror 10 is formed by joining triangular prisms 2A and 2B whose two cross sections form a right-angled triangle at an inclined surface, and joining the joining surface to a half mirror surface. M is a quadratic prism half mirror 1, and the heads 3A and 3B are adjacent to each other across the half mirror surface M such that the light emitting dots of the head 3B are located between the light emitting dots (light emitting elements) of the head 3A. By disposing the light from the heads 3A and 3B by installing them on two side surfaces, the light emitting element density in one line (one scanning line) can be increased by 2
Can be doubled.

Alternatively, as shown in FIG. 2 (b), a prism type half mirror 11 is formed by joining triangular prisms 2A and 2B each having a right-angled triangular cross section on each inclined surface, and joining the joining surface to a half mirror surface M. The prismatic half mirrors 1A, 1B, and 1C are formed in such a manner that their half mirror surfaces M are joined in an L-shape in cross section so as to be parallel. By installing the light emitting element array heads 3A to 3D on two adjacent side surfaces of the two quadrangular prism type half mirrors 1A and 1C except for the half mirror 1B with the half mirror surface M interposed therebetween, the light emitting element Quadruple the density. At this time, the head 3A
The light emitting dots of the heads 3B to 3D are set so as not to overlap each other between the light emitting dots.

In FIG. 2, the heads 3A to 3D do not necessarily need to be directly installed on the prism half mirrors 10, 11, and the prism half mirrors 10, 11 are
Although it is a necessary condition to be in the optical path of A to 3D, direct installation is preferable because position adjustment can be easily performed.

In the example shown in FIG. 2, when the boundaries of the light emitting dots of the respective heads are adjacent to each other and the apparent area of the synthesized light emitting dots is doubled or quadrupled, the light emitting element density is doubled. In addition to quadrupling, the combined light emitting dots are turned on and off by each light emitting dot of each head to perform area gradation, so that two or four or more gradations can be preferably displayed.

Further, as shown in FIGS. 3A and 3B, light-shielding films 20 and 21 are provided on the side surfaces of the prism type half mirrors 10 and 11 except for the installation surfaces of the heads 3A to 3D and the light emission surface. Alternatively, this configuration prevents light that has deviated from a predetermined optical path from returning to the optical path again to generate an abnormal image such as a ghost. The light-shielding films 20 and 21 are preferably made of a material that largely absorbs light from the light-emitting element. The light-shielding films 20 and 21 are formed by applying a known dark-colored coating material such as a black fiber or a black paint by a method such as sticking or coating.

As shown in FIG. 4A, photoconductors 5A and 5B may be arranged for two outgoing light beams from the prism type half mirror 10, respectively, and at this time, printing is performed at two places at the same time. And printing efficiency is doubled. Alternatively, as shown in FIG.
For each of the four outgoing light beams from 1,
5F can also be arranged, and in this case, printing can be performed simultaneously at four places, and the printing efficiency is quadrupled.

Further, a set of zoom lenses may be used in place of the one aspherical lens 4. With such a configuration, the pixel density and the size of the image can be freely adjusted. Further, by controlling the driving of at least one head to increase or decrease the light emitting element density, it is possible to adjust the light emitting element density to the optimum with respect to the magnification of the zoom lens. Etc. are prevented. The zoom lens can be used as long as the imaging plane is fixed and the magnification is changed, and a known method in which a plurality of lenses are combined and the lenses move in the optical axis direction is used. Good. A plurality of aspherical lenses 4 or zoom lenses may be provided. However, it is preferable to provide one aspherical lens 4 or the like in terms of uniform printing quality, prevention of separation and superposition of images, and easy adjustment of the optical axis.

On the other hand, in the present invention, one line is formed by superimposing the light emitting dots of a plurality of heads. For example, in the case of FIG. 2A, the light emitting dots of the heads 3A and 3B are superposed. When one line is formed in total,
The emission intensity can be easily doubled. Or head 3
If the light emission intensity of each of the light emission dots A and 3B is set to two levels by controlling the applied voltage, it is possible to display 2 × 2 four gradations. Further, when the light emission intensity of one of the heads is set to three levels, 6 × 2 × 3 gradation display is performed, and an arbitrary gradation display can be performed.

Thus, the present invention provides a simple configuration with 12
A high-density head and a high-resolution optical system of a solid-state scanning method exceeding 00 DPI can be provided, and a gradation display can be performed.

As the prism type half mirror of the present invention, the above quadrangular prism type half mirror has less distortion of the light beam shape than other flat half mirrors, flat optical waveguides, optical fiber couplers and the like. This is preferable in that the optical axis can be easily adjusted and the optical loss is small. In addition, the half mirror surface may be formed so that incident light is transmitted and reflected almost half by half, and is formed of a known dielectric multilayer film or the like.

Further, as the light emitting element of the present invention, LED
Device, semiconductor laser device, EL (Electro Luminescent)
) An element, a plasma cell, a fluorescent element, a liquid crystal shutter, or the like can be used, but an LED element is preferable in terms of high emission luminance, low driving voltage (5 V), miniaturization, and mass productivity.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0023]

Embodiments of the present invention will be described below.

Example 1 As shown in FIG. 2A, a prism type half mirror 10 was used for a light source section, and the density of LED elements in one line was doubled as a result. At this time, as shown in FIG. 1, a light source unit that combines and emits light from each head, one aspheric lens 4 that enlarges the light to form an image, and a photoconductor 5 provided in the image forming unit An image forming apparatus provided with:

Specifically, the heads 3A and 3B each composed of an LED array were set to 1200 DPI, and were combined by the prism type half mirror 10 to 2400 DPI. The length of each head was 54 mm, and the total number of dots was 5120 dots. When the light emission signal of 2400 DPI is enlarged by the aspherical lens 4 having a magnification of 4 times, the photosensitive member 5
Above, the pixel density was 600 DPI, and the length of the signal for one scan was 216 mm. As a result, an image having a pixel density of 600 DPI can be printed on A4 (Japanese Industrial Standards A row 4th) size paper, and a high quality image can be obtained by the high resolution characteristics of the aspherical lens 4.

At this time, in order to obtain an optically good image-forming surface by magnifying 4 times by the aspherical lens 4, the object-image distance is preferably set to 50 mm to 100 mm. The distance between the object and the image was 75 mm because the diameter of the aspherical lens 4 was about 20 mm, the distance between the head and the lens was 15 mm, and the distance between the lens and the imaging surface was 60 mm.
In this case, the distance between the object and the image may be bent by a mirror or the like to reduce the size of the entire apparatus.

Example 2 As shown in FIG. 2B, a prism type half mirror 11 was used in the light source section, and the density of LED elements in one line was quadrupled as a result. In this case, the half mirror surface M is the vertex L of the L-shaped corner.
_The two mirrors are arranged in parallel to the direction toward _0, and the two square prism prism half mirrors 1A and 1C except for the half mirror 1B at the L-shaped corner are adjacent to each other with each half mirror surface M interposed therebetween. When the heads 3A to 3D are installed on the side surfaces, light from the four heads 3A to 3D can be combined. That is, the prism type half mirror 11 has a configuration in which a new half mirror is provided at the position of the heads 3A and 3B of the prism type half mirror 10 in FIG. Other configurations are the same as in the first embodiment.

The specific configuration of the head is as follows.
D was set to 1200 DPI, respectively, and combined by the prism type half mirror 11 to obtain 4800 DPI. The length of each head was 54 mm, and the total number of light emitting dots was 10240 dots. At this time, it is not necessary to arrange the LED elements of the other heads 3B to 3D completely in a straight line between the LED elements of the head 3A. You may. Alternatively, it is also possible to arrange the LED elements so as to partially overlap each other on a straight line and control the light emission luminance of the LED elements so that the optical axes of the LED elements do not substantially overlap.

When the light emission signal of 4800 DPI is magnified by the aspherical lens 4 having a magnification of 4 times, 120
The pixel density is 0 DPI, and the signal length of one scan is 21.
6 mm. As a result, 120 A4 size paper
An image with a pixel density of 0 DPI could be printed, and a high-quality image was obtained due to the high resolution characteristics of the aspherical lens 4.

Each of the heads 3A to 3D is 600 DP
In the case of I, the images were multiplexed to 2400 DPI, and an image having a pixel density of 600 DPI could be printed on A4 size paper.

Further, in this embodiment, the heads 3A to 3D
If one of them is synthesized without emitting light, the LED element density can be tripled.

(Embodiment 3) In the same manner as in Embodiment 1, a prism type half mirror 10 is used for the light source section, and as shown in FIG. 3 (a), the surface excluding the installation surfaces of the heads 3A and 3B and the light emission surface. Was provided with a light shielding film 20. The light-shielding film 20 was formed by applying a black pigment.

Using this light source section, 6 sheets of A4 size paper
When an image having a pixel density of 00 DPI was printed, an abnormal image such as a ghost did not occur at all, and a higher quality image was obtained.

In the same manner as in the second embodiment, a prism type half mirror 11 is used for the light source unit, and as shown in FIG.
1 was provided. The light shielding film 21 was formed in the same manner as the light shielding film 20.

Using this light source unit, one sheet of A4 size paper
When an image with a pixel density of 200 DPI was printed, no abnormal image occurred, and a higher quality image was obtained.

(Embodiment 4) In the same manner as in Embodiment 1, a prism type half mirror 10 is used for the light source section, and as shown in FIG.
A and 5B were arranged. In this case, the two emitted lights are the same combined signal (synthesized image), and the same image could be printed simultaneously at two locations.

Further, in the same manner as in the second embodiment, the prism type half mirror 11 is used for the light source unit, and as shown in FIG.
Was placed. In this case, assuming that the signals from the heads 3A to 3D are S _A , S _B , S _C , and S _D , respectively, the four outgoing lights are S _A + S _B , S _A + S _B + S _C + S as shown in the figure.
_D (two) and S _C + S _{D were} three kinds of composite signals. Accordingly, three types of composite images could be printed simultaneously at four locations.

(Embodiment 5) In the same manner as in Embodiment 2, a prism type half mirror 11 is used for the light source unit, and a set of zoom lenses (not shown) is arranged instead of one aspheric lens 4. . The zoom lens is configured by combining a plurality of lenses, and the magnification is variable from 0.1 to 20. With this zoom lens, an image can be reduced, and for example, a function of partially inserting a graphic print can be obtained.

Further, in order to adjust the LED element density to be optimum for various magnifications of the zoom lens, the following adjustment was made. For example, 4800 DPI is 1 /
When reduced to 2, the total dot length is 27m at 9600 DPI
m, and image collapse occurs, so the total number of dots is reduced to 1/2 to 1/3 to 4800 to 3200 DP
I to prevent image collapse and the like. Conversely, when enlarging with a zoom lens, the dot density becomes coarse, so the light emitting element density was set to the maximum of 4800 DPI. At this time, the speed in the sub-scanning direction (vertical direction) can be reduced in order to increase the pixel density in the vertical direction of the image.

[0040]

According to the present invention, the light from the light emitting element array head can be synthesized by the prism type half mirror to easily increase the light emitting element density to more than 1200 DPI, and as a result, a high quality image can be obtained. Can be printed. The prism type half mirror of the present invention can be easily configured by combining prisms and the like, and by using a high-resolution aspherical lens as a lens, high printing quality is ensured and the product yield is increased, and productivity is improved. Also improve. Furthermore, a plurality of images can be printed simultaneously by simultaneously exposing a plurality of composite signals emitted from the prism type half mirror onto the photoconductor.

[Brief description of the drawings]

FIG. 1 is a perspective view of a basic configuration of an image forming apparatus of the present invention.

FIG. 2 is a side view of a light source unit according to the present invention.

FIG. 3 is a side view of another light source unit of the present invention.

FIG. 4 is a side view of a basic configuration of another image forming apparatus of the present invention.

[Explanation of symbols]

 1: prism type half mirror 2A: triangular prism 2B: triangular prism 3A: LED array head 3B: LED array head 3C: LED array head 3D: LED array head 4: aspherical lens 5: photoreceptor 10: quadrangular prism Type half mirror 11: prism prism type half mirror

Claims (1)

[Claims] 1. A plurality of light emitting element array heads in which a large number of light emitting elements are linearly arranged at predetermined intervals, and light emitting dots of the other light emitting element array head are positioned between light emitting dots of one light emitting element array head. Or a prism type half mirror installed in an optical path of these light emitting element array heads so as to form one line by superposing light emitting dots of a plurality of light emitting element array heads. An image forming apparatus, wherein light emitted from a mirror is formed on a photosensitive member through an aspheric lens.