JPS62266517A - Laser printer - Google Patents

Abstract

PURPOSE:To form an image by highly accurate scanning and to attain color printing or the like of high quality by providing the titled device with a rotary hologram disk and an f-theta lens in addition to the required numbers of laser light sources and photosensitive bodies. CONSTITUTION:Laser beams 4a-7a are projected to the same plane (plane in the radius direction of the rotary hologram disk 1) parallel with a rotary shaft 3 of the disk 1 and made incident upon a diffraction grating 2a and the incident angles of respective laser beams 4a-7a to the diffraction grating 2a are different each other. Laser beams 4b-7b diffracted by the diffraction grating 2 are made incident upon the f-theta lens 8. On the other hand, photosensitive bodies 9a-9d corresponding to respective laser light sources 4-7 are arranged on an image forming position based upon the f-theta lens 8 so as to be vertically positioned on the same plane. Since the laser beam 4a-7a are made incident upon the same diffraction grating 2 and diffracted, no shear is generated in the scanning speed and scanning phase of respective beams and accurate scanning can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention is directed to emitting laser beams each modulated by a different image signal from a plurality of laser light sources, for example, 2 to 4, and forming an image on a corresponding photoconductor to generate an electrostatic charge. The present invention relates to a digital electrophotographic laser printer that forms a latent image, develops it to make it visible, and then transfers it onto the same transfer medium to obtain a single color image or a monochrome image for overlay.

BACKGROUND OF THE INVENTION In recent years, laser printers have become increasingly important as output devices in office automation equipment. The practical use and development of color printing using such a laser printer is also active, and various proposals have been made.

As one example, as shown in Japanese Unexamined Patent Publication No. 58-95361, a single rotating polygon mirror is used in common, and the laser beams emitted from multiple laser light sources are reflected and scanned by different reflecting surfaces of the mirror. Some devices are designed to form an image on a photoreceptor. In other words, it uses a rotating polygon mirror, which is the most common type of laser printer. In the case of such a rotating polygon mirror, a highly accurate mirror surface is required, which requires advanced processing techniques and is expensive.

If the accuracy of this rotating polygon mirror is poor, when different reflecting surfaces of the rotating polygon mirror are used as described above, the difference in flatness between each reflecting surface will appear as a difference in scanning speed, and each reflecting surface will An error in the indexing angle between the two images appears as a phase difference, which deteriorates the image quality.

This is particularly noticeable when printing in color. Further, since there are parts where the scanning direction is reversed, a buffer memory and its control circuit are required, and control is troublesome.

Furthermore, the optical system includes 4 f-θ lenses and 4 mirrors.
The number of parts required is large, and precision is required for each part, resulting in high costs.

Furthermore, as shown in Japanese Unexamined Patent Publication No. 54-13/139, there is also a system in which one rotating polygon mirror and one f-0 lens are shared by a plurality of laser light sources. However, in this method, although the f-theta lens is -, a large number of mirrors are used after the second f-theta lens (on the photoreceptor side) to form an image on each photoreceptor. be. Therefore, the number of parts is large, and the precision between each mirror and the assembly precision must be high, resulting in high cost and lack of reliability.

Purpose The present invention has been made in view of the above points, and has a simple structure with a small number of parts, and improves the accuracy of the scanning speed and phase of a laser beam on a plurality of photoreceptors to perform high-quality printing. The purpose is to obtain a laser printer that can.

Structure In order to achieve the above object, the present invention includes a plurality of laser light sources that emit laser beams each modulated by a different image signal, and a number of photoreceptors corresponding to these laser light sources. In a laser printer that obtains a single image by superimposing and transferring images formed on these photoreceptors onto a single transfer medium, a rotating hologram disk having at least one diffraction grating;
one f-theta lens, and a plurality of laser light sources that emit laser beams at different angles of incidence on one and the same diffraction grating on a plane parallel to the rotation axis of the rotating hologram disk. , a photoreceptor corresponding to each laser light source is installed at a position where a laser beam emitted from these laser light sources, diffracted by the diffraction grating, and passed through the f-0 lens is imaged by the r-θ lens. This is a characteristic feature.

Hereinafter, one embodiment of the present invention will be described based on the drawings. This embodiment basically uses hologram technology. Laser printers using such hologram technology are, for example, rRicoh electrical
Report N O, l O, D
It is known from ``Hologram Scanner for Laser Printer'' in E CEMI3 E R, 1983J, and uses a rotating hologram disk as a deflection function similar to a rotating polygon mirror.

First, Figure 1 shows a conceptual diagram, and one ′
A rotating hologram disk 1 is provided in a substantially horizontal state. This rotating hologram disk 1 has, for example, six diffraction gratings (holograms) 2 divided into six at 60° in the circumferential direction, which are manufactured by a holographic method. These diffraction gratings 2 are, for example, linear grating holograms, and the grating material is a surface relief type transmission grating using photoresist. The rotating hologram disk 1 is rotated in one direction about the rotating shaft 3 by a motor or the like. Here, one diffraction grating 2 corresponds to one reflecting surface of a rotating polygon mirror, and scans one line. On the lower side of such a rotating hologram disk 1, four laser light sources 4, 5, and 6.7 are provided assuming a plurality of four-color prints, for example, RGB+black. These laser light sources 4 to 7 each include a collimator optical system and the like, and each have laser beams 4a and 5a of the same wavelength modulated by different image signals.

6a and 7a are emitted to one diffraction grating 2a of the rotating hologram disk 1. To explain the more specific positional relationship, these laser beams 4a, 5a, 6a, 7a are on the same plane (plane in the radial direction of the rotating hologram disk l) parallel to the rotation axis 3 of the rotating hologram disk 1. The laser beams 4a, 5a, 6 are incident on the diffraction grating 2a.
a.

The angles of incidence of the diffraction gratings 7a on the diffraction grating 2a are different.

As a result, these laser beams 4a, 5a, 6a, and 7a incident on the diffraction grating 2a are diffracted at different angles to form laser beams 4b and 5b.

8b and 7b. Laser beams 4b and 5b are thus diffracted by the diffraction grating 2a.

One r-0 lens 8 is provided, into which the beams 6b and 7b are incident. Here, since this f-theta lens 8 is a general point-symmetric f-theta lens, the scanning line (described later) is curved and causes a difference in scanning speed. An anamorphic f-theta lens having a different shape depending on the direction is used. And this r-θ
Laser beams 4b, 5b, 6b, 7 incident on lens 8
b is emitted as laser beams 4c, 5c, 6c, and 7c. At the imaging positions of the laser beams 4c, 5c, 6c, and 7c by the f-theta lens 8, there are photoreceptors 9a, 9b, which correspond to the laser light sources 4, 5, and 6.7, respectively.
9c and 9d are arranged vertically in the same plane. More specifically, these photoreceptors 9a, 9b, 9c
, 9d are orthogonal to the rotation axis 3 of the rotating hologram disk 1, and horizontal scanning lines 4d, 5d, respectively.
.

6d, 7d are assumed, and the imaging points of the laser beams 4c, 5c, 6c, 7c at the start of scanning are scanning lines 4d,
5d, 6d, and 7d (for example, on the near side).

With this configuration, as the rotating hologram disk 1 rotates, the laser beams 4c, 5c, 6c, and 7c are horizontally deflected by the diffraction grating 2a, and are directed onto the photoreceptors 9a, 9b.
, 9c, 9(l) scans on the scanning lines 4d, 5d, 6d, 7d, and at the end of the line the laser beam 4
c', 5c'.

6c', 7c'. In this way, each photoreceptor 9
When one line scanning on a, 9b, 9c, and 9d is completed, the laser beam! Laser beam 4a from 4, 5, 6.7,
5a, 6a, and 7a are similarly deflected and scanned by the next diffraction grating 2b of the rotating hologram disk 1 to perform the next one-line scan. In this way, the photoreceptors 9a, 9b, 9
c, 94 have respective laser beams 4a, 5a, 6a, 7
Since electrostatic latent images corresponding to a are formed, a color print can be obtained by developing these with respective toners, etc., and then sequentially overlapping and transferring them onto a sheet of transfer paper, etc.

In this way, according to this embodiment, the plurality of laser light sources 4,
5, 6.7 and photoreceptors 9a, 9b, 9c.

In addition to 9d, one rotating hologram disk 1 and one f
-O lens 8 may be provided, the number of parts can be reduced, and costs can be reduced.

In one rotating hologram disk 1, the laser beams 4a, 5a, Ga, and 7a are incident on the same diffraction grating 2 and diffracted, so it is similar to using different reflecting surfaces of a conventional rotating polygon mirror. Compare the scanning speed and scanning phase between each beam.

There is no deviation and the accuracy is high. Therefore, high quality color printing etc. can be performed with high reliability.

Using the principle shown in FIG. 1, a practical laser printer can be constructed as shown in FIG. 2.

In this figure, a motor 10 that rotationally drives the rotating hologram disk 1 is shown. In addition, in order to make the overall configuration more compact and to take into account the transportability of the transfer paper 12 fed from the transfer paper cassette 11, the photoreceptors 9a, 9b, 9c, and 9d are arranged in order to make the transport path approximately horizontal. The f-theta lens 8 and these photoreceptors 9a, 9b, and 9c are arranged side by side in a substantially horizontal state.

A single mirror 13 is interposed between the mirror 9d and the mirror 9d. Chargers 14a, 14 are placed around each photoreceptor 9a, 9b, 9c, 9d according to a well-known electrophotographic process.
b, 14c, 15d, developing devices 15a, 15b, 15c,
15d, transfer charger 16a, 16b, 16c, 16
d, cleaning devices 17a, 17b, L7c, 17d
etc. are arranged. Then, the transfer paper cassette 11
The transfer paper 12 fed by the paper feed rollers 18 and the registration rollers 19 is transferred to the photoreceptors 9a, 9b, and 9c.

A conveyor belt 20 is provided to sequentially convey the sheets 9d, and a fixing device 21 and a discharge roller 22 are provided on the discharge side of the conveyor belt 20. Furthermore, a beam detector 23 is provided at one end of the image forming line of the photoreceptor 9il for determining scanning timing.

In such a configuration, the image forming operation is the same as in the case of FIG. 1, and the image processing operation around each photoreceptor 9a, 9b, 9c, and 9d is also the same as in a general digital electrophotographic color printer. It is done.

Effects As described above, in addition to the required number of laser light sources and photoreceptors, the present invention provides one rotating hologram disk and one r-
Since the θ lens is provided and these are configured in a predetermined positional relationship, it can be constructed with a small number of parts and at low cost. Since the laser beams are incident on the laser beam and diffracted, there is no difference in scanning speed or scanning phase between each laser beam, and it is possible to perform high-precision scanning to form images, resulting in high-quality color printing, etc. This can be done at

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a conceptual perspective view, and FIG. 2 is a schematic side view. 1... Rotating hologram disk, 2... Diffraction grating,
3... Rotation axis, 4, 5, 6.7... Laser light source, 4
a. 5 a + 6 a + 7 a...Laser beam, 8...f'-0 lens, 9a, 9b, 9c, 9d
・=Photoreceptor, 12...Transfer paper (transfer medium)

Claims (1)

[Claims] A plurality of laser light sources each emitting a laser beam modulated by a different image signal and a number of photoreceptors corresponding to these laser light sources are provided, and images formed by the laser beams on these photoreceptors are unified. A laser printer that obtains one image by overlapping transfer onto two transfer media includes one rotating hologram disk having at least one diffraction grating and one f-theta lens; A plurality of laser light sources are installed that emit laser beams at different incident angles to one and the same diffraction grating on a plane parallel to the rotation axis, and the laser beams emitted from these laser light sources are diffracted by the diffraction grating. The f-θ of the laser beam passing through the f-θ lens
A laser printer characterized in that a photoreceptor corresponding to each laser light source is installed at an image formation position by a lens.