JPH06217086A - Optical scanning device - Google Patents

Abstract

PURPOSE:To scan a body to be scanned by two beams at the same time and to prevent the generation of bending of scanning lines in a simple constitution. CONSTITUTION:The two laser beams emitted from light source units 1a and 1b modulated according to picture data of adjacent two lines are made incident on one rotary polygonal mirror 4 through beam shaping use slits 2a and 2b and cylindrical lens 3a and 3b, and are deflected by reflecting them by dissimilar surfaces of the rotary polygonal mirror 4. Then they are reflected by cylindrical mirrors 6a and 6b through ftheta lens 5a and 5b and led to the adjacent position on a photosensitive body 7, then scanned mutually in reverse directions 8a and 8b simultaneously at the prescribed intervals on the photosensitive body 7 which rotates at a constant speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in an image forming apparatus such as a laser beam printer which forms an image by scanning an object to be scanned with a light beam.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a laser printer, it has been proposed to speed up image processing by scanning a photosensitive member with a plurality of light beams. In such a method of scanning with a plurality of light beams, for example, as shown in JP-A-58-105117, a beam scanning area of one line is divided in the beam scanning direction and each divided area is divided into separate areas. There are a method of scanning with a beam and a method of simultaneously scanning a plurality of lines with a plurality of beams as shown in, for example, Japanese Patent Laid-Open No. 63-50809.

[0003]

However, the former method of dividing the beam scanning area of one line and scanning it has a problem that it is difficult to match the joints of a plurality of beams.

In the latter method of simultaneously scanning a plurality of lines with a plurality of beams, conventionally, a plurality of beams are scanned in parallel in the same direction, as disclosed in Japanese Patent Laid-Open No. 63-50809. Method is used,
In this method, a beam combining element using a beam splitter or the like for combining a plurality of beams, a half-wave plate, or a 1-wave plate is used.
There has been a problem that a quarter wavelength plate is required and an optical element for adjusting the beam pitch is required, which complicates the configuration. Further, since a plurality of beams pass through the same scanning lens, at least one beam does not pass through the optical axis of the scanning lens, which causes a problem that the scanning line is bent on the photoconductor. .

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical scanning device capable of simultaneously scanning an object to be scanned with two beams with a simple structure and preventing the occurrence of bending of a scanning line.

[0006]

The optical scanning device of the present invention comprises:
A first light source unit that generates a light beam that is modulated according to the scanning direction and the scanning speed based on the image data of one line of the image data of two adjacent lines; A second light source unit for generating a light beam modulated in accordance with the scanning direction and the scanning speed based on the image data of the other one line, and deflecting each light beam from each light source unit by a different surface 1 One rotating polygon mirror and two optical systems for guiding the two light beams deflected by the rotating polygon mirror to positions close to each other in the sub-scanning direction on one scanned object and scanning them in opposite directions to each other It is a thing.

In this optical scanning device, the respective light beams which are modulated by the image data of one separate line and emitted from the respective light source sections are deflected by different surfaces of the rotary polygon mirror, and are scanned by the respective optical systems. They are guided to close positions on the body and scan in opposite directions.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 relate to an embodiment of the present invention.

FIG. 1 is an explanatory view showing the structure of the optical scanning device of this embodiment, and FIG. 2 is an explanatory view of the optical scanning device of FIG. 1 as seen from the axial direction of the photoconductor. As shown in these figures, the optical scanning device according to the present embodiment generates separate light beams.
One light source unit 1a, 1b and each light source unit 1a,
Beam shaping slits 2a and 2b for shaping the laser beam from 1b, and beam shaping slits 2a and 2b
One rotating polygon mirror 4 for deflecting the passing laser beam by different surfaces, and an optics provided between the rotating polygon mirror 4 and the beam shaping slits 2a, 2b to correct the surface tilt of the rotating polygon mirror 4. Cylindrical lenses 3a and 3b forming a part of the system, and an fθ lens 5a for correcting the scanning speed of each laser beam deflected by the rotary polygon mirror 4 and for focusing the laser beam in the vicinity of the photoconductor 7. 5b and each of the laser beams after passing through the fθ lenses 5a and 5b are guided to a close position on the photoconductor 7 and scanned in opposite directions, and a part of an optical system for correcting the surface tilt of the rotary polygon mirror 4 is configured. Cylindrical mirror 6a, 6b
It has and.

Each of the light source units 1a and 1b includes a laser diode which is driven in accordance with image data and emits a modulated laser beam, and a collimator lens which collimates the divergent laser beam emitted from the laser diode. It is configured.

In this optical scanning device, each light source unit 1
The laser beams emitted from a and 1b pass through the beam shaping slits 2a and 2b and the cylindrical lenses 3a and 3b, respectively, and enter the rotary polygon mirror 4. In this embodiment, in particular, as shown in FIG. 1, the rotary polygon mirror 4 is composed of eight surfaces, and the laser beams from the light source units 1a and 1b are incident on the rotary polygon mirror 4 in a parallel state. The two surfaces of the mirror 4 which are adjacent to each other with one of the eight surfaces separated are reflected in opposite directions, and are deflected so that the scanning directions are opposite to each other. The respective laser beams deflected by the rotary polygon mirror 4 are fθ lenses 5a and 5b, respectively.
2 through the cylindrical mirrors 6a and 6b to reach the photoconductor 7 and rotate on the photoconductor 7 rotating at a constant speed.
At the same time, a laser beam of a book scans in the opposite directions 8a and 8b at a predetermined interval.

In the image forming apparatus having this optical scanning device, the photoconductor 7 is uniformly charged in accordance with the usual xerographic process, and the photoconductor is formed by two laser beams modulated according to the image data. An electrostatic latent image is formed on the electrostatic latent image 7, and a toner is attached to the electrostatic latent image by a developing device to make it visible as a toner image, and the toner image is transferred to a sheet by a transfer device.

Next, the positional relationship between the two laser beams on the photoconductor 7 will be described with reference to FIGS. 3 and 4. Here, the resolution of the image forming apparatus using the optical scanning apparatus of the present embodiment is 400 dots / inch, and the fθ lens 5
The focal lengths of a and 5b are F, the number of faces of the rotary polygon mirror 4 is 8,
The beam scanning width on the photoconductor 7 is 300 mm, and the beam scanning efficiency is 70%. The beam scanning efficiency η is η
= [Scanning width / {(4π / number of faces of rotating polygon mirror) × F}] ×
It is represented by 100 (%). Under the above conditions, the surface speed of the photoconductor 7 (speed in the direction perpendicular to the beam scanning direction)
Is 25.4 (mm) / 4 with respect to the beam scanning period T.
00 (dots) × 2 = 127 (μm / T). Therefore, in order to make the intervals of the scanning lines equal, as shown in FIG. 3, the interval between the laser beam 11a from the light source unit 1a and the laser beam 11b from the light source unit 1b is set to 63.5 μm.

Actually, since the photosensitive member 7 is rotating at a constant speed in the moving direction indicated by the arrow 12, the two scanning lines formed by the two laser beams 11a and 11b have the positional relationship shown in FIG. To do this, use two laser beams 11
It is necessary to set the positional relationship between a and 11b as shown in FIG. That is, based on the laser beam 11a, the scanning start position of the laser beam 11b is + 2η × 6 in the direction opposite to the moving direction 12 of the photoconductor 7 from the position shown in FIG.
The laser beam 11b is moved to a position moved by 3.5 μm.
The scanning end position of is the position moved by −2η × 63.5 μm in the direction opposite to the moving direction 12 of the photoconductor 7 from the position shown in FIG. As a result, when the scanning efficiency η = 0.7, the relative positional relationship between the laser beams 11a and 11b is that the scanning start position of the laser beam 11a is more sensitive than the scanning end position of the laser beam 11b as shown in FIG. Body rotation direction 12
25.4 μm before the laser beam 11b
The scanning start position of is 152.4 μm before the scanning end position of the laser beam 11a with respect to the rotation direction 12 of the photoconductor.

The adjustment of the positional relationship between the laser beams 11a and 11b is performed by adjusting the cylindrical mirror 6b when the laser beam 11a is used as a reference.

Next, the modulation of the laser beam in the image forming apparatus using the optical scanning device of this embodiment will be described. First, in the image forming apparatus, one page of image data is decomposed into pixels as shown in FIG. 5, and is represented by an M × N matrix. Where M is the number of lines on one page, N
Is the number of pixels in one line, and D _mn (1 ≦ m ≦ M, 1 ≦ n
≦ N) indicates the image data of the nth pixel on the m line.

FIG. 6 is a block diagram showing a structure relating to the modulation of the laser beam in the image forming apparatus using the optical scanning device of this embodiment. As shown in this figure, the image forming apparatus includes a 2-line data buffer 21 for storing image data 20 for two lines, and a 2-line data buffer 21.
An odd line data buffer 22 for storing the odd line data stored in, an even line inversion circuit 23 for inverting the output order of the even line data stored in the 2-line data buffer 21, and an odd line data buffer 22. Drive the laser diode of the light source unit 1a according to the output data of the first laser drive circuit 24a that modulates the laser beam, and drive the laser diode of the light source unit 1b according to the output data of the even line inversion circuit 23. And a second laser drive circuit 24b for modulating the laser beam.

The even line inversion circuit 23 is composed of, for example, a line buffer whose data writing direction and data reading direction are opposite to each other.

In FIG. 6, the image data 20 is sequentially stored in the 2-line data buffer 21 by two lines.
The odd line data stored in the 2-line data buffer 21 is temporarily stored in the odd line data buffer 22 and then input to the first laser drive circuit 24a. On the other hand, the even line data stored in the 2-line data buffer 21 is inverted in the data output order by the even line inversion circuit 23 and is input to the second laser drive circuit 24b. Further, the timing of starting the reading of data from the odd line data buffer 22 and the timing of starting the reading of data from the even line inverting circuit 23 are the scanning start end side of the laser beam deflected by the rotary polygon mirror 4 and the scanning region. It is synchronized based on the output of a beam detector (not shown) that receives an external beam. The data read speed of the odd line data buffer 22 and the even line inversion circuit 23 corresponds to the scanning speed.

FIG. 7A shows the first laser drive circuit 24a.
Image data supplied to the second laser drive circuit 24b, and FIG. 7B shows image data supplied to the second laser drive circuit 24b. As shown in these figures, when the data of the odd-numbered lines to the first laser driving circuit 24a is supplied in the order of D ₁₁ to D _1N, the second laser driving circuit as shown in FIG. 7 (b) 24
Data of even lines are supplied to b in the order of D _{2N to} D ₂₁ . Similarly, when data of odd lines is supplied to the first laser driving circuit 24a, data of even lines is supplied to the second laser driving circuit 24b in the reverse order.

Instead of reversing the data writing direction and the data reading direction in the even line inversion circuit 23, the even line inversion circuit 23 is configured by a line buffer in which the data writing direction and the data reading direction are the same, and the even line inversion circuit is used. When the data to be written to the circuit 23 is read from the 2-line data buffer 21, the 2-line data buffer 2
The data may be read out in the direction opposite to that at the time of writing data to 1.

As described above, according to this embodiment, 2
Since two lines are simultaneously scanned by one beam, the image processing can be speeded up, and it is not necessary to align the seams of the beams as in the case where the scanning region is divided into plural scans. Further, since two laser beams are scanned using different surfaces of one rotating polygon mirror, a beam combining element or a beam combining element is required as compared with the case where two laser beams are combined and deflected on the same surface of the rotating polygon mirror. The optical element for adjusting the pitch of the beam is not required and the configuration is simple, and moreover,
Adjustment of the optical system becomes easy. Further, in the present embodiment, both of the two beams can pass near the optical axes of the fθ lens 5a and 5b, so that two laser beams are combined and deflected on the same plane of the rotary polygon mirror. It is possible to prevent such bending of the scanning line.

In the present invention, the two optical systems for each laser beam are not limited to the arrangements shown in FIGS. 1 and 2, but the two optical systems should be symmetrical as shown in FIGS. 1 and 2. With the above configuration, the configuration becomes simpler and the adjustment becomes easier.

Further, in the present invention, the two lines simultaneously scanned by the two beams are not limited to the two adjacent lines, but may be two lines shifted by a plurality of lines.

[0025]

As described above, according to the present invention, 2
Since two light beams from one light source unit are deflected by different surfaces of one rotating polygon mirror and are guided to positions close to each other on the one scanning target in the sub-scanning direction, they are scanned in opposite directions. Two lines can be simultaneously scanned with a simple structure, and there is an effect that the processing can be speeded up without the need to align the joints of a plurality of beams. Further, since the two light beams deflected by the rotary polygon mirror can respectively pass through the optical axis of the optical system, it is possible to prevent the scanning line from being bent.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the optical scanning device in FIG. 1 viewed from an axial direction of a photoconductor.

FIG. 3 is an explanatory diagram showing two scanning lines by two laser beams in one embodiment.

4 is a diagram for realizing the positional relationship of the scanning lines in FIG.
It is explanatory drawing which shows the positional relationship of the laser beam of a book.

FIG. 5 is an explanatory diagram showing image data for one page.

FIG. 6 is a block diagram showing a configuration related to modulation of a laser beam in an image forming apparatus using the optical scanning device of the embodiment.

7 is an explanatory diagram showing image data supplied to the laser drive circuit in FIG.

[Explanation of symbols]

1a, 1b ... Light source unit, 4 ... Rotating polygon mirror, 5a, 5
b ... fθ lens, 6a, 6b ... Cylindrical mirror,
7 ... Photoreceptor

Claims (1)

[Claims] 1. A first light source unit for generating a light beam modulated in accordance with a scanning direction and a scanning speed based on image data of one line of image data of two adjacent lines, and 2. A second light source unit that generates a light beam that is modulated according to the scanning direction and the scanning speed based on the image data of the other one line of the image data of the line; One rotating polygon mirror that is deflected by different surfaces and two light beams that are deflected by this rotating polygon mirror
An optical scanning device, comprising: two optical systems that guide two scanning objects to positions close to each other in the sub-scanning direction and scan in opposite directions.