JPH0461466A - Laser image forming device - Google Patents

Abstract

PURPOSE:To reduce uneven density of a picture without slowing down an image forming speed by scanning an overwritten line at picture forming with a different reflecting face of a rotary polygon mirror at each overwrite and scanning plural lines at one main scanning by the reflecting face of the rotary polygon mirror. CONSTITUTION:Since a scanning control section 9 controls a laser beam radiating overlappingly to a line after radiation so as to be subject to main scanning on a different reflecting face of a rotary polygon mirror 4, plural number of times of main scanning implemented to a same line in the case of picture formation are executed on a different reflecting face at each scanning without fail. Moreover, plural lines are scanned at one main scanning on the reflecting face of the rotary polygon mirror 4. Thus, the uneven density of the picture is reduced without slowing down the image forming speed at picture forming.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention irradiates multiple lines at the same time with multiple laser diodes, scans the same line multiple times with different reflecting surfaces of a rotating polygon mirror, and eliminates accuracy errors of the rotating polygon mirror. The present invention relates to a laser imaging device that reduces image unevenness caused by.

Problems to be Solved by the Prior Art and the Invention Conventionally used laser imaging devices modulate a laser beam output from a laser diode (hereinafter referred to as LD) or the like based on image information. The laser beam is polarized by a rotating polygon mirror and scanned over the photoreceptor.
This forms an image.

The rotating polygon mirror used in such a laser imaging device plays an important role in forming an image, and has many advantages such as a large polarization angle and no spectral property. On the other hand, however, since it is very difficult to manufacture them precisely, each reflecting surface has slight unevenness in reflectance, sagging, and errors in assembly. For this reason, in an image formed by scanning using each reflective surface, variations in density occur periodically in the direction in which each scanning line is lined up.

For example, a rotating polygon mirror is composed of 10 reflecting surfaces, and the scanning line density in the sub-scanning direction on the photoreceptor is 10 lines 7 mm.
In this case, the above-mentioned density variations occur repeatedly every 1 mm. The repetition of this variation is III
If this occurs every approximately Il, density unevenness in the obtained image becomes noticeable.

Various techniques have been proposed to reduce density unevenness caused by such causes, one of which is
For example, there is a technique as disclosed in Japanese Patent Laid-Open No. 179274/1983. This technique performs overwriting by scanning the l line multiple times using different reflecting surfaces of a rotating polygon mirror using a modulation signal based on the same image information, thereby reducing density unevenness in the image.

In this way, the density unevenness of the image can certainly be reduced, but on the other hand, there arises the problem that the image forming speed increases in inverse proportion to the number of times of overwriting.

The present invention has been made to solve the above-mentioned problems, and provides a laser imaging device that can reduce density unevenness in images without slowing down the sub-scanning speed during image formation. For the purpose of providing.

Means for Solving the Problems In order to achieve the above object, the present invention provides that when the laser beams respectively output from a plurality of laser beam output means are reflected and scanned by the same reflective surface of a rotating polygon mirror, the photoconductor an optical system configured to simultaneously scan a plurality of different lines in the sub-scanning direction of the photoreceptor; , while outputting a modulated signal based on image information for one different line to the plurality of laser beam output means, the laser beam output means for irradiating the laser beam over the already irradiated line is a modulated signal output means for outputting a modulated signal based on the same image information as that output during irradiation; and a modulated signal outputted from the laser beam output means based on the same image information from the modulated signal output means. The present invention is characterized by comprising scan control means for performing main scanning of the laser beam using a different reflecting surface of the rotating polygon mirror each time an already irradiated line is irradiated with the laser beam.

Function The present invention having the above-described configuration functions as follows.

A plurality of laser beams are output from the plurality of laser beams toward the photoreceptor. These laser beams are reflected by the same reflecting surface of the rotating polygon mirror and simultaneously irradiate a plurality of different lines onto the photoreceptor in the sub-scanning direction. Therefore, as the rotating polygon mirror rotates, these laser beams are simultaneously main-scanned over the photoreceptor.

A modulation signal based on one line of image information for image formation is output from the modulation signal output means to each laser beam output means.

Overwriting is performed in conjunction with sub-scanning of the photoreceptor, and during this overwriting, the laser beam output means that irradiates the laser beam over the already irradiated line includes a modulation signal output means. A modulation signal based on the same image information as that output during irradiation of the irradiated line is given from .

Further, during this overwriting, the scanning control means controls the laser beam to be irradiated to overlap the already irradiated line so that it is main scanned by each different reflecting surface of the rotating polygon mirror. Therefore, multiple main scans performed on the same line during image formation are always performed on a different reflective surface for each scan, so it is possible to reduce density unevenness in the image, and Since a plurality of lines can be scanned in one main scan by the reflecting surface of the rotating polygon mirror, overwriting can be performed without slowing down the image forming speed.

EXAMPLE Hereinafter, a laser imaging apparatus of the present invention will be explained based on the drawings.

FIG. 1 shows an overview of the laser imaging device according to the present invention, and each L
Laser beam Bl oscillated from D1a, lb, lc
, B2. B3 is made into parallel light by collimator lenses 2a, 2b, and 2c, respectively, and then reflected by reflective prisms 3a and 3b.
, 3c, and is reflected by the same reflecting surface of a polygon mirror 4, which is a rotating polygon mirror that rotates at high speed. As the polygon mirror rotates, the reflection angle of each of the laser beams B1 to B3 on the reflecting surface changes, and each of the laser beams B1 to B3 is directed to a photoreceptor, which is a photoreceptor, as shown in FIG. Different lines of the drum 5 are scanned in the longitudinal direction. That is, main scanning is performed during image formation. When this main scanning is performed once, these laser beams B1 to B3 scan three adjacent lines at the same time.

These laser beams B1 to B3 are each focused by an fθ lens 6, and are imaged on the negatively charged photoreceptor drum 5, thereby reducing the charged potential at that position. Then, an electrostatic latent image is formed on the photoreceptor drum 5 by rotation of the photoreceptor drum 5 at a constant speed, that is, by repeating this main scanning along with the sub-scanning. Further, a reflecting mirror 7 is provided on the optical path to reflect one of the laser beams and make it incident on the laser beam detection sensor 8, and the laser beam detection sensor 8 detects the reflected laser beam and detects each laser beam. It outputs a scan start signal that aligns the main scan start positions of laser beams.

A scan control section 9 functioning as a scan control means synchronizes the rotational speed of the polygon mirror 4 and the sub-scanning speed of the photoreceptor drum 5 so that each laser beam is main-scanned one line at a time. ing.

After an electrostatic latent image is formed by repeating the main scanning and sub-scanning as described above, toner, which is a colored pigment, is selected for this electrostatic latent image area, although not shown. The toner image is transferred to the paper surface by adhesion, and the paper is heated to melt the toner and fix it to the paper, thereby obtaining a desired image.

Here, an outline of the process in which image formation is performed using three laser beams as in this embodiment will be explained. When the polygon mirror 4 first starts rotating at a predetermined rotation speed,
As shown in FIG. 2, only one of the LDs 1a to 1c outputs a laser beam with a very low energy level (SOS level) that does not contribute anything to forming a latent image (
In FIG. 2, it is LDla). This laser beam is main-scanned in the longitudinal direction of the photosensitive drum 5 on the reflective surface of the polygon mirror 4 . During this scanning process, the laser beam passes through the reflection mirror 7 and passes through the laser beam detection sensor 8.
detected by. When a scanning start signal is output from the laser beam detection sensor 8 based on this detection, a laser beam with an energy level (image forming level) sufficient to form a latent image from only the LDla is output at first. The other LDlb and LDlc are set to off level.

This laser beam is applied to the first polygon mirror 4, for example.
The first line of the photoreceptor drum 5F is irradiated by the reflective surface. At this time, a modulation signal based on the image information of the first line is applied to LDla. In this way, when one main scan is completed and the first line image is formed, the energy level of the LD (LDla- in Figure 2) that first outputs the SOS level laser beam is used to create an image. level to SOS level. At the same time, the photosensitive drum 5 is sub-scanned by one line. Here, when the beam diameter of the laser beam used is, for example, 100μ, the sub-scanning amount for one line is 100μ.

Thereafter, as described above, when the SOS level laser beam is detected by the laser beam detection sensor 8, the energy level of the laser beam output from LDla and LDIb is set to the image forming level, The second reflective surface of the polygon mirror 4 directs the laser beam from LDla to the second line on the photoreceptor drum 5, and similarly the laser beam from LDlb to the second line of the photosensitive drum 5.
Each is irradiated on the first line. At this time, LDla
The modulated signal based on the image information of the second line is
A modulation signal based on the image information of the first line row is applied to each of the lbs. When main scanning is performed in this manner, the first line is overwritten by a different LD and reflective surface, and at the same time, a new image for the second line is formed. When the main scanning is completed, the energy level of the LD1a is lowered from the image forming level to the SOS level, and the energy levels of the other LDs are lowered to the off level, and the photosensitive drum 5 is sub-scanned by one line.

When the SOS level laser beam from LDla is detected by the laser beam detection sensor 8 again,
This time, the energy level of the laser beam output from all LD1a to IC is set to the image forming level, and the third reflective surface of the polygon mirror 4 directs the laser beam from the LD1a to the third line on the photoreceptor drum 5. In, LD
The laser beam from lb is irradiated on the second line, and the laser beam from LDlc is irradiated on the first line. The modulation signal inside is 1
1 rubel). At this time, LDla has the third
A modulation signal based on the image information of the second line is applied to LDlb, a modulation signal based on the image information of the second line is applied to LDlc,
A modulation signal based on the image information of the first line is applied to each. When main scanning is performed in this manner, the first and second line rows are overwritten again by different LDs and reflective surfaces, and at the same time, a new third line image is formed.

The above operations are repeated for each line to form one image. In the case of the above example, all lines are overwritten three times using different LDs and different reflective surfaces, so the influence unique to each reflective surface of the polygon mirror is weakened, and the imaging speed is reduced. The density unevenness of the image can be reduced without reducing the image density. In the above example, three LDs were used, but although there are varying degrees of reduction in density unevenness,
A certain amount of reduction is possible by using a plurality of LDs. If N laser beams are used when an N-sided polygon mirror is used, the density unevenness can be almost completely eliminated. However, in order to reliably obtain the above effect, it must be noted that overwriting lines must be performed using a different reflective surface each time.

Next, a more specific operation of this laser imaging device will be explained based on the block diagram of the control device shown in FIG.

In the figure, the clock signal PCLK given to the horizontal timing generator 10 and the horizontal readout counter 11 is a clock signal for each pixel forming an image,
Horizontal timing generator 10 and vertical read counter 12a
The signal SO8 given to ~12c is a scan start signal output from the laser beam detection sensor 8. Image information for one page is stored in each of the image memories 13a to 13c. The reason why three image memories storing the same image information are provided is that it is necessary to provide image information independently to each of the three LDs 1a to 1c. The three pieces of image information are created by copying the image information stored in one image memory to the other two image memories. These image memories 13a-1
3C customer traffic is 8 bits per dot, 4 bits per 100.
It is 16 megabytes as 096 x 4096 dots.

Further, the upper 12 bits of the address are assigned to a vertical address, and the lower 12 bits are assigned to a horizontal address.

When entering the print cycle, both the horizontal read counter 11 and the vertical read counters 12 to 12c are cleared.
Wait for the scanning start signal SO8.

When the first scanning start signal SO8 is manually input, the horizontal timing generator 10 starts counting the clock signal PCLK, and when the counted value reaches a predetermined value, the horizontal readout counter 11 and the gate buffers 14a to 14c output an image. Indicates the start of a region. In the image area, the horizontal read counter 11 is counted up in accordance with the clock signal PCLK.

On the other hand, in response to the clock signal PCLK, the image memory 13a
Data at addresses corresponding to the main scanning direction on 13c are sequentially sent to D/A converters 15a to 15c through gate buffers 14a to 14c, respectively, and converted into analog signals. These analog signals are sent to the laser drive circuit 1.
6a to 16c, and LDla to LD accordingly.
lc output modulation is performed. When the output of all modulation signals based on one line of simultaneously scanned image information is completed by performing the above operations, the horizontal timing generator 10 outputs the horizontal reading counter 11 and the gate buffer 14a.
~14c, instructs to end the image area.

As a result, the horizontal read counter 11 stops counting the clock signal PCLK, and the gate buffer lla
~11c is closed and waits for the next scan start signal SOS.

On the other hand, the vertical read counters 12a to 12c count addresses in the sub-scanning direction of the image memories 13a to 13c to be read. Specifically, this count is
Scanning start signal SO8 from laser beam detection sensor 8
Each time the vertical reading counter 12a is outputted, the vertical reading counter 12a
, 3.4. . . . n, o, o, the vertical read counter 12b counts 0. 1.2.3.4. -, n,
0. Further, the vertical read counter 12c
is 0°0.1, 2, 3, 4. . . , n is repeatedly counted.

Horizontal read counter 11 and vertical read counter 1 below
Based on each count of 2a to 12c, LDl
The image data corresponding to each line formed by each of the a-LDlcs is transferred to the gate buffers 14a to 14a.
14c. To explain again using the above example, when the first scan start signal 5JSO8 is output from the laser beam detection sensor 8, the count value of the vertical readout counter 12a is 1, and the count values of the vertical readout counters 12b and 12c are 0. Therefore, the image data of the first line of the image memory 12a is sequentially read out by the horizontal reading counter 11, and the image of the first line is formed by the LDla. Of course, at this time, no image data is given to the other LDlb and LDlc, so no laser beam is output from these LDs. Next, when the scan start signal SO8 is output,
Since the count value of the vertical read counter 12a is 2, the count value of the vertical read counter 12b is 1, and the count value of the vertical read counter 12c is 0, the image memory 12
The image data of the second line of a is horizontal read counter 1
The image data of the first line of the image memory 12b is sequentially read out by the horizontal read counter 11, and the image of the first line is formed by LDlb. It will be done. At this time, no laser beam is output from the LDlc. Furthermore, when the scan start signal SO8 is output, the count value of the vertical read counter 12a becomes 3, the count value of the vertical read counter 12b becomes 2, and the count value of the vertical read counter 12c becomes 1. The image data of the 3rd line row is sequentially read out by the horizontal reading counter 11, and the image of the 3rd line row is formed by the LDla, and the image data is stored in the image memory 12b.
The image data of the second line row of the horizontal read counter 11
The images are sequentially read out by the LDIb, the second line image is formed by the LDIb, and the first line image is formed by the LDIC. And finally, LDlc
Only the n-th line image is formed, and all image forming operations are completed.

According to the embodiment of the present invention in which one image is formed by repeatedly performing the above-described operations, the following effects can be expected.

1. Since a new line is written even when the same line is being overwritten, density unevenness in the image can be reduced without reducing the image forming speed.

2. When overwriting the same line, the overwriting laser beam line completely overlaps the already written line, which increases the energy intensity modulation width and reduces the dynamic range of the image. can be raised.

For the reason described in 3.2, the edges of the lines are not disturbed and a clear image can be obtained.

Next, an embodiment will be described in which the technology and concept of the present invention are applied to a laser image forming apparatus that forms a color image.

FIG. 4 is a schematic diagram of a laser image forming apparatus that forms a color image using photographic film or paper as a photoreceptor. In the figure, the same members as in FIG. 1 are designated with the same symbols.

The LDs used here output laser beams with different wavelengths, for example, LDI
A outputs a laser beam with a wavelength of 450 nm, LDIB outputs a laser beam with a wavelength of 55 nm, and LDIC outputs a laser beam with a wavelength of 650 nm. For photosensitive materials such as photographic film or paper, 4
A material is used that produces yellow in response to a laser beam with a wavelength of 50 nm, magenta in response to a laser beam in a 550 nm wavelength, and cyan in response to a laser beam in a 650 nm wavelength. A color image can be obtained by irradiating such three laser beams with different wavelengths onto the same line. In the figure, 2a to 2b are collimator lenses, and the laser beam B5 output from each LDIA to IC
~ B7 is made into parallel light. 3a to 3c are reflecting prisms that reflect the laser beams B5 to B7 in the same direction and output them to the polygon mirror 4.

As the polygon mirror rotates, each of the laser beams B5 to B7 is focused by the fθ lens 6, reflected by the folding mirror 18, passes through the window glass 19, and travels along different lines of the photosensitive area 20 longitudinally. scanned in the direction. Similarly in this embodiment, when main scanning by the polygon mirror 4 is performed once, these laser beams B5 to B7 scan three adjacent lines at the same time. The photosensitive material 20 is sandwiched between a platen 25 and a roller 26 and fed in a predetermined direction. That is, sub-scanning is performed. The photosensitive material on which a latent image is formed by the main scanning of the laser beams B5 to B7 and the sub-scanning of the photosensitive material 20 is later developed by a photographic developing machine. Although not shown, in order to finely adjust the energy level between the laser beams output from each LD, a polarizing beam splitter is installed on the optical path from the collimator lens to the reflection prism.
An attenuator such as the following may be provided.

FIG. 5 is a block diagram of a control device in this laser imaging device. This block diagram has substantially the same configuration as that shown in FIG. 3, and the same members as those shown in FIG. 3 are given the same reference numerals.

This block diagram differs from the one in FIG. 3 in the image data written to the image memories 13a to 13c. When forming a color image, image data for each color of yellow, cyan, and magenta is required, so for example, the image memory 13a stores yellow image data, and the image memory 13b stores magenta image data. , cyan image data is written into the image memory 13c, respectively. The operation of each part in this block diagram is exactly the same as the operation of each part in the block section of FIG. 3, so a description of the operation will be omitted.

The laser image forming apparatus configured as described above forms a color image, for example, in the following manner.

First, on the first line, a laser beam from the LDIA modulated based on yellow image data is irradiated from the first reflective surface of the polygon mirror 4. Next, on the second line, the LDI is modulated based on the yellow image data.
A laser beam from A and a laser beam from LDIB modulated on the first line based on magenta image data are simultaneously irradiated from the second reflecting surface of the polygon mirror 4. Then, the laser beam from the LDIA modulated based on the yellow image data is applied to the third line, the laser beam from the LDIB modulated based on the magenta image data is applied to the second line, and the laser beam from the LDIB is modulated based on the magenta image data to the third line. At the same time, laser beams from the LDIC modulated based on the cyan image data are irradiated from the third reflecting surface of the polygon mirror 4. When images are created by repeating these operations, the laser beams of different wavelengths irradiated on the same line are necessarily scanned on different surfaces of the polygon mirror, which makes it possible to eliminate density unevenness in color images. This means that it can be reduced.

Effects of the Invention As is clear from the above explanation, according to the present invention, a line to be overwritten during image formation is scanned by a different reflective surface of a rotating polygon mirror each time overwriting is performed, and Since a plurality of lines are scanned in one main scan by the reflecting surface of the rotating polygon mirror, density unevenness in the image can be reduced without slowing down the image forming speed.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a laser imaging device according to the present invention, FIG. 2 is a diagram showing an example of the energy level output from each laser diode during scanning, and FIG.
FIG. 4 is a block diagram of a control device in the laser imaging device shown in FIG. 4. FIG. 5 is a schematic configuration diagram of a laser imaging device according to another embodiment of the present invention. FIG. FIG. 2 is a block diagram of a control device in the image forming apparatus. 1a to 1c...Laser diode, (laser beam output means), 2a to 2c...Collimator lens, 3a to 3c...
・Reflection prism, 4... Polygon mirror (rotating polygonal fit), 5...
Photoreceptor, 6... fθ lens, 7... Reflection mirror 8... Laser beam detection sensor, 9... Scanning control section (scanning control means), 16a-16c... Laser drive circuit (
modulation signal output means). Figure 4

Claims (1)

[Claims] When the laser beams respectively output from the plurality of laser beam output means are reflected by the same reflecting surface of the rotating polygon mirror and scanned, a plurality of different laser beams are generated in the sub-scanning direction of the photoreceptor. an optical system configured to main-scan lines simultaneously; and a modulation signal based on image information for a different line for each line irradiated by the plurality of laser beam output means as the photoreceptor is sub-scanned. to the plurality of laser beam output means, and to the laser beam output means that irradiates the laser beam over the already irradiated line, the same image information that was output when irradiating the already irradiated line. a modulation signal output means for outputting a modulation signal based on the same image information; and a modulation signal output means for outputting a modulation signal based on the same image information from the modulation signal output means, for directing the main scanning of the laser beam output from the laser beam output means to the irradiated line. A laser imaging device comprising: scanning control means for performing irradiation using a different reflecting surface of the rotating polygon mirror for each irradiation.