JP3487482B2 - Optical scanning device for multicolor image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to an optical scanning device used in an optical writing system such as a digital copying machine and a laser printer, and in particular, an electrostatic latent image is formed on a photoconductor by a plurality of beams. The present invention relates to an optical scanning device of a multicolor image forming apparatus that obtains a multicolor image by superimposing the images.

[0002]

[Prior art]

1. In order to reduce the printing time, in recent years, four photoconductor drums are juxtaposed in the conveying direction of the output paper and are simultaneously exposed by laser beams (hereinafter simply referred to as beams) corresponding to the photoconductor drums, respectively, and toners of different colors are used. 2. Description of the Related Art Digital copying machines and laser printers, which form images in color by sequentially superposing images developed by the developing means, have been put into practical use. As one of them, although it is not a known technique, a. A plurality of laser light sources that emit a single beam are provided as a pair facing each other with a deflecting unit in between, and each beam emitted from each laser light source is distributed and scanned by using the same deflecting unit, and is connected to the photoconductors arranged in parallel. An optical scanning device of a multicolor image forming apparatus for forming an image has been proposed (Japanese Patent Laid-Open No. 4-127115).

On the other hand, in order to shorten the printing time, b. A multi-beam method has been studied in which a plurality of beams are simultaneously scanned at the same time to increase the recording speed, and as a semiconductor laser recording device used in such a multi-beam writing system, a method of synthesizing the beams of a plurality of semiconductor lasers is a special feature. It is known from, for example, Kaihei 7-72407.

Therefore, by combining the above technique with the above technique, c. A plurality of laser light sources for emitting two beams of a first beam and a second beam are provided as a pair facing each other with a deflecting means in between, and each beam emitted from each laser light source is used by the same deflecting means. An optical scanning device of a multicolor image forming apparatus, which is configured to perform a divided scan and form an image on photoconductors juxtaposed to each other, has been proposed as a known technique.

2. Further, in the multi-beam scanning system, if the scanning line positions are not exactly aligned, color misregistration occurs and image quality deteriorates. As a countermeasure, in a laser printer that forms an image for each of a plurality of photoconductors by an image forming station and then transfers these images onto a recording medium, the relative position deviation of these images is measured by a measuring device. Japanese Patent Laid-Open No. 62-242969 discloses a technique relating to a laser beam printer provided with a color misregistration correction means for correcting the writing timing of each image based on the measured values.

[0006]

[Problems to be Solved by the Invention]

1. In the proposed technique of the above c, due to its configuration, there is the following relationship between the beam and the scanning line. I. When each of the laser light sources is set so that the emission direction of the second beam is the same as that of the first beam, the first beam and the second beam of the two light sources facing each other with the deflecting means in between are used. The scanning locus in the main scanning scanning direction on the surface to be scanned is symmetrical. That is, the scanning locus in the main scanning direction by the first beam and the scanning locus in the main scanning direction by the second beam in one of the opposing light sources, the preceding and succeeding order in the sub-scanning direction, and the scanning trajectory in the other light source in the opposite direction. The scanning locus of the one beam in the main scanning direction and the scanning locus of the second beam in the main scanning direction in the sub-scanning direction are in reverse order.

B. Since the light sources are arranged in a facing relationship with the deflecting means in between, the main scanning directions of the facing light sources on the surface to be scanned are opposite to each other.

C. On the other hand, as a print control system of a laser printer, image information to be written is divided into even-numbered row data and odd-numbered row data and stored in the image memory in advance, and these odd-numbered row data and even-numbered row data are stored in the order of beam detection. A method is generally adopted in which the write controller is controlled by distributing the data to control the laser modulator and corresponding data.

In the above-mentioned proposed technique c having the characteristics of a and b, the control method of c is adopted, and the first beam and the second beam are detected by a common sensor in order to simplify the beam detection means. Then, of the two beams of the first beam and the second beam emitted from one light source, the first detected beam has, for example, odd row data, and the next detected beam has even row data. If the writing control is performed, the beam order is reversed between the beams from the light sources facing each other in the main scanning direction and the sub-scanning direction, as described in a and b above. Therefore, for the beam from one of the two light sources facing each other, for example, the beam for scanning odd rows is controlled by the odd row data, and the beam for scanning the even rows is controlled by the even row data. Assuming no problem, with respect to the other light source, the beam scanning the odd rows is scanned with the even row data, and the beam scanning the even rows is scanned with the odd row data, and the image itself is not established.

In order not to cause such a problem,
In order to match the line position with the line data, if a printing control system different from the above-mentioned control system is adopted, the image forming apparatus can be realized, but in that case, the control system becomes complicated. .

2. The technique for preventing color misregistration described in Japanese Patent Application Laid-Open No. Sho 6
Since the technique disclosed in Japanese Patent Publication No. 2-242969 is not intended for a laser light source that emits two beams,
It cannot be applied as it is as a measure against color misregistration in an optical scanning device using a laser light source that emits two beams as in the proposed technique of c.

In view of the above, according to the first and second aspects of the present invention, a simple print control system generally used in multi-beam scanning is used to enable multi-beam image formation of one light source and two beams, and image formation speed. It is an object of the present invention to provide an optical scanning device of a multicolor image forming apparatus that can improve the image quality.

According to the inventions of claims 3 to 4, there is provided an optical scanning device of a multicolor image forming apparatus capable of obtaining a high-quality image with less color misregistration when forming an image by multi-beams of one light source and two beams. The purpose is to provide.

[0014]

In order to achieve the above object, the present invention has the following constitution. (1) A plurality of laser light sources that emit two beams, a first beam and a second beam, are provided as a pair facing each other with a deflecting means in between, and each beam emitted from each laser light source is the same deflecting means. In the optical scanning device of the multi-color image forming apparatus, in which the second beam in each of the laser light sources is scanned at a predetermined angle in the main scanning direction with respect to the first beam in a multicolor image forming apparatus in which images are distributed and scanned using The emission directions of the beams of the laser light sources facing each other are set to be symmetrical with respect to the first beam in the main scanning direction. 1).

(2) A plurality of laser light sources for emitting two beams, a first beam and a second beam, are provided as a pair facing each other with a deflecting means in between, and each beam emitted from each laser light source is the same. In the optical scanning device of the multicolor image forming apparatus, in which the second beam in each of the laser light sources is scanned in a sub-scanning direction with respect to the first beam, the light beam is distributed and scanned using the deflecting means of FIG. The laser beams are emitted at a predetermined angle apart from each other, and the emission directions of the beams of the laser light sources facing each other are set so that the direction of the second beam is symmetrical with respect to the first beam in the sub-scanning direction. (Claim 2).

(3) A plurality of laser light sources for emitting two beams, a first beam and a second beam, are provided as a pair facing each other with a deflecting means in between, and each beam emitted from each laser light source is the same. In the optical scanning device of the multi-color image forming apparatus, in which the scanning is performed separately by using the deflecting means, and the images are formed on the photoconductors juxtaposed to each other, one of an odd-row forming beam and an even-row forming beam is formed in each station. Was used to measure the station interval, and the writing start timing was set based on the measured value (claim 3).

(4) In the optical scanning device of the multicolor image forming apparatus described in (3), an odd-row forming beam, an even-row forming beam and an odd-row forming beam or an even row of the adjacent deflecting surface are provided for each station. A color misregistration detecting unit that detects a relative positional deviation of an image formed by using a forming beam, and a color misregistration amount detected by the color misregistration detecting unit is selected as a first row forming beam. And a timing switching means for performing the switching.

(5) In the optical scanning device of the multicolor image forming apparatus described in (4), the sub-scanning beam pitch at each station is set to be slightly shifted from the recording density (claim 5).

[0019]

DETAILED DESCRIPTION OF THE INVENTION

(1) An example of an optical scanning device of a multicolor image forming apparatus common to the invention described in each claim will be described with reference to FIGS. In these drawings, reference numerals 11, 12, 13, and 14 respectively denote a light source unit including a semiconductor laser and a collimator lens (not shown),
It constitutes the light source according to the present invention.

All of these light source units have at least the components shown in FIG. That is, the first
Semiconductor laser LD1, second semiconductor laser LD2, first collimating lens L1, second collimating lens L
It has a half-wave plate L3, a reflecting surface L4, a polarization beam splitter L5, and the like. First semiconductor laser LD1
The first beam emitted further is converted into parallel light by the collimator lens L1 and transmitted through the polarization beam splitter L5. The second beam emitted from the second semiconductor laser LD2 is converted into parallel light by the collimating lens L2, and
The polarization plane is rotated by the half-wave plate L3 and the reflection plane L
4, polarized beam splitter L5 is deflected in this order,
The first beam is emitted in a direction opened at a predetermined angle in a predetermined direction. In this way, each light source unit 11-1
4 emits two beams, a first beam and a second beam, respectively.

These light source units 11, 12, 13,
Denoted at 14 are opposed to each other with a polygon mirror 15 as a deflecting unit in between, and are supported and mounted on a mounting surface formed on the optical housing 10. here,
The average incident angle θ of the light source units 11 and 14 forming a pair facing the polygon mirror 15 is set to approximately 60 °, and the average incident angle θ of the light source units 12 and 13 forming another pair is set to approximately 75 °.

These light source units 11, 12, 13,
The first beam and the second beam respectively emitted from 14 are deflected by the polygon mirror 15, and are the first optical system to be incident on the optical path after the polygon mirror, and have the fθ characteristic of a spherical surface or a coaxial aspherical surface. After passing through fθ mirrors 16 and 17 which are concave curved surface mirrors as image forming elements, further toroidal lenses 18 and 19 which form a plane tilt correction system,
A drum-shaped photosensitive member 28, 29, 30, which serves as an image forming station, is a surface to be scanned through 20, 21 and
An image is formed in a spot shape on the surface 31 and is scanned in the main scanning direction to record a latent image. Here, it is assumed that the first beam passes through the optical axes of the toroidal lenses 18 to 21, and the second beam passes through a position displaced from the optical axes of the toroidal lenses 18 to 21.

These latent images are written with information to be visualized with cyan toner for the photoconductor 31 constituting the first station, and similarly, for the photoconductor 30 constituting the second station. What is written with information to be visualized with magenta toner, the photosensitive member 29 that constitutes the third station is written with information that is to be visualized with yellow toner, and constitutes the fourth station. The photoconductor 28 is written with information to be visualized with black toner.

Each of these latent images is visualized with toner of a predetermined color at each station, and the photoconductor 31 and the photoconductor 3 located at an early position in the sub-scanning direction.
0, the photoconductor 29, and the photoconductor 28 are sequentially transferred onto the output paper to form a color image.

The polygon mirror 15 has a thickness of 3 mm and is constructed by stacking it in two stages with the phases on the motor reference plane aligned with each other. As shown in FIG. 4, the f.theta. The distance between the centers in the sub-scanning direction is 3 mm and the resin is integrally formed in two steps.
The θ mirrors are inclined in opposite directions in the sub-scanning direction by a predetermined angle so that the beams are distributed to the respective stations with respect to the incident light beams so that the emitted lights are directed in the directions in which they diverge from each other. Similarly to the fθ mirror 16, the fθ mirror 17 provided oppositely with the polygon mirror 15 in between is vertically stacked in two stages, and the normal direction of the fθ mirror 17 is also opposite to the sub-scanning direction. It is tilted.

As shown in FIG. 3, with respect to the first beam and the second beam emitted from the light source unit 11 and the light source unit 12, respectively, the first beam and the second beam are detected by the synchronization detection sensor 32 via the mirror 35. Before and after is detected, and write control is performed based on the detected information. Similarly, the first beams emitted from the light source unit 13 and the light source unit 14, respectively,
Regarding the second beam, the synchronization detection sensor 33 detects the front and rear of the first beam and the second beam via the mirror 36, and the writing control is performed based on the detection information. The reference numeral 34 indicates the light source unit 11
2 shows a beam detector as a write end detector for detecting the write end of the first beam from the.

In FIG. 5, in an image memory 40-1 for writing a cyan image, data relating to the cyan image is divided into even-numbered row data and odd-numbered row data and stored. The synchronization detection sensor 32 includes the light source unit 11
The first beam, the second beam from the light source unit 12, and the first beam and the second beam from the light source unit 12, and the synchronization detection sensor 33 detects the first beam from the light source unit 13, the second beam, and the first beam from the light source unit 14. One beam and a second beam are detected. These beams are set so that they do not enter the same synchronization detection sensor at the same time, that is, they enter later in time.

For example, when the beam is detected by the synchronous detection sensor 32, the first detected beam out of the total four beams from the light source units 11 and 12 and 3 are detected.
The write position counter 40-2 determines that the beam detected second is the preceding beam, the beam detected second and the beam detected fourth is the trailing beam, and a gate signal for setting the write position for each beam. (GATE signal) is output to the write control unit 40-3. In response to this gate signal, the writing control unit 40-3 reads the odd-numbered row data from the image memory 40-1 for the preceding beam and the even-numbered row data from the image memory 40-1 for the succeeding beam. Reading is performed, the LD modulators of the semiconductor lasers of the corresponding beams are respectively controlled to put image data on the beams, and writing is performed. The synchronization detection sensor 33 also performs similar detection for each beam from the light source units 13 and 14, and causes the writing position counter 40-2 and the writing control unit 40-3 to function to perform writing control.

(2) Example of the invention according to claim 1 The emission direction of the second beam with respect to the first beam in FIG. 6 is as follows for each of the light source units 11-14.
It is assumed that they are all set and arranged in the same relationship. For example, regarding the light source unit 100 shown in FIG. 12, when the light source unit 100 alone is viewed, when the optical path of the first beam is aligned with the three-dimensional coordinate axis z axis, the emission direction of the second beam is in the first quadrant. . In this coordinate axis, the x axis corresponds to the main scanning direction and the y axis corresponds to the sub scanning direction. It is assumed that such a light source unit 100 is used for the light source units 11-14. Then, as shown in an enlarged manner in FIG. 8, the first beam and the second beam emitted from the light source unit 14 are deflected by the lower part of the polygon mirror 15 and reflected by the lower part of the fθ mirror 17, Toroidal lens 2 via mirror 23
1, and is further deflected by the mirror 25 to form an image on the photoconductor 31 which is the first station. At this time, the second beam forms an image at a preceding position in the sub-scanning direction, and the first beam forms an image at a following position.

Similarly, the first beam and the second beam emitted from the light source unit 13 are deflected by the upper stage of the polygon mirror 15, reflected by the upper stage of the fθ mirror 17, and toroidal through the mirror 27. Lens 2
Photosensitive member 3 which is the second station as it passes 0
Image at 0. At this time, the first beam is imaged at the preceding position in the sub-scanning direction, and the second beam is imaged at the following position.

Similarly, the first beam and the second beam emitted from the light source unit 12 are deflected by the upper stage of the polygon mirror 15, reflected by the upper stage of the fθ mirror 16, and toroidal through the mirror 26. Lens 1
An image is formed on the photoconductor 29, which is the third station, after passing through 9. In this case, unlike the beam from the light source unit 11, after the light is emitted from the toroidal lens 19, it does not pass through the mirror, so the second beam of the beams emitted from the toroidal lens 19 is coupled to the preceding position in the sub-scanning direction. The first beam is imaged, and the first beam is imaged at the following position.

Similarly, the first beam and the second beam emitted from the light source unit 11 are polygon mirrors 15.
The light is deflected by the lower part of the fθ mirror, reflected by the lower part of the fθ mirror 16, and transmitted through the toroidal lens 18 via the mirror 22 and then imaged on the photoconductor 28 which is the fourth station via the mirror 24. At this time, the first beam is imaged at the leading position in the sub-scanning direction, and the second beam is imaged at the trailing position.

Regarding the main scanning direction, the polygon mirror 1
Since the rotation direction of 5 is a constant direction, the main scanning direction of the beam from the light source unit 11 and the main scanning direction of the beam from the light source unit 14, which are provided to face each other with the polygon mirror 15 in between, respectively. Arrows A and B in FIGS.
As shown in, the relationship is reversed. Similarly, the light source unit 1
The main scanning direction of the beam from 2 and the main scanning direction of the beam from the light source unit 13 also have an inverse relationship as shown by arrows A and B.

Regarding the linearity of the scanning locus, in each station (photoconductor 28 to 31), each light source unit 1
As shown in FIG. 7, the writing scan lines by the beams from 1 to 12 are linearly scanned because the first beam passes through the optical axes of the toroidal lenses 18 to 21, and the second beam is toroidal lenses. 18-2
Since the light beam passes through a position deviated from the optical axis of No. 1, it is scanned into a curved shape as shown in FIG.

FIG. 1 shows the relationship between the scanning locus of a beam scanned under such conditions and the image data placed on the beam.
Take a look at each station while referring to. In each station, the positional relationship between the first beam and the second beam in the sub-scanning direction is as described in FIG.
In the station and the fourth station, the first beam is the leading beam and the second beam is the trailing beam, and in the first and third stations, the second beam is the leading beam and the first beam is the trailing beam.

Therefore, the first beam scans the odd-numbered row positions and the second beam scans the even-numbered row positions in the second station and the fourth station respectively, and the second beam scans the odd number in the first station and the third station. Row, first
The beam scans each even row. Also, the first beam in the main scanning direction at each of these stations,
Regarding the predecessor-posterior relationship of the second beam, assuming that the beam spot is located at the position indicated by the black circle for the first beam at the first station, the beam spot of the second beam is the position indicated by the white circle delayed in the main scanning direction. It is in.

Therefore, in the printing control method described with reference to FIG. 5, in the first station, the first beam for scanning even rows is written with odd data, and the second beam for scanning odd rows is written with even data. Becomes Regarding the fourth station which is scanned by the light source unit 11 facing the light source unit 14 which scans the first station, the first beam for scanning odd rows is written with odd data and the second beam for scanning even rows. Will be written with even data.

Similarly, for the second station, the first beam scanning odd rows is written with odd data,
The second beam for scanning even rows is written with even data. Regarding the third station which is scanned by the light source unit 12 opposite to the light source unit 13 which scans the second station, the second beam for scanning odd rows is written with even data and the first beam for scanning odd rows. Will be written with odd data.
Therefore, the line positions and the image data do not match in the first and fourth stations and the second and third stations, and as a result, a correct image cannot be formed. This is
This is as described in the section of the problem to be solved by the invention.

The present invention solves such a problem.
In each station, the line position and the image data are matched.

In FIG. 1, in order to eliminate the discrepancy between the row position and the image data, in the first station, the second beam, which is scanned later than the first beam in the main scanning direction, precedes the first beam. Just do it. In this way, the preceding second beam is first detected by the synchronization detection sensor 3
Since the second beam for scanning the odd rows is written with the odd data, the first beam for scanning the even rows is written with the even data. Become. In order to do so, the light source unit 14 for scanning the first station is the same as the light source unit 100 shown in FIG.
The direction of emission of the second beam is not the position in the first quadrant, but y
What is set so as to pass through a position in the fourth quadrant that is symmetrical with respect to the axis may be used.

This means that in the relationship between the light source unit 11 and the light source unit 14 which face each other with the polygon mirror 15 in between, the direction of the second beam is symmetrical with respect to the first beam in the main scanning direction. It means that you should do it. That is, assuming that the emission direction of the second beam of the light source unit 11 is the position in the first quadrant, the light source unit 14
The emission direction of the second beam is set to the position on the fourth quadrant.

That is, of the laser light sources, the emission directions of the beams of the laser light sources facing each other with the deflecting means in between are the emission directions of the second beam with respect to the first beam passing through the origin of one light source in the first quadrant. In the other direction, the emission direction of the second beam with respect to the first beam passing through the origin is the direction in the fourth quadrant that is symmetrical to the direction of the second beam in the one light source.

The same applies to the relationship between the light source unit 12 and the light source unit 13 that face each other with the polygon mirror 15 in between. That is, when the emission direction of the second beam of the light source unit 13 is the direction within the first quadrant, the emission direction of the second beam of the light source unit 12 is the direction within the fourth quadrant that is symmetrical with respect to the y axis. . By doing so, the second station in the third station in FIG.
Since the beam spot of the beam precedes the beam spot of the first beam, the second beam scanning the odd row is written with odd data, and the first beam scanning the even row is written. Will be written with even data.

As described above, according to the present invention, the beam emission directions of the laser light sources facing each other are set so that the direction of the second beam is symmetrical to the direction of the first beam, thereby making the print control system complicated. In addition, it is possible to form a multicolor image by a multi-beam without using a small number of synchronization detection sensors.

(3) Example of the invention described in claim 2 In the invention described in claim 1, as described with reference to FIG.
Since the second beam scanning the odd rows writes with the odd data and the first beam scanning the even rows writes with the even data, the discrepancy between the row position and the image data is eliminated. However, as described with reference to FIG. 7, of the two beams of the first beam and the second beam emitted from the same light source, the position deviated from the optical axis with respect to the beam passing through the optical axes of the toroidal lenses 18 to 21. Since the scanning trajectory of the beam passing through is curved,
In FIG. 1, when the odd-numbered rows are linearly scanned and the even-numbered rows are curved line scanning in the second and fourth stations, the odd-numbered rows are curved line scanning and the even-numbered rows are linearly scanned in the first and third stations. However, this does not eliminate the occurrence of inconsistency in the bending characteristics. Such inconsistency of the bending characteristics between the stations becomes an obstacle to high-quality image output. Therefore, the invention of claim 2 specifies the emission directions of the first beam and the second beam in each light source unit so as to prevent such inconsistencies in the bending characteristics. Now, with reference to FIG. 1 described in (2) above, consider the state before the invention according to claim 1 is implemented. That is, it is assumed that the emission directions of the second beams are the same as the emission directions of the first beam in each of the light source units 11 to 12,
The relationship between the writing beam, the scanning locus, and the writing data in each station (photoconductors 28 to 31) is shown in FIG.

That is, in the first station, the scanning locus by the second beam is curved and is located in the odd-numbered rows, and the scanning locus by the first beam is linear and is located in the even-numbered rows. The main scanning direction is arrow B. Since the first beam precedes the second beam in the main scanning direction, the first beam for scanning even rows performs writing with odd data, whereas the first beam scans for odd rows. The second beam to be scanned is written with even data. Therefore, the line position and the image data do not match in the first station.

In the second station, the scanning locus by the first beam is located in a straight line in odd rows, and the scanning locus in the second beam is curved and located in even rows. The main scanning direction is an arrow B. Since the first beam precedes the second beam in the main scanning direction, the first beam for scanning odd rows writes with odd data, whereas the first beam scans even rows. The second beam to be scanned is written with even data. Therefore, the line position and the image data match in the second station.

In the third station, the scanning locus by the second beam is curved and is located in an odd numbered row.
The beam scanning locus is a straight line and is located in even rows. The main scanning direction is arrow A. Since the first beam precedes the second beam in the main scanning direction, the first beam for scanning even rows performs writing with odd data, whereas the first beam scans for odd rows. The second beam to be scanned is written with even data. Therefore, the line position and the image data do not match at the third station.

In the fourth station, the scanning locus by the first beam is located in a straight line in odd rows, and the scanning locus in the second beam is curved and located in even rows. The main scanning direction is an arrow A. Since the first beam precedes the second beam in the main scanning direction, the first beam for scanning odd rows writes data by odd data, while the first beam scans even rows. The second beam to be scanned is written with even data. Therefore, the line position and the image data match in the second station.

In order to eliminate such a discrepancy between the row position and the image data in FIG. 2, for the first station, the scanning trajectory of the second beam should be symmetrical with respect to the first beam, that is, , 'Can be moved so as to scan the position. Similarly, in the third station as well, it may be moved so that the scanning locus by the second beam becomes a symmetrical position with respect to the first beam, that is, by scanning the position of '. By doing so, in the first station and the third station, the scanning positions of the first beam and the second beam are switched between the odd-numbered row and the even-numbered row, so that the mismatch between the row position and the image data is resolved. The bending characteristics between the stations are also matched.

In order to do so, with respect to the light source unit 14 for scanning the first station, in the optical unit 100 shown in FIG. 12, the emission direction of the second beam is not at the (first quadrant) position but at the first position. What is set on two quadrants so as to pass through a position symmetrical to the position of the first quadrant may be used.

This means that in the relationship between the light source unit 11 and the light source unit 14 which face each other with the polygon mirror 15 in between, the direction of the second beam is symmetrical with respect to the first beam in the sub-scanning direction. It means that you should do it. That is, assuming that the emission direction of the second beam of the light source unit 11 is the position in the first quadrant, the light source unit 14
Of the second beam ′ of the second beam symmetric with respect to the x-axis
It is located in the quadrant.

The same applies to the relationship between the light source unit 12 and the light source unit 13 which face each other with the polygon mirror 15 in between. That is, assuming that the emission direction of the second beam of the light source unit 13 is on the first quadrant, the emission direction of the second beam ′ of the light source unit 12 is on the second quadrant position symmetrical with respect to the x axis. is there.

By doing so, it is possible to eliminate the inconsistency between the row position and the image data, and at the same time to avoid the inconsistency of the curve characteristics of the beam between the stations, and to obtain a high quality color image.

(4) Example of the invention according to claim 3 A latent image for a multicolor image is written on each of a plurality of photoconductors juxtaposed with each other, visualized, and then transferred onto a recording member conveyed in the sub-scanning direction. In the method of forming a color image by using the above-described method, the timing of writing an image in the image forming station including these photoconductors, that is, the timing of placing image information on a beam is basically a color image by one light source and one beam. The station interval may be measured using one of the odd-row forming beam and the even-row forming beam by using the technique applied in the forming apparatus, and the writing timing may be set based on the measured value.

For example, the first station (photoconductor 31)
Consider the timing of writing in the second station (photoconductor 30) with respect to the timing of writing in. In FIG. 4, a photo sensor 38 is provided at a position downstream of the fourth station (photoconductor 28) in the sub-scanning direction so that the edge of the writing line on the recording paper can be detected via the condenser lens 39. It has become.

Therefore, at a certain known time, a line is written on the photoconductor 31 of the first station by the odd-row forming beam of the first light source unit 14, and then at a timing after a time of Δt from the known time. Lines are written on the photoconductor 30 of the second station by the odd-row forming beam of the second light source unit 13, and each is developed into a visible image and transferred onto a recording paper (or an intermediate transfer belt), and then a photo sensor. When these written line intervals ΔM are measured by 38, the rotation speed of the photoconductor 30 = the rotation speed of the photoconductor 31 = the feed speed of the recording paper =
Since v is known, the accurate distance L between the first station and the second station is calculated from these values of v, ΔM, and Δt.
1 can be calculated (see FIG. 4). Therefore,
By calculating "L1 / v", the photoconductor unit 1
Each writing time t1 to the photoconductors 31 and 30 at which the odd-row forming beam from 4 and the odd-row forming beam from the photoconductor unit 13 can be accurately overlapped on the recording paper.
Can be obtained by the calculation formula of t1 = L1 / v (see FIG. 9).

By the same method, the accurate distance L2 between the first station and the third station and the accurate distance L3 between the first station and the fourth station can be obtained (see FIG. 4). Therefore, the time interval t2 from the time of writing by the odd-row forming beam from the photoconductor unit 14 to the time of writing by the odd-row beam from the photoconductor unit 12 so that the writing lines by each beam can be accurately overlapped. The time interval t3 from the time of writing by the odd-numbered row forming beam from the photoconductor unit 14 to the time of writing by the odd-numbered row beam from the photoconductor unit 11 is also t, respectively.
It can be obtained as 2 = L2 / v and t3 = L3 / v.

Therefore, if the timing of writing is set by accurately matching these t1, t2, and t3, the images of the respective beams can be accurately overlapped, but in reality, per surface of the polygon mirror 15 It cannot be accurately adjusted within the scanning cycle of. Therefore, these t
Writing is performed by the reflected light from the polygonal surface at the timing closest to 1, t2, and t3.

A method therefor will be described. When the scanning period per one surface of the polygon mirror 15 is CLK, the value of CLK can be accurately measured. The value when this CLK value is multiplied by an arbitrary integer k1 is t
1 '. That is, t1 ′ = K1 × CLK. In this equation, the actual value of k1 that can take the value closest to t1 is obtained, and the timing of writing at the first station determines the timing of writing at the second station with the timing of t1 ′ calculated from the actual value. Similarly for the writing timing in the third station and the writing timing in the fourth station, t2 ′ = K2 × CLK,
With t3 ′ = K3 × CLK, the actual values of integers K2 and K3 that can take the values most approximate to t2 ′ and t3 ′ are obtained, and t2 ′ and t3 ′ calculated from the obtained actual values
The timing of writing in the third station and the fourth station is determined.

In the above description, the writing timing is set by using the odd row forming beam for each light source unit, but it is also possible to use the even row forming beam for each light source unit.

Since the photo sensor 38 cannot discriminate colors, when setting t1 to t3, detection is performed by a line separated from the reference color by an arbitrary interval, for example, 1 inch. Alternatively, if the same line is scanned in the main scanning direction by dividing the section for each beam, the trajectories of the respective beams deviate in the main scanning direction, so that the overlapping states can be compared without overlapping in the sub-scanning direction. Kaisho 62-2
42969, see FIG. 3).

(5) Example of Invention of Claim 4 In the example of the above (4), the writing timing at the n-th color station is set by using one of the even-numbered row and the odd-numbered row. Therefore, in reality, with respect to one reflecting surface of the polygon mirror, the same idea that only one beam exists makes it possible to select the reflecting surface of the polygon mirror that scans the scanning position where the color shift can be minimized. .

In this example, paying attention to the fact that two beams exist for one reflecting surface of the polygon mirror,
Among these two beams, the beam existing at a position where the color shift can be further reduced is selected as the first row forming beam to form an image.

FIG. 10 shows the output of the line image on the recording paper written by the same polygon mirror 15 read by the photosensor 38 shown in FIG. In the output waveform shown in FIG. 10, the line images formed on the recording paper are sequentially read by the single photosensor 38. Therefore, the images are sequentially formed in the sub-scanning direction, and the line with less color shift is the first line. In order to select it as the forming beam, the reflecting surface of the polygon mirror is made different to form line images sequentially in the sub-scanning direction.
In order to make it easier to read and compare the outputs by using the above-mentioned 8, the detection output of the scanning locus for each reflecting surface of the polygon mirror is first detected.
The colors are also shown in phase.

The first output is the second output from the top, and the r-plane writes an odd-numbered row and an even-numbered row adjacent to the first-color, and an arbitrary interval from these first-color writing lines. This is the detection output of the photosensor 38 when the image of the nth color is written on the odd-numbered rows and the even-numbered rows adjacent thereto by the r-plane at a (target interval).

The second output is shown at the top, and is higher than the reflecting surface r when the image of the nth color in the first output is written in the rotation direction of the polygon mirror for the nth color. , The read output by the photosensor 38 when an odd-numbered row and an even-numbered row adjacent to this are written for the first color by the r-1 surface adjacent to the delayed side.

The third output is shown at the bottom, and is higher in the rotation direction of the polygon mirror than the reflecting surface r when the image of the nth color in the first output is written for the nth color. , The detection output of the photosensor 38 when an odd-numbered row and an even-numbered row adjacent thereto are written for the first color by the r + 1 surface adjacent to the advanced side.

Of these three outputs, for example, with respect to the output of the scanning beam by the r-plane, the interval L12 from the odd-numbered row of the first color (for example, this is the leading row) to the odd-numbered row of the n-th color is measured. , Suppose that it was slightly off the target interval. To minimize the amount of this deviation,
Of either one row before or after the odd row of the nth color on the r-plane, the row with the smallest deviation from the target interval is selected as the first row, and the data for the first row is set as the beam for scanning this row. Make sure to write on it. In other words, r
The odd-numbered row data corresponding to the odd-numbered row data of the first color is written on the beam for scanning the line of the even-numbered row located at the interval L12 from the odd-numbered row of the first color, or the Either the odd-numbered row of the first color or the odd-numbered row data corresponding to the odd-numbered row data of the first color is written on the beam for scanning the line of the even-numbered row and the writing is selected.

In the above example, the odd-numbered row of the first color by the r-plane is considered as a reference, but the same thing can be said when the even-numbered row of the first color by the r-plane is used as a reference. That is, it is assumed that the distance L15 from the even-numbered row of the first color (for example, the leading row) to the even-numbered row of the n-th color is measured and is slightly deviated from the aimed distance. In order to minimize the amount of this deviation, one of the rows before and after the even row of the nth color on the r-plane, which has the smallest deviation from the above-mentioned target interval, is selected as the first row. The data for the first row is written on the beam for scanning the row. In other words, the even-numbered row data corresponding to the even-numbered row data of the first color is written on the beam for scanning the line of the odd-numbered row at the position of the interval L14 from the even-numbered row of the r-side, or the r-plane From the even line of the first color
It is selected whether the beam for scanning the odd-numbered rows of the r + 1 plane at the position of 16 is written with the even-row data corresponding to the even-row data of the first color of the r-plane.

In this example, the photo sensor 38 constitutes an example of the color shift detecting means in the invention described in claim 4. Further, the timing switching means for selecting the beam with the smallest color shift amount as the head row forming beam is the synchronous detection sensors 32 and 33 capable of detecting the rotational position of the polygon mirror 15, and the beam detection output from these sensors. Can be input and the predetermined image information can be placed at a predetermined timing by a writing control unit. In this example, since the row data and the row position are rearranged by originally using the beam for scanning the odd row as the even row as described above, it is possible to place the odd row data on the preceding beam. The write control unit 40-3 described with reference to FIG. 5 for controlling is not used.

(6) Example of the Invention of Claim 5 In the example of (5), the color shift is eliminated by finely adjusting the sub-scanning beam pitch. In FIG. 11, when the pitch of each row indicated by the thick line is P, originally, writing on the thick line at the top by the first beam by the nth color first row data and by the second beam by the reference color first row data is performed. Is performed, the second beam is written on the nth color second row data on the next thick line, and the first beam is written on the reference color second row data, and the nth line is written on the next thick line. Writing by the first beam based on the color third row data and writing by the second beam based on the reference color third row data should be performed.

However, the middle position between the rows where the beam of the reference color has the maximum deviation, that is, the middle position of the thick line as shown by the thin line in the figure, that is, the position of P / 2 (ΔPmax
= P / 2 = 31.75 μm), if no adjustment is made, the scanning lines of the reference color will be located at the middle positions of the thick lines at intervals of the pitch P as shown by the thin lines.

Therefore, regarding the first row, writing with the first beam of the nth color first row data is performed at the position on the top thick line, and the reference color first row data is provided at the position on the next thin line. Writing with two beams is performed. Similarly, for the second row, the second thick line is used for writing the nth color second row data by the second beam, and the next thin line is used for writing the reference color second row data by the first beam. Similarly, for the third row, writing of the nth color third row data by the first beam on the third thick line and writing of the reference color third row data by the second beam on the thin line next to this thick line are performed. Done.

In this case, the case where the first beam of the reference color is shifted with respect to the second beam of the reference color to adjust the deviation will be described. In this example, the polygon mirror 15
In the case where two beams are simultaneously incident on one of the reflection surfaces and an image is written by scanning two lines simultaneously, the shift amount appears as it is as a variation of the line pitch. The maximum value at which the influence of the fluctuation of the line pitch on the image is allowed is 10 μm which is 10% of the beam diameter of 100 μm. Therefore, as shown in FIG. 11B, the second beam of the reference color is fixed, and the scanning position of the first beam of the reference color shown in FIG. 11A is indicated by the arrow within the allowable shift amount of 10 μm. Shift in the direction of. In this example, a case where the maximum value of 10 μm is shifted will be described.

Then, the relationship between the pitch ΔP ′ changed by the shift and the pitch P before the change is ΔP ′ <ΔP
(∵ΔP ′ = ΔP−10 μm), that is, the shift causes the shifted beam to come closest to the top thick line which is the scanning line of the first beam by the nth color first row data. 11 (1), the first beam of the reference color shown in FIG. 11 (1) after this shift is used as the writing beam of the first row of the reference color. It is changed so that the second beam of the reference color of 2) carries the third line data instead of the first line data.

As described above, the writing of the first row is the combination of the shifted first beam of the reference color and the first beam of the nth color, and the writing of the second row is the writing of the second beam of the reference color and the second beam of the nth color. A combination of beams is used. Writing the third row is a combination of the first beam of the reference color and the first beam of the nth color after shifting. Writing of the fourth row is the second beam of the reference color and the second beam of the nth color. Will be a combination of.

As a result, the maximum deviation between colors can be calculated as ΔP'ma.
By setting x = P / 2-10 μm = 21.75 μm, it is possible to suppress the amount of misrecognition or less.

Means for such a shift will be described. In FIG. 12, a nut 103N is screwed onto the shaft of the stepping motor 103, and the nut 103N
Is brought into contact with the lower part of one end side of the light source unit 100. On the other hand, the light source unit 100 is configured to be rotatable about the extension line of the first beam passing through the optical axis as the rotation center.
Then, the tip of the nut 103N is brought into contact with the lower surface of one end side of the light source unit 100, and the nut 103N and the light source unit are always kept in contact with each other by pressing the nut 103N from the opposite upper side by the urging means. Leave. Further, a long groove is formed in the nut N in the vertical direction, and a shaft provided on the immovable member is slidably engaged with the long groove. The rotation stopping means causes the nut N to move up and down in response to the driving of the stepping motor 103.

By doing so, by driving the stepping motor 103, the nut N can be moved up and down, and the light source unit 100 can be tilted up and down about the optical axis. Shift control becomes possible.

[0081]

According to the first aspect of the present invention, one of the first beam and the second beam by one laser light source is detected by the synchronization detection means common to the preceding beam, and the print control is common to each station. It is possible to realize high speed color printing by multi-beam with a simple structure.

According to the second aspect of the present invention, the beam curvature characteristics of the beams of the laser light sources can be matched on the surface to be scanned, so that a high-quality color image with less color misregistration can be obtained.

According to the third, fourth, and fifth aspects of the present invention, the initial setting work of each station can be simplified, the work efficiency can be improved, and a high-quality image with little color shift can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram illustrating scanning trajectories of a first beam and a second beam in each station.

FIG. 2 is a diagram illustrating a scanning locus by a first beam and a second beam in each station.

FIG. 3 is a plan view of an optical scanning device according to the present invention.

FIG. 4 is a front view of an optical scanning device according to the present invention.

FIG. 5 is a block diagram of a print control system of the optical scanning device according to the present invention.

FIG. 6 is a perspective view illustrating a configuration of a laser light source that outputs two beams in the optical scanning device according to the present invention.

FIG. 7 is a diagram illustrating a beam bending characteristic.

FIG. 8 is a partially enlarged front view of the optical scanning device shown in FIG.

FIG. 9 is a time chart explaining the timing of image writing in each light source unit.

FIG. 10 is a diagram schematically illustrating a detection output by a sensor of an image formed by a scanning beam by an arbitrary reflection surface of a polygon mirror and reflection surfaces on both sides of the reflection surface.

FIG. 11 is a diagram explaining that row data to be placed on a beam is changed by shifting one of the two beams in order to eliminate the positional deviation.

FIG. 12 is a diagram illustrating a configuration of a light source unit and a beam emission direction.

[Explanation of symbols]

15 Polygon mirrors 16 and 17 (as deflecting means) fθ mirrors 28, 29, 30 and 31 (as image forming elements) Photoconductor 32 (constituting a station) 32 Synchronous detection sensors 33 and 34 Beam detector First beam 2 beams

Claims (5)

(57) [Claims] 1. A plurality of laser light sources for emitting two beams, a first beam and a second beam, are provided as a pair facing each other with a deflecting means in between, and each beam emitted from each laser light source is the same. In an optical scanning device of a multi-color image forming apparatus, which is configured to perform scanning separately by using a deflecting unit and form an image on photoconductors juxtaposed to each other, the second beam in each laser light source is in the main scanning direction with respect to the first beam. The emission directions of the beams of the laser light sources facing each other are set so as to be emitted at a predetermined angle, and the direction of the second beam is set to be symmetrical with respect to the first beam in the main scanning direction. An optical scanning device for a multi-color image forming apparatus. 2. A plurality of laser light sources for emitting two beams, a first beam and a second beam, are provided as a pair facing each other with a deflecting means in between, and each beam emitted from each laser light source is the same. In an optical scanning device of a multicolor image forming apparatus, in which a deflecting means is used to perform scanning in a divided manner to form images on photoconductors arranged side by side, the second beam in each laser light source is in the sub-scanning direction with respect to the first beam. The laser beams are emitted at a predetermined angle, and the emission directions of the beams of the laser light sources facing each other are set so that the direction of the second beam is symmetrical with respect to the first beam in the sub-scanning direction. An optical scanning device for a multi-color image forming apparatus. 3. A plurality of laser light sources for emitting two beams, a first beam and a second beam, are provided as a pair facing each other with a deflecting means in between, and each beam emitted from each laser light source is the same. In an optical scanning device of a multicolor image forming apparatus in which a deflecting means is used to perform scanning in a distributed manner so as to form an image on photoconductors juxtaposed to each other, one of an odd-row forming beam and an even-row forming beam is formed in each station. An optical scanning device of a multicolor image forming apparatus, characterized in that the station interval is measured by using the measured value, and the writing start timing is set based on the measured value. 4. An optical scanning device of a multicolor image forming apparatus according to claim 3, wherein an odd row forming beam is provided for each station.
Color shift detecting means for detecting relative position shift of an image formed using the even-numbered row forming beam and the odd-numbered row forming beam of the adjacent deflection surface, or the color detected by the color shift detecting means. An optical scanning device of a multicolor image forming apparatus, comprising: a timing switching unit that selects a beam having the smallest amount of color shift as a leading row forming beam. 5. An optical scanning device of a multicolor image forming apparatus according to claim 4, wherein the sub-scanning beam pitch at each station is set to be slightly shifted from the recording density. Optical scanning device.