JP2003334989A - Writing control method, writing controller, and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that the toner image of each color is shifted by approximately one line. <P>SOLUTION: In the writing control method of an imaging method for forming a color image by superposing a plurality of images obtained by performing scanning of n lines (n>0) per operation, scanning corresponding to the image information from (i+1)-th line is started, where i is an integer for minimizing |t1+T×(i/n)-t2|, if t1<t2 when writing of an image other than a reference image is started, assuming the time interval of generating a main scanning sync signal is T, the time after detecting an imaging start signal before detecting the main scanning sync signal is t1 when writing of the reference image is started, and the time after detecting the imaging start signal before detecting the main scanning sync signal is t2 when writing of an image other than the reference image is started. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a write control method,
The present invention relates to a writing control device and an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, for an image carrier moving in the sub-scanning direction, image information in the main-scanning direction is detected based on a main-scanning synchronization signal detected after an image formation start signal in the sub-scanning direction is detected. There is known an image forming apparatus such as a copying machine, a printer, a facsimile or the like, which has a scanning writing device that performs scanning according to the above to write an image. FIG. 2 shows an example of such an image forming apparatus.

In FIG. 2, 1 is an optical writing device as a scanning writing device which is an exposure device, and 2 is a photoconductor driving device (not shown) in which an image is written by being scanned by the optical writing device 1 in the main scanning direction according to image information. A drum-shaped photoconductor as an image bearing member, which is a member to be scanned and is driven to rotate in the sub-scanning direction at an image writing position, 3 is a cleaning device for cleaning the photoconductor 2, and 4 is a photoconductor 2. Charging device for charging like, 5K, 5C, 5M,
5Y is a developing device for developing the electrostatic latent image on the photoconductor 2 into a toner image of each color of black, cyan, magenta, and yellow, and 6 is the same peripheral speed as the photoconductor 2 by a driving means (not shown). A transfer drum serving as an intermediate transfer member that is rotated and provided with a marker M is a sub-device 61 that detects the marker M on the transfer drum 6 and generates a recording start signal in the sub-scanning direction which is an image formation start signal in the sub-scanning direction. Detecting means as a scanning direction image forming start signal generating means, 7 is a fixing device, 8 is a transfer sheet as a recording medium, and 9 is a recording start signal in the sub-scanning direction input from the detecting means 61 to control the entire example. A controller 10 as a control means for controlling the transfer paper 8 is a paper feeding device for feeding the transfer paper 8.

Next, the operation of this example will be described. When the image forming operation is started, the surface of the photoconductor 2 is charged to a predetermined potential by the charging device 4. The photoconductor 2 rotates in the direction of the arrow in the figure, and the charged surface of the photoconductor 2 is then sequentially modulated by the optical writing device 1 with the image information of each color of black color, cyan color, magenta color, and yellow color. The beam is repeatedly scanned and exposed in the main scanning direction.
At this time, the exposed portion of the photoconductor 2 becomes conductive and the surface charge is discharged from the inner surface of the photoconductor 2 to the ground, whereby the exposed portion becomes an image portion and the non-exposed portion becomes a non-image portion. As a result, electrostatic line images corresponding to the image information of each color are sequentially formed on the photoconductor 2.

Next, the electrostatic latent images corresponding to the image information of the respective colors on the photoconductor 2 are developed by the developing devices 5K, 5C, 5M, respectively.
Developed by 5Y. Each developing device 5K, 5C, 5M,
5Y is black, cyan, magenta,
A developer carrying member carrying a developer containing toners of each color of yellow is provided, and a non-image part potential and an image part potential of the electrostatic latent image on the photoconductor 2 are supplied to the developer carrying body from a power supply device (not shown). The toner on the developer carrying member is selectively adhered to the image portion on the photoconductor 2 by applying an electric potential in the middle between and. In this example, the developing devices 5K, 5C, 5M and 5Y are attached by a revolver system, and four developing devices 5
By rotating K, 5C, 5M, and 5Y integrally by a revolver mechanism (not shown), the developing device facing the photoconductor 2 is switched, and the rotation operation causes the developing device to be selectively selected to face the photoconductor 2. The developing device develops the electrostatic latent image on the photoconductor 2 to form a toner image.

The toner image of the first color formed on the photoconductor 2 by the developing device that has been selected as an alternative is the primary transfer mechanism (not shown) in the primary transfer portion, which is a region near the photoconductor 2 and the transfer drum 6. Is transferred onto the transfer drum 6. A revolver mechanism (not shown) that integrally rotates the developing devices 5K, 5C, 5M, and 5Y completes the development of the electrostatic latent images corresponding to the image information of the first color on the photoconductor 2 when the developing devices 5K, 5C, and 5M and 5Y are integrally rotated, and a developing device that develops an electrostatic latent image corresponding to the second color image information on the photoconductor 2 is opposed to the photoconductor 2.

The toner image of the first color on the transfer drum 6 is carried to the primary transfer portion again by the rotation of the transfer drum 6. At this time, each part of this example is controlled by the controller 9 so that the toner image of the second color formed on the photoconductor 2 by the developing device reaches the primary transfer portion, and the second color on the photoconductor 2 is controlled at the primary transfer portion. Toner image is transferred onto the transfer drum 6 by a primary transfer mechanism (not shown) so as to be superimposed on the toner image of the first color.

When the revolver mechanism (not shown) completes the development of the electrostatic latent image corresponding to the image information of the second color on the photoconductor 2, the developing devices 5K, 5C, 5M and 5Y are integrally rotated to integrally rotate the photoconductor. The developing device for developing the electrostatic latent image corresponding to the image information of the third color on the second side is opposed to the photoconductor 2. Each part of this example is controlled by the controller 9 so that the toner image of the third color formed on the photoconductor 2 by the developing device reaches the primary transfer part.
The upper third-color toner image is transferred onto the transfer drum 6 by a primary transfer mechanism (not shown) so as to be superimposed on the first-color toner image and the second-color toner image.

When the revolver mechanism (not shown) finishes the development of the electrostatic latent image corresponding to the image information of the third color on the photoconductor 2, the developing devices 5K, 5C, 5M and 5Y are integrally rotated to rotate the photoconductor. The developing device that develops the electrostatic latent image corresponding to the image information of the fourth color on 2 is opposed to the photoconductor 2. Each part of this example is controlled by the controller 9 so that the toner image of the fourth color formed on the photoconductor 2 by the developing device reaches the primary transfer part, and the photoconductor 2 is transferred at the primary transfer part.
A full-color image is formed by superimposing the toner image of the fourth color on the transfer drum 6 by a primary transfer mechanism (not shown) so as to be superimposed on the toner image of the first color, the toner image of the second color, and the toner image of the third color. It

On the other hand, the transfer paper 8 is fed from a paper feeding device 10 to a registration roller (not shown), and the registration roller 8 sends the transfer paper 8 in accordance with the full-color image on the transfer drum 6. When the full-color image is formed on the transfer drum 6, the secondary transfer mechanism (not shown) that has been retracted or stopped until then operates, and the full-color image on the transfer drum 6 is transferred from the registration roller to the transfer paper 8 by the secondary transfer mechanism. Then, the secondary transfer is performed collectively. The transfer paper 8 onto which the full-color image has been transferred has the full-color image fixed by the fixing device 7, and is discharged to the outside of the device.

FIG. 3 shows the configuration of the optical writing device 1. The optical writing device 1 includes a light source 11, and the light source 11
Are sequentially modulated by a modulation unit (not shown) according to the image information of each color of black, cyan, magenta, and yellow, and are sequentially modulated by the image information of each of black, cyan, magenta, and yellow. A laser beam is emitted as the generated light beam.

The laser beam from the light source 11 is collimated by the collimator lens 15 and then deflected by the deflecting / reflecting surface thereof by the rotary polygon mirror 12 as a scanning means. The rotary polygon mirror 12 is rotationally driven by a driving unit (not shown) to repeatedly scan in the main scanning direction. The laser beam from the rotary polygon mirror 12 is narrowed down by the imaging lens 13 and imaged as a laser spot on the photoconductor 2. The rotary polygon mirror 12 is rotationally driven by a driving unit (not shown) to repeatedly scan the photoconductor 2 in the main scanning direction, and the laser spot forms an electrostatic latent image on the photoconductor 2.

Here, the light receiving element 14 as the main scanning synchronization signal generating means is arranged outside the image range within the laser beam scanning range, receives the laser beam from the rotary polygon mirror 12, detects it, and detects it. A main scanning synchronizing signal that determines the recording start position (horizontal registration) in the scanning direction is generated.

On the other hand, the recording start signal in the sub-scanning direction, which is the image formation start signal in the sub-scanning direction that determines the recording start position (vertical registration) in the sub-scanning direction, which is the image formation start position in the sub-scanning direction, is the transfer drum. 6, a light receiving means for detecting reflected light or transmitted light obtained by irradiating light on a marker provided on 6 or a marker provided on the photoconductor 2, rotation start timing of the registration roller, transfer paper 8 to the registration roller. Immediately after that, a detection signal from a paper detection sensor, a rotary encoder incorporated in the photoconductor driving means, or the like is detected and generated. There are various methods of generating the recording start signal in the sub-scanning direction, but in this example, the detection unit 61 detects the marker M provided on the transfer drum 6 to generate the recording start signal in the sub-scanning direction.

The main scanning synchronizing signal from the light receiving element 14 and the recording start signal in the sub scanning direction from the detecting means 61 are sent to the controller 9, and the controller 9 sends the main scanning synchronizing signal from the light receiving element 14 and the detecting means 61. The optical writing device 1 is instructed to perform optical writing (exposure) on the photoconductor 2 in accordance with the recording start signal in the sub-scanning direction.

FIG. 4 shows the operation timing of this example. For convenience of description, the time when the recording start signal in the sub-scanning direction from the detecting means 61 is detected by the controller 9 is set to t = 0 and the time when optical writing corresponding to the image information of each color is set to t = 0, and the light receiving element 14 performs main scanning. When the time interval for generating the synchronization signal is T, and the optical writing device 1 performs optical writing according to the image information of the first color, the controller 9 first outputs the main scanning synchronization signal from the light receiving element 14 after t = 0. At time t1, and when the optical writing device 1 performs optical writing according to the image information of the second color, the time at which the controller 9 first detects the main scanning synchronization signal from the light receiving element 14 after t = 0. T2 is the time at which the controller 9 first detects the main scanning synchronization signal from the light receiving element 14 after t = 0 when performing optical writing according to the image information of the third color in the optical writing device 1. 3, controller 9 is a time of t4 initially to detect the main scanning synchronization signal from the light receiving element 14 to t = 0 after the case of performing optical writing corresponding to the image information of the fourth color in the optical writing device 1. Here, the transmission time of each signal is ignored.

When the controller 9 detects the first main scanning synchronizing signal from the light receiving element 14 after detecting the recording start signal from the detecting means 61 in the sub-scanning direction, it instructs the optical writing device 1 to perform optical writing (exposure). To do. FIG. 6 shows the operation flow of this example. First, the controller 9 periodically checks the recording start signal in the sub-scanning direction from the detecting means 61 to determine whether or not the recording start signal in the sub-scanning direction is detected (step 1). When the recording start signal in the sub-scanning direction is detected, the time t is set to 0 (step 2). Next, the controller 9 periodically checks the main scanning synchronization signal from the light receiving element 14 to determine whether or not the main scanning synchronization signal is detected (step 3), and outputs the main scanning synchronization signal from the light receiving element 14 to the main scanning synchronization signal. If detected, the optical writing device 1 is instructed to perform optical writing (exposure) (step 4). The above operation flow is independently performed by the optical writing according to the image information of each color by the optical writing device 1.

[0018]

In the above image forming apparatus, since the main scanning synchronizing signal and the recording start signal in the sub-scanning direction are generally not synchronized, optical writing according to the image information of the first color is performed. The angle of the rotary polygon mirror 12 when the recording start signal in the sub-scanning direction from the detecting means 61 reaches the controller 9 when starting the detecting means when starting the optical writing according to the image information of the second color. It is different from the angle of the rotary polygon mirror 12 when the recording start signal from 61 in the sub-scanning direction reaches the controller 9. That is, when the optical writing corresponding to the image information of each color is started, the detection unit 6 is used.
The angles of the rotary polygon mirrors 12 when the recording start signal from 1 reaches the controller 9 do not become equal to each other.

Therefore, as shown in FIG. 4, t1, t2,
t3 and t4 do not become equal values, and t = 0 to t = T
It is the time between. Therefore, a color shift phenomenon occurs in which the toner images of the respective colors formed on the photoconductor 2 and transferred on the transfer belt 6 in a superimposed manner are displaced in the sub-scanning direction. For example, as shown in FIG. 4, the optical writing according to the image information of the first color and the optical writing according to the image information of the second color are performed as shown in FIG.
If the time difference between 1 and t2 is large, the optical writing start (exposure start) time shifts by nearly T, and as a result, the toner image of the first color and the toner image of the second color are one line as shown in the lower part of FIG. It will shift closer.

In the present specification, the "line" refers to a set of pixels having the same position in the sub-scanning direction among the pixels forming the image information, and is a line which is scanned earlier in time when an image is formed. The first line, the second line, the third line, etc., each line toward the line to be scanned later in time.
・ ・ Shall be expressed as Even in the case of using a scanning writing device that forms a plurality of lines with one scanning by a multi-beam light source, etc., as shown in FIG. 21, the first line, the second line, the third line ...・ Express.

As a technique for preventing the color shift as described above, there is a method of controlling the exposure depending on whether t1 to t4 are equal to or more than a predetermined value. In this method, for example, when the value of t1 is T / 2 or more, optical writing (exposure) is started at time t1, and when the value of t1 is less than T / 2, exposure is started at time t1 + T. . When exposure is started at time t1 + T, the optical writing device may be stopped at time t1 or the laser may not be emitted while the optical writing device is operating.

FIG. 5 shows the positional relationship of dots of each color when this conventional method is used in the situation shown in FIG. The dots indicated by the dotted line in FIG. 5 indicate the time t1 + T.
It is a dot at time t1 when the exposure is not started when the exposure is started. However, in this method, time t1 is immediately before time T / 2, and time t2
Immediately after time T / 2, it is impossible to prevent the toner image of the first color and the toner image of the second color from deviating by nearly one line.

Further, there is an image forming apparatus described in Japanese Patent Application Laid-Open No. 11-212009 as a technique combining such a system with multi-beam. However, this image forming apparatus reduces the positional deviation of the image information of the first line of each color, and does not prevent the toner image of each color from being displaced by nearly one line. The present invention is directed to a writing control method, a writing control device, and an image forming apparatus capable of preventing color misregistration of a toner image due to a lack of synchronization between a main scanning synchronization signal and an image formation start signal in the sub scanning direction. The purpose is to provide.

[0024]

In order to achieve the above object, the invention according to claim 1 is directed to an object to be scanned moving in the sub-scanning direction after an image formation start signal in the sub-scanning direction is detected. Using a scanning writing device that writes an image by performing scanning according to image information in the main scanning direction based on the detected main scanning synchronization signal, the scanning writing device uses n lines per scan according to image information. In the writing control method of the image forming method of forming a color image by superimposing a plurality of images obtained by performing scanning of (n> 0), the time interval at which the main scanning synchronization signal is generated is T, and the scanning writing device is At time t1, the time elapsed from the detection of the image formation start signal to the detection of the main scanning synchronization signal when the writing of the predetermined reference image is started is When the time that elapses from the detection of the image formation start signal to the detection of the main scanning synchronization signal when starting the writing of an image other than the image to be written is t2, and when t1 <t2, the scanning is performed. When the writing device starts writing an image to be written other than the reference image, i is set to | t1 + T ×
When (i / n) -t2 | is set to the minimum integer, the scanning / writing device is caused to start scanning according to the image information from the (i + 1) th line.

According to the second aspect of the present invention, the main scanning direction is detected based on the main scanning synchronizing signal detected after the image forming start signal in the sub scanning direction is detected for the scanned object moving in the sub scanning direction. A scanning writing device for writing an image by performing scanning according to image information, and the scanning writing device obtained by scanning n lines (n> 0) per scan according to the image information. In a writing control device of an image forming apparatus that forms a color image by superimposing a plurality of images,
The time interval at which the main scanning synchronization signal is generated is T, and the time that elapses from the detection of the image formation start signal to the detection of the main scanning synchronization signal when the writing of a predetermined reference image is started by the scanning writing device. Is t1, and the time that elapses from the detection of the image formation start signal to the detection of the main scanning synchronization signal when the writing of an image to be written other than the reference image is started by the scanning writing device is set to t2. When t1 <t2, when starting writing of an image to be written other than the reference image by the scanning writing device, i is set to | t1 +
When T × (i / n) −t2 | is set to the minimum integer, the scanning / writing device is caused to start scanning in accordance with image information from the (i + 1) th line.

According to a third aspect of the present invention, in the writing control apparatus according to the second aspect, when t1> t2, the scanning writing apparatus starts writing an image to be written other than the reference image. , M is | t1 + T ×
When (m / n) -t2 | is set to the minimum integer, the scanning / writing device delays image information by -m lines to start scanning.

The invention according to claim 4 is the invention according to claim 2 or 3.
In the writing control device described above, when starting writing of the reference image in the scanning writing device, j is set to | t
When 1-T × (j / n) | When starting the writing of the image which is the writing target of | t1-T × (j / n) + T ×
When (k / n) -t2 | is set to the minimum integer, the scanning / writing device is caused to start scanning according to image information from the (k + 1) th line.

According to a fifth aspect of the present invention, the main scanning direction is detected based on the main scanning synchronizing signal detected after the image forming start signal in the sub scanning direction is detected for the object to be scanned moving in the sub scanning direction. Equipped with a scanning writing device to write images to
In the writing control device of the image forming apparatus, which forms a color image by superposing images of a plurality of colors obtained by the scanning and writing device performing a plurality of times of scanning in accordance with image information of a plurality of colors, the main scanning synchronization The time interval at which a signal is generated is T, and the time that elapses from the detection of the image formation start signal to the first detection of the main scanning synchronization signal when the scanning writing device writes an image of a predetermined reference color. t1, when the time elapsed from the detection of the image formation start signal to the first detection of the main scanning synchronization signal when writing an image of a color other than the reference color by the scanning writing device is t2, The writing of the image of the reference color according to the image information of the reference color by the scanning writing device is t1 after the image formation start signal in the sub-scanning direction is detected. When the main scanning synchronization signal is detected when the time elapses, the writing of an image of a color other than the reference color by the scanning writing device is started when t1 is smaller than a predetermined time and | t1-t2 | When the time is less than the time t,
When 2 has elapsed, it is performed according to the image information from the first line, and when t1 is smaller than the predetermined time, | t1-t2 |
Is greater than or equal to the predetermined time, when t2 has elapsed from the detection of the image formation start signal, the process is performed according to the image information from the second line, and when t1 is greater than or equal to the predetermined time, | t
When 1−t2 | is less than the predetermined time, the process is performed according to the image information from the first line when t2 has elapsed from the detection of the image formation start signal, and when t1 is the predetermined time or more, | t1 When -t2 | is equal to or longer than the predetermined time, it is performed according to the image information from the first line when t2 + T has elapsed from the detection of the image formation start signal.

According to a sixth aspect of the present invention, the main scanning direction is detected on the basis of the main scanning synchronizing signal detected after the image forming start signal in the sub scanning direction is detected with respect to the scanned object moving in the sub scanning direction. Equipped with a scanning writing device to write images to
In the writing control device of the image forming apparatus, which forms a color image by superposing images of a plurality of colors obtained by the scanning and writing device performing a plurality of times of scanning in accordance with image information of a plurality of colors, the main scanning synchronization The time interval at which a signal is generated is T, and the time that elapses from the detection of the image formation start signal to the first detection of the main scanning synchronization signal when the scanning writing device writes an image of a predetermined reference color. t1, when the time elapsed from the detection of the image formation start signal to the first detection of the main scanning synchronization signal when writing an image of a color other than the reference color by the scanning writing device is t2, The writing of the image of the reference color according to the image information of the reference color by the scanning writing device is performed in the sub-scanning direction when t1 is less than a predetermined time. t after the image formation start signal is detected
When the main scanning synchronization signal is detected when 1 has elapsed, the main scanning synchronizing signal is detected, and the image forming start signal in the sub scanning direction is detected when t1 is equal to or longer than a predetermined time. When the main scanning synchronization signal is detected when t1 has elapsed after the writing, the writing is performed according to the image information from the second line, and the writing of the image of the color other than the reference color by the scanning writing device is performed by t1. When | t1−t2 | is shorter than the predetermined time and less than the predetermined time, t2 is detected from the detection of the image formation start signal.
Is performed according to the image information from the first line, and t1 is smaller than the predetermined time and | t1-t2 |
Is greater than or equal to the predetermined time, when t2 has elapsed from the detection of the image formation start signal, the process is performed according to the image information from the second line, and when t1 is greater than or equal to the predetermined time, | t
When 1-t2 | is less than the predetermined time, the process is performed according to the image information from the second line when t2 has elapsed from the detection of the image formation start signal, and when t1 is the predetermined time or more, | t1 When -t2 | is equal to or longer than the predetermined time, it is performed according to the image information from the first line when t2 has elapsed from the detection of the image formation start signal.

The invention according to claim 7 is the invention according to claim 5 or 6.
In the writing control device described above, t1 is an average value of the time from the detection of the image formation start signal to the writing time of the first line of the image already written.

According to an eighth aspect of the present invention, in the writing control apparatus according to any one of the second to seventh aspects, the scanning writing device starts scanning the earliest as the reference image or the image of the reference color. It uses images.

According to a ninth aspect of the present invention, in the writing control device according to any one of the second to seventh aspects, the scanning writing device has already started scanning as the reference image or the image of the reference color. A virtual image obtained by averaging the positions of the image in the sub-scanning direction is used.

According to a tenth aspect of the present invention, in the writing control apparatus according to any one of the second to seventh aspects, a writing target other than the reference image or the reference color image written by the scanning writing apparatus is written. When the image is a chromatic image, the other chromatic image is preferentially selected as the reference image or the image of the reference color.

The invention according to claim 11 is the write control device according to any one of claims 2 to 7, wherein a write target other than the reference image or the image of the reference color is written by the scanning writing device. The image having a high correlation with the image is selected as the reference image.

According to a twelfth aspect of the present invention, in the write control device according to any one of the fifth to seventh aspects, the predetermined time is T / 2.

The invention according to claim 13 is the invention according to claims 2 to 12.
1 is provided with the write control device.

According to a fourteenth aspect of the present invention, in the image forming apparatus having the write control apparatus according to the eighth aspect, means for converting image information in the first color space into information in the second color space, And a means for determining the strength of correlation of each color image in the second color space according to the amount of information of each color image in one color space, and the color image from the information in the second color space. Is formed.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION In the first embodiment of the present invention, in the above-described image forming apparatus shown in FIG. 2, a controller 9 performs a writing control (exposure control) as shown in FIG. 1 (exposure control section). ) 91 and a recording device (for example, a storage device) 92. The exposure controller 91 and the recording device 92 constitute a writing control device that controls the optical writing operation of the above-described optical writing device 1 shown in FIG.

The exposure controller 91 is connected to the recording device 92, and records data in the recording device 92 or acquires data from the recording device 92 as required. The exposure control unit 91 has a main scanning synchronization signal (main scanning synchronization signal from the light receiving element 14) used when starting optical writing of each color and a recording start signal (sub scanning direction) used when starting optical writing of each color ( A recording start signal in the sub-scanning direction) from the detection means 61 is input, and the exposure control section 91 sends an optical writing (exposure) start signal to the optical writing device 1 in accordance with the main scanning synchronization signal and the recording start signal in the sub-scanning direction. send.

FIG. 7 shows a processing flow performed by the exposure control unit 91 of the first embodiment. FIG. 7A is a flow relating to the exposure control according to the image information of the first color.
(B) is a flow relating to exposure control according to image information for the second and subsequent colors. Since the exposure control according to the image information of the second color, the third color, and the fourth color is the same, t2, t3, and t4 are represented by t2 in the description of FIG. 7B.

When controlling the exposure according to the image information of the first color, as shown in FIG. 7A, the exposure controller 91
Periodically checks the recording start signal in the sub-scanning direction from the detecting means 61 to determine whether or not the recording start signal in the sub-scanning direction is detected (step 1). If detected, the time t is set to t = 0 (step 2). Next, the exposure control unit 91 periodically checks the main scanning synchronization signal from the light receiving element 14 to determine whether the main scanning synchronization signal is detected (step 3), and if the main scanning synchronization signal is detected, , Time t when the main scanning synchronization signal is detected
1 is recorded on the recording device 92 (step 4), and the optical writing device 1 is caused to start exposure (step 5).

On the other hand, when controlling the exposure according to the image information of the second and subsequent colors, as shown in FIG. 7B, the exposure control section 91 responds to the image information of the first color from the storage device 92. The time t1 which is the main scanning synchronization signal detection time when starting the exposure is acquired (step 1), and the recording start signal in the sub scanning direction from the detecting means 61 is periodically checked to check the recording start signal in the sub scanning direction. Is detected (step 2), and if the recording start signal in the sub-scanning direction is detected, the time is t
= 0 is set (step 3). Next, the exposure controller 9
No. 1 periodically checks the main scanning synchronization signal from the light receiving element 14 to determine whether or not the main scanning synchronization signal is detected (step 4). If the main scanning synchronization signal is detected, t1 is predetermined. It is judged whether or not the time is smaller than T / 2, for example (step 5).

If t1 <T / 2, the exposure control unit 91 uses the times t1 and t2 at which the main scanning synchronization signal is detected to determine whether | t1-t2 | is smaller than a predetermined time, for example, T / 2. It is determined whether or not (step 6). Exposure control unit 91
If | t1−t2 | is smaller than T / 2 in the determination in step 6, the optical writing device 1 starts exposure according to the image information from the image information of the first line at t = t2 (step 8). ), | T1-t2 | is larger than T / 2, at t = t2, the optical writing device 1 is caused to start exposure according to the image information from the image information of the second line (step 7). That is, in step 7, 1
Image formation by exposure according to the image information of the line is not performed. In the image forming apparatus of the first embodiment, it is assumed that the image information sent from the scanner or the computer is stored in the image information storage means (not shown) in the controller 9 in the form of a bit map. The exposure control unit 91 controls whether to start the exposure from the image information or to start the exposure from the image information of the second line.
It is controlled by the image information read start address of the image information storage means when sending to.

On the other hand, if t1 ≧ T / 2, the exposure control section 91 determines whether or not | t1-t2 | is smaller than a predetermined time, for example, T / 2 (step 9). The exposure control unit 91 determines that | t1−t2 | is T / 2 in the determination of step 9.
If it is smaller than t2, at t = t2, the optical writing device 1 is caused to start the exposure according to the image information from the image information of the first line (step 11), and if | t1-t2 | At t = t2 + T, the optical writing device 1 is caused to start exposure according to the image information from the image information of the first line (step 10). In the case of step 10, the optical writing device 1 delays the image information by one line and performs scanning. As can be seen from the above description, in steps 10 and 11, dots formed by exposure according to image information of the first color are formed at positions closer to the dots by exposure according to image information of two or more colors. Such an exposure start time is selected.

FIG. 8 shows dot positions formed by the first embodiment for the situation shown in FIG. In the situation shown in FIG. 8, t1 is smaller than T / 2 in the exposure of the first color and | t1-t in the exposure of the second color and the exposure of the third color.
2 | is T / 2 or more, and | t1 in the exposure of the fourth color
-T2 | is smaller than T / 2. Therefore, step 6,
By performing steps 7 and 8, the exposure of the second color and the exposure of the third color are started from the image information of the second line, and the exposure of the first color and the exposure of the fourth color are started from the image information of the first line. By performing the exposure control in this way, t1 becomes T /
When it is smaller than 2, the positional deviation of the image information of the second and subsequent lines of the second color, the third color, and the fourth color can be suppressed to half or less of the dot pitch for the image information of the first color.

In the first embodiment, step 5,
Even if t1 is T / 2 or more by providing 9, 10, and 11, the positional deviation of the image information of the second and subsequent lines of the second color, the third color, and the fourth color can be adjusted to the dot pitch relative to the image information of the first color. I try to keep it below half. This allows
In all situations, the positional deviation of the image information of the second and subsequent lines of the second color, the third color, and the fourth color can be suppressed to half the dot pitch or less with respect to the image information of the first color.

FIG. 9 shows step 9 in the first embodiment.
The execution results of 10 and 11 are shown. In the situation shown in FIG. 9, t
1 is T / 2 or more, | t1-t2 | is T / 2 or more in the exposure of the second and fourth colors, and | t1-t2 | is smaller than T / 2 in the exposure of the third color. Therefore, by performing Steps 9, 10, and 11, the exposure of the second color and the fourth color starts at the times t2 + T and t4 + T, and the exposure of the third color starts at the time t3. That is, in the exposure of the second and fourth colors, the image information is delayed by one line and scanning is performed. By performing the exposure control in this way, when t1 is T / 2 or more, the positional deviation of the image information of the second color, the third color, and the fourth color is reduced to half the dot pitch of the image information of the first color or less. Can be suppressed.

As described above, according to the first embodiment, the positional deviation of the image information of the other colors with respect to the image information of the first color or the second color, which is the reference color, can be suppressed to half the dot pitch or less. It is possible to prevent the color shift of the toner image due to the lack of synchronization between the scanning synchronization signal and the image formation start signal in the sub-scanning direction. In addition, step 5,
The predetermined time to be compared with t1 and | t1-t2 | in 6 and 9 is T / 2, but a similar effect can be obtained with a value around T / 2. Also, at steps 5, 6, and 9, t1, | t
The predetermined time to be compared with 1-t2 |
Even with a smaller value, it is possible to reduce the positional deviation of the image information of other colors with respect to the image information of the reference color.

Next, a second embodiment of the present invention will be described. The image forming apparatus according to the second embodiment is similar to the first embodiment.
In, the process of the exposure control unit 91 is performed as follows. FIG. 10 shows a processing flow performed by the exposure control unit 91 of the second embodiment. FIG. 10A is a flow relating to optical writing (exposure) control according to the image information of the first color,
FIG. 10B is a flow relating to optical writing (exposure) control according to the image information of the second and subsequent colors. Since the exposure control according to the image information of the second color, the third color, and the fourth color is the same, t2, t3, and t4 are represented as t2 in the description of FIG.

When performing the exposure control according to the image information of the first color, as shown in FIG. 10A, the exposure control section 91.
Periodically checks the recording start signal in the sub-scanning direction from the detecting means 61 to determine whether or not the recording start signal in the sub-scanning direction is detected (step 1). If detected, the time t is set to t = 0 (step 2). Next, the exposure control unit 91 periodically checks the main scanning synchronization signal from the light receiving element 14 to determine whether the main scanning synchronization signal is detected (step 3), and if the main scanning synchronization signal is detected, , Time t when the main scanning synchronization signal is detected
1 is stored in the recording device 92 (step 4).

Next, the exposure controller 91 determines that t1 is T / 2.
Is smaller than (step 5), t1 is T
If it is smaller than / 2, the optical writing device 1 is caused to start exposure according to the image information from the image information of the first line at time t1 (step 6). In addition, the exposure control unit 91
If t1 is T / 2 or more, at the time t1, the optical writing device 1 starts the exposure according to the image information from the image information of the second line (step 7). That is, in step 7, image formation is not performed by exposure according to the first line of the image information.

On the other hand, when performing the exposure control according to the image information of the second and subsequent colors, the exposure controller 91 responds to the image information of the first color from the storage device 92 as shown in FIG. 10B. T1 which is the main scanning synchronization signal detection time when the exposure is performed
(Step 1), the recording start signal in the sub-scanning direction from the detection means 61 is periodically checked to determine whether the recording start signal in the sub-scanning direction is detected (step 2), and the sub-scanning is performed. If the recording start signal in the direction is detected, the time is set to t
= 0 is set (step 3). Next, the exposure controller 9
1 periodically checks the main scanning synchronization signal from the light receiving element 14 to determine whether the main scanning synchronization signal is detected (step 4). If the main scanning synchronization signal is detected, t1 is a predetermined time. , For example, it is determined whether it is smaller than T / 2 (step 5).

If t1 <T / 2, the exposure control unit 91 uses the times t1 and t2 when the main scanning synchronization signal is detected to determine whether | t1-t2 | is smaller than a predetermined time, for example, T / 2. It is determined whether or not (step 6). Exposure control unit 91
If | t1−t2 | is smaller than T / 2 in the determination in step 6, the optical writing device 1 starts exposure according to the image information from the image information of the first line at t = t2 (step 8). ), | T1-t2 | is larger than T / 2, at t = t2, the optical writing device 1 is caused to start exposure according to the image information from the image information of the second line (step 7). That is, in step 7, image formation is not performed by exposure according to the first line of the image information.

If t1 ≧ T / 2, the exposure control section 91 determines whether or not | t1-t2 | is smaller than T / 2 (step 9). If | t1−t2 | is smaller than T / 2 in the determination of step 9, the exposure control unit 91 starts the exposure of the optical writing device 1 from the image information of the second line at t = t2 according to the image information. (Step 11), if | t1-t2 | is T / 2 or more, t = t
2, the optical writing device 1 from the image information of the first line
To start exposure according to the image information (step 1
0). That is, in steps 10 and 11, the first color 2
Depending on whether or not the dots of the second color and thereafter are formed in the positions close to the dots of the line, whether to start the image formation of the second color and thereafter from the first line or the second line is selected. .

FIG. 11 shows an example of dot positions formed according to the second embodiment. In FIG. 11, t1 is T / 2 or more in the exposure according to the image information of the first color, and | t1-t in the exposure according to the image information of the second and fourth colors.
2 | is T / 2 or more, and | t1-t2 | is smaller than T / 2 in the exposure according to the image information of the third color. Therefore, by carrying out steps 5, 6, and 7 in FIG.
The exposure according to the image information of the color is performed from the second line. By performing steps 9, 10, and 11 in FIG. 10B, the exposure according to the image information of the second and fourth colors starts from the image information of the first line, and the exposure according to the image information of the third color. Starts from the image information of the second line.
By performing the exposure control in this way, when t1 is T / 2 or more, the positional deviation of the image information of the second and subsequent lines of the second color, the third color, and the fourth color is changed to the dot information with respect to the image information of the first color. It can be reduced to less than half the pitch.

In the second embodiment, further, FIG.
By providing the steps 6, 7, and 8 of (1), even in a situation where t1 is smaller than T / 2, the positional deviation is suppressed to half the dot pitch or less. This makes it possible to suppress the positional deviation of the image information to less than half the dot pitch in all situations. In the second embodiment, for the situation shown in FIG. 11, the “second color” is the color for which image formation is performed first, the “first color” is the color for which image formation is second, and t1
Let t be the timing at which the main scanning synchronization signal arrives when performing exposure according to the second color image information, and t2 be the timing at which the main scanning synchronization signal arrives when performing exposure according to the first color image information. The lower part of 11 is the execution result of steps 6, 7, and 8.

As shown in FIG. 11, when the image formation is performed in the order of the second color → the first color → the third color → the fourth color, t
2 is smaller than T / 2, and | t1-t2 | is T / 2 or more in the exposure according to the image information of the first and third colors, and | t1-t in the exposure according to the image information of the fourth color.
2 | is smaller than T / 2. Therefore, steps 6, 7,
By carrying out step 8, the exposure corresponding to the image information is started from the second line at the times t1 and t3 in the exposure according to the image information of the first color and the third color, and the exposure is performed at the time t4 in the exposure according to the image information of the fourth color. The exposure according to the image information is started from the first line. By performing exposure control in this way, t
When 2 is smaller than T / 2, the first color, the third color,
The positional deviation of the image information of the fourth color can be suppressed to half or less of the dot pitch of the image information of the second color.

As described above, according to the second embodiment, the positional deviation of the image information of the other colors with respect to the image information of the first color or the second color, which is the reference color, can be suppressed to half or less of the dot pitch. It is possible to prevent the color shift of the toner image due to the lack of synchronization between the scanning synchronization signal and the image formation start signal in the sub-scanning direction. In addition, step 5,
The predetermined time to be compared with t1 and | t1-t2 | in 6 and 9 is T / 2, but a similar effect can be obtained with a value around T / 2. Also, at steps 5, 6, and 9, t1, | t
The predetermined time to be compared with 1-t2 |
Even with a smaller value, it is possible to reduce the positional deviation of the image information of the other colors with respect to the image information of the first color or the second color that is the reference color.

Next, a third embodiment of the present invention will be described. In the image forming apparatus according to the third exemplary embodiment, the image forming apparatus according to the first exemplary embodiment is used.
Is different from the optical writing (exposure) control according to the image information of the second color of the exposure control unit 91 as described below. FIG. 12 shows a flow of optical writing (exposure) control according to the image information of the second and subsequent colors in the third embodiment. The flow shown in FIG. 12 is almost the same as the flow shown in FIG. 7B, but only steps 1, 12, and 13 are different from the flow shown in FIG. 7B. In the third embodiment, the exposure control according to the image information of the second, third, and fourth colors is the same, and t2, t3, and t4 are represented by t2.

The exposure controller 91, as shown in FIG.
In step 1, ta1 is acquired from the recording device 92 instead of t1. ta1 is an average value of the exposure times according to the image information of the first line of the color for which the image formation has already been performed, and t1 when the image currently being formed is the second color image
1. If the image currently being formed is the image of the third color, the average value of t1 and t2, and the image currently being formed is 4
In the case of a color image, the average value of t1, t2, and t3 is obtained.

In other words, in the third embodiment, the exposure control section 91 uses the exposure time corresponding to the image information of the first line in the already image-formed (exposed) color as the reference and the second and subsequent colors. The exposure start control is performed according to the image information. Therefore, in the third embodiment, the positional deviation of the dots of the third and subsequent colors can be made smaller than that in the first embodiment in which t1 is used as a reference. Here, the average value ta1 is substantially used for the exposure according to the image information of the third color and thereafter, but in the third embodiment, the image information of the second color is used for the commonization of the circuit for obtaining the average value ta1. For the corresponding exposure, the average value ta1 is obtained using the same circuit as the exposure for the image information of the third and subsequent colors.

The exposure control unit 91 uses steps 7, 8, 1
From 0 and 11 to step 12, in step 12, ta1 is set using the exposure start time corresponding to the new image information of the first line determined in steps 7, 8, 10 and 11.
To recalculate. It is assumed that the exposure control unit 91 virtually performs exposure according to the image information of the first line even when a color is not actually exposed according to the image information of the first line when ta1 is calculated. Get the exposure start time. Therefore, ta1 can take a negative value. Next, the exposure controller 9
In step 13, 1 stores the newly calculated ta1 in the storage device 92.

FIG. 13 shows an example of dot positions formed according to the third embodiment. In this example, ta1 is smaller than T / 2, | t1-t4 | is smaller than T / 2, and | ta when forming an image in which exposure is performed according to the image information of the fourth color.
1-t4 | is larger than T / 2. In the first embodiment,
When the image is formed by performing the exposure according to the image information of the fourth color, the exposure at time t4 is the image information of the first line because | t1-t4 | is smaller than T / 2. But,
Actually, t4 is the average time of the exposure start times according to the image information of the second line, ta1 + T, rather than the average time ta1 of the exposure start times according to the image information of the first line.
When the exposure corresponding to the image information is started from the second line, the positional deviation of the image information is smaller. In the third embodiment, since | ta1−t4 | is larger than T / 2, step 7 is executed and the exposure is started from the second line. That is, the image information is delayed by one line. Therefore, the image of the fourth color has less deviation from the average position of the images of the first, second, and third colors, and the color misregistration is reduced. As described above, according to the third embodiment, it is possible to prevent the color shift of the toner image due to the lack of synchronization between the main scanning synchronization signal and the image forming start signal in the sub scanning direction. Also,
By using, as the reference image, a virtual image obtained by averaging the positions in the sub-scanning direction of the image that has already started scanning by the optical writing device, it is possible to further reduce the positional deviation of the images that start scanning after the third scanning. .

Next, a fourth embodiment of the present invention will be described. The image forming apparatus of the fourth embodiment differs from the second embodiment only in the exposure control according to the image information of the second and subsequent colors performed by the exposure controller 91. Specifically, in the fourth embodiment, in the flow shown in FIG. 10B, the exposure control unit 91 sets t1 in step 1 to ta1 as in step 1 shown in FIG. 12, and immediately before END in FIG. Two steps similar to steps 12 and 13 shown in are added and the two steps are executed after steps 7, 8, 10 and 11.

As a result, in the fourth embodiment, the exposure control section 91 sets the exposure start time according to the image information of the first line of the color for which the image has already been formed as an average to 2 times.
The exposure start control is performed according to the image information after the color. Therefore, in the fourth embodiment, it is possible to further reduce the positional deviation of the dots formed by the exposure according to the image information of the third and subsequent colors, as compared with the first embodiment in which t1 is used as a reference. As described above, according to the fourth embodiment, it is possible to prevent the color shift of the toner image due to the lack of synchronization between the main scanning synchronization signal and the image forming start signal in the sub scanning direction.

Next, a fifth embodiment of the present invention will be described. In the image forming apparatus according to the fifth embodiment, a multi-beam light source is used as the light source 11 of the optical writing device 1 in the first embodiment, and n light sources (n> 0) are used from this one light source.
The light beam of is output. For convenience of explanation, in the following, n light beams forming a multi-beam are first and second beams in the sub-scanning direction in order from a light beam which scans corresponding to image information having a small number of lines. Expressed as eyes.

In the optical writing device 1, the light source is modulated in accordance with the image information by the modulation means (not shown) and emits n laser beams which are sequentially and repeatedly modulated with the image information of the same color. The operation is sequentially performed by the image information of each color of black color, cyan color, magenta color, and yellow color, so that black color, cyan color,
Emitting n laser beams sequentially modulated by the image information of each color of magenta and yellow. The n laser beams from the light source are collimated by the collimator lens 15 as shown in FIG. 3, and then are deflected by the deflecting / reflecting surface by the rotary polygon mirror 12 as the scanning means. The rotary polygon mirror 12 is rotationally driven by a driving unit (not shown) to repeatedly scan in the main scanning direction. The laser beam from the rotary polygon mirror 12 is formed by the imaging lens 1
It is narrowed down by 3 and is imaged as a laser spot on the photoconductor 2 at regular intervals in the sub-scanning direction. The rotary polygon mirror 12 is rotationally driven by a driving unit (not shown) so that the laser spot repeatedly scans the photoconductor 2 in the main scanning direction to form an electrostatic latent image on the photoconductor 2.

FIG. 17 shows a control flow of the exposure control section 91 in the fifth embodiment. The flow regarding the optical writing (exposure) control according to the image information of the first color is the same as the flow shown in FIG. The optical writing (exposure) control according to the image information is performed as in the first embodiment.

FIG. 17 shows an optical writing (exposure) control flow according to the image information of the second and subsequent colors. Second color, third color,
Since the optical writing (exposure) control according to the image information of the fourth color is the same, in the description of FIG. 17 and FIG.
2, t3 and t4 are represented as t2.

When performing the exposure control for the second and subsequent colors, the exposure control section 91 performs the optical writing (exposure) control flow shown in FIG. 17 according to the image information for the second and subsequent colors for each laser beam. First, the exposure control unit 91 acquires from the storage device 92 the main scanning synchronization signal detection time t1 when the exposure according to the image information of the first color is started (step 1), and periodically from the detection means 61. The recording start signal in the sub-scanning direction is checked to determine whether the recording start signal in the sub-scanning direction has been detected (step 2). If the recording start signal in the sub-scanning direction is detected, the time is set to t = 0. Set (step 3).

Next, the exposure control section 91 periodically checks the main scanning synchronization signal from the light receiving element 14 to determine whether or not the main scanning synchronization signal is detected (step 4). If the exposure control unit 91 detects the main scanning synchronization signal, | t1
Recursive calculation is performed to obtain i such that + T × (i / n) −t2 | becomes the smallest, and such i is acquired (step 5). In the recursive calculation, i is -n + 1 or more and n-
Do this for integers less than or equal to 1.

Next, the exposure control unit 91 determines whether i is larger than 0 (step 6). If i> 0, the exposure start time according to the second color image information is behind the exposure start time according to the first color image information.
The image information for the second color should be written from a line that overlaps the image information for the first color with the least amount of positional deviation.
Therefore, if i> 0, the exposure controller 91 causes the optical writing device 1 to start exposure according to the image information from the image information of the (i + 1) th line at time t2 (step 7). In the multi-beam light source, in order to emit the laser beam modulated by the image information from the image information of the (i + 1) th line to perform the exposure, the line and the light source may be appropriately associated with each other. When i = 0, the image information of the first line is written in the first beam, but when i = 1, the image information of the second line is written in the first beam.

On the other hand, if i ≦ 0, the exposure start time corresponding to the image information of the first color is delayed or substantially the same as the exposure start time corresponding to the image information of the second color, so that the image information of the second color is obtained. Should be delayed as necessary to start the exposure according to the second color image information at the time when the positional deviation is the smallest. Therefore, the exposure controller 91
If ≦ 0, the optical writing device 1 is caused to start exposure according to the image information from the image information of the first line at time t2-T × (i / n) (step 8). In the case of step 8, the optical writing device 1 delays the image information by i lines and performs scanning.

FIG. 18 shows an example of dot positions formed according to the fifth embodiment. In FIG. 18, the case of n = 4 is shown, and the writing dot position is represented by a signal of four beams, that is, a signal shown by a solid line and a signal shown by three dotted lines following it. In the exposure of the second and third colors starting at t2 and t3 which are later than t1, the execution of step 7 causes t2 and t
The writing dots in No. 3 are in the fourth line (i =
3) It is a writing dot of the third line (i = 2) (the number of lines is shown in the dot of FIG. 18).

On the other hand, in the exposure of the fourth color which starts at t4 which is earlier than t1, the exposure is started from the second beam of the four beams by the execution of step 8 (i = -1 and the image information is delayed by one line. Made). In the fifth embodiment, by such processing of the exposure control unit 91, the positional deviation of the image information of the second color, the third color, and the fourth color can be suppressed to half or less of the dot pitch with respect to the image information of the first color. .

Since the exposure control section 91 starts image recording by exposure from a predetermined line as described above, the image formation start line is selected by address selection of the bitmap image stored in the image forming apparatus. In addition, an appropriate beam is selected from the n beams forming the multi-beam as a substantial exposure start beam. Further, when determining the dot formation positions for the third and subsequent colors, t1 is set in the fifth embodiment.
However, as described in the third embodiment, the average time t of the first lines in the colors formed so far is
It may be based on a1.

As described above, according to the fifth embodiment, there is a lapse of time from the detection of the image forming start signal in the sub-scanning direction to the detection of the main-scanning synchronization signal when writing the image of the first color as the predetermined reference image. Even when the time elapsed from the detection of the image forming start signal in the sub-scanning direction to the detection of the main scanning synchronization signal when writing an image other than the reference image is longer than the time, The positional deviation with respect to the reference image can be suppressed to half the dot diameter or less, and the color deviation of the toner image due to the lack of synchronization between the main scanning synchronization signal and the image forming start signal in the sub scanning direction is prevented. be able to.

Further, in the case of writing the image of the first color as the predetermined reference image, the time other than the reference image is more than the time elapsed from the detection of the image forming start signal in the sub-scanning direction to the detection of the main scanning synchronization signal. Even when the time that elapses from the detection of the image formation start signal in the sub-scanning direction to the detection of the main scanning synchronization signal when writing an image is short, the misalignment of the images other than the reference image with respect to the reference image is dot It is possible to suppress the diameter to half or less, and it is possible to prevent the color shift of the toner image due to the lack of synchronization between the main scanning synchronization signal and the image forming start signal in the sub scanning direction.

Next, a sixth embodiment of the present invention will be described. In the sixth embodiment, an optical writing device having the same multi-beam light source as in the fifth embodiment is used as the optical writing device 1 in the second embodiment, and one light source outputs n beams.

FIG. 19 shows a control flow of the exposure controller 91 in the sixth embodiment. FIG. 19A is a flow relating to control of optical writing (exposure) according to image information of the first color, and FIG. 19B is a flow relating to control of optical writing (exposure) according to image information of the second and subsequent colors. Is. Since the control of the optical writing (exposure) according to the image information of the second color, the third color, and the fourth color is the same, t2, t3, and t4 are represented as t2 in the description of FIG. 19B.

When the exposure control section 91 controls the optical writing (exposure) according to the image information of the first color, the exposure control section 91 shown in FIG.
As shown in (a), the recording start signal in the sub-scanning direction from the detecting means 61 is periodically checked to determine whether the recording start signal in the sub-scanning direction is detected (step 1), and the sub-scanning is performed. When the recording start signal of the direction is detected, the time t is set to t = 0 (step 2).

Next, the exposure control section 91 periodically checks the main scanning synchronization signal from the light receiving element 14 to determine whether or not the main scanning synchronization signal is detected (step 3), and outputs the main scanning synchronization signal. If detected, the time t1 at which the main scanning synchronization signal is detected is stored in the recording device 92 (step 4). Next, the exposure control unit 91 calculates j such that | t1−T × (j / n) | is minimized by recursive calculation in the range of j = 0 to n−1 (step 5), and this calculation is performed. Using j obtained in step 1, the optical writing device 1 is caused to start exposure according to the image information from the image information of the (j + 1) th line at time t1 (step 6).

When the exposure control unit 91 controls the exposure according to the image information of the second and subsequent colors, as shown in FIG. 19B, the exposure control unit 91 outputs the exposure according to the image information of the first color from the storage device 92. The time t1 which is the main scanning synchronization signal detection time at time is acquired (step 1), and then | t1−T × (j / n) |
Is calculated by recursive calculation in the range of j = 0 to n-1 (step 2). After that, the exposure control section 91 periodically checks the recording start signal in the sub-scanning direction from the detecting means 61 and determines whether or not the recording start signal in the sub-scanning direction is detected (step 3), and the sub-scanning is performed. When the recording start signal of the direction is detected, the time is set to t = 0 (step 4). Next, the exposure control unit 91 periodically checks the main scanning synchronization signal from the light receiving element 14 and determines whether or not the main scanning synchronization signal is detected (step 5).

When the exposure control section 91 detects the main scanning synchronization signal, | t1-T * (j / n) + T * (i / n) -t.
Recursive calculation is performed to obtain i such that 2 | becomes the smallest, and such i is acquired (step 6). The recursive calculation is performed for an integer in which i is −n + 1 or more and n−1 or less.

Next, the exposure control unit 91 determines whether i is larger than 0 (step 6). If i> 0, time t1−T × (starting formation of dots (which may be virtual dots that are not actually formed) corresponding to the first line by exposure according to the image information of the first color j
/ N), the exposure start time corresponding to the image information of the second color is delayed, so that the image of the second color should be formed from a line that overlaps the image of the first color with the least displacement. . Therefore, if i> 0, the exposure controller 91 causes the optical writing device 1 to start exposure according to the image information from the image information of the (i + 1) th line at time t2 (step 8). In the multi-beam light source, in order to emit the laser beam modulated by the image information from the image information of the (i + 1) th line to perform the exposure, the line and the light source may be appropriately made to correspond to each other. For example, when i = 0 Is 1
Image information of the first line can be written by the beam eye, but i
When = 1, the image information of the second line is written by the first beam.

On the other hand, if i ≦ 0, the image of the second color is obtained with respect to time t1-T × (j / n) when dots corresponding to the first line are formed by exposure according to the image information of the first color. Since the exposure start time according to the information is early or almost the same, the exposure according to the image information of the second color is delayed as necessary so that the exposure according to the image information of the second color is performed at the time when the positional deviation is the smallest. Should start. Therefore, the exposure control unit 91 causes the optical writing device 1 to start exposure according to the image information from the image information of the first line at time t2-T × (i / n) (step 9). In the case of this step 9, the optical writing device 1 performs exposure by delaying the image information by i lines.

FIG. 20 shows an example of dot positions formed in the sixth embodiment. In this example, n = 4, and the writing dot position is represented by a signal for four beams, that is, a signal indicated by a solid line and a signal indicated by three dotted lines subsequent thereto. By executing step 6 in FIG. 19A, the dots of the first color are formed from the second beam (j = 1). In the exposure of the second color and the third color started at t2 and t3 which are later than t1, the execution of step 8 in FIG.
The dots at 2 and t3 are on the 5th line (i =
4) The fourth line (i = 3) is set (the number of lines is shown in the dots in FIG. 20).

On the other hand, the exposure of the fourth color, which is started at t4 earlier than t1, is started from the first line (i = 0) of the fourth beam by performing step 9 in FIG. 19 (b). In the sixth embodiment, by such processing of the exposure control unit 91, the positional deviation of the image information of the second color, the third color, and the fourth color can be suppressed to half or less of the dot pitch with respect to the image information of the first color. The image forming position in the sub scanning direction can be stabilized.

Since the exposure controller 91 starts image recording by exposure from a predetermined line as described above, the image forming start line is selected by address selection of the bitmap image stored in the image forming apparatus. In addition, an appropriate beam is selected from the n beams forming the multi-beam as a substantial exposure start beam. Further, when determining the dot formation positions for the third and subsequent colors, t1 is set in the sixth embodiment.
However, as described in the fourth embodiment, the average time t of the first lines in the colors formed so far is
a1 may be used as the reference, and in the fifth and sixth embodiments, a virtual image obtained by averaging the positions in the sub-scanning direction of the image already started to be scanned by the scanning writing device is used as the reference image. It is possible to further reduce the positional deviation of the image that starts scanning thereafter. Also,
In the fifth and sixth embodiments, n is an integer of 1 or more, and n = 1.

As described above, according to the sixth embodiment, the positional deviation of the images of the second, third, and fourth colors, which are images other than the reference image, with respect to the image of the first color as the reference image is less than half the dot pitch. Therefore, the image forming position in the sub-scanning direction can be stabilized.

Next, a seventh embodiment of the present invention will be described. In the seventh embodiment, the method of selecting the reference image when the optical writing (exposure) timing control target in the first embodiment is the exposure according to the image information of the cyan color, the magenta color, and the yellow color is the above-described method. Is different. Specifically, the amount of image information of red (hereinafter referred to as R), green (hereinafter referred to as G), and blue (hereinafter referred to as B) colors is used at the time of exposure according to image information of cyan, magenta, and yellow. The reference image is selected so that the influence of the positional deviation of the image information is minimized. FIG. 22 shows an image processing circuit included in the controller 9 of the seventh embodiment. In FIG. 22, 954 is a compression / expansion circuit that entropy-codes the data to compress or expands the original data, and 955 is a compression / expansion circuit 954.
A page memory for storing the data compressed by 1.951 is a logarithmic conversion circuit for converting a signal linear to the reflectance into a signal linear to the density. 952 is a filter circuit including a smoothing filter. Is a gradation processing circuit for processing the data so as to express a halftone by using dithering, error diffusion or the like. Digital image information read from an image input device such as a scanner or a network is sent to the compression / expansion circuit 954 as an R color signal, a G color signal, and a B color signal. The compression / expansion circuit 954 converts the image information read from the image input device into J
It is compressed using a compression method such as PEG2000 or JBIG. The code compressed by the compression / expansion circuit 954 is held in the page memory 955, and the compression code is read out from the page memory 955 at the time of creating the second version, and the compression / expansion circuit 95 is loaded.
In step 4, the data is decrypted in the reverse order of the compression and sent to the next step. The Log conversion circuit 951 performs table conversion for converting the characteristics of the signal decoded by the compression / expansion circuit 954 from the reflectance space as the first color space to the density space as the second color space, and R The color signal, the G color signal, and the B color signal are converted into image information of cyan color, magenta color, yellow color, and black color. The filter circuit 952 performs various filter processes on the image information from the Log conversion circuit 951. The gradation processing circuit 953 prepares a dither table for the image information from the filter circuit 952, performs middle gradation processing, and sends the processed image information to the optical writing device 1.

Here, while the exposure start timing is determined only from the recording start signal of the present embodiment, the exposure start timing is determined by further obtaining the compression code amount for each color from the compression / expansion circuit 954 ( (See FIG. 23). Specifically, the exposure control unit 91 acquires the compression code amount Fr of R color, the compression code amount Fg of G color, and the compression code amount Fb of B color from the compression / expansion circuit 954. Here, the compression code amount is the size on the page memory 955 of the compression code obtained as a result of the compression processing performed by the compression / expansion circuit 954, and the larger the image information amount, the larger the compression code amount. In addition, in the seventh embodiment, the storage device 92 stores the time when the main scanning synchronization signal is detected by the exposure control unit 91 regarding the exposure according to the image information of all the colors that has already started. For example, the storage device 92 stores the times t1 and t2 at which the main scanning synchronization signal is detected when starting the exposure of the first color and the second color when performing the exposure according to the image information of the third color. When exposure is performed according to the image information of the fourth color, the times t1, t2, and t3 at which the main scanning synchronization signal is detected when the exposure of the first color, the second color, and the third color are started are stored.

In the seventh embodiment, the exposure start timing control according to the black image information may be any of the exposure start timing control in each of the above-described embodiments. Cyan (hereinafter C) color,
The control of the exposure start timing according to the image information of magenta (hereinafter referred to as M) color and yellow (hereinafter referred to as Y) color is performed according to FIG.

The control flow of the exposure start timing according to the image information of C color, M color, and Y color performed by the exposure control unit 91 of the seventh embodiment will be described below with reference to FIG. here,
The flow when the exposure according to the image information of C color is a control target is shown. The flow when the exposure according to the image information of M color is a control target is shown in FIG.
May be Fr. Further, in the flow in the case where the exposure according to the image information of Y color is the control target, Y in FIG. 24 may be C and Fb may be Fr.

In FIG. 24, the exposure control section 91 first determines whether or not the control target is the exposure according to the image information of the first color (there is no exposure according to the image information of the color that has started first). It is determined (step 1), and if the control target is the exposure according to the image information of the first color, the “flow of the exposure start timing control according to the image information of the first color” is shown in, for example, FIG. Exposure start timing control is performed (step 2). When the control target is not the exposure according to the image information of the first color, the exposure control unit 91 determines whether the exposures according to the image information of the M color and the Y color are both started (step 3). .

If the judgment result of step 3 is N (exposure according to the image information of M color and Y color has not started yet), the exposure control section 91 determines the image information of M color and Y color. It is determined whether either one of the exposures according to (3) has already started (step 4). If the determination result of step 4 is N (either one of the exposures according to the image information of M color or Y color has not been started), the exposure control unit 91 uses the image of K color as the reference image for the "second color". The subsequent exposure start timing control flow according to the image information ", for example, the exposure control shown in FIG. 10B is performed (step 5).

If the result of the judgment at step 4 is Y (either one of the exposures according to the image information of M color or Y color has been started), the exposure control section 91 makes an image of M color or Y color. "Exposure start timing control flow according to image information of second and subsequent colors", for example, with reference to the written image that has already started among exposures according to information, for example, FIG.
The exposure start timing control shown in is performed (step 6).

In steps 4, 5, and 6, the exposure controller 91 performs one of the features of the seventh embodiment, that is, the chromatic image is used as a reference image with another chromatic image as much as possible. . Since a chromatic color image overlaps with another chromatic color image to form an image of a target color, color misregistration can be made inconspicuous by using another chromatic color image as a reference image as much as possible.

On the other hand, if the result of the judgment in step 3 is Y (exposure according to the image information of M color and Y color has already started), the exposure control unit 91 determines the exposure control device 91.
Acquires Fg and Fb from the storage device 92 (step 7), compares the Fg and Fb, and determines whether or not Fg> Fb (step 8). When the determination result of step 8 is Y (Fg> Fb), the exposure control unit 91 uses the Y-color image as a reference image to “exposure start timing control flow according to image information of second and subsequent colors”. For example, the exposure start control shown in FIG. 10B is performed (step 9).

When the result of the determination in step 8 is N (Fg ≦ Fb), the exposure control section 91 uses the M color image as a reference image and "exposure start timing according to the image information of the second and subsequent colors. Control flow ", for example, exposure control shown in FIG. 10B is performed (step 10).

Steps 8, 9, and 10 are steps 1 of the seventh embodiment.
Control is performed to select a color image having a higher correlation, which is one of the features, as a reference image. Explaining this in detail, the fact that Fg> Fb means that the image information amount of G color is larger than the image information amount of B color. On the contrary, Fg <Fb means that the image information amount of G color is smaller than the image information amount of B color. For example, when the image is composed of only G color, the image information amount of G color is large, but the image information amount of B color is 0 (because information such as header is generally present in the compression code, B color is The image information amount of is not 0). Therefore, when Fg> Fb, preventing the color shift of the G color image information rather than the B color image information leads to effectively reducing the deterioration of the image quality.

Here, the R color is formed from the M color and the Y color,
Since the G color is formed from the C color and the Y color, and the B color is formed from the C color and the M color, if the Y color image is used as the reference image at the start of exposure according to the C color image information, the G color The color shift of the image is reduced, and the color shift of the B color image is reduced by using the M color image as a reference image. Therefore, when Fg> Fb, it is effective from the viewpoint of reducing the color misregistration if the Y-color image is used as the reference image at the start of exposure according to the C-color image information.
After all, in the seventh embodiment, an image of a color having a higher correlation is selected as the reference image. As described above, when the exposure according to the M color image information is the control target, M may be C and Fg may be Fr, and the exposure corresponding to the Y color image information is the control target. Y for C in some cases
And Fb may be Fr.

As described above, according to the seventh embodiment, by using the image in which the scanning writing device starts scanning the earliest as the reference image, it is possible to maximize the image in which the positional deviation is reduced by the simple process. You can increase. Also,
When the image to be written other than the reference image is a chromatic color image, the other chromatic color image is preferentially selected as the reference image to reduce the displacement of the chromatic color image and improve the image quality. Can be improved. Furthermore, by selecting an image having a high correlation with the image to be written other than the reference image as the reference image, it is possible to reduce the positional deviation of the image having a high correlation and improve the image quality.

In the second to sixth embodiments, the method of selecting the reference image when the exposure timing control target is the exposure according to the image information of cyan, magenta and yellow is the same as in the seventh embodiment. , Cyan, magenta,
At the time of exposure according to the image information of yellow color, R color, G color, B
A method may be used in which the reference image is selected using the color image information amount so that the influence of the positional deviation of the image information is minimized. Next, an eighth embodiment of the present invention will be described. The eighth embodiment is basically the same as the third embodiment, except for the following two points. The selection method of the reference image is different. Specifically, the image of the color whose exposure has started immediately before is always selected as the reference image.
The exposure start control flow in this case is the same as the exposure start control flow shown in FIG. 12 if ta1 relating to the exposure of the color started immediately before the exposure to be started is replaced with ta1 as an average value. Specifically, FIG.
In step 12 of the exposure start control flow shown in
2 should be a new ta1. In this case, there is a possibility that a color shift of nearly one line may occur between the first-color image and the fourth-color image, the second-color image and the fourth-color image, and the like. The exposure start order is an order in consideration of color correlation.
For example, when the exposure start order is K color → C color → Y color → M color, the color shift of C color is reduced with respect to K color.
The color shift of the Y color is reduced with respect to the C color, and the color shift of the M color is reduced with respect to the Y color.

In the eighth embodiment, as a result of performing the exposure start control as described above, the color misregistration between the C color and the Y color forming the G color, which greatly contributes to the luminance information, is reduced, and the C color and the K color are further reduced.
Since the color shift from the color is reduced and the color shift from the G color to the K color is relatively small, the reproducibility of the luminance information is good. In this way, by always selecting the immediately preceding image as the reference image and selecting the color order in advance so as to reduce the color misregistration in such a case, the image can be processed with a simpler algorithm than that of the seventh embodiment. It is possible to reduce the color misregistration. Further, since the same processing can be performed for the exposure control according to the image information of each color, the circuit can be simplified and the processing time can be shortened.

In the eighth embodiment, the image of the color whose exposure was started immediately before was selected as the reference image, but the image of the color whose exposure was started two exposures before the exposure to be started is selected as the reference image. However, it is also possible to set the exposure start order suitable for it in advance.

According to the eighth embodiment, an image having a high correlation with the image to be written other than the reference image is selected as the reference image, so that the image having a high correlation can be effectively selected. In addition, the above-mentioned Embodiments 1, 2, 4 to.
In the seventh embodiment, the same reference image selection method as in the eighth embodiment may be used, and the exposure start order may be the order in consideration of color correlation as in the eighth embodiment.

The present invention can be applied to the image forming apparatus shown in FIGS. 14 and 16, and the exposure control can be similarly performed by using the controller 9 similar to the controller in each of the first to eighth embodiments. . The image forming apparatus shown in FIG. 14 is a tandem type image forming apparatus. This image forming apparatus has four image stations 100K, 100C, 100 on an intermediate transfer belt 6a as an intermediate transfer member.
M and 100Y are arranged. Each image station 1
00K, 100C, 100M, and 100Y are common except that the colors of the toner images to be formed are different, and only one image station 100Y is extracted and shown in FIG. Note that in the following description, the reference numerals of the elements shown in FIG.
When adding M, Y, and K, it means the elements belonging to the image stations 100K, 100C, 100M, and 100Y, respectively.

14 and 15, the intermediate transfer belt 6a has a structure in which a seamless belt is stretched around the driving roller 65, the tension roller 66, and the secondary transfer counter roller 63, and the intermediate transfer belt 6a is provided on the intermediate transfer belt 6a. A cleaner 67 for removing secondary transfer residual toner and the like is installed. Furthermore, each image station 100K, 1
The detection device 61 (61K, 61C, 61M, 6 as a detection means individually provided in 00C, 100M, 100Y
1Y) is a device for detecting the marker on the intermediate transfer belt 6a.
When it is detected by 1, the recording start signal in the sub-scanning direction is generated. An exposure device 1 (1Y, 1M, 1C, 1K) as an optical writing device that is a scanning writing device,
The marker and the detection means 61 are the same as those of the image forming apparatus shown in FIG.

The marker on the intermediate transfer belt 6a is the detection device 661 (61K, 61C, 61M, 61Y) in each image station 100K, 100C, 100M, 100Y.
When detected by the controller 9, the controller 9 detects the
Image station 100K, 100 that detected the marker at
For C, 100M, and 100Y, the same light-receiving element as the light-receiving element 14 in the exposure apparatus 1 (1Y, 1M, 1C, 1K) in the exposure apparatus 1 (1Y, 1M, 1C, 1K) after the marker detection is performed. (1Y, 1M, 1C, 1) as described above in response to the main scanning synchronization signal from the element).
K) is caused to start exposure according to the image information of each color of K color, C color, M color, and Y color.

Each image station 100K, 100C,
For 100M and 100Y, the charging device 4 is
(4K, 4C, 4M, 4Y) uniformly charges the photoconductor 2 (2K, 2C, 2M, 2Y) as an image carrier, which is a scanned object, and the charged photoconductor 2 is charged. Exposure device 1
Exposes each of K color, C color, M color, and Y color according to the image information, forms an electrostatic latent image corresponding to the image information of each color, and forms an electrostatic latent image corresponding to the image information of each color. The developing device 5 (5K, 5C, 5M, 5Y) develops the latent image to form toner images of K color, C color, M color, and Y color on the photoconductor 2, respectively. The toner image of each color formed on the second transfer roller 62 (6
2K, 62C, 62M, 62Y) to be superposed on the intermediate transfer belt 6a and primary-transferred to form a full-color image. The photoconductor 2 (2K, 2C, 2M, 2Y) and the intermediate transfer belt 6a are rotationally driven at the same peripheral speed by a drive source (not shown).

On the other hand, the transfer paper 8 as a recording medium is fed from the paper feeding device 10 to a registration roller (not shown), and the registration roller 8 sends the transfer paper 8 according to the full-color image on the intermediate transfer belt 6a. Intermediate transfer belt 6a
The full-color image formed on top of the
Secondary transfer is performed on the transfer paper 8 by the electric field formed between the secondary transfer roller 64 and the secondary transfer counter roller 63. The transfer paper 8 on which the full-color image is secondarily transferred is fixed by the fixing device 7.
Then, the full-color image is fixed and discharged to the outside of the apparatus. After the primary transfer of the toner image, the photoconductor 2 (2K, 2C, 2M, 2Y) is cleaned by the cleaning device 3 (3K, 3C, 3M,
3Y), and the intermediate transfer belt 6a is cleaned by the cleaning device 67 after the secondary transfer of the full-color image.

In this image forming apparatus, each exposure device 1
The exposure start times of Y, 1M, 1C, and 1K are selected at a timing such that the toner images of the respective colors are superposed on the intermediate transfer belt 6a as in the above embodiment. The order of image formation is from upstream to downstream in the moving direction of the intermediate transfer belt 6a, that is, a Y-color toner image, an M-color toner image, a C-color toner image,
The order is the K color toner image. Therefore, the Y color toner image is used as the first color toner image, the M color toner image is used as the second color toner image, the C color toner image is used as the third color toner image, and the K color toner image is used as the fourth color toner image. By performing the exposure start control by the exposure control unit 91 in the controller 9 as in the first to fourth embodiments, color misregistration can be prevented.

The image forming apparatus shown in FIG. 16 is an image forming apparatus in which the image stations 102 and 103 and the exposure device 1a are arranged below the intermediate transfer belt 6b as an intermediate transfer member, and the fixing device 7 is provided. Here, the image stations 102 and 103 have the same configuration except the color of the toner in the developing device. 2MY and 2CK are photoconductors as image bearing bodies that are the objects to be scanned, 3MY and 3CK are cleaning devices, 4MY and 4CK are charging devices, 5Ka and 5K
Ca, 5Ma, and 5Ya are developing devices that form toner images of black color, cyan color, magenta color, and yellow color by development. The exposure apparatus 1a is a well-known exposure apparatus that performs exposure by reflecting light beams from two light sources (not shown) with a rotating polygon mirror as one scanning means.
As in the case of 4, the two light beams from the rotary polygon mirror are respectively detected by two light receiving elements (not shown in the figure, but are labeled with 14MY and 14CK for convenience) as main scanning synchronizing signal generating means. The intermediate transfer belt 6b includes rollers 68 and 69.
The photoconductors 2MY and 2CK and the intermediate transfer belt 6b are rotatably driven at the same peripheral speed by a driving source (not shown).

Next, the operation of this image forming apparatus will be outlined. The detection device 61MY of the detection devices 61MY and 61CK as the sub-scanning direction recording start signal generating means detects a predetermined marker on the intermediate transfer belt 6b to generate a recording start signal in the sub-scanning direction to the controller 9. Send,
Next, when the main scanning synchronization signal from the light receiving element 14MY reaches the controller 9, the exposure of the exposure apparatus 1MY is started as in the above embodiment. In this case, the exposure apparatus 1MY
First, a light beam modulated with image information of Y color or M color, for example, Y color, from a light source for the upstream image station 102 is deflected by a rotating polygon mirror, and the photoconductor in the image station 102 is deflected. The exposure according to the Y-color image information of 2MY is started.

In the image station 102, when the exposure is started, the surface of the photoconductor 2MY is charged to a predetermined potential by the charging device 4MY in time for the exposure. The surface of the charged photoconductor 2MY is exposed by the exposure device 1a to form an electrostatic latent image corresponding to Y color image information, and the electrostatic latent image on the photoconductor 2MY is one of the developing devices 5Y and 5M. Developed by one. The developing devices 5Y and 5M are selectively retracted from the photoconductor 2MY, or alternatively, the developing devices 5Y and 5M perform the developing operation by advancing to the developing position and applying a developing bias from a power supply device (not shown). The non-execution can be controlled. Here, the electrostatic latent image on the photoconductor 2MY is first developed by the developing device 5Y to become a Y-color toner image. The Y-color toner image formed on the photoconductor 2MY is primarily transferred to the intermediate transfer belt 6b by a transfer unit (not shown).

Next, the detection device 61CK detects a predetermined marker on the intermediate transfer belt 6b to generate a recording start signal in the sub-scanning direction and send it to the controller 9, after which a main scanning synchronization signal is sent from the light receiving element 14CK. When it reaches the controller 9, the exposure device 1a deflects the light beam modulated by the image information of K color from the light source for the image station 103 by the rotating polygon mirror, and starts the exposure of the photoconductor 2CK in the image station 103.

In the image station 103, when the exposure is started, the surface of the photoconductor 2CK is charged to a predetermined potential by the charging device 4CK in time for the exposure. The surface of the charged photoconductor 2CK is exposed by the exposure device 1a to form an electrostatic latent image corresponding to the K color image information, and the electrostatic latent image on the photoconductor 2 is one of the developing devices 5C and 5K. Developed by one. The developing devices 5C and 5K are selectively retracted from the photoconductor 2CK, or alternatively, the developing devices 5C and 5K are selectively advanced to a developing position and a developing bias is applied from a power supply device (not shown) to perform the developing operation. It is configured so that non-execution can be controlled.
The electrostatic latent image on K is first developed by the developing device 5K and then K
It becomes a color toner image. The K-color toner image formed on the photoconductor 2CK is primarily transferred onto the intermediate transfer belt 6b by the transfer means (not shown) so as to be superposed on the Y-color toner image.

The image on which the Y-color toner image and the K-color toner image are superposed on the intermediate transfer belt 6b is moved by the rotation of the intermediate transfer belt 6b and is again moved to the image station 1.
Reach 02. At this time, in the image station 102, the developing device at the developing position is switched to the developing device 5M, and the detection device 61MY detects a predetermined marker on the intermediate transfer belt 6b to generate a recording start signal in the sub-scanning direction. And send it to the controller 9.

Then, the main scanning synchronization signal is received by the light receiving element 14M.
Upon reaching the controller 9 from Y, the exposure apparatus 1 deflects the light beam modulated by the image information of M color from the light source for the image station 102 by the rotating polygon mirror to start the exposure of the photoconductor 2MY in the image station 102. To do.

In the image station 102, when the exposure is started, the surface of the photoconductor 2MY is charged to a predetermined potential by the charging device 4MY in time for the exposure. The surface of the charged photoconductor 2MY is exposed by the exposure device 1a to form an electrostatic latent image corresponding to the image information of M color, and the electrostatic latent image on the photoconductor 2MY is developed by the developing device 5M to be M. It becomes a color toner image. M formed on the photoconductor 2MY
The color toner image is primarily transferred onto the intermediate transfer belt 6b by a transfer unit (not shown) so as to be superimposed on the Y color toner image and the K color toner image.

Y color toner image on the intermediate transfer belt 6b, K
The color toner image and the M color toner image are superimposed and the image moves by the rotation of the intermediate transfer belt 6b and reaches the image station 103. At this time, in the image station 103, the developing device at the developing position is switched to the developing device 5C, and the detecting device 61MY causes the intermediate transfer belt 6 to operate.
The recording start signal in the sub-scanning direction is generated by detecting a predetermined marker on b, and is sent to the controller 9.

Then, the main scanning synchronization signal is received by the light receiving element 14C.
Upon reaching the controller 9 from K, the exposure apparatus 1 deflects the light beam, which is modulated by the image information of C color from the light source for the image station 103, by the rotating polygon mirror, and the C color of the photoconductor 2CK in the image station 103 is changed. The exposure according to the image information is started.

In the image station 103, when the exposure is started, the surface of the photoconductor 2CK is charged to a predetermined potential by the charging device 4CK in time for the exposure. The surface of the charged photoconductor 2CK is exposed by the exposure device 1a to form an electrostatic latent image corresponding to the C color image information, and the electrostatic latent image on the photoconductor 2CK is developed by the developing device 5C to C.
It becomes a color toner image. The C-color toner image formed on the photoconductor 2CK is primarily transferred onto the intermediate transfer belt 6b by the transfer means (not shown) so as to be superimposed on the Y-color toner image, the K-color toner image and the M-color toner image. As a result, a full-color image is formed.

On the other hand, the transfer paper 8 as a recording medium is fed from the paper feeding device 10 to a registration roller (not shown), and this registration roller sends the transfer paper 8 in accordance with the full-color image on the intermediate transfer belt 6b. Intermediate transfer belt 6b
The full-color image formed above is secondarily transferred onto the transfer paper 8 by a transfer unit (not shown). The transfer paper 8 to which the full-color image has been secondarily transferred is fixed with the fixing device 7 to the full-color image, and is discharged to the outside of the device. Photoconductor 2M
Y and 2CK are cleaned by the cleaning devices 3MY and 3CK after the primary transfer of the toner image, and the intermediate transfer belt 6b is cleaned by a cleaning device (not shown) after the secondary transfer of the full-color image.

In this image forming apparatus, a Y-color toner image, a K-color toner image, an M-color toner image, and a C-color toner image are sequentially formed, and each color toner image is formed.
The first color is Y and the second color is K
It is possible to control the exposure according to the image information of each color in the same manner as in the first to fourth embodiments, assuming that the third color is K color and the fourth color is C color cyan. In the case of this image forming apparatus, in consideration of the delicate eccentricity of the photoconductors 2MY and 2CK, the image of the developing color of the developing device held in the same image station is always used as the reference image. good.

In addition to the above, according to the present invention, an image forming apparatus for superimposing toner images of respective colors on a photoconductor, an image for directly transferring a toner image from a photoconductor to a recording medium without using an intermediate transfer body is used. It is also applicable to a forming device. Further, the present invention is, for example, a photosensitive member that blows toner (including ink) from a rotating nozzle according to image information and moves in the sub-scanning direction,
It is also applicable to an image forming apparatus that forms an image by an image forming process other than electrophotography, such as forming a toner image by scanning the intermediate transfer member or recording paper in the main scanning direction according to image information. is there. In short, the present invention is applicable to any image forming apparatus that superimposes a plurality of images formed by using a scanning writing device capable of forming a latent image or an image.

[0128]

As described above, according to the present invention, the reference time is more than the time elapsed from the detection of the image forming start signal in the sub-scanning direction to the detection of the main scanning synchronization signal when writing a predetermined reference image. Even when the time from the detection of the image formation start signal in the sub-scanning direction to the detection of the main scanning synchronization signal when writing an image other than the image is long, the misalignment of the image other than the reference image with respect to the reference image Can be suppressed to less than half of the dot diameter,
It is possible to prevent the color shift of the toner image due to the lack of synchronization between the main scanning synchronization signal and the image forming start signal in the sub scanning direction.

Further, in the case of writing an image other than the reference image, the time is longer than the time elapsed from the detection of the image formation start signal in the sub-scanning direction to the detection of the main scanning synchronization signal in the case of writing the predetermined reference image. Even when the time that elapses from the detection of the image formation start signal in the sub-scanning direction to the detection of the main scanning synchronization signal is short, it is possible to suppress the misalignment of images other than the reference image with respect to the reference image to less than half the dot diameter. It is possible to prevent the color shift of the toner image due to the lack of synchronization between the main scanning synchronization signal and the image forming start signal in the sub scanning direction.

Further, it is possible to stabilize the image forming position in the sub-scanning direction, and it is possible to maximize the number of images in which positional deviation is reduced by simple processing. Further, it is possible to further reduce the positional deviation of the images that start the scanning after the third scanning. Further, it is possible to reduce the positional deviation of the chromatic color image and improve the image quality. In addition, it is possible to reduce the positional deviation of highly correlated images and improve the image quality. Further, it is possible to effectively select an image having a high correlation.

[Brief description of drawings]

FIG. 1 is a block diagram showing a controller according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of an image forming apparatus.

FIG. 3 is a plan view showing a configuration of an optical writing device in the image forming apparatus.

FIG. 4 is a diagram showing an operation timing of the image forming apparatus.

FIG. 5 is a diagram showing a positional relationship of each color dot according to a conventional method.

FIG. 6 is a flowchart showing an operation flow of the image forming apparatus.

FIG. 7 is a flowchart showing a processing flow performed by the exposure control unit of the first embodiment.

FIG. 8 is a diagram showing an example of dot positions formed in the first embodiment.

FIG. 9: Steps 9, 10, 1 in the first embodiment
It is a figure which shows the implementation result of 1.

FIG. 10 is a flowchart showing a processing flow performed by an exposure control unit according to the second embodiment of the present invention.

FIG. 11 is a diagram showing an example of dot positions formed according to the second embodiment.

FIG. 12 is a flowchart showing a flow of exposure control according to image information of second and subsequent colors according to the third embodiment of the present invention.

FIG. 13 is a diagram showing an example of dot positions formed according to the third embodiment.

FIG. 14 is a cross-sectional view showing another example of the image forming apparatus.

FIG. 15 is a cross-sectional view showing one image station in the image forming apparatus.

FIG. 16 is a cross-sectional view showing another example of the image forming apparatus.

FIG. 17 is a flowchart showing a control flow of an exposure control section according to the fifth embodiment of the present invention.

FIG. 18 is a diagram showing an example of dot positions formed according to the fifth embodiment.

FIG. 19 is a flowchart showing a control flow of an exposure control section according to the sixth embodiment of the present invention.

FIG. 20 is a diagram showing an example of dot positions formed in the sixth embodiment.

FIG. 21 is a diagram for explaining a line.

FIG. 22 is a block diagram showing an image processing circuit included in the controller according to the seventh embodiment of the present invention.

FIG. 23 is a block diagram showing a controller according to the seventh embodiment.

FIG. 24 is a flowchart showing a control flow of an exposure control section in the seventh embodiment.

[Explanation of symbols]

1 Optical writing device 2 photoconductor 9 Controller 14 Light receiving element 61 detection means 91 Exposure control unit 92 storage device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/113 H04N 1/04 104A 5C072 (72) Inventor Atsuga Matsuura 1-3 Nakamagome, Ota-ku, Tokyo No. 6 ・ F-term in Ricoh Co., Ltd. (reference) 2C262 AB15 BA01 BC19 EA10 FA01 FA03 FA06 GA04 2C362 BA51 BA52 BA70 BA71 BB32 BB38 BB46 CA22 CA39 2H076 AB05 AB12 AB31 AB67 AB68 EA01 2H300 EB02 EB08 EB12 EC02 EC08 EF03 EG03 E04H34EG02 EH35 EJ09 EJ15 EK03 EL07 FF05 GG23 GG27 HH12 QQ13 RR20 RR21 RR45 RR49 RR50 SS12 5C051 AA02 CA07 DB02 DB07 DB30 DC03 DE02 EA01 FA01 5C072 AA03 BA19 HA02 HA13 HB11 HB13 QA14 AUA18 XA

Claims (14)

[Claims] 1. A scanning object which moves in the sub-scanning direction,
This scanning writing device uses a scanning writing device that writes an image by performing scanning according to image information in the main scanning direction based on a main scanning synchronization signal detected after an image formation start signal in the sub scanning direction is detected. In the write control method of the image forming method for forming a color image by superimposing a plurality of images obtained by scanning n lines (n> 0) per scan according to image information. The time interval at which a signal is generated is T, the time that elapses from the detection of the image formation start signal to the detection of the main scanning synchronization signal when the writing of a predetermined reference image is started by the scanning writing device is t1, The main scanning synchronization signal is detected from the detection of the image formation start signal when the writing of the image to be written other than the reference image is started by the scanning writing device. When the time elapsed until detection is t2 and t1 <t2, i is set to | t1 + T × (i when starting writing of an image to be written other than the reference image by the scanning writing device. / N) -t2
A writing control device which causes the scanning writing device to start scanning in accordance with image information from the (i + 1) th line when | is an integer that minimizes. 2. A scanning object that moves in the sub-scanning direction,
The scanning writing device includes a scanning writing device that writes an image by performing scanning according to image information in the main scanning direction based on the main scanning synchronization signal detected after the image formation start signal in the sub scanning direction is detected. In the write control device of the image forming apparatus, which forms a color image by superimposing a plurality of images obtained by performing scanning of n lines (n> 0) per scan according to image information, the main scanning synchronization signal Is T, the time that elapses from the detection of the image formation start signal to the detection of the main scanning synchronization signal when the writing of a predetermined reference image is started by the scanning writing device is t1, and the scanning is performed. From the detection of the image formation start signal when the writing device starts writing an image that is a writing target other than the reference image, the main scanning synchronization signal When the time elapsed until the knowledge is set to t2 and t1 <t2, i is set to | t1 + T × (i when starting writing of an image to be written other than the reference image by the scanning writing device. / N) -t2 |
Is a minimum integer, the scanning writing device is caused to start scanning according to image information from the (i + 1) th line. 3. The writing control device according to claim 2, wherein when t1> t2, m is set to | t1 + T when the scanning writing device starts writing an image to be written other than the reference image. X (m / n) -t2 |
A writing control device characterized by delaying image information by m lines and starting scanning. 4. The writing control device according to claim 2, wherein j is made to be | t1−T × (j / n) | is minimum when the writing of the reference image is started by the scanning writing device. When it is a non-negative integer, the scanning / writing device is caused to start scanning in accordance with image information from the j + 1th line, and k is started when the scanning / writing device starts writing an image to be written other than the reference image. ｜
When the sum of t1−T × (j / n) + T × (k / n) −t2 |
A writing control device characterized in that scanning according to image information is started from a line. 5. An object to be scanned that moves in the sub-scanning direction,
A scanning writing device for writing an image in the main scanning direction based on a main scanning synchronization signal detected after the detection of the image formation start signal in the sub scanning direction is provided, and the scanning writing device performs plural times of scanning for each of plural colors. In a writing control device of an image forming apparatus that forms a color image by superimposing images of a plurality of colors obtained by performing according to image information, a time interval at which the main scanning synchronization signal is generated is set to T, and the scanning writing device is set to In the case of writing an image of a predetermined reference color by the above, the time that elapses from the detection of the image formation start signal to the first detection of the main scanning synchronization signal is t1, and a color other than the reference color is detected by the scanning writing device. When the image is written, the time elapsed from the detection of the image formation start signal to the first detection of the main scanning synchronization signal is t
In the case of 2, the writing of the image of the reference color according to the image information of the reference color by the scanning writing device is performed when the time t1 elapses after the image formation start signal in the sub-scanning direction is detected. Is detected, and the writing of an image of a color other than the reference color by the scanning writing device is performed when t1 is smaller than a predetermined time.
When t1−t2 | is less than the predetermined time, it is performed according to the image information from the first line when t2 has elapsed from the detection of the image formation start signal, and when t1 is smaller than the predetermined time, | When t1−t2 | is equal to or longer than the predetermined time, when t2 has elapsed from the detection of the image formation start signal, the process is performed according to the image information from the second line, and
When 1 is the predetermined time or more and | t1-t2 | is less than the predetermined time, the process is performed according to the image information from the first line when t2 has elapsed from the detection of the image formation start signal. Is greater than or equal to the predetermined time and | t1-t2 | is greater than or equal to the predetermined time, it is performed according to the image information from the first line when t2 + T has elapsed from the detection of the image formation start signal. Write control device. 6. An object to be scanned which moves in the sub-scanning direction,
A scanning writing device for writing an image in the main scanning direction based on a main scanning synchronization signal detected after the detection of the image formation start signal in the sub scanning direction is provided, and the scanning writing device performs plural times of scanning for each of plural colors. In a writing control device of an image forming apparatus that forms a color image by superimposing images of a plurality of colors obtained by performing according to image information, a time interval at which the main scanning synchronization signal is generated is set to T, and the scanning writing device is set to In the case of writing an image of a predetermined reference color by the above, the time that elapses from the detection of the image formation start signal to the first detection of the main scanning synchronization signal is t1, and a color other than the reference color is detected by the scanning writing device. When the image is written, the time elapsed from the detection of the image formation start signal to the first detection of the main scanning synchronization signal is t
In the case of 2, the writing of the image of the reference color according to the image information of the reference color by the scanning writing device detects the image formation start signal in the sub-scanning direction when t1 is less than a predetermined time. After the time t1 has elapsed, the main-scanning synchronization signal is detected to perform the operation in accordance with the image information from the first line. When t1 is a predetermined time or more, the image forming start signal in the sub-scanning direction is generated. Is performed according to the image information from the second line by the detection of the main scanning synchronization signal when t1 has elapsed after the detection of the, and the writing of the image of a color other than the reference color by the scanning writing device is performed. t1 is smaller than the predetermined time and | t1-
When t2 | is less than the predetermined time, the process is performed according to the image information from the first line when t2 has elapsed from the detection of the image formation start signal, and when t1 is smaller than the predetermined time and | t1- When t2 | is equal to or longer than the predetermined time, it is performed according to the image information from the second line when t2 has elapsed from the detection of the image formation start signal. When | is less than the predetermined time, it is t2 from the detection of the image formation start signal.
When t1 is equal to or longer than the predetermined time and | t1−t2 | is equal to or longer than the predetermined time, t2 is detected from the detection of the image formation start signal. A writing control device characterized in that when the time has elapsed, it is performed according to the image information from the first line. 7. The writing control device according to claim 5, wherein t1 is an average value of time from the detection of the image formation start signal to the writing time of the first line of the image already written. Characteristic write control device. 8. The writing control device according to claim 2, wherein an image in which the scanning writing device starts scanning earliest is used as the reference image or the image of the reference color. Write control device. 9. The writing control device according to claim 2, wherein an image which has already started to be scanned by the scanning writing device as the reference image or the image of the reference color is in the sub-scanning direction. A writing control device using a virtual image in which positions are averaged. 10. The writing control device according to claim 2, wherein an image to be written other than the reference image or the image of the reference color written by the scanning writing device is a chromatic color. Write control device, the other chromatic color image is preferentially selected as the reference image or the reference color image. 11. The writing control device according to claim 2, wherein a correlation with an image to be written other than the reference image or the image of the reference color is written by the scanning writing device. A writing control device, wherein a high image is selected as the reference image. 12. The write control device according to claim 5, wherein the predetermined time is T / 2. 13. An image forming apparatus comprising the write control device according to claim 2. 14. An image forming apparatus having the write control device according to claim 11, wherein the image information in the first color space is converted into information in the second color space, and each color in the first color space. A color image is formed from the information in the second color space, and means for determining the strength of the correlation between the color images in the second color space according to the amount of information in the image. Image forming apparatus.