JP4138260B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a superimposed image misregistration technique in a multicolor image forming apparatus that fixes and outputs a multicolor image.
[0002]
[Prior art]
Regarding the misregistration of the superimposed image, that is, the color misregistration in the conventional multicolor image forming apparatus, in the quadruple drum type image forming apparatus shown in FIG. 2, the K (black) photoreceptor, M (magenta) photoreceptor, and Y ( A specific toner mark is formed on the conveyance belt 14 by the yellow) photoreceptor and the C (cyan) photoreceptor, and the toner mark is read by the sensor 21, and the toner mark line thickness, length, positional deviation, toner mark The color misregistration is corrected by detecting the misregistration of each color image from the mutual positional relationship and the toner mark inclination degree (details of detection will be described later).
[0003]
Since the toner mark for detecting misalignment on the conveyance belt 14 becomes unnecessary after reading by the sensor 21, it is necessary to remove the toner mark from the conveyance belt, and is provided on the downstream side of the conveyance belt of the sensor. The toner mark was cleaned by the cleaning member (see FIG. 4).
[0004]
[Problems to be solved by the invention]
As described above, through a series of processes such as image formation of a positional deviation detection toner mark on the conveyance belt, color misregistration correction by reading the toner mark, and removal of the toner mark from the conveyance belt, many processes are performed. The function of correcting the misalignment of the superimposed image of the color image forming apparatus is achieved.
[0005]
The toner mark removal process in this series of misregistration correction functions includes the fact that the toner mark has been written to more than half the total length of the conveyor belt, and the toner mark on the conveyor belt has been electrostatically peeled off. Due to the insufficiency and incompleteness of the removal due to this, the time required for the toner mark removal process occupies a considerable time in the entire process time of the positional deviation correction function.
[0006]
An object of the present invention is to shorten the execution time of the entire color misregistration correction by shortening the cleaning time of the toner mark.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention mainly adopts the following configuration.
[0008]
A plurality of image forming units are arranged along the conveying direction of the conveying belt, a multicolor image is formed by the superimposed image by the image forming unit, and a predetermined toner pattern is conveyed for alignment of the superimposed image An image forming apparatus that forms an image on a belt, detects a color shift amount of each color by reading a toner pattern formed on the transport belt, and performs color shift correction based on the detected color shift amount,
At the time of cleaning in which the toner pattern on the transport belt is electrostatically attracted and removed by a bias roller after the toner pattern is read, the speed of the transport belt is made higher than the speed of the transport belt at the time of forming the toner pattern. An image forming apparatus.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
A color image forming apparatus according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram showing an overall configuration of a color image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration example of a toner mark and a toner mark detection sensor in a positional deviation amount detection pattern formed on the conveyance belt. FIG. 3 is a diagram showing a specific example of the positional deviation amount detection pattern and a pattern example when color misregistration occurs. FIG. 4 is a view showing a cleaning mechanism for cleaning the toner mark on the transport belt according to the present embodiment. FIG. 5 is a flowchart showing a toner mark cleaning operation according to this embodiment.
[0010]
First, a configuration example of a color image forming apparatus according to the present invention will be described with reference to FIG. As shown in FIG. 1, in this color image forming apparatus, a plurality of image forming units as electrophotographic process units are arranged along a conveyance path of a recording sheet that is a recording medium, and the sheet includes each image forming unit. The images of different colors are sequentially transferred onto the paper every time the image passes through the image, and finally a color image is obtained by superimposing the four colors. The apparatus shown in FIG. 1 is a so-called four-drum type image forming apparatus.
[0011]
Each image forming unit is disposed around a drum-shaped black photoconductor 1K, a magenta photoconductor 1M, a yellow photoconductor 1Y, and a cyan photoconductor 1C that function as an image forming medium. Black charging device 2K, magenta charging device 2M, yellow charging device 2Y, cyan charging device 2C, black developing device 3K, magenta developing device 3M, yellow developing device 3Y, cyan developing device 3C, etc. It is composed of
[0012]
A laser scanner 8 is used as an exposure device that exposes the photoreceptors 1K, 1M, 1Y, and 1C of each image forming unit. The laser scanner 8 reflects the laser beam from the laser light source by the polygon scanner 9, Further, the optical path is bent by the respective fθ lenses 10K, 10M, 10Y, and 10C and the deflecting mirrors 11K, 11M, 11Y, and 11C to be guided to the photosensitive members 1K, 1M, 1Y, and 1C, and the surface of each photosensitive member is exposed. It has become. Further, in this laser scanner 8, the polygon scanner 9 rotates to move the laser beam in the axial direction of each photoconductor to perform main scanning, and the rotation of each photoconductor causes the axial direction of each photoconductor. Sub-scanning is performed in a direction orthogonal to.
[0013]
In forming a color image, the color separation image signal obtained in advance by the color image reading device 6 is subjected to color conversion processing by the image processing unit 7 based on the intensity level, and black (K), magenta ( M), yellow (Y), and cyan (C) color image data are converted and output to the laser scanner 8. When image formation is started, first, the surfaces of the photoreceptors 1K, 1M, 1Y, and 1C are uniformly charged by the charging devices 2K, 2M, 2Y, and 2C in the dark, and then a laser as an exposure device. A laser beam modulated by the image data of each color output from the image processing unit 7 is emitted from the scanner 8, and a pattern corresponding to the image to be output is exposed by the laser beam, and an electrostatic latent image is formed on the surface of each photoconductor. An image is formed.
[0014]
The electrostatic latent images formed on the photoconductors are developed by the developing devices 3K, 3M, 3Y, and 3C to form toner images of the respective colors, and these toner images are formed on the photoconductors for the respective colors. A color image is obtained by superimposing and transferring the transfer positions of the respective colors, which are the opposing portions of 1K, 1M, 1Y, and 1C and the transfer devices 4K, 4M, 4Y, and 4C, onto the sheet that is sequentially conveyed by the conveyance belt. Then, the transferred paper is separated from the conveying belt 14 and sent to the fixing device 15, and after the color image is fixed by the fixing device 15, the paper is discharged to a paper discharge unit (not shown). In addition, after the toner image is transferred to the paper, the toner remaining on the photoconductors 1K, 1M, 1Y, and 1C is removed by the cleaning devices 5K, 5M, 5Y, and 5C provided corresponding to the photoconductors. Preparations for the next image formation are made.
[0015]
Each color image is aligned with the timing at which the recording paper fed from the paper supply unit 12 is conveyed from the registration unit 13 to the transfer position of each color by the conveyance belt 14 and on each of the photoconductors 1K, 1M, 1Y, and 1C. This is performed by setting the exposure start time of each color by the laser scanner 8 so that the timing at which the toner image is moved to the transfer position is the same for each color toner image.
[0016]
In the color image forming apparatus configured as described above, the color at a position where it should originally overlap due to an error in the distance between the axes of the photoconductors, an error in the photoconductor parallelism, an installation error of an optical system such as a folding mirror, a writing timing error, etc. There is a problem that images are not overlapped and an image whose position is shifted between colors is formed. Even if these are adjusted initially, not only will they shift due to replacement of the image forming unit, maintenance, product transportation, etc., but the error will change over time due to the temperature expansion of the mechanism after forming multiple images, so It will be necessary to make adjustments in a shorter range.
[0017]
The types of main color shifts that occur in the image forming apparatus described above are roughly classified as follows.
[0018]
As "color shift in the sub-scanning direction"
(1) Skew (diagonal shift). That is, it is caused by a parallelism error between the exposure unit and the photosensitive member. In the example of the positional deviation amount detection pattern shown in FIG. 3A, the M vertical line is written slightly obliquely with respect to the K vertical line. Color shift. Specifically, as shown in (2) of FIG. 3, the KM distance of the left detection pattern is different from the KM distance of the right detection pattern. The distance between M is longer. Such a phenomenon is treated as skew, and the mirror angle is adjusted so that the left and right scanning lines of M are parallel to that of K.
[0019]
(2) Sub-scanning resist misalignment. That is, the color is shifted in the paper transport direction due to an exposure unit, an inter-axial error of the photosensitive member, an error in writing timing, and the like. In the example of the positional deviation amount detection pattern shown in FIG. This is a color shift in which the M vertical lines are written slightly deviated back and forth with respect to the vertical lines.
[0020]
As "color shift in the main scanning direction"
(3) Main scanning registration misalignment. That is, the color is shifted in the writing direction due to a deviation of the exposure unit in the main scanning direction, an error in writing timing, and the like. In the example of the positional deviation amount detection pattern shown in FIG. The start point and the end point of the vertical line are color shifts that are written slightly shifted back and forth in the main scanning direction. Specifically, as shown in (3) of FIG. 3, first, the distance between the horizontal line and the oblique line at an angle of 45 degrees is obtained. At this time, if there is a deviation, the horizontal line and the oblique line move in the left-right direction, but the distance between the horizontal line and the oblique line is shortened in the illustrated example by the amount (b) moved in the left-right direction due to the movement of the oblique line. In this way, the main scanning registration deviation can be obtained.
[0021]
(4) Magnification deviation. That is, the length of the scanning line differs between colors due to an optical path length error, a writing frequency error, and the like. In the example of the misregistration amount detection pattern shown in FIG. This is a color shift in which the direction length is written slightly longer or shorter than the set value. Specifically, as shown in (4) of FIG. 3, in the left and right detection patterns, if the distance between the horizontal line and the oblique line is the original length a, no magnification shift has occurred. However, if the distance between the horizontal line and the oblique line in the left and right detection patterns is different, that is, if the distance b between the horizontal line and the oblique line in the right detection pattern is shorter than the original length a by α in the illustrated example, a magnification deviation occurs. Will be. However, when both the left and right detection patterns have the same length and the line-to-line distances are different, it is a main scanning deviation.
[0022]
Regarding the color misregistration described above, there is a method for forming a specific toner mark (registration mark) on the conveyor belt 14, reading the mark with an attached sensor, recognizing the misregistration of each color image, and adjusting this. Proposed. As shown in FIG. 2, the color misregistration amount is detected by forming a toner mark of each color in each image forming unit before normal image formation, and transferring the toner mark of each color to the transport belt 14. The positional deviation amount detection pattern 20 is formed by transferring the image on the top.
[0023]
Then, from the detection result of each mark of the misregistration amount detection pattern 20, a method of obtaining the resist misregistration amount of each color and correcting the resist position is adopted. In FIG. 2, the positional deviation amount detection pattern 20 including toner marks formed on the conveyance belt 14 by each image forming unit, and the toner that is provided at the most downstream side of the conveyance belt 14 and detects the toner mark of the positional deviation amount detection pattern 20. A mark detection sensor 21 is shown. Here, the toner marks of the positional deviation amount detection pattern 20 are formed at both ends of the conveyance belt 14, and the registration position deviations at both ends of the conveyance belt 14 are detected by the corresponding toner mark detection sensors 21.
[0024]
Describing the mechanism of misregistration detection with such a configuration, the misregistration amount detection pattern 20 on the conveyor belt 14 is usually perpendicular to the sheet conveyance direction (sub-scanning direction) by the conveyor belt 14 and parallel to the main scanning direction. It is formed by a horizontal line-shaped toner mark and an oblique line-shaped toner mark having a specific angle (for example, 45 °) with respect to the main scanning direction. A toner mark detection sensor 21 is placed at a position where these toner marks pass. The toner mark detection sensor 21 is a sensor that detects the timing at which the toner mark has passed, and each registration position shift is determined by the passage time.
[0025]
(1) of FIG. 3 describes four specific examples of the positional deviation amount detection pattern to be written on the conveyor belt. The reason why the number n of pattern repetitions is set to a plurality of times such as 4 or 8 in (1) of FIG. 3 is to obtain a statistical process of color misregistration based on a plurality of pattern results and to ensure its accuracy. is there. According to the example of (1) in FIG. 3, in the case of (2) and (4), the total length of the pattern reaches about 6 times the one-rotation length of the OPC drum. Here, in the case of the structure example in which the circumference of the conveyor belt is 777 mm, the pattern total length of 565 mm is written for a length exceeding 70% of the conveyor belt.
[0026]
In the pattern example of (1) in FIG. 3, four lines in the main scanning direction and four lines inclined at 45 degrees in the sub-scanning direction in the order of K (black), M (magenta), Y (yellow), and C (cyan). Are written on the conveyor belt in that order, and numerical values such as the line length A, the line width w, and the line interval d are measured by a sensor to calculate the color shift in the main scanning direction and the color shift in the sub-scanning direction. For example, the image frequency of the laser diode is adjusted so as to eliminate the color shift.
[0027]
4 (1), four photosensitive drums 31, 32, 33, and 34 in a four-drum system, a conveyor belt 35, a conveyor belt drive roller 36, a positional deviation amount detection pattern reading sensor 37, and a reflector 38 are shown. , And a related configuration of the cleaning member 39. Here, the cleaning member 39 removes a detection pattern that is no longer necessary after the detection pattern written on the conveyor belt 35 has been read by the reading sensor 37. The cleaning pattern is not limited to the detection pattern on the conveyor belt, but is used to clean the conveyor belt with scattered toner and paper dust. In FIG. 4 (1), the reflection type is exemplified as the pattern reading mechanism. However, the pattern reading mechanism is not limited to this and may be a transmission type.
[0028]
FIG. 4B shows a detailed structure of the cleaning member 39. In this structural example, a bias roller 40 and a cleaning blade 41 are provided. The bias roller 40 electrostatically attracts paper dust and toner on the transport belt and removes them from the transport belt. A cleaning blade 41 is provided in contact with the bias roller 40 in the counter-rotating direction to scrape off the toner on the bias roller 40. The waste toner is collected in a waste toner bottle by a screw (not shown).
[0029]
The timing for writing the positional deviation amount detection pattern on the conveyor belt 14 is the same as when the image forming apparatus starts up on the day, when the temperature in the apparatus rises (detects that the temperature exceeds a predetermined temperature), and the photosensitive drum. Alternatively, when the developing unit is replaced, when a predetermined number of color copies are executed, or as required by the user, color misregistration of the multicolor image is corrected each time at these timings.
[0030]
The image forming apparatus according to the embodiment of the present invention is characterized in that the detection pattern on the conveyor belt is removed by the cleaning member 39 after the positional deviation amount detection pattern written on the conveyor belt 35 is read by the reading sensor 37. In order to shorten the cleaning time, the speed of the conveying belt at the time of detection pattern cleaning is made faster than that at the time of image formation of the detection pattern. Here, since the speed of the conveyor belt at the time of color image creation and the conveyor belt speed at the time of detection pattern imaging are the same, the conveyor belt speed at the time of detection pattern cleaning is faster than the conveyor belt speed at the time of color image formation. Yeah.
[0031]
Specifically, removal of the detection pattern on the conveyor belt will be described. In the configuration example of electrostatic toner adsorption by the bias roller 40 and mechanical toner separation by the cleaning blade, the pattern reading sensor shown in FIG. The detection pattern on the conveyor belt that has passed through 37 cannot be completely removed by a single cleaning operation by the cleaning member 39. In practice, the detection pattern on the conveyor belt is detected by passing the detection pattern through the cleaning member several times. The pattern toner can be completely removed. Therefore, by increasing the speed of the conveying belt at the time of cleaning the detection pattern, it is possible to greatly reduce the time for performing color misregistration correction as a whole.
[0032]
The image forming apparatus according to the present embodiment is capable of forming a black and white image according to user settings in addition to being able to form a color image. The speed of the conveyor belt when forming a black and white image is the same as that when forming a color image. For example, it is transported at a speed approximately 50% higher. In other words, the driving of the conveyor belt has two speeds (when forming a multicolor image and when forming a black and white image) in order to achieve the original function of the image forming apparatus. Accordingly, it is possible to shorten the cleaning time by switching the conveying belt speed at the time of detection pattern cleaning to the existing conveying belt speed at the time of monochrome image formation. Here, the speed of the conveyor belt at the time of detection pattern cleaning is not used as the speed of other functions, but at a dedicated high speed, for example, at a speed of 50% or more, faster than at the time of color image formation or monochrome image formation. Therefore, it is natural that the time for cleaning can be shortened.
[0033]
FIG. 5 shows operation modes of the detection pattern imaging mode and the cleaning mode. According to FIG. 5, it is determined whether or not to form an alignment pattern (position shift amount detection pattern), and if it is a pattern image formation mode, it is combined with the transfer drive roller 36 (see (1) in FIG. 4). The rotational speed of the drive motor is set to the rotational speed during normal image formation. On the other hand, in the cleaning mode, an instruction is given to the rotational speed setting circuit of the driving motor of the transfer driving roller 36 so that the rotational speed is increased by α as compared with the pattern imaging rotational speed, and the rotational speed is set. Increase to increase the conveyor belt speed. Here, the flowchart of FIG. 5 is an example of setting the pattern image forming mode and the cleaning mode, and the cleaning mode may be set after the pattern image forming mode ends. Furthermore, the end of reading the pattern of the reading sensor 37 shown in FIG. 4 may be detected, and the cleaning mode may be selected based on this detection.
[0034]
【The invention's effect】
According to the present invention, the cleaning time that is not directly related to the color misregistration correction is shortened by making the belt speed at the time of cleaning the misregistration amount detection pattern faster than that at the time of image formation or image formation. Thus, the overall color misregistration correction execution time can be greatly shortened.
[0035]
Further, by setting the cleaning belt speed to the belt speed at the time of monochrome image formation, the cleaning time can be shortened without adding extra means.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an overall configuration of a color image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration example of a toner mark and a toner mark detection sensor in a positional deviation amount detection pattern formed on a conveyance belt.
FIG. 3 is a diagram illustrating a specific example of a positional deviation amount detection pattern and a pattern example when color misregistration occurs.
FIG. 4 is a diagram illustrating a cleaning mechanism that cleans toner marks on a conveyance belt according to the present exemplary embodiment.
FIG. 5 is a flowchart illustrating a toner mark cleaning operation according to the exemplary embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Drum-shaped photoconductor 3 Developing device 4 Transfer device 5 Photoconductor cleaning device 6 Color image reading device 8 Laser scanner 9 Polygon scanner 12 Paper feed unit 14 Conveying belt 15 Fixing device 16 LED (light emitting element)
18 Photodetector 20 Misregistration detection patterns 31, 32, 33, 34 Photoconductor 35 Conveying belt 36 Conveying belt driving roller 37 Pattern reading sensor 38 Reflecting plate 39 Cleaning member 40 Bias roller 41 Cleaning blade

Claims (3)

A plurality of image forming units are arranged along the conveying direction of the conveying belt, a multicolor image is formed by the superimposed image by the image forming unit, and a predetermined toner pattern is conveyed for alignment of the superimposed image An image forming apparatus that forms an image on a belt, detects a color shift amount of each color by reading a toner pattern formed on the transport belt, and performs color shift correction based on the detected color shift amount,
At the time of cleaning in which the toner pattern on the transport belt is electrostatically attracted and removed by a bias roller after the toner pattern is read, the speed of the transport belt is made higher than the speed of the transport belt at the time of forming the toner pattern. An image forming apparatus. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the speed of the conveying belt at the time of cleaning is matched with the conveying belt speed at the time of black-and-white image formation. The image forming apparatus according to claim 1, wherein
An image forming apparatus characterized in that a conveying belt speed during cleaning is increased based on detection of completion of reading of the toner pattern.

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